The Cerebellum and its Disorders

The Cerebellum and its Disorders ‘In this volume, the editors have brought together an outstanding group of contributors who have accomplished the daunting task of thoroughly reviewing the basic sciences relevant to the cerebellum as well as the major clinical disorders affecting the cerebellum. Although the emphasis of the volume is on clinical aspects of cerebellar function, the book contains excellent reviews of the current status of the embryology, anatomy, physiology, and pharmacology of the cerebellum. The coverage is both complete and up to date. With its combination of excellent basic and clinical science, this book is extremely valuable for students, investigators, and practitioners with interests in the cerebellum and diseases affecting its function. The book has been written by experts in the field, the writing is lucid, the chapters are thorough, and the coverage is extraordinary.’ From the Foreword by Sid Gilman   Department of Neurology, University of Michigan

The cerebellum was for many years a relatively neglected component of the central nervous system. Recently, however, there have been major advances in the understanding of motor and nonmotor operations of the cerebellum, including its role in cognition, and important discoveries in the genetics of the cerebellar ataxias. This is a comprehensive text on the cerebellum and its disorders. It ranges from embryology and basic neuroanatomy to a thorough survey of the sporadic and hereditary disorders of the cerebellum. Models of cerebellar function and clinical-pathophysiological correlations are thoroughly covered, and there is an extensive and authoritative review of recent advances in the genetics of cerebellar diseases. The chapters are written by the leading international authorities on the cerebellum, including many of those who made fundamental discoveries in the field. The first comprehensive text on the cerebellum to be published for many years, this book will be essential reading for a wide range of basic and clinical neuroscientists, neurologists and others studying or treating cerebellar disorders. Mario-Ubaldo Manto is attached to the Cerebellar Ataxias Unit of the Free University of Brussels, and is Secretary of the Fondation de l’Ataxie Cérébelleuse. Massimo Pandolfo is Head of Service in Neurology, Free University of Brussels. He was formerly Adjunct Professor in the Department of Neurology at McGill University, Montreal.

The Cerebellum and its Disorders

Edited by

Mario-Ubaldo Manto Cerebellar Ataxias Unit Free University of Brussels Belgium

and

Massimo Pandolfo Department of Neurology Free University of Brussels Belgium

                                                     The Pitt Building, Trumpington Street, Cambridge, United Kingdom    The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY 10011-4211, USA 10 Stamford Road, Oakleigh, VIC 3166, Australia Ruiz de Alarcón 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http://www. cambridge.org © Cambridge University Press 2002 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2002 Printed in the United Kingdom at the University Press, Cambridge Typeface Utopia 8.5/12pt.

System QuarkXPress™ [  ]

A catalogue record for this book is available from the British Library ISBN 0 521 77156 0 hardback

Every effort has been made in preparing this book to provide accurate and up-to-date information which is in accord with accepted standards and practice at the time of publication. Nevertheless, the authors, editors and publisher can make no warranties that the information contained herein is totally free from error, not least because clinical standards are constantly changing through research and regulation. The authors, editors and publisher therefore disclaim all liability for direct or consequential damages resulting from the use of material contained in this book. Readers are strongly advised to pay careful attention to information provided by the manufacturer of any drugs or equipment that they plan to use.

Contents

List of contributors Preface Acknowledgments Foreword by Sid Gilman

page ix xvii xix xxi

PA RT I I N T R O D U C T I O N 11 Embryology of the cerebellum Mario-Ubaldo Manto

3

12 Neuroanatomy of the cerebellum Fernand Colin, Laurence Ris, and Emile Godaux

6

13 High-resolution cerebellar anatomy Arthur W. Toga and Colin Holmes

30

14 Neurotransmitters in the cerebellum Ole P. Ottersen and Fred Walberg

38

15 Structure and function of the cerebellum Amy J. Bastian and W. Thomas Thach

49

PA RT II T H E O R I E S O F C E R E B E L L A R CONTROL 16 Models of cerebellar function Steve G. Massaquoi and Helge Topka

69

PA RT I I I C L I N I C A L S I G N S A N D PAT H O PH Y S I O LO G I C A L C O R R E L AT I O N S 17 Clinical signs of cerebellar disorders Mario-Ubaldo Manto 18 Pathophysiology of clinical cerebellar signs Helge Topka and Steve G. Massaquoi

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19 The role of the cerebellum in affect and psychosis Jeremy D. Schmahmann

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23 Other cerebellotoxic agents Mario-Ubaldo Manto and Jean Jacquy

342

PA RT V I A DVA N C E S I N G R A F TS PA RT I V S P O R A D I C D I S E A S E S 10 Congenital malformations of the cerebellum and posterior fossa Joseph R. Madsen, Tina Young Poussaint, and Patrick D. Barnes 11 Multiple system atrophy and idiopathic late-onset cerebellar ataxia José Berciano

24 Cerebellar grafts Lazaros C. Triarhou 161

PA RT V I I N E U R O PAT H O LO G Y 178

12 Corticobasal degeneration Mario-Ubaldo Manto and Jean Jacquy

198

13 Cerebellar stroke Serge Blecic and Julien Bogousslavsky

202

14 Immune diseases Pierre Duquette

228

15 Infectious diseases: radiology and treatment of cerebellar abscesses Jeffrey Weinberg

237

16 Other infectious diseases Mario-Ubaldo Manto

248

17 Cerebellar disorders in cancer Jerzy Hildebrand and Danielle Balériaux

265

18 Posterior fossa trauma Matthias Maschke, Uwe Dietrich, and Dagmar Timmann-Braun

288

25 Neuropathology of the inherited ataxias Arnulf H. Koeppen

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PA RT V I I I D O M I N A N T LY I N H E R I T E D P R O G R E S S I V E ATAX I A S 26 Spinocerebellar ataxia type 1 Xi Lin, Harry T. Orr, and Huda Y. Zoghbi

409

27 Spinocerebellar ataxia type 2 Stefan-M. Pulst

419

28 Spinocerebellar ataxia type 3 S.H. Subramony and Paraminder J.S. Vig

428

29 Spinocerebellar ataxia type 4 Ying-Hui Fu and Louis J. Ptacek

440

30 Spinocerebellar ataxia type 5 445 Christina L. Liquori, Lawrence J. Schut, H. Brent Clark, John W. Day, and Laura P.W. Ranum 31 Spinocerebellar ataxia type 6 Marina Frontali and Carla Jodice

19 Thyroid hormone and cerebellar development 305 Noriyuki Koibuchi 20 Endocrine disorders: clinical aspects Mario-Ubaldo Manto and Henryk Zulewski

369

32 Autosomal dominant cerebellar ataxia with progressive pigmentary macular dystrophy Giovanni Stevanin, Anne-Sophie Lebre, Cecilia Zander, Géraldine Cancel, Alexandra Dürr, and Alexis Brice

451

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21 Alcohol toxicity in the cerebellum: fundamental aspects 327 Roberta Pentney

33 Spinocerebellar ataxia type 8 Melinda L. Moseley, Lawrence J. Schut, John W. Day, and Laura P.W. Ranum 34 Dentatorubral-pallidoluysian atrophy Shoji Tsuji

481

22 Alcohol toxicity in the cerebellum: clinical aspects Mario-Ubaldo Manto and Jean Jacquy

35 Molecular mechanisms of triplet repeat expansions in ataxias Robert D. Wells

PA RT V TOX I C AG E N T S

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Contents

PA RT I X R E C E S S I V E ATAX I A S 36 Friedreich’s ataxia Massimo Pandolfo

505

37 Early-onset inherited ataxias Guiseppe De Michele and Alessandro Filla

519

38 Ataxia telangiectasia and variants Susan Perlman, Jacques-Olivier Bay, Nancy Uhrhammer, and Richard A. Gatti

531

39 Ataxia in mitochondrial disorders 548 Massimo Zeviani, Carlo Antozzi, Mario Savoiardo, and Enrico Bertini 40 Episodic ataxias as ion channel diseases Maria Cristina D’Adamo, Paulo Imbrici, and Mauro Pessia

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Index

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Contributors

Carlo Antozzi MD Neurologist Neuromuscular Research Department National Neurological Institute ‘Carlo Besta’ Via Celoria 11 Milan 20133 Italy E-mail: [email protected] Danielle Balériaux MD Professor and Head Clinique de Neuroradiologie l’Hôpital Erasme Université Libre de Bruxelles 808 Route de Lennik B-1070 Brussels Belgium E-mail: [email protected] Patrick D. Barnes MD Director of Neuroradiology Department of Radiology Children’s Hospital 300 Longwood Avenue Boston Massachusetts 02115 USA

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Amy J. Bastian PT, PhD Assistant Professor Physical Therapy and Neurobiology Program in Physical Therapy Washington University Medical School 4444 Forest Park Boulevard Box 8502 St Louis Missouri 63108 USA E-mail: [email protected] Jacques-Olivier Bay MD, PhD Centre Jean Perrin Departement d’Oncologie Moléculaire 63000 Clermont-Ferrand France José Berciano PhD Professor and Chair of Neurology Service of Neurology University Hospital ‘Marqués de Valdecilla’ University of Cantabria 39008 Santander Spain E-mail: [email protected] Enrico Bertini MD Chief of the Unit of Molecular Medicine Department of Neurosciences Division of Neurology Bambino Gesù Hospital Piazza S. Onofrio 4 Rome 00165 Italy E-mail: [email protected] Serge Blecic MD Associate Professor of Neurology Service de Neurologie l’Hôpital Erasme Université Libre de Bruxelles 808 Route de Lennik B-1070 Brussels Belgium E-mail: [email protected]

Julien Bogousslavsky MD Professor and Chair University Department of Neurology Service de Neurologie Centre Hospitalier Universitaire Vaudois 11 Rue de Bugnon CH-1011 Lausanne Switzerland E-mail: [email protected] Alexis Brice MD Head Neurogenetics Group INSERM U289 l’Hôpital de la Salpêtrière 47 boulevard de l’Hôpital 75651 Paris Cedex 13 France E-mail: [email protected] Géraldine Cancel PhD Neurogenetics Group INSERM U289 l’Hôpital de la Salpêtrière 47 boulevard de l’Hôpital 75651 Paris Cedex 13 France E-mail: [email protected] H. Brent Clark MD, PhD Professor Department of Laboratory Medicine/Pathology University of Minnesota Box 174 Mayo 420 Delaware Street SE Minneapolis Minnesota 55455 E-mail: [email protected] Fernand Colin Formerly, Professor of Neurophysiology Faculté de Médecine Laboratoire de Physique Biomedicale Université Libre de Bruxelles 808 Route de Lennik B-1070 Brussels Belgium E-mail: [email protected]

List of contributors

Maria Cristina D’Adamo PhD Student Department of Vascular Medicine and Pharmacology Istituto di Ricerche Farmacologiche ‘Mario Negri’ Consorzio Mario Negri Sud 66030 Santa Maria Imbaro Chieti Italy E-mail: [email protected] John W. Day MD, PhD Associate Professor Department of Neurology Institute of Human Genetics University of Minnesota Minneapolis USA E-mail: [email protected] Guiseppe De Michele MD Senior Lecturer in Neurology Department of Neurological Sciences Medical School Federico II University Via S. Pansini 5 I-80131 Naples Italy E-mail: [email protected]. Uwe Dietrich MD Resident in Neuroradiology Department of Neuroradiology University Clinic Essen Hufelandstrasse 55 45122 Essen Germany Pierre Duquette MD Professor of Neurology Director, Notre-Dame MS Clinic Chairman, Neurology Division Service de Neurologie l’Hôpital Notre-Dame 3e Pavillon Deschamps – H 3135 1560 est, rue Sherbrooke Montreal Quebec H2L 4M1 Canada E-mail: [email protected]

Alexandra Dürr MD, PhD Head of the DNA and Cell Bank Neurogenetics Group INSERM U289 Neurogenetics Group l’Hôpital de la Salpêtrière 47 boulevard de l’Hôpital 75651 Paris Cedex 13 France E-mail: [email protected] Alessandro Filla MD Associate Professor of Neurology Department of Neurological Sciences Medical School Federico II University Via S. Pansini 5 I-80131 Naples Italy E-mail: afi[email protected] Marina Frontali MD Senior Researcher Istituto di Medicina Sperimentale del CNR Via Fosso del Cavaliere 00133 Rome Italy E-mail: [email protected] Ying-Hui Fu PhD Associate Professor Department of Neurobiology and Anatomy University of Utah Salt Lake City Utah 84112 USA E-mail: [email protected] Richard A. Gatti MD Department of Pathology UCLA School of Medicine Los Angeles California 90095-1732 USA E-mail: [email protected]

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Emile Godaux MD PhD Professor and Head of the Department of Neuroscience Laboratoire de Neurosciences Faculty of Medicine Université de Mons-Hainaut 20 Place du Parc 7000 Mons Belgium E-mail: [email protected] Jerzy Hildebrand MD, PhD Professor and Head of Neurology Service de Neurologie l’Hôpital Erasme Université Libre de Bruxelles 808 Route de Lennik B 1070 Brussels Belgium E-mail: [email protected] Colin Holmes PhD Research Associate Laboratory of Neuro Imaging Room 4238 Reed Building Department of Neurology UCLA School of Medicine 710 Westwood Plaza Los Angeles California 90095-1769 USA E-mail: [email protected] Paolo Imbrici PhD Postdoctoral Fellow Department of Vascular Medicine and Pharmacology Istituto di Ricerche Farmacologiche ‘Mario Negri’ Consorzio Mario Negri Sud 66030 Santa Maria Imbaro Chieti Italy E-mail: [email protected]

Jean Jacquy MD, PhD Professor of Pathology of the Central Nervous System, and Head Department of Neurology Centre Hospitalier Universitaire de Charleroi (CHU) Université Libre de Bruxelles 92 Boulevard Paul Janson 6000 Charleroi Belgium E-mail: [email protected] Carla Jodice MD Assistant Professor of Genetics Department of Biology Tor Vergata University Via della Ricerca Scientifica 00100 Rome Italy E-mail: [email protected] Arnulf H. Koeppen MD Professor of Neurology Neurology Service Veterans Affairs Medical Center Albany New York 12208 USA E-mail: [email protected] Noriyuki Koibuchi MD, PhD Professor Department of Physiology Gunma University School of Medicine Maebashi Gunma 371–8511 Japan E-mail: [email protected] Anne-Sophie Lebre MS PhD Student Neurogenetics Group INSERM U289 Hôpital de la Salpêtrière 47 boulevard de l’Hôpital 75651 Paris Cedex 13 France E-mail: [email protected]

List of contributors

Xi Lin MD, PhD Postdoctoral Associate Howard Hughes Medical Institute Baylor College of Medicine Houston Texas 77030 USA E-mail: [email protected] Christina L. Liquori BS Graduate Student Department of Genetics, Cell Biology, and Development Institute of Human Genetics Box 206 UMHC 420 Delaware Street SE University of Minnesota Minneapolis 55455 USA E-mail: [email protected] Joseph R. Madsen MD Associate in Neurosurgery Department of Neurosurgery Children’s Hospital 300 Longwood Avenue Boston Massachusetts 02115 USA E-mail: [email protected]>Harvard.edu Mario-Ubaldo Manto MD, PhD Director Cerebellar Ataxias Unit Belgian National Research Foundation Centre Hospitalier Universitaire de Charleroi (CHU) 92 Boulevard Paul Janson 6000 Charleroi Belgium E-mail: [email protected] Matthias Maschke MD Resident in Neurology Department of Neurology University Clinic Essen Hufelandstrasse 55 45122 Essen Germany E-mail: [email protected]

Steve G. Massaquoi MD, PhD Assistant Professor Department of Electrical Engineering and Computer Science and Division of Health Sciences and Technology Massachusetts Institute of Technology Cambridge Massachusetts USA E-mail: [email protected] Melinda L. Moseley MMC 206 515 Delaware St. S.E. Department of Genetics, Cell Biology and Development Institute of Human Genetics University of Minnesota USA E-mail: [email protected] Harry T. Orr PhD Professor and Director Institute of Human Genetics University of Minnesota Minneapolis Minnesota 55455 USA E-mail: [email protected] Ole P. Ottersen MD, PhD Professor of Anatomy Department of Anatomy Institute of Basic Medical Sciences University of Oslo P.O. Box 1105 Blindern N-0317 Oslo Norway E-mail: [email protected] Massimo Pandolfo MD Service de Neurologie Université Libre de Bruxelles l’Hôpital Erasme Route de Lennik 808 B-1070 Bruxelles Belgium E-mail: [email protected]

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Roberta Pentney PhD Professor of Anatomy and Cell Biology Department of Anatomy and Cell Biology School of Medicine and Biomedical Sciences State University of New York at Buffalo 317 Farber Hall Buffalo New York 14214-3000 USA E-mail: [email protected]ffalo.edu

Laura P.W. Ranum PhD Associate Professor Department of Genetics, Cell Biology, and Development Institute of Human Genetics Box 206 UMHC 516 Delaware Street SE University of Minnesota Minneapolis 55455 USA E-mail: [email protected]

Susan Perlman MD Department of Neurology UCLA School of Medicine Los Angeles California 90095 USA

Laurence Ris Laboratoire de Neurosciences Université de Mons-Hainaut 20 Place du Parc 7000 Mons Belgium

Mauro Pessia PhD Unit Chief Department of Vascular Medicine and Pharmacology Istituto di Ricerche Farmacologiche ‘Mario Negri’ Consorzio Mario Negri Sud 66030 Santa Maria Imbaro Chieti Italy E-mail: [email protected]

Mario Savoiardo MD Head Division of Neuroradiology National Neurological Institute ‘Carlo Besta’ Via Celoria 11 Milan 20133 Italy E-mail: [email protected]

Louis J. Ptacek MD Associate Professor Department of Neurology and Human Genetics Associate Investigator Howard Hughes Medical Institute University of Utah Salt Lake City Utah 84112 USA E-mail: [email protected] Stefan-M. Pulst MD Professor of Medicine UCLA School of Medicine 8631 W. 3rd Street Los Angeles California 90048 USA E-mail: [email protected]

Jeremy D. Schmahmann MD Director Ataxia Unit Cognitive/Behavioral Neurology Unit Massachusetts General Hospital Burnham 823 Fruit Street Boston Massachusetts 02114 USA E-mail: [email protected] Lawrence J. Schut MD Assistant Professor Department of Neurology CentraCare Clinic St Cloud Minnesota USA

List of contributors

Giovanni Stevanin PhD Post-Doctoral Fellowship of the Société de Secours des Amis des Sciences Neurogenetics Group INSERM U289 l’Hôpital de la Salpêtrière 47 boulevard de l’Hôpital 75651 Paris Cedex 13 France E-mail: [email protected] S.H. Subramony MD Professor of Neurology Department of Neurology University of Mississippi Medical Center 2500 North State Street Jackson Mississippi 39216 USA E-mail: [email protected] W. Thomas Thach MD Professor of Neurobiology and Neurology Department of Anatomy and Neurobiology Washington University School of Medicine 4566 Scott Avenue Box 8108 St Louis Missouri 63110-1031 USA E-mail: [email protected] Dagmar Timmann-Braun MD Professor of Neurology Department of Neurology University Clinic Essen Hufelandstrasse 55 45122 Essen Germany E-mail: [email protected] Arthur W. Toga PhD Professor of Neurology and Director Laboratory of Neuro Imaging Department of Neurology Room 4238, Reed Building UCLA School of Medicine 710 Westwood Plaza Los Angeles California 90095-1769 USA E-mail: [email protected]

Helge Topka MD, PhD Assistant Professor Department of Neurology University of Tübingen Hoppe-Seyler-Strasse 3 72076 Tübingen Germany E-mail: [email protected] Lazaros C. Triarhou MD, MSc, PhD Formerly Professor of Pathology (Neuropathology) and Medical Neurobiology PO Box 18039 54007 Thessaloniki (11) Greece E-mail: [email protected] Shoji Tsuji MD, PhD Professor Department of Neurology Brain Research Institute Niigata University 1 Asahimachi Niigata 951 Japan E-mail: [email protected] Nancy Uhrhammer PhD Departement d’Oncologie Moléculaire Centre Jean Perrin 63000 Clermont-Ferrand France Paraminder J.S. Vig PhD Associate Professor (Research) Department of Neurology University of Mississippi Medical Center 2500 North State Street Jackson Mississippi 39216 USA E-mail: [email protected] Fred Walberg MD, PhD Professor Emeritus Department of Anatomy Institute of Basic Medical Sciences University of Oslo PO Box 1105 Blindern N-0317 Oslo Norway E-mail: [email protected]

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Jeffrey S. Weinberg MD Assistant Professor Department of Neurosurgery University of Texas M. D. Anderson Cancer Center 1515 Holcombe Boulevard Box 442 Houston Texas 77030–4095 E-mail: [email protected] Robert D. Wells PhD Professor and Director Center for Genome Research Institute of Biosciences and Technology Texas A&M University System Health Science Center 2121 W. Holcombe Boulevard Houston Texas 77030-3303 USA E-mail: [email protected] Tina Young Poussaint MD Neuroradiologist Department of Radiology Children’s Hospital 300 Longwood Avenue Boston Massachusetts 02115 USA E-mail: [email protected] Cécilia Zander MS PhD Student Neurogenetics Group INSERM U289 l’Hôpital de la Salpêtrière Paris France E-mail: [email protected]

Massimo Zeviani MD, PhD Head of the Division of Biochemistry and Genetics National Neurological Institute ‘Carlo Besta’ Via Celoria 11 Milan 20133 Italy E-mail: [email protected] Huda Y. Zoghbi MD Professor, Departments of Pediatrics, Neurology, Neuroscience, and Molecular and Human Genetics Howard Hughes Medical Institute Baylor College of Medicine One Baylor Plaza Mail Stop 225 Houston Texas 77030 E-mail: [email protected] Henryk Zulewski MD Laboratory of Molecular Endocrinology Massachusetts General Hospital Harvard Medical School 50 Blossom Street Boston Massachusetts 02114 USA

Preface

Our knowledge of cerebellar functions has increased exponentially during the last two decades. Powerful new neuroimaging techniques and the spectacular development of molecular biology are probably the most striking examples of developments that have completely changed the field. We started the project that led to this book because we were convinced that the time was ripe for an updated, comprehensive text attempting to summarize this new knowledge and present it in a coherent, systematic fashion. In preparing this book, our aim was to present the current perspective on the functional roles of the cerebellum as well as on the clinical and pathophysiological aspects of cerebellar diseases. We wanted to provide a comprehensive review of the major advances of these last years. The Cerebellum and its Disorders is divided into nine parts, each giving an overview of a particular area. In each chapter the latest discoveries are presented in the context of their clinical relevance. In Part I, the fundamental aspects of cerebellar structure and functions are covered. This part serves as the basis for those that follow. Part II addresses the main models of cerebellar function that have been proposed so far. Part III includes an overview of cerebellar symptoms and their pathophysiology, including the emerging concepts on the cognitive roles of the cerebellum and their clinical implications. Part IV addresses the broad spectrum of sporadic cerebellar disorders. Part V deals with the effect of toxic agents on the cerebellum. Part VI covers the growing area of cerebellar grafts. Part VII summarizes the neuropathology of cerebellar disorders. Parts VIII and IX are dedicated to the genetics of dominant and recessive cerebellar ataxias, respectively. For each chapter, we attempted to provide the most accurate and updated information. The exceptional quality of

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the contributors, all internationally renowned researchers and clinicians from around the world, is a guarantee in this sense. The book edited by Sid Gilman, James Bloedel, and Richard Lechtenberg in 1981 long remained the referMario-Ubaldo Manto, Brussels Massimo Pandolfo, Brussels

ence work in the area of diseases of the cerebellar system. We hope that this volume will take its place and remain a major reference in the rising discipline of ataxiology.

Acknowledgments

The completion of this book was dependent upon the committed efforts of the authors. We are particularly grateful to them. They took time out from their busy research, teaching schedules, and clinical duties. We gratefully acknowledge the precious help of all the editorial staff of Cambridge University Press. We were extremely fortunate to work with Dr Richard Barling, Publishing Director, who brought to this book a level of enthusiasm that inspired us. His colleagues coordinated the work with thoughtfulness and intelligence. We are also impressed by the meticulous work of Jane Smith who carefully read each chapter. The book could not have been completed without their tireless efforts.

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Foreword

During the last two decades, research in basic neuroscience has advanced at an astonishing pace. The advances stem from a growing interest in the nervous system by scientists, the rapid adaptation of molecular biological techniques to basic neuroscience research, and improvements in technology such as the widespread use of neural cell cultures and brain slices for examining the interactions between neurotransmitters and neurotransmitter receptors. Advances in clinical neurology have occurred in parallel, stemming in part from progress in the basic sciences and in part from the development of new technologies, notably structural and functional imaging, including computed tomography, magnetic resonance imaging, angiography, positron emission tomography and single photon emission computed tomography. As in the case of basic neuroscience, molecular biological and particularly molecular genetic approaches have enhanced the identification of specific neurological disorders, notably these resulting from dominant genetic inheritance. The growth of information in both basic neuroscience and clinical neurology has led to the development of new pharmaceuticals for many disorders, including epilepsy, stroke, movement disorders, and multiple sclerosis, to name just a few. The rapid expansion of new knowledge in the basic and clinical aspects of neuroscience pertains to the cerebellum and its afferent and efferent pathways as well as to the rest of the nervous system. Information has accumulated rapidly concerning the embryology, anatomy, physiology, and pharmacology of the cerebellum. Knowledge has also expanded about the clinical aspects of cerebellum function and cerebellar disorders. As an example, we now have a new classification of the dominantly inherited ataxias and growing insight into the underlying biochemical disorders at a molecular level. Functional imaging techniques have given new information about the myriad stimuli that

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activate the cerebellum, not only sensory and motor, but also cognitive. Moreover, cerebellar function has been linked to specific higher cognitive processes, including affect. In this volume, the editors have brought together an outstanding group of contributors who have accomplished the daunting task of thoroughly reviewing the basic sciences relevant to the cerebellum as well as the major clinical disorders affecting the cerebellum. Although the emphasis of the volume is on clinical aspects of cerebellar function, the book contains excellent reviews of the current status of the embryology, anatomy, physiology, and

pharmacology of the cerebellum. The coverage is both complete and up to date. With its combination of excellent basic and clinical science, this book is extremely valuable for students, investigators, and practitioners with interests in the cerebellum and diseases affecting its function. The book has been written by experts in the field, the writing is lucid, the chapters are thorough, and the coverage is extraordinary. Sid Gilman   Department of Neurology University of Michigan

Part I

Introduction

1

Embryology of the cerebellum Mario-Ubaldo Manto Cerebellar Ataxias Unit, Free University of Brussels, Belgium

The development of the cerebellum Although cerebellum differentiates early during embryogenesis, it only reaches its final configuration several months after birth (Koop et al., 1986 ; Lechtenberg, 1993). The neural tube is initially composed of a pair of neural folds which will fuse in the midline dorsally. The embryonic neural groove closes to become the neural tube at four weeks of gestation. The fusion proceeds from the most rostral region to the most caudal. When the rostral neuropore closes, three brain vesicles can be identified: the forebrain, the midbrain, and the hindbrain (three-vesicle stage). The hindbrain is also called rhombencephalon. At five weeks, the forebrain and the hindbrain both subdivide (five-vesicle stage). The hindbrain is generating the metencephalon rostrally and the myelencephalon caudally. Metencephalon and myelencephalon are separated by the pontine flexure of rhombencephalon. Cerebellum was thought to originate exclusively from metencephalon, but it has been shown that caudal mesencephalon also participates in the genesis of the rostral parts of cerebellum. The superior vermis begins to be formed at about seven to eight weeks of gestation, and the fusion of the inferior vermis continues up to about 18 weeks. The superior rhombic lip and the adjacent parts proliferate to generate the rudiment of the cerebellum (Fig. 1.1A). The central cavity of rhombencephalon becomes the fourth ventricle. In the following weeks, cerebellar development is characterized macroscopically by an expansion in four directions: rostrally, caudally, dorsally, and laterally. At the fifth month, the cerebellum of the fetus clearly shows two identifiable lobar masses laterally: the cerebellar hemispheres (Fig. 1.1B).

Fig. 1.1 A: illustration of the cerebellar rudiment in a fetus at the third month of gestation (sagittal section). B: Cerebellar hemispheres can be identifiable as two lobar masses located laterally at the fifth month of gestation (posterior view).

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Fig. 1.2 This figure illustrates the genesis of fissures. Posterolateral fissure (A) emerges before the primary fissure (B). Subsequently, the secondary fissure and the prepyramidal fissures appear (C), followed by a development of the anterior lobe rostrally (D).

Genesis of fissures Transverse fissures appear progressively on the surface. The first to emerge is the posterolateral fissure (Fig. 1.2), under which flocculi and subsequently the nodulus can be distinguished. The flocculus and superior cerebellar peduncle are discernible at day 45 (O’Rahilly et al., 1988). The posterolateral fissure is usually apparent by week nine. At this stage, the flocculonodular lobe is the most caudal. At the end of the third month, the primary fissure appears and demarcates the anterior lobe from the posterior parts of cerebellum. In addition, two grooves can be distinguished: the secondary fissure, which isolates the uvula, and the prepyramidal fissure, which demarcates the pyramid.

Migration of primitive cells and genesis of deep cerebellar nuclei All cerebellar neuroblasts arise from a germinal matrix consisting of a neuroepithelial ventricular zone and the rhombic lip. The ventricular neuroepithelium is responsible for the generation of the nuclear cells and Purkinje cells. The origin of the interneurons in the cerebellar cortex

Fig. 1.3 The three successive migration stages of primitive cells. (I) Genesis of nuclear neuroblasts from the ventricular epithelium. (II) Radial outward migration of Purkinje neuroblasts and tangential migration of the external granular layer (EGL). (III) Inward migration of granule cell neuroblasts which emerge from the EGL. The interneurons are not illustrated.

is both the metencephalon and the mesencephalon, unlike the granule cells. Indeed, these neurons arise from the external granular layer, which originates exclusively from the metencephalon. Golgi cell neuroblasts have the same origin as nuclear neuroblasts and Purkinje neuroblasts, whereas the external granular layer will also produce basket cell neuroblasts and stellate cell neuroblasts. The migration of primitive cells over the surface of cerebellum begins at about 11–12 weeks of gestation. Three migration stages can be identified (Fig. 1.3). The first stage

Embryology of the cerebellum

is characterized by the generation of nuclear neuroblasts from the ventricular epithelium. The deep cerebellar nuclei appear between 11 and 12 weeks. There is an intense growth of the dentate nuclei between week 20 and week 25 (Mihajlovic and Zecevic, 1986). At the second stage, a radial outward migration of Purkinje neuroblasts occurs, as well as a tangential migration of the external granular layer. Purkinje precursors are grouped in clusters initially. The Purkinje cell layer is apparent as a one-cell-thick layer of cells between weeks 17 and 28. The synapses between parallel fibers and Purkinje cells form at week 24. The third stage is characterized by an inward migration of the external granular layer, occurring at about 30 weeks after conception and persisting after birth. The neuronal migration is under the influence of critical factors, including the recently identified genes reeler and disabled (dab1). The reeler gene encodes for reelin, an extracellular matrix glycoprotein secreted by the external granular layer, whereas dab1 codes for cytoplasmic protein which is an adaptor molecule expressed and tyrosinephosphorylated in the developing nervous system. During the growth of cerebellum, cells expressing Dab1 protein are next to those secreting reelin. In mice with targeted disruption of the dab1 gene, foliation is absent and Purkinje cells are clumped in clusters. Dab1 protein might act in a parallel pathway or downstream of reelin, leading to the transformation of embryonic Purkinje cell clusters into the adult parasagittal bands (Gallagher et al., 1998). During the development of cerebellum, the number of Purkinje cells determines the size of the population of granule neurons. Purkinje cells are able to control the mitotic activity of granule cell neuroblasts within the exter-

nal granular layer. Interestingly, knockout mice for the Math 1 gene (a gene encoding a transcription factor specifically expressed in the precursors of the external granular layer) show an absence of the external granular layer (Ben-Arie et al., 1997). The Math 1 gene seems to be required in granule cell lineage. The external granular layer will disappear progressively during the first year of life (Lechtenberg, 1993).

iReferencesi Ben-Arie, N., Bellen, H.J., Armstrong, D.L. et al. (1997). Math 1 is essential for genesis of cerebellar granule neurons. Nature 13: 169–72. Gallagher, E., Howell, B.W., Soriano, P., Cooper, J.A. and Hawkes, R. (1998). Cerebellar abnormalities in the disabled (mdab1-1) mouse. J Comp Neurol 14: 238–51 Koop, M., Rilling, G., Herrmann, A. and Kretschmann, H.J. (1986). Volumetric development of the fetal telencephalon, cerebral cortex, diencephalon, and rhombencephalon including the cerebellum in man. Bibl Anat 28: 53–78 Lechtenberg, R. (1993). Embryogenesis of cerebellum. In: Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 13–16. New York: Marcel Dekker. Mihajlovic, P. and Zecevic, N. (1986). Development of the human dentate nucleus. Hum Neurobiol 5: 189–97 O’Rahilly, R., Mullet, F., Hutchins, G.M. and Moore, G.W. (1988). Computer ranking of the sequence of appearance of 40 features of the brain and related structures in staged human embryos during the seventh week of development. Am J Anat 182: 295–317.

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Neuroanatomy of the cerebellum Fernand Colin1, Laurence Ris2, and Emile Godaux2 1 2

formerly, Department of Neurophysiology, Free University of Brussels, Belgium Laboratory of Neurosciences, University of Mons-Hainaut, Belgium

Introduction In humans, the cerebellum overlies the posterior parts of the pons and medulla, occupying a large part of the posterior fossa. Structurally, the cerebellum consists of four pairs of deep nuclei, embedded in white matter, and is surrounded by a cortical mantle of gray matter. Unlike in the cerebral cortex, the cytoarchitecture of the cerebellum is remarkably uniform. This chapter reviews the fundamental aspects of the macroscopic and microscopic anatomy of the cerebellum, with emphasis on aspects of functional importance.

In addition, some species have developed a tremendous enlargement of particular parts. Cetacea have an enlarged dorsal part of the paraflocculus. In weak electric fish, the valvula, related to the lateral line, is so huge that it covers the brain completely. It is remarkable that these fish, which rely on measurement of the self-induced electric field along the lateral line to guide their movements in muddy water, have a very limited motor repertoire (Nieuwenhuys and Nicholson, 1969).

Macroscopic anatomy Evolution Cartilaginous fish have a transversal eminence at the level of the octavo-lateral line system (Schnitzlein and Faucette, 1969). Even in the lower species, the afferent pathway is not limited to the VIIIth nerve. Trigeminal somesthetic projections and a genuine spinocerebellar tract are present. The cytoarchitecture of the cerebellum has evolved with few refinements. In most teleosts and amphibians the cerebellum is a single leaf with lateral auricles (Fig. 2.1). In reptiles and birds, this original leaf duplicates in the rostral direction as a foliated fan-like structure, named the vermis because of its worm-like appearance. The posterior portions (the flocculus and paraflocculus) and their lateral expansions (the auricles) are the oldest phylogenetic part, making up the vestibulocerebellum. From birds to primates the number of folia increases significantly (22 in pigeons and 260 in humans). In parallel with this rostro-caudal expansion and the development of the cerebral cortex, there has been a continuous medio-lateral expansion of the hemispheres. The area of transition between the vermis and the hemispheres is called the intermediate region.

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Figures 2.2 and 2.3 illustrate the macroscopic anatomy of human cerebellum and a section showing the deep cerebellar nuclei, respectively.

Nomenclature The nomenclature of the subdivisions of the cerebellum in animals differs from that used in human anatomy. The folia are separated by shallow grooves and deeper fissures. Lobules are shown in Fig. 2.4A. In humans, Jansen divided the cerebellum into three main parts: (a) the anterior lobe, (b) the posterior lobe, and (c) the paraflocculus and flocculus, separated by fissura prima and fissura postero-lateralis respectively (see Fig. 2.2; Jansen, 1969). Larsell suggested a different nomenclature which is widely used in animals and is illustrated on the left of Fig. 2.4B (Larsell, 1970). Voogd noticed that the posterolateral fissure, instead of establishing rostro-caudal separation, introduced a medio-lateral division between the vermis and the lateral part of the posterior lobe up to Larsell’s lobule VI (Fig. 2.4B; Voogd, 1964). This is consistent with the fact that a strip of white matter divides the gray layer on the surface, and, in particular, interrupts the course of the

Neuroanatomy of the cerebellum

Fig. 2.1 Evolution. In amphibians (frogs) and many teleosts, the cerebellum is reduced to a single folium (A). From reptiles to primates, the number of folia increases (B, C, D). In fishes the cerebellum is often reduced to a single folium, but can be larger and have a rostral expansion, the valvula (E). At the level of the valvula, the granular layer lies under the pial surface and does not fold; granule cells do not migrate internally. Only the Purkinje and the molecular layers are folded, forming fine ridges. In mormyrids (F, G), the valvula is so huge that it covers all parts of the brain (F: side view). Viewed from above (G), the upper posterior part appears striated by the ridges, while the rest is smooth because it presents the unfolded granular layer. The cerebellum itself is completely embedded in the valvula and is not visible. Nevertheless, it is well developed and has four folia. (Modified from Voogd and Glickstein, 1998.)

parallel fibers. This rise of the white matter up to the surface might be due to secondary cortical atrophy, because it is absent in lower mammals and during the early stage of development in higher mammals such as cats. On the basis of mossy fiber projections to the cerebellar cortex, Dow considered three main areas: the flocculonodulus (vestibulocerebellum), the vermal anterior and posterior lobes with mainly spinal connections (paleocerebellum), and a medio-lateral part having principally cortico-ponto-cerebellar connections (neocerebellum) (Dow, 1942). Pontocerebellar and spinocerebellar afferents are mixed in the intermediate zone.

Afferences and efferences Afferences enter the cerebellum through three pairs of peduncles: the inferior peduncle or restiform body, the large middle peduncle or brachium pontis, and the superior peduncle or brachium conjunctivum (see Fig. 2.2B).

Efferences from the cerebellar nuclei leave the cerebellum through the superior and the inferior peduncles. The number of afferent fibers exceeds the number of efferences by a ratio of about 40:1. Three types of fibers enter the cerebellum: the climbing fibers, the mossy fibers, and the cholinergic/monoaminergic afferents. The climbing fibers arise exclusively from the contralateral inferior olive. They cross the midline and ascend in the restiform body. These fibers are thin (2 m), myelinated and relatively slow conducting (20 m/s). They fire at low frequency (1 Hz). Complete specific chemical destruction of the inferior olive by 3-acetylpyridine (3AP) is followed by degeneration of all climbing fibers in all areas of the cerebellar cortex (Desclin, 1974; Desclin and Colin, 1980). The mossy fibers arise from a large spectrum of ipsilateral and contralateral sources. They are large, myelinated, fast conducting and fire at high frequency. Finally, the cerebellum receives diffusely distributed cholinergic and mono-aminergic afferents.

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Fig. 2.3 The deep cerebellar nuclei. A section of human cerebellum in the plane of superior cerebellar peduncles showing the deep cerebellar nuclei: fastigial nucleus medially, globosus nucleus, emboliformis nucleus, and dentate nucleus more laterally.

The olivo-cerebellar system The cerebellar cortex Overview

Fig. 2.2 The human cerebellum. (A) Superior view showing the anterior lobe (red) and the rostral part of the posterior lobe. They are separated by the primary fissure (fissura prima). (B) Anterior–inferior view after transection of the cerebellar peduncles. The focculo-nodular lobe and the posterolateral fissure (fissura posterolateralis) are exposed. (C) Inferior view showing the posterior part of the posterior lobe and the flocculonodular lobe.

The cerebellar cortex and a set of central nuclei make up the basic structure of the cerebellum (Fig. 2.5). Mossy and climbing fibers excite the cortex and the nuclei, which are themselves inhibited by the cortex. Axons from the nuclei are the only output of the cerebellum. The cerebellar cortex contains more neurons and synapses than the rest of the brain. In order to pack such a huge number of interconnected elements into the smallest volume, the cerebellar cortex has a unique crystal-like structure. The folium is the morphological unit. Afferents and efferents run in the middle, and the three-layered cortex lies on both sides (Figs. 2.6 and 2.7).

The Purkinje cell Purkinje cells are arranged as a monolayer, the ganglionic layer, separating the outer molecular from the inner granular layer. In humans, the number of Purkinje neurons is estimated to about 15 million. Their pear-shaped soma has a 30-m short axis. A single axon leaves the lower rounded pole as a thin initial segment called the pre-axon. After about 30 m, it widens and becomes myelinated. In the granular layer these axons give off numerous collaterals whose course is oriented perpendicularly to the folium axis. They form the dense infra-ganglionic and supraganglionic plexus. Purkinje cells are gamma-aminobutyric

Neuroanatomy of the cerebellum

Fig. 2.4 Human and Larsell–Voogd’s nomenclature. (A) Human nomenclature, schematic representation of Jansen and Dow. (B) Link with the schematic representation of Larsell and Voogd. Stars mark fissura posterolateralis according to Voogd (see text for explanation). (Modified from Voogd and Glickstein, 1998.)

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Fig. 2.5 Model of the cerebellum. PC, Purkinje cell; m.f., mossy fiber; c.f., climbing fiber. (Modified from Ito, 1984.)

response of three to ten spikes at the level of the soma. The extracellular response was coined the ‘complex spike’ by Thach (Thach, 1967; see Chapter 5). It is not certain that each spike is conducted along the thin pre-axon. Despite this powerful excitation, two important inhibitory effects of the climbing fiber have been discovered. (a) When the 1 Hz background activity is stopped, either by 3-AP selective destruction (Colin et al., 1980) or by cooling the inferior olive, the spontaneous discharge rate of the Purkinje cell doubles. Conversely, when the climbing fiber frequency is experimentally driven above 1 Hz, the spontaneous activity decreases sharply, and above 5 Hz the Purkinje cell activity is limited to the complex spike response. This inhibition disappears within 10 s. (b) Experimentally, when the climbing fiber is stimulated simultaneously with the parallel fibers, the responsiveness of the latter decreases progressively. This inhibition persists for a long time after the climbing fiber ‘conjunctive’ stimulation (long-term depression). During development, Purkinje cells are innervated by several climbing fibers (Crépel, 1982). A single climbing fiber gives off about ten collaterals spreading in the parasagittal plane. Each of them reaches a single Purkinje cell. The number of olivary cells is thus about one-tenth of the number of Purkinje cells.

The granule cells acid-(GABA)ergic (Ito and Yoshida, 1964). Their targets are the deep nuclei and vestibular nuclei. Branches of the supra-ganglionic plexus inhibit the basket and stellate cells in the molecular layer (Llinas and Precht, 1969), and branches of the infra-ganglionic plexus inhibit the Golgi and the Lugaro cells in the granular layer. All these intracortical interneurons are themselves inhibitory. Some collaterals inhibit neighboring Purkinje cells (Bernard and Axelrad, 1993). A single primary dendrite emerges from the outer pole and fans out by branching inside a 35-m, thin, flat slice perpendicular to the folium axis. The width of this arbor is about 300 m. The terminal part of the dendrite is covered with numerous spines (80 000) which make small excitatory synapses with the parallel fibers (Fig. 2.7C). A single ascending climbing fiber winds around the smooth proximal part. This unmyelinated terminal contains 50-nm round synaptic vesicles, clustered in several hundreds of varicose enlargements, each of which abuts onto one to six stubby spines protruding from the dendrite. This unique connection between climbing fibers and Purkinje cell is the most powerful excitatory synapse in the brain. A single incoming spike produces a large excitatory post-synaptic potential (EPSP) of about 10 ms, which induces a repetitive

Granule cells are the main component of the granular layer. They are round or oval cells, with a diameter of 5–8 m. Nuclei appear naked because of the thinness of the rimming cytoplasm and the absence of discrete Nissl granules. In humans, the total number of granule cells has been evaluated to be between 1010 and 1011, with about 3 to 7 million cells/mm3. Each mossy fiber branches many times in several directions and folia. Their terminals end up in the granular layer, making a clubby enlargement called a ‘rosette’. This ending is part of a complex synaptic globular arrangement enclosed in a few sheets of glial membranes, the glomerulus (Fig. 2.7A). Rosettes make special ‘en marron’ excitatory synaptic contacts with clawshaped terminal branches of the granule cell dendrites. A single rosette makes synapses with about 100 different dendrites. Each granule cell presents about four to five dendrites. In addition to granule cell excitation, the rosette may stimulate an appendage of a descending dendrite of Golgi cells. Moreover, axons of Golgi cells make inhibitory synapses on the branches of the granule dendrites in close proximity to the excitatory synapses with the mossy fiber. The unmyelinated thin axon of the granule cells ascends vertically in the molecular layer, where it bifurcates in two branches (T-shaped) running parallel to the axis of the

Neuroanatomy of the cerebellum

Fig. 2.6 Stereodiagram of the cerebellar cortex. Note that the axon and the dendrite of the Golgi cell expand in all directions. Brush cells and Lugaro cells are not represented. (Modified from Eccles et al., 1967, and from Carpenter, 1985.)

folium in opposite directions. The mean diameter of these parallel fibers is around 0.2 m and the length of one branch has been evaluated to be between 2 and 7 mm. Synaptic vesicles are confined in varicose swellings which form excitatory synapses with the spines of the Purkinje cell dendrite. About 400 000 parallel fibers cross one Purkinje dendritic arbor, and about 80 000 parallel fibers make a single synapse with the 80 000 spines on one Purkinje cell. In addition to extracerebellar mossy fibers, two types of proprio-cerebellar mossy fibers are known: the first come from collaterals of axons of the nuclear cells (see Fig. 2.5), and the second emerge from the so-called unipolar brush cells (Fig. 2.8) (Mugnaini and Floris, 1994; Takács et al., 1999). The latter are densely stained with antiserum to calretinin, a calcium-binding protein. They reside in the granular layer. Their size is intermediate between that of granule cells and that of Golgi cells. They are characterized

by a single, thick dendrite terminating in a brush-like tip consisting of several branchlets. Unipolar brush cells are concentrated in the vestibulocerebellum. They are also found with a relatively high density in the lingula, at moderate-to-low density in other folia of the vermis, and in intermediate cortex. They are rare in lateral regions of cerebellum and in the dorsal paraflocculus. Interestingly, they are also located in the cochlear nucleus, a cerebellar-like structure (Floris et al., 1994). The functional role of the unipolar brush cells is not understood. Mossy fiber terminals form a special synapse with their dendrites, characterized by a long synaptic cleft with many sites of vesicle clustering. The neurotransmitter is trapped in the cleft for a long time. A single spike in the mossy fiber produces a 500 ms spike burst. This is an example of chemical integration. Their axon branches in the granular layer and, like ordinary mossy fibers, ends with a rosette which excites granule cell dendrites (Rossi et al., 1995; Fig. 2.8A).

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The synapse between parallel fibers and Purkinje cell The Purkinje cell has distinctive ultrastructural and biochemical features. Its agranular endoplasmic reticulum is extremely developed. Its membrane contains inositol 1,4,5-triphosphate (IP3) and ryanodine receptors (Kano et al., 1995). The complex spike activates voltage-controlled calcium channels and calcium entry triggers a huge calcium calcium release (CCR) from the reticulum (Llano et al., 1994). The level of cGMP is also very high in Purkinje cells and is increased during stimulation of the climbing and parallel fibers. This is probably related to the activation of guanylate-cyclase by nitric oxide (NO) liberated from the parallel fibers (see also Chapter 4). Recently, an endogenous substrate for a cyclic guanosine monophosphate (cGMP)-dependent protein kinase specific to Purkinje cells has been identified (Endo et al., 1999). Calcium entry and NO liberation during the simultaneous (‘conjunctive’) activation of the climbing and parallel fiber EPSPs are thought to be the first step of the chain leading to longterm depression of the synaptic transmission between parallel fibers and Purkinje cell dendrite (for a review see Crépel et al., 1996). This plasticity is widely proposed as a chemical memory trace enabling the cerebellar cortex to store critical information necessary for the control of movements. Stimulation of the parallel fibers alone induces a long-term potentiation of these synapses. Longterm depression and long-term potentiation could be respectively writing and erasing mechanisms.

The inhibitory interneurons The excitation on the Purkinje cell is balanced by the activity of inhibitory interneurons located in the molecular and granular layers.

Inhibitory interneurons of the molecular layer Fig. 2.7 Ultrastructure of some connections in the cerebellar cortex. (A) Ultastructure of a glomerulus. The enlarged extremity of a mossy fiber (the ‘rosette’) makes synaptic contacts with some dendrites of granule cells and a Golgi cell. It also receives synaptic contacts from axons of the Golgi cell. (Modified from Eccles et al., 1967.) (B) Ultrastructure of the synapse between basket cell axons and a Purkinje cell. (Modified from Eccles et al., 1967.) (C) Ultrastructure of Purkinje cell dendrites showing the dendritic spines and the synapses coupling parallel fibers to dendritic spines.

The basket cells are just above the ganglionic layer, with a ratio of one per six Purkinje cells (see Fig. 2.6). The dendritic tree expands into a hemi-ellipsoid whose base is centered on the soma. The top reaches the pial surface. The long axis is oriented perpendicular to the axis of the folium and is shorter than the long axis of the Purkinje cell dendrite (220 versus 350 m). The short axis is larger than the width of the Purkinje cell dendrite (60 versus 35 m). Basket cell dendrites have long spines, which also make synapses with the parallel fibers. So far, there is no evidence of plasticity at the level of these synapses. The basket cell axon runs on both sides over 350 m, perpendicular to the long axis of the folium, above the row of Purkinje cells (see Fig. 2.6). It gives off descending collaterals that surround the Purkinje cell soma, forming a basket-like structure, hence their name. The lower end of

Neuroanatomy of the cerebellum

Fig. 2.8 Summary of the olivo-cerebellar layout. (A) Intracortical circuits. Pc, Purkinje cells; gr, granule cells; pf, parallel fibers; ba, basket and stellate cells; Go, Golgi cells; Lc, Lugaro cells; bc, brush cells; mf, mossy fibers. Feedforward paths: (1) Direct excitation by the climbing fiber (not represented).Indirect excitation by the mossy fibers, via the granule cells. (2) Indirect excitation by the mossy fibers, via the brush cells, followed by the granule cells (in the vermis only).

the basket closely encircles the pre-axon in a peculiar structure called ‘pinceau’ (see Fig. 2.7B). The pre-axon is known to be the trigger zone of the axonal spike. One basket cell inhibits only eight to nine Purkinje cells. Basket cells are found only in birds and mammals. Stellate cells are located in the outer two-thirds of the molecular layer (see Fig. 2.6). Their soma is smaller than the soma of the Purkinje cells. Their dendrites make inhibitory synapses with the Purkinje cell dendrites outside the basket. Their axon is short. The total number of inhibitory interneurons in the

(3) Indirect inhibition by mossy fibers, via the granule cells, followed by the basket and stellate cells. (4) Indirect inhibition by the mossy fibers, via the Golgi cells (soma or descending dendrite), followed by the granule cells. The Golgi cells sense and gate the mossy fiber excitatory input. Feedback paths: (1) Collateral inhibition by the Purkinje axon recurrent collaterals. (2) Inhibition: by the Purkinje axon collaterals, via the Lugaro cells, followed by basket and stellate cells (disinhibition of the basket and stellate cells). (3) Excitation: by the Purkinje axon collaterals, via basket and stellate cells (disinhibition of the Purkinje cell). (4) Excitation: by the Purkinje axon collaterals, via the Golgi cells, followed by the granule cells (disinhibition of the granule cell). (B) Connections between the cerebellum and the precerebellar nuclei. B1: Connections with the mossy fiber precerebellar nuclei. Pc, gr and pf as in (A); lrn, lateral reticular nucleus; nu, cerebellar nuclei. The positive feedback between nu and lrn has been shown to oscillate when the negative feedback loop between nu and pc is abolished by picrotoxine (see Ito, 1984). These positive and negative feedback loops may be conceived respectively as providing and controlling the mean firing rate of pc and nu. These two loops have a ringing time in the ms range. B2–3: Connections with the inferior olive. cf, climbing fiber; oi, inferior olive; da, nucleus of Darkschevich. Two possibilities are considered. (B2) Due to the low frequency of the cf system and the scanty (doubtful) projection of cf to nu, cf collaterals to the nuclei are neglected. Furthermore, after a very short powerful excitation, cf are inhibitory on the pc. The B2 scheme emphasizes the inhibition of the climbing fibers. The loop pc, nu, oi, pc is a negative feedback and the loop pc, nu, da, oi, pc is a positive feedback. The interpretation is similar to that given in B1, except that the ringing time is now in the 10 seconds range. (B3) The focus is given to the excitation of cf on pc. The two loops of B2 have opposite effects. cf collaterals introduce an additional loop – nu, da, oi, nu – which is a positive feedback. These loops have a ringing time in the 1-second range.

molecular layer seems to have been underestimated. It has been shown that they outnumber the Purkinje cell by a ratio of 10:1 (Andersen et al., 1992; Pouzat and Hestrin, 1997). Purkinje cells, basket cells, and stellate cells share the same parallel fiber input.

Inhibitory interneurons of the granular layer Two types of inhibitory interneurons are located in the granular layer: the Lugaro cells and the Golgi cells (see Figs. 2.6 and 2.8). The Lugaro cells have a small fusiform soma and a

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horizontally expanding dendrite, both in the outer granular layer just under the Purkinje cells. Soma and dendrites receive massive innervation from Purkinje cell axon collaterals. The axon of the Lugaro cell ascends in the molecular layer and makes numerous symmetrical GABAergic synapses with the soma and dendrites of basket and stellate cells (Lainé and Axelrad, 1998). Golgi cells have a 6–16 m soma. They are outnumbered by the Purkinje cells (1:3). Golgi cells have vesicular nuclei and definite chromophilic bodies. The main excitatory synaptic input comes from the parallel fibers on the dendritic arbor, expanding about equally along the longitudinal and transversal dimensions of the folium. Dendrites of neighboring cells do not overlap. Golgi cells were said to have a descending dendrite directly stimulated by the rosettes of the mossy fibers, but more recent work points to excitation at the level of the soma. Golgi cells are inhibited by Purkinje cell collaterals. In the granular layer, branches of the axon occupy a field which is a mirror image of the dendritic one. As mentioned earlier, Golgi neurons inhibit the synaptic transmission between mossy fiber rosettes and granule cell dendrites. From their connections, Golgi cells sense and regulate the mossy fiber input. This gate is also controlled by Purkinje cells.

The cerebellar nuclei The dorso-caudal part of the lateral vestibular nucleus receives vermal Purkinje cell axons (Ito, 1984). This area is thus equivalent to a cerebellar nucleus. The cerebellar nuclei are the target of the Purkinje cell axons. Fish and amphibians have a single cerebellar nucleus; reptiles and birds have a medial and a lateral nucleus; lower mammals have a medial, an interpositus, and a lateral nucleus. In higher mammals, the interpositus is divided into an anterior and posterior part. In humans, the fastigial nucleus corresponds to the medial nucleus, the globosus to the anterior interpositus, the emboliformis to the posterior interpositus, and the dentate to the lateral nucleus, albeit the emboliform nucleus is often difficult to distinguish from the dentate. The size of the lateral group increases with the size of the cerebral cortex. In humans, the dentate nucleus contains 90% of the cerebellar nuclear neurons. The dentate nucleus appears as a convoluted band, having the shape of a folded bag, with the hilus directed medially (Carpenter, 1985). Two parts may be distinguished: a rostro-medial or magnocellular region, and a postero-lateral or parvocellular region. The dentate nucleus is composed mainly of large multipolar neurons. The largest soma have a diameter of 35 m in the medial group. Cells of the emboliform nucleus are similar to

those found in the dentate, whereas globosus nucleus includes both large and small multipolar neurons. Fastigial nucleus also contains cells of different sizes, with the smaller ones clustered in ventral areas of the nucleus. Nucleofugal fibers are excitatory everywhere except in the inferior olive. Glutamate has been shown to be the neuromediator (Schwarz and Schmitz, 1997; see also chapter 4). Nuclear cells receive a dense Purkinje cell innervation. On average, the ratio between Purkinje and nuclear cells is 26 :1 (Ito, 1984). A given nuclear cell receives about 14 terminals from the same Purkinje cell among about 12 000 other inhibitory terminals. The axon of one Purkinje cell gives off 500 terminals which contact 35 nuclear cells, and one nuclear cell receives terminals from 860 different Purkinje cells. Intranuclear recurrent collaterals have been described. These collaterals stimulate small non-projecting interneurons. Their number does not exceed 10% of the total neuronal population of the cerebellar nuclei. The overall inhibitory input to the nuclear cell represents 62% of the total synaptic input. The excitatory input on the nuclear cell comes from collaterals of the climbing and mossy fiber afferents. The arguments supporting the existence of climbing fiber collaterals have been reviewed by Ito (1984; see also De Zeeuw et al., 1997). It is difficult to conclude from studies of lesions of the inferior olive or from tracer studies whether collaterals of climbing fibers do exist, because ascending climbing fibers to the cerebellar cortex cross the cerebellar nuclei. The final evidence of the reality of climbing fiber input to cerebellar nuclei would be the ultrastructural demonstration of degenerating synaptic buttons after 3AP destruction of the inferior olive. So far, this evidence is still lacking. Despite a painstaking search of his material, Desclin failed to find such proof, although degenerating terminals were abundantly demonstrated in the molecular layer (unpublished results). At most, the climbing fiber collaterals are scant. Even if they were abundant, their impact on the global synaptic input would probably be negligible because of their low frequency. Thus, the excitatory input from the mossy fibers is the major excitatory input to the nuclear cells. Whatever their origin, they send collaterals to the nuclei, except the fibers emerging from the pontine nuclei. All nucleofugal fibers send collaterals which end in the granular layer as mossy fiber rosettes (see Fig. 2.5; Ito, 1984). The nucleo-cortical projections reach mostly the areas from which they receive Purkinje cell axons (BuisseretDelmas, 1988; Buisseret-Delmas and Angaut, 1988; Trott et al., 1998). However, several exceptions are known. For instance, the dentate projects to the vermis, but the Purkinje cells of the vermis do not send projections to the

Neuroanatomy of the cerebellum

Fig. 2.9 Architecture of the inferior olive. Different components of the inferior olive of the cat are represented in the lower part as six transverse slices. Above, the three main components are represented separately as their projection on a horizontal plane. DAO, dorsal accessory olive; MAO, medial accessory olive; PO, principal olive; MAO is the lower one, PO should be put above it mentally, and DAO on top. n,  nucleus of Kooy; dc, dorsal cap; dmcc, dorsomedial cell column; vlo, ventral lateral outgrowth. (Modified from Ito, 1984.)

dentate nucleus. So, these connections may be viewed either as a negative feedback loop or as an open loop communication between different areas of cerebellum.

The inferior olive The main subdivisions of the cat inferior olive are presented in Fig. 2.9. A major advance in the understanding of

the functional anatomy started in 1964 when Voogd discovered that the white matter of the cerebellum was divided into long longitudinal strips (Voogd, 1964; Fig. 2.10B). Anterograde degeneration studies and horseradish peroxidase (HRP) retrograde tracing have delineated eight major bands (A, X, B, C1, C2, C3, D1, and D2), each of which projects to well-circumscribed regions of the cerebellar nuclei and receives climbing fibers from specific areas of the inferior olive (Voogd and Glickstein, 1998; Fig. 2.10A). Stimulation of limb nerves also evokes climbing fiber responses along sagittal bands. However, in a given band, the map of a different body part evoked by natural stimuli is discontinuous, like a mosaic. The flocculus is divided into eight longitudinal, thin strips corresponding in pairs to four small parts of the inferior olive. These microzones correspond to functional micromodules. For example, the median H band has been shown to control the horizontal vestibulo-ocular reflex. Thus, the anatomical and functional unit of the olivocerebellar system consists of a sagittal band of cortex receiving climbing fibers from a small part of the inferior olive and sending its output to a small part of the nuclei. A given area in the inferior olive corresponds to a definite area in the output structure. By contrast, the organization of the mossy fiber input is not topologically coupled with the output system. This anatomical and functional subdivision of the olivocerebellar system finds support from the demonstration of a corresponding biochemical and immunological heterogeneity of the Purkinje cells distributed sagittally (Fig. 2.10C). This was disclosed first for the distribution of 5nucleotidase (Ito, 1984), then for the distribution of acetylcholinesterase, and, more recently, for the distribution of zebrin I and zebrin II (Hawkes et al., 1985; Gravel et al., 1987; Leclerc et al., 1992). The distributions are roughly congruent (for a review see Hawkes and Gravel, 1991). A sagittal distribution was also found for the muscarinic receptor in the rat (Jaarsma et al., 1995). The inferior olivary complex in humans comprises approximately 1.5 million cells. The size of these cells may vary slightly. The dendritic arbor expands widely around the soma, with a tendency to bend centrally. The olivary cell has some very distinctive features. In 1974, Llinas et al. discovered the existence of gaps between dendrites and described strong electrotonic coupling between cells (Llinas et al., 1974). The olivary complex is organized in functional units of cells, which tend to fire synchronously and project to the same sagittal band. Dendrites of olivary cells bear spines with a long, thin neck. Five to six spines from different cells cluster in glomerular structures where they make gap junctions.

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Fig. 2.10 Organization of the olivo-cerebellar system. (A) The eigth Voogd’s sagittal bands A to D2 with their projections to the cerebellar nuclei and the inferior olive. ANT, anterior lobe; ANS, ansiform lobule; B, the  nucleus of Kooy; D, dorsomedial cell column; DAO, dorsal accessory olive; DC, dorsal cap; dl, dorsal leaf; DR rostromedial dentate; FL, flocculus; IA anterior interpositus; IC, interstitial cell group; IP, posterior interpositus; LV, lateral vestibular nucleus; MAO, medial accessory olive; PFL, paraflocculus; PFLD, dorsal paraflocculus; PFLV, ventral paraflocculus; PMD, paramedian lobule; PO, principal olive; SI, lobule simplex; vl, ventral leaf; VLO, ventrolateral outgrowth; NO, nodulus; PY, pyramis; UV, uvula; F, fastigius. (B) Transverse section at the level of IA, stained for acetylcholinesterase. A to D2 bands can easily be recognized. bc, brachium conjunctivum; cr, restiform body. (C) Zebrin II bands 1 to 6. (Reprinted from Trends in Neurosciences, Vol. 21, Voogd, J. and Glickstein, M. The anatomy of the cerebellum, pp. 370–5, © 1998, with permission from Elsevier Science.)

Lucifer yellow intracellular injection shows a spread among up to eight cells. However, after injection of harmaline (a drug which greatly increases the spontaneous tendency of the olivary cell membrane potential to oscillate around 10 Hz) and picrotoxin, Llinas et al. found that up to 100 cells could fire simultaneously (Llinas and Volkind, 1973). Two categories of synapses were found on the spines (De Zeeuw et al., 1998). Firstly, symmetrical inhibitory GABAergic synapses were shown to originate from a population of small nuclear cells. The projection was congruent with the modular architecture of the olivo-cerebellar system. Secondly, asymmetrical synapses with rounded vesicles were also discovered. They were shown to be projections from the mesodiencephalic junction nuclear groups,

mainly from the nucleus of Darkschewitsch, which receives a projection from the cerebellar nuclei (De Zeeuw et al., 1998). Depending on the importance attributed to the efficacy of the climbing fiber collaterals, these two inputs, mesodiencephalic and nuclear, can be viewed differently (see Fig. 2.8B 2–3). Olivary cells are equipped with a set of conductances allowing them to fire at very low frequency between 1 and 10 Hz (Llinas and Yarom, 1981, 1986). The upper limit is established by a very long afterhyperpolarization of 100 ms. Nevertheless, the mean frequency is very close to 1 Hz in every species. Thus, the inferior olive translates its afferent inputs into a well-controlled, low-frequency discharge in time and distributed to a precise cluster of sagittally organized Purkinje cells in space.

Neuroanatomy of the cerebellum

The cerebellar afferent systems The mossy fiber system Overview Mossy fibers have numerous origins: somesthetic, vestibular, acoustic, visual, and cortical. Except for a few fibers of the vestibular nerve, they relay at least once along their course to the cerebellum. They have been traced by numerous neuronatomical techniques, completed by electrophysiological methods. The immense wealth of data available was obtained from experiments on animals: rats, rabbits, cats and, less frequently, primates. Extrapolation to humans should be cautious because the cerebral cortex takes over functions assumed at a lower level in animals. The pyramidal tract has a conspicuous importance in humans, whereas the rubrospinal tract regresses. However, if the human pyramidal paths contain about one million fibers, the extrapyramidal pathways have still about 20 times more fibers. These descending pathways control the transfer of neural information at relays along both the mossy and climbing fiber paths.

The spinocerebellar tracts A single spinocerebellar tract is described in fish. In mammals, 11 climbing or mossy fiber paths, crossed or uncrossed, were reviewed by Matsushita et al. (1979). They end mainly in the anterior lobe, the paramedian lobule, and pyramis of the posterior lobe. The classical dorsal and ventral spinocerebellar tracts of Flechsig and Gowers will be presented first.

The dorsal spinocerebellar tract The dorsal spinocerebellar tract (DSCT; Flechsig’s tract) arises from Clarke’s column, located medially at the base of the dorsal horn in the thoracic and upper lumbar segments. DSCT is an uncrossed tract conveying information mainly from the hind limbs and entering the cerebellum via the inferior cerebellar peduncle. Clarke’s cells are large and receive collaterals from the dorsal and lateral funiculi. Terminals make large synapses with large, rounded synaptic vesicles. Monosynaptic 5-mV EPSPs of short duration and short afterhyperpolarization are common. Three of them can trigger the spike. No more than 15–20 afferent fibers impinge upon a single Clarke’s neuron. These features ensure transmission characterized by high frequency (up to 500 Hz), high speed of conduction, and small receptive fields. The high accuracy in time and space of the DSCT is much like the transmission in the dorsal columns. DSCT cells are either proprioceptive or exteroceptive. The majority of proprioceptive cells are distinct cells

stimulated either by muscle spindles primary Ia and secondary group II endings or by tendon Ib endings. These neurons are spontaneously active, even in the absence of group I afferents. The mean frequency increases linearly with the length of the muscle, but the discharge is not as regular as in the primary afferents. A given cell is monosynaptically stimulated by a single muscle or a small group of agonist muscles and is disynaptically inhibited by group I afferents from antagonists, like the motoneurons themselves. However, no recurrent inhibition of the Renshaw type was found. The influence of supraspinal descending tracts is weak except for inhibition by the pyramidal tract. The exteroceptive cells are monosynaptically activated by cutaneous low-threshold, fast-adapting hairy and highthreshold, slowly adapting pressure receptors. Receptor fields are relatively small (1–100 cm2).

The ventral spinocerebellar tract The ventral spinocerebellar tract (VSCT; Gower’s tract) arises from the third to sixth lumbar segments. Like the DSCT, the VSCT conveys information from the hind limb. Axons cross the midline, ascend ventrally to DSCT in spinal cord, cross a second time at the level of the ipsilateral brachium conjunctivum, and end bilaterally in the anterior lobe. All VSCT neurons receive strong polysynaptic input from the ipsilateral flexor reflex afferents (FRA). FRA are defined as those myelinated fibers which evoke the flexor reflex in the spinal preparation. They include low-threshold and high-threshold cutaneous fibers, groups II and III muscle afferents, and high-threshold joint afferents (Oscarsson, 1973). Components of the FRA can be inhibitory or excitatory. Their receptive fields are large (one or several limbs) and their effects are polysynaptic, mediated by a pool of interneurons which are strongly excited or inhibited by descending tracts. FRA are the major input of spinocerebellar tracts. Obviously, these tracts are more suitable for monitoring the state of activity of the interneuron pool commanding motoneurons than for conveying accurate peripheral sensory information (Fig. 2.11A). These interneurons are controlled by very limited areas of the sensorimotor cortex (Asanuma et al., 1971; Oscarsson, 1973). This observation contrasts with the diffuse effects of FRA. VSCT cells are also influenced by group I muscle receptors. Oscarsson considered two main type of cells (Oscarsson, 1973): (a) Ib-VSCT cells are monosynaptically activated by tendon organ Ib fibers. They are located laterally in Rexed laminae V–VII. Their EPSPs are small. They are activated simultaneously at the level of different articulations of the same limb. The corresponding muscles

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Fig. 2.11 (A) and (B) Type of information transferred by the spinocerebellar paths. (A) Information about the excitation state of the lower motor centers following Lundberg and Oscarsson. (Modified from Oscarsson, 1973.) (B) Information about the motoneuron itself through the border cells of Cooper and Sherington (SBC). FRAc and FRAp, flexor reflex afferents from center and periphery of the receptive fields, respectively; CN, corticonuclear extrapyramidal pathway; PT, pyramidal tract; Ret Sp, reticulospinal pathways; SBC, spinal border cell; MN, motoneuron. (Modified from Bloedel, 1973.) (C) The three subdivisions of the lateral reticular nucleus (LRN): the lateral parvocellular, the medial magnocellular, and the anterior subtrigeminal. The first two are often collectively named mLRN. (D) The vSCP path to the LRN. VST, vestibulo-spinal tract; bVFRT, bilateral ventral flexor reflex tract; VN, lateral vestibular nucleus.

Neuroanatomy of the cerebellum

presumably contract together during movement or maintenance of posture. (b) SCC-VSCT cells (border cells of Cooper and Sherrington) are located along the antero-lateral border of the anterior horn. They are activated monosynaptically by Ia and a few by Ib afferents, but about 30% of them are not activated by group I afferents. Disynaptic inhibition from Ia afferents occurs in about 50% of this neuronal population. These cells are morphologically indistinguishable from motoneurons. DSCT and VSCT activities are modulated synchronously during stepping in the mesencephalic preparation. Interestingly, rhythmical DSCT activity disappears after section of the dorsal roots or after curarization, but not the VSCT activity. Horseradish peroxidase retrograde tracing studies have shown few (5%) labeled cells in various motor nuclei of the cranial nerves. The similarity with the motoneuron-like cells of origin of VSCT suggests a similar function. Thus, part of VSCT cells shares the same synaptic input as true motoneurons, except the recurrent Renshaw inhibition. This would represent an example of corollary discharge or efference copy (Fig. 2.11B; Bloedel, 1973).

The cuneocerebellar tract The cuneocerebellar tract (CCT) is the forelimb equivalent of the DSCT. The proprioceptive cells are found in the external cuneatus nucleus. Their functional properties are similar to those of the DSCT cells. However, their receptive fields are smaller, each muscle being somatotopically represented. Some cells receive only group II afferents from spindle secondaries. The cells of origin of the exteroceptive component are intermingled with the lemniscal neurons in the rostral part of the main cuneatus nucleus. Again, their functional properties are similar to those of the corresponding part of the DSCT, but their receptive fields are smaller.

The rostral spinocerebellar tract The rostral spinocerebellar tract (RSCT) is the forelimb equivalent of the VSCT. The cell bodies are located in the rostral Clarke’s column. Axons reach the cerebellum partly through the brachium conjunctivum and partly through the restiform body and terminate bilaterally in the anterior lobe. DSCT is uncrossed and has only ipsilateral receptive fields. Flexor reflex afferents (FRA) are predominantly excitatory.

Vestibular afferents The vestibular nerves and vestibular nuclei contribute to the mossy fiber input. The primary afferents project mainly

to the ipsilateral vestibulocerebellum: the flocculus, ventral paraflocculus, nodulus, and uvula. This ipsilateral projection is small compared with the amount of fibers projecting bilaterally from the vestibular nuclei. Whereas primary afferents reach different parts of the vestibular nuclei depending on the canal of origin, there is no similar segregation in the vestibular nuclei projection. Fibers from the vestibular nuclei project diffusely bilaterally to the vermis, the flocculus, the paraflocculus, the paramedian lobule, the fastigial and the interpositus nucleus, but not to the lateral cerebellum.

Acoustic, visual and trigeminal afferents Click sounds evoke mass responses in lobules VI, VII, and VIII. Stimulation of visual cortex likewise produces potentials in a similar area, corresponding to the audiovisual representation in cerebellum. Concerning trigeminal afferents, the primary afferent cells of the mesencephalic root have been reported to send collaterals to the restiform body, but this is still questioned. Secondary cells of different parts of the trigeminal nucleus project ipsilaterally to several areas of the posterior lobe.

The reticular precerebellar nuclei The lateral reticular nucleus (LRN) The lateral reticular nucleus (LRN) is located in the lower medulla, lateral to the inferior olive. The nucleus is divided into three parts: lateral parvocellular, medial magnocellular, and anterior subtrigeminal. Their borders are blurred (Fig. 2.11C). The destination of the mossy fibers issued from the LRN has been a matter of debate. Fibers ascend trough the brachium conjunctivum. It is now accepted that the projection is bilateral, with an ipsilateral dominance and poor somatotopy in the classical Dow’s spinal areas (the anterior lobe and the paramedian lobule). The complex spinal input to LRN has been well known since the tremendous work from Lund’s group (Clendenin et al., 1974, 1975; Ekerot, 1990a, 1990b, 1990c) and others. Nevertheless, the spinal tracts provide less than 5% of the overall synaptic input to the LRN (Ito, 1984). 1. Bilateral ventral flexor reflex tract. This first and most important component is activated monosynaptically by the bilateral ventral flexor reflex tract (bVFRT) of Lundberg and Oscarsson. About 50% of the cells in the main LRN (parvocellular and magnocellular parts) respond to a direct stimulation of the bVFRT (Clendenin et al., 1974). Axons cross the midline at the spinal level before ascending in the ventral funiculus. Cell bodies are activated or inhibited by FRA stimulation of the four limb nerves (Fig. 2.11D). The bVFRT shares some interesting properties with the VSCT: both

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respond best to FRA stimulation and both are controlled by descending paths. 2. Other spinal pathways. The ipsilateral forelimb (iF) tract is activated only by ipsilateral nerve stimulation of the forelimb (Clendenin et al., 1974). The responding neurons are localized in the dorso-lateral portion of the magnocellular part. The projection is ipsilateral in the anterior lobe and in the paramedian lobule. Its input comprises cutaneous and high-threshold muscle afferents. It has been shown with intracellular recordings in the LRN cells (Ekerot, 1990a, 1990b, 1990c) that ipsilateral forelimb tract cells are excitatory or inhibitory on the LRN cells. Suprathreshold EPSPs can trigger bursts of spikes at 500 Hz. The C3-C4 propriospinal neurons (C3-C4PNs) are activated strongly by the pyramidal tract and weakly by the rubrospinal tract. They stimulate the motoneurons, and their axon gives off ascending collaterals to the LRN. Once more, this pathway forwards information to the cerebellum about the state of the pool of interneurons at the junction between the descending command and the motoneurons. The dorsal column nuclei and the trigeminal nerve activate the LRN through a polysynaptic common path which is still poorly defined. 3. Pyramidal and rubrospinal input. The pyramidal and rubrospinal contralateral tracts powerfully stimulate the mLRN. Projections from the sensorimotor cortex are not congruent with the spinal input. The rubrospinal input arises from the magnocellular part (caudal portion) of the nucleus and projects to the magnocellular and subtrigeminal subdivision of the LRN. LRN receives additional input from the superior colliculus and the lateral vestibular nucleus. 4. Input from the cerebellar nuclei. The LRN receives a powerful excitatory input from the medial and interpositus nuclei, to which it sends excitatory collaterals (Dietrichs, 1983; Matsushita and Ikedda, 1976; see Fig. 2.8B 1). The rostral part of the LRN projects to the lateral nucleus, and the caudal part projects to the medial nucleus (Parenti et al., 1996). This suggests that a given area of the LRN is coupled with a definite part of a nucleus, which itself is linked to a particular Voogd’s band and a precise part of the inferior olive. In other words, LRN is also topologically linked to the output of the system. Another aspect of this reciprocal excitatory connection is the possibility of a positive feedback (Kitai et al., 1974a, 1974b). Ringing has been experimentally demonstrated in this loop (Ito, 1984). Several other mossy fiber precerebellar nuclei have similar reciprocal excitatory connections with the cerebellar nuclei. It has

been suggested that they provide a controlled bias excitatory background activity averaged over multiple inputs (spinal and cortical) which can be modulated by the ongoing Purkinje cell inhibition. If so, it makes sense that each nuclear output unit should have its own control, explaining congruence between precerebellar and cerebellar nuclei structures (Parenti et al., 1996).

Other reticular precerebellar nuclei The nucleus reticularis tegmenti pontis (NRTP) is situated dorsally to the median lemniscus. Its main input comes from Brodmann’s areas 1 to 6. The projection of the cortical fibers is organized in rostro-caudal slabs, reminiscent of the cortical projection in the pontine nuclei. However, the cerebellar destination is the contralateral anterior lobe and the paramedian lobule, the spinal areas, and the vermal part of lobules VI and VII (Ito, 1984). NRTP supplies collaterals to the lateral and interpositus nuclei. Fibers reach the cerebellum through the brachium pontis. NRTP receives input from the vestibular nuclei and from the pretectal areas. Indeed, NRTP relays visual information to the flocculus. Like the LRN, NRTP receives a massive input from the cerebellar nuclei through the brachium conjunctivum. The paramedian reticular nucleus (PRN) is located between the root of the hypoglossal nerve and the raphe. It receives a large spectrum of afferents from the spinal cord up to the cerebral cortex. Projection fibers ascend in the restiform body and reach the anterior lobe, the vermal posterior lobe, and the flocculus. The perihypoglossal nuclei send projections to the anterior lobe, pyramis, uvula, and fastigial nuclei. They receive afferents from the fastigial nucleus and flocculo-nodular lobe. One of them, the nucleus prepositus hypoglossi, has attracted special attention because it projects to the oculomotor nuclei through collaterals of fibers reaching the flocculo-nodular region. This nucleus has reciprocal connections with the vestibular and cerebellar nuclei and receives visual and somesthetic inputs. It plays a determinant role in the control of gaze.

The pontine nuclei The organization of the pontine nuclei was reviewed authoritatively by Brodal and Bjaalie in 1992. In humans, the pontine nuclei make up 37% of the brainstem volume. On each side, 19 million corticopontine fibers impinge upon 10 million pontine neurons, whereas only 1 million fibers reach the pyramidal tract. Cytoarchitecture is uniform among the nuclei, which form a homogeneous population spread out by the pyramidal and extrapyramidal descending fibers. Less than 5% of

Neuroanatomy of the cerebellum

Fig. 2.12 Corticopontine mossy fiber input in the monkey. (A) Areas 4 and 6 are the major input. Primary sensory areas 3, 1, 2, parietal areas 5 and 7, and supratemporal areas contribute also. In the monkey, unlike in the cat, there is no visual occipital input. Each area projects to a given area of the cerebellar cortex (B), and to a longitudinal slab at the level of the pontine nuclei (C). At a smaller scale, a small area of the cortex projects to several points in the pontine slab and in the cerebellar cortex area, in agreement with the fractured somatotopy of the mossy fiber input. (Modified from Brodal and Bjaalie, 1992.)

the pontine neurons are GABAergic. These presumed interneurons have a single very long dendrite. Projecting cells to the cerebellum (95%) give off mossy fibers with scanty collaterals to the nuclei. The dendritic arbor measures 200–350 m. Corticopontine fibers make asymmetric synapses with rounded vesicles only on the dendrite. Presynaptic GABAergic axoaxonal buttons have been described as well as dendrodendritic serial synapses. These ultrastructural details suggest that some computation is applied to the information forwarded at this level, although the overwhelming number of projecting cells over the number of interneurons and the low (2:1) convergence of the corticopontine fibers suggest a rather straightforward transfer. No recurrent collaterals have been found.

Fig. 2.13 Fractured somatotopy. The patchy nature of the mossy fiber projection from different skin areas to the intermediate part of the ipsilateral cerebellar cortex is in sharp contrast with the sagittal strip projection of the climbing fiber system. Each Voogd’s band and even each microzone receives mossy fibers from different areas of the skin and probably from spinal and cortical motor centers. Lob. ant., anterior lobe; Lob. sim., lobule simplex; PY, pyramis; UV, uvula; PFL, paraflocculus; PML, paramedian lobule. (Modified from Voogd and Glickstein, 1998.)

The organization of the cortico-ponto-cerebellar connections in the monkey is illustrated in Fig. 2.12. The anterior part of the frontal lobe and the lower part of the temporal lobe do not project on the pontine nuclei. The visual areas have no projection in the monkey, but such projections are found in other species, such as the cat. The maximal density of projections comes from areas 4 and 6. Cortical areas corresponding to the hand are deemphasized (Serapide et al., 1994). Each large Brodmann’s area projects to one or two slabs oriented rostro-caudally in the pons. Each slab projects mainly contralaterally to the cerebellar hemisphere in a well-defined region. Within a given area, a small point of cortex may project to several points in a slab and on the cerebellar surface. This has been called ‘fractured somatotopy’ (Fig. 2.13) which is a typical feature of the mossy fiber system (Shambes et al., 1978). However, it was shown recently, using very small injections of tracer in the basal pontine nuclei, that the projection in the cerebellar cortex could be oriented along sagittal strips much like the climbing fiber projections (Serapide et al.,

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1994). About 10% of the pontocerebellar projection is ipsilateral. Some mossy fibers send collaterals to the opposite side, branching inside the cerebellar white matter.

The climbing fiber system The climbing fiber input arises from all levels of the central nervous system, from the spinal cord to the motor cortex.

Spinal olivo-cerebellar tracts Fibers arise contralaterally in the spinal cord, at the lumbar level from Rexed’s laminae IV to VIII (Ito, 1984), and bilaterally at the upper thoracic and cervical levels (Buisseret-Delmas and Batini, 1978; Buisseret-Delmas, 1980). From the segmental level, information reaches specific parts of the inferior olive through different tracts: the ventral funiculus spino-olivary cerebellar path (VFSOCP), the dorsal (DF-SOCP), the dorso-lateral (DLFSOCP), and the lateral (LF-SOCP). Each of them is divided into several subdivisions, depending on the actual destination in the inferior olive and Voogd’s projection band in the anterior lobe and the paramedian lobule. Each of them has functional specificities in terms of peripheral receptor modality, conduction velocity, number of synaptic relays, transmission fluctuations, and sensitivity to anesthetic agents, to dopamine and clonidine. The most important VF-SOCPs are illustrated in Fig. 2.14. The reader is referred to Apps (1999) for an up-to-date description. Unfortunately, the influence of descending pathways on the spinal transmission has not been investigated. Indirect evidence points to properties analogous to those of the VSCT. FRA are the preferred modality of stimulation. Evoked responses fluctuate like the flexor reflex and transmission is very sensitive to drugs. Oscarsson (1973) suggested that most spinal paths forward information about the state of the spinal motor centers. Interestingly, when the response to natural stimuli was investigated in behaving animals, complex spikes could be easily evoked after slight touch of the paw or small mobilization of an articulation, but they were blocked or modulated during stepping (Apps and Lee, 1999). Complex spikes were also triggered when stepping was interrupted in the decerebrated ferret (Lou and Bloedel, 1992).

Brainstem and mesodiencephalic input to the inferior olive The inferior olive and the vermal b-zone receive projections from the sensory spinal root of the trigeminal nerve. Nuclei of the mesodiencephalic junction make excitatory connections with the inferior olive, particularly the nucleus of Darkschewitsch. Sensory complex spike responses

known to be inhibited during active movements were also shown to be inhibited at the level of the inferior olive by stimulation of the red nucleus (Horn et al., 1998). The anterior parvocellular portion of the red nucleus, which is the most important portion in humans, sends a dense projection to the principal and medial accessory olive. This part of the red nucleus receives collaterals of fibers arising from the dentate nucleus and projecting to the ventral lateral nucleus (NVL) of the thalamus. Stimulation of the rubrospinal tract powerfully inhibits the dorsal accessory olive (DAO) responses to light tactile stimuli at the spinal level (Weiss et al., 1990).

Cortical input to the inferior olive The cortical afferences project to the medial and dorsal accessory olive. The cortical input originates from layer V of the motor cortex only. This area is also the origin of the densest projection towards the pontine nuclei.

Visual and vestibular inputs to the inferior olive These inputs have been studied in detail because it was expected that elucidating their function in the plasticity of the vestibulo-ocular reflex (VOR) would help in the understanding of the cerebellar control of movement. The structures involved are the dorsal cap, the  nucleus, the dorsal part of the ventro-lateral outgrowth, and their projections to the flocculo-nodular lobe (Fig. 2.15). The specific visual stimulus is a posterior to anterior displacement of the visual field at slow speed, less than one degree per sescond. The relays from the optic nerve to the dorsal cap are the ipsilateral nucleus of the optic tract (NOT) and the accessory optic system. Descending and medial vestibular nuclei have been shown to be GABAergic and project on the  nucleus. The visual input has been interpreted by Ito as an error message meaning that the gain of the VOR was no longer appropriate.

The cerebellar efferent systems Overview All parts of the cerebellar cortex send fibers to the deep nuclei. Three approximate rostro-caudal longitudinal zones have been identified: (a) a vermal zone which projects to the fastigial nucleus, (b) an intermediate zone whose Purkinje cells are connected with interposed nuclei, and (3) a lateral zone projecting to the dentate nuclei. The nuclear excitatory outputs to the cerebellar cortex, the precerebellar nuclei, and the inhibitory output to the inferior olive may be considered as building blocks of the

Neuroanatomy of the cerebellum

Fig. 2.14 The spino-olivo-cerebellar paths. The five main pathways with their preferred primary afferents, their spinal relays, and their sagittal ipsilateral and bilateral projections to the anterior lobe. The projection areas in Larsell’s lobules IV and V are indicated by hatching (see keys) in upper diagrams. The course and relays of the paths are shown in the lower diagrams. Interrupted vertical lines indicate the midline of the neuraxis. Intermed., pars intermedia; Hemiv., hemivermis; Ipsilat., ipsilateral; Bilat., bilateral; IO, inferior olive; DF, dorsal funiculus; DLF, dorsolateral funiculus; LF, lateral funiculus; VF, ventral funiculus; FRA, flexor reflex afferents. (Modified from Oscarsson, 1973.)

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internal cerebellar machinery. They have been described above and are illustrated in Fig. 2.8B. With the exception of the vermal Purkinje cell axons to the lateral vestibular nucleus, the cerebellar output arises exclusively from the cerebellar nuclei. The cerebellar nuclei receive collaterals from the mossy and climbing fibers on their way to the cerebellar cortex. However, this input is not a mere copy of the cortical afference. Climbing fiber collaterals are sparse and do not make the powerful synapse they make with the Purkinje cell. Collaterals from the pontine nuclei are scanty, too. It seems that this is also true for the mossy fiber spinal input. Instead, a wealth of collaterals comes from the reticular precerebellar nuclei like LRN and NRTP. These findings are in agreement with the relatively poor somatotopy found in the cerebellar nuclei compared to that found in the cerebellar cortex. However, responses of a single muscle or of a small group of agonists can be evoked by low-intensity stimulation of the nuclei. Somatotopy must be considered as being mapped on muscles or primary motor cortex instead of being mapped on the sensory surface.

The fastigial nucleus

Fig. 2.15 Visual and vestibular input to the inferior olive. The nucleus climbing fiber projections terminate upon Purkinje cells in the contralateral uvula and nodulus. The GABAergic Purkinje cells of these structures project onto the subjacent vestibular nuclei (not illustrated). The vestibular primary afferent projections to the nodulus and to the vestibular nuclei are shown. The medial and descending vestibular nuclei project to the ipsilateral -nucleus (heavy line) and bilaterally to the nodulus and uvula (dashed lines). The dorsal cap receives a visual projection from the contralateral eye via the nucleus of the optic tract, and also receives a cholinergic input from the contralateral nucleus prepositus hypoglossi. The dorsal cap projects to the contralateral flocculus and ventral aspect of the nodulus. The vestibular secondary afferent cholinergic projection to the nodulus is also illustrated. , -nucleus; dc, dorsal cap; DVN, MVN, descending and medial vestibular nuclei; FLOC, flocculus; NOT, nucleus of the optic tract; NPH, nucleus prepositus hypoglossi; SC, superior colliculus; 9 a–d, uvula; 10, nodulus. (Modified from Barmack et al., 1993.)

The fastigial nucleus projects bilaterally to the vestibular and reticular nuclei (Fig. 2.16A). The crossed projection arches around the brachium conjunctivum, forming the hook bundle (uncinate fasciculus), before entering the contralateral restiform body. Uncrossed efferent fibers send projections in brainstem through the restiform body. The main targets of fastigial efferences in brainstem are reticular and vestibular nuclei. The fastigial efferences are involved in the control of the reticulospinal and vestibulospinal tracts. Their effects on the spinal  and  motoneurons are complex. An ascending projection crosses within the cerebellum and reaches the tectum and many thalamic nuclei (for a review see Ito, 1984).

The interpositus nucleus The interpositus nucleus is divided into anterior and posterior parts (AIN and PIN). The AIN projects mainly to the NVL of the contralateral thalamus and adjacent areas of the ventral anterior (NVA), ‘area X,’ and NVPL (Fig. 2.16B). The fibers send collaterals to the caudal magnocellular part of the red nucleus. They impinge upon the proximal dendrite, whereas cerebral cortical fibers make distal synapses. Their EPSPs are distinct. It has been shown that lesion of the contralateral interpositus nucleus is followed within a few days by secondary colonization of the freed

Neuroanatomy of the cerebellum

Fig. 2.16 Projections of the cerebellar nuclei. (A) Projections of the medial (fastigial) nucleus (1). Bilateral descending projections with preponderance of the contralateral side through the hook bundle (4); superior (5), lateral (6), medial (7) and inferior (8) vestibular nuclei. The precerebellar nuclei: lateral reticular (9), perihypogossal (10) and others. The medial bulbar reticular formation (12), the parasolitarius nucleus (13), and the upper cervical segments. A bilateral ascending projection with contralateral dominance to: the periaqueductal gray (14), the mesodiencephalic nuclei: interstitial (15), of Darkschewitsch (16), and scantly to other thalamic nuclei, the center median (17) and midline nuclei (18). (B) Projections from the interpositus anterior and posterior nuclei (2,2), the lateral dentate nucleus (3); contralateral projections to the tegmental reticular nucleus (19), the periaqueducal gray (14), the mesodiencephalic nuclei; interstitial (15), of Darkschewitsch (16), the two parts of the red nucleus (20) at the origin of the rubrospinal tract (interpositus) and of the rubro-olivary projection (dentate). Projections to the thalamic nuclei: mainly to the ventral lateral (21), ventral anterior (22) and ventral posterolateral (23) groups. Scant projections to the center median (17) and midline nuclei (18). (Modified from Jansen, 1969.)

dendritic surface by the cortical fibers (Tsukahara et al., 1983). The AIN sends fibers to the NRTP, the pontine nuclei, and the superior colliculus. The PIN projection to the thalamus is less dense and, in the red nucleus, is limited to its medial part.

to the rostral intralaminar thalamic nuclei, chiefly the central lateral nucleus (CLN), and (b) the collaterals reach the anterior parvocellular part of the contralateral red nucleus.

The thalamo-cortical relay The lateral-dentate nucleus The dentate nucleus projects mainly to the thalamus (NVL, NVPL, ‘area X’), like the interpositus. However, there are two differences with the projections of the interpositus: (a) a small number of fibers from the dentate nucleus project

The NVL, the NVPL and NVA nuclei are the major sites that receive cerebellar nucleofugal projections. Neurons in the NVL, NVPL, and NVA project to the cerebral cortex. Inputs from the contralateral dentate and interpositus nuclei terminate densely in these nuclei, whereas the fastigial input

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is more restricted and bilateral. The cerebellothalamic projection is characterized by large unitary EPSPs. Detailed electrophysiological studies revealed a topographic organization in cats. The interpositus projects mainly to the NVL nucleus, which in turn projects to the motor cortical area controlling the distal forelimbs. The lateral cerebellar nucleus projects to a more medial and dorsal region of the NVL nucleus which is principally connected to the motor area that controls the axial musculature and shoulder (Rispal-Padel et al., 1973). VA neurons of cats also receive inputs from both the interpositus and lateral cerebellar nuclei, but in contrast to NVL neurons projecting to the motor cortex, NVA neurons project to the parietal cortex (Sasaki et al., 1972). The pattern of cerebellocerebral projections in monkeys is different. The fastigial nucleus projects bilaterally to the hindlimb area of the motor cortex and the parietal cortex. The interpositus nucleus projects contralaterally to the trunk area of the motor cortex and the premotor cortex. The dentate nucleus projects contralaterally to the forelimb area of the motor cortex, premotor cortex, and prefrontal association cortex. The lateral part of the cerebellum is linked with the parietal association cortex in cats, but to the forelimb area of the motor cortex, premotor cortex, and prefrontal association cortex in monkey. Recently, using retrograde transneuronal transport of herpes virus injected in the primary motor area of the monkey, it was shown that this cortical area mapped contralaterally, in both in the interpositus and dentate nuclei (Middleton and Strick, 1994; Hoover and Strick, 1999). In the interpositus, NIA posterior projects to the arm area, NIP anterior to the leg area, and NIP posterior to the face area. The proportion of labeled cells was higher in the dentate and they were found in separate parts for arm, leg, and face. The primary motor area is not the only projection area of the dentate because a large volume (70%) was free of labeled cells. Previous work from the same group found a circumscribed area of the dentate related to the prefrontal Brodmann area 46, suggesting a participation in cognitive functions. A fine somatotopical organization has been suggested for the cerebello-thalamo-cortical projection. Axons from a small area of the dentate nucleus of monkeys terminate within the NVL in an elongated rod-like zone, which in turn projects to a small area of the motor cortex (Strick 1976; Asanuma et al., 1983). The finding that there might be a relationship between distinct regions of the deep cerebellar nuclei and distinct areas in cerebral cortex has led to the hypothesis that cerebellar output is composed of separate ‘output channels’ (Middleton and Strick, 1997).

Cerebro-cerebellar loops Functional cerebro-cerebellar loops were postulated (Allen and Tsukahara, 1974). However, their anatomical demonstration is difficult because transynaptic labeling methods are required and these techniques are still in the early stages of development. Electrophysiological mapping gives information about departure and destination, but nothing about intermediate relays. Functional studies with single photon emission computed tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) provide additional information in favor of the existence of cerebro-cerebello-cerebral loops. Unfortunately, these new methods still lack the required accuracy in space and time to establish (a) that the loop is actually closed, and (b) that the ringing time is actually that predicted by the conduction times and the synaptic delays. The most commonly cited loop is the cortico-pontocerebello-thalamo-cortical loop. The afferent pathway (‘feedforward limb’) is the crossed projection from pontine nuclei, and the efferent pathway (‘feedback limb’) includes the cerebellar cortico-nuclear projections, the efferences from the deep nuclei, and the thalamo-cortical relay. The projections from deep cerebellar nuclei are directed towards ‘motor’ thalamic nuclei (NVL, NVPL, X) and intralaminar thalamic nuclei. Motor nuclei project to motor cortex, premotor cortex, supplementary motor area, as well as prefrontal, posterior parietal, and temporal regions. Intralaminar nuclei project towards association areas and limbic cortices (Schmahmann and Pandya, 1997). This loop is usually thought to be excitatory. However, because the pontine nuclei give few collaterals to the nuclei (if any), the path must loop through the inhibitory Purkinje cells. The motor cortex is the only cortical input to the medial and dorsal accessory olive (Ito, 1984), which is related to the A and B Voogd’s bands and to the fastigial nucleus. However, this nucleus has only a scant projection to the motor area (Hoover and Strick, 1999). Instead, this nucleus controls the vestibulospinal and reticulospinal tracts. Therefore, this path is an open side path to the cortical extrapyramidal system. Surprisingly, loops have not been considered for the climbing and mossy fiber systems separately. For the mossy fiber system, given that the corticopontine patchy input spreads over many Voogd’s bands and since there are virtually no collaterals to the nuclei, close and open inhibitory loops might coexist.

Neuroanatomy of the cerebellum

Aminergic and cholinergic inputs The cerebellum and the inferior olive receive a diffuse aminergic innervation. Noradrenergic fibers arise mostly from the locus ceruleus, but also from A1, A2, and A3 nuclei, whereas dopaminergic fibers arise from nucleus A10. Serotoninergic fibers arise from the raphe nuclei (Ito, 1984; Kerr and Bishop, 1991). Noradrenergic fibers are supposed to form synapses with the distal dendrites of the Purkinje cells, in contrast to serotoninergic fibers which do not synapse upon Purkinje cells. The serotoninergic innervation of the inferior olive can be temporarily destroyed by injection of 5,6-dihydroxytyramine or 5,7-dihydroxytyramine. Interestingly, this treatment suppresses tremor induced by the injection of harmaline. In the vermal area, Purkinje cells fire complex spikes at the frequency of the tremor and the simple spikes disappear (De Montigny and Lamarre, 1973). Cholinesterase has been found in the cerebellum and in the inferior olive, and muscarinic receptors have been identified in the cerebellum (Jaarsma et al., 1995; see also Chapter 4).

Connections with autonomic centers The cerebellum receives direct and indirect projections from autonomic centers: the sensory nuclei of the IXth and Xth nerves, and the parabrachial nucleus (Ito, 1984; Nisimaru et al., 1991; Kondo et al., 1998). Cerebellar stimulation can change the heart rate and the respiration frequency, but these effects were usually considered to result from projections of the fastigial nucleus to the brainstem reticular formation. Stimulation of the vagus nerve evokes responses in the cerebellar cortex (Zheng et al., 1982; Ito, 1984). Connections with the hypothalamus have been demonstrated by Haines, and colleagues (1990). These connections are reciprocal for the lateral and interpositus nuclei. The fastigial nucleus receives a hypothalamic projection, but does not itself project to the hypothalamus. Fibers from the hypothalamus ending in the cerebellar nuclei are considered to be collaterals of projections to the cerebellar cortex.

xReferencesx Allen, G.I. and Tsukahara, N. (1974). Cerebrocerebellar communication systems. Physiol Rev 54: 957–1005. Andersen, B.B., Korbo, L. and Pakkenberg, B. (1992). A quantitative

study of the human cerebellum with unbiased stereological techniques, J Comp Neurol 326: 549–60. Apps, R. (1999). Movement-related gating of climbing fibre input to cerebellar cortical zones. Progr Neurobiol 57: 537–62. Apps, R. and Lee, S. (1999). Gating of transmission in climbing fibre paths to cerebellar cortical C1 and C3 zones in the rostral paramedian lobule during locomotion in the cat. J Physiol (Lond) 516: 875–83. Asanuma, C., Thach, W.T. and Jones, E.J. (1983). Anatomical evidence for segregated focal grouping of efferent cells and their terminal ramifications in the cerebellothalamic pathway of the monkey. Brain Res Rev 5: 267–97. Asanuma, H., Stoney, S.D. Jr and Thompson, W.D. (1971). Characteristics of cervical interneurones which mediated cortical motor outflow to distal forelimb muscles of cat. Brain Res 27: 79–95. Barmack, N.H., Fagerson, M., Fredette, B.J., Mugnaini, E. and Shojaku, H. (1993). Activity of neurons in the beta nucleus of the inferior olive of the rabbit evoked by natural vestibular stimulation. Exp Brain Res 94: 203–15. Bernard, C. and Axelrad, H. (1993). Effects of recurrent collateral inhibition on Purkinje cell activity in the immature rat cerebellar cortex – an in vivo electrophysiological study. Brain Res 626: 234–58. Bloedel, J.R. (1973). Cerebellar afferent systems: a review. In Progress in Neurobiology, Vol. 2 Part 1, ed. J.A. Kerkut and J.W. Phillis, pp. 3–67. Oxford: Pergamon Press. Brodal, P. and Bjaalie, J.G. (1992). Organization of the pontine nuclei. Neurosci Res 13: 83–118. Buisseret-Delmas, C. (1980). An HRP study of the afferents to the inferior olive in cat. I. Cervical and dorsal column nuclei projections. Arch Ital Biol 118: 270–86. Buisseret-Delmas, C. (1988). Sagittal organization of the olivocerebellonuclear pathway in the rat. I. Connections with the nucleus fastigii and the nucleus vestibularis lateralis. Neurosci Res 5: 475–93. Buisseret-Delmas, C. and Angaut, P. (1988). The cerebellar nucleocortical projections in the rat. A retrograde labelling study using horseradish peroxidase combined to a lectin. Neurosci Lett 84: 255–60. Buisseret-Delmas, C. and Batini, C. (1978). Topology of the pathways to the inferior olive: an HPR study in cat. Neurosci Lett 10: 207–14. Carpenter M.B. (1985). Core Text of Neuroanatomy, 3rd edn. Baltimore: Williams and Wilkins. Clendenin, M., Ekerot, C.F. and Oscarsson, O. (1974). The lateral reticular nucleus in the cat. III. Organization of component activated from ipsilateral forelimb tract. Exp Brain Res 21: 501–13. Clendenin, M., Ekerot, C.F. and Oscarsson, O. (1975). The lateral reticular nucleus in the cat. IV. Activation from dorsal funiculus and trigeminal afferents. Exp Brain Res 24: 131–44. Colin, F., Manil, J. and Desclin, J.C. (1980). The olivocerebellar system. I. Delayed and slow inhibitory effects: an overlooked salient feature of the cerebellar climbing fibers. Brain Res 187: 3–27.

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28

F. Colin, L. Ris, and E. Godaux

Crépel, F. (1982). Regression of functional synapses in the immature mammalian cerebellum. Trends Neurosci 5: 266–9. Crépel, F., Hemart, N., Jaillard, D. and Daniel, H. (1996). Cellular mechanisms of long-term depression in the cerebellum. Behav Brain Sci 19: 347. De Montigny, C. and Lamarre, Y. (1973). Rythmic activity induced by harmaline in the olivo-cerebello-bulbar system of the cat. Brain Res 53: 81–95. De Zeeuw, C.I., Simpson, J.I., Hoogenraad, G.C., Galjart, N., Koekkoek, S.K.E. and Ruigrok, T.J.H. (1998). Microcircuitry and function of the inferior olive. Trends Neurosci 21: 391–400. De Zeeuw, C.I., Van Alphen, A.M., Hawkins, R.K. and Ruigrok, T.J.H. (1997). Climbing fibre collaterals contact neurons in the cerebellar nuclei that provide a GABAergic feedback to the inferior olive. Neuroscience 80: 981–6. Desclin, J.C. (1974). Histological evidence supporting the inferior olive as the major source of cerebellar climbing fibers in the rat. Brain Res 77: 365–84. Desclin, J.C. and Colin, F. (1980). The olivocerebellar system II. Some ultrastructural correlates of inferior olive destruction in the rat. Brain Res 187: 29–46. Dietrichs, E. (1983). Cerebellar nuclear afferents from the lateral reticular nucleus in the cat. Brain Res 288: 320–4. Dow, R.S. (1942). The evolution and anatomy of the cerebellum. Biol Rev 17: 179–220. Eccles, J.C., Ito, M. and Szentagothai, J. (1967). The Cerebellum as a Neuronal Machine, New York, Heidelberg: Springer-Verlag. Ekerot, C.F. (1990a). The lateral reticular nucleus in the cat. VI. Excitatory and inhibitory afferent paths. Exp Brain Res 79: 109–19. Ekerot, C.F. (1990b). The lateral reticular nucleus in the cat. VII. Excitatory and inhibitory projection from the ipsilateral forelimb tract (iF tract). Exp Brain Res 79:120–8. Ekerot, C.F. (1990c). The lateral reticular nucleus in the cat. VIII. Excitatory and inhibitory projection from the bilateral ventral flexor reflex tract (bVFRT). Exp Brain Res 79: 129–37. Endo, S., Suzuki, M., Sumi, M. et al. (1999). Molecular identification of human G-substrate, a possible downstream component of the cGMP-dependent protein kinase cascade in cerebellar Purkinje cells. Proc Natl Acad Sci USA 96: 2467–72. Floris, A., Dino, M., Jacobowitz, D.M. and Mugnaini, E. (1994). The unipolar brush cells of the rat cerebellar cortex and cochlear nucleus are calretinin-positive: a study by light and electron microscopic immunocytochemistry. Anat Embryol 189: 495–520. Gravel, C., Eisenman, L.M., Sasseville, R. and Hawkes, R. (1987). Parasagittal organization of the rat cerebellar cortex: direct correlation between antigenic Purkinje cell bands revealed by mabQ113 and the organization of the olivocerebellar projection. J Comp Neurol 265: 294–331. Haines, D.E., May, P.J. and Dietrichs, E. (1990). Neuronal connections between the cerebellar nuclei and hypothalamus in Macaca fascicularis: cerebello-visceral circuits. J Comp Neurol 299: 106–22. Hawkes, R., Colonnier, M. and Leclerc, R. (1985). Monoclonal anti-

bodies reveal sagittal banding in the rodent cerebellar cortex. Brain Res 333: 359–65. Hawkes, R. and Gravel, C. (1991). The modular cerebellum. Prog Neurobiol 36: 309–27. Hoover, J.E. and Strick, P.L. (1999). The organization of cerebellar and basal ganglia outputs to primary motor cortex as revealed by retrograde transneuronal transport of herpes simplex virus type 1. J Neurosci 19: 1446–63. Horn, K.M., Hamm, T.M. and Gibson, A.R. (1998). Red nucleus stimulation inhibits within the inferior olive. J Neurophysiol 80: 3127–36. Ito, M. (1984). The Cerebellum and Neural Control. New York: Raven Press. Ito, M. and Yoshida, M. (1964). The cerebellar-evoked monosynaptic inhibition in Deiters’ neurones. Experientia 20: 515–16. Jaarsma, D., Levey, A.I., Frostholm, A., Rotter, A. and Voogd, J. (1995). Light-microscopic distribution and parasagittal organisation of muscarinic receptors in rabbit cerebellar cortex. J Chem Neuroanat 9: 241–59. Jansen, J. (1969). On cerebellar evolution and organization from the point of view of a morphologist. In Neurobiology of Cerebellar Evolution and Development, ed. R. Llinas, pp. 881–93. Chicago: American Medical Association. Kano, M., Garaschuk, O., Verkhratsky, A. and Konnerth, A. (1995). Ryanodine receptor-mediated intracellular calcium release in rat cerebellar Purkinje neurones. J Physiol (Lond) 487: 1–16. Kerr, C.W.H. and Bishop, G.A. (1991). Topographical organization in the origin of serotoninergic projections to different regions of the cat cerebellar cortex. J Comp Neurol 304: 502–15. Kitai, S.T., De France, J.F., Hatada, K. and Kennedy, D.J. (1974a). Electrophysiological properties of lateral reticular nucleus cells. II. Synaptic activation. Exp Brain Res 21: 419–32. Kitai, S.T., Kennedy, D.T., Defrance, J.F. and Hatada, K. (1974b). Electrophysiological properties of lateral reticular nucleus cells. I. Antidromic activation. Exp Brain Res 21: 403–18. Kondo, M., Sears, T.A., Sadakane, K. and Nisimaru, N. (1998). Vagal afferent projections to lobule VIIa of the rabbit cerebellar vermis related to cardiovascular control. Neurosci Res 30: 111–17. Lainé, J. and Axelrad, H. (1998). Lugaro cells target basket and stellate cells in the cerebellar cortex. Neuroreport 9: 2399–403. Larsell, O. (1970). The Comparative Anatomy and Histology of the Cerebellum from Monotremes to Apes. Minneapolis: University of Minnesota Press. Leclerc, N., Schwarting, G.A., Herrup, K., Hawkes, R. and Yamamoto, M. (1992). Compartmentation in mammalian cerebellum: Zebrin II and P-path antibodies define three classes of sagittally organized bands of Purkinje cells. Proc Natl Acad Sci USA 89: 5006–10. Llano, I., DiPolo, R. and Marty, A. (1994). Calcium-induced calcium release in cerebellar Purkinje cells. Neuron 12: 663–73. Llinas, R., Baker, R. and Sotelo, C. (1974). Electrotonic coupling between neurons in cat inferior olive. J Neurophysiol 37: 560–71. Llinas, R. and Precht, W. (1969). Recurrent facilitation by disinhibition in Purkinje cells of the cat cerebellum. In Neurobiology of

Neuroanatomy of the cerebellum

Cerebellar Evolution and Development, ed. R. Llinas, pp. 619–27. Chicago: American Medical Association. Llinas, R. and Volkind, R. (1973). The olivo-cerebellar system: functional properties as revealed by harmaline-induced tremor. Exp Brain Res 18: 69–87. Llinas, R. and Yarom, Y. (1981). Electrophysiology of mammalian inferior olivary neurones in vitro. Different types of voltagedependent ionic conductances. J Physiol (Lond) 315: 549–67. Llinas, R. and Yarom, Y. (1986). Oscillatory properties of guinea-pig inferior olivary neurones and their pharmacological modulation: an in vitro study. J Physiol (Lond) 376: 163–82. Lou, J.S. and Bloedel, J.R. (1992). Responses of sagittally aligned Purkinje cells during perturbed locomotion: relation of climbing fiber activation to simple spike modulation. J Neurophysiol 68: 1820–33. Matsushita, M., Hosoya, Y. and Ikeda, M. (1979). Anatomical organization of the spinocerebellar system in the cat as studied by retrograde transport of horseradish peroxidase. J Comp Neurol 184: 81–106. Matsushita, M. and Ikedda, M. (1976). Projections from the lateral reticular nucleus to the cerebellar cortex and nuclei in the cat. Exp Brain Res 24: 403–21. Middleton, F.A. and Strick, P.L. (1994). Anatomical evidence for cerebellar and basal ganglia involvement in higher cognitive function. Science 266: 458–61. Middleton, F.A. and Strick, P.L. (1997). Cerebellar output channels. In: The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 61–82. San Diego: Academic Press. Mugnaini, E. and Floris, A. (1994). The unipolar brush cell: a neglected neuron of the mammalian cerebellar cortex. J Comp Neurol 339: 174–80. Nieuwenhuys, R. and Nicholson, C. (1969). A surview of the general morphology, the fiber connections, and the possible functional significance of the gigantocerebellum of the mormyrid fishes. In Neurobiology of Cerebellar Evolution and Development, ed. R. Llinas, pp. 107–34. Chicago: American Medical Association. Nisimaru, N., Okahara, K. and Nagao, S. (1991). Olivocerebellar projection to the cardiovascular zone of rabbit cerebellum. Neurosci Res 12: 240–50. Oscarsson, O. (1973). Functional organization of spinocerebellar paths. In Handbook of Sensory Physiology, Vol. II, Somatosensory System, ed. A. Iggo, pp. 339–80. Berlin–Heidelberg–New York: Springer Verlag. Parenti, R., Cicirata, F., Pantò, M.R. and Serapide, M.F. (1996). The projections of the lateral reticular nucleus to the deep cerebellar nuclei. An experimental analysis in the rat. Eur J Neurosci 8: 2157–67. Pouzat, C. and Hestrin, S. (1997). Developmental regulation of basket/stellate cell – Purkinje cell synapses in the cerebellum. J Neurosci 17: 9104–12. Rispal-Padel, L., Massion, J. and Grangetto, A. (1973). Relations between the ventrolateral thalamic nucleus and motor cortex and their possible role in the central organization of motor control. Brain Res 60: 1–20.

Rossi, D.J., Alford, S., Mugnaini, E. and Slater, N.T. (1995). Properties of transmission at a giant glutamatergic synapse in cerebellum: the mossy fiber–unipolar brush cell synapse. J Neurophysiol 74: 24–42. Sasaki, K., Matsuda, Y., Kawaguchi, S. and Mizuno, N. (1972). On the cerebello-thalamo-cerebral pathway for the parietal cortex. Exp Brain Res 16: 89–103. Schmahmann, J.D. and Pandya, D.N. (1997). The cerebrocerebellar system. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 31–60. San Diego: Academic Press. Schnitzlein, H.N. and Faucette, J.R. (1969). General morphology of the fish cerebellum. In Neurobiology of Cerebellar Evolution and Development, ed. R. Llinas, pp. 77–106. Chicago: American Medical Association. Schwarz, C. and Schmitz, Y. (1997). Projection from the cerebellar lateral nucleus to precerebellar nuclei in the mossy fiber pathway is glutamatergic: a study combining anterograde tracing with immunogold labeling in the rat. J Comp Neurol 381: 320–34. Serapide, M.F., Cicirata, F., Sotelo, C., Pantó, M.R. and Parenti, R. (1994). The pontocerebellar projection: longitudinal zonal distribution of fibers from discrete regions of the pontine nuclei to vermal and parafloccular cortices in the rat. Brain Res 644: 175–80. Shambes, G.M., Beermann, D.H. and Welker, W. (1978). Multiple tactile areas in cerebellar cortex: another patchy cutaneous projection to granule cell columns in rats. Brain Res 157: 123–8. Strick, P.L. (1976). Anatomical analysis of ventrolateral thalamic input to primate motor cortex. J Neurophysiol 39: 1020–31. Takács, J., Markova, L., Borostyanköi, Z., Görcs, T.J. and Hámori, J. (1999). Metabotrop glutamate receptor type 1a expressing unipolar brush cells in the cerebellar cortex of different species: a comparative quantitative study. J Neurosci Res 55: 733–48. Thach, W.T. (1967). Discharge of Purkinje and cerebellar nuclear neurons during rapidly alternating arm movements in the monkey. J Neurophysiol 31: 785–96. Trott, J.R., Apps, R. and Armstrong, D.M. (1998). Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 2. The C2 zone. Exp Brain Res 118: 298–315. Tsukahara, N., Fujito, Y. and Kubota, M. (1983). Specificity of the newly-formed corticorubral synapses in the kitten red nucleus. Exp Brain Res 51: 45–56. Voogd, J. (1964). The cerebellum of the cat. Thesis, University of Leiden. Voogd, J. and Glickstein, M. (1998). The anatomy of the cerebellum. Trends Neurosci 21: 370–5. Weiss, C., Houk, J.C. and Gibson, A.R. (1990). Inhibition of sensory responses of cat inferior olive neurons produced by stimulation of red nucleus. J Neurophysiol 64: 1170–84. Zheng, Z.H., Dietrichs, E. and Walberg, F. (1982). Cerebellar afferent fibres from the dorsal motor vagal nucleus in the cat. Neurosci Lett 32: 113–18.

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High-resolution cerebellar anatomy Arthur W. Toga and Colin Holmes Laboratory of Neuro Imaging, UCLA School of Medicine, Los Angeles, California, USA

Introduction Jansen and Brodal began their treatise on the cerebellum by pointing out its great morphological diversity across species, which appeared striking even within the mammals (Jansen and Brodal, 1954). While intriguing the early anatomists, this fascinating anatomy presents considerable challenges to current methods for imaging, mapping, and measuring morphology. These tasks are further complicated by today’s focus on functional imaging, which requires that the brain be mapped in vivo. The cerebellum’s gross features and major landmarks are easily distinguished with non-invasive techniques such as conventional magnetic resonance imaging (MRI), but novel techniques are required to discern its individual folia and deep nuclei. While the creation of stereotaxic atlas systems for the cerebral hemispheres has greatly facilitated the exchange and comparison of structural and functional data, the most ubiquitous stereotaxic systems and atlas spaces fail to define the cerebellum sufficiently in terms of its placement or delineation. This chapter describes progress in each of these problem areas. Specifically, it describes the use of a high-resolution cryosectioning approach that produces full-color, three-dimensional image volumes of in-situ anatomy and a multi-scan MRI approach to achieve superior in-vivo image volumes of cerebellar anatomy. It also describes efforts to rectify the standard cerebral atlases with multisubject mappings of this structure by use of informatics techniques and a deformable brain atlas.

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Post-mortem anatomy Human neuroanatomy From the early developmental, topological, and statistical descriptions of the cerebellum (Smith, 1902; Larsell, 1947; Jansen and Brodal, 1954; Blinkov and Glezer, 1968), anatomists have spent the intervening years creating finer resolution atlases of the cellular nature of the cerebellum, culminating in the stereology (Nairn et al., 1989; Henery and Mayhew, 1989; Mayhew et al., 1990; Andersen et al., 1992) and chemoarchitectonics (Rakic and Sidman, 1970; Braak and Braak, 1983; Powers et al., 1989; Yu et al., 1996) of modern histological and immunocytochemical surveys. These descriptions have been derived from post-mortem, histologically treated tissue samples. These, coupled with detailed templates that establish the boundaries and names of structures, result in atlases of the brain. Several histological collections have been produced as an anatomic reference for the human brain (Vogt and Vogt, 1942; Yakovlev, 1970), along with several atlases (Angevine et al., 1961; Larsell, 1967; Duvernoy, 1995), as well as an early form of probabilistic atlas (Afshar et al., 1978). Although providing a significant resource for morphometric studies (Kaufman and Galaburda, 1989; Kretschmann et al., 1989; Arnold et al., 1991), these data are limited because they do not enable visualization of the human brain as a three-dimensional structure or allow interpretation of complex spatial relationships between its substructures. Attempts to utilize the histologic material for digital reconstruction techniques have failed due to a paucity of source data and spatial inconsistencies (Kazarnovskaya et al., 1991). In several cases the cerebellum receives only cursory treatment or is absent altogether. When it is included, the detail of the delineations is not high. Although three-dimensional

High-resolution cerebellar anatomy

reconstructions of deep nuclear histology have begun to appear in the literature (Yamaguchi and Goto, 1997), they lack intensity of information and are laborious to produce. In addition, the use of histologic material incorporates artifacts caused by the staining and slide mounting process. In the cerebellum, each of these deficiencies is exacerbated due to its highly divided nature. MR-based atlases (Evans et al., 1991; Lehmann et al., 1991) have the advantage of intrinsic three-axis registration, but do not provide sufficient spatial resolution or anatomic contrast for comprehensive anatomic delineation. Here, too, the cerebellum has been described incompletely.

Cryosectioning Several years ago, the authors initiated a project to overcome some of the limitations listed above. We sought to create a description of brain anatomy that surpassed the resolution of in-vivo (i.e., MRI) techniques but retained the tomographic and three-dimensional attributes of in-situ sampling. We also wanted to collect data that had sufficiently high resolution and retained the texture and color available in histologically treated tissue. The product of our efforts was a method of digitally acquiring images from the block face of cryosectioned whole brain. This enabled reconstructions of unparalleled resolution, in full color, of the entire three-dimensional volume. The cerebellum was sampled along with the cerebrum and, as a benefit of a high sampling frequency of isotropic pixels, could be sliced in any orientation favorable to the question at hand. The technical details of the technique for whole human head and brain cryosectioning and digital image capture have been described elsewhere (Toga et al., 1993, 1994a, 1994b). These methods allow the collection of serially sectioned full-color images of brain within and without the cranium using a high-resolution ((1024  1024)24-bit) camera (Fig. 3.1). Digitization of the block face itself during the ongoing sectioning process (Quinn et al., 1993) preserves the spatial integrity of the data volume and reduces the time to produce comprehensive reconstructions. The results yield a three-dimensional volume. The spatial resolution of images derived from surface photography of sectioned anatomic specimens is higher than the limits of conventional MRI and can be increased either by the use of higher pixel count instruments, or by the capture of smaller (hence magnified) fields of view. The combination of cryosectioning and specimen surface photography provides the means for acquiring anatomic image data and the potential for the simultaneous collection of specimen tissue for histological analysis (Rauschning, 1986; Pech, 1988). Such methods have been used to yield high-

Fig. 3.1 Cryotome apparatus. The macrocryotome apparatus consists of a hydraulic sled on which the tissue is mounted, within a block of water ice. This powered sled drives the tissue block under a cryotome knife, to a stable position, where the freshly cut blockface is imaged by a camera whose focal plane is fixed at the level of the knife. This setup permits the collection of very high-quality digital images that are suitable for threedimensional reconstruction, such as that in the inset.

resolution, morphologically detailed imagery for correlation with other imaging modalities such as MR and computed tomography (CT) (Ho. et al., 1988; Philippou et al., 1990) or histology (Hirsch et al., 1989; Courchesne et al., 1989). Cryoplaned specimens have also been used in the production of digital atlases along with conventional film photography taken from the surface of the preparations (Bohm et al.,1983; Gerke et al., 1992). However, such atlases, based on secondary reconstruction of non-registered serial images, suffer from alignment and sampling problems.

High-resolution digital anatomy We were able to appreciate the natural color of the nonperfused brain (Fig. 3.2). The color quality demonstrated in these full-color images provided subtle texture and contrast characteristics that were not as readily apparent in similar monochrome images. Since these images of the block face are not histologically processed, the blood that remained in the non-perfused, fresh frozen tissue facilitated gray/white matter discrimination and made apparent many of the observed subnuclei and other smaller structures. As pointed out by Duvernoy and colleagues

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Fig. 3.2 Reconstructions of cryosectioned cerebellum. This figure demonstrates the quality of reconstructions possible with the cryosection apparatus described in Fig. 3.1. A mid-sagittal (A) and a parasagittal (B) view of the tissue block, reconstructed from the original coronal sections show the fine detail viewable within the cerebellar folia and deep nuclei. The full-color images allow the different tissue types (gray matter: brownish red; white matter: cream or tan; vessels: dark purple, blue, red; embedding media: bright white) to be clearly distinguished. Transverse sections (C, D) and enlargement (D) show the level of detail available, and the discrete edges of the dentate nuclei that facilitate segmentation.

lobules generally separated slightly along these structures. The remaining finer fissures were also clearly determined, whereas in some cases intrafoliar divisions were more difficult to visualize, especially in the depths where the tissue was tightly pressed together and partial volume effects became problematic. The deep nuclei of the cerebellum were evident, with the dentate being most easily observed in any plane (Fig. 3.2C and 3.2D). The fastigial and emboliform were less well distinguished, however, and the cell clusters forming the globus nucleus were quite difficult to make out. Associated structures in the brainstem, such as the olivary nucleus of the pons, were also finely discriminated in the cryosection volumes (Fig. 3.2A). The results of these post-mortem experiments produced unparalleled anatomic detail of the cerebellum while retaining tomographic three-dimensional spatial relationships. Further, the cerebellar anatomy was studied relative to the rest of the brain, and hence was amenable to modern brain mapping and atlasing strategies. These atlas strategies require a complete brain volume for correct placement within a coordinate system, within which comparisons between different modalities of the same subject (such as magnetic resonance, histology or even ante and post mortem) can be made. In addition, atlas strategies enable the comparison of data from different subjects with appropriate application of brain warping mathematical algorithms (Toga, 1998).

In-vivo human cerebellar anatomy (Duvernoy et al., 1983), the angioarchitectonic structure of the cerebellar cortex defines three lamina co-extensive with the molecular, Purkinje, and granular layers of the cerebellar cortex, a fact that results in intracortical contrast in our images. The embedding medium used to fix the brain en bloc to the cryotome stage was colored to facilitate distinction between brain and background. This was especially beneficial when examining the cerebellum, because of the relatively smaller folia and interstitial spaces. This difference was especially appreciated when edited data were compared with original digital images that contained the supporting ice block. Collection of the cerebellum in this way allowed for the observation of both lobular and deep nuclear anatomy. From the peduncles to the tips of the folia, the cerebellar white matter was clearly visible. Frequently, penetrating vessels appeared within the fibers as puncta (if cut across) or as dark blue striations (if imaged parallel to the plane of section). The larger fissures (e.g., primary, secondary, horizontal, posterolateral) were clearly visible (Fig. 3.2A) as the

There is a variety of robust computational methods for the registration of three-dimensional volumes between and within subjects and scanning modalities (Collins et al., 1994; Friston et al., 1995; Lancaster et al., 1995). In our approach, these tools are applied to intramodality scans from the same subject, with the result being post hoc enhancement of the signal-to-noise ratio through averaging. As each scan can be kept short, this gain comes without the cost of long individual scan times and therefore allows the production of higher quality images than those available from single MR scanning protocols. To evaluate this process, we scanned a single subject multiple times, compared the result of averaging these scans to single high-resolution scans, and examined the usefulness of the resulting volume in other brain-mapping applications (Holmes et al., 1998). The resulting collection of T1-weighted scans (minimum 1 mm isotropic voxels) was registered and averaged from 27 different scanning sessions of the same individual. The product of this was vastly superior imagery describing the anatomy of the whole brain, including the cerebellum

High-resolution cerebellar anatomy

(Fig. 3.3). The averaging reduced the noise inherent in MRI and resulted in better edge detection as well as discrimination of subnuclei. This intramodality, intrasubject averaging also helped the quality of T2 and proton dense images from the same sessions (not shown). Coupled with the cryosectioned data, these approaches provide a unique advantage for describing cerebellar anatomy and, when placed within a common reference system, can be used to interpret traditional MRI scans from other subjects. In contrast to standard clinical MRI (Fig. 3.3A), the averaging technique revealed not only the larger fissures, but also the fine divisions between and within the folia. Additionally, enhancing the contrast of the image allowed the dentate nucleus to be visualized in-vivo (Fig. 3.3C, 3.3D). While it is remarkable that the dentate is visible at all, the images still do not allow for segmentation, for which cryosection resolution is necessary (Fig. 3.4). These data have been replicated in additional serial intrasubject studies, to be published elsewhere.

Informatics and human brain mapping There are numerous aspects to brain mapping that are beyond the scope of this chapter. However, the ability to integrate diverse information describing brain structure and function is an essential element to brain mapping and particularly important in the study of the cerebellum. The cerebellum has recently received considerable attention from several different avenues of investigation (Desmond et al., 1998; Elliott and Dolan, 1998; Schmahmann et al., 1999) suggesting that our understanding of its structure and function can be greatly enhanced with the application of integrative methodologies. From microscopic to wholebrain organization, data can be acquired at many scales from subjects in various experimental conditions, at differing ages, and in a range of developmental or disease states. High-resolution post-mortem techniques, such as cryosectioning (as described above), can be used to bridge the gap between lower resolution in-vivo techniques, such as MRI, and ultra high-resolution methods, such as neurochemical and molecular mapping. Taking advantage of these different studies at different scales requires an approach that can register all of them into a single common representation. In this manner, a more complete characterization of regional anatomy and the integration of functional information at a very fine structural level can be achieved. One of the most critical elements to achieving such a multimodal representation is the ability to establish an accurate and adaptable anatomic reference system with

Fig. 3.3 High-resolution T1 MR. A total of 27 T1 MR scans were registered and averaged to produce panels A and B, which are sagittal (A) and transverse (B) planes reconstructed at 0.5 mm from a composite T1 volume. This technique produces images on a par with older cryosectioning techniques that are suitable for exploration of in-vivo anatomical mapping at the level of individual folia. Within the transverse plane (B), there is a suggestion of contrast in the region where the dentate would be expected to be seen, but this image is not robust or suitable for segmentation. Using higher field strengths, (3 Tesla, C, D), the dentate nucleus becomes apparent in as little as ten averages (1.0 mm3 T1 MR, different subject from A and B). Although visible, the boundaries of this structure are not sharp enough to permit accurate segmentation, due to partial volume effects and the large initial sampling (1.0 mm) relative to the size of the structure itself (0.25–0.5 mm).

which to index specific locations (Toga and Mazziotta, 1996). Unfortunately, the cerebellum has rarely received the attention the cerebrum has in establishing a welldefined and widely accepted reference system. Reference systems must provide sufficient anatomic information to achieve cytoarchitectural levels of detail on a comprehensive whole-brain scale. In addition, its basis must be able to accommodate the demands of all brain data modalities including data collected post mortem as well as in vivo. The result of such a reference system will be that anatomical descriptions based upon cryosectioned tissues can be used to interpret anatomies observed in vivo from MRI, for example. There are, however, at least two significant problems in defining a single reference system: (a) there is variability between the anatomies of different people, some generally

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Fig. 3.4 Surface reconstruction of cryosectioned dentate nucleus. Using the three-dimensional volume reconstruction of the cerebellum, the dentate nucleus was manually segmented and a surface was computed from the resulting binary volume. This surface was colored using a point-for-point transfer of the color data from the volume to the vertices of the surface. The left (A) and right (B) dentate nuclei from one subject are rendered, as observed from a position dorsal and caudal to the nuclei. This demonstrates both the resolution and potential for segmentation available from cryosection, and the utility of the full-color acquisition.

uninteresting that must be removed (such as variability from overall size) and other types that are the object of mapping (such as intersubject variability); and (b) the resolution of the data used to define the reference system may make difficult the incorporation of data from other more or less spatially resolving imaging equipment. To remove gross intrasubject variability, atlases are built in a commonly available and well-understood stereotaxic space (Talairach et al., 1967; Talairach and Tourneau 1988), where the normal variability arising from factors such as height and weight is reduced and where cross-center comparisons and data sharing can be performed. Studies of the residual anatomical variability within the common stereotaxic space have employed mean intensity (Evans et al., 1994) or probabilistic representations (Collins et al., 1995), but are still limited by detail in cerebellar regions and by the resolution of current anatomical MRI acquisitions. The development of the method by which the quality of standard MR images and the visibility of in-vivo fine neuroanatomical structures are enhanced allows us to bridge the gap between the relatively well-accepted atlases from MRI (Collins et al., 1995), and the cryosectioned brain data (Toga et al., 1997), and can also be applied to premortem and post-mortem data. Assuming that the anatomical descriptions obtained from the cryosectioned data and the multiscan MRI average are to form the basis for an atlas of the cerebellum, how can it be used for reference against anatomies of other

subjects? In both basic science investigations and clinical diagnosis, it is essential to determine quantitatively the severity of subtle deviations from normal brain structure and function. This exercise is especially difficult in the cerebellum, because its internal geometry is highly individual in character and there is evidence in some species that, depending on the position of the head and neck during image acquisition, the relationship to the rest of the brain may vary more than for other structures (Absher et al., 1992; Toga et al., 1993). Striking variations exist, across normal subjects, in the size, configuration, and complexity of brain substructures (Toga et al., 1993; Thompson et al., 1996). These complex variations have complicated the goals of comparing and integrating functional data from many subjects, and of developing standardized atlases of the human brain.

Deformable brain atlases In view of the complex structural variability between individuals, a fixed digital atlas, representing the anatomy of a single human brain, will fail to serve as a faithful representation of the brains of new subjects. It would, however, be ideal if an atlas could be elastically deformed to fit a new image set from an incoming subject. Transforming individual datasets into the shape of a single reference anatomy, or onto a three-dimensional digital brain atlas, removes subject-specific shape variations and allows subsequent comparison of brain function between individuals (Hardy et al., 1992). Conversely, high-dimensional warping algorithms can also be used to transfer all the information in a three-dimensional digital brain atlas onto the scan of any given subject, while respecting the intricate patterns of structural variation in their anatomy. Such deformable atlases (Gee et al., 1993; Miller et al., 1993) can be used to carry three-dimensional maps of functional and vascular territories into the coordinate system of different subjects, as well as information on different tissue types and the boundaries of cytoarchitectonic fields and their neurochemical composition. Deformable atlases rely on high-dimensional warping algorithms to drive them into precise structural correspondence with target brain images. The fine external features of the cerebellum make it ideally suited to a surface-based warping procedure, recently devised and implemented in our laboratory (Thompson and Toga, 1996). This algorithm was designed to calculate the high-dimensional deformation field relating the brain anatomies of an arbitrary pair of subjects or within the same subject over time, and to transfer functional information between subjects or

High-resolution cerebellar anatomy

integrate that information on a single anatomic template. High spatial accuracy can be guaranteed by using a large set of corresponding anatomic surfaces to constrain the complex transformation of one subject’s anatomy into the shape of another. These surfaces include critical functional interfaces such as the vermis and hemispheres, as well as numerous cytoarchitectonic and lobar boundaries in three dimensions. Connected systems of parametric meshes model deep internal fissures, or sulci, lobules or other readily observable boundaries whose trajectories represent critical functional divisions. These sulci are sufficiently extended inside the brain to reflect subtle and distributed variations in neuroanatomy between subjects. The parametric form of the system of connected surface elements allows us to represent the relation between any pair of anatomies as a family of high-resolution displacement maps carrying the surface systems of one individual onto another in stereotaxic space. The algorithm then calculates the high-dimensional volumetric warp (typically with 384  256  3 3D 0.1 billion degrees of freedom), deforming one three-dimensional scan into structural correspondence with the other. Integral distortion functions are used to extend the deformation field required to elastically transform these surface systems into structural correspondence with their counterparts in the target scan. Three-dimensional warping algorithms provide a method for calculating local and global shape changes and give valuable information about normal and abnormal growth and development. Deformable atlases not only account for the anatomic variations and idiosyncrasies of each individual subject, but they offer a powerful strategy for exploring and classifying age-related, developmental or pathologic variations in anatomy. More fundamentally, they also provide a method for spatially normalizing the anatomies of different brains. While the more esoteric of these algorithms may lie outside the reach of smaller laboratories, the development of distributed computing resources and the automation of warping algorithms may ultimately allow remote users to submit their own images for normalization to regional or national computational centers. Such a facility for consistent cross-center normalization and registration could supply a much more robust basis for comparing experimental or clinical data obtained from different subjects or different research centers than exists at the present time.

Conclusion The use of novel methods to describe the anatomy of the cerebellum, coupled with sophisticated atlas and warping

approaches, makes the study of this structure considerably more tractable. Increasing the spatial resolution of the source data provides obvious advantages in distinguishing details of the anatomy. However, most techniques that provide cytoarchitectural or chemoarchitectural information do so destructively and without benefit of threedimensional whole-brain reference. The cryosectioning and MRI averaging methods described here offer unique bridging modalities that help extend detailed neuroanatomic information into a multisubject deformable atlas framework.

Acknowledgments Thanks go to the staff of the Laboratory of Neuro Imaging, without whom this work would not have been possible. This work was supported, in part, by the National Center for Research Resources (P41-RR13642), the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health (NINDS/NIMH NS38753), the National Library of Medicine (LM/MH05639), the National Science Foundation (BIR 93-22434), and by a Human Brain Project grant to the International Consortium for Brain Mapping, funded jointly by NIMH and NIDA (P20 MH/DA52176).

xReferencesx Absher, J.R., Toga, A.W., Banerjee, P.K., Collins, R.C. and Santori, E.M. (1992). Neuroanatomic variability of rat brains. Neurosci Abstracts 18: 330. Afshar, F., Watkins, E.S. and Yap, J.C. (1978). Stereotaxic Atlas of the Human Brainstem and Cerebellar Nuclei: a Variability Study. New York: Raven Press. Andersen, B. B., Korbo, L. and Pakkenberg, B. (1992). A quantitative study of the human cerebellum with unbiased stereological techniques. J Comp Neurol 326(3): 549–60. Angevine, J.B. Jr, Mancall, E.L. and Yakolev, P.I. (1961). The Human Cerebellum: an Atlas of Gross Topography in Serial Sections, 1st edn. Boston: Little, Brown. Arnold, S.E., Hyman, B., vanHoesen, G. and Damasio, A. (1991). Some cytoarchitectural abnormalities of the entorhinal cortex in schizophrenia. Arch Gen Psychiatry 48: 625–32. Blinkov, S.M. and Glezer, I.I. (1968). The Human Brain in Figures and Tables; a Quantitative Handbook. Translated from the Russian by Basil Haigh. New York: Basic Books. Bohm, C., Greitz, T., Kingsley, D., Berggren, B. and Olsson, L. (1983). Adjustable computerized stereotaxic brain atlas for transmission and emission tomography. Am J Neuroradiol 4: 731–3. Braak, E. and Braak, H. (1983). On three types of large nerve cells in the granular layer of the human cerebellar cortex. Anat Embryol 166: 67–86.

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Collins, D.L., Holmes, C.J., Peters, T.M. and Evans, A.C. (1995). Automatic 3-D model-based neuroanatomical segmentation. Hum Brain Map 3: 190–208. Collins, D.L., Neelin, P., Peters, T.M. and Evans, A.C. (1994). Automatic 3D intersubject registration of MR volumetric data in standardized Talairach space. J Comput Assist Tomogr 18: 192–205. Courchesne, E., Press, G., Murakami, J. et al. (1989). The cerebellum in sagittal planes – anatomic–MR correlation. 1. The vermis. Am J Roentgenol 10:659–65. Desmond, J.E., Gabriele, J.D. and Glover, G.H. (1998). Dissociation of frontal and cerebellar activity in a cognitive task: evidence for a distinction between selection search. NeuroImage 7(4): 368–76. Duvernoy, H.M. (1995) The Human Brain Stem and Cerebellum: Surface, Structure, Vascularization, and Three-dimensional Sectional Anatomy with MRI. New York: Springer-Verlag. Duvernoy, H.S., Delon, S. and Vannson, J.L. (1983). The vascularization of the human cerebellar cortex. Brain Res Bull 11(4): 419–80. Elliott, R. and Dolan, R.J. (1998). Activation of different anterior cingulate foci in association with hypothesis testing and response selection. NeuroImage 8(1): 17–29. Evans, A., Marret, S., Torrescorzo, J., Ku, S. and Collins, L. (1991). MRI–PET correlation in three dimensions using a volume of interest (VOI) atlas. J Cereb Blood Flow Metab 11: 169–78. Evans, A.C., Kamber, M., Collins, D.L. and MacDonald, D. (1994). An MRI-based probabilistic atlas of neuroanatomy. In Magnetic Resonance Scanning and Epilepsy, ed. S.D. Shorvon, pp. 263–74. New York: Plenum Press. Friston, K.J., Ashburner, J., Frith, C.D., Poline, J-B., Heather, J.D. and Frackowiak, R.S.J. (1995). Spatial registration and normalization of images. Hum Brain Map, 3: 165–89. Gee, J.C., Reivich, M. and Bajcsy, R. (1993). Elastically deforming 3D atlas to match anatomical brain images. J Comput Assist Tomogr 17: 225–36. Gerke, M., Schutz, T. and Kretschmann, H. (1992). Computer assisted reconstruction and statistics of the limbic system. Anat Embryol 186: 129–36. Hardy, T., Brynildson, L.R., Gray, K.G. and Spurlock, D. (1992). Three-dimensional whole-brain mapping. Stereotact Funct Neurosurg 58: 141–3. Henery, C.C. and Mayhew, T.M. (1989). The cerebrum and cerebellum of the fixed human brain: efficient and unbiased estimates of volumes and cortical surface areas. J Anatomy 167: 167–80. Hirsch, W., Kemp, S., Martinez, A., Curtin, H., Latchaw, R. and Wolf, G. (1989). Anatomy of the brainstem: correlation of in vitro MR images with histologic sections. Am J Neuroradiol 10: 923–8. Ho, P., Yu, S., Czervionke, L. et al. (1988). MR and cryomicrotomy of C1 and C2 roots. Am J Neuroradiol 9: 928–31. Holmes, C.J., Hoge, R., Collins, L., Woods, R., Toga, A.W. and Evans, A.C. (1998). Enhancement of magnetic resonance images using registration for signal averaging. J Comput Assist Tomogr 22(2): 324–33.

Jansen, J. and Brodal, A. (1954). Aspects of Cerebellar Anatomy. Oslo: Anatomical Institute, University of Oslo, J.G. Tanum. Kaufmann, W.E. and Galaburda, A. (1989). Cerebrocortical microdysgenesis in neurologically ill subject: a histologic study. Arch Neurol 39: 238–44. Kazarnovskaya, M., Borodkin, S., Shabalov, V., Krivosheina, V. and Golanov, A. (1991). Three dimensional computer model of subcortical structures of human brain. Comput Biol Med 21(6): 451–7. Kretschmann, H.J., Schleicher, A., Grottschrieber, J.F. and Kullmann, W. (1989). The Yakolev Collection. J Neurosci 43: 111–26. Lancaster, J.L., Glass, T.G., Lankipalli, B.R., Downs, H., Mayberg, H. and Fox, P.T. (1995). A modality-independent approach to spatial normalization of tomographic images of the human brain. Hum Brain Map 3: 209–23. Larsell, O. (1947). The development of the cerebellum in man in relation to its comparative anatomy. J Comp Neurol 87: 85–129. Larsell, O. (1967). The Comparative Anatomy and Histology of the Cerebellum from Myxinoids through Birds, ed. J. Jansen. Minneapolis: University of Minnesota Press. Lehmann, E.D., Hawkes, D., Hil, D et al. (1991). Computer aided interpretation of SPECT images of the brain using an MRI derived neuroanatomic atlas. Med Inform (Lond) 16: 151–66. Mayhew, T. M., MacLaren, R. and Henery, C.C. (1990). Fractionator studies on Purkinje cells in the human cerebellum: numbers in right and left halves of male and female brains. J Anat 169: 63–70. Miller, M.I., Christensen, G.E., Amit, Y. and Grenander, U. (1993). Mathematical textbook of deformable neuroanatomies. Proc Natl Acad Sci USA 90: 11944–8. Nairn, J. G., Bedi, K.S., Mayhew, T.M. and Campbell, L.F. (1989). On the number of Purkinje cells in the human cerebellum: unbiased estimates obtained by using the ‘fractionator’. J Comp Neurol 290(4): 527–32. Pech, P. (1988). Correlative investigations of craniospinal anatomy and pathology with computed tomography, magnetic resonance imaging and cryomicrotomy. Acta Radiol (Suppl. Stockholm) 372: 127–8. Philippou, M., Stenger, G., Goumas, P., Hillen, B. and Huizig, E. (1990). Cross-sectional anatomy of the nose and paranasal sinuses: a correlative study of computer tomographic images and cryosections. Rhinology 28: 221–30. Powers, R.E., O’Connor, D.T. and Price, D.L. (1989). Noradrenergic systems in human cerebellum. Brain Res 481(1): 194–9. Quinn, B., Ambach, K.A. and Toga, A.W. (1993). Three-dimensional cryomacrotomy with integrated computer-based technology in neuropathology. Lab Invest 68: 121A. Rakic, P. and Sidman, R.L. (1970). Histogenesis of cortical layers in human cerebellum, particularly the lamina dissecans. J Comp Neurol 139(4): 473–500. Rauschning, W. (1986). Surface cryoplaning: a technique for clinical anatomical correlations. Uppsala J Med Sci 91: 251–5. Schmahmann, J.D., Doyon, J., McDonald, D. et al. (1999). Three dimensional MRI atlas of the human cerebellum in proportional stereotaxic space. NeuroImage 10: 233–60.

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Smith, G.E. (1902). The primary divisions of the mammalian cerebellum. J Anat Physiol 16: 381–5. Talairach, J., Szikla, G., Tournoux, P. et al. (1967). Atlas d’Anatomie Stéréotaxique du Télencéphale. Paris: Masson. Talairach, J. and Tourneau, P. (1988). Co-planar Stereotaxic Atlas of the Human Brain. New York: Thieme. Thompson, P., Schwartz, C., Lin, R.T., Khan, A.A. and Toga, A.W. (1996). 3D statistical analysis of sulcal variability in the human brain. J Neurosci 16(13): 4261–74. Thompson, P. and Toga, A.W. (1996). A surface-based technique for warping 3-dimensional images of the brain. IEEE Trans Med Imaging 15(4): 402–17. Toga, A.W. and Mazziotta, J.C. (1996). Brain Mapping: the Methods. San Diego: Academic Press. Toga, A.W., ed. (1998). Brain Warping. San Diego: Academic Press. Toga, A.W., Ambach, K.L., Quinn, B.C., Hutchin, M. and Burton, J.S. (1994a). Post mortem anatomy from cryosectioned whole human brain. J Neurosci Methods 54(2): 239–52. Toga, A.W., Ambach, K.L. and Schluender, S. (1994b). High-resolution anatomy from in situ human brain. NeuroImage 1(4): 334–44.

Toga, A.W., Goldkorn, A., Ambach, K., Chao, K., Quinn, B.C. and Yao, P. (1997). Postmortem cryosectioning as an anatomic reference for human brain mapping. Comput Med Imaging Graph 21(2): 131–41. Toga, A.W., Woods, R.P., Huang, C., Mazziotta, J. Cand Cai, R. (1993). Anatomic variability as measured with a 3D reconstructed Talairach atlas. Brain PET 93. Ann Nucl Med 7: 582–3. Vogt, C. and Vogt, O. (1942). Morphologische gestaltungen unter normalen und pathologen bedingungen: ein hirnanatomischer beitrag zu ihrer kenntnin. J Psychol Neurol 50: 11–310. Yakovlev, P. (1970). Whole brain serial histological sections. In Neuropathology: Methods and Diagnosis, ed. C.G. Tedeschi, pp. 371–8. Boston: Little Brown. Yamaguchi, K. and Goto, N. (1997). Three-dimensional structure of the human cerebellar dentate nucleus: a computerized reconstruction study. Anat Embryol 196(4): 343–8. Yu, M.C., Cho, E., Luo, C.B., Li, W.W., Shen, W.Z. and Yew, D.T. (1996). Immunohistochemical studies of GABA and parvalbumin in the developing human cerebellum. Neuroscience 70(1): 267–76.

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Neurotransmitters in the cerebellum Ole P. Ottersen and Fred Walberg Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, Norway

Introduction The aim of this chapter is to provide a brief overview of the neurotransmitters in the cerebellum, with a focus on the cerebellar cortex. We have chosen to devote most of the chapter to the recent advances in our understanding of ‘fast’ synaptic transmission and to provide a critical appraisal of some of the novel methods that have made these advances possible. Emphasis is placed on neurochemical and immunocytochemical data and how these data have led to the identification of cerebellar transmitters. Important issues that can be dealt with only superficially within the format of the present chapter include the diversity and synaptic localization of receptors, and their regulation and functional properties. Additional information and references may be sought in a recent review (Takumi et al., 1998) and in the studies of Somogyi and his colleagues (Baude et al., 1994; Nusser et al., 1994, 1996, 1998). The anatomy of the cerebellum is detailed in Chapter 2. For an exhaustive review of the chemoarchitecture of the cerebellum, the reader is referred to Voogd et al. (1996). The bibliography in this chapter is far from complete and is biased toward recent studies. References to earlier literature can be found in previous reviews (Ottersen and Storm-Mathisen, 1984; Mugnaini and Oertel, 1985; Ottersen, 1993).

The major afferent fiber systems to the cerebellar cortex Mossy and climbing fibers constitute the major afferent pathways to the cerebellar cortex (for references see Palay and Chan-Palay, 1974). It has long been known that these pathways are excitatory and that they have separate

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origins; the most important ones being the pontine nuclei and the inferior olive, respectively. The mossy fiber system is by far the more massive and establishes contacts with dendritic digits of granule cells. The latter cells are themselves excitatory (see below) and constitute the second leg in a disynaptic excitatory input to the Purkinje cells. In contrast, the climbing fibers excite the Purkinje cells directly, through their synapses on Purkinje cell dendritic thorns (Fig. 4.1). Both of the major afferent pathways mediate fast excitation (Ito, 1984) and it is thus not surprising that glutamate, now considered as the predominant fast excitatory transmitter in the central nervous system (CNS) (Seeburg, 1993; Hollmann and Heinemann, 1994), has been identified as a likely transmitter in these systems. However, the path leading to this conclusion has been long and tortuous, particularly in the case of the climbing fibers. As for the mossy fibers, a breakthrough came in 1986 with the demonstration that their terminals are enriched in glutamate (Somogyi et al., 1986). The latter study was based on a novel method that permits the contents of glutamate and other amino acids to be assessed in electron microscopically identified cell profiles. The basic features of this method are the use of antibodies that recognize specific amino acids following their fixation in situ by glutaraldehyde (Storm-Mathisen et al., 1983; also see Liu et al., 1989), and the subsequent visualization of the bound antibodies by IgG-coupled gold particles (for a review see Ottersen, 1989). By quantitation of the subcellular distribution of glutamate-signaling gold particles, it was later found that glutamate is associated with the synaptic vesicles of the mossy fibers (Ji et al., 1991) and that their glutamate pool can be released by depolarization with high potassium ion concentration (Ottersen et al., 1990a). Thus, it could be concluded that the glutamate within the mossy fibers is compartmentalized as expected of a transmitter

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PCN

Fig. 4.1 Schematic diagram showing the major cell types in the cerebellar cortex and their presumed transmitters. Stellate and basket cells (S and B) are indicated in black (for GABA); the Golgi cells (G) are shown in bottom left to top right stripes to indicate that they contain GABA (the probable transmitter) as well as glycine (not yet proved to have a transmitter role in these cells). The light shading of the Purkinje cells (P) points to their content of GABA and taurine (the latter amino acid may act as an osmoregulator rather than transmitter). Excitatory, presumed glutamatergic, systems are drawn in dark shading (mf, mossy fibers; GR and pf, granule cells and their parallel fibers; UBC, unipolar brush cells), whereas the top left to bottom right stripes of the climbing fibers (cf) leave open the possibility that these fibers use a signal molecule in addition to glutamate (see text). CN, cerebellar nuclei; PCN, precerebellar nuclei; IO, inferior olive. (Modified from Voogd et al., 1996.)

pool, and that it responds as such to experimental manipulations. The importance of this resides in the fact that much of the glutamate in the brain serves metabolic purposes unrelated to synaptic transmission (Ottersen et al., 1992). Hence, the mere presence of glutamate in a nerve terminal is insufficient evidence for transmitter identity. A transmitter role of glutamate in the synapses between mossy fibers and granule cells is supported by several lines of evidence. Notably, the postsynaptic elements have been shown to display several types of glutamate receptor, including N-methyl--aspartate (NMDA) and aminohydroxymethylisoxazolepropionate (AMPA) receptors (Cox et al., 1990; Gallo et al., 1992; Petralia and Wenthold, 1992), and pharmacological data point to glutamate as their likely endogenous ligand (Garthwaite and Brodbelt, 1990). It must not be overlooked that the mossy fiber system is heterogeneous and that subpopulations may use other transmitters instead of (or in addition to) glutamate. More than 20 years ago, Kan et al. (1978) demonstrated that some mossy fibers contain choline acetyl transferase (ChAT), suggesting that they use acetylcholine as transmitter. This notion has been strengthened by subsequent immunocytochemical studies, but there is still no consensus as to

the detailed extent and origin of the cholinergic fibers. Ojima et al. (1989; rat) concluded that ChAT-positive fibers distributed preferentially to lobules IXc and X, while Barmack et al. (1992a; rat, cat, rabbit, and monkey) traced ChAT-immunolabeled fibers to lobules IX and X, anterior vermis, and flocculus/ventral paraflocculus. The medial vestibular nucleus and nucleus prepositus hypoglossi have been proposed as the major sources of cholinergic fibers to the cerebellar cortex (Barmack et al., 1992b), although the cerebellar nuclei may also contribute (Ikeda et al., 1991). Some ChAT-immunopositive mossy fibers from the vestibular nuclei have been shown to contact unipolar brush cells (Mugnaini et al., 1997). The nucleo-cortical fibers may be particularly heterogeneous with respect to transmitter content. As noted above, a subpopulation of these may use acetylcholine as transmitter (Ikeda et al., 1991); others may depend on glutamate (Hamori, et al., 1990) or gamma-aminobutyric acid (GABA) (Chan-Palay et al., 1979; Hamori and Takacs, 1989; Hamori et al., 1990; Batini et al., 1992). The involvement of GABA would violate the general principle that all afferent ‘fast’ amino acid transmitters to the cerebellar cortex are excitatory. Mossy fibers have also been shown to contain a number

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of peptides that are unlikely to act as fast transmitters but which may serve modulatory functions. These include enkephalin (ENK), cholecystokinin (CCK), corticotrophin releasing factor (CRF), and calcitonin gene-related peptide (CGRP). A detailed description of these peptides is beyond the scope of the present chapter; the reader is referred to the review of Voogd et al. (1996). The climbing fibers are now believed to use glutamate as transmitter, like the majority of the mossy fibers. The climbing fibers are as strongly enriched in glutamate as the latter (Ottersen et al., 1992) and face thorns that express high concentrations of AMPA receptors (Landsend et al., 1997). Further, early studies showed that the climbing fibers take up and retrogradely transport D-[3H]aspartate to their perikarya in the inferior olive (Wiklund et al., 1984). The latter finding would also be consistent with the idea that the climbing fibers use -aspartate as transmitter, in addition to or instead of -glutamate. This is because the glutamate transporters that are identified by use of the metabolically inert tracer -[3H]aspartate do not differentiate between -aspartate and -glutamate (Danbolt et al., 1994). In fact, -aspartate was long held to be a likely climbing fiber transmitter. Supporting this view were slice experiments showing that evoked release of endogenous aspartate from the cerebellar cortex could be reduced by lesions of the inferior olive by 3-acetylpyridine (Toggenburger et al., 1983; Vollenweider et al., 1990). However, by use of specific antibodies and quantitative immunogold analyses, it could be demonstrated that the level of -aspartate in climbing fiber terminals was low, as compared with the average tissue level and with the level of this amino acid in the parent cell bodies in the inferior olive (Zhang et al., 1990). Several explanations have been put forward to reconcile these data (Ottersen, 1993). Perhaps the most likely of these is that a relative shortage of oxygen and energy substrates during the preparation and incubation of brain slices leads to a build-up of -aspartate in nerve terminals that contain only sparse amounts of this amino acid under physiological conditions (Gundersen et al., 1998). One must also leave open the possibility that immunogold analyses fail to reveal the entire endogenous pool of transmitter -aspartate, either because this pool is released during the preparation of the tissue, or because it is inaccessible to immunogold detection. Another excitatory amino acid that has been implicated in climbing fiber neurotransmission is homocysteic acid (HCA; Cuénod et al., 1989). Like -aspartate, this sulfurcontaining amino acid is released in smaller quantities than normal following lesions of the inferior olive (Vollenweider et al., 1990). However, later studies of the cerebellar cortex showed that HCA-like immunoreactivity

is largely confined to glial elements, including the Bergmann fibers (Grandes et al., 1991; Zhang and Ottersen, 1992, 1993). This rules out a transmitter role of HCA in climbing fibers. The possibility remains that HCA is engaged in an unorthodox signaling process involving release from glial cells. In conclusion, there is little doubt that the climbing fibers use an excitatory amino acid as transmitter (although N-acetylaspartylglutamate has been proposed as an additional candidate; Renno et al., 1997). In an elegant experiment supporting this view, Takahashi et al. (1996) showed that injections of -aspartate into Purkinje cells prolonged the excitatory postsynaptic current (EPSC) at climbing fiber synapses. The most likely explanation of this finding is that the injected -aspartate inhibits an excitatory amino acid transporter that normally contributes to the removal of transmitter from the synaptic cleft (also see Otis et al., 1997). Candidate transporters are excitatory amino acid transporter type 4 (EAAT4), which is concentrated at specific membrane domains in Purkinje cell spines (Dehnes et al., 1998), and EAAT3 (formerly EAAC1), which is more generally distributed in neuronal plasma membranes (Rothstein et al., 1994). Like the mossy fibers, the climbing fibers contain a number of peptides with possible modulatory functions (for a review see Voogd et al., 1996). Some are only transiently expressed during development (e.g., somatostatin and CGRP). There are also notable species differences. Enkephalin serves as an example, being present in the opossum (King et al., 1986) but not in the other species that have been investigated. Several of the peptides are concentrated in parasagittal bands of the cerebellar cortex. The distribution of CRF, ENK, and CCK has been reviewed by King et al. (1992).

Parallel fibers It was mentioned above that the granule cells with their parallel fibers serve as the second leg of a disynaptic excitatory input to the Purkinje cells. There are few fiber systems in the brain for which the evidence favoring glutamate as a transmitter is more compeling than in the case of the parallel fibers. An important piece of evidence came with the study of Young et al. (1974), who observed that a granule cell loss (caused by virus infection) was accompanied by a decreased content of glutamate and glutamate/aspartate uptake in the cerebellar cortex. Subsequent investigations based on similar paradigms confirmed and extended this study by showing that the content, uptake, as well as the

Neurotransmitters in the cerebellum

release of glutamate depend on intact granule cells (for reviews see Ito, 1984; Ottersen and Storm-Mathisen, 1984). A direct demonstration of glutamate in identified parallel fiber terminals became possible with the advent of the postembedding immunogold technique for glutamate (Somogyi et al., 1986; Ottersen, 1987). The nerve terminal pool of glutamate can be depleted by high [K] consistent with its involvement in synaptic transmission (Ottersen et al., 1990a; also see preceding section). The Purkinje cell spines apposed to parallel fibers are equipped with high densities of AMPA receptors, as shown at high anatomical resolution in the electron microscope (Baude et al., 1994; Nusser et al., 1994; Landsend et al., 1997). The postsynaptic densities of these synapses also contain 2-receptors (Landsend et al., 1997). The 2-receptors are classified as glutamate receptors due to their sequence homology with the latter, but they fail to bind glutamate, and their biological role is therefore unclear. However, knockout studies have indicated that the 2receptors play a role in synaptic plasticity and cerebellar development (Kashiwabuchi et al., 1995; Kurihara et al., 1997), and a mutation of this receptor has been identified as a likely cause of the neurological deficits in the Lurcher mice (Zuo et al., 1997). Interestingly, the 2-receptors are restricted to those parallel fiber synapses that are established with Purkinje cell dendritic spines (Landsend et al., 1997). No such receptors were detected postsynaptic to parallel fibers apposed to cerebellar interneurons. The latter finding suggests that, although all parallel fiber synapses may use glutamate as transmitter, they may be heterogeneous in other respects. Studies of the electron microscopic distribution of glutamate transporters have provided another example of this. Using the postembedding immunogold technique, it was reported that GLAST (the predominant glial glutamate transporter in the cerebellum; Torp et al., 1994; Lehre et al., 1995) is more abundant around parallel fiber–Purkinje cell synapses than around parallel fiber–interneuron synapses (Chaudhry et al., 1995). This reflects the more elaborate glial investment of the former type of synapse and the preferential expression of GLAST at those glial plasma membrane domains that surround the synaptic cleft (Chaudhry et al., 1995). These anatomical data suggest – as do physiological studies (Barbour et al., 1994) – that the two types of synapse differ as to the degree by which glial glutamate transport contributes to the termination of transmitter action. While the data supporting a transmitter role of glutamate in parallel fibers are indeed overwhelming, it remains to be clarified how their transmitter pool is replenished. It is widely assumed that the bulk of transmitter glutamate is synthesized through phosphate-activated glutaminase

(PAG; Kvamme et al., 1988). Recently, the availability of new antibodies to PAG has made it possible to analyze the precise subcellular distribution of this enzyme in a semiquantitative manner (Laake et al., 1999). It was found that PAG was strongly enriched in mossy fiber terminals, as could be expected on the basis of their presumed glutamatergic nature (see above). However, the parallel fibers showed a modest level of PAG immunoreactivity (although clearly higher than that in glial cells). It is possible that direct presynaptic uptake of glutamate contributes more to transmitter replenishment in the parallel fiber synapses than in other synapses (such as those of mossy fibers), although alternative explanations of their low PAG content must also be considered (Laake et al., 1999).

Purkinje cells The Purkinje cell – the only output neuron in the cerebellar cortex – is the archetypical GABAergic cell in the mammalian brain. Following early pharmacological studies of the postsynaptic inhibition of Purkinje cells on Deiters neurons (Ito and Yoshida, 1964; Obata et al., 1967), the case for GABA as the Purkinje cell transmitter was reinforced by the finding that the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) is specifically associated with these cells (Fonnum et al., 1970). Several immunocytochemical studies with antibodies to GAD or GABA have revealed rather low signals in the Purkinje cell bodies. It is now clear that GAD (Mugnaini and Oertel, 1985) as well as GAD mRNA (Wuenschell et al., 1986; Willcutts and Morrison-Bogorad, 1991) are present throughout the Purkinje cell population and that negative results in early studies are probably explained by methodological factors. It has also been proposed that newly synthesized GAD is rapidly transported into the axon and that its short transit time in the cell body may foil attempts to reveal its reaction product or the enzyme itself. In contrast, the nerve terminals of the Purkinje cells are consistently enriched in GAD as well as GABA (Ottersen and StormMathisen, 1984; Mugnaini and Oertel, 1985; Ottersen et al., 1988a). Could the Purkinje cells (or subpopulations of these) use other signal substances, in addition to GABA? The neuroactive amino acid taurine is concentrated in the Purkinje cells and is enriched in their terminals relative to their cell bodies (Ottersen et al., 1988a). However, it still remains to be shown that taurine is released from the Purkinje cell terminals under physiological conditions. It is possible that taurine in Purkinje cells simply acts as an organic osmolyte. Thus, hypo-osmotic stress causes a transfer of taurine

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from Purkinje cell bodies to neighboring glial cells (Nagelhus et al., 1993), which can be reversed by injections of hypertonic saline. This neuronal–glial exchange of taurine could serve to maintain the Purkinje cell volume in the face of osmotic changes. One of the many peptides that have been identified in Purkinje cells is the pituitary adenylate cyclase-activating polypeptide (PACAP; Nielsen et al., 1998; Skoglosa et al., 1999). It was suggested that PACAP could act as a cerebellar transmitter (Nielsen et al., 1998), but this hypothesis awaits rigorous testing. The effect of this peptide on apoptosis and cerebellar development is well documented (Skoglosa et al., 1999; Vaudry et al., 1999). Notably, it has been reported that PACAP, through interaction with specific receptors, increases proliferation (or inhibits programmed cell death) of granule cells, and stimulates their migration (Vaudry et al., 1999). Purkinje cells have been reported to show a transient expression of ChAT and CGRP, and subpopulations of Purkinje cells in adult rat cerebellum contain somatostatin (see Voogd et al., 1996, for references).

Inhibitory interneurons GABA is not only a well-established transmitter of Purkinje cells, but is also assumed to be the predominant transmitter of cerebellar interneurons (the unipolar brush cell seems to be an exception to this rule; see below). The inhibitory nature of stellate and basket cells was established more than 30 years ago (Andersen et al., 1964; Eccles et al., 1966) and immunocytochemical studies have revealed GABA as well as GAD in stellate and basket cells, as well as in the Golgi cells of the granule cell layer (for reviews see Ottersen and Storm-Mathisen, 1984; Mugnaini and Oertel, 1985). These types of inhibitory interneuron are also equipped with uptake mechanisms for GABA, as shown by autoradiography (Hökfelt and Ljungdahl, 1970; Schon and Iversen, 1972) and, more recently, by use of antibodies to GABA transporters (Radian et al., 1990; Morara et al., 1996; Itouji et al., 1996; Yan and Ribak, 1998). Further evidence has been provided by immunogold studies that have revealed GABAA receptors postsynaptic to interneuron terminals in the molecular as well as the granule cell layer of the cerebellar cortex (see Somogyi et al., 1996, and Nusser et al., 1998, for references). The study by Nusser et al. (1998) suggests that phasic and tonic inhibition of granule cells are mediated by different combinations of GABAA receptor subunits. GABA may not be the only inhibitory signal substance of cerebellar interneurons. One of the first studies that

pointed to a role of glycine in cerebellar neurotransmission was that of Wilkin et al. (1981). This study demonstrated high-affinity uptake of radiolabeled glycine in a subpopulation of Golgi cells. With the advent of amino acid immunocytochemistry, it could be shown that as many as 70% of the Golgi cells coexpressed GABA and glycine (Ottersen et al., 1988b) and that both amino acids could be depleted by high [K] (Ottersen et al., 1990b). A colocalization of GABA and glycine has been reported for numerous nerve terminal populations in the lower brainstem and spinal cord and is consistent with data suggesting that GABA and glycine are carried by the same vesicular transporter (Burger et al., 1991; Christensen et al., 1991). In other words, those GABAergic neurons that are equipped with a machinery for glycine synthesis (or uptake) would be expected to display both amino acids in their synaptic vesicles. Recent physiological data from the spinal cord confirm that a single synaptic vesicle may contain a mixture of GABA and glycine (Jonas et al., 1998). It remains to be determined whether the glycine-containing Golgi cell terminals in the cerebellum are apposed to postsynaptic membranes carrying glycine receptors. A majority of the granule cells in cerebellar slices do respond to exogenous glycine (as well as exogenous GABA), but the spontaneous synaptic currents were eliminated by bicuculline, suggesting that they were mediated by GABA only (Kaneda, 1995). In contrast, Golgi cells themselves have been reported to receive both glycinergic and GABAergic inputs (Dieudonne, 1995). Further attesting to the chemical heterogeneity of Golgi cells are data showing that some of them (less than 5%; Illing, 1990) display ChAT-immunoreactivity (Illing, 1990; Ikeda et al., 1991). These studies were done in the cat, where ChAT immunopositive neurons occurred in the vermis as well as in the hemispheres. ChAT-immunoreactive Golgi cells have not been identified in rats. Immunocytochemical studies have also revealed that a subpopulation of Golgi cells contain [met]enkephalin-arg-gly-leu (rat; Ibuki et al., 1988). This peptide was coexpressed with GABA. In contrast to the Golgi cells, the stellate and basket cells appear to be chemically uniform. At one stage it was thought that subpopulations of stellate cells used taurine as transmitter, but it was later shown that taurine is largely restricted to Purkinje cells (Madsen et al., 1985; Ottersen, 1988). A lesser known interneuron in the cerebellar cortex is the Lugaro cell, a fusiform cell type located just beneath the Purkinje cell layer. The Lugaro cells were recently found to project to basket and stellate cells and to be uniformly GABA immunoreactive (Laine and Axelrad, 1998). Some of the Lugaro cells also contain glycine (Ottersen et al., 1987).

Neurotransmitters in the cerebellum

Among the interneurons, the unipolar brush cell (Mugnaini et al., 1997) is exceptional in that it is enriched in glutamate and is presynaptic to glutamate receptors (Nunzi and Mugnaini, 1999). These observations suggest that the unipolar brush cell is glutamatergic. The axons of this cell type contact granule cells and other unipolar brush cells, and presumably also Golgi cells (Nunzi and Mugnaini, 1999; see also Chapter 2).

Monoaminergic input to the cerebellum Beaded fibers, differing morphologically from mossy and climbing fibers, terminate in all layers of the cerebellar cortex. This ‘third afferent system’ constitutes the monoaminergic input to the cerebellum and serves a series of modulatory roles. The noradrenergic input from the locus ceruleus has been reported to modulate the responses of cerebellar neurons to glutamate and GABA (for references to early literature, see Ottersen, 1993). In a recent study by Kondo and Marty (1998), it was found that noradrenaline increased the firing rate of stellate cells, but reduced the probability of evoked GABA release. This was interpreted to suggest that noradrenaline differentially affects action potentialdependent and action potential-independent transmitter release. It has also been proposed that activation of the noradrenergic input may potentiate the depressant effects of ethanol on Purkinje cells (Wang et al., 1999). Purkinje cells appear to be the main target of the noradrenergic input to the cerebellar cortex (Voogd et al., 1996). Serotonin fibers to the cerebellum were found to originate in different parts of the brainstem reticular formation, including the paramedian and lateral reticular nuclei, the periolivary reticular formation, and the lateral tegmental field (cat; Kerr and Bishop, 1991). These results were obtained by combining retrograde tracing with immunocytochemical detection of fixed serotonin. No doublelabeled cells were detected in the raphe nuclei. This negative finding is surprising and opens the possibility that the well-documented raphe–cerebellar projection contains a transmitter other than serotonin. Serotonin fibers appear to reach all parts of the cerebellum except lobule X (cat; Kerr and Bishop. 1991), and application of serotonin has been reported to inhibit glutamate release from mossy fibers (Maura et al., 1991) and to modulate responses to GABA (Strahlendorf et al., 1989). Recent data suggest that the serotoninergic input to the cerebellum regulates the activity and expression of glial GABA transporters (Voutsinos et al., 1998). It is still unclear whether the cerebellum has a biologi-

cally significant dopamine innervation (see Voogd et al., 1996, for a critical discussion of this issue).

Hypothalamic input to the cerebellum Fibres from the posterior, lateral, and dorsal hypothalamic areas, and the lateral mammillary and periventricular nuclei have been traced to the cerebellar cortex, with a preferential distribution in the flocculus and vermis (Dietrichs, 1984). The hypothalamic input to the cerebellum is believed to give rise to the histamine-immunopositive fibers that reach all cortical layers, as described in the rat (Inagaki et al., 1988) and guinea-pig (Airaksinen and Panula, 1988). Histamine H1 receptors are preferentially expressed on Purkinje cell dendrites (Rotter and Frostholm, 1986).

Nitric oxide We have chosen to discuss nitric oxide (NO) under a separate heading because the properties of this signal substance set it apart from the classical transmitters. A gaseous molecule, NO can diffuse freely from cell to cell independently of synaptic specializations. It is synthesized from arginine by NO synthase, which comes in several isoforms. Garthwaite et al. (1988) made the important discovery that activation of NMDA receptors in the cerebellum leads to cyclic guanosine monophosphate (cGMP) formation through stimulation of NO synthesis. Granule cells have been identified as a main source of NO, and glial cells as a main site of cGMP formation. The neuronal isoform of NO synthase is found in granule cells and parallell fibers as well as basket cells (Bredt et al., 1990, 1991), while cGMP immunoreactivity occurs in many cell types, with a predominance in Bergmann glia and astrocytes (see de Vente et al., 1989, and references therein). Immunocytochemical analyses of cGMP in Purkinje cells have given inconsistent results (compare de Vente et al., 1989, with Sakaue et al., 1988). A release of NO from parallel fibers has been demonstrated by use of electrochemical probes (Shibuki and Kimura, 1997) and is believed to play a part in long-term depression (LTD), a form of plasticity in the parallel fiber–Purkinje cell synapse which may be involved in motor learning (Daniel et al., 1998; Levenes et al., 1998). NO synthesis in neurons may depend on a supply of precursor arginine from glial cells (Grima et al., 1997), thus pointing to an important mode of neuronal–glial interaction. It has been suggested that NO from unipolar brush cells is involved in vestibular compensation after unilateral labyrinthectomy (Kitahara et al., 1999).

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A more comprehensive survey of the extensive literature on NO must be sought elsewhere (e.g., Voogd et al., 1996; Daniel et al., 1998; Levenes et al., 1998).

Conclusion For the major afferent fiber systems to the cerebellar cortex, the output neurons (Purkinje cells), and main categories of interneuron, the principal transmitters have now been identitified beyond reasonable doubt. The simple picture that has emerged during the last decade is that glutamate mediates transmission of climbing, mossy, and parallel fibers, while GABA is the predominant transmitter of the Purkinje cells as well as the basket, stellate, and Golgi cells. Superimposed on the glutamate and GABA circuitries, and exerting a modulatory role on these, are monoaminergic inputs from well-defined serotonin-containing and noradrenaline-containing cell groups in the brainstem. There is also compelling evidence that NO plays a key role in cerebellar physiology, most importantly as an essential factor in LTD. This type of synaptic plasticity seems to depend on an interaction between several molecules, including NO, glutamate (the principal transmitter of parallel fibers), and a number of ion channels and intracellular signal cascades (Daniel et al., 1998). Faced with the simplicity of this general scheme, one must not forget that our understanding of cerebellar neurotransmission is still far from complete. Among the other outstanding questions are: (1) To what extent is release of the principal transmitter accompanied by a corelease of other signal substances? (2) Does co-release occur onto postsynaptic membranes containing the appropriate receptors, and, if so, how do the co-released substances interact? These questions are particularly relevant in the case of the Golgi cells (shown to colocalize GABA and glycine), mossy fibers (some of which may coexpress glutamate and acetylcholine), and Purkinje cell terminals (containing GABA as well as taurine). Another lacuna in our knowledge is to what extent the postsynaptic response to the principal transmitter is regulated by the spatial disposition and subunit profile of the major ionotropic and G-protein coupled receptors. Data obtained so far (Baude et al., 1994; Nusser et al., 1994, 1998) indicate that such factors may contribute significantly to the repertoire of postsynaptic responses in the cerebellum. In fact, it seems reasonable to speculate that the diversity of synaptic responses is ensured primarily by the spatial arrangement, subunit composition, and properties of the postsynaptic receptors, and that transmitter heterogeneities play a more modest role.

On a more general level, one needs to clarify the role of glial cells in synaptic transmission. Glial processes are intimately apposed to certain types of cerebellar synapse and express transporters and receptors for the major amino acid transmitters (see above). The functional implications of this are only beginning to be unravelled. Further, although touched upon only briefly in the present review, it is clear that glial cells are biochemically coupled to surrounding neurons, providing metabolic intermediates and transmitter precursors. Evidence is also accruing that they release bona fide neuroactive substances. But the mechanisms effecting this release await characterization. Over the entire field looms the grand question: to what extent can knowledge about cerebellar neurotransmission contribute to better insight in the functional role of the cerebellum at large? Novel methodologies allowing selective knockout of receptors (Kashiwabuchi et al., 1995) and targeted ablation of specific cell populations (Watanabe et al., 1998) provide valuable information, but such approaches must be accompanied by efforts to understand better the properties and behavior of neuronal ensembles. Only then can we start to bridge the gap between synapse physiology and cerebellar function.

xReferencesx Airaksinen, M.S. and Panula, P. (1988). The histaminergic system in the guinea pig central nervous system: an immunocytochemical mapping study using an antiserum against histamine. J Comp Neurol 273: 163–86. Andersen, P., Eccles, J.C. and Voorhoeve, P.E. (1964). Postsynaptic inhibition of cerebellar Purkinje cells. J Neurophysiol 27: 1139–53. Barbour, B., Keller, B.U., Llano, I. and Marty, A. (1994). Prolonged presence of glutamate during excitatory synaptic transmission to cerebellar Purkinje cells. Neuron 12: 1331–43. Barmack, N.H., Baughman, R.W. and Eckenstein, F.P. (1992a). Cholinergic innervation of the cerebellum of rat, rabbit, cat, and monkey as revealed by choline acetyltransferase activity and immunohistochemistry. J Comp Neurol 317: 233–49. Barmack, N.H., Baughman, R.W., Eckenstein, F.P. and Shojaku, H. (1992b). Secondary vestibular cholinergic projection to the cerebellum of rabbit and rat as revealed by choline acetyltransferase immunohistochemistry, retrograde and orthograde tracers. J Comp Neurol 317: 250–70. Batini, C., Compoint, C., Buisseret-Delmas, C., Daniel, H. and Guegan, M. (1992). Cerebellar nuclei and the nucleocortical projections in the rat: retrograde tracing coupled to GABA and glutamate immunohistochemistry. J Comp Neurol 315: 74–84. Baude, A., Molnar, E., Latawiec, D., McIlhinney, R.A. and Somogyi, P. (1994). Synaptic and nonsynaptic localization of the GluR1

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subunit of the AMPA- type excitatory amino acid receptor in the rat cerebellum. J Neurosci 14: 2830–43. Bredt, D.S., Glatt, C.E., Hwang, P.M., Fotuhi, M., Dawson, T.M. and Snyder, S.H. (1991). Nitric oxide synthase protein and mRNA are discretely localized in neuronal populations of the mammalian CNS together with NADPH diaphorase. Neuron 7: 615–24. Bredt, D.S., Hwang, P.M. and Snyder, S.H. (1990). Localization of nitric oxide synthase indicating a neural role for nitric oxide. Nature 347: 768–70. Burger, P.M., Hell, J., Mehl, E., Krasel, C., Lottspeich, F. and Jahn, R. (1991) GABA and glycine in synaptic vesicles: storage and transport characteristics. Neuron 7: 287–93. Chan-Palay, V., Palay, S.L. and Wu, J-Y. (1979). Gammaaminobutyric acid pathways in the cerebellum studied by retrograde and anterograde transport of glutamic acid decarboxylase antibody in vivo injections. Anat Embryol 157: 1–14. Chaudhry, F.A., Lehre, K.P., van Lookeren Campagne, M., Ottersen, O.P., Danbolt, N.C. and Storm-Mathisen, J. (1995). Glutamate transporters in glial plasma membranes: highly differentiated localizations revealed by quantitative ultrastructural immunocytochemistry. Neuron 15: 711–20. Christensen, H., Fykse, E.M. and Fonnum, F. (1991). Inhibition of gamma-aminobutyrate and glycine uptake into synaptic vesicles. Eur J Pharmacol 207: 73–9. Cox, J.A., Felder, C.C. and Henneberry, R.C. (1990). Differential expression of excitatory amino acid receptor subtypes in cultured cerebellar neurons. Neuron 4: 941–7. Cuénod, M., Do, K.-Q., Vollenweider, F., Zollinger, M., Klein, A. and Streit, P. (1989). The puzzle of the transmitters in the climbing fibers. In The Olivocerebellar System in Motor Control, ed. P. Strata, pp. 162–76. Berlin: Springer Verlag. Danbolt, N.C., Storm-Mathisen, J. and Ottersen, O.P. (1994). Sodium/potassium-coupled glutamate transporters, a ‘new’ family of eukaryotic proteins: do they have ‘new’ physiological roles and could they be new targets for pharmacological intervention? Progr Brain Res 100: 53–60. Daniel, H., Levenes, C. and Crepel, F. (1998). Cellular mechanisms of cerebellar LTD. Trends Neurosci 21: 401–7. de Vente, J., Bol, J.G. and Steinbusch, H.W. (1989). Localization of cGMP in the cerebellum of the adult rat: an immunohistochemical study. Brain Res 504: 332–7. Dehnes, Y., Chaudhry, F.A., Ullensvang, K., Lehre, K.P., StormMathisen, J. and Danbolt, N.C. (1998). The glutamate transporter EAAT4 in rat cerebellar Purkinje cells: a glutamate-gated chloride channel concentrated near the synapse in parts of the dendritic membrane facing astroglia. J Neurosci 18: 3606–19. Dietrichs, E. (1984). Cerebellar autonomic function: direct hypothalamocerebellar pathway. Science 223: 591–3. Dieudonne, S. (1995). Glycinergic synaptic currents in Golgi cells of the rat cerebellum. Proc Natl Acad Sci USA 92: 1441–5. Eccles, J.C., Llinas, R. and Sasaki, K. (1966). The inhibitory interneurones within the cerebellar cortex. Exp Brain Res 1: 1–16. Fonnum, F., Storm-Mathisen, J. and Walberg, F. (1970). Glutamate decarboxylase in inhibitory neurons. A study of the enzyme in Purkinje cell axons and boutons in the cat. Brain Res 20: 259–75.

Gallo, V., Upson, L.M., Hayes, W.P., Vyklicky, L.Jr, Winters, C.A. and Buonanno, A. (1992). Molecular cloning and developmental analysis of a new glutamate receptor subunit isoform in cerebellum. J Neurosci 12: 1010–23. Garthwaite, J. and Brodbelt, A.R. (1990). Glutamate as the principal mossy fiber transmitter in rat cerebellum: pharmacological evidence. Eur J Neurosci 2: 177–80. Garthwaite, J., Charles, S.L. and Chess-Williams, R. (1988). Endothelium-derived relaxing factor release on activation of NMDA receptors suggests role as intercellular messenger in the brain. Nature 336: 385–8. Grandes, P., Do, K.Q., Morino, P., Cuenod, M. and Streit, P. (1991). Homocysteate, an excitatory transmitter candidate localized in glia. Eur J Neurosci 3: 1370–3. Grima, G., Benz, B. and Do, K.Q. (1997). Glutamate-induced release of the nitric oxide precursor, arginine, from glial cells. Eur J Neurosci 9: 2248–58. Gundersen, V., Chaudhry, F.A., Bjaalie, J.G., Fonnum, F., Ottersen, O.P. and Storm-Mathisen, J. (1998). Synaptic vesicular localization and exocytosis of -aspartate in excitatory nerve terminals: a quantitative immunogold analysis in rat hippocampus. J Neurosci 18: 6059–70. Hamori, J. and Takacs, J. (1989). Two types of GABA-containing axon terminals in cerebellar glomeruli of cat: an immunogold-EM study. Exp Brain Res 74: 471–9. Hamori, J., Takacs, J. and Petrusz, P. (1990). Immunogold electron microscopic demonstration of glutamate and GABA in normal and deafferented cerebellar cortex: correlation between transmitter content and synaptic vesicle size. J Histochem Cytochem 38: 1767–77. Hökfelt, T. and Ljungdahl, A. (1970). Cellular localization of labeled gamma-aminobutyric acid (3H-GABA) in rat cerebellar cortex: an autoradiographic study. Brain Res 22: 391–6. Hollmann, M. and Heinemann, S. (1994). Cloned glutamate receptors. Ann Rev Neurosci 17: 31–108. Ibuki, T., Okamura, H., Miyazaki, M., Kimura, H., Yanaihara, N. and Ibata, Y. (1988). Colocalization of GABA and [Met]enkephalinArg6-Gly7-Leu8 in the rat cerebellum. Neurosci Lett 91: 131–5. Ikeda, M., Houtani, T., Ueyama, T. and Sugimoto, T. (1991). Choline acetyltransferase immunoreactivity in the cat cerebellum. Neurosci 45: 671–90. Illing, R.-B. (1990). A subtype of cerebellar Golgi cells may be cholinergic. Brain Res, 522: 267–74. Inagaki, N., Yamatodani, A., Ando-Yamamoto, M., Tohyama, M., Watanabe, T. and Wada, H. (1988). Organization of histaminergic fibers in the rat brain. J Comp Neurol 273: 283–300. Ito, M. (1984). The Cerebellum and Neural Control. New York: Raven Press. Ito, M. and Yoshida, M. (1964). The cerebellar-evoked monosynaptic inhibition of Deiters’ neurons. Experientia 20: 515–19. Itouji, A., Sakai, N., Tanaka, C. and Saito, N. (1996). Neuronal and glial localization of two GABA transporters (GAT1 and GAT3) in the rat cerebellum. Brain Res Mol Brain Res 37: 309–16. Ji, Z.Q., Aas, J.E., Laake, J., Walberg, F. and Ottersen, O.P. (1991). An electron microscopic, immunogold analysis of glutamate and

45

46

O.P. Ottersen and F. Walberg

glutamine in terminals of rat spinocerebellar fibers. J Comp Neurol 307: 296–310. Jonas, P., Bischofberger, J. and Sandkuhler, J. (1998). Corelease of two fast neurotransmitters at a central synapse. Science 281: 419–24. Kan, K.-S., Chao, L.-P. and Eng, L.F. (1978). Immunohistochemical localization of choline acetyltransferase in rabbit spinal cord and cerebellum. Brain Res 146: 221–9. Kaneda, M., Farrant, M. and Cull-Candy, S.G. (1995). Whole-cell and single-channel currents activated by GABA and glycine in granule cells of the rat cerebellum. J Physiol 485: 419–35. Kashiwabuchi, N., Ikeda, K., Araki, K. et al. (1995). Impairment of motor coordination, Purkinje cell synapse formation, and cerebellar long-term depression in GluR 2 mutant mice. Cell 81: 245–52. Kerr, C.W.H. and Bishop, G.A. (1991). Topographical organization in the origin of serotoninergic projections to different regions of the cat cerebellar cortex. J Comp Neurol 304: 502–15. King, J.S., Cummings, S.L. and Bishop, G.A. (1992). Peptides in cerebellar circuits. Progr Neurobiol 39: 423–42. King, J.S., Ho, R.H. and Bishop, G.A. (1986). Anatomical evidence for enkephalin immunoreactive climbing fibres in the cerebellar cortex of the opossum. J Neurocytol 15: 545–59. Kitahara, T., Tekeda, N., Kubo, T. and Kiyama, H. (1999). Nitric oxide in the flocculus works the inhibitory neural circuits after unilateral labyrinthectomy. Brain Res 815: 405–9. Kondo, S. and Marty, A. (1998). Differential effects of noradrenaline on evoked, spontaneous and miniature IPSCs in rat cerebellar stellate cells. J Physiol 509: 233–43. Kurihara, H., Hashimoto, K., Kano, M. et al. (1997). Impaired parallel fiber–Purkinje cell synapse stabilization during cerebellar development of mutant mice lacking the glutamate receptor delta2 subunit. J Neurosci 17: 9613–23. Kvamme, E., Svenneby, G. and Torgner, I.A. (1988). Glutaminases. In Glutamine and Glutamate in Mammals, ed. E. Kvamme, pp. 53–67. Boca Raton, FL: CRC. Laake, J.H., Takumi, Y., Eidet, J. et al. (1999). Postembedding immunogold labelling reveals subcellular localization and pathwayspecific enrichment of phosphate activated glutaminase in rat cerebellum. Neurosci 88: 1137–51. Laine, J. and Axelrad, H. (1998). Lugaro cells target basket and stellate cells in the cerebellar cortex. Neuroreport 9: 2399–403. Landsend, A.S., Amiry-Moghaddam, M., Matsubara, A. et al. (1997). Differential localization of delta glutamate receptors in the rat cerebellum: coexpression with AMPA receptors in parallel fiber–spine synapses and absence from climbing fiber–spine synapses. J Neurosci 17: 834–42. Lehre, K.P., Levy, L.M., Ottersen, O.P., Storm-Mathisen, J. and Danbolt, N.C. (1995). Differential expression of two glial glutamate transporters in the rat brain: quantitative and immunocytochemical observations. J Neurosci 15: 1835–53. Levenes, C., Daniel, H. and Crepel, F. (1998). Long-term depression of synaptic transmission in the cerebellum: cellular and molecular mechanisms revisited. Progr Neurobiol 55: 79–91. Liu, C.J., Grandes, P., Matute, C., Cuenod, M. amd Streit, P. (1989).

Glutamate-like immunoreactivity revealed in rat olfactory bulb, hippocampus and cerebellum by monoclonal antibody and sensitive staining method. Histochem 90: 427–45. Madsen, S., Ottersen, O.P. and Storm-Mathisen, J. (1985). Immunocytochemical visualization of taurine: neuronal localization in the rat cerebellum. Neurosci Lett 60: 255–60. Maura, G., Carbone, R., Guido, M., Pestarino, M. and Raiteri, M. (1991). 5-HT2 presynaptic receptors mediate inhibition of glutamate release from cerebellar mossy fibre terminals. Eur J Pharmacol 202: 185–90. Morara, S., Brecha, N.C., Marcotti, W., Provini, L. and Rosina, A. (1996). Neuronal and glial localization of the GABA transporter GAT-1 in the cerebellar cortex. Neuroreport 7: 2993–6. Mugnaini, E., Dino, M.R. and Jaarsma, D. (1997). The unipolar brush cells of the mammalian cerebellum and cochlear nucleus: cytology and microcircuitry. Prog Brain Res 114: 131–50. Mugnaini, E. and Oertel, W.H. (1985). An atlas of the distribution of GABAergic neurons and terminals in the rat CNS as revealed by GAD immunocytochemistry. Handbook Chem Neuroanat 4: 436–608. Nagelhus, E.A., Lehmann, A. and Ottersen, O.P. (1993). Neuronal–glial exchange of taurine during hypo-osmotic stress: a combined immunocytochemical and biochemical analysis in rat cerebellar cortex. Neurosci 54: 615–31. Nielsen, H.S., Hannibal, J. and Fahrenkrug, J. (1998). Expression of pituitary adenylate cyclase activating polypeptide (PACAP) in the postnatal and adult rat cerebellar cortex. Neuroreport 9: 2639–42. Nunzi, M.G. and Mugnaini, E. (1999). UBC axons form a sizeable portion of the mossy fibers in the vestibulocerebellum. Soc Neurosci Abstr 5: 1403. Nusser, Z., Mulvihill, E., Streit, P. and Somogyi, P. (1994). Subsynaptic segregation of metabotropic and ionotropic glutamate receptors as revealed by immunogold localization. Neurosci 61: 421–7. Nusser, Z., Sieghart, W. and Somogyi, P. (1998). Segregation of different GABAA receptors to synaptic and extrasynaptic membranes of cerebellar granule cells. J Neurosci 18: 1693–703. Nusser, Z., Sieghart, W., Stephenson, F.A. and Somogyi, P. (1996). The alpha 6 subunit of the GABAA receptor is concentrated in both inhibitory and excitatory synapses on cerebellar granule cells. J Neurosci 16: 103–14. Obata, K., Ito, M., Ochi, R. and Sato, N. (1967). Pharmacological properties of the postsynaptic inhibition by Purkinje cell axons and the action of gamma-aminobutyric acid on deiters neurones. Exp Brain Res 4: 43–57. Ojima, H., Kawajiri, S-I. and Yamasaki, T. (1989). Cholinergic innervation of the rat cerebellum: qualitative and quantitative analyses of elements immunoreactive to a monoclonal antibody against choline acetyltransferase. J Comp Neurol 290: 41–52. Otis, T.S., Kavanaugh, M.P. and Jahr, C.E. (1997). Postsynaptic glutamate transport at the climbing fiber–Purkinje cell synapse. Science 277: 1515–18. Ottersen, O.P. (1987). Postembedding light- and electron microscopic immunocytochemistry of amino acids: description of a

Neurotransmitters in the cerebellum

new model system allowing identical conditions for specificity testing and tissue processing. Exp Brain Res 69: 167–74. Ottersen, O.P. (1988). Quantitative assessment of taurine-like immunoreactivity in different cell types and processes in rat cerebellum: an electronmicroscopic study based on a postembedding immunogold labelling procedure. Anat Embryol 178: 407–21. Ottersen, O.P. (1989). Quantitative electron microscopic immunocytochemistry of neuroactive amino acids. Anat Embryol 180: 1–15. Ottersen, O.P. (1993). Neurotransmitters in the cerebellum. Rev Neurol (Paris) 149: 629–36. Ottersen, O.P., Davanger, S. and Storm-Mathisen, J. (1987). Glycine-like immunoreactivity in the cerebellum of rat and Senegalese baboon, Papio papio: a comparison with the distribution of GABA-like immunoreactivity and with [3H]glycine and [3H]GABA uptake. Exp Brain Res 66: 211–21. Ottersen, O.P., Laake, J.H. and Storm-Mathisen, J. (1990a). Demonstration of a releasable pool of glutamate in cerebellar mossy and parallel fibre terminals by means of light and electron microscopic immunocytochemistry. Arch Ital Biol 128: 111–25. Ottersen, O.P., Madsen, S., Storm-Mathisen, J., Somogyi, P., Scopsi, L. and Larsson, L.I. (1988a). Immunocytochemical evidence suggests that taurine is colocalized with GABA in the Purkinje cell terminals, but that the stellate cell terminals predominantly 0contain GABA: a light- and electronmicroscopic study of the rat cerebellum. Exp Brain Res 72: 407–16. Ottersen, O.P., Storm-Mathisen, J. and Laake, J.H. (1990b). Cellular and subcellular localization of glycine studied by quantitative electron microscopic immunocytochemistry. In Glycine Neurotransmission, ed. O.P. Ottersen and J. Storm-Mathisen, pp. 303–28. Chichester: Wiley. Ottersen, O.P. and Storm-Mathisen, J. (1984). Neurones containing or accumulating transmitter amino acids. In Handbook of Chemical Neuroanatomy, Vol. 3, ed. A. Björklund, T. Hökfelt and M.J. Kuhar, pp. 141–246. Amsterdam: Elsevier/North. Ottersen, O.P., Storm-Mathisen, J. and Somogyi, P. (1988b). Colocalization of glycine-like and GABA-like immunoreactivities in Golgi cell terminals in the rat cerebellum: a postembedding light and electron microscopic study. Brain Res 450: 342–53. Ottersen, O.P., Zhang, N. and Walberg, F. (1992). Metabolic compartmentation of glutamate and glutamine: morphological evidence obtained by quantitative immunocytochemistry in rat cerebellum. Neuroscience 46: 519–34. Palay, S.L. and Chan-Palay, V. (1974). Cerebellar Cortex. Berlin, Heidelberg, New York: Springer Verlag. Petralia, R.S. and Wenthold, R.J. (1992). Light and electron immunocytochemical localization of AMPA-selective glutamate receptors in the rat brain. J Comp Neurol 318: 329–54. Radian, R., Ottersen, O.P., Storm-Mathisen, J., Castel, M. and Kanner, B.I. (1990). Immunocytochemical localization of the GABA transporter in rat brain. J Neurosci 10: 1319–30. Renno, W.M., Lee, J.H. and Beitz, A.J. (1997). Light and electron microscopic immunohistochemical localization of N-acetylaspartylglutamate (NAAG) in the olivocerebellar pathway of the rat. Synapse 26: 140–54.

Rothstein, J.D., Martin, L., Levey, A.I. et al. (1994). Localization of neuronal and glial glutamate transporters. Neuron 13: 713–25. Rotter, A. and Frostholm, A. (1986). Cerebellar histamine-H1 receptor distribution: an autoradiographic study of Purkinje cell degeneration, staggerer, weaver and reeler mutant mouse strains. Brain Res Bull 16: 205–14. Sakaue, M., Kuno, T. and Tanaka, C. (1988). Novel type of monoclonal antibodies against cyclic GMP and application to immunocytochemistry of the rat brain. Jpn J Pharmacol 48: 47–56. Schon, F. and Iversen, L.L. (1972). Selective accumulation of [3H]GABA by stellate cells in rat cerebellar cortex in vivo. Brain Res 42: 503–7. Seeburg, P.H. (1993). The TIPS/TINS lecture: the molecular biology of mammalian glutamate receptor channels. Trends Pharmacol Sci 14: 297–303. Shibuki, K. and Kimura, S. (1997). Dynamic properties of nitric oxide release from parallel fibres in rat cerebellar slices. J Physiol 498: 443–52. Skoglosa, Y., Patrone, C. and Lindholm, D. (1999). Pituitary adenylate cyclase activating polypepetide is expressed by developing rat Purkinje cells and decreases the number of cerebellar gamma-amino butyric acid positive neurons in culture. Neurosci Lett 265: 207–10. Somogyi, P. Fritschy, J.M., Benke, D., Roberts, J.D. and Sieghart, W. (1996). The gamma 2 subunit of the GABAA receptor is concentrated in synaptic junctions containing the alpha 1 and beta 2/3 subunits in hippocampus, cerebellum and globus pallidus. Neuropharmacology 35: 1425–44. Somogyi, P., Halasy, K., Somogyi, J., Storm-Mathisen, J. and Ottersen, O.P. (1986). Quantification of immunogold labelling reveals enrichment of glutamate in mossy and parallel fibre terminals in cat cerebellum. Neurosci 19: 1045–50. Storm-Mathisen, J., Leknes, A.K., Bore, A.T et al. (1983). First visualization of glutamate and GABA in neurones by immunocytochemistry. Nature 301: 517–20. Strahlendorf, J.C., Lee, M. and Strahlendorf, H.K. (1989). Modulatory role of serotonin on GABA-elicited inhibition of cerebellar purkinje cells. Neurosci 30: 117–25. Takahashi, M., Sarantis, M. and Attwell, D. (1996). Postsynaptic glutamate uptake in rat cerebellar Purkinje cells. J Physiol 497: 523–30. Takumi, Y., Bergersen, L., Landsend, A.S., Rinvik, E. and Ottersen, O.P. (1998). Synaptic arrangement of glutamate receptors. Prog Brain Res 116: 105–21. Toggenburger, G., Wiklund, L., Henke, H. and Cuénod M. (1983). Release of endogenous and accumulated amino acids from slices of normal and climbing fiber-deprived rat cerebellar slices. J Neurochem 41: 1606–13. Torp, R., Danbolt, N.C., Babaie, E. et al. (1994). Differential expression of two glial glutamate transporters in the rat brain: an in situ hybridization study. Eur J Neurosci 6: 936–42. Vaudry, D., Gonzalez, B.J., Basille, M., Fournier, A. and Vaudry, H. (1999). Neurotrophic activity of pituitary adenylate cyclase-activating polypeptide on rat cerebellar cortex during development. Proc Natl Acad Sci USA 96: 9415–20.

47

48

O.P. Ottersen and F. Walberg

Vollenweider, F.X., Cuénod, M. and Do, K.Q. (1990). Effect of climbing fiber deprivation on release of endogenous aspartate, glutamate, and homocysteate in slices of rat cerebellar hemispheres and vermis. J Neurochem 54: 1533–40. Voogd, J., Jaarsma, D. and Marani, E. (1996). The cerebellum: chemoarchitecture and anatomy. In Handbook of Chemical Neuroanatomy, Vol. 12: Integrated Systems of the CNS, Part III, ed. L.W. Swanson, A. Björklund and T. Hökfelt, pp. 1–369. Amsterdam: Elsevier Science. Voutsinos, B., Dutuit, M., Reboul, A. et al. (1998). Serotoninergic control of the activity and expression of glial GABA transporters in the rat cerebellum. Glia 23: 45–60. Wang, Y., Freund, R.K. and Palmer, M.R. (1999). Potentiation of ethanol effects in cerebellum by activation of endogenous noradrenergic inputs. J Pharmacol Exp Ther 288: 211–20. Watanabe, D., Inokawa, H., Hashimoto, K. et al. (1998). Ablation of cerebellar Golgi cells disrupts synaptic integration involving GABA inhibition and NMDA receptor activation in motor coordination. Cell 95: 17–27. Wiklund, L., Toggenburger, G. and Cuénod, M. (1984). Selective retrograde labelling of the rat olivocerebellar climbing fiber system with D-[3H]aspartate. Neuroscience 13: 441–68. Wilkin, G.P., Csillag, A., Balazs, R., Kingsbury, A.E., Wilson, J.E. and Johnson, A.L. (1981). Localization of high affinity [3H]glycine transport sites in the cerebellar cortex. Brain Res 216: 11–33 Willcutts, M.D. and Morrison-Bogorad, M. (1991). Quantitative in situ hybridization analysis of glutamic acid decarboxylase messenger RNA in developing rat cerebellum. Dev Brain Res 63: 253–64.

Wuenschell, C.W., Fisher, R.S., Kaufman, D.L. and Tobin, A.J. (1986). In situ hybridization to localize mRNA encoding the neurotransmitter synthetic enzyme glutamate decarboxylase in mouse cerebellum. Proc Natl Acad Sci USA 83: 6193–7. Yan, X.X. and Ribak, C.E. (1998). Developmental expression of gamma-aminobutyric acid transporters (GAT-1 and GAT-3) in the rat cerebellum: evidence for a transient presence of GAT-1 in Purkinje cells. Brain Res Dev Brain Res 111: 253–69. Young, A.B., Oster-Granite, M.L., Herndon, R.M. and Snyder, S.H. (1974). Glutamic acid: selective depletion by viral induced granule cell loss in hamster cerebellum. Brain Res 73: 1–13. Zhang, N. and Ottersen, O.P. (1992). Differential cellular distribution of two sulphur-containing amino acids in rat cerebellum. An immunocytochemical investigation using antisera to taurine and homocysteic acid. Exp Brain Res 90: 11–20. Zhang, N. and Ottersen, O.P. (1993). In search of the identity of the cerebellar climbing fiber transmitter: immunocytochemical studies in rats. Can J Neurol Sci 20 (Suppl. 3): S36–S42. Zhang, N., Walberg, F., Laake, J.H., Meldrum, B.S. and Ottersen, O.P. (1990). Aspartate-like and glutamate-like immunoreactivities in the inferior olive and climbing fibre system: a light microscopic and semiquantitative electron microscopic study in rat and baboon (Papio anubis). Neuroscience 38: 61–80. Zuo, J., De Jager, P.L., Takahashi, K.A., Jiang, W., Linden, D.J. and Heintz, N. (1997). Neurodegeneration in Lurcher mice caused by mutation in 2 glutamate receptor gene. Nature 388: 769–73.

5

Structure and function of the cerebellum Amy J. Bastian1 and W. Thomas Thach2 2

1 Department of Physical Therapy and Neurobiology Department of Anatomy and Neurobiology, Washington University Medical School, St Louis, Missouri, USA

Introduction The output of the cerebellum projects to all components of the voluntary and postural motor systems except the basal ganglia. The output is generated by the deep cerebellar nuclei and by the vestibular nuclei (the ‘deepest’ of the deep cerebellar nuclei); the output is excitatory. The cerebellum controls the activities of the many antagonist and synergist muscles that are used automatically in most normal movements. The cerebellum combines and coordinates their timing, duration, and amplitude of activity. It helps in the learning of new motor skills and in modifying old ones, such that they may be performed with perfect coordination and automatically. Damage of the lateral cerebellar hemisphere cortex and dentate nucleus causes a curved trajectory, overshoot of endpoint, terminal tremor on the finger-nose-finger and heel-knee-shin tests, and irregularity of rapid alternating pronation–supination of the wrist and finger-to-thumb tests. Damage of the midline cerebellar cortex and fastigial nuclei causes falls to the side of the lesion, especially on heel-to-toe gait. There is increasing evidence that the extreme lateral, posterior, and inferior regions of cerebellar cortex and the lateral inferior portions of the dentate nucleus may control performance of so-called ‘cognitive’ tasks that do not involve overt movement (see also Chapter 9; Fiez et al., 1992).

Neuronal activity in the cerebellar nuclei The output from the cerebellum is generated by its deep nuclei. Each deep cerebellar nucleus appears to have a separate somatotopic representation of the body, with the head caudal, tail rostral, trunk lateral, and extremities medial (Orioli and Strick, 1989; Asanuma et al., 1983a, 1983b, 1983c, 1983d). In the absence of movement, the

nuclear cells fire at high maintained rates of approximately 40–50 Hz (Fig. 5.1A). Through this activity, the cerebellum modulates its target structures, presumably to help maintain optimum sensitivity to their other inputs. During movement, firing rates increase and decrease above and below their baseline. In addition, increases in cerebellar nuclear firing rate precede and help to increase the discharge frequency in its target structures, thus helping to initiate movement. There is also evidence that the cerebellum combines the functions resident in the downstream generators into novel combinations (Holmes, 1939; Thach et al., 1992a) The deep nuclei appear to control differentially the medial and lateral motor systems and their respective functions. The vestibular and medial cerebellar nuclei (fastigius) are concerned with the control of eye movements, equilibrium, upright stance, and gait. The intermediate nuclei (interpositus) appear to be concerned with modulation of stretch, contact, placing and other reflexes. The lateral nucleus (dentate) appears to be concerned with voluntary movement of the extremities, including reaching and grasping for objects.

Fastigius Single-unit recordings done in the fastigius relate to eye movements, control of head orientation, and control of musculature activity during stance and gait. The fastigius receives input from the vermal cerebellar cortex, the vestibular complex, the lateral reticular nucleus, the superior colliculus (via the pons), and the spinocerebellar pathways. Single-unit recordings in the fastigius and vermal cerebellar cortex of decerebrate cats have shown neural discharge to be correlated with both walking and scratching movements (Antziferova et al., 1980; Andersson and Armstrong, 1987). Recordings in the interpositus and dentate nucleus did not to relate to these behaviors

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(a) Fig. 5.1 Maintained discharge of a dentate nucleus neuron (a) and a Purkinje cell (b), each recorded extracellularly from an awake, behaving monkey, during rest (a), movement of ipsilateral wrist (b), ipsilateral shoulder (c), contralateral wrist (d), and contralateral shoulder (e), respectively. The ‘simple’ and ‘complex’ spikes are distinguished in (b) and shown individually in (c). In (c) the top trace shows the relationship between simple and complex spikes over a couple of seconds; the bottom traces show simple and complex spikes individually and together over shorter periods of time to demonstrate the different waveform patterns. (Reproduced from Thach, 1968, with permission from Journal of Neurophysiology.)

(Arshavsky et al., 1980). These observations are consistent with the idea that the fastigius nucleus is specific for the control of stance and gait. Other recordings done in the fastigius suggest that this nucleus can be functionally divided into rostral and caudal components (Buttner et al., 1991). The rostral fastigius

appears to be involved in the descending control of somatic musculature (Buttner et al., 1991) and may help control head orientation and combined eye–head gaze shifts (Pelisson et al., 1998). The caudal fastigius appears to be involved in oculomotor functions, including saccade generation (Ohtsuka and Noda, 1990, 1991; Fuchs et al.,

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(b) Fig. 5.1 (cont.)

1993) and smooth pursuit (Fuchs et al., 1994). Adaptation of the size of saccades may also depend on the cerebellum (Optican and Robinson, 1980; Scudder et al., 1998).

Interpositus Single-unit recordings done in the intermediate zone of the cerebellar cortex and interpositus nucleus have shown firing in relation to the antagonist muscle group being used (Smith and Bourbonnais, 1981; Frysinger et al., 1984; Wetts et al., 1985). When a holding position is suddenly perturbed, there is a reflex movement that returns the perturbed part to the hold position. Neurons in the interpositus fire when the holding position is perturbed, and in doing so appear to control the antagonist muscle that ‘checks’ the return movement to the prior hold position (Vilis and Hore, 1977, 1980; Thach, 1978; Strick, 1983).

Interpositus neurons have also been shown to modulate in relation to sensory feedback including that from tremor accompanying movement (Thach, 1978; Soechting et al., 1978; Vilis and Hore, 1980; Schieber and Thach, 1985). This is consistent with the idea that the interpositus is involved in somesthetic reflex behaviors, controlling the antagonist muscle to damp the tremor (Vilis and Hore, 1977, 1980; Elble et al., 1984). Smith and his colleagues have evidence supporting the hypothesis that a main role of the interpositus is to control whether the pattern of activity in muscles acting at a joint is reciprocal or co-contraction (Smith and Bourbonnais, 1981; Frysinger et al., 1984; Wetts et al., 1985). During behavior when co-contraction was employed, nuclear cells fired as if activating each of the two sets of agonist and antagonist muscles, and Purkinje cells in the intermediate cortex were silent (Fig. 5.2). In

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(c) Fig. 5.1 (cont.)

behavior in which agonists and antagonists were reciprocally active, both nuclear cells and Purkinje cells fired in similar patterns. The interpretation was that alternating firing in the Purkinje cells created (through inhibition) the alternating patterns in the nuclear cells, and thus the alternation in the agonist and antagonist muscles. Other work suggests that the interpositus contributes to stretch reflex excitability via control of the discharge of gamma motor neurons (Gilman, 1969; Soechting et al., 1978; Schieber and Thach, 1985).

Dentate Single-unit studies have shown that cell activity in the dentate precedes the onset of movement and may also

precede motor cortex cell activity (Thach, 1975, 1978; Lamarre et al., 1983). Dentate cells preferentially fire at the onset of movements that are triggered by mental associations with either visual or auditory stimuli. In one study, recordings were made in the motor cortex, dentate nucleus, interpositus nucleus, and the muscles as monkeys made wrist movements in response to stimuli (Thach, 1978). In tasks in which a light triggered movement, the order of activity was dentate, motor cortex, interpositus, then muscles. When a transient force perturbed the wrist, the firing order was muscles, interpositus, motor cortex, then dentate. These results suggest that the dentate helps to initiate movements that are triggered by stimuli which are mentally associated with the movement, while

Structure and function of the cerebellum

(a)

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Fig. 5.2 Purkinje cells tend to cease (a) and interposed/dentate nuclear cells to increase (b) firing during precision pinch which, unlike alternating movements (Fig. 5.1), are accompanied by cocontraction (rather than reciprocal action) of forearm agonist and antagonist muscles. (a) Upper left, three traces of a Purkinje cell simple spike and complex spike (dotted) discharge during pinch. Below, output of pinch force transducer. Middle and right, EMG, Purkinje cell simple and complex spike rasters and histograms. (From Smith and Bourbonnais, 1981, with permission, from Journal of Neurophysiology.) (b) Discharge of a dentate nuclear neuron during pinch. (From Wetts et al., 1985, with permission.)

the interpositus is more involved in compensatory or corrective movements initiated via feedback from the movement itself. Similar findings have been reported in other studies, where the dentate responded strongly when movements were triggered by either visual signals or auditory signals, but not when triggered by somesthetic signals (Lamarre et al., 1983). Finally, both dentate and interpositus activity has also been speculated to relate more to movements involving multiple joints than to movements involving single joints. Neither the dentate nor the interpositus codes exclusively for any specific parameter (velocity, amplitude, duration) during single-jointed movements (Brooks and Thach, 1981; Elble et al., 1984; Schieber and Thach, 1985; Thach et al., 1992a; van Kan et al., 1993). In sum, the dentate plays a role in initiating movements requiring a mental interpretation of the visual or auditory signal, and both the dentate and interpositus are increasingly active during multijointed movements.

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Neuronal activity in the cerebellar cortex Purkinje cell discharge related to limb movements: simple spikes Purkinje cell simple spike activity occurs at high spontaneous rates, even if an animal is at rest (Fig. 5.1B). Simple spike activity is driven by mossy fiber inputs to granule cells, and is known to modulate weakly during passive movement (Bauswein et al., 1983) and strongly during active movement (Thach, 1968, 1970; Harvey et al., 1977; Bauswein et al., 1983). Purkinje cells receive a massive convergence of mossy fiber inputs (via parallel fibers), placing them in a position to integrate or combine inputs from a variety of sources. In addition, Purkinje cell activity in different regions of the cerebellum probably encodes distinct parameters, given that regions of the cerebellar cortex receive different inputs. Many groups have studied movement-related Purkinje cell activity in the intermediate and lateral hemispheres of lobules IV–VI (Mano and Yamamoto, 1980; Frysinger et al., 1984; Fortier et al., 1989, 1993; van Kan et al., 1993; Fu et al., 1997; Coltz et al., 1999). These regions of the cerebellum receive peripheral somatosensory inputs via the dorsal spinocerebellar pathway, information from spinal interneuronal pools via the ventrospinocerebellar pathway, and cortical information via the pontine nuclei (see also Chapter 2). Thus, this region of the cerebellum is likely to integrate sensory information from the periphery with information from spinal interneurons and cortical motor commands. During a single-joint movement, simple spike discharge can have a nonreciprocal relation to movement direction (flexion or extension), but may be more related to the speed of movement (Mano and Yamamoto, 1980). Others have also shown that simple spike discharge is phasic during a movement, and speculated that it may correlate with the speed or velocity of the movement (Mano and Yamamoto, 1980; Marple-Horvat and Stein, 1987; van Kan et al., 1993; Coltz et al., 1999). A recent study tested whether Purkinje cell tuning was best related to the direction of movement, speed of movement, or to the direction–speed interaction (velocity). Results showed that simple spike discharge was tuned to both direction and speed, but was best related to the velocity of the movement (Coltz et al., 1999). Simple spike discharge can also be reciprocal during a single-joint movement, and this may relate to the pattern of muscle activity (Thach, 1970; Frysinger et al., 1984). Studies of multijointed reaching movements have shown that simple spike activity changes in a graded manner with the direction of the reaching movement (Fortier et al., 1989, 1993; Fu et al., 1997; Coltz et al., 1999). Some investi-

gators have interpreted this tuning as coding specifically for direction (Fu et al., 1997), while others speculate that the tuning relates more to the control of specific muscle groups (Fortier et al., 1989). One study that compared tuning in motor cortex and the cerebellum during a multijointed radial reaching task found that cerebellar cells tended to be tuned more broadly in a much more graded fashion compared with the reciprocal tuning in motor cortex (Fortier et al., 1993). Cerebellar neurons (both Purkinje and nuclear cells) showed much greater trial-totrial variability compared to motor cortical cells (Fortier et al., 1993).

Purkinje cell discharge related to limb movements: complex spikes Purkinje cell complex spike activity occurs at very low rates (1–3 Hz, see Fig. 5.1b and 5.1c), and is thought to occur randomly when an animal is at rest (Keating and Thach, 1995; Miall et al., 1998; but see Lang et al., 1999). The role of complex spikes during limb movements is currently a subject of debate. According to the Marr–Albus–Ito hypothesis, the role of the complex spike is to signal an error (Albus, 1971) or provide a teaching signal (Marr, 1969) to the Purkinje cell. Either of these signals is thought to decrease the effectiveness of concurrently active parallel fiber–Purkinje cell synapses (Albus, 1971; Ito et al., 1982). It is by this mechanism that Purkinje cell output is thought to be shaped through a trial-and-error learning process (Thach et al., 1992a). In contrast to the motor learning hypothesis, others believe that the complex spike may serve as a motor clock (Lamarre and Mercier, 1971; Llinas and Yarom, 1986; Lang et al., 1999) or as a ‘synchronizing pulse’ to assist the onset or cessation of simple spike activity (Mano et al., 1986). There are several studies of complex spike activity during limb movement that support the learning hypothesis. Gilbert and Thach (1977) showed increases in complex spike firing rates during adaptation to a novel load during a wrist-holding task. In a specific group of Purkinje cells, this increase in complex spike activity was coupled with a decrease in simple spike activity (Gilbert and Thach, 1977). Once the task was successfully learned, complex spike firing returned to baseline. During a multi-jointed arm movement, Ojakangas and Ebner (1992, 1994) also found increased complex spike activity when learning a new gain between the hand and a visual cursor on a computer screen. They found that complex spike activity was equally likely to occur in the early, middle or late stages of the movement. In contrast to the findings of Gilbert and Thach, they found that complex spike activity did not relate to long-term decreases in simple spike activity

Structure and function of the cerebellum

(Ojakangas and Ebner, 1992, 1994). Instead, complex spikes related to a brief 10–20 ms suppression of simple spike activity. Based on these findings, they concluded that the complex spike activity may encode a velocity-related error signal and may function by evoking short-term changes in simple spike activity (Ojakangas and Ebner, 1994). Recent work from Kitazawa and colleagues (1998) showed that complex spikes may encode specific information about the errors occurring during a multijointed reaching movement. They found that complex spikes occurring early during a reaching movement may help to encode the absolute direction and destination of the arm. Complex spikes occurring at the end of the movement were found to encode the relative endpoint errors of the reach (Kitazawa et al., 1998). Thus, complex spikes were hypothesized to carry directional information about the reach endpoint error. In contrast to this finding, Dugas and Smith (1992) found that Purkinje cell complex spike activity did not relate to specific errors during a grasping task. In this study, monkeys performed movement trials in which they had to grasp and lift a device. On select blocks of trials, a perturbation was applied to the hand-held object. Following the perturbation, there were reflex-like increases or decreases in simple spike activity, but no changes in complex spike activity related to the slip error. They concluded that the receptive fields for simple and complex spike activity were not the same. In contrast to the motor learning hypothesis, others have proposed that complex spike activity subserves motor clock or synchronization functions. The motor clock hypothesis is based on the presumed periodic discharge in the inferior olive (Lamarre and Mercier, 1971; Llinas and Yarom, 1986; Lang et al., 1999). Initially, this idea was based on the effects of harmaline, a drug which causes 10 Hz tremor in experimental animals (Lamarre and Mercier, 1971) and a correlated synchronous discharge in inferior olive cells in slice preparations (Llinas and Yarom, 1986). In a recent study, Llinas and colleagues found that spontaneous complex spike activity in rats occurred at an average firing rate of 1 Hz and had a clear rhythmicity of 10 Hz (Lang et al., 1999). This is in contrast to the findings of Keating and Thach (1995), who found that complex spike activity is random in non-behaving monkeys. For a more complete description of the motor clock hypothesis, see the section entitled Timer.

Damage of the cerebellar nuclei Fastigius Ablations done in the nucleus fastigius in cats and monkeys have been shown to impair dramatically those movements requiring the control of equilibrium, like unsupported sitting, stance, and gait (Fig. 5.3; Botterell and Fulton, 1938; Thach et al., 1992b). Longitudinal splitting of the cerebellum at midline also gives rise to very significant and long-lasting disturbances of equilibrium. In humans, it has been shown that lesions in the vermal and intermediate zones of the anterior lobe preferentially impair movements requiring equilibrium control (Mauritz et al., 1979; Horak and Diener, 1993). These data suggest that the fastigius may be preferentially involved in movements like gait and stance.

Interpositus Ablations of the nucleus interpositus in monkeys consist primarily of tremor (Fig. 5.4; Vilis and Hore, 1980; Thach et al., 1992a). Temporary inactivation using cooling probes positioned at both the interpositus and dentate nuclei has been shown to elicit tremor that is dependent on proprioceptive feedback but is uninfluenced by vision (Flament et al., 1984). In studies of unconstrained movements of monkeys (Thach et al., 1992b), interpositus inactivation disturbed gait minimally but caused a large-amplitude 3–5 Hz action tremor as the animals reached out for food (see Fig. 5.3). These studies support the idea that the interpositus in monkeys is most concerned with the balance of agonist–antagonist muscle activity of the limb as it moves. It has been speculated that the interpositus normally uses abundant afferent input from the periphery to generate predictive signals that will decrease alternating stretch reflexes that cause limb oscillation. Others have proposed that the interpositus also plays a more prominent role in the coordination of forelimb movements. Bloedel and colleagues have recently demonstrated that muscimol injections into the same regions of the cerebellar interpositus nuclei that control withdrawal reflexes also impair the control of limb flexion and precision placement of the paw during both locomotion and reaching tasks (Bracha et al., 1999). They propose that the interposed nuclei control the ipsilateral ‘action primitives’ and that inactivating the interposed nuclei affects these primitives across several modes of action (Bracha et al., 1999). Houk and colleagues have found that inactivations in the anterior versus posterior interpositus differentially disrupt grasping and reaching movements, respectively

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Fig. 5.3 Major deficits produced by microinjection of muscimol or kainic acid into different regions of the cerebellum. F indicates the standing and walking deficit seen after muscimol injections into the fastigius. I indicates arm position (tremor) during reaching after muscimol injection into the interpositus. D indicates the deficits in reaching and pinching after muscimol injection into the dentate. (From Thach et al., 1992a, with permission, from the Annual Review of Neuroscience, Volume 15, © 1992, by Annual Reviews, www.AnnualReviews.org.).

(see Mason et al., 1998). They propose that the anterior and posterior interpositus are involved in coordinating distal and proximal musculature together via climbing fiber input to Purkinje cells (Mason et al., 1998).

Dentate Ablations done in the dentate nucleus of monkeys have been shown to cause slight reaction time delays, poor endpoint control, and impaired multijointed movements beyond deficits found in single-jointed movements. In several studies, lesions of the dentate nucleus produced very slight delays in the onset of motor cortex cell activity (Meyer-Lohman et al., 1975; Spidalieri et al., 1983; Thach et

al., 1992a). This was shown to be due to loss of phasic dentate activity rather than of tonic support, because no change in the resting motor cortex cell firing rate was found after dentate cooling (Meyer-Lohman et al., 1975). Lesions of the dentate also produce a slight delay in reaction time of the movement when triggered by light or sound (Trouche and Beaubaton, 1980; Spidalieri et al., 1983). Abnormal endpoint control has been reported following dentate ablation in both single-jointed movements and multijointed movements. In single-jointed movements, dentate ablation has been reported to cause monkeys to overshoot very slightly (Thach et al., 1992a) or moderately (Flament and Hore, 1986). In studies of monkeys making unconstrained multijointed movements,

Structure and function of the cerebellum

Fig. 5.4 Oscillations in limb position occur when the interposed and dentate nuclei are inactivated by cooling. (A) Effects of cooling on responses to transient passive displacement of the limb. Position, velocity, and electromyographic responses in biceps and triceps following a torque-pulse perturbation applied to the limb maintained in a stationary position by a trained monkey. Prior to cooling, the limb returns to its original position upon termination of the external torque; only minimal overshooting is evident on the position trace. During cooling, the limb returns with marked overshoot; sequential corrections produce oscillations. (B) Effects of cooling on movement trajectories. As in the case of passive movement, cooling of deep nuclei during voluntary movement produces oscillations in the trajectory. (Adapted from Vilis and Hore, 1977.)

dentate inactivation resulted in profoundly impaired reaching patterns with abnormally increased angulation of the shoulder and elbow and excessive overshoot of the target (Thach et al., 1992b). Dentate inactivation also caused the animals to have difficulty pinching small bits of food out of a narrow well; instead, the animals used one finger as a scoop to retrieve the food (Thach et al., 1992b). In sum, dentate ablation impairs movements requiring the coordination of multiple joints to a greater extent than movements of a single joint. Further, inactivation of the dentate nucleus also causes slight impairment of the initiation of movements that are triggered by vision or mental percepts. The dentate may facilitate motor cortical cells, particularly for movements triggered teleceptively.

Theories concerning the mechanism of cerebellar operation Tonic reinforcer The cerebellum exerts a tonic reinforcing effect on other motor generators – vestibular, reticular, and motor cortex (via thalamus). As such, it would be responsible for the tuning and fine adjustment of these structures so that they respond optimally to their non-cerebellar driving inputs. This idea was first suggested by Rolando on the basis of increased movement upon galvanic stimulation of the cerebellum. Luciani championed the idea of a reinforcing tone with his interpretation of the behavioral deficits after cerebellar ablation in animals, a principal component of which was ‘atonia.’ Holmes endorsed this interpretation from his own analysis of behavioral deficits in human subjects with cerebellar lesions (Holmes, 1939; Dow and Moruzzi, 1958; Dow, 1987). It has since been shown that the output of the cerebellum is excitatory, and that it is

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tonically active even in the absence of movement (Eccles et al., 1967; Thach, 1968). Granit et al. (1955) and Gilman (1969) emphasized how tone could be controlled by the cerebellum by an excitatory input to gamma motor neurons and their control over stretch reflexes. However, because the cerebellum also projects to alpha motor neurons, and because cerebellar nuclear discharge changes tonically in relation to different held postures and phasically in relation to different movements, it has become clear that the basic cerebellar function must be more complex than originally supposed. The direct descendant of this theory is that of sensorimotor ‘optimization,’ wherein the cerebellum contributes a constantly changing influence to provide ‘fine control’ to posture and movement (Bloedel, 1992).

Timer A number of studies of the cerebellum have suggested pure timing functions. The first of these by Braitenberg (1967) viewed the parallel fiber–Purkinje cell arrangement in a long beam as a way of implementing a ‘tapped delay line.’ In this hypothesis, a wave of activity coming down the parallel fiber could be ‘tapped off’ at successive Purkinje cells, each ‘tap’ occurring at an incremental delay after the onset of the wave. This could be used to time movements, the ‘timer’ operating in the range of up to 50 ms or so. Llinas and Lamarre have independently proposed motor clock functions for the cerebellum on the basis of presumed periodic discharge in the inferior olive (Lamarre and Mercier, 1971; Llinas and Yarom, 1986). This presumption was founded on the effects of harmaline, which induced a whole-body 10 Hz tremor in experimental animals (Lamarre and Mercier, 1971) and a correlated synchronous discharge in inferior olive cells in slice preparations (Llinas and Yarom, 1986). Because ablation of the olive then abolished the tremor, it was assumed that the olivary discharge caused the tremor. A number of other findings seemed to uphold the interpretation, such as a tendency in undrugged animals for the olive to fire periodically and in synchrony, and gap junctions in the olive which might synchronize cell discharge. The generalization has been questioned by others who, in the awake performing monkey, find that olivary discharge is not only non-periodic, but indeed is random (Keating and Thach, 1995). Ivry and colleagues (1988) have proposed clock functions based on other evidence. Patients with lateral cerebellar injury are impaired in their ability to perceive differences in intervals between tone pairs of the order of 0.5 s. This has been interpreted as indicative of a general clock not only for movement but also for perception.

Finally, Houk (1988) has proposed that motor programs are encoded as tonic reverberating activity within several closed-loop systems that make up the basic movement program generators. In voluntary movement, the loops are excited by a higher cerebral input, and continue to reverberate closed-loop (all the while generating movement) until they are turned off. The cerebellar cortex is supposed to turn them off: upon recognizing (through trialand-error learning) the ‘context’ in which movement should stop, the Purkinje cell output flipflops from a low bistable condition of no discharge to one of high maintained discharge. This is purported to inhibit the maintained activity in the deep nuclei and to stop the activity reverberating in the movement program generator circuits. In all these formulations, the supposition is that the cerebellum (or the olive) controls timing and timing only of muscle activity. Against these ideas is the absence of any demonstrated clock-like periodicity in cerebellar nuclear cell discharge, and the presence of graded tonic discharge correlating with muscle pattern and force, limb position, and movement direction that would seem unlike what a clock would produce.

Command–feedback comparator Several reviews suggested models incorporating linear systems principles (Evarts and Thach, 1969; Allen and Tsukahara, 1974). The lateral cerebellum received command from association cortex and feedback from motor cortex, and projected back to and helped initiate and correct command signals from motor cortex. Intermediate cerebellum received command from motor cortex, feedback from spinal cord, and projected to red nucleus and helped execute and correct error in the ongoing movement. These models were consistent with the early discharge of lateral cerebellar neurons (dentate nucleus) in the initiation of movement, and the later discharge of intermediate (interpositus) neurons. They did not make clear how the relatively slow neural feedback signals could make the same kind of error corrections that electronic feedback can.

Combiner–coordinator Flourens (1824) first proposed that the role of the cerebellum was to coordinate movements, and Babinski (1899, 1906) supported these interpretations by finding in cerebellar patients loss of coordination of compound movements without impairment of force in simpler movements. Pellionisz and Llinas (1980) developed a mathematical model for translating one reference frame (such as body

Structure and function of the cerebellum

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Fig. 5.5 (A) Single trials of the torques produced by one control and one cerebellar subject making fast reaches to the target. At the elbow, the control subject produced a flexor muscle torque (gray line) that was a mirror image of the extensor interaction torque (small dotted line), offsetting it to the appropriate degree. At the elbow, the cerebellar subject produced a flexor muscle torque that did not mirror the extensor interaction torque. Because of this, the elbow extension was caused by an interaction torque that was not appropriately countered by a muscle torque. A similar pattern was apparent at the shoulder. (B) Kinematics of the same reach shown in (A). Bold lines are the path of the wrist (W) and index finger (I) as the subject moved to the target (shaded circle). Also shown are the elbow (E) and shoulder (S) angular movements versus time. Note the abnormally curved wrist and index path, and target overshoot produced by the cerebellar subject. (From Bastian et al., 1996, with permission, from Journal of Neurophysiology.)

musculature) to another (such as movements in space), but for static positions only, and without stating specifically how it might be implemented by the circuitry. Fujita (1982) gave a similar tensor algebra description of a coordination model, but also gave appropriate mathematics for dynamics as well as statics. Kawato and colleagues have proposed that the intermediate cerebellum learns an inter-

nal model of body mechanics, allowing the cerebellum to adjust for the complex dynamics (interaction torques) inherent in multijointed movements (Schweighofer et al., 1998a, 1998b). This model was, in part, based on the finding that cerebellar patients are impaired in adjusting for interaction torques that occur during fast reaching movements (Fig. 5.5; Bastian et al., 1996; Topka et al., 1998).

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Thach et al. (1992a) speculate, and Bastian et al. (1998) give evidence, on how the long parallel fibers might be used to combine the activities of lower motor pattern generators, motor neurons, and muscles so as to provide many unique patterns of coordinated movement.

Sensory processor A number of studies suggest that the basic function of the cerebellum is in monitoring and adjusting the acquisition of sensory information (Paulin, 1993; Gao et al., 1996; Bower, 1997). Paulin (1993) has proposed that the cerebellum may be best characterized as a sensory tracking system. This hypothesis was based on a review of anatomical and physiological data from many different vertebrates. The proposed cerebellar tracking function would allow an animal to track its own movements, as well as the movements of other objects, and could contribute to motor control by providing this information to motor structures. Data from lower animals, such as the weakly electric fish, suggest that the cerebellum may predominantly play a role in tracking exteroreceptive and proprioceptive inputs (Bullock, 1986). Bower and colleagues have put forward the idea that the cerebellum is not itself responsible for any specific motor function, but instead facilitates the efficiency with which sensory data are acquired (Gao et al., 1996; Bower, 1997). In support of this idea, a functional magnetic resonance imaging (fMRI) study showed that the dentate nucleus was active during a passive sensory task (with little or no motor output), but inactive during finger movements not associated with tactile sensory discrimination (Gao et al., 1996). In contrast to this finding, a more recent fMRI study of patients who have severe pansensory neuropathies showed movement-related cerebellar activation in the absence of visual or somatosensory input (Weeks et al., 1999). Many other studies have shown that cerebellar patients have significant motor deficits with no appreciable sensory deficit (Hallett et al., 1975, 1991; Brown et al., 1990; Hore et al., 1991; Goodkin et al., 1993; Manto et al., 1994; Bastian et al., 1996; Topka et al., 1998). There have been very few reports of sensory deficits following cerebellar damage (Angel, 1980; Grill et al., 1994). One report showed that a patient with cerebellar damage had abnormal weight perception or ‘barognosis’ (Angel, 1980). Yet, weight estimation, is not a ‘purely’ sensory task, given that it relies partially on movement of the limb holding the weight. Others have reported that cerebellar patients can have subtle deficits in kinesthesia. Specifically, cerebellar patients were shown to have slight deficits in the perception of velocity (difficulty

distinguishing differences of less than 15°/s) of finger displacements (Grill et al., 1994).

Motor learning According to the Marr–Albus–Ito Motor Learning Theory, the cerebellum is the controller of movements that are made automatically, without having to think about them (Marr, 1969; Albus, 1971; Ito, 1972, 1984, 1989; Palay and Chan-Palay, 1974; Thach et al., 1992b). The cerebellum gains this control through trial-and-error practice, linking a certain behavioral context to the movement response. When one initially tries to learn a new pattern of movements, such as a piece of music on the piano, one has to concentrate mentally, and the result is the painfully slow playing of each note, one at a time, and with great effort. With time, control of the process passes from the frontal cerebral cortex to the cerebellum. Repeated occurrence of the context in which the movement is made causes it to become linked to the response. Occurrence of the context alone may then ‘trigger’ the onset of the movement. The context may be a very large and complex composition of signals representing intent and the status of the internal and external milieu at a point in time. The response may involve a very large number of movement generators, muscles, and joints. The occurrence of the context automatically triggers the occurrence of the response. Novel linkages define novel movements and their ‘fine control and coordination.’ Because learned movement is stereotyped, movement components may be triggered by contexts early in the performance, thus to anticipate and prevent errors, and to build sequences of movements. The cerebellar circuitry is uniquely built and seems likely to be able to implement the many components in a context, the many components in a response, the many context– response linkages that are the basis of our stored learned movement repertoire, and the process of learning them. Damage of the cerebellum causes the inability to make automatic, rapid, smoothly coordinated movements, and to learn new, complex movements. One can still move, by virtue of the action of frontal cerebral cortex and the actions of sensory inputs on each of the motor program generators. But each component of the movement has to be thought out: the movement is slow, and it is irregular, because the agonist, antagonist, synergist, and fixator muscles cannot be linked together in time, amplitude, and combination. This theory takes into account the structural plan of the cerebellar cortex, and what functions it might perform.

Structure and function of the cerebellum

Parallel fibers, Purkinje cell beams, and coordination of linked nuclear cells One of the main historic objections to a cerebellar role in coordination was the lack of any special feature in its structure which suggested such a function. This is no longer the case. In each nuclear body representation, the mapping is of the caudo-rostral dimension of the body onto the sagittal dimension of the nucleus. The hindlimbs are represented anteriorly, the head (at least for dentate and interpositus nuclei) posteriorly; distal parts are medial, proximal parts lateral. This orientation would suggest that the myotomes, running orthogonal to the long axis of the body, run primarily in the coronal dimension and thus roughly parallel to the trajectory of the parallel fibers. Because the parallel fibers are connected to the nuclear cells by Purkinje cells, a coronal ‘beam’ of parallel fibers would control, through inhibitory modulation, the nuclear cells that influence the synergistic muscles in the myotome. The parallel fiber in this way would be a single neural element spanning and coordinating the activities of multiple synergic muscles and joints. Direct anatomical studies show parallel fibers to be on the average just under 10 mm for the chicken, a little over 5 mm for the cat, and about 6 mm for the monkey, with the range of lengths being roughly the mean 2 mm (Mugnaini, 1983). For the macaque monkey, a 6 mm stretch of cortex projects onto the width of one nucleus or slightly greater. Thus, a beam of Purkinje cells under the influence of a set of parallel fibers of the same origin and length affects a beam of nuclear cells across an entire nucleus. Depending on which portion of the body map the cortical beam projects, that nuclear beam influences the synergic muscles across several joints in the limb, or the muscles of the eye, head, neck, and arm, or whatever, depending on the pattern of projection and the folial orientation in the horizontal plane. Parallel fiber beams can also bridge and link between the deep cerebellar nuclei. A link occurring across the two fastigial nuclei would effectively link the two sides of the body in stance and gait (Bastian et al., 1998). A link across the fastigius and interpositus nuclei would effectively link locomotion and reflex sensitivity. Finally, a link across the interpositus and dentate nuclei would effectively link reach and reflex sensitivity. Support for the participation of the cerebellum in motor learning comes from both human and animal studies. Ablation of the cerebellar cortex prevents adaptation and learning from occurring, and removes any adaptation previously wrought (Robinson, 1976; McCormick et al., 1981; McCormick and Thompson, 1984; Yeo et al., 1984). The adaptation and learning deficits can be independent of the

performance deficits. Neural recording during behavior has shown that the mossy fiber–granule cell–Purkinje cell–nuclear cell route through the cerebellum is the operational one (Thach, 1968, 1975, 1978; Fortier et al., 1989). Its high-frequency discharge correlates with behavior. The climbing fiber–Purkinje cell route does not directly control moment-to-moment behavior. Its low frequency discharge increases only when signaling errors in performance, and during adaptation or learning of movement (Simpson and Alley, 1974; Gilbert and Thach, 1977; Gellman et al., 1985; Ojakangas and Ebner, 1994; but see Dugas and Smith 1992). Conjoint electrical stimulation of mossy and climbing fibers depresses (long-term depression, LTD) those parallel fiber–Purkinje cell synapses that are concurrently active, and spares those parallel fiber–Purkinje cell synapses that are inactive (Ito et al., 1982; Ekerot and Kano, 1985; Strata, 1985; Kano and Kato, 1987). Failing to find Purkinje cells carrying a signal appropriate to control behavior which had been adapted, Lisberger (1988) has suggested that the cerebellum plays a role in learning by recognizing the error in behavior and computing a correction factor, which is then down-loaded into synapses on the vestibular nuclei in the brainstem.

Cerebellar contributions to cognition In humans, lesions of a large part of the cerebellum are clinically ‘silent’. That is, they may cause little or none of the motor deficits that traditionally characterize a cerebellar lesion. One such region is in the lateral and inferior portion of the posterior lobe, which is supplied by the posterior inferior cerebellar artery (PICA). Occlusion of this artery is common. Yet, unless the branches to the brainstem are also involved, cerebellar infarction may give rise to little or no obvious deficit, and go unrecognized. By contrast, human functional imaging studies of ‘purely mental’ tasks (such as generating verbs to noun stimuli) with the motor vocal component subtracted out (Petersen et al., 1989; Raichle et al., 1994) activate the postero-lateral cerebellum. Correspondingly, lesions of the region impair the performance and especially the learning of these same cognitive tasks (Fiez et al., 1992). Language tasks activate this region on the right side of the cerebellum (Petersen et al., 1989; Raichle et al., 1994), tasks involving spatial operations activate it on the left (Van Mier et al., 1995). Specific tasks whose learning or performance has been shown to be related to these cognitive cerebellar regions consist of the perception of time (Ivry et al., 1988), and the learning of object shapes (Roland et al., 1988), verbal associations (right side only – Petersen et al., 1989: Fiez et al., 1992;

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Raichle et al., 1994), Tower of Toronto (Fiez et al., 1992) and Insanity (Kim et al., 1994) games with sequential moves, association/dissociation of word meaning and word color (Stroop Test – Fiez et al., 1992), tactile mazes (left side only – Van Mier et al., 1995), spatial locations (Joyal et al., 1996), and prism-adaptation of pointing to (Weiner et al., 1983) and throwing at visual targets (Martin et al., 1996). Performance of these tasks also requires (and is more critically impaired by) lesions of the cerebral ‘association’ cortex. Thus, language is more obviously impaired by lesions of the left cerebral hemisphere than by lesions of the right cerebellum. Similarly, operations in extrapersonal space are more obviously impaired by lesions of the right cerebral hemisphere than by lesions of the left cerebellum. Finally, intent and operations in time and future are more obviously impaired by cerebral frontal lobe lesions than by any cerebellar lesion. There have been many case reports of disorders of attention, spontaneity of movement, control of affective state, and various cognitive performances. There are also reports of autism produced by cerebellar lesion, and claims of cerebellar atrophy related to schizophrenia. Schmahmann and Sherman (1998), on the basis of a study of a number of patients and a review of the literature, posit a more general ‘cerebellar cognitive affective syndrome’ (see also Chapter 9). In this syndrome, there may be deficits in planning, setshifting, verbal fluency, language abilities including grammatism and prosody, abstract reasoning and working memory, visual–spatial organization and memory, personality structure with blunting of affect or disinhibited and inappropriate behavior, and an overall lowering of intelligence. The constancy of the relation of a cerebellar lesion to a behavioral abnormality and of the specificity of the location of the lesion site to the specific behavioral abnormality have been questioned by others (cf Thach, 1996). The so-called ‘motor’ and ‘cognitive’ regions of the cerebellum have distinct input and output connections, consistent with their differing specializations. The cerebellar motor regions receive from vestibular and spinocerebellar pathways, and sensorimotor cortex via the pons: the region projects back to these areas. The cerebellar cognitive regions receive from nonprimary frontal, parietal, and occipital association cortex via the pons and project back to them via the thalamus: the projections are reciprocal (Middleton and Strick, 1994; Schmahmann and Sherman, 1998). Yet, the cerebellar circuity – the network wiring within the cerebellum – is remarkably similar for the two areas. The sameness of the circuitry suggests that some common computation is performed in the two areas on the different sets of input information. It has been suggested that the motor cerebellum may

combine simple movement elements and link them together to a novel stimulus or context. An extension of this hypothesis is that the cognitive cerebellum may also combine simple cerebral ‘cognitive units’ into larger complexes, linking them by trial-and-error learning to a triggering context (Thach, 1996). Such a mechanism might provide for the mental subroutines that form unconscious ‘backgrounds’ to the ‘foreground’ of conscious thoughts (Thach, 1998).

xReferencesx Albus, J.S. (1971). A theory of cerebellar function. Math Biosci 10: 25–61. Allen, G.I. and Tsukahara, N. (1974). Cerebro-cerebellar communication systems. Physiol Rev 54: 957–1006. Angel, R.W. (1980). Barognosis in a patient with hemiataxia. Ann Neurol 7(1): 73–7. Andersson, G. and Armstrong, D.M. (1987). Complex spikes in Purkinje cells in the lateral vermis (b zone) of the cat cerebellum during locomotion. J Physiol 385: 107–34. Antziferova, L.I., Arshavsky, Y.I., Orlovsky, G.N. and Pavlova, G.A. (1980). Activity of neurons of cerebellar nuclei during fictitious scratch reflex in the cat.I. Fastigial nucleus. Brain Res 200: 239–48. Arshavsky, Y.I., Yu.I., Orlovsky, G.N., Pavlova, G.A. and Perret, C. (1980). Activity of neurons of cerebellar nuclei during fictitious scratch reflex in the cat. II. The interpositus and lateral nuclei. Brain Res 200: 249–58. Asanuma, C., Thach, W.T. and Jones, E.G. (1983a). Cytoarchitectonic delineation of the ventral lateral thalamic region in the monkey. Brain Res Rev 5: 219–35. Asanuma, C., Thach, W.T. and Jones, E.G. (1983b). Distribution of cerebellar terminations and their relation to other afferent terminations in the ventral lateral thalamic region of the monkey. Brain Res Rev 5: 237–65. Asanuma, C., Thach, W.T. and Jones, E.G. (1983c). Anatomical evidence for segregated focal groupings of efferent cells and their terminal ramifications in the cerebellothalamic pathway of the monkey. Brain Res Rev 5: 267–99. Asanuma, C., Thach, W.T. and Jones, E.G. (1983d). Brainstem and spinal projections of the deep cerebellar nuclei in the monkey, with observations on the brainstem projections of the dorsal column nuclei. Brain Res Rev 5: 299–322. Babinski, J. (1899). De l’asynergie cérébelleuse. Rev Neurol 7: 806–16. Babinski, J. (1906). Asynergie et inertie cérébelleuses. Rev Neurol 14: 685–6. Bastian, A.J., Martin, T.A., Keating, J.K. and Thach, W.T. (1996). Cerebellar ataxia: abnormal control of interaction torques across multiple joints. J Neurophysiol 76: 492–509. Bastian, A.J., Mink, J.W., Kaufman, B.A. and Thach, W.T. (1998). Posterior vermal split syndrome. Ann Neurol 44(4): 601–10.

Structure and function of the cerebellum

Bauswein, E., Kolb, F.P., Leimbeck, B. and Rubia, F.J. (1983). Simple and complex spike activity of cerebellar Purkinje cells during active and passive movements in the awake monkey. J Physiol (Lond) 339: 379–94. Bloedel, J.R. (1992). Functional heterogeneity with structural homogeneity: how does the cerebellum operate? Behav Brain Sci 3:1–39. Botterell, E.H. and Fulton, J.F. (1938). Functional localization in the cerebellum of primates. II. Lesions of midline structures (vermis) and deep nuclei. J Comp Neurol 69: 47–62. Bower, J.M. (1997). Control of sensory data acquisition. Int Rev Neurobiol 41: 489–513. Bracha, V., Kolb, F.P., Irwin, K.B. and Bloedel, J.R. (1999). Inactivation of interposed nuclei in the cat: classically conditioned. Exp Brain Res 126(1): 77–92. Braitenberg, V. (1967). Is the cerebellar cortex a biological clock in the millisecond range? Prog Brain Res 25: 2334–46. Brooks, V.B. and Thach, W.T. (1981). Cerebellar control of posture and movement. In Handbook of Physiology, the Nervous System, Section 1, Vol. 2, ed. V.B. Brooks, pp. 877–946. Bethesda: American Physiology Society. Brown, S.H., Hefter, H., Mertens, M. and Freund, H-J. (1990). Disturbances in human arm movement trajectory due to mild cerebellar dysfunction. J Neurol Neurosurg Psychiatry 53: 306–13. Bullock, T.H. (1986). Significance of findings on electroreception for general neurobiology. In Electroreception, ed. by T.H. Bullock and W. Heilingenberg, pp. 651–74. New York: Wiley. Buttner, U., Fuchs, A.F., Markert-Schwab, G. and Buckmaster, P. (1991). Fastigial nucleus activity in the alert monkey during slow eye and head movements. J Neurophysiol 65(6): 1360–71. Coltz, J.D., Johnson, M.T. and Ebner, T.J. (1999). Cerebellar Purkinje cell simple spike discharge encodes movement velocity in primates during visuomotor arm tracking. J Neurosci 19(5): 1782–803. Dow, R.S. (1987). Cerebellum, pathology: symptoms and signs. In The Encyclopedia of Neuroscience, Vol. 1, ed. G. Adelman, pp. 203–6. Boston: Birkhauser Boston. Dow, R.S. and Moruzzi, G. (1958). The Physiology and Pathology of the Cerebellum. Minneapolis: University of Minnesota Press. Dugas, C. and Smith, A.M. (1992). Responses of cerebellar Purkinje cells to slip of a hand-held object. J Neurophysiol 67(3): 483–95. Eccles, J.C., Ito, M. and Szentagothai, J. (1967). The Cerebellum as a Neuronal Machine, New York: Springer-Verlag. Ekerot, C-F. and Kano, M. (1985). Long-term depression of parallel fibre synapses following stimulation of climbing fibres. Brain Res 342: 357–60. Elble, R.J., Schieber, M.H. and Thach, W.T. (1984). Activity of muscle spindles, motor cortex, and cerebellar nuclei during action tremor. Brain Res 323: 330–4. Evarts, E.V. and Thach, W.T. (1969). Motor mechanisms of the CNS: cerebro-cerebellar inter-relations. Annu Rev Physiol 31: 451–98. Fiez, J.A., Petersen, S.E., Cheney, M.K. and Raichle, M.E. (1992). Impaired non-motor learning and error detection associated with cerebellar damage. Brain 115: 155–78.

Flament, D. and Hore, J. (1986). Movement and electromyographic disorders associated with cerebellar dysmetria. J Neurophysiol 55: 1221–33. Flament, D., Vilis, T. and Hore, J. (1984). Dependence of cerebellar tremor on proprioceptive but not visual feedback. Exp Neurol 84(2): 314–25. Flourens, P. (1824). Recherches Expérimentales sur les Propriétés et les Fonctions du Système Nerveux, dans les Animaux Vertébrés. Paris: Crevot. Fortier, P.A., Kalaska, J.F. and Smith, A.M. (1989). Cerebellar neuronal activity related to whole-arm reaching movements in the monkey. J Neurophysiol 62: 198–211. Fortier, P.A., Smith, A.M. and Kalaska, J.F. (1993). Comparison of cerebellar and motor cortex activity during reaching: directional tuning and response variability. J Neurophysiol 69(4): 1136–49. Fu, Q.G., Flament, D., Coltz, J.D. and Ebner, T.J. (1997). Relationship of cerebellar Purkinje cell simple spike discharge to movement kinematics in the monkey. J Neurophysiol 78(1): 478–91. Fuchs, A.F., Robinson, F.R. and Straube, A. (1993). Role of the caudal fastigial nucleus in saccade generation. I. Neuronal discharge pattern. J Neurophysiol 70(5): 1723–40. Fuchs, A.F., Robinson, F.R. and Straube, A. (1994). Participation of the caudal fastigial nucleus in smooth-pursuit eye movements. I. Neuronal activity. J Neurophysiol 72(6): 2714–28. Fujita, M. (1982). Adaptive filter model of the cerebellum. Biol Cybern 45: 195–206. Frysinger, R.C., Bourbonnais, D., Kalaska, J.F. and Smith, A.M. (1984). Cerebellar cortical activity during antagonist cocontraction and reciprocal inhibition of forearm muscles. J Neurophysiol 51: 32–49. Gao, J.H., Parsons, L.M., Bower, J.M., Xiong, J., Li, J. and Fox, P.T. (1996). Cerebellum implicated in sensory acquisition and discrimination rather than motor control. Science 26: 545–7. Gellman, R., Gibson, A.R. and Houk, J.C. (1985). Inferior olivary neurons in the awake cat: detection of contact and passive body displacement. J Neurophysiol 54: 40–60. Gilbert, P.F.C. and Thach, W.T. (1977). Purkinje cell activity during motor learning. Brain Res 128: 309–28. Gilman, S. (1969). The mechanism of cerebellar hypotonia. Brain 92: 621–38. Goodkin, H.P., Keating, J.G., Martin, T.A. and Thach, W.T. (1993). Preserved simple and impaired compound movement after infarction in the territory of the superior cerebellar artery. Can J Neurol Sci 20 (Suppl. 3): S93–104. Granit, R., Homgren, B. and Merton, P.A. (1955). The two routes for excitation of muscle and their subservience to the cerebellum. J Physiol (Lond) 130: 213–34. Grill, S.E., Hallett, M., Marcus, C. and McShane, L. (1994). Disturbances of kinaesthesia in patients with cerebellar disorders. Brain 117: 1433–47. Hallett, M., Berardelli, A., Matheson, J., Rothwell, J. and Marsden, C.D. (1991). Physiological analysis of simple rapid movements in patients with cerebellar deficits. J Neurol Neurosurg Psychiatry 53: 124–33.

63

64

A.J. Bastian and W.T. Thach

Hallett, M., Shahani, B.T. and Young, R.R. (1975). EMG analysis of patients with cerebellar deficits. J Neurol Neurosurg Psychiatry 38: 1163–9. Harvey, R.J., Porter, R. and Rawson, J.A. (1977). The natural discharges of Purkinje cells in paravermal regions of lobules V and VI of the monkey’s cerebellum. J. Physiol (Lond) 271: 515–36. Holmes, G. (1939). The cerebellum of man. The Hughlings Jackson memorial lecture. Brain 62: 1–30. Hore, J., Wild, B. and Diener, H-C. (1991). Cerebellar dysmetria at the elbow, wrist, and fingers. J Neurophysiol 65: 563–71. Horak, F.B. and Diener, H.C. (1993). Cerebellar control of postural scaling and central set. J Neurophysiol 72: 479–93. Houk, J.C. (1988). Cooperative control of limb movements by the motor cortex, brainstem and cerebellum. In Models of Brain Function, ed. R.M.J. Cotterill, Cambridge: Cambridge University Press. Ito, M. (1972). Neural design of the cerebellar control system. Brain Res 40: 80–2. Ito, M. (1984). The Cerebellum and Neural Control. New York: Appleton-Century-Crofts. Ito, M. (1989). Long-term depression. Ann Rev Neurosci 12: 85–102. Ito, M., Sakurai, M. and Tongroach, P. (1982). Climbing induced depression of both mossy fiber responsiveness and glutamate sensitivity of cerebellar Purkinje cells. J Physiol (Lond) 324: 113–34. Ivry, R.B., Keele, S.W. and Diener, H.C. (1988). Dissociation of the lateral and medial cerebellum in movement timing and movement execution. Exp Brain Res 73: 167–80. Joyal, C.C., Meyer, C., Jacquart, G., Mahler, P., Caston, J. and Lalonde, R. (1996). Effects of midline and lateral cerebellar lesions on motor coordination and spatial orientation. Brain Res 739(1–2): 1–11. Kano, M. and Kato, M. (1987). Quisqualate receptors are specifically involved in cerebellar synaptic plasticity. Nature 325: 276–9. Keating, J.G. and Thach, W.T. (1995). Nonclock behavior of inferior olive neurons: interspike interval of Purkinje cell complex spike discharge in the awake behaving monkey is random. J Neurophysiol 73: 1329–40. Kim, S.G., Ugurbil, K. vand Strick, P.L. (1994). Activation of a cerebellar output nucleus during cognitive processing. Science 12: 949–51. Kitazawa, S., Kimura, T. and Yin, P-B. (1998). Cerebellar complex spikes encode both destinations and errors in arm movements. Nature 392: 494–7. Lamarre, Y. and Mercier, L.A. (1971). Neurophysiological studies of harmaline-induced tremor in the cat. Can J Physiol Pharmacol 49: 1049–58. Lamarre, Y., Spidalieri, G. and Chapman, C.E. (1983). A comparison of neuronal discharge recorded in the sensori-motor cortex, parietal cortex, and dentate nucleus of the monkey during arm movements triggered by light, sound or somesthetic stimuli. Exp Brain Res 7(Suppl.): 140–56. Lang, E.J., Sugihara, I., Welsh, J.P. and Llinas, R. (1999). Patterns of spontaneous Purkinje cell complex spike activity in the awake rat. J Neurosci 19(7): 2728–39.

Lisberger, S.G. (1988). The neural basis for learning of simple motor skills. Science 242: 728–35. Llinas, R. and Yarom, Y. (1986). Oscillatory properties of guinea-pig inferior olivary neurones and their pharmacological modulation: an in vitro study. J Physiol (Lond) 376: 163–82. Mano, N., Kanazawa, I. and Yamamoto, K. (1986). Complex-spike activity of cerebellar Purkinje cells related to wrist tracking movement in monkey. J Neurophysiol 56: 137–58. Mano, N. and Yamamoto, K. (1980). Simple spike activity of cerebellar Purkinje cells related to visually guided wrist tracking movement in the monkey. J Neurophysiol 43: 713–28. Manto, M., Godaux, E. and Jacquy, J. (1994). Cerebellar hypermetria is larger when the inertial load is artificially increased. Ann Neurol 35: 45–52. Marple-Horvat, D.E. and Stein, J.F. (1987). Cerebellar neuronal activity related to arm movements in trained rhesus monkeys. J Physiol (Lond) 394: 351–66. Marr, D. (1969). A theory of cerebellar cortex. J Physiol (Lond) 202: 437–70. Martin, T.A., Keating, J.G., Goodkin, H.P., Bastian, A.J. and Thach, W.T. (1996). Throwing while looking through prisms: I. Focal olivocerebellar lesions impair adaptation. Brain 119: 1183–98. Mason, C.R., Miller, L.E., Baker, J.F. and Houk, J.C. (1998). Organization of reaching and grasping movements in the primate cerebellar. J Neurophysiol 79(2): 537–54. Mauritz, K.H., Dichgans, J. and Hufschmidt, A. (1979). Quantitative analysis of stance in late cortical cerebellar atrophy of the anterior lobe and other forms of cerebellar ataxia. Brain 102: 461–82. McCormick, D.A., Lavond, D.G., Clark, G.A., Kettner, R.E., Rising, C.E. and Thompson, R.F. (1981). The engram found? Role of the cerebellum in classical conditioning of nictitating membrane and eyelid responses. Bull Psychon Soc 18: 103–5. McCormick, D.A. and Thompson, R.F. (1984). Cerebellum: essential involvement in the classically conditioned eyelid response. Science 223: 296–9. Meyer-Lohman, J., Conrad, B., Matsunami, K. and Brooks, V.B. (1975). Effects of dentate cooling on precentral unit activity following torque pulse injections into elbow movements. Brain Res 94: 237–51. Miall, R.C., Keating, J.G., Malkmus, M. and Thach, W.T. (1998). Simple spike activity predicts occurrence of complex spikes in cerebellar Purkinje cells. Nat Neurosci 1(1): 13–15. Middleton, F.A. and Strick, P.L. (1994). Anatomical evidence for cerebellar and basal ganglia involvement in higher cognitive function. Science 266: 458–61. Mugnaini, E. (1983). The length of cerebellar parallel fibers in chicken and rhesus monkey. J Comp Neurol 220: 7–15. Ohtsuka, K. and Noda, H. (1990). Direction-selective saccadicburst neurons in the fastigial oculomotor region of the macaque. Exp Brain Res 81(3): 659–62. Ohtsuka, K. and Noda, H. (1991). Saccadic burst neurons in the oculomotor region of the fastigial nucleus of macaque monkeys. J Neurophysiol 65: 1422–34. Ojakangas, C.L. and Ebner, T.J. (1992). Purkinje cell complex and

Structure and function of the cerebellum

simple spike changes during a voluntary arm movement learning task in the monkey. J Neurophysiol 68(6): 2222–36. Ojakangas, C.L. and Ebner, T.J. (1994). Purkinje cell complex spike activity during voluntary motor learning: relationship to kinematics. J Neurophysiol 72(6): 2617–30. Optican, L.M. and Robinson, D.A. (1980). Cerebellar-dependent adaptive control of primate saccadic system. J Neurophysiol 44: 1058–76. Orioli, P.J. and Strick, P.L. (1989). Cerebellar connections with the motor cortex and the arcuate premotor area: an analysis employing retrograde transneuronal transport of WGA-HRP. J Comp Neurol 288: 612–26. Palay, S.L., and Chan-Palay, V. (1974). Cerebellar Cortex. Cytology and Organization. New York: Springer-Verlag. Paulin, M.G. (1993). The role of the cerebellum in motor control and perception. Brain Behav Evol 41: 39–50. Pelisson, D., Goffart, L. and Guillaume, A. (1998). Contribution of the rostral fastigial nucleus to the control of orienting gaze shifts in the head-unrestrained cat. J Neurophysiol 80(3): 1180–96. Pellionisz, A. and Llinas, R. (1980). Tensorial approach to the geometry of brain function: cerebellar coordination via metric tensor. Neuroscience 2: 1125–36. Petersen, S.E., Fox, P.T., Posner, M.I., Minten, M. and Raichle, M.E. (1989). Positron emission tomographic studies of the processing of single words. J Cog Neurosci 1: 153–70. Raichle, M.E., Fiez, J.A., Videen, T.O. et al. (1994). Practice-related changes in human brain functional anatomy during nonmotor learning. Cereb Cortex 4: 2–26. Robinson, D.A. (1976). Adaptive gain control of the vestibuloocular reflex by the cerebellum. J Neurophysiol 39: 954–69. Roland, P.E., Eriksson, L., Widen, L. and Stone-Elander, S. (1988). Changes in regional cerebral oxidative metabolism induced by tactile learning and recognition in man. Eur J Neurosci 1: 3–17. Schieber, M.H. and Thach, W.T. (1985). Trained slow tracking II. Bidirectional discharge patterns of cerebellar nuclear, motor cortex, and spindle afferent neurons. J Neurophysiol 55: 1228–70. Schmahmann, J.D. and Sherman, J.C. (1998). The cerebellar cognitive affective syndrome. Brain 121: 561–79. Schweighofer, N., Arbib, M.A. and Kawato, M. (1998a). Role of the cerebellum in reaching movements in humans. I. Distributed inverse dynamics control. Eur J Neurosci 10(1): 86–94. Schweighofer, N., Spoelstra, J., Arbib, M.A. and Kawato, M. (1998b). Role of the cerebellum in reaching movements in humans. II. A neural model of the intermediate cerebellum. Eur J Neurosci 10(1): 95–105. Scudder, C.A., Batourina, E.Y. and Tunder, G.S. (1998). Comparison of two methods of producing adaptation of saccade size and implications for the site of plasticity. J Neurophysiol 79(2): 704–15. Simpson, J.I. and Alley, K.E. (1974). Visual climbing fiber input to rabbit vestibulocerebellum: a source of direction-specific information. Brain Res 82: 302–8. Smith, A.M. and Bourbonnais, D. (1981). Neuronal activity in cerebellar cortex related to control of prehensile force. J Neurophysiol 45: 286–303.

Soechting, J.F., Burton, J.E. and Onoda, N. (1978). Relationships between sensory input, motor output and unit activity in interpositus and red nuclei during intentional movement. Brain Res 152: 65–79. Spidalieri, H.J., Busby, L. and Lamarre, Y. (1983). Fast ballistic arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey II. Effects of unilateral dentate lesion on discharge of precentral cortical neurons and reaction. J Neurophysiol 50: 1359–79 Strata, P. (1985). Inferior olive: functional aspects. In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans and W. Precht, pp. 231–46. Berlin: Springer-Verlag. Strick, P.L. (1983). The influence of motor preparation on the response of cerebellar neurons to limb displacements. J Neurosci 3: 2007–20. Thach, W.T. (1968). Discharge of Purkinje and cerebellar nuclear neurons during rapidly alternating arm movements in the monkey. J Neurophysiol 31: 785–97. Thach, W.T. (1970). Discharge of cerebellar neurons related to two maintained postures and two prompt movements. II. Purkinje cell output and input. J Neurophysiol 33: 537–47. Thach, W.T. (1975). Timing of activity in cerebellar dentate nucleus and cerebral motor cortex during prompt volitional movement. Brain Res 88: 233–41. Thach, W.T. (1978). Correlation of neural discharge with pattern and force of muscular activity, joint position, and direction of intended next movement in motor cortex and cerebellum. J Neurophysiol 41: 654–78. Thach, W.T. (1996). On the specific role of the cerebellum in motor learning and cognition: clues from PET activation and lesion studies in humans. Behav Brain Sci 19: 411–31. Thach, W.T. (1998). What is the role of the cerebellum in motor learning and cognition? Trends Cog Sci 2: 331–7. Thach, W.T., Goodkin, H.G. and Keating, J.G. (1992a). Cerebellum and the adaptive coordination of movement. Ann Rev Neurosci 15: 403–42. Thach, W.T., Kane, S.A., Mink, J.W. and Goodkin, H.P. (1992b). Cerebellar output: multiple maps and motor modes in movement coordination. In The Cerebellum Revisited, ed. R. Llinas and C. Sotelo, pp. 283–300. New York: Springer-Verlag. Topka, H., Konczak, J., Schneider, K., Boose, A. and Dichgans, J. (1998). Multi-joint arm movements in cerebellar ataxia: abnormal control of movement dynamics. Exp Brain Res 119(4): 493–503. Trouche, E. and Beaubaton, D. (1980). Initiation of a goal-directed movement in the monkey. Exp Brain Res 40: 311–21. van Kan, P.L., Houk, J.C. and Gibson, A.R. (1993). Output organization of intermediate cerebellum of the monkey. J Neurophysiol 69: 57–73. Van Mier, H., Tempel, L., Perlmutter, J.S., Raichle, M.E. and Petersen, S.E. (1995). Generalization of practice-related effects in motor learning using the dominant and nondominant hand measured by PET. Soc Neurosci Abstr 21: 1441. Vilis, T. and Hore, J. (1977). Effects of changes in mechanical state of limb on cerebellar intention tremor. J Neurophysiol 40: 1214–24.

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Vilis, T. and Hore, J. (1980). Central neuronal mechanisms contributing to cerebellar tremor produced by limb perturbations. J Neurophysiol 43: 279–91. Weeks, R.A., Gerloff, C., Honda, M., Dalakas, M.C. and Hallett, M. (1999). Movement-related cerebellar activation in the absence of sensory input. J Neurophysiol 82(1): 484–8. Weiner, M.J., Hallett, M. and Funkenstein, H.H. (1983). Adaptation to lateral displacement of vision in patients with lesions of the central nervous system. Neurology 33: 766–72.

Wetts, R., Kalaska, J.F. and Smith, A.M. (1985). Cerebellar nuclear cell activity during antagonist cocontraction and reciprocal inhibition of forearm muscles. J Neurophysiol 54: 231–44. Yeo, C.H., Hardiman, M.J. and Glickstein, M. (1984). Discrete lesions of the cerebellar cortex abolish the classically conditioned nictitating membrane response of the rabbit. Behav Brain Res 13: 261–6.

Part II

Theories of Cerebellar Control

6

Models of cerebellar function Steve G. Massaquoi1 and Helge Topka2 1

Department of Electrical Engineering and Computer Science and Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, USA 2 Department of Neurology, University of Tübingen, Germany

Introduction Especially because the circuitry of the cerebellum is strikingly uniform and has been relatively well characterized anatomically and physiologically, many investigators have been prompted to devise theories to explain its function. Over the centuries, many conceptions of cerebellar function have been put forward, and it still cannot be said that a consensus view has been achieved. However, despite their seeming diversity, theories of cerebellar function have converged significantly. Useful summaries and reviews of the more historical ideas can be found in several places (Llinas, 1981; Pellionisz, 1985; Thach et al., 1992). In order to afford better quantitative analysis and to take advantage of our growing computer simulation capabilities, models of cerebellar function have been formulated increasingly in mathematical terms. This chapter focuses on these models and attempts to introduce them from a qualitative engineering perspective, with a bare mimimum of mathematical detail. Specifically, it reviews the basic character of cerebellar function, describing it as an adaptive modulator or ‘controller’ of movement, rather than as a principal driver of movement. It then describes the types of signal processing that are thought to occur in the cerebellum and the essential features of the neuronal architecture that would implement these proposed types of computation. The central theoretical principles of controller design that are used to understand and evaluate cerebellar models are then outlined. Specifically, feedforward, feedback, internal model-based, and discontinuous control strategies are discussed. Finally, several specific mathematical models have been selected to highlight important concepts in the evolution of the quantitative thinking about the cerebellum.

Characteristics of cerebellar system function The cerebellar system as an adaptive controller Motor control In humans, the most evident critical functions of the cerebellum are to assist the assessment, stabilization and control of movement, posture, and autonomic function. In these regards, most current views of the cerebellum consider the organ to operate broadly as an adaptive controller in the engineering sense (Goodwin and Sin, 1984; Slotine and Li, 1991). A slightly more general view that takes into account some non-motor functions is discussed in the next section. A controller, in a movement generation system, is a component that performs certain types of signal processing that are used to optimize or at least improve the characteristics of movement. In general, the function of motor controllers is to enhance the stability of the system, in the sense of making it recover more quickly, more completely, and with less oscillation following a perturbation, and to enhance its tracking ability – that is, the timeliness, precision, smoothness, and accuracy with which a system executes a commanded motion. Shock absorbers, electronic suspensions, and automatic pilots are examples of progressively more sophisticated controllers. The action of the controller typically becomes more important as the dynamic aspects of the task become more demanding. An example would be the situation in which a massive and/or highly interlinked, multicomponent system must be moved rapidly through a complex trajectory. On the other hand, a controller is not primarily responsible for generating or storing the movement plan or program. Thus, it plays a fundamentally assistive role in movement control. Given that the cardinal signs of cerebellar dysfunction are tremor and ataxia that is especially prominent in rapid multijoint movements, and not

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apraxia, paralysis or protracted non-oscillatory involuntary movement (as in dystonia), it is clear why the cerebellum can be viewed as a motor controller. Also, because the cerebellum is a principal site of plasticity during motor learning (Gilbert and Thach, 1977; Ito, 1984; Watanabe, 1985; Lisberger, 1988; Pascual-Leone et al., 1993; Topka et al., 1993, 1998c), it functions in particular as an adaptive, or self-tuning controller (Goodwin and Sin, 1984). If one seeks a more detailed and precise description of cerebellar function, it is essential to bear in mind that ‘the cerebellum’ is best thought of as a collection of separate suborgans that have the same, or at least very similar, neural architectures. Because of this essential anatomical commonality, all suborgans presumably perform somewhat similar elemental signal processing. However, given their distinct neuroanatomical connections, the functional role of each cerebellar subregion is different. Moreover, several extracerebellar centers are so intimately related to cerebellar operation that they are often usefully considered to be part of a functional ‘cerebellar system’. These areas include the following nuclei: red, pontine, lateral reticular, pontine reticular tegmental, paramedian reticular, vestibular, perihypoglossal, inferior olivary, as well as the ‘cerebellar’ thalamic nuclei (Bloedel and Courville, 1981; Brodal, 1981). Often, descriptions in the literature of the function of ‘the cerebellum’ are best related to particular segments of ‘the cerebellar system’. In particular, it is frequently overlooked that it is the comparatively small anterior lobe that appears to be most specifically dedicated to movement control. Both the diversity in the types of other brain centers that are interconnected with the cerebellar system, and the multiplicity of possible signal processing operations that might be used to improve motor control, contribute to much of the apparent disparity between theories of ‘cerebellar function’. For example, the cerebellum has been viewed as a context-dependent motor pattern generator (Marr, 1969; Albus, 1971; Thach et al., 1992; Houk et al., 1993; Thach, 1996) or calibrator (Contreras-Vidal et al., 1997) timing device (Braitenberg, 1967; Ivry and Keele, 1989; Keele and Ivry, 1990; Buonomano and Mauk, 1994), signal predictor/controller (Miall et al., 1993), body state estimator (Paulin, 1989, 1997), sensory signal optimizer (Bower, 1995, 1997), regulator of reflex gains, spindle sensitivity and/or stiffness (Gilman and MacDonald, 1967; Gilman, 1969; MacKay and Murphy, 1979a, 1979b; Gilman et al., 1981; Smith, 1996), regulator of temporal integration (Robinson, 1989; Leigh and Zee, 1991), sensorimotor coordinate transformer (Pellionisz and Llinas, 1979; Pellionisz, 1985), and a wave-variable processor (Massaquoi and Slotine, 1996). In fact, none of these conceptions is fundamentally inconsis-

tent with the idea of an adaptive controller and it is likely that many or all of these are very reasonable descriptions of at least some aspect of cerebellar system function. The complexity of cerebellar system function is understandable considering the different features of animal motor control that might benefit from adaptive optimization. In addition to fostering basic stability and accuracy during self-paced movement, an animal motor control system must also be able to: modulate reflexive movements and/or trigger programmed responses quickly and accurately in response to changes in environment (e.g., perceived features during tactile exploration, altered terrain or suddenly detected threats); produce externally guided and often predictive movements in order to track and intercept moving targets; execute all types of motions with precise timing; and adapt quickly to maintain good motor control in the presence of varying environmental loads and disturbances (e.g., added masses, fluid and frictional resistances, and impacts) as well as with physiological or pathophysiological changes in body capacities (e.g., fatigue, age or injuries). Moreover, as subregions of the cerebellum have been implicated in autonomic control (Reis et al., 1973) and in aspects of cognition (Schmahmann, 1997), it appears that cerebellar action concerns a range of brain processes, not only those related directly to the precision control of voluntary movement.

‘Sensory control’ and ‘cognitive control’ Given the neuroanatomical connections of the cerebellum, it is clear that the structure is well positioned to process many types of information, both sensory and nonsensory, and both internally and externally derived, for a variety of purposes. The feedback motor control strategy proposed for the cerebellum in many models implies that cerebellar-based sensory signal processing is fundamental to normal movement control. Thus, this strategy is inherently a sensorimotor one. A more sensory-oriented sensorimotor theory has recently been put forth by Bower (1995, 1997). However, the theory does not imply that cerebellar processing of sensory information is not also used to support non-motor brain functions. Paulin (1989, 1997) and Gao et al. (1996) have emphasized that cerebellar processing may be involved in purely perceptual tasks involving movement of an external system. In fact, this view can be generalized further to suggest that the cerebellum is well suited and important for processing time-varying signals in general (Ivry and Keele, 1989; Keele and Ivry, 1990; Ivry and Diener, 1991; Massaquoi and Hallett, 1998). For example, cerebellar prediction might be applied to signals from exteroceptors and teleceptors to enable the brain to better interpret and anticipate external motions

Models of cerebellar function

and events. While such a capacity might be used to help in the interception of a moving target, the information might also be used, for example, for non-motor decision making. Paulin (1989) also points to the prominent development of the cerebellum in animals such as electroceptive fish that apparently must contend with complex sensory processing tasks but execute only very ordinary movements (see also Chapter 2). Ito (1997) has more recently emphasized the idea that cerebellar functional microcomplexes may subserve cognitive control functions. Moreover, a range of perceptual, cognitive, and even affective defects may be caused by cerebellar dysfunction (Schmahmann, 1991; Schmahmann and Pandya, 1997). Presumably, wider use of directed neuropsychological testing would reveal a greater prevalence of perceptual and other cognitive deficits following, especially, posterior lobe lesions. The critical nature of the cerebellar role in motor control is clear. The fact that the large volume of cerebellar tissue may be more closely correlated with certain sensory functions in various animals is of unclear significance. It is quite plausible that the volume of dedicated tissue is most directly related to the complexity and/or flexibility of the particular signal processing that is required, whether for motor or non-motor purposes, and less directly to its relative importance to the animal. Certainly, relatively small portions of the cerebellum may subserve critical functions (e.g., balance, oculomotor control). From a clinical point of view, the perceptual and cognitive dysfunctions in cerebellar disorders are almost uniformly much less disabling than are the motor deficits. We are just beginning to have quantitatively detailed theories of how the cerebellum functions in sensorimotor control. These are the focus of this chapter. Comparable theories of cerebellar function in perception and cognition await future modeling efforts. It is to be hoped that these will be able to be formulated using many of the same principles that are outlined here.

Unique aspects of cerebellar system signal processing It is evident that the frontal cerebrum, basal ganglia, and brainstem centers also function importantly in executive control, and that these structures may exhibit plasticity as well (Phillips and Carr, 1987; Pascual-Leone et al., 1993, 1994; Houk and Wise, 1995; Bloedel and Bracha, 1997). What, then, is the neural signal processing that can be considered unique to the cerebellar system? The answer to this question has not been established. However, it can be noted that at their cores virtually all models of cerebellar function incorporate the idea of storage and adaptation of gain settings or functions, in some form or another. ‘Gain’ here

means linear or non-linear amplification or attenuation (i.e., scaling) of neuronal signals. From the perspective of engineering control theory, this is quite plausible, because the mathematical representation of the input–output behavior of many types of controllers includes importantly some scaling, linear or non-linear, of the input signals. Because of the comparatively slow signal conduction in cerebellar parallel fibers (see below), many but not all models also suggest that the delaying of signals is also a fundamental aspect of cerebellar processing. The cerebellum is also felt by many to implement internal models of the body’s physical dynamics. Hence, the cerebellum has been considered to be able to represent the behavior of differential equations. This implies, in turn, that it contains mechanisms that perform temporal (i.e., mathematical) integration and/or differentiation of signals. Also, in general, as mentioned above, the cerebellum appears somehow to be specially involved in the processing of timevarying signals. Finally, the great divergence and convergence of input information within the cerebellum have prompted many to propose the fundamental role of the cerebellum in the establishment of novel input–output associations or of sensory–motor transformations. Available evidence is most compelling that the unique function of the cerebellum proper is quickly to store, adapt, and utilize a very large number (perhaps of the order of a trillion)1 of very precise input-to-output gains and possibly input-to-output delay settings for a variety of signal processing purposes. Although signal transmission gains and delays are associated with various other parts of the nervous system, and some of these may also be ultimately adaptable, it appears likely that the cerebellum is uniquely specialized to modify and store these settings with great precision, stability, and rapidity. Thus, although in many circumstances cerebellar damage does not eliminate motor learning altogether, it typically markedly degrades and slows the process (Welsh and Harvey, 1989; PascualLeone et al., 1993; Thach, 1996; Topka et al., 1998c). As discussed below, physiological evidence (Allen and Tsukahara, 1974) also suggests that cerebellar systems consisting of cerebellar cortical circuits together with certain brainstem nuclei may also be able to approximate mathematical integration (Leigh and Zee, 1991). Moreover, approximate mathematical differentiation can be performed by signal processing that uses suitable combinations of gains and delays. Therefore, it is highly plausible that the cerebellar system may be uniquely suited to represent at least certain aspects of body dynamics. The cerebellum undoubtedly derives great operational power from its ability to functionally integrate many types of information including primary sensory data as well as

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Fig. 6.1 Schematic diagram of the principal signal pathways within a cerebellar microcomplex that might be related to voluntary control of limb movements. Other cerebellar signal processing tasks would be handled by variants of this basic structure. PC: Purkinje cells; PF: parallel fibers; GC: granule cells; MF: mossy fibers; DCN: deep cerebellar nuclear cells or lateral vestibular nuclear cells (here, dentate or interposed nuclear cells); Th: thalamus; RN: red nucleus (or other post-cerebellar nucleus); PCN: precerebellar nuclei (e.g., pontine, pontine lateral reticular, pontine reticular tegmental); CF: climbing fiber; IO: inferior olivary nucleus. Each structure represents many neurons acting approximately in parallel. Note that, for clarity, not all of the mossy fiber paths or deep nuclear output paths are shown. (Figure adapted from Massaquoi, 1999.)

highly processed internal signals. Particular cerebellar outputs can therefore become associated with a particular internal and external world state, or context (Thach, 1996) among a large universe of such states. At least some very important processes attributed to the cerebellum, such as regulation of vestibulo-ocular reflexes, appear not to depend upon great convergence of information, though they still depend on gain adaptation. Furthermore, although there remains debate on aspects of this point, it is at least very often, if not always, the case that novel sensorimotor associations made within the cerebellum also exist outside of the cerebellum, in parallel. The spinal cord, brainstem, and cerebral association cortices are, of course, highly capable of functionally integrating information from a very large number of diverse sources. Thus, it appears to be the character of the cerebellar large-scale associational capability that is unique, not simply its existence. Similarly, although sensory–motor coordinate transformation is apparently performed by some regions of the cerebellum, it presumably must also occur in many other parts of the sensorimotor control system (e.g., suprasegmental reflex pathways).

Several examples of important cerebellar processing involve modification of the temporal characteristics of time-varying signals. However, other cerebellar processes do not. In the cerebellum-mediated adaptation to wedge prism spectacles (Thach et al., 1992), for example, it appears that a fixed offset (bias) is learned that applies just as much to correcting static eye position as to correcting eye movements. Thus, marked ongoing time-variation does not appear to be an essential characteristic of signals that are processed by the cerebellum. Indeed, many cerebellar signals, especially in the dentate, appear to be steady for significant periods of time during movements (e.g., Robertson and Grimm, 1975). At this point, the challenge in cerebellar system modeling appears to be one of determining the precise manner in which gain settings or functions and possibly delay settings are stored, adapted, and utilized to benefit motor and other types of neural signal processing.

Essential cerebellar system microcircuitry Functional microcomplexes Any satisfactory theory of cerebellar signal processing must explain how the process is implemented by the cerebellar system microcircuitry. Detailed reviews of the circuitry can be found in Chapter 2. Figure 6.1, which is adapted from the formulations of Ito (1984, 1997), Oscarsson (1979), Allen and Tsukahara (1974), and ultimately from Eccles (Eccles et al., 1967), summarizes the principal neuronal processing elements of the cerebellum as they might be organized in a functional module. The particular function represented is that of voluntary limb movement control. Other cerebellar functions appear to be mediated by the same type of cerebellar cortical circuitry, though possibly interacting with different deep cerebellar nuclei and/or other brain centers. This basic cerebellar system neural connectivity is conserved from amphibians, to reptiles, birds, and mammals (Llinas, 1981). Specifically, from the point of view of motor control, there are two primary input pathways.2 The mossy fibers convey information from a wide range of sources, including peripheral sensory receptors and many central nervous system centers, while the climbing fibers convey signals specifically from the inferior olive. Cerebellar system output is from deep cerebellar nuclei or from the lateral vestibular nucleus. Most mossy fibers possess collaterals that impinge directly upon deep nuclear cells yielding a direct, rapid input–output connection. Other branches of the mossy fibers synapse upon granule cells, which in turn give rise to long, thin, relatively slowly conducting parallel fibers.

Models of cerebellar function

Parallel fibers then interact with many Purkinje cells, as well as with Golgi, basket and stellate cells (not shown).3 Because Purkinje cells in turn synapse upon (specifically inhibit) deep nuclear cells, a parallel signal pathway from mossy fiber input to deep cerebellar nuclear cell output is formed. Climbing fibers synapse strongly upon Purkinje cells and also give off collaterals to deep cerebellar nuclear cells. The climbing fiber–Purkinje cell–deep nuclear cell system represents the second major cerebellar input–output pathway (see also Chapter 2). Purkinje cells, either individually or certainly in small groups, are generally viewed as having continuously graded responses to parallel fiber input under experimental and physiological conditions (e.g., Llinas, 1981; Ito and Kano, 1982; Ito et al., 1982; Fortier et al. 1989). However, on–off, switch-type responses have also been described under experimental conditions and in simulations (Houk et al., 1990; Berthier et al., 1993; Jaeger and Bower, 1994; Yuen et al., 1995). It is conceivable that both operating modes may occur in normal cerebellar operation. In either case, the role of the Purkinje cells in most theories is to receive inputs from a large number of parallel fibers, and to transmit a net signal to cells of either a deep cerebellar nucleus or the lateral vestibular nucleus. The manner in which Purkinje cells do this is considered to be modulated by climbing fiber activity, as described below. Drawing upon the observations and thoughts of Eccles (Eccles et al., 1967), Oscarsson (1979), and others, Ito (1984) has argued that the intracerebellar circuits shown in Fig. 6.1 constitute a fundamental, or canonical, cerebellar functional module (cerebellar cortico-nuclear microcomplex; Ito, 1984) that is repeated throughout the organ. According to this idea, all cerebellar processing is attributable to collections of these modules, each possibly communicating with different extracerebellar centers. Each module itself consists of many neurons operating in parallel. For example, in humans each parallel fiber synapses on many hundred Purkinje cells, there is a convergence of about 60 000 parallel fibers onto each Purkinje cell, and of about 860 Purkinje cells onto each deep nuclear neuron (Ito, 1984). It is worth noting that if many of the parallel fibers received similar information from the same source (e.g., stretch receptors in the same muscle), the parallel processing and convergence could yield essentially an averaging of information. To the extent that the noise processes in the receptors’ (or other input pathways’) signals are uncorrelated, this could provide a significant increase in the net signal quality at the deep nuclear cell output.

Fig. 6.2 Schematic diagrams of possible functional signal pathways through a cerebellar microcomplex, as depicted in Fig. 6.1. Here, the dark, vertical bars represent Purkinje cells viewed on edge. Their output signals travel to deep nuclear cells and thence to post-cerebellar nuclei. Presumably, signal summation could occur at either or both nuclei. (a) Input signals u1(t) and u2(t), sometimes conveyed via precerebellar nuclear cells (open circles in afferent paths) to mossy and parallel fibers (via granule cells), are scaled by weights (gains) that represent the strengths of the parallel fiber-to-Purkinje cell (1, 2), and mossy fiber-to-deep nuclear cell (0) synapses. (b) The input signal, u(t), encounters a significant time delay, t, along its parallel fiber path before exiting via the Purkinje cell. Depending on the values of the scaling factors 0 and 1, the net result can approximate differentiation of the input signal (see text for details). (Figure adapted from Massaquoi 1999.)

Possible linear signal processing Figure 6.2 gives examples of two elementary signal processing functions that theoretically could be performed easily by the cerebellar cortex. The first (Fig. 6.2a) is scaling of the input signal u1(t) by the factor (0  1), together with scaling of a second input signal u2(t) by the factor 2. Thus, the output signal y(t) is a linear combination of the inputs: y(t) (0  1) u1(t)  2u2(t). Berthier et al. (1993) use statistical arguments to indicate how populations of on–off-type Purkinje cells could cause a nuclear cell group (within a recurrent loop) to display a net graded reduction in activity as parallel fiber activity increases. Depending upon the action of climbing fibers, the graded reduction in output as a function of parallel fiber activity would be more or less steep. Essentially, then, populations of on–off-type Purkinje cells could also implement a net cerebellar input–output gain of the type described above. The second operation (Fig. 6.2b) consists of forming a particular linear combination of an input signal u(t) with a version of itself that has been delayed by Tpf , u(t  Tpf ). Tpf is likely to be no more than 35 ms (Thach et al., 1992). If it is also true that 0 1, then:

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y(t) 0 u(t)  u(t  Tpf ) approx.  dy/dt. In this way, scaling and approximate differentiation of signals may be achieved very simply. Other cerebellar circuit implementations of differentiation-like processing have been proposed (Hassul and Daniels, 1977; Fujita, 1982), and other linear combinations of signals might also have value to a motor control system. The possibility that linear functional modules could be used for temporal integration of neural signals is discussed in the section entitled ‘Prominent cerebellar system models’. Ito has not argued which precise computations are performed by cerebellar modules, and the computations considered here have not been established experimentally. However, they represent simple interpretations of how the cerebellar cortex might function in a number of circumstances. The idea that cerebellar modules store and adapt gains, and can thereby generate at least linear combinations of inputs, with or without delays, is a parsimonious one that is consistent with several current models. As reviewed below, however, a number of investigators have attributed somewhat different signal processing to the basic cerebellar microcircuitry. Finally, it should be borne in mind that Golgi, stellate and basket cells, which are neglected in Figs. 6.1 and 6.2, undoubtedly have important functions in regulating the distribution and quality of the signals that are processed by the Purkinje cells. Many schemes have been proposed (see the models of Albus, Kettner et al. and Schweighofer et al. which are described in this chapter). Much more work needs to be done to determine the detailed function of these neuronal elements within cerebellar cortical circuitry (e.g., Maex and De Schutter, 1998).

the transmission gain of the Purkinje cell activation with respect to parallel fiber activity can be adaptively depressed. Interestingly, Kano (1996) and others have noted that long-term potentiation (LTP) of inhibitory input to Purkinje cells (e.g., from basket and/or stellate cells) also may accompany climbing fiber activity. Kano argues that this may reinforce the changes on the Purkinje cell produced by convergent activity of parallel and climbing fibers. The above stimulation studies paralleled behavioral electrophysiological recording studies by Gilbert and Thach (1977) and many others (see Simpson et al., 1996), who have shown that climbing fiber activity typically occurs in association with unanticipated behavioral events. Classically, whenever a monkey manipulated a novel load, or a cat’s paw inadvertently struck an obstacle, a burst of climbing activity was generated. Together, these findings have suggested to many that the climbing fibers convey behavioral error signals that determine when and to what extent the Purkinje cells are to adapt their input sensitivities. It can thus be readily appreciated how behavioral errors could result in a change in the net input–output gain of the net transmission from mossy fiber input to deep nuclear cell output. To date, it appears that most analyses of climbing fiber-induced plasticity changes have focused on motor behavior. Presumably, if the cerebellum is involved in cognitive control, climbing fiber activity should appear in relation also to cognitive tasks. This awaits further investigation.

Theoretical considerations Feedforward and feedback control strategies

Adaptation of circuit behavior Importantly, Ito et al. (1982; Ito and Kano, 1982), Ekerot (1985), Kano (1996), and many others (see Simpson et al., 1996 for a review) have confirmed the early predictions of Marr (1969) and Albus (1971) that, in response to climbing fiber activation, the sensitivity of Purkinje cells to parallel fiber input (e.g., 1, 2 in Fig. 6.2) can be modified. Specifically, Ito (Ito and Kano, 1982; Ito et al., 1982) and Ekerot (1985) showed that, if climbing fiber activation occurs within several milliseconds of parallel fiber activity, the strength of the Purkinje cell synapse with that particular parallel fiber becomes reduced to some extent. This reduction, termed long-term depression (LTD), lasted for at least an hour, and no upper limit for the duration has currently been found. (However, the experimental conditions are difficult to maintain for long periods.) This means that

If it is assumed, as is done in most cerebellar system modeling, that the system operates to an important degree as an adaptive motor controller, then the problems that it must solve and the principles by which it must function can be specified. By considering the system to be a controller, we assume that for every movement there exists a motor plan or program, however crude, that is generated elsewhere. For voluntary movements, this formulation presumably takes place in the cerebrum. For certain involuntary patterned behaviors, the movement plan may be formed at brainstem or even spinal levels. If one considers, for example, the particular task of moving a limb, it is clear that at some point the movement plan takes the form of a specified series of joint angles that are to be achieved over time, i.e., a planned or programmed joint trajectory. The detailed physiology of this process has not been

Models of cerebellar function

established.4 However, in any case, the job of the controller, as represented schematically in Fig. 6.3, is to assist the conversion of the programmed or reference trajectory into an acceptably faithful movement. In particular, the controller should determine, for any given reference trajectory, the specific commands that must be sent to the actuators, in this case the muscles, to cause the limb to move satisfactorily. Often, a close match with the reference trajectory is sought. At other times, perhaps a smoothed version of the reference command would be desirable. In either situation, both feedforward and feedback control strategies can be used to address this problem.

Feedforward control The idea in feedforward control (Fig. 6.3a) is to be able to calculate the correct motor commands in advance of the movement. To be generally effective, this strategy depends on the presence of quantitative knowledge (an internal representation) of what commands, as indicated by electromyogram (EMG) signals, for example, are required to produce any given desired movement. In an engineering approach, the problem is frequently solved in reverse. That is, given the basic principles of muscle physiology and biomechanics that specify how the muscles and skeleton convert EMG signals into motions (i.e., that define the forward dynamics of the system to be controlled, or the ‘plant’ P in Fig. 6.3), the reverse relationship P1 is determined. This can often be done by mathematically ‘inverting’5 the forward dynamics (e.g., see Slotine and Li, 1991). On the other hand, if P1 can be learned directly (by whatever means), there is no need to begin formally with P. In practice, the inverse dynamics are ultimately only approximated, even if very closely (generally by computer), so that one speaks of basing control on an (approximate) inverse ˆ 1. dynamics model P Feedforward use of such a model as in Fig. 6.3a has the great advantage of being able to reproduce any desired trajectory, with faithfulness limited only by the accuracy of the inverse dynamics model. Specifically, we have from Fig. 6.3a that: ˆ 1 ) (PP ˆ 1)  (1)  , actual (P)(P ref ref ref ref ˆ 1  P 1 . where the approximation is because, in practice, P ˆ 1 is to P1, the closer However, it is clear that the closer P ˆ 1 determines directly the actual will be to ref . Thus, P command signals needed to accelerate and decelerate the body part properly, as well as those needed to compensate for any biomechanical interaction forces that occur during motion. These are all functions that have been attributed to the cerebellum (e.g., Holmes, 1939; Thach et al., 1992; Bastian et al., 1996; Massaquoi and Hallett, 1996, 1998;

Fig. 6.3 Various strategies for controlling and stabilizing a musculoskeletal system P that is subject to exogenous disturbances, Pd.. ref represents the desired or reference joint angles over time (i.e., the reference joint trajectory). actual is the response (movement) of the system; fb is the feedback (sensed) position signal; emg refers to the electromyogram. Note that all signals are functions of time. In vivo, there exist time delays along each of the signal pathways. The shaded regions suggest the areas of possible cerebellar contribution. In (b) and (c), the small circular summing junction represents the primary motor cortex together with brainstem or spinal motor nuclei. The differencing junction represents, as yet, not fully specified cerebral sensorimotor regions. As a simplification, the net effects of spinal reflex arcs are considered to be lumped into P. (a) A pure feedforward control scheme that employs an adaptive ˆ 1. (b) An adaptive linear inverse dynamics model P feedforward/feedback control system (servo) that processes the angle error signal, e, and its derivative, e• , the angular velocity error. Bc and Kc are adjustable gains that are used to scale the signals before summation. (c) An adaptive composite control ˆ 1, used in a scheme that employs an inverse dynamics model, P feedforward path, a linear feedforward/feedback controller, and a forward model-based feedback control path.

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Topka et al., 1998a, 1998b). Moreover, dynamic models are defined to some extent in terms of various gains and differentiations or integrations that are to be applied to their input signals. As suggested previously, it may therefore be feasible for cerebellar microcircuitry to compute at least some aspects of dynamic models. For these reasons, some investigators (e.g., Kawato et al., 1987) have modeled the cerebellum or parts of the cerebellum as a feedforward controller that principally implements an inverse dynamics model. The potentially large disadvantage of pure feedforward control is that, under several important circumstances, a satisfactory inverse dynamics model is not achievable. The first situation is when it is theoretically impossible fully to invert the forward dynamics. For example, the output (e.g., force) capacities of physical actuators such as muscles have hard upper limits. Therefore, desired movements that call for accelerations that exceed the muscles’ capacities cannot be achieved. Hence, the forward dynamics are only invertible for less-demanding desired trajectories. A second situation is when the body interacts with any novel object (load) or disturbance, i.e., when there is uncertainty and fundamental unpredictability of the movement dynamics. This problem is especially serious for any system that operates in an open (unpredictable) environment, as does a human. In situations where new dynamics become constant for a period of time, or where they recur at reasonably predictable intervals (e.g., ground contact during walking), this second problem can be addressed by adapting the feedforward controller until it substantially learns the new inverse dynamics. That is, over ˆ 1 → P 1 . If multiple inverse models can be stored, time P new then the residual problem becomes one of determining precisely when best to shift between different internal inverse dynamics models. Adaptation of an internal inverse dynamics model is a central feature of the models of Kawato (Kawato et al., 1987; Kawato, 1990; Kawato and Gomi, 1992), Gomi (Gomi and Kawato, 1992) Schweighofer et al. (1998a, 1998b) described below. However, because incorrectly specified inverse dynamics can result in extremely poor control, this type of scheme depends upon some other method of maintaining satisfactory control during the period in which the new inverse dynamics are being learned. Hence, in some schemes an auxiliary stabilizing controller (e.g., a feedback controller, see below) is needed to operate in conjunction with inverse model adaptation. Yet, if the novel dynamics are truly unpredictable, feedforward control can never be used alone, irrespective of the amount of learning. A third important circumstance in which the feedforward design is unsatisfactory is when the controller

does not have sufficient complexity or power to represent or calculate the inverse dynamics fully. As discussed below, this case may also be relevant to physiological systems.

Feedback control The second fundamental approach to control is to send forward a very simple movement command, often just the reference trajectory itself, and then to use feedback signals that report the actual state (position and velocity) of the controlled system to refine the command. In a common situation (Fig. 6.3b), the signals to the actuators are generated by processing the discrepancy (error) between the desired and actual states. The job of the feedback controller is to improve the use of these error signals to produce highly effective commands. This approach has the major advantage of not requiring knowledge or explicit internal representation of the musculoskeletal inverse dynamics. Using this design, a control system may be able to approximate the inverse dynamics implicitly over a very wide range of conditions. For example, feedback control systems can yield acceptable control and stability in the presence of actuator limitations (saturations) as well as random disturbances and other dynamic uncertainties. Moreover, effective feedback controllers may have simple structures even when the dynamics of the controlled system are very complex. Often, the role of the feedback controller is simply to amplify the error signal and possibly to perform simple dynamic filtering (i.e., to apply a number of mathematical differentiations and/or integrations). Figure 6.3b shows a simple feedback control system that uses proportional and derivative processing of the error signal.6 The particular type of system shown in Fig. 6.3b is a servomechanism. For such control systems, the desired output is used as the input, and the controller (the shaded regions in Fig. 6.3) output is computed as a continuous function of the error. Because passive stiffnesses (e.g., spring-like muscles) as well as spinal reflexes and suprasegmental stretch responses can all be viewed as servomechanisms (McIntyre and Bizzi, 1993), the servo principle can be viewed as the basis for several closely related theories of motor control, including impedance control (Hogan, 1984a, 1984b, 1985), equilibrium point control (Bizzi et al., 1984; Flash, 1987; Latash and Goodman, 1994), the -model (Feldman, 1986) and others (see Houk and Rhymer, 1981). A potentially serious disadvantage of servos is that their tracking accuracy in practice is generally considerably less than that of well-tuned feedforward control systems. This is because the activity of any servo depends fundamentally upon the existence of some error, even if only transient.

Models of cerebellar function

Thus, the implicit representation of inverse dynamics is necessarily only approximate. Still, for well-designed servo controllers, the error can usually be made very small, and it may well tend to zero in the steady state (over time). A second important limitation of feedback control systems occurs when there is either significant noise or delay in the feedback signal, as certainly happens in biological nervous systems. In this case, the signal that arrives at the controller is not completely accurate, and therefore the control signals that are issued to the muscles are no longer fully appropriate. If severe, these distortions of sensory feedback, especially the delays, can give rise to system oscillations (e.g., tremor) or gross instability (e.g., flailing). Moreover, there is a basic trade-off between performance and stability associated with changing the gains in the feedback loop. Large gains tend to improve performance, i.e., they reduce the discrepancy between the actual and desired postures and motions. However, large gains ordinarily also increase the vulnerability of the system to instability due to delays. Therefore, feedback systems often require special designs to achieve small performance errors in the presence of degraded sensory information or delays (Goodwin and Sin, 1984; de Carvalho, 1993). The role of the cerebellum in feedback control of movement has been examined intensively and there is little doubt that it is very significant (Gilman and MacDonald, 1967; Murphy et al., 1975; MacKay and Murphy, 1979a, 1979b; Gilman et al., 1981; Hore and Vilis, 1984; Hore and Flament, 1986). Therefore, a major focus of modeling is to explain how a cerebellar feedback system might cope with delays and/or sensory noise. In engineering control systems and cerebellar system models, feedforward and feedback control strategies are typically combined (e.g., Fig. 6.3c, and Kawato et al., 1987; Atkeson and Reinkensmeyer, 1990; Kawato, 1990; Gomi and Kawato, 1992; Kawato and Gomi, 1992; Schweighofer et al., 1998a, 1998b). The feedforward controller supplies the best estimate of the needed control signals, and a servo control system ‘cleans up’ any residual error due to inaccuracies in the inverse dynamics model or to external disturbances.

Sensory features of servo controllers A further aspect of servo structure warrants mention in regard to sensory control hypotheses of cerebellar function. By its construction, the servo error signal is fundamentally both a motor command and a sensory information signal. Any structure that processes such an error signal may appear to exhibit either motor or sensory character, both, or neither (when the error is zero), depending upon the particular situation. Consider, for

example, the task of voluntarily moving a finger through space. Because air offers little resistance to motion, under servo control the actual finger motion would nearly match the desired trajectory. Therefore, the servo error signal and the signals at the output of the controller (Kc and Bc in Fig. 6.3b) may be very small. If the cerebellum functions to some extent as a servo controller, then, some findings of relatively crude neurophysiological assessment techniques, such as functional magnetic resonance imaging (MRI), may incorrectly suggest that the structure is inactive in such a task (e.g., Parsons and Fox, 1997). Consider the task of sliding the finger tip along a surface at constant velocity. Suppose that some part of the cerebellum could provide the time integral of the slip velocity as measured by cutaneous receptors. Such a signal would estimate the distance that the finger has moved along the surface. Steady finger movement could be viewed as being controlled by a cerebellar servo that uses a constant velocity (steadily increasing position) intended movement as a reference signal, and compares this to the cutaneously derived distance moved estimate, rather than to signals from proprioceptors (as when moving through air). If the surface has friction or viscosity, there will be a steady-state mismatch between the commanded and estimated position signals. This error and its derivative will appear (scaled) at the output of the controller. The magnitude of this mismatch is proportional to the viscosity of the surface and to the speed of finger movement. If the motor command is steady, the steadiness of the error signal, or equivalently the smallness of its time derivative, is then a direct indicator of the uniformity of the surface. Thus, servo controller-derived signals based on cutaneous slip during movement could be used as a special type of sensory information that would be provided by active exploration of surfaces. On the other hand, consider the task of holding the finger still while monitoring the velocity of a material moving across the tip. In this case, it could be easily conceived that the velocity of the movement command signal is simply zero, and the output from the summing junction in Fig. 6.3.b (i.e., from motor cortex or spinal cord) is being suppressed by whatever mechanism enables body parts to be maintained in a passive state. In this case, the error signal becomes large (specifically equal to fb ) and therefore the output of the controller is large, even though there is no finger motion. Here, the steadiness of the derivative of the error signal ˙fb indicates the uniformity of the surface, but only if it can be assumed that the material is being dragged across the the finger tip with constant force. The magnitude of the friction in the surface cannot be determined from the slip rate alone (without additional

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force information from the skin). Overall, then, passive assessment of surface characteristics by monitoring slip would be less reliable and less informative than active exploration. However, some useful surface information could still be obtained from the servo circuitry during passive monitoring. Thus, if the cerebellum were to function at least in part as a servo controller, its activity could be seen to be much greater during active or passive interaction with a surface than during free movement through air. Moreover, its output could be highly useful for analysis of the environment. Concluding from this that the cerebellum is a sensory signal processor that could be very important in guiding tactile exploration would be highly appropriate; however, concluding that the structure is not fundamentally related to classical motor control would not be. In principle, the reference command can be viewed as specifying the desired motion to be achieved, or the sensory signal to be expected. Therefore, the error signal may be viewed as giving information about the quality of motion that has occurred, about the success in acquiring anticipated sensory signals during active exploration, or about the characteristics of sensory information acquired during passive monitoring. Feedback controller circuitry could thus be employed for a variety of sensorimotor purposes.

Internal model-based versus non-model-based control In the motor neurophysiological context, the term ‘internal (dynamic) model’ is taken to mean a collection of neural circuits whose output mimics the behavior of some part of the body or physical environment. It is clear from engineering movement control systems that performance usually benefits substantially by having a faithful dynamic model of some type within the controller. In some sense mirroring the central role of an inverse dynamic model to feedforward control, an internal forward dynamic model (Fig. 6.3c) may greatly improve feedback control. Figure 6.3c includes a forward model-based feedback control system design (dashed lines) in which corollary command signals c are used to produce surrogate feedback signals ˆfb . These surrogate signals approximate the behavior of the actual feedback signals that would occur in the absence of, or with reduced, noise or delays.7 Thus, the internal forward model functions as a body state estimator or observer (Luenberger, 1979). By suitable construction, such observers can easily function as predictors as well (Goodwin and Sin, 1984). As the cerebellum has been implicated in body state estimation/prediction (Grill et al., 1994, 1997) it is natural that several interpretations of

cerebellar system function have included forward internal dynamic models. As mentioned above, the cerebellar system is an attractive candidate for implementation of internal dynamic models also, because it may contain adjustable gains or functions and delays, as well as integrator-like behavior. Particular examples of the internal model interpretation of cerebellar function are the Smith Predictor (Miall et al., 1993) and Kalman filter models (Paulin, 1989). Other investigators strongly consider that the cerebellum implements both forward and inverse dynamics models (Kawato et al., 1987; Wolpert et al., 1998). Another application of internal models that may be relevant to cerebellar system modelling is in model reference adaptive control (Houk and Rhymer, 1981; Goodwin and Sin, 1984; Slotine and Li, 1991) In this scheme (not shown), an independent dynamic model that possesses some desirable behavior is used as an ideal toward which the actual control circuitry should attempt to push the plant’s behavior. Typically, the difference between the ideal model’s output and the system’s actual behavior is used as an error signal to the adaptive controller. This technique may allow the adaptation of the plant’s controlled behavior to reach a satisfactory endpoint short of precise matching of the input command. This is useful, for example, when the input signal is unavoidably abrupt or noisy, and therefore when a completely faithful output would be undesirable and/or difficult to achieve within the limitations of the control system. Some models of cerebellar function are essentially model reference control schemes (Kawato, 1990; Gomi and Kawato, 1992; Kawato and Gomi, 1992). A potential limitation in the use of internal dynamic models is the complexity of the circuitry or computation that is required to represent or operate the model. For example, sinusoidal head oscillations considered by Paulin (1997) are well described by linear dynamics. A suitable internal model can be created by coupling two integrating circuits via simple gains. However, the dynamics of a multilink appendage such as an arm are non-linear and much more complicated (see Slotine and Li, 1991). They cannot be simulated using only linear gains, delays, and integrators. Certainly, artificial neural network-based and other non-linear controllers have been designed that are very powerful (Kawato et al., 1987; Miller et al., 1990; Slotine and Li, 1991) and could, in principle, represent body dynamics fully. It is also conceivable that the cerebellum could be involved in triggering, linking, and/or modulating the behavior of oscillator circuits or other elemental dynamic circuits elsewhere in the nervous system. This might produce more complex internal signals than would be generated by the cerebellum alone. However, whether natural neural systems have sufficient non-linear computational

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ability to represent body dynamics fully8 remains an open question. Moreover, the training time requirements of any proposed internal model must be considered. Training certain types of powerful but complex internal models may be extremely slow, and therefore such models may be unrealistic. It also must be considered that limited prediction can be performed by circuits consisting simply of delays and gains that are not organized to form internal dynamic models, i.e., by linear filters which are elaborations of the circuit shown in Fig. 6.2 (e.g., see restricted complexity direct adaptive prediction: Goodwin and Sin, 1984). A variant of this idea has been suggested for the cerebellum by Pellionisz and Llinas (1979). In their model, prediction was generated by multiple signal differentiations (in a manner that is slightly more complex, but analogous, to the differencing filter shown in Fig. 6.2b). Because of the potential sensitivity of differentiators to noise and the limited lookahead time that is achievable in practice, the feasibility of such an approach to biological signal prediction is not clear. However, the significance of these potential problems depends on the details of the biological implementation (e.g., the presence or absence of significant signal averaging), the frequency content of the signals being predicted, and how far ahead the prediction needs to be. For certain signals in the sensorimotor system, averaged differencing filter-based predictions of a few hundred milliseconds may not be unreasonable. This is an area for future modeling and physiological investigation. Explicit model-based designs are especially attractive from an analytical point of view, because they compartmentalize the estimation of body state or the computation of inverse dynamics. They contrast with schemes in which the adaptive controller receives both command and feedback information and, over time (i.e., with practice), learns to generate command signals that improve motor performance, even though the output signal need not represent either inverse dynamics or estimates of body state. The servo shown in Fig. 6.3b is a particular case of this idea in which the command and feedback information enter together as an error signal. However, more general nonexplicit model-based designs exist (Goodwin and Sin, 1984). This general approach is termed (feedforward/feedback) direct adaptive control, and may yield performance that is as good as that based on explicit internal models. Certain models, notably those of Berthier et al. (1993), Kettner et al. (1997) and Schweighofer et al. (1998a, 1998b) are of this type. Other models (Massaquoi and Slotine, 1996; Massaquoi, 1999), though not adaptive, similarly do not rely on explicit internal models. Ultimately, the distinction between explicit internal

model-based and non-explicit internal model-based control is not sharp. For example, in a direct adaptive control scheme, depending on its design, the controller may come to have internal portions that are similar to either forward or inverse models without precisely representing either.

Discontinuous control The preceding theoretical considerations concern the way the cerebellar system may function in an effectively continuous manner to assist the production of stable, precise movements given a continuous command trajectory or a fixed position to be maintained. It is clear that such considerations might also apply to cerebellar system involvement in autonomic control of internal variables such as blood pressure or heart rate which are effectively continuous. However, it is not evident how such control mechanisms might contribute to behavior or cognition. It is therefore important to consider other modes in which the cerebellar system might function. For example, the servo and continuous model-based designs should be distinguished carefully from lookup table-based control schemes (Raibert and Wimberly, 1984; Atkeson and Reinkensmeyer, 1990; Barto, 1990), wherein the control signals that are generated under very similar circumstances may be arbitrarily different from each other. That is, the control is discontinuous. Typically, the particular output to be emitted in response to each distinct feedforward or feedback signal has been pre-stored, possibly via a learning procedure. In this situation, novel feedback signals, for example due to unanticipated disturbances, initially do not trigger responses that are systematically appropriate (unless a continuous-type controller is employed in parallel, as in Atkeson and Reinkensmeyer, 1990). Rather, specific new entries in the lookup table must be created (learned) for each specific new disturbance. It clearly may take a very long time for such a system to develop even basic general behavioral competence if used by itself. Thus, feedback-driven lookup table mechanisms may share some of the computational simplicity of servos in terms of freedom from an explicit representation of complete dynamics.9 However, like pure feedforward controllers, lookup mechanisms deal much less well with uncertainty (although they similarly often perform much better than servos once they are well trained). Many automatic behaviors of humans seem to be driven by such discrete, learned stimulus–response-type control (Houk and Rhymer, 1981). This has led to several influential models of cerebellar function (Marr, 1969; Albus, 1971; Kettner et al., 1997) based on context–response linkages

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(Thach, 1996). Because of their possibly highly discontinuous output, these lookup table-based control mechanisms can be thought of as programmed output controllers. Importantly, programmed control is likely to involve structures beyond the cerebellum (Brooks, 1985, 1986; Diener et al., 1993; Thach, 1996). It appears that the lateral cerebellar hemispheres, which consist largely of the posterior lobe, are also particularly important to human timing functions (Dichgans and Diener, 1984; Ivry et al., 1988; Ivry and Keele, 1989; Keele and Ivry, 1990). There are various theoretical mechanisms that could account for human timing, including delay lines (Braitenberg, 1967), oscillators and integrators (Miall, 1996), and intrinsic neural network dynamics (Buonomano and Mauk, 1994). Some of these have suggested models in which the cerebellum emits signals at precise time intervals (Braitenberg, 1967; Buonomano and Mauk, 1994). Such signals, which also do not necessarily involve internal dynamic modeling, presumably could either generate action directly, or could be used to trigger or suppress the activity of other centers in a timely manner. It can therefore be envisioned that such signals could be useful in regulating cognitive activity, including higher levels of motor programming. However, as yet, no model has compellingly linked these theoretical timing mechanisms to either cognitive or motor behavior. In the end, as with the distinction between explicit model-based and non-model-based control, the distinction between discontinuous control and continuous control is not sharp. In theory, various intermediate and hybrid approaches exist (e.g., Atkeson and Reinkensmeyer, 1990; Barto, 1990). Moreover, the interpretation may depend on the time scale and the particular physiological system that is being considered. Many human control signals may change arbitrarily from one second to another. However, it may be the case that the same signals are necessarily much more continuous from one hundredth of a second to the next hundredth. Presumably, because of some of their complementary characteristics, both continuous and discontinuous control mechanisms are employed by the nervous system (Houk and Rhymer, 1981). Moreover, it is conceivable that different subregions of the cerebellum might operate in different ways. For example, the anterior intermediate cerebellum might facilitate continuous control of limb dynamics without use of an explicit model, while the posterior lateral cerebellum might cooperate with the cerebrum to implement programmed control and also perform state estimation and prediction using a more explicit internal model-like mechanism. Thus, the control theoretic principles outlined above appear to be very useful in characterizing the

possibilities for the modes of cerebellar control. However, in attempting to define detailed and comprehensive models of ‘cerebellar function’, they should be applied flexibly. Careful study will be required to determine the applicability of different control–theoretic concepts to different cerebellar regions.

Prominent cerebellar system models Over the past 30 years, several theories of cerebellar system operation have been presented in mathematical form, allowing systematic analysis and simulation. Several of the more comprehensive and/or detailed models are reviewed briefly below. We recognize that, within the scope of this chapter, it is impossible to provide more than a cursory introduction to these models or this growing area of investigation. The reader is encouraged to pursue the literature references given.

Repository for programmed motor responses The models of Marr and Albus The idea that the cerebellum is a memory site for programmed motor responses that can be rapidly evoked by association with certain specific sensorimotor contexts was put forth by Brindley (1969), Marr (1969), and Albus (1971) in some of the earliest mathematical models of cerebellar function. Ito (1972) also noticed context-related cerebellar plasticity, but developed a model of a different basic form. The core concept of the Marr–Albus models is that the cerebellum stores context–response linkages (Thach, 1996). Here, ‘context’ refers to the entire set of signals carried by mossy fibers that relate the state of the brain and body. The cerebellum is posited to develop (learn with practice) a chain of associations between cerebellumgenerated motor commands and the states of the brain and body that can then be replayed without constant cerebral participation, and therefore presumably with much reduced conscious attention. The central mechanism was postulated to be the representation of each specific firing pattern of (some number) N incoming mossy fibers by a unique binary pattern of parallel fiber activity. Specifically, at any point in time, N of perhaps 100N possible parallel fibers would be active (transmit the value 1), while the rest would remain inactive (transmit the value 0). In the parlance of artificial neural network theory (Barto, 1990), the parallel fiber activity pattern thus would represent a sparse expansive recoding (Albus, 1971; Kettner et al., 1997) of the activity of incoming mossy fibers. It was proposed that, through the action

Models of cerebellar function

of climbing fibers, the Purkinje cells would then learn a particular firing pattern that would become associated with (triggered by) each unique parallel fiber activity pattern. Specifically, the Purkinje cell response depended upon the sum of the activities of the impinging parallel fibers, each scaled by the strength of a trainable synaptic weight (gain). Overall, then, the relationship between the input mossy fibers, the parallel fibers and the Purkinje cell output cells was viewed to be equivalent to that of a perceptron (Rosenblatt, 1961; Hertz et al., 1991) with one hidden layer. This scheme has been shown to be able to store a large number of input–output relationships. In the model, the output of the Purkinje cells was then directed via deep nuclear cells to brainstem and/or spinal motor centers to produce movement. Each motion produced a change in the activity of the mossy fibers, thereby creating a new context which, in turn, could trigger a subsequent motor control command from the Purkinje cells. For a novel movement, the motion was proposed to be directed initially from the cerebral cortex via the red nucleus, inferior olive, climbing fibers, Purkinje and cerebellar deep nuclear cells. After learning, the Purkinje cell output would be able to assume full, or nearly full, control of the motion using mossy fiber input as a substitute for climbing fiber input, and thus free the cerebral cortex. The Albus model especially is qualitatively consistent with cerebellar physiology in many ways and has been very influential. The general idea that cerebro-cerebellar interaction affords increased automaticity of movement is longstanding and remains current (Thach, 1996). The model’s postulate that the correlated firing of climbing and parallel fibers leads to changes in the synaptic strength between parallel fibers and Purkinje cells was a particularly important prediction that was ultimately verified ten years later by Ito et al. (Ito and Kano, 1982; Ito et al., 1982). This postulate helped entrench the idea that climbing fibers convey signals that ‘teach’ Purkinje cells to adapt, and thereby began to connect cerebellar learning theory with engineering notions of adaptive control (Goodwin and Sin, 1984). Aspects of the Marr–Albus model persist in most current models. However, a closer analysis is warranted with regard to the details of the proposed mechanism. First, the Marr–Albus models assume that novel movements are controlled principally via a red nucleus – climbing fiber – Purkinje cell motor pathway. Presumably, acquired red nuclear and inferior olivary lesions would therefore prevent acquisition of all novel movements (and Purkinje cell lesions would produce paralysis of all movements). The formulation does not suggest why cerebellar lesions should be specifically characterized by ataxia and tremor rather than by paralysis, or perhaps dyskinesias. So,

clearly, some modifications of the model are necessary. As noted even by Albus (1971), climbing fibers are readily activated by certain types of peripheral input (Llinas, 1981; Ebner and Bloedel, 1985; Simpson et al., 1996) in addition to central commands. Therefore, most current models consider climbing fibers to convey error signals instead of the motor command itself, which is appropriately considered to be conveyed by corticospinal, rubrospinal, and other extracerebellar pathways. The modern error signal idea is more consistent with engineering adaptive control algorithms (Goodwin and Sin, 1984; Slotine and Li, 1991) and therefore with the idea of the cerebellum as an adaptive controller. Second, and conversely, in the presence of bradykinesia, apraxia or chorea, for example, the cerebellum does not appear to be able to produce correctly paced or properly organized movements, regardless of how well practised the movements had been. One interpretation of this observation is that cerebral motor system lesions cause the cerebellum to maladapt and to lose its stored, programmed responses. An alternative interpretation, however, is that the cerebellum never stores full programs itself. Rather, it functions to support context-dependent rapid triggering and smooth concatenation of motor programs (Brooks, 1985, 1986; Diener et al., 1993; Massaquoi and Hallett, 1998) that reside and are organized (and possibly become disorganized) elsewhere, often in the cerebrum, but possibly also in the brainstem. Thus, the cerebellar system may facilitate programmed output control, but is probably not its sole author. The latter view is consistent with the fact that there is a very significant projection from the lateral cerebellum (via the thalamus) to a range of frontal cerebral areas not limited to primary motor cortex (Sasaki, 1985). Moreover, well-practised movement is apparently accompanied by increasing prefrontal cortex–lateral cerebellar interaction, rather than exclusive takeover of motor control by the cerebellum (Sasaki, 1985).10 Finally, cerebellar dysfunction may be associated with certain mild to moderate derangements of cognition and affect (Schmahmann, 1997), but not with frank dementia or apraxia. Thus, it is even less desirable to consider the cerebellum as a primary repository for ‘cognitive programs.’ The support-role view of the cerebellar system potentially provides a more attractive, unified conception of its function in the programming of both movement and other cognitive activities. The question regarding cerebellar storage of voluntary motor programs is a higher level analog of the continuing debate regarding whether the cerebellum is the primary storage site for certain classically conditioned responses (e.g., see Schmahmann, 1997). Some have argued that the

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cerebellum is the repository (Woodruff-Pak et al., 1990; Thompson and Kim, 1996) for new sensory–motor conditioned response linkages. However, others suggest that it is simply a modulator or optimizer of conditioned responses that have significant representation elsewhere (Welsh and Harvey, 1989; Kelly et al., 1990; Bloedel and Bracha, 1997). For simple behaviors, the distinction may be minor, because the principal specifications of many classically conditioned responses are those of a certain response amplitude (possibly expressible as a scaling of a stimulus signal) and its latency (e.g., Welsh and Harvey, 1989). Similarly, the acquisition of a certain fixed bias signal to correct for prism-displaced vision (Weiner et al., 1983; Thach, 1996) may be interpreted as the learning of the correct scaling of some tonic signal before it is added to a motor command. Thus, if conditioned responses or context-dependent bias signals are considered to be rudimentary motor programs, then it seems possible that the important functional details of the program (gain and delay) may reside substantially in the cerebellum – whether or not a crude extracerebellar component exists as well. With higher level programs, presumably more of the program specification (such as a correct sequence of submovements) resides outside of the cerebellum.

The oculomotor predictive tracking model of Kettner et al. A detailed model of cerebellar function in controlling eye movements that is influenced strongly by the Marr–Albus program storage concept has been recently developed by Kettner et al. (1997). In this model, mossy fibers convey various combinations of eye position, velocity and retinal slip (mismatch between eye and target position) information, as well as their derivatives, all with realistic delays. Contexts are defined in terms of unique patterns of mossy fiber activity levels that are assessed every 10 ms. During each 10-ms epoch, the mossy fiber activity pattern is converted into a binary parallel fiber activity pattern. During each epoch, the ‘on’ parallel fibers then activate Purkinje cells (one controlling vertical eye motion, the other horizontal motion) via adjustable synaptic weights. In contrast to the Marr–Albus models, climbing fibers convey error signals. These consist of the vertical and horizontal components of the retinal slip that are sent to the respective motion-controlling Purkinje cells. As in the Marr–Albus models, depending upon the approximate coincidence of parallel fiber and climbing fiber activity, the weights are adjusted at the particular parallel fiber–Purkinje cell synapses that are active during the epoch. In computer simulations wherein the model is given the task of learning to track a visual target moving along a

somewhat complex two-dimensional spatial trajectory, the model learns high-fidelity tracking within about 300 practice trials. The trained performance of the model is comparable and, in fact, is better than the visual pursuit tracking of monkeys trained on the same task. A particularly impressive feature of the model is its ability to produce tracking with very little, if any, time lag, even though there are delays of up to 100 ms in the transmission of retinal slip information to the learning mechanism. This means that the model, as do the monkeys, learns to track predictively. The developed reliance on predicted target motion was demonstrated more specifically by a second feature of the tracking. Lengthy training was given on a trajectory in which the target relatively infrequently made sudden, identical deviations from its usual pattern. Later, it was observed that, whenever a target deviation occurred, both the model and the monkeys’ eyes routinely continued along the usual (predicted) target trajectory for about 80–90 ms after the target deviation. Only after this delay did a corrective saccade intervene to realign the eye with the target, whereupon excellent tracking resumed. The learning of predictive pursuit is facilitated first by a time-lagged ‘eligibility trace’ (Kettner et al., 1997) that allows synaptic modifications to be made for a period well after (30–600 ms) tracking error occurs. In this way, learning is not compromised by the realistic 100 ms delay in the transmission of retinal slip information via the climbing fiber system. Second, the information in mossy fibers that is available to the Purkinje cell adaptive synapses includes signals lagged up to 120 ms. The latter mechanism is widely used for training predictors (Goodwin and Sin, 1984; Kawato et al., 1987). This model, like the Marr–Albus models, essentially creates an extremely large lookup table in which the entries specify the control output needed, in this case for each 10-ms epoch within the entire complex position–time trajectory. These signals are those needed to overcome the inertial and viscous forces of the eye. Thus, the Kettner et al. and Marr–Albus models describe the cerebellum as a feedback-driven, context–response controller rather than as a servo mechanism. As demonstrated by Kettner et al. (1997), and as is characteristic of such programmedoutput controllers, the model can learn to develop appropriate responses to a novel perturbation, but only after very many practice trials. The model of Kettner et al. demonstrates clearly the general feasibility of the Marr–Albus-like model formulation in a fairly challenging setting. Several considerations remain regarding this model, including: 1. The model-tracking performance is in general more precise than that of the monkeys. This may well be due to greater precision in the model computation and the

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fact that the model did not incorporate noise. However, the relative imperfections of the monkeys’ behavior appears somewhat systematic. This may therefore indicate that the model structure itself differs from the natural system in some systematic way. 2. In the latter regard, a possibly important model simplification is its method of representing parallel fiber activity. While the idea of binary activity on parallel fibers that was proposed by Marr is useful for perceptron-like (Hertz et al., 1991) models, more recent studies (Maex and De Schutter, 1998) indicate that parallel fibers fire at graded frequencies, as do mossy fibers. 3. It is not clear how quickly the model learns in comparison with the monkeys. The time course of the learning potentially provides important further information about the realism of the postulated adaptive mechanism.

Adjustable generator of muscle activation patterns Houk et al. (1990, 1993) have put forth a model that also seeks to account for the increased automaticity and movement modulation that the cerebellar system affords. Specifically, it draws attention to the interaction between the cerebellum and reverberatory circuits in the brainstem involving the red nucleus, lateral pontine reticular tegmental nucleus, and the interposed deep cerebellar nuclei (see Fig. 6.1); Tsukahara, 1972; Allen and Tsukahara, 1974). It is proposed that this self-reinforcing neural activity, which is not included in many other models, assists in driving movements in a manner that affords modulation by Purkinje cells. In particular, movements are considered to be driven by a recurrent interaction between cerebral and cerebellar modules, the strength of which is regulated by the intensity of Purkinje cell firing. According to the model, these cerebro-cerebellar ensembles comprise adjustable pattern generators (APGs) (Houk et al., 1993) The Purkinje cell activity within each APG is determined by feedback signals that monitor the extent of movement progression. In this way, movement normally arrests in a timely fashion. The APG formulation predicts plausibly that Purkinje cell lesions would cause hypermetria because of a failure in Purkinje cell-mediated suppression of APG activity. Also apparently realistically, movement is driven by ongoing interaction between cerebrum and cerebellum in a cooperative manner. The model predicts less realistically that paralysis would result from cerebellar deep nuclear lesions. While clinically this does not occur, severe hypotonia may result from massive lesions of the deep cerebellar nuclei (Massaquoi and Hallett, 1998). Thus, the reverberatory circuits might have a role in supporting motor strength, if not accounting entirely for it.11

Arrays of APGs can be coupled to an adaptive mechanism and used to account for motor learning of an arm trajectory (Berthier et al., 1993). The model appears to give a plausible account of the acquisition of novel movement kinematics and emphasizes the distributed representation of motor programs between the cerebrum and cerebellum. However, the arm model contains no dynamics, and therefore the question of dynamic compensation is not addressed.

Regulator of temporal integration Reverberatory neural activity of the type noted by Houk et al. (1990, 1993) has also been described in oculomotor neurocircuitry. Specifically, there appear to be positive feedback circuits that involve the nucleus prepositus hypoglossi, oculomotor nuclei, and the vestibulocerebellum (Leigh and Zee, 1991). In the oculomotor context, an interpretation of this reverberation is a mechanism that facilitates temporal (mathematical) integration of angular velocity signals to produce angular position commands (Robinson, 1989; Leigh and Zee., 1991).12 This operation is used by both the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) (Ito, 1984; Leigh and Zee., 1991). Because perfect integration represents behavior that is only quasi-stable (that is, enduring though non-increasing signal from a transient input), a neuronal integrator must be tuned very precisely to have a very long decay time and not become frankly unstable. The vestibulocerebellum is considered to be instrumental in this tuning (Robinson, 1989; Leigh and Zee, 1991). The oculomotor integrator normally has a decay time constant of at least 20 s. If the flocculus is ablated, this falls to around 1.3 s (Zee et al., 1981). The rapid decay allows the eyes to drift back from the gaze direction (with decelerating slow phases) until a corrective saccade occurs, whereupon the process repeats. Thus, gaze-evoked nystagmus is seen commonly in cerebellar disease affecting the flocculus and with lesions in the region of the vestibular or perihypoglossal nuclei. Congenital nystagmus and certain vertical nystagmus which is seen in some cerebellar disorders have accelerating ‘slow’ phases and can be interpreted as the result of the opposite problem, an unstable integrator (Leigh and Zee, 1991). A simple model of these phenomena (Fig. 6.4, lower portion) consists of a ‘leaky’ integrator (with a time constant near 1.3 s) in the brainstem, which operates within a reverberatory circuit whose loop and input–output gains are adjusted by the flocculus in association with vestibular neurons. It can be shown that, under simple assumptions, as the flocculovestibular-based gain  (0  1) is

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increased, the integrator becomes less leaky (Robinson, 1989; Massaquoi, 1999). Also, for sufficiently high flocculovestibular gains, the integrator becomes unstable. Thus, in regard to gaze-evoked nystagmus, certain brainstem lesions could be expected to decrease  by reducing 0. Similarly, if cerebellar congenital defects or cerebellar disease compromised 1, it would follow that  could become too large. Unclear by this model, however, is how flocculectomy causes decelerating slow phase nystagmus. Presumably, either some coincident deleterious effect on the brainstem occurs, or the model is too simple (or very possibly both). A similar view of cerebellar regulation of integration via linear gain adjustment is used implicitly by Houk et al. (1990, 1993) and explicitly by Massaquoi and Slotine (1996) in arm movement control models. Because integrators can be used to build internal dynamic models, many other cerebellar system models are implicitly consistent with a cerebellar role in temporal integration.

Sensorimotor coordinate transformer and predictor Fig. 6.4 A simplified summary model of flocculus-modulated PD control of the vestibulo-ocular reflex (VOR) adapted from Ito (1984), Lisberger (1988), Robinson (1976), and Leigh and Zee (1991). The shaded regions represent the floccular cortex and the pathway symbol conventions are as in Figs. 6.1 and 6.2. Head angular velocity information ˙head enters from the semicircular canals. One copy of the signal flows directly to the oculomotor neurons (OMN) via vestibular nuclear neurons (VN), and in the process becomes scaled by some factor (). Another copy of the signal is processed by a floccular corticonuclear microcomplex that scales it by  (0  1) (upper functional module). A third copy travels to a vestibular neuron (in lower functional module) associated with a self-exciting neural circuit that includes a ‘leaky integrator’ (LNI) involving the medial vestibular nucleus and nucleus prepositus hypoglossi, and another path through the flocculus. The output of this module, ˆ head, is a much less ‘leaky’ integral of the negative head velocity (which approximates the negative of the head angular displacement) scaled by  (0  1). Because of unavoidable signal transmission delays in the system, ˆ head must lag, and therefore not completely match,  head. The dynamics of the eye muscles and ball (together Poc)determine eye position (eye) from the net muscle command (emg). Adaptation of the floccular modules is stimulated by inferior olive (IO) activity that presumably contains retinal slip and retinal slip velocity signals (eret, e˙ret ). * indicates the point at which introduction of a retinal slip velocity signal (e˙ret) enables the circuitry also to mediate the optokinetic reflex (OKR; see text).

Pellionisz and Llinas (1979; Pellionisz, 1985) were impressed by the fact that a large amount of cerebellar input is from sensory receptors, while much, if not most, of its output is directed to motor centers, and that the coordinate frames of sensory information and motor output are different. In particular, the sensory and motor spaces have different geometries and, because of muscle redundancies, different dimensions. Pellionisz argued that the principal function of the cerebellum was the efficient mathematical transformation of signals from sensory to motor coordinates. The theory dealt primarily with kinematic relationships. Although it postulated an important role for the cerebellum in the temporal (i.e., mathematical) differentiation of signals, it did not include mathematical integration and generally did not address most of the dynamic aspects of cerebellar control. Specifically, it did not argue why and under what circumstances the sensory–motor coordinate transformation performed by extracellular pathways was insufficient. Thus, it did not seem capable of explaining why low-acceleration (i.e., dynamically less demanding) movement is typically near normal in the presence of cerebellar lesions (see, for example, Massaquoi and Hallett, 1996). In the context of current models, the major contributions of the Pellionisz–Llinas viewpoint appear to have been to argue that cerebellar operation can be represented mathematically by a matrix of gains, i.e., as a linear multi-input–multi-output function, and that linear signal prediction is likely to be an important aspect of cerebellar function.

Models of cerebellar function

Adaptive timer/adaptive linear filter Braitenberg (1967) and others (Braitenberg and Atwood, 1958; Braitenberg and Onesto, 1962) called attention to the fact that parallel fibers are among the most slowly conducting (perhaps 0.2 m/s; see Ito, 1984) fibers in the brain. They described how Purkinje cells arrayed along a ‘beam’ of active parallel fibers become activated in strict sequence, with highly reproducible time intervals. Thus, cerebellar output could change at precisely defined intervals. This suggested that the cerebellum used such tapped delaylines to implement a ‘timer in the millisecond range’ (Braitenberg, 1967). Thach and colleagues (1992) have pointed out more recently that parallel fibers in monkeys (and presumably similarly in humans) may be up to 6 mm long. Therefore, in principle, time intervals of the order of 30 ms could be computed by the cerebellum.13 It is not clear how such timing would be used by the nervous system. Tapped delay-lines seem to be an unlikely mechanism for timing the intervals between commands to different muscle groups in compound movements, for at least two reasons: First, motor programs may easily call for delays in excess of 30 ms, and second, the delay between muscle activations depends sensitively on movement execution speed. Therefore, a different delay would have to be stored for every different execution speed attempted. Other models of timing functions performed by the cerebellar cortex have been developed, such as that by Buonomano (Buonomano and Mauk, 1994), based on other types of proposed cerebellar cortical dynamics. The model has a delay storage range of at least 350 ms, which would allow it to account for the timing of certain conditioned responses. However, as it is a programmed-outputtype model, it accepts to take into account the timing of muscle synergies. On the other hand, if the gains of the Purkinje cells along Braitenberg–Atwood tapped delay-lines can be adjusted independently, the structure might implement an adaptive linear filter (Haykin, 1991). This idea is particularly attractive, because such linear filters are highly suitable for general purpose signal processing in engineering systems (Goodwin and Sin, 1984; Haykin, 1991). In particular, they may be used for smoothing, averaging, approximate differentiation for prediction of signals, as well as to implement many types of controllers (Goodwin and Sin, 1984). Fujita (1982) and others (Calvert and Meno, 1972; Hassul and Daniels, 1977) introduced the perspective of filter design and linear systems frequency domain analysis to cerebellar modeling. Fujita’s adaptive linear filter model of the cerebellum (Fujita, 1982) captured this idea, though it attributed delays to Golgi cell–granule cell interaction

rather than to distance travelled along parallel fibers. It also proposed that phase advance could be generated by mossy fiber granule cell–Golgi cell interaction. This is similar to the effect of the differentiation-like circuit proposed in Fig. 6.2b. The tapped phase advance/delay line concept remains a potentially very useful one.

Internal dynamics model-based observer/controller The adaptive control model of Ito Building upon his own work in the cerebellum, including the demonstration of climbing fiber-mediated parallel fiber–Purkinje cell synapse modification (Ito and Kano, 1982; Ito et al., 1982), Oscarsson’s (1979) and others’ ideas about cerebellar modular architecture, and influenced by the engineering theories of adaptive control, and the adaptive linear filter model of Fujita (1982), Ito proposed that the cerebellum could be understood in terms of arrays of functional corticonuclear microcomplexes (Ito, 1984), each of which could compute a certain input–output function. He proposed that this input–output relationship is modifiable by error signals that are conveyed by the climbing fibers, and that in different situations it might represent a simple adaptable input–output gain or a more complete adaptive dynamic model, as in Figs. 6.3a and 6.3b. In the former case, a corticonuclear microcomplex connected within a positive feedback loop could account for cerebellar function in integrator tuning. Or, if located in the forward path, a microcomplex could implement a direct adaptive feedback servo controller, as in Fig. 6.3b. Other classic examples of Ito’s adaptive controller concept are Robinson’s (1976) and Lisberger’s (1988) models of cerebellar regulation of the gain of the VOR angular velocity component. This system (Fig. 6.4, upper portion) uses angular velocity signals from the semicircular canals to control the angular velocity of eye movement to compensate for head rotation, thereby enabling maintenance of steady visual fixation. To function properly, the ocular response must have angular velocity and angular displacement that are of equal magnitude and in the opposite direction to the head rotation. However, the ratio of the eye rotational velocity to the (negative of) the head velocity signal, as conveyed by transvestibular neural pathways and the oculomotor system, is some composite factor Poc that is not necessarily equal to unity.14 In particular,  is determined by the strength of signal transmission in the brainstem, and Poc may change slowly over time due to changing properties of the oculomotor system (e.g., muscle fatigue). It appears that the cerebellum is capable of adjusting this net signal transmission gain so that it does becomes closer to unity.15 Specifically, the floccular cortex

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appears to provide an additional forward path with a gain  (0  1) that can be continuously readjusted (upper microcomplex in Fig. 6.4). If this angular velocity control circuit is augmented by a position control component (Fig. 6.4, lower portion), as described above, then the total command to the eye muscles becomes: ˆ . emg (  )˙head   head And, therefore, the eye position is given by:

eye Poc((  )˙head  ˆ head).

learning. Unfortunately, as it does not incorporate neural signal transmission delays, its applicability to several important features of cerebellar function and dysfunction, especially the characteristic target overshoot that occurs in limb ataxia, is unclear. Other models based on Ito’s ideas that also include long-loop feedback circuits with delays tend specifically to predict ataxia with overshoot and possibly tremor as a consequence of cerebellar injury. Many include, or are consistent with, some form of internal prediction of signals to circumvent instabilities potentially associated with feedback and delays.

It can be then argued that  and  can be tuned so that

eye Poc(b ˙head  c ˙head) Poc (b  c )˙head for some values b and c. That is,

eye Poc(b (d/t) c)head. Therefore, if b and c can be selected so that [b(d/t) c] Poc1, then eye head, and the eye movement is thus able to compensate well for head rotation16. In the above control scheme, the cerebellum effectively mediates linear proportional-derivative (PD) control. It does this by starting with a derivative signal as input and then integrating. This is in mild contrast to the feedback PD control described in Fig. 6.3b in which differentiation is performed. As in Fig. 6.3a, the flocculus is postulated here by adapting  and to approximate the inverse dynamics P1 oc . This proposal is reasonable if Poc represents fairly simple linear dynamics consisting of signal scaling and integraconsists of linear scaling and differentiation tion. Then P1 oc (or equivalently, linear scaling and integration of the derivative signal ˙eye). That the cerebellum may compute linear inverse dynamics in eye control has received experimental support.17 It should also be noted that the same circuitry could also be used to modulate the OKR (Ito, 1984) by processing the retinal slip velocity e˙ret (by injecting it at * in Fig. 6.4). In this circumstance, the same circuitry functions as an adaptive linear PD feedback controller to assist visual tracking. Composite models that describe cerebellar involvement with both VOR and OKR have been developed (e.g., Ito, 1984; Gomi and Kawato, 1992). Thus, in contrast to the feedback-driven lookup tablebased formulations, models based upon Ito’s microcomplex concept rely on continuous functions of input signals, including error signals, to support, rather than to drive, movement. A detailed, adaptive arm control model inspired by Ito’s microcomplex architecture has been proposed by Contreras-Vidal et al. (1997). The model addresses much important cerebral, cerebellar, and spinomuscular physiology, including some aspects of motor

The models of Kawato et al., Gomi, Miall et al., Paulin and Wulpert et al. Following Ito, Kawato et al. (1987; Kawato, 1990; Kawato and Gomi, 1992), Gomi and Kawato (1992), Miall et al. (1993), Paulin (1989, 1997), and, more recently, Schweighofer et al. (1998a, 1998b) and Wolpert et al. (1998), have directly or indirectly emphasized the likelihood that cerebellar circuits embody internal dynamic models, either forward or inverse (or both). Although quite similar in style, the models have significant differences in detail. An early model of Kawato et al. (1987), based on known cerebellar and motor system pathways, proposed that the intermediate (presumably anterior) cerebellum implements an adaptive non-linear forward dynamic model of body dynamics. A similar proposal for the intermediate cerebellum was made by Miall et al. (1993) as part of an overall Smith predictor structure (de Carvalho, 1993). Another similar proposal is made by Paulin (1989) for the cerebellum (without indication of cerebellar subregion) based on Kalman filter theory (Goodwin and Sin, 1984; Paulin, 1989). These models are potentially, but not necessarily, non-linear. In each case, the function of the forward model is as an observer that yields a predictive surrogate feedback signal. Paulin noted that in rabbits (Collewijn, 1985), following extended training of the VOR using slow head oscillations, compensatory ocular oscillations of the same frequency may persist while the head is being moved at a different frequency, and even when the head is at rest. This suggests that an internal model of the original head oscillation dynamics was acquired to assist the eyes in compensating for the movement, and that its activity then persisted inappropriately. The subjective sense of ‘sea legs’ on land following a long boat trip in heavy seas is presumably a similar phenomenon.18 Paulin further emphasizes that such internal models need not be limited to simulating the human body’s own dynamics. Internal models could, in principle, simulate the dynamic behavior of external objects (Paulin, 1997). An important problem for future investigations will be to define better the nature of

Models of cerebellar function

cerebellar system-based internal models. To what extent are they non-linear? How rapidly can they be trained? Is all prediction dynamic model based? The models of Kawato et al. (1987) and Kawato–Gomi (Kawato, 1990; Gomi and Kawato, 1992; Kawato and Gomi, 1992) also suggest that the lateral cerebellum implements an adaptive non-linear inverse model that functions in a purely or partially feedforward manner. These investigators have developed a method for adaptively approximating inverse dynamics (feedback–error–learning) that assumes the existence of a stable, basic, underlying feedback control system. This scheme proposes that the climbing fibers convey a copy of the output of the underlying feedback control system as an ‘error’ signal. The feedforward system then learns to take over control by adapting until the output of the feedback control system has become zero. This is a form of model reference direct adaptive control. The explicit demonstration of an effective and plausible learning rule is a valuable contribution of the model. The model of Miall et al. (1993) suggests that the lateral cerebellum implements a second Smith predictor forward model in an outer feedback loop which contains the intermediate cerebellum-based Smith predictor forward model described above, in an inner feedback loop. Smith predictors are controllers that are specifically designed to compensate for significant signal transmission delays within a feedback control system (de Carvalho, 1993). Miall et al. (1993) point out that Smith predictors (as do other controllers that use forward internal dynamic models within negative feedback loops) have the effect of calculating inverse dynamics implicitly (see Fig. 6.3c). A Kalman filter-based controller (Goodwin and Sin, 1984; Paulin, 1989) has a slightly simpler structure and, although it can be used very effectively as a predictor to compensate for delays, it is designed specifically to have optimal performance in the presence of certain types of sensory noise (Anderson and Moore, 1979). Miall et al. (1993) and Paulin (1989, 1997) discuss, but do not indicate explicitly, how their models would learn the proper forward dynamics and delays.19 This is an important issue, because the stability of Smith predictors can be very sensitive to model mismatch (de Carvalho, 1993) – a problem that typically increases with the complexity and non-linearity of the plant – and training complex filters can be very slow. On the other hand, as high-performance servos, the Smith predictor and Kalman filter formulations have the fundamentally attractive feature that they can manage both trajectory tracking and unanticipated disturbances. Because of the very low gain of the underlying feedback controller hypothesized by the Kawato–Gomi models, these models would not be able to

account for the rapid, stable recoveries that humans can make following a perturbation. Higher gain feedback cannot be used in the Kawato–Gomi model because, unlike the Smith predictor or Kalman filter, there is no explicit forward model, or other means of managing the associated delay-related instabilities.

The intermediate cerebellar model of Schweighofer et al. Schweighofer et al. (1998a, 1998b) have produced a sophisticated model of cerebellar control of multijoint arm movement that is based upon a fusion of the previous models of Kawato and Gomi described above, and a cerebellar oculomotor control model developed previously by Schweighofer et al. (1996a, 1996b). The model concerns the proposed role of the intermediate (presumably anterior) cerebellum in using feedback–error–learning to assist the cerebrum in managing arm movement dynamics. Here, although described as acquisition of an internal inverse dynamics model, this is only approximately true. In this model, the intermediate cerebellum is (appropriately) not considered to lie in an exclusively feedforward path, i.e., its input does not consist of the desired trajectory alone. Rather, it accepts feedback signals as well as inverse dynamics-like feedforward signals. Thus, it functions as a direct adaptive feedforward/feedback controller. In addition, part of the feedforward inverse dynamcs control is relegated to the motor cortex so that dynamical control is distributed within the motor system. This also appears to be a realistic feature of the model. In comparison to most other models, the model of Schweighofer et al. (1998a, 1998b) incorporates a large amount of physiological detail. Mathematical representations are proposed for the membrane voltage behavior of most of the principal cerebellar neurons, as well as for signals in spinal cord, muscles, and for separate sensory and motor regions of the cerebral cortex. The intracerebellar neuronal connection architectures and connection strengths are specified initially according to plausible random distributions, and the cerebellar neuronal dynamics are fairly realistically non-linear, with output firing rates determined by sigmoidal functions of membrane potential (Hertz et al., 1991). The model relegates explicit, adaptive control of interjoint dynamics to the cerebellum, which is consistent with the impressions of several investigators (Thach et al., 1992; Goodkin et al., 1993; Bastian et al., 1996; Topka et al., 1998a, 1998b).20 Unfortunately, an important model omission is the effective delay that is associated with the (excitation–contraction) coupling of EMG to muscle that has been modeled as a low-pass filter (Lacquaniti et al., 1982; Fuglevand and Winter, 1993). The

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effective delay may be of the order of at least 50 ms and, when combined with neural signal transmission delays, might well result in an unstable model (see, for example, Massaquoi, 1999). The model’s performance was assessed in several ways. First, through simulations, it was examined in terms of its ability to learn to control the dynamics of a model twojoint arm that was commanded to practice a relatively slow multiline segment-tracing task. Before the action of the cerebellum was incorporated, the basic motor system model generated inappropriate curvature and overshoot that are roughly similar to ataxic movements that can be seen in patients with cerebellar degeneration during reaching movements (Massaquoi and Hallett, 1996). With the cerebellar model added, the tracing had improved significantly along most segments after 2000 practice trials, although it never closely approached human accuracy. The behavior of the internal signals in the model Purkinje, interposed nuclear, and inferior olivary cells was then examined and found to have several qualitatively realistic features. Purkinje cells showed a variety of firing patterns owing to their different parallel fiber and climbing fiber inputs, and they had apparently acquired directional tuning (Fortier et al., 1989) spontaneously. Nuclear cells displayed velocity-like firing patterns as seen experimentally (Van Kan et al., 1993). Also, as expected, inferior olivary activity diminished substantially after learning. The model of Schweighofer et al. (1998a, 1998b) represents a recent culmination of, particularly, Ito’s view of cerebellar function (Ito, 1984). It appears to merge control system principles with cerebellar physiology with considerable success. Importantly, its attention to physiological detail affords scrutiny and evaluation of the behavior of individual neurons and neuronal ensembles. Its principal weaknesses appear to be its potential for instability in the presence of physiological signal transmission delays, the large number of practice trials that is required for its training, and the limited performance that it exhibits when trained. Just the same, the model remains an important benchmark and a useful point of departure for future cerebellar system modeling.

Wave-variable processor A model of intermediate (anterior) cerebellar function proposed by Massaquoi and Slotine (1996) sought to address the problem of feedback motor control in the presence of signal transmission delays. Its central premise is that the interaction between the intermediate cerebellum and spinal cord may represent wave-variable-based communication. The idea is based on a teleoperation theory devel-

oped by Niemeyer and Slotine (1991; Niemeyer, 1996). Wave variables are simply special linear combinations of command and feedback signals that can be exchanged between a master and remote (slave) site in a manner that can ensure stable control irrespective of transmission delays. The linearity and simplicity of the transformations which are independent of plant complexity are particularly attractive for implementation by cerebellar and spinal circuitry. The transformation scheme is also consistent with the fact that the signals that ascend, especially, the rostral and ventral spinocerebellar tracts are noted to consist of combinations of multiple inputs, including force feedback signals and corollary signals from internal pathways (Bloedel and Courville, 1981). The net result is that wavevariable processing would enable the motor system to operate principally as a simple linear servo mechanism despite system delays and without explicit, potentially complex internal models. The wave-variable control model can thus be viewed as extending a long line of internal model-free servo-type hypotheses (Merton, 1953; Bizzi et al., 1984; Hogan, 1985; Feldman, 1986; Flash, 1987; McIntyre and Bizzi, 1993; Latash and Goodman, 1994) through its specific proposal for the nature of the cerebellar system’s contribution to servo motor control. A simple formulation of the model (Massaquoi and Slotine, 1996) was used to simulate the rapid elbow movements of monkeys. Physiologically realistic values were used for the neural transmission and muscle activation properties, and a stable movement under feedback control was demonstrated that closely mimicked the monkey’s performance. Reduction of the model’s intermediate cerebellar output to motor cortex yielded a 2.5 Hz largeamplitude oscillation similar to cerebellar outflow tremor (Massaquoi and Hallett, 1998). Finally, during movement the signals at the model’s interpositus nucleus21 closely matched signals recorded from the monkeys, including those that were not strictly velocity like. As expected for servo-type systems, wave-variable-based arm control models also display physiologically rapid recoveries following external perturbations. A more physiologically detailed, two-joint arm control model has been developed (Massaquoi, 1999) that adds the postulated role of the lateral anterior cerebellum in wavevariable processing for enhanced multijoint feedback control. The two-joint control model closely reproduces the high-speed trajectories of healthy humans (Massaquoi and Hallett, 1996), while generating signals that closely resemble dentate nuclear signals observed during monkeys’ arm movements. When model cerebellar gains are reduced, the ataxic trajectories of patients with cerebellar degeneration (Massaquoi and Hallett, 1996) can be

Models of cerebellar function

closely approximated. Finally, the model is able to suggest the physiological bases for the distinctive anatomical lesion sites that are associated with cerebellar tremor, ataxia with terminal tremor, ataxia with little tremor and pure clumsiness, as in the dysarthria–clumsy hand syndrome (Fisher, 1967). As in the APG model of Houk et al. (1993), reverberatory neural circuits involving the interposed nuclei are included in the wave-variable arm control models. Along the lines of Paulin’s (1989) and Robinson’s (1989) thoughts, these are interpreted as being signal integrators. It may be noted that for slow movements, limbs behave approximately as damped masses that convert velocity-like commands (commands that are non-zero only during intended motion) into new limb configurations (positions). For these movements, the wave-variable controller’s internal integrator behaves somewhat as a crude internal model of forward dynamics, because it converts a velocity-like wave-variable command signal into a position-like surrogate feedback signal – and, specifically, one that is quasipredictive of the limb’s actual configuration. However, this analogy does not apply to the high-frequency behavior of limbs (e.g., that associated with rapid accelerations or decelerations). Moreover, because of its linearity, the wavevariable cerebellar control system can, in principle, never fully model the non-linear dynamics of the two-joint arm. Interestingly, though, it may be precisely because of such a limited ability to internally model body dynamics that normal human tracking is fairly imperfect at high accelerations (Massaquoi and Hallett, 1996; Massaquoi, 1999). It seems as if the wave-variable controller’s integrator primarily serves to provide just enough dynamic modeling to compensate for delays. Overall, the gross structure of the wave-variable models is very similar to that of the model of Schweighofer et al. (1998a, 1998b) and the models have many similar functional characteristics in tracking tasks. Fundamentally, the wave-variable arm-control models place greater emphasis on feedback control and they thereby account better for disturbance rejection and simplify the feedforward signal (command) that is required for movement. Whether this is a realistic simplification is a matter for further study. An important present limitation of the wave-variable models is that an adaptation scheme has not been given. Therefore, the ability of these models to account for motor learning has not been demonstrated. Although the internal circuitry required for wave-variable processing is fairly simple, it has also not been established whether wavevariable relations could be learned over time, beginning with randomly distributed neural connection parameters in a manner analogous to that in the models of Kettner et

al. (1997) and Schweighofer et al. (1996a, 1996b). It is conceivable that these transformations are ‘hard-wired’ (genetically encoded). However, it would be especially attractive if the proper computation could be shown to arise naturally through cerebellar adaptation.

xReferencesx Albus, J.S. (1971). A theory of cerebellar function. Math Biosci 10: 25–61. Allen, G.I. and Tsukahara, N. (1974). Cerebrocerebellar communication systems. Physiol Rev 54: 957–1006. Anderson, B.D. and Moore, J.B. (1979). Optimal Filtering. Englewood Cliffs, NJ: Prentice-Hall. Atkeson, C.G. and Reinkensmeyer, D.J. (1990). Using associative content-addressable memories to control robots. In Neural Networks for Control, ed. W.T.I. Miller, R. Sutton and P.J. Werbos, pp. 254–85. Cambridge, MA: MIT Press. Barto, A.G. (1990). Connectionist learning for control. In Neural Networks for Control, ed. W.T.I. Miller, R. Sutton and P.J. Werbos, pp. 5–65. Cambridge, MA: MIT Press. Bastian, A. J., Martin, T. A. and Keating, J. G. (1996). Cerebellar ataxia: abnormal control of interaction torques across multiple joints. J Neurophysiol 76: 492–509. Berthier, N. E., Singh, S. P., Barto, A. G. and Houk, J. C. (1993). Distributed representation of limb motor programs in arrays of pattern generators. J Cogn Neurosci 5: 56–78. Bizzi, E., Accornero, N., Chappele, W. and Hogan, N. (1984). Posture control and trajectory formation during arm movement. J Neurosci 4: 2738–44. Bloedel, J. R. and Bracha, V. (1997). Duality of cerebellar motor and cognitive functions. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 613–34. San Diego: Academic Press. Bloedel, J. R. and Courville, J. (1981). Cerebellar afferent systems. In Handbook of Physiology: the Nervous System II, ed. J.M. Bookhart, V.B. Mountcastle, V.B. Brooks and S.R. Geiger, pp. 735–829. Bethesda, MD: American Physiological Society. Bower, J.M. (1995). The cerebellum as a sensory acquisition controller. Hum Brain Map 2: 255–6. Bower, J.M. (1997). Control of sensory data acquistion. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 489–513. San Diego: Academic Press. Braitenberg, V. (1967). Is the cerebellar cortex a biological clock in the millisecond range? Prog Brain Res 25: 334–46. Braitenberg, V. and Atwood, R.P. (1958). Morphological observations on the cerebellar cortex. J Comp Neurol 109: 1–33. Braitenberg, V. and Onesto, N. (1962). The cerebellar cortex as a timing organ. In Proceedings of the First International Congress on Cybernetic Medicine, ed. Giannini, pp. 1–19. Naples: Societa Internazionale di Medicina Cibernetica Brindley, G. S. (1969). The use made by the cerebellum of the information that it receives from sense organs. Int Brain Res Org Bull 3: 80.

89

90

S.G. Massaquoi and H. Topka

Brodal, A. (1981). Neurological Anatomy in Relation to Clinical Medicine. New York: Oxford University Press. Brooks, V.B. (1985). How are ‘move’ and ‘hold’ programs matched? In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans and W. Precht, pp. 1–21. New York: Springer-Verlag. Brooks, V.B. (1986). The Neural Basis of Motor Control. New York: Oxford University Press. Buonomano, D. V. and Mauk, M. D. (1994). Neural network model of the cerebellum: temporal discrimination and the timing of motor responses. Neural Comput 6: 38–55. Calvert, T.W. and Meno, F. (1972). Neural systems modelling applied to the cerebellum. IEEE Trans Syst Man and Cybern SMC-2: 363–74. Cannon, S.C. and Robinson, D.A. (1985). An improved neuralnetwork model for the neural integrator of the oculomotor system: more realistic neuron behavior. Biol Cybern 53: 93–108. Cannon, S.C., Robinson, D.A. and Shamma, S. (1983). A proposed neural network for the integrator of the oculomotor system. Biol Cybern 49: 127–36. Collewijn, H. (1985). Integration of adaptive changes of the optokinetic reflex, pursuit and the vestibulo-ocular reflex. In Adaptive Mechanisms of Gaze Control, ed. A. Berthoz and G. Melvill-Jones. Amsterdam: Elsevier Contreras-Vidal, J.L., Grossberg, S. and Bullock, D. (1997). A neural model of cerebellar learning for arm movement control: corticospino-cerebellar dynamics. Learning and Memory 3: 475–502. de Carvalho, M.J.L. (1993). Dynamical Systems and Automatic Control. New York, London: Prentice Hall. Dichgans, J. and Diener, H.C. (1984). Clinical evidence for functional compartmentalization of the cerebellum. In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans, J. and W. Precht, pp. 126–47. New York: Springer-Verlag. Diener, H. C., Hore, J., Ivry, R. and Dichgans, J. (1993). Cerebellar dysfunction of movement and perception. Can J Neurol Sci 20: S62–9. Ebner, T. J. and Bloedel, J. R. (1985). Rhythmic properties of climbing fiber afferent responses to peripheral stimuli. In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans and W. Precht, pp. 260–2. New York: Springer-Verlag. Eccles, J. C., Ito, M. and Szentagothai, J. (1967). The Cerebellum as a Neuronal Machine. New York: Springer-Verlag. Ekerot, C.-F. (1985). Climbing fibre actions of Purkinje cells – plateau potentials and long-lasting depression of parallel fibre responses. In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans, and W. Precht, pp. 268–74. New York: Springer-Verlag. Feldman, A.G. (1986). Once more on the equilibrium-point hypothesis (lambda model) for motor control. J Mot Behav 18 17–54. Fisher, C.M. (1967). A lacunar stroke: the dysarthria–clumsy hand syndrome. Neurology 17: 614–17. Flash, T. (1987). The control of hand equilibrium trajectories in multi-joint arm movements. Biol Cybern 57: 257–74. Fortier, P.A., Kalaska, J.F. and Smith, A.M. (1989). Cerebellar neuronal activity related to whole-arm reaching movements in the monkey. J Neurophysiol 62: 198–211.

Fuglevand, A.J. and Winter, D.A. (1993). Models of recruitment and rate coding organization in motor-unit pools. J Neurophysiol 70: 2470–88. Fujita, M. (1982). Adaptive filter model of the cerebellum. Biol Cybern 45: 195–206. Gao, J.-H., Parsons, L.M., Bower, J.M., Xiong, J., Li, J. and Fox, P. (1996). Cerebellum implicated in sensory acquisition and discrimination rather than motor control. Science 272: 545–7. Gilbert, P.F. and Thach, W.T. (1977). Purkinje cell activity during motor learning. Brain Res 128: 309–28. Gilman, S. (1969). Fusimotor fiber responses in the decerebellate cat. Brain Res 14: 218–21. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Philadelphia: F.A. Davis. Gilman, S. and MacDonald, W.I. (1967). Cerebellar facilitation of muscle spindle activity. J Neurophysiol 30: 1494–512. Gomi, H. and Kawato, M. (1992). Adaptive feedback control models of the vestibulocerebellum and spinocerebellum. Biol Cybern 68: 105–14. Goodkin, H. P., Keating, J. G., Martin, T. A. and Thach, W. T. (1993). Preserved simple and impaired compound movement after infarction in the territory of the superior cerebellar artery. Can J Neurol Sci Suppl. 3: S93–104. Goodwin, G. C. and Sin, K. S. (1984). Adaptive Filtering Prediction and Control. Englewood Cliffs, NJ: Prentice-Hall. Grill, S.E., Hallett, M., Marcus, C. and McShane, L. (1994). Disturbances of kinaesthesia in patients with cerebellar disorders. Brain 117: 1433–47. Grill, S. E., Hallett, M. and McShane, L. M. (1997). Timing of onset of afferent responses and of use of kinesthetic information for control of movement in normal and cerebellar-impaired subjects. Exp Brain Res 113: 33–47. Hassul, M. and Daniels, P. (1977). Cerebellar dynamics. The mossy fiber input. IEEE Trans Biomed Eng 24: 449–56. Haykin, S. (1991). Adaptive Filter Theory. Englewood Cliffs, NJ: Prentice Hall. Hertz, J., Krogh, A. and Palmer, R.G. (1991). Introduction to the Theory of Neural Computation. Redwood City, CA: Addison-Wesley. Hogan, N. (1984a). Adaptive control of mechanical impedance by coactivation of antagonist muscles. IEE Trans Aut Contr AC-29: 681–90. Hogan, N. (1984b). An organizing principle for a class of voluntary movements. J Neurosci 4: 2745–54. Hogan, N. (1985). The mechanics of multi-joint posture and movement control. Biol Cybern 52: 315–31. Holmes, G. (1939). The cerebellum of man. Brain 62: 1–30. Hore, J. and Flament, D. (1986). Evidence that a disordered servolike mechanism contributes to tremor in movements during cerebellar dysfunction. J Neurophysiol 56: 123–36. Hore, J. and Vilis, J. (1984). A cerebellar-dependent efference copy mechanism for generating appropriate muscle responses to limb perturbations. In Cerebellar Functions, ed. E.A. Bloedel. New York: Springer-Verlag. Houk, J.C., Kiefer, J. and Barto, A. (1993). Distributed motor commands in the limb premotor network. Trends Neurosci 16: 27–33.

Models of cerebellar function

Houk, J. C. and Rhymer, W. Z. (1981). Neural control of muscle length and tension. In Handbook of Physiology: the Nervous System II, ed. J.M. Bookhart, V.B. Mountcastle, V. B. Brooks and S.R. Geiger, pp. 257–323. Bethesda, MD: American Physiological Society. Houk, J.C., Singh, S.P., Fisher, C. and Barto, A.G. (1990). An adaptive sensorimotor network inspired by the anatomy and physiology of the cerebellum. In Neural Networks for Control, ed. W.T.I. Miller, R. Sutton and P.J. Werbos, pp. 301–48. Cambridge, MA: MIT Press. Houk, J.C. and Wise, S.P. (1995). Distributed modular architectures linking basal ganglia, cerebellum, and cerebral cortex: their role in planning and controlling action. Cereb Cortex 5: 95–110. Ito, M. (1972). Neural design of the cerebellar motor control system. Brain Res 40: 81–4. Ito, M. (1984). The Cerebellum and Neural Control. New York: Raven Press. Ito, M. (1997). Cerebellar microcomplexes. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 475–87. San Diego: Academic Press. Ito, M. and Kano, M. (1982). Long-lasting depression of parallel fiber–Purkinje cell transmission induced by conjunctive stimulation of parallel fibers in the cerebellar cortex. Neurosci Lett 33: 253–8. Ito, M., Sakurai, M. and Tongroach, P. (1982). Climbing fiber induced depression of both mossy fiber responsiveness and glutamate sensitivity of cerebellar Purkinje cells. J Physiol (Lond) 324: 113–34. Ivry, R. and Diener, H. C. (1991). Impaired velocity perception in patients with lesions of the cerebellum. J Cogn Neurosci 3: 355–66. Ivry, R.B. and Keele, S.B. (1989). Timing functions of the cerebellum. J Cogn Neurosci 1: 136–52. Ivry, R.B., Keele, S.W. and Diener, H.C. (1988). Dissociation of the lateral and medial cerebellum in movement timing and movement execution. Exp Brain Res 73: 167–80. Jaeger, D. and Bower, J. M. (1994). Prolonged responses in rat cerebellar Purkinje cells following activation of the granular cell layer: an intracellular in vitro and in vivo investigation. Exp Brain Res 100: 200–14. Kano, M. (1996). Long-lasting potentiation of GABAergic inhibitory synaptic transmission in cerebellar Purkinje cells: its properties and possible mechanisms. In BBS Special Issue: Controversies in Neuro Sciences IV: Motor Learning and Synaptic Plasticity, ed. S. Harnad, pp. 354–61. Cambridge: Cambridge University Press. Katayama, M. and Kawato, M. (1993). Virtual trajectory and stiffness ellipse during multijoint arm movement predicted by neural inverse models. Biol Cybern 69: 353–62. Kawato, M. (1990). Feedback–error–learning neural network for supervised motor learning. In Advanced Neural Computers, ed. R. Eckmiller, pp. 365–72. Amsterdam: Elsevier. Kawato, M., Furukawa, K. and Suzuki, R. (1987). A hierarchical neural-network model for control and learning voluntary movement. Biol Cybern 57: 169–85. Kawato, M. and Gomi, H. (1992). A computational model of four

regions of the cerebellum based on feedback-error learning. Biol Cybern 68: 95–103. Keele, S. and Ivry, R. (1990). Does the cerebellum provide a common computation for diverse tasks? Ann NY Acad Sci 608: 179–211. Kelly, T.M., Zuo, C.-C. and Bloedel, J.R. (1990). Classical conditioning of the eyeblink reflex in the decerebrate–decerebellate rabbit. Behav Brain Res 38: 7–18. Kettner, R.E., Mahamud, S., Leung, H.-C. et al. (1997). Prediction of complex two-dimensional trajectories by a cerebellar model of smooth pursuit eye movement. J Neurophysiol 77: 2115–30. Lacquaniti, F., Licata, F. and Soechting, J.F. (1982). The mechanical behavior of human forearm response in transient perturbations. Biol Cybern 44: 35–46. Latash, M. L. and Goodman, S. R. (1994). An equilibrium-point model of electromyographic patterns during single-joint movements based on experimentally reconstructed control signals. J Electromyogr Kinesiol 4: 230–41. Leigh, J. R. and Zee, D. S. (1991). The Neurology of Eye Movements. Philadelphia: F.A. Davis. Lisberger, S. G. (1988). The neural basis for learning of simple motor skills. Science 242: 728–35. Llinas, R. (1981). Electrophysiology of the cerebellar networks. In Handbook of Physiology: the Nervous System II, ed. J.M. Bookhart, V.B. Mountcastle, V.B. Brooks. and S.R. Geiger, pp. 831–76. Bethesda, MD: American Physiological Society. Luenberger, D.G. (1979). Introduction to Dynamic Systems. New York: John Wiley & Sons. MacKay, W.A. and Murphy, J.T. (1979a). Cerebellar influence on proprioceptive control loops. In Cerebro–Cerebellar Interactions, ed. J. Massion and K. Sasaki, pp. 141–62. Amsterdam, New York: Elsevier/North-Holand Biomedical Press. MacKay, W.A. and Murphy, J.T. (1979b). Cerebellar modulation of reflex gain. Prog Neurobiol 13: 361–417. Maex, R. and De Schutter, E. (1998). Synchronization of golgi and granule cell firing in a detailed network model of the cerebellar granule cell layer. J Neurophysiol 80: 2521–37. Marr, D. (1969). A theory of cerebellar cortex. J Physiol (Lond) 202: 437–70. Massaquoi, S.G. (1999). Modelling the function of the cerebellum in scheduled linear servo control of simple horizontal planar arm movements. PhD Thesis, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA. Massaquoi, S.G. and Hallett, M. (1996). Kinematics of initiating a two-joint arm movement in patients with cerebellar ataxia. Can J Neurol Sci 23: 3–14. Massaquoi, S.G. and Hallett, M. (1998). Ataxia and other cerebellar syndromes. In Parkinson’s Disease and Movement Disorders, ed. J. Jankovic and E. Tolosa, pp. 523–686. Baltimore: Williams & Wilkins. Massaquoi, S.G. and Slotine, J.-J.E. (1996). The intermediate cerebellum may function as a wave-variable processor. Neurosci Lett 215: 60–4. McIntyre, J. and Bizzi, E. (1993). Servo hypotheses for the biological control of movement. J Mot Behav 25: 193–202.

91

92

S.G. Massaquoi and H. Topka

Merton, P.A. (1953). Speculations on the servo control of movement. In The Spinal Cord, ed. J.L. Malcom, A.B. Gray. and G.A.W. Wolstenholme. Boston: Little, Brown & Co. Miall, C. (1996). Models of neural timing. In Time, Internal Clocks and Movement, ed. M.A. Pastor and J. Artieda, pp. 69–94. Amsterdam: Elsevier. Miall, R. C., Weir, D. J., Wolpert, D. M. and Stein, J. F. (1993). Is the cerebellum a Smith predictor? J Mot Behav 25: 1993. Miller, W. T. I., Sutton, R. S. and Werbos, P. J. (1990). Neural Networks for Control, Neural Network Modeling and Connectionism, Vol. 3. Cambridge, MA: MIT Press. Murphy, J.T., Kwan, H.C. and MacKay, W.A. (1975). Physiological basis of cerebellar dysmetria. Can J Neurol Sci 2: 279–84. Niemeyer, G. (1996). Using wave variables in time delayed force reflecting teleoperation. PhD Thesis. Boston: Department of Aeronautics and Astronautics, Massachusetts Institute of Technology. Niemeyer, G. and Slotine, J.-J.E. (1991). Stable adaptive teleoperation. IEEE J Ocean Eng 16: 152–62. Ogata, K. (1990). Modern Control Engineering. Engelwood Cliffs, NJ: Prentice-Hall, Inc. Oscarsson, O. (1979). Functional units of the cerebellum–sagittal zones and microzones. Trends Neurosci 2: 143–5. Parsons, L. M. and Fox, P. T. (1997). Sensory and cognitive functions. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 255–71. San Diego: Academic Press. Pascual-Leone, A., Grafman, J., Clark, K. et al. (1993). Procedural learning in Parkinson’s disease and cerebellar degeneration. Ann Neurol 34: 594–602. Pascual-Leone, A., Grafman, A.J. and Hallett, M. (1994). Modulation of cortical motor output maps during the development of implicit and explicit knowledge. Science 265: 1600–1. Paulin, M. (1989). A Kalman filter theory of the cerebellum. In Dynamic Interactions in Neural Networks: Models and Data, ed. M.A. Arbib and S. Amari. New York: SpringerVerlag. Paulin, M.G. (1997). Neural representations of moving systems. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 515–33. San Diego: Academic Press. Pellionisz, A. and Llinas, R. (1979). Brain modeling by tensor network theory and computer simulation. The cerebellum: distributed processor for predictive coordination. Neroscience 4: 323–48. Pellionisz, A.J. (1985). Tensorial brain theory in cerebellar modelling. In Cerebellar Functions, ed. J.R. Bloedel, J. Dichgans and W. Precht, pp. 201–29. New York: Springer-Verlag. Phillips, A.G. and Carr, G.D. (1987). Cognition and the basal ganglia: a possible substrate for procedural knowledge. Can J Neurol Sci 14: 381–5. Raibert, M. H. and Wimberly, F. C. (1984). Tabular control of balance dynamics in a legged system. IEEE Trans Sys Man Cybern SMC-14: 334–9. Reis, D.J., Doba, N. and Nathan, M.A. (1973). Predatory attack, grooming, and consummatory behaviors evoked by electrical stimulation of cat cerebellar nuclei. Science 182: 845–7.

Robertson, L.T. and Grimm, R.J. (1975). Responses of primate dentate neurons to different trajectories of the limb. Exp Brain Res 23: 447–462. Robinson, D.A. (1976). Adaptive gain control of the vestibulocular reflex by the cerebellum. J Neurophysiol 39: 954–69. Robinson, D.A. (1989). Integrating with neurons. Ann Rev Neurosci 12: 33–45. Rosenblatt, F. (1961). Principles of Neurodynamics: Perceptrons and the Theory of Brain Mechanisms. Washington, DC: Spartan. Sasaki, K. (1985). Cerebro–cerebellar interaction and organization of a fast and stable hand movement: cerebellar participation in voluntary movement and motor learning. In Cerebellar Functions, ed. J. Bloedel, pp. 70–85. New York: Springer-Verlag. Schmahmann, J.D. (1991). An emerging concept. The cerebellar contribution to higher function. Arch Neurol 48: 1178–87. Schmahmann, J.D. (1997). The Cerebellum and Cognition. International Review of Neurobiology, Vol. 41. San Diego: Academic Press. Schmahmann, J.D. and Pandya, D.N. (1997). The cerebrocerebellar system. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 31–60. San Diego: Academic Press. Schweighofer, N., Arbib, M.A. and Dominey, P.F. (1996a). A model of the cerebellum in adaptive control of saccadic gain. I. The model and its biological substrate. Biol Cybern 75: 19–28. Schweighofer, N., Arbib, M.A. and Dominey, P.F. (1996b). A model of the cerebellum in adaptive control of saccadic gain. II. Simulation results. Biol Cybern 75: 29–36. Schweighofer, N., Arbib, M.A. and Kawato, M. (1998a). Role of the cerebellum in reaching movements in humans. I. Distributed inverse dynamics control. Eur J Neurosci 10: 86–94. Schweighofer, N., Spoelstra, J., Arbib, M. and Kawato, M. (1998b). Role of the cerebellum in reaching movements in humans. II. A neural model of the intermediate cerebellum. Eur J Neurosci 10: 95–105. Shidara, M., Kawano, K., Gomi, H. and Kawato, M. (1993). Inversedynamics model eye movement control by Purkinje cells in the cerebellum. Nature 365: 50–2. Simpson, J.I., Wylie, D.R. and De Zeeuw, C.I. (1996). On climbing fiber signals and their consequence(s). In BBS Special Issue: Controversies in Neuro Sciences IV: Motor Learning and Synaptic Plasticity, ed. S. Harnad, pp. 384–98. Cambridge: Cambridge University Press. Slotine, J.-J.E. and Li, W. (1991). Applied Nonlinear Control. Engelwood Cliffs, NJ: Prentice Hall. Smith, A.M. (1996). Does the cerebellum learn strategies for the optimal time-varying control of joint stiffness? In BBS Special Issue: Controversies in Neuro Sciences IV: Motor Learning and Synaptic Plasticity, ed. S. Harnad, pp. 399–410. Cambridge: Cambridge University Press. Thach, W.T. (1996). On the specific role of the cerebellum in motor learning and cognition: clues from pPET activation and lesion studies in man. In BBS Special Issue: Controversies in Neuro Sciences IV: Motor Learning and Synaptic Plasticity, ed. S. Harnad, pp. 411–31. Cambridge: Cambridge University Press. Thach, W.T., Goodkin, H.P. and Keating, J.G. (1992). The cerebellum

Models of cerebellar function

and the adaptive coordination of movement. Ann Rev Neurosci 15: 403–42. Thompson, R.F. and Kim, J. . (1996). Memory systems in the brain and localization of a memory. Proc Natl Acad Sci 93: 13438–44. Topka, H., Konczak, J. and Dichgans, J. (1998a). Coordination of multi-joint arm movements in cerebellar ataxia: analysis of hand and angular kinematics. Exp Brain Res 119: 483–92. Topka, H., Konczak, J., Schneider, K., Boose, A. and Dichgans, J. (1998b). Multijoint arm movements in cerebellar ataxia: abnormal control of movement dynamics. Exp Brain Res 119: 493–503. Topka, H., Massaquoi, S.G., Benda, N. and Hallett, M. (1998c). Motor skill learning in patients with cerebellar degeneration. J Neurol Sci 158: 164–72. Topka, H., Valls-Solle, J., Massaquoi, S.G. and Hallett, M. (1993). Deficit in classical conditioning in patients with cerebellar degeneration. Brain 116: 961–9. Tsukahara, N. (1972). The properties of the cerebello-pontine reverberating circuit. Brain Res 40: 67–71. Van Kan, P.L.E., Houk, J.C. and Gibson, A.R. (1993). Output organization of intermediate cerebellum of the monkey. J Neurophysiol 69: 57–73. Watanabe, E. (1985). Role of the primate flocculus in adaptation of the vestibulo-ocular reflex. Neurosci Res 3: 20–38. Weiner, M.J., Hallett, M. and Funkenstein, H.H. (1983). Adaptation to lateral displacement of vision in patients with lesions of the central nervous system. Neurology 33: 766–72. Welsh, J. P. and Harvey, J. A. (1989). Cerebellar lesions and the nictitating membrane reflex: performance deficits of the conditioned and unconditioned response. J Neurosci 9: 299–311. Wolpert, D.M., Miall, R.C. and Kawato, M. (1998). Internal models in the cerebellum. Trends Cogn Sci 2: 338–47. Woodruff-Pak, D., Thompson, R.F. and Logan, C.G. (1990). Neurobiological substrates of classical conditioning across the life-span. Ann NY Acad Sci 608: 150–78. Yuen, G.L., Hockberger, P.E. and Houk, J.C. (1995). Bistability in cerebellar Purkinje cell dendrites modeled with high-threshold calcium and delayed rectifier potassium channels. Biol Cybern 73: 375–88. Zee, D.S., Atsumi, Y., Butler, P.H. and Gucer, G. (1981). Effects of ablation of flocculus and paraflocculus on eye movements in primate. J Neurophysiol 46: 878–99.

Endnotes 1. This would be at least 60 000 synapses per Purkinje cell 15 000 000 Purkinje cells (Ito, 1984). 2. The cerebellum also receives rich innervation from monoamineargic cells of the brainstem (Brodal, 1981). These circuits are targets of attempted pharmacotherapy because they are suspected of being involved in global modulation of the intensity of cerebellar operation. 3. Llinas (1981) and Bower (1997) have emphasized that perhaps the most important synapses between granule cells and Purkinje cells occur along the rising rather than transverse

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(parallel fiber) portions of the granule cell axon. This may result in dominant Purkinje cell activation near the granule cell rather than far along a ‘beam’ of parallel fibers. The possible implications of this view are discussed by Bower. This view does not contradict the circuit description offered here. Rather, it provides a different interpretation of the circuit behavior. Indeed, there are many complexities, including how tasks specified in external world coordinates are translated into joint coordinates, whether or not the movement is specified in terms of various checkpoints, and how commands in joint coordinates are transformed to the appropriate muscle length coordinates. Some or all of these issues may ultimately concern cerebellar function. However, for the moment they will not be addressed. In terms of formal motor control system analysis, ‘inversion’ means to determine the integral or differential equation that yields inputs (actuator input signals) for any desired outputs (movements). Some have argued that the problem of finding an inverse model is generally not ‘well posed’ because the set of applied forces that yield the desired trajectory is not unique. This is due to the fact that many muscles antagonize others, therefore different combinations of muscle activation levels may result in the application of the same net forces to the joints. However, if the limb stiffness is specified and the tensions in each of the contributing muscles are minimized in some sense (Katayama and Kawato, 1993), the problem becomes uniquely solvable. This yields so-called PD control (Ogata, 1990; de Carvalho, 1993). Derivative control provides phase lead (limited prediction) that can help to compensate for signal delays. Incorporation of an integrator in addition (PID control, not shown) could enhance the system’s management of steady disturbances such as gravity or elastic resistances. Typically, information from the actual feedback signal is still used to some extent. However, the surrogate feedback signal may be given more weight. While the nervous system need not represent differential equations explicitly in the same algebraic form that we write them, it must still embody the information in these equations in some manner and therefore the complexity of the neural representation must bear some relationship to the complexity of the dynamics. After all, technically, a servo is a special (and particularly important) case of a table lookup mechanism wherein ‘adjacent’ table entries are infinitessimally close to one another and have values that are determined by a simple continuous rule (function) applied to an error signal (Barto, 1990). And correlated activity changes are seen in positron emission tomography (PET) studies (Thach, 1996). For example, the model of Massaquoi and Slotine (1996) uses reverberatory circuitry in parallel with other pathways and thereby circumvents the issue of paralysis. Cannon et al. (1983; Cannon and Robinson, 1985) and Robinson (1989) have pointed out that, in the oculomotor

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13. 14.

15.

16.

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system, integration may be implemented by lateral inhibitory neuronal networks. In principle, this does not exclude the facilitation of integration by positive feedback. In any case, these investigators’ proposal for cerebellar involvement in integrator regulation is functionally similar to that considered here. But see also Bower (1997), who is not convinced of the tapped delay-line interpretation. For the moment, we neglect the dynamics of the oculomotor system and consider Poc to be effectively a fixed or slowly varying parameter. Note that the cerebellar role is much more significant when the VOR gain must be adapted to values very different from unity (Leigh and Zee, 1991). The angular velocity component (  )˙head in the emg is presumably used to help compensate for viscous components of Poc and signal lag. Shidara et al. (1993) note that multiple parafloccular Purkinje cells in monkey appear to compute such dynamic signals during smooth visual tracking. To what extent the Purkinje cell ensemble is thought to have fully computed the inverse dynamics depends upon what type of inputs the ensemble receives and what other systems might contribute to the motor command at the same time. In any case, it is note-

18.

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20. 21.

worthy that they found that the Purkinje cell activity scaled well with target stimulus velocity. This suggests that the oculomotor system and the Purkinje ensemble signal processing are both substantially linear. This is also reminiscent of the predictive tracking exhibited by monkeys as modeled by Kettner et al. (1997), and therefore suggests that lookup table-type mechanisms can provide alternative means for producing internal model-like behavior. This method consists essentially of storing and then recalling specific behaviors, rather than generating them de novo using a general purpose internal model. These authors suggest that reinforcement learning mechanisms (Miller et al., 1990) should also be considered in explaining cerebellar adaptation, not simply error-driven schemes. This is an important point. However, Paulin’s major concern regarding the difficulties that error-driven adaptation methods may have with delays (Paulin, 1989) may be at least partially addressed by the eligibility trace concept of Kettner et al. (1997). Note, however, that motor cortical control of biarticular muscles may also have potent effects on interjoint dynamics. The monkey interpositus nucleus is the homolog of the human interposed nuclei.

Part III

Clinical Signs and Pathophysiological Correlations

7

Clinical signs of cerebellar disorders Mario-Ubaldo Manto Cerebellar Ataxias Unit, Free University of Brussels, Belgium

Clinically relevant anatomy

Clinical symptoms of cerebellar disorders

The reader is referred to Chapter 2 of Part I for a detailed description of the anatomy of the cerebellum. Basically, the cerebellum is divided into ten lobules, which are shown in Fig. 7.1a. Two major fissures subdivide the cerebellum into three lobes: the anterior and posterior lobes are demarcated by a primary fissure, and a postero-lateral fissure separates the posterior lobe and the flocculonodular lobe (Fig. 7.1b; Gilman et al., 1981). This latter lobe is also called the vestibulocerebellum. Mainly on the basis of phylogenetic studies, the cerebellum has been divided into archicerebellum, paleocerebellum and neocerebellum (Fig. 7.1c). There is an approximate relationship between this nomenclature and the projections of afferent pathways towards the cerebellum (Brodal, 1981). The term spinocerebellum is also used to designate paleocerebellum, because important projections are directed from the spinal cord towards the paleocerebellum, whereas the terms neocerebellum and pontocerebellum are used equally to designate this most recent part of cerebellum. In clinical practice, there are basically three sagittal areas, including cortical and subcortical structures (Fig. 7.1d): a vermal zone in relation to the fastigial nucleus; a paravermal or intermediate zone associated with the interpositus nucleus; and a lateral zone whose Purkinje cells project to the dentate nucleus (Fig. 7.1d). Midline zone includes the vermis and flocculo-nodular lobe. Table 7.1 indicates main afferent and efferent pathways for each of these three sagittal zones. The three sagittal zones described here should not be confused with the sagittal bands of the cerebellum (see Chapter 2).

Pathological conditions usually affect cerebellar function through discrete mechanisms, which often combine (Gilman et al., 1981): decrease in blood flow, edema, mechanical compression, invasion of cerebellar parenchyma, inflammatory and/or immune processes, and direct cytotoxic effect. Concomitant involvement of surrounding structures in the posterior fossa, in particular the brainstem and meninges, is common, impeding circulation of the cerebrospinal fluid. When confronted with a patient suspected of having a cerebellar disease, there are general principles which must be taken into account: 1. focal cerebellar lesions located laterally generate signs ispilaterally, but expanding lesions may occasionally produce a false localization of clinical signs; 2. diffuse cerebellar diseases, such as degenerative ataxic affections, usually cause relatively symmetric deficits; 3. cerebellar deficits due to non-progressive disease tend to undergo attenuation with time; 4. symptomatology suggestive of cerebellar damage may be encountered in patients presenting lesions along the afferent or efferent cerebellar pathways outside the cerebellum. As a rule, the symptoms of cerebellar disorders will be influenced more by the location and the rate of progression of the disease than by the pathological characteristics (Gilman et al., 1981; Lechtenberg, 1993). For instance, an infection and a tumor may produce remarkably similar symptoms if they develop in the same location and have the same rate of progression. Patients with slowly progressive tumors may be remarkably asymptomatic for a long time, whereas a rapidly expanding lesion such as a hemorrhage will be accompanied by severe symptoms in most cases (Dow and Moruzzi, 1958; Gilman et al., 1981).

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Table 7.1 Main afferent and efferent pathways of the vermal, paravermal, and lateral regions of the cerebellum Zone

Afferent

Deep cerebellar nuclei

Efferent

Vermal

Spinal cord Vestibular nuclei Reticular nuclei Spinal cord Cerebral cortex Brainstem Cerebral cortex Pons

Fastigial nuclei

Vestibular nuclei Reticular nuclei Spinal cord Thalamus Red nucleus

Paravermal

Lateral

Interpositus nuclei

Dentate nuclei

Thalamus Cerebral cortex Brainstem

(a) Fissures and lobules Lingula

Primary fissure

I II, III

Central lobe Anterior quadrang. lobule Posterior quadrang. lobule

IV V

Superior semilunar lobule

VI VII

sil

VIII

Posterolateral fissure

Inferior semilunar lobule

Uvula

Ton

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IX

Gracile lobule Biventer lobule Paraflocculus

X

Nodulus

(b) Division in lobes

Flocculus

(c) Phylogenetic division

(d) Sagittal areas

Anterior lobe

Paleocerebellum

Vermal zone

Posterior lobe

Neocerebellum

Intermediate zone

Flocculonodular lobe

Archicerebellum

Lateral zone

Fig. 7.1 The four major divisions of the cerebellum: (a) division into ten lobules; (b) division into three lobes: anterior, posterior, and flocculo-nodular; (c) phylogenetic division into paleocerebellum, neocerebellum, and archicerebellum; (d) division into three sagittal areas: vermal, paravermal (intermediate) and lateral regions. The cerebellum is shown unfolded in one plane.

Clinical signs of cerebellar disorders

Table 7.2 Symptoms in a prospective series of 115 cases with cerebellar disorders

Table 7.3 Symptoms in a group of 49 patients presenting lesions restricted to the cerebellum

Symptoms

Number of patients (%)

Symptoms

Number of patients (%)

Gait difficulties Headache Nausea, vomiting Dizziness Clumsiness in limbs Speech difficulties Tremor Blurred vision, impaired visual acuity Diplopia Feebleness Sensory complaints Fatigability Memory difficulties Impotence Swallowing difficulties Illusion of movement in environment Hearing loss Tinnitus Limb or facial weakness Urinary incontinence

89 (77) 84 (73) 58 (50) 38 (33) 37 (32) 32 (28) 16 (14) 15 (13) 14 (12) 12 (10) 8 (7) 7 (6) 6 (5) 6 (5) 5 (4) 5 (4) 4 (3) 4 (3) 4 (3) 4 (3)

Gait difficulties Headache Dizziness Clumsiness in limbs Speech difficulties Blurred vision Feebleness Fatigability

37 (76) 32 (65) 29 (59) 26 (53) 15 (31) 12 (24) 8 (16) 4 (8)

Table 7.2 lists the symptoms noted in a prospective series of 115 ataxic patients. The diagnoses were: cerebellar stroke (n 45), hereditary cerebellar ataxia or idiopathic late-onset cerebellar atrophy (ILOCA) (n 34), inflammatory disease (n 12), trauma (n 9), tumor (n 8), and sequelae of drug intoxication (n 7). All these patients exhibited predominant cerebellar signs and presented lesions in the cerebellum, although not exclusively for some of them, as demonstrated by brain magnetic resonance imaging (MRI). Gait difficulties and headache were the two most common symptoms, followed by nausea/vomiting and dizziness. In the subgroup of patients with lesions restricted to the cerebellum (n 49), the most frequent complaints were gait difficulties, headache, dizziness, and clumsiness in the limbs (Table 7.3). In particular, the most common complaint was headache in the case of stroke or tumor, and the most frequent symptom in the case of diffuse cerebellar atrophy was gait unsteadiness. Half of the patients presenting clumsiness in the upper limbs had difficulties eating or writing. Headaches in cerebellar disorders are usually reported very early in the course of the disease and in many cases are influenced by postural changes. Pain may be associated with nausea or vomiting, which arise from brainstem irritation. Headache may be the first or only complaint in the

case of tumor, abscess or stroke. In some patients, pain may be restricted to a region around or behind the eye(s), to the parietal or occipital region (Lechtenberg and Gilman, 1978a; Gilman et al., 1981). There are two situations in which headache may suggest the correct diagnosis. First, any child who complains of headache in the morning in association or not with nausea, vomiting, clumsiness or gait difficulties should be investigated to rule out a cerebellar tumor. In this case, vomiting may not be preceded by a period of nausea, but may be projectile, consisting of forceful vomiting with little or no warning (Stewart and Holmes, 1904; Gilman et al., 1981; Lechtenberg, 1993). Second, severe dull headache of abrupt onset in a hypertensive patient exhibiting gait ataxia and vomiting is indicative of intracerebellar hemorrhage. The first division of the trigeminal nerve innervates the surface of the tentorium cerebelli, explaining the frontal location of headache in posterior fossa expanding lesions, by a mechanism of referred pain (Feindel et al., 1960). Occipital location of pain, sometimes associated with sensations of neck stiffness, reflects involvement of the meninges at the level of the foramen magnum, which is innervated by the first cervical roots and vagus nerve (Kimmel, 1961).

Clinical signs Definition of ataxia The term ataxia was originally coined to describe dysequilibrium in tabes and has been used latterly to depict the jerky or poorly coordinated character of movement or posture (Holmes, 1917; Trouillas et al., 1997). It is applied in the routine clinical examination of a disorder of coordination when strength and sensation deficits cannot explain

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the loss of coordination. Garcin defined ataxia as ‘a disturbance of coordination which, quite independently of any motor weakness, alters the direction and extent of voluntary movement and impairs the sustained voluntary or reflex muscle contractions necessary for maintaining posture and equilibrium’ (Garcin, 1969). Many clinicians and researchers use the term ataxia to describe hereditary degenerative diseases of the cerebellum, although the terminology is more appropriate once the diagnosis has been established (Lechtenberg, 1993). This is typically the case for Friedreich’s ataxia and dominant spinocerebellar atrophies (see Part VII).

Historical aspects The triad of Luciani In the nineteenth century, Luciani undertook several important neurophysiological experiments to clarify the roles of the cerebellum (Luciani, 1891). In particular, he investigated the effects of cerebellar lesions in dogs and primates, and addressed the question of the function of the cerebellum in control of voluntary movements. He observed three elemental deficits ipsilateral to the lesion: atonia, asthenia, and astasia. He defined atonia as a reduction in resistance of the limbs to passive manipulations, compared asthenia to a paresia in movement, and defined astasia as the involuntary oscillations appearing during movement. Later, he added a fourth sign: dysmetria, designating errors in the metrics of motion (Manni and Petrosini, 1997). Luciani observed that cerebellar signs following a first injury could recover, and that deficits could reappear when the contralateral motor cortex was removed. This is one of the first descriptions of the compensation and decompensation of cerebellar deficits. However, despite the major input provided by Luciani, this author denied that one of the fundamental roles of the cerebellum is coordination in voluntary movements.

Babinski’s hypothesis Babinski considered that the synergic function and the fight against inertia were the two crucial roles of the cerebellum (Table 7.4; Babinski, 1899, 1902, 1906). He depicted asynergia as an inability to combine each of the elements of a movement into a complex motor action, hence the feature of decomposition of the movement. Babinski suggested that intention tremor consisting of rhythmic oscillations during a movement was a manifestation of

Table 7.4 Dual role of the cerebellum: Babinski’s hypothesis

Clinical sign

Asynergia

Defective adaptation to inertia

Intention tremor Irregular gait

Overshooting Adiadochokinesia Ataxia of stance – titubation Scanning speech Catalepsy

asynergia. Furthermore, he defined inertia as a property of a body to remain motionless or in movement until modification by an external force (‘cette propriété qu’ont les corps de rester dans leur état de repos ou de mouvement jusqu’à ce qu’une cause étrangère les en tire’). Babinski also described disorders of rapid successive movements, or adiadochokinesia. Cerebellar catalepsy, sometimes called Babinski phenomenon, relates to the ability to keep the hips and knees flexed during a long period while supine. Catalepsy occurs in case of extensive cerebellar damage such as bilateral hemorrhage. Limb manipulation reveals hypotonia. Babinski suggested that catalepsy was related to a deficient adaptation to inertia (Babinski, 1906).

The major influence of Holmes At the beginning of the twentieth century, Holmes described in detail the clinical deficits in soldiers of the First World War (Holmes, 1917). These patients exhibited cerebellar lesions following gunshot and shrapnel wounds. Holmes considered five fundamental cerebellar deficits: hypotonia, static tremor, asthenia, fatigability, and atasia. He included in astasia both dysmetria and intention tremor. Holmes observed that intention tremor was characterized by an oscillatory rhythmic activity during execution of the movement. He named the oscillations appearing during postural tasks static tremor (Holmes, 1904, 1917). He pointed out that asthenia was always more obvious in the upper than in the lower limb, and was usually greater in the proximal than in the distal muscles (Holmes, 1922). He insisted that asthenia was frequently absent in slowly progressive diseases of the cerebellum. Fatigability was described as an inability to perform and to maintain muscular work against resistance. Holmes reported the case of a patient who was unable to keep his arm outstretched for more than 60 s, as a consequence of an ipsilateral gunshot wound (Holmes, 1922).

Clinical signs of cerebellar disorders

Table 7.5 Clinical signs according to the sagittal zone affected

quantified scale of cerebellar ataxic signs (Trouillas et al., 1997).

Zone

Signs

Ocular motor movements

Vermal

Oculomotor disturbances Dysarthria Head tilt Ataxia of stance Ataxic gait Titubation No syndrome defined Dysarthria Oculomotor disturbances Dysarthria Head tilt Dysmetria Intention tremor Action tremor Hypotonia Dysdiadochokinesia Decomposition of movements Dysrhythmokinesia Impaired check, excessive rebound Ataxia of stance Ataxic gait

Examination of eye movements

Paravermal Lateral

Clinical signs of damage to the cerebellar area Table 7.5 lists the clinical signs as a function of the sagittal zone affected (Gilman et al., 1981; Dichgans, 1984). Oculomotor deficits associated with ataxia of stance and gait indicate a midline zone disease, whereas lateral lesions are more likely to produce a combination of limb dysmetria, intention tremor, hypotonia, dysdiadochokinesia, impaired check, and excessive rebound. A syndrome purely restricted to the paravermal zone has not been described in human, but isolated dysarthria has been reported in intermediate zone damage (Lechtenberg and Gilman, 1978b; Amarenco et al., 1991). Cerebellar dysarthria is also observed in lesions located in the cerebellar hemispheres (Gilman et al., 1981; Silveri et al., 1994).

Classification of clinical signs Ther cerebellar signs can be divided into four categories (Trouillas et al., 1997): (a) oculomotor disturbances, (b) dysarthria, (c) deficits of limb movements, and (d) abnormalities of gait and posture. The reader is referred to the International Cooperative Ataxia Rating Scale (ICARS) for a

First, the observer checks the stability of gaze by holding an index finger in front of the patient, at an approximate distance of 30 cm. A static ocular misalignment is specifically looked for. Then, the patient is asked to look at the finger, which is maintained motionless in a lateral position (on the left, on the right; no more than 30 degrees) and then in upwards and downwards position. Next, the saccades are tested by placing the index fingers in each of the patient’s temporal visual fields. The patient is asked to keep the eyes in a primary position and then to look laterally at one of the fingers (Trouillas et al., 1997). Latency, precision, and velocity of saccades are estimated. Then, to test vestibular suppression and assess the vestibulo-ocular reflex (VOR), the patient sits on a rotating chair and fixates on an object that moves synchronously with head movements. The chair is rotated at a constant velocity and movements of the eyes are observed. Normally, the subject can suppress the effects of the VOR during fixation of an object by rotating the head. The rotation of the chair is then stopped suddenly and the eye movements are evaluated by looking for a post-rotatory nystagmus. Additionally, a rotating drum is used to assess the optokinetic response, bearing in mind that the drum test also investigates pursuit. The patient is asked to count the stripes. Finally, Frenzel goggles may be useful to estimate eye movements without the subject fixating. Table 7.6 lists the ocular signs observed in patients with cerebellar disease (Holmes, 1922; Baloh et al., 1975; Leigh et al., 1981; Cogan et al., 1982; Kattah et al., 1983; Thurston et al., 1987; Pierrot-Deseilligny et al., 1990). These oculomotor signs are described below.

Oculomotor deficits and location of the lesion in the cerebellum In cerebellar diseases, disorders of extra-ocular movements are usually due to a lesion at the level of (a) the dorsal vermis or fastigial nucleus, (b) the flocculus and paraflocculus, and/or (c) the uvula and nodulus (Furman et al., 1990; Waterson et al., 1992; Lewis and Zee, 1993; Vahedi et al., 1995). Table 7.7 lists the oculomotor deficits according to the topography of the cerebellar lesion. While the dorsal vermis and underlying fastigial nuclei are determinant in initiation, precision, and dynamics of saccades, the flocculus and paraflocculus are involved primarily in stabilization of a visual image on the retina (Fetter et al., 1994).

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Table 7.6 Oculomotor alterations in cerebellar diseases Fixation deficits instability of gaze (unsteady fixation) flutter macrosaccadic oscillations Ocular misalignment skew deviation Disorders of pursuit saccadic pursuit Saccade deficits dysmetria: hypermetria, hypometria Nystagmus gaze-paretic (gaze-evoked) nystagmus centripetal nystagmus rebound nystagmus downbeat nystagmus (DBN) Primary position upbeat nystagmus Periodic alternating nystagmus (PAN) Disorders of VOR and optokinetic response Notes: VOR: vestibulo-ocular reflex.

Table 7.7 Correlation between localization of lesion in cerebellum and oculomotor disorders Structure

Deficits

Dorsal vermis/fastigial nucleus (lobules VI, VII)

Dysmetria of saccades Flutter Macrosaccadic oscillations Saccadic pursuit Gaze-evoked nystagmus Rebound nystagmus Downbeat nystagmus Saccadic pursuit Abnormal gain of VOR Abnormal optokinetic response Periodic alternating nystagmus

Flocculus/paraflocculus

Nodulus Ventral uvula Notes: VOR: vestibulo-ocular reflex.

Disorders of fixation Flutter designates brief oscillations of the eyes, typically conjugate, during attempted fixation or movement of the eyes (see Fig. 7.2A; Cogan, 1954; Cogan et al., 1982; Wiest et al., 1997). Oscillations are usually horizontal, and occur in both the dark and the light (Goldberg and Jampel, 1963). Macrosaccadic oscillations comprise repetitive cycles of square wave jerks (Cogan et al., 1982), which are characterized by spontaneous small saccades in opposite directions

during fixation. Macrosaccadic oscillations are often reduced or may even disappear in complete darkness. When saccadic oscillations are involuntary, multidirectional, and conjugate, the term opsoclonus is used. Opsoclonus was initially described by Orzechowski (1927; Leigh and Zee, 1991). The expression ‘dancing eyes’ refers to the same phenomenon. Opsoclonus may be associated with myoclonus, in the so-called ‘Kinsbourne syndrome’ (Kinsbourne, 1962).

Skew deviation Skew deviation designates a disorder of static ocular alignment in which one eye is higher than the other (Lewis and Zee, 1993). This vertical ocular misalignment is often due to a brainstem lesion located at the mesencephalic or ponto-mesencephalic level. It also occurs following lesions in the cerebellum, in the medulla, in the peripheral vestibular apparatus or in the vestibular cortex. Skew deviation results from imbalance of otolith inputs. The diagnosis of skew deviation should be considered when vertical diplopia is not explained by cranial nerve palsies, myasthenia or disease of the extraocular muscles. Alternating skew deviation, in which the side of the higher eye changes depending upon whether gaze is directed to the right or to the left, may be observed in patients presenting lesions located in the posterior fossa, including those restricted to the cerebellum.

Ocular tilt reaction Ocular tilt reaction (OTR) combines head tilt, conjugated eye cyclotorsion, skew deviation, and impairment of vertical perception. OTR is a brainstem otolith-ocular reflex of probable utricular origin. Partial OTR can result from unilateral lesions in caudal parts of the cerebellum, such as an infarct in the territory of the posterior inferior cerebellar artery (Mossman and Halmagyi, 1997).

Disorders of pursuit Saccadic pursuit means a stepwise decomposition of pursuit movements (Fig. 7.2B). Non-smooth pursuit movements are a very common finding in cerebellar patients, consisting of fast/slow movements (‘catch-up saccades’) of square waves or contaminated by a superimposed nystagmus (Cogan et al., 1982). However, specificity of saccadic pursuit is very low. A similar deficit may be observed in Parkinson’s disease and many other movement disorders (Corin et al., 1972).

Disorders of saccades An abnormality very suggestive of cerebellar disease is ocular hypermetria, defined as an inaccurate saccade with

Clinical signs of cerebellar disorders

Fig. 7.2 Oculomotor disturbances in cerebellar patients recorded with electro-oculography (EOG). Deflection upwards indicates eye movement to the right, and deflection downwards to the left. (A) Flutter in a patient presenting cerebellar cortical atrophy. The patient is attempting to maintain fixation on a stationary target. Note the involuntary brief oscillations (arrow). (B) Saccadic pursuit in a patient presenting a bilateral hemorrhage in the cerebellum. Movements are jerky. The thin trace corresponds to the target moving sinusoidally; the thick trace corresponds to eye movements. (C) Ocular dysmetria made of overshoot (hypermetria) or undershoot (hypometria) in a patient presenting a cerebellar tumor. Dysmetric saccades are followed by oscillations until fixation. (D) Nystagmus in a patient with cerebellar cortical atrophy. Gaze to the left is associated with gaze-evoked nystagmus, with drifting of eyes to the right. When the eyes return to the primary position, a nystagmus in the opposite direction (rebound) occurs.

overshooting of the target (Selhorst et al., 1976; Fig. 7.2C). Usually, centripetally directed dysmetric saccades are larger than centrifugally directed saccades (Lewis and Zee, 1993). Although dysmetria is observed for both eyes, it can be asymmetric, when it is called disconjugate dysmetria. Hypermetria will often be followed by one (or more) short latency corrective saccade or by a glissadic movement (Weber and Daroff, 1972). Glissades are common in patients presenting diffuse cerebellar atrophy. The other form of dysmetria, hypometria or undershooting, is less specific (Fig. 7.2C).

Nystagmus Nystagmus consists of rhythmic oscillatory movements of one or both eyes, with a fast and a slow component in opposite directions.

Gaze-paretic nystagmus Gaze-paretic nystagmus, also called gaze-evoked nystagmus, is a slow drift of the eyes, which are supposed to maintain an eccentric position, interrupted by repetitive saccades tending to return the gaze toward the desired position (Fig. 7.2D; Avanzini et al., 1979). It is the most

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Table 7.8 Cerebellar diseases associated with rebound nystagmus Idiopathic late-onset cerebellar atrophy (ILOCA) Hereditary cerebellar ataxias Degeneration of the olivo-cerebellar circuit Cerebellar hemorrhage Cerebellar ischemia Intoxication with phenytoin or lithium salts Hyperpyrexia

common form of nystagmus in disorders of the cerebellum (Gilman et al., 1981). About half of the patients with a cerebellar midline lesion present with this nystagmus, whereas only 30% of patients with a lateral lesion will exhibit it. The amplitude of the fast component of nystagmus may be larger in gaze directed towards a cerebellar lesion (Lechtenberg, 1993). When the fast component of nystagmus has a large amplitude, it is often called ‘coarse’ nystagmus. With a prolonged attempt to maintain eccentric gaze, gaze-evoked nystagmus tends to change direction: the velocity of centripetal drift diminishes and the slow phases can change direction (Leech et al., 1977).

1986). Both smooth pursuit and optokinetic response are usually disturbed in cerebellar patients with DBN (Yee et al., 1984). However, DBN may be associated with a severe deficit in smooth pursuit and relatively normal optokinetic response (Yee et al., 1979). An intermittent DBN provoked by extension and rotation of the head should raise the possibility of a cerebellar lesion compressing the brainstem, such as an arachnoid cyst. Recently, a periodic form of DBN due to hypomagnesemia has been described (Du Pasquier et al., 1998). Upbeat nystagmus (UBN) is a primary-position nystagmus with the fast phase in an upward direction. It has been associated predominantly with drug overdose, lesions of the midbrain, lower brainstem and midline zone of the cerebellum (Kanaya et al., 1994; Hirose et al., 1998).

Ocular bobbing Ocular bobbing refers to a fast downward movement of both eyes followed by a slow drift back toward midposition (Fig. 7.3B). Forms limited to one eye usually occur in association with contralateral oculomotor palsy (‘monocular bobbing’). Ocular bobbing is observed in cerebellar lesions generating brainstem compression, or in basilar artery occlusion (Fisher, 1964).

Rebound nystagmus

Periodic alternating nystagmus

Rebound nystagmus (Fig. 7.2D), relatively specific but lacking any localizing value in the cerebellum, refers to a transient nystagmus observed during the return to a primary position after maintaining eccentric gaze (Hood et al., 1973). Its duration is usually only a few seconds. Table 7.8 lists the cerebellar disorders in which a rebound nystagmus has been clearly described. Rebound nystagmus may be a transient phenomenon in cerebellar stroke or drug intoxication. Unusually, healthy subjects exhibit rebound nystagmus after prolonged lateral gaze when the eyes return to the primary position and when lights are turned off.

Periodic alternating nystagmus (PAN) is a horizontal jerk nystagmus characterized by a spontaneous nystagmus in the primary direction of gaze, beating in one direction for one or two minutes, followed by a silent phase, and then by reappearance of nystagmus in the opposite direction (Fig. 7.3C; Kennard et al., 1981; Di Bartolomeo and Yee, 1988; Furman et al., 1990). It may be congenital or acquired. It may be observed in cases of vestibulo-cerebellar disease, and has been reported in prion diseases. In patients presenting cerebellar atrophy, PAN has been found in association with a periodic alternating skew deviation.

Downbeat/upbeat nystagmus

Differential diagnosis with a ‘peripheral vestibular nystagmus’

Downbeat nystagmus (DBN), a source of disabling oscillopsia, is a primary-position nystagmus characterized by fast ocular movements downwards (Fig. 7.3A). DBN is observed in diseases at the cervico-medullary junction or in hereditary ataxic diseases, where it is sometimes the predominant clinical feature (Harada et al., 1998). It is often present at a variable degree in Chiari malformations and may even be the warning sign of the disease (Zee et al., 1974; Yee et al., 1984). DBN may also be observed following drug intoxication, especially with lithium salts and anticonvulsants, or following alcohol intake. It is often exacerbated on lateral gaze and with convergence (Furman et al.,

The peripheral vestibular nystagmus has the following characteristics: (a) it is usually a rotatory/horizontal nystagmus; (b) it tends to be inhibited by fixation (in contrast to a nystagmus of cerebellar origin) and is therefore more intense when visual fixation is removed using Frenzel lenses; (c) it is most pronounced on gaze away from the side of vestibular involvement; (d) it may appear after shaking the patient’s head vigorously 15–20 times in the horizontal plane;

Clinical signs of cerebellar disorders

Fig. 7.3 Schematic illustrations of (A) downbeat nystagmus, (B) ocular bobbing, and (C) periodic alternating nystagmus.

(e) it is elicited by the Hallpike–Dix maneuver in the case of benign paroxysmal positional vertigo (BPPN). In addition, patients often complain of vertigo and/or tinnitus and there may be an associated reduced or extinguished caloric response (irrigation with cold/warm water).

VOR and optokinetic responses During the vestibular suppression test, intermittent deviation of the eyes occurs in cerebellar patients, with corrective saccades (Takemori, 1977; Zee, 1977; Cogan et al., 1982). The corrections may be obvious in acute and in chronic cerebellar diseases. Furthermore, patients exhibit exaggerated movements related to the fast or slow component in nystagmus during testing of the optokinetic response. In the case of acute cerebellar injury, the optokinetic response may be totally disrupted.

Oculomotor signs as indicators of extracerebellar disease Observing a patient with a degenerative ataxic disease, both slowing of saccadic eye movements and vertical and/or horizontal gaze palsy suggest extracerebellar manifestations (Wessel et al., 1998). For instance, reduction in the velocity of saccades may be obvious in spinocerebellar ataxia type 2 (see Part VII). Patients may need to move their head because of ophthalmoparesis or gaze apraxia (Lechtenberg, 1993). In addition, patients may complain of a decrease in visual acuity, which may be due to optic nerve atrophy or retinal degeneration (Rabiah et al., 1997; see also ‘Non-cerebellar signs,’ below).

Dysarthria Examination of speech The patient is asked to maintain a sustained vowel phonation (‘ah’ and ‘ee’), to repeat syllables, to produce monosyllabic words, to repeat a standard sentence, and to read aloud a text such as the Grandfather Passage (Darley et al., 1975). The observer evaluates clarity, rhythm, and fluency of speech. To evaluate speed of speech, the observer measures the time taken to pronounce a fixed number of words using a tape-recorder. Such recordings often prove to be a very useful tool for the clinical follow-up. Not exceptionally, patients remain unaware of their dysarthria a long time after the beginning of speech difficulties. In cerebellar diseases, speech tends to be slow, with slurring. However, comprehension is spared and paraphrasias are absent. Words become unintelligible because of temporal dysregulation (Kent et al., 1997). Speech may become explosive, with a staccato rhythm and a nasal character. The scanning aspect of speech is the most easily recognized deficit (Zentay, 1937; Gilman et al., 1981). Its main clinical characteristics are given in Table 7.9. The term dysprosody is also used to describe speech deficits in cerebellar patients, referring to disturbed melodic aspects of speech. Table 7.10 shows the clinical deficits in speech production in a group of 21 patients presenting pure cerebellar signs due to a stroke (n 11), ILOCA (n 7) or a cerebellar tumor (n 3). Brain MRI showed no lesion outside the cerebellum and all these patients had normal somatosensory evoked potentials and normal brainstem auditory evoked potentials. Analysis was done on tape recordings of speech. Scanning speech, slowness, and slurring were the most

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Table 7.9 Characteristics of scanning speech Hesitations Accentuation of some syllables Omission of appropriate pauses Addition of inappropriate pauses

Table 7.10 Speech abnormalities in a group of 21 patients presenting isolated cerebellar signs Abnormality

n (%)

Scanning speech Slowness Slurring Syllables or words not understandable Addition of pauses Loss of intonation Voice tremor

15 (71) 13 (62) 10 (48) 6 (29) 5 (24) 5 (24) 2 (10)

Fig. 7.4 The area over the left superior paravermal region most frequently involved in cerebellar dysarthria. (Modified from Lechtenberg and Gilman, 1978b.)

common deficits. In a large series of 162 patients with a focal cerebellar disease, Lechtenberg and Gilman observed 31 patients exhibiting dysarthria (Lechtenberg and Gilman, 1978b; Gilman et al., 1981). Interestingly, they found that 22 out of the 31 patients with dysarthria had a predominantly or exclusively left hemisphere disease and two patients had a vermal disease. The superior paravermal segment of the left hemisphere about lobules VI and VII corresponded to this region (Fig. 7.4). It has been suggested that, as a result of asymmetric development of language, damage to the left intermediate cerebellar cortex might be one of the main causes of cerebellar dysarthria (Amarenco et al., 1991; Lechtenberg, 1993).

‘Cerebellar mutism’ is an absence of speech without other aphasic symptomatology or alteration of consciousness, appearing after posterior fossa surgery for tumor in pediatric patients (Rekate et al., 1985; Ammirati et al., 1989; Dietze and Mickle, 1990; Ferrante et al., 1990). Its occurrence is rare in adults (Van Calenbergh et al., 1995). Mutism usually appears within 12 to 48 hours of surgery (Dailey et al., 1995) and lasts 1.5 to 12 weeks after onset. Cerebellar dysarthria is observed after resolution of the muteness. Association with hydrocephalus and postsurgical edema participate in its pathogenesis (van Dongen et al., 1994).

Limb movements Examination of upper limb movements The patient sits in a comfortable position. (a) In the finger-to-nose test, the patient is asked to make movements of one upper limb, with the hand first resting on the thigh and then touching the nose with the index finger. (b) In the finger-to-finger test, the patient touches the examiner’s index finger, which is moved and stopped in different locations in space. (c) The patient is then asked to maintain the upper limbs motionless and parallel to the floor, with the elbows extended and the hands in supination. Next, the patient has to maintain the two index fingers medially, pointing at each other at a distance of about 1 cm. This maneuver is called the index-to-index test. (d) Pronation–supination movements are tested by asking the patient to maintain the forearms vertically and to perform successive pronation/supination movements of the hands. Alternate movements of the hands can also be tested with the tapping test over the thigh, the patient placing palmar and dorsal surfaces alternately. (e) Muscle tone is assessed by passively moving the wrists, elbows, and shoulders. Another way to estimate the degree of hypotonia is to grasp the patient’s forearm and to shake the relaxed hand (Gilman et al., 1981). (f) The patient is then asked to draw slowly and accurately in space a square with one index finger. The observer specifically looks for inaccuracy in movement and difficulties in changing direction. (g) In Barany’s test, the patient’s eyes are closed, the arms are extended horizontally in front of the subject, then redirected straight up over the head, and finally to the initial position. (h) The horizontal pointing maneuver (Fig. 7.5) is used to estimate fast proximal movements towards a defined target area in space. (i) During the Stewart–Holmes maneuver, the patient is

Clinical signs of cerebellar disorders

(k) For handwriting, the patient is settled in front of a table. A sheet of paper with a predrawn spiral is affixed to the table, and the patient copies the spiral three times.

Examination of lower limb movements Several tests are used. (a) The knee–tibia maneuver is executed in a supine position. The patient is asked to raise one leg and place the heel on the contralateral knee, which is motionless. The patient slides the heel down the tibial surface in a slow and regular way up to the ankle. The heel is then raised again up to the resting knee. (b) The same test is also applied by asking the patient to maintain the heel on the knee for several seconds (heel-to-knee). (c) In the great toe–finger test, the patient touches the index finger of the examiner with one great toe. (d) The patient is also requested to elevate the legs with a 90° flexion of the hips and knees. This position is sustained for at least 30 s and the examiner specifically looks for oscillations of the trunk and lower limbs. (e) Muscle tone is estimated by passively moving the patient’s ankles, knees and the hips.

Dysmetria

Fig. 7.5 The horizontal pointing maneuver towards a fixed area in space. The right upper limb is the moving limb. The left upper limb is maintained motionless. The subject has to make a very quick horizontal movement. The right index finger must stop within a triangular target area delineated by the left index finger and the left thumb.

asked to flex the elbow forcefully while the observer tries to extend the joint by holding the forearm of the patient (Stewart and Holmes, 1904). The examiner then abruptly releases the forearm and notes if the subject strikes the shoulder or the chest with his or her hand. (j) Decomposition of movement may be assessed by asking the patient to make a pointing movement towards the wrist of the examiner, which is maintained horizontally at the height of the patient’s shoulder and at an approximate distance of 85% of the patient’s upper limb’s length. This index-to-wrist maneuver is a clinical application from the neurophysiological study by Bastian and Thach in 1995.

Limb dysmetria is a cardinal sign of cerebellar disease. As for eye movements, dysmetria is divided into hypermetria and hypometria. Dysmetria is an error in trajectory, which was viewed by Holmes in terms of disturbed range, rate, and force of movement (Holmes, 1917, 1922; Gilman et al., 1981). Hypermetria, or overshooting of a target (‘excessive range of movement’ according to Holmes), is more evident when the movement is made as fast as possible. Hypometria, a premature arrest before reaching the target, is less frequently observed. Both hypermetria and hypometria are often followed by corrective movements. Dysmetria tends to be most marked for aimed movements of small amplitudes and is present equally for proximal and distal joints (Hore et al., 1991). In elderly patients presenting a cerebellar stroke involving outflow pathways, initial hypermetria may turn into hypometria, as a result of an aberrant recovery process (Fig. 7.6). This shift from one type of dysmetria to the other is detectable clinically by observing fast movements of one joint. In the case of chronic cerebellar syndrome, cerebellar hypermetria is increased when a mass is added to the hand, because patients cannot adapt themselves to increased inertia (Manto et al., 1994). This increase of hypermetria is observed for both proximal and distal movements. In acute cerebellar lesions, such as a cerebellar stroke, this artificial

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immediately after a cerebellar injury, whereas intention tremor may increase in the following days or weeks. The worsening of intention tremor predominates at the level of the proximal joints (Fig. 7.7).

Action tremor

Fig. 7.6 Shift from hypermetria to hypometria during the aberrant recovery from a cerebellar stroke. In the days following the cerebellar lesion, the wrist movements, which were initially hypermetric, become hypometric (instead of normometric) as a result of aberrant compensation.

increase of hypermetria may be apparent only after a period of several days (Manto et al., 1995b). The same procedure may also be used to unravel silent cerebellar lesions (Manto et al. 1995a). These findings confirm Babinski’s view of the role of the cerebellum in fighting against inertia. As underlined by Lechtenberg, dysmetric movements may result from severely impaired position sense, but if the patient is still able to describe the direction of the movement without looking, the deficit is likely to be of cerebellar origin. Alternatively, these movements are due to injury to the afferent/efferent pathways to the cerebellum (Lechtenberg, 1993).

Intention or kinetic tremor The terms intention tremor and kinetic tremor are both used to describe oscillations that are exaggerated at the end of a voluntary movement. However, the word ‘intention’ may be misleading, because it is the act of moving that generates the oscillations and not the intention to make a movement. Kinetic tremor is tested mainly during finger-to-nose or knee–tibia tests. The kinetic tremor may be present at initiation or during the whole range of movement (Holmes, 1939). The tremor is perpendicular to the main direction of the intended movement. Intention tremor tends to be predominant over proximal musculature (Gilman et al., 1981; Lechtenberg, 1993). In some patients, kinetic tremor clearly worsens if the movement is made under visual guidance, in comparison to when the movement is guided by proprioceptive information alone (Sanes et al., 1988). However, it is difficult to find a direct bedside application of this observation. In contrast to dysmetria, intention tremor tends to be improved with the addition of inertia (Chase et al., 1965; Hewer et al., 1972). A second difference between these two major cerebellar signs is that dysmetria is maximal

This tremor was called static tremor by Holmes. Action tremor appears generally during postural tasks requiring precision (Table 7.11; Brown et al., 1997): index-to-index test, heel-to-knee test, arms outstretched or legs maintained fixed against gravity from the supine position. Tremor appears progressively after several seconds, essentially in the line of gravity (Holmes, 1904, 1922). In the heelto-knee test, oscillations begin in the line of gravity and rapidly evolve into unwanted lateral movements. A typical 3 Hz leg tremor may be observed during the sustained leg elevation with 90° flexion in the knee and hip joints. This tremor often has a waxing and waning amplitude with spindle formation, and predominates in one leg (Fig. 7.8). It is highly suggestive of anterior lobe cerebellar pathology, but may be encountered also in cases of diffuse cerebellar disease (Silfverskiöld, 1977; Mauritz et al., 1979; Harayama et al. 1983; Manto et al., 1996). Chronic alcohol ingestion is the most frequent cause of this tremor (Table 7.12). Brown et al. (1997) have described a cerebellar axial postural tremor predominating proximally, and occurring in any posture. The head and shoulders are mainly involved. Interestingly, this tremor: (a) is not limited to precision tasks, (b) is characterized by a systematic variation in frequency, and (c) may be observed in the absence of significant intention tremor. This peculiar postural tremor could share a common pathophysiology with palatal tremor (see below). Table 7.13 lists the main differential diagnoses of cerebellar tremor (Cleeves and Findley, 1989; Findley, 1996).

Essential tremor Essential tremor is a postural tremor mainly involving the hands, arms, and head. Its frequency is usually between 5 and 8 Hz. Clinically, some patients with essential tremor exhibit a kinetic tremor which cannot be distinguished from the kinetic tremor associated with cerebellar lesions proven by MRI. However, essential tremor has not been considered so far as a manifestation of a genuine cerebellar dysfunction, although there is growing evidence that the cerebellum is involved in the genesis of essential tremor (Wills et al., 1994).

Palatal tremor Palatal tremor is also called rhythmic palatal myoclonus. It may be associated with hypertrophy of the contralateral

Clinical signs of cerebellar disorders

Fig. 7.7 Increase of the intensity of intention tremor at the level of the proximal joints (shoulder), but not at the level of the distal joints (wrist) in the days following a stroke in the territory of the superior cerebellar artery. This observation contrasts with the finding of reduction of hypermetria in the days following a cerebellar injury.

Table 7.11 Postural tremor in cerebellar diseases Tremor

Lesion

Precipitants

Distribution

Frequency (Hz)

Precision tremor

Nuclei SCP Hemisphere ? Outflow tract Nigro-striatal

Precision tasks

Distal

2–5

Fatigue Any posture Any posture

Proximal/distal Proximaldistal Distalproximal

Irregular 2–10 2.5–5

Asthenic tremor Axial postural tremor Midbrain tremor

Notes: SCP: Superior cerebellar peduncle. Source: This table is modified from Brown et al. (1997).

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Table 7.12 Causes of postural 3-Hz leg tremor Alcohol consumption () Lithium intoxication Sequelae of neuroleptic malignant syndrome (NMS) Hypothyroidism

Fig. 7.8 This figure illustrates the 3-Hz leg tremor observed mainly in patients presenting atrophy of the anterior lobe. Typically, the tremor predominates in one leg and has a spindlelike aspect.

inferior olivary nucleus as a result of a lesion in the contralateral central tegmental tract or in the ipsilateral dentate nucleus (Lapresle 1979).

position at rest, may be associated with hypotonia, especially for patellar and triceps reflexes (Holmes, 1922, 1939). Nevertheless, the amplitude and velocity of reflexes are normal, unlike hyperreflexia in pyramidal tract dysfunction. In addition, cutaneous reflexes are normal in cerebellar diseases. Hypotonia affecting the facial muscles is difficult to diagnose and can mimick facial palsy in advanced cases. Table 7.14 lists the main differential diagnoses of hypotonia. Cerebellar fits are spasms associated with intermittent opisthotonos phenomena (Stewart and Holmes, 1904). They are observed in expanding posterior fossa and, rarely, in Chiari malformations. Exceptionally, a stroke in the territory of the superior cerebellar artery involving the cortex in the anterior lobe, but sparing the deep cerebellar nuclei, will generate extensor posture of the neck, trunk, and legs (Ringel and Culberson, 1988). These observations of increased extensor tone might be due to an extensor tone disinhibition by lesioning of the cerebellar inhibitory efferences to the vestibular nuclei (Sprague and Chambers, 1953). Cerebellar fits are considered as part of cerebellar seizures (McCrory et al., 1999), which can also present as episodes of hemifacial contractions in infants presenting a cerebellar tumor (Harvey et al., 1996). These hemifacial seizures are characterized by deviation of the head and eye, autonomic signs, and normal consciousness. Hemifacial seizures are rare.

Decomposition of movements Disorders of muscle tone Hypotonia is a decline in resistance to the passive manipulation of limbs. It is often more intense in children. In adults, it is usually associated with severe cerebellar damage and occurs at the acute stage of the disease, followed by a rapid trend towards return to normal. It may be so marked that gravity is sufficient to change the spontaneous posture of the limbs (Holmes, 1922; Dow and Moruzzi, 1958). Joints or limbs seem more relaxed (Lechtenberg, 1993). The reduced consistency on palpation of the muscle is, however, difficult to perceive. Hypotonia tends to be more pronounced in the proximal joints. Pendular tendon reflexes, characterized by limbs oscillating around the

Cerebellar injuries cause jerky movements, both for singlejoint and multijoint movements. Compound movements tend to be decomposed into their elemental components, showing a lack of synergy. Consequently, the movements become less fluid (Topka et al., 1998). In the index-to-wrist maneuver, the movements of the shoulder and elbow are asynchronous. For slow movements requiring several joints, decomposition is manifested by errors in the direction and rate of movement. No rhythmic activity is identified in this ataxia of slow movements. Decomposition of movement is often accompanied by the loss of ability to generate independent finger movements: when the patient performs successive tapping

Clinical signs of cerebellar disorders

Table 7.13 Differential diagnoses of cerebellar tremor affecting the limbs Tremor

Type or disease

Characteristics

Postural tremor

Physiologic tremor

Usually asymptomatic Hands predominantly affected Frequency: 8–13 Hz Higher amplitude than physiologic tremor

Enhanced physiologic tremor, e.g., drugs (epinephrine, norepinephrine, theophylline, amphetamine, caffeine, steroids) Essential tremor

Family history Head affected Favorable effect of alcohol Frequency: 5–8 Hz

Rest tremor

Parkinson’s diseases and ‘Parkinson-plus’ syndromes

‘Pill rolling’ Reduction by movement Frequency: 4–6 Hz

Midbrain tremor

Multiple sclerosis Tumor Trauma Stroke

At rest, postural and kinetic Frequency: 2.5–5 Hz

Rhythmic myoclonus Peripheral neuropathy

Irregular, shock-like contractions Variable amplitude CIDP, paraproteinemia HSMN (Roussy–Levy syndrome) Diabetes, uremia

Psychogenic tremor

Postural Involves distal muscles in arms Abrupt onset Variable amplitude and frequency Reduction by distraction Favourable effect of placebo

Notes: CIDP: chronic inflammatory demyelinating polyneuropathy; HSMN: hereditary sensorimotor neuropathies.

Table 7.14 Differential diagnoses of hypotonia Cerebellar lesion Extensive brainstem damage Spinal shock Anterior horn cell disease Polyradiculitis and polyneuropathy Floppy syndrome in children

movements of the index finger against the thumb (the index–thumb test), all the fingers flex at the same time. This involuntary flexion of other fingers is observed in the ‘sign of the piano’: the attempt to move the thumb and index finger alone is associated with a successive flexion of the third, the fourth, and the fifth finger, followed by a phase of immobility of the fingers. This ‘sign of the piano’ is observed during the early phase of a stroke at the level of

the superior cerebellar artery disrupting the cerebellar outflow tract.

Dysdiadochokinesia When alternate sequential movements are performed, cerebellar patients exhibit a deficit consisting of irregular and often slowed movements (Fig. 7.9). An abnormal sway of the elbow is detected in advanced cases (Holmes, 1939; Trouillas et al., 1997). The movement may be so disorganized that the alternate character of the task cannot be identified.

Dysrhythmokinesia (arrhythmokinesis) Dysrhythmokinesia is a disturbed rhythm in a repetitive sequence of movements. It is often observed in tapping procedures (Wertham, 1929) and is one of the characteristics of adiadochokinesia. In some patients with lesions

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check may be tested during the Stewart–Holmes test. When the forearm is released, the contraction of the biceps persists and there is a delay in the response of the triceps muscle. Therefore, the patient hits himself with the hand.

Impaired isotonic force production, or isometrataxia This is an underestimated cerebellar deficit. Cerebellar patients are unable to maintain constant forces during skilled tasks requiring hand or finger use (Mai et al., 1989). Isometrataxia is tested by asking the patient to exert a slight and constant pinch force (using the index finger and thumb) between the lateral parts of the examiner’s thumb; the examiner will feel an irregular pressure, in the absence of tremor of the hand. Figure 7.10 illustrates this deficit. The difficulty in identifying this sign comes from its usual association with action tremor, which masks isometrataxia. However, the two major differences between isometrataxia and isometric tremor are: (1) the absence of rhythm in isometrataxia, and (2) the fact that isometrataxia is observed for slight contractions, whereas isometric tremor tends to occur during forceful contraction of muscles, as underlined by Lou and Jankovic (Lou and Jankovic, 1993). Isometrataxia may be observed in the first hours after a stroke in the territory of the postero-inferior cerebellar artery (PICA).

Sensitivity and specificity of clinical tests in the upper limbs

Fig. 7.9 Adiadochokinesia: alternate movements of pronation–supination in (A) a healthy subject, (B) a patient presenting a stroke in the territory of the superior cerebellar artery, and (C) a patient presenting Friedreich’s ataxia. Note the difficulties of changing direction in B (arrows) and the severe disturbances in C.

involving the dentato-thalamic tract, the disturbances in the rhythm of movement contrast with the relative accuracy of movement. Affected professional musicians often complain of this aberrant rhythm generation.

Check and rebound Disturbed check is observed by asking the patient to maintain the upper limbs extended with the hands pronated and by exerting a tap on the wrist. As a result, a large displacement of the limb appears, followed by an overshooting of the initial position and successive oscillations around the primary position. Impaired check induces a large movement called excessive rebound. The lack of

In practice, many clinicians use the following tests in the upper limbs: maintaining the arms in a fixed position against gravity, the finger-to-nose test, rapid alternate movements of the hands, fine finger movements, handwriting, passive manipulation of the wrists, elbows, and shoulders, the Stewart–Holmes’ test, and Barany’s test. Adding the horizontal pointing maneuver to this list, the study of sensitivity and specificity shows that the two tests characterized by the highest sensitivities are the finger-tonose test and the evaluation of muscle tone (Fig. 7.11). The highest specificities are observed for the finger-to-nose test and the horizontal pointing test. Therefore, the predictive value is best for the finger-to-nose test (Fig. 7.12).

Ataxia of stance and gait Stance is a prerequisite for walking (Nutt and Horak, 1997). The observation that, to some extent, stance and gait may be considered as different functions is also valid for cerebellar patients. Gait may be seen as resulting from balance and locomotor tasks. Balance tasks include standing in an upright position (antigravity task), anticipatory adjustments preceding movements, and postural responses

Clinical signs of cerebellar disorders

Fig. 7.10 The phenomenon of isometrataxia. This figure shows the superimposition of force curves produced during a pinch task (aimed force level: 5 N) in (A) a control subject, (B) a patient presenting cerebellar cortical atrophy (CCA), and (C) a patient presenting a stroke in the territory of the postero-inferior cerebellar artery (C). In (B), note the rhythmic character of the oscillations corresponding to action tremor, also confirmed by Fast Fourier Transform analysis. In (C), the patient is unable to maintain a constant force. The curves are irregular in the absence of tremor. Note the absence of initial overshoot in (B) and in (C).

triggered by external forces. Locomotor tasks include the integration of the body to the changing environment, taking into account the rhythmic character of locomotion. Balance and locomotor tasks may be defective in the case of cerebellar dysfunction.

Ataxia of stance Examination of stance Quiet stance is tested with the patient’s eyes open and closed. The patient is first asked to stand on one foot, then with the feet in tandem, and then with the feet together. A simple and reliable test is the spread of the feet in a natural

position in the absence of support (Trouillas et al., 1997): the patient is requested to find a comfortable position with the eyes open. The distance between medial malleoli is measured. The assumption that ataxia of stance in isolated cerebellar diseases is not influenced by eye closure (Romberg test) is false, as pointed out by Mauritz et al. in 1979 and Diener et al. in 1984, although the exacerbating effect of closing the eyes might be less evident than in proprioceptive deficits or in the so-called vestibular ataxia (Mauritz et al., 1979; Diener et al., 1984; Trouillas et al., 1997). Ataxia of stance is characterized by an inability to maintain the body in a stationary position (Fig. 7.13). Body sway is increased and the trunk tends to lurch from side to side or to drift to one side (Gilman et al., 1981). This is called lateropulsion and sometimes leads to falls, which are a mattern of concern for the patient (Gilman et al., 1981; Amarenco et al., 1990; Shan et al., 1995). Lateropulsion is usually towards the site of the lesion, and may be associated with pseudolabyrinthine signs (Amarenco et al., 1990). Rhythmic extensions–flexions of the feet may occur. In the Romberg test, eye closure tends to increase the body sway, as underlined previously. This is particularly evident in cerebellar anterior lobe disease. These patients may present titubation, characterized by rhythmic oscillations of the head, trunk or entire body, due to ‘irregular and discontinuous contractions of the muscles that should maintain the attitude’ (Holmes, 1917). Titubation was considered by Holmes as a form of static tremor. Oscillations occur in an anterior–posterior plane, in a lateral plane or are rotatory. Whereas vestibulocerebellar lesions tend to produce a lowfrequency sway ( 1 Hz) in all directions, lesions of the anterior lobe are rather associated with a 3 Hz sway predominating in the anterior–posterior direction (Diener et al., 1984). When the amplitudes of oscillations are small, titubation is often overlooked (Lou and Jankovic, 1993). Figure 7.14 illustrates the wide-based character of stance in cerebellar disorders, as attested to by the increased spread of the feet in a natural position by comparison with healthy subjects. This characteristic widened base in cerebellar patients might result from the increased body sway and/or might be used to lower the center of gravity of the body. In addition to increased sway and a broad-based stance, patients also exhibit distorted anticipatory adjustments and defective postural responses to external forces. For instance, the patient falls in the direction opposite to the one in which a force is applied (Horak and Diener, 1994). Indeed, patients have difficulties scaling the magnitude of postural responses appropriately.

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Fig. 7.11 Sensitivity and specificity of nine clinical tests in the upper limbs. The tests have been prospectively used in 79 patients with a unilateral or bilateral cerebellar disease (mean age: 59 years; range: 38–70 years; 46 males, 33 females). Patients had cerebellar ataxia in one or two limbs due to a stroke (n 42), an ILOCA (n 30), a tumor (n 5), or a direct trauma (n 2). None had pyramidal or extrapyramidal signs, and sensations were normal. Patients with cerebellar degeneration did not present postural hypotension or incontinence. Brain MRI disclosed isolated cerebellar lesions in all. The study also included 44 control subjects without neurological disease (mean age: 54 years; range: 29–68 years; 24 males, 20 females).

Ataxia of gait Examination of gait Gait is tested during a 10-m test, with a half-turn. Walking in a straight line, walking in tandem, and walking backward are then observed. These maneuvers can, indeed, unravel a subtle gait deficit that would be overlooked by the examination of regular gait. Ataxic gait has several features. It is irregular and often broad based. Successive steps are spaced in a staggering way, followed by corrections. The rhythm of gait is distorted and its speed is often reduced. This pattern of gait mimicks that of alcohol intoxication. During gait, truncal instability sometimes takes the aspect of a tremor (titubation, see previous section). Bastian et al. have reported an interesting observation in

children with transection of the posterior inferior cerebellar vermis, involving lobules VI to X (Bastian et al., 1998). They exhibited an abnormal tandem gait, contrasting with a preservation of regular gait and standing. Speech tasks and reaching movements were adequately executed, suggesting an important role of the posterior inferior cerebellar vermis in tandem gait. The authors have suggested the denomination posterior vermal split syndrome. Lesions at the level of the flocculo-nodular lobe are responsible for unsteady gait. In about half of these patients, the initiation of walking while lying down improves the ataxic character of gait, in contrast to gait ataxia following anterior lobe disease or bilateral lesions in the cerebellar hemispheres. Some patients presenting frontal lesions may exhibit

Clinical signs of cerebellar disorders

Fig. 7.12 Predictive values of clinical tests in the upper limbs (likelihood ratio of the positive test). See the caption of Fig. 7.11 for details.

Fig. 7.13 Illustration of the sway path in (A) a healthy subject, (B) a patient exhibiting cerebellar ataxia following a bilateral ischemic stroke (superior cerebellar artery), and (C) a patient presenting atrophy of the anterior lobe associated with alcohol consumption. Note the multidirectional oscillations in bilateral stroke and the anterior–posterior oscillations in the case of damage to the anterior lobe.

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Table 7.15 Clues suggesting a psychogenic gait ataxia Historical clues Abrupt onset Spontaneous remissions Somatizations Search for a compensation Context of litigations Clinical clues Inconsistent character of gait Gait influenced by distraction Self-inflicted injuries Discrepancies in neurological examination Remission with placebo administration Abnormal psychiatric interview Fig. 7.14 Spread of the feet in a natural position in healthy subjects (open circles) and in cerebellar patients (filled circles). Recordings in a control group including 25 healthy subjects aged from 14 to 76 years and in a group of 25 patients with a cerebellar disease aged from 13 to 78 years. Subjects were asked to find a comfortable position, and the distance between internal malleoli was measured using an opto-electronic system.

what has been called Bruns’ ataxia or ‘frontal ataxia’. Clinically, patients have difficulties arising and, once in an erect position, they fail to bring their body over their feet. Coordination between the trunk and lower limbs is poor, with feet crossing. Frontal ataxia has been assumed to share similar mechanisms with true cerebellar gait ataxia. However, crossing the legs during gait is very unusual in cerebellar patients, and other cerebellar signs are lacking in ‘frontal ataxia’. Disruption of subcortical–frontal circuits generates this form of apraxia of gait.

Psychogenic ataxic gait This is one of the most frequent presentations of hysterical gait disorders (Keane, 1989). A detailed history is often a critical step in making the diagnosis. Spontaneous remissions, multiple somatizations, and search for a compensation are important points to look for (Table 7.15). A previous history of work in the field of health is worth considering. On neurological examination, useful clues for differential diagnosis are changes of gait pattern with suggestion or after placebo administration, self-inflicted injuries reported to be due to falls, and disparities in neurological examination (e.g., ataxic gait and a normal heel-to-knee test). The psychogenic Romberg test is characterized by increase of body sway following a silent latency and is influenced by distraction (Lempert et al., 1991). The occurrence of psychogenic ataxic gait

superimposed on a true cerebellar ataxia is unfortunately not exceptional, as observed for other psychogenic movement disorders (Galvez-Jimenez and Lang, 1997), and a ‘normal’ interview with a psychiatrist is not sufficient to reject the possibility of a psychogenic gait disorder. In our cerebellar ataxia unit, we have observed two patients with a psychogenic ataxic gait combined with kinetic-like tremor in the upper limbs. In one patient exhibiting bilateral tremor, there was an intermittent lack of cooperation during evaluation, which was suggestive of malingering, and the placebo had an excellent effect. In addition, this patient exhibited uneconomic postures of the trunk with wastage of muscular energy (Lempert et al., 1991). In the other patient, unilateral pseudo-ataxic movements were observed during the centrifugal phase of the finger-to-nose test, whereas the patient performed very accurate centripetal movements. Moreover, giving slight cutaneous taps over the contralateral hand induced a reproducible disappearance of the tremor and gait disorder.

Tilted or rotated posture of head, pelvis or body Tilted head, or head tilt, indicates a lateral deviation of the head. Cerebellar patients may also exhibit a rotated posture of the head (Dow and Moruzzi, 1958; Gilman et al., 1981). Such head rotation around the longitudinal axis was observed by Luciani in the nineteenth century (Luciani, 1891). The sensitivity and specificity of head tilt or rotated head are low and there is no correlation between these signs and the lateralization of the cerebellar lesion. Persistent disturbances of stance may lead to head tilt, pelvic tilt or body tilt. Body tilt may result in skeletal abnormalities, such as scoliosis, which are also encountered in genetic diseases such as Friedreich’s ataxia (see Part VII).

Clinical signs of cerebellar disorders

Cognitive deficits in cerebellar patients The cerebellum has extensive connections with higher brain structures. Anatomical, physiological, and neuroimaging studies suggest that the cerebellum is involved in the organization of higher order functions (Schmahmann and Sherman, 1998). However, except for language, the role of the cerebellum in cognitive tasks is currently a matter of debate (Daum et al., 1993; Barinaga, 1996; GomezBeldarrain et al., 1997; Gomez-Beldarrain and GarciaMonco, 1998; Thach, 1998). Schmahmann and Sherman have suggested that cerebellar patients may present important cognitive and behavioral changes, termed the ‘cerebellar cognitive affective syndrome’ (Schmahmann and Sherman, 1998). This syndrome includes impairment of executive functions such as planning and working memory, deficits in visuospatial skills, linguistic deficiencies such as agrammatism, and inappropriate behavior. In particular, behavioral changes might be clinically prominent in patients presenting lesions involving the posterior lobe of the cerebellum and the vermis. Attention errors and abnormal visuospatial skills could be the two main cognitive deficits (Malm et al., 1998). The concept of ‘dysmetria of thought’ or ‘cognitive dysmetria’ has been proposed, by extension to the observations of motor deficits (Andreasen et al., 1996). This is an important concept. It has been hypothesized that cognitive deficits in cerebellar patients are due to disruption of the neural circuits connecting the prefrontal cortex, parietal lobe, temporal lobe, and paralimbic zones with cerebellar structures. Further investigations are required in order to increase our knowledge of the deficits in cognitive operations in cerebellar patients. The direct implications for clinical practice need to be clarified.

Cerebellar influence on visceral function Autonomic signs appearing in patients presenting lesions restricted to the cerebellum have usually been interpreted as resulting from increased intracranial pressure and damage to the brainstem. However, there is evidence that pure cerebellar lesions may affect autonomic control in the absence of brainstem lesions or hydrocephalus (Haines et al., 1997). Voluntary movements may trigger a vasomotor response, such as face flushing, and pupil dilatation. Bradycardia and hyperventilation have also been described. Lesions of the fastigial nucleus and involvement of the anterior lobe have been incriminated. Visceral responses might result from the impairment of the reciprocal connections between the hypothalamus and cerebellar nuclei/cortex (Haines et al., 1997; see also Chapter 2).

Table 7.16 Extracerebellar signs Clinical sign

Associated disease

Papilledema

Expanding mass

Optic neuritis

Multiple sclerosis

Facial nerve palsy Hearing loss Tinnitus

Brainstem compression (cerebellopontine angle)

‘Apraxia of gait’

Hydrocephalus

Non-cerebellar signs A substantial number of patients with cerebellar disease have concomitant clinical signs indicating involvement of extracerebellar structures. Some are listed in Table 7.16. Papilledema often arises from obstruction of the flow of cerebrospinal fluid at the foramina of Luschka and Magendie, or at the aqueduct of Sylvius.

Acknowledgments M-U. Manto was supported in his research by the Bureau des Relations Internationales (ULB) and by the Belgian American Educational Foundation (BAEF). M-U. Manto is a David and Alice van Buuren Fellow of the BAEF.

xReferencesx Amarenco, P., Chevrie-Muller, C., Roullet, E. and Bousser, M-G. (1991). Paravermal infarct and isolated cerebellar dysarthria. Ann Neurol 30: 211–13. Amarenco, P., Roullet, E., Hommel, M., Chaine, P. and Marteau, R. (1990). Infarction in the territory of the medial branch of the posterior inferior cerebellar artery. J Neurol Neurosurg Psychiatry 53: 731–5. Ammirati, M., Mirzai, S. and Samii, M. (1989). Transient mutism following removal of a cerebellar tumor. Child Nerv Syst 5: 12–14. Andreasen, N.C., O’Leary, D.S., Cizadlo, T. et al. (1996). Schizophrenia and cognitive dysmetria: a positron-emission tomography study of dysfunctional prefrontal-thalamic-cerebellar circuitry. Proc Natl Acad Sci USA 93: 9985–90. Avanzini, G., Girotti, F., Crenna, P. and Negri, S. (1979). Alterations of ocular motility in cerebellar pathology. An electro-oculographic study. Arch Neurol 36: 274–80. Babinski J. (1899). De l’asynergie cérébelleuse. Rev Neurol 7: 806–16. Babinski J. (1902). Sur le rôle du cervelet dans les actes volitionnels

117

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M-U. Manto

nécessitant une succession rapide de mouvements (diadococinésie). Rev Neurol 10: 1013–15. Babinski J. (1906). Asynergie et inertie cérébelleuse. Rev Neurol 14: 685–6. Baloh, R.W., Konrad, H.R. and Honrubia, V. (1975). Vestibulo-ocular function in patients with cerebellar atrophy. Neurology 25: 160–8. Barinaga, M. (1996). The cerebellum: movement coordinator or much more? Science 272: 482–3. Bastian, A.J., Mink, J.W., Kaufman, B.A. and Thach, W.T. (1998). Posterior vermal split syndrome. Ann Neurol 44: 601–10 Bastian, A.J. and Thach, W.T. (1995). Cerebellar outflow lesions: a comparison of movement deficits resulting from lesions at the levels of the cerebellum and thalamus. Ann Neurol 38: 881–92. Brodal, A. (1981). Neurological Anatomy in Relation to Clinical Medicine, 3rd edn. New York: Oxford University Press. Brown, P., Rothwell, J.C., Stevens, J.M., Lees, A.J. and Marsden, C.D. (1997). Cerebellar axial postural tremor. Mov Disord 12: 977–84. Chase, R.A., Cullen, J.K., Sullivan, S.A. and Ommaya, A.K. (1965). Modification of intention tremor in man. Nature 206: 485–7. Cleeves, L. and Findley, L.J. (1989). Tremors. Med Clin North Am 73: 1307–19. Cogan, D.G. (1954). Ocular dysmetria, flutter-like oscillations of the eyes, and opsoclonus. Arch Ophthalmol, 51: 318–35. Cogan, D.G., Chu, F.C. and Reingold, D.B. (1982). Ocular signs of cerebellar disease. Arch Ophthalmol 100: 755–60. Corin, M.S., Elizan, T.S. and Bender, M.B. (1972). Oculomotor function in patients with Parkinson’s disease. J Neurol Sci 15: 251–65. Dailey, A.T., McKhann, G.M. and Berger, M.S. (1995). The pathophysiology of oral pharyngeal apraxia and mutism following posterior fossa tumor resection in children. J Neurosurg 83: 467–75. Darley, F.L., Aronson, A.E. and Brown, J.R. (1975). Motor Speech Disorders. Philadelphia: W.B. Saunders. Daum, I., Ackermann, H., Schugens, M.M., Reimold, C., Dichgans, J. and Birbaumer, N. (1993). The cerebellum and cognitive functions in human. Behav Neurosci 107: 411–19. Di Bartolomeo, J.R. and Yee, R.D. (1988). Periodic alternating nystagmus. Otolaryngol Head Neck Surg 99: 552–7. Dichgans, J. (1984). Clinical symptoms of cerebellar dysfunction and their topodiagnostical significance. Hum Neurobiol 2: 269–79. Diener, H.C., Dichgans, J., Bacher, M. and Gompf, B. (1984). Quantification of postural sway in normals and patients with cerebellar disease. EEG Clin Neurophysiol 57: 134–42. Dietze, D.D. and Mickle, J.P. (1990). Cerebellar mutism after posterior fossa surgery. Pediatr Neurosurg 16: 25–31. Dow, R.S. and Moruzzi, G. (1958). The Physiology and Pathology of the Cerebellum. Minneapolis: University of Minnesota Press. Du Pasquier, R., Vingerhoets, F., Safran, A.B. and Landis, T. (1998). Periodic downbeat nystagmus. Neurology 51: 1478–80. Feindel, W., Penfield, W. and McNaughton, F.L. (1960). The tentorial nerves and localization of intracranial pain in man. Neurology 10: 555–63. Ferrante, L., Mastronardi, L., Acqui, M. and Fortuna, A. (1990).

Mutism after posterior fossa surgery in children. J Neurosurg 72: 959–63. Fetter, M., Klockgether, T., Schultz, J.B., Faiss, J., Koenig, E. and Dichgans, J. (1994). Oculomotor abnormalities and MRI findings in idiopathic cerebellar ataxia. J Neurol 241: 234–41. Findley, L.J. (1996). Classification of tremors. J Clin Neurophysiol 13: 122–32. Fisher, C.M. (1964). Ocular bobbing. Arch Neurol 11: 543–6. Furman, J.M.R., Baloh, R.W. and Yee, R.D. (1986). Eye movement abnormalities in a family with cerebellar vermian atrophy. Acta Otolaryngol 101: 371–7. Furman, J.M., Wall, C. and Pang, D.L. (1990). Vestibular function in periodic alternating nystagmus. Brain 113: 1425–39. Galvez-Jimenez, N. and Lang, A.E. (1997). Psychogenic movement disorders. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 715–32. New York: McGraw-Hill. Garcin, R. (1969). The ataxias. In Handbook of Clinical Neurology, ed. P.J. Vinken and G.W. Bruyn, pp. 309–55. Amsterdam: NorthHolland Publishing Company. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Goldberg, R.T. and Jampel, R.S. (1963). Flutter-like oscillations of the eyes in cerebellar disease. Am J Ophthalmol 55: 1229–33. Gomez-Beldarrain, M. and Garcia-Monco, J.C. (1998). The cerebellar cognitive affective syndrome. Brain 121: 2202–3. Gomez-Beldarrain, M., Garcia-Monco, J.C., Quintana, J.M., Llorens, V. and Rodeno, E. (1997). Diaschisis and neuropsychological performance after cerebellar stroke. Eur Neurol 37: 82–9. Haines, D.E., Dietrichs, E., Mihailoff, G.A. and McDonald, E.F. (1997). The cerebellar-hypothalamic axis: basic circuits and clinical observations. In The Cerebellum and Cognition, ed. J.D. Schmahmann, pp. 83–107. San Diego: Academic Press. Harada, H., Tamaoka, A., Watanabe, M., Ishikawa, K. and Shoji, S. (1998). Downbeat nystagmus in two siblings with spinocerebellar ataxia type 6 (SCA 6). J Neurol Sci 160: 161–3. Harayama, H., Ohno, T. and Miyatake, T. (1983). Quantitative analysis of stance in ataxic myxoedema. J Neurol Neurosurg Psychiatry 46: 579–81. Harvey, A.S., Jayakar, P., Duchowny, M. et al. (1996). Hemifacial seizures and cerebellar ganglioglioma: an epilepsy syndrome of infancy with seizures of cerebellar origin. Ann Neurol 40: 91–8. Hewer, R.L., Cooper, R. and Morgan, M.H. (1972). An investigation into the value of treating intention tremor by weighting the affected limb. Brain 95: 579–90. Hirose, G., Ogasawara, T., Shirakawa, T. et al. (1998). Primary position upbeat nystagmus due to unilateral medial medullary infarction. Ann Neurol 43: 403–6. Holmes, G. (1904). On certain tremors in organic brain lesions. Brain 27: 327–75. Holmes, G. (1917). The symptoms of acute cerebellar injuries from gunshot wounds. Brain 40: 461–535. Holmes, G. (1922). Clinical symptoms of cerebellar disease and their interpretation. The Croonian lecture III. Lancet 2: 59–65.

Clinical signs of cerebellar disorders

Holmes, G. (1939). The cerebellum of man. The Hughlings Jackson memorial lecture. Brain 62: 1–30. Hood, J.D., Kayan, A. and Leech, J. (1973). Rebound nystagmus. Brain 96: 507–26. Horak, F.C. and Diener, H.C. (1994). Cerebellar control of postural scaling and central set in stance. J Neurophysiol 72: 479–93. Hore, J., Wild, B. and Diener, H.C. (1991). Cerebellar dysmetria at the elbow, wrist, and fingers. J Neurophysiol 65: 563–71. Kanaya, T., Nonaka, S., Kamito, M., Unno, T., Sako, K. and Takei, H. (1994). Primary position upbeat nystagmus localizing value. J Otorhinolaryngol Relat Spec 56: 236–8. Kattah, J.C., Kolsky, M.P., Guy, J. and O’Doherty, D. (1983). Primary position vertical nystagmus and cerebellar ataxia. Arch Neurol 40: 310–14. Keane, J.R. (1989). Hysterical gait disorders: 60 cases. Neurology 39: 586–9. Kennard, C., Barger, G. and Hoyt, W.F. (1981). The association of periodic alternating nystagmus with periodic alternating gaze. A case report. J Clin Neuroophthalmol 1: 191–3. Kent, R.D., Kent, J.F., Rosenbek, J.C., Vorperian, H.K. and Weismer, G. (1997). A speaking task analysis of the dysarthria in cerebellar disease. Folia Phoniatr Logop 49: 63–82. Kimmel, D.L. (1961). Innervation of spinal dura mater and dura mater of the posterior cranial fossa. Neurology 11: 800–9. Kinsbourne, M. (1962). Myoclonic encephalopathy in infants. J Neurol Neurosurg Psychiatry 25: 271–9. Lapresle, J. (1979). Rhythmic palatal myoclonus and the dentatoolivary pathway. J Neurol 220: 223–30. Lechtenberg, R. (1993). Signs and symptoms of cerebellar disease. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 31–43. New York: Marcel Dekker. Lechtenberg, R. and Gilman, S. (1978a). Localization of function in the cerebellum. Neurology 28: 376. Lechtenberg, R. and Gilman, S. (1978b). Speech disorders in cerebellar disease. Ann Neurol 3: 285–90. Leech, J., Gresty, M., Hess, K. and Rudge, P. (1977). Gaze failure, drifting eye movements, and centripetal nystagmus in cerebellar disease. Br J Ophthalmol 61: 774–81. Leigh, R.J., Robinson, D.A. and Zee, D.S. (1981). A hypothetical explanation of periodic alternating nystagmus: instability in the optokinetic–vestibular system. Ann NY Acad Sci 374: 629–35. Leigh, R.J. and Zee, D.S. (1991). The Neurology of Eye Movements, 2nd edn. Philadelphia: F.A. Davis. Lempert, T., Brandt, T., Dieterich, M. and Huppert, D. (1991). How to identify psychogenic disorders of stance and gait. A video study in 37 patients. J Neurol 238: 140–6. Lewis, R.F. and Zee, D.S. (1993). Ocular motor disorders associated with cerebellar lesions: pathophysiology and topical localization. Rev Neurol (Paris) 149: 665–77. Lou, J-S. and Jankovic, J. (1993). Origin and treatment of tremor in cerebellar disease. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 45–63. New York: Marcel Dekker. Luciani, L. (1891). Il Cerveletto: Nuovi Studi de Fisiologia Normale e Patologica. Instituto di studi superiori pratici e di perfezionamento. Florence: Le Monnier.

Mai, N., Diener, H.C. and Dichgans, J. (1989). On the role of feedback in maintaining constant grip force in patients with cerebellar disease. Neurosci Lett 99: 340–4. Malm, J., Kristensen, B., Karlsson, T., Carlberg, B., Fagerlund, M. and Olsson, T. (1998). Cognitive impairment in young adults with infratentorial infarcts. Neurology 51: 433–40. Manni, E. and Petrosini, L. (1997). Luciani’s work on the cerebellum a century later. Trends Neurosci 20: 112–16. Manto, M., Godaux, E. and Jacquy, J. (1994). Cerebellar hypermetria is larger when the inertial load is artificially increased. Ann Neurol 35: 45–52. Manto, M., Godaux, E. and Jacquy, J. (1995a). Detection of silent cerebellar lesions by increasing the inertial load of the moving hand. Ann Neurol 37: 344–50. Manto, M., Goldman, S. and Hildebrand, J. (1996). Cerebellar gait ataxia following neuroleptic malignant syndrome. J Neurol 243: 101–2. Manto, M., Jacquy, J., Hildebrand, J. and Godaux, E. (1995b). Recovery of hypermetria after a cerebellar stroke occurs as a multistage process. Ann Neurol 38: 437–45. Mauritz, K.H., Dichgans, J. and Hufschmidt, A. (1979). Quantitative analysis of stance in late cortical cerebellar atrophy of the anterior lobe and other forms of cerebellar ataxia. Brain 102: 461–82. McCrory, P.M., Bladin, P.F. and Berkovic, S.F. (1999). The cerebellar seizures of Hughlings Jackson. Neurology 52: 1888–90. Mossman, S. and Halmagyi, G.M. (1997). Partial ocular tilt reaction due to unilateral cerebellar lesion. Neurology 49: 491–3. Nutt, J.G. and Horak, F.B. (1997). Gait and balance disorders. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 649–60. New York: McGraw-Hill. Orzechowski, K. (1927). De l’ataxie dysmétrique des yeux: remarques sur l’ataxie des yeux dite myoclonique (opsoclonie, opsochorie). J Psychol Neurol 35: 1–18. Pierrot-Deseilligny, C., Amarenco, P., Roulle, E. and Marteau, R. (1990). Vermal infarct with pursuit eye movement disorders. J Neurol Neurosurg Psychiatry 53: 519–21. Rabiah, P.K., Bateman, J.B., Demer, J.L. and Perlman, S. (1997). Ophthalmologic findings in patients with ataxia. Am J Ophthalmol 123: 108–17. Rekate, H.L., Grubb, R.L., Aram, D.M., Hahn, J.F. and Ratcheson, R.A. (1985). Muteness of cerebellar origin. Arch Neurol 42: 697–8. Ringel, R.A. and Culberson, J.L. (1988). Extensor tone disinhibition from an infarction within the midline anterior cerebellar lobe. J Neurol Neurosurg Psychiatry 51: 1597–9. Sanes, J.N., LeWitt, P.A. and Mauritz, K.H. (1988). Visual and mechanical control of postural and kinetic tremor in cerebellar system disorders. J Neurol Neurosurg Psychiatry 51: 934–43. Schmahmann, J.D. and Sherman, J.C. (1998). The cerebellar cognitive affective syndrome. Brain 121: 561–79. Selhorst, J.B., Stark, L., Ochs, A.L. and Hoyt, W.F. (1976). Disorders in cerebellar ocular motor control. I. Saccadic overshoot dysmetria. An oculographic, control system and clinico-anatomical analysis. Brain 99: 497–508. Shan, D.E., Wang, V. and Chen, J.T. (1995). Isolated lateropulsion of the trunk in cerebellar infarct. Clin Neurol Neurosurg 97: 195–8.

119

120

M-U. Manto

Silveri, M.C., Leggio, M.G. and Molinari, M. (1994). The cerebellum contributes to linguistic production: a case of agrammatic speech following a right cerebellar lesion. Neurology 44: 2047–50. Silfverskiöld, B.P. (1977). A 3 C/sec leg tremor in a ‘cerebellar’ syndrome. Acta Neurol Scand 55: 385–93. Sprague, J.M. and Chambers, W.W. (1953). Regulation of posture in intact and decerebrate cat. I. Cerebellum, reticular formation, vestibular nuclei. J Neurophysiol 16: 451–63. Stewart, T.G. and Holmes, G. (1904). Symptomatology of cerebellar tumors. A study of forty cases. Brain 27: 522–91. Takemori, S. (1977). Visual suppression test. Ann Otol Rhinol Laryngol 86: 80–5. Thach, W.T. (1998). Cerebellum in motor learning and cognition? Trends Cogn Neurosci 2: 331–7. Thurston, S.E., Leigh, R.J., Abel, A. and Dell’Osso, L.F. (1987). Hyperactive vestibulo-ocular reflex in cerebellar degeneration. Pathogenesis and treatment. Neurology 37: 53–7. Topka, H., Konczak, J., Schneider, K., Boose, A. and Dichgans, J. (1998). Multijoint arm movements in cerebellar ataxia: abnormal control of movement dynamics. Exp Brain Res 119: 493–503. Trouillas, P., Takayanagi, T., Hallett, M. et al. (1997). International cooperative ataxia rating scale for pharmacological assessment of the cerebellar syndrome. J Neurol Sci 145: 205–11. Vahedi, K., Rivaud, S., Amarenco, P. and Pierrot-Deseilligny, C. (1995). Horizontal eye movement disorders after posterior vermis infarction. J Neurol Neurosurg Psychiatry 58: 91–4. Van Calenbergh, F., Van De Laar, A., Plets, C., Goffin, J. and Casaer, P. (1995). Transient cerebellar mutism after posterior fossa surgery in children. Neurosurgery 37: 894–8. van Dongen, H.R., Catsman-Berrevoets, C.E. and van Mourik, M. (1994). The syndrome of ‘cerebellar’ mutism and subsequent dysarthria. Neurology 44: 2040–6.

Waterson, J.A., Barnes, G.R. and Grealy, M.A. (1992). A quantitative study of eye and head movements during smooth pursuit in patients with cerebellar disease. Brain 115: 1343–58. Weber, R.B. and Daroff, R.B. (1972). Corrective movements following refixation saccades: type and control system analysis. Vision Res 12: 467–75. Wertham, F.I. (1929). A new sign of cerebellar disease. J Nerv Ment Dis 69: 486–93. Wessel, K., Moschner, C., Wandinger, K.P., Kompf, D. and Heide, W. (1998). Oculomotor testing in the differential diagnosis of degenerative ataxic disorders. Arch Neurol 55: 949–56. Wiest, G., Safoschnik, G., Schnaberth, G. and Mueller, C. (1997). Ocular flutter and truncal ataxia may be associated with enterovirus infection. J Neurol 244: 288–92. Wills, A.J., Jenkins, I.H., Thompson, P.D., Findley, L.J. and Brooks, D.J. (1994). Red nuclear and cerebellar but no olivary activation associated with essential tremor: a positron emission tomographic study. Ann Neurol 36: 636–42. Yee, R.D., Baloh, R.W. and Honrubia, V. (1984). Episodic vertical oscillopsia and downbeat nystagmus in a Chiari malformation. Arch Ophthalmol 102: 723–5. Yee, R.D., Baloh, R.W., Honrubia, V., Lau, C.G. and Jenkins, H.A. (1979). Slow build-up of optokinetic nystagmus associated with downbeat nystagmus. Invest Ophthalmol Vis Sci 18: 622–9. Zee, D.S. (1977). Suppression of vestibular nystagmus. Ann Neurol 1: 207. Zee, D.S., Friendlich, A.R. and Robinson, D.A. (1974). The mechanism of downbeat nystagmus. Arch Neurol 30: 227–37. Zentay, P.J. (1937). Motor disorders of the central nervous system and their significance for speech: cerebral and cerebellar dysarthrias. Laryngoscope 47: 147–56.

8

Pathophysiology of clinical cerebellar signs Helge Topka1 and Steve G. Massaquoi2 2

1 Department of Neurology, University of Tübingen, Germany Department of Electrical Engineering and Computer Science and Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, USA

Introduction Disorders of the cerebellum may have a large number of etiologies and, therefore, may be associated with a multitude of clinical signs. However, only a small number of clinical signs may be viewed as being specific for cerebellar dysfunction. These clinical hallmarks of cerebellar dysfunction include inaccurate, dysmetric limb movements, disordered gait, dysarthric speech, nystagmus, abnormal oculomotor control, as well as involuntary movements such as terminal and postural tremors. During recent years, a large number of studies have helped to clarify to a considerable extent both the role of the cerebellum in normal movement and the pathophysiological consequences of cerebellar dysfunction. This chapter reviews the major clinical signs of cerebellar disorders and attempts to interpret these signs in the framework of current concepts of normal and pathologic cerebellar motor physiology. The neuroanatomy of the cerebellum is extensively reviewed in Chapter 2. This chapter briefly emphasizes two fundamental features of cerebellar neuroanatomy that seem to be critical for understanding its physiology. These two features are the organization of its input–output pathways and the consequent compartmentalization of cerebellar functions. The microarchitecture of the cerebellum is remarkably homogenous across different cerebellar subdivisions. In particular, the cerebellar cortical circuitry consisting of two input pathways, the mossy fiber/parallel fiber system and the climbing fiber system, and a single output pathway, the Purkinje cells that connect the cerebellar cortex with the deep nuclei, is remarkably homogeneous across different cerebellar subdivisions. While mossy fibers originate chiefly from pontine nuclei and project to Purkinje cells indirectly via granular cells and parallel fibers, climbing fibers represent direct projections

from the inferior olive to the dendritic tree of Purkinje cells. Despite the microarchitectural homogeneity of cerebellar cortex, due to differences in the input–output patterns that characterize each cerebellar subdivision (Dow and Moruzzi, 1958; Brodal, 1981; Gilman et al., 1981), lesions of different aspects of the cerebellum are associated with a different and distinct pattern of clinical deficits. Lesions of the lateral cerebellar hemispheres and the dentate nucleus predominantly cause dysmetria of movements of the ipsilateral upper limbs, whereas lesions of the anterior lobe are associated with postural ataxia, and oculomotor symptoms are consequences of lesions within cerebellar flocculus and fastigial nuclei. This phenomenon has been referred to as functional compartmentalization (Dichgans, 1984). Functional compartmentalization notwithstanding, it seems reasonable to assume that all cerebellar signs, as different as they may appear clinically, share a few common pathophysiologic mechanisms. Therefore, in this chapter, clinical features are grouped and discussed with respect to the known or presumed underlying pathophysiologic mechanisms.

Cerebellar control of voluntary movement Terminology The majority of clinical signs that help to identify cerebellar dysfunction in a patient are summarized by the Greek term ataxia,which literally means ‘without order’. While chronic damage, even to large proportions of the cerebellum, does not cause any obvious muscle weakness, movements directed toward a target are usually slower than normal, the acceleration of the limb is reduced, and movements are less accurate, either stopping before the target is

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reached (hypometria) or, more frequently, overshooting the target (hypermetria). In addition to these inaccuracies in limb placement (dysmetria), a number of other terms have been used historically to describe what was felt to represent clinical hallmarks of cerebellar damage. Among the more frequently used terms are dyssynergia and dysdiadochokinesis. Dysdiadochokinesis refers to the difficulties cerebellar patients exhibit when asked to perform rapid alternating movements. The term dyssynergia was originally coined by Babinski (1899) and refers to the disordered coordination of different muscles or muscle groups that is associated with cerebellar dysfunction. Somewhat related to dyssynergia is a phenomenon that is referred to as ‘decomposition’ of movement (Holmes, 1939). Depending on the spatial layout of a multijoint arm movement, patients tend to use larger hand paths to move the hand from start to target than would be required if they were to connect start and target positions using the shortest distance, a roughly straight line. This phenomenon was thought to reflect a specific inability to generate simultaneous movements of adjacent joints and, therefore, was thought to represent decomposition of a compound movement into its constituent parts.

Pathophysiology of dysmetria One of the first researchers who provided quantitative measurements of voluntary movements in cerebellar ataxia was the British neurologist Gordon Holmes (Holmes, 1917, 1939). He studied grasping movements in patients with unilateral cerebellar lesions and noted some 200 ms delay in movement initiation, a decrease in phasic muscle strength, and a prolongation of the time required to produce maximal muscular force in the arm ipsilateral to the lesion. Subsequently, many studies have attempted to identify elementary cerebellar motor control functions by restricting their analyses to movements about a single joint as opposed to more natural, but kinematically and kinetically more complex, multijoint movements. A large number of single-joint studies not only investigated the temporospatial characteristics of voluntary movements (kinematics), but also yielded detailed analyses of the electromyographic pattern of muscle activation associated with the movement. Due to their short durations of a few hundred milliseconds, rapid single-joint movements must be guided, at least initially, without feedback and, therefore, have been termed ballistic movements. In healthy subjects, ballistic single-joint movements are characterized by short reaction or motor preparation times, high peak velocities, and nearly symmetric and bell-shaped velocity profiles. A characteristic three-phase pattern of

Fig. 8.1 Disorder in agonist electromyographic activity (Ag) ipsilateral to a cerebellar lesion. Records are superimposed averages of 15–20 movements made between targets separated by 5, 30 and 60 degrees. (A) Finger movements, (B) elbow movements. Acc, acceleration. (Adapted from Hore et al. (1991), Journal of Neurophysiology 65: 563, with permission.)

electromyographic activity that consists of an initial agonist burst, an overlapping burst in the antagonist, and a subsequent second agonist burst (Wacholder, 1923) is associated with rapid ballistic movements. Patients with cerebellar dysfunction that involves the limbs exhibit several distinct abnormalities when executing single-joint movements (Fig. 8.1). Compared to healthy subjects, movement initiation is delayed, as indicated by increased reaction or motor preparation times, and movements are dysmetric. At the level of movement kinematics, peak acceleration may be reduced, and dysmetria is associated with asymmetries in the velocity profiles due to a disordered relationship between the accelerative and decelerative phases of the movements. Both, a mismatch of amplitudes or durations of movement acceleration and deceleration have been reported (Flament and Hore 1986; Hore et al., 1991; Hallett and Massaquoi, 1993). Analysis of electromyographic activity revealed not only that reduced accelerations are due to a somewhat delayed and more gradual rise in agonist activity (Hore et al., 1991; Hallett et al., 1975; Wild et al., 1996), but, most importantly, demonstrated that movement dysmetria is caused by a delay in antagonist muscle activity, which is supposed to brake the movement (Fig. 8.2). In some patients, a selective decrease in the rate of rise of the antagonist activity may be observed (Manto et al., 1996). The rebound phenomenon seems to be due to abnormalities in the recruitment and activation of particular antagonistic muscles Specifically, the rebound test

Pathophysiology of clinical cerebellar signs

Fig. 8.2 Delayed antagonist electromyographic activity (Ant) associated with hypermetria. Records are averages of 15–20 flexions on the normal side and on the cerebellar affected side made about (A) the elbow, (B) the wrist, and (C) the finger. Records are synchronized to the start of the movement (time 0s). Target distance is 30 degrees. Ag, agonist EMG activity; Pos, position; Vel, velocity; Acc, acceleration. (Adapted from Hore et al. (1991). Journal of Neurophysiology; 65: 563, with permission.)

assesses the rapidity of activation of the elbow extensor muscles when a forceful elbow flexion against the examiner is abruptly released. Abnormalities in the recruitment of agonist and antagonist muscles are not likely to be explained by an alteration of movement strategies in the face of cerebellar motor deficits. Rather, they are likely to represent a genuine deficit in generating normal levels of phasic muscular forces (Wild et al., 1996). As a result, the inertia of the limb is managed poorly and therefore both acceleration and deceleration rates are diminished. Both single-joint studies and studies involving transcranial magnetic stimulation of motor cortex in human subjects suggest that reduced peak accelerations and disordered electromyographic activity during execution of a movement in cerebellar ataxia are related to diminution of facilitatory cerebellar output to motor cortical areas of agonist and antagonist muscles (Spidalieri et al., 1983; Butler et al., 1992; Topka et al., 1994; Wessel et al., 1996).

Dyscoordination of movement While the term ‘decomposition of movement’ was introduced by Holmes early in the twentieth century (Holmes, 1939), the observation that patients with cerebellar disorders experience difficulties in coordinating movements about several adjacent joints had been made earlier by a number of researchers and had sparked a long-lasting controversy as to the exact pathophysiological basis of this motor problem. Hughlings Jackson (1870) and others (Luciani 1893) felt that all motor difficulties observed in cerebellar disorders may be explained by a summation of elementary motor deficits that affect a single joint. Flourens (1824) and Babinski (1906) argued that a major role of the cerebellum in controlling movements was to orchestrate movements of adjacent joints in order to provide for coordinated movement of a limb. From today’s point of view, several lines of reasoning suggest that the full clinical picture of ataxic multijoint

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movements may not be completely explained by merely summing up the motor deficits that occur during movements about each single joint involved. Some 30 muscles of the upper arm, the forearm, and the shoulder girdle are involved in moving the arm during a simple reaching movement. To maintain stable posture during the movement of the arm, the central nervous systems needs to control several additional muscles of the trunk and in the legs. Thus, in standing human subjects, movements of the upper limbs have to be preceded, accompanied, and followed by muscular activation in postural muscles of the trunk and the legs that have to be adapted to compensate for changes in the center of gravity potentially jeopardizing stable posture. Thus, the activities of a large number of muscles which subserve different aspects of the motor task need to be orchestrated in order to provide for normal, accurate, and fast movement. In their comprehensive review, Thach and colleagues (1992) interpreted pertinent neuroanatomical and neurophysiological data and suggested that, indeed, the architecture of cerebellar cortex and outflow pathways is compatible with the notion of a specific role of the cerebellum in (multijoint) coordination per se. A clinical observation that simple movements may well be preserved after ischemia in the territory of the superior cerebellar artery while compound movements exhibit severe ataxia (Goodkin et al., 1993) may provide some support for this hypothesis (but see also Massaquoi and Hallett, 1996). However, as noted above, single-joint movement abnormalities are a well-established consequence of cerebellar dysfunction. Even so, given the dynamic considerations described below, in many circumstances, multijoint coordination may be more demanding of cerebellar integrity. Therefore, at times ataxia in multijoint movements may be more apparent than in single-joint movements. Theoretical considerations emphasize the need for special central nervous system control of multijoint coordination. In a one degree of freedom movement such as a single-joint movement, the force F (or torque) generated by a muscle and the acceleration A (or angular acceleration) of a limb segment are proportional to each other by Newton’s second law of motion. This is not the case, however, for a mechanical system with more than one degree of freedom, such as a whole human arm. For example, the torques generated at either the shoulder or elbow are not in general proportional to the angular acceleration at either of the two joints. This is because of the effects of joint interaction forces in the multi-degree of freedom human arm which enable muscles to accelerate joints they do not span (Zajac, 1993). It would, therefore, seem advantageous for there to be central control of these

joint interactions as well as of inertial forces at each single joint. In the case of multijoint movements, the relationship between the change in behavior of the movement over time (kinematics) and the forces that drive movements (dynamics) may be described by sets of non-linear equations of motion (Hollerbach and Flash 1982; Schneider and Zernicke 1990; Bastian et al., 1996) and is accessible to experimental quantification. Given an observed motion of the hand, the shoulder, and the elbow, one can compute the torques that produced the movement by using an inverse dynamics model. In this approach, the upper limb is modeled as two or more interconnected rigid links or segments (upper arm, forearm, wrist) with frictionless joints (shoulder, elbow, wrist). Certain inverse dynamics models also allow for parsing the net forces acting at a given joint into force components that originate from muscular activation (MUS), external forces (EXT) including gravity and other disturbances, and dynamic inertial and interaction forces (DYN). The net torque (NET) is then simply the sum of all positive and negative torque components: NET MUSEXTDYN. From a theoretical point of view, the most important component of dynamic movement variables related to the coordination of multiple joints of a limb are dynamic interaction forces. Direction and temporal patterns of muscular and dynamic interaction forces during a rapid elbow flexion movement are illustrated in Fig. 8.3. In order for coordinated movement to occur, dynamic interaction forces have to be accurately assessed and monitored by the central nervous system and, since muscular activation represents the only dynamic movement variable that is actively controlled by the nervous system, muscle activation at the joint involved has to be modified accordingly. The concept that voluntary activation of a muscle has to be adjusted to compensate for the physical consequences of movement was first proposed by the Russian physiologist Bernstein in 1967. Bernstein hypothesized that the role of the central nervous system in controlling multijoint movements is to provide for muscular activation that takes dynamic and external forces into account. It takes advantage of them if these forces support the goal of the movement or compensates for them if they oppose the goal of the movement. Subsequently, physiological studies in healthy subjects have provided experimental evidence in support of this hypothesis by showing that dynamic interaction forces during multijoint movements are sufficiently large to influence movement trajectories – if not adequately compensated for (Hollerbach

Pathophysiology of clinical cerebellar signs

Fig. 8.3 Illustration of temporal pattern and direction of muscular and dynamic interaction forces during a rapid elbow flexion movement in a healthy subject. The subject was instructed to perform the elbow flexion as fast as possible while fixating the shoulder joint. Elbow flexion is driven by muscular forces (MUS Elbow), which in turn generate passive interaction forces at the shoulder joint (DYN Shoulder) that have a similar time course but different signs. To cancel DYN Shoulder, muscular activation at the shoulder joint (MUS Shoulder) exactly matching the time course of DYN is required. (Modified from Neuroscience Letters 261 (1–2), A. Boose, J. Dichgans and H. Topka. Deficits in phasic muscle force generation explain insufficient compensation for interaction torque in cerebellar patients, pp. 53–6 (1999), with permission from Elsevier Science.)

and Flash 1982; Sainburg et al., 1995; Virji-Babul and Cooke 1995). The concept that a major role of the cerebellum may be in the management of movement physics was proposed earlier by Braitenberg (1987) on theoretical grounds. During recent years, several studies have provided experimental evidence suggesting that dyscoordination of movement in cerebellar ataxia may in fact originate from deficient compensation of dynamic interaction forces during voluntary movement. Massaquoi and Hallett (1996) noted characteristic sluggishness and curvature in ataxic two-joint arm movements. The abnormalities were attributed to deficient cerebellar management of forces, both at each joint and, potentially, between the joints. Bastian and colleagues (1996) performed a kinetic analysis of torques generated at each joint during slow–accurate and fast– accurate reaching movements. Particularly during fast reaching movements, patients with cerebellar disorders produced abnormal torque profiles compared to healthy subjects, with inappropriate levels of shoulder muscle torque and elbow muscle torques that did not vary appropriately with the dynamic interaction torques that occurred at the elbow. Several kinematic characteristics of cerebellar limb ataxia, therefore, were shown to result from an abnormal influence of dynamic joint interactions and to reflect a critical role of cerebellar pathways in generating

muscle torques that predict and compensate for joint interaction torques. Fig. 8.4 provides an example of deficient control of dynamic interaction forces in patients with degenerative cerebellar disorders. Magnitudes of dynamic interaction and other forces are scaled to the square of movement speed, an observation which is probably related to the fact that cerebellar clinical signs such as dysmetria are more prominent during fast movements. A role of the cerebellum in scaling dynamic movement variables is also in accord with the presumed involvement of cerebellar pathways in motor adaptation processes. At this point, the exact mechanisms that lead to an abnormal control of interaction torques are not known. In principle, the generation of inadequate muscular torques may result from an impairment in generating sufficient levels of torques or rates of torque increase, or from an inaccurate assessment and prediction of the mechanical consequences of movements of one limb segment on adjacent joints. Indirect evidence for the notion that a difficulty in generating muscle forces with sufficient rapidity may contribute to ataxia of limb movements came from a study that investigated the kinematics of initiating a twojoint arm movement (Massaquoi and Hallett 1996). Recent studies provide further support for the hypothesis that deficits in generating normal magnitudes of phasic muscle forces known from single-joint studies may significantly

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Fig. 8.4 Effects of insufficient compensation of dynamic joint interactions. Movements are performed as in Fig. 8.3. Examples of single movements of a healthy subject (SLA-N, left panel) and two patients (AHA-C, MKU-C, right panels). In healthy subjects, small-amplitude motion at the shoulder joint occurs, violating the instruction to some extent. Motion about the shoulder joint exactly matches the temporal pattern of dynamic interaction forces originating from active elbow motion. In patients, passive shoulder joint motion and the temporal pattern of dynamic interaction forces do not match (upper right panel). In some instances, patients tend to overcompensate (lower panel). (Modified from Neuroscience Letters 261 (1–2), A. Boose, J. Dichgans and H. Topka. Deficits in phasic muscle force generation explain insufficient compensation for interaction torque in cerebellar patients, pp. 53–6 (1999), with permission from Elsevier Science.)

contribute to the dyscoordination of fast multijoint movements in cerebellar ataxia (Topka et al., 1998; Boose et al., 1999). Quantitative analysis of muscular forces during vertical multijoint pointing movements reveals that cerebellar hypermetric movements are associated with smaller peak muscular torques and smaller rates of torque change at elbow and shoulder joints. The patient’s deficit in generating appropriate magnitudes of muscular force are prominent during two different phases of the pointing movement. Peak muscular forces at the elbow are reduced during the initial phase of the movement when simultane-

ous shoulder joint flexion generated an extensor influence upon the elbow joint. When attempting to terminate the movement, gravitational and dynamic interaction as well as inertial forces cause overshooting extension at the elbow joint. Interestingly, the timing of shoulder and elbow joint muscle torques that is characterized by a large degree of synchronicity (Gottlieb et al., 1996) in normal subjects is preserved in cerebellar patients, despite severe kinematic abnormalities of ataxic movements (Topka et al., 1998). A clinical test to evaluate the processing of dynamic limb interactions may be to ask the patient to perform a rapid

Pathophysiology of clinical cerebellar signs

movement of one extended arm while standing or sitting unsupported. While normal subjects will be able to stabilize the position of the trunk during such a movement of the arm, patients with cerebellar disorders will show involuntary movements of the trunk and perhaps the legs that represent the propagation of dynamic interaction forces to remote parts of the body. These findings clearly demonstrate cerebellar involvement in controlling ‘parasitic’ forces during voluntary movement, the exact relationship between movement dynamics and cerebellar neuronal processing has yet to be established. The observation that sensory deafferentation results in deficits controlling movement dynamics that are reminiscent of cerebellar dysfunction (Sainburg et al., 1993, 1995) but affect different phases of the movement has prompted the notion that cerebellar pathways may be part of a three-stage control system consisting of anticipatory mechanisms, error correction, and mechanisms of postural control (Sainburg et al., 1999). In such a scheme, the cerebellum may contribute by holding an internal model or representation of the biomechanic properties of the body that is continuously updated and recalibrated by afferent sensory information (Sainburg et al., 1999; Ghez and Sainburg, 1995). While it is well known that lesions of the lateral cerebellar hemispheres and the dentate nuclei (Meyer-Lohmann et al., 1977; Hore and Vilis, 1984; Tsujimoto et al., 1993; Lu et al., 1998), are in general associated with disordered limb movements, there may also exist functional partitioning within cerebellar pathways that provides more detail regarding the nature of the dysfunction associated with localized lesions. Specifically, theories of cerebellar function (Allen and Tsukahara, 1974) link the function of monitoring of ongoing movement execution as well as error correction more to the intermediate cerebellum, including the interposed nuclei, and anticipatory activation more to the lateral aspects of the cerebellar hemisphere, including the dentate. Thus, in addition to poorly controlled muscle activation within simple single-joint and multijoint movements, patients with cerebellar disease also characteristically fail to trigger properly sequences of submovements within a more complex movement. Studies by Ivry and Keele (1989) have suggested that the medial portions of the cerebellum may be more influential in promoting promptness of movements once they are triggered (implementation timing), whereas the lateral cerebellum may be more important in triggering movements at correct latencies (clock timing) following previous movements or presumably other cues. Dysdiadochokinesis is a sign of failed movement coordination that is due in large part to failure to properly syn-

chronize movements. In the examination for dysdiadochokinesis, the patient is asked to perform rapidly alternating pronations and supinations of the lower arm while simultaneously moving the hand and forearm up and down. When done correctly, the hand pats a surface alternately with the palm and dorsum in a regular rhythm. Typically, patients with diffuse cerebellar lesions will have slowed, poorly rhythmic movements that have irregular amplitude. In such a motorically challenging test, poor overall performance presumably is due to both faulty accelerations and dysmetria within each of the simple motions, as well as in the synchronizing and pacing of the submovements. Dysdiadochokinesis is especially prominent in patients with lateral cerebellar lesions (Gilman et al., 1981), consistent with the ideas of Keele and Ivry (Ivry and Keele, 1989; Ivry, 1997), that deficits in ‘clock timing’ are particularly brought out by this test.

Ataxia of gait and posture Gait is frequently disordered in patients with cerebellar diseases. In degenerative cerebellar ataxias, for example, gait difficulties are among the first clinical symptoms to occur, and represent a significant cause of functional deficits in ambulation as the disease progresses (Klockgether et al., 1998). Cerebellar dysfunction chiefly degrades maintenance of steady posture and causes difficulties coordinating movements of the trunk and the legs, yielding an irregular, staggering gait. Lesions of the vermis and the anterior lobe of the cerebellum are associated with increased body sway, which is omnidirectional with lower vermal lesions and may be more prominent in anterior –posterior directions with upper vermal and intermediate lesions (Dichgans and Fetter, 1993). Despite the importance of disordered gait for the patient’s functional capabilities, only a few studies have addressed the pathophysiology of cerebellar gait disorders. Patients may show reduced step and stride length, a somewhat reduced cadence, and an increased variability in all quantitative gait measurements. However, overall, the pattern of abnormalities that can be observed in patients does not seem to differ in principle from the pattern that is associated with other multijoint movements (Palliyath et al., 1998). Thus, it appears that cerebellar gait disorders, being dependent on multijoint control of lower limbs and the trunk, share to a large extent the pathophysiology of other multijoint movements and, therefore, like dyscoordination of isolated limb movements, appear to be related to an insufficient control of dynamic interaction forces during gait. This view is in accord with earlier observations that demonstrated deficient coordination of postural

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adjustments if patients were asked to perform limb movements during quiet stance (Diener et al., 1992). One study emphasized the role of the posterior cerebellar vermis in coordinating bilateral movements of the legs as children who underwent transsection of this portion of the cerebellum were severely impaired in tandem gait, but showed only few abnormalities with other leg movements such as regular gait, standing or hopping (Bastian et al., 1998). On the other hand, tandem gait seems to represent a rather difficult motor task compared to normal gait and standing and, therefore, it is somewhat unclear if difficulties in tandem gait represent a specific cerebellar deficit in coordinating both legs.

Cerebellar tremors Cerebellar disorders may be associated with three different forms of tremor: postural tremor, kinetic or terminal tremor and titubation. Unless extracerebellar pathology is involved, tremor does not occur at rest, i.e., when the patient attempts to relax muscles fully. Typical clinical tests of terminal or kinetic tremor are finger-to-nose and heel-to-shin tests. A tremor of 4–7 Hz may be apparent when the movement is initiated. However, it usually decreases in amplitude as the movement progresses and is most severe during termination of the movement. Initially, it was felt that the occurrence of terminal tremor is related to the intention to move (‘intention tremor’) (Holmes, 1904). However, since then it became clear that the occurrence of tremor is related rather to termination of a movement and, hence, it seems more appropriate to use the term terminal or kinetic tremor for this form of oscillatory movement (Gilman et al., 1981). Postural tremor is evoked if subjects are asked to hold the arm against gravity or during forceful isometric voluntary contraction (Gilman et al., 1981). In general, tremor frequencies may vary according to the body part involved. Truncal tremor in the lower limbs as observed in anterior lobe damage varies between 3 and 4 Hz (Dichgans and Fetter, 1993), tremors of the upper limbs during maintained posture may show frequencies in the range of 3–8 Hz during movement. The tremors may occur bilaterally or ipsilateral to a cerebellar lesion. In cases of postural tremor, the oscillation may be facilitated by eye closure and by body displacement. The pathophysiological basis of terminal and postural cerebellar tremors has yet to be established. Interestingly, cerebellar tremors are less frequently associated with cerebellar degenerative disorders, but are more frequently seen

in patients with demyelinating disorders of the brain such as multiple sclerosis. Both in animal experiments (Carrea and Mettler, 1947, 1955; Flament and Hore, 1988) and in patients (Gilman et al., 1981, Nakamura et al., 1993, Bastian and Thach, 1995; Topka et al., 1999), lesions restricted to the superior cerebellar peduncle, or to other points along the cerebellar outflow pathway to motor cortical areas via thalamus, are sufficient to cause terminal and postural tremors. Several lines of evidence support the notion that cerebellar tremors are generated within central motor loops. Hore and Flament (1986; Flament and Hore, 1986) observed terminal tremor during targeted limb movements after cooling of the cerebellar nuclei, and hypothesized that cerebellar pathways may critically be involved in stabilizing a limb during maintained posture or after brisk voluntary movements. To counteract oscillation that may otherwise accompany the termination of a brisk movement, the central nervous system generates bursts of muscle activity that do not seem to be simple stretch reflexes. Rather, the bursts appear to anticipate and thereby are able to suppress the oscillations. Cooling of the cerebellar nuclei interferes with the normal predictive nature of the suppressive bursts both in electromyographic recordings from muscles and in cortex. Without the properly timed suppressive bursts, positional corrections of the limb become driven by nonanticipatory spinal and transcortical (long-loop) stretch responses (Flament and Hore, 1986; Hore and Flament, 1986). Due to delays in the feedback loop, a mismatch develops between the movement phase and the corrective muscle activity. Thus, transcortical reflex activity may tend to reinforce oscillations rather than dampen them. In human cerebellar disease, enhancement of long-loop stretch reflexes frequently occurs (Mauritz et al., 1981; Friedemann et al., 1987), possibly reflecting a compensatory effort aimed at improving movement and postural control. This in turn causes additional detrimental effects on the control of corrective muscle activity. Indirect evidence that feedback loops are involved in the generation of cerebellar tremors originates from animal experiments showing that sensory influences strongly affect cerebellar tremors (Flament et al., 1984) and from demonstrations in humans that blocking peripheral inputs from the hand temporarily reduces tremor during hand writing (Dash, 1995). Recent induction of a cerebellar-like postural and terminal tremor in healthy subjects by repetitive TMS (rTMS) of the primary motor cortex may provide a means of investigating the pathophysiology of cerebellar tremors in more detail (Topka et al., 1999). In analogy to patients with cerebellar disorders, rTMS seems to induce tremor by enhancing the activity of non-anticipatory transcortical

Pathophysiology of clinical cerebellar signs

reflex loops. Thus, in general, cerebellar-like tremor may be due to any relative deficiency in cerebellum-dependent predictive responses in relation to the contribution of nonpredictive transcortical responses to posture and movement stabilization (Massaquoi and Slotine 1996). Titubation refers to low-frequency rhythmic oscillations of the head, in some cases also the trunk, either in anterior–posterior or lateral directions. Titubation may occur in conjunction with or without tremor elsewhere in the body. The pathophysiological basis of titubation is not clear. Conceivably, titubation represents a type of postural tremor that predominantly affects neck and upper truncal muscles.

Hypotonia Hypotonia refers to decreased resistance to passive movement of a limb and typically is tested by repetitively moving, for example, the lower limb after the patient has been asked to relax the limb to the fullest extent possible. In this particular situation, hypotonia is diagnosed if the provoking movement evokes excessive swinging of the foot. While hypotonia frequently is considered to be a sign that is typical of cerebellar dysfunction (Gilman et al., 1981), particularly in the early stages of acute cerebellar disorders, systematic studies that document the magnitude and the time course of this sign are lacking. One reason for this may lie in the difficulties that are associated with quantitatively assessing the tone of a limb and, in particular, from lack of a generally accepted definition of normal tone. In addition, the pathophysiology of hypotonia remains obscure. One study exists that suggests that hypotonia may be related to disordered processing of primary muscle spindle afferents (Kornhauser et al., 1982). However, the significance of this finding remains unclear, given that a number of other studies failed to demonstrate (Gorassini et al., 1993) or questioned cerebellar involvement in monitoring and controlling muscle spindle afferents (Gilman et al., 1976).

Control of eye movements Cerebellar pathways are involved in the control of saccadic and smooth pursuit eye movements as well as in brainstem reflexes involving oculomotor control such as the vestibulo-ocular (VOR) and optokinetic reflexes (OKR). Anatomically, the flocculo-nodular lobe and the paraflocculi of the cerebellum are strongly interconnected with the

vestibular nuclei suggesting that cerebellar pathways are important for modification of the (VOR) and (OKR), whereas the flocculus and probably also the dorsal vermis participate in controlling saccadic and smooth pursuit eye movements. Most commonly, patients present with horizontal gazeevoked nystagmus (a sign of floccular dysfunction), inaccuracies in saccadic eye movements (ocular dysmetria, a dysfunction of the dorsal vermis) and disordered control of eye movements during smooth pursuit (Zee et al., 1976; Fetter et al., 1994; Arpa et al., 1995). In most patients with cerebellar disorders, the severity of symptoms correlates well with the degree of atrophy of the flocculus and the dorsal vermis (Fetter et al., 1994; Arpa et al., 1995). Gaze-evoked nystagmus that predominantly affects eye movements in the horizontal plane results from deficits in voluntarily holding eccentric conjugated gaze and in some cases may be accompanied by downbeat nystagmus and rebound nystagmus when bringing the eyes back to the primary position. Gaze-evoked nystagmus is thought to originate from deficient cerebellar control of the neural integration of saccade velocity-related signals in the brainstem (Cannon and Robinson 1987). Cerebellar pathways are also essentially involved in stabilizing retinal images of moving targets. As a consequence, smooth pursuit eye movements are interrupted by saccades in patients with cerebellar dysfunction. An earlier view that the flocculus is the major anatomical site of cerebellar retinal image stabilization has been challenged in recent years, as several animal studies demonstrated the existence of pursuitrelated single units also in the posterior vermis in primates and the occurrence of smooth-pursuit deficits in patients with vermal lesions (Pierrot-Deseilligny et al., 1990). Ocular dysmetria refers to inaccuracies of saccadic eye movements that more frequently overshoot than undershoot the target. In a clinical examination, the subject is asked to focus alternately on two targets (fingers) positioned approximately 30° from the midline. Unlike healthy subjects, who are able to perform accurate saccades, sometimes with slight undershoot, patients will require additional corrective after-saccades. A wealth of evidence suggests that ocular dysmetria is related to lesions of the vermal portions of the cerebellum, while the flocculus is involved in adjusting velocities and amplitudes of saccades resulting in pulse-step mismatches (post-saccadic drifts of the eye) in the case of dysfunction. The VOR provides a means to stabilize retinal image during head movements. Two abnormalities are present in patients with cerebellar disorders, in particular with lesions to the flocculus. Firstly, the gain of the VOR that represents the ratio between head and eye velocities is

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somewhat increased with floccular lesions (Robinson 1976). Secondly, visual suppression of the VOR by fixation of a visual target that moves simultaneously with the subject is reduced (Dichgans et al., 1978). At this point, it is widely accepted that cerebellar pathways, in particular target neurons in the brainstem, play an essential role in modulating and adapting the gain of the vestibulo-ocular reflex according to environmental changes (Lisberger, 1988). Optokinetic (OKN) nystagmus is evoked physiologically when watching a target that rapidly moves in one direction. Patients with cerebellar disorders may present with either exaggerated or dampened excursions of the eyes with such a stimulus. Here, the cerebellum seems to be involved mainly in the initiation of OKN (the direct path or smooth pursuit component of the OKN), while steadystate OKN is much less afflicted by cerebellar lesions. Finally, suppression of the VOR by changing the otolith input (vestibular tilt dumping) is reduced in patients with lesions of the nodulus and uvula. These patients also frequently show signs of disinhibition of the VOR with periodic alternating nystagmus.

1992), has been challenged recently as cerebellar dysarthria has also been shown in patients with pathology limited to the right cerebellar hemisphere (Ackermann et al., 1992). These abnormalities in speech production seem to resemble motor problems that are associated with other forms of voluntary movements such as limb movements or gait. In addition to supporting the motor aspects of speech, cerebellar pathways may also participate in more cognitive aspects of speech such as grammatism. Anatomical connections appear to support the possibility of cerebellar participation in higher cognitive functions in general (for an extensive review see Schmahmann and Sherman 1998). Nonetheless, in regard to a role for the cerebellum in grammar formation in particular, existing experimental evidence is not convincing. Agrammatism was reported in single patients who suffered a right-sided cerebellar infarction (Silveri et al., 1994). However, recent functional imaging studies demonstrate that cerebellar involvement in speech production is related to the articulation rather than to cognitive processing (Ackermann et al., 1998).

Cerebellar dysarthria

Is there a single elementary cerebellar function common to all cerebellar motor functions?

Cerebellar dysfunction not only degrades eye and limb movements, but also affects production of speech, in particular movements during articulation. Like other forms of voluntary movement, speech production is inaccurate and exhibits an abnormal modulation of pitch and loudness. The latter is thought to represent a characteristic feature of cerebellar dysarthria and is frequently referred to as ‘scanning’ speech. During recent years, a number of studies have begun to analyze speech in cerebellar disorders in quantitative terms. These studies document that dysarthric speech results from slowing down of articulatory movements and suffers from articulatory impreciseness (Lechtenberg and Gilman 1978; Ackermann et al., 1992) and imperfect syllable timing (Ackermann and Ziegler 1994). To some extent, also, abnormal kinematics, i.e., ataxia of breathing movements, may contribute to cerebellar dysarthria (Murdoch et al., 1991). The topography of cerebellar control of speech is not entirely clear. A number studies investigating the distribution of cerebellar pathology in patients showed lesions that were restricted to a small region of the paravermal aspect of the superior cerebellar hemispheres (Lechtenberg and Gilman 1978; Amarenco et al., 1991; Ackermann et al., 1992). The initial view that exclusively left-sided cerebellar lesions represent speech functions (Lechtenberg and Gilman 1978; Amarenco et al., 1991; Ackermann et al.,

At this point, this question has not been sufficiently answered. Recent experimental evidence has helped to develop a theoretical framework that may trace the seemingly different cerebellar motor functions to a single (or a set of) elementary basic function (for a more detailed discussion of models of cerebellar functions see Chapter 6). Clearly, cerebellar pathways are critically involved in dealing with the physics of movements and, consequently, clinical signs of cerebellar dysfunction can be explained by deficits in controlling dynamic movement variables. However, it is unclear if this aspect of cerebellar motor control is pointing to a primary role of the cerebellum in motor control or is secondary to yet another and more basic deficit. At this point, serious doubts remain as to whether cerebellar neuronal structures are capable of computing movement dynamics directly, as the findings in single-joint and multijoint limb movements might suggest. As outlined later in this book, alternative approaches to motor control exist that are based on feedback that enables implicit management of movement dynamics. In order to address this issue, a number of questions have to be resolved. One major argument against explicit control of dynamic movement variables by the central nervous system has always been the need for explicit or implicit computation of muscular torque series that is associated with such a

Pathophysiology of clinical cerebellar signs

control mechanism. Based on the very influential ‘equilibrium point’ hypothesis (Bizzi et al., 1976; Feldman et al., 1990; Feldman 1986), researchers felt that the central nervous system may be able to control limb stiffness and rest length independently. In principle, by adjusting the values of these two parameters, the limb may then be moved from one resting state to the other, i.e., from a start position, to a target position without explicit calculation of the movement dynamics. Continuous movement may then be viewed as motions toward a series of targets. While this mechanism would be advantageous for the central nervous system as it reduces the requirement for explicit computation of torque series, it may not be sufficient to enable rapid adaptation of motor output to external and internal pertubation as frequently as required in a natural environment and, therefore, the general applicability of the equilibrium point hypothesis remains unclear. One other potential argument against the notion of explicit cerebellar computation of movement dynamics stems from anatomical studies. To date, no peripheral receptor has been identified that is capable of measuring the force components of different origin during movement. Therefore, it is unclear how the central nervous system would be able to monitor rapid changes in single components of movement dynamics as they occur during execution of a limb movement. On the other hand, it is conceivable that cerebellar management of movement physics does not critically depend on a breakdown of the force components. The total applied force, as measured by Golgi tendon organs, may provide for sufficient information to be used to estimate the acceleration of limb segments. Another objection against the notion of cerebellar computation of movement dynamics is raised on rather technical grounds. At this point, several sets of the equation of motions have been used to compute the force components acting at a given joint. It is important to note, however, that the equations of motion differ in various aspects. First of all, there are differences with respect to the coordinate frame that is used to assess angular motion. While some formulations calculate inverse dynamics based on joint angles (i.e., forearm versus upper arm), others perform these calculations based on body segment position in absolute space (i.e., forearm versus right horizontal). This difference may look somewhat technical at first sight; however, since the time course and the magnitude of calculated torque components depend on the coordinate frame used, it has some implications for neurobiological interpretations. At this point, sufficient experimental data are not available to help to decide if the human nervous system uses any one of these reference frames or is able to

switch between different reference frames according to task requirements. Another important difference between different sets of equations of motion used in previous studies concerns the definition of the various torque components, which is not unified across different groups. These difficulties in defining and calculating dynamic movement variables demonstrate that, for example, dynamic interaction forces are not invariant under coordinate transformation and, thus, at least in the form they are computed using these approaches, are very unlikely to represent a motor control variable of direct biological significance. In particular, the nature and the value of the partitioning of forces remain unclear at this point. One may argue that there are also biological reasons to believe that movement dynamics are not the primary variable controlled by cerebellar pathways. Clearly, cerebellar dysfunction not only degrades limb movements and gait, but also causes dysarthria and, in particular, difficulties in the control of extraocular eye muscles (see above). Considering the biomechanics of the human eye, in particular its small moment of inertia and the lack of multiple ‘joints’, it is not easy to see how deficient control of dynamic interaction forces may explain oculomotor deficits associated with cerebellar disorders. On the other hand, the smallness of its inertia and its lack of ‘joints’ do not mean that its dynamics are trivial. The desired speed and accuracy of its response as well as the dynamics of its actuators, the eye muscles, the noisiness and calibration requirements of the motion sensors (e.g., semicircular canal afferents) are all potentially demanding aspects of ocular sensorimotor control. It seems that the cerebellum may have other roles in the control of movement in addition to that of managing joint interaction torques. An earlier influential hypothesis suggested that the regularity of cerebellar microarchitecture may point to a role of cerebellar circuitry in detecting temporal sequences (Ivry and Keele 1989; Braitenberg 1967; Keele and Ivry 1990). To date, the role of the cerebellum as a central timekeeper is still highly controversial. A large body of evidence supports the idea that cerebellar pathways play an important role in controlling temporal movement variables such as the timing between antagonistic muscles during rapid single-joint movements, the relative timing between activation of postural muscles and limb muscles during motor preparation and execution, or the acquisition of a novel temporal relationship of two distinct stimuli as is required in classical conditioning (Topka et al., 1993). There is also some evidence that cerebellar pathways may not only be involved in controlling temporal variables of movement execution but may also be relevant for time perception (Ivry and Keele 1989; Diener et al., 1993; Jueptner et al.,

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1995). On the other hand, attempts to directly localize clock functions to neurons in the inferior olive or cerebellar cortex have failed (Keating and Thach 1997). One major problem with certain cerebellar timing theories has been in relation to the quantitative anatomy of cerebellar cortex. In mammals, the average length of cerebellar cortical parallel fibers allows for detection of, maximally, 10 ms, whereas even rapid movements require temporal control of at least some 200 ms. In order to resolve this issue, Braitenberg and colleagues proposed that several sets of parallel fibers may be involved in processing temporal information in tidal waves that may last up to 200 ms (Braitenberg et al., 1997). However, several theoretical concerns remain and the proposed models require further experimental verification. An alternative set of hypotheses suggests that the orthogonal organization of the cerebellar cortex may point to a role of the cerebellar neuronal machinery in the detection of sensory sequences of a movement rather than controlling primarily temporal aspects (Miall 1997; Bower 1997). This concept emphasizes the role of the cerebellum in the processing of sensory information and has received support from various sources. Functional imaging studies demonstrated that the lateral cerebellar output nucleus is highly activated during a passive and active sensory discrimination task whether or not the task involves movement (Gao et al., 1996), suggesting that the cerebellum pays attention to sensory consequences of other than motor acts. Along these lines, other studies have shown perceptual deficits in patients with cerebellar disorders during the preparation and execution of limb movements, the processing of visual information, as well as during the processing of speech stimuli. Paulin (1993; 1997), also emphasizing the role of the cerebellum in processing sensory information suggested that one major function of the cerebellum may be in constructing neural representations of moving systems, including the body, its parts, and objects in the environment. Additional experimental evidence is required in order to confirm such a theory of cerebellar function, however, the principal concept of the cerebellum monitoring internally and externally generated movements of the body and adapting motor output appropriately seems to represent one model that explains the various seemingly different functions of the cerebellum in controlling eye, limb, and body movements, as well as motor learning and adaptation processes (for a detailed discussion of models of cerebellar functions see Chapter 6).

iReferencesi Ackermann, H., Vogel, M., Petersen, D. and Poremba, M. (1992). Speech deficits in ischaemic cerebellar lesions. J Neurol 239: 223–7. Ackermann, H., Wildgruber, D., Daum, I. and Grodd W. (1998). Does the cerebellum contribute to cognitive aspects of speech production? A functional magnetic resonance imaging (fMRI) study in humans. Neurosci Lett 247: 187–90. Ackermann, H. and Ziegler, W. (1994). Acoustic analysis of vocal instability in cerebellar dysfunctions. Ann Otol Rhinol Laryngol 103: 98–104. Allen, G. I. and Tsukahara, N. (1974). Cerebrocerebellar communication systems. Physiol Rev 54: 957–1006. Amarenco, P., Chevrie, M.C., Roullet, E. and Bousse,r M.G. (1991). Paravermal infarct and isolated cerebellar dysarthria. Ann Neurol 30: 211–13. Arpa, J., Sarria, J., Cruz, M.A. et al., (1995). Electro-oculogram in multiple system and late onset cerebellar atrophies. Rev Neurol 23: 969–74. Babinski, J. (1899). De l’asynergie cerebelleuse. Rev Neurol 7: 806–16. Babinski, J. (1902). Sur le rôle cervelet dans les actes volitionnels nécessitant une succession rapide de mouvements (diadococinésie). Rev Neurol 10: 1013–15. Babinski, J. (1906). Asynergie et inertie cerebelleuse. Rev Neurol 14: 685–6. Bastian, A. J., Martin, T. A., Keating, J.G. and Thach, W.T. (1996). Cerebellar ataxia: abnormal control of interaction torques across multiple joints. J Neurophysiol 76: 492–509. Bastian, A.J., Mink, J.W., Kaufman, B.A. and Thach, W.T. (1998). Posterior vermal split syndrome. Ann Neurol 44: 601–10. Bastian, A.J. and Thach, W.T. (1995). Cerebellar outflow lesions: a comparison of movement deficits resulting from lesions at the levels of the cerebellum and thalamus. Ann Neurol 38: 881–92. Bernstein, N. (1967). The Co-ordination and Regulation of Movement. Oxford: Pergamon Press. Bizzi, E., Polit, A. and Morasso, P. (1976). Mechanisms underlying achievement of final head positions. J. Neurosci 39: 435–44. Boose, A., Dichgans, J. and Topka, H. (1999). Deficits in phasic muscle force generation explain insufficient compensation for interaction torque in cerebellar patients. Neurosci Lett 261: 53–6. Bower, J.M. (1997). Control of sensory data acquisition. Int Rev Neurobiol 41: 489–513. Braitenberg, V. (1967). Is the cerebellar cortex a biological clock in the millisecond range? Prog Brain Res 25: 334–46. Braitenberg, V. (1987). The cerebellum and the physics of movement: some speculations. In Cerebellum and Neuronal Plasticity, ed. M. Glickstein, C. Yeo and J. Stein, pp. 193–207. New York, London: Plenum Press. Braitenberg, V., Heck, D. and Sultan, F. (1997). The detection and generation of sequences as a key to cerebellar function: experiments and theory. Behav Brain Sci 20: 229–45; discussion 245–77.

Pathophysiology of clinical cerebellar signs

Brodal, A. (1981).Neurological Anatomy New York, Oxford: Oxford University Press. Butler, E.G., Horne, M.K. and Hawkins, N.J. (1992). The activity of monkey thalamic and motor cortical neurones in a skilled, ballistic movement. J Physiol (Lond) 445: 25–48. Cannon, S.C. and Robinson, D.A. (1987). Loss of the neural integrator of the oculomotor system from brain stem lesions in monkey. J Neurophysiol 57:1383–409. Carrea, R.M.E. and Mettler, F.A. (1947). Physiologic consequences following extensive removal of cerebellar cortex and deep cerebellar nuclei and effect of secondary cerebral ablation in the primate. J Comp Neurol 87: 169–288. Carrea, R.M.E. and Mettler, F.A. (1955). Function of the brachium conjunctivum and related structures. J. Comp. Neurol 102: 151–322. Dash, B.M. (1995). Role of peripheral inputs in cerebellar tremor. Mov Disord 10: 622–9. Dichgans, J. (1984). Clinical symptoms of cerebellar dysfunction and their topodiagnostical significance. Hum Neurobiol 2: 269–79. Dichgans, J. and Fetter, M. (1993). Compartmentalized cerebellar functions upon the stabilization of body posture. Rev Neurol Paris 149: 654–64. Dichgans, J., von Reutern, G.M. and Römmelt, U. (1978). Impaired suppression of vestibular nystagmus by fixation in cerebellar and non-cerebellar patients. Arch Psychiatr Nervenkr 226: 183–99. Diener, H.C., Dichgans, J., Guschlbauer, B., Bacher, M., Rapp, H. and Klockgether, T. (1992). The coordination of posture and voluntary movement in patients with cerebellar dysfunction. Mov Disord 7: 14–22. Diener, H.C., Hore, J., Ivry, R. and Dichgans, J. (1993). Cerebellar dysfunction of movement and perception. Can J Neurol Sci 20 Suppl. 3: S62–9. Dow, R.S. and Moruzzi, G. (1958).The Physiology and Pathology of the Cerebellum. Minnesota: University of Minnesota Press. Feldman, A.G. (1986). Once more the equilibrium point hypothesis (l model) for motor control. J Motor Behav 18: 17–54. Feldman, A.G., Adamovich, S.V., Ostry, D.J. and Flanagan, J.R. (1990). The origin of the electromyograms – explanations based on the equilibrium point hypothesis. In Multiple Muscle Systems: Biomechanics and Movement Organization, ed. J.M. and S.L.-Y. Winters, Woo, pp. 195–213. New York: Springer-Verlag. Fetter, M., Klockgether, T., Schulz, J.B., Faiss, J., Koenig, E. and Dichgans, J. (1994). Oculomotor abnormalities and MRI findings in idiopathic cerebellar ataxia. J Neurol 241: 234–41. Flament, D. and Hore, J. (1986). Movement and electromyographic disorders associated with cerebellar dysmetria. J Neurophysiol 55: 1221–33. Flament, D. and Hore, J. (1988). Comparison of cerebellar intention tremor under isotonic and isometric conditions. Brain Res 439: 179–86. Flament, D., Vilis, T. and Hore, J. (1984). Dependence of cerebellar tremor on proprioceptive but not visual feedback. Exp Neurol 84: 314–25. Flourens, P. (1824).Recherches Experimentales sur les Proprites et les

Fonctions du Système Nervaux, dans les Animaux Vertebres. Paris: Crevot. Friedemann, H.H., Noth, J., Diener, H.C. and Bacher, M. (1987). Long latency EMG responses in hand and leg muscles: cerebellar disorders. J Neurol Neurosurg Psychiatry 50: 71–7. Gao, J.H., Parsons, L.M., Bower, J.M., Xiong, J., Li, J. and Fox, P.T. (1996). Cerebellum implicated in sensory acquisition and discrimination rather than motor control [see comments]. Science 272: 545–7. Ghez, C. and Sainburg, R. (1995). Proprioceptive control of interjoint coordination. Can J Physiol Pharmacol 73: 273–84. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Philadelphia: F.A. Davis. Gilman, S., Carr, D. and Hollenberg, J. (1976). Kinematic effects of deafferentation and cerebellar ablation. Brain 99: 311–30. Goodkin, H.P., Keating, J.G., Martin, T.A. and Thach, W.T. (1993). Preserved simple and impaired compound movement after infarction in the territory of the superior cerebellar artery. Can J Neurol Sci 20: S93–104. Gorassini, M., Prochazka, A. and Taylor, J.L. (1993). Cerebellar ataxia and muscle spindle sensitivity. J Neurophysiol 70: 1853–62. Gottlieb, G.L., Song, Q., Hong, D.A., Almeida, G.L. and Corcos, D. (1996). Coordinating movement at two joints: a principle of linear covariance. J Neurophysiol 75: 1760–4. Hallett, M. and Massaquoi, S.G. (1993). Physiologic studies of dysmetria in patients with cerebellar deficits. Can J Neurol Sci 20 Suppl. 3: S83–92. Hallett, M., Shahani, B. and Young, R.R. (1975). EMG analysis in patients with cerebellar deficits. J Neurol Neurosurg Psychiatry 38: 1163–9. Hollerbach, J.M. and Flash, T. (1982). Dynamic interactions between limb segments during planar arm movement. Biol. Cybern 44: 67–77. Holmes, G. (1904). On certain tremors in organic brain lesions. Brain 27: 327–75. Holmes, G. (1917). The symptoms of acute cerebellar injuries due to gunshot injuries. Brain 40: 461–535. Holmes, G. (1939). The cerebellum of man. (The Hughling Jackson memorial lecture.) Brain 62: 1–30. Hore, J. and Flament, D. (1986). Evidence that a disordered servolike mechanism contributes to tremor in movements during cerebellar dysfunction. J Neurophysiol 56: 123–36. Hore, J. and Vilis, T. (1984). Loss of set in muscle responses to limb perturbations during cerebellar dysfunction. J Neurophysiol 51: 1137–48. Hore, J., Wild, B. and Diener, H.C. (1991). Cerebellar dysmetria at the elbow, wrist, and fingers. J Neurophysiol 65: 563–71. Ivry, R. (1997). Cerebellar timing systems. Int Rev Neurobiol 41: 555–73. Ivry, R.B. and Keele, S.W. (1989). Timing functions of the cerebellum. J Cogn Neurosci 1: 136–52. Jackson, J.H. (1870). A study of convulsions. In Selected Writings of John Hughlings Jackson (1932), ed. L. Taylor, pp. 8–36. New York: Basic Books.

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Jueptner, M., Rijntjes, M., Weiller, C. et al., (1995). Localization of a cerebellar timing process using PET. Neurology 45: 1540–5. Keating, J.G. and Thach, W.T. (1997). No clock signal in the discharge of neurons in the deep cerebellar nuclei. J Neurophysiol 77: 2232–4. Keele, S.W. and Ivry, R. (1990). Does the cerebellum provide a common computation for diverse tasks? A timing hypothesis. Ann NY Acad Sci 608: 179–207. Klockgether, T., Ludtke, R., Kramer, B. et al., (1998). The natural history of degenerative ataxia: a retrospective study in 466 patients. Brain 121(Pt 4): 589–600. Kornhauser, D., Bromberg, M.B. and Gilman, S. (1982). Effects of lesions of the fastigical nucleus on static and dynamic responses of muscle spindle primary afferents in the cat. J. Neurophysiol 47: 977–86. Lechtenberg, R. and Gilman, S. (1978). Speech disorders in cerebellar disease. Ann Neurol 3: 285–90. Lisberger, S.G. (1988). The neural basis for learning of simple motor skills. Science 242: 728–35. Lu, X., Hikosaka, O. and Miyachi, S. (1998). Role of monkey cerebellar nuclei in skill for sequential movement. J Neurophysiol 79: 2245–54. Luciani, L. (1893). Das Kleinhirn. Neue Studien zur normalen und pathologischen Physiologie. Leipzig: Besold. Manto, M., Godaux, E. and Jacquy, J. (1994). Cerebellar hypermetria is larger when the inertial load is artificially increased. Ann Neurol 35: 45–52. Manto, M., Godaux, E., Jaquy, J. and Hildebrand, J. (1996). Cerebellar hypermetria associated with a selective decrease in the rate of rise of antagonist activity. Ann Neurol 39: 271–4. Massaquoi, S.G. and Hallett, M. (1996). Kinematics of initiating a two-joint arm movement in patients with cerebellar ataxia. Can J Neurol Sci 23: 3–14. Massaquoi, S.G. and Slotine, J.J. (1996). The intermediate cerebellum may function as a wave-variable processor. Neurosci Lett 215: 60–4. Mauritz, K.H., Schmitt, C. and Dichgans, J. (1981). Delayed and enhanced long latency reflexes as the possible cause of postural tremor in late cerebellar atrophy. Brain 104: 97–116. Meyer-Lohmann, J., Hore, J. and Brooks, V.B. (1977). Cerebellar participation in generation of prompt arm movements. J Neurophysiol 40: 1038–50. Miall, R.C. (1997). Sequences of sensory predictions. Behav Brain Sci 20: 258–9. Murdoch, B.E., Chenery, H.J., Stokes, P.D. and Hardcastle, W.J. (1991). Respiratory kinematics in speakers with cerebellar disease. J Speech Hear Res 34: 768–80. Nakamura, R., Kamakura, K., Tadano, Y. et al., (1993). MR imaging findings of tremors associated with lesions in cerebellar outflow tracts: report of two cases. Mov Disord 8: 209–12. Palliyath, S., Hallett, M., Thomas, S.L. and Lebiedowska, M.K. (1998). Gait in patients with cerebellar ataxia. Mov Disord 13: 958–64. Paulin, M.G. (1993). The role of the cerebellum in motor control and perception. Brain Behav Evol 41: 39–50.

Paulin, M.G. (1997). Neural representations of moving systems. Int Rev Neurobiol 41: 515–33. Pierrot-Deseilligny, C., Amarenco, P., Roullet, E. and Marteau, R. (1990). Vermal infarct with pursuit eye movement disorders. J Neurol Neurosurg Psychiatry 53: 519–21. Robinson, D.A. (1976). Adaptive gain control of vestibuloocular reflex by the cerebellum. J. Neurophysiol 39: 954–69. Sainburg, R.L., Ghez, C. and Kalakanis, D. (1999). Intersegmental dynamics are controlled by sequential anticipatory, error correction, and postural mechanisms. J Neurophysiol 81: 1045–56. Sainburg, R.L., Ghilardi, M.F., Poizner, H. and Ghez, C. (1995). Control of limb dynamics in normal subjects and patients without proprioception. J Neurophysiol 73: 820–35. Sainburg, R.L., Poizner, H. and Ghez, C. (1993). Loss of proprioception produces deficits in interjoint coordination. J Neurophysiol 70: 2136–47. Schmahmann, J.D. and Sherman, J.C. (1998). The cerebellar cognitive affective syndrome. Brain 121(Pt 4): 561–79. Schneider, K. and Zernicke, R.F. (1990). A Fortran package for the planar analysis of limb intersegmental dynamics from spatial coordinate–time data. Adv Eng Software 12: 123–8. Silveri, M.C., Leggio, M.G. and Molinari, M. (1994). The cerebellum contributes to linguistic production: a case of agrammatic speech following a right cerebellar lesion. Neurology 44: 2047–50. Spidalieri, G., Busby, L. and Lamarre, Y. (1983). Fast ballistic arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey. II. Effects of unilateral dentate lesion on discharge of precentral cortical neurons and reaction time. J Neurophysiol 50: 1359–79. Thach, W.T., Goodkin, H.P. and Keating, J.G. (1992). The cerebellum and the adaptive coordination of movement. Annu Rev Neurosci 15: 403–42. Topka, H., Konczak, J., Schneider, K., Boose, A. and Dichgans, J. (1998). Multijoint arm movements in cerebellar ataxia: abnormal control of movement dynamics. Exp Brain Res 119: 493–503. Topka, H., Mescheriakov, S., Boose, A. et al., (1999). A cerebellarlike terminal and postural tremor induced in normal man by transcranial magnetic stimulation. Brain 122: 1551–62. Topka, H., Valls-Sole, J., Massaquoi, S.G. and Hallett, M. (1993). Deficit in classical conditioning in patients with cerebellar degeneration. Brain 116: 961–9. Topka, H., Wild, B. and Dichgans, J. (1994). Motor cortex excitability during motor preparation in patients with cerebellar degeneration. Mov Dis 9: 125. Tsujimoto, T., Gemba, H. and Sasaki, K. (1993). Effect of cooling the dentate nucleus of the cerebellum on hand movement of the monkey. Brain Res 629: 1–9. Virji-Babul, N. and Cooke, J.D. (1995). Influence of joint interactional effects on the coordination of planar two-joint arm movements. Exp Brain Res 103: 451–9. Wacholder, K. (1923). Untersuchungen über die Innervation und Koordination der Bewegungen mit Hilfe der Aktionsströme. Pflügers Arch Ges Physiol 199: 625–50. Wessel, K., Tegenthoff, M., Vorgerd, M., Otto, V., Nitschke, M.F. and

Pathophysiology of clinical cerebellar signs

Malin, J.P. (1996). Enhancement of inhibitory mechanisms in the motor cortex of patients with cerebellar degeneration: a study with transcranial magnetic brain stimulation. Electroencephalogr Clin Neurophysiol 101: 273–80. Wild, B., Klockgether, T. and Dichgans, J. (1996). Acceleration deficit in patients with cerebellar lesions. A study of kinematic and EMG-parameters in fast wrist movements. Brain Res 713: 186–91.

Zajac, F.E. (1993). Muscle coordination of movement: a perspective. J Biomechanics 26: 109–24. Zee, D.S., Yee, R.D., Cogan, D.G., Robinson, D.A. and Engel, W.K. (1976). Ocular motor abnormalities in hereditary cerebellar ataxia. Brain 99: 207–34.

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The role of the cerebellum in affect and psychosis Jeremy D. Schmahmann Cognitive/Behavioral Neurology Unit, Massachusetts General Hospital, Boston, USA

Introduction Contemporary investigations provide substantial clinical and experimental support for the hypothesis generated in the early part of the twentieth century that the cerebellum participates in a multitude of nervous system functions beyond that of motor control. Executive functions such as strategy formation, self-monitoring, reasoning, and working memory; visual–spatial learning and analysis; and linguistic processing, among other cognitive paradigms, have all been shown to require a cerebellar contribution both in normal subjects and in patients with acquired cerebellar lesions. The role of the cerebellum in the modulation of emotion also appears to be critically important in both health and disease states. The focus of this chapter, therefore, is directed toward the cerebellar contribution to behaviors associated with the experience and expression of emotion. It summarizes anatomic investigations demonstrating substrates that could sustain a cerebellar contribution to nonmotor as well as motor behaviors, and describes contemporary clinical studies that report changes in behavior, personality, and affect following lesions of the cerebellum. It includes data from morphologic and functional neuroimaging experiments that support a wider role of the cerebellum in nervous system function, and specifically that suggest an important contribution of the cerebellum to the regulation of affect and to psychosis. The chapter concludes with an examination of the dysmetria of thought hypothesis, and discusses how this theory harmonizes with models of cerebellar function proposed by other contemporary theorists. Our thesis is that the cerebellum is an essential node in the distributed neural circuitry subserving cognitive and affective functions as well as other functions traditionally thought to be under cerebellar influence; that there is a topographic organization of behaviors in the

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cerebellum, and that the phylogenetically older fastigial nucleus, vermis, and flocculonodular lobe are the ‘limbic cerebellum’; and that the study of the cerebellum may provide new insights into instinctive behaviors and disorders of emotion and thought. Readers are referred to earlier accounts for more detailed analysis of the cerebellar role specifically in cognitive experience (see, for example, Leiner et al., 1986; Schmahmann and Pandya, 1997; Schmahmann, 1991, 1997a, 1997b, 1998; Schmahmann and Sherman, 1998).

Affect and emotion – a definition The term ‘affect’ was originally used by Freud (1953) to denote the signal of some kind of danger to one’s selfregard and existence. The term has been used more generally for some time, however (MacLean, 1969; Kaplan and Sadock, 1985), to imply a mood state, both as it is subjectively experienced and in its outward manifestations. Affect is embedded within the complex phenomenon of emotion that draws on multiple anatomic and physiologic substrates. As part of the essential behavioral repertoires of all mammals, emotions serve, amongst other things, to protect against harm, provide stimulus for pleasure and for self-preservation, and provide reward for appropriate socialization. The feelings that accompany emotional states are arguably the privilege of higher primates, but in the absence of a common language with nonhuman primates and other species, this is of necessity a matter of conjecture. The experience and display of feelings and emotions have long been of interest to the humanities and to science. In the early part of the current scientific era, Papez (1937) elucidated the anatomic substrates for emotion, dividing emotional life into an interoceptive component (perception of

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emotion) subserved by the cingulate gyrus, and an exteroceptive component (display of emotion) subserved by the hypothalamus. The question posed by the present discussion is whether the cerebellum has been inadvertently omitted from the discussion concerning emotion and its interaction with cognition. Plainly stated, should Papez’s circuit include the cerebellum?

Early accounts Luigi Rolando (1809) demonstrated that cerebellar lesions produced aberrations of movement, but Marie-Jean-Pierre Flourens (1824) concluded that the principal result of cerebellar extirpation is impairment of muscular coordination. Of considerable interest, however, is the following observation of Flourens: in all the animals and at all ages, slight interference with the cerebellum always causes a slight lack of coordination of movement which always increases with the interference; and the total loss of the cerebellum always causes the total loss of those faculties which regulate movement. However, there remains the very peculiar observation that even with this regularity and with this exact repetition of the phenomena, the movements that have become disorderly because of the cerebellum always correspond in the different animals to their dominant movements. In birds that fly much, it is in flight that the disorder mainly appears; in animals that walk it shows up in the gait; in birds that swim in their swimming (quoted in Clarke and O’Malley, 1996, p. 660).

This notion that the cerebellar lesion first impairs the highest achievement of the animal has implications for the current discussion. Could Flourens’ observation also presage the cerebellar role in the human condition, i.e., that the dominant human achievement (implying all that the mind–brain interaction embodies) ‘becomes disorderly’ because of the cerebellar lesion? Case reports of patients with cerebellar agenesis and cerebellar atrophy or degeneration first appeared in the early nineteenth century, starting possibly with Combettes (1831). These have been discussed elsewhere (Schmahmann, 1991, 1997a), but in essence they describe patients in whom intellectual, emotional, social, and other behavioral parameters were sufficiently disordered as to define and/or overwhelm their characters and personality styles. By the mid-twentieth century, patients with cerebellar degeneration were described who developed dementia and/or psychosis particularly in the later stages of the illness (e.g., Akelaitis, 1938; Schut, 1950; Keddie, 1969; see Schmahmann, 1997a). These early accounts were hampered by limited clinicopathological correlations and documentation of possibly coexistent cerebral pathology.

Three hierarchical systems supporting behavior and affect Experimental observations in three different hierarchically organized behaviors and anatomic systems heralded the scientific journey into the domain of a cerebellar contribution to affect. First, there were early indicators of a connection in the cat between cerebellum and arousal. These included descriptions by Moruzzi and Magoun (1949) of flattening of the electroencephalographic pattern by fastigial nucleus stimulation; of Snider et al. (1949) that single shock stimulation of the culmen or fastigial nucleus produced evoked responses in the bulbar reticular formation; of Scheibel et al. (1955) that cerebellar stimulation produced increased, decreased, or altered patterns of electrical activity within the brainstem reticular formation; and of Manzoni et al. (1968) that fastigial stimulation influences the sleep–wake cycle. These and other studies (see Dow and Moruzzi, 1958; Schmahmann, 1997a) explored the core function upon which emotional and cognitive experiences are superimposed, for without an adequate level of alertness there is no conscious engagement in the psychic world or the external environment. Second, the demonstration that autonomic phenomena are influenced by cerebellar stimulation in cats made it apparent that the cerebellum participates in regulating the internal milieu. Autonomic changes included the inhibition of respiratory and vasomotor carotid sinus reflexes by stimulation of the anterior vermis (Moruzzi, 1940), and bradycardia, hypotension, mydriasis, altered gastrointestinal motility, length of gestational period and piloerection were induced by anterior lobe cortex or fastigial nucleus stimulation (Rasheed et al., 1970; Doba and Reis, 1972; Martner, 1975). More recent studies of cerebellar influences on vasomotor tone (Andrezik et al., 1984; Paton and Spyer, 1990; Reis and Golanov, 1997) and on vagally mediated respiratory reflexes (Xu and Frazier, 1997) have confirmed and extended the earlier conclusions that the cerebellum is one of the neural structures that influence autonomic parameters. The third set of early observations that address the affective function of the cerebellum relates to the phenomenon of sham rage that is produced in cats by hypothalamic stimulation (Bard, 1928). Moruzzi (1947) showed that anterior cerebellar stimulation could alter patterns of responsiveness in cats with sham rage, and Zanchetti and Zoccolini (1954) localized this effect to the vermis and fastigial nucleus. Berntson et al. (1973) showed eating and grooming responses in cats by stimulation of the fastigial nucleus and superior cerebellar peduncle. Complex oral behaviors were elicited in the rat

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by fastigial nucleus stimulation (Ball et al., 1974), and selfstimulation (previously considered quintessentially an amygdala function) was induced by stimulation of the rostral anterior lobe and the fastigial nucleus (Micco, 1974). Reis et al. (1973) showed that low intensities of fastigial nucleus stimulation produced grooming and ingestive behaviors, but at higher intensities of stimulation, predatory attack and sham rage were elicited. These early observations in the domains of reticular, autonomic, and limbic behaviors provided experimental support for the notion that cerebellum influences arousal, autonomic behavior, and emotional responsiveness to internal and environmental stimuli. These conclusions, however, did not fit with the motor cerebellar assumptions that were starting to become firmly embedded in the thinking about the cerebellum. The investigations of Luciani (1891) and Ferrier and Turner (1893) in monkeys, along with the clinical reports of influential figures including Babinski (1899) and Holmes (1939) firmly established the cerebellum as an organ of motor control. For reasons that may relate as much to the unmistakable ataxia in certain forms of cerebellar disease as to the divergence of the disciplines of psychiatry and neurology until the emergence of cognitive neuroscience as an integrated field in the last two decades, the conventional notion in the medical and scientific literature has been that the cerebellum is exclusively a motor control organ. This conclusion seems to have been premature.

Further behavioral observations Snider and Stowell (1942) recorded electrical potentials in the cerebellum of a cat following cutaneous stimulation of the periphery and following visual stimuli (flashing lights) and auditory stimuli (clicking sounds). In addition, they observed that stimulation of the cerebral cortex in auditory and visual regions produced cerebellar potentials in regions that overlap those resulting from the peripheral stimulation. These seminal observations led to two main conclusions. First, there is topography of function in cerebellum, confirming the hypothesis of Louis Bolk (1906) derived from comparative morphometric analysis, and laying to rest the unitary concept of cerebellar function that originated with the work of Rolando (1809) and Flourens (1824) and that was further championed by Luciani (1891). Second, the responses to cutaneous auditory and visual stimulation necessitated a revision of the notion that cerebellar afferents relate purely to proprioceptive information. These observations led Snider (1950) to suggest that the cerebellum is the great modulator of

neurologic function and he wondered what its role in neurology and psychiatry may ultimately prove to be. A theoretical advance in the approach to cerebellar function that pertains directly to its role in affect was derived from James Prescott’s unusual conclusions from observations of severe behavioral pathology in Harlow’s monkeys raised with maternal deprivation and sensory isolation (Harlow and McKinney, 1971). Prescott postulated that somatosensory input, particularly movement stimulation, was important in the development of appropriate emotional behaviors, whereas its absence could result in violent aggressive behavior (quoted in Heath, 1997). He concluded that the rocking, head banging, and other selfstimulation behaviors observed in the Harlow’s monkeys were a result of cerebellar ‘denervation supersensitivity’ such that minimal sensory stimuli would provoke unusual behavioral patterns. This hypothesis has not been specifically validated, although Heath (1972) observed abnormal electrical potentials in the cerebellar dentate nucleus and the anterior septum of the Harlow’s monkeys, suggesting an identifiable physiologic correlate of the environmentally induced aberrant behavior. Prescott’s views, however, did prompt investigations into the relationship between cerebellum and aggression. Berman et al. (1978) demonstrated reduced aggression in rhesus monkeys that received destructive lesions that involved the vermis, consistent with the work of Peters and Monjan (1971) showing that aggressive adult squirrel monkeys were rendered tame after lesions that damaged the vermis, but not by lesions of the cerebellar hemispheres alone. Riklan et al. (1974) implanted electrodes over the superior surface of the cerebellum in patients in an attempt to control epilepsy. This group reported that in addition to achieving better seizure control, patients also experienced improvement in aggression, anxiety, and depression, although it is possible that the clinical improvement was related in part to the seizure abatement. Heath et al. (1974) recorded increased neuronal discharges in the cerebellar fastigial nucleus of an emotionally disturbed patient that correlated with the patient’s experience of fear and anger. Similar recordings had been performed by Nashold and Slaughter (1969), who stimulated the cerebellar dentate nucleus and superior cerebellar peduncle and reported that their patient had a subjective experience of an unpleasant sensation and of feeling scared. In 11 patients with severe emotional dyscontrol, Heath (1977) implanted subdural electrodes for chronic stimulation over the superior aspect of the cerebellar cortex and reported extraordinary improvements in the behavior of these patients such that those who were confined to institutions could be released to the community and live essentially normal lives. These experimental

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and therapeutic manipulations in patients have not been replicated, and presently stand alone as an intriguing set of data pointing to a clinically relevant relationship between cerebellum, personality, and mood. The observations derived from clinical reports, physiological studies in patients and animals, and lesion–behavior correlations together constitute a body of information about cerebellar function that is entirely inconsistent with an exclusively motor control view, that developed separate from it, and that has an internal consistency even in its embryonic form that needs to be replicated, verified, and explained.

Anatomic substrates ‘Is emotion a magic product or is it a physiologic process which depends on an anatomic mechanism?’ In attempting to answer his question, Papez (1937) proposed ‘that the hypothalamus, the anterior thalamic nuclei, the gyrus cinguli, the hippocampus, and their interconnections constitute a harmonious mechanism which may elaborate the functions of central emotion, as well as participate in emotional expression.’ The limbic system as defined by Papez has been shown in clinical and experimental studies for over half a century to be critical for the experience and expression of emotion. If the cerebellum has a role in affective experience and expression, then there must of necessity be an appropriate anatomic substrate that can support this. Furthermore, such a substrate should permit the cerebellum to influence the constituent elements of affect, namely, arousal (reticular system), autonomic functions (hypothalamus), and both the interoceptive (cingulate) and exteroceptive components (other limbic structures) of emotional behavior. Furthermore, Damasio (1999) has emphasized that the experience of feeling is fundamentally influenced by one’s conscious awareness and interpretation of one’s own mood. There is thus an interdependency between emotion and cognition, and there are correspondingly extensive interconnections between the limbic system and the cortical association areas (see Pandya and Yeterian, 2000). It is therefore also pertinent to the present discussion of the anatomic systems underlying the cerebellar modulation of affect to consider the cerebellar incorporation into the distributed neural circuits that support cognitive operations in humans and nonhuman primates.

Cerebellar connections with the reticular system Some of the more recent studies demonstrating reciprocal connections between the cerebellum and brainstem

reticular nuclei are as follows. An area of the fastigial nucleus in beagles that produces increases in blood pressure and heart rate when stimulated projects to the medial, lateral, and paramedian reticular nuclei as well as to vestibular nuclei, nucleus tractus solitarius, nucleus gigantocellularis, and nucleus pontis caudalis (Andrezik et al., 1984). In a wheat germ agglutinin–horseradish peroxidase (WGA– HRP) study, the fastigial ‘ocular motor region’ in monkeys was shown to receive afferents from a number of brainstem structures including the mesencephalic and medullary reticular formation, the pontine raphe, and the pontine reticular tegmental nucleus; and it sends efferent fibers to the central mesencephalic reticular formation, the periaqueductal gray, and thalamus (Noda et al., 1990). The lateral reticular nucleus receives afferents mostly from the contralateral rostral fastigial nucleus (Qvist, 1989) and projects to all the cerebellar nuclei (Qvist, 1989; Gonzalo-Ruiz and Leichnetz, 1990). The vermal lobule VII in monkeys (‘ocular motor vermis,’ also neocerebellar vermis) receives afferents from nuclei in the pons, including the pontine raphe and reticular tegmental nucleus of the pons, and sends projections to the fastigial nucleus. Cerebellar nuclear projections that ascend through the superior cerebellar peduncle are also destined for the nonspecific intralaminar thalamic nuclei, most notably central lateral, paracentral, paraventricular, and parafascicular nuclei (Miller and Strominger, 1977; Person et al., 1986; Gonzalo-Ruiz and Leichnetz, 1990; Aumann and Horne, 1996). These thalamic nuclei project widely throughout the cerebral hemispheres and may play a role in arousal and nociception.

Cerebellar connections with the hypothalamus The central anatomic substrates that form the basis of autonomic function include principally the hypothalamus, certain brainstem nuclei, including those subserving taste (nucleus tractus solitarius), as well as structures concerned with pain modulation, including the periaqueductal gray and the intralaminar or nonspecific thalamic nuclei including the central lateral and paracentral nuclei. Dietrichs (1984) and Haines and Dietrichs (1984) demonstrated reciprocal connections between the hypothalamus and the cerebellum. Projections arise from multiple hypothalamic nuclei and terminate in all layers of the cerebellar cortex and in the deep cerebellar nuclei (Fig. 9.1). All the cerebellar nuclei send efferents back to the hypothalamus (Haines et al., 1997). The nucleus tractus solitarius receives heavy projections from the fastigial nucleus (Andrezik et al., 1984), and the fastigial projections to the intralaminar thalamic nuclei have been referred to above.

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Fig. 9.1 Diagrammatic representation of efferent projections of the hypothalamus to the cerebellum and to the pontine nuclei and the lateral reticular nucleus. Those cell groups listed under hypothalamus and not in parentheses are the prime source of hypothalamocerebellar fibers; those listed in parentheses give rise to fewer projections. Cells number 1, 2, and 3 are indicative of (1) hypothalamic cells that project only to the cortex, (2) hypothalamic cells that project to the cortex and send collaterals into the cerebellar nuclei, and (3) hypothalamic cells that project only to the cerebellar nuclei. Cerebellar projections back to the hypothalamus but not shown here arise from all cerebellar nuclei and terminate in the lateral, posterior, and dorsal hypothalamic areas as well as in the dorsomedial and paraventricular hypothalamic nuclei. DHAr, dorsal hypothalamic area; DMNu, dorsomedial hypothalamic nucleus; DNu, dentate (lateral cerebellar) nucleus; ENu, emboliform (anterior interposed) nucleus; FNu, fastigial (medial cerebellar) nucleus; GNu, globose nucleus; LHAr, lateral hypothalamic area; LMNu, lateral mammillary nucleus; MMNu, medial mammillary nucleus; PHAr, posterior hypothalamic area; PVZo, periventricular zone; SMNu, supramammillary nucleus; SupChNu, suprachiasmatic nucleus; SupOpNu, supraoptic nucleus; TMNu, tuberomammillary nucleus; TubCin, tuber cinereum; VMNu, ventromedial nucleus. (From Haines et al., 1997, with modified legend.)

The role of the cerebellum in affect and psychosis

Cerebellar connections with the limbic system Connections between the cerebellum and the limbic system have been shown by both physiological studies and anatomic tracing techniques. The hypothalamus, anterior thalamic nuclei, cingulate gyrus, and hippocampus are closely related to the fiber pathways of the fornix, mammillothalamic tract, median forebrain bundle, and cingulum bundle. The limbic structures are also interconnected with the ventral tegmental area (VTA), periaqueductal gray, and interpeduncular nuclei. Snider and Maiti (1976) described projections from the fastigial nucleus of cat to the VTA, interpeduncular nucleus, periaqueductal gray, and locus ceruleus; the interpositus and dentate nuclei project to the interpeduncular nucleus and the VTA. The mesorhombencephalic component of the VTA has also been shown in monkeys to project back to the cerebellum (Oades and Halliday, 1987). The medial mammillary bodies are closely linked with the limbic anterior thalamic nuclei through the mammillothalamic tract, and they are also in communication with the cerebellum by way of their projections to the nuclei of the basilar pons (Haines and Dietrichs, 1984; Aas and Brodal, 1988). Electrical stimulation of the cerebellum has been shown to produce a number of effects on the physiology of limbic system structures. Cerebellar stimulation studies have resulted in evoked responses in hippocampus and amygdala (Whiteside and Snider, 1953; Heath and Harper, 1974), and altered and/or arrested abnormal or epileptiform discharges in the hippocampus (Mutani, 1967; Babb et al., 1974). Heath et al. (1978) demonstrated in cats and rats that stimulation of the rostral vermis, fastigial nucleus, and intervening midline folia of the cerebellum resulted in facilitation of units in the septal region, inhibition of units in the hippocampus, and a mixed pattern of physiological responses in the amygdala (some units were facilitated, and some inhibited). In contrast, stimulation of the lateral cerebellar hemispheres and dentate nucleus yielded no changes in activity, and stimulation of the posterior vermis produced inconsistent septal facilitation and no hippocampal response. These findings provided support for their contention that ‘the fastigial nucleus is an integral part of the network for emotion and for epilepsy.’ Snider and Maiti (1976) demonstrated that focal stimulation of the septum induced after-discharges in septum as well as in hippocampus and amygdala; however, simultaneous cerebellar stimulation was effective in the elimination of the tonic phase. The reciprocal anatomic connections between cerebellum and hypothalamus discussed above with respect to autonomic functions are also of interest with regard to the

limbic system, because of the phenomenon of sham rage produced by hypothalamic and fastigial nucleus stimulation, and the amelioration of aggression by cerebellar cortical stimulation in humans. In addition to its role in the interoceptive experience of emotions, the cingulate gyrus also supports initiation, motivation, and goal-directed behaviors (Devinsky et al., 1995). The anterior cingulate is further divided into an affect region that modulates autonomic activity and internal emotional responses, and a cognition division engaged in response selection associated with skeletomotor activity and responses to noxious stimuli. It has been implicated in depression (Ebert and Ebmeier, 1996) and in obsessive–compulsive disorder (Rauch et al., 1994). Direct cingulate projections into the feedforward limb of the cerebrocerebellar circuits through the basilar pons were shown in monkeys by Vilensky and Van Hoesen (1981): the rostral cingulate projecting to medial pontine nuclei, the caudal cingulate to more lateral regions. A cingulo-pontine connection in cats was documented by Brodal et al. (1991), who found considerable overlap in the pons between terminal fibers originating in the cingulate gyrus and pontine cells retrogradely labeled following injection of tracer into the cerebellar ventral paraflocculus, leading to the conclusion that the ventral paraflocculus (hemispheric lobule IX) receives limbic input. These studies together reveal that cerebellum is interconnected with multiple different elements of the traditional Papez limbic circuit subserving emotion, although it is important to recognize that there is still a considerable amount of detail missing from our understanding of these pathways.

Cerebellar connections with associative/neocortical systems The available details of the associative connections with the cerebellum have been reviewed previously (Schmahmann, 1996; Schmahmann and Pandya, 1997; Middleton and Strick, 1997). In summary, the cerebellum is linked with the cerebral cortex predominantly via a two-stage feedforward limb in which the pontine nuclei serve as the obligatory synaptic step between the corticopontine pathway and the mossy fiber-mediated pontocerebellar pathway. The twostage feedback system from the cerebellum back to the cerebral cortex has the thalamus as the obligatory synaptic step between the cerebellothalamic and thalamocortical pathways. Both the feedforward and feedback limbs are critical components of this circuit because of the specific information carried to the cerebellum by the input and the cerebral regions that are the recipients of the cerebellar feedback. The associative and paralimbic corticopontine

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pathways in rhesus monkeys were investigated in a series of papers by Schmahmann and Pandya (summarized in Schmahmann, 1996; Schmahmann and Pandya, 1997). In these studies it was demonstrated that there is a specific ordering of corticopontine projections such that each cerebral architectonic area commits fibers to a predictable trajectory in the cerebral white matter and cerebral peduncle that lead to a unique mosaic of patches of terminations in precisely arranged regions of the basilar pons (Fig. 9.2). Thus, the prefrontal cortical projections arise mostly in dorsolateral and dorsomedial prefrontal cortices, and terminate in the medial pons in its rostral third. The posterior parietal projections arise from both gyral and sulcal cortices, including the multimodal caudal regions, and terminate throughout the rostrocaudal extent of the pons in the intermediate and lateral sectors, with a degree of topographic organization determined by the site of origin in the cortex. The temporal lobe projections arise from the multimodal regions of the cortex of the upper bank of the superior temporal sulcus, as well as from the superior temporal gyrus and supratemporal plane, and terminate in the lateral and dorsolateral pontine regions. The parastriate cortices at the dorsomedial and dorsolateral convexity, as well as the posterior parahippocampal gyrus, project to the lateral and dorsolateral pontine regions in a pattern that interdigitates with the other terminations in this area. The cingulate cortex projections to the pons have been described above, and the anterior insular cortex, an important cortical component of the autonomic and pain modulation systems, also has been shown to have pontine connections (Glickstein et al., 1985). The details of the pontocerebellar system await further elucidation, but information derived from earlier work (Brodal, 1979) and more recent trans-synaptic anterograde tracer studies (Strick, 1999) suggests that the prefrontal connections (through the medial pons) project predominantly to focal areas of the neocerebellar hemispheres in crus I and crus II of the ansiform lobule. The climbing fiber system that originates in the inferior olive is the other major source of afferents to the cerebellum. The inferior olive receives little, if any, direct input from the cerebral cortex. Its major source of descending afferents that arise from the red nucleus carry mostly sensorimotor information, but it also receives some associative cortical input indirectly from brainstem reticular nuclei and through the zona incerta that conveys information arising from the cingulate gyrus, prefrontal cortex, and posterior parietal cortices (Shah et al., 1997). Brainstem neurotransmitter systems in the raphe (serotonin), locus ceruleus (norepinephrine), ventral tegmental area (dopamine), and possibly histaminergic structures receive

diffuse cerebral cortical input and in turn convey their efferents to widespread cerebellar regions, conferring perhaps a background tone upon which the mossy fiber and climbing fiber systems exert their more specific and topographically precise influence. The cerebellar cortical feedback to the cerebral cortex originates in the corticonuclear projection and is arranged in an orderly manner with medial cortical areas committing efferents to the midline nuclei (mostly fastigial nucleus), and lateral cerebellar cortices projecting to the lateral (dentate) nuclei (Jansen and Brodal, 1940; Chambers and Sprague, 1955; Haines, 1989). The dentate nucleus itself had for some time been recognized to be architectonically heterogeneous, and Dow (1942) further elaborated upon this by defining a dorsomedial part with minimal gyration and large neurons, and a ventrolateral part that is heavily folded and contains small neurons. Dow recognized that the dorsomedial part was phylogenetically older, whereas the ventrolateral part was more recently evolved. Leiner et al. (1986) later postulated that the newer ventrolateral dentate that developed along with the expanded neocerebellar hemispheres evolved in concert with the cerebral association areas (prefrontal cortex in particular) and would play a role in language processing, a prediction that subsequent studies have tended to support. The projections of the cerebellar nuclei to the thalamus and the thalamocortical projection have been extensively studied, but the availability of transneuronal viral tracers that replicate in synaptic neurons and amplify the detectable signal at second-order sites has provided new insights into this feedback circuitry (Fig. 9.3). These data show that a cortical association area such as area 46 sends efferents (via the pons: Schmahmann and Pandya, 1997) to the cerebellar cortex, which in turn sends information back to area 46 (via the ventrolateral dentate nucleus and thalamus: Middleton and Strick, 1994). It is likely that this pattern is reproduced throughout the cerebrocerebellar system, such that cortical areas projecting to cerebellum receive information back from the cerebellum. This evolving body of anatomic information linking the cerebellum in both feedforward and feedback directions with the association areas of the cerebral cortex that are known to subserve complex behaviors, including executive function, linguistic processing, and visuospatial awareness, provides the final component of the link between the cerebellum and those behaviors (arousal, autonomic, limbic, associative) necessary to support the complex functions inherent in emotion and affect.

The role of the cerebellum in affect and psychosis

Fig. 9.2 Composite color-coded summary diagram illustrating the distribution within the basilar pons of the rhesus monkey of projections derived from associative cortices in the prefrontal (purple), posterior parietal (blue), temporal (red), and parastriate and parahippocampal regions (orange), and from motor, premotor, and supplementary motor areas (green). The medial (A), lateral (B), and ventral (C) surfaces of the cerebral hemisphere are shown at upper left. The plane of section through the basilar pons is at lower left, and the rostrocaudal levels of the pons I through IX are shown on the right. Cerebral areas that have been shown to project to the pons by other investigators using either anterograde or retrograde tracers are depicted in white; those areas studied with both anterograde and retrograde tracers and found to have no pontine projections are shown on the hemispheres in yellow; and those with no pontine projections according to retrograde studies by other investigators are shaded in gray. The dashed lines in the hemisphere diagrams represent the sulcal cortices. In the pons diagrams, the dashed lines represent the pontine nuclei, and the solid lines depict the traversing corticofugal fibers. (From Schamahmann, 1996.)

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Fig. 9.3 Lateral view of a cebus monkey brain (top) to show the location of injections of McIntyre-B strain of herpes simplex virus type 1 in the primary motor cortex (M1arm), ventral premotor cortex (PMVarm), and areas 9 and 46. The resulting retrogradely labeled neurons in the cerebellar dentate nucleus (bottom) are indicated by solid dots. (Adapted from Middleton and Strick, 1997.)

Clinical observations Against the background of the early clinical observations, experimental investigations, and the consideration of anatomic substrates that could subserve a cerebellar contribution to affect, it is useful to consider the contemporary systematic clinical reports that have addressed the nature of the affective disturbances resulting from cerebellar

lesions and that have brought forth a credible challenge to established notions in psychiatry and neurology by postulating a cerebellar role in the pathophysiology of the psychoses. Reports in the 1980s and early 1990s described impairments in subsets of neuropsychological domains in patients with cerebellar degeneration syndromes (BrackeTolkmitt et al., 1989; Grafman et al., 1992; Appollonio et al., 1993) and following phenytoin toxicity (Botez et al., 1985),

The role of the cerebellum in affect and psychosis

but no systematic investigation studied patients with lesions confined to the cerebellum, or investigated the behavioral phenomena outside of selected cognitive processes. In 1998, Schmahmann and Sherman described 20 adult patients with lesions confined to the cerebellum. Thirteen had strokes, three had post-infectious cerebellitis, three had cerebellar cortical atrophy, and one had surgical excision of the vermis and adjacent regions bilaterally for low-grade glioma. The principal findings of the study were that patients with large unilateral or bilateral cerebellar lesions that involved the posterior lobe of the cerebellum (including lobule VI, crus I, crus II, and lobule VIIB; see Schmahmann et al., 1999) manifested a constellation of impairments that were clinically relevant, detectable on bedside mental state tests, and distinct enough to constitute a syndrome consequent upon cerebellar injury that was named the cerebellar cognitive affective syndrome (Fig. 9.4). These characteristically included impairments in executive functions such as planning, set-shifting, verbal fluency, abstract reasoning, and working memory; difficulties with spatial cognition including visual–spatial organization (Fig. 9.5); and memory and language deficits including agrammatism and dysprosodia. As a consequence, patients performed poorly on IQ tests for a period of four to six months following the injury. In addition, an observation that was also striking to nurses, physicians, and family members, was that of changes in personality and affect that were so prominent as to overwhelm the cognitive difficulties in some cases. The affective changes included a combination of passivity, flattening or blunting of emotion, and little observable emotional expression, sometimes simultaneous with or alternating with a disinhibited, inappropriately jocular, flippant, silly or child-like behavior style. These changes in affective display, personality style, and social interactions were most notable when the lesions involved the vermal region of the cerebellum. The phenomenon of mutism that develops within one to two days following surgery involving the inferior aspect of the vermis in children with cerebellar tumors has been reported for over a decade. In their study of these patients with posterior fossa syndrome, Pollack et al. (1995) further described a characteristic behavior change manifesting as a regressive, withdrawn, and apathetic state, sometimes with inconsolable whining and a silliness that persisted for days to weeks. Levisohn et al. (2000) studied children who underwent surgical resection of cerebellar tumors but who did not receive radiation therapy or methotrexate, which are known to produce cognitive impairment. Neuropsychological evaluations in these children showed a variety of disturbances in cognitive performance that

resembled those seen in adults with the cerebellar cognitive affective syndrome (Fig. 9.6), including agrammatism and a mild dysarthria that persisted for up to six months in the subset of children who experienced postoperative mutism. Furthermore, like the adults, those with vermal lesions showed behavioral changes that extended beyond the cognitive domain, and included most prominently a flattening of affect and a silly, disinhibited, regressive quality to their interactions. Riva and Giorgi (2000) have observed similar phenomena in their series of 26 children following resection of cerebellar tumors. In addition to impairment in verbal intelligence and complex language tasks following right cerebellar hemisphere lesions, and deficient nonverbal tasks and prosody after left cerebellar hemisphere lesions, children with vermal involvement developed either postoperative mutism or affective and social behavioral alterations, the severity of which varied in terms of clinical expression. In four patients with vermis medulloblastoma, postoperative behavioral disturbances included irritability, a decreased ability to tolerate the company of others, and a general tendency to avoid physical and eye contact. These features were so prominent in one previously healthy child, and associated with complex repetitive and rhythmic rocking movements, stereotyped linguistic utterances, and general lack of empathy, that she met DSM-IV criteria for a diagnosis of autism. The mother of one patient who underwent resection of a midline astrocytoma reported her surprise at witnessing a prominent and persistent behavior change in her son (Schmahmann, unpublished case). The child’s personality style had been characterized by impulsiveness and assertiveness to the point of aggression from the age of five. The tumor became clinically apparent by virtue of nausea, vomiting, vertigo, and ataxia, and at the age of 12 was resected. The patient’s personality abruptly changed from the moment that he recovered from the anesthesia. He became passive, immature, and child-like, and showed no hint of the previous aggressive behavior. He has remained unchanged for six years. This anecdotal report of a permanent behavior change following cerebellar surgery is consistent with the contemporary studies mentioned above that examined sizable groups of patients, but it also raises for reconsideration the studies on personality, aggression, and emotion performed by the laboratories of Cooper and of Heath in the 1970s, discussed above. These findings have been relegated to obscurity, largely as a consequence of the fact that there was no prevailing or accepted context in which to understand or explain them, and possibly also because they were so startling and at first glance seemingly unbelievable. The demonstration that cerebellar lesion or stimulation

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Fig. 9.4

The role of the cerebellum in affect and psychosis

Fig. 9.5 T2-weighted MRI images of the brain of a patient with infarction in the territory of the posterior inferior cerebellar artery bilaterally, in the horizontal section at left, and in the territory of the right superior cerebellar artery, in the parasagittal image in the center. Perseverative copying of a two-loop diagram is shown on the right. (From Schmahmann and Sherman, 1998.)

experiments produce changes in affect as well as cognitive operations leads directly into the consideration of the potential role for the cerebellum in the psychoses. There have been descriptions of psychoses in patients with cerebellar lesions, either acquired or congenital (as in cerebellar agenesis) that have appeared in the psychiatric and neurologic literature since the early 1800s. In the early 1980s, with the widening utility of computerized tomographic scans, observations concerning cerebellar vermian atrophy or hypoplasia in patients with psychiatric presentations began to appear in the literature (e.g., Lippmann et al., 1982 Moriguchi, 1981), and these findings were compared to post-mortem analyses as well. Vermian atrophy determined by prominence of cerebellar fissures in the midline and enlargement of the fourth ventricle were judged to be anatomical features indicative of cerebellar involvement in these diseases. The report of Heath et al. (1979) of psychopathology in patients with midline cerebellar anomalies identified on computerized tomography (CT) was consistent with these observations, but nevertheless did not provide ultimately conclusive evidence for a causal relationship. The question continued to be addressed in earnest, however, in reviews such as that of S.R. Snider (1982), and in Frick’s (1982) whimsical query as to whether

the cerebellum could possibly be the anatomic substrate of the ego. The observations (Courchesne et al., 1988) of decreased vermal volumes on magnetic resonance imaging (MRI) in early infantile autism (previously known as juvenile schizophrenia), neuronal loss in roof nuclei, and Purkinje cell loss in posterolateral cerebellar cortex in postmortem studies of the same disease (Bauman and Kemper, 1985) added to the debate about a cerebellar involvement in the pathophysiology of these behavioral/psychiatrically defined illnesses. These observations laid the foundation for questioning whether the abnormal cerebellum contributes to or causes the psychopathology of these illnesses based on the fact that the cerebellum is part of the neural circuitry subserving affect and cognition, and because impairment of the normal cerebellar input to the neural circuit results, at least in part, in the ultimate aberrant behaviors.

Neuroimaging observations Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have revealed cerebellar activation by tasks within multiple cognitive domains

Fig. 9.4 Distribution graphs of the z-scores for patients (grouped according to disease type and location), showing their performance on neuropsychological tests. Diamonds represent bilateral postero-inferior cerebellar artery (PICA) infarction; circles represent unilateral PICA infarction; squares represent superior cerebellar artery (SCA) infarction; triangles represent cerebellitis; crosses represent cerebellar cortical atrophy. Intellectual function: Picture, Verbal and Full Scale Intelligence Quotient; Executive function: Wisconsin Card Sorting Test, animal naming, F-A-S-verbal fluency test, Trails A and B; Visuospatial/Visual construction: Hooper Visual Orientation Test, object assembly; Reasoning and abstraction: picture arrangement, arithmetic, picture completion, comprehension, similarities; Verbal and visual memory: Rey complex figure memory, visual reproduction I and II, logical Memory I and II; Attention and orientation: digit symbol; Language function: information, vocabulary, Peabody Picture Vocabulary Test – Revised, Boston Naming Test. (From Schmahmann and Sherman, 1998.)

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neocerebellum with a complex topographic organization that awaits further precise delineation (Fig. 9.7). Imaging studies have also provided some support for the hypothesis that the phylogenetically older cerebellar fastigial nucleus, vermis, and flocculonodular lobes may be the equivalent of the ‘limbic cerebellum.’ The experience and anticipation of pain, thirst, hunger, and smell are closely linked with affective experience, and therefore activation of the cerebellum in studies of the neural correlates of these functions is worthy of consideration here.

Pain

Fig. 9.6 Drawings of the Rey–Osterrieth figure by a six-year-old boy, 11 months following resection of a left cerebellar cystic astrocytoma. (A) Copy, (B) immediate recall, (C) delayed recall (20 minutes). (From Levisohn et al., 2000.)

including executive, linguistic, mnemonic, attentional, and visual/spatial functions in addition to sensorimotor paradigms. There appears to be a functional topography within the cerebellum, as suggested by a meta-analysis of published studies charted onto a semi-flattened map of the human cerebellar cortex (Schmahmann et al., 1998) derived from the three-dimensional MRI atlas of the human cerebellum (Schmahmann et al., 2000). This work suggested that there is a ‘sensorimotor cerebellum’ located in the anterior lobe (rostral to the primary fissure), with a secondary representation in lobules VIII/IX, and a ‘cognitive cerebellum’ in lobule VI and VII at the vermis and in their hemispheric extensions into lobule VI, and crus I and II of lobule VIIA (ansiform lobe) and lobule VIIB. Whereas language is represented in quite a restricted manner at the vermis and right hemisphere in lobule VI and crus I, other cognitive functions are distributed throughout the

In a PET study, Svensson et al. (1997) found significant increases in regional cerebral blood flow (rCBF) in a number of brain regions in subjects who received painful stimuli to the skin or muscles. These included primary (SI) and secondary (SII) somatosensory cortices, inferior parietal lobule, anterior insular, anterior cingulate, lateral prefrontal, and premotor cortices as well as thalamus, lenticular nucleus, and cerebellum. Derbyshire and Jones (1998) used PET to demonstrate significantly increased rCBF responses to tonic noxious stimulation compared with non-noxious stimulation in the anterior cingulate cortex bilaterally, in the lentiform nucleus and posterior insular cortex contralaterally, and in the ipsilateral thalamus, cerebellum, prefrontal cortex, and anterior insular cortex. In a PET study of the brain mechanisms subserving the processing of pain intensity (Coghill et al., 1999), painful thermal stimuli applied to the upper arm activated the anterior insula, anterior cingulate, SII, thalamus, and putamen bilaterally; contralateral primary association cortex and supplementary motor area (SMA); and ipsilateral ventral premotor areas. Pain intensity-related activation was noted in the cerebellum, ipsilateral more than contralateral, in the anterior lobe, and mostly in vermal lobule III and paravermal lobule IV/V (according to the cerebellar atlas of Schmahmann et al., 2000, based on published coordinates). Becerra et al. (1999) observed positive signal changes on fMRI in frontal gyri, anterior and posterior cingulate gyrus, thalamus, motor cortex, somatosensory cortex (SI and SII), SMA, insula, and cerebellum in subjects who received painful thermal stimulation; and low-level negative signal changes were present in the amygdala and hypothalamus. Ploghaus et al. (1999) determined using fMRI that the expectation of pain activated sites within the medial frontal lobe, insular cortex, and cerebellum distinct from, but close to, locations mediating pain experience itself. This suggested that anticipation of pain can in its own right cause the mood changes and behavioral adaptations that exacerbate the suffering

The role of the cerebellum in affect and psychosis

experienced by chronic pain patients, and further implicates the cerebellum in the neural circuitry subserving this system.

Thirst and hunger Cerebellar activation was noted during a recent PET study of thirst in subjects who received intravenous boluses of hypertonic saline (Parsons et al., 2000). Activation was most prominent in the vermal and paravermal regions in both the anterior and posterior lobes, and in the fastigial nucleus. Activation was not related to motor behavior or to a computation of the degree of thirst, but instead seemed to correlate with changes in thirst/satiation state and possibly also the intention for gratification by drinking that is inherent in the consciousness of thirst. Observations with similar significance were noted in the PET study of Tataranni et al. (1999) with respect to the neural correlates of hunger and satiation of appetite. Hunger was associated with significantly increased rCBF in the hypothalamus and a number of limbic and paralimbic structures (hippocampus and parahippocampal, insular, anterior cingulate, and orbitofrontal cortices) as well as in precuneus, thalamus, caudate, putamen, and bilaterally in lobule V of the cerebellum in the paravermian regions (see Schmahmann et al., 2000). Satiation was associated with increased rCBF in more restricted cerebral cortical sites.

Smell Sobel et al. (1998) demonstrated by fMRI that the cerebellum is involved in olfaction in the human. Odorantinduced activation patterns were seen primarily in posterior lateral regions of the hemispheres, whereas the act of sniffing (with no odorant) induced activation primarily in anterior central regions. Sniff volume is inversely proportional to odor concentration, and so the authors hypothesized that the cerebellar role in olfaction is to maintain this inverse proportionality with an accurate and rapid feedback mechanism that monitors the sensory input (odor concentration) and modulates the motor output (sniff volume). Thus, the cerebellum receives olfactory information for modulating the sniff, which in turn modulates further olfactory input.

Mood Early PET studies of emotion by Reiman et al. (1989) revealed activation in the cerebellar vermis by lactateinduced panic in subjects prone to panic disorders. Reiman et al. (1997) later investigated the structural basis

Fig. 9.7 Diagram illustrating topographic organization of functions in the human cerebellum. The results of a metaanalysis of functional imaging studies of the human cerebellum are represented on a semi-flattened map. Cerebellar cortical activation sites are shown as 1-cm diameter circles for arm, leg, mouth, and eye movement (light gray enclosed by black outline), motor imagery (gray), and linguistic processing tasks (black). Roman numerals refer to the cerebellar lobules. The cerebellar fissures are identified by name on the right. (Adapted from Schmahmann et al., 1998.)

of externally generated emotions by performing functional imaging scans while their subjects watched film clips that generated feelings of happiness, sadness, or disgust. Cerebellar activation was noted laterally in both hemispheres (lobule VI), as well as in the occipitotemporoparietal and anterior temporal cortices, hypothalamus, amygdala, and hippocampus. Lane et al. (1997) demonstrated that the emotional responses were generated by sadness rather than happiness or disgust, and lobule IV in the vermis and the intermediate aspect of lobule V on the

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right were activated as well. Beauregard et al. (1998) also demonstrated that, in subjects passively viewing an emotionally laden film clip aimed at inducing a transient state of sadness, there was activation in the cerebellum as well as in medial and inferior prefrontal cortices, middle temporal cortex, and caudate nucleus.

Depression Morphologic differences in the cerebella of patients with depression have been studied using high-resolution, thinslice MRI morphometry. Soares and Mann (1997) reviewed the available literature and concluded that unipolar depression is associated with smaller frontal lobes, cerebellum, caudate and putamen, and bipolar disorder is associated with a larger third ventricle, smaller cerebellum, and perhaps a smaller temporal lobe. Shah et al. (1992) observed a decreased size of the cerebellar vermis and brainstem in major depression. DelBello et al. (1999) detected a significant reduction in size of vermal lobules VIII through X in patients with multiple episodes of depression compared to first-episode patients or healthy volunteers, suggesting that cerebellar vermal atrophy may be a later neurodegenerative event in patients with bipolar disorder who have had multiple affective episodes. Functional imaging studies to date have not specifically focused on the cerebellum in depression, although the PET study of Dolan et al. (1992) reported rCBF to be increased in the cerebellar vermis and decreased in the left anterior medial prefrontal cortex in depressed patients with cognitive impairments compared with patients with depression but no cognitive impairment. Other studies using PET and single photon emission tomographic scans (SPECT) have observed decreased rCBF bilaterally in severe unipolar depression in frontal and anterior temporal cortices, anterior cingulate gyrus, and caudate nucleus (Mayberg et al., 1994; Awata et al., 1998). Moreover, refractory depression unresponsive to medical treatment seems to correlate with hypometabolism in the anterior cingulate cortex (Mayberg et al., 1994; Awata et al., 1998) and prefrontal regions (Awata et al., 1998). The lack of reporting of cerebellar hypoperfusion in depression could conceivably be related in part to the practice of using the cerebellum as the baseline from which cerebral activation or perfusion is subtracted (e.g., Vasile et al., 1997).

Schizophrenia A cerebellar role in schizophrenia has been postulated for some time, as discussed earlier, both as a consequence of the pathoanatomic findings of cerebellar vermal

hypoplasia, large fourth ventricles, and focal lesions of the vermis in patients with psychotic disorders, and because of the considerable body of anatomic and physiologic investigations suggesting a role for the cerebellum in affect, emotion, and aggression. Recent functional imaging studies that have addressed the question of a role for the cerebellum in schizophrenia have done so with the specific intention of addressing the dysmetria of thought hypothesis (Schmahmann, 1991, 1996, 1998), with the understanding that disruption of the anatomic circuits that subserve the cerebellar contribution to cognitive operations can result in the disordered thinking that characterizes schizophrenia. Volkow et al. (1992) studied medicated schizophrenics and found lower absolute and relative metabolism in the cerebellum compared to controls, whereas using PET in neuroleptic-naïve patients with schizophrenia, Andreasen et al. (1997) defined decreased metabolic activity in prefrontal, inferotemporal and parietal cortices, but increased metabolic activity in the cerebellum, thalamus, and retrosplenial cortex. In tests of word list recall (Crespo-Facorro et al., 1999), schizophrenic patients performed at similar levels to controls, but in the schizophrenics there was decreased activation in the cerebellum as well as in the frontal and temporal lobe areas and thalamus. This suggested to the investigators that there is an impairment in the neural circuitry that has been shown to link the cerebellum with the higher order areas of the cerebral hemispheres (Schmahmann, 1991, 1996; Schmahmann and Pandya, 1997; Middleton and Strick, 1997), and they have drawn on this and related findings in support of the dysmetria of thought hypothesis as an integrative concept for the pathophysiology of schizophrenia, although they have amended the terminology (‘cognitive dysmetria,’ Andreasen et al., 1998). The substantial advances in anatomic neuroimaging that MRI provided have been applied to the cerebellum in studies that reveal a relationship between large cerebellar size and greater intelligence (Paradiso et al., 1997), as well as the vermal hypoplasia described in autism and in schizophrenia. Yates et al. (1987) were initially unable to confirm earlier reports linking cerebellar atrophy with schizophrenia, but when they performed automated volumetric measures of subregions of the vermis in schizophrenics (Nopoulos et al., 1999), they found that the anterior lobe vermis was smaller than in controls, and was positively correlated with total cerebellar volume, reduced temporal lobe volume, and full scale IQ. Further, lower cerebellar volume in schizophrenics was associated with the duration of negative and psychotic symptoms and with psychosocial impairment (Wassink et al., 1999). Vermal

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lobules VIII–X have been shown to have decreased volumes in children with attention deficit/hyperactivity disorder (Berquin et al., 1998), fragile X syndrome (Mostofsky et al., 1998), and dyslexia (Nicolson et al., 1999). In schizophrenics the vermal region has been shown to have a decreased size but increased cerebellar blood volume (Loeber et al., 1999). It thus appears that the cerebellar vermal region is consistently implicated in functional imaging studies of arousal, autonomic function, and affect in normal individuals; that it is abnormal morphologically and functionally in patients with psychosis; that it is implicated in disturbances of emotional modulation and psychosis, and in patients with acquired lesions producing pronounced affective impairment. These findings are consistent with the early studies of autonomic and complex behavioral changes in animals subjected to fastigial nucleus stimulation, and there are new and added dimensions considering the recent findings of vermal activation by behaviors that are essential for emotional experience and expression.

Synthesis and hypothesis There is increasing evidence that, in the functional and clinical domains, the cerebellar role in the nervous system extends considerably beyond the conventional notion of motor control, and that, indeed, control of motor performance is but one of a multitude of functions subserved by the cerebellum (in the same way as motor performance is but one of a multitude of functions subserved by the cerebral hemispheres). The prerequisites for emotional experience and expression include arousal, autonomic, and complex behavioral paradigms that are influenced both by the internal milieu and by the external environment. The studies summarized in this chapter together provide evidence that the cerebellum is anatomically linked with systems that subserve these functions; that cerebellar stimulation influences these parameters; and that cerebellar lesions, whether naturally occurring or surgically induced in patients or experimental animals, have an impact on behaviors that define affective experience in normal individuals and psychopathology in disease states. Further, the available experimental and clinical evidence provides some support for the hypothesis concerning topography of function in cerebellum, such that the ‘limbic cerebellum,’ comprised of the vermis, fastigial nucleus, and possibly flocculonodular lobe, is integrally linked with the limbic system, and indeed should be considered an extension of Papez circuit; whereas the ‘cognitive cerebellum’ is linked with para-

limbic areas and association cortices concerned with the integration of emotional experiences into the repertoire of perceptions and behaviors required for normal psychological and social interactions. What the cerebellum is doing in this circuit is a matter of hypothesis and debate. The discussion about localization versus unitary function in the cerebellum is likely to be resolved in the same way as it was for the cerebral cortex. Both are correct and, indeed, they are complementary. The cerebellum occupies, as it were, an intermediate position between the cerebral cortex and the basal ganglia (Table 9.1). Like the cerebral cortex, the cerebellar cortex is truly a cortical structure, with major afferents from external regions, communication between neural elements within cerebellar cortex, and a resultant efferent return to the deep cerebellar nuclei before information leaves the cerebellum for other brain structures. Unlike the cerebral cortex, however, the cerebellum has an essentially uniform, monotonously repetitive architecture. Whereas immunohistochemistry has identified that cerebellar cortex contains anatomically identifiable parasagittal bands (Hawkes et al., 1993) that appear to have connectional and physiologic specificity (Hallem et al., 1999), there are no ‘Brodmann areas’ in the cerebellum. The homogeneity of the cerebellar cortical architecture is more reminiscent of the basal ganglia than it is of the cerebral cortex. The caudate and putamen, for example, have a similar histology and the regions within these structures cannot be readily differentiated from each other using light microscopy. The anatomic connections between the caudate putamen and other brain regions, however, are topographically very precise. There is thus a unitary principle of architecture, but a localizationist organizing principle of the connectivity. In this paradigm, the cerebellum as a cortical structure is interposed between the architectonic heterogeneity and matching connectional specificity of the cerebral cortex, on the one hand, and the architectonic homogeneity (as used here) and the complex connectional heterogeneity of the basal ganglia, on the other. This principle of anatomic organization of the cerebellum (and the functional units of cerebellum, namely, the cerebellar corticonuclear microcomplex, Ito, 1993) directly informs the following hypothesis about the specific function performed by the cerebellum. The histology suggests that the transformations performed by the cerebellum are invariant throughout the structure. There is, however, anatomic specificity linking each cerebral cortical area with unique patterns of termination in the basilar pons, that in turn link with specific regions of cerebellar cortex (although more work on this important link is still needed).

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Table 9.1 Summary of the features that place the cerebellum in an ‘intermediate’ position between cerebral cortex and basal ganglia when viewed from the perspective of architecture, anatomic connections, and functional topography Cerebellum

Caudate–putamen–pallidum

Cerebral cortex

Cytoarchitecture

Essentially a monotonously repeating cortical pattern

Essentially constant throughout

Heterogeneous Varies according to each cortical area

Anatomic specificity

Strongly supported by topography of cerebro-cerebellar pathways and cerebellar corticonuclear projections

Confirmed by topography of cortical and other subcortical connections

Connections tightly determined by cortical architecture

Functional topography

Documented in motor system, and supported by motor/ cognitive/affective–autonomic topography clinically and by functional neuroimaging

Documented in both motor and cognitive domains

Varies, according to each cortical area

Unit transform

Homogeneous Homogeneous Universal Cerebellar Transform (UCT) (Possibly error prevention, detection, correction)

Heterogeneous Unique to each cortical area

Clinical deficit following injury

Universal Cerebellar Impairment (UCI) dysmetria

Impairment common to these structures ? Initiation failure

Impairment unique to each cortical area

Heterogeneity of deficit determined exclusively by connections (Dysmetria of movement manifests as ataxia; dysmetria of thought manifests as cerebellar cognitive–affective syndrome and psychosis)

Heterogeneity of deficit determined exclusively by connections

Heterogeneous deficits determined by the architecture of each cortical area as well as the connections

The cerebellar corticonuclear projection is then transmitted to specific areas of the thalamus before returning to those cerebral areas from which the projection originated. The cerebellum thus performs a universal cerebellar transform (UCT) on the information to which it has access, whether that information subserves arousal, autonomic functions, affective behaviors, cognitive operations, or sensorimotor processes. The larger hypothesis that derives from this concept is that the UCT, or ‘cerebellumizing,’ is matched by unique functional transforms that are specific to other architectonic stations (such as caudate nucleus, area 46 etc.) that comprise the interconnected neural circuits that subserve brain function. Thus, the universal cerebellar transform can be viewed in two ways: (1) how it manifests, and (2) what the computations consist of. With respect to the former, we have previously hypothesized (Schmahmann, 1991, 1996, 1998) that the cerebellum acts to maintain behaviors around a homeostatic baseline, to compare the consequences of

actions with the intended outcome, and to match reality with perceived reality. The cerebellum modulates behaviors and serves as an oscillation dampener, smoothing out performance in all domains. The loss of the UCT then leads to dysmetria, a lack of coordination that then defines the universal cerebellar impairment (UCI). This UCI manifests as dysmetria of movement (or ataxia), dysmetria of spatial orientation (or dysequilibrium), or dysmetria of thought (manifesting as the different elements of the cerebellar cognitive affective syndrome, including psychotic thought and disturbances of emotional experience and expression). Impaired modulation of affect and mismatch of reality with perception of reality are central and defining features of the psychoses including schizophrenia and related disorders, and bipolar affective disorders and related illnesses, and so the role of the cerebellum in the pathophysiology of these conditions becomes plausible in the context of the dysmetria of thought hypothesis. The nature of the computation performed by the

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corticonuclear microcomplex is yet more uncertain, but it must of necessity be derived from an understanding of the neuronal architecture, physiology, and chemistry. Ito (1993, 1997) has proposed that the cerebellum provides an internal model for neural function including cognition and emotion, and that it acts as a controller of these systems using adaptive mechanisms for the detection of errors. In addition to error detection, it is possible that the cerebellar corticonuclear microcomplex is equipped for the prevention and correction of errors in order to maintain behavior around the intended homeostatic baseline. It cannot be stated presently which of a number of theories (see Schmahmann, 1997b) is correct concerning the essential computations performed by the cerebellum, or whether the dysmetria of thought hypothesis derived in part from the anatomic organization of the cerebrocerebellar system is an overarching concept that satisfactorily incorporates the various theories. The absence of this central piece of knowledge, however, does not diminish the importance of the recent advances in understanding the contributions that the cerebellum makes to the organization of behavior, including the modulation of affect. The theoretical paradigm shift that the cerebellum performs its unique computations in a topographically precise manner on diverse streams of information relating to almost all aspects of behavior has brought to life the ideas and contributions of earlier investigators, and opened the way to a new era of cognitive neuroscience in the new millennium, one that focuses on the cerebellar role in affective disorders, and more specifically on the role of the cerebellum in the pathophysiology of the elusive psychotic disorders.

Acknowledgments This chapter is reprinted in large part from Schmahmann (2000), Journal of Neurolinguistics, supported in part by a grant from the McDonnell – Pew Program in Cognitive Neuroscience. The constructive reviews of the original manuscript by Lawrence M. Parsons, PhD and Deepak N. Pandya, MD are gratefully acknowledged.

xReferencesx Aas, J-E. and Brodal, P. (1988). Demonstration of topographically organized projections from the hypothalamus to the pontine nuclei: an experimental study in the cat. J Comp Neurol 268: 313–28. Akelaitis, A.J. (1938). Hereditary form of primary parenchymatous

atrophy of the cerebellar cortex associated with mental deterioration. Am J Psychiat 94, 1115–40. Andreasen, N.C., O’Leary, D.S., Flaum, M. et al. (1997). Hypofrontality in schizophrenia: distributed dysfunctional circuits in neuroleptic-naïve patients. Lancet 349, 1730–4. Andreasen, N.C., Paradiso, S. and O’Leary, D.S. (1998). ‘Cognitive dysmetria’ as an integrative theory of schizophrenia: a dysfunction in cortical-subcortical-cerebellar circuitry? Schizophr Bull 24: 203–18. Andrezik, J.A., Dormer, K.J., Foreman, R.D. and Person, R.J. (1984). Fastigial nucleus projections to the brain stem in beagles: pathways for autonomic regulation. Neuroscience 11: 497–507. Appollonio, I.M., Grafman, J., Schwartz, V., Massaquoi, S. and Hallett, M. (1993). Memory in patients with cerebellar degeneration. Neurology 43: 1536–44. Aumann, T.D. and Horne, M.K. (1996). Ramification and termination of single axons in the cerebellothalamic pathway of the rat. J Comp Neurol 376: 420–30. Awata S., Ito, H., Konno, M. et al. (1998). Regional cerebral blood flow abnormalities in late-life depression: relation t refractoriness and chronification. Psychiat Clin Neurosci 52: 97–105. Babb, T.L., Mitchell, A.G. Jr and Crandall, P.H. (1974). Fastigiobulbar and dentatothalamic influences on hippocampal cobalt epilepsy in the cat. Electroencephalogr Clin Neurophysiol 36: 141–54. Babinski, J.F.F. (1899). De l’asynergie cérébelleuse. Rev Neurol 7: 806–16. Ball, G., Micco, D. Jr and Berntson, G. (1974). Cerebellar stimulation in the rat. Complex stimulation bound oral behaviors and self-stimulation. Physiol Behav 13: 123–7. Bard, P. (1928). A diencephalic mechanism for the expression of rage with special reference to the sympathetic nervous system. Am J Physiol 84: 490. Bauman, M. and Kemper, T.L. (1985). Histoanatomic observations of the brain in early infantile autism. Neurology 35: 866–74. Beauregard, M., Leroux, J.M., Bergman, S. et al. (1998). The functional neuroanatomy of major depression: an fMRI study using an emotional activation paradigm. Neuroreport 9: 3253–8. Becerra, L.R., Breiter, H.C., Stojanovic, M. et al. (1999). Human brain activation under controlled thermal stimulation and habituation to noxious heat: an fMRI study. Magn Reson Med 41: 1044–57. Berman, A.J., Berman, D. and Prescott, J.W. (1978). The effects of cerebellar lesions on emotional behavior in the rhesus monkey. In The Cerebellum, Epilepsy and Behavior, ed. I.S. Cooper, M. Riklan and M. Snider. New York: Plenum Press. Reprinted in The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: 111–19, 1997. Berntson, G., Potolicchi, S. Jr and Miller, N. (1973). Evidence for higher functions of the cerebellum: eating and grooming elicited by cerebellar stimulation in cats. Proc Natl Acad Sci USA 70: 2497–9. Berquin, P.C., Giedd, J.M., Jacobsen, L.K. et al. (1998). Cerebellum in attention-deficit hyperactivity disorder: a morphometric MRI study. Neurology 50: 1087–93.

153

154

J.D. Schmahmann

Bolk, L. (1906). Das Cerebellum der Säugetiere. Haarlem: De Erven F. Bohn. Botez, M.I., Gravel, J., Attig, E. and Vezina J-L. (1985). Reversible chronic cerebellar ataxia after phenytoin intoxication: possible role of cerebellum in cognitive thought. Neurology 35: 1152–7. Bracke-Tolkmitt, R., Linden, A., Canavan, A.G.M. et al. (1989). The cerebellum contributes to mental skills. Behav Neurosci 103: 442–6. Brodal, P. (1979). The pontocerebellar projection in the rhesus monkey: an experimental study with retrograde axonal transport of horseradish peroxidase. Neuroscience 4: 193–208. Brodal, P., Bjaali, J.G. and Aas, J.E. (1991). Organization of cinguloponto-cerebellar connections in the cat. Anat Embryol (Berl) 184: 245–54. Chambers, W.W. and Sprague, J.M. (1955). Functional localization in the cerebellum. I. Organization in longitudinal corticonuclear zones and their contribution to the control of posture, both extrapyramidal and pyramidal. J Comp Neurol 103: 105–29. Clarke, E. and O’Malley C.D. (1996). The Human Brain and Spinal Cord. San Francisco: Norman Publishing Co. Coghill, R.C., Sang, C.N., Maisog, J.M. and Iadarola, M.J. (1999). Pain intensity processing within the human brain: a bilateral, distributed mechanism. J Neurophysiol 82: 1934–43. Combettes (1831). Absence complète du cervelet, des pédoncules postérieurs et de la protubérance cérébrale chez une jeune fille morte dans sa onzième année. Bull Soc Anat de Paris 5: 148–57. Courchesne, E., Yeung-Courchesne, R., Press, G.A., Hesselink, J.R. and Jernigan, T.L. (1988). Hypoplasia of cerebellar vermal lobules VI and VII in autism. N Engl J Med 318: 1349–54. Crespo-Facorro, B., Paradiso, S., Andreasen, N.C. et al. (1999). Recalling word lists reveals ‘cognitive dysmetria’ in schizophrenia: a positron emission tomography study. Am J Psychiatry 156: 386–92. Damasio, A.R. (1999). The Feeling of What Happens: Body and Emotion in the Making of Consciousness. New York: Harcourt Brace. DelBello, M.P., Strakowski, S.M., Zimmerman, M.E., Hawkins, J.M. and Sax, K.W. (1999). MRI analysis of the cerebellum in bipolar disorder: a pilot study. Neuropsychopharmacology 21: 63–8. Derbyshire, S.W. and Jones, A.K. (1998). Cerebral responses to a continual tonic pain stimulus measured using positron emission tomography. Pain 76: 127–35. Devinsky, O., Morrell, M.J. and Vogt, B.A. (1995). Contributions of anterior cingulate cortex to behaviour. Brain 118: 279–306. Dietrichs, E. (1984). Cerebellar autonomic function: direct hypothalamocerebellar pathway. Science 223: 591–3. Doba, N. and Reis, D.J. (1972). Changes in regional blood flow and cardiodynamics evoked by electrical stimulation of the fastigial nucleus in the cat and their similarity to orthostatic reflexes. J Physiol (Lond) 227: 729–47. Dolan, R.J., Bench, C.J., Brown, R.G., Scott, L.C., Friston, K.J. and Frackowiak, R.S. (1992). Regional cerebral blood flow abnormalities in depressed patients with cognitive impairment. J Neurol Neurosurg Psychiatry 55: 768–73.

Dow, R.S. (1942). The evolution and anatomy of the cerebellum. Biol Rev Cambridge Philosoph Soc 17: 179–220. Dow, R.S. and Moruzzi, G. (1958). The Physiology and Pathology of the Cerebellum. Minneapolis: University of Minnesota Press. Ebert, D. and Ebmeier K.P. (1996). The role of the cingulate gyrus in depression: from functional anatomy to neurochemisty. Biol Psychiatry 39: 1044–50. Ferrier, D. and Turner, W.A. (1893). A record of experiments illustrative of the symptomatology and degenerations following lesions of the cerebellum and its peduncles and related structures in monkeys. Philosoph Trans Roy Soc, s B 185: 719–78. Flourens, P. (1824). Recherches experimentales sur les Proprietes et les Fonctions du Systeme Nerveux dons les Animaux Vertebres. Paris: Crevot. Freud, S. (1953). Neuropsychosis of Defense, Standard Edition of the Complete Psychological Works of Sigmund Freud, Vol. 3, p. 47. London: Hogarth Press. Frick, R.B. (1982). The ego and the vestibulocerebellar system. Psychoanal Q 51: 93–122. Glickstein, M., May, J.G. III and Mercier, B.E. (1985). Corticopontine projection in the macaque: the distribution of labelled cortical cells after large injections of horseradish peroxidase in the pontine nuclei. J Comp Neurol 235: 343–59. Gonzalo-Ruiz, A. and Leichnetz, G.R. (1990). Connections of the caudal cerebellar interpositus complex in a new world monkey (Cebus apella). Brain Res Bull 25: 919–27. Grafman, J., Litvan, I., Massaquoi, S., Stewart, M., Sirigu, A. and Hallett, M. (1992). Cognitive planning deficit in patients with cerebellar atrophy. Neurology 42: 1493–6. Haines, D.E. (1989). HRP study of cerebellar corticonuclearnucleocortical topography of the dorsal culminate lobule – lobule V – in a prosimian primate (Galago): with comments on nucleocortical cell types. J Comp Neurol 2: 274–92. Haines, D.E. and Dietrichs, E. (1984). An HRP study of hypothalamo-cerebellar and cerebello-hypothalamic connections in squirrel monkey (Saimiri scieureus). J Comp Neurol 229: 559–75. Haines, D.E., Dietrichs, E., Mihailoff, G.A. and McDonald, E.F. (1997). The cerebellar-hypothalamic axis: basic circuits and clinical observations. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Hallem, J.S., Thompson, J.H., Gundappa-Sulur, G., Hawkes, R., Bjaalie, J.G. and Bower, J.M. (1999). Spatial correspondence between tactile projection patterns and the distribution of the antigenic Purkinje cell markers anti-zebrin I and anti-zebrin II in the cerebellar folium crus IIA of the rat. Neuroscience 93: 1083–94. Harlow, H.F. and McKinney, W.T. (1971). Nonhuman primates and psychoses. J Autism Chilhood Schizophrenia 1: 368–75. Hawkes, R., Blyth, S., Chockkan, V., Tano, D., Ji, Z. and Mascher, C. (1993). Structural and molecular compartmentation in the cerebellum. Can J Neurol Sci 20 (Suppl 3): S29–35. Heath, R.G. (1972). Electroencephalographic studies in isolationraised monkeys with behavioral impairment. Dis Nerv Sys 33: 157–63.

The role of the cerebellum in affect and psychosis

Heath, R.G. (1977). Modulation of emotion with a brain pacemaker. Treatment for intractable psychiatric illness. J Nerv Ment Dis 165: 300–17. Heath, R.G. (1997). Foreword. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: xxiii–xxv. Heath, R.G., Cox, A.W. and Lustick, L.S. (1974). Brain activity during emotional states. Am J Psychiatry 131: 858–62. Heath, R.G., Dempesy, C.W., Fontana, C.J. and Myers, W.A. (1978). Cerebellar stimulation: effects on septal region, hippocampus, and amygdala of cats and rats. Biol Psychiatry 13: 501–29. Heath, R.G., Franklin, E.D. and Shraberg, D. (1979). Gross pathology of the cerebellum in patients diagnosed and treated as functional psychiatric disorders. J Nerv Ment Dis 167: 585–92. Heath, R.G. and Harper, J.W. (1974). Ascending projections of the cerebellar fastigial nucleus to the hippocampus, amygdala, and other temporal lobe sites: evoked potential and histological studies in monkeys and cats. Exp Neurol 45: 2682–7. Holmes, G. (1939). The cerebellum of man (Hughlings Jackson Memory Lecture). Brain 62: 1–30. Ito, M. (1993). Cerebellar learning in vestibulo-ocular reflex. Trends Cogn Sci 2: 313–21. Ito, M. (1997). Cerebellar microcomplexes. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Jansen, J. and Brodal, A. (1940). Experimental studies on the intrinsic fibers of the cerebellum. II. The cortico-nuclear projection. J Comp Neurol 73: 267–321. Kaplan, H.I. and Sadock, B.J. (1985). Modern Synopsis of Comprehensive Textbook of Psychiatry/IV, 4th edn. Baltimore: Williams and Wilkins. Keddie, K.M.G. (1969). Hereditary ataxia, presumed to be of the Menzel type, complicated by paranoid psychosis, in a mother and two sons. J Neurol Neurosurg Psychiatry 32: 82–7. Lane, R.D., Reiman, E.M., Ahern, G.L., Schwartz, G.E. and Davidson, R.J. (1997). Neuroanatomical correlates of happiness, sadness, and disgust. Am J Psychiatry 154: 926–33. Leiner, H.C., Leiner, A.L. and Dow, R.S. (1986). Does the cerebellum contribute to mental skills? Behav Neurosci 100: 443–54. Levisohn, L., Cronin-Golomb, A. and Schmahmann, J.D. (1997). Neuropsychological sequelae of cerebellar tumors in children. Soc Neurosci Abstr 23: 496. Levisohn, L., Cronin-Golomb, A. and Schmahmann, J.D. (2000). Neuropsychological consequences of cerebellar tumour resection in children: cerebellar cognitive affective syndrome in a paediatric population. Brain 123: 1041–50. Lippmann, S., Manshadi, M., Baldwin, H., Drasin, G., Rice, J. and Alrajech, S. (1982). Cerebellar vermis dimensions on computerized tomographic scans of schizophrenic and bipolar patients. Am J Psychiat 139: 667–8. Loeber, R.T., Sherwood, A.R., Renshaw, P.F., Cohen, B.M. and Yurgelun-Todd, D.A. (1999). Differences in cerebellar blood volume in schizophrenia and bipolardisorder. Schizophr Res 37: 81–9. Luciani L. (1891). Il Cerbelletto: Nuovi Studi di Fisiologia Normale e Pathologica. Firenze: Le Monnier.

MacLean, P. (1969). The hypothalamus and emotional behavior. In The Hypothalamus, ed. W. Haymaker, E. Anderson and W.J.H. Nauta, pp. 659–78. Springfield, IL: Charles C Thomas. Manzoni, T., Sapienza, S. and Urbano, A. (1968). EEG and behavioral sleeplike effects induced by the fastigial nucleus in unrestrained unanesthetized cats. Arch Ital Biol 106: 61–72. Martner, J. (1975). Cerebellar influences on autonomic mechanisms. Acta Physiol Scand 425: 1–42. Mayberg, H.S., Brannan, S.K., Mahurin, R.K. et al. (1997). Cingulate function in depression: a potential predictor of treatment response. Neuroreport 8: 1057–61. Mayberg, H.S., Lewis, P.J., Regenold, W. and Wagner, H.N. Jr (1994). Paralimbic hypoperfusion in unipolar depression. J Nucl Med 35: 929–34. Micco, D.J. Jr (1974). Complex behaviors elicited by stimulation of the dorsal pontine tegmentum in rats. Brain Res 75: 172–6. Middleton, F.A. and Strick, P.L. (1994). Anatomical evidence for cerebellar and basal ganglia involvement in higher cognitive function. Science 266: 458–61. Middleton, F.A. and Strick, P.L. (1997). Cerebellar output channels. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: 61–82. Miller, R.A. and Strominger, N.L. (1977). An experimental study of the efferent connections of the superior cerebellar peduncle in the rhesus monkey. Brain Res 133: 237–50. Moriguchi, I. (1981). A study of schizophrenic brains by computerized tomography scans. Folia Psychiat Neurol Jpn 35: 55–72. Moruzzi, G. (1940). Paleocerebellar inhibition of vasomotor and respiratory carotid sinus reflexes. J Neurophysiol 3: 20–32. Moruzzi, G. (1947). Sham rage and localized autonomic responses elicited by cerebellar stimulation in the acute thalamic cat. Proceedings of the XVII International Congress on Physiology, Oxford, pp. 114–15. Moruzzi, G. and Magoun, H.W. (1949). Brainstem reticular formation and activation of the EEG. Electroencephalogr Clin Neurophysiol 1: 455–73. Mostofsky, S.H., Mazzocco, M.M., Aakaly, G. et al. (1998). Decreased cerebellar posterior vermis size in fragile X syndrome: correlation with neurocognitive performance. Neurology 50: 121–30. Mutani., R. (1967). Cobalt experimental hippocampal epilepsy in the cat. Epilepsia 8: 223–40. Nashold, B.S. and Slaughter, D.G. (1969). Effects of stimulating or destroying the deep cerebellar regions in man. J Neurosurg 31: 172–86. Nicolson, R.I., Fawcett, A.J., Berry, E.L., Jenkins, I.H., Dean, P. and Brooks, D.J. (1999). Association of abnormal cerebellar activation with motor learning difficulties in dyslexic adults. Lancet 353: 1662–7. Noda, H., Sugita, S. and Ikeda, Y. (1990). Afferent and efferent connections of the oculomotor region of the fastigial nucleus in the macaque monkey. J Comp Neurol 302: 330–48. Nopoulos, P.C., Ceilley, J.W., Gailis, E.A. and Andreasen, N.C. (1999). An MRI study of cerebellar vermis morphology in patients with schizophrenia: evidence in support of the cognitive dysmetria concept. Biol Psychiatry 46: 703–11.

155

156

J.D. Schmahmann

Oades, R.D. and Halliday, G.M. (1987). Ventral tegmental (A10) system: neurobiology. 1. Anatomy and connectivity. Brain Res 434: 117–65. Pandya, D.N. and Yeterian, E.G. (2000). The anatomical substrates of emotional behavior: the role of the cerebral cortex. In Handbook of Neuropsychology, Vol. 5, Emotional Behavior and its Disorders, ed. F. Boller, and J. Grafman. New York: Elsevier. Papez, J.W. (1937). A proposed mechanism of emotion. Arch Neurol Psychiatry 38: 725–44. Paradiso, S., Andreasen, N.C., O’Leary, D.S., Arndt, S. and Robinson, R.G. (1997). Cerebellar size and cognition: correlations with IQ, verbal memory, and motor dexterity. Neuropsychiatry Neuropsychol Behav Neurol 10: 1–8. Parsons, L.M., Denton, D., Egan, G. et al. (2000). Neuroimaging evidence implicating cerebellum in support of sensory/cognitive processes associated with thirst. Proc Natl Acad Sci USA 97: 2332–6. Paton, J.F. and Spyer, K.M. (1990). Brain stem regions mediating the cardiovascular responses elicited from the posterior cerebellar cortex in the rabbit. J Physiol (Lond) 427: 533–52. Person, R.J., Andrezik, J.A., Dormer, K.J. and Foreman, R.D. (1986). Fastigial nucleus projections in the midbrain and thalamus in dogs. Neuroscience 18: 105–20. Peters, M. and Monjan, A.A. (1971). Behavior after cerebellar lesions in cats and monkeys. Physiol Behav 6: 205–6. Ploghaus, A., Tracey, I., Gati, J.S. et al. (1999). Dissociating pain from its anticipation in the human brain. Science 284: 1979–81. Pollack, I.F., Polinko, P., Albright, A.L., Towbin, R. and Fitz, C. (1995). Mutism and pseudobulbar symptoms after resection of posterior fossa tumors in children: incidence and pathophysiology. Neurosurgery 37: 885–93. Qvist, H. (1989). The cerebellar nuclear afferent and efferent connections with the lateral reticular nucleus in the cat as studied with retrograde transport of WGA-HRP. Anat Embryol (Berl) 179(5): 471–83. Rasheed, B.M.A., Manchanda, S.K. and Anad, B.K. (1970). Effects of the stimulation of paleocerebellum on certain vegetative functions in the cat. Brain Res 20: 293–308. Rauch, S.L., Jenike, M.A., Alpert, N.M. et al. (1994). Regional cerebral blood flow measured during symptom provocation in obsessive–compulsive disorder using oxygen 15-labeled carbon dioxide and positron emission tomography. Arch Gen Psychiatry 1: 62–70. Reiman, E.M., Lane, R.D., Ahern, G.L. et al. (1997). Neuroanatomical correlates of externally and internally generated human emotion. Am J Psychiatry 154: 918–25. Reiman, M., Raichle, M.E., Robins E. et al. (1989). Neuroanatomical correlates of a lactate-induced anxiety attack. Arch Gen Psychiatry 46: 493–500. Reis, D.J., Doba, N. and Nathan, M.A. (1973). Predatory attack, grooming and consummatory behaviors evoked by electrical stimulation of cat cerebellar nuclei. Science 182: 845–7. Reis, D.J. and Golanov, E.V. (1997). Autonomic and vasomotor regulation in The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: 121–49.

Riklan, M., Marisak, I. and Cooper, I.S. (1974). Psychological studies of chronic cerebellar stimulation in man. In The Cerebellum Epilepsy and Behavior, ed. I.S. Cooper, M. Riklan and R.S. Snider, pp. 285–342 . New York: Plenum Press. Riva, D. and Giorgi, C. (2000). The cerebellum contributes to higher function during development: evidence from a series of children surgically treated for posterior fossa tumors. Brain 123: 1051–61. Rolando, L. (1809). Saggio sopra la Vera Struttura del Cervello dell’Uomo e degli Animali e sopra le Funzioni del Sistema Nervoso. Sassari: Stampeía da S.S.R.M. Privilegiata. (Quoted in Dow and Moruzzi, 1958.) Scheibel, M., Scheibel, A., Mollica, A. and Moruzzi, G. (1955). Convergence and interaction of afferent impulses on single units of reticular formation. J Neurophysiol 18: 309–31. Schmahmann, J.D. (1991). An emerging concept: the cerebellar contribution to higher function. Arch Neurol 48: 1178–87. Schmahmann, J.D. (1996). From movement to thought: anatomic substrates of the cerebellar contribution to cognitive processing. Hum Brain Map 4: 174–98. Schmahmann, J.D., ed. (1997a). The Cerebellum and Cognition, San Diego: Academic Press. Int Rev Neurobiol 41. Schmahmann, J.D. (1997b) Rediscovery of an early concept. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: 3–27. Schmahmann, J.D. (1998). Dysmetria of thought. Clinical consequences of cerebellar dysfunction on cognition and affect. Trends Cogn Sci 2: 362–70. Schmahmann, J.D. (2000). The role of the cerebellum in affect and psychosis. J Neuroling 13: 189–214. Schmahmann, J.D., Doyon, J., Toga, A.W., Petrides, M. and Evans, A.C. (2000). MRI Atlas of the Human Cerebellum. San Diego: Academic Press. Schmahmann, J.D., Loeber, R.T., Marjani, J. and Hurwitz, A.S. (1998). Topographic organization of cognitive function in the human cerebellum. A meta-analysis of functional imaging studies. NeuroImage 7: S721. Schmahmann, J.D. and Pandya, D.N. (1989). Anatomical investigation of projections to the basis pontis from posterior–parietal association cortices in rhesus monkey. J Comp Neurol 289: 53–73. Schmahmann, J.D. and Pandya, D.N. (1997). The cerebrocerebellar system. In The Cerebellum and Cognition, ed. J.D. Schmahmann. San Diego: Academic Press. Int Rev Neurobiol 41: 31–60. Schmahmann, J.D. and Sherman, J.C. (1998). The cerebellar cognitive affective syndrome. Brain 121: 561–79. Schut, J.W. (1950). Hereditary ataxia. Arch Neurol Psychiatry 63: 535–68. Shah, S.A., Doraiswamy, P.M., Husain, M.M. et al. (1992). Posterior fossa abnormalities in major depression: a controlled magnetic resonance imaging study. Acta Psychiatr Scand 85: 474–9. Shah, V.S., Schmahmann, J.D., Pandya, D.N. and Vaher, P.R. (1997). Associative projections to the zona incerta: possible anatomic substrates for extension of the Marr–Albus hypothesis to nonmotor learning. Soc Neurosci Abstract 23: 1829. Snider, R.S. (1950). Recent contributions to the anatomy and physiology of the cerebellum. Arch Neurol Psych 64: 196–219.

The role of the cerebellum in affect and psychosis

Snider, R.S. and Maiti, A. (1976). Cerebellar contributions to the Papez circuit. J Neurosci Res 2: 133–46. Snider, R.S., McCulloch, W.S. and Magoun, H.W. (1949). A cerebello-bulbo-reticular pathway for suppression. J Neurophysiol 12: 325–34. Snider, R.S. and Stowell, A. (1942). Evidence of tactile sensibility in the cerebellum of the cat. Fed Proc 1: 82. Snider, S.R. (1982). Cerebellar pathology in schizophrenia – cause or consequence? Neurosci Behav Rev 6: 47–53. Soares, J.C. and Mann, J.J. (1997). The anatomy of mood disorders – review of structural neuroimaging studies. Biol Psychiatry 41: 86–106. Sobel, N., Prabhakaran, V., Hartley, C.A. et al. (1998). Odorantinduced and sniff-induced activation in the cerebellum of the human. J Neurosci 18: 8990–9001. Strick, P.L. (1999). Symposium: basal ganglia, cerebellum and motor control. Soc Neurosci Abstract 25: 528. Svensson, P., Minoshima, S., Beydoun, A., Morrow, T.J. and Casey, K.L. (1997). Cerebral processing of acute skin and muscle pain in humans. J Neurophysiol 78: 450–60. Tataranni, P.A., Gautier, J.F., Chen, K. et al. (1999). Neuroanatomical correlates of hunger and satiation in humans using positron emission tomography. Proc Natl Acad Sci USA 96: 4569–74. Vasile, R.G., Sachs, G., Anderson, J.L., Lafer, B., Matthews, E. and

Hill, T. (1997). Changes in regional cerebral blood flow following light treatment for seasonal affective disorder: responders versus nonresponders. Biol Psychiatry 42: 1000–5. Vilensky, J.A. and Van Hoesen, G.W. (1981). Corticopontine projections from the cingulate cortex in the rhesus monkey. Brain Res 205: 391–5. Volkow, N.D., Levy, A., Brodie, J.D. et al. (1992). Low cerebellar metabolism in medicated patients with chronic schizophrenia. Am J Psychiatry 149: 686–8. Wassink T.H., Andreasen N.C., Nopoulos, P. and Flaum, N. (1999). Cerebellar morphology as a predictor of symptom and psychosocial outcome in schizophrenia. Biol Psychiatry 45: 41–8. Whiteside, D.G. and Snider, R.S. (1953). Relation of cerebellum to upper brain stem. J Neurophysiol 16: 397–413. Xu, F. and Frazier, D.T. (1997). Involvement of the fastigial nuclei in vagally mediated respiratory responses. J Appl Physiol 82: 1853–61. Yates, W.R., Jacoby, C.G. and Andreasen, N.C. (1987). Cerebellar atrophy in schizophrenia and affective disorder. Am J Psychiatry 144: 465–7. Zanchetti, A. and Zoccolini, A. (1954). Autonomic hypothalamic outbursts elicited by cerebellar stimulation. J Neurophysiol 17: 475–83.

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Sporadic Diseases

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10

Congenital malformations of the cerebellum and posterior fossa Joseph R. Madsen1, Tina Young Poussaint2, and Patrick D. Barnes2 2

Introduction Congenital anomalies of the cerebellum cover a broad range of entities, with the scale of the malformation varying from the microscopic, even molecular, to the macroscopic. It is the latter extreme of anomalies in the gross anatomical structure of the cerebellum for which surgical intervention may be indicated. The major surgical entities are (a) the Chiari malformations, which represent herniation of the lower parts of the midline cerebellum through the foramen magnum, and (b) the Dandy–Walker malformation and its variants, involving failure of formation of part of the midline structures of the cerebellum and compression by a fluid-filled cyst. In both cases, surgical intervention is aimed at decompressing these structures. To an increasing degree, surgical decision-making is determined by precise anatomical diagnosis, revealed by new imaging techniques. This chapter describes both the diagnostic schemes and the surgical interventions available and on the horizon today.

Normal embryology and development The cerebellum has the longest period of embryological development of any major structure of the brain (Lemire et al., 1975; see also Chapter 2). Neuroblastic proliferation in the cerebellar plates is recognized at 32 days, but neuronal migration from the plates is not complete until one year postnatally. As a result of this extended ontogenesis, the cerebellum is vulnerable to teratogenic insult for longer than most parts of the central nervous system (CNS). During weeks 8–13 (all dates approximate) intense neuroblastic activity causes extraventricular ballooning of the cerebellum, which then starts to subdivide (Kollias et al., 1993). The first division, at about 8–9 weeks, is by the

1 Department of Neurosurgery Department of Radiology, Children’s Hospital, Boston, Massachusetts, USA

flocculo-nodular fissure, which separates the flocculus and the nodulus of the vermis from the rest of the cerebellum. The flocculo-nodular lobe, also called the archicerebellum, is the most primitive part of the cerebellum. It is also called the vestibular cerebellum, because vestibular fibers project densely in this lobe, which is involved in the control of eye movements and body equilibrium, including stance and gait. The next subdivision results from the formation of the primary fissure separating the anterior lobe from the remainder of the cerebellum at about 10–11 gestational weeks. The anterior, or rostral, vermis precedes the development of the posterior vermis, the culmen being first to develop (tenth gestational week), followed by the lingula, central lobule, pyramis, uvula and nodulus (thirteenth week), and the declive, folium and tuber (fourteenth week) (Lemire et al., 1975). Formation of the vermis antedates that of the cerebellar hemispheres by 30–60 days. The vermis of the anterior lobe and the pyramis, uvula, and paraflocculus are called the paleocerebellum (Gilman et al., 1981), also known as the spinocerebellum due to numerous projections from the spinal cord. The remainder of the cerebellum constitutes the neocerebellum, also called the cerebro-cerebellum due to its connections to the cerebral cortex.

Imaging modalities Imaging techniques may be classified as structural or functional. Structural imaging modalities provide spatial resolution based primarily on anatomic or morphologic data. These include radiography, ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), angiography, myelography, cisternography, and ventriculography. Functional imaging modalities provide spatial resolution based on physiologic or metabolic data. These

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Table 10.1 Congenital malformations of cerebellum Chari malformation (I, II, III, IV) Cystic posterior fossa and hindbrain malformations Dandy–Walker malformation Dandy–Walker variant Megacisterna magna Blakes’s pouch cyst Other developmental abnormalities Joubert’s syndrome Partial or complete absence (hypoplasia) of inferior vermis Tectocerebellar dysraphia Global cerebellar hypoplasia Lhermitte–Duclos syndrome Macrocerebellum

include Doppler ultrasonography, single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance angiography (MRA), perfusion and diffusion MRI, cerebrospinal fluid (CSF) flow MRI, functional magnetic resonance imaging (fMRI), and magnetic resonance spectroscopy (MRS). The imaging modalities useful for assessing the developmental and congenital malformations of the cerebellum are emphasized below. Congenital and developmental abnormalities of the CNS (Table 10.1) may result from defective formation, postformational destruction or disordered maturation. These are best classified according to gestational timing and include (a) disorders of dorsal and ventral neural tube development, (b) disorders of neural, glial, and mesenchymal development, encephaloclastic processes, and (c) disorders of myelination and cortical maturation (van der Knaap and Valk, 1988). Within the spectrum of developmental malformations of the cerebellum, the Chiari malformations and associated spinal malformations arise between three and four weeks’ gestation and result from disorders of dorsal neural tube development. Between five and ten weeks’ gestation, disorders of ventral neural tube development result and include the Dandy–Walker continuum and hindbrain anomalies, such as cerebellar hypoplasia and aplasia. Ultrasonography is useful in fetal and neonatal screening and especially for the unstable infant who cannot be examined in the radiology department. It is readily accessible, fast, portable, and provides real-time and multiplanar images (Teele and Share, 1991; Barnes et al., 1993a, 1993b; Barkovich, 1995). It requires a path that is not impeded by bone or air for cranial and spinal imaging. Thus, it is limited to the fetus, the infant with an open fontanel or

suture, the child with an immature or dysplastic cranium or spine and surgical exposure. In addition to standard imaging of the brain through the anterior and posterior fontanel, posterior fossa structures may be scanned through the mastoid fontanel to delineate the brainstem and the cerebellar hemispheres, vermis, and fourth ventricle (Yousefzadeh and Naidich, 1985; Buckley et al., 1997). Transcranial Doppler techniques can be useful to identify infants and newborns with elevation in intracranial pressure and for assessing the need for, and optimal timing of, shunt placement (Chadduck and Seibert, 1989; Lui et al., 1990). Computed tomography is the primary modality for imaging when the acoustic window is no longer available for ultrasonography. It is especially important for detecting gross formational anomalies and for acute or emergent presentations such as macrocephaly, increased intracranial pressure, headache, shunt malfunction, and suspected postoperative complication. Magnetic resonance imaging provides more complete delineation of complex CNS anomalies for diagnosis, treatment, prognosis, and genetic counseling. In addition, MRI is indicated for treatment beyond simple shunting of hydrocephalus. Examples include the management of the sequelae of the Chiari II malformation after closure of the myelomeningocele and shunting of hydrocephalus (McLone and Naidich, 1992), and the management of the posterior fossa cystic anomalies regarding the decision for cyst shunting versus combined cyst and ventricular shunting (Altman et al., 1992). Also, MRI is useful to delineate the more subtle anomalies with the hindbrain malformations, such as disorders of migration and cortical organization, and disorders of proliferation, differentiation, and histiogenesis. In addition, motion-sensitive MRI techniques such as those used to demonstrate CSF flow may be useful in the evaluation, both preoperatively and postoperatively, of abnormalities of CSF dynamics, such as hydrocephalus and hydrosyringomyelia, and abnormalities of brain motion, such as the Chiari malformations. (Gammal et al., 1987; Castillo et al., 1991; Poncelet et al., 1992; Wolpert et al., 1995).

The Chiari malformations The first description of a Chiari malformation was given in 1883 by John Cleland, who described dissections of brains in children with hindbrain abnormalities (Cleland, 1883). In 1891, Hans von Chiari described a series of patients with malformations of the posterior fossa in which inferior extension of the cerebellar tonsils through a large foramen

Malformations of the cerebellum and posterior fossa

Fig. 10.1 Chiari I malformation. Unusual presentation with unilateral sixth nerve palsy in a child with asymmetric (right greater than left) displacement of the tonsils (left). Sagittal T1 MR image demonstrates cerebellar tonsils well below the foramen magnum. Operative photographs (after craniectomy, C1 laminectomy, and dural opening) show views before (middle) and after (right) coagulation of the pia over the tonsils.

magnum was the primary abnormality (Chiari, 1891). Four anomalies of the hindbrain were classified by Chiari: type I was a displacement of the cerebellar tonsils below the foramen magnum without displacement of the medulla caudally; type II was a displacement of the inferior vermis associated with a caudal displacement of lower pons and medulla and presence of lumbar meningomyelocele; type III was a displacement of brainstem with herniation of cerebellum in a meningocele; and type IV was a generalized hypoplasia.

Chiari I malformation Chiari I malformation occurs less commonly in children than in adults, hence the developmental defect is so-called ‘adult’ Chiari malformation. It is defined as an extension of the cerebellar tonsils below the foramen magnum of at least 3–5 mm, although a tonsillar herniation of less than 5 mm does not exclude the diagnosis (Aboulezz et al., 1985; Barkovich et al., 1986; Elster and Chen, 1992; Mikulis et al., 1992; Ball and Crone, 1995; Milhorat et al., 1999). It is embryologically unrelated to the other Chiari malformations. Clinical presentations include headache or neck pain, nystagmus, cranial nerve palsies, or progressive scoliosis. It is estimated that up to 75% of cases develop paroxysmal symptoms, including headaches, dizziness, vertigo, and vomiting. Positional changes, coughing or sneezing may all precipitate symptoms. Craniocervical dysgenesis

with atlanto-occipital assimilation, Klippel–Feil syndrome (Spinos et al., 1985), spina bifida occulta, and basilar invagination may occur. Occasionally, the symptoms can be quite asymmetric, such as a unilateral cranial nerve palsy (Fig. 10.1). In two-thirds of the cases, the tonsils extend to C1. In 25%, there may be extension as far as C3. The Chiari I malformation differs from the Chiari II malformation not only because of the absence of associated myelomeningocele, but also because supratentorial anomalies are usually lacking. It is an abnormality of hindbrain development, often with a significant postnatal, or ‘acquired,’ component (Dure et al., 1989; Barnes et al., 1993b; Huang and Constantini, 1994). The Chiari I malformation is rarely observed at birth. It is more often seen later in childhood or adolescence. The progressive extension of the tonsils below the foramen magnum with age may be related to the known continuation of postnatal growth and maturation of the cerebellum up to four years of age in opposition to the unyielding tentorium above and skull base below. The phenomenon is accentuated especially if there is early fusion of the synchondroses or other abnormality of the skull base. There may be associated findings such as hydrosyringomyelia (Fig. 10.2) and scoliosis, particularly in childhood (Dure et al., 1989; Barnes et al., 1993a). Characteristically, the tonsils are pointed inferiorly. Increased tonsillar motion (hypervelocity) may be the cause of the hydrosyringomyelia by transmitting excessive pressure into the spinal

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Fig. 10.2 Chiari I malformations with hydrosyringomyelia. Sagittal T1 image demonstrates Chiari I malformation with (A) midcervical spinal cord syrinx, and (B) diffuse cord hydrosyringomyelia.

cord (Oldfield et al., 1994; Wolpert et al., 1995). The cisterna magna is often small. Hydrocephalus is present in 25% of patients and has been postulated as the cause of tonsillar herniation due to a pressure effect (De La Paz et al., 1983). Surgical treatment of a Chiari I malformation is performed in the prone position with the neck in flexion. A vertical incision is made and the musculature is swept off the occipital bone and C1 lamina. One useful surgical trick is to preserve a cuff of fascia on the occipital bone for later

watertight closure of the back to the skull. Bone from the lower posterior fossa down to the foramen magnum is removed, and usually the middle part of the C1 lamina is removed as the sole cervical exposure needed. Care must be taken to avoid the vertebral arteries and the venous plexes around these arteries. A ligamentous band between the foramen magnum and C1, the atlanto-occipital membrane, is usually firmly adherent to the dura and often can be left in place and simply divided when the dura is opened

Malformations of the cerebellum and posterior fossa

to give additional space to the cervicomedullary junction. Care must be taken to avoid bleeding or air entry from occipital sinus and other vascular structures while opening the dura, but in general a Y-shaped opening gives excellent exposure of the herniated tonsils and the cervicomedullary junction just below the lower tips of the tonsils. After identification of vascular structures, dissection can be carried down between the tonsils to identify the fourth ventricle, to be sure there is good outflow from the fourth ventricle into the CSF space. The pia of the tonsils can then be coagulated slightly to cause the tonsillar tissue to retract upward into a more normal position to help ensure that the outflow of CSF will be kept open (see Fig. 10.1). In some extreme cases, or where a syrinx exists and it is uncertain whether the pathways will remain open, a thin, flexible piece of tubing may be left in the fourth ventricle to keep this opening patent; however, it is needed only occasionally in practice. A generous dural graft is used to increase the volume of space around the craniocervical junction and help avoid future symptoms.

Chiari II malformation The Chiari II malformation is a complex anomaly involving the entire neuraxis. It is the most common Chiari malformation in the pediatric population. The malformation is classified as a disorder of dorsal induction, because almost all patients have an associated myelomeningocele, usually in the lumbar region. This is the Arnold–Chiari malformation. Several theories concerning the pathogenesis have been postulated. The traction theory proposes that the primary cause is the myelomeningocele. The cord is tethered and pulls the brainstem and cerebellum into the upper cervical canal. The hydrodynamic theory suggests that primary hydrocephalus forces reopening of the closed neural tube, which produces the myelomeningocele and downward herniation of the hindbrain. The overgrowth theory proposes that an excess of neural tissue prevents closure of the vertebral arches. A large supratentorium then forces the hindbrain inferiorly. Teratological theories stem from animal models in which varying teratogens have simulated the deformity. An alternative theory postulates the lack of distension of the embryonic ventricular system due to leakage of the myelomeningocele as the cause of the malformation. The lack of distension of the fourth ventricle prevents enlargement of the subsequent bony confines of the posterior fossa. The volume of the posterior fossa is then fixed in capacity and is inadequate for the subsequent growth of the cerebellum (Naidich et al., 1983). Clinically, there is a spectrum of severity ranging from asymptomatic to brainstem dysfunction including

apnea. All the symptoms described for Chiari I malformation may be observed. The rhombencephalon contains most of the characteristic features of the Chiari II malformation. Some form of cerebellar dysplasia is not uncommon. In contrast to the normal coronal orientation, there may be dorsal angulation of the cerebellar fissures with consequent non-visualization of the folia on the sagittal view. The cerebellum and brainstem are inferiorly displaced through a wide foramen magnum (Fig. 10.3). Owing to this impaction, the pyramis, uvula, and nodulus may be compressed and necrotic. Prepontine migration of the cerebellum at the level of the middle cerebellar peduncle gives the brainstem a ‘triple peak’ or ‘angel wing’ appearance on axial views. Due to the low-lying, sickle-shaped tentorium, upward bulging of the cerebellum is seen on the coronal images, the so-called towering cerebellum. Inferior vermian pegs lying posterior to the medulla and fourth ventricle are a constant feature (Wolpert et al., 1987). The dentate ligaments hold the upper cervical cord in position, and as the medulla and cerebellum impact downward on the upper cervical canal, tethering occurs. If the medulla is displaced below these ligaments, a cervicomedullary kink is formed, which is seen in 70% of patients (Naidich et al., 1983; Wolpert et al., 1987). The cervicomedullary deformities are classified according to shape and contents (Naidich et al., 1983); three types may occur. In the first, there is an inferior vermian peg alone. In the second, the fourth ventricle is elongated and descends anterior to the vermian peg. In the third, the medulla is buckled below the cervical cord, forming the cervicomedullary kink, which does not usually extend below C4. The fourth ventricle is usually collapsed, but may be dilated, particularly if it is trapped. As a result of herniation, the exiting cranial nerves may at times make an upward turn to reach their skull base foramina. The most important complications are hydrocephalus (often after myelomeningocele closure) and isolation of the fourth ventricle following ventricular shunting. The latter may be a neurosurgical emergency. Mesencephalic abnormalities involving the aqueduct and colliculi are often present (Naidich et al., 1980a). The aqueduct is dysfunctional and may be shortened, stretched or dilated, but not necessarily occluded (Naidich et al., 1983). Pressure from the occipital lobes at the level of the tentorial hiatus may cause compression of the midbrain (Masters, 1978). A constant feature of the Chiari II malformation is the abnormal appearance of the colliculi. The tectum may be bulbous or beaked. Although the collicular fusion may be intrinsic, hydrocephalus may cause this appearance.

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A

Fig. 10.3 Chiari II malformations. (A) Sagittal T1 image demonstrates towering cerebellum, small fourth ventricle, and corpus callosal dysgenesis. (B) Chiari II can also be associated with hydrosyringomyelia.

Controversy exists over treatment for neurological symptoms referable to possible brainstem compression at the foramen magnum. In patients with a cervicomedullary kink extending to or below C4, the majority have been symptomatic and surgical decompression has been recommended (Curnes et al., 1989). Others, however, found no correlation between the degree of hindbrain herniation and symptomatology (Wolpert et al., 1987). Aplasia or hypoplasia of the cranial nerve nuclei, including the basal pontine nuclei and olivary nuclei, and disorganization of the brainstem nuclei have been described in autopsy specimens and may be intrinsic to the anomaly (Gilbert et al., 1986). Disorganization of brainstem nuclei

may be the basis for neurological symptoms. If so, posterior decompression may not be beneficial (Wolpert et al., 1988). Hydrosyringomyelia is seen in 70% to 80% of cases (Naidich et al., 1983). The more severe the cerebellar herniation in Chiari I or II, the more likely that hydrosyringomyelia is present. Abnormalities of the corpus callosum are common and may occur in up to 80% of patients with Chiari II malformation (Barkovich, 1995). Complete agenesis occurs in 33% of patients (Wolpert et al., 1987). Although anteroinferior pointing of the frontal horns of the lateral ventricles is a non-specific finding seen in other congenital anomalies, it is a constant feature of the Chiari II

Malformations of the cerebellum and posterior fossa

malformation (Naidich et al., 1980a). The supratentorial CSF spaces are commonly prominent, most notably the quadrigeminal plate cistern, interhemispheric fissure, and cistern of the velum interpositum, especially after shunting. Colpocephaly, a disproportionate enlargement of the occipital horns, may also be present (Herskowitz et al., 1985; Noorani et al., 1988). Stenogyria, a defect of the cerebral cortical pattern, may be seen located in the medial aspect of the occipital lobes and may result from dysplasia of the hemispheres medial to the atria. The falx may be thinned anteriorly, allowing interdigitations of the medial surfaces of the cerebral hemispheres to occur. The tentorium is low, inserting sometimes close to the foramen magnum, and often has a sickle shape. Hydrocephalus often occurs after surgical closure of the myelomeningocele. This may result from obstruction of the outlet foramina of the fourth ventricle, aqueduct stenosis, obliteration of the subarachnoid spaces at the level of the foramen magnum, and/or obstruction at the level of the dysplastic tentorium (McLone and Naidich, 1992). Luckenshadel, or craniofenestria, a condition characterized by marked thinning of the occipital or parietal bones, is identified in 85% of patients with Chiari II malformation when examined before six months of age. After that, it becomes unrecognizable (Naidich et al., 1980b, 1983). Clival and petrous bone scalloping is identified in a majority of patients, secondary to pressure from the cerebellum. The petrous scalloping occurs above the jugular tubercles and internal auditory canals.

Clinical management and surgical treatment Previously, the major causes of death in open neural tube defects were meningitis, hydrocephalus, and consequences of repeated urinary tract infections including renal failure. As the medical management of these conditions has improved, the brainstem symptoms caused by the Chiari II malformation have become among the leading causes of death and morbidity in these patients. About one-third of all patients with Chiari II malformations develop brainstem symptoms by the age of five, and one-third or more of these children die, often as a result of respiratory failure (Oakes, 1996). The nature of clinical presentation is significantly affected by age: neonates typically show rapid neurological deterioration over a period of several days, while older patients experience a more insidious symptom progression. Acute presentation of Chiari II symptoms may be a neurological emergency in as many as one-fifth of patients with myelomeningocele (Pollack et al., 1992). The symptoms may affect respiration, pharyngeal coordination, including swallowing, and vocal cord functions (stridor). Earlier onset of symptoms por-

tends a more dangerous situation, with the worst cases having onset and progression of symptoms in the first three months. The issue of how many of the Chiari symptoms result from local pressure, and are therefore amenable to decompression, and how many result from disorganization of brainstem tracts and synaptic organization, is a particularly troublesome and sometimes ethical dilemma for the surgeon. For example, in infants who fail to initiate ventilatory patterns at the beginning of life, the prognosis with any kind of management appears very poor. Either dysplasia of the brainstem or damage from the prenatal compression of the Chiari may be responsible, but surgical intervention is not likely to provide much relief of symptoms in either case. On the other hand, most patients who undergo decompressive surgery for Chiari II malformations have a substantial improvement in symptoms, with the degree of improvement depending significantly on the timing of surgery and patient selection. Surgery for the Chiari II malformation is more difficult than surgical treatment of Chiari I, because the patients are often younger and more unstable and the anatomical findings are very complex, with profound anomalies of both the vascular anatomy and the anatomy of cerebellar and brainstem structures. The torcular, or junction of the sagittal and transverse sinuses, can be remarkably low, sometimes as low as the foramen magnum, making suboccipital craniectomy extremely dangerous. Furthermore, identification of cerebellar and fourth ventricular structures may be very difficult within the cervical canal. Finally, the need for multiple levels of cervical laminectomy in an infant may cause delayed cervical instability. Because patients with Chiari II malformations almost invariably have open neural tube defects and hydrocephalus requiring shunting, it is crucial to rule out shunt malfunction as the cause of the patient’s symptoms prior to undertaking a decompressive operation. Surgical exploration of the shunt is often indicated as the definitive test of adequate shunt function prior to surgery on the Chiari malformation (Oakes, 1996). Surgery is performed in the prone position with the neck flexed. The operating microscope is used after opening the dura to obtain optimal recognition of structures. The vermis and medulla are often quite adherent and difficult to separate. Considerable exploration may be needed to find an area of decreased adhesion to allow entry into the fourth ventricle (Fig. 10.4). Once the fourth ventricle is well exposed and the CSF pathways have been re-established, a dural graft is used to repair the dural opening. Because of the possibility that at least part of the consequences of the Chiari malformation may be a result of the

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Fig. 10.4 Operative view of Chiari II decompression, showing a displaced fourth ventricle at the level of C4–5 in this patient with spina bifida and hydromyelia.

open neural tube defect in the lumbosacral area, and the disastrous potential consequences of this malformation in itself, the possibility has recently been entertained of closing the neural tube defects in utero. Such an approach has significant ethical concerns, including the risk incurred to the mother in an attempt to prevent later complications in the fetus or child. Early investigations into surgically created models of neural tube defect suggested that neurotoxic effects of amniotic fluid on the spinal cord may be mitigated if the defect can be covered early enough in pregnancy (Heffez,et al., 1990). More recent experiments with animals (Fig. 10.5) and preliminary experience with human fetal surgery (Adzick et al., 1998; Tulipan et al., 1998; Tulipan and Bruner, 1999) have suggested that the major benefit of such intervention may be in the pre-emption of the hindbrain herniation. Thus, fetal surgery for myelomeningocele may eventually be considered in the armamentarium against the type II Chiari malformation.

Chiari III malformation The Chiari III malformation is comprised of a cervicooccipital cephalocele with hindbrain dysplasia. It has variable features of Chiari II malformation associated with a low occipital or high cervical cephalocele and herniation of dysplastic, gliotic brain, often with heterotopias, and/or the ventricles into the cephalocele (Fig. 10.6A). Anomalies of the venous drainage may be associated with the encephalocele. Surgical treatment is individualized to close optimally or reduce the encephalocele, and sometimes drain cavities of entrapped fluid.

Chiari IV malformation The Chiari IV malformation represents severe cerebellar hypoplasia and has been placed in a separate category in

Fig. 10.5 Experimental antenatal treatment of hindbrain herniation in fetal lambs. A surgically created lumbar neural tube defect (NTD) in the lamb results in herniation of cerebellar contents through the foramen magnum at birth. The defect is created at 75 days of gestation. If treated at 100 days of gestation, the hindbrain herniation is not seen. (Images courtesy of Dr Russell Jennings, Children’s Hospital, Boston.)

the van der Knaap and Valk classification (Fig. 10.6B). It is unrelated to the other Chiari malformations and is characterized by a small brainstem, large posterior fossa CSF spaces, and absence or severe hypoplasia of the cerebellum and vermis.

Cystic posterior fossa and hindbrain malformations Dysgeneses of the paleocerebellum include the Dandy– Walker–Blake continuum, Joubert syndrome, rhombencephalosynapsis, and tectocerebellar dysraphia (Byrd and Naidich, 1988; Altman et al., 1992; Kollias et al., 1993). Aplasia of the vermis may be complete or partial. Because of its craniocaudal pattern of formation, partial aplasia always involves the caudal rather than the rostral part of the vermis. Dysgenesis of the neocerebellum includes cerebellar aplasia, hypoplasia, and dysplasia (Byrd and Naidich, 1988; Altman et al., 1992; Kollias et al., 1993). The vermis in these cases may be small in size but is otherwise normal. Combinations of paleocerebellar and neocerebellar malformations may occur. The majority of forms of cerebellar dysgenesis are paleocerebellar (before the third gestational month). Neocerebellar dysgenesis may occur

Malformations of the cerebellum and posterior fossa

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Fig. 10.6 Other Chiari malformations. (A) Chiari III malformation: occipital encephalocele and stigmata of Chiari II in posterior fossa. (B) Chiari IV malformation: severe hypoplasia of cerebellum and vermis, and small brainstem.

any time between the seventh gestational week and the first postnatal year.

The Dandy–Walker–Blake continuum The association of a posterior fossa cyst and cerebellar dysgenesis was described initially by Sutton in 1887. Dandy and Blackfan later described a malformation of the posterior fossa in which the inferior vermis was absent and the fourth ventricle ballooned to form a cystic lesion posterior to the cerebellum (Dandy and Blackfan, 1914). There was no communication between the cyst and the perimedullary cistern. They postulated atresia or postnatal obstruction of the foramen of Magendie as the cause of the abnormality. Taggart and Walker also postulated that the cause was in-utero atresia of the foramen of Magendie (Taggart and Walker, 1942). Benda coined the term Dandy–Walker malformation and commented that the foramen may be patent in the malformation (Benda, 1954). Since these initial investigations, many descriptions and postulates concerning pathology have appeared in the literature, including the theory that the retrocerebellar arachnoid cyst represents persistence of the primitive Blake’s pouch (Benda, 1954; Haller et al., 1971; Gardner et

al., 1975; Sawaya and McLaurin, 1981; Raybaud, 1982; Barkovich et al., 1989). Probably the best single unifying concept is that of impaired permeability of the membranous roof of the fourth ventricle together with vermian dysgenesis. Although the pathogenesis is still uncertain, it is clear that the primary defect in posterior fossa cystic malformations is not obstruction of the foramen of Magendie alone. More recent reviews classifying posterior fossa cystic lesions have considered that there is a spectrum (i.e., the Dandy–Walker–Blake continuum) of malformations involving the fourth ventricle and cerebellum, including the Dandy–Walker malformation, the so-called Dandy– Walker variant, the megacisterna magna, and the retrocerebellar cyst (Blake’s pouch cyst) (Barkovich et al., 1989; Strand et al., 1993). The Dandy–Walker–Blake continuum accounts for 2–4% of cases in large series of patients with hydrocephalus (Hirsch et al., 1984).

Dandy–Walker malformation Dandy–Walker malformation (Fig. 10.7) is characterized by hypoplasia of the cerebellar hemispheres, hypoplasia or absence of the inferior cerebellar vermis, and marked

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C Fig. 10.7 Dandy–Walker malformation. (A) and (B) Sagittal T1 and axial T2 images demonstrate absence of cerebellar vermis, torcular/lambdoid inversion and dilatation of the fourth ventricle. (C) Another case demonstrates callosal dysgenesis.

dilatation of the fourth ventricle so that it balloons posteriorly into the remainder of the cerebellum, which is anterolaterally displaced. The posterior fossa is enlarged, and the tentorial insertion and confluence of dural venous sinuses are elevated above the lambda, accounting for ‘torcular-lambdoid inversion,’ often with a wide, vertically oriented incisura. The falx cerebelli is absent. Hydro-

cephalus is variable and may not be present at birth. There is no correlation between the size of the posterior fossa expansion, vermian hypoplasia, and the degree of hydrocephalus (Hart et al., 1972). The exit foramina of the fourth ventricle may be patent or occluded. Histologically, the wall of the Dandy–Walker cyst is composed of an inner layer of ependyma, an intermediate layer of attenuated neuroglial tissue, and an outer layer of pia-arachnoid (Altman et al., 1992). The large majority of Dandy–Walker cases are sporadic, but about 1–2% are familial (Pollock and Johnson, 1993). The prevalence of Dandy–Walker malformation among siblings is about 2% and the recurrence risk in subsequent pregnancies is estimated to between 0.5% and 5%. The diagnosis of Dandy–Walker malformation is made in four children out of five by one year of age. The most common clinical signs are macrocephaly with hydrocephalus and cerebellar dysfunction. The patients exhibit nystagmus and truncal ataxia. They may also present cranial nerve palsies, seizures, opisthotonos,

Malformations of the cerebellum and posterior fossa

apnea, and hemiparesis. Associated anomalies have been described, including complete or partial agenesis of the corpus callosum (25% of patients), polymicrogyria, cortical heterotopias, occipital encephalocele, agenesis of brainstem pyramids, infundibular hamartomas, and holoprosencephaly (minority of patients). Systemic anomalies include polydactylism, syndactylism, Klippel–Feil syndrome, Sjögren–Larsson syndrome, cardiac malformations, urinary tract abnormalities, and Cornelia de Lange’s syndrome (Hart et al., 1972; Barkovich et al., 1989).

Dandy–Walker variant Harwood-Nash and Fitz first coined the term Dandy– Walker variant to encompass those entities not satisfying all the criteria for the true Dandy–Walker malformation (Barkovich et al., 1989). In this entity there is posterior evagination of the tela choroidea of the fourth ventricle with partial vermian agenesis but without torcular elevation (Fig. 10.8) (Raybaud, 1982; Barkovich et al., 1989). If a lesion does not satisfy the criteria for a true Dandy–Walker malformation and cannot be ascribed either to a megacisterna magna or to a retrocerebellar cyst, it is probably best described anatomically without placement in a single category (Kollias et al., 1993; Strand et al., 1993).

Megacisterna magna The megacisterna magna is defined as a prominent CSF space posterior to the cerebellum without vermian agenesis or significant mass effect, although there may be an effaced or scalloped appearance of the cerebellum or occipital bone which mimics mass effect (Fig. 10.9). The cisterna magna is larger in the premature than in the more mature fetus or infant, or than in older children. The megacisterna magna may represent a subtle disturbance of midline brain development (Lemire et al., 1975). In one study, 8 of 14 infants with a large cisterna magna had neurologic abnormalities, including ataxia and hypotonia (de Souza et al., 1994). The architecture of the fourth ventricle is normal. The torcular may be normal or elevated in position and the posterior fossa may be normal or large in size. Minor positional asymmetry of the dural venous sinuses may be present, along with minor tentorial, falx, and inner table cranial deformities.

Blake’s pouch cyst The Blake’s pouch cyst (retrocerebellar arachnoid cyst) is the posterior evagination of the tela choroidea, but without cerebellar agenesis (Fig. 10.10). The cause of the cyst may

Fig. 10.8 Dandy–Walker variant, with hypoplasia of the inferior vermis but no torcular elevation.

be a developmental variation of the meninx primitiva, which surrounds the neural tube during the differentiation of the mesenchyme, or an abnormal development of the inferior membranous area, with persistence of Blake’s pouch (Gilles and Rockett, 1971). The retrocerebellar cyst is thus thought to be due to maldevelopment of the anterior and posterior membranous areas around the fifth week of gestation (Barkovich et al., 1989). The anterior membranous area is incorporated into the developing cerebellum, and the posterior membranous area forms the foramen of Magendie (Hart et al., 1972; Raybaud, 1982; Barkovich et al., 1989). If the anterior membranous area fails to incorporate into the cerebellum and the posterior membranous area is malformed, the foramen of Magendie will balloon outward. Normally there is absorption of the ependymal lining and the pouch involutes or is incorporated as the arachnoid-lined cisterna magna. The inner wall of the cyst is lined with ependyma or astroglial membrane, with an outer layer of arachnoid elements (Gilles and Rockett, 1971). Similarity between these histological features and those of the Dandy–Walker malformation support the theory that the two entities are related. Failure of involution of the Blakes’ pouch results in the posterior fossa cystic malformation (Strand et al., 1993). Mass effect is often present and the cerebellum may be displaced anteriorly. The torcular may or may not be elevated, although the

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Fig. 10.9 Megacisterna magna. (A) Sagittal T1 image and (B) axial T2 image demonstrate a prominent CSF space behind the cerebellum without mass effect or vermian agenesis.

tentorium may bulge. The cyst may extend through the tentorium. The cysts may or may not communicate with the subarchnoid space (Galassi et al., 1982). The term ‘arachnoid cyst’ should probably be reserved for those cysts that do not communicate with the subarachnoid space. Multiplanar MRI, CT ventriculography or CT cisternography is often indicated to distinguish the different cystic malformations. In cases of hydrocephalus, patency of the aqueduct and communication of the cyst with the fourth ventricle and subarachnoid spaces are the critical factors in deciding whether to shunt only the cyst or to shunt both the cyst and the ventricles in order to prevent upward or downward herniation when only one compartment is shunted. A CT cisternogram (Galassi et al., 1982) or a CSF MRI flow study may be necessary in some cases to distinguish a megacisterna magna (communication with the subarachnoid spaces) from a retrocerebellar arachnoid cyst or an encysted megacisterna magna (non-communication).

Surgical treatment

Fig. 10.10 Blake’s pouch cyst. There is a large retrocerebellar cyst with an intact cerebellum not communicating with the CSF.

The surgical treatment of a Dandy–Walker malformation involves diversion of the CSF from the ventricular space or the posterior fossa cystic space, or both, to another drainage location such as the peritoneal cavity. The main tactical

Malformations of the cerebellum and posterior fossa

Fig. 10.11 Dramatic response of a very large Dandy–Walker cyst to shunting; the CT image on the right shows significant restitution of cerebellar volume eight years after shunting of a Dandy–Walker malformation at birth (shown in the MRI on the left).

question for the surgeon is which of these spaces should be shunted. Advantages of shunting the posterior fossa space include the lack of choroid plexus to plug the shunt and the theoretical possibility that, as the posterior fossa cystic space closes in, the shunt may be less likely to over-drain. Advantages of shunting the ventricle include the fact that the symptoms often occur from the hydrocephalus itself and, if the spaces do not communicate well, it is desirable to ensure treatment of the ventricular dilatation. Passing a catheter through brain results in a ‘gasket effect’ around the most peripheral parts of the ventricular catheter, so there is less likelihood of fluid leakage out into the subcutaneous space. Opinion is mixed among pediatric neurosurgeons about which space should be preferentially shunted. At Boston Children’s Hospital, the practice has been to perform an MRI scan to determine the patency of the aqueduct connecting the ventricular system to the fourth ventricular cyst. If there seems to be good communication, the cyst is shunted preferentially to the ventricular system. If the ventricular system seems to be significantly more distended than the posterior fossa, it may be shunted first. In either event, if continued

pressure symptoms indicate that the unshunted space is exerting pressure and causing symptoms, a modification of the shunt is made with a Y-connector to drain both spaces. The response of the cerebellum to shunting often includes dramatic restitution of tissue volume (Fig. 10.11).

Other cerebellar developmental abnormalities Joubert’s syndrome Joubert’s syndrome is characterized morphologically by absence of all or part of the cerebellar vermis, dysplasia of the cerebellar nuclei and brainstem, and anomalies of the inferior olives and spinal tracts (Fig. 10.12) (Lemire et al., 1975). The pyramidal decussations may be completely absent (Kendall et al., 1990; Altman et al., 1992). The condition is inherited as an autosomal recessive disorder. In one series, all seven children showed hypoplasia of the brainstem in addition to cerebellar vermal dysgenesis (Kendall et al., 1990). As a result of vermian, superior cerebellar peduncle and midbrain abnormalities, axial MRI

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Fig. 10.12 Joubert’s syndrome. (A) Sagittal T1 image and (B) axial T2 image demonstrate absence of the cerebellar vermis and dysplasia of the brainstem.

may show a very suggestive sign, called the ‘molar tooth’ aspect (Maria et al., 1997). Patients with Joubert’s syndrome often have pendular or rotatory eye movements, retinal dystrophy, and ataxia (Joubert et al., 1969). The children are usually mentally retarded. They also present episodic hyperpnea (breathing at a rate up to 180/min), which may alternate with episodes of apnea not associated with abnormalities of the arterial blood gases. However, the breathing pattern is usually normal during sleep. An autistic behavior as well as hemifacial spasms have been reported. Other midline central malformations such as meningoencephaloceles, neuronal heterotopias, and dysgenesis of the corpus callosum may be found. In addition, Joubert’s syndrome may be associated with multicystic kidney disease and hepatic fibrosis. Because of the deficits of respiratory control, children with Joubert’s syndrome are very sensitive to the respiratory depressant effects of anesthetic agents (Habre et al., 1997).

Partial or complete absence (hypoplasia) of the inferior vermis Partial or total absence of the inferior vermis may occur as an isolated anomaly or in association with Down

syndrome (Altman et al., 1992; Kollias et al., 1993; Demaerel et al., 1995). This results from failure of development of the cerebellar midline primordia. Many of the cases ascribed to the Dandy–Walker variant may represent vermian or cerebellar hypoplasia. Usually the inferior lobules are hypoplastic. The cerebellar peduncles, pons, and brainstem may be small. The fourth ventricle, basal cisterns, vallecula, and cisterna magna are prominent. If accompanied by clinical signs of cerebellar and brainstem dysfunction, the appearances are probably the result of Joubert’s syndrome. Cases associating inferior vermal hypoplasia and hypogonadism have been reported. This may be inherited as an autosomal recessive pattern (Abs et al., 1990). Cerebellar vermis hypoplasia may also occur in association with oligophrenia, ataxia, coloboma, and hepatic fibrosis (COACH syndrome: Verloes and Lambotte, 1989).

Tectocerebellar dysraphia This is an entity consisting of vermian hypoplasia or aplasia and dorsal traction of the brainstem resulting in ventrolateral displacement of the cerebellar hemispheres and fusion of the tectum. It has features which overlap those of the Dandy–Walker malformation, Chiari II

Malformations of the cerebellum and posterior fossa

malformation, and posterior fossa ventriculocele. It is usually associated with an occipital cephalocele (Altman et al., 1992; Demaerel et al., 1995). When associated with an occipital cephalocele (inverse cerebellum with occipital cephalocele), the encephalocele contains hypoplastic cerebellar hemispheres which are attached to a dorsal extension of the tectum.

cerebellar hemisphere may be seen in patients with somatic hemihypertrophy. Diffuse enlargement of the cerebellum has been reported in patients with Alexander’s disease.

xReferencesx

Global cerebellar hypoplasia Global cerebellar hypoplasia may be primary or may occur in patients with Tay–Sachs disease, Menkes’ kinky-hair disease, and spinal muscular atrophy (Altman et al., 1992; Kollias et al., 1993; de Souza et al., 1994). In all these cases, the subarachnoid spaces surrounding the cerebellum are prominent, resemble cystic malformations, and must be distinguished from other posterior fossa cystic lesions.

Rhomboencephalosynapsis Rhomboencephalosynapsis is characterized by fusion of the two cerebellar hemispheres with absence of the vermis (Truwit et al., 1991; Demaerel et al., 1995). The dentate nuclei, the superior cerebellar peduncles, and the thalami may also be fused. Anomalies of the limbic system and hydrocephalus may also occur (Byrd and Naidich, 1988). Isaac and Best suggested that the fusion of dentate nuclei occurs at about 100 days of gestation, as a possible consequence of the effect of a teratogen (Isaac and Best, 1987).

Lhermitte–Duclos syndrome In 1920, Lhermitte and Duclos described an abnormality characterized by a sharply marginated focal enlargement of the cerebellum. Affected children exhibit macrocephaly, seizures, and mild cerebellar deficits. Microscopically the granular cells are replaced by abnormal ganglion cells providing the name cerebellar gangliocytoma (Lhermitte and Duclos, 1920). The cerebellar histologic characteristics are explained by a failure in migration of the Purkinje cells and reactive hypertrophy of granule cells, which are in-utero events.

Macrocerebellum The cerebellum may be diffusely enlarged but have otherwise normal neuroimaging features. A small group of children with large cerebelli, delayed white matter myelination, and a clinical syndrome of global developmental delay, abnormalities of tone, and oculomotor apraxia has been described (Bodensteiner et al., 1997). Enlargement of the

Aboulezz, A.O., Sartor, K., Geyer, C.A. and Gado, M.H. (1985). Position of cerebellar tonsils in the normal population and in patients with Chiari malformation: a quantitative approach with MR imaging. J Comp Assist Tomogr 9: 1033–6. Abs, R., Van Vleymen, E., Parizel, P.M., Van Acker, K., Martin, M., and Martin, J.J. (1990). Congenital cerebellar hypoplasia and hypogonadotropic hypogonadism. J Neurol Sci 98: 259–65. Adzick, N.S., Sutton, L.N., Crombleholme, T.M. and Flake, A.W. (1998). Successful fetal surgery for spina bifida [letter] [see comments]. Lancet 352: 1675–6. Altman, N., Naidich, T. and Braffman, B.H. (1992). Posterior fossa malformations. Am J Neuroradiol 13: 691–724. Ball, W.S. Jr and Crone, K.R. (1995). Chiari I malformation: from Dr Chiari to MR imaging [editorial; comment]. Radiology 195: 602–4. Barkovich, A. (1995). Pediatric Neuroimaging. New York: Raven Press. Barkovich, A.J., Kjos, B.O., Norman, D. and Edwards, M.S. (1989). Revised classification of posterior fossa cysts and cystlike malformations based on the results of multiplanar MR imaging. Am J Roentgenol 153: 1289–300. Barkovich, A.J., Wippold, F.J., Sherman, J.L. and Citrin, C.M. (1986). Significance of cerebellar tonsillar position on MR. Am J Neuroradiol 7: 795–9. Barnes, P.D., Brody, J.D., Jaramillo, D., Akbar, J.U. and Emans, J.B. (1993a). Atypical idiopathic scoliosis: MR imaging evaluation. Radiology 186: 247–53. Barnes, P.D., O’Tuama, L. and Tzika, A. (1993b). Investigating the pediatric central nervous system. Curr Opin Pediatr 5: 643–52. Benda, C. (1954). The Dandy–Walker syndrome, or the so-called atresia of the foramen Magendie. J Neuropathol Exp Neurol 13(14). Bodensteiner, J.B., Schaefer, G.B., Keller, G.M., Thompson, J.N. and Bowen, M.K. (1997). Macrocerebellum: neuroimaging and clinical features of a newly recognized condition. J Child Neurol 12: 365–8. Buckley, K.M., Taylor, G.A., Estroff, J.A., Barnewolt, C.E., Share, J.C. and Paltiel, H.J. (1997). Use of the mastoid fontanelle for improved sonographic visualization of the neonatal midbrain and posterior fossa. Am J Roentgenol 168: 1021–5. Byrd, S.E. and Naidich, T.P. (1988). Common congenital brain anomalies. Radiol Clin North Am 26: 755–72. Castillo, M., Hudgins, P.A., Malko, J.A., Burrow, B.K. and Hoffman, J.C. Jr (1991). Flow-sensitive MR imaging of ventriculoperitoneal shunts: in vitro findings, clinical applications, and pitfalls [see comments]. Am J Neuroradiol 12: 667–71.

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J.R. Madsen, T. Young Poussaint, and P.D. Barnes

Chadduck, W.M. and Seibert, J.J. (1989). Intracranial duplex Doppler: practical uses in pediatric neurology and neurosurgery. J Child Neurol 4 (Suppl.): S77–86. Chiari, H. (1891). Ueber Veränderungen des Kleinhirns infolge von Hydrocephalie des Grosshirns. Deutsche Medicinische Wochenschrift, 17: 1172–5. Cleland, J. (1883). Contribution to the study of spina bifida, encephalocele and anencephaly. J Anat Physiol 17: 257. Curnes, J.T., Oakes, W.J. and Boyko, O.B. (1989). MR imaging of hindbrain deformity in Chiari II patients with and without symptoms of brainstem compression [see comments]. Am J Neuroradiol 10: 293–302. Dandy, W. and Blackfan, K. (1914). Internal hydrocephalus: an experimental, clinical, and pathologic study. Am J Dis Children 8: 406. De La Paz, R., Brody, T. and Buonanno, F. (1983). Nuclear magnetic resonance imaging of Arnold–Chiari type I malformation with hydromyelia. J Comp Assist Tomogr 7: 126. Demaerel, P., Wilms, G., Halpin, S.F., Casaer, P. and Baert, A. (1995). Uncommon posterior cranial fossa anomalies: MRI with clinical correlation. Neuroradiology 37: 72–6. de Souza, N., Chaudhuri, R., Bingham, J. and Cox, T. (1994). MRI in cerebellar hypoplasia. Neuroradiology 36: 148–51. Dure, L.S., Percy, A.K., Cheek, W.R. and Laurent, J.P. (1989). Chiari type I malformation in children. J Pediatr 115: 573–6. Elster, A.D. and Chen, M.Y. (1992). Chiari I malformations: clinical and radiologic reappraisal. Radiology 183: 347–53. Galassi, E., Tognetti, F., Gaist, G., Fagioli, L., Frank, F. and Frank, G. (1982). CT scan and metrizamide CT cisternography in arachnoid cysts of the middle cranial fossa: classification and pathophysiological aspects. Surg Neurol 17: 363–9. Gammal, T.E., Allen, M.B. Jr, Brooks, B.S. and Mark, E.K. (1987). MR evaluation of hydrocephalus. Am J Roentgenol 149: 807–13. Gardner, E., O’Rahilly, R. and Prolo, D. (1975). The Dandy–Walker and Arnold–Chiari malformations. Clinical, developmental, and teratological considerations. Arch Neurol 32: 393–407. Gilbert, J.N., Jones, K.L., Rorke, L.B., Chernoff, G.F. and James, H.E. (1986). Central nervous system anomalies associated with meningomyelocele, hydrocephalus, and the Arnold–Chiari malformation: reappraisal of theories regarding the pathogenesis of posterior neural tube closure defects. Neurosurgery 18: 559–64. Gilles, F.H. and Rockett, F.X. (1971). Infantile hydrocephalus: retrocerebellar ‘arachnoidal’ cyst. J Pediatr 79: 436–43. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Habre, W., Sims, C. and D’Souza, M. (1997). Anaesthetic management of children with Joubert syndrome. Paediatr Anaesth 7: 251–3. Haller, J.S., Wolpert, S.M., Rabe, E.F. and Hills, J.R. (1971). Cystic lesions of the posterior fossa in infants: a comparison of the clinical, radiological, and pathological findings in Dandy–Walker syndrome and extra-axial cysts. Neurology 21: 494–506. Hart, M.N., Malamud, N. and Ellis, W.G. (1972). The Dandy–Walker syndrome. A clinicopathological study based on 28 cases. Neurology 22: 771–80.

Heffez, D.S., Aryanpur, J., Hutchins, G.M. and Freeman, J.M. (1990). The paralysis associated with myelomeningocele: clinical and experimental data implicating a preventable spinal cord injury. Neurosurgery 26: 987–92. Herskowitz, J., Rosman, N.P. and Wheeler, C.B. (1985). Colpocephaly: clinical, radiologic, and pathogenetic aspects. Neurology 35: 1594–8. Hirsch, J.F., Pierre-Kahn, A., Renier, D., Sainte-Rose, C. and HoppeHirsch, E. (1984). The Dandy–Walker malformation. A review of 40 cases. J Neurosurg 61: 515–22. Huang, P.P. and Constantini, S. (1994). ‘Acquired’ Chiari I malformation. Case report. J Neurosurg 80: 1099–102. Isaac, M. and Best, P. (1987). Two cases of agenesis of the vermis of cerebellum with fusion of the dentate nuclei and cerebellar hemispheres. Acta Neuropathol (Berl) 74: 278–80. Joubert, N., Eisenring, J., Robb, J. and Andermann, F. (1969). Familial agenesis of the cerebellar vermis: a syndrome of hyperapnea, abnormal eye movements, ataxia, and retardation. Neurology 19: 813–25. Kendall, B., Kingsley, D., Lambert, S.R., Taylor, D. and Finn, P. (1990). Joubert syndrome: a clinico-radiological study. Neuroradiology 31: 502–6. Kollias, S.S., Ball, W.S. Jr and Prenger, E.C. (1993). Cystic malformations of the posterior fossa: differential diagnosis clarified through embryologic analysis [see comments]. Radiographics 13: 1211–31. Lemire, R., Loeser, J., Leech, R. and Alvord, E. (1975). Normal and Abnormal Development of the Human Nervous System. Hagerstown, MD: Harper and Row. Lhermitte, J. and Duclos, P. (1920). Sur un ganlioneurome diffus du cortex du cervelet. Bull Assoc Fançaise Etude Cancer 9: 99M12. Lui, K., Hellmann, J., Sprigg, A. and Daneman, A. (1990). Cerebral blood-flow velocity patterns in post-hemorrhagic ventricular dilation. Childs Nerv Syst 6: 250–3. Maria, B.L., Hoang, K.B., Tusa, R.J. et al. (1997). ‘Joubert syndrome’ revisited: key ocular motor signs with magnetic resonance imaging correlation. J Child Neurol 12: 423–30. Masters, C.L. (1978). Pathogenesis of the Arnold–Chiari malformation: the significance of hydrocephalus and aqueduct stenosis. J Neuropathol Exp Neurol 37: 56–74. McLone, D.G. and Naidich, T.P. (1992). Developmental morphology of the subarachnoid space, brain vasculature, and contiguous structures, and the cause of the Chiari II malformation. Am J Neuroradiol 13: 463–82. Mikulis, D.J., Diaz, O., Egglin, T.K. and Sanchez, R. (1992). Variance of the position of the cerebellar tonsils with age: preliminary report. Radiology 183: 725–8. Milhorat, T.H., Chou, M.W., Trinidad, E.M. et al. (1999). Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery 44: 1005–17. Naidich, T., McLone, D. and Fulling, K.H. (1983). The Chiari II malformation: Part IV. The hindbrain deformity. Neuroradiology 25: 179–97. Naidich, T.P., Pudlowski, R.M. and Naidich, J.B. (1980a). Computed tomographic signs of Chiari II malformation. II: Midbrain and cerebellum. Radiology 134: 391–8.

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Naidich, T.P., Pudlowski, R.M., Naidich, J.B., Gornish, M. and Rodriguez, F.J. (1980b). Computed tomographic signs of the Chiari II malformation. Part I: Skull and dural partitions. Radiology 134: 65–71. Noorani, P.A., Bodensteiner, J.B. and Barnes, P.D. (1988). Colpocephaly: frequency and associated findings. J Child Neurol 3: 100–4. Oakes, W.J. (1996). The Chiari malformations of the child. In Principles of Spinal Surgery, ed. A.H. Menezes and V.K.H. Sonntag, pp. 379–94. New York: McGraw-Hill. Oldfield, E.H., Muraszko, K., Shawker, T.H. and Patronas, N.J. (1994). Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment [see comments]. J Neurosurg 80: 3–15. Pollack, I.F., Pang, D., Albright, A.L. and Krieger, D. (1992). Outcome following hindbrain decompression of symptomatic Chiari malformations in children previously treated with myelomeningocele closure and shunts. J Neurosurg 77: 881–8. Pollock, J.M. and Johnson, M.H. (1993). Dandy–Walker malformation. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 147–62. New York: Marcel Dekker. Poncelet, B.P., Wedeen, V.J., Weisskoff, R.M. and Cohen, M.S. (1992). Brain parenchyma motion: measurement with cine echo-planar MR imaging [see comments]. Radiology185: 645–51. Raybaud, C. (1982). Cystic malformations of the posterior fossa. Abnormalities associated with the development of the roof of the fourth ventricle and adjacent meningeal structures. J Neuroradiol 9: 103–33. Sawaya, R. and McLaurin, R.L. (1981). Dandy–Walker syndrome. Clinical analysis of 23 cases. J Neurosurg 55: 89–98. Spinos, E., Laster, D.W., Moody, D.M., Ball, M.R., Witcofski, R.L. and Kelly, D.L. Jr (1985). MR evaluation of Chiari I malformations at 0.15 T. Am J Roentgenol 144: 1143–8. Strand, R.D., Barnes, P.D., Poussaint, T.Y., Estroff, J.A. and Burrows, P.E. (1993). Cystic retrocerebellar malformations: unification of the Dandy–Walker complex and the Blake’s pouch cyst. Pediatr Radiol 23: 258–60.

Sutton, J.B. (1887). The lateral recesses of the fourth ventricle: their relation to certain cysts and tumors of the cerebellum, and to occipital meningocele. Brain 9: 352. Taggart, J. and Walker, A. (1942). Congenital atresia of the foramens of Luschka and Magendie. Arch Neurol Psychiatry 48: 583. Teele, R. and Share, J. (1991). Ultrasonography of Infants and Children. Philadelphia: WB Saunders. Truwit, C.L., Barkovich, A.J., Shanahan, R. and Maroldo, T.V. (1991). MR imaging of rhombencephalosynapsis: report of three cases and review of the literature. Am J Neuroradiol 12: 957–65. Tulipan, N. and Bruner, J.P. (1999). Fetal surgery for spina bifida [letter; comment]. Lancet 353(9150): 406; discussion 407. Tulipan, N., Hernanz-Schulman, M. and Bruner, J.P. (1998). Reduced hindbrain herniation after intrauterine myelomeningocele repair: a report of four cases. Pediatr Neurosurg 29: 274–8. van der Knaap, M.S. and Valk, J. (1988). Classification of congenital abnormalities of the CNS. Am J Neuroradiol 9: 315–26. Verloes, A. and Lambotte, C. (1989). Further delineation of a syndrome of cerebellar vermis hypo/aplasia, oligophrenia, congenital ataxia, coloboma and hepatic fibrosis. Am J Genet 32: 227–32. Wolpert, S.M., Anderson, M., Scott, R.M., Kwan, E.S. and Runge, V.M. (1987). Chiari II malformation: MR imaging evaluation. Am J Roentgenol 149: 1033–42. Wolpert, S.M., Bhadelia, R.A., Bogdan, A.R. and Cohen, A.R. (1995). Chiari I malformations: assessment with phase-contrast velocity MR [published erratum appears in Am J Neuroradiol 1995, 16(1): A11]. Am J Neuroradiol 15: 1299–308. Wolpert, S.M., Scott, R.M., Platenberg, C. and Runge, V.M. (1988). The clinical significance of hindbrain herniation and deformity as shown on MR images of patients with Chiari II malformation. Am J Neuroradiol 9: 1075–8. Yousefzadeh, D. and Naidich, T.P. (1985). US anatomy of the posterior fossa in children: correlation with brain sections. Radiology 156: 353–61.

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Multiple system atrophy and idiopathic late-onset cerebellar ataxia José Berciano Service of Neurology, University Hospital ‘Marqués de Valdecilla’, University of Cantabria, Santander, Spain

Multiple system atrophy: introduction The term multiple system atrophy (MSA) was created by Graham and Oppenheimer (1969), as a general label applicable to numerous subtypes of presenile neuronal degeneration, among them olivo-ponto-cerebellar atrophy (OPCA) being one of the better known. After describing the clinicopathological study of a case with orthostatic hypotension and atrophy of multiple neuronal systems, Graham and Oppenheimer implicitly included within MSA Shy–Drager syndrome, striatonigral degeneration, and OPCA, although they were in favor of retaining the eponym Shy–Drager syndrome for cases with MSA and orthostatic hypotension. In this way, credit should be given to the British authors for dividing the anatomical hallmark of primary orthostatic hypotension into two groups: (a) cases in which degeneration of intermediolateral cell columns and autonomous ganglia is part of the MSA pathological framework, as in the early description by Shy and Drager (1960); and (b) cases in which pathological findings are those of idiopathic Parkinson’s disease, and therefore the eponym Shy–Drager syndrome is not applicable. Concerning OPCA, it is worth noting that Graham and Oppenheimer did not make any distinction between familial and sporadic forms. Thus, the concept of MSA emerged, in 1969, not as a new clinicopathological picture but as an all-embracing term of several previously reported syndromes (OPCA, Shy–Drager syndrome and striatonigral degeneration), whose nosology was then well known, though with undoubted overlappings. More recently, Quinn (1989, 1994) reviewed the concept of MSA, proposing that it is not an embracing term but a substitute for other classical eponyms, that are now focused on sporadic OPCA, Shy–Drager syndrome and striatonigral degeneration. Quinn recognized two MSA subtypes: (a) striatonigral degeneration type (with predominant parkinsonian semeiology); and (b) OPCA type

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(with predominant cerebellar semeiology). As almost all MSA patients do have dysautonomic manifestations to some degree (it will be seen below that this is by no means always the case), Quinn recommended avoiding the use of the term ‘MSA of SDS type’. The consistent finding of glial cytoplasmic inclusions in MSA brains (see below) has been another starting point for lumping classical syndromes under the MSA umbrella. Given the complex nosology of MSA, the nosology of sporadic OPCA, striatonigral degeneration, and Shy–Drager syndrome is reviewed first before that of MSA itself. Idiopathic late onset cerebellar ataxia (ILOCA) is discussed in the following paragraph on OPCA.

Olivo-ponto-cerebellar atrophy Historical review and classification In 1900, Déjerine and Thomas described the case of a patient with a sporadic and progressive clinical picture beginning at the age of 53, characterized by progressive gait ataxia, dysarthria, impassive face, hyperreflexia, hypertonia, and urinary incontinence. The man died 2.5 years after onset. At autopsy there was atrophy of the griseum pontis, inferior olivary nuclei, and cerebellum, with demyelination of middle and inferior cerebellar peduncles. I reviewed the pathological material of this case (at the Laboratoire Déjerine, Paris), which comprised preparations of the spinal cord, medulla-pons-cerebellum and basal ganglia (in the last case, just one transverse section passing through anterior white commissure) (Berciano, 1978). Although the presence of OPCA lesions were confirmed (Fig. 11.1) no apparent lesions in the basal ganglia could be found (sections stained with the Weigert–Pal method). Déjerine and Thomas considered

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that their case should be included among non-familial primary cerebellar degenerations under the designation of ‘atrophie olivo-ponto-cérébelleuse.’ So, sporadic OPCA was originally included within cerebellar ataxias. However, at this time, such a description of olivo-pontocerebellar lesions was not unheard of. In fact, nine years previously, Menzel had reported a family with four affected members in two generations and onset of symptoms around the age of 30 years (Menzel, 1891). The clinical picture consisted of a progressive cerebellar-plus syndrome, including spasmodic torticollis and rigidity. At autopsy there was OPCA together with degeneration of substantia nigra and spinal cord, and flattening of subthalamic nuclei, though, unfortunately, Menzel did not give histological details of this structure. Retrospectively, this family could be considered as an example of autosomal dominant cerebellar ataxia (ADCA) type I (Harding, 1984). Both in the early paper by Déjerine and Thomas (1900) and later on in the doctoral thesis by Loew (1903–4) – under the tutelage of Déjerine himself – OPCA was considered to be atypical when there were hereditary factors (as in Menzel’s observation), lesions extending beyond the OPCA framework or a clinical picture not limited to cerebellar semeiology. The concept of atypical OPCA fell into disuse with the recognition of familial OPCA and of the many combinations of lesions that frequently accompany olivopontine degeneration (Welte, 1939; Rosenhagen, 1943). Concerning extrapyramidal rigidity, it is worth noting that Scherer (1933) was the first author to recognize that parkinsonism, often associated with OPCA, does not correlate with the severity of cerebellar lesions, but correlates with the severity of lesions of the nigrostriatal system (see below). Greenfield (1954) divided the pathological framework of ataxias into six main categories: (a) familial cerebellar, type Menzel (familial OPCA); (b) familial cerebellar, type Holmes (cortical cerebellar atrophy); (c) sporadic cerebellar, type Déjerine–Thomas (sporadic OPCA); (d) sporadic cerebellar, type Marie–Foix–Alajouanine (sporadic CCA); (e) spinal forms (Friedreich’s ataxia); and (f) dentato-rubral atrophy (Ramsay–Hunt syndrome). In this way, OPCA was divided into two forms: sporadic (Déjerine–Thomas type) and familial (Menzel type). This classification was in use until the advent of the clinicogenetic classification of the ataxias at the beginning of the 1980s (Harding, 1984). With the successive publication of clinicopathological studies of OPCA, its nosological complexity was evident to

Fig. 11.1 Olivo-ponto-cerebellar lesions in the case reported by Déjerine and Thomas (1900). Both transverse sections are stained with the Weigert–Pal method. (A) This section through medulla and cerebellum shows demyelination of the cerebellar white matter and olivocerebellar fibers. (B) This section through the upper half of the pons shows demyelination of middle cerebellar peduncles.

the point that it is difficult to find ‘pure’ cases of OPCA, that is, with lesions restricted to griseum pontis, inferior olivary nuclei, and cerebellum, and a clinical picture consisting of isolated cerebellar ataxia (Berciano, 1982, 1998).

Clinical picture and pathology The following brief review of the clinical picture of sporadic OPCA starts from published reviews of the literature concerning cases with pathological confirmation (Berciano, 1978, 1982, 1998). The age at onset of symptoms varied between 0 and 66 years (mean, 50); it is timely to remember that OPCA may be the pathological framework not only of ILOCA but also of sporadic congenital, infantile or juvenile ataxias and several ADCA subtypes. Duration of disease ranged from 4 months to 20 years (mean, 6 years); undoubtedly, the mean duration in clinical series is higher. Figure 11.2 shows the frequencies of symptoms and signs in both sporadic and familial OPCA. Global ataxia

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Fig. 11.2 Histogram showing frequencies of symptoms and signs in familial OPCA (FOPCA) and sporadic OPCA (SOPCA). (Adapted from Berciano, 1978, 1982, 1998.)

Fig. 11.4 (A) Severe loss of neurons and gliosis in the substantia nigra of a patient suffering from sporadic OPCA with extrapyramidal rigidity. The arrow indicates the only preserved pigmented neuron, and the arrowhead indicates the presence of melanin within the neuropil. Note the absence of Lewy bodies. (B) Control section of the substantia nigra at the same magnification as (A).

Fig. 11.3 Histogram showing frequencies of the main associated lesions in familial OPCA (FOPCA) and sporadic OPCA (SOPCA). (Adapted from Berciano, 1978, 1982, 1998.)

(static, kinetic, and dysarthria) is the predominant semeiology. Sooner or later, however, there appear non-cerebellar manifestations, the most frequent of them being as follows: parkinsonism, pyramidal and other spinal signs (e.g., amyotrophy or sensory loss), subcortical dementia, abnormal movements, urinary incontinence, dysphagia (sometimes with laryngeal palsy), supranuclear ophthalmoplegia, and sleep disturbances. Both in familial and sporadic OPCA, there may be presynaptic parkinsonism with good response to levodopa (Pascual et al., 1991). The pathological hallmark of this polymorphic clinical picture is a complex degeneration involving not only the olivo-ponto-cerebellar system but many others (Fig. 11.3).

In contrast with Parkinson’s disease, degeneration of the substantia nigra is not accompanied by the presence of Lewy bodies (Fig. 11.4). Evident degeneration of striatum is uncommon in OPCA , both familial and sporadic. When it does occur in a sporadic form, it is retrospectively indistinguishable from SND (e.g., cases 72/29 and 1873 in Scherer’s paper [1933] would be considered at present as examples of SND). Glial cytoplasmic inclusions have been reported in both sporadic and familial OPCA (see below).

From ILOCA to sporadic OPCA To continue with the nosology of sporadic OPCA from the perspective of ataxic syndromes, this is important, because, as will be seen at once, the nosology of MSA has mainly emerged from the study of parkinsonian patients, overlooking the fact

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Fig. 11.5 CT scan in a patient with sporadic OPCA. (A) A section through the middle pons showing widening of the cerebellar hemispheric sulci, visualization of the lateral cerebellar cisterns (arrowheads), increased fourth ventricle width and surface, and enlarged prepontine and cerebello-pontine cisterns (arrows). (B) A section through the mesencephalon showing marked atrophy of the superior vermis and enlargement of the perimesencephalic cisterns.

that, in the vast field of general neurology, there are patients with ILOCA whose clinical course is quite different from that of SND or SDS. This sporadic subgroup represents around 15% of all patients with degenerative ataxias (Harding, 1981), that is, a prevalence ratio of 3/100 000 for a total prevalence of 20/100 000 (Polo et al., 1991). The clinical picture of ILOCA may be pure cerebellar ataxia or cerebellar-plus syndrome, with onset usually after the age of 20 years (Harding, 1981, 1984). Neuroimaging studies usually show isolated cerebellar atrophy in the first case, suggesting that the pathological framework is CCA. Contrariwise in cases with additional non-cerebellar semeiology, neuroimaging generally reveals a combination of brainstem and cerebellar atrophy (Fig. 11.5) suggestive of OPCA (Ramos et al., 1987; Klockgether et al., 1990; Ormerod et al., 1994). Difficulties of nosologic delimitation appear when confronting MSA, defined following ad-hoc criteria (see below), and sporadic OPCA as a variant of ILOCA. With the idea of illustrating this question, three ILOCA series are reviewed below. In her original paper, Harding (1981) reported 18 cases with cerebellar-plus syndrome with a mean age of onset of 45 years. Non-cerebellar semeiology did not significantly

differ from that of her ADCA-I patients. Being exclusion criteria of MSA (Quinn, 1989, 1994), outstanding semeiology in this series includes the following features: dementia (22%), ophthalmoplegia (11%), hypoesthesia (11%), and areflexia (17%). Also atypical for MSA was the presence of chorea in one case. In contrast with MSA, it is worth noting that only one case had had incipient parkinsonism, despite the prolonged clinical course (12.56 7.51 years). Polo et al. (1991) reported six ILOCA patients with cerebellar-plus syndrome. Onset ranged from the age of 28 to 45 years (median, 38) and duration from 11 to 19 years (follow-up between 3 and 13 years). Non-cerebellar features were as follows: pyramidal signs (five cases), dysphagia (three cases), sensory neuropathy or areflexia (three cases), dementia (one case), urinary incontinence (one case) and chorea (one case). Neither parkinsonism nor orthostatic hypotension was observed. Ormerod et al. (1994) described 11 ILOCA patients with onset between the ages of 39 and 73 years (mean, 56) and duration between 3 and 15 years (mean, 7). Non-cerebellar additional clinical features were as follows: polyneuropathy (four cases), dementia (three cases), parkinsonism (two cases), supranuclear ophthalmoplegia (two cases), dysautonomia (one case) and optic atrophy (one case).

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Fig. 11.6 Algorithm outlining the author’s suggested approach to the diagnosis of a patient with ILOCA. The period of four years for ‘pure’ cerebellar syndrome is based on the fact that additional non-cerebellar symptoms usually come later (Klockgether et al., 1990). Sporadic OPCA patients may also have presynaptic parkinsonism, although rarely.

From these three series it is clear that the term sporadic OPCA is still applicable, as a presumptive or demonstrated pathological label, for cases of ILOCA and cerebellar-plus syndrome (exceptionally, for cases with pure cerebellar ataxia), often without evidence of parkinsonism or dysautonomia. This clinical picture is quite different from that of MSA (see below), although evolution of ILOCA to MSA may occur (Gilman and Quinn, 1996). Rarely is any ILOCA phenotype caused by one of the dynamic mutations associated with ADCA (de-novo mutation) (Ranum et al., 1994; Silveira et al., 1996). A recent study demonstrated that 22% of sporadic ataxia patients had expanded CAG repeats, the SCA6 gene mutation linked to CCA being the most frequently observed (Futamura et al., 1998). These findings suggest that patients with ataxia even without a family history should be examined for a CAG repeat expansion, although in our experience genetic study in ILOCA is systematically negative (Pujana et al., 1999). In an attempt

to clarify this further, the diagnostic algorithm that appears in Fig. 11.6 is proposed. For historical reasons and in order to avoid semantic confusion, the eponym sporadic OPCA (Déjerine–Thomas type) should be used in the first place to designate a subset of ILOCA patients and in the second place for MSA, when there is clinical, neuroimaging or eventually pathological evidence of olivopontine degeneration (see below). Furthermore, the term sporadic OPCA is also applicable to sporadic early onset cerebellar ataxia patients (see above).

Striatonigral degeneration Historical review The term SND was introduced by Adams et al. (1961, 1964) to designate the disease of four patients with progressive

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

parkinsonism beginning between the ages of 47 and 59 years, and with a duration ranging from 1 to 7 years. The authors indicated that the clinical picture was typical of PD, although the possibility of SND should be considered when other neurological signs appear, such as ‘cerebellar tremor or ataxia, chorea, choreoathetosis or dystonia, and possibly mental disturbances or pyramidal and pseudobulbar signs.’ Macroscopically, Adams et al. (1961, 1964) found a reduction of the putamen and, to a lesser degree, of caudate nuclei and globus pallidus, which exhibited a brownish pigmentation. There was paleness of the substantia nigra. Microscopically, there was severe neuronal loss and gliosis of putamen and substantia nigra and, to a lesser extent, of globus pallidus, caudate nuclei, locus ceruleus, subthalamic nuclei, griseum pontis, inferior olivary nuclei, cerebellum, and spinal cord. As in Huntington’s disease, the degenerative process mainly involved small putaminal neurons. Adams et al. correlated macroscopic pigmentation of the putamen with the gliosis and lipofuscin deposit observed. Wisely, they thought that such abnormal macroscopic findings could be due to abnormal iron deposit, even though such a feature was only seen in one case. In contrast with PD, the presence of Lewy bodies in substantia nigra occurred in only one case. Adams et al. (1964) concluded their paper as follows: ‘Thus, in presenting this new syndrome, we make no claim to it representing a new disease. Instead, it is possibly a variant of paralysis agitans or Huntington’s chorea, and presently classifiable only as degenerative. As such it deserves separate categorization until the causal factors and mechanisms of all the degenerative disease have been disclosed.’ Certainly, it was not a ‘new syndrome,’ because this clinicopathological syndrome had already been reported in detail by Scherer (1933) 30 years before. Surprisingly, despite both Van Bogaert and Adams being aware of Scherer’s papers, these are not mentioned in the seminal paper reporting SND (Berciano et al., 1999).

Clinical picture and pathology The following is a brief review of the nosology of SND, starting from data taken from my review of 48 clinicopathological cases published up to 1976 (Berciano, 1978) and the comprehensive reviews by Zarranz Imirizaldu and Rivera Pomar (1984), and Fearnley and Lees (1990). The age of onset ranged from 40 to 73 years (mean, 60), and duration from 1 to 13 years (mean, 6). The clinical course of SND is, therefore, significantly shorter than that of PD. The cardinal manifestation is a parkinsonian syndrome, with response to levodopa in up to 40% of cases; thus, the clini-

Fig. 11.7 Macroscopic lesions in striatonigral degeneration. (A) Note atrophy of the caudate and putamen, and gray discoloring of the atrophic putamen. (B) Note marked and extensive paleness of the substantia nigra.

cal diagnosis of PD made in some cases at the time of autopsy is hardly surprising. There are, however, several differences between SND and PD (Fearnley and Lees, 1990). At onset, rest tremor is observed in 10% of SND cases, whereas it occurs in 75% of PD cases. Asymmetrical extrapyramidal rigidity is noted in 66% of cases with SND and in 88% of cases with PD. Early unexplained falls, rare in PD, occur in one-third of SND cases. Other atypical signs for PD that may be present in SND are as follows: dysphagia, dysphonia, cerebellar ataxia, sleep disturbances, disproportionate antecollis, pyramidal signs, urinary incontinence, nystagmus, and orthostatic hypotension. Helpful early pointers to the diagnosis of SND include a variable combination of unexplained falls, autonomic dysfunction, absence of rest tremor, and failure to respond to levodopa. By definition, fundamental lesions in SND are atrophy of striatum and substantia nigra. Figure 11.7 illustrates the characteristic macroscopic lesions. Nigral atrophy is diffuse, although predominating in ventrolateral, ventrointermediate and lateral zones. Striatal pathology mainly involves small and medium-sized neurons (GABAergic), though large neurons (cholinergic) are not spared (Fig. 11.8). The posterior two-thirds of the putamen is usually more involved. Neuronal loss is accompanied by gliosis and pigment deposits, including hemosiderin, hematin, lipofuscin, and neuromelanin. There is demyelination of striopallidal fibers. Immunocytochemical studies with

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dopa (Fearnley and Lees, 1990), and that D-2 striatal receptors are preserved (Brooks et al., 1992) in a similar percentage of cases (see below). Certainly, such features would not have been expected to occur when applying strict neuropathological criteria, that is, presence of severe putaminal cell loss. This specific problem emerges in cases of MSA–SND subtype whose pathological framework is just a degeneration of substantia nigra and other brainstem nuclei or cerebellum (Wenning et al., 1994b). Contrariwise to presynaptic and postsynaptic parkinsonism characteristic of classical SND, in this ‘presumed SND’ parkinsonism is presynaptic and therefore preservation of both striatal D2 receptors and levodopa response is hardly surprising (Pascual et al., 1991). For such transitional cases, the eponym MSA seems to be very helpful. As in OPCA (see above), associated lesions in SND are constant, the most frequent being localized as follows (Berciano, 1978): cerebellum (33%), inferior olivary nuclei or olivocerebellar fibres (40%), griseum pontis or pontocerebellar fibres (33%), locus ceruleus (52%), and spinal cord (25%). After identification of glial cytoplasmic inclusions (see above and below), these have been a constant pathological finding.

Fig. 11.8 Putaminal microscopic lesions in striatonigral degeneration. (A) Note the almost complete neuron loss accompanied by gliosis and spongiosis of the neuropil (Hematoxylin–eosin). (B) Perl staining showing coarse ironpositive pigments (arrows); note also the presence of gemistocytic gliosis (arrowheads).

antibodies against metenkephalin, substance P, and calbindin-D28K have shown that the efferent striatal system may be involved, even in the absence of apparent striatal degeneration (Ito et al., 1996). In classical neuropathology, the inclusion of a case within a given syndrome implied demonstration of a clear and prevailing degeneration of specific neuronal systems (e.g., putamen and nigra for SND, or griseum pontis cerebellum and inferior olivary nuclei for OPCA). This criterion has not always been applied. Thus, the label of SND has been used for cases in which striatal pathology is merely a gliosis without neuron loss (Fearnley and Lees, 1990), or the label OPCA has presumptively been applied to cases in which neuroimaging studies did not reveal brainstem and cerebellar atrophy (the hallmark of OPCA) (Wenning et al., 1994c). Not having biological markers available, the overuse of eponyms contributes to making the borderlines of these neuropathological syndromes somewhat hazy. It has been stated that 40% of SND cases do respond to levo-

Neuroimaging studies Magnetic resonance imaging (MRI) is a useful technique in separating PD and SND (Schwarz et al., 1996; Savoiardo and Grisoli, 1998). In SND there may be abnormal putaminal signal, as illustrated in Fig. 11.9. Unfortunately, this feature is neither constant nor pathognomonic, as has been reported in other atypical parkinsonisms (e.g., progressive supranuclear palsy). Eidelberg et al. (1993) used 18F-fluorodeoxyglucose and positron emission tomography (PET) to estimate regional and global brain metabolic rates in SND, PD, and control subjects (ten in each group). Normalized glucose metabolism was significantly reduced in the caudate and putamen in the SND group as compared with PD and normal controls. Putaminal hypometabolism in the SND group significantly correlated with motor disability. MRI, performed in eight cases, showed putaminal hyposignal in four; interestingly, MRI abnormalities were observed as of year 5 of the clinical course. In contrast with OPCA, where a uniform pattern of posterior fossa atrophy is observed, computed tomography (CT) scan reveals cerebellar and brainstem atrophy in only 39% and 18% of cases, respectively (Wenning et al., 1994b). Certainly, these percentages are in agreement with pathological findings showing cerebellar or pontine atrophy in one-third of cases (see above). Be that as it may, diagnosis

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Fig. 11.9 Striatonigral degeneration. T2-weighted axial (A) and coronal (B) sections showing marked putaminal hypointensity and a tiny line of hyperintensity (arrows). Putaminal deposit of paramagnetic substances (see Fig. 11.8 and text) accounts for the hypointensity, whereas the hyperintensity is consistent with an increased amount of water associated with cell loss and gliosis.

of SND is based upon clinical criteria (atypical parkinsonism, usually with pyramidal and dysautonomic features), neuroimaging findings, either positive or negative, giving support to clinical diagnosis. Conversely, diagnosis of OPCA relies on demonstrating a characteristic pattern of atrophy in CT or MRI studies in a patient with progressive cerebellar-plus syndrome (rarely, pure cerebellar ataxia). It should be kept in mind that the clinical pictures of the pure spinal form of ataxia and of OPCA are indistinguishable and therefore presumptive use of the label OPCA is only justified when there is neuroimaging evidence of brainstem and cerebellar atrophy.

Shy–Drager syndrome Historical review In 1960, Shy and Drager described the first autopsy study of a case with primary orthostatic hypotension. Their patient was a male who, at the age of 49, developed a progressive clinical picture consisting of impotence, dimin-

ished libido, orthostatic syncopes, constipation, and urinary disturbances. On examination, there was orthostatic hypotension, iris atrophy, anisocoric pupils, and atonia of bladder and anal sphincter. Together with these dysautonomic features there was cerebellar ataxia, impassive face, rest tremor, hypertonia, dysarthria, and difficulty in ocular convergence due to paresis of rectus internus muscles. The patient died 6.5 years after onset. Autopsy revealed degeneration of sympathetic intermediolateral columns, autonomous ganglia, posterior columns, spinocerebellar tracts, Clarke’s columns, anterior gray horns, cerebellum, striatum, inferior olivary nuclei, griseum pontis, brainstem pigmented nuclei (without Lewy bodies), and ambiguus, hypoglossus, and oculomotor nuclei. After noting the similarity of their observation to that previously reported by Crichtley and Greenfield (1948) (an example of sporadic OPCA), Shy and Drager wrote: ‘It is suggested that a primary degenerative nervous system disorder may be one etiological factor in orthostatic hypotension. It would appear that this is a recognizable clinical syndrome.’

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Clinical picture and pathology In my doctoral thesis I reviewed 31 clinicopathological SDS cases published up to 1976 (Berciano, 1978). This series was divided into three main categories that are briefly developed here. Eight cases (26%) belonged to PD (see above). The mean age of onset was 65 years. Dysautonomic features were the outstanding semeiology. In four cases there was parkinsonism and in two others spinal signs. Pathologically there was degeneration of the intermediolateral columns, sympathetic ganglia and brainstem pigmented nuclei, accompanied by the presence of Lewy bodies. Nowadays, such a clinicopathological hallmark is considered not a MSA but a form of Lewy body disease. When there is outstanding dysautonomia, the eponym pure autonomic failure is applied. In comparison to MSA, dysautonomic dysfunction in pure autonomic failure is more distal, which accounts for the reduced plasmatic levels of norepinephrine (Van Ingelghem et al., 1994). Nineteen (61%) cases, including that described by Shy and Drager (1960), could be categorized as examples of SDS or MSA. Ages of onset varied between 40 and 73 years (mean, 51) and duration between 0.5 and 12 years (mean 4). By definition, a variable although outstanding combination of dysautonomic features (see above) occurred in all patients. However, this was regularly accompanied by pyramidal signs (ten cases), extrapyramidal rigidity (15 cases), spinal non-pyramidal signs (ten cases), cerebellar ataxia (ten cases), cranial nerve dysfunction (seven cases), respiratory disturbances (four cases), and myoclonus (one case). Subsequently, laryngeal palsy and sleep disturbances were reported. Pathological studies in this SDS group consistently revealed degeneration of intermediolateral columns, sometimes accompanied by involvement of autonomous ganglia. When mentioned, another consistent finding was atrophy of the nigra and/or locus ceruleus without Lewy bodies. OPCA was found in 11 (58%) cases and striatal atrophy in 12 (63%) cases. Other less frequent lesions were localized in the following structures: posterior columns, Clarke’s columns, spinocerebellar tracts, brainstem motor nuclei, vestibular nuclei, dentate nuclei, central tegmental tracts, medial longitudinal bundle or supraoptic nuclei. As in SND (see above and below), glial cytoplasmic inclusions are also a constant finding. The four remaining cases were included in the intermediate form, a concept now obsolete. In short, the eponym SDS means autonomic failure associated with central nervous system dysfunction attributable to MSA, as underlined by Quinn et al. in 1995. This

author entirely agrees that inappropriate use of the eponym SDS has led it to be applied to cases of PD with dysautonomia. The present use of such terminology is discussed below.

Multiple system atrophy Having reviewed the nosology of ILOCA, sporadic OPCA, SND, and SDS, the study of MSA, as an encompassing term of these three clinicopathological syndromes, is straightforward.

Definition and terminology As biological markers are not yet available, MSA definition must be descriptive (Quinn 1989, 1994). In this way, MSA can be defined as a sporadic degenerative disease of the nervous system that causes a clinical syndrome in which many combinations of extrapyramidal, pyramidal, cerebellar, and autonomic features may occur. The pathological hallmark of the disease is the presence of glial and neuronal cytoplasmic inclusions on a set of a highly variable topographic histopathological process going from minimal lesions, just involving the nigra and locus ceruleus, to fully developed olivo-ponto-cerebellar atrophy or striatonigral degeneration (see above) with or without atrophy of intermediolateral columns and Onuf’s nucleus. The use of confusing terms such as ‘multisystem degeneration’ for MSA is inappropriate and now discouraged. Gilman et al. (1999) recommend classifying patients as having MSA-P if parkinsonian features predominate, or MSA-C if cerebellar features predominate. Furthermore, Gilman et al. propose that these terms are intended to replace the SND and OPCA types of MSA (Quinn 1989, 1994); this proposal is timely as neither putaminal nor olivopontine degeneration is a constant finding in MSA-P or MSA-C, repectively (see below). On the other hand, the authors consider that the term Shy–Drager syndrome has been widely misused and therefore is no longer useful (see also the section below, Clinical picture).

Epidemiology As diagnosis of definite MSA requires autopsy confirmation, precise data of prevalence are lacking. Around 10% of patients with parkinsonism have MSA, giving a prevalence ratio of 16.4 per 100 000 (Quinn, 1989, 1994). A yearly incidence of three new cases per 100 000 has been estimated in a population aged between 50 and 99 years (Bower et al., 1997).

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Pathology and pathophysiology In an extensive review of the literature, Wenning et al. (1997) analyzed 203 pathologically proven cases and established that the more severe lesions involve the following structures (percentages of normal findings in brackets): nigra (8.6%), putamen (14.6%), caudate (45.2%), globus pallidus (25.5%), inferior olivary nuclei (22.1%), pons (39.2%), cerebellar cortex (16.9%), dentate nuclei (68.8%), intermediolateral columns (31.7%), anterior horn cells (51.9%), and pyramidal tracts (45.2%). Other involved structures were as follows: cerebral cortex (78.4%), thalamus (77.6%), subthalamic nuclei (59.4%), locus ceruleus (12.8%), vestibular nuclei (43.6%), dorsal motor nucleus (29.6%), nucleus ambiguus (58.3%), and Onuf’s nucleus (35.7%). It is worth noting that in this series the prominent semeiology was parkinsonism (87%), dysautonomia (74%), cerebellar ataxia (54%), and pyramidal signs (49%). Characteristic glial or neuronal inclusions (see below) were identified in all cases in which they were sought. Overall, nigrostriatal cell loss correlated with disease severity at the time of death (Wenning et al., 1994a, 1995). The latest, but not the best, recorded levodopa response tended to be inversely related to the degree of putamen degeneration. It has been established that one-third of MSA patients have a good or excellent initial motor response to levodopa. Such a response was sustained until death, however, in only 7% of them. Good levodopa response could be accounted for by relative preservation of the putamen (presynaptic parkinsonism) in some cases. The substrate of levodopa unresponsiveness in MSA is uncertain. Although loss of striatal dopamine receptors plays a part, much of the levodopa resistance and its heterogeneity between patients is probably due to the variable degeneration of additional cell populations within the basal ganglia (see above), involving other neurotransmitter systems. Tremor was unrelated to cell loss at any site. Ataxia correlated with the degree of olivo-ponto-cerebellar lesions. The presence of associated cerebellar pathology was, however, unrelated to the presence of cerebellar signs in life, a feature that can be attributed to the fact that conspicuous extrapyramidal rigidity does not evolve into cerebellar semeiology (Rosenhagen, 1943), that is, extrapyramidal signs usually mask cerebellar semeiology (Berciano, 1982, 1998). After the first description by Papp et al. in 1989, glial cytoplasmic inclusions have been a constant finding in MSA brains (see Lantos, 1998, for review). Inclusions have been decribed in five cellular sites (Lantos, 1998): in oligodendroglial cytoplasm and nucleus, in neuronal cytoplasm and nucleus, and in axons. The comparison of the

Fig. 11.10 Glial cytoplasmic inclusions in the cerebellar cortex of a patient with multiple system atrophy showing positive immunostaining for (A) ubiquitin and (B) -synuclein. (Courtesy of Professor Isidro Ferrer, Department of Neuropathology, Hospital Príncipes de España, Hospitalet de Llobregat, Barcelona, Spain.)

severity of oligo-dendroglial degeneration (glial cytoplasmic inclusion density) with that of neuronal alerations reveals a striking preponderance of oligo-dendroglial lesions and indicates that degeneration of neither axons nor neuronal cell bodies is a prerequisite for the formation of glial cytoplasmic inclusions. GCIs are shown by modified Bielschowsky silver impregnation and, to a limited extent, with antisera to ubiquitin (Fig. 11.10), tau protein or -crystalin. Semiquantitative studies have demonstrated that structures with high GCI density (more than 300 per mm2) include the supplementary motor and primary motor cortical areas with their subjacent white matter, the dorsolateral larger part of the putamen, the dorsolateral smaller part of the caudate nucleus, the ponticuli substantiae grisae, the globus pallidus, the internal and the external capsules, the reticular formation, the

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basis pontis, the middle cerebellar peduncles, and the cerebellar white matter (Papp and Lantos, 1994). In electron micrographs, GCIs are mainly composed of twisted and straight tubular structures with their external surface coated by a fuzzy or granular material. GCIs are different from neurofibrillary tangles observed in Alzheimer’s disease. GCIs are characteristic but not pathognomic of MSA, as they have also been reported in other neurodegenerative diseases, including familial OPCA (Daniel et al., 1995; Gilman et al., 1996; Berciano and Ferrer, 1996). However, the diagnostic value relies on their density and distribution (just described), which are certainly specific of MSA (Lantos, 1998). GCIs exhibit pronounced -synuclein immunoreactivity (Fig. 11.10), which is also observed in degenerating neurites and neuronal inclusions. Alpha-synuclein immunoreactivity seems to be more sensitive than ubiquitin immunoreactivity as a neuropathological marker for the MSA lesions (Gai et al., 1998). Insoluble -synuclein has been shown to be a structural component of the filaments in Lewy bodies of PD, dementia with Lewy bodies, Lewy body variant of Alzheimer’s disease, and Hallervorden–Spatz disease, which have been dubbed ‘-synucleinopathies’, whereas the tangle diseases are ‘tauopathies’ (Tu et al., 1998; Golbe, 1999). Alpha-synuclein is a small, soluble and flexible monomeric protein of 140 amino acids with little or no secondary structure. It is abundantly expressed in the central nervous system and associated with neuronal membranes. The normal function of -synuclein is unknown, although, as other small proteins, it may regulate protein–protein interactions, thereby binding to another protein and assuming a more rigid structure (Golbe, 1999). In brain, a role in the regulation or support of synaptic plasticity seems likely (Clayton and George, 1998). Strong immunostaining of GCIs suggests that oligo-dendroglial cells also produce synuclein. Because the solubility of -synuclein may be due to abundant negatively charged glutamic acid residues in the C-terminal half of this protein, abnormal modifications of this region may be an early step in the aggregation of the protein into neuronal and glial inclusions. However, the detection of other proteins in GCIs and Lewy bodies suggests that the formation of filamentous inclusions from altered -synuclein may require additional proteins that serve as pathological chaperones. As missense mutations in the -synuclein gene have only been reported in a few PD pedigrees, it has been proposed that post-translational modifications change the biophysical properties of -synuclein, rendering it insoluble (Tu et al., 1998). Together with the presence of insoluble -synuclein,

further evidence of neuronal loss comes from the demonstration of increased levels of neurofilament protein in the cerebrospinal fluid of MSA patients compared with that of PD patients (Holmberg et al., 1998). It has been suggested that in MSA the formation of GCIs is the primary lesion which, through oligo-dendroglia–myelin–axon–neuron complex, secondarily will affect nerve cells (Lantos, 1998). This hypothesis is difficult to reconcile with the growing evidence of neuronal dysfunction in MSA. Furthermore, the same argument could be applied to other neurodegenerative diseases in which the presumptive pathogenetic mechanism is that neurons rather than oligo-dendroglia play the pivotal role, despite glia inclusions being a prominent finding (e.g., corticobasal degeneration). As stated by Daniel et al. (1995), the presence of GCIs may merely represent a limited repertoire of responses of glia and neurons to a variety of stimuli, resulting in morphological similarities between clinically distinct neurodegenerative diseases. In any case, the presence of GCIs in MSA is an intringuing finding indicative of white matter involvement, a notion that had already been emphasized by Scherer in 1933.

Etiology MSA is a sporadic and idiopathic disorder (Quinn, 1989, 1994; Wenning et al., 1993; Wenning and Granata, 1998). Up to now, several studies have failed to identify genetically determined vulnerability to neuronal degeneration (see Lantos, 1998, and Wenning and Granata, 1998, for review). Impaired debrisoquine metabolism caused by mutations in the CYP2D6 gene or dynamic mutations associated with autosomal dominant cerebellar ataxia (ADCA) do not occur in MSA patients (Bandmann et al., 1997). The absence of optimized MSA animal models is an additional obstacle in scrutinizing the etiology of the disease (Wenning and Granata, 1998). Autoantibodies to glutamate receptor subunit GluR2 have recently been described in a sporadic OPCA patient (Gahring et al., 1997). However, the possible pathogenetic role of autoimmunity in MSA awaits confirmation of this finding in further MSA patients.

Clinical picture In-depth discussions of the nosology of MSA by Quinn (1989, 1994) and Wenning et al. (1994a, 1995, 1997) form the basis of the overview below. The mean age of onset is 52.2 9.0 years (range, 31 to 78) and the mean age at death is 60.5 8.7 years (range, 34 to 84). Extrapyramidal rigidity is the initial symptom in 46% of

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

cases, although 91% of them eventually develop parkinsonian semeiology, this being outstanding in 82% of cases. Rigidity and akinesia predominate; both are asymmetrical in 74% of cases. Any tremor is present in 66% of cases, but a classical pill-rolling rest tremor in only 9%. Up to 29% of cases show good response (>50%) to levodopa at some stage of treatment, although just 13% retained this at latest follow-up. Levodopa dyskinesias, with orofacial predominance, appear in 53% of cases (Hughes et al., 1992). Hypokinetic dysarthria, often mixed with other components (e.g., spasmodic or scanning), is common. Onset with cerebellar ataxia (static, kinetic, or both) occurs in 5% of cases, though any cerebellar signs are noted in 47% throughout the clinical course. In any case, isolated cerebellar semeiology is only an outstanding sign in 9% of cases. This is an obvious differential feature from sporadic OPCA (see above). Undoubtedly, ascertainment bias accounts for the difference, as most MSA series are reported by neurologists interested in extrapyramidal disorders, whereas clinicopathological studies of sporadic OPCA are done by general neurologists. Autonomic failure is considered an almost constant feature in MSA (Penney, 1995). This is the case when including here sphincter disturbances, a semeiology that is by no means always dysautonomic. Urodynamic studies have demonstrated that 48% of MSA patients do have detrusor hyperreflexia and 29% atonic detrusor (Beck et al., 1994), that is, dysautonomic failure is the cause of urinary disturbances in a minority of cases. As in ADCA, detrusor hyperreflexia is probably due to hyperactivity of the micturition pontine center as a result of diminution of inhibitory impulses coming from basal ganglia and substantia nigra (Kirby et al., 1986; Beck et al., 1994). A further mechanism of urinary incontinence is denervation of the external sphincter of the urethra as a consequence of degeneration of somatic Onuf’s nucleus (Mannen et al., 1982). It is obvious that, in most MSA cases, sphincter disturbances cannot be assigned to dysautonomia. In fact, urinary dysfunction is not different from that observed in ADCA or multiple sclerosis, where autonomic failure is not an integral part of the clinical picture. Symptomatic orthostatic hypotension (more than three syncopal attacks), the cardinal manifestation of SDS (see above), occurred in only 15 out of 100 MSA cases reported by Wenning et al. (1994a). Subclinical orthostatic hypotension was recorded, however, in 68% of cases. Other dysautonomic symptoms include male erectile dysfunction, constipation and decreased sweating. Male erectile dysfunction is an early and almost constant manifestation, but it has low specificity (Gilman et al., 1999) as it usually accompanies any kind of sphincter disturbance, which is

also an almost constant feature of MSA (Wild and Fowler, 1996). The author agrees with the notion that the term SDS has been widely misused (see above). While accepting a precise definition of the syndrome, such as autonomic failure plus central nervous system dysfunction attributable to MSA, there are occasional reported cases (e.g., those described by Shy and Drager themselves) in which dysautonomic features and urinary incontinence were the outstanding or the unique semeiology for years. For clinicians, the diagnostic and therapeutic approaches to these cases are quite different from those of MSA-P or MSA-C subtypes. Here, MSA of Shy–Drager type would be a useful diagnostic label; MSA-D MSA with predominant dysautonomic features could alternatively be used. The burial of Shy and Drager syndrome (Quinn et al., 1995; Gilman et al., 1999) seems to be premature. Furthermore, misinterpretation of Shy and Drager’s paper (1960) should not lead us to ignore the magnificent work of these authors, who accurately indicated that the disorder is a recognizable, distinct syndrome (Koeppen, 1999; see above). Pyramidal signs, that is, extensor plantar responses with hyperreflexia, occur in 61% of MSA patients. Corticospinal signs can contribute to the diagnosis, but are less important than abnormalities in the other domains. Both OPCA and MSA patients may develop dysphagia, probably due to superior esophageal sphincter dysfunction and, more rarely, laryngeal palsy (Berciano, 1982, 1998; Quinn, 1989, 1994). Like the striated muscles of the urethral and anal sphincters, the cricopharyngeus and posterior cricoarytenoid muscles are probably tonically and rhythmically active as a result of spontaneous discharge of reticular interneurons adjacent to the nucleus ambiguus. Conceivably, the tonic firing of these motor neurons (Onuf’s nucleus and nucleus ambiguus), which differs from the neuronal firing of other skeletal muscles, accounts for the conjoint tendency to degenerate in OPCA and MSA (Berciano, 1998). It is worth noting that the respiratory stridor resulting from paralysis of the abductor of vocal cords may be an inaugural manifestation of MSA. Although cognitive deterioration is not generally considered to be an integral feature of MSA, a recent neuropsychological study showed a distinct pattern of cognitive deficits suggesting a prominent frontal-lobe-like component (Robbins et al., 1992). Thus, a significant proportion of MSA patients failed specific tests investigating attention, speed of thinking, and spatial working memory. Pillon et al. (1995) found that dysexecutive syndrome of SND is similar to that of PD and less severe than in PSP. In any case, clinicopathological studies of MSA with symptoms of dementia are exceptional (Konagaya et al., 1999).

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Table 11.1 Clinical domains, features, and criteria used in the diagnosis of multiple system atrophy (MSA) I.

Autonomic and urinary dysfunction A. Autonomic and urinary features 1. Orthostatic hypotension (by 20 mmHg systolic or 10 mmHg diastolic) 2. Urinary incontinence or incomplete bladder emptying B. Criterion for autonomic failure or urinary dysfunction in MSA Orthostatic fall in blood pressure (by 30 mmHg systolic or 5 mmHg diastolic) or urinary incontinence (persistent, involuntary partial or total bladder emptying, accompanied by erectile dysfunction in men) or both II. Parkinsonism A. Parkinsonian features 1. Bradykinesia (slowness of voluntary movement with progressive reduction in speed and amplitude during repetitive actions) 2. Rigidity 3. Postural instability (not caused by primary visual, vestibular, cerebellar, or proprioceptive dysfunction) 4. Tremor (postural, resting, or both) B. Criterion for parkinsonism in MSA Bradykinesia plus at least one of items 2 to 4 III. Cerebellar dysfunction A. Cerebellar features 1. Gait ataxia (wide-based stance with steps of irregular length and direction) 2. Ataxic dysarthria 3. Limb ataxia 4. Sustained gaze-evoked nystagmus B. Criterion for cerebellar dysfunction in MSA Gait ataxia plus at least one of items 2 to 4 IV. Corticospinal tract dysfunction A. Corticospinal tract features 1. Extensor plantar responses with hyperreflexia B. Corticospinal tract dysfunction in MSA: no corticospinal tract features are used in defining the diagnosis of MSA Notes: A feature (A) is a characteristic of the disease and a criterion (B) is a defining feature or composite of features required for diagnosis Source: Reprinted with permission from Neurologia, Vol. 14, Gilman et al., Consenso sobre el diagnóstico de atrofia multisistémica, pp. 425–8, © 1999.

Parallel to OPCA, in MSA there may be a group of other manifestations, namely: nystagmus, saccadic ocular pursuit, hypometric saccadic eye movements, slowing of horizontal saccadic eye movements, myoclonus, hypopallesthesia, sleep disturbances, acroerythrocyanosis, disproportionate antecollis, and other dystonic postures including the recently reported Pisa syndrome (Colosimo, 1998).

Diagnosis Diagnosis relies mainly on clinical data. Quinn proposed clinical and neuropathological diagnostic criteria for MSA that have been extensively used. These criteria have recently been updated by a Consensus Conference and appear in Tables 11.1 and 11.2; exclusion criteria are summarized in Table 11.3 (Gilman et al., 1999).

Litvan et al. (1997) determined the accuracy of the clinical diagnosis of MSA starting from 105 autopsy-confirmed cases of MSA and related disorders (MSA, n 16; non-MSA, n 89). For the first visit (median, 42 months after the onset), the raters’ sensitivity (median, 56%; range, 50–69%) and positive predictive values (median, 76%; range, 61–91%) for the clinical diagnosis were not optimal. For the last visit (74 months after the onset) the raters’ sensitivity (median, 80%; range 56–94%) and positive predictive values (median, 80%; range, 77–92%) had improved. Primary neurologists correctly identified 25% and 50% of the patients with MSA at their first and last visits, respectively. False-negative and false-positive misdiagnoses frequently occurred in patients with PD and PSP. Early severe autonomic failure, absence of cognitive impairment, early cerebellar symptoms, and early gait disturbances were identified as the best predictive features to diagnose MSA.

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Table 11.2 Diagnostic categories of multiple system atrophy (MSA) III. Possible MSA: one criterion plus two features from separate other domains. When the criterion is parkinsonism, a poor levodopa response qualifies as one feature (hence only one additional feature is required) III. Probable MSA: criterion for autonomic failure/urinary dysfunction plus poorly levodopa-responsive parkinsonism or cerebellar dysfunction III. Definite MSA: pathologically confirmed by the presence of a high density of glial cytoplasmic inclusions in association with a combination of degenerative changes in the III. nigrostriatal and olivo-ponto-cerebellar pathways Notes: The features and criteria for each clinical domain are shown in Table 11.1. Source: Reprinted with permission from Neurologia, Vol. 14, Gilman et al., Consenso sobre el diagnóstico de atrofia multisistémica, pp. 425–8, © 1999.

Table 11.3 Exclusion criteria for the diagnosis of multiple system atrophy (MSA) III. History Symptomatic onset under 30 years of age Family history of a similar disorder Systemic diseases or other identifiable causes for features listed in Table 11.1 Hallucinations unrelated to medication III. Physical examination DSM criteria for dementia Prominent slowing of vertical saccades or vertical supranuclear gaze palsy Evidence of focal cortical dysfunction such as aphasia, alien limb syndrome, and parietal dysfunction III. Laboratory investigation Metabolic, molecular genetic, and imaging evidence of an alternative cause of features listed in Table 11.1 Source: Reprinted with permission from Neurologia, Vol. 14, Gilman et al., Consenso sobre el diagnóstico de atrofia multisistémica, pp. 425–8, © 1999.

Helpful pointers to MSA diagnosis include rapid progression, relative symmetry, absence of tremor at onset, and lack of response to levodopa. Even taking current diagnostic criteria into account, the sensitivity for the clinical diagnosis of MSA is low. To find biological markers is a pressing need. Postural hypotension is best investigated using a tilt table.

Plasma norepinephrine responses to postural changes can be monitored. Electrophysiological studies may reveal subclinical polyneuropathy in MSA (Golbe, 1998). An external urethral sphincter electromyogram usually reveals denervation in patients with MSA but not in those with PD (Beck et al., 1994). Unfortunately, sphincter denervation is not pathognomonic of MSA, as this finding has already been described in PSP (Valldeoriola et al., 1995). Routine hematological and biochemical studies are normal. The diagnostic value of an increased level of neurofilament protein in cerebrospinal fluid (see above) remains to be established. As genetic studies to detect denovo mutations of ADCA genes have been almost always negative, investigation of dynamic mutations is probably not worthwhile (see above) (Bandmann et al., 1997; Pujana et al., 1999). Neuroimaging studies may help to differentiate between MSA and PD. However, at the time of interpretation it should be borne in mind that the extent of MSA pathology is variable (see above). Therefore, the lack of uniform features on CT or MRI studies is hardly surprising. Wenning et al. (1994b) described CT findings in 33 MSA patients. All patients had autonomic dysfunction, all but one had parkinsonism, and 13 had cerebellar signs. CT scan was normal in 21%. Moderate or severe infratentorial atrophy, either cerebellar or pontine, was found in 42%. Interestingly, only 8 of the 13 patients with cerebellar ataxia had cerebellar atrophy. Supratentorial involvement was much less common and severe. It is concluded that CT imaging is of limited diagnostic value in individual patients with MSA. The diagnostic role of MRI in SND has already been reviewed (see above). More recently, Schrag et al. (1998) determined the sensitivity, specificity, and positive predictive values of a selection of abnormal findings in the putamen and infratentorial structures on MRI for distinguishing between MSA, PD, and age-matched controls. The specificity of the combined infratentorial and putaminal abnormal findings approached 100%. However, the sensitivity of those findings was limited, as a sizeable minority of patients with SND type of MSA had no abnormality on MRI, although the diagnosis could be made clinically. Undoubtedly, such a minority corresponds to cases in which the pathological framework is absence of lesions or at most gliosis without apparent neuronal loss (see above). In any case, MRI is useful to support a diagnosis of MSA versus PD, the absence of any of these changes in patients with SND-type MSA not excluding the diagnosis of MSA. However, it remains to be established whether MRI changes are specific to MSA, as patients with other

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conditions that occur in the differential diagnosis were not included (Counsell and Hughes, 1999). Magnetic resonance spectroscopy (MRS) study localized to the lentiform nucleus has shown different neuroimaging patterns in PD, MSA–OPCA and MSA–SND (Davie et al., 1995). The SND group showed a significant reduction in the N-acetylaspartate (NAA)/creatine ratio compared with the control ratio. In MSA–OPCA, the ratio was also significantly reduced, although to a lesser extent. In PD the ratio was normal. The reduction of the NAA/creatine ratio probably reflects neuronal loss. The choline/creatine ratio was significantly reduced in the MSA–SND group only, a finding indicative of impaired membrane turnover. It is worth noting that in this study it was not possible to establish a correlation between levodopa responsiveness in the MSA group and the degree of reduction in the NAA/creatine ratio. Thus, MRS is a useful, non-invasive technique to help differentiate MSA from PD. PET and to some degree single photon emission computed tomography (SPECT) remain largely research techniques. As a whole, studies using these techniques in MSA have demonstrated striatal hypometabolism, reduction of striatal 18F-fluorodopa uptake, and inconstant diminution of striatal non-opioid dopaminergic receptors (Brooks et al., 1990, 1992; Gilman et al., 1994; Schulz et al., 1994; Rinne et al., 1995; Antonini et al., 1997). MSA, PSP, and PD show a variable reduction of 18Ffluorodopa uptake, ranging from minimal reduction or normal findings in PD to moderate in MSA or severe reduction in PSP (Brooks et al., 1990). However, 18F-fluorodopa measurements may not distinguish between PD and MSA (Antonini et al., 1997). Results regarding dopamine D2 receptors in MSA are not homogeneous. A study of striatal D2 receptors with 11 C-raclopride has demonstrated variable findings in MSA, ranging between marked loss to similar findings to those observed in PD (Brooks et al., 1992). Such findings prompted Brooks et al. to conclude that failure of MSA patients to respond to levodopa cannot therefore be due to loss of striatal D2 sites alone, but must reflect loss of other basal ganglia connections. Now, almost a decade after Brooks’ results were reported, there is evidence arguing against this contention. Also, using 11C-raclopride as radioligand and PET, Antonini et al. (1997), in nine patients with degenerative parkinsonism and poor or no response to levodopa, found clear 11C-raclopride binding compared to PD patients and controls. Furthermore, in this study the measurement of striatal dopamine D2 binding was more sensitive than glucose metabolism in assessing the extent of neuronal degeneration. Using SPECT, two independent groups from Germany have also reported reduced levels of

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I-iodobenzamide (a specific dopamine antagonist with high affinity for D2 receptor) in patients with degenerative parkinsonism and no or poor levodopa response (Schulz et al., 1994; Schwarz et al., 1997). Undoubtedly, preservation of striatal D2 receptors in some cases correlates with the absence of or minimal putaminal lesions in about 15% of MSA brains (see above), and this percentage could be greater early in the clinical course. However, PET studies using D1 or striatal receptor ligands have revealed more clear evidence of striatal dysfunction that may help to differentiate MSA from PD. It is worth noting, however, that in the only autopsy study investigating striatal receptors by means of radiometric techniques, there was loss of putaminal postsynaptic D2 receptors in both MSA brains investigated, whereas D1 receptors were reduced only in one (Churchyard et al., 1993). The pathological study of these two cases showed marked neuron loss and gliosis in the middle and caudal portions of the putamen, accompanied by a corresponding and regional selective loss of postsynaptic D2 receptors. Once again, the characteristic variability of MSA pathological framework (see above) accounts for non-concordance between PET–SPECT studies and post-mortem autoradiography. Further investigations are needed to clarify this question. Using PET with [18F] fluorodeoxyglucose, Gilman et al. (1994) studied local metabolic rates for glucose (lCMRglc) in patients with MSA, sporadic OPCA, and dominant OPCA in comparison with normal control subjects. In all three syndromes there was significant lCMRglc reduction in the cerebellum and brainstem, but putamen hypometabolism occurred only in the MSA group. Several patients in this series had minimal atrophy and substantially reduced lCMRglc, a finding that indicates that PET study may be useful as a diagnostic test in patients with presumptive diagnosis of MSA or OPCA and normal CT or MRI. Both in the MSA and sporadic OPCA groups, but not in dominant OPCA, hypometabolism was observed in forebrain and cerebral cortical structures. The authors interpreted this finding as consistent with the possibility that, in many cases, sporadic OPCA will evolve into MSA (see above). However, during the period of study (1988–94, see Gilman et al., 1994), only one of the 33 sporadic OPCA patients had developed extrapyramidal and autonomic symptoms.

Differential diagnosis MSA should be distinguished from other parkinsonian, cerebellar-plus or dysautonomic-plus syndromes (Golbe, 1998). The distinctions between MSA and ILOCA syndrome have already been reviewed (see above).

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

MSA is most frequently misdiagnosed as PD. Clinical pointers indicated above are helpful in distinguishing MSA from PD and PAF. Furthermore, neuroimaging techniques showing abnormal basal ganglia signal or posterior fossa atrophy lend support to MSA diagnosis. PSP shares semeiology with MSA. Dysautonomia is not an integral part of the PSP clinical picture. Furthermore, supranuclear ophthalmoplegia in PSP involves vertical gaze, whereas in MSA it involves horizontal gaze. Hyperextension of the head, disproportionate nuchal rigidity, and apraxia of eyelid opening are suggestive of PSP. Highly asymmetric signs and the presence of signs of cortical dysfunction such as apraxia and cortical sensory loss in corticobasal degeneration, allow one to distinguish progressive supranuclear palsy from MSA. Focal myoclonus and asymmetric frontoparietal atrophy on MRI also argue in favor of corticobasal degeneration. Multi-infarct states may mimic not only MSA but also many other neurodegenerative syndromes. Stepwise progression, coexistence of vascular risk factors, and the presence of vascular lesions on MRI scan give support to a vascular syndrome. The characteristic absence of mental impairment in MSA is the main differential feature from the long list of diseases causing parkinsonian or cerebellar syndrome and dementia (e.g., Alzheimer’s disease, Creutzfeldt–Jakob disease, or diffuse Lewy body disease).

Prognosis MSA is a relentlessly progressive and incapacitating disease (Quinn, 1989, 1994; Wenning et al., 1994a). Complications from the disease include gait imbalance and postural instability with frequent falling, dysphagia that can produce aspiration pneumonia, and laryngeal dysfunction that may result in sudden death. The increasing immobility and inability to care for oneself eventually lead to significant debilitation, requiring complete help for the patient’s activities of daily life. However, as MSA is a heterogeneous syndrome, its clinical course is not uniform. In a series of autopsy-proven cases, mean survival was 8.0 years (Hughes et al., 1992), whereas in a series of 100 clinically diagnosed MSA patients, the median actuarially corrected survival was 9.5 years (Wenning et al., 1994a). Better survival is linked to cases of younger onset and predominant cerebellar semeiology. Disease progression is much faster than in the hereditary ataxias (Klockgether et al., 1998).

Table 11.4 Symptomatic treatment of multiple system atrophy A. Extrapyramidal signs Carbidopa/levodopa Dopamine agonists: pergolide, bromocriptine B. Autonomic failure 1. Orthostatic hypotension elastic support stockings, abdominal binders head-up tilt of the bed at night increased salt intake fluorocortisone (↓ salt loss, ↑ plasma volume) midodrine, clonidine, ephedrine (vasoconstriction) indomethacin, propranolol (prevent vasodilatation) caffeine, octreotide (↓ postprandial hypotension) desmopressin (↓ nocturnal polyuria) erythropoietin (↑ red cell mass) 2. Urinary disturbances oxybutinin, propantheline urinary acidification intermittent or continuous urinary catheterization 3. Constipation dietary fiber liquid ingestion bulk agents, laxatives 4. Respiratory difficulties/sleep disturbances clonazepam tracheostomy 5. Dysphagia appropriate diet percutaneous gastrostomy C. Psychosocial support D. Occupational therapy E. Speech therapy

Treatment Symptomatic treatment is summarized in Table 11.4. Levodopa may provide some benefit for the extrapyramidal rigidity, bradykinesia, and postural instability, but is effective in less than half of MSA cases and rarely more than moderately so (Hughes et al., 1992; Golbe, 1998). As in PD, treatment may be initiated with Sinemet 25/100, 0.5 to 1 tablet twice a day, and increased every few days to efficacy or toxicity. Good levodopa responsiveness could be linked to relative putaminal preservation (see above). Dopaminergic side-effects may appear, with oral dyskinesias predominating (Hughes et al., 1992); their treatment does not differ from that of PD. If there is no response, dopamine agonists such as pergolide or bromocriptine in maximally tolerable doses may also be used. These

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medications should be discontinued if there is no beneficial effect after a reasonable period (three to six months) of treatment. Postural hypotension is exacerbated by prolonged recumbency, at mealtimes, on physical exertion, coughing, and defecation. It is recommended that physical exertion should not closely follow mealtimes. Orthostatic hypotension is usually worsened by dopaminergic drugs, and treatment with elastic support stockings, head-up tilt of the bed at night, increased salt intake, and adding fluorocortisone (starting at 0.1 mg/daily and increasing to a maximun of four tablets per day in two divided doses) or midodrine (starting at 2.5 mg three times a day and increasing to 10 mg three times a day) may be necessary (Koening and Mathias, 1996; Golbe, 1998). If these drugs are unsuccessful, inhibition of vasodilator prostaglandin synthesis may be initiated with indomethacin (25 mg three times a day with meals, increasing to 50 mg three times a day). Alternatives include the alpha-adrenergic agonist clonidine (0–1 mg twice a day, increasing to 0.3 mg twice a day), ephedrine (starting at 25 mg three times a day), and propranolol (starting at 20 mg twice a day). Urinary disturbances due to detrusor hyperreflexia are treated with a peripherally acting anticholinergic agent such as oxybutinin (5–10 mg at bedtime) or propantheline (15–30 mg at bedtime). The impotence of MSA may respond to yohimbine (5.6 mg one to three times daily) (Wild and Fowler, 1996; Golbe, 1998). In all cases, treatment of urinary disturbances should be carried out in close collaboration with an expert in neuro-urology. Sleep disturbances usually respond well to clonazepam (0.5 mg at bedtime). Obstructive sleep apnea and laryngeal paresis may require tracheostomy. However, the patient’s quality of life should be taken into account if a tracheostomy is proposed. There is no proven treatment for the ataxia in MSA–OPCA (Golbe, 1998). Psychosocial support is most important. Physical, occupational, and speech therapies may be essential to reduce the patient’s disability and to maintain independent functioning for longer. Gait training and assistive devices to prevent falling will avoid further debilitation of the patient (Lai, 1998).

Acknowledgments I am grateful to Mr John Hawkins for stylistic revision and to Mrs Marta de la Fuente for secretarial help. The writing of this chapter was supported by ‘Fundación La Caixa’ (Grant No. 98/017–00) and ‘Fondo de Investigación Sanitaria’ (Grant No. 99/0046–01).

Addendum After submitting this chapter, we have reported a postmortem autoradiographic study analyzing with specific markers the dopamine presynaptic terminals and dopamine D2 receptors in the putamen of four Parkinson’s disease, one striatonigral degeneration, and six control brains (González et al., 2000). Dopamine uptake transporter was dramatically decreased (>90%) in the striatum of both Parkinson’s disease and striatonigral degeneration. Dopamine D2 receptors were preserved in Parkinson’s disease, but clearly reduced (>76%) in the striatonigral degeneration putamen. As indicated under the section on the diagnosis of multiple system atrophy (above), these data corroborate the observations by Churchyard et al. (1993) and confirm that levodopa response is closely associated with the preservation of striatal dopamine D2 receptors.

xReferencesx Adams, R.D., Van Bogaert, L. and Van der Eecken H. (1961). Dégénérescences nigro-striées et cerebello-nigro-striées (unicité et variabilité pathologique des dégénérescences préséniles à forme de rigidité extrapyramidale). Psychiatr Neurol (Basel) 142: 219–59. Adams, R.D., Van Bogaert, L. and Van der Eecken, H. (1964). Striatonigral degeneration. J Neuropath Exp Neurol 23: 584–608. Antonini, A., Leenders, K.L., Vontobel, P. et al. (1997). Complementary PET studies of striatal neuronal function in the differential diagnosis between multiple system atrophy and Parkinson’s disease. Brain 120: 2187–95. Bandmann, O., Sweeney, M.G., Daniel, S.E. et al. (1997). Multiplesystem atrophy is genetically distinct from identified inherited causes of spinocerebellar degeneration. Neurology 49: 1598–604. Beck, R.O., Betts, C.D. and Fowler, C.J. (1994). Genitourinary dysfunction in multiple system atrophy: clinical features and treatment of 62 cases. J Urol 151: 1336–41. Berciano, J. (1978). Nuevas contribuciones al conocimiento clínico y patológico de la atrofia olivopontocerebelosa. Doctoral thesis, Universidad of Bilbao, Spain. Berciano, J. (1982). Olivopontocerebellar atrophy. A review of 117 cases. J Neurolog Sci 53: 253–72. Berciano, J. (1998). Olivopontocerebellar atrophy. In Parkinson’s Disease and Movement Disorders, 3rd edn, ed. J. Jankovic and E. Tolosa, pp. 263–95. Baltimore: Williams Wilkins. Berciano, J., Combarros, O., Polo, J.M., Pascual, J. and Oterino, A. (1999). An early description of striatonigral degeneration. J Neurol 246: 462–6. Berciano, J. and Ferrer, I. (1996). Neuronal and glial cytoplasmic inclusions in familial olivopontocerebellar atrophy. Ann Neurol 40: 819–20.

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Bower, J.H., Maraganore, D.N., McDonnell, S.K. and Rocca, W.A. (1997). Incidence of progressive supranuclear palsy and multiple system atrophy in Olmsted County, Minnesota, 1976 to 1990. Neurology 49: 1284–8. Brooks, D.J., Ibanez, V., Sawle, G.V. et al. (1992). Striatal D2 receptors status in patients with Parkinson’s disease, striatonigral degeneration, and progressive supranuclear palsy measured with 11Craclopride and positron emission tomography. Ann Neurol 31: 184–92. Brooks, D.J., Salmon, E.P., Mathias, C.J., Quinn, N., Leenders, K.L. and Bannister, R. (1990). The relationship between locomotor disability, autonomic dysfunction, and the integrity of the striatal dopaminergic system in patients with multiple system atrophy, pure autonomic failure, and Parkinson’s disease, studied with PET. Brain 113: 1539–52. Churchyard, A., Donnan, G.A., Hughes, A. et al. (1993). Dopa resistance in multiple system atrophy: loss of postsynaptic D2 receptors. Ann Neurol 34: 219–26. Clayton, D.F. and George, J.M. (1998). The synucleins: a family of proteins involved in synaptic function, plasticity, neurodegeneration and disease. Trends Neurosci 21: 249–54. Colosimo, C. (1998). Pisa syndrome in a patient with multiple system atrophy. Mov Disord, 13: 607–9. Counsell, C. and Hughes, A. (1999). Clinical usefulness of MRI in multisystem atrophy. J Neurol Neurosurg Psychiatry 66: 694. Critchley, M. and Greenfield, J.G. (1948). Olivo-ponto-cerebellar atrophy. Brain 71: 343–64. Daniel, S.E., Greddes, J.F. and Revesz, T. (1995). Glial cytoplasmic inclusions are not exclusive to multiple system atrophy. J Neurol Neurosurg Psychiatry 58: 262. Davie, C.A., Wenning, G.K., Barker, G.J. et al. (1995). Differentiation of multiple system atrophy from idiopathic Parkinson’s disease using proton magnetic resonance spectroscopy. Ann Neurol 37: 204–10. Déjerine, J. and Thomas, A. (1900). L’atrophie olivo-ponto-cérébelleuse. Nouvelle Iconographie de la Salpêtrière 13: 330–70. Eidelberg, D., Tatikawa, S., Moeller, J.R. et al. (1993). Striatonigral hypometabolism distinguishes striatonigral degeneration from Parkinson’s disease. Ann Neurol 53: 518–27. Fearnley, J.M. and Lees, A.J. (1990). Striatonigral degeneration: a clinico-pathologic study. Brain 113: 1823–32. Futamura, N., Matsumura, R., Fujimoto, Y., Horikawa, H., Sazumura, A. and Takayanagi, T. (1998). CAG repeat expansions in patients with sporadic ataxia. Acta Neurol Scand 98: 55–9. Gahring, L.C., Rogers, S.W. and Twyman, R.E. (1997). Autoantibodies to glutamate receptor subunit GluR2 in nonfamilial olivopontocerebellar degeneration. Neurology 48: 494–500. Gai, W.P., Power, J.H.T., Blumbergs, P.C. and Blessing, W.W. (1998). Multiple system atrophy: a new -synuclein disease? Lancet 352: 547–8. Gilman, S., Koeppe, R.A., Junck, L., Kluin, K.J., Lohman, M. and St Laurent, R. (1994). Patterns of cerebral glucose metabolism detected with positron emission tomography differ in multiple system atrophy and olivopontocerebellar atrophy. Ann Neurol 36: 166–75.

Gilman, S. and Quinn, N.P. (1996). The relationship of multiple system atrophy to sporadic olivopontocerebellar atrophy and other forms of idiopathic late onset cerebellar atrophy. Neurology 46: 1197–9. Gilman, S., Low, P., Quinn, N.P. et al. (1999). Consenso sobre el diagnóstico de atrofia multisistémica. Neurología 14: 425–8. Gilman, S., Sima, A.A.F., Junck, K. et al. (1996). Spinocerebellar ataxia type I with multiple system degeneration and glial cytoplasmic inclusions. Ann Neurol 39: 241–55. Golbe, L.I. (1998). Multiple system atrophy. In Neurobase, ed. S. Gilman, G.W. Goldstein and S.G. Waxman. San Diego: Arbor Publishing. Golbe, L.I. (1999). Alpha-synuclein and Parkinson’s disease. Mov Disord 14: 6–9. González, A.M., Berciano, J., Figols, J., Pazos, A. and Pascual, J. (2000). Loss of dopamine uptake sites and dopamine D2 receptors in striatonigral degeneration. Brain Res 852: 228–32. Graham, J.G. and Oppenheimer, D.R. (1969). Orthostatic hypotension and nicotine sensitivity in a case of multiple system atrophy. J Neurol Neurosurg Psychiatry 32: 28–34. Greenfield, J.G. (1954). The Spino-cerebellar Degenerations. Oxford: Backwell. Harding, A.E. (1981). ‘Idiopathic’ late onset cerebellar ataxia. A clinical and genetic study of 36 cases. J Neurolog Sci 51: 259–71. Harding, A.E. (1984). The Hereditary Ataxias and Related Disorders. Edinburgh: Churchill Livingstone. Holmberg, B., Rosengren, L., Karlsson, J.E. and Johnels, B. (1998). Increased cerebrospinal fluid levels of neurofilament protein in progressive supranuclear palsy and multiple-system atrophy compared with Parkinson’s disease. Mov Disord 13: 70–7. Hughes, A.J., Colosimo, C., Kleeforfer, B., Daniel, S.E. and Lees, A.J. (1992). The dopaminergic response in multiple system atrophy. J Neurol Neurosurg Psychiatry 55: 1009–13. Ito, H., Kusaka, H., Matsumoto, S. and Imai, T. (1996). Striatal efferent involvement and its correlation to levodopa efficacy in patients with multiple system atrophy. Neurology 47: 1291–9. Kirby, R., Fowler, C., Gosling, J. and Bannister, R. (1986). Urethrovesical dysfunction in progressive autonomic failure with multiple system atrophy. J Neurol Neurosurg Psychiatry 49: 554–62. Klockgether, T., Lüdtke, R., Kramer, B. et al. (1998). The natural history of degenerative ataxia: a retrospective study in 466 patients. Brain 121: 589–600. Klockgether, T., Schroth, G., Diener, H.C. and Dichgans, J. (1990). Idiopathic cerebellar ataxia of late onset: natural history and MRI morphology. J Neurol Neurosurg Psychiatry 53: 297–305. Koening, E. and Mathias, C.J. (1996). Autonomic dysfunction. In Neurological Disorders. Course and Treatment, ed. T. Brandt, L.R. Caplan, J. Dichgans, H.C. Diener and C. Kennard, pp. 1035–48. San Diego: Academic Press. Koeppen, A.H. (1999). Editorial. J Neurol Sci 163, 4–5. Konagaya, M., Sakai, M., Matsuoka, Y., Konagaya, Y. and Hashizume, Y. (1999). Multiple system atrophy with remarkable frontal lobe atrophy. Acta Neuropathol (Berlin) 97: 423–8. Lai, E.C. (1998). Striatonigral degeneration. In Neurobase, ed. S.

195

196

J. Berciano

Gilman, G.W. Goldstein and S.G. Waxman. San Diego: Arbor Publishing. Lantos, P.L. (1998). The definition of multiple system atrophy: a review of recent developments. J Neuropathol Exp Neurol 57: 1099–111. Litvan, I., Goetz, C.G., Jankovic, J. et al. (1997). What is the accuracy of the clinical diagnosis of multiple system atrophy. Arch Neurol 54: 937–44. Loew, P. (1903–4). L’atrophie olivo-ponto-cérébelleuse. Doctoral thesis, University of Paris. Mannen, T., Iwata, M., Toyokura, Y. and Nagashima, K. (1982). The Onuf’s nucleus and the external sphincter muscles in amyotrophic lateral sclerosis and Shy–Drager syndrome. Acta Neuropathol 58: 225–60. Menzel, P. (1891). Beitrage zur Kenntniss der hereditären Ataxie und Kleinhirnatrophie. Arch Psychiatr Nervenkrankh 22: 160–90. Ormerod, I.E.C., Harding, A.E., Miller, D.H. et al. (1994). Magnetic resonance imaging in degenerative ataxic disorders. J Neurol Neurosurg Psychiatry 57: 51–7. Papp, M.I., Kahn, J.E. and Lantos, P.L. (1989). Glial cytoplasmic inclusions in the CNS of patients with multiple system atrophy (striatonigral degeneration, olivopontocerebellar atrophy and Shy Drager syndrome). J Neurol Sci 94: 79–100. Papp, M.I. and Lantos, P.L. (1994). The distribution of oligodendroglial inclusions in multiple system atrophy and its relevance to clinical symptomatology. Brain 117: 235–43. Pascual, J., Pazos, A., Del Olmo, E., Figols, E., Leno, C. and Berciano, J. (1991). Presynaptic parkinsonism in olivopontocerebellar atrophy: clinical, pathological and neurochemical evidence. Ann Neurol 30: 425–8. Penney, J.B. (1995). Multiple systems atrophy and non-familial olivopontocerebellar atrophy are the same disease. Ann Neurol 37: 553–4. Pillon, B., Gonider-Khouja, N., Deweer, B. et al. (1995). Neuropsychological pattern of striatonigral degeneration: comparison with Parkinson’s disease and supranuclear palsy. J Neurol Neurosurg Psychiatry 58: 174–9. Polo, J.M., Calleja, J., Combarros, O. and Berciano, J. (1991). Hereditary ataxias and paraplegias in Cantabria, Spain. An epidemiological and clinical study. Brain 114: 855–66. Pujana, M.A., Corral, J., Gratacòs, M. et al. (1999). Spinocerebellar ataxia in Spanish patients: genetic analysis of familial and sporadic cases. Hum Genet 104: 516–22. Quinn, N. (1989). Multiple system atrophy – the nature of the beast. J Neurol Neurosurg Psychiatry 52 (Suppl.): 78–89. Quinn, N. (1994). Multiple system atrophy. In Movement Disorders 3, ed. C.D. Marsden and S. Fahn, pp. 262–81. London: Butterworths. Quinn, N.P., Wenning, G. and Marsden, C.D. (1995).The Shy-Drager syndrome. What did Shy and Drager really describe? Arch Neurol 52: 656–7. Ramos, A., Quintana, F., Díez, C., Leno, C. and Berciano, J. (1987) CT findings in spinocerebellar degeneration. Am J Neuroradiol 8: 635–40. Ranum, L.P.W., Chung, M., Banfi, S. et al. (1994). Molecular and

genetic correlations in spinocerebellar ataxia type I: evidence for familial effects of the age at onset. Am J Hum Genet 55: 244–52. Rinne, J.O., Burn, D.J., Mathias, C.J., Quinn, N.P., Marsden, C.D. and Brooks, D.J. (1995). Positron emission tomography studies on the dopaminergic system and striatal opioid binding in the olivopontocerebellar atrophy variant of multiple system atrophy. Ann Neurol 37: 568–73. Robbins, T.W., James, M., Lange, K.W., Owen, A.M., Quinn, N.P. and Marsden, C.D. (1992). Cognitive performance in multiple system atrophy. Brain 115: 271–91. Rosenhagen, H. (1943). Die primäre Atrophie des Brückenfüsses und der unteren Oliven (dargestellt nach klinischen und anatomischen Beobachtungen). Arch Psychiatr Nervenkrankh 116: 163–228. Savoiardo, M. and Grisoli, M. (1998). Magnetic resonance imaging of movement disorders. In Parkinson’s Disease and Movement Disorders, ed. J. Jankovic and E. Tolosa, pp. 967–90. Baltimore: Williams & Wilkins. Scherer, H.J. (1933). Extrapyramidale Störungen bei de olivopontocerebellären Atrophie. Ein Beitrage zum Problem des lokalen vorseitigen Alterns. Z Gesamte Neurol Psychiatr 145: 406–19. Schrag, A., Kingsley, D., Phatouros, C. et al. (1998). Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry 65: 65–71. Schulz, J.B., Klockgether, T., Petersen, D. et al. (1994). Multiple system atrophy: natural history, MRI morphology and dopamine receptor imaging with 123IBZM-SPECT. J Neurol Neurosurg Psychiatry 57: 1047–56. Schwarz, J., Tatsch, K., Gasser, T., Arnold, G. and Oertel, W.H. (1997). 123IBZM binding predicts dopaminergic responsiveness in patients with parkinsonism and previous dopaminomimetic therapy. Mov Disord 12: 898–902. Schwarz, J., Weiss, S., Kraft, E. et al. (1996). Signal changes on MRI and increases in reactive microgliosis, astrogliosis, and iron in the putamen of two patients with multiple system atrophy. J Neurol Neurosurg Psychiatry 60: 98–101. Shy, G.M. and Drager, G.A. (1960). A neurologic syndrome associated with orthostatic hypotension. Arch Neurol 2: 511–27. Silveira, I., Lopes-Cendes, J., Kish, S. et al. (1996). Frequency of spinocerebellar ataxia type 1, dentatorubropallidoluysian atrophy, and Machado–Joseph disease mutations in a large group of spinocerebellar ataxia patients. Neurology 46: 214–18. Tu, P., Galvin, J.E., Baba, M. et al. (1998). Glial cytoplasmic inclusions in white matter oligodendrocytes of multiple system atrophy brains contain insoluble -synuclein. Ann Neurol 44: 415–22. Valldeoriola, F., Valls-Solé, J., Tolosa, E.S. and Marti, M.J. (1995). Striatal and sphincter denervation in patients with progressive supranuclear palsy. Mov Disord 10: 550–5. Van Ingelghem, E., Van Zandijcke, M. and Lammens, M. (1994). Pure autonomic failure: a new case with clinical, biochemical and necropsy data. J Neurol Neurosurg Psychiatry 57: 745–7. Welte, E. (1939). Die Atrophie des Systems des Brückenfüsses und der unteren Oliven. Arch Psychiatr Nervenkrankh 109: 649–98. Wenning, G.K., Ben-Shlomo, Y., Magalhães, M., Daniel, S.E. and

Multiple system atrophy and idiopathic late-onset cerebellar ataxia

Quinn, N.P. (1994a). Clinical features and natural history of multiple system atrophy. An analysis of 100 cases. Brain 177: 835–45. Wenning, G.W., Ben-Shlomo, Y., Magalhães, M., Daniel, S.E. and Quinn, N.P. (1995). Clinicopathological study of 35 cases of multiple system atrophy. J Neurol Neurosurg Psychiatry 58: 160. Wenning, G.K. and Granata, R. (1998). Multiple system atrophy: more on the nature of the beast. Neurologia 13: 105–10. Wenning, G.K., Jäger, R., Kendall, B., Kingsley, D., Daniel, S.E. and Quinn, N. (1994b). Is cranial computerized tomography useful in the diagnosis of multiple system atrophy? Mov Disord 9: 333–6. Wenning, G.K., Quinn, N., Magalhães, M., Mathias, C. and Daniel, S.E. (1994c). ‘Minimal change’ multiple system atrophy. Mov Disord 9: 161–6.

Wenning, G.K., Tison, F., Ben-Shlomo, Y., Daniel, S.E. and Quinn, N.P. (1997). Multiple system atrophy: a review of 203 pathologically proven cases. Mov Disord 12: 133–47. Wenning, G.K., Wagner, S., Daniel, S. and Quinn, N.P. (1993). Multiple system atrophy: sporadic or familial? Lancet 342: 681. Wild, B. and Fowler, C.J. (1996). Neurogenic disorders of micturation, defecation and sexual function. In Neurological Disorders. Course and Treatment, ed. T. Brandt, L.A. Caplan, J. Dichgans, H.C. Diener and C. Kennard, pp. 1049–62. San Diego: Academic Press. Zarranz Imirizaldu, J.J. and Rivera Pomar, J.M. (1984). Degeneración estrionígrica. In Heredodegeneraciones Espinocerebelosas (VI Congreso Nacional de Neurología), ed. P. Salisachs, J. Berciano and A. Codina, pp. 95–115. Barcelona: Gráficas Poutuca.

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Corticobasal degeneration Mario-Ubaldo Manto1 and Jean Jacquy2 1 2

Cerebellar Ataxias Unit Department of Neurology, Free University of Brussels, Belgium

Introduction

Table 12.1 Clinical signs in corticobasal degeneration

Corticobasal degeneration (CBD), also called corticobasal ganglionic degeneration (CBGD), was first described by Rebeiz et al. (1967, 1968). It is a slowly progressive, sporadic disease, usually appearing after the age of 50 and affecting both sexes equally (Rinne et al., 1994). CBD is now classified in the group of tauopathies, due to inclusions related to abnormally phosphorylated protein tau (Tolnay and Probst, 1999).

Major features

Minor features

Asymmetric akinetic-rigid syndrome Cortical sensory loss Apraxia Astereognosis Abnormal graphestesia Tactile extinction Dysphasia Pyramidal signs Alien hand Dystonia of limbs Myoclonus Tremor

Blepharospasm Choreoathetosis

Clinical features The main clinical features are given in Table 12.1. In the series of Rinne et al., 20 patients over the age of 36 presented with complaints related to a jerky, stiff or clumsy upper limb (Rinne et al., 1994). Similar symptoms related to gait occurred in ten patients. In most of the cases, patients exhibit an asymmetric akinetic-rigid syndrome. Cortical signs are often associated: apraxia, cortical sensory loss, dysphasia, and pyramidal signs. In addition, a dystonic posture of the hand occurs in the majority of patients. ‘Alien hand’ is a sign suggestive of CBD (Doody and Jankovic, 1992). It includes failure to recognize ownership of one’s limb when visual cues are removed, a feeling that part of the body is foreign, and autonomous activity perceived as independent of voluntary control (Doody and Jankovic, 1992). Myoclonus is often focal and stimulus sensitive at the beginning of the disease (Chen et al., 1992). Neuropsychiatric disturbances are more frequent than previously thought, including depression, apathy, irritability, and agitation (Litvan et al., 1998). Cerebellar dysfunction has not received much attention in CBD. However, a veritable cerebellar syndrome may occur in CBD, but cerebellar ataxia is often masked by the extrapyramidal syndrome and by a concomitant parietal

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Cerebellar ataxia Cognitive impairment Supranuclear gaze deficit

ataxia. The presence of tremor in CBD is one of the reasons for the difficulty associated with clinically demonstrating cerebellar dysfunction in the disease. Tremor is rapid (5–8 Hz), irregular, and has a jerky component, often combined with myoclonic discharges. A kinetic tremor may be observed, characterized by an intensity that increases with velocity of movement. The addition of a mass to the limb attenuates tremor and exacerbates hypermetric movements, especially at the proximal level. However, testing is often difficult, due to various combinations of rigidity, dystonia, and apraxia.

Diagnostic studies Brain computed tomography and magnetic resonance imaging With progression of the disease, serial brain computed tomography (CT) and brain magnetic resonance imaging

Corticobasal degeneration

SPECT/PET studies Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) studies suggest asymmetric involvement of cortical structures around peri-rolandic cortex and thalamus (Eidelberg et al., 1991).

Neuropathological findings

Fig. 12.1 Illustration of wrist flexion movements towards a fixed target located at 15 degrees in a patient presenting CBD. Movements are recorded on the patient’s left side. The patient exhibited a marked akinetic–rigid syndrome, alien hand sign, and a stimulus-sensitive myoclonus on the right side. On the left side, neurological examination showed a mild rigidity associated with kinetic tremor and adiadochokinesia. Movements were hypermetric.

(MRI) will demonstrate an asymmetric atrophy at the level of frontoparietal cortex, correlating with laterality of clinical signs. Cerebellar atrophy can be found. Interestingly, cerebellar atrophy tends to be symmetrical, by contrast with atrophy in frontoparietal areas.

Electrophysiological studies Electroencephalogram (EEG) recording shows a slowing, which is also often asymmetrical. Electrophysiological investigations are useful to analyze tremor and myoclonus. Action myoclonus is not preceded by a cortical discharge, and there is no enlargement of sensory evoked potentials (SEP) (Thompson et al., 1994). In hand muscles, reflex myoclonus following median nerve stimulation has a latency of about 40 ms. Jerks are due to hypersynchronous, short-duration bursts of electromyogram (EMG) activity. Analysis of ballistic movements may demonstrate a hypermetria (Fig. 12.1). Hypermetria may be associated with a delayed onset latency of antagonist EMG activity, which is highly suggestive of cerebellar dysfunction (see Chapter 8). The overshoot tends to be higher in the limb that is less affected by rigidity and dystonia.

Macroscopically, asymmetry in cortical atrophy at the level of frontoparietal areas is characteristic. Anterior frontal cortex is occasionally affected, whereas temporal and occipital cortex are unremarkable. Microscopic analysis demonstrates gliosis and neuronal loss. Swollen and achromatic ‘ballooned’ neurons are distinguishing, though they are not a specific histopathologic feature. They are found in cortical and subcortical areas. Among subcortical nuclei, degeneration of substantia nigra is usually the most evident (Watts et al., 1994). The thalamus, red nucleus, dentate nucleus, and inferior olive also show variable degrees of cell loss. Marked neuronal degeneration at the level of the dentatorubrothalamic pathway has been highlighted in some patients (Litvan et al., 1996). Neuropil threads and occasionally neurofibrillary tangles are observed, including in brainstem nuclei such as the inferior olivary nuclear complex. The neuropil threads have a more distinct profile in CBD than in Alzheimer’s disease or progressive supranuclear palsy (Komori et al., 1997).

Pathogenesis of cerebellar ataxia There are several causes of cerebellar ataxia in CBD: involvement of olivocerebellar tracts, of the afferent pontocerebellar pathway, of the dentate nucleus and its efferent pathways. Ataxia is also related to parietal disease, which generates combinations of sensory and pseudocerebellar ataxia.

Differential diagnosis Corticobasal degeneration is a pathologically and clinically heterogeneous disorder with substantial overlap with other neurodegenerative disorders (Schneider et al., 1997). Signs of cerebral cortex involvement and lack of benefits from anti-parkinsonian therapy are important clues for differential diagnosis with Parkinson’s disease. Multiple system atrophy is a differential diagnosis of CBD in a patient exhibiting a degenerative disease with cerebellar and extracerebellar signs (Table 12.2).

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Table 12.2 Differential diagnosis of corticobasal degeneration

Disease

Occurrence of cerebellar signs

Parkinson’s disease Parkinson’s disease with dementia Progressive supranuclear palsy Lewy body disease Pick’s disease Multiple system atrophy Wilson’s disease Neuronal ceroid lipofuscinosis Creutzfeldt–Jakob disease

        

Alien hand sign is also observed in multiple infarcts. However, the association of alien hand sign with cortical reflex myoclonus is indicative of CBD (Doody and Jankovic, 1992).

Treatment Treatment provides small benefits. Levodopa and dopamine agonists may improve the extrapyramidal features slightly. Clonazepam is often administered to treat myoclonus or tremor, and has some effect in cerebellar ataxia, whereas the effect of baclofen is often very limited. Botulinum toxin may improve dystonic posture of the hand. Neuropsychological aspects should not be underestimated in the management of patients with CBD. Physiotherapy, occupational therapy, and speech rehabilitation are recommended to keep some degree of functional independence (Watts et al., 1997). At an advanced stage, dysphagia becomes so marked that a gastrostomy may be necessary.

Prognosis Usually, the disease progresses slowly over a period of four to eight years, leading to death.

Conclusions Little effort has been devoted so far to describing the cerebellar involvement in CBD. This is partly explained by the fact that extrapyramidal signs mask cerebellar deficits and

by the prominent parietal involvement. Clinical and experimental investigations are required to define better the impacts of cerebellar dysfunction in CBD, including thorough neuropsychological studies considering recent advances in the understanding of the roles of cerebellum in cognition (Schmahmann, 1997). Neuroradiological studies should include quantitative volumetric measurements of posterior fossa structures. In the future, functional imaging techniques might prove to be interesting methods to investigate cerebellar dysfunction in CBD and the role of cerebello-parietal connections in the impairment of voluntary movement.

Acknowledgments M-U. Manto is supported by the Belgian National Research Foundation, the Bureau des Relations Internationales (ULB), and the Belgian American Educational Foundation (BAEF).

xReferencesx Chen, R., Ashby, P. and Lang, A.E. (1992). Stimulus-sensitive myoclonus in akinetic-rigid syndromes. Brain 115: 1875–88. Doody, R.S. and Jankovic, J. (1992). The alien hand and related signs. J Neurol Neurosurg Psychiatry 55: 806–10. Eidelberg, D., Dhawan, V., Moeller, J.R. et al. (1991). The metabolic landscape of corticobasal ganglionic degeneration: regional asymmetries studied with positron emission tomography. J Neurol Neurosurg Psychiatry 54: 856–82. Komori, T., Arai, N., Oda, M. et al. (1997). Morphologic difference of neuropil threads in Alzheimer’s disease, corticobasal degeneration and progressive supranuclear palsy: a morphometric study. Neurosci Lett 233: 89–92. Litvan, I., Cummings, J.L. and Mega, M. (1998). Neuropsychiatric features of corticobasal degeneration. J Neurol Neurosurg Psychiatry 65: 717–21. Litvan, I., Hauw, J.J., Bartko, J.J. et al. (1996). Validity and reliability of the preliminary NINDS neuropathologic criteria for progressive supranuclear palsy and related disorders. J Neuropathol Exp Neurol 55: 97–105. Rebeiz, J.J., Kolodny, E.H. and Richardson, E.P. (1967). Corticodentatonigral degeneration with neural achromasia: a progressive disorder of late adult life. Trans Am Neurol Assoc 92: 23–6. Rebeiz, J.J., Kolodny, E.H. and Richardson, E.P. (1968). Corticodentatonigral degeneration with neural achromasia. Arch Neurol 18: 20–33. Rinne, J.O., Lee, M.S., Thompson, P.D. and Marsden, C.D. (1994). Corticobasal degeneration: a clinical study of 36 cases. Brain 117: 1183–96.

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Schmahmann, J.D. (1997). The Cerebellum and Cognition. San Diego: Academic Press. Schneider, J.A., Watts, R.L., Gearing, M., Brewer, R.P. and Mirra, S.S. (1997). Corticobasal degeneration: neuropathologic and clinical heterogeneity. Neurology 48: 959–69. Thompson, P.D., Day, B.L., Rothwell, J.C., Brown, P., Briton, T.C. and Marsden, C.D. (1994). The myoclonus of corticobasal degeneration: evidence of two forms of corticobasal reflex myoclonus. Brain 117: 1197–207. Tolnay, M. and Probst, A. (1999). Review: tau protein pathology in

Alzheimer’s disease and related disorders. Neuropathol Appl Neurobiol 25: 171–87. Watts, R.L., Brewer, R.P., Schneider, J.A. and Mirra, S.S. (1997). Corticobasal degeneration. In Movement Disorders, ed. R.L. Watts and W.C. Koller. New York: McGraw-Hill. Watts, R.L., Mirra, S.S. and Richardson, E.P. (1994). Corticobasal ganglionic degeneration. In Movement Disorders, ed. C.D. Marsden and S. Fahn. London: Butterworth.

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Cerebellar stroke Serge Blecic1 and Julien Bogousslavsky2 1 2

Service de Neurologie, l’Hôpital Erasme, Free University of Brussels, Belgium Service de Neurologie, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland

Introduction Before the advent of computed tomography (CT) and magnetic resonance imaging (MRI), descriptions of cerebellar infarctions were mainly based upon necropsy findings and neurosurgical reports (Amarenco, 1995). CT and MRI techniques have led to a comprehensive description of the clinical features and distribution of cerebellar strokes, allowing clinicians to make precise clinico-anatomic correlations before the death of the patient. The cerebellum is supplied by three main arteries arising from the vertebrobasilar system: the two vertebral arteries and the basilar artery. The complex formed by the cerebellum, brainstem, and brain occipital areas receives about one-third of the cardiac output (Mettler, 1948). Because the cerebellum and brainstem are supplied by the same arteries, they are frequently damaged together when artery occlusion occurs. Stroke in the territory of cerebellar arteries may be life threatening. However, edematous stroke in the cerebellum may have a relatively good functional outcome if emergency surgery is performed. Therefore, early recognition of the clinical pictures of cerebellar stroke is of the utmost importance.

Vascularization of cerebellum Vertebrobasilar system The vertebral artery is divided into four segments. The first segment (V1) courses directly from its origin (the subclavian artery) to the transverse foramen of C6. The second segment (V2) is within the transverse foramen from C6 to C2–C1. Usually, the third segment (V3) begins at the transverse foramen of C2 and emerges on the surface of the costo-transverse foramen of the atlas. It passes behind the

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posterior arch of C1 and is then located between the atlas and the occiput. The third segment of the vertebral artery is covered by the atlanto-occipital membrane, formed by different layers of fascia, muscles, and nerves. The vertebral arteries enter the skull by way of the foramen magnum, the distal portion of the vertebral artery (V4) being exclusively intracranial. Histologically, the fourth part of the vertebral artery is different from the others, due to the decrease in proportion of the elastic lamina. In roughly two-thirds of the population, vertebral arteries are asymmetric. The left vertebral artery is dominant in about 50% of the population. The right vertebral artery is larger of the two in less than 20% of subjects, and the arteries are of equal size in the remaining 30%. Around the level of the pontobulbar junction, both vertebral arteries unite to form the basilar artery. This artery is located anteriorly to the brainstem. At the level of the midbrain, the basilar artery bifurcates into the two posterior cerebral arteries, which are part of the circle of Willis.

Arterial supply of the cerebellum The vascularization of cerebellar cortex The vascularization of cerebellar cortex can be divided into (a) a pial network and (b) intracortical vessels (Duvernoy et al., 1983). The pial vessels are dense and form vascular laminae within the sulci. The intracortical vessels are subdivided into short, middle, and deep vessels. Three vascular layers are observed and there is an approximate correlation between these vascular layers and the three layers in cerebellar cortex. Indeed, the superficial vascular layer is located in the molecular layer, the middle in the Purkinje cell layer, and the deep in the granular layer. The vascularization of Purkinje cells is peculiar, because arteries parallel to the surface of cerebellum (parallel arteries) are in close relationship with Purkinje neurons.

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Presumably, the Purkinje cells take nutritive substances via these parallel arteries. Capillaries and veins are scarce in the Purkinje cell layer, when compared to the arterial supply.

The anterior inferior cerebellar artery

From the origin of the vertebral artery, the first cerebellar branch is the posterior inferior cerebellar artery (PICA). It is the largest branch arising from the vertebral artery, usually emerging from the intradural segment (V4) of the corresponding vertebral artery, at a distance varying from 15 to 28 mm of the origin of the basilar artery (Mettler, 1948; Amarenco et al., 1998). Sometimes, the PICA originates from the vertebral artery on one side and from the basilar artery on the other side. Rarely, it originates from the ascending pharyngeal artery. The PICA is lacking in up to 10% of subjects and is hypoplastic in 5% of cases. The second cerebellar artery is the anterior inferior cerebellar artery (AICA). The AICA arises from the first third of the basilar artery (in 75% of individuals), usually about 1 cm rostrally to the junction of the vertebral arteries. Rarely, the AICA emanates from the middle third and exceptionally from the last third of the vertebral artery. The point where the AICA originates is often different from one side to the other. The superior cerebellar artery (SCA) arises generally from the top or from the rostral part of the basilar artery, usually before the division into the posterior cerebral arteries.

This irrigates a ponto-cerebellar territory (see Fig. 13.1, parts IV to VII). The artery courses laterally over the pons, inferior to the seventh and eighth cranial nerves. It crosses the sixth nerve and reaches the cerebello-pontine angle. This position in the cerebello-pontine angle may be a useful anatomic reference point (Gilman et al., 1981). Small rami of the AICA supply the fifth cranial nerve, although this nerve may be supplied by an independent vessel arising from the basilar artery. The AICA gives off internal auditory and labyrinthine arteries. Unusually, the AICA may arise in common with the internal auditory artery. The AICA supplies a fairly constant territory in the brainstem: the lateral region of the pons, including the facial nucleus, the lateral lemniscus, the spinothalamic tract, the superior, lateral, and medial vestibular nuclei, and the cochlear nucleus. After having given rise to the internal auditory artery, it divides into two branches. The first branch of the AICA (or lateral branch) supplies the lateral part of the biventer lobule. The second (or medial) branch plunges between the tonsilla and the biventer lobule, emerging dorsally to the uvula, and provides the arterial supply for the remainder of the inferior surface of the cerebellum. As a rule, the AICA supplies the middle cerebellar peduncle in all cases and nearly always supplies the flocculus. The terminal branches of AICA anastomose with branches of the superior cerebellar artery (SCA), in the posterior superior fissure.

The posterior inferior cerebellar artery

The superior cerebellar artery

This artery supplies the posterior and caudal part of the cerebellum (see Fig. 13.1, parts I to VII). The PICA is a sinuous artery, with several loops. It runs dorsally and laterally around the medulla oblongata, usually passing between the superficial origins of the vagus nerve and the internal, or accessory, part of the spinal nerve. It passes obliquely and caudally into the ponto-cerebellar angle, and continues its way dorsally about the restiform body to reach the tonsil. When it reaches the edge of the tonsil, it makes a cranial loop and gives off the medial (mPICA) and the lateral (lPICA) branches. The mPICA irrigates the inferior vermis and the inferior part of the inferior semilunar lobule, gracilis lobule, and tonsil. The lPICA supplies inferior parts of the biventer lobule, as well as the inferior semilunar and gracilis lobules, and the ventrolateral part of the tonsil. The only portion of the medulla that is always supplied by the PICA is the dorsal medullary area, which is also vascularized by the posterior spinal arteries. This territory includes the middle and inferior vestibular nuclei, the restiform body, the dorsal nucleus of the vagus, the area postrema, and the gracilis and cuneiform nuclei.

This is larger than the two other cerebellar arteries. It passes between the trochlear and the third occulomotor nerve. The SCA is a major source of arterial blood for the superior part of cerebellum (see Fig. 13.1, parts V to XII). The SCA has a short trunk which divides into a medial branch (mSCA) and a lateral branch (lSCA). These two branches pass around the superior cerebellar peduncle. The SCA supplies the dorsolaterotegmental zone of the upper pons, which includes the superior cerebellar peduncle, lateral lemniscus, spinothalamic tract, and the root of the contralateral fourth cranial nerve. The inferior colliculus is also supplied in part by the SCA. Several branches go rostrally along the side of the central lobule to curve over the ventral edge of the superior cerebellar surface, supplying the medial half of the superior cerebellar surface, the lobulus simplex, the superior semilunar lobule, the culmen, the central lobule, the tuber, and the lingula of the vermis. Velar branches of the medial rami pass along the anterior medullary velum to supply the choroidal plexus of the fourth ventricle and the rostral part of the bed of the deep cerebellar nuclei.

The three main cerebellar arteries

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Fig. 13.1 Arterial vascularization of human brainstem and cerebellum. The 12 serial sections (4 mm thick) presented here are based on a bicommissural plane passing through the anterior and posterior commissures. (Modified by Laurent Tatu and Thierry Moulin, from Tatu et al. (1996). Arterial territories of human brain: brainstem and cerebellum. Neurology 47: 1125–35, with permission.) Arterial groups to the medulla (sections I to IV). Anteromedial group arising from: anterior spinal artery (sections I, II, III) anterior spinal and vertebral arteries (section IV). Anterolateral group arising from: anterior spinal and vertebral arteries (section I) anterior spinal and posterior inferior cerebellar arteries (sections II, III) anterior spinal and vertebral arteries (section IV). Lateral group arising from: posterior inferior cerebellar artery (sections I, II, III) vertebral artery (section IV). Posterior group arising from: posterior spinal artery (sections I, II) posterior inferior cerebellar artery (sections III, IV). Arterial groups to the pons (sections V to X). Anteromedial group arising from: foramen cecum arteries (basilar artery) (section V, part a of sections VI and VII) pontine arteries (basilar artery) (section VIII, part a of sections VI, VII, IX, and X) interpeduncular fossa arteries (part a of sections IX and X). Anterolateral group arising from: pontine arteries (basilar arteries) (sections V, VI, VII, VIII, IX, X). Lateral group arising from: vertebral and anterior inferior cerebellar arteries (section V) pontine arteries (basilar artery) (sections IX, part b of sections VI and VII) anterior inferior cerebellar artery (part b of sections VI and VII) pontine arteries and anterior inferior cerebellar artery (section VIII) superior cerebellar artery (section X). Posterior group arising from: superior cerebellar artery (sections IX and X). Arterial groups to the midbrain (sections XI and XII). Anteromedial group arising from: interpeduncular fossa arteries (sections XI, XII). Anterolateral group arising from: collicular and posteromedial choroidal arteries (section XI) collicular, posteromedial and anterior choroidal arteries (section XII). Lateral group arising from: collicular artery (section XI) collicular, posteromedial choroidal and posterior cerebral arteries (section XII). Posterior group arising from: superior cerebellar and collicular arteries (section XI) collicular and posteromedial choroidal arteries (section XII).

Anatomic structures of sections I to XII 28 1 Corticospinal tract 29 2 Medial lemniscus 30 2 Medial longitudinal 31 fasciculus 32 3 Spinothalamic tract 33 4 Spinal trigeminal tract and 34 nuclei 35 5 Gracile and cuneate nuclei 36 6 Nucleus of the solitary tract 37 7 Dorsal motor vagal nucleus 38 8 Hypoglossal nucleus 39 9 Inferior olivary nucleus 40 10 Inferior cerebellar peduncle 41 11 Vestibular nucleus 42 12 Nucleus prepositus 43 13 Facial nucleus 44 14 Superior olivary nucleus 45 15 Abducens nucleus 46 16 Pontine nuclei 47 17 Motor trigeminal nucleus 48 18 Principal sensory trigeminal 49 nucleus 50 19 Nucleus ceruleus 51 20 Superior cerebellar peduncle 52 21 Substantia nigra 53 22 Inferior colliculus 54 23 Trochlear nucleus 24 Superior colliculus V 25 Oculomotor nucleus VII 26 Red nucleus VIII 27 Mammillary body IX

Optic tract Lateral geniculate body Medial geniculate body Pulvinar Mammillothalamic tract Column of fornix Caudate nucleus Putamen Anterior commissure Tonsil Biventer lobule Inferior semilunar lobule Pyramid of vermis Uvula Superior semilunar lobule Tuber of vermis Middle cerebellar peduncle Dentate nucleus Folium of vermis Nodulus Flocculus Declive Simple lobule Culmen Quadrangular lobule Central lobule Ala of the central lobule Trigeminal nerve Facial nerve Vestibulocochlear nerve Glossopharyngeal nerve

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Fig. 13.2 Cerebellar venous anatomy. The three venous groups can be identified in this schematic drawing: the Galenic group, emptying in the vein of Galen, the petrosal group, draining in the superior and inferior petrosal sinuses, and the posterior group, which anastomoses with the superior vermian vein and which drains into the straight sinus.

Venous drainage of the cerebellum Compared to the venous system above tentorium cerebelli and to the arteries of the vertebrobasilar system, the venous system in the posterior fossa has received little attention. The blood of the bed of the deep cerebellar nuclei is returned by veins which correspond only roughly to the arteries. Venous networks differ from the arterial system in that (1) they drain a larger area, and (2) they commonly show anatomical variations between subjects. The veins of the folia are formed by the confluence of a cortical capillary plexus into subpial networks, which join into trunks ascending in the sulci, forming with other nets. Three main groups of veins are found: the superior (Galenic) group, the anterior (petrosal group), and the posterior (tentorial) group (Fig. 13.2).

Veins of the superior group drain the upper brainstem and superior cerebellum. The superior vermian vein converges with the precentral vein to form the superior cerebellar vein, which empties in the vein of Galen. The vessels of the anterior group drain the anterior portion of the brainstem and cerebellum. They drain into the superior and inferior petrosal venous sinus. The superior petrosal vein is a major venous collector around the pons and can be identified with MRI in up to 95% of subjects (Braun et al., 1996). The vessels of the posterior group drain the inferior part of cerebellar vermis and medial parts of the cerebellar hemispheres. Tonsillar veins empty in the paramedian inferior vermian veins, which drain into the straight sinus. The inferior cerebellar hemispheric veins drain the inferomedial surface of the cerebellar hemisphere into the transverse sinus.

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Infarctions into the territory of cerebellar arteries The incidence of cerebellar infarction in large series of patients with stroke is approximately 1.5–3%, with an average patient age of about 60 years. In the Lausanne stroke registry, cerebellar infarctions accounted for 1.9% of 1000 consecutive initial strokes (Bogousslavsky et al., 1988). As already mentioned, the cerebellum shares its arterial supply with the brainstem. Therefore, both cerebellum and brainstem are frequently involved together when artery occlusion occurs (Macdonnel et al., 1987). We can differentiate several occlusion patterns: infarction within a single territory of a cerebellar artery (territorial infarct involving PICA, AICA or SCA), small infarction and border zone infarcts, multiple infarcts distributed into different artery territories, and cerebellar hemorrhages. The neurological deficits may be transient and resolve completely, may persist, or may even worsen in the days following admission. A transient ischemic attack (TIA) in the vertebrobasilar arterial system consists of an episode of focal neurologic deficit with complete resolution within 24 hours.

Posterior inferior cerebellar artery infarctions PICA infarcts are amongst the most frequent cerebellar infarctions (Amarenco, 1993; Marinkovic et al., 1995). In the series of Amarenco and co-authors, who studied 64 autopsy cases of cerebellar infarctions, about 50% involved the SCA territory, 28/64 the PICA territory, and 10 involved both PICA and SCA territories (Amarenco et al., 1990a; Amarenco and Hauw, 1990; Amarenco, 1993). In the series of Kase et al. (1985, 1993) PICA infarcts accounted for half of their patients with cerebellar infarctions. Until recently, it was often difficult to differentiate between PICA infarcts and lateral medullary infarcts (Wallenberg’s syndrome). It has been shown that the lateral region of the medulla is supplied by three or four small perforating branches arising from the end of the V4 portion of the vertebral artery between the PICA ostium and the basilar artery. Partial PICA territory infarcts are the most frequent findings (Amarenco, 1993; Kase et al., 1993). Whole PICA territory infarcts have been found in only 7% of the autopsy series. Occasionally, this special pattern can be associated with other cerebellar infarctions such as AICA or SCA infarctions (Amarenco, 1991; Canaple and Bogousslavsky, 1999). However, PICA strokes are less frequently associated with extracerebellar strokes in the vertebrobasilar system than AICA or SCA infarcts.

Table 13.1 Symptoms in territorial cerebellar infarctions Symptoms

SCA

AICA

PICA

Deafness Dizziness Drowsiness Tinnitus Vertigo Nausea/vomiting Hallucination Headache and/or facial pain (ipsilateral) Pain of limbs and trunk Sleep disorders

       

       -

       

 

 

 

Notes: SCA: superior cerebellar artery; AICA: antero-inferior cerebellar artery, PICA: postero-inferior cerebellar artery. : never; : very common.

Clinical features The symptoms and clinical signs of territorial infarctions are given in Table 13.1 and Table 13.2, respectively. According to the neurological presentation, six patterns of PICA infarctions can be distinguished. 1. The first pattern is the dorsal lateral medullary syndrome, which is found in about one-quarter to onethird of patients. Clinically, the lateral medullary infarction (also called Wallenberg’s syndrome) includes vertigo, nystagmus, ipsilateral Horner’s sign, appendicular ataxia, ipsilateral Vth, IXth, and Xth cranial nerve palsies, and contralateral loss of pain and temperature sensation (Wallenberg, 1895, 1901; Fisher et al., 1961). In the acute phase of a Wallenberg’s syndrome, saccadic lateropulsion and spontaneous nystagmus in light, with the horizontal fast component beating to the contralateral normal side, are very common (Waespe and Wichmann, 1990). 2. The second pattern consists of PICA territory infarcts sparing the medulla. Patients present vertigo, appendicular and gait ataxia, and nystagmus. In many series, nystagmus is the most frequent sign, found in 65–75% of the cases (Kase et al., 1993; Amarenco et al., 1994). Nystagmus is either horizontal or vertical. Axial lateropulsion, ipsilateral to the lesion, is also a major point and was found in one-quarter of the patients described by Amarenco and colleagues (Amarenco, 1993; Amarenco et al., 1994). This lateropulsion appears in absence of a similar deficit in the limbs. Headache is also usual, being reported in about one-third of the patients by Kase and colleagues in 1993. Headache is

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Table 13.2 The clinical signs of territorial cerebellar infarctions PICA

AICA

SCA

Ipsilateral signs

Horner’s syndrome Impaired facial pain and temperature sensation Dysmetria of limbs Kinetic tremor

Horner’s syndrome Impaired facial pain and temperature sensation Facial palsy Deafness Dysmetria of limbs

Horner’s syndrome Dysmetria of limbs Kinetic tremor Asynergia Hypotonia Choreiform/athetotic movements

Contralateral signs

Impaired pain and temperature sensation over body

Partial impairment of pain and temperature sensation over body

Partial deafness Loss of pain and temperature sensation over face and body Hemifacial weakness IVth nerve palsy IIIrd nerve palsy

Non-lateralizing signs

Ataxia of stance/gait Ocular dysmetria Nystagmus Dysarthria Dysphagia Impaired state of consciousness Bradycardia

Ataxia of stance/gait Nystagmus Dysarthria Dysphagia Impaired state of consciousness

Ataxia of stance/gait Ocular dysmetria Ocular flutter/square waves Vertical gaze palsy Dysarthria* Impaired state of consciousness

Notes: * A predominance of cerebellar dysarthria in left cerebellar lesions has been reported. Italics: major clinical deficits. For other abbreviations, see Table 13.1.

cervical, occipital, cervico-occipital, and occasionally peri-auricular, or with ocular extension. Brainstem compression can occur in nearly 25% of the patients (Kase et al., 1993). 3. An autopsy study by Duncan led to identification of the third form, also called the isolated acute vertigo form. Clinically, it is difficult to differentiate this form from symptoms that occur in peripheral labyrinthitis. In the case of Duncan, autopsy showed a recent infarction, located in the medial and the caudal part of the PICA territory (Duncan et al., 1975). This patient had experienced an acute episode of vertigo and died three weeks after myocardial infarction. Symptoms were the consequence of the involvement of the cerebellar nodulus, which is normally supplied by the PICA. 4. Vertigo accompanied by ipsilateral axial lateropulsion of trunk and gaze, and dysmetria of limbs constitutes the fourth pattern of PICA infarction (Bogousslavsky and Regli, 1984; Ranalli and Sharpe, 1986; Amarenco et al., 1990b). Patients may also present (a) an isolated vertigo, or (b) a Wallenberg’s syndrome if the medulla is affected. In addition, stroke may be clinically silent. The partial territory infarction described here corresponds

to the syndrome of the mPICA, involving the cerebellar region adjacent to the fourth ventricle (Amarenco, 1993). MRI shows an infarction that is usually of triangular shape, with a base oriented dorsomedially and the ventral point towards the fourth ventricle (Fig. 13.3). 5. Barth et al. (1994) have defined the fifth pattern of PICA infarction. These authors reported that patients with vertigo and ipsilateral dysmetria had an infarction in the territory of the lateral branch of the PICA. This rare pattern of infarction had been described previously by Amarenco (1993). 6. Finally, the sixth pattern involves in the presence of multiple territorial cerebellar infarcts (PICA). Together with AICA and SCA infarctions, PICA infarctions may lead to a pseudotumoral presentation, or present with coma and tetraplegia. Neurological signs vary according to the arterial territories involved (Amarenco et al., 1994; Canaple and Bogousslavsky, 1999).

Anterior inferior cerebellar artery infarctions AICA infarcts are rare (Amarenco, 1993). However, the increasing use of MRI will probably reveal a higher

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pattern, including vertigo, vomiting, tinnitus, and dysarthria as main symptoms. Ipsilateral facial palsy, facial sensory loss, and Horner’s syndrome are often observed. Appendicular dysmetria, contralateral loss of sensation, hearing loss, conjugate lateral gaze palsy, dysphagia, and ipsilateral motor weakness (due to contralateral involvement of the corticopontine tract) may also be found. Because some signs are similar to those of Wallenberg’s syndrome, AICA infarction can be misdiagnosed as a lateral medullary infarction. This first pattern accounts for one-third to one-half of patients with AICA territory infarcts found in the different series (Amarenco, 1993). 2. The second form is isolated vertigo, mimicking a labyrinthitis. Whereas vertigo occurring in PICA infarction is due to involvement of the nodulus, vertigo in AICA infarct is due to damage of the flocculus (Amarenco et al., 1990a, 1990b; Amarenco, 1993). 3. Massive infarction of AICA is frequently associated with brainstem infarction and cerebellar infarcts in the territory of all three cerebellar arteries. Massive infarction of AICA results from a proximal occlusion of the artery. Patients present coma, tetraplegia, and ophthalmoplegia (Canaple and Bogousslavsky, 1999). 4. Isolated cerebellar signs have been reported exceptionally (Philips et al., 1988).

Superior cerebellar artery infarctions

Fig. 13.3 Axial T2-weighted magnetic resonance imaging showing an infarction in the territory of the medial branch of the posterior inferior cerebellar artery (mPICA), with a typical triangular shape.

incidence than expected. AICA territory infarctions are usually small and most of them are confined to the middle cerebellar peduncle, the caudal pons, and the flocculus (Amarenco, 1993). When the PICA is absent or hypoplastic, the AICA may take over the whole territory usually supplied by the PICA. In this condition, AICA territory infarction can mimic PICA territory infarct. Figure 13.4 illustrates an infarction in the territory of the AICA.

Clinical features AICA infarction differs strikingly from PICA or SCA strokes in terms of associated brainstem signs. Four clinical presentations can be observed. 1. The first clinical picture, the classic syndrome, was described in 1943 by Adams. It is the most frequent

SCA infarctions are probably the most common cerebellar infarctions after PICA infarcts. SCA infarctions are usually accompanied by brainstem infarctions, most often involving mesencephalon and the upper part of the pons, or by involvement of supratentorial artery territories. In autopsy cases of full territorial infarctions, ischemic lesions are found in occipital/temporal lobes and in thalamosubthalamic areas in more than 70% of cases (Amarenco and Hauw, 1990; Amarenco et al., 1991b).

Clinical features Seven different clinical patterns are recognized. 1. Kase et al. and Amarenco et al. clarified the classical SCA syndrome, which is probably very rare, accounting for less then 3% of the autopsy cases (Kase et al., 1993; Amarenco and Hauw, 1990). The classic form was initially described by Mills in 1912 and by Guillain et al. in 1928. The syndrome includes ipsilateral limb dysmetria, ipsilateral Horner’s syndrome, contralateral loss of pain and temperature and, more rarely, contralateral fourth nerve palsy. Sleep disorders can occur, resulting from involvement of the locus ceruleus. Rarely, the

Cerebellar stroke

Fig. 13.4 Sagittal magnetic resonance imaging showing an infarction in the territory of the anterior inferior cerebellar artery (AICA).

lateral lemniscus is involved. This might explain the hearing loss occasionally reported. Movement disorders consisting of ipsilateral slow movements of large amplitude have been noted (Davison et al., 1935; Cossa and Richard, 1955). In addition, palatal myoclonus, as well as myoclonus of the jaw, may develop several weeks after the stroke (Freeman and Jaffe, 1941). 2. The rostral basilar artery syndrome occurs in about 20–25% of SCA occlusion. Patients complain of visual defects, diplopia, dizziness, paresthesias, jerky movements, and weakness. Drowsiness and Balint’s syndrome have been reported, resulting from occipitotemporal lobe damage. The thalamo-mesencephalic involvement predominates in other patients: sensory loss, contralateral Horner’s syndrome, hemianopia, behavioral abnormalities, memory loss, abulia. Furthermore, subthalamic lesion may generate hemiballic movements. Mesencephalic involvement can also induce an isolated third nerve palsy, a more complex vertical gaze palsy, or even a Parinaud syndrome. Third

nerve palsy may be associated with contralateral movement disorders of limbs (Benedikt’s syndrome), with contralateral dysmetria of limbs (Claude’s syndrome), or with contralateral motor weakness (Weber’s syndrome). 3. Concomitant infarction in anterior circulation may mask SCA occlusion, because of brachiofacial weakness and aphasia. This pattern is typically associated with cardioembolism. 4. The vestibular form of SCA infarcts was reassessed by Amarenco et al. in 1991 (Amarenco et al., 1991b; Amarenco, 1993). The main symptoms are headache, unsteadiness, dizziness, and vomiting. Neurological examination shows dysmetria and kinetic tremor. Nystagmus is also an important feature, as well as other brainstem signs, which were found in one-third of the patient of Kase and colleagues (1993). Dysarthria is frequently found in SCA infarcts and could be considered as a hallmark in this pattern (Amarenco, 1993). 5. The lateral SCA syndrome is due to anterior rostral cerebellar involvement. This pattern of infarction includes

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cerebellar infarction. The clinical features include coma at onset with tetraplegia and ophthalmoplegia (Canaple and Bogousslavsky, 1999). Coma from onset is due to embolic obstruction of the rostral end of the basilar artery.

Border zone cerebellar infarctions

Fig. 13.5 Axial T2-weighted magnetic resonance imaging showing infarction within the territory of the lateral branch of the superior cerebellar artery (lSCA) (large arrow). Note the concomitant infarctions in the pons (small arrow).

mainly ipsilateral limb dysmetria and ipsilateral axial lateropulsion. Gait unsteadiness and dysarthria can also be observed. In some instances, the lateral SCA syndrome simulates a dysarthria–clumsy hand syndrome (Tougeron et al., 1988). Patients with lSCA infarct can exhibit horizontal nystagmus and contrapulsion of ocular saccades. Figure 13.5 shows an infarct in the territory of the lSCA. 6. The medial SCA syndrome may present with gait ataxia, or ataxia of limbs associated with increased tone in extensor muscles (Ringer and Culberson, 1989). An isolated cerebellar dysarthria has also been reported (Amarenco et al., 1991a). 7. Finally, SCA infarction can be a part of multiple

Border zone infarcts have probably been underestimated by both clinical and necropsy studies (Amarenco et al., 1993). The advent of MRI has allowed the identification of these watershed cerebellar strokes. They are defined as small infarctions, located chiefly at the boundaries between SCA and PICA territories on the surface of the cortex, and between SCA and PICA in the deep cerebellar white matter (Amarenco, 1995). The affected areas usually measure less than 2 cm in diameter (Rodda, 1971). Amarenco proposed classifying them into three groups: A. Cortical border-zone infarcts, distributed perpendicular to the cortex and parallel to the penetrating arteries: these infarcts are the most frequent and are located at the boundary zones between SCA and PICA territories (Fig. 13.6A). Similar infarcts have been reported between the territories of PICA and AICA. B. Cortical dorsal infarcts parallel to the cortex (Fig. 13.6B): these are rarely found because of the abundance of anastomotic arterial network between the cortical and superficial branches of SCA and PICA. C. Small deep infarcts, corresponding to the deep border zone: these are located in the border zone of AICA and the lateral branches of PICA territories, or in the border zone between vermal branches of the two SCA (Amarenco, 1995). The clinical signs of border-zone infarcts are not fundamentally different from those found after infarction in a single cerebellar artery territory. Symptoms may be transient or recurrent. Some patients exhibit position-related symptoms even years after stroke: light-headedness, vertigo, disequilibrium. These symptoms might reflect a low flow state in the vertebrobasilar circulation. Combinations of different pattern of infarctions (i.e., PICA SCA . . .) can also be found.

Lacunar infarctions A controversy still exists regarding the existence of lacunar infarctions in the cerebellum. In the deep cerebral white or gray matter or in brainstem, small penetrating branches arise from middle-sized arteries (Fisher, 1977). By contrast, the anatomical characteristic of cerebellar arteries showing a progressive reduction in diameter of the vessels

Cerebellar stroke

A

territory infarctions. The commonest association was PICA SCA, found in approximately half of the patients, followed by infarction in all cerebellar territories (SCAAICA PICA). The combination of PICAAICA was never found in this study. Multiple small infarctions were found in different cerebellar arteries. The pathological mechanism remained unknown, but the authors suggested that rather than being border-zone infarcts, as initially thought, these infarcts could be end-zone strokes, suggesting that multiple emboli arise either from the heart or from an arterial source.

Course/outcome

B

Fig. 13.6 Schematic drawing of cortical border zone infarctions. (A) Axial view, showing infarcts perpendicular to the cortex, between penetrating arteries from the PICA and the SCA. (B) Posterior (on the left) and axial (on the right) views of infarcts parallel to the cortex, between superficial cortical branches. Those perpendicular to the cortex are the most frequent and those parallel to the cortex are the least frequent. (Modified from Amarenco, 1993.)

does not favor the genesis of lacunar infarction. Small infarctions found in the cerebellum are rather in the category of border-zone infarctions and could also be due to small emboli (Amarenco, 1993, 1995).

Multiple cerebellar infarctions Until the recent study of Canaple and Bogousslavsky in 1999, multiple cerebellar infarctions had been poorly studied. Historically, they had the reputation of bad prognosis, because all the studies were necropsy series. Since the advent of new radiological techniques, very precise clinical and radiological correlations have been performed in patients with multiple cerebellar infarctions. In their prospective study, Canaple and Bogousslavsky found that 16.5% of patients with cerebellar infarctions had multiple

The course of cerebellar infarction differs according to the territory involved (Barinagarrementeria et al., 1997). PICA infarctions lead to brainstem compression and tonsillar herniation in 25% of the patients (Kase et al., 1993). Acute hydrocephalus is seen in up to 20% of the patients and, in about 10% of cases, death can be ascribed to edema in posterior fossa. This pseudotumoral infarction is a rapidly progressive cerebellar swelling, initially described by Menzies in 1893. A delayed impairment of consciousness is observed in 90% of the cases, appearing from a few hours up to eight to ten days after stroke onset, with a mean of five days. However, pseudotumoral presentation occurs in patients presenting full PICA territory infarction. In fact, most of PICA territory are only partial territory infarcts, which have a more benign course (Amarenco et al., 1990b; Kase et al., 1993). Because the large majority of AICA has been described in autopsy series (Amarenco, 1993), one could assume that this type of infarction is lethal. However, with the advent of MRI, it appears that such infarction could have a better outcome. In different series, most deaths were due to pulmonary infections and other general conditions rather than to the stroke itself (Sypert and Alvord, 1975; Amarenco, 1993; Kase et al., 1993). Nevertheless, the prognosis of proximal occlusion of AICA is worse than in the case of terminal branch occlusion, and AICA infarct may herald massive basilar artery thrombosis. In nearly 20% of the cases, SCA infarctions can have a pseudotumoral presentation (Amarenco and Hauw, 1990; Amarenco, 1993). However, a benign outcome with minimal disabling, or even asymptomatic, infarction is common in partial SCA territory infarction (Kase et al., 1993). For instance, a favorable outcome in patients with lateral SCA infarction has been reported (Barth et al., 1993).

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Pathophysiology of cerebellar infarction Different mechanisms can provoke an ischemic stroke within the vertebrobasilar system.

Large artery diseases Atherosclerosis As for the carotid artery system, atherosclerosis is the commonest cause of stroke in the western world. Vertebral as well as basilar artery plaques without or with calcified and/or ulcerated lesions can be identified in these vessels. However, several authors underlined that ulceration of plaques is probably less frequent within the vertebrobasilar arteries than within the carotid artery system (Fisher and Ojemann, 1986). When ulcerated plaques are demonstrated, they are mainly found in the V1 segment of the vertebral artery, usually together with involvement of the subclavian artery (Pelouze, 1989). Ulcerated plaques can also be observed in the aortic arch (Amarenco et al., 1992). Both vertebral arteries are equally involved by the atherosclerotic process, and vertebral arteries can be affected throughout their entire course from the subclavian artery to the foramen magnum. The final step of atherosclerosis is clot formation, which is usually limited to the site of atherosclerosis, in contrast to what happens in carotid artery disease in which the thrombus generally extends to distal arteries. When occlusion occurs into the intracranial part of the vertebral artery, the thrombus extends into the basilar artery (Castaigne et al., 1973). The basilar artery seems to be less often involved by the atherosclerotic mechanism then the first part of vertebral artery. Castaigne et al. (1973) have shown that the proximal part of the basilar artery is more regularly involved. Usually, the atherosclerotic process reaches the orifice of the SCA and of the AICA. The top of the basilar artery and the division into posterior cerebral arteries can also be affected by the extension of atherosclerotic plaque. PICA occlusions are due to atherothrombosis in about 50% of cases (Amarenco et al., 1990a, 1990b). SCA occlusions are more frequently due to cardioembolism (Amarenco et al., 1994), whereas AICA occlusions are due to atherosclerosis in nearly all cases, especially in diabetics. This exclusivity is probably due to the anatomical conformation of AICA (Amarenco, 1993). In the study of Canaple and Bogousslavsky (1999), large artery disease was also, by far, the main cause of stroke.

Dissections Dissection of the vertebral or the basilar artery is probably as frequent as dissection of the carotid artery. Embolism as well as hemodynamic mechanisms participate in the genesis of stroke associated with dissections. In patients younger than 40 years, arterial occlusion resulting from vertebral artery dissection is the most common mechanism of cerebellar infarction (Barinagarrementeria et al., 1997). The most affected part is the extracranial vertebral artery, either above its origin from the subclavian artery or at the end of the V2 segment, particularly in front of the C2 vertebra (Easton and Sherman, 1977; Levine and Welch, 1988; Frumkin and Baloh, 1990). The first reports concerned traumatic dissections consecutive either to neck manipulations or to severe trauma. Recent studies have demonstrated that vertebral dissections can occur after minor trauma, particularly in sportsmen after normal sport practice (Blecic et al., 1999). Spontaneous dissections can also occur in different congenital pathologies such as Marfan’s, Ehlers–Danlos’, Grönblad–Stranberg syndromes, fibromuscular dysplasia, and systemic vasculitis (Youl et al., 1990; Dunac et al., 1998). Although the recurrence rate of dissection in the general population is around 1%, Schievink et al. (1994, 1996) have found in different selected families a recurrence rate of 50% in patients with former dissection. The basilar artery is less commonly involved than the vertebral artery. Most of the cases were either found in autopsy series or are isolated case reports (Ringle et al., 1977; Alexander et al., 1979). Coma at onset is usual found after basilar artery dissection. Clinical symptoms are due to massive infarction within the basilar artery territory distribution. A connective tissue disease could be the cause of dissection in such cases. (Schievink et al., 1994, 1996)

Embolism The most common clinical presentation of embolic stroke remains a sudden deficit, maximal at onset. Embolism results from cardiac disease, or may be due to artery-toartery embolism from atherosclerotic occlusion of the vertebral artery, from vertebral artery dissection (see previous paragraph), or from ulcerated plaques in the aortic arch. Cardiac origin embolism accounts for about 40–45% of strokes in the cerebellum. Cardioembolism is the most frequent cause of occlusion of the SCA (Struck et al., 1991). Considering the largest published series, the cause of PICA infarction is cardioembolism in about 50% of cases. Cardioembolism is also the cause of multiple cerebellar infarctions and responsible for the clinical presentation of

Cerebellar stroke

basilar syndrome (Caplan, 1980; Chaves et al., 1994; Canaple and Bogousslavsky, 1999). Moreover, cardioembolism is more frequently the presumed cause of border-zone infarct than previously assumed, accounting for about 50% of cases (Mounier-Vehier et al., 1995). The cardiac diseases which increase the risk of embolism are atrial fibrillation, valvular disease, a recent myocardial infarction, congestive heart failure, and patent foramen ovale. In young patients, embolism from a cardiac source results primarily from patent foramen ovale and rheumatic valvular disease (Barinagarrementeria et al., 1997).

Low-flow Systemic hypoperfusion is rarely the cause of cerebellar infarction. However, this pathological condition could be one of the causes of border-zone infarctions, in addition to small or end (pial) artery disease due to intracranial atheroma or hypercoagulable states, to large artery (vertebral or basilar) occlusive disease, and to brain embolism. The cerebellum seems relatively protected against low-flow, probably because of the rich anastomotic network. In a post-mortem series of patients who presented anoxic encephalopathy due to cardiorespiratory failure, borderzone infarctions were found in watershed areas of the anterior, middle, and posterior cerebral arteries, but not in the cerebellum (Sevestre et al., 1988).

Small artery disease (lipohyalinosis) This process, involving small penetrating branches, affects the brainstem (lacunar infarction) rather than the cerebellum. Lipohyalinosis leads to stroke by a progressive subintimal proliferation that occludes the lumen and leads to a distal lacuna. As underlined previously, this kind of infarction is very rarely found in the cerebellum (Amarenco, 1995).

Other causes of stroke Saccular aneurysm of the distal part of the vertebral artery or of the basilar artery can provoke infarction into different cerebellar artery territories. The mechanism is probably a clot phenomenon into the aneurysmal sac. The pathophysiologic mechanism is aneurysm to artery embolism. The most common sites are the distal part of the basilar artery near the division into the posterior cerebellar arteries, and the vertebral/ PICA junction. Infectious disease can also provoke stroke within the territory of cerebellar arteries. Particularly, aspergillosis was

found to have peculiar tropism for the posterior circulation vessels (Walsh et al., 1985). Indeed, aspergillosis is a cause of occlusion of distal branches of the cerebellar arteries. Both small infarctions and hemorrhages can occur. Walsh et al. have emphasized that the mechanism of arterial occlusion is an angiitis resulting from invasion of blood vessels. A second putative mechanism could be a cardioembolism due to fungal endocarditis. Ischemia may develop in patients presenting a complicated migraine. Vasculitis, as seen in systemic lupus erythematosus, granulomatous angiitis, syphilis, and isolated central nervous system vasculitis, can also be the cause of cerebellar infarction (Caplan, 1991). Drug abuse (smoked, snorted or intravenously administered cocaine) is also responsible for cerebellar ischemic strokes. The mechanisms are multiple and overlap: vasculitis, vasospasm, sudden onset of hypertension, cardiac arrhythmias (Daras et al., 1991).

Cerebellar hemorrhage Overall, cerebellar hemorrhages represent approximately 10% of all cerebellar strokes. They usually have a clinical presentation similar to ischemic stroke. Thus, differential diagnosis on a clinical basis only is often very difficult. Nevertheless, the sudden onset of occipital headache, with dizziness, vomiting, and ataxia of stance/gait, is most characteristic of a hemorrhage (Gilman et al., 1981). The clinical course can imitate a pseudotumoral infarct. Not exceptionally, patients are comatose by the time of hospital admission and about 15% of patients go into coma in the days following the onset of symptoms. Brain CT and MRI are helpful to differentiate hemorrhage from ischemia (Fig. 13.7). The most frequent territory is the deep region around the dentate nucleus, supplied by an anastomotic network formed by the long perforating branches of SCA and the cortical arteries which supply the cerebellar cortex. This area is particularly vulnerable to hypertension peaks, which are the most common causative factor. Artery rupture leads to hemorrhages in the ipsilateral hemisphere, the middle cerebellar peduncle, with or without rupture in the fourth ventricle, and extending up the brainstem. Cerebellar hemorrhage may also result from rupture of an aneurysm. Posterior fossa aneurysms account for about 8–15% of all intracranial aneurysms. In most cases, posterior fossa aneurysms occur at the bifurcation of the basilar artery into the posterior cerebral arteries or along the basilar artery. Aneurysms can also occur at the junction of PICA/vertebral arteries or along the cerebellar arteries

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Fig. 13.7 Axial T1-weighted magnetic resonance imaging showing two hemorrhagic areas in the right cerebellar hemisphere. Note the compression of the brainstem. This patient suffered from arterial hypertension.

(Hudgins et al., 1983). The presentation may be a picture of classic subarachnoid hemorrhage, and a clinically significant vasospasm may occur (Hudgins et al., 1983). In the series of Redekop et al. (1997), including 49 patients with 52 aneurysms of the upper basilar artery (mean age, 50 years, range, 23–74 years), 35 patients presented with subarachnoid hemorrhage, with a grading varying from I to IV according to the Hunt and Hess Scale. Ruptured aneurysms of cerebellar arteries almost always coexist with intraventricular hemorrhage and hydrocephalus (Kallmes et al., 1997). In the particular case of giant aneurysm of the basilar artery, the presentation can be similar to a tumor in the posterior fossa. Complications of anticoagulation therapy, angiomas, hemangioblastomas, arteriovenous malformations, brain metastases, trauma, and coagulation disorders are the other causes of cerebellar hemorrhages.

Cerebellar hemorrhagic infarction Cerebellar hemorrhage may also develop after a primary infarct. In the majority of cases, imaging studies do not show blood initially, and hemorrhagic infarction is detected on routine serial scans performed during the first 15 days after stroke onset (Chaves et al., 1996). The stroke mechanism is usually embolic from cardiac and intraarterial sources, such as in the anterior circulation.

Diagnostic studies Magnetic resonance imaging Conventional magnetic resonance imaging MRI is by far the best diagnostic test to evaluate patients with ischemic cerebellar stroke. Indeed, all studies showed a dramatic superiority of MRI over other diagnostic

Cerebellar stroke

techniques. MRI delineates the precise localization of the lesion in the three dimensions. Conventional MRI also allows one to detect early occlusion of major intracranial arteries. A precise definition of infarct localization is of considerable importance for clinicians, because a better definition of the territory involved enables one to discover a stroke etiology at an early stage. For instance, AICA infarctions are more often associated with atherosclerosis, whereas SCA infarctions are more often associated with cardioembolism. This is of interest for patients to whom early treatments could be administered (Tohgi et al., 1993). In the case of acute hemorrhage, brain CT still plays an important role in the diagnosis or follow-up of the patients.

Magnetic resonance angiography Magnetic resonance angiography (MRA) is a complement to MRI in the definition of cerebellar infarct, mainly to investigate the vertebral and basilar arteries. This technique has many advantages, the principal one being that it is non-invasive. However, this advantage is counterbalanced by technical problems, such as the need to use different head and neck coils for imaging, the possibility of overlapping vessels, and shadows. Nevertheless, in the study of Bogousslavsky and colleagues (1993), MRA was very effective in diagnosing the etiology of posterior circulation infarct. Indeed, these authors could determinate the arterial cause of stroke in 70 consecutive patients included in a prospective study (Bogousslavsky et al., 1993).

either stenosis or occlusion, and even vertebral artery dissection (Trattnig et al., 1990). Transcranial Doppler (TCD) is also a useful non-invasive technique to assess cerebral hemodynamics. In addition, TCD might be an interesting method for detecting emboli, for instance using microbubbles and the Valsalva maneuver where there is suspicion of patent foramen ovale. TCD can evaluate quantitatively the vertebrobasilar system. However, the problems of transmission of ultrasound through the cranium should not be underestimated; the anatomic variability of basal arteries must be known; and the evaluation is clearly more difficult than for the anterior circulation. The development of two-dimensional transcranial color-coded sonography (TCCS), which provides both anatomical and functional information about the major cerebral vessels, and the use of echo-enhancing agents (Levovist) are promising techniques which are increasingly applied for strokes in the anterior circulation (Ringelstein, 1998; Goertler et al., 1998). Their role in the diagnosis of posterior circulation stroke remains to be determined.

Single-photon emission computed tomography Single-photon emission computed tomography (SPECT) with 99Tc-HMPAO shows an ipsilateral decrease in blood flow in the territory of the cerebellar infarction. A contralateral hemispheric diaschisis may be associated, and is more severe in mixed brainstem and cerebellar infarction than in pure cerebellar infarcts (Rousseaux and Steinling, 1999).

Conventional angiography Intra-arterial angiography used to be the principal diagnostic test to evaluate the vertebral and basilar arteries. Its superiority has dramatically decreased, especially with the increasing use of MRA and ultrasound techniques. Angiography should be performed only when the quality of MRA is not sufficient to propose a diagnosis. This is particularly true in the case of artery dissections (Trattnig et al., 1990). Moreover, conventional angiography is still indicated if an aneurysm or another vascular malformation is suspected.

Ultrasound Because of the anatomy of the vertebrobasilar system, ultrasound of the posterior circulation arteries is less advantageous than for carotid arteries. However, continuous wave Doppler and B-mode ultrasound (duplex system) remains the first examination to be performed. Studies of the shapes of velocity curves in the VA course can indicate

Blood studies Blood studies should include cell counts, hematocrit, lipid levels, glucose level, and coagulation studies. Detailed coagulation investigations are indicated in patients with unexplained strokes after a careful evaluation, previous thrombotic episodes, or a positive family history for thrombosis.

Cardiac studies Electrocardiography (ECG) is a routine procedure in the large majority of centers dealing with stroke patients. It may reveal an arrhythmia or signs of congestive heart failure. Transesophageal echocardiography (TEE) with contrast injection and 24-hour Holter monitoring are required when the history and clinical examination suggest a cardiac cause. TEE has the advantage of a superior resolution for the posterior cardiac structures, such as left atrium and appendage and atrial septum, as well as of

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Table 13.3 Treatment of cerebellar stroke Identification and management of risk factors Control of vital functions Intensive supervision Ischemia Thrombolysis* Anticoagulants Antiplatelet agents Surgical procedure

Hemorrhage Surgical procedure

External ventricular drainage and monitoring of intracranial pressure Suboccipital craniectomy Evacuation of the lesion External ventricular drainage and monitoring of intracranial pressure Suboccipital craniectomy Clot evacuation/CT-guided aspiration Vascular malformations: surgery and/or interventional neuroradiology, management of vasospasm

Rehabilitation after the acute phase of stroke Notes: *In selected cases only.

the aorta. It is superior to transthoracic echocardiography (TTE) for identifying potential cardiac sources of emboli, including left atrial thrombi, valvular vegetations, thoracic aortic plaque, and patent foramen ovale (paradoxical embolism).

Lumbar puncture Lumbar puncture is performed for patients presenting a severe and unexplained headache if brain CT is negative. Mass effect (especially in the posterior fossa) on CT scan is a contraindication.

Other diagnostic tests Spiral CT scanning of brain circulation is a new technique, available for examining the blood vessels. Compared to MRI, this technique has the disadvantage of requiring a large amount of contrast medium. However, the short time needed for examination may be useful for patients who cannot undergo MRI scanning. So far, positron emission tomography (PET) has not been widely used in cerebellar stroke, although the oxygen extraction fraction may be a good predictor in tissue viability. PET studies might be a helpful tool in patient assessment for future treatments.

Treatments Risk factors such as hypertension, diabetes mellitus, hyperlipemia, and cigarette smoking should be identified and dealt with appropriately (Table 13.3). General management in the acute phase includes cardiac and pulmonary care, fluid and ion balance restoration, metabolic maintenance, blood pressure control, and prevention of bed sores and phlebitis (Blecic and Bogousslavsky, 1995). The dysphagia, dysarthria, clumsiness of limbs, and the high risk of falls should not be underestimated. As for strokes located in other territories, there is no consensus yet concerning the treatment to apply in patients with infarction within the posterior circulation. Indeed, most of the studies are dedicated to single cases only, or were not randomized when they addressed large populations.

Thrombolysis Thrombolysis is probably the most promising treatment for acute ischemic stroke. Recent thrombotic occlusions into the vertebrobasilar system arteries will probably constitute a first-choice indication. In fact, reperfusion gives patients the best chance of surviving a stroke without disability. In 1988, Hacke and collaborators treated 65 consecutive patients with severe ischemia of brainstem in whom artery occlusions were demonstrated angiographically.

Cerebellar stroke

Forty-three were treated either by urokinase or streptokinase within 24 hours of stroke onset. Other patients were treated either with anticoagulants or with antiplatelet therapy. The better outcome was found in patients treated with thrombolytic therapy: 19/43 patients had artery reperfusion and 10 out of 19 had a very good clinical outcome. Conversely, in the group of patients treated with anticoagulants or with antiplatet therapy, only 3/22 patients survived, all with severe neurological deficit (Hacke et al., 1988). Other studies have shown similar results (Hennerici et al., 1991). In an attempt at obtaining a consensus, del Zoppo (1992) concluded that thrombolysis could be very effective only in selected patients, and when they were treated within a few hours. Whether the timing of therapy is more important than specific dose is uncertain (Marshall and Mohr, 1997). The ideal route of administration of the treatment has not yet been determined (del Zoppo, 1992).

Anticoagulants Heparin could play a role in the acute treatment of patients with ischemic stroke, but this opinion remains conjectural and unproven. No study has demonstrated any benefical role of anticoagulants in a population of patients with stroke located in the vertebrobasilar system. Patients with TIA due to basilar artery stenosis could benefit the most from warfarin (Amarenco et al., 1998). Long-term oral anticoagulation is given for patients with cardioembolic infarction: atrial fibrillation, myocardial infarction, intracardiac thrombus, or valvular disease (prothrombin time: 1.2 to 2.5 times control).

Antiplatelet agents Most of the studies which assessed the possible beneficial role of aspirin and other antiplatelet agents in ischemic stroke have unfortunately excluded from their analysis vertebrobasilar stroke. In the secondary prevention of ischemic stroke, the European Stroke Prevention Study (Sivenius et al., 1991) and the Ticlopidine–Aspirin Stroke Study (Hass et al., 1989) have demonstrated that antiplatelet therapy is as efficient in patients presenting a stroke in the vertebrobasilar circulation as it is for those with a stroke in the carotid artery system.

Surgery Anastomoses and bypass Transposition of the vertebral artery to the carotid artery has occasionally been tried. However, no larger study has

shown efficacy of this method (Amarenco et al., 1998). Bypass, which is efficient for the common and internal carotids, is rarely performed for vertebral arteries, although endarteriectomies of the origin of the vertebral artery have been tested.

Decompressive surgery Decompressive surgery is efficient in reducing brainstem compression. Most authors advise external ventricular drainage and/or suboccipital craniectomy before the occurrence of coma when acute hydrocephalus develops. A CT scan showing isolated hydrocephalus and compression of the fourth ventricle even in the absence of cerebellar hypodensity should raise the possibility of pseudotumoral cerebellar infarction and prompt neurosurgical treatment. In the series of Mathew et al., including 48 patients with hematoma and 71 patients with infarction, early surgery in both cerebellar hemorrhage and infarct (either external ventricular drainage or evacuation of the lesion) associated with early presentation and CT signs of brainstem compression and acute hydrocephalus, led to a good outcome in most cases (Mathew et al., 1995). Ultimately, 75% of the patients with a hematoma required a surgical procedure, whereas most patients with an infarct were successfully managed conservatively. Although ventricular drainage may be a life-saving procedure in the case of cerebellar stroke with coma at onset, surgery is not recommended in cases of severe weakness, because there is a correlation between hemiplegia or tetraplegia and massive pontine infarction. The state of consciousness is a determinant factor in the treatment strategy (Cioffi et al., 1985). The following guidelines can be proposed. 1. The patient is clinically stable and alert, and brain CT scan shows no or moderate hydrocephalus: medical treatment, and close clinical/radiological follow-up. 2. The patient is alert but brain CT scan demonstrates marked hydrocephalus: medical treatment and monitoring of intracranial pressure. Ventricular drainage is performed if pressure 350 cmH2O. 3. The patient is deteriorating clinically: medical treatment and ventricular drainage. If no rapid clinical improvement occurs, a suboccipital craniectomy is performed. Resection of the lesion may be also considered. MRI and MRA might be useful tools in determining at an early stage the patients who could benefit most from surgical treatment, especially by accurately imaging the brainstem (Heros, 1992; Kanis et al., 1994; Jauss et al., 1999).

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Management of vascular malformations Surgical treatment is often advisable in the case of a ruptured aneurysm. For instance, clipping of the aneurysm neck is often an essential step for aneurysms at the PICA/vertebral junction (Hudgins et al., 1983). The indications of interventional neuroradiology are growing, in particular, the use of coils. Embolization of arteriovenous malformations may facilitate the resection of the lesion. The general management of vasospasm is also applicable in posterior circulation: ‘triple H’ therapy (hemodilution, hypertension, hypervolemia), calcium channel blockers, recombinant tissue plasminogen activator, and percutaneous transluminal angioplasty (Chiappetta et al., 1998).

Neuroprotective therapy of acute ischemic stroke These promising therapies are based on the principle that delayed neuronal injury occurs after ischemia (Hickenbottom and Grotta, 1998; Devuyst and Bogousslavsky, 1999). Each step of the ‘ischemic cascade’ is a potential therapeutic target. The main drugs that are currently being tested in humans are calcium channel antagonists, N-methyl--aspartate receptor antagonists, the free radical scavenger tirilizad, and the anti-intercellular adhesion molecule-1 (ICAM-1) antibody.

Cerebellar vein thrombosis Cerebellar venous infarction has been rarely reported (Bousser and Russel, 1997). The thrombosis usually follows occlusion of the surface veins draining into the transverse sinus or of the superior vermian vein, which reaches the great vein of Galen. Thrombosis of the vein of Galen or the straight sinus may be a devastating condition, usually affecting cerebellar structures bilaterally, as well as rostral brainstem and supratentorial structures. If obstruction occurs simultaneously in the vein of Galen and the basal veins, death follows rapidly (Andeweg, 1999). Like other infarctions following cerebral vein occlusion, the cerebellar lesion can be either hemorrhagic or ischemic, and is usually accompanied by edema. Major complications are tonsillar or upward cerebellar herniation with brainstem compression. Clinically, nausea, vomiting, severe progressive headaches, cranial nerve palsies, ataxia, and impairment of consciousness are the main features, resulting principally from increased intracranial pressure in the posterior fossa (Rousseaux et al., 1988). Symptoms may have a sudden onset or a progressive course over several weeks. Causes are variable. Pregnancy, oral contraceptives,

hyperosmolar state in diabetic patients, coagulation disorders such as antithrombin III deficiency or resistance to C active protein (R-APC), and infection are the main predisposing factors (Bousser and Russel, 1997). Mastoiditis with cholesteatoma, as well as extension from thrombophlebitis of the cavernous sinus into the cerebellar venous system following facial pyodermitis or sphenoethmoidal sinusitis have been described (Macdonald et al., 1988; Nayak et al., 1994). A rare complication of surgery which should not be overlooked is contralateral cerebellar hemorrhagic infarction following pterional craniotomies. Papanastassiou et al. (1996) have reported five cases of patients who were initially undergoing craniotomy for unruptured aneurysms or meningioma. The symptoms of obstructive hydrocephalus and brainstem compression developed from the immediate postoperative period to 24 hours later. The diagnosis is usually made with MRI and MRA, which disclose vein occlusion. In addition, non-contrast and contrast-enhanced TCCS may be helpful in the evaluation of posterior fossa sinuses, increased venous blood flow velocity being used as an indirect criterion for venous thrombosis (Stolz et al., 1999). Treatments include anticoagulants, monitoring of intracranial pressure, and the surgical removal of the lesion in the case of a swollen cerebellar infarct (Bousser and Russel, 1997). Endovascular thrombolysis may prove to be a useful treatment in selected cases. Antibiotics are indicated in the case of infection.

xReferencesx Adams, R.D. (1943). Occlusion of anterior inferior cerebellar artery. Arch Neurol Psychiatry 49: 765–70. Alexander, C.B., Burger, P., Goree, J.A. (1979). Dissecting aneurysms of the basilar artery in 2 patients. Stroke 10: 294–7. Amarenco, P. (1991). The spectrum of cerebellar infarctions. Neurology 41: 973–9. Amarenco, P. (1993). Les infarctus du cervelet et leurs mécanismes. Rev Neurol (Paris) 149: 728–48. Amarenco, P. (1995). Cerebellar stroke syndrome. In Stroke Syndromes, ed. J. Bogousslavsky and L. Caplan, pp. 344–57. Cambridge: Cambridge University Press. Amarenco, P., Caplan, L.R. and Pessin, M.S. (1998). Vertebrobasilar occlusive disease. In Stroke, ed. H.J.M. Barnett, J.P. Mohr, B.M. Stein and F.M. Yatsu, pp. 513–98. New York: Churchill Livingstone. Amarenco, P., Chevrie-Muller, C., Roullet, E. and Bousser, M.G. (1991a). Paravermal infarct and isolated cerebellar dysarthria. Ann Neurol 30: 211–13.

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Amarenco, P., Duyckaerts, C., Tzourio, C., Henin, D., Bousser, M.G. and Hauw, J.J. (1992). The prevalence of ulcerated plaques in the aotic arch in patients with stroke. N Engl J Med 326: 221–5. Amarenco, P. and Hauw, J.J. (1990). Cerebellar infarction in the territory of the superior cerebellar artery: a clinicopathologic study of 33 cases. Neurology 40: 1383–90. Amarenco, P., Hauw, J.J. and Gautier, J.C. (1990a). Arterial pathology in cerebellar infarction. Stroke 21: 1299–305. Amarenco, P., Kase, C.S., Rosengart, A., Pessin, M.S., Bousser, M.G. and Caplan, L.R. (1993). Very small (border zone) cerebellar infarcts. Causes, mechanisms, distribution and clinical features. Brain 116: 161–86. Amarenco, P., Levy, C., Cohen, A., Touboul, P.J., Roullet, E. and Bousser, M.G. (1994). Causes and mechanisms of territorial and non territorial cerebellar infarcts in 115 consecutive cases. Stroke 25: 105–12. Amarenco, P., Roullet, E., Gougon, C., Cheron, F., Hauw, J.J. and Bousser, M.G. (1991b). Infarction in the anterior rostral cerebellum. Neurology 41 253–8. Amarenco, P., Roullet, E., Hommel, M., Chaine, P. and Marteau, R. (1990b). Infarction in the territory of the medial branch of the posterior inferior cerebellar artery. J Neurol Neurosurg Psychiatry 53: 731–5. Andeweg, J. (1999). Consequences of the anatomy of deep venous outflow from the brain. Neuroradiology 41: 233–41. Barinagarrementeria, F., Amaya, L.E. and Cantu, C. (1997). Causes and mechanisms of cerebellar infarction in young patients. Stroke 28: 2400–4. Barth, A., Bogousslavsky, J. and Regli, F. (1993). The clinical and topographic spectrum of cerebellar infarcts; a clinical– magnetic resonance imaging correlation study. Ann Neurol 33: 451–6. Barth, A., Bogousslavsky, J. and Regli, F. (1994). Infarcts in the territory of the lateral branch of the posterior inferior cerebellar artery. J Neurol Neurosurg Psychiatry 57: 1073–6. Blecic, S. and Bogousslavsky, J. (1995). General management of patients with ischaemic stroke: clinical features and epidemiology. Curr Opin Neurol 8: 30–7. Blecic, S., Jeangette, S. and Bier, J.C. (1999). Stroke in sportsmen. Frequency, etiology and outcome: an analysis of 20 cases. Neurology 52(6): 241. Bogousslavsky, J. and Regli, F. (1984). Lateropulsion axiale isolée lors d’ un infarctus cérébelleux flocculo-nodulaire. Rev Neurol (Paris) 140: 140–3. Bogousslavsky, J., Regli, F., Maeder, P., Meuli, R. and Nader, J. (1993). The etiology of posterior circulation infarcts: a prospective study using magnetic resonance imaging and magnetic resonance angiography. Neurology 43: 1528–33. Bogousslavsky, J., Van Melle, G. and Regli, F. (1988). The Lausanne stroke registry: analysis of 1000 consecutive patients with first stroke. Stroke 19: 1083–92. Bousser, M.G. and Russel, R.R. (1997). Cerebellar vein thrombosis. In Major Problems in Neurology, ed. M.G. Bousser and R.R. Russel, pp. 40–2. London: W.B. Sauders Company Ltd. Braun, M., Bracard, S., Huot, J.C., Roland, J. and Picard, L. (1996).

Pontine veins. MRI cross-sectional anatomy. Surg Radiol Anat 18: 315–21. Canaple, S. and Bogousslavsky, J. (1999). Multiple large and small cerebellar infarcts. J Neurol Neurosurg Psychiatry 66: 739–45. Caplan, L.R. (1980). Top of the basilar syndrome. Neurology 30: 72–9. Caplan, L.R. (1991). Migraine and vertebrobasilar ischemia. Neurology 41: 55–61. Castaigne, P., Lhermitte, F., Gauthier, J.C. et al. (1973). Arterial occlusions in the vertebro-basilar system. A study of 44 patients with post-mortem data. Brain 96: 133–54. Chaves, C.J., Caplan, L.R., Chung, C.S. et al. (1994). Cerebellar infarcts in the New England Medical Center Posterior Circulation Stroke Registry. Neurology 44: 1385–90. Chaves, C.J., Pessin, M.S., Caplan, L.R. et al. (1996). Cerebellar hemorrhagic infarction. Neurology 46: 346–9. Chiappetta, F., Brunori, A. and Bruni, P. (1998). Management of intracranial aneurysms: ‘state of the art’. J Neurosurg Sci 42(Suppl. 1): 5–13. Cioffi, F.A., Bernini, F.P., Punzo, A. and D’Avanzo, R. (1985). Surgical management of acute cerebellar infarction. Acta Neurochir 74(3–4): 105–12. Cossa, P. and Richard, S. (1955). Sur deux cas de syndrome de l’artère cérébelleuse supérieure (ou de ses branches). Rev Neurol (Paris) 92: 633–5. Daras, M., Tuchman, A.J. and Marks, S. (1991). Central nervous system infarction related to cocaine abuse. Stroke 22: 1320–5. Davison, C., Goodhart, S.P. and Savitsky, N. (1935). The syndrome of the superior cerebellar artery and its branches. Arch Neurol Psychiatry 33: 1143–74. del Zoppo, G.J. (1992). Fibrinolytic therapy. In Vertebrobasilar Arterial Disease, ed. R. Berguer and L.R. Caplan, pp. 179–92. St Louis: Quality Medical Publishing. Devuyst, G. and Bogousslavsky, J. (1999). Clinical trial update: neuroprotection against acute ischaemic stroke. Curr Opin Neurol 12: 73–9. Dunac, A., Blecic, S., Jeangette, S., Bier, J.C., Rossetti, P and, Hildebrand, J. (1998). Stroke due to artery dissection. Role of collagen disease. Cerebrovasc Dis 8: 18. Duncan, G.W., Parker, S.W. and Fisher, C.M. (1975). Acute cerebellar infarction in the PICA territory. Arch Neurol 32: 364–8. Duvernoy, H., Delon, S. and Vannson, J.L. (1983). The vascularization of the human cerebellar cortex. Brain Res Bull 11: 419–80. Easton, J.D. and Sherman, D.G. (1977). Cervical manipulation and stroke. Stroke 8: 594–7. Fisher, C.M. (1977). Bilateral occlusion of basilar artery branches. J Neurol Neursurg Psychiatry 40: 566–7. Fisher, C.M., Karnes, W.E. and Kubick, C.S. (1961). Lateral medullary infarction: the pattern of vascular occlusion. J Neuropathol Exp Neurol 20: 323–79. Fisher, C.M. and Ojemann, R.J. (1986). A clinicopathological study of carotid endarterectomy plaques. Rev Neurol (Paris) 123: 142–56. Freeman, W. and Jaffe, D. (1941). Occlusion of superior cerebellar artery. Report of a case with necropsy. Arch Neurol Psychiatry 46: 115–26.

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S. Blecic and J. Bogousslavsky

Frumkin, L. and Baloh, R.W. (1990). Wallenberg’s syndrome following neck manipulations. Neurology 40: 611–15. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Goertler, M., Kross, R., Baeumer, M. et al. (1998). Diagnostic impact and prognostic relevance of early contrast-enhanced transcranial color-coded duplex sonography in acute stroke. Stroke 29: 955–62. Guillain, G., Bertrand, Y. and Péron, P. (1928). Le syndrome de l’artère cérébelleuse supérieure. Rev Neurol (Paris) 2: 835–43. Hacke, W., Zeumer, H., Ferbert, A., Bruckmann, H. and del Zoppo, G.J. (1988). Intra-arterial thrombolitic therapy improves outcome in patients with acute vertebrobasilar occlusive disease. Stroke 19: 1216–22. Hass, W.K., Easton, J.D., Adams, H.P. Jr et al. (1989). A randomized trial comparing ticlopidine hydrochloride with aspirin for the prevention of stroke in high-risk patients. N Engl J Med 321: 501–7. Hennerici, M., Hacke, W., von Kummer, R. et al. (1991). Intravenous tissue plasminogen activator for the treatment of acute thromboembolic ischemia. Cerebrovasc Dis 1: 124–8. Heros, R.C. (1992). Surgical treatment of cerebellar infarction. Stroke 23: 937–8. Hickenbottom, S.L. and Grotta, J. (1998). Neuroprotective therapy. Semin Neurol 18: 485–92. Hudgins, R.J., Day, A.L., Quisling, R.G., Rhoton, A.L. Jr, Sypert, G.W. and Garcia-Bengochea, F. (1983). Aneurysms of the posterior inferior cerebellar artery. A clinical and anatomical analysis. J Neurosurg 58: 381–7. Jauss, M., Krieger, D., Hornig, C., Schramm, J. and Busse, O. (1999). Surgical and medical management of patients with massive cerebellar infarctions: results of the German–Austrian Cerebellar Infarction Study. J Neurol 246: 257–64. Kallmes, D.F., Lanzino, G., Dix, J.E. et al. (1997). Patterns of hemorrhage with ruptured posterior inferior cerebellar artery aneurysms: CT findings in 44 cases. Am J Roentgenol 169: 1169–71. Kanis, K.B., Ropper, A.H. and Adelman, A.S. (1994). Homolateral hemiparesis as an early sign of cerebellar mass effect. Neurology 44: 2194–7. Kase, C.S., Norrving, B., Levine, S.R. et al. (1993). Cerebellar infarction: clinical and anatomic observations in 66 cases. Stroke 24: 76–83. Kase, C.S., White, J.L., Joslyn, J.N., Williams, J.P. and Mohr, J.P. (1985). Cerebellar infarction in the superior cerebellar artery distribution. Neurology 35: 705–11. Levine, S.R. and Welch, K.M. (1988). Superior cerebellar artery infarction and vertebral artery dissection. Stroke 19: 1431–4. Macdonald, R.L., Findlay, J.M. and Tator, C.H. (1988). Sphenoethmoidal sinusitis complicated by cavernous sinus thrombosis and pontocerebellar infarction. Can J Neurol Sci 15: 310–13. Macdonnel, R.A., Kalnins, R.N. and Donnan, G.A. (1987). Cerebellar infarction: natural history, prognosis and pathology. Stroke 19: 847–55.

Marinkovic, S., Kovacevic, M., Gibo, H., Milisavljevic, M. and Bumbasirevic, L. (1995). The anatomical basis for the cerebellar infarcts. Surg Neurol 44: 450–61. Marshall, R.S. and Mohr, J.P. (1997). Ischemic stroke. In Neurological Emergencies, ed. R.A.C. Highes, pp. 12–87. London: British Medical Group. Mathew, P., Teasdale, G., Bannan, A. and Oluoch-Olunya, D. (1995). Neurosurgical management of cerebellar haematoma and infarct. J Neurol Neurosurg Psychiatry 59: 287–92. Menzies, W.F. (1893). Thrombosis of inferior cerebellar artery. Brain 15: 436–9. Mettler, F.A. (1948). Arterial supply of the cerebellum. In Neuroanatomy, ed. F.A. Mettler, pp. 175–80. New York: C.V. Mosby. Mills, C.K. (1912). Preliminary note on a new symptom complex due to lesion of the cerebellum and cerebello-rubro-thalamic system. J Nerv Ment Dis 39: 73–6. Mounier-Vehier, F., Degaey, I., Leclerc, X. and Leys, D. (1995). Cerebellar border zone infarcts are often associated with presumed cardiac sources of ischaemic stroke. J Neurol Neurosurg Psychiatry 59: 87–9. Nayak, A.K., Karnad, D., Mahajan, M.V., Shah, A. and Meisheri, Y.V. (1994). Cerebellar venous infarction in chronic suppurative otitis media. A case report with review of four other cases. Stroke 25: 1058–60. Papanastassiou, V., Kerr, R. and Adams, C. (1996). Contralateral cerebellar hemorrhagic infarction after pterional craniotomy: report of five cases and review of the literature. Neurosurgery 39: 841–51. Pelouze, G.A. (1989). Plaque ulcérée de l’ostium de l’artère vertébrale. Rev Neurol (Paris) 145: 478–81. Philips, P.C., Lorentsen, K.J., Shropshire, L.C. and Ahn, H.S. (1988). Congenital odontoid aplasia and posterior circulation stroke in childhood. Ann Neurol 23: 410–13. Ranalli, P.J. and Sharpe, J.A. (1986). Contrapulsion of saccades and ipsilateral ataxia: a unilateral disorder of the rostral cerebellum. Ann Neurol 20: 311–13. Redekop, G.J., Durity, F.A. and Woodhurst, W.B. (1997). Management-related morbidity in unselected aneurysms of the upper basilar artery. J Neurosurg 87: 836–42. Ringelstein, E.B. (1998). Echo-enhanced ultrasound for diagnosis and management in stroke patients. Eur J Ultrasound 3 (Suppl.): S3–15. Ringer, R.A. and Culberson, J.L. (1989). Extensor tone disinhibition from an infarction within the midline anterior cerebellar lobe. J Neurol Neurosurg Psychiatry 52: 1597–9. Ringle, S., Harrison, S.H., Noremberg, M. and Austin, J.H. (1977). Fibromuscular dysplasia: multiple ‘spontaneous’ dissecting aneurysms of the major cervical arteries. Ann Neurol 1: 301–6. Rodda, R. (1971). The vascular lesions associated with cerebellar infarcts. Proc Aust Assoc Neurol 8: 101–10. Rousseaux, M., Lesoin, F., Barbaste, P. and Jomin, M. (1988). Pseudotumoral cerebellar infarction of venous origin. Rev Neurol (Paris) 144: 209–11. Rousseaux, M. and Steinling, M. (1999). Remote regional cerebral

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blood flow consequences of focused infarcts of the medulla, pons and cerebellum. J Nucl Med 40: 721–9. Schievink, W.I., Mokri, B. and O’Fallon, W.M. (1994). Recurrent spontaneous cervical-artery dissection. N Engl J Med 330: 393–7. Schievink, W.I., Mokri, B., Piepgras, D.G. and Kuiper, J.D. (1996). Recurrent spontaneous arterial dissections. Risk in familial versus nonfamilial disease. Stroke 27: 622–4. Sevestre, H., Vercken, J.B., Henin, D. et al. (1988). Anoxic encephalopathy after cardiocirculatory insufficiency. Neuropathological study of 16 cases. Ann Med Interne (Paris) 139: 245–50. Sivenius, J., Riekkinen, J., Smets, P., Laakso, M. and Lowenthal, A. (1991). The European Stroke Prevention Study (ESPS): results by arterial distribution. Ann Neurol 29: 596–600. Stolz, E., Kaps, M. and Dorndorf, W. (1999). Assessment of intracranial venous hemodynamics in normal individuals and patients with cerebral venous thrombosis. Stroke 30: 70–5. Struck, L.K., Biller, J. and Bruno, A. (1991). Superior cerebellar artery territory infarction. Cerebrovasc Dis 1: 71–5. Sypert, G.W. and Alvord, E.C. (1975). Cerebellar infarction. A clinicopathological study. Arch Neurol 32: 357–63. Tatu, L., Moulin, T., Bogousslavsky, J. and Duvernoy, H. (1996). Arterial territories of human brain; brainstem and cerebellum. Neurology 47: 1125–35.

Tohgi, H., Takahashi, S., Chibra, K. and Hirata, Y. (1993). Cerebellar infarction. Clinical and neuroimaging analysis in 293 patients. Stroke 24: 1697–701. Tougeron, A., Samson,Y., Schaison, M., Artigou, J.Y. and Bousser, M.G. (1988). Syndrome dysarthrie-main malhabile causé par infarctus cérébelleux. Rev Neurol (Paris) 41: 253–8. Trattnig, S., Hubsch, P., Shuster, H. and Polzleitner, D. (1990). Color-coded Doppler imaging of normal vertebral arteries. Stroke 21: 1222–5. Waespe, W. and Wichmann, W. (1990). Oculomotor disturbances during visual–vestibular interaction in Wallenberg’s lateral medullary syndrome. Brain 113: 821–46. Wallenberg, A. (1895). Acute bulbäraffection. Arch Psychiatr 27: 504–40. Wallenberg, A. (1901). Anatomischer befund in einem als ‘Acute bulbäraffection’. Arch Psychiatr 34: 923–59. Walsh, T.J., Hier, D.B. and Caplan, L.R. (1985). Aspergillosis of the central nervous system: clinicopathological analysis of 17 patients. Ann Neurol 18: 574–82. Youl, B.D., Coutellier, A., Dubois, B., Leger, J.M. and Bousser, M.G. (1990). Three cases of spontaneous extracranial vertebral artery dissection. Stroke 21: 618–25.

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Immune diseases Pierre Duquette Service de Neurologie, l’Hôpital Notre-Dame, Montreal, Quebec, Canada

Multiple sclerosis Introduction Multiple sclerosis (MS) is the most common chronic neurological disorder in young and middle-aged adults. It involves exclusively the central nervous system (CNS). It is an inflammatory disorder consecutive to the formation of venule-centered areas, or plaques, scattered haphazardly. These plaques contain reactive cells and harbor myelin and axonal damage. Whether remyelination is a constant feature is at issue, but, if it is present, it is clearly ineffective at restoring myelin and axonal integrity. The consensus is that MS is an atypical autoimmune disorder (Reder and Antel, 1983). A genetic contribution to the etiology has been deduced from family studies (Sadovnick et al., 1997, 1998). MS is twice as common in women than it is in men, and affects predominantly Caucasians (Whitacre et al., 1999). The most classical clinical manifestation of MS is a relapse, which is an acute or subacute episode of neurological dysfunction lasting several weeks, followed by a remission. Relapses are unpredictable in time course, severity, duration, and site of lesion. MS course is usually protracted, only five or six years of overall longevity being lost (Sadovnick et al., 1992). Although still incurable, therapeutic breakthroughs have been attained that partially decrease the formation of new plaques (Paty and Hartung, 1999). Multiple sclerosis seems to be a modern affliction, there apparently being no mention of this disease in ancient medical texts, or in those of the Middle Ages. The earliest accounts of MS are of St Lidwina of Schiedam of Holland (1380–1433) by Godfried Sonderbank, and by Sir Frederick d’Este from the UK (1794–1848) in his diary (Firth, 1948). Cruveilhier (in 1835) and Carswell (1838) brought medical attention to the disease, which was described in a masterful fashion by Charcot in 1868 (Francis et al., 1996).

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Epidemiology The prevalence of MS in ‘developed countries’ inhabited by people from Northern European extraction varies from 100 to over 200 cases per 100 000, and shows a striking geographical variation. Equatorial countries have a low incidence. The disease is increasingly more common with distance from the equator, in either hemisphere. This variation is partially due to the Northern European, and especially Scandinavian, ancestry of the affected populations, but there is also an environmental influence (Sadovnick and Ebers, 1993). MS is almost non-existent among African Blacks, and is rare in Orientals, as well as in NorthAmerican Indians (Sadovnick et al., 1997).

Clinical manifestations Manifestations of MS are protean. The most common, and often most disabling, symptom is fatigue, an unexplained, peculiar sensation of exhaustion unrelated to physical or disease activity, sometimes present upon awakening (Reder and Antel, 1983). Sensory manifestations are the most common initial feature of MS, and are almost universal during its course. They can reflect spinothalamic, posterior columns, or dorsal entry zone lesions. Pain, especially in the legs, is common in wheelchair-bound patients. Lhermitte’s symptom, an electric shock-like sensation felt along the spine or the limbs, although not exclusive to MS, is one of its most evocative manifestations. Optic neuritis, usually unilateral, is also common. Not all cases of initial optic neuritis go on to develop MS, the risk being higher in young women with silent magnetic resonance imaging (MRI) brain lesions (Beck et al., 1993). Impairment of oculomotor pathways can become manifest as nystagmus or, typically, as internuclear ophthalmoplegia (a dissociation of horizontal eye movements). Weakness, or paresis, is more marked in the lower extremities; it is associated with spasticity and increased deep

Immune diseases

tendon reflexes. Together with a Babinski sign, they reflect the longer course of the corticospinal fibers to the legs in the spinal cord. Function of the bladder (failure to store) and of the rectum (failure to empty) is frequently impaired (Schoenberg, 1983), as is the sexual response (erectile dysfunction, decreased sensations in the clitoris and vagina). Cognitive impairment is now acknowledged to be common, even at early stages, presenting as impaired memory, decreased concentration, and mental fatigue (Rao et al., 1991). Depression can be secondary to the many losses incurred, or due to brain lesions. Heat sensitivity is a frequent occurrence. Uhthoff’s sign is also common; it is a temporary decrease of vision occurring during exercise, or upon taking a hot bath. It reflects decreased conductivity in demyelinated axons. Charcot’s triad of cerebellar signs is comprised of nystagmus, scanning speech, and intention tremor. Cerebellar impairment is a poor omen in MS and is a major factor leading to incapacity. The characteristic intention tremor seen in MS is that of an oscillating tremor at 5 to 7 Hz moving in a plane perpendicular to the direction of the intended movement. When severe, it appears at the slightest intention of movement. It is associated with a clumsiness resulting in irregularities of rapidly alternating movements, and with hypotonia (Paty and Ebers, 1998). After a course of 20 years, an MS patient characteristically is in a wheelchair, because of spastic paraparesis and truncal ataxia. Sphincteric function is unpredictable, an action tremor impairs arm function, speech is disturbed, visual acuity is low, and social and family life is perturbed by emotional and cognitive dysfunction.

Disease course MS typically evolves by relapses, followed after three to six weeks by a remission, as in optic neuritis. This relapsing–remitting pattern is most common in young women with an early onset. After 10 to 20 years, relapses gradually cease and are replaced by a slow progression, this pattern being designated as secondary progressive MS (Weinshenker and Ebers, 1987). Primary progression occurs in 15% to 20% of patients, and is most common in men with a later onset; these patients rarely have superimposed relapses (progressive–relapsing course) (Lublin and Reingold, 1996).

Pathology Multiple sclerosis plaques are found throughout the brain and spinal cord in both gray and white matter, but the most likely sites are periventricular and periaqueductal. Gray

Fig. 14.1 Unstained gross coronal section of the brain. Note the typical dark-colored periventricular and parenchymatous lesions. (Reproduced with permission from An Atlas of Multiple Sclerosis, ed. C.M. Posner, Parthenon Publishing, 1998.)

matter is affected, for it contains myelinated fibers. Plaques are of varying ages, unlike the monophasic lesions of postinfectious and postvaccinal encephalomyelitis. Typical acute plaques spread out from the postcapillary venules. The initial lesion is a cuff of macrophages and CD4 lymphocytes that surround vessels lined with major histocompatibility complex class II endothelial cells (Traugott et al., 1985; Raine, 1991). The early plaques are hypercellular and inflammatory, and show ongoing diffuse demyelination and swollen astrocytes at the edges. Compact myelin is phagocytosed by infiltrating macrophages. Demyelination predominates, but there is some axonal loss (Trapp et al., 1998). As the MS plaque ages, inflammation and edema resolve. The relative number of CD8 cells, B cells, and monocytes increases (Lassmann et al., 1994). A glial scar, demyelinated axons, and occasional inflammatory cells are the residue. Remyelination is present in many active plaques, but is inefficient at restoring myelin and axonal integrity, probably because it is impeded by the immune mechanisms responsible for plaque formation.

Etiological hypotheses The prevailing etiological hypothesis for MS evokes an autoimmune attack against myelin, and possibly axons, in genetically predisposed individuals. The higher incidence of MS in women is probably related to the known influence of sex hormone on immune functions. It is well known that

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Fig. 14.2 Section of the cervical spine showing a large lesion. Luxol fast blue–PAS stain. (Courtesy of Professor H. Lassmann, Institute of Brain Research, Vienna, Austria.)

most autoimmune diseases are more common in women than in men (Whitacre et al., 1999). For instance, Sjögren’s disease occurs 20 times more frequently in women. Although there appears to be an autoimmune attack against myelin and myelin-forming cells in the brain and spinal cord, MS cannot be called a true autoimmune disease. T-cell and antibody reactivity has been tested against numerous virus and brain antigens, but no target antigen has been clearly demonstrated. Cloned T-cells from MS patients show excessive reactions to myelin antigens in some studies, but not in all. It is possible that the immune response evolves through ‘epitope spreading,’ generating responses to a number of CNS antigens. These antigens include heat shock protein-65, which is highly conserved between bacteria and humans, and is crossreactive with the myelin antigen cyclic nucleotide phosphohydrolase (Birnbaum et al., 1996). Heat shock protein and cyclic nucleotide phosphohydrolase are two of many possible infectious and myelin (also myelin basic

protein, proteolipid protein, myelin oligodendrocyte glycoprotein) antigens that could trigger antigen-specific responses or be involved in a gradual shift in immune reactivity over time, i.e., ‘epitope spreading.’ The lack of a causative antigen suggests that regulation of immune responses may be abnormal and that oligodendroglia may be innocent bystanders that are damaged by unregulated inflammation. However, this theory does not explain the specificity of the process. Lymphocytes and monocytes might enter the CNS because of non-specific adhesion to endothelial cells by cellular adhesion molecules, cross the blood–brain barrier, and become activated within the CNS where, along with macrophages, cytokines, and proteins of the complement system, they destroy myelin and axons (Cossette et al., 1998). Multiple etiologies have been proposed. These include: (1) viruses, with a direct damage to oligodendroglia, retrovirus incorporation in oligodendroglia and T-cells, and immune reactivity to shared determinants

Immune diseases

Fig. 14.3 Unstained gross axial section of the cerebellum. Note the typical involvement of the dentate nuclei and periventricular lesions (arrows). (Reproduced with permission from An Atlas of Multiple Sclerosis, ed. C.M. Posner, Parthenon Publishing, 1998.)

between oligodendroglia and viruses; human herpes virus6 and endogenous retroviruses were implicated recently (Myhr et al., 1998); (2) bacteria; (3) defective function or repair in oligodendroglia; (4) diet (affects membrane composition, macrophage function, and prostaglandin synthesis); (5) genetic (predisposition to respond to brain antigens, decreased control of the immune response to brain antigens) (Reder, 1999). Recovery from relapses is also presumably immune mediated. In CNS lesions of experimental allergic encephalomyelitis, an experimentally induced animal model of MS, inhibitory Th2 cytokines, immunoglobulins, and glucocorticoids wax as the clinical symptoms wane. The cytokine profile during exacerbations and remissions of MS may parallel this model (Reder et al., 1994; Reder, 1999).

Genetics Multiple sclerosis is not a disorder with a mendelian pattern of inheritance but, in most exhaustive analyses, a little over 20% of unrelated MS patients have another

member of their family who is affected. For relatives of an affected patient, the degree of risk of acquiring the disease is directly related to the amount of gene sharing (Sadovnick, 1993). Monozygotic twins have a concordance of 30%, while the risk for fraternal twins is close to the risk of non-twin sibs (Sadovnick et al., 1993). This constitutes the strongest evidence for the role of genetic factors (Ebers and Sadovnick, 1994). First-degree relatives have a 10–70-fold increased risk of developing MS compared to the general population (Hogancamp et al., 1997). It has been determined that, for the first-degree relatives of an affected patient with onset before the age of 20 and one parent affected, the risk of MS is 20%, close to the level of non-dominant inheritance (Sadovnick et al., 1998). Unaffected twins often have abnormal MRIs (Mumford et al., 1994), but their T-cell responses to myelin basic protein are normal (Martin et al., 1993). The large number of unaffected monozygotic twins may be the strongest argument for an environmental contribution to MS. The maximal contribution of genetics to the etiology of MS is estimated at 40%.

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Blood

Hemato-encephalic barrier

Helper T-lymphocyte

Active lymphocyte

T

T

Central nervous system

Th Microglial astrocyte IL-2 IL-4, 10

Antigen Macrophage –

TGFβ –

Th1

TGFβ

T

B

–

IFN-γ

IL-2 LT TNFα NO

TGFβ

Antibody

–

–

SEP?

IL-4, 5, 6 Th2

T

Suppressor T-lymphocyte

C5b-9 TNFa OH* NO Proteases

Antibody B

Myelin

Fig. 14.4 Proposed etiopathogenesis of multiple sclerosis. (Reproduced with permission from Cossette et al. (1998), Médecine Sciences, Vol. 14, pp. 37–43.)

Studies in adoptees, half-sibs, and conjugal MS have demonstrated that the observed familial aggregation in MS – that is, the relative excess of MS among biological relatives compared to the general population – is entirely determined by genes, with no impact from the shared environment (Ebers et al., 1995). Results of random genome screens have been reported: several loci have been identified, none having a strong impact on susceptibility. MS has been known since 1970 to be associated with HLA-alleles of the major histocompatibility complex, but the meaning of this association is still unknown (Ebers et al., 1996). Current thinking holds that genetic susceptibility to MS is determined by multiple genes, each having a minor, and in most instances probably unnecessary, role. Environmental causes have been suggested, but none is clearly a direct cause of MS.

Diagnosis In typical cases, the diagnosis of MS is easily reached on clinical grounds. Two spontaneously resolving episodes separated in time and in space (i.e., involving separate sites in the CNS) in a previously healthy young adult suffice to establish a definitive diagnosis (Poser et al., 1983). Clinical diagnosis can be confirmed by the demonstration of oligoclonal bands in the immunoglobulin fraction of the cerebrospinal fluid (CSF), or by multiple lesions of the brain and spinal cord evidenced in particular by MRI.

Treatment There is no curative therapy of MS. Beta-interferons (IFN) and glatiramer acetate can decrease the frequency and severity of relapses and reduce signs of MRI activity. Their efficacy is maintained for at least five years; they are

Immune diseases

Fig. 14.5 T2-weighted (left) and gadolinium–EDTA-enhanced (right) axial MRIs showing a number of ovoid lesions. Although many areas of increased signal intensity are seen on T2-weighting, other such areas (arrows) not revealed by T2-weighting are clearly seen with gadolinium–EDTA enhancement. This phenomenon is relatively uncommon.

quite well tolerated, having shown no severe toxicity, although very long-term effects are unknown. Their effect on established progression is less clear (Paty and Hartung, 1999). In a European trial including patients with secondary progressive MS, IFN-1b was shown to reduce the rate of progression (European Study Group on Interferon -ib in Secondary Progressive MS, 1998). In similar conditions, IFN-1a was ineffective in halting progression, except in a post-hoc analysis showing that women derived a benefit, while men did not (Freedman M., personal communication). Numerous clinical trials of agents attempting to abrogate the immune response are in progress. Innumerable methods of immunosuppression have been tried in MS, none having given satisfying and reproducible results (Paty and Ebers, 1998). A comprehensive symptomatic approach to the treatment of MS is being developed; it eases the many problems patients have to face in their daily lives (Frohman, 1999). The treatment of cerebellar deficits poses a great challenge. Rubral-type action tremor is most common in the upper extremities, but can spread to the head, the trunk, and the lower extremities. It is usually resistant to

pharmacological intervention. Surgical lesions to thalamic structures can ablate the tremor, often at the expense of dysarthria, dysphagia, cognitive deterioration, and increased limb weakness. It is a last-resort choice. Chronic stimulation of subthalamic nuclei, with implanted electrodes, holds better promise, but has been tried in only a small number of patients (Frohman, 1999).

Miller Fisher syndrome Miller Fisher syndrome is a postinfectious polyneuropathy comprising cerebellar-like ataxia and areflexia, with motor manifestations usually restricted to weakness of the extraocular muscles (Fisher, 1956). Elevated CSF protein levels, good recovery, and transitional cases link Miller Fisher syndrome strongly to the Guillain–Barré syndrome. However, some believe that cerebellar-like deficits and ophthalmoplegia are better attributed to a CNS disorder involving mainly the brainstem. In Miller Fisher syndrome, antiganglioside antibodies are found in over 90% of patients at clinical presentation. They disappear over time, as recovery occurs (Vincent, 1998).

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Other immune diseases causing cerebellar ataxia A number of other immune-mediated conditions may involve the cerebellum. Although cerebellar ataxia seems a rare complication, these diseases should not be underestimated, because cerebellar deficits may be reversible with treatment.

Cerebellar ataxia associated with celiac disease Celiac disease is a malabsorption syndrome characterized by intolerance to dietary gluten and typical lesions of the small intestine. In genetically susceptible individuals, a state of heightened immunological responsiveness to dietary gluten can be demonstrated. Antigliadin antibodies and antiendomysium antibodies are markers of celiac disease. Neurological complications occur in about 8% to 10% of patients; they include peripheral neuropathy, progressive multifocal leukoencephalopathy, cerebellar progressive myoclonic ataxia, dementia, and myopathy (Cooke and Thomas-Smith, 1966; Hadjivassiliou et al., 1996, 1997, 1998). The mechanisms responsible for neurological complications remain unclear. They could result from nutritional deficiencies, but supplementation rarely brings improvement. Antigliadin antibodies have been suggested to be directly or indirectly neurotoxic. Ataxia is the commonest, and sometimes the sole, manifestation of celiac disease. Hadjivassiliou et al. (1998) have reported a group of 28 patients with celiac disease and ataxia. The mean age at onset of ataxia was 54, with a range from 18 to 75, and a male/female ratio of 3/1. Interestingly, 16 patients had no history of gastrointestinal symptoms. Gait ataxia was present in all, and limb ataxia in most of them. Those with severe gait ataxia had a longer disease duration. Nystagmus was noted in only three patients; no patient had extrapyramidal features; 19 presented evidence of peripheral neuropathy on neurophysiological studies. Six patients had evidence of cerebellar atrophy on MRI. Biopsy of duodenum demonstrated lymphocytic infiltration in two patients and revealed abnormalities suggestive of celiac disease in 11. Autopsy was available in two cases: there was lymphocytic infiltration of the cerebellum, damage to the posterior columns of the spinal cord, and sparse infiltration of peripheral nerves. Gluten ataxia results from this combination of damage to the cerebellum, spinal cord, and peripheral nerves (Hadjivassiliou et al., 1998). Some authors have reported improvement of ataxia and peripheral neuropathy on a gluten-free diet (Ward et al., 1985; Kaplan et al., 1988; Beversdorf et al., 1996). Patients may experience a complete resolution of

ataxic symptoms if the diagnosis is made very early and a strict gluten-free diet is given (Hadjivassiliou et al., 1998).

Cogan’s syndrome Cogan’s syndrome is an uncommon and probably underdiagnosed disease of young adults, giving rise to episodes of acute interstitial keratitis with vestibuloauditory dysfunction (Cogan, 1945; Manto and Jacquy, 1996). From 2% to 50% of patients have neurological manifestations, consisting mainly of meningoencephalitis, seizures, organic mental syndrome, and peripheral neuropathy. Thrombosis of the posterior inferior cerebellar artery has been reported (Norton and Cogan, 1959; Fair and Levi, 1960), as well as acute multifocal cerebellar lesions mimicking cerebellar infarctions (Manto and Jacquy, 1996). Cogan syndrome should be included in the differential diagnosis of cerebellar lesions when they are accompanied by eye and ear symptoms. The pathogenesis consists of a vasculitis which may involve many tissues. Lesions suggestive of polyarteritis nodosa have been observed in some cases. Steroids may improve cerebellar ataxia (Manto and Jacquy, 1996).

Behçet’s disease Behçet’s disease is an uncommon, relapsing and remitting, multisystem inflammatory disorder with the triad of oral ulceration, genital ulceration, and uveitis (Behçet, 1937; Hadfield et al., 1997). Neurological manifestations arise in up to 42% of patients. The term neuro-Behçet’s disease is coined when they occur. The most frequent neurological picture is that of a relapsing–remitting meningoencephalitis, most frequently affecting the brainstem. Superimposed venous thrombosis is a complication of Behçet’s disease. The patients may exhibit waxing and waning neurological deficits (Hadfield et al. 1996). The neuroradiologic findings sometimes simulate those of MS (Hadfield et al., 1996). The pathology reveals foci of chronic inflammation in the vicinity of a blood vessel; fibroid necrosis is absent.

Cerebellar ataxia with glutamic acid decarboxylase antibodies Glutamic acid decarboxylase (GAD) catalyses the conversion of glutamate to -aminobutyric acid. The GAD65 isoform has been found to be a major antigen in the stiffman syndrome, polyendocrine autoimmune syndrome, and insulin-dependent diabetes mellitus. Recently, an association between cerebellar ataxia and GAD antibodies has been reported in three patients with accompanying

Immune diseases

insulin-dependent diabetes mellitus and polyendocrine autoimmune syndrome (Saiz et al., 1997). The physiological role of GAD antibodies in cerebellar ataxia remains unclear. Purkinje cells, affected in most types of cerebellar degeneration, contain high levels of GAD. It is not clearly understood how an intracellular antigen can be affected by circulating antibodies. One explanation could be the ability of Purkinje cells to uptake immunoglobulin G (IgG) from the CSF. Alternatively, surface HLA-antigens have been suggested as presenting the intracellular antigen to circulating antibodies. Cerebellar ataxia may respond to intravenous immunoglobulins (Abele et al., 1999).

Systemic lupus erythematosus Antibodies directed against Purkinje cells have been reported in patients with lupus ataxia (Shimomura et al., 1993). A pancerebellar syndrome of subacute progression associated with cerebellar atrophy is highly suggestive of papaneoplastic cerebellar degeneration. The case of a 27year-old woman with systemic lupus erythematosus who presented with a subacute pancerebellar syndrome has been reported (Manto et al., 1996). Serum and CSF anti-Yo, anti-Hu, and anti-Ri were not found. Brain MRI showed cerebellar atrophy. The cerebellar ataxia improved markedly following treatment with steroids.

xReferencesx Abele, M., Weller, W., Merscheriakov, S., Burk, K., Dichgans, J. and Klockgether, T. (1999). Cerebellar ataxia with glutamic acid decarboxylase antibodies. Neurology 52: 857–9. Beck, R.W., Cleary, P.A., Trobe, J.D. et al. (1993). The effect of corticosteroids for acute optic neuritis on the subsequent development of multiple sclerosis. The Optic Neuritis Study Group. N Engl J Med 326: 581–8. Behçet, H. (1937). Über die rezidivierende Aphtöse durch ein Virus verursachte Geschwüre am Auge und an den Genitalien. Dermatol Wochenschr 105: 1152–7. Beversdorf, D., Moses, P., Reeves, A. and Dunn, J. (1996). A man with weight loss, ataxia, and confusion for 3 months. Lancet 347(8999): 446. Birnbaum, G., Kotilinek, L., Schlievert, P. et al. (1996). Heat shock proteins and experimental autoimmune encephalomyelitis (EAE). Immunization with a peptide of the myelin protein 2, 3 cyclic nucleotide 3 phosphodiesterase that is cross-reactive with a heat shock protein alters the course of EAE. J Neurosci Res 44: 381–96. Cogan, D.G. (1945). Syndrome of nonsyphilitic intersitial keratitis and vestibuloauditory symptoms. Arch Ophthalmol 33: 144–9.

Cooke, W.T. and Thomas-Smith, W. (1966). Neurological disorders associated with adult celiac disease. Brain 89: 683–722. Cossette, P., Duquette, P. and Antel, J.P. (1998). Le rôle des cytokines et de molécules d’adhérence cellulaire dans la formation des lésions de la sclérose en plaques. Méd-Sci 14: 37–43. Ebers, G.C., Duquette, P. and Risch, N.A. (1996). A full genome search in multiple sclerosis. Nature Genet 13: 1–6. Ebers, G.C. and Sadovnick, A.D. (1994). The role of genetic factors in multiple sclerosis susceptibility. J Neuroimmunol 54: 1–17. Ebers, G.C., Sadovnick, A.D. and Risch, N.J. (1995). The Canadian Collaborative Study Group. A genetic basis for familial aggregation in multiple sclerosis. Nature 377: 150–1. European Study Group on Interferon -1b in Secondary Progressive MS (1998). Placebo-controlled multicentre randomized trial of interferon -1b in treatment of secondary progressive multiple sclerosis. Lancet 352: 1491–7. Fair, J.R. and Levi, G.A. (1960). Keratitis and deafness. Am J Ophthalmol 49: 1017–21. Firth, D. (1948). The Case of Augustus D’Esté. Cambridge: Cambridge University Press. Fisher, M. (1956). An unusual variant of acute idiopathic polyneuritis syndrome of ophthalmoplegia, ataxia and areflexia. N Engl J Med 255: 57–65. Francis, G.S., Duquette, P. and Antel, J.P. (1996). Inflammatory demyelinating diseases of the central nervous system. In Neurology in Clinical Practice, ed. W.G. Bradley, R.B. Daroff, G.M. Fenichel and C.D. Marsden, pp. 1307–43. Boston: Butterworth– Heinemann. Frohman, E.M. (1999). Treatment for patients with relapsing remitting MS. In Multiple Sclerosis: Experimental and Applied Therapeutics, ed. R. Rudick and D. Goodkin. London: Dunitz. Hadfield, M.G., Aydin, F., Lippman, H.R., Kubal, W.S. and Sanders, K.M. (1996). Neuro-Behçet’s disease. Clin Neuropathol 15: 249–55. Hadfield, M.G., Aydin, F., Lippman, H.R. and Sanders, K.M. (1997). Neuro-Behçet’s disease. Clin Neuropathol 16: 55–60. Hadjivassiliou, M., Chattopadhyay, A.K., Davies-Jones, G.A., Gibson, A., Grunewald, R.A. and Lobo, A.J. (1997). Neuromuscular disorder as a presenting feature of coeliac disease. J Neurol Neurosurg Psychiatry 63: 770–5. Hadjivassiliou, M., Gibson, A., Davies-Jones, G.A., Lobo, A.J., Stephenson, T.J. and Milford-Ward, A. (1996). Does cryptic gluten sensitivity play a part in neurological illness? Lancet 347: 369–31. Hadjivassiliou, M., Grunewald, R.A., Chattopadhyay, A.K. et al. (1998). Clinical, radiological, and neuropathological characteristics of gluten ataxia. Lancet 352: 1582–5. Hogancamp, W.E., Rodriguez, M. and Weinshenker, B.G. (1997). The epidemiology of multiple sclerosis. Mayo Clin Proc 72: 871–8. Kaplan, J.G., Pack, D., Horoupian, D., DeSouza, T., Brin, M. and Schaumburg, H. (1988). Distal axonopathy associated with chronic gluten enteropathy: a treatable disorder. Neurology 38: 642–5. Lassmann, H., Suchanek, G. and Ozawa, K. (1994). Histopathology

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and the blood–cerebrospinal fluid barrier in multiple sclerosis. Ann Neurol 36: S42–6. Lublin, F.D. and Reingold, S.C. (1996). Defining the clinical course of multiple sclerosis: results of an international survey. Neurology 46: 907–11. Manto, M-U. and Jacquy, J. (1996). Cerebellar ataxia in Cogan syndrome. J Neurol Sci 136: 189–91. Manto, M-U., Rondeaux, P., Jacquy, J. and Hildebrand, J.G. (1996). Subacute pancerebellar syndrome associated with systemic lupus erythematosus. Clin Neurol Neurosurg 98: 157–60. Martin, R., Voskuhl, R., Flerlage, M., McFarlin, D.E. and McFarland, H.F. (1993). Myelin basic protein-specific T cell responses in identical twins discordant or concordant for multiple sclerosis. Ann Neurol 34: 524–35. Mumford, C.J., Wood, N.W., Kellar, W.H., Thorpe, J.W., Miller, D.H. and Compston, D.A. (1994). The British Isles survey of multiple sclerosis in twins. Neurology 44: 11–15. Myhr, K.M., Riise, T., Barrett-Connor, E. et al. (1998). Altered antibody pattern to Epstein–Barr virus but not to other herpes viruses in multiple sclerosis: a population based case-control study from western Norway. J Neurol Neurosurg Psychiatry 64: 539–42. Norton, H.W.D. and Cogan, D.G. (1959). Syndrome of nonsyphilitic interstitial keratitis and vestibuloauditory symptoms: long-term follow-up. Arch Ophthalmol 61: 695–7. Paty, D.W. and Ebers, G.C. (1998). Clinical features. In Multiple Sclerosis, ed. D.W. Paty and G.C. Ebers, pp. 135–91. Contemporary Neurology Series, Vol. 50. Philadelphia: F.A. Davis. Paty, D.W. and Hartung, H-P. (1999). Management of relapsing–remitting multiple sclerosis: diagnosis and treatment guidelines. Eur J Neurol 6: S1–29. Poser, C.M., Paty, D.W. and Scheinberg, L. (1983). New diagnostic criteria for multiple sclerosis: guidelines for research protocols. Ann Neurol 13: 227–31. Raine, C.S. (1991). Multiple sclerosis: a pivotal role for the T cell in lesion development. Neuropathol Appl Neurobiol 17: 265–74. Rao, S.M., Leo, G.J., Bernardin, L. and Unverzagt, F. (1991). Cognitive dysfunction in multiple sclerosis. I. Frequency, patterns, and prediction. Neurology 41: 685–91. Reder, A. (1999). Review of Multiple Sclerosis, 3rd edn. Santiago: Arbor Publishing. Reder, A.T. and Antel, J.P. (1983). Clinical spectrum of multiple sclerosis. Neurol Clin 1: 573–99. Reder, A.T. and Thapar, M., Sapugay, A.M. and Jensen, M.A. (1994). Prostaglandins and inhibitors of arachidonate metabolism suppress experimental allergic encephalomyelitis. J Neuroimmunol 54: 117–27.

Sadovnick, A.D. (1993). Familial recurrence risks and inheritance of multiple sclerosis. Curr Opin Neurol Neurosurg 6: 189–94. Sadovnick, A.D., Armstrong, H., Rice, G.P.A. et al. (1993). A population-based study of multiple sclerosis in twins: update. Ann Neurol 33: 281–5. Sadovnick, A.D., Dyment, D. and Ebers, G.C. (1997). Genetic epidemiology of multiple sclerosis. Epidemiol Rev 19: 99–106. Sadovnick, A.D. and Ebers, G.C. (1993). Epidemiology of multiple sclerosis: a critical overview. Can J Neurol Sci 20: 17–29. Sadovnick, A.D., Ebers, G.C., Wilson, R.W. and Paty, D.W. (1992) Life expectancy in patients attending multiple sclerosis clinics. Neurology 42: 991–4. Sadovnick, A.D., Yee, I.M.L., Ebers, G.C. and Risch, N.J. (1998). The effect of age of onset and parental disease status on sib risks for multiple sclerosis. Neurology 50: 719–23. Saiz, A., Arpa, J., Sagasta, A. et al. (1997). Autoantibodies to glutamic acid decarboxylase in three patients with cerebellar ataxia, late-onset insulin-dependent diabetes mellitus, and polyendocrine autoimmunity. Neurology 49: 1026–30. Schoenberg, H. (1983). Bladder and sexual dysfunction in multiple sclerosis. In Neurologic Clinics, ed. J.P. Antel, pp. 601–13. Philadelphia: W.B. Saunders. Shimomura, T., Kuno, N., Takenaka, T., Maeda, M. and Takahashi, K. (1993). Purkinje cell antibody in lupus ataxia. Lancet 342: 375–6 Trapp, B.D., Peterson, J., Ransohoff, R.M., Rudick, R., Mörk, S. and Bö, L. (1998). Axonal transection in the lesions of multiple sclerosis. N Engl J Med 338: 278–85. Traugott, U., Scheinberg, L.C. and Raine, C.S. (1985). On the presence of Ia-positive endothelial cells and astrocytes in multiple sclerosis lesions and its relevance to antigen presentation. J Neuroimmunol 8: 1–14. Vincent, A. (1998). Antibody-mediated disorders of the neuromuscular junction: the Lambert–Eaton myasthenia syndrome, acquired neuromyotonia, and conditions associated with antiglycolipid antibodies. In Clinical Neuroimmunology, ed. J. Antel, G. Birnbaum and H-P. Hartung, pp. 360–73. Oxford: Blackwell Sciences. Ward, M.E., Murphy, J.T. and Greenberg, G.R. (1985). Celiac disease and spinocerebellar degeneration with normal vitamin E status. Neurology 35: 1199–201. Weinshenker, B.G. and Ebers, G.C. (1987). The natural history of multiple sclerosis. Can J Neurol Sci 14: 255–61. Whitacre, C.C., Blankenhorn, E., Brinley, F.J. et al. (1999). A gender gap in autoimmunity. Science 238: 1277–8.

15

Infectious diseases: radiology and treatment of cerebellar abscesses Jeffrey S. Weinberg Department of Neurosurgery, University of Texas, Houston, USA

Introduction The first case of a surgically treated cerebellar abscess was in 1887, by Schwartze (Braun, 1890). However, Charles Ballance was the first neurosurgeon to treat a cerebellar abscess diagnosed by cerebellar findings (Ballance, 1908, 1927). Even though the majority of brain abscesses occur in the supratentorial compartment, many do present in the cerebellum, especially as a complication of otogenic infections. Cerebellar abscess can occur at any age, but the incidence is higher in children between the ages of three and eight and in young adults, with a peak incidence between the second and third decade. It is estimated that 8–18% of purulent brain abscesses are located in the cerebellum (Beller et al., 1973; Gilman et al., 1981). Much of what we know about the treatment of cerebellar abscesses is generalized from treatment protocols developed for the management of supratentorial abscesses. The difference in management is based on the fact that the posterior fossa is a closed compartment with a small, fixed volume. When a mass lesion presents in the cerebellum, the pressure on surrounding structures can result in fourth ventricular compression, obstructive hydrocephalus, brainstem compression, and tonsillar herniation. Cerebellar abscesses thus require immediate attention, and at times urgent surgical intervention. This chapter focuses on the radiologic appearance of a cerebellar abscess, the histology, and the medical and surgical management options available.

Overview The presentation of patients with cerebellar abscess is relatively consistent. Briefly, the majority of patients present after experiencing an otogenic infection (Pennybacker,

1948; Nager, 1967; Morgan and Wood, 1975; Shaw and Russell, 1975; van Dellen et al., 1987; Brydon and Hardwidge, 1994; Kurien et al., 1998). Most patients have acute disease, although a small minority develop a cerebellar abscess after chronic disease. Children may develop cerebellar abscesses as a complication of cyanotic heart disease (Shaw and Russell, 1975; van Dellen et al., 1987; Nadvi et al., 1997) or, in rare cases, secondary to a dermal sinus (Schijman et al., 1986; Brydon and Hardwidge, 1994; Nadvi et al., 1997). Other causes include tuberculosis (Leblanc, 1981; Unnikrishnan et al., 1989; Brydon and Hardwidge, 1994; Shahzadi et al., 1996; Nadvi et al., 1997; Oshinowo et al., 1998), trauma (Osenbach and Loftus, 1992), postoperative complication (Eagleton, 1919; Nadvi et al., 1997), and metastatic septic emboli (Eagleton, 1919; Osenbach and Loftus, 1992; Matsuoka et al., 1995). Septic emboli cause vessel thrombosis and tissue infarction. This leads to an area of relative hypoxia, decreased inflammation, decreased angiogenesis, and decreased capsule formation (Osenbach and Loftus, 1992). Cerebellar infection occurs via direct extension from the petrous temporal bone directly into the cerebellum, or via retrograde thrombosis from the lateral inferior petrosal or superior petrosal sinuses (Eagleton, 1919; Nager, 1967; Wispelwey and Scheld, 1990). The location of the otogenic process can predict the subsequent location of the cerebellar abscess. Petrous apex osteitis or labyrinthitis can yield medial and deep cerebellar abscesses (Krayenbuhl, 1967; Shaw and Russell, 1975), while osteitis at the sinodural angle or lateral sinus thrombophlebitis can lead to lateral or superficial abscesses (Nager, 1967). Two studies have indicated that cerebellar abscesses present most frequently in summer months (Brydon and Hardwidge, 1994; Nadvi et al., 1997). Clinically, most patients present with headaches followed by ataxia (Morgan and Wood, 1975; Shaw and

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Russell, 1975; Shahzadi et al., 1996). Many patients are found to have nystagmus and papilledema on physical examination. These findings are due either to the abscess itself or to hydrocephalus from mass effect on the fourth ventricle. The symptoms are related to the location and size of the abscess, number of lesions, organisms, immune status of the patient, edema, and intracranial pressure (Gormley and Rosenblum, 1996). At presentation, cerebellar abscesses are less likely to be encapsulated than extracerebellar abscesses because they present early due to mass effect (Morgan and Wood, 1975). In the pre-computed tomography (CT) era, the diagnosis of cerebellar abscess was more difficult and was based solely on history of otogenic disease in the presence of cerebellar complaints and findings. Angiography and ventriculography were frequently performed to classify the cerebellar pathology (Shaw and Russell, 1975). Since the development of CT and magnetic resonance imaging (MRI), the diagnosis of brain abscess can be made earlier and more conclusively. Most cerebellar abscesses are noted in the hemispheres, with a smaller proportion diagnosed in the vermis (van Dellen et al., 1987; Matsuoka et al., 1995; Nadvi et al., 1997). Hydrocephalus, primarily seen in adult patients (Kurien et al., 1998), is frequently present at diagnosis (van Dellen et al., 1987; Nadvi et al., 1997). Laboratory data, including cerebrospinal fluid (CSF) and serum analysis, are of limited value in the diagnosis of a brain abscess. In patients with large posterior fossa mass lesions, lumbar puncture may be complicated by acute tonsillar herniation and death (Haerer, 1992). CSF obtained via lumbar puncture is often non-diagnostic. Frequently, CSF analysis reveals pleocytosis, a normal or slightly increased protein, and a low glucose (Heineman et al., 1971; Carey et al., 1972; Morgan and Wood, 1975; Shaw and Russell, 1975). Up to 50% of CSF culture specimens from brain abscess patients may be positive (Heineman et al., 1971; Morgan and Wood, 1975; Shahzadi et al., 1996). Serum examination will frequently reveal leukocytosis (Carey et al., 1972; Mampalam and Rosenblum, 1988; Wispelwey and Scheld, 1990; Osenbach and Loftus, 1992), with a white blood cell count greater than 11 000 cells/ml in 30% (Mampalam and Rosenblum, 1988) and greater than 20 000 cells/ml in 10% of patients (Carey et al., 1972). The erythrocyte sedimentation rate may be elevated in up to 90% of patients (Carey et al., 1972).

Radiology of brain abscesses With the development of CT scanning, MRI, and magnetic resonance spectroscopy (MRS) techniques, the diagnosis

of a brain abscess can be made with increased accuracy. The importance of early diagnosis cannot be understated: it allows for rapid institution of medical therapies, including antibiotics and, in certain situations, steroids, as well as surgical intervention when indicated, thus preventing the high morbidity and mortality associated with untreated lesions.

CT scan A CT scan with and without contrast is commonly the first imaging study obtained in evaluating a patient with signs and symptoms of intracranial pathology. CT imaging of brain abscess can be correlated with the stages of abscess formation as described below. The degree and pattern of contrast enhancement can define the stage of cerebritis, capsule formation, and necrosis, and can help differentiate abscesses from other pathology with similar imaging findings. Whereas originally defined in the supratentorial compartment, the imaging characteristics can be applied to the cerebellum as well. The early cerebritis stage, at days one to three of abscess formation, is characterized initially by a low-density, nonenhancing lesion. Contrast enhancement changes from mild peripheral enhancement to thick and ring-like, encompassing the diameter of the cerebritis. With delayed imaging, the capsule enhancement does not fade, and the core cerebritis does not enhance. As noted above, a true capsule is not observed histologically at this time. The late cerebritis stage is identified on CT scans as a hypodense, necrotic core, surrounded by a hyperdense capsule, which enhances brightly with contrast. With delayed scanning, enhancement spreads from the periphery to the core, giving the appearance of a homogeneous lesion. Core enhancement occurs because new capillaries that form during angiogenesis lack tight junctions and can leak contrast (Schoefl, 1963; Cancilla et al., 1974). As the abscess progresses to early capsule formation, the necrotic center becomes smaller, and the capsule becomes thicker. Even on non-enhanced images, the capsule appears as a dense ring surrounding the hypodense necrotic center. Enhancement is brightest immediately after contrast injection. The capsule is now thicker, and there is less contrast diffusion into the core. Due to increased vascularity of the cortical gray matter as compared to the periventricular zone, the capsule may be thicker in the more lateral peripheral part versus the more medial periventricular portion. At day 14 and later, only the peripheral capsule enhances; there is minimal to no contrast diffusion into the center, even with delayed imaging (Figs. 15.1 and 15.2). A surrounding area of low density, consistent with edema,

Radiology and treatment of cerebellar abscesses

Fig. 15.1 Contrast-enhanced CT scan demonstrates a left lateral cerebellar contrast-enhancing lesion adjacent to the petrous temporal bone. The thick enhancing capsule, hypodense core, peripheral hypodense region consistent with edema, and peripheral location are characteristic of a cerebellar abscess.

may accompany all stages. Even after treatment, the rim continues to enhance, and may persist for up to eight months (Whelan and Hilal, 1980; Dobkin et al., 1984). A summary of these imaging characteristics is found in Table 15.1. Steroid administration may have an effect on contrast enhancement of brain abscess (Enzmann et al., 1979, 1982, 1983, Lyons et al., 1982; Britt and Enzmann, 1983). While steroids have been shown not to limit the amount of enhancement in a late-staged abscess (i.e., one with a wellformed collagenous capsule), they may reduce the enhancement in abscesses in the early and late cerebritis stages (Enzmann et al., 1982). However, the differential diagnosis of a ring-enhancing lesion as described above includes more than just abscesses. Tumors, including high-grade gliomas and metastases, granulomas, radiation necrosis, infarction, and resolving hematomas, may appear as similar ringenhancing lesions (Whelan and Hilal, 1980; Britt and Enzmann, 1983; Osenbach and Loftus, 1992; Osborn, 1994). The peripheral edema, central necrosis, and specific

pattern ring enhancement help confirm the diagnosis of abscess (Nielson and Gyldensted, 1977; Whelan and Hilal, 1980; Braun et al., 1982; Enzmann et al., 1983).

Magnetic resonance imaging MRI is now the diagnostic test of choice to determine the nature of a ring-enhancing lesion. Non-enhanced as well as gadolinium-enhanced scans must be obtained, as well as T1- (short TR/short TE) and T2- (long TR/long TE) weighted images. One significant advantage of MRI is its ability to identify multiple small lesions that are smaller than can be resolved by the CT scanner, or are located in an area of bony artifact or scatter. The parenchyma surrounding a brain abscess is usually edematous, owing to the increased vascularity and the permeability of the new blood vessels (Schoefl, 1963; Cancilla et al., 1974). This edema is present as mild hypointensity on T1-weighted and as bright hyperintensity on T2-weighted images. The interface between abscess and surrounding edematous parenchyma is exaggerated due to

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Fig. 15.2 Contrast-enhanced CT scan reveals a contrast-enhancing right lateral cerebellar lesion. There is obvious mass effect, surrounding edema, and complete obliteration of the fourth ventricle. There is obstructive hydrocephalus, as evidenced by the dilated temporal horns of the lateral ventricles.

Table 15.1 Summary of CT scan characteristics of cerebellar abscesses Stage

Core

Capsule

Early cerebritis

Hypo, non-enhancing

Initially mild enhancement; progresses to ring enhancement

Late cerebritis

Initially hypo, non-enhancing; progresses to mild, homogeneous enhancement

Hyper, bright enhancement

Early capsule

Hypo, minimal enhancement

Thick, hyperdense; brightly enhances

Late capsule

Hypo, non-enhancing

Mild enhancement

Notes: Hypo hypodense; hyper hyperdense.

the increased sensitivity of MRI to water content (Haimes et al., 1989). Serial scanning reveals resolution of edema with successful treatment. The core also has characteristic findings on MRI and is consistent with increased protein content seen in both abscess and tumor. On T1 sequences, the necrotic core is

hyperintense relative to CSF, and hypointense relative to white matter. T2 imaging reveals an isointensive to hyperintense core relative to CSF and gray matter (Sze and Zimmerman, 1988). In larger abscesses, concentric areas of alternating relative hypointensity and hyperintensity are visualized on T2 in the central core. Abscess rupture,

Radiology and treatment of cerebellar abscesses

which can further help differentiate an abscess from other pathological entities and which may not be apparent on CT scan, will appear hyperintense on long TR/intermediate TE images. The collagenous capsule characterizes the border between the core and peripheral edema. This capsule is readily appreciated in MR images on both T1 and T2 sequences. Compared to white matter, an isointense to slightly hyperintense rim is noted on T1 studies and is further delineated by the surrounding edema. On T2 sequencing, the capsule appears hypointense relative to gray matter and hypointense to isointense relative to white matter. The hypointensity of the rim is believed to be due to macrophage activity at the abscess periphery. The rate of capsule formation is proportionate to the organism, the number of organisms, infection origin, immune response, antibiotic and steroid administration (Britt et al., 1981; Britt and Enzmann, 1983). As with CT scanning, the mesial wall is noted to be thinner than the subcortical wall. The signal characteristics are consistent with abscess but can be rarely seen with other intraparenchymal pathology, including metastases, granulomas, and gliomas (Fleming et al., 1987; Gupta et al., 1988). From the late cerebritis stage, the smooth, thin-walled rim enhances with gadolinium (Sze and Zimmerman, 1988). Haimes et al. (1989) performed delayed MRI on patients for up to one year after treatment, and were able to characterize the radiographic changes noted in brain abscesses. Within one week after surgery, the imaging characteristics remained the same as preoperatively, but the size changed, based on the amount of fluid aspirated. Between nine weeks and one year, the peripheral edema and mass effect decreased as did the size of the abscess. The rim showed a progressive decrease in hypointensity (believed to be due to decreased macrophage activity) and, by 15 weeks, the rim and necrotic core had resolved. At one year, only mild T1 hypointensity and mild T2 hyperintensity remained, without mass effect. A summary of the MRI findings is given in Table 15.2.

Magnetic resonance spectroscopy MRS is gaining widespread use for the diagnosis of brain abscess. MRS can aid MRI in diagnosing a brain abscess and can be used to follow the abscess after treatment has been initiated. Spectroscopy works by identifying the chemical state of certain metabolites, yielding in-vivo information about cellular physiology in specific locations. The MRS of a brain abscess identifies many metabolites that are not observed in other brain pathology. Certain elements are specific to brain abscess, and it is for this

Table 15.2 Summary of MRI characteristics of cerebellar abscesses Region

T1

T2

Edema

Hypo

Hyper

Core

Hyper to CSF Hypo to white matter

Iso/hyper to CSF and gray matter

Capsule

Iso/hyper to white matter; may enhance with gadolinium

Hypo to gray matter; hypo/iso to white matter

Notes: Hyper hyperintense; hypo hypointense; iso isointense.

reason that MRS has become so useful in diagnosing and following brain abscesses. Spikes for amino acids (alanine, glycine, valine, leucine, isoleucine, and phenylalanine), aspartate, lactate, pyruvate, succinate, and lipids are seen in the MRS of brain abscess. In comparison, tumors such as glioblastoma have increased choline and smaller spikes for N-acetyl-aspartate, creatine, lactate, and lipids, and no spikes for amino acids or acetate (Poptani et al., 1995a, 1995b; Remy et al., 1995; Dev et al., 1998). The difference in the spectra is due to the difference in cellular biology between the two. A brain abscess is characterized by a central area of bacterial anaerobic activity, yielding lactate as a byproduct of pyruvate metabolism. Neutrophilic activity is responsible for proteolysis, leading to the production of amino acids. Cell membrane necrosis results in the formation of free fatty acids, and thus lipids. It has been suggested that following the lactate/amino acid ratio during treatment for the abscess may be an easy way to follow the effect of treatment (Poptani et al., 1995a, 1995b; Dev et al., 1998).

Nuclear medicine imaging The recent development of sophisticated nuclear medicine studies has enhanced our ability to diagnose and follow brain abscesses. Leukocyte scintigraphy works by re-injecting radiolabeled autologous leukocytes and identifying inflammatory foci using a gamma counter. Recent evidence has suggested that 99mTc-hexamethylpropyleneamine oxime (99mTc-HMPAO) is well suited for radioactive imaging of brain abscesses. In a recent study using 99mTcHMPAO, 23 patients with ring-enhancing lesions consistent with an abscess or neoplasm were studied. Ten of the 23 patients had an abscess as confirmed by histopathological examination of the excised tissue. Leukocyte scintigraphy

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was able to identify all ten patients without error for a diagnostic accuracy of 100%. In addition, C-reactive protein levels were noted to be elevated in nine of ten cases. In the presence of steroids, the authors indicated that leukocyte scintigraphy would be inaccurate, while C-reactive protein levels would still be elevated (Grimstad et al., 1992). Leukocyte scintigraphy is inaccurate in the presence of steroids, while similar work with labeled white blood cells has yielded comparable findings (Belloti et al., 1986). In certain cases, tumors may incite inflammation and yield a falsepositive result (Osenbach and Loftus, 1992).

Histology of brain abscesses Much of what we know about the histology of brain abscess has been derived from a series of experiments by Britt and his colleagues (Enzmann et al., 1979, 1983; Britt et al., 1981; Britt and Enzmann, 1983; Britt, 1985). Using a dog model, they injected bacteria into the brain, sacrificed the animals at predetermined intervals, and then studied brain slices with a variety of histological stains. In addition, later experiment with CT scanning yielded the radiographic correlates of brain abscess, described below. Histological examination of the abscess in the dog model identified five distinct zones that developed and progressed over four stages. The five zones, from the center and moving outward, are: (1) necrotic center, which initially contains cerebritis with acute inflammatory cells and later develops to full necrosis; (2) inflammatory zone, consisting of macrophages and fibroblasts; (3) capsular zone, composed of reticulin fibers and collagen; (4) cerebritis, with neovascularization, perivascular inflammatory cells, and migrating fibroblasts; and (5) surrounding parenchyma, which contains reactive astrocytosis and edema (Britt et al., 1981). The stages of abscess development begin with the early cerebritis stage, from days one to three post-inoculation of bacteria. During this phase, there is an acute inflammatory reaction, with a predominance of polymorphonuclear leukocytes (PMN). By day three, angiogenesis begins at the periphery, and fibroblasts begin to appear in the cerebritis zone. Days four to nine comprise the late cerebritis stage. This is the time of maximum cerebritis and is characterized by further development of necrosis, with PMNs surrounded by macrophages and further development of neovascularity. At the periphery, collagen deposition by the fibroblasts progresses, and is ultimately surrounded by astrocytosis and edema. The amount of edema can be correlated with angiogenesis. The new vessels created do not have a com-

plete blood–brain barrier, and evidence exists that proteinrich fluid may seep out into the surrounding tissue (Schoefl, 1963). By day 10 to 13, the early capsular stage develops. The central zone consists of necrotic debris, and actually shrinks in size as macrophages appear in greater quantities. In addition, the increase in the number of fibroblasts accounts for the appearance of a thicker collagenous capsule. The glial reaction in the periphery progresses, and the edematous zone may slightly decrease in size. In a majority of abscesses, the capsule closer to the cortical surface is larger or thicker than the part in proximity to the ventricle. This is believed to be due to the enhanced blood flow to the cortex but not to the periventricular white matter. This results in increased angiogenesis in the subcortical area, yielding more vessels, more oxygen and subsequently, more fibroblasts, creating a proportionally larger capsule. From day 14, the necrotic center continues to coalesce. The number of inflammatory cells decreases as the fibroblast number increases. The edema of zone five continues to decrease in size; however, the number of reactive astrocytes continues to increase. Ultimately, a thick capsule surrounding a zone of necrosis remains.

Treatment Medical management Data support the contention that many brain abscesses may be treated with a trial of antibiotics and steroids prior to resorting to surgical intervention. However, many of these studies were described for cerebral abscesses and not cerebellar abscesses. As stated previously, because of the small volume of the posterior fossa, a relatively small abscess may present with symptoms due to the location, mass effect, and presence of obstructive hydrocephalus. Therefore, surgical intervention may be warranted earlier in the course of cerebellar abscess than in cerebral abscess. Steroids may be used judiciously in the treatment of a brain abscess. They decrease inflammation and edema, resulting in decreased mass effect from the abscess. However, they can impede the host’s immune response by decreasing local polymorphonuclear cell and macrophage infiltration, capillary permeability, neovascularity, and local bacteria clearing (Quartey et al., 1976; Gormley and Rosenblum, 1996). Quartey et al. (1976) performed a randomized controlled study examining the use of steroids in an animal model. Bacteria were injected intracerebrally in 40 rabbits which were subsequently treated with and

Radiology and treatment of cerebellar abscesses

without steroids, and with and without antibiotics. Quartey et al. confirmed what had been suspected previously: steroids decreased the formation of an abscess capsule (Long and Meacham, 1968; Quartey et al., 1976; Bohl et al., 1981; Schroeder et al., 1987), the abscess cultured positive in the presence of steroids, there was decreased edema and necrosis and minimal perivascular lymphocytic cuffing. Without steroids, there was sterile resolution of the abscess, giant cells, and a glial–fibrous scar. Steroids have also been implicated in decreased antibiotic penetration, thus requiring an increased dose of antibiotics in their presence (Ilavsky and Foley, 1953; Jawetz and Merrill, 1954). Additionally, steroids decrease the amount of enhancement seen in imaging studies (Enzmann et al., 1979; Whelan and Hilal, 1980; Enzmann et al., 1982; Lyons et al., 1982). Antibiotics should be started immediately upon diagnosis of a brain abscess. If possible, a culture should be obtained prior to initiation of broad-spectrum, empiric antibiotic therapy, followed by tailoring the drug and dose to the particular organism. In addition, early diagnosis by aspiration or biopsy allows one to diagnose other pathology that may be in the differential diagnosis when the diagnosis of a brain abscess is circumspect. The blood–brain barrier prevents penetration of most antibiotics; therefore, only antibiotics that are lipophilic, non-ionized, and nonprotein bound can penetrate (Gormley et al., 1997). Abscess levels of antibiotics are dependent upon the presence of leukocyte enzymes, pH, hypoxia, number of organisms, and length of antibiotic treatment (Gormley et al., 1997). However, the use of antibiotics does not guarantee a cure. Black et al. (1973) examined the concentration of antibiotics in an animal model of brain abscess. They noted that whereas therapeutic levels of antibiotics may be found in the abscess cavity, viable organisms were still able to be cultured. In addition, they concluded that the abscess environment decreases the bactericidal activity of an antibiotic. Antibiotics have the greatest usage as a sole treatment for brain abscess in patients with small lesions, and in those who are in the cerebritis stage. The success of antimicrobial treatment is proportional to the type of antibiotic (bacteriocidal or bacteriostatic), the route of administration, dosage, duration of treatment, host response, and the drug concentration in the abscess (Everett and Strausbaugh, 1980; Garvey, 1983). In 1971, Heineman et al. examined six cases of intracranial abscesses treated successfully with antibiotics alone. They noted that the earlier the diagnosis, the better the chance of treatment with pharmacotherapy alone. In addition, medical treatment was more successful if the abscess was in the cerebritis stage, without a capsule. This was confirmed in the CT era for cerebellar abscesses by

van Dellen et al. (1987). Further evidence suggests that antibiotic treatment may even prevent the conversion of an area of cerebritis to an encapsulated abscess (Dyste et al., 1988). Multiple retrospective reviews have yielded evidence that abscesses of less than 2.0–3.0 cm in maximum diameter can be completely treated with antibiotic therapy alone (Rosenblum et al., 1980; Dyste et al., 1988). To summarize, steroids are useful in abscesses that produce mass effect and significant perilesional edema. Antibiotics should be initiated after a culture has been obtained. If the lesion is small, empiric treatment with antibiotics for aerobic and anaerobic bacteria should be initiated and can be tailored to the flora of the primary site of infection. Serial imaging studies should be performed and, if progression is demonstrated, surgical intervention is indicated. In the case of an abscess larger than 2.5 cm in diameter, surgical intervention is indicated, followed by antibiotic therapy for six weeks.

Surgical management Surgical intervention is warranted initially in the presence of an abscess greater than 2.5 cm in diameter or in the case of unsuccessful treatment. Surgery is also indicated to obtain a tissue diagnosis when the radiographic imaging is inconclusive or in the case of a patient who is immunocompromised and may have a rare type of bacteria or a non-abscess lesion (Osenbach and Loftus, 1992). Surgical treatment may include aspiration and drainage, and resection. There are few data to support a recommendation regarding placement of an indwelling catheter into the surgical cavity after aspiration or excision. Due to the fixed volume of the posterior fossa and the possibility of hydrocephalus, placement of an externalized ventricular drain is also an option. Since the earliest published series on the treatment of cerebellar abscess (Eagleton, 1919), the management algorithm has undergone a variety of changes. This is due to improved and earlier diagnosis with CT and MRI, and a variety of new antibiotics. The result has been improved prognosis of these potentially dangerous lesions. Aspiration is the least invasive of the surgical methods of treatment. It has the advantage of being performed under local anesthesia, usually by a single burr hole, and provides for a rapid decompression and decreased mass effect. This is a perfect method for those patients who are too ill to undergo general anesthesia and a full craniectomy and resection. It is also the treatment of choice when multiple abscesses are present (Dyste et al., 1988; Shahzadi et al., 1996). Decreasing the size of an abscess may improve the local environment with respect to antibiotic efficacy (Black

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et al., 1973; Shahzadi et al., 1996). It is an insufficient method for the treatment of abscesses in the cerebritis stage, although a culture obtained from an abscess in this stage is likely to be positive and will allow for correct antibiotic treatment (van Dellen et al., 1987). Also, in the posterior fossa, a simple aspiration is less traumatic and may not provoke postoperative edema (Brydon and Hardwidge, 1994; Shahzadi et al., 1996). CT guidance allows for directed aspiration of an abscess through a prior incision for a mastoidectomy (Pennybacker, 1948; Coin et al., 1983). Stereotaxis may be utilized to aspirate multiple lesions or for deep-seated lesions (Dyste et al., 1988; Stapleton et al., 1993; Mamelak et al., 1995; Shahzadi et al., 1996). The transtentorial hiatus route has been utilized for the rare vermian lesions (Matsuoka et al., 1995). There is less risk of stimulating local cerebellar edema (Brydon and Hardwidge, 1994). Recently, aspiration has successfully been performed using endoscopy (Fritsch and Manwaring, 1997). This allows the surgeon direct visualization of the abscess cavity and for complete irrigation of the cavity. There are many proponents of open excision of cerebellar lesions. Resection of the entire capsule and core components provides a large sample for bacterial culture as well as a complete decrease in mass effect. It is effective for traumatic abscesses that may have retained foreign body fragments. These retained fragments are often responsible for delayed abscess formation (Hagan, 1971; Rish et al., 1981). Fungal abscesses are difficult to cure with simple antibiotics or aspiration alone. Fungal organisms are frequently found in the capsule of abscesses, making simple eradication impossible (Britt, 1985). Gas in an abscess may be an indication of gas-producing organisms or, in some cases, a dural fistula. This may especially be true in cases that occur as postoperative complications or in communication with a sinus cavity (Young and Frazee, 1984). Aspiration may be insufficient treatment for multiloculated abscesses, which require complete excision (Osenbach and Loftus, 1992). However, excision is inappropriate for abscesses in eloquent locations (e.g., the brainstem) or for lesions in the cerebritis stage (Fujino et al., 1990; Osenbach and Loftus, 1992) and may be associated with local contamination of the surrounding parenchyma or CSF cavities (Pennybacker, 1948). Unless patients with multiple abscesses have one that is unquestionably in need of resection, they should be managed with aspiration (Dyste et al., 1988; Shahzadi et al., 1996). In patients who present with a cerebellar abscess as a direct complication of an otogenic infection, some believe that an abscess resection should be performed at the same operation as the surgery for the mastoidectomy (Wright and Grimaldi, 1973; Shaw and Russell, 1975; Kurien et al., 1998).

Outcome The mortality associated with cerebellar abscesses was much higher in the pre-CT era. In Pennybacker’s 1947 series, two groups of nine patients were surgically treated with a combination of excision and aspiration, with and without intraoperative irrigation with penicillin (Pennybacker, 1948). The overall mortality was 8 of 18, or 44%. However, eight of nine patients treated with intraoperative antibiotic irrigation survived. Besides receiving penicillin, seven patients in the first group underwent aspiration as a primary procedure, whereas seven patients underwent complete excision of the abscess in the second group. Of the patients who died, the one in the antibiotic group died from pulmonary complications of treatment, not because of the abscess itself. In the pre-penicillin group, five patients died from acute and chronic meningitis and two from increased intracranial pressure. Of these two, one had upward herniation 12 days after abscess aspiration, and the other died as a result of a missed second cerebellar abscess. In their review of 47 cases, Shaw and Russell (1975) had an overall mortality of 41% (19 patients). An otogenic source was identified in 44 cases, whereas the other three lesions were metastatic in origin. Three patients did not have surgical intervention. Of the other 41, 16 had an aspiration, 4 had aspiration and a delayed excision, 2 had a partial excision, and 19 had a complete excision, whereas the last 3 had a negative exploration. A worse outcome was achieved if the patient was treated more than two weeks after symptom onset and if the patient was unarousable on admission. Eleven of 16 patients who underwent aspiration died, whereas 14 of 19 patients who underwent complete excision as the primary procedure survived. The authors concluded that resection was correlated with improved survival and should be the treatment of choice. Morgan and Wood (1975) found that improved survival was also correlated with earlier treatment. They were also among the first to demonstrate that cerebellar abscesses present earlier in the course of disease than supratentorial abscesses and thus are less likely to be well encapsulated. Van Dellen et al. (1987) were the first to realize the benefit of CT scanning in the diagnosis and treatment of cerebellar abscess. Thirty-four of 158 patients with brain abscesses had an abscess in the cerebellum. In all cases, diagnosis was made by CT scan. All patients were managed with aspiration of the abscess, and a ventricular drain was placed at the same time if hydrocephalus was present. Antibiotics were prescribed for six weeks. The mortality rate was 29%, and the morbidity rate was 21%. Cerebritis (rather than abscess), hydrocephalus on the admission CT scan, and a depressed mental status were negative

Radiology and treatment of cerebellar abscesses

prognostic factors. The authors advocated a ‘watchful waiting’ management for patients with cerebellar cerebritis without hydrocephalus, while treating with antibiotics. Any patient with fourth ventricular effacement or displacement with or without overt hydrocephalus should have urgent ventricular drainage. Brydon and Hardwidge (1994) reviewed their experience with 15 patients with cerebellar abscesses treated in the CT era. In all but three cases, CT scans allowed diagnosis of the abscess at presentation. In two of the remaining three patients, the CT scans revealed coexisting supratentorial abscesses, and in the third, the abscess developed during treatment for a temporal subdural empyema. Seven patients underwent aspiration, whereas the remainder underwent total or partial resection. The mortality rate in this series was 13%. Although there was a higher incidence of the need for temporary ventricular drainage and permanent ventriculo-peritoneal shunts in patients undergoing aspiration, there was no difference in mortality rate, number of complications, and residual symptoms between the two surgical groups. Brydon and Hardwidge concluded that, without a difference in mortality or longterm outcome, the benefits of aspiration (less traumatic and no spillage of contents) outweigh the benefits of excision and recommended aspiration as the treatment of choice. Only recently has the value of external ventricular drainage been elucidated. Nadvi et al. (1997) performed a prospective trial over a 13-year period, examining the benefit of urgent ventricular drainage in patients with cerebellar abscesses. In the first group of 34 patients, the cerebellar abscess was immediately drained via burr hole aspiration; this was followed by placement of a ventricular drain if overt hydrocephalus was present and by mastoidectomy (if indicated) during the same anesthesia. In the second set of 43 patients, emergency ventricular drainage was immediately performed if there was overt hydrocephalus or incipient hydrocephalus, the latter defined by the presence of temporal horns on two or more consecutive cuts on the CT scan. The overall mortality rate was 19.5%; however, the differences in mortality rates for both groups were a statistically significant 29% and 11.6%, respectively (p0.005). In the early group, five of ten patients who ultimately died were able to follow commands on admission. Three of the post-mortem examinations revealed hydrocephalus, indicating the potential for death from hydrocephalus in presumably stable patients. There were statistically more patients with good outcomes in the second group (86% versus 64.7%, p0.05). The authors concluded that, regardless of the patient’s clinical status, hydrocephalus is an absolute indication for ventricular drainage.

Summary Cerebellar abscesses are insidious lesions that require immediate treatment. Steroids are useful in the acute period for obvious perilesional edema. Early ventricular drainage should be instituted if radiographic evidence of hydrocephalus is present. Aspiration and/or excision for diagnosis and relief of mass effect should be performed immediately, followed by institution of the appropriate antibiotics. If diagnosed early in their course, rapid treatment of these lesions can result in improved outcomes.

xReferencesx Balance, C. (1908). Discussion on the diagnosis of the intracranial complications of ear disease. Br Med J 2: 1265–70. Balance, C. (1927). Remarks and reminiscences. Br Med J 1: 64–8. Beller, A.J., Sahar, A. and Praiss, I. (1973). Brain abscess. Review of 89 cases over a period of 30 years. J Neurol Neurosurg Psychiatry 36: 757–68. Belloti, C., Aragno, M., Medina, M. et al. (1986). Differential diagnosis of CT-hypodense cranial lesions with indium-111-oxinelabeled leukocytes. J Neurosurg 64: 750–3. Black, P., Graybill, J.R. and Charache, P. (1973). Penetration of brain abscess by systemically administered antibiotics. J Neurosurg 38: 705–9. Bohl, I., Wallenfang, T., Bothe, H. et al. (1981). The effect of glucocorticoids in the combined treatment of experimental brain abscess in cats. Adv Neurosurg 9: 125–33. Braun, E. (1890). Die ergfolge der trepanation bei dem otitis-chen hirnabscess. Arch Ohren 29: 161–200. Braun, I., Chambers, E., Leeds, N. and Zimmerman, R.D. (1982). The value of unenhanced scans in differentiating lesions producing ring enhancement. Am J Neuroradiol 3: 643–7. Britt, R. (1985). Brain abscess. In Neurosurgery, ed. R. Wilkins and S. Rengachary, pp. 1928–56. New York: McGraw-Hill. Britt, R.H. and Enzmann, D.R. (1983). Clinical stages of human brain abscesses on serial CT scans after contrast infusion. Computerized tomographic, neuropathological, and clinical correlations. J Neurosurg 59: 972–89. Britt, R.H., Enzmann, D.R. and Yeager, A.S. (1981). Neuropathological and computerized tomographic findings in experimental brain abscess. J Neurosurg 55: 590–603. Brydon, H.L. and Hardwidge, C. (1994). The management of cerebellar abscess since the introduction of CT scanning. Br J Neurosurg 8: 447–55. Cancilla, P., Robert, C. and Frommes, S. (1974). Regeneration of cerebral capillaries after local freezing injury (abstract). J Neuropathol Exp Neurol 33: 182–3. Carey, M., Chou, S. and French, L. (1972). Experience with brain abscesses. J Neurosurg 34: 652–6. Coin, C.G., Hucks-Folliss, A.G. and Mehegan, C.C. (1983).

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Computed-tomographically guided percutaneous transmastoid drainage of a cerebellar abscess. Surg Neurol 20: 387–90. Dev, R., Gupta, R., Poptani, H., Roy, R., Sharma, S. and Husain, M. (1998). Role of in vivo proton magnetic resonance spectroscopy in the diagnosis and management of brain abscesses. Neurosurgery 42: 37–43. Dobkin, J., Healton, E., Dickinson, P. and Brust, J.C. (1984). Nonspecificity of ring-enhancement in ‘medically cured’ brain abscesses. Neurology 34: 139–44. Dyste, G.N., Hitchon, P.W., Menezes, A.H., VanGilder, J.C. and Greene, G.M. (1988). Stereotaxic surgery in the treatment of multiple brain abscesses. J Neurosurg 69: 188–94. Eagleton, W. (1919). Cerebellar abscess. J Am Med Assoc 73: 1060–3. Enzmann, D.R., Britt, R.H. and Placone, R. (1983). Staging of human brain abscess by computed tomography. Radiology 146: 703–8. Enzmann, D.R., Britt, R., Placone, R.J., Obana, W., Lyons, B. and Yeager, A.S. (1982). The effect of short-term corticosteroid treatment on the CT appearance of experimental brain abscesses. Radiology 145: 79–84. Enzmann, D.R., Britt, R.H. and Yeager, A.S. (1979). Experimental brain abscess evolution: computed tomographic and neuropathologic correlation. Radiology 133: 113–22. Everett, E. and Strausbaugh, L. (1980). Antimicrobial agents and the central nervous system. Neurosurgery 6: 691–714. Fleming, C., Zimmerman, R., Haimes, A. et al. (1987). The diagnostic significance of rim intensity and edema patterns in the differentiation of intracranial mass lesions on MRI (abstract). Am J Neuroradiol 8: 454. Fritsch, M. and Manwaring, K.H. (1997). Endoscopic treatment of brain abscess in children. Minim Invasive Neurosurg 40: 103–6. Fujino, H., Tobayashi, T., Goto, I., Nagata, E. and Shima, F. (1990). Cure of a man with solitary abscess of the brain-stem. J Neurol 237: 265–6. Garvey, G. (1983). Current concepts of bacterial infection of the central nervous system. Bacterial meningitis and bacterial brain abscess. J Neurosurg 59: 735–44. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Gormley, W., delBusto, R., Saravolatz, L. et al. (1997). Cranial and intracranial bacterial infections. In Neurological Surgery, ed. J. Youmans, pp. 3191–220. Philadelphia: W.B. Saunders. Gormley, W. and Rosenblum, M. (1996). Cerebral abscess. In The Practice of Neurosurgery, Vol. III, ed. G. Tindall, P. Cooper and D. Barrow, pp. 3343–54. Baltimore: Williams & Wilkins. Grimstad, I.A., Hirschberg, H. and Rootwelt, K. (1992). 99mTchexamethylpropyleneamine oxime leukocyte scintigraphy and C-reactive protein levels in the differential diagnosis of brain abscesses. J Neurosurg 77: 732–6. Gupta, R., Jena, A., Sharma, A., Guha, D.K., Khushu, S. and Gupta, A.K. (1988). MR imaging of intracranial tuberculomas. J Comput Assist Tomogr 12: 280–5. Haerer, A. (1992). DeJong’s The Neurologic Examination, 5th edn. New York: J.P. Lippincott.

Hagan, R. (1971). Early complications following penetrating wounds of the brain. J Neurosurg 34: 132–41. Haimes, A.B., Zimmerman, R.D., Morgello, S. et al. (1989). MR imaging of brain abscesses. Am J Roentgenol 152: 1073–85. Heineman, H.S., Braude, A.I. and Osterholm, J.L. (1971). Intracranial suppurative disease. Early presumptive diagnosis and successful treatment without surgery. J Am Med Assoc 218: 1542–7. Ilavsky, J. and Foley, E. (1953). Observations on antibiotic treatment of bacterial infections of cortisone treated mice. Proc Soc Exp Biol Med 84: 211–14. Jawetz, E. and Merrill, E. (1954). Effect of cortisone on the therapeutic efficacy of antibiotics in experimental infections. Arch Intern Med 93: 850–61. Krayenbuhl, H. (1967). Abscess of the brain. Clin Neurosurg 14: 25–44. Kurien, M., Job, A., Mathew, J. and Chandy, M. (1998). Otogenic intracranial abscess: concurrent craniotomy and mastoidectomy – changing trends in a developing country. Arch Otolaryngol Head Neck Surg 124: 1353–6. Leblanc, R. (1981). Tuberculous brain abscess: report of a case with computed tomography correlation. Neurosurgery 8: 88–91. Long, W. and Meacham, W. (1968). Experimental method for producing brain abscesses in dogs with evaluation of the effect of dexamethasone and antibiotic therapy on the pathogenesis of intracerebral abscesses. Surg Forum 19: 437–8. Lyons, B., Enzmann, D., Britt, R., Obana, W.G., Placone, R.C. and Yeager, A.S. (1982). Short term high dose corticosteroids in computed tomographic staging of experimental brain abscess. Neuroradiology 23: 279–84. Mamelak, A., Mampalam, T. and Rosenblum, M. (1995). Improved management of multiple brain abscesses: a combined surgical approach based on a review of 16 cases. Neurosurgery 36: 76–86. Mampalam, T. and Rosenblum, M. (1988). Trends in the management of bacterial brain abscesses: a review of 102 cases over 17 years. Neurosurgery 23: 451–8. Matsuoka, T., Yamada, K., Matsuda, Y., Kamite, Y. and Uozumi, T. (1995). CT-guided stereotactic operation for cerebellar abscess by the transtentorial hiatus approach: a case report. No Shinkei Geka 23: 69–72. Morgan, H. and Wood, M.W. (1975). Cerebellar abscesses: a review of seventeen cases. Surg Neurol 3: 93–6. Nadvi, S.S., Parboosing, R. and van Dellen, J.R. (1997). Cerebellar abscess: the significance of cerebrospinal fluid diversion. Neurosurgery 41: 61–6; discussion 66–7. Nager, G. (1967). Mastoid and paranasal sinus infections and their relation to the central nervous system. Clin Neurosurg 14: 288–313. Nielson, H. and Gyldensted, C. (1977). Computed tomography as a guide in the diagnosis and follow-up of brain abscesses. Radiology 135: 663–71. Osborn, A. (1994). Diagnostic Neuroradiology. St Louis: Mosby–Year Book. Osenbach, R.K. and Loftus, C.M. (1992). Diagnosis and management of brain abscess. Neurosurg Clin N Am 3: 403–20.

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Oshinowo, A.G., Blount, B.W. and Golusinski, L.L. (1998). Tuberculous cerebellar abscess. J Am Board Fam Pract 11: 459–64. Pennybacker, J. (1948). Cerebellar abscess. Treatment by excision with the aid of antibiotics. J Neurol Neurosurg Psychiatry 11: 1–12. Poptani, H., Gupta, R., Jain, V., Roy, R. and Pandey, R. (1995a). Cystic intracranial mass lesion: possible role of in vivo MR spectroscopy in its differential diagnosis. Magn Reson Imaging 13: 1019–29. Poptani, H., Gupta, R., Roy, R., Pandey, R., Jain, V.K. and Chhabra, D.K. (1995b). Characterization of intracranial mass lesions with in vivo proton MR spectroscopy. Am J Neuroradiol 16: 1593–603. Quartey, G.R., Johnston, J.A. and Rozdilsky, B. (1976). Decadron in the treatment of cerebral abscess. An experimental study. J Neurosurg 45: 301–10. Remy, C., Grand, S., Lai, E. et al. (1995). 1H MRS of human brain abscesses in vivo and in vitro. Magn Reson Med 34: 508–14. Rish, B., Caveness, W., Dillon, J., Kistler, J.P., Mohr, J.P. and Weiss, G.H. (1981). Analysis of brain abscess after penetrating craniocerebral injuries in Vietnam. Neurosurgery 9: 535–41. Rosenblum, M.L., Hoff, J.T., Norman, D., Edwards, M.S. and Berg, B.O. (1980). Nonoperative treatment of brain abscesses in selected high-risk patients. J Neurosurg 52: 217–25. Schijman, E., Monges, J. and Cragnaz, R. (1986). Congenital dermal sinuses, dermoid and epidermoid cysts of the posterior fossa. Childs Nerv Syst 2: 83–9. Schoefl, G. (1963). Studies on inflammation. III. Growing capillaries: their structure and permeability. Virchows Arch (Pathol Anat) 337: 97–141.

Schroeder, K., McKeever, P., Schaberg, D. and Hoff, J.T. (1987). Effect of dexamethasone on experimental brain abscess. J Neurosurg 66: 264–9. Shahzadi, S., Lozano, A.M., Bernstein, M., Guha, A. and Tasker, R.R. (1996). Stereotactic management of bacterial brain abscesses. Can J Neurol Sci 23: 34–9. Shaw, M.D. and Russell, J.A. (1975). Cerebellar abscess. A review of 47 cases. J Neurol Neurosurg Psychiatry 38: 429–35. Stapleton, S.R., Bell, B.A. and Uttley, D. (1993). Stereotactic aspiration of brain abscesses: is this the treatment of choice? Acta Neurochir 121: 15–19. Sze, G. and Zimmerman, R.D. (1988). The magnetic resonance imaging of infections and inflammatory diseases. Radiol Clin N Am 26: 839–59. Unnikrishnan, M., Chandy, M.J. and Abraham, J. (1989). Posterior fossa abscesses. A review of 33 cases. J Assoc Physicians India 37: 376–8. van Dellen, J.R., Bullock, R. and Postma, M.H. (1987). Cerebellar abscess: the impact of computed tomographic scanning. Neurosurgery 21: 547–50. Whelan, M. and Hilal, S. (1980). Computed tomography as a guide in the diagnosis and follow-up of brain abscesses. Radiology 135: 663–71. Wispelwey, B. and Scheld, M. (1990). Brain abscess. In Principles and Practice of Infectious Disease, ed. G.L. Mandell, R. Douglas and J.E. Bennett, pp. 777–88. New York: Churchill Livingstone. Wright, J. and Grimaldi, P. (1973). Otogenic intracranial complications. J Laryngol Otol 87: 1085–96. Young, R. and Frazee, J. (1984). Gas within intracranial abscess cavities: an indication for surgical excision. Ann Neurol 16: 35–9.

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Other infectious diseases Mario-Ubaldo Manto Cerebellar Ataxias Unit, Free University of Brussels, Belgium

CEREBELLITIS

Table 16.1 Clinical presentation of cerebellitis

Cerebellitis is an inflammatory process characterized by an acute or subacute onset of cerebellar ataxia following an infection, in general of viral origin. The primary infection occurs usually at the level of the gastrointestinal tract or the respiratory airways (Cohen and Lipton, 1990; Klockgether et al., 1993). Ataxia may also appear after the skin rash of an exanthematous infection or after a vaccination. Most frequently, cerebellitis is observed in children aged one to six years and in young adults, although ataxia may also develop in the elderly. In children, it is estimated that about 0.05–0.10% of all children with varicella infection present cerebellar ataxia. Cerebellitis in young adults affects males more than female, with a M/F ratio varying from 2 :1 up to 4.3 :1. In some series, a marked predominance of males has been observed (Klockgether et al., 1993).

Pure cerebellar syndrome Cerebellar signs associated with extracerebellar signs Dystonic rigidity of neck and limbs Acute hydrocephalus Miller–Fisher syndrome Bickerstaff’s brainstem encephalitis Opsoclonus–myoclonus (Kinsbourne syndrome)

Clinical presentation Body temperature is not a reliable clinical sign, and fever may have completely disappeared at the time of neurological presentation (Cleary et al., 1980). Ataxia appears within several hours, several days or develops slowly over a period of one to four weeks. The cerebellar syndrome is isolated or appears as part of a diffuse inflammatory complication in the brain (Table 16.1). In children, the most frequent picture is an association of sudden limb clumsiness and gait unsteadiness with muscle hypotonia. Overall, limb ataxia is accompanied in 75% of cases by oculomotor disturbances. Figure 16.1A illustrates the cerebellar signs observed during the acute stage in a series including nine patients aged 12 to 64 presenting cerebellitis in the absence of clinical evidence of extracerebellar involve-

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ment. Relative frequencies of different types of oculomotor deficits are shown in Fig. 16.1B. Very similar cerebellar deficits were reported by Klockgether et al. in 1993 in a series including 11 patients, except for dysmetria of saccades, which were more commonly found in their series, and opsoclonus, which was observed in one of our patients. Cerebellar signs may also be associated with extracerebellar signs, in particular brainstem signs (Yuki et al., 1997; Aylett et al., 1998). In this latter case, patients exhibit concomitantly cranial nerve palsies, especially of the VIIth nerve, unilateral or bilateral sensory disturbance, increased tendon reflexes, extensor plantar responses, and increased muscle tone, which sometimes takes the form of dystonic rigidity of the neck and limbs (Alfaro, 1993). Vertigo and vomiting, exacerbated or not by change of position, reflect involvement of vestibulocerebellar connections or brainstem structures, and occasionally precede ataxia of limbs and gait. Seizures and drowsiness occur when cerebellitis is part of a generalized meningoencephalitis or acute diffuse encephalomyelitis (ADEM), which typically includes meningeal signs and significant alteration in mental state. Tendon areflexia associated with a cerebellar syndrome should raise the possibility of a concomitant Guillain–Barré syndrome, while the association of ophthalmoplegia, areflexia, and ataxia points to a Miller Fisher syndrome

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Fig. 16.1 Cerebellar signs in a group of nine patients presenting with cerebellitis. (A) Oculomotor disturbances are the most common cerebellar signs. (B) Impaired smooth pursuit is the most common oculomotor deficit, followed by dysmetria of saccades, and impaired suppression of the vestibulo-ocular reflex (VOR).

(Fisher, 1956; see Chapter 14). Another clinical presentation is Bickerstaff’s brainstem encephalitis, an immune disease involving mainly brainstem structures and overlapping not only with Miller Fisher syndrome, but also with Guillain– Barré syndrome (Yuki et al., 1997).

Agents implicated Table 16.2 lists the diseases preceding cerebellitis in children (Cleary et al., 1980; Gilman et al., 1981; Nigro et al.,

1983; Klockgether et al., 1993). Varicella, measles, mumps, and rubella are by far the most common. Whooping cough has been recently identified as a potential trigger for cerebellitis in adolescence (Setta et al., 1999). In addition, Coxiella burnetii has also been found as a cause of acute cerebellitis (Sawaishi et al., 1999). Coxiella burnetii is the agent of Q fever, which presents as a flu-like disease associated with atypical pneumonia. Table 16.3 indicates the vaccinations which have been implicated in the genesis of cerebellitis (Sunaga et al., 1995; Mancini et al., 1996). Toro et al. described in 1977 a series of accidents of antirabies

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Table 16.2 Infectious diseases associated with cerebellitis in children Varicella Measles Mumps Rubella Infectious mononucleosis Whooping cough Legionellosis Parvovirus B19 infection Hepatitis A Q fever

Table 16.3 Cerebellitis following vaccination Diphtheria–tetanus–poliomyelitis Mumps–measles–rubella Varicella Influenza Hepatitis B

Table 16.4 Infectious agents associated with cerebellitis in adults Epstein–Barr virus (EBV) Influenza Parainfluenza Enterovirus: poliovirus, coxsackie virus, echovirus Herpes simplex virus (HSV) Varicella zoster virus (VZV) Cytomegalovirus (CMV) Adenovirus HIV-1 Borrelia burgdorferi Mumps virus Mycoplasma pneumoniae Legionella pneumophila Salmonella typhi Plasmodium falciparum Legionella pneumophila Rickettsia

vaccination with suckling mouse brain vaccine. One of the patients presented a chronic encephalomyelopathy with demyelinating plaques affecting cerebellum and extracerebellar structures (Toro et al., 1977). Table 16.4 lists the agents that have been associated with cerebellitis in adults (Senanayake, 1987; Silpapojakul et al., 1991; Alfaro, 1993; Klockgether et al., 1993; Senanayake and de Silva, 1994; Manto, 1995; Wiest et al., 1997; Zagardo et

al., 1998). It is noteworthy that cerebellar ataxia is a common complication of enteric fever (Wadia et al., 1985), occurring in about 2.3% of cases. Typically, ataxic signs develop in the second week and last about 5 to 15 days. Some infectious diseases may be accompanied by cerebellar ataxia during the acute infectious episode. For instance, acute attacks of falciparum malaria include cerebellar signs (Senanayake and de Silva, 1994). In this case, Plasmodium falciparum is supposed to be the direct cause of ataxia (Chitkara et al., 1984). Patients are febrile and respond dramatically to antimalarials, with complete recovery within 48–72 hours. Although the list of infectious agents implicated directly or indirectly in the genesis of cerebellitis is growing, the causative agent cannot be identified in up to 35% of the cases, even with use of the most recent techniques such as polymerase chain reaction (PCR).

Pathogenesis The pathogenesis of postinfectious cerebellitis is multifactorial. Different mechanisms coexist, whatever the infectious agent. In viral infections, direct viral replication and postinfectious demyelination are among the causes of ataxia. Active viral replication can be demonstrated using PCR (see below). The virus might enter the central nervous system (CNS) via the bloodstream or via peripheral nerves (Anderson, 1997). In addition, allergic or immune mechanisms are likely to play a determinant role in demyelination course (Johnson et al., 1985). Indeed, familial association, a known epidemiological feature of autoimmune diseases, has been described and argues in favor of an immune-mediated phenomenon with a genetic predisposition (Woody et al., 1989; Korn-Lubetzki and Kleinman, 1994). Moreover, a latent interval of several days to several weeks between initial infection and cerebellar dysfunction is suggestive of a delayed antigen–antibody reaction, with the possibility of molecular mimicry between antigens of infectious agents and epitopes in the cerebellum. This mechanism would be involved in the disseminated foci of perivenous lymphocytic infiltrates in ADEM (Hart and Earle, 1975). In favor of the immunological hypothesis are also: (1) the favorable response to steroids seen in some patients; (2) immune activation with increased levels of tumor necrosis factor , interleukin 2 and interleukin 6 in blood and cerebrospinal fluid (CSF) samples with postinfectious ataxia (de Silva et al., 1992); and (3) demonstration of serum antibodies to gangliosides (GM1, GM2, and GT1b) (Komatsu et al., 1998). Because

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high levels of interleukin 2 as well as interleukin 6 might cause lesions to the cerebellum (Holliday et al., 1995; Karp et al., 1996), these molecules might contribute to the genesis of cerebellar lesions. The case of whooping cough provides other insights to the understanding of the pathogenesis of cerebellitis, although the association of cerebellitis and pertussis infection is probably rare. Indeed, Bordetella pertussis has unique characteristics among bacteria (Pittman, 1984). It is localized and multiplies on the cilia of the epithelial lining of the respiratory tract, but does not invade tissues. The bacteria liberate an exotoxin called lymphocytosispromoting factor (LPF), which is the key to understanding the pathogenesis of the disease. LPF, a membraneassociated protein, shares the molecular structure of bacterial exotoxins. The cerebellum could be one of the most vulnerable brain regions to LPF (Askelöf and Bartfai, 1979). LPF catalyze ribosylation of a guanine nucleotide-binding protein, leading to a marked increase in the cellular levels of 3, 5 cyclic guanosine monophosphate (cGMP) (Askelöf and Gillenius, 1982), an irreversible effect in cells with no renewal (Pittman, 1984). This second messenger plays a major role in neurotransmission in the cerebellum, especially for climbing fibers. The harmaline-induced tremor is an example of the effects of increase in cerebellar cGMP following synchronous activation of inferior olive cells (Lorden et al., 1988). Thus, cerebellitis associated with whooping cough seems to be a model of a cerebellar syndrome triggered by a bacterial exotoxin. Another activator of cGMP production is nitric oxide, which plays a crucial role in cerebellar function. In situations of viral or bacterial infections, massive quantities of nitric oxide are released, leading to cell death (McCann, 1997). Further studies are required to analyze the exact consequence(s) of nitric oxide release in the genesis of cerebellitis. The cerebellar degeneration associated with human immunodeficiency virus (HIV) infection remains of unexplained origin. Cerebellar syndrome was the first manifestation of HIV infection in 30% of the patients presented by Tagliati et al. in 1998. The cerebellar involvement occurs in the absence of cognitive deficit, being thus distinct from cerebellar ataxia associated with HIV dementia (Navia et al., 1986). There is no evidence of direct HIV infection, or of a concomitant opportunistic infection or malignancy such as primary CNS lymphoma. Neuropathological examination shows notably focal degeneration of granular cell layer (Fig. 16.2) and axonal swellings in the inferior olivary. One possible mechanism is a direct neuronal toxicity of HIV virus, as suggested by the tenfold increase of neuronal death when cerebellar granular cells are exposed to gp120, a HIV coat protein (Savio and Levi, 1993). Apoptosis is an

alternative mechanism which could explain granular cell loss (Tagliati et al., 1998). Another possible but controversial factor is fever. There are studies suggesting that high fever might contribute to the deleterious effect on cerebellar neurons. Indeed, Purkinje cells and deep cerebellar nuclei cells are particularly vulnerable to high fever (Freeman and Dumoff, 1944; Lefkowitz et al., 1983; Yaqub et al., 1987). However, the role of fever in the genesis of ataxia in cerebellitis remains unclear, particularly when patients develop ataxia after an afebrile period of up to several weeks (Senanayake and de Silva, 1994).

Diagnosis The association of (a) acute or subacute cerebellar ataxia following an infectious episode of viral type, (b) lymphocytic pleocytosis in CSF, and (c) microbiological evidence of infection is highly suggestive of a cerebellitis. A history of orchitis or parotitis may point to mumps; myalgia and myocarditis suggest coxsackie infection; and rash indicates possible enterovirus infection (Anderson, 1997). A history of insect bite may precede Lyme or rickettsial disease.

Blood studies Bacteriological cultures are often unhelpful, including viral isolation attempts on human fetal fibroblast, rhesus kidney or human epithelial cells (HEp-2). A confirmation of the seroconversion will be looked for by testing sera for antibodies during the acute and convalescent phases. Blood films should be scrutinized for malaria parasites for patients at risk.

Cerebrospinal fluid studies Opening pressure is normal or slightly elevated. Pleocytosis in CSF is found in the majority of patients, with a white cell count up to 250/L and with a predominance of lymphocytes from 60% to 99%. Absence of pleocytosis is an exception to the rule (Applebaum et al., 1953; Johnson and Milbourn, 1970). Elevated protein level up to 300 mg/dl can be found. The CSF immunoglobulin G/albumin ratio is normal in about 40% of cases, and increased in the remaining 60%. Oligoclonal bands are a rare finding in isolated cerebellitis. Glucose level is either normal or slightly reduced. Culture of virus may be confirmatory in some settings.

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Fig. 16.2 High-power photomicrograph of the cerebellum in a patient presenting cerebellar degeneration associated with human immunodeficiency virus infection. Degeneration of the cerebellar cortex. The granular cell layer is involved. (Reproduced with permission from Tagliati et al. (1998). Cerebellar degeneration associated with human immunodeficiency virus infection. Neurology 50: 244–51.)

Polymerase chain reaction

Magnetic resonance imaging

The PCR of virus DNA in peripheral blood leukocytes and CSF is a very useful technique for confirmation of diagnosis. For instance, varicella cerebellitis may be disclosed before development of skin manifestations, at a pre-eruptive stage (Dangond et al., 1993). Chickenpox exanthema and positive VZV serum antibody titer are confirmatory, but may present in a delayed fashion. Not only does demonstration of viral nucleic acid in CSF indicate viral CNS invasion and allow for earlier treatment, but this also prevents unnecessary procedures.

Brain magnetic resonance imaging (MRI) may demonstrate: (1) inflammatory lesions in the white matter of the cerebellar hemispheres, taking a hyperintense aspect on T2-weighted images; (2) diffuse lesions in cerebellar cortex; or (3) round-shaped lesion at the level of a cerebellar peduncle (Hayashi et al., 1989; Hayakawa and Katoh, 1995). Radiologic evidence of cerebellar swelling occurs in about 10–15% of the cases, with possible herniation of the tonsil and obstructive hydrocephalus (Aylett et al., 1998; Sawaishi et al., 1999; Fig. 16.3). After contrast administration, the cerebellum shows abnormal enhancement with variable degrees (Bakshi et al., 1998). In cases of ADEM, demyelinating areas will be revealed as disseminated areas in brain, which may become confluent for some of them. In patients who recover clinically, MRI abnormalities either persist (Horowitz et al., 1991) or show a resolution in concordance with neurological examination.

Electroencephalography Non-specific slowing in the electroencephalogram (EEG) recording, as well as abnormal somatosensory evoked potentials (SEP), visual evoked potentials (VEP), or brainstem auditory evoked potentials (BAEP) indicate a widespread involvement in CNS in most of the cases.

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A

B

Fig. 16.3 MRI in a boy presenting severe cerebellitis caused by Coxiella burnetii. (A) An axial T2-weighted image showing diffuse high signal intensity predominating in the cortex of the right cerebellar hemisphere. (B ) A T1-weighted sagittal image demonstrating that the brainstem is compressed dorsally by the swollen vermis. The tonsil is partially herniated into the foramen magnum. (Reproduced with permission from Sawaishi et al. (1999). Acute cerebellitis caused by Coxiella burnetii. Annals of Neurology 45: 124–7.)

Computed tomography Computed tomography (CT) is often unhelpful when compared with MRI.

Single photon emission computed tomography Tc-99m HMPAO single photon emission computed tomography (SPECT) shows reduction in cerebellar perfusion. Correlation with the extent of cerebellar signs is better than with MRI in some cases (San Pedro et al., 1998; Nagamitsu et al., 1999). Using I123-iomazenil (IMP), Nagamitsu and colleagues found no abnormal signal intensities on MRI in five children with postinfectious acute cerebellar ataxia, contrasting with the reduced regional cerebral blood flow (rCBF) in the cerebellum (Nagamitsu et al., 1999; Fig. 16.4).

Differential diagnosis Acute diffuse encephalomyelitis, which may present with signs of involvement of optic nerves or spinal cord, is a differential diagnosis of demyelinating diseases of CNS, in particular multiple sclerosis. A major feature in favor of the diagnosis of ADEM is its monophasic course, with all lesions having similar characteristics. By contrast, multiple sclerosis is a progressive disease, with relapsing–remitting or progressive course. ADEM may mimick the progressive run of multiple sclerosis (Toro et al., 1977). Labyrinthitis and migraine should be considered in the differential diagnosis of cerebellitis. Labyrinthitis is associated with vertigo and nausea, and is characterized by a lack of ataxia in limbs. Migraine may present with recurrent ataxia in children. Postinfectious acute sensory neuropathy can manifest with ataxia, but this is very rarely

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Table 16.5 Causes of opsoclonus-myoclonus (Kinsbourne syndrome) Postinfectious Epstein–Barr virus, enterovirus, herpes zoster, lymphocytic choriomeningitis, mumps, rubella Metabolic encephalopathies Paraneoplastic Neuroblastoma (mediastinum), leukaemia, Hodgkin’s disease, lung cancer, breast or gynecologic cancer, renal cancer Cranial trauma Hydrocephalus Thalamic hemorrhage Brainstem lesion Toxics Traditional herbal medicine consumption, cocaine, chlordecone Progressive encephalomyelitis with rigidity Sarcoidosis Idiopathic

Fig. 16.4 Axial brain MRI at three different levels, including cerebellum (left panel), in a patient with postinfectious cerebellitis. No abnormality in structure and signal intensity is found in (A) T1-weighted and (B) T2-weighted images. By contrast, 123I-IMP SPECT demonstrates a decreased regional cerebral blood flow (rCBF) in the region of the cerebellum in this patient (C; left panel). (D) SPECT images at the same levels obtained in a control subject: normal regional cerebral blood flow. (Reproduced with permission from Nagamitsu et al., 1999.)

encountered in children. The accidental ingestion of toxics such as drugs (diphantoin) or ethanol should be specifically looked for. Conditions associated with opsoclonus–myoclonus are listed in Table 16.5 (Cogan, 1968; Shetty and Rossman, 1972; Kuban et al., 1983; Casado et al., 1994; Hasaerts et al., 1998; Sheth et al., 1995; Pohl et al., 1996; Wiest et al., 1997; Adamlekun and Hakim, 1998; Tabarki et al., 1998; see also

Chapter 7). Metabolic encephalopathies and paraneoplastic phenomena are the main differential diagnosis of parainfectious opsoclonus–myoclonus. In patients presenting autoimmune deficiency syndrome (AIDS), prevalent brainstem and cerebellar signs are a possible presentation of cytomegalovirus (CMV) encephalitis (Pierelli et al., 1997). This peculiar presentation should be distinguished from rhombencephalitis due to Listeria monocytogenes. Moreover, the differential diagnosis of cerebellopathy associated with HIV infection includes HIV-related vestibulopathy, myelopathy, and ataxic sensory neuropathy (Dal Pan et al., 1994; Castellanos et al., 1994; Pappas et al., 1995). In some instances, rubella infection acquired in utero also causes a chronic progressive panencephalitis with prominent ataxia (Gilman et al., 1981). Children exhibit microcephaly, cataract, and hearing deficit with a stationary course until adolescence. At that time, mental deterioration develops along with cerebellar ataxia, myoclonic jerks, and choreiform movements, finally leading to death after several years. The disease presents numerous similarities with subacute sclerosing panencephalitis.

Treatment The two main treatments are antibiotics and steroids. Intravenous acyclovir 10 mg/kg three times a day for 10–15 days is effective to reduce the duration and severity of the

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primary infection, such as varicella, if given very early after infection. It is not effective if treatment does not start for several days or weeks. Acyclovir treatment initiated after the onset of skin rash does not interfere with the subsequent immunological response (Dangond et al., 1993). Ceftriaxone is one of the treatments of choice for cerebellitis associated with Lyme disease. Usual doses are 2 g twice daily by the intravenous route for a period of two weeks (Manto, 1995). Minocycline at a dose of 4 mg/kg per day is recommended if the suspected agent is Coxiella burnetii (Sawaishi et al., 1999). For corticosteroids, typical regimens include oral prednisolone 1 to 5 mg/kg per day during 10 to 15 days, followed by a gradual withdrawal. Higher doses up to 1 g/day for five days of methylprednisolone are administered in cases of diffuse encephalomyelitis. Nevertheless, effects of steroids on the clinical course of cerebellitis remain a matter of debate due to the self-limiting character of the disease in many cases. In the case of cerebellitis associated with enterovirus infection, steroids should be used cautiously because they might potentiate the infection (Tabarki et al., 1998). Short-term treatment with adrenocorticotrophic hormone (ACTH) reduces symptoms in up to 85% of children with opsoclonus–myoclonus. Prednisone is less effective. Symptomatic treatment of nausea, vomiting, and vertigo should not be delayed. Nausea usually responds well to metoclopramide or domperidone, and even better to ondansetron. For vertigo, neuroleptics may be useful. When transtentorial and transforaminal herniations occur as a result of an expanding inflammatory process, emergency posterior fossa decompression with external ventricular drainage is often required, but cases with herniated tonsil compressed by swollen vermis may respond to glycerol and dexamethasone (Asenbauer et al., 1997; Sawaishi et al., 1999). Plasmapheresis has been proposed for Miller Fisher syndrome and Bickerstaff’s encephalitis (Yuki, 1995). In addition, high-dose immunoglobulin therapy (0.4 g/kg per day for five days) has been reported to be effective to stop the progression of ataxia in Miller Fisher syndrome (Zifko et al., 1994; see also Chapter 14). However, large studies including detailed investigations of cerebellar function are lacking.

Prognosis/outcome The short-term and long-term prognoses of cerebellitis are usually favorable in children and adults before the age of 40. About 80–90% of patients will recover sufficiently to return to normal life, but neurological examination will

Fig. 16.5 Brain MRI in the sagittal plane (T1-weighted image) demonstrating severe cerebellar atrophy in a patient who presented cerebellitis associated with whooping cough. The infection occurred at the age of 15.

still demonstrate minor to moderate cerebellar deficits in 10–40% of them, according to age category. Complete recovery occurs between one and 30 weeks (Klockgether et al., 1993) in the majority of patients. The cerebellar syndrome after falciparum malaria carries an excellent prognosis, whatever the age of the patient (Senanayake and de Silva, 1994). Unfortunately, not all patients will recover completely from cerebellitis. Some clinical signs noted during the acute phase of the disease have a bad prognosis. This is the case for yawning and hiccoughs, even when they are observed in previously healthy subjects (Pierelli et al., 1997). These signs indicate severe lesions in the posterior fossa. At middle term and at long term, patients may suffer permanent sequelae, from mild to severe, especially the elderly (Mardh et al., 1975; Klockgether et al., 1993). Patients with sequelae often show moderate to severe atrophy of the cerebellum, indicating irreversible neuronal loss. Cerebellar atrophy is a complication found in particular in patients older than 60 years (Klockgether et al., 1993), but it may also occur as a complication of cerebellitis in young patients (Fig. 16.5) and, rarely, in children

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(Hayakawa and Katoh, 1995). The pathogenesis of atrophy is poorly understood. Why some patients only develop cerebellar atrophy is not established. The severity of the initial infectious episode might contribute to cerebellar atrophy, as well as physical and immunological mechanisms (Klockgether et al., 1993), and a genetic predisposition.

xReferencesx Adamolekun, B. and Hakim, J.G. (1998). Opsoclonus–myoclonus associated with traditional medicine ingestion: case report. East Afr Med J 75: 120–1. Alfaro, A. (1993). Cerebellar encephalitis in adults. J Neurol 240: 505–6. Anderson, M. (1997). Cerebral infection. In Neurological Emergencies, ed. R.A.C. Hughes, pp. 225–71. London: British Medical Journal. Applebaum, E., Rachelson, M.H. and Dolgopol, V.B. (1953). Varicella encephalitis. Am J Med 15: 223–30. Asenbauer, B., McConachie, N.S., Allcutt, D., Farrell, M.A. and King, M.D. (1997). Acute near-fatal parainfectious cerebellar swelling with favorable outcome. Neuropediatrics 28: 122–5. Askelöf, P. and Bartfai, T. (1979). Effect of whooping-cough vaccine on cyclic-GMP levels in the brain. FEMS Microbiol Lett 6: 223–5. Askelöf, P. and Gillenius, P. (1982). Effect of lymphocytosis-promoting factor from Bordetella pertussis on cerebellar cyclic GMP levels. Infect Immun 36: 958–61. Aylett, S.E., O’Neill, K.S., De Sousa, C. and Britton, J. (1998). Cerebellitis presenting as acute hydrocephalus. Childs Nerv Syst 14: 139–41. Bakshi, R., Bates, V.E., Kinkel, P.R., Mechtler, L.L. and Kinkel, W.R. (1998). Magnetic resonance imaging findings in acute cerebellitis. Clin Imaging 22: 79–85. Casado, J.L., Gil-Peralta, A., Graus, F., Arenas, C., Lopez, J.M. and Alberca, R. (1994). Anti-Ri antibodies associated with opsoclonus and progressive encephalomyelitis with rigidity. Neurology 44: 1521–2. Castellanos, F., Mallada, J., Ricart, C. and Zabula, J.A. (1994). Ataxic neuropathy associated with human immunodeficiency virus conversion. Arch Neurol 51: 236. Chitkara, A.J., Anand, N.K. and Saini, L. (1984). Cerebellar syndrome in malaria. Indian Paediatr 21: 908–10. Cleary, T.G., Henle, W. and Pickering, L.K. (1980). Acute cerebellar ataxia associated with Epstein–Barr virus infection. J Am Med Assoc 243: 148–9. Cogan, D.G. (1968). Opsoclonus, body tremulousness and benign encephalitis. Arch Ophthalmol 79: 545–51. Cohen, B.A. and Lipton, H.L. (1990). The cerebellum and CNS infection. In Infections of the Nervous System, ed. D. Schlossberg, pp. 143–52. New York, Berlin, Heidelberg: Springer-Verlag. Dal Pan, G.J., Glass, G.D. and McArthur, J.C. (1994). Clinicopathologic correlations of HIV-1-associated vacuolar

myelopathy: an autopsy-based case-control study. Neurology 44: 2159–64. Dangond, F., Engle, E., Yessayan, L. and Sawyer, M.H. (1993). Preeruptive varicella cerebellitis confirmed by PCR. Pediatr Neurol 9: 491–3. de Silva, H.J., Hoang, P., Dalton, H., de Silva, N.R., Jewell, D.P. and Peiris, J.B. (1992). Immune activation during cerebellar dysfunction following Plasmodium falciparum malaria. Trans R Soc Trop Med Hyg 86: 129–31. Fisher, C.M. (1956). An unusual variant of acute idiopathic polyneuritis (syndrome of ophthalmoplegia, ataxia and areflexia). N Engl J Med 255: 55–7. Freeman, W. and Dumoff, E. (1944). Cerebellar syndrome following heat stroke. Arch Neurol Psychiatry 51: 67–72. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Hart, M.N. and Earle, K.M. (1975). Haemorrhagic and perivenous encephalitis: a clinical and pathological review of 28 cases. J Neurol Neurosurg Psychiatry 38: 585–91. Hasaerts, D.E., Gorus, F.K. and De Meirleir, L.J. (1998). Dancing eye syndrome and hyperphosphatasemia. Pediatr Neurol 18: 432–4. Hayakawa, H. and Katoh, T. (1995). Severe cerebellar atrophy following acute cerebellitis. Pediatr Neurol 12: 159–61. Hayashi, T., Ichiyama, T. and Kobayashi, K. (1989). A case of acute cerebellar ataxia with an MRI abnormality. Brain Dev 11: 435–6. Holliday, J., Parsons, K., Curry, J., Lee, S.Y. and Gruol, D.L. (1995). Cerebellar granule neurons develop elevated calcium responses when treated with interleukin-6 in culture. Brain Res 673: 141–8. Horowitz, M.B., Pang, D. and Hirsch, W. (1991). Acute cerebellitis: case report and review. Pediatr Neurosurg 17: 142–5. Johnson, R. and Milbourn, P.E. (1970). Central nervous system manifestations of chickenpox. Can Med Assoc J 102: 831–4. Johnson, R.T., Griffin, D.E. and Gendelman, H.E. (1985). Postinfectious encephalomyelitis. Semin Neurol 5: 180–90. Karp, B.I., Yang, J.C., Khorsand, M., Wood, R. and Merigan, T.C. (1996). Multiple cerebral lesions complicating therapy with interleukin-2. Neurology 47: 417–24. Klockgether, T., Döller, G., Wüllner, U., Petersen, D. and Dichgans, J. (1993). Cerebellar encephalitis in adults. J Neurol 240: 17–20. Komatsu, H., Kuroki, S., Shimizu, Y., Takada, H. and Takeuchi, Y. (1998). Mycoplasma pneumoniae meningoencephalitis and cerebellitis with antiganglioside antibodies. Pediatr Neurol 18: 160–4. Korn-Lubetzki, I. and Kleinman, Y. (1994). Familial occurrence of cerebellar encephalitis. J Neurol 241: 349–50. Kuban, K.C., Ephros, M.A., Freeman, R.L., Laffell, L.B. and Bresnan, M.J. (1983). Syndrome of opsoclonus–myoclonus caused by Coxsackie B3 infection. Ann Neurol 13: 69–71. Lefkowitz, D., Ford, C.S., Rich, C., Biller, J. and McHenry, J.R. (1983). Cerebellar syndrome following neuroleptic induced heat stroke. J Neurol Neurosurg Psychiatry 46: 183–6. Lorden, J.F., Stratton, S.E., Mays, L.E. and Oltmans, G.A. (1988). Purkinje cell activity in rats following chronic treatment with harmaline. Neuroscience 27: 465–72.

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Mancini, J., Chabrol, B., Moulene, E. and Pinsard, N. (1996). Relapsing acute encephalopathy: a complication of diphtheria–tetanus–poliomyelitis immunization in a young boy. Eur J Pediatr 155: 136–8. Manto, M. (1995). Cerebellitis associated with Lyme disease. Lancet 345: 1060. Mardh, P-A., Ursing, B. and Lind, K. (1975). Persistent cerebellar symptoms after infection with Mycoplasma pneumoniae. Scand J Infect Dis 7: 157–60. McCann, S.M. (1997). The nitric oxide hypothesis of brain aging. Exp Gerontol 32: 431–40. Nagamitsu, S., Matsuishi, T., Ishibashi, M. et al. (1999). Decreased cerebellar blood flow in postinfectious acute cerebellar ataxia. J Neurol Neurosurg Psychiatry 67: 109–12. Navia, B.A., Jordan, B.D. and Price, R.W. (1986). The AIDS dementia complex: I. Clinical features. Ann Neurol 19: 517–24. Nigro, G., Castellani Pastoris, M., Mazzotti Fantasia, M. and Midulla, M. (1983). Acute cerebellar ataxia in pediatric legionellosis. Pediatrics 72: 847–9. Pappas, D.G. Jr., Roland, J.T. Jr, Lim, J., Lai, A. and Hillman, D.E. (1995). Ultrastructural findings in the vestibular end-organs of AIDS cases. Am J Otol 16: 140–5. Pierelli, F., Tilia, G., Damiani, A. et al. (1997). Brainstem CMV encephalitis in AIDS: clinical case and MRI features. Neurology 48: 529–30. Pittman, M. (1984). The concept of pertussis as a toxin-mediated disease. Ped Inf Dis 3: 467–86. Pohl, K.R., Pritchard, J. and Wilson, J. (1996). Neurological sequelae of the dancing eye syndrome. Eur J Pediatr 155: 237–44. San Pedro, E.C., Mountz, J.M., Liu, H.G. and Deutsch, G. (1998). Postinfectious cerebellitis: clinical significance of Tc-99m HMPAO brain SPECT compared with MRI. Clin Nucl Med 23: 212–16. Savio, T. and Levi, G. (1993). Neurotoxicity of HIV coat protein gp120, NMDA receptors, and protein kinase C: a study with rat cerebellar granule cell cultures. J Neurosci Res 34: 265–72. Sawaishi, Y., Takahashi, I., Hirayama, Y. et al. (1999). Acute cerebellitis caused by Coxiella burnetii. Ann Neurol 45: 124–7. Senanayake, N. (1987). Delayed cerebellar ataxia: a new complication of falciparum malaria? Br Med J 294: 1253–4. Senanayake, N. and de Silva, H.J. (1994). Delayed cerebellar ataxia complicating falciparum malaria: a clinical study of 74 patients. J Neurol 241: 456–9. Setta, F., Baecke, M., Jacquy, J., Hildebrand, J., Monseu, G. and Manto, M. (1999). Cerebellar ataxia following whooping cough. Clin Neurol Neurosurg 101: 56–61. Sheth, R.D., Horwitz, S.J., Aranoff, S., Gingold, M. and Bodensteiner, J.B. (1995). Opsoclonus myoclonus syndrome secondary to Epstein–Barr virus infection. J Child Neurol 10: 297–9. Shetty, T. and Rossman, N.P. (1972). Opsoclonus in hydrocephalus. Arch Ophthalmol 88: 585–9. Silpapojakul, K., Ukkachoke, C., Krisanapan, S. and Silpapojakul, K. (1991). Rickettsial meningitis and encephalitis. Arch Intern Med 151: 1753–7. Sunaga, Y., Hikima, A., Ostuka, T. and Morikawa, A. (1995). Acute

cerebellar ataxia with abnormal MRI lesions after varicella vaccination. Pediatr Neurol 13: 340–2. Tabarki, B., Palmer, P., Lebon, P. and Sebire, G. (1998). Spontaneous recovery of opsoclonus–myoclonus syndrome caused by enterovirus infection. J Neurol Neurosurg Psychiatry 64: 406–7. Tagliati, M., Simpson, D., Morgello, S., Clifford, D., Schwartz, R.L. and Berger, J.R. (1998). Cerebellar degeneration associated with human immunodeficiency virus infection. Neurology 50: 244–51. Toro, G., Vergara, I. and Roman, G. (1977). Neuroparalytic accidents of antirabies vaccination with suckling mouse brain vaccine. Clinical and pathological study of 21 cases. Arch Neurol 34: 694–700. Wadia, R.S., Ichaporia, N.R., Kiwalkar, R.S., Amin, R.B. and Sardesai, H.V. (1985). Cerebellar ataxia in enteric fever. J Neurol Neurosurg Psychiatry 48: 695–7. Wiest, G., Safoschnik, G., Schnaberth, G. and Mueller, C. (1997). Ocular flutter and truncal ataxia may be associated with enterovirus infection. J Neurol 244: 288–92. Woody, R.C., Street, R.W., Charlton, R.K. and Smith, S. (1989). Histocompatibility determinants in chidhood postinfectious encephalomyelitis. J Child Neurol 4: 204–7. Yaqub, B.A., Daif, A.K. and Panayiotopoulos, C.P. (1987). Pancerebellar syndrome in heat stroke: clinical course and CT findings. NeuroRadiology 29: 294–6. Yuki, N. (1995). Successful plasmapheresis in Bickerstaff’s brain stem encephalitis associated with anti-GQ1b antibody. J Neurol Sci 131: 108–10. Yuki, N., Wakabayashi, K., Yamada, M. and Seki, K. (1997). Overlap of Guillain–Barre syndrome and Bickerstaff’s brainstem encephalitis. J Neurol Sci 145: 119–21. Zagardo, M.T., Shanholtz, C.B., Zoarski, G.H. and Rothman, M.I. (1998). Rhombencephalitis caused by adenovirus: MR imaging appearance. Am J Neuroradiol 19: 1901–3. Zifko, U., Drlicek, M., Senautka, G. and Grisold, W. (1994). High dose immunoglobulin therapy is effective in the Miller Fisher syndrome. J Neurol 241: 178–9.

P RO G R E S S I V E M U LT I F O C A L L E U KO E N C E PH A LO PAT H Y Introduction Progressive multifocal leukoencephalopathy (PML) is a devastating demyelinating disease occurring in patients with altered cell-mediated immune status, first described by Anstrom et al. in 1958 (see also Brink and Miller, 1996). PML was rare four decades ago, and mainly encountered in patients presenting lymphoproliferative diseases (Brooks and Walker, 1984). The advent of AIDS pandemia has been accompanied by a marked increase in the incidence of PML. It is estimated that about one patient in 20 with AIDS

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will develop PML during the course of HIV infection, with a male to female ratio of 1.8:1. Inherited immunodeficiency states are also predisposing conditions (Katz et al., 1994).

Clinical presentation In most cases, PML presents as a focal neurological deficit progressing over several weeks or months, although acute neurologic deterioration is reported (Chaisson and Griffin, 1990; Morriss et al., 1997). Altered mental status, visual deficits, and motor weakness are the most common neurological signs. Cerebellar signs occur in about 13% of patients, mainly in adults. A cerebellar presentation has been described (Jones et al., 1982; Brooks and Walker, 1984; Morriss et al., 1997). Due to predominant involvement of brain white matter, seizures are unusual. Fever is rarely observed, except when another cause exists concomitantly.

Agent PML is due to a neurotropic Papovavirus, first identified as virus-like particles in oligodendrocytic nuclei in brain tissue (Zu Rhein and Chou, 1965; Silverman and Rubenstein, 1965; Richardson, 1988). The tropism of the virus for oligodendroglia, the myelin-producing cells, is an important characteristic. In 1971, Padgett et al. gave the pathogen the name of JC virus, according to the initials of a patient in whom the virus was isolated. JC virus is an ubiquitous agent, persisting for life in the kidney.

Figure 16.6 This figure illustrates a cerebellar white matter lesion due to PML in a 7-year-old boy presenting HIV infection acquired perinatally. He exhibited slurred speech and ataxia. CT with contrast injection demonstrates a non-enhancing, lowdensity lesion in right cerebellar white matter, middle cerebellar peduncle, and dorsolateral pons. (Reproduced with permission from Morriss et al. (1997). Progressive multifocal leukoencephalopathy in an HIV-infected child. Neuroradiology 39: 142–4.)

Pathophysiology

Diagnosis

The mechanism of persistence of JC virus is unclear (Brink and Miller, 1996). JC virus is believed to be transported to the brain by infected B-lymphocytes. JC virus DNA is found in brain in the absence of PML (White et al., 1992). The virus might generate latent infection in the nervous system, with reactivation in the case of immunosuppression or following direct interaction with the HIV agent. Alternatively, JC virus might spread from the kidney to the CNS. In the course of PML, oligodendrocytes undergo cytolytic destruction, resulting in loss of myelin. Exceptionally, primary involvement of cerebellar cortex occurs (Sweeney et al., 1994).

PML should be suspected in immunocompromised patients presenting slowly progressive neurological deficits and radiological evidence of white matter disease in the absence of mass effect.

Cerebrospinal fluid studies Routine studies are often unhelpful. However, pleocytosis is found in up to 20% of cases, and protein levels are increased in up to one patient in three (Tornatore et al., 1994). IgG antibodies against JC virus are usually not detectable. Detection of JC virus DNA is a more powerful technique (Gibson et al., 1993), confirming clinical diagnosis in about 60–70% of cases.

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(a)

(b)

Figure 16.7 Axial T2-weighted MRI showing (a) high signal lesion without mass effect, and (b) low signal lesion in T1-weighted sequence. See Fig. 16.6 for details. (Reproduced with permission from Morriss et al. (1997). Progressive multifocal leukoencephalopathy in an HIVinfected child. Neuroradiology 39: 142–4.)

Brain computed tomography

Proton magnetic resonance spectroscopy

Brain CT may demonstrate a low-density lesion in white matter, in the absence of mass effect. The occipito-parietal region is the most commonly involved area. In patients exhibiting cerebellar ataxia, the lesion often involves cerebellar white matter, middle cerebellar peduncle, and dorsolateral pons (Morriss et al., 1997; Fig. 16.6).

Proton magnetic resonance spectroscopy (MRS) demonstrates low levels of N-acetyl aspartate (NAA), increased choline-containing compounds, excess lactate and lipids (Chang et al., 1997). These MRS findings are consistent with neuropathologic observations of cell loss, cell membrane and myelin breakdown, and increased glial activity in PML lesions.

Brain magnetic resonance imaging Brain MRI is more sensitive than CT and is a method of choice for white matter diseases (Whiteman et al., 1993). Lesions are usually asymmetrical, often appear as low signal intensity changes in T1-weighting, and are characterized by high signal intensity in T2 images (Fig. 16.7). Demarcation between gray and white matter is often sharp. In the majority of cases, lesions are not enhanced by gadolinium. Atypical cases have been described, with gadolinium enhancement in cerebellar and extracerebellar regions (Rosas et al., 1999).

Histological findings Histological abnormalities of tissues from biopsies or autopsies include demyelination, hypertrophic oligodendrocytes with intranuclear inclusions, and bizarre giant astrocytes. Foci of necrosis and inflammatory infiltrates may also be observed. Complementary methods have been developed to disclose the presence of JC virus, such as in-situ hybridization (Aksamit, 1993), immunochemistry or immunofluorescence. PCR is an attractive method, demonstrating viral DNA sequences in brain tissues.

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Table 16.6 Treatments of progressive multifocal leukoencephalopathy Drug

Reference

Cytosine arabinoside (A-C) Alpha-2A interferon Camptothecin Cidofovir Abacavir

Portegies et al. (1991); Hall et al. (1998) Berger et al. (1992) Kerr et al. (1993) Sadier et al. (1998); Brambilla et al. (1999) Sadier et al. (1998)

Telenti et al. found viral DNA in brain tissue from 20 of 24 patients with PML, while brain tissue from 17 autopsies of controls did not show viral DNA (Telenti et al., 1990). The technique of in-situ PCR has disclosed localization of virus DNA in oligodendrocytes and bizarre astrocytes (Ueki et al., 1994).

Prognosis/outcome In non-AIDS patients, improvement of primary immunodeficiency may be associated with PML remission (Selhorst et al., 1978). AIDS patients usually die within the year following diagnosis of PML. Only about 9% of patients are alive after one year (Berger et al., 1998a, 1998b). Survival for longer than 16 months has been described in a woman without overt immune disorder and who presented multiple cerebellar lesions (Rosas et al., 1999). Predictive factors for prolonged survival include PML as a presenting manifestation of AIDS, a high CD4 lymphocyte count at disease onset, and contrast enhancement on CT or MRI (Berger et al., 1998a). It has been shown that HIV RNA viral load is correlated with prognosis. Recently, HIV RNA viral load has been recognized as a critical parameter to assess the effectiveness of therapy.

xReferencesx

Differential diagnosis Lack of mass effect and absence of contrast enhancement on brain MRI are two significant features for the differential diagnosis between PML and lymphoma or cerebral abscesses. Other diagnoses to consider are low-grade glial neoplasm and infarct (Morriss et al., 1997).

Treatment Several drugs have been tried, both experimentally and clinically, with the aim of inhibition of virus replication or modification of underlying disease status (Table 16.6; Brink and Miller, 1996). Although favorable responses have been described in case reports (O’Brien and Honavar, 1997), clinical results have been conflicting in many cases. The role of specific antiretroviral treatments, such as zidovudine or specific viral protease inhibitors, in HIV-related PML should not be underestimated (Brink and Miller, 1996), because highly active antiretroviral therapy (HAART) improves the survival of patients (Clifford et al., 1999). New drugs like cidofovir, a viral DNA polymerase inhibitor used for the treatment of cytomegalovirus (CMV) infection in AIDS, and abacavir, a nucleoside analog, seem promising (Brambilla et al., 1999).

Aksamit, A.J. (1993). Nonradioactive in situ hybridisation in progressive multifocal leukoencephalopathy. Mayo Clin Proc 68: 899–910. Anstrom, K.E., Mancall, E.L. and Richardson, E.P. Jr (1958). Progressive multifocal leukoencephalopathy: hitherto unrecognised complication of chronic lymphatic leukemia and Hodgkin’s disease. Brain 81: 93–111. Berger, J.R., Pall, L., McArthur, J. et al. (1992). A pilot study of recombinant alpha-2A interferon in the treatment of AIDS related PML. Neurology 42: 257. Berger, J.R., Levy, R.M., Flomenhoft, D. and Dobbs, M. (1998a). Predictive factors for prolonged survival in acquired immunodeficiency syndrome-associated progressive multifocal leukoencephalopathy. Ann Neurol 44: 341–9. Berger, J.R., Pall, L., Lanska, D. and Whiteman, M. (1998b). Progressive multifocal leucoencephalopathy in patients with HIV infection. J Neurovirol 4: 59–68. Brambilla, A.M., Castagna, A., Novati, R. et al. (1999). Remission of AIDS-associated progressive multifocal leukoencephalopathy after cidofovir therapy. J Neurol 246: 723–5. Brink, N.S. and Miller, R.F. (1996). Clinical presentation, diagnosis and therapy of progressive multifocal leukoencephalopathy. J Infect 32: 97–102. Brooks, B.R. and Walker, D.L. (1984). Progressive multifocal leukoencephalopathy. Neurol Clin 2: 299–313. Chaisson, R.E. and Griffin, D.E. (1990). Progressive multifocal leukoencephalopathy in AIDS. J Am Med Assoc 264: 79–82. Chang, L., Ernst, T., Tornatore, C. et al. (1997). Metabolite abnormalities in progressive multifocal leukoencephalopathy by proton magnetic resonance spectroscopy. Neurology 48: 836–45. Clifford, D.B., Yiannoutsos, C., Glicksman, M. et al. (1999). HAART

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improves prognosis in HIV-associated progressive multifocal leukoencephalopathy. Neurology 52: 623–5. Gibson, P.E., Knowles, W.A., Hand, J.F. and Brown, D.W.G. (1993). Detection of JC virus DNA in the cerebrospinal fluid from patients with progressive multifocal leukoencephalopathy. J Med Virol 39: 278–81. Hall, C.D., Dafni, U., Simpson, D. et al. (1998). Failure of cytarabine in progressive multifocal leukoencephalopathy associated with human immunodeficiency virus infection. AIDS Clinical Trials Group 243 Team. N Engl J Med 338: 1345–51. Jones, H.R., Hedley Whyte, E.T., Friedberg, S.R., Kelleher, J.E. and Krolikowski, J. (1982). Primary cerebellopontine multifocal leucoencephalopathy diagnosed premortem by cerebellar biopsy. Ann Neurol 11: 199–202. Katz, D.A., Berger, J.R., Hamilton, B., Major, E.O. and Donovan Post, M.J. (1994). Progressive multifocal leukoencephalopathy complicating Wiskott–Aldrich syndrome. Arch Neurol 51: 422–6. Kerr, D.A., Chang, C.F., Gordon, J., Bjornisti, M-A. and Khalili, K. (1993). Inhibition of human neurotropic virus (JCV) DNA replication in glial cells by camptothecin. Virology 196: 612–18. Morriss, M.C., Rutstein, R.M., Rudy, B., Desrochers, C., Hunter, J.V. and Zimmerman, R.A. (1997). Progressive multifocal leukoencephalopathy in an HIV-infected child. Neuroradiology 39: 142–4. O’Brien, M.D. and Honavar, M. (1997). Progressive multifocal leucoencephalopathy treated with cytosine arabinoside: 12 year follow-up and postmortem findings. J Neurol Neurosurg Psychiatry 62: 427–8. Padgett, B.L., Walker, D.L., Zu Rhein, G.M., Eckroade, R.J. and Dessel, B.H. (1971). Cultivation of papova-like virus from human brain with progressive multifocal leukoencephalopathy. Lancet i: 1257–60. Portegies, P., Algra, P.R., Hollak, C.E.M. et al. (1991). Response to cytarabine in progressive multifocal leukoencephalopathy in AIDS. Lancet 337: 680–1. Richardson, E.P. (1988). Progressive multifocal leucoencephalopathy 30 years later. N Engl J Med 318: 315–16. Rosas, M.J., Simoes-Ribeiro, F., An, S.F. and Sousa, N. (1999). Progressive multifocal leukoencephalopathy: unusual MRI findings and prolonged survival in a pregnant woman. Neurology 52: 657–9. Sadier, M., Chinn, R.J., Healy, J., Nelson, M.R. and Gazzard, B.G. (1998). Successful treatment of HIV associated progressive multifocal leucoencephalopathy. J Neurol Neurosurg Psychiatry 65: 418. Selhorst, J.B., Ducy, K.F., Thomas, J.M. and Reggelson, W. (1978). Remission and immunologic reversals. Neurology 28: 337. Silverman, L. and Rubenstein, L.J. (1965). Electron microscopic observation on a case of progressive multifocal leukoencephalopathy. Acta Neuropathol 5: 215–24. Sweeney, B.J., Manji, H., Miller, R.F., Harrison, M.J., Gray, F. and Scaravilli, F. (1994). Cortical and subcortical JC virus infection: two unusual cases of AIDS associated progressive multifocal leukoencephalopathy. J Neurol Neurosurg Psychiatry 57: 994–7. Telenti, A., Aksamit, A.J., Proper, J. Jr and Smith, T.F. (1990).

Detection of virus DNA by polymerase chain reaction in patients with progressive multifocal leukoencephalopathy. J Infect Dis 162: 858–61. Tornatore, C., Amemiya, K., Atwood, W., Conant, K. and Major, E.O. (1994). JC virus: current concepts and controversy in the molecular virology and pathogenesis of progressive multifocal leukoencephalopathy. Rev Med Virol 4: 197–219. Ueki, K., Richardson, E.P., Henson, J.W. and Louis, D.N. (1994). In situ polymerase chain reaction demonstration of JC virus in progressive multifocal leukoencephalopathy, including an index case. Ann Neurol 36: 670–3. White, F.A., Ishaq, M., Stoner, G.L. and Frisque, R.J. (1992). JC virus DNA is present in many human brain samples from patients without progressive multifocal leukoencephalopathy. J Virol 66: 5726–34. Whiteman, M.L., Post, M.J.D., Berger, J.R., Tate, L.G., Bell, M.D. and Limonte, L.P. (1993). Progressive multifocal leukoencephalopathy in 47 HIV-seropositive patients: neuroimaging with clinical and pathologic correlation. Radiology 187: 233–40. Zu Rhein, G.M. and Chou, S.M. (1965). Particles resembling papovavirus in human cerebral demyelinating disease. Science 148: 1477–9.

WHIPPLE’S DISEASE

Introduction Whipple’s disease was first described at the beginning of the twentieth century by Whipple, who found the presence of rod-shaped structures in the intestine and mesenteric lymphatic tissues and suggested that a bacillus might be responsible for the disease (Whipple, 1907). Several decades later, sophisticated techniques such as electron microscopy studies have confirmed this hypothesis (Fredricks and Relman, 1997). From the epidemiological point of view, the disease affects mainly patients from Europe and North America. Most of those affected are middle-aged (Keren, 1993). About 10% of patients with Whipple’s disease present neurological complications (Weiner and Utsinger, 1986).

Clinical presentation The clinical manifestations are given in Table 16.7 (Perkin and Murray-Lyon, 1998). Gastrointestinal and articular signs are predominant features (Verhagen et al., 1996; Ramzan et al., 1997). Small intestine involvement results in malabsorption with weight loss. CNS signs can appear in isolation (Romanul et al., 1977), but Whipple’s disease

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Table 16.7 Clinical features of Whipple’s disease Gastrointestinal tract Abdominal pain Diarrhea Steatorrhea Weight loss Joints Arthralgias Polyarthritis Cardiac Congestive heart failure Pericarditis, myocarditis Valvular deformity Nervous system Dementia Ophthalmoplegia Myoclonus Myorhythmia Seizures Cerebellar ataxia Insomnia, hyperphagia, polydipsia

confined to the CNS is exceptional. When convergence nystagmus is associated with mandibular, tongue and neck involuntary movements with a dystonic bruxism-like aspect, the term oculomasticatory myorhythmia is used (Tison et al., 1992; Perkin and Murray-Lyon, 1998). This sign is pathognomonic. Myorhythmia tends to be repetitive, at a frequency of 2–4 Hz. Cerebellar signs include scanning speech, limb and truncal ataxia (Knox et al., 1976; Adams et al., 1987). Ataxic gait generates frequent falls.

Agent The organism is an intracellular Gram-positive actinomycete, called Tropheryma whippelii (Relman et al., 1992). This agent can be cultured from intestinal biopsy specimens when interleukin-4 (IL-4) is added. Experimental data suggest that IL-4 renders macrophages open to the infectious agent (Schoedon et al., 1997).

Pathophysiology Light and electron microscopy studies have demonstrated that bacilli are found in the lamina propria of small intestine, but also in lymph nodes, CNS, heart, lungs, and liver. Patients with Whipple’s disease do not seem to present a specific immune abnormality. However, the bacillus prob-

ably interferes with cytokine production (Relman et al., 1992; Fredricks and Relman, 1997). The following brain regions are preferentially affected: insular cortex, cingulate gyrus, basal ganglia, hypothalamus, and cerebellum (Perkin and Murray-Lyon, 1998). Ventricular ependymal zones are also injured, leading to ependymitis. Pathological studies have shown nodules and granuloma in these regions.

Diagnosis The diagnosis of Whipple’s disease is often difficult for the neurologist, in particular when digestive signs are not predominant.

Endoscopy Endoscopic examination of duodenum shows thickened folds of mucosa (Petrides et al., 1998). Duodenal or jejunal biopsy may disclose periodic acid-Schiff (PAS)-positive foamy macrophages within lamina propria. Both optic and electron microscopic studies should be performed.

Cerebrospinal fluid studies There is often an increase in protein level in the CSF and elevation of cell count is usual. Occasionally, macrophages containing PAS-positive material are identified.

Brain biopsy Stereotactic brain biopsy may be helpful (Mendel et al., 1999) to diagnose Whipple’s disease, but all efforts should be made to reach a diagnosis with other methods before considering biopsy.

Polymerase chain reaction PCR assay performed on intestinal tissues, on brain tissues, on CSF fluid or even on a vitreous specimen detects a portion of the 16S ribosomal RNA gene sequence, which is specific for Whipple’s disease (Relman et al., 1992). PCR is a highly sensitive and specific method to confirm the diagnosis and to identify suspicious cases (Lynch et al., 1997; Sommer et al., 1998; Delanty et al., 1999), demonstrating T. whippelii-specific DNA sequences in samples taken from histologically negative zones of intestine.

Magnetic resonance imaging Brain MRI shows areas of decreased intensity in T1 sequence and increased intensity in T2 sequence

Other infectious diseases

(Schnider et al., 1995), in general with gadolinium enhancement. This enhancement may be confined to ependymal structures. Rarely, multiple ring-enhancing intracerebral mass lesions are demonstrated by MRI (Wroe et al., 1991). A hydrocephalus due to meningo-ependymitis involving aqueduct has been reported (Lapointe et al., 1980).

Treatment If initiated early in the course of the disease, antibiotics may limit or stop the progression of CNS signs, including cerebellar ataxia. The response is usually observed first for oculomotor signs. Myorhythmia may improve with antibiotic treatment (Colcher and Hurtig, 1997). Penicillin, chloramphenicol and trimethoprim-sulphamethoxazole, streptomycin, doxycycline, and third-generation cephalosporins have been recommended. According to Singer, the preferred method of treatment is the parenteral administration of 1.2 million units of penicillin G/day and streptomycin 1 g/day for a period of two weeks. This first phase of treatment is followed by administration of cotrimoxazole (trimethoprim 160 mg and sulfamethoxazole 800 mg) twice a day (Singer, 1998). Cotrimoxazole seems to be more efficacious than tetracyclines in the treatment of cerebral Whipple’s disease (Feurle and Marth, 1994). Antibiotics should be given for at least four months and up to two years (Albers et al., 1989; Singer, 1998). MRI lesions become less hypointense on T1-weighted sequence and less hyperintense on T2-weighted sequence with treatment (Duprez et al., 1996).

Prognosis/outcome Neurological signs indicate a worse prognosis, and most patients retain moderate to marked deficits. In particular, cerebellar signs may remain disabling sequelae. Disease recurs in about one-third of cases, and there is a high incidence of relapsing episodes if treatment is stopped prematurely. Antibiotics should be restarted in the case of recurrence of Whipple’s disease (Knox et al., 1976).

xReferencesx Adams, M., Rhyner, P.A., Day, J., DeArmond, S. and Smuckler, F.A. (1987). Whipple’s disease confined to the central nervous system. Ann Neurol 21: 104–8.

Albers, J.W., Nostrant, T.T. and Riggs, J.E. (1989). Neurologic manifestations of gastrointestinal disease. Neurol Clin 7: 525–48. Colcher, A. and Hurtig, H.I. (1997). Systemic illnesses that cause movement disorders. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 733–41. New York: McGraw-Hill. Delanty, N., Georgescu, L., Lynch, T., Paget, S. and Stubgen, J.P. (1999). Synovial fluid polymerase chain reaction as an aid to the diagnosis of central nervous system Whipple’s disease. Ann Neurol 45: 137–8. Duprez, T.P., Grandin, C.B., Bonnier, C. et al. (1996). Whipple disease confined to the central nervous system in childhood. Am J Neuroradiol 17: 1589–91. Feurle, G.E. and Marth, T. (1994). An evaluation of antimicrobial treatment for Whipple’s disease. Tetracycline versus trimethoprim-sulfamethoxazole. Dig Dis Sci 39: 1642–8. Fredricks, D.N. and Relman, D.A. (1997). Cultivation of Whipple’s bacillus: the irony and the ectasy. Lancet 350: 1262–3. Keren, D.F. (1993). Whipple’s disease: the causative agent defined. Its pathogenesis remains obscure. Medicine 72: 355–8. Knox, D.L., Bayless, T.M. and Pittman, F.E. (1976). Neurologic disease in patients with treated Whipple’s disease. Medicine 55: 467–76. Lapointe, L.R., Lamarche, J., Salloum, A. and Beaudry, R. (1980). Meningo-ependymitis in Whipple’s disease. Can J Neurol Sci 7: 163–7. Lynch, T., Odel, J., Fredericks, D.N. et al. (1997). Polymerase chain reaction-based detection of Trophyrema whippelii in central nervous system Whipple’s disease. Ann Neurol 42: 120–4. Mendel, E., Khoo, L.T., Go, J.L., Hinton, D., Zee, C.S. and Apuzzo, M.L. (1999). Intracerebral Whipple’s disease diagnosed by stereotactic biopsy: a case report and review of the literature. Neurosurgery 44: 203–9. Perkin, G.D. and Murray-Lyon, I. (1998). Neurology and the gastrointestinal system. J Neurol Neurosurg Psychiatry 65: 291–300. Petrides, P.E., Muller-Hocker, J., Fredricks, D.N. and Relman, D.A. (1998). PCR analysis of T. whippelii DNA in a case of Whipple’s disease: effect of antibiotics and correlation with histology. Am J Gastroenterol 93: 1579–82. Ramzan, N.N., Loftus, E. Jr, Burgart, L.J. et al. (1997). Diagnosis and monitoring of Whipple disease by polymerase chain reaction. Ann Intern Med 126: 520–7. Relman, D.A., Schmidt, T.M., MacDermott, R.P. and Falkow, S. (1992). Identification of the uncultured bacillus of Whipple’s disease. N Engl J Med 327: 293–301. Romanul, F.C.A., Radvany, J. and Rosales, R.K. (1977). Whipple’s disease confined to the brain: a case studied clinically and pathologically. J Neurol Neurosurg Psychiatry 40: 901–9. Schnider, P., Trattnig, S., Kollegger, H. and Auff, E. (1995). Am J Neuroradiol 16: 1328–9. Schoedon, G., Goldenberger, D., Forrer, R. et al. (1997). Deactivation of macrophages with interleukin-4 is the key to the isolation of Trophyerma whippelii. J Infect Dis 176: 672–7. Singer, R. (1998). Diagnosis and treatment of Whipple’s disease. Drugs 55: 699–704. Sommer, S., Rozot, P., Wagner, M., Xenard, L. and Poveda, J.D.

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(1998). Uveitis in Whipple disease: identification of Trophyrema whippelii by PCR. J Fr Ophthalmol 21: 588–90. Tison, F., Louvet-Giendaj, C., Henry, P., Lagueny, A. and Gaujard, E. (1992). Permanent bruxism as a manifestation of the oculofacial syndrome related to systemic Whipple’s disease. Mov Disord 7: 82–5. Verhagen, W.I., Huygen, P.L., Dalman, J.E. and Schuurmans, M.M. (1996). Whipple’s disease and the central nervous system. A case report and a review of the literature. Clin Neurol Neurosurg 98: 299–304.

Weiner, S.R. and Utsinger, P. (1986). Whipple’s disease. Arthritis Rheum 15: 157–67. Whipple, G.H. (1907). A hitherto undescribed disease characterized anatomically by deposits of fat and fatty acids in the intestinal and mesenteric lymphatic tissues. J Hopkins Hosp Bull 18: 382–91. Wroe, S.J., Pires, M., Harding, B., Youl, B.D. and Shorvon, S. (1991). Whipple’s disease confined to the CNS presenting with multiple intracerebral mass lesions. J Neurol Neurosurg Psychiatry 54: 989–92.

17

Cerebellar disorders in cancer Jerzy Hildebrand1 and Danielle Balériaux2 2

Introduction Several mechanisms are involved in the neurologic insults seen in cancer patients. The most common lesions are due to primary or metastatic tumors. A second group of disorders is caused either by specifically antineoplastic treatments such as surgery, radiation or chemotherapy (Hildebrand, 1990) or by supportive therapies frequently used in cancer patients. The incidence of central nervous system (CNS) infections and of vascular lesions is also increased in patients with malignant diseases. In addition, infectious agents (Armstrong, 1976, 1977) and the causes of stroke (Graus et al., 1985) differ from those found in a general population. Finally, when all these etiologies are ruled out, one has to consider the possibility of paraneoplastic disorders resulting from a remote effect of cancer on the nervous system (Posner, 1995). In fact, all these pathogenic mechanisms are represented in the cerebellar disorders occurring in cancer patients. The incidence of cerebellar lesions in a cancer population is not easy to assess from the literature. Gait ataxia is probably the most conspicuous sign of cerebellar dysfunction, but not all cancer patients described as ataxic have a cerebellar lesion. For example, it is unclear whether ataxia observed in patients treated with procarbazine or hexamethylmelamine is caused by a cerebellar or a peripheral nerve lesion. In all the diseases considered in this chapter, the cerebellar insult has been clearly established.

1 Service de Neurologie Clinique de Neuroradiologie, l’Hôpital Erasme, Free University of Brussels, Belgium

placement of posterior fossa structures (herniations), obstructive hydrocephalus, and intracranial hypertension. Acute upwards transtentorial herniation of brainstem and cerebellar structures starts by loss of upwards gaze and may evolve into loss of consciousness and death. Obstructive hydrocephalus frequently complicates upwards transtentorial herniation. Tonsillar herniation may be caused by posterior fossa lesions or, less frequently, may complicate central transtentorial herniation due to supratentorial mass. Tonsillar displacement in the foramen magnum produces stiffness of the neck, head tilt and, less commonly, ataxia and nystagmus. Eventually, medullary compression causes respiratory irregularities, apnea, and death. Tonsillar herniation may be favored by inappropriate lumbar puncture. The cardinal manifestations of intracranial hypertension are: headache, vomiting, and papilledema. Headache is the most common presenting symptom. It tends to be occipital in posterior fossa space-occupying lesions, and is exacerbated at night, by coughing, straining or Valsalva maneuver. Vomiting may be sudden and occur without nausea. Papilledema is a classical sign of intracranial hypertension in older children and adults, whereas enlarged head, tense fontanels, and separation of cranial sutures indicate intracranial hypertension in infants and younger children. Patients may complain of transient visual obscuration. In the late stages, intracranial hypertension may produce bradycardia and systemic hypertension. Sixth nerve palsy is common in intracranial hypertension but has no localizing value.

Clinical presentation Diseases and therapy Cerebellar symptoms and signs are due either to intrinsic lesions of the cerebellum, which are considered elsewhere in this volume, or to mass effect. The latter is mainly associated with tumors or cerebellar hematomas creating dis-

Cerebellar diseases associated with neoplasia are summarized in Table 17.1.

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Table 17.1 Main causes of cerebellar lesions in cancer patients Lesions

Causes

Neoplastic

1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 2.

Treatment-induced

1. Chemotherapy 1. 5-fluorouracil 1. cytosine arabinoside 2. Supportive treatments 1. phenytoin 1. lithium 3. Superficial siderosis

Primary tumors Intrinsic Medulloblastomas Astrocytomas Extrinsic Brainstem gliomas Hemangioblastomas Ependymomas Meningiomas Schwannomas (neurinomas) Epidermoids and dermoid tumors Primary CNS lymphomas Lhermitte–Duclos disease Metastases

Vascular

Cerebrovascular lesions

Infectious

Abscess

Paraneoplastic

1. 2. 3. 4. 5. 6.

Anti-Yo syndrome Anti-Hu syndrome Anti-Ri syndrome Anti-CV2 syndrome Anti-Tr syndrome Anti-Ma1 syndrome

Neoplastic lesions Cerebellar symptoms and signs may be caused by tumors originating in the cerebellum or by extrinsic neoplasms of the posterior fossa. Many intrinsic cerebellar tumors, including medulloblastomas and astrocytomas, or extrinsic malignancies, such as fourth ventricle ependymomas or brainstem gliomas, occur preferentially in children. In adults the most common parenchymal cerebellar malignancies are metastases, whereas extrinsinc posterior fossa tumors are meningiomas and schwannomas (neurinomas). However, both schwannomas and meningiomas may occur in patients with type 1 neurofibromatosis (or von Recklinghausen’s disease), usually diagnosed during the first decade of life, or with type 2 neurofibromatosis, which is usually diagnosed during the second or third decade.

Medulloblastomas These are the most common type of primitive neuroectodermal tumors (PNET), accounting for 20% of all primary brain tumors in children. Their peak incidence is between five and ten years. In children, they typically arise from the vermis. In adults, they account for less than 4% of all primary tumors, and their origin tends to shift laterally. Medulloblastoma may be associated with hereditary diseases, such as the basal cell nevus syndrome (Gorlin’s syndrome) or ataxia-telangiectasia. Medulloblastomas are fast-growing tumors and tend to invade the fourth ventricle and the leptomeninges or to produce distant spinal leptomeningeal seedings. Posterior fossa extension causes cranial nerve palsies, which may be seen in addition to signs of intracranial hypertension, and gait ataxia, which are the most common presenting features. The main radiological characteristics are illustrated in Fig. 17.1. Pathologically, medulloblastomas are characterized by high-density cellularity and frequent mitoses (Fig. 17.2).

Therapy The management of medulloblastoma combines surgery, radiation, and chemotherapy. The results of two large trials aiming primarily to test adjuvant chemotherapy are in favor of extensive tumor resection. In the Société Internationale d’Oncologie Pédiatrique (SIOP) study (Tait et al., 1990), the five-year survival of patients with biopsy was significantly (p0.05) shorter than (33%) that of children with subtotal (52.1%) or total (50.8%) resection. However, in a series of 67 medulloblastomas patients without disseminated disease operated on at the Children’s Hospital of Philadelphia, the groups with subtotal and total resection had similar relapse rates (Sutton et al., 1996). In the Children Cancer Study Group (CCSG) study (Evans et al., 1990) there was only a trend towards longer survival in patients with more extensive tumor removal. In conclusion, an extensive removal of medulloblastoma tissue is desirable, but taking increased risks to remove small amounts of tumor from critical areas seems unjustified. Radiation therapy remains the mainstay in the treatment of medulloblastoma, and the main factor resulting in a 50–70% cure rate at five years and over 40% at ten years. Because of cognitive and growth dysfunction induced by radiation therapy, numerous attempts have been made to reduce radiation doses (Jenkin, 1996). Despite these attempts, the standard irradiation of the posterior fossa (the dominant site for recurrence) remains 5000–5500 cGy delivered in 30 fractions. Below 5000 cGy, there is a rapid fall in tumor control. Optimal doses for the rest of the craniospinal axis are more controversial. It is still uncertain

Cerebellar disorders in cancer

A

B

Fig. 17.1 Medulloblastoma: typical MRI appearance. Medulloblastomas are most commonly located in the inferior portion of the vermis. (A) Sagittal T1-weighted image: hypointense mass (arrow) sitting within the fourth ventricle. (B) Axial T2-weighted image: the tumor is heterogeneous with ill-defined margins. (C) Sagittal and (D) coronal post-contrast T1-weighted image: the tumor enhances strongly and heterogeneously.

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C

D

Fig. 17.1 (cont.)

Cerebellar disorders in cancer

whether the commonly used irradiation with 3600 cGy given in 20 fractions can be lowered even in nonmetastatic medulloblastoma. A pilot study combining adjuvant chemotherapy (vincristine, CCNU and cisplatin) with a craniospinal irradiation reduced to 1800 cGy yielded a 69% progression-free survival of four years (Goldwein et al., 1993). However, it is still undetermined whether and to what extent the classical dose of 3600 cGy can be lowered by concomitant chemotherapy without decreasing the rate of long-term cures. The most appropriate use of chemotherapy in the treatment of medulloblastoma remains unsettled. Two pivotal trials have shown that patients with average risk do not benefit from adjuvant chemotherapy consisting either of vincristine plus CCNU (Tait et al., 1990) or vincristine, CCNU, and prednisolone (Evans et al., 1990). However, high-risk patients (i.e., children under two to four years, patients with larger tumors, and metastases) benefit from adjuvant chemotherapy. In addition, two other studies (Neidhardt, 1983; Krischer et al., 1991) failed to demonstrate the value of adjuvant chemotherapy in unselected medulloblastoma patients. Of course, the regimens tested may not be the most efficient. The addition of cisplatin to vincristine plus CCNU yielded an overall progression-free survival of 85 6% (Packer et al., 1994; Cohen and Packer, 1996) in a non-randomized study. In many centers, chemotherapy is also used to delay radiation therapy until the age of 36 months to reduce the effect of irradiation on cognitive function and growth. Unfortunately, about half of these infants relapse during chemotherapy and need to be irradiated and sometimes reoperated. Whereas the use of adjuvant chemotherapy remains questionable in average-risk patients, the rate of response of recurrent medulloblastoma to various chemotherapy regimens is high (see Table 6, p. 13 in Hildebrand, 1992). Medulloblastomas are one of the best illustrations of the apparent divergence in response to chemotherapy when the drug is used either as adjuvant or as rescue therapy. We suggest a therapeutic algorithm (Fig. 17.3), but it should be kept in mind that (a) delaying radiation therapy in children under three years has not withstood the test of time, and (b) the best chemotherapy regimen remains to be established.

Cerebellar astrocytomas Cerebellar astrocytomas account for 10–20% of brain malignancies in childhood. The peak incidence is from birth to nine years of age. Their pathology ranges from the most common and benign juvenile pilocytic astrocytoma to grade II infiltrating fibrillary astrocytoma (Fig. 17.4) and rare grade IV glioblas-

Fig. 17.2 Neuropathology of medulloblastoma. The tumor is characterized by a very high cell density. Cells are isomorphic with hyperchromatic nuclei. There are numerous mitoses. (Courtesy of Dr I. Salmon and Dr N. Nagy.)

Fig. 17.3 Therapeutic algorithm in medulloblastoma. VCR, vincristine; CCNU, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea.

toma. Pilocytic astrocytomas represent 80–85% of cerebellar astrocytomas and need to be recognized because their prognosis is particularly favorable. Over 90% of patients are alive ten years after the diagnosis has been made (Winston et al., 1977). Histologically the tumors are formed by fascicles of elongated bipolar astrocytes. Microvascular proliferation is common in pilocytic astroctyoma and probably accounts for their enhancement after contrast media administration on magnetic resonance imaging

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A

B

C

D

E

Figure 17.4 Left cerebellar cystic grade II astrocytoma: MRI aspects. (A) and (B) Sagittal T1-weighted images: large partially cystic mass inducing tonsillar herniation (arrow). The solid component has welldefined borders and is moderately hypointense. The associated cyst is definitely more hypointense and clearly identified on this pulse sequence. (C) Axial T2-weighted image: the solid nodule exhibits a slightly hyperintense heterogeneous signal, and has well-defined margins. The cyst is uniformly hyperintense. (D) Sagittal and (E) coronal post-contrast T1-weighted images: the solid component enhances strongly and homogeneously. Contrast enhancement is also seen within the cyst wall.

Cerebellar disorders in cancer

(MRI) and computerized tomography (CT) scan, a feature which, in the case of pilocytic astrocytoma, is not an indication of malignancy. Vascular proliferation (Fig. 17.5) and nuclear atypia probably also explain why juvenile pilocytic astrocytomas are occasionally overgraded. Even without undergoing a malignant transformation, pilocytic astrocytomas may metastasize (Mamelak et al., 1994). Compared to medulloblastomas, astrocytomas arise more frequently in the cerebellar hemispheres, and unilateral appendicular dysmetria may be an early sign which is overshadowed by gait ataxia and signs of intracranial hypertension as the tumor progresses.

Therapy The management of cerebellar astrocytoma is related to malignancy grade. Although apparent cures lasting over 20 years are observed even after partial surgical removal, total resection is recommended in pilocytic astrocytomas. Adjuvant radiation therapy and chemotherapy for an incompletely resected pilocytic cerebellar astrocytoma have not been proven to improve prognosis. Infiltrative grade II and high-grade cerebellar astrocytomas are much less amenable to total resection. In the treatment of grade II cerebellar astrocytoma, the benefit of adjuvant radiation and chemotherapy remains unproven. Adjuvant radiation therapy follows operation in high-grade tumors, but the use of adjuvant chemotherapy remains questionable in cerebellar glioblastoma. However in supratentorial glioblastoma, adjuvant administration of vincristine and CCNU has been shown to be effective at least in one study performed in children (Sposto et al., 1989) and, by analogy, cerebellar high-grade gliomas are also treated by chemotherapy in some centers.

Surgery plays no role in the management of infiltrating gliomas of the pons. Even diagnostic stereotactic biopsy is progressively abandoned in children (Levivier et al., 1998), and the diagnosis relies on the fairly typical MRI appearance (Fig. 17.6). Radiation therapy using 5000 to 55 000 cGy in 180 to 200 cGy daily fractions remains the mainstay treatment of infiltrating brainstem glioma (Littman et al., 1980). Recurrent tumors may respond to chemotherapy including etoposide (VP16), cisplatin, cyclophosphamide, and vincristine, but the efficacy of adjuvant chemotherapy remains unproven (Jenkin et al., 1987).

Brainstem gliomas

Hemangioblastomas

Two-thirds of brainstem gliomas occur before the age of 20 years, making up 10–20% of all pediatric brain tumors. A second small peak occurs during the fourth decade, but in adults brainstem gliomas comprise less than 2% of all brain neoplasia. Schematically, these tumors are located in three distinct sites: the tectum, the cervicomedullary junction, and the pons. The advent of MRI has greatly improved their diagnosis. Approximately 70% of all brainstem gliomas infiltrate the pons (Fig. 17.6A). They are the most malignant forms and may extend into the cerebellar peduncules (Fig. 17.6B). Cranial nerve palsies are a common presenting sign, and brainstem gliomas may produce cerebellar symptoms and signs, including gait ataxia and nystagmus.

Hemangioblastomas are rare tumors. They may be a manifestation of von Hippel–Lindau disease, a syndrome combining retinal angiomatosis and cerebellar ataxia caused by hemangioblastoma (Table 17.2). Retinal hemangioblastomas are multiple in 40–65% of cases. In 15% of cases, hemangioblastomas occur in the spinal cord and in 10% in the brainstem. In fact, von Hippel–Lindau disease predisposes to the development of many other neoplasias such as endolymphatic sac tumors, renal cell carcinoma or renal cysts, pheochromocytoma, and pancreatic tumors or cysts (Richard et al., 1998). Up to 20–40% of the patients die due to renal carcinoma, but the most common cause of death is CNS hemangioblastomas. Some hemangioblastomas may produce erythropoietin or erythropoietin-like substance creating hyperglobulinemia and hyperviscosity

Fig. 17.5 Cerebellar pilocytic astrocytoma. The tumor is made of elongated cells. Note the absence of mitoses and necrosis, but the presence of vessels of small size without endothelial proliferation (Courtesy of Dr I. Salmon and Dr N. Nagy.)

Therapy

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A

B

C

D

Fig. 17.6 MRI of brainstem glioma. (A) Sagittal T1-weighted image: widening of the pons and medulla by an ill-defined, slightly hypointense tumor (arrow). (B) Axial T2-weighted image: the glioma is moderately hyperintense and extends into the right middle cerebellar peduncle (arrow). (C) Sagittal and (D) coronal post-contrast T1-weighted images: only mild contrast uptake is seen within the center of the lesion. The tumor is partly exophytic, bulging within the floor of the fourth ventricle.

state. The incidence of polycythemia is estimated to be 5–30%. There is a correlation between the degree of erythropoiesis and the size of the tumor. Rare familial cases of cerebellar hemangioblastomas occur without other manifestations of von Hippel–Lindau disease. Cerebellar hemangioblastomas have also been described in association with multiple endocrine neoplasia and with primary hyperparathyroidism. The mean age at diagnosis is about 30 years for von Hippel–Lindau disease and about 50 years for patients with sporadic disease. Most patients with von Hippel–Lindau disease will have presented symptoms by the age of 50 years. Von Hippel–Lindau disease is dominantly transmitted. The severity of its clinical expression varies considerably

inside the pedigree. The gene is located on chromosome 3p. Cerebellar hemangioblastoma presents a fairly typical aspect on both CT and MRI (Fig. 17.7), with a large cystic component found in 80% of all the cases, and a small mural nodule. They may be strictly solid in 20% of cases. Hemangioblastomas are located in the cerebellar hemisphere in 80% of cases, in the vermis in 15% of cases, and in the floor of the fourth ventricule in 5% of cases.

Therapy Cerebellar hemangioblastomas are treated surgically. Screening of members of families with von Hippel–Lindau disease is recommended above the age of ten years (Table 17.3).

Cerebellar disorders in cancer

Table 17.2 Features of von Hippel–Lindau disease

Common

Rare

Type of lesion/location

Incidence (%)

Retinal hemangioblastoma Cerebellar hemangioblastoma Kidney (cyst, carcinoma) Pheochromocytoma Pancreas (adenoma, cyst, islet cell tumor) Epididymal cyst Liver (cyst, carcinoma) Temporal bone adenoma Cyst of broad ligament Skin hemangioblastoma Spleen (cyst) Lung (cyst) Adrenal cortical angioma Sympathetic paraganglioma

40–65 20–80 30–60 15–60 15–40 10–25

Platinum derivatives – used alone or in combination – are amongst the first-choice drugs (see Table 4, p. 10, in Hildebrand, 1992).

Meningiomas Posterior fossa meningiomas (Fig. 17.11) originating from the cerebellar tentorium, cerebellar convexity, and pontocerebellar angle cause cerebellar signs, often associated with cranial nerve lesions and intracranial hypertension.

Therapy Total surgical resection is the usual goal. In patients with partial tumor removal, adjuvant radiation therapy is often used (Barbaro et al., 1987). Preliminary encouraging results have been observed with progesterone receptor antagonist (Grunberg et al., 1987) and long-term administration of hydroxyurea (Schrell et al., 1997). However, both studies await further confirmation.

Schwannomas (neurinomas) Ependymomas Cerebellar ependymomas represent 10–20% of all posterior fossa tumors before the age of 15 years, surpassed in frequency only by medulloblastomas and astrocytomas. In children, two-thirds of ependymomas arise typically from the floor of the fourth ventricle (Fig. 17.8). The most common clinical presentation is intracranial hypertension caused by the filling of the fourth ventricle, but ependymomas may cause localizing cerebellar signs and are sometimes indistinguishable from medulloblastomas, even on MRI (Figs. 17.9 and 17.10).

Therapy Macroscopically, total resection is the main therapeutic step as the extent of tumor removal is the main prognostic factor for survival (Healey et al., 1991). Subtotal resection is usually followed in patients over three years of age by an irradiation with 5000 to 5500 cGy in 180 to 200 cGy daily fractions. The use of adjuvant cranial radiation therapy after macroscopically total tumor removal is based on retrospective studies (Rousseau et al., 1994). Also, prophylactic spinal irradiation remains controversial, as craniospinal dissemination occurs in only about 10% of the patients. In some centers, patients with undifferentiated posterior fossa ependymomas are treated by craniospinal irradiation. The benefit of adjuvant chemotherapy has not been demonstrated, but in children under three years of age chemotherapy has been used to delay irradiation. Chemotherapy is also used to treat recurrent tumors.

The vast majority of intracranial schwannomas originate from the vestibular nerve, and 80% of all tumors located in the cerebello-pontine angle are vestibular schwannomas. The presenting symptoms and signs are related to the impairment of the acoustico-facial complex. In countries with easy access to CT and MRI, the diagnosis is fortunately often made at this stage. However, large tumors may cause cerebellar symptoms and signs in addition to other cranial nerve and brainstem deficits.

Therapy Microsurgery has allowed a 90–100% rate of complete resection (Flickinger et al., 1997), but not all patients are candidates for operation. The treatment of vestibular schwannomas ranges from expectant follow-up, usually considered in elderly patients with mild disability and quiescent tumors, to urgent tumor removal. At the present time there is also an increasing competition between microsurgery and stereotactic radiation therapy (also referred to as radiosurgery) in the treatment of tumors less than 3 cm in diameter (Pollock et al., 1995).

Epidermoid and dermoid tumors Epidermoid and dermoid tumors are benign congenital cysts deriving from embryonic ectoderm (Smith, 1989). Epidermoids are occasionally traumatic, but this pathogenesis is not found in the intracranial location. Both epidermoid and dermoid tumors are rare and account for less than 1% of all primary intracranial tumors. Posterior fossa epidermoid tumors are mainly found in the cerebellopontine angle (Fig. 7.12). Their peak incidence is in the

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Fig. 17.7 Left cerebellar hemangioblastoma: MRI features. (A) Axial T1-weighted image: well-delineated cystic lesion with a small isointense solid nodule (arrow). (B) Axial T2-weighted image: the solid nodule is hypointense, contrasting with the hyperintense cystic component. (C) Axial and (D) coronal post-contrast T1-weighted images: only the solid nodule enhances strongly, while no contrast uptake is seen within the wall of the cyst.

Table 17.3 Screening in members of families with von Hippel–Lindau disease Detailed physical examination Ophthalmologic evaluation Brain MRI CT scan/ultrasound evaluation of the abdomen Urinary analysis (VMA, catecholamines) Notes: VMA, Vanillic mandelic acid.

fourth decade. Intracranial dermoids typically occupy the vermis and the fourth ventricule. They are usually diagnosed during the first two decades of life, either by the development of an intracranial hypertension or by an acute aseptic meningitis following cyst rupture.

Primary CNS lymphomas (PCNSL) Most primary CNS lymphomas (PCNSL) are highly malignant non-Hodgkin’s lymphomas and over 80% are B phenotype. In immunocompetent patients, the median age of presentation is during the sixth decade. In this group of patients, the incidence of PCNSL has increased several fold during recent decades. PCNSL are also associated with congenital (Wiskott–Aldrich syndrome) or acquired

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Fig. 17.8 Brain MRI in a fourth ventricle ependymoma. The MR differentiation of ependymomas from other gliomas is mainly related to location and morphology with images of moulding of the fourth ventricle. There are no differences in signal behavior or enhancement patterns. (A) Sagittal T1-weighted image: lobulated mass almost entirely filling the fourth ventricle. The tumor is inhomogeneously hypointense (arrow). (B) Proton density MR scan and (C) T2-weighted image: the tumor is hyperintense. (D) Sagittal and (E) axial postcontrast T1-weighted images: a strong heterogeneous enhancement is seen in this case.

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Fig. 17.9 Plastic fourth ventricle ependymoma. MRI shows that the tumor is extruding into the right pontocerebellar cisterna and extending into the upper cervical canal through the foramen magnum. (A) Sagittal T1-weighted image; (B) axial T2-weighted image and (C) axial post-contrast T1-weighted image. In this case, the tumor is characterized by a heterogeneous signal and enhances only moderately.

immunodeficiency disorders (transplantation, human immune deficiency virus, infection, immunosuppressive chemotherapy). In immunocompromised patients, these tumours are diagnosed at a younger age. PCNSL are preferentially located around the lateral ventricles and in basal ganglia. However, about 20% involve the brainstem and the cerebellum. PCNSL are isointense to slightly hypointense to gray matter on T1-weighted images and are isointense to slightly hyperintense on T2-weighted images. Gadolinium enhancement is homogeneous in immunocompetent patients and ring like in AIDS patients. At diagnosis, approximately 10% of patients have ocular involvement that may be demonstrated by slit-lamp. When radiological features suggest PCNSL, diagnostic biopsy should be performed before the administration of glucocorticosteroids because, in PCNSL, these have a cytolytic effect, which may take place within 24 hours and compromise the pathological diagnosis.

Therapy

Fig. 17.10 Large ependymoma in a two-year-old child. Sagittal post-contrast T1-weighted image shows not only tumor extension to the foramen magnum, but also upwards growth with obstruction of the aqueduct (arrow) and tentorial herniation.

The treatment of PCNSL combines methotrexate-based chemotherapy and irradiation. It has increased the median expected survival from a few to over 40 months. However, older patients treated with this combination develop an unacceptably high rate of severe cognitive disorders, and irridiation tends to be delayed or even abandoned in elderly patients.

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Fig. 17.11 MR aspects of posterior fossa meningioma. (A) Axial T1-weighted image: almost isointense mass surrounded by a thin hypointense rim corresponding to entrapped CSF (arrow). (B) Axial T2-weighted image: the meningioma is slightly hyperintense; the aspect is homogeneous. (C) and (D) axial post-contrast T1-weighted images: homogeneous and intense contrast uptake by the lesion that partially invades the adjacent right transverse sinus (arrow). (E) Coronal contrast-enhanced T1-weighted image and (F) twodimensional phase contrast coronal MR angiography: the invasion of the right lateral sinus is confirmed by this non-invasive angiographic approach (arrow).

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Fig. 17.12 Epidermoid tumor of the pontocerebellar angle cistern: MRI findings. (A) Axial T2-weighted image (black arrow: tumor) and (B) axial post-contrast T1-weighted image. Epidermoid tumors are difficult to depict on MRI due to their signal behavior being similar to that of CSF: hypointense on T1-weighted image and hyperintense on T2-weighted image. In addition, they do not enhance after contrast administration.

Lhermitte–Duclos disease Also known as dysplastic cerebellar gangliocytoma, the disease may present radiologically as an expending cerebellar lesion (Fig. 17.13). The disease may recur after surgical resection and is observed in association with Cowden’s phakomatosis. It has been classified for these reasons into the neoplastic gangliocytoma category by some authors (Williams et al., 1992), whereas others regard this condition as a malformation (see Chapter 10).

Cerebellar metastases Posterior fossa metastases represent about 10% of parenchymal brain metastases. According to Delattre et al., pelvic (prostate or uterus) and gastrointestinal neoplasia are overrepresented primary tumors compared to supratentorial brain metastases (Delattre et al., 1988). Occipital headaches and vomiting – with or without nausea – and gait ataxia are the most common presenting symptoms and signs. Intracranial hypertension occurs rapidly, usually within a few weeks, in untreated patients.

Therapy Corticosteroid administration is the most effective symptomatic treatment, which relieves cerebellar symptoms and signs within 24 to 48 hours. Cerebellar metastases being potentially resectable, the general principles of brain metastasis management are applicable to their treatment (Hoang-Xuan and Delattre, 1992). Surgery is considered first in patients with: (a) totally removable metastases, (b) good general condition and an expected survival of six months or more, (c) reduced or medically controlled systemic cancer.

External irradiation with 3000 cGy in ten fractions remains the mainstay treatment in operated and nonoperated patients. External stereotactic irradiation, particularly the Linac radiosurgical technique, is indicated in spherical lesions of 3 cm in diameter or less. Surgery and various radiotherapeutic techniques may only control local disease, but in about 50% of patients with brain metastases, death is caused by systemic cancer lesions (Cairncross et al., 1980). In chemosensitive tumors, chemotherapy may control both the brain seedings and the systemic malignant spread. The blood–brain barrier is largely destroyed around brain metastases, and drug selection will be guided by the chemosensitivity of the primary tumor rather than by the ability of the drug to cross the blood–brain barrier. This assertion is illustrated by the success obtained in the treatment of not only germ cell tumor brain metastases but also metastases originating from breast cancer (Rosner et al., 1986). Figure 17.14 summarizes the successive steps of cerebellar metastases therapy.

Treatment-related lesions Anticancer chemotherapy Cerebellar injury related to anticancer chemotherapy is uncommon and is mainly caused by 5-fluorouracil (5-FU) and cytosine arabinoside (Ara-C). High doses of 5-FU are associated with a pancerebellar syndrome characterized by gait ataxia, limb dysmetria, nystagmus, and dysarthria (Moertel et al., 1964). Patients may exhibit a combination of cerebellopathy and encephalopathy resembling a Wernicke–Korsakoff syndrome. Doses of Ara-C above 3

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Fig. 17.13 MRI features of Lhermitte–Duclos disease. (A) Axial T1-weighted image and (B) contrast-enhanced T1-weighted image: left heterogeneous low signal intensity mass displacing the fourth ventricle to the right. After contrast injection, typical linear enhancement is noted within dilated venous structures. (C) Axial and (D) coronal T2-weighted images: characteristic appearance with folial, tigroid pattern of increased signal intensity areas.

g/m2 may produce cerebellar manifestations ranging from reversible nystagmus to an irreversible florid pancerebellar syndrome (Herzig et al., 1987), which often follows an episode of somnolence and encephalopathy. Moreover, cerebellar ataxia may be associated with a neuronopathy. Ara-C-related cerebellopathy has been mainly observed for cumulative doses superior to 24 g. Patients more than 50 years old are at risk for severe cerebellar toxicity. Experimentally, Ara-C triggers a cascade of new mRNA and protein synthesis, which leads to apoptotic cell death in cultured cerebellar granule cells. A cerebellar toxicity of methotrexate (MTX) has also been described (Wizniter et al., 1987). In children treated for acute lymphoblastic leukemia with intrathecal MTX before five years of age, structural deficits in cerebellar lobuli VI–VII have been found (Lesnik et al., 1998).

Supportive therapy Phenytoin is probably the most common anti-epileptic drug used in neuro-oncology. Dose-related reversible nystagmus and ataxia are seen for serum concentrations greater than 20 g/ml. Cerebellar atrophy has been rarely observed and only after prolonged phenytoin administration, and must therefore be very rare in cancer patients. Lithium salts are used in the treatment of psychotic disorders including in cancer patients where its prophylactic administration has been advocated to prevent corticosteroid-induced psychosis (Falk et al., 1979). Cerebellar signs are predominant manifestations of lithium neurotoxicity. They have been confirmed by pathological studies (Schneider and Mirra, 1994). Lithium neurotoxicity may be enhanced by coadministration of carbamazepine, neuroleptics or concomitant hyperthermia.

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Cerebrovascular diseases

Fig. 17.14 Management of cerebellar metastases.

Therapy Cerebellar toxicity associated with high-dose 5-FU or Ara-C requires discontinuation of its administration. Cerebellar signs due to phenytoin administration usually subside when the doses are lowered. If this is not the case, phenytoin should be replaced by another anti-epileptic agent.

Superficial siderosis Surgery, radiotherapy, and chemotherapy have improved the outlook for primary cerebellar tumors. As a result, late or very late complications of treatment are now being established (Anderson et al., 1999). Slowly progressive bilateral sensorineural hearing loss associated with gait and limb ataxia and appearing in the 5 to 25 years after surgery for a primary cerebellar tumor should raise the possibility of superficial siderosis (Anderson et al., 1999). Although this late complication is probably uncommon, it has been under-recognized. MRI is very suggestive, disclosing a hypointense rim of iron coating in particular at the level of the cerebellum, brainstem, and cranial nerves on T2-weighted spin-echo sequences (Anderson et al., 1999). It may be that surgery provides a bleeding source in the brain, with access to the cerebrospinal fluid (CSF). The particular vulnerability of the cerebellum and vestibulocochlear nerves is explained by the ability of glial cells to synthesize ferritin, a precursor of hemosiderin (Koeppen and Dentinger, 1988). The vestibulocochlear nerve has a long glial sheath extending into the pontine cistern, where it is in contact with CSF.

No work seems to have specifically addressed the issue of cerebellar stroke in cancer patients. Assuming the causes are similar to those of the cerebrosvascular diseases usually found in association with malignancies, the mechanisms of stroke seen in cancer patients differ from those found in the general population. Graus et al. (1985) studied the incidence of CVD from both the clinical and pathological points of view in a large cancer population. After metastases, CVDs were the most common CNS insult, found in 14.6% of their patients; half of them were symptomatic. Unlike in a general population, ischemic and hemorrhagic lesions were equally frequent, but the latter were more often symptomatic. The main cause of intraparenchymal hematomas was intratumoral hemorrhage or coagulopathy, and hypertension was the third most frequent etiology. The most frequent causes of symptomatic ischemic CVD in cancer patients were disseminated intravascular coagulation and emboli originating from nonbacterial or septic endocarditis, all conditions frequently causing multiple lesions. Amongst cerebellar tumors, metastases are the most likely to bleed, particularly when they originate from germ cell tumors, melanomas and, to a lesser extent, lung carcinoma. The malignancy most commonly associated with coagulation disorders is leukemia.

Therapy Hematomas presenting with mass effect will be removed surgically whenever patients’ condition and coagulation status permit. When the hemorrhage is caused by cerebellar metastases, radiation therapy and chemotherapy may help to stop bleeding. Treatment of infections and correction of coagulation disorders causing CVD are a useful therapeutic adjunct.

Cerebellar infections Central nervous system infections account for only about 0.2% of all neurologic complications seen in cancer patients. They occur preferentially in immunosuppressed and neutropenic individuals, especially in patient with leukemia or lymphoma. They are mainly caused by opportunistic organisms such as Nocardia asteroides, Aspergillus, Cryptococcus neoformans or Toxoplasma gondii, which are much less pathogenic in immunocompetent patients. In addition, neurosurgery and cerebral shunts favor CNS infections caused by Staphylococcus aureus or epidermidis. Cerebellitis or cerebellar abscesses are discussed in Chapter 15. The treatment is primarily medical, but neurosurgery is performed in patients who do not respond to antibiotics or show signs of acute mass effect.

Cerebellar disorders in cancer

Table 17.4 Paraneoplastic cerebellar degeneration (PCD) syndromes Antibody

Antigen

PNS other than PCD

Associated tumour(s)

Comments

Anti-Hu ANNA-1 Type-IIa

Neuronal nuclear protein 35–40 kD

Limbic encephalitis Encephalomyelitis, Sensory neuronopathy

SCLC Neuroblastoma (R) Non-SCLC (R) Prostate carcinoma (R)

Anti-Hu titers must be high Antigen present in all tumors

Anti-Yo PCA-1, APCA-1 Type 1

Purkinje cell Cytoplasmic protein 34 kD and 62 kD

Ovarian or breast carcinoma Other gynecologic carcinoma

Antigen found in the tumor only if PNS≈ present

Anti-Ri ANNA-2 or Type IIb

Mainly nuclear neuronal protein 55 kD and 80 kD

Opsoclonus Myoclonus Encephalomyelitis (R)

Breast carcinoma Gynecologic carcinoma

Antigen found in the tumor only if PNS present

Anti-CV2

Oligodendrocyte cytoplasmic protein 66 kD

Limbic encephalitis Encephalomyelitis Lambert–Eaton syndrome

Predominantly SCLC Uterine sarcoma Malignant thymoma

Antigen expressed in oligodendrocytes but cell loss is neuronal

Anti-Tr

Cell body and dendrites of Purkinje cell

Anti-Ma1

Neuronal protein 37 kD

Hodgkin’s disease Brainstem dysfunction

Parotid, breast, colon carcinoma

Antigen expressed in brain and testis

Notes: Abbreviations: SCLC, small cell lung carcinoma; PNS, paraneoplastic neurological syndrome; (R), rare.

Paraneoplastic cerebellar degeneration Paraneoplastic cerebellopathies are among the most common, most typical, and best-defined paraneoplastic syndromes involving the CNS. They may be identified by antibodies present in the serum and the CSF in approximately 50% of the patients. These antibodies are characteristic not only of the paraneoplastic syndrome but also of the underlying cancer (Table 17.4). In the majority of patients, the development of neurologic paraneoplasia precedes the diagnosis of the underlying malignancy. In this case, the malignancy often follows a more indolent course than in patients without neurologic paraneoplasia. Patients are often more disabled by the paraneoplastic cerebellar degeneration than by the malignant disease. Six types of paraneoplastic cerebellar degeneration have been identified.

Anti-Yo syndrome Anti-Yo antibodies are associated with isolated subacute paraneoplastic cerebellar degeneration. The disorder usually starts as gait ataxia, followed by limb and truncal dysmetria, dysarthria, and intention tremor. Patients may complain of nystagmus-related oscillopsia. The neurological signs are purely cerebellar, evolve in weeks to months, and remain stable thereafter. Late CT and MRI scan may

reveal cerebellar atrophy or remain normal. CSF shows inflammatory changes, including possible oligoclonal bands. Pathological lesions consist of diffuse and severe loss of Purkinje cells and thinning of granular and molecular layers (Fig. 17.15). Anti-Yo antibodies are directed towards cytoplasmic proteins of 34 and 62 kD found only in the Purkinje cells. Indirect immunostaining reveals a characteristic coarse pattern. Yo antigens are expressed in ovary and breast carcinoma only in patients with paraneoplastic cerebellar degeneration (Furneaux et al., 1990). The main characteristics of anti-Yo antibodies are the following: They are found in over 50% of paraneoplastic cerebellar degeneration in women with breast or ovary carcinoma. Their presence in paraneoplastic cerebellar degeneration associated with other cancers is exceptional. They are not found in neurologically normal individuals with cancer, in healthy controls, or in cerebellar degeneration of other causes (Jaeckle et al., 1985). They have occasionally been found in high titers in patients with ovarian carcinoma without clinical cerebellar signs (Brashaer et al., 1989; Drlicek et al., 1997). Anti-Yo syndrome has to be distinguished from the subacute cerebellar syndrome associated with systemic

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Fig. 17.15 A section through cerebellar cortex in a patient presenting paraneoplastic cerebellar degeneration associated with anti-Yo antibodies. There is complete disappearance of Purkinje cells. (Courtesy of Dr J.J. Vanderhaeghen.)

immune diseases, namely systemic lupus erythematosus and Sjögren’s syndrome in which antibodies staining cytoplasmic elements in cerebellar neurons are detected (Terao et al., 1994).

Anti-Hu syndrome Anti-Hu antibodies, first identified in a patient with paraneoplastic sensory neuronopathy, are in fact a manifestation of a multifocal encephalomyelitis where lesions can be found anywhere between cortex and sensory ganglia. The clinical manifestations of the paraneoplastic encephalomyelitis are largely determined by the most affected areas. When lesions predominate in the cerebellum, clinical manifestations may be similar to paraneoplastic cerebellar degeneration associated with anti-Yo antibodies. Hu antigen is a 35–40 kD nuclear protein expressed in all CNS neurons, and also in small cell lung carcinoma, and neuroblastoma (Tora et al., 1997). High titers of anti-Hu are characteristic of paraneoplastic encephalomyelitis and of sensory neuronopathy, but they are found in low titers in about 16% of patients with small cell lung carcinoma

without neurologic paraneoplastic manifestations (Dalmau et al., 1990).

Anti-Ri syndrome Anti-Ri antibodies are associated with opsoclonus, myoclonus, dysmetria, and ataxia. Encephalomyelitis is occasional. Opsoclonus, the cardinal sign, is characterized by involuntary chaotic, multidirectional eye saccades. Myoclonus is often evoked or enhanced by voluntary movements. Ataxia associated with anti-Ri antibodies is predominantly truncal. Anti-Ri syndrome develops over one week to a few months. The most striking clinical feature is fluctuations with possible recovery similar to what may be observed in non-paraneoplastic opsoclonus–myoclonus syndrome. A favorable outcome may be related to the paucity of pathological lesions, including in the midbrain. Anti-Ri syndrome is associated almost exclusively with breast carcinoma. Ri antigens are 55 kD and 80 kD proteins present in all neurons of the CNS. Like Yo antigens, but unlike Hu or calcium channel antigens, Ri antigens have

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Fig. 17.16 CV2 antigen expression by oligodendrocytes in the superior cerebellar peduncle of an adult rat brain obtained by (A) indirect immunofluorescence (200) or (B) immunoperoxidase (400) using the serum of a patient containing anti-CV2 autoantibodies. This patient presented a subacute paraneoplastic cerebellar degeneration associated with a small cell lung carcinoma. (Courtesy of Dr J. Honnorat.)

been found in cancer tissue only in patients with specific antibody. Anti-Ri antibodies have the following characteristics: They were not found in controls or in 87 women with breast cancer without neurological signs (Luque et al., 1991), but were found in high titers (Brashaer et al., 1989) in 7 out of 181 women with ovarian cancer but no clinical signs of neurological paraneoplasia. They are not found in association with opsoclonus occurring in patients with small cell lung carcinoma or neuroblastoma. They were exceptionally found in non-paraneoplastic conditions (Casado et al., 1994).

Anti-CV2 syndrome Anti-CV2 antibodies have been found more recently in 11 out of 45 patients with various paraneoplastic neurological syndromes. Cerebellar ataxia, reported in 6 of 11 patients, was the most common clinical sign (Honnorat et al., 1996). CV2 antigen is a 66 kD cytoplasmic protein expressed in a subpopulation of oligodendrocytes and is also called POP 66 (paraneoplastic oligodendrocyte protein) (Fig. 17.16). Serum anti-CV2 antibodies were found in only two cancer patients without paraneoplastic neuropathy out of 1061 controls (de la Sayette et al., 1998). Exceptionally, anti-CV2, anti-Hu, and anti-Ri antibodies are found in the same patient in association with small cell lung carcinoma, indicating that multiple immune responses against onconeuronal antigens may occur concomitantly (Honnorat et al., 1998).

Anti-Tr syndrome Anti-Tr syndrome is a paraneoplastic cerebellar degeneration associated with Hodgkin’s disease. Clinically, the cere-

bellopathy resembles the syndromes described above. However, unlike in most paraneoplasias, the patients are predominantly males and the cerebellar disease usually follows the diagnosis of the neoplasia. Serum antibodies, identified by Graus et al. as anti-Purkinje cell antibodies, were found in their series in 75% of patients with Hodgkin’s disease-related paraneoplastic cerebellar degeneration (F. Graus, personal communication). Anti-Tr antibodies are found in the serum and CSF of patients with paraneoplastic cerebellar degeneration and Hodgkin’s disease, but not in cerebellar patients without Hodgkin’s disease or in patient’s with Hodgkin’s disease without paraneoplastic cerebellar degeneration (Graus et al., 1997).

Anti-Ma1 syndrome Dalmau et al. (1999) have identified antibodies reacting with 37 kD proteins in patients exhibiting brainstem and cerebellar dysfunction. Autopsy revealed deep cerebellar white matter inflammatory infiltrates and loss of Purkinje cells (Fig. 17.17). Neuronal degeneration was also found in the brainstem. The antibodies, called anti-Ma1, recognize a protein expressed in neurons and in testis.

Therapy Based upon the still not proven assumption that anti-Hu and anti-Yo antibodies may be involved in the pathogenesis of paraneoplastic cerebellar degeneration, several immunomodulating therapies, including plasmapheresis, gammaglobulins, immunoadsorption (Barchelor et al., 1998), and immunosuppressive drugs have been tested. The results of these trials were generally negative, although the lack of therapeutic effect may be due to the fact that

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plastic cerebellar degeneration associated with Hodgkin’s disease may respond to the treatment of the underlying tumor (Posner, 1995). The spontaneous remissions observed in the anti-Ri syndrome make the evaluation of any therapy difficult.

Diagnostic work-up

Fig. 17.17 Neuropathological findings in a patient with anti-Ma1 antibodies. (A) Section in cerebellar cortex disclosing severe loss of Purkinje cells and Bergmann astrogliosis. (B) Perivascular and interstitial inflammatory infiltrates in the brainstem. (Reproduced with permission from Dalmau et al. (1999). Ma1, a novel neuron-specific and testis-specific protein, is recognized by the serum of patients with paraneoplastic neurological disorders. Brain 122: 27–39.)

treatments were given too late, when the loss of Purkinje cells had already been completed (Graus et al., 1992). Occasional improvements have indeed been observed in early-treated patients (Stark et al., 1995; Counsell et al., 1994). Usually, a successful treatment of the underlying cancer does not affect the course of paraneoplastic cerebellar degeneration, but again there are anecdotal exceptions. Data concerning the response of paraneoplastic cerebellar degeneration associated with CV2 antibodies are still scarce, but one patient improved dramatically after tumor excision (de la Sayette et al., 1998). Also, some paraneo-

The first-choice examination in patients with cerebellar pathology and possibly malignant disease is brain MRI, which is clearly superior to CT scan in exploring posterior fossa. A diagnostic algorithm based on MRI scan is shown in Fig. 17.18. MRI may show focal lesions, be normal, or show a diffuse atrophy. 1. Neoplasia is suspected when MRI demonstrates a focal abnormality, especially when the lesion produces a mass effect and is enhanced by gadolinium. In operable patients, the final diagnosis will be made by the examination of the surgical material. In adults, the most common malignant cerebellar tumors are metastases. In children, malignant pathologies are mostly primary tumors. However, all primary posterior fossa malignancies, especially astrocytoma and medulloblastoma, may either develop or recur during adulthood. Non-operable patients with highly probable metastatic lesions may either be treated by radiation and chemotherapy, or have a diagnostic biopsy. The decision to perform such biopsy largely relies upon individual judgement and clinical situation. Even in patients known to have a malignant disease, biopsy may reveal an unexpected and potentially curable pathology. We propose that stereotactic biopsy should be performed in the following circumstances: When patients are not known to have a systemic cancer, or when the primary tumor is unlikely to produce brain metastases. When a cerebellar hemorrhagic lesion occurs in patients without coagulation disorders, or without a long history of systemic hypertension. In such patients, the likelihood of intratumoral bleeding is high. When a lesion, first suspected of being an abscess, does not respond to adequate antibiotic therapy. 2. Normal MRI or the presence of diffuse cerebellar atrophy suggests drug-induced or paraneoplastic etiology. (a) The history should either reveal or rule out the use of drugs toxic to the cerebellum such as 5-FU, AraC, phenytoin or lithium. Excessive alcohol

Cerebellar disorders in cancer

Fig. 17.18 Diagnostic algorithm based upon MRI in patients suspected to have a cerebellar cancer or a paraneoplastic disease.

consumption, which favors the development of several cancers, is also a major cause of cerebellar atrophy in adults. In addition, systemic lupus erythematosus and Sjögren’s syndrome should be searched for when faced with a subacute cerebellar syndrome of unknown origin (Terao et al., 1994). (b) When specific antibodies (summarized in Table 17.4) are found either in the serum or in the CSF, the diagnosis of paraneoplastic cerebellar degeneration may be accepted even if the primary tumor is not obvious. The presence of such antibodies justifies a search for an underlying malignancy, looking particularly for treatable tumors such as Hodgkin’s disease, breast or ovary carcinomas (see Table 17.4 for the correspondence between various antibodies and associated neoplasia). Falsepositive high titers of specific antibodies are, indeed, exceptional.

xReferencesx Anderson, N.E., Sheffield, S. and Hope, J.K. (1999). Superficial siderosis of the central nervous system: a late complication of cerebellar tumors. Neurology 52: 163–9. Armstrong, D. (1976). Infectious complications of neoplastic disease: their diagnosis and management, Part I. Clin Bull 6: 135–41.

Armstrong, D. (1977). Infectious complications of neoplastic disease: their diagnosis and management, Part II. Clin Bull 7: 13–20. Barbaro, N.M., Gutin, P.H., Wilson, C.B. et al. (1987). Radiation therapy in the treatment of partially resected meningiomas. Neurosurgery 20: 525–8. Barchelor, T.T., Platten, M. and Hochberg, F.H. (1998). Immunoadsorption therapy for paraneoplastic syndromes. J Neurooncol 40: 131–6. Brashaer, H.R., Greenlee, J.E., Jaeckle, K.A. and Rose, J.W. (1989). Anticerebellar antibodies in neurologically normal patients with ovarian neoplasms. Neurology 39: 1605–9. Cairncross, J.G., Kim, J.H. and Posner, J.B. (1980). Radiation therapy for brain metastases. Ann Neurol 7: 529–41. Casado, J.L., Gil-Peralta, A., Graus, F. et al. (1994). Anti-Ri antibodies associated with opsoclonus and progressive encephalomyelitis with rigidity. Neurology 44: 1521–2. Cohen, B.H. and Packer, R.J. (1996). Chemotherapy for medulloblastomas and primitive neuroectodermal tumors. J Neurooncol 29: 55–68. Counsell, C.E., McLeod, M. and Grant, R. (1994). Reversal of subacute paraneoplastic cerebellar syndrome with intravenous immunoglobulin. Neurology 44: 1184–5. Dalmau, J., Furneaux, H.M., Gralla, R.J. et al. (1990). Detection of the anti-Hu antibody in the serum of patients with small cell lung cancer – a quantitative Western blot analysis. Ann Neurol 27: 544–52. Dalmau, J., Gultekin, S.H., Voltz, R. et al. (1999). Ma1, a novel neuron- and testis-specific protein, is recognized by the serum of patients with paraneoplastic neurological disorders. Brain 122: 27–39.

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de la Sayette, V., Bertran, F., Honnorat, J. et al. (1998). Paraneoplastic cerebellar syndrome and optic neuritis with antiCV2 antibodies: clinical response to excision of the primary tumor. Arch Neurol 55: 405–8. Delattre, J.Y., Kroll, G., Thaler, H.T. et al. (1988). Distribution of brain metastases. Arch Neurol 45: 741–4. Drlicek, M., Bianchi, G., Bogliun, G. et al. (1997). Antibodies of the anti-Yo and anti-Ri type in the absence of paraneoplastic neurological syndromes: a long-term survey of ovarian cancer patients. J Neurol 244: 85–9. Evans, A.E., Jenkin, R.D.T., Sposto, R. et al. (1990). Results of a prospective randomized trial of radiation therapy with and without CCNU, vincristine and prednisone. J Neurosurg 72: 572–82. Falk, W.E., Mahnke, M.W. and Postkanzer, D.C. (1979). Lithium prophylaxis of corticotropin-induced psychosis. J Am Med Assoc 241: 1011–12. Flickinger, J.C., Kondziolka, D. and Lunsford, L.D. (1997). Vestibular schwannoma in cancer of the nervous system. In Cancer of the Nervous System, ed. P.Mc.L. Black and J.S. Loeffler, pp. 404–13. Cambridge, MA: Blackwell Science. Furneaux, H.M., Rosenblum, M.K., Dalmau, J. et al. (1990). Selective expression of Purkinje-cell antigens in tumor tissue from patients with paraneoplastic cerebellar degeneration. N Engl J Med 322: 1844–51. Goldwein, J.W., Radcliffe, J., Packer, R.J. et al. (1993). Results of a pilot study of low-dose craniospinal radiation therapy plus chemotherapy for children younger than 5 years with primitive neuroectodermal tumors. Cancer 71: 2647–52. Graus, F., Dalmau, J., Valldeoriola, F. et al. (1997). Immunological characterization of a neuronal antibody (anti-Tr) associated with paraneoplastic cerebellar degeneration and Hodgkin’s disease. J Neuroimmunol 74: 55–61. Graus, F., Rogers, L.R. and Posner, J.B. (1985). Cerebrovascular complications in patients with cancer. Medicine (Baltimore) 64: 16–35. Graus, F., Vega, F., Delattre, J.Y. et al. (1992). Plasmapheresis and antineoplastic treatment in CNS paraneoplastic syndromes with antineuronal autoantibodies. Neurology 42: 536–40. Grunberg, S.M., Daniels, A.M., Muensch, H. et al. (1987). Correlation of meningioma hormone receptor status with hormone sensitivity in tumor stem-cell assay. J Neurosurg 66: 405–8. Healey, E.A., Barnes, P.D., Kupsky, W.J. et al. (1991). The prognostic significance of postoperative residual tumour in ependymoma. Neurosurgery 28: 666–72. Herzig, R.H., Hines, J.D., Herzig, G.P. et al. (1987). Cerebellar toxicity with high-dose cytosine arabinoside. J Clin Oncol 5: 927–32. Hildebrand, J., ed. (1990). Neurological Adverse Reactions to Anticancer Drugs. Berlin: Springer-Verlag. Hildebrand, J. (1992). Treatment of primary brain tumours. In Management in Neuro-Oncology, ed. J. Hildebrand, pp. 3–22. Berlin: Springer- Verlag. Hoang-Xuan, K. and Delattre, J.Y. (1992). Treatment of brain metastases. In Management in Neuro-Oncology, ed. J. Hildebrand, pp. 23-40. Berlin: Springer-Verlag.

Honnorat, J., Aguera, M., Guillon B. et al. (1998). Association of antineuronal autoantibodies in a patient with paraneoplastic cerebellar syndrome and small cell lung carcinoma. J Neurol Neurosurg Psychiatry 62:425–6. Honnorat, J., Antoine, J.C., Derrington, E. et al. (1996). Antibodies to a subpopulation of glial cells and a 66 kDa developmental protein in patients with paraneoplastic neurological syndromes. J Neurol Neurosurg Psychiatry 61: 270–8. Jaeckle, K.A., Graus, F., Houghton, A. et al. (1985). Autoimmune response of patients with paraneoplastic cerebellar degeneration to a Purkinje cell cytoplasmic protein antigen. Ann Neurol 18: 592–600. Jenkin, D. (1996). The radiation treatment of medulloblastoma. J Neurooncol 29: 45–54. Jenkin, R.D., Boesel, C., Ertel, I. et al. (1987). Brainstem tumors in childhood: a prospective randomized trial of irradiation with and without adjuvant CCNU, VCR, and prednisolone. J Neurosurg 66: 227–33. Koeppen, A.H. and Dentinger, M.P. (1988). Brain hemosiderin and superficial siderosis of the central nervous system. J Neuropathol Exp Neurol 47: 249–70. Krischer, J.P., Ragab, A.H., Kun, L. et al. (1991). Nitrogen mustard, vincristine, procarbazine, and prednisone as adjuvant chemotherapy in the treatment of medulloblastoma. J Neurosurg 74: 905–9. Lesnik, P.G., Ciesielski, K.T., Hart, B.L. et al. (1998). Evidence for cerebellar-frontal subsystem changes in children treated with intrathecal chemotherapy for leukemia: enhanced data analysis using an effect size model. Arch Neurol 55: 1561–8. Levivier, M., Massager, N. and Brotchi, J. (1998). Management of mass lesions of the brain stem. Crit Rev Neurosurg 8: 338–45. Littman, P., Jarret, P., Bilaniuk, L.T. et al. (1980). Pediatric brainstem gliomas. Cancer 45: 2787–92. Luque, F.A., Furneaux, H.M., Ferziger, R. et al. (1991). Anti-Ri: an antibody associated with paraneoplastic opsoclonus and breast cancer. Ann Neurol 29: 241–51. Mamelak, A.N., Prados, M.D., Obana, W.G. et al. (1994). Treatment options and prognosis for multicentric juvenile pilocytic astrocytoma. J Neurosurg 81: 24–30. Moertel, C.G., Reitemeier, R.J., Bolton, C.F. and Shorter, R.G. (1964). Cerebellar ataxia associated with fluorinated pyrimidine therapy. Cancer Chemother Rep 41: 15–18. Neidhardt, M.K. (1983). (On behalf of the Medulloblastoma Study Committee of the Society of Pediatric Oncology-GPO.) Therapeutic approach to medulloblastoma and results: the West German Treatment Study (interim results). 13th International Congress on Chemotherapy, Vienna 208: 29–33. Packer, R.J., Sutton, L.N., Elterman, R. et al. (1994). Outcome for children with medulloblastoma treated with radiation and cisplatin, CCNU, and vincristine chemotherapy. J Neurosurg 81: 690–8. Pollock, B.E., Lunsford, L.D., Kondziolka, D. et al. (1995). Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery 36: 215–25.

Cerebellar disorders in cancer

Posner, J.B. (1995). Paraneoplastic syndromes. In Neurologic Complications of Cancer, pp. 352–84. Philadelphia: F.A. Davis. Richard, S., Campello, C., Taillandier, L. et al. (1998). Haemangioblastoma of the central nervous system in von Hippel–Lindau disease. French VHL Study Group. J Intern Med 243: 547–53. Rosner, D., Nemoto, T. and Lane, W.W. (1986). Chemotherapy induces regression of brain metastases in breast carcinoma. Cancer 58: 832–9. Rousseau, P., Habrand, J.L., Sarrazin, D. et al. (1994). Treatment of intracranial ependymoma of children: review of a 15-year experience. Int J Radiat Oncol Biol Phys 28: 381–6. Schneider, J.A. and Mirra, S.S. (1994). Neuropathologic correlates of persistent neurologic deficit in lithium intoxication. Ann Neurol 36: 928–31. Schrell, U.M., Rittig, M.G., Anders, M. et al. (1997). Hydroxyurea for treatment of unresectable and recurrent meningiomas. Decrease in the size of meningiomas in patients treated by hydroxyurea. J Neurosurg 86: 840–5. Smith, A.S. (1989). Myth of the mesoderm: ectodermal origin of dermoids. Am J Neuroradiol 10: 449. Sposto, R., Ertel, I.J., Jenkin, R.D. et al. (1989). The effectiveness of chemotherapy for treatment of high grade astrocytoma in children: results of a randomized trial. J Neurooncol 7: 165–77. Stark, E., Wurster, U., Patzold, U. et al. (1995). Immunological and

clinical response to immunosuppressive treatment in paraneoplastic cerebellar degeneration. Arch Neurol 52: 814–18. Sutton, L.N., Phillips, P.C. and Molloy, P.T. (1996). Surgical management of medulloblastoma. J Neurooncol 29: 9–21. Tait, D.M., Thornton-Jones, H., Bloom, H.J. et al. (1990). Adjuvant chemotherapy for medulloblastoma: the first multicentre control trial of the International Society of Paediatric Oncology (SIOP I). Eur J Cancer 26: 464–9. Terao, Y., Sakai, K., Kato, S. et al. (1994). Antineuronal antibody in Sjogren’s syndrome masquerading as paraneoplastic cerebellar degeneration. Lancet 343: 790. Tora, M., Graus, F., de Bolos, C. and Real, F.X. (1997). Cell surface expression of paraneoplastic encephalomyelitis/sensory neuronopathy-associated Hu antigens in small-cell lung cancers and neuroblastomas. Neurology 48: 735–41. Williams, D.W., Elster, A.D., Ginsberg, L.E. et al. (1992). Recurrent Lhermitte–Duclos disease: report of two cases and association with Cowden’s disease. Am J Neuroradiol 13: 287–90. Winston, K., Gilles, F.H., Leviton, A. and Fulchiero, A. (1977). Cerebellar gliomas in children: clinical considerations and a proposed classification. J Natl Cancer Inst 58: 833–8. Wizniter, M., Packer, R.J., Rorke, L.B. and Meadows, A.T. (1987). Cerebellar sclerosis in pediatric cancer patients. J Neurooncol 4: 353–60.

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Posterior fossa trauma Matthias Maschke1, Uwe Dietrich2, and Dagmar Timmann-Braun1 1 2

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Department of Neurology Department of Neuroradiology, University Clinic Essen, Germany

Introduction

Epidemiology

Primary (direct) or secondary (indirect) traumatic injuries of brain structures localized within the posterior fossa (i.e., cerebellum and brainstem) are called ‘posterior fossa trauma’ (Fisher et al., 1958; Tsai et al., 1980). Primary traumatic injuries are commonly subdivided into open/closed head injuries, and intra-/extra-axial lesions. Open head injuries are characterized by opening of the subarachnoid space to the outside with liquorrhea, and are caused by penetrating injuries or by fractures. In closed head injuries the subarachnoid space remains intact. Intra-axial brain lesions lead to intraparenchymal damage, namely cerebellar or brainstem concussion and contusion, diffuse axonal injury due to shearing forces and delayed post-traumatic intracerebellar hematomas. Extra-axial injuries include epidural hematomas, subdural hematomas, and subarachnoid hemorrhages. Furthermore, vascular lesions may occur due to traumatic dissection of the vertebral arteries with subsequent infarction of the cerebellum and/or brainstem. Secondary traumatic brain lesions develop after the primary impact and are usually due to pathologic brain responses to the primary injury (e.g., brain edema, infection, elevated intracranial pressure, brain herniation) (Zimmerman, 1991; Keidel and Miller, 1996). Despite advances in the understanding of the pathophysiology of primary and secondary brain injuries and in the management of patients with severe head trauma, posterior fossa trauma remains a life-threatening condition, which allows no delay in diagnosis and management. This chapter gives an overview of types, clinical and radiological presentation of posterior fossa trauma. The chapter also describes the pathophysiology and management of posterior fossa trauma. Special operative techniques are not described.

Traumatic brain injury is known as a leading cause of death in children (Vaughan, 1983) and young adults (Goldstein, 1990). The peak incidence occurs in young men. About 100 000 patients/year with traumatic brain injury will suffer from lifelong disability and about 2% of them will live in a persistent vegetative state (Goldstein, 1990). The major causes of head injury are car or motorcycle accidents (49%), and accidental falls in the elderly (29%). Motorcycling is one of the main risk factors for major brain injury (Rivara et al., 1988). Another well-identified risk factor is alcohol intake (Luna et al., 1984; Kraus et al., 1989). Ethanol consumption is associated with an increased risk of motor vehicle crashes and assaults, in particular between the ages of 25 and 50. Trauma may also result from abuse in infants and in children (non-accidental craniocerebral trauma) (Kalsbeek et al., 1980; Johnson and Faerber, 1995). It has been estimated that in infants hospitalized for head trauma, 64% of all head injuries and more than 90% of significant intracranial injuries are associated with child abuse (Billmire and Myers, 1985). Major injuries within the posterior fossa are reported in 3.3% of all head trauma (Tsai et al., 1980). Parenchymal (intra-axial) lesions are found more often than extra-axial hematomas (Gean, 1994). Brainstem injuries (36% of all posterior fossa trauma) are more frequent than cerebellar injuries (25%), epidural hematomas (25%), and subdural hematomas (14%) (Tsai et al., 1980).

Posterior fossa trauma

Types of posterior fossa trauma Intra-axial lesions Concussion A concussion is a clinical syndrome defined by a transient impairment of neural function, likewise an alteration of consciousness, due to mild head trauma (Ommaya and Gennarelli, 1974). Patients may describe amnesia for the events preceding and immediately following the trauma. The cause of disturbances of consciousness after concussion remains controversial, but theories include sudden dysfunction of the reticular system within the brainstem, and global ischemia (Jane et al., 1985). Patients with concussion are at risk for developing a post-traumatic concussion syndrome with headache, fatigue, anxiety, and loss of balance (Levin et al., 1987).

Because shearing forces are intense at the mesencephalon–diencephalon junction, the periventricular region, the cortical gray matter–white matter junction, and the corpus callosum, diffuse axonal injuries occur mainly in these brain areas. Diffuse axonal injury is the most common type of traumatic primary brainstem injury (Gentry et al., 1989). Diffuse axonal injury is one of the mechanisms of cerebellar injury in chronic traumatic encephalopathy associated with boxing. Repeated subconcussive head injuries lead to lesions in frontotemporal regions, in basal ganglia, and in the cerebellum (Johnson, 1969; Corsellis et al., 1973). This traumatic encephalography may develop several months or years later, and includes disinhibition, memory impairment, parkinsonian deficits, and cerebellar signs, mainly intention tremor and lack of coordination in the limbs. Dysarthria is relatively common.

Secondary traumatic lesions Contusion Contusion refers to an intraparenchymal lesion due to forces that act on the brain at the impact site of the head trauma. Brain contusions (and traumatic intraparenchymal hematomas) can be subdivided according to their pathogenesis and aspect on imaging into fracture contusion, coup contusion, and contrecoup contusion (Gean, 1994). One example of the coup–contrecoup injury is impact on the occiput, the coup site, which leads to a contrecoup lesion in the contralateral frontal lobe. Contusion and traumatic hematoma are not distinct entities, given the fact that microhemorrhages occur around vessels in a contusion and may coalesce into a focal rounded hematoma with increasing severity of head trauma. This coalescence of microhemorrhages into an intracerebral hematoma often develops several hours to a few days after the primary contusion. The name ‘delayed traumatic intracerebral hemorrhage or hematoma’ has been coined (Gudeman et al., 1979). Cerebellar and brainstem contusions are rare compared to the incidence of all intracranial contusions (12%) and occur only with severe head trauma (Gean, 1994). However, in severe head injury, brainstem lesions, contusions, and diffuse axonal injuries are common and are detected by magnetic resonance imaging (MRI) in more than 60% of patients (Firsching et al., 1998).

Diffuse axonal injury The immediate, focal, and irreversible damage to axons by shearing forces has been termed ‘diffuse axonal injury’ (Adams et al., 1982; Gennarelli, 1982). Axonal injuries are caused by the rotational acceleration–deceleration of the skull and brain during the moment of head impact.

Secondary traumatic brainstem lesions may result from herniation of medial structures of the temporal lobe through the tentorial opening (uncal herniation) or from expanding mass lesions of the posterior fossa (Gean, 1994). This may lead to herniation of the cerebellar tonsils through the foramen magnum, resulting in compression of the medulla oblongata (foraminal herniation). Acute downward herniation of the brain often results in brainstem ischemia by elongation and narrowing of long penetrating arteries within the pons. As a consequence of the brainstem ischemia, the vascular endothelium is damaged and reperfusion may generate bleeding (‘Duret hemorrhage’; Klintworth, 1968; Fig. 18.1).

Extra-axial lesions Epidural hematoma Epidural hematomas in the posterior fossa constitute 4–13% of all epidural hematomas and are observed more commonly in children (Johnson and Farber, 1995). Epidural hematomas are located between the outer (periosteal) layer of the dura mater and the inner table of the skull and develop in the moment of impact, when the dura is forcefully stripped away from the skull. In contrast to subdural hematomas, epidural hematomas are usually situated at the coup site. Skull fractures are identified in up to 95% of epidural hematomas in adults (Pozzati et al., 1989; Knuckey et al., 1989). The origins of blood are the disrupted meningeal vessels, diploic veins or dural sinuses. Epidural hematomas of the posterior fossa are more frequently of venous than of arterial origin. Venous epidural hematomas are the most common traumatic space-occupying masses in the posterior fossa (Pozzati et al., 1989).

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Subarachnoid hemorrhage Concomitant subarachnoid hemorrhage is often seen in craniocerebral trauma. In 70% of patients with moderate or severe subarachnoid hemorrhage vasospasms of the basal arteries may complicate the disease (Kassell et al., 1990). In up to 25% of these patients, vasospasm leads to brain infarction, which is associated with poor outcome after head trauma. In a few cases, vasospasm or focal stenosis may be due to atlanto-occipital dislocation without subarachnoid hemorrhage (Lee et al., 1991).

Traumatic vascular lesions Traumatic vascular lesions consist of ruptures of the vessel walls (known as dissection) and of direct vessel damage by penetrating head injuries. Dissection may lead to an occlusion of the artery or embolization and consecutive brain ischemia. Vertebral arteries are more often involved in traumatic dissection than carotid arteries (Reid and Weigelt, 1988; Laitt et al., 1996). Thus, brainstem or cerebellar infarction is more frequent than infarction of supratentorial structures following traumatic artery dissection in neck vessels. Some patients with dissections have pseudoaneurysms with limited rupture into the space surrounding the artery (Leys et al., 1997). Traumatic aneurysms of cerebellar arteries resulting from a skull fracture have also been reported (Morard and de Tribolet, 1991). This rare complication must be suspected when an unusual pattern of subarachnoid hemorrhage is seen on computerized tomography (CT) scan. Fig. 18.1 Brainstem injury. CT scan of a young man with delayed hemorrhage within the pons (open triangle) secondary to head injury associated with brain swelling and subarachnoid hemorrhage. Secondary injury of the brainstem is known as Duret hemorrhage following injury of the perforating arteries of the basilar artery caused by downward herniation. Note right temporal subgaleal hematoma.

Subdural hematoma A subdural hematoma consists of a blood collection caused by traumatic disruption of cerebral veins. It is located between the inner (meningeal) layer of the dura mater and the arachnoid. Subdural hematomas are not always the result of the direct impact in head trauma, because shearing forces also disrupt cerebral veins (Gennarelli and Thibault, 1982). A subdural hematoma within the posterior fossa is the rarest of traumatic brain injuries, accounting for only 0.5% of all intracranial injuries (Miles and Medlery, 1974; Tsai et al., 1980).

Clinical presentation The clinical presentation of patients with traumatic head injury of the posterior fossa depends on: (1) the type of trauma (intra-axial versus extra-axial lesions); (2) the localization of the brain injury (cerebellum and/or brainstem); and (3) accompanying brain injuries (especially concomitant damage to cerebral hemispheres or spinal cord injuries). The severity of the head trauma is determined by the disturbance of consciousness and the loss of brainstem function.

General presentation Patients with posterior fossa trauma complain of headache and exhibit a combination of brainstem and cerebellar deficits. In many cases, the initial clinical picture is dominated by impaired state of consciousness up to coma and

Posterior fossa trauma

Table 18.1 Glasgow Coma Scale Category

Reaction

Score

Eyes open

Spontaneously To command To pain stimuli Absent

4 3 2 1

Motor reaction

Follows commands Localizes stimuli Normal flexor withdrawal Abnormal flexion Extension posture No movement

6 5 4 3 2 1

Oriented Confused Isolated words Inarticulate sounds None

5 4 3 2 1

Verbal reactions

brainstem signs (e.g., cranial nerve deficits, paraparesis or tetraparesis, flaccid areflexia) (Tsai et al., 1980). In all head trauma, the Glasgow Coma Scale (GCS) provides an internationally established assessment tool to quantify the severity of the trauma (Table 18.1; Teasdale and Jennett, 1974). According to this scale, head trauma may be classified into mild (minor), moderate, and severe brain trauma. A mild brain trauma is indicated by 13–15 points on the GCS, a moderate brain trauma by 9–12 points, and a severe brain trauma by 3–8 points (Miller, 1986).

Traumatic brainstem lesions As indicated previously, posterior fossa trauma is frequently associated with moderate to severe disturbances of brainstem functions. The clinical parameters of brainstem dysfunction are pupil size and reaction to light, oculomotor function, best motor response, and alteration of cardiovascular parameters (e.g., blood pressure, heart rate, and respiration). Brainstem lesions may be subdivided into lesions of the diencephalon, midbrain, lower midbrain/rostral pons, and caudal pons/rostral medulla (Table 18.2; Keidel and Miller, 1996).

Traumatic cerebellar lesions The clinical presentation of traumatic lesions of the cerebellum has been described in great detail by Holmes in his classic papers (1917, 1939). Unilateral lesions of the cere-

bellar hemispheres lead to loss of muscle tone and weakness on the ipsilateral side in the acute phase, ipsilateral limb ataxia with decomposition of movements, dysdiadochokinesis, dysmetria, and intention tremor. Patients often report vertigo with rotation to the ipsilateral side. Speech is dysarthric. Ataxia of stance and gait as well as truncal ataxia are present in patients with medial lesions. However, cerebellar symptoms may be overshadowed by changes of consciousness and other brainstem symptoms due to concomitant brainstem injuries in head injuries, as stated above (Tsai et al., 1980).

Hematoma within the posterior fossa In 20–50% of cases, patients with epidural hematoma may show a lucid interval between the time of injury and onset of clinical detoriation (Tsai et al., 1980). Lucid intervals may last from a few seconds to a few days, but usually last a few hours. Vomiting and headaches are frequent in epidural hematoma. Other symptoms and signs result from compression of the cerebellum and brainstem. In adults, a subdural hematoma is commonly accompanied by cerebral contusion and is often an indicator of severe brain injury. In many cases, adult patients with an acute traumatic subdural hematoma are comatose on admission. However, it should be highlighted that in children delayed progressive impairment of consciousness is more common than in adults (Menkes, 1985; Johnson and Faerber, 1995).

Vertebral artery dissection Vertebral artery dissection may occur after a severe or even a minor head and neck trauma, for instance when the head is rapidly rotated. Clinically it is characterized by a sudden cervico-occipital pain on the ipsilateral side, and deficits of brainstem function, which often occur bilaterally (Leys et al., 1997). The most common neurological deficit is an incomplete or complete lateral medullary syndrome (Wallenberg’s syndrome) due to occlusion of the posterior inferior cerebellar artery (Hufnagel et al., 1999). Therefore, neurological examination should specifically look for a unilateral Horner’s syndrome (ptosis, miosis, enophthalmus) and for contralateral loss of pain and temperature sensation.

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Table 18.2 Signs and symptoms of different anatomic levels of brainstem lesions

Diencephalon

Midbrain

Lower midbrain, rostral pons

Caudal pons, rostral medulla

Eupnea, sometimes Cheyne–Stokes type

Cheyne–Stokes type, sometimes hyperpnea and tachypnea

Apneustic breathing with long apnea phases

Ataxic breathing

Pupil size

Narrow

Medium, unrounded shape

Narrow

Narrow

Pupil reaction

Reactive

No reaction

No reaction

No reaction

Oculomotor system

Conjugated, OCR retained

OCR dissociated

OCR dissociated

Absent

Motor system

Resistance, positive plantar responses

Decortication posture

Decerebration posture

Sleep

Breathing

Notes: OCR oculocephalic reflex. Source: Modified from Keidel and Miller (1996).

Imaging Computed tomography and magnetic resonance imaging Computed tomography imaging should be performed first in a patient with an acute head trauma, because of its sensitivity in detecting acute hemorrhage, mass lesions, and diffuse brain swelling, all complications which might require urgent surgical intervention. The short time to run the examination, the practicability of emergency care during the time of examination, and the cost-effectiveness are additional advantages. Scans of high quality are essential (Tsai et al., 1980) and contrast enhancement may be valuable in screening for vascular injury. CT scan is a less reliable method than MRI in the detection of non-hemorrhagic and small contusions or later stages of hematoma in the posterior fossa (Gentry et al., 1988a, 1988b). This is mainly due to beam-hardening streak artefacts, which are caused by the occipital bone. MR evaluation should be done if the patient is stabilized and if the primary CT imaging was not sufficient to explain neurological deficits or a comatose state in a patient with head trauma. The multiplanar capability of MRI is particularly useful in the anatomic localization of lesions (Johnson and Faerber, 1995). MR images should include at least two imaging planes using T1-weighted and T2weighted sequences. T2-weighted images are especially sensitive for the majority of traumatic lesions (Johnson and Faerber, 1995).

Intra-axial lesion Cerebellar injuries: computed tomography findings Presentation of cerebellar contusion on non-contrast CT imaging is an ill-defined hypodense area caused by edema within the cerebellum, and in some cases punctuate hyperdense areas indicating small perifocal hemorrhages. Cerebellar hematoma appears on CT scans as a circumscribed, hyperdense, space-occupying mass within the cerebellum (Gean, 1994; Fig. 18.2). Dissolution of the hematoma leads to a decrease in hyperdensity of the mass. Two to three weeks later, an isodense aspect of the lesion can be found on CT scan. Secondary swelling of the surrounding parenchymal areas may cause obliteration of the basal cisterns located in the posterior fossa, which can be recognized with sequential CT scans. Progressive obliteration of the posterior fossa cisterns indicates additional brainstem injury and carries a poor prognosis (Tsai et al., 1980). Compression of the fourth ventricle and aqueduct may lead to a dilatation of the third and lateral ventricles (i.e., noncommunicating hydrocephalus), which is also reliably detected by sequential CT scans. About one week after the injury, contrast-enhanced CT scan may reveal a ringenhancement surrounding the hematoma, which should not be mistaken for intracerebral neoplasm or abscess.

Cerebellar injuries: magnetic resonance imaging findings Magnetic resonance imaging findings of cerebellar hematoma or contusion depend on the time interval to the primary injury and on the MR sequence used. On T1weighted images a contusion appears as a mild mass effect, whereas T2-weighted images show an ill-defined hyperintense lesion. The signal abnormality on T2-

Posterior fossa trauma

A

B

Fig. 18.2 Cerebellar contusion. CT scans of a 14-year-old girl showing a coup contusion in the cerebellum, and a contrecoup contusion in the frontal cortex. (A) Axial CT scan demonstrating a small hyperdense hematoma of the right cerebellar hemisphere and a smaller left frontobasal hematoma. Both contusions have a small surrounding edema with low attenuation. (B) Bone window reveals an occipital fracture (arrow) and an overlying soft tissue swelling indicating the impact site.

weighted images is the result of an increase of tissue water content within the lesion (i.e., edema). The appearance of hematoma on T1-weighted images or T2-weighted images changes across the days after the primary injury due to changes of the biochemistry of hemoglobin, which is located in the clot of the hematoma. Briefly, the evolution of a hematoma can be divided into five stages, with a different appearance of each stage on MR imaging, as summarized in Table 18.3. Delayed post-traumatic cerebellar hematoma may be suspected by MRI, if the primary CT scan reveals no cerebellar hematoma and a subsequent MRI shows hyperintense parenchymal lesions on T2weighted images in a patient with a severe head trauma (Tanaka et al., 1988). Follow-up CT scans will reveal these hemorrhagic changes in the majority of cases.

Brainstem injuries Before the advent of CT, the diagnosis of brainstem injury was usually made post-mortem. Detection of a hemor-

rhage in acute brainstem contusion on CT scans is possible and seems almost as reliable as on MRI, provided the quality of the image is good (Gean, 1994). Radiological features are not different from those of a cerebellar hematoma, described above. In contrast, brainstem edema is nearly invisible on CT imaging until the edema is signaled by the obliteration of the surrounding cisterns (Tsai et al., 1980). This edema must be distinguished from low-density artefacts. MRI is more sensitive in detecting edema than CT scans.

Diffuse axonal injury Diffuse axonal injury within the posterior fossa is characterized by edematous lesions of the cerebellum and brainstem. CT imaging may also detect punctate hemorrhages. In severe diffuse axonal injury, CT scans may reveal a diffuse hypodensity of the cerebellar hemispheres with ill-defined cerebellar folia and compression of the brainstem and obliteration of the basal cisterns and the fourth ventricle (Fig.

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Table 18.3 Staging of intracerebral hematoma on MRI Stage

Time interval to primary injury

Hemoglobin oxygenation state

T1WI

T2WI

Hyperacute Acute Early subacute Late subacute Chronic

6 hours 6–24 hours Few days Days to weeks Months to years

Oxyhemoglobin Deoxyhemoglobin Methemoglobin Methemoglobin Ferritin/hemosiderin

Dark Isointense Bright Bright Isointense

Bright Dark Dark Bright Dark

Notes: T1WI T1-weighted images; T2WI T2-weighted images. Source: Modified from Gean (1994).

18.3). Frequently, severe axonal injuries of the cerebellum are accompanied by lesions of other regions, most commonly within the cerebral gray–white matter interface, subcortical white matter, corpus callosum, and basal ganglia, which is detectable on MRI (Fig. 18.4). MRI is superior in the detection of non-hemorrhagic lesions, especially with newer imaging techniques like fluid attenuated inversion recovery (FLAIR) imaging (Parizel et al., 1998) or magnetization transfer imaging (McGowan et al., 1999).

A

Extra-axial lesions Epidural hematoma On CT imaging epidural hematoma appears as a high density lesion with a lenticular form (biconvex) (Tsai et al., 1980; Fig. 18.5). An acute epidural hematoma may also present as a heterogeneous mass with both hyperdense and hypodense areas, which might indicate active bleeding (Greenberg et al., 1985). The space-occupying effect of an epidural hematoma may lead to compression of the cerebellum and/or brainstem and obliteration of the basal cisterns. The lucid interval may defer CT examination until a long time after the trauma, so that non-contrast CT may not show the typical hyperdense biconvex aspect (Tsai et al., 1980). Post-contrast CT is sometimes necessary to confirm the presence of the epidural hematoma. On MRI an acute epidural hematoma presents as an isointense mass on T1-weighted image and has a hypointense appearance on T2-weighted image. Compression of brain structures or basal cisterns is also visible on MRI. The subacute and chronic stages of epidural hematoma resemble those of intraparenychmal hematomas, due to change of the biochemistry of hemoglobin (see Table 18.3).

Subdural hematoma On CT imaging, acute subdural hematoma within the posterior fossa appears as a more or less homogeneous hyperdense mass, which is located between the skull and the

B

Fig. 18.3 Infratentorial brain swelling in diffuse axonal injury. A 66-year-old woman presenting with a small right supratentorial subdural hematoma on the right side and diffuse brain swelling (A) CT examination of the posterior fossa revealed severe swelling with effacement of the fourth ventricle and of subarachnoid spaces, probably due to downward herniation. (B) Bone window demonstrates a linear skull fracture (arrow) through the internal occipital protuberance.

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Fig. 18.4 Diffuse axonal injury. Diffuse axonal injury in a child with prolonged coma and normal CT scans. MRI revealed multiple areas of increased signal intensity of the corpus callosum (small arrows) and the upper vermis (closed triangle) on sagittal T2-weighted images (A), and high signal intensity of the vermis (closed triangle) on axial T2-weighted images (B). Callosal lesions are the most common locations of diffuse axonal (shearing) injury, whereas cerebellar lesions are rare. Note hyperintense signal of the right temporal lobe, indicating postcontusional edema – open triangle – on (B).

cerebellum. It is often concavoconvex with tapered ends (Tsai et al., 1980; Peyster and Hoover, 1982). Subdural hematoma can occur without concomitant injury of the cerebellum. Atypical findings on CT scans consist of an isodense or minimally hyperdense presentation of acute subdural hematoma, which has been attributed to anemia, mixture with cerebrospinal fluid, and disseminated intravascular coagulation (Greenberg et al., 1985; Boyko et al., 1991). Traumatic subdural hematoma is usually unilateral in adults and bilateral in children. MRI is superior to CT imaging in the demonstration of small subdural hematomas, because of reduced impact of bone artefacts. On MRI, a typical appearance of acute subdural hematoma is an isointense concavoconvex space-occupying mass on T1-weighted image, with a hypointense feature on T2-weighted image (Fig. 18.6).

Subarachnoid hemorrhage CT scan is more sensitive than MRI to disclose subarachnoid hemorrhage at the acute stage, showing high-density fluid within the cisterns and sulci, around the falx of cerebellum or in ventricles.

Traumatic vascular lesions Traumatic dissections of the vertebral arteries are a cause of ischemic infarction of the cerebellum and/or brainstem (Fig. 18.7A). CT scans may detect cerebellar infarction, but MRI is clearly superior to CT in the detection of brainstem infarction (Gean, 1994). MRI may show the intramural hematoma and narrowing of the lumen of the artery on T2weighting. Vessel occlusion or pseudoaneurysm may be demonstrated using MR angiography (Friedman et al., 1995). If a dissection of one or both vertebral arteries is clinically suspected in a patient with traumatic head injury or whiplash injury, and if the results of MRI and/or Doppler sonography of the arteries remain unclear, intra-arterial angiography of the neck vessels should be performed (Fig. 18.7B). Conventional angiography still remains the gold standard, although its role will probably decline in the future (Leys et al., 1997).

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Fig. 18.5 Epidural hematoma of the posterior fossa. A 23-year-old male patient admitted with a longitudinal fracture (closed triangles) of the right temporal bone extending into the sulcus of sigmoid sinus (A) on axial CT scans with bone window. (B) Soft tissue window reveals a biconvex high-attenuation collection representing epidural hematoma (open arrow) of the posterior fossa. (C) Unlike a subdural hematoma, an epidural hematoma can extend above the tentorium and to the supratentorial space.

Positron emission tomography and single photon emission tomography Single photon emission computed tomography (SPECT) and positron emission tomography (PET) are more sensitive than CT or MRI in the detection of brain abnormalities in patients with mild or moderate traumatic brain injury. Even in patients with normal CT or MRI, areas of hypoperfusion and hypometabolism may be detected. These are commonly localized within the basal ganglia and thalami, frontal and temporal lobes, regardless of impact site (Ruff et al., 1994; Abdel-Dayem et al., 1998). Supratentorial lesions are frequently accompanied by a depression of metabolism and blood flow in the contralateral cerebellar hemisphere. This is termed ‘crossed

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Fig. 18.6 Bilateral subdural hematoma of the posterior fossa. (A) Axial non-contrast MRI of an infant showing subdural hematomas overlying both cerebellar hemispheres with fluid–fluid levels (the so-called ‘hematocrit effect’). This is explained by sedimentation of erythrocytes with high signal intensity on T1-weighted image (arrows), whereas supernatant fluid represents serum and has low signal intensitity (asterisks). (B) On T2-weighted image the dependent parts of the hematoma are dark (arrows), whereas the serum is bright and remains isointense to CSF. Hematoma with high signal on T1-weighted image and low signal on T2-weighted image suggest intracellular methemoglobin.

cerebellar diaschisis’ and was first been shown using PET by Baron et al. (1980) in patients with supratentorial infarction. ‘Crossed cerebellar diaschisis’ may also be detected by SPECT (Feeney and Baron, 1986; Kim et al., 1997), and has been shown in patients with focal traumatic head injury (Alavi et al., 1997). The clinical significance of crossed cerebellar diaschisis remains unclear. Patients do not exhibit cerebellar deficits in most of the cases. The correlation with outcome is not established either.

Pathophysiology Traumatic brain lesions damage tissue directly and indirectly and are mostly accompanied by post-traumatic brain edema. Besides morphologically apparent direct mechanical axonal and neuronal injuries, there are progressive events in the minutes and hours after the trauma: release of free oxygen radicals, lipid peroxidation of cell membranes, opening of ion channels to calcium influx, release of cytokines, and synthesis of vasoreactive substances (Miller, 1997). Metabolic changes are likely to be involved in the extension of the lesions after the trauma. The turnover of catecholamines (e.g., norepinephrine) increases in the first 30

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Fig. 18.7 Dissection of the vertebral artery. (A) Infarction of the cerebellum in postero-inferior cerebellar artery (PICA) territory (arrows) detected by MRI following dissection of the left vertebral artery, which is shown by angiography in (B). Note the irregularity of the vessel wall and consecutive arterial occlusion (arrow) in (B).

minutes in and around the site of brain injury after head trauma, and decreases over the next 6–24 hours (DunnMeyenell et al., 1994; Levin et al., 1995). The early increase in catecholamine turn-over seems to be protective, maybe due to stabilizing of the blood–brain barrier, whereas the later decline in function might impede recovery of function (Dunn-Myenell et al., 1998). Interestingly, noradrenergic agonists given 24 hours after traumatic brain injury accelerate the recovery of function in rats (Sutton and Feeney, 1992). There are several reports that have shown a close link of endothelin elevation after traumatic brain injury to cerebral vasospasm and oxidative stress leading to an increase in lesion size (Armstead, 1996). Substances showing antagonistic activity to the endothelin receptors and given postinjury attenuate cortical neuronal injury, but do not prevent delayed Purkinje cell death in the cerebellum (Sato and Noble, 1998). The cerebellum, and, especially, the Purkinje cells show distinct subcellular and cellular responses to traumatic

brain injury. Recent studies revealed a special vulnerability of Purkinje cells of the vermis to lateral and midline percussion brain injury in rats. This may be a consequence of alterations in the local environment triggered by disturbances of the blood–brain barrier, excitotoxicity (toxicity to enhanced excitation of neurons mediated by glutamate), and/or cytotoxic cytokines or molecules like nitric oxide (Mautes et al., 1996). Survival of neurons after traumatic brain injury depends on trophic support by neurotrophins such as nerve growth factor. The neurotrophic effects of nerve growth factor are mediated by cell receptors. In normal adults, only a few cerebellar Purkinje cells display nerve growth factor receptors. Interestingly, experimental traumatic cerebellar injury induces a re-expression of nerve growth factor receptors in the cerebellum, which is restricted to Purkinje cells (Martinez-Murillo et al., 1998). These receptors might be involved in the enhancement of repair processes and plasticity. Repair processes after traumatic cerebellar

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injury are also mediated by hormonal systems such as the cerebellar renin–angiotensin system. Angiotensin II levels increase in the astroglia around a cerebellar lesion as a result of a traumatic injury (Lippoldt et al., 1994). Given the fact that angiotensin II was shown to induce the expression and secretion of nerve growth factor in cultured cells (Creedon and Tuttle, 1991), the role of the cerebellar renin–angiotensin system in repair processes after posterior fossa trauma deserves further studies

Management The principles of first management of patients with posterior fossa trauma are similar to those applied in patients with supratentorial traumatic brain lesions. There are three priorities: (1) the control of vital functions, (2) the control of raised intracranial pressure, and (3) the relief of space-occupying lesions. The primary goals are the early limitation of primary brain damage and the prevention of secondary brain injuries (Miller, 1997).

1996). The intracranial pressure should be maintained below 25 mmHg. A prime objective of monitoring headinjured patients with severe trauma is to measure the cerebral perfusion pressure (CPP) – CPP blood pressure (BP)  ICP – and the level of arterial oxygenation. Cerebral perfusion pressure should be maintained at 60 mmHg. Commonly, the management of elevated intracranial pressure includes hyperventilation (which results in a reduction of cerebral blood volume) (Grant et al., 1989), administration of osmotic agents (mannitol), diuretics (Pickard and Czosnyka, 1993), and hypnotic agents (such as barbiturates, which act as metabolic depressants) (Piatt and Schiff, 1984; Chesnut and Marshall, 1993). Drainage of cerebrospinal fluid is indicated in patients with development of occlusive hydrocephalus. Moreover, in patients with profound brain edema and elevated intracranial pressure that is not treatable by conservative therapeutic approaches, surgical decompression is recommended (Miller, 1993). There is no place for steroid therapy in head trauma (Miller, 1997).

Relief of space-occupying lesions Control of vital functions First, patients with head trauma have to be evacuated carefully from the accident site, with the avoidance of movements of the cervical spine until spinal injury has been excluded. For the same reason, the helmets of motorcyclists have to be removed very cautiously. The next step is clearance of the upper airways and immediate intubation of patients with prolonged unconsciousness. Blood pressure and heart frequency have to be monitored continuously. Intravenous colloid or crystalloid fluids are administered if the blood pressure drops. Further decreases of blood pressure should be treated by the intravenous administration of catecholamines (Keidel and Miller, 1996). Immediately after stabilization of the vital parameters at the accident site, the patient should be admitted to an intensive care unit or a special trauma unit if available. After admission, a CT examination of the head and cervical spine is performed in order to exclude intracranial or spinal lesions, which may require immediate surgical treatment. It is also crucial at this point to determine all the injuries outside the nervous system.

Control of intracranial pressure In patients with severe head injury, the intracranial pressure (ICP) should be monitored continuously using an intraventricular catheter or extraventricular fluid couple system (subarachnoid screw) (von Rosen and Guazzo,

The treatment of an epidural hematoma of the posterior fossa is surgical evacuation. Alternatively, careful clinical monitoring and repeated CT scans may be used in a few cases with very small epidural hematomas in the absence of compression of the cerebellum and/or brainstem and slight obliteration of basal cisterns. Subdural hematomas within the posterior fossa have to be removed immediately by the neurosurgeon (Marshall, 1990). The treatment of intra-axial cerebellar or brainstem hematomas is more variable. The decision about whether operative evacuation of a hematoma should be undertaken depends on the localization and size of the hematoma, secondary brain lesions, and the extension of the hematoma on repeated CT scans. There are no defined criteria for the time point of the surgical intervention (Soloniuk et al., 1990). However, surgery of cerebellar hematomas is considered if the patient deteriorates clinically, or when compression of the brainstem is visible and there is increasing obliteration of the basal cisterns. In contrast, brainstem hematoma is not treatable by surgery, because of potential irreversible damage of essential structures within the brainstem. After surgical removal of epidural, subdural, and large cerebellar hematomas, and in patients with a primary severe head trauma without visible intracranial lesions, repeated CT scans are often required to detect rebleeding, delayed intraparenchymal hematoma, or diffuse brain swelling.

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Vertebral artery dissection Anticoagulation with intravenous heparin is recommended in the case of dissection of the vertebral artery to prevent further thrombus propagation and thromboembolism. However, hemorrhagic infarcts and subarachnoid hemorrhage from intradural dissection are considered by many authors as relative contraindications. Warfarin is subsequently administered for a period of one to three months (Leys et al., 1997). The natural history of extracranial residual aneurysms is to resolve or to improve and, when they persist, they never rupture. Therefore, there is no rationale for an invasive approach (Leys et al., 1997). Antiplatelet agents are usually given in the case of residual aneurysm. By contrast, the natural history of traumatic intracranial aneurysm is unpredictable. The high mortality rate and the possibility of efficient surgery make surgical treatment mandatory.

Long-term complications This section focuses on four recently recognized long-term complications of head trauma, particularly involving the cerebellum and its major connections with the brainstem.

‘Delayed-onset cerebellar syndrome,’ ‘delayed-onset intention tremor,’ and ‘rubral tremor’ A minority of patients with moderate or severe head trauma develop cerebellar features between three weeks and two years after the initial head trauma. This syndrome is called ‘delayed-onset’ or ‘post-traumatic-delayed cerebellar syndrome’ (Louis et al., 1996). Symptoms consist of nystagmus, dysarthria, limb ataxia including intention tremor, dysmetria, dysdiadochokinesis, and ataxia of gait. In a few patients, this syndrome may be progressive. Some patients with mild or moderate traumatic brain injury and normal CT scans or MRI develop ‘delayed-onset intention tremor’ without other cerebellar signs and symptoms (Iwadate et al., 1989). The topographic distribution of primary lesions is not uniform, but most lesions are localized within the thalamus and brainstem. Both ‘delayed-onset cerebellar syndrome’ and ‘delayedonset intention tremor’ are thought to be caused by disruption of cerebellar outflow pathways, particularly the cerebello-rubro-thalamic tract and the cerebello-rubroolivary pathway (Larochelle et al., 1970; Iwadate et al., 1989; Louis et al., 1996). The syndromes might be due to post-traumatic postsynaptic supersensitivity or secondary reorganization of involved pathways (Louis et al., 1996).

There might be a shared pathophysiology with the posttraumatic midbrain tremor (‘rubral tremor’), characterized clinically by rest, postural and kinetic oscillations, which also begins typically weeks or months after the brainstem trauma. A continuum between ‘delayed-onset cerebellar syndrome,’ ‘delayed-onset intention tremor,’ and midbrain tremor is possible. Some patients may experience slight to moderate reduction of the tremor following administration of clonazepam. Furthermore, stereotactic surgery (e.g., thalamotomy) can partly alleviate the post-traumatic tremor. This technique should be used in selected cases only.

‘Crossed cerebellar atrophy’ Atrophy of the contralateral cerebellar hemisphere has been described in patients with traumatic cerebral lesions years after the initial lesion (Baudrimont et al., 1983; Chung, 1985; Tien and Ashdown, 1992; Verstichel et al., 1993). ‘Crossed cerebellar atrophy’ might be caused by anterograde degeneration of the cortico-ponto-cerebellar tract or by retrograde trans-synaptic degeneration of the cerebello-rubro-thalamic tract (Chung, 1985; Tien and Ashdown, 1992). Likewise, atrophy has been found in the red nucleus ipsilateral to the primary cerebral lesion, in the contralateral superior cerebellar peduncle, and in the contralateral dentate nucleus (Chung, 1985; Tien and Ashdown, 1992), all parts of the cerebello-rubro-thalamic tract (Marchi, 1891). Like ‘crossed cerebellar diaschisis,’ it is unclear whether ‘crossed cerebellar atrophy’ leads to clinical symptoms of cerebellar dysfunction (Tien and Ashdown, 1992).

Olivary hypertrophy Olivary hypertrophy, also called pseudohypertrophy, is thought to be a consequence of lesions within the dentatorubro-olivary pathway (Guillain–Mollaret triangle). The lesions are usually of traumatic, vascular, inflammatory, infectious or neoplastic origin. Clinically, it is commonly associated with palatal tremor (synonyms: palatal myoclonus, palatal myorhythmia) made of rhythmic involuntary movements of the soft palate at a frequency of 0.5–3 Hz (Elble, 1997). Symptomatic palatal tremor is frequently associated with brainstem deficits or cerebellar signs. Other segmental myoclonias, such as ‘wing beating’ in upper extremities, may be present. Furthermore, symptomatic palatal tremor persists during sleep, unlike the essential form (essential palatal tremor). Annoying ear clicking is frequent in the latter, but rare in the former (Elble, 1997).

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Unilateral or bilateral enlargement and signal abnormalities of the inferior olivary nucleus are detected by MRI in up to 10–39% of patients with intra-axial lesions within the cerebellum and brainstem due to head trauma (Birbamer et al., 1994; Deuschl et al., 1994; Kawata et al., 1996). The changes are usually more significant in proton density weighted images than in T2-weighted images (Birbamer et al., 1994). The abnormal signals in inferior olives should not be overlooked or misinterpreted as primary traumatic lesions. When unilateral olivary hypertrophy is seen on MRI, palatal tremor and cerebellar signs are contralateral. The time interval between the occurrence of trauma and the detection of olivary hypertrophy varies between four weeks and several years. A disturbance of the electrotonic coupling between cells in inferior olives has been proposed (Deuschl et al., 1994). These cells normally discharge with a firing frequency of about 2 Hz. Botulinum toxin may be useful to resolve the tremor.

Superficial siderosis Superficial siderosis of the central nervous system is characterized by deposition of hemosiderin on the leptomeninges on the surface of the forebrain, cerebellum, brainstem, cranial nerves, and spinal cord (Noetzel, 1940). Most cases of superficial siderosis are due to repeated hemorrhages from tumors, vascular malformations or subdural hematomas, but recent studies also found superficial siderosis in patients with former head trauma (Bracchi et al., 1993). The main clinical manifestations are cerebellar signs associated with progressive bilateral hearing loss. CT imaging may show cerebellar atrophy and enlargement of the basal cisterns. MRI is superior in the detection of superficial siderosis due to the paramagnetic effect of hemosiderin, which appears as a hypointense rim around the cerebellum and cranial nerves on T2-weighted images (Fig. 18.8; Bracchi et al., 1993). The pathophysiology is explained in Chapter 17). Experimental therapy consists of the application of iron-chelating agents, but there are no studies demonstrating beneficial effects on clinical deficits.

Rehabilitation Patients who survive moderate or severe head trauma should be referred to a rehabilitation care unit after acute management, in order to improve their performance of activities of daily living. Therapeutic motor training may increase mobility. Residential-based services appear to

Fig. 18.8 Superficial siderosis of brainstem and cerebellum. Axial non-contrast MRI with deposition of hemosiderin on the leptomeninges on the surface of the cerebellum (open arrow), brainstem (closed arrow), and cranial nerves as shown by T2weighted images.

produce greater functional improvement, whereas homebased services are more effective in maintaining community integration (Willer et al., 1999). Whether special training techniques improve cerebellar symptoms after head injury remains unclear, because of the lack of controlled clinical studies. Some improvement of postural stability after postural training has been reported in patients with cerebellar dysfunction (Gill-Body et al., 1997; Horak et al., 1997). Thus, in brain-injured patients, intense physical therapy might result in favorable plastic neuronal changes and, therefore, a better outcome.

Conclusion Trauma in posterior fossa should be recognized immediately to allow early medical and surgical intervention.

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Delay in diagnosis may result in subsequent fatal brainstem injury. Thorough and repeated clinical examination is essential. The three priorities of treatment are control of vital functions, management of raised intracranial pressure, and evacuation of space-occupying lesions. Specific long-term complications of traumatic lesions of the cerebellar outflow pathways have been recognized, including ‘delayed-onset cerebellar syndrome,’ ‘rubral tremor,’ and ‘crossed cerebellar atrophy.’ Olivary hypertrophy with symptomatic palatal tremor may occur following lesions of the dentato-rubro-olivary pathway.

xReferencesx Abdel-Dayem, H.M., Abu-Judeh, H., Kumar, M. et al. (1998). SPECT brain perfusion abnormalities in mild or moderate traumatic brain injury. Clin Nucl Med 23: 309–17. Adams, J.H., Graham, D.I., Murray, L.S. and Scott, G. (1982). Diffuse axonal injury due to non-missile head injury in humans: an analysis of 45 cases. Ann Neurol 12: 557–63. Alavi, A., Mirot, A., Newberg, A. et al. (1997). Fluorine-18-fDG evaluation of crossed cerebellar diaschisis in head injury. J Nucl Med 38: 1717–20. Armstead, W.M. (1996). Role of endothelin in pial vasoconstriction and altered responses to vasopressin after brain injury. J Neurosurg 85: 901–7. Baron, J.C., Bousser, M.G., Comar, D. and Castaigne, P. (1980). ‘Crossed cerebellar diaschisis’ in human supratentorial infarction. Trans Am Neurol Assoc 105: 459–61. Baudrimont, M., Gray, F., Meininger, V., Escourolle, R. and Castaigne, P. (1983). Crossed cerebellar atrophy following hemispheric lesions occurring in adulthood. Rev Neurol (Paris) 139: 485–95. Billmire, M.E. and Myers, P.A. (1985). Serious head injury in infants: accident or abuse? Pediatrics 75: 340–2. Birbamer, G., Gerstenbrand, F., Aichner, F. et al. (1994). MRimaging of post-traumatic olivary hypertrophy. Funct Neurol 9: 183–7. Boyko, O.B., Cooper, D.F. and Grossman, C.B. (1991). Contrastenhanced CT of acute isodense subdural hematoma. Am J Neuroradiol 12: 341–3. Bracchi, M., Savoiardo, M., Triulzi, F. et al. (1993). Superficial siderosis of the CNS: MR diagnosis and clinical finding. Am J Neuroradiol 14: 227–36. Chesnut, R.M. and Marshall, L.F. (1993). Management of severe head injury. In Neurological and Neurosurgical Intensive Care, ed. A.H. Ropper, pp. 203–46. New York: Raven Press. Chung, H.D. (1985). Retrograde crossed cerebellar atrophy. Brain 108: 881–95. Corsellis, J.A., Bruton, C. and Browne, D.F. (1973). The aftermatch of boxing. Psychol Med 3: 270–303.

Creedon, D. and Tuttle, J.B. (1991). Nerve growth factor synthesis in vascular smooth muscle. Hypertension 18: 730–41. Deuschl, G., Toro, C., Valls-Sole, J., Zeffiro, T., Zee, D.S. and Hallett, M. (1994). Symptomatic and essential palatal tremor. 1. Clinical, physiological and MRI analysis. Brain 117: 775–88. Dunn-Meyenell, A.A., Hassanain, M. and Levin, B.E. (1998). Norepinephrine and traumatic brain injury: a possible role in post-traumatic edema. Brain Res 800: 245–52. Dunn-Meyenell, A., Pan, S. and Levin, B.E. (1994). Focal traumatic brain injury causes widespread reductions in rat brain norepinephrine turnover from 6 to 24 hours. Brain Res 660: 88–95. Elble, R.J.(1997). The pathophysiology of tremor. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 405–17. New York: McGraw-Hill,. Feeney, D.M. and Baron, J.C. (1986). Diaschisis. Stroke 17: 817–30. Firsching, R., Woischneck, D., Diedrich, M. et al. (1998). Early magnetic resonance imaging of brainstem lesions after severe head injury. J Neurosurg 89: 707–12. Fisher, R.G., Kim, J.K. and Sachs, E. (1958). Complications in posterior fossa due to occipital trauma, and their operability. J Am Med Assoc 167: 176–82. Friedman, D., Flanders, A., Thomas, C. and Millar, W. (1995). Vertebral artery injury after acute cervical spine trauma: rate of occurrence as detected by MR angiography and assessment of clinical consequences. Am J Roentgenol 164: 443–7. Gean, A.D. (1994). Imaging of Head Trauma. New York: Raven Press. Gennarelli, T.A. (1982). Cerebral concussion and diffuse brain injuries. In Head Injuries, ed. P.R. Cooper PR, pp. 83–97. Baltimore: Williams and Wilkins. Gennarelli, T.A. and Thibault, L.E. (1982). Biomechanics of acute subdural hematoma. J Trauma 22: 680–6. Gentry, L.R., Godersky, J.C. and Thompson, B. (1988a). MR imaging of head trauma: review of the distribution and radiologic features of traumatic lesions. Am J Roentgenol 150: 663–72. Gentry, L.R., Godersky, J.C., Thompson, B. and Dunn, V.D. (1988b). Prospective comparative study of intermediate-field MR and CT in the evaluation of closed head trauma. Am J Roentgenol 150: 673–82. Gentry, L.R., Godersky, J.C. and Thompson, B.H. (1989). Traumatic brainstem injury: MR imaging. Radiology 171: 177–87. Gill-Body, K.M., Popat, R.A., Parker, S.W. and Krebs, D.E. (1997). Rehabilitation of balance in two patients with cerebellar dysfunction. Phys Ther 77: 534–52. Goldstein, M. (1990). Traumatic brain injury: a silent epidemic. Ann Neurol 27: 327. Grant, R., Condon, B., Patterson, J., Wyper, D.J., Hadley, M.D.M. and Teasdale, G.M. (1989). Changes in cranial CSF volume during hypercapnia and hypocapnia. J Neurol Neurosurg Psychiatry 52: 218–22. Greenberg, J., Cohen, W.A. and Cooper, P.R. (1985). The ‘hyperacute’ extra-axial intracranial hematoma: computed tomography findings and clinical significance. Neurosurgery 17: 48–56. Gudeman, S.K., Kishore, P.R., Miller, J.D., Girevendulis, A.K., Lipper, M.H. and Becker, D.P. (1979). The genesis and significance of

Posterior fossa trauma

delayed traumatic intracerebral hematoma. Neurosurgery 5: 309–13. Holmes, G. (1917). The symptoms of acute cerebellar injuries due to gunshot injuries. Brain 40: 461–535. Holmes, G. (1939). The cerebellum of man (Hughlings Jackson Memorial Lecture). Brain 62: 1–30. Horak, F.B., Henry, S.M. and Shumway-Cook, A. (1997). Postural perturbations: new insights for treatment of balance disorders. Phys Ther 77: 517–33. Hufnagel, A., Hammers, A., Schönle, P.W., Böhm, K.D. and Leonhardt, G. (1999). Stroke following chiropractic manipulation of the cervical spine. J Neurol 246: 683–8. Iwadate, Y., Saeki, N., Namba, H., Odaki, M., Oka, N. and Yamaura, A. (1989). Post-traumatic intention tremor: clinical features and CT findings. Neurosurg Rev 12(Suppl .1): 500–7. Jane, J.A., Steward, O. and Gennarelli, T. (1985). Axonal degeneration induced by experimental non-invasive minor head injury. J Neurosurg 62: 96–100. Johnson, J. (1969). Organic psychosyndromes due to boxing. Br J Psychiatry 115: 45–53. Johnson, M.H. and Faerber, E.N. (1995). Trauma. In CNS Magnetic Resonance Imaging in Infants and Children, pp. 98–115. Mac Keith Press. Kalsbeek, W.D., McLaurin, R.L., Harris, B.S. and Miller, J.D. (1980). The National Head and Spinal Cord Injury Survey: major findings. J Neurosurg 53: S19–31. Kassell, N.F., Torner, J.C., Haley, E.C., Jane, J.A., Adams, H.P. and Kongable, G.L. (1990). The International Cooperative Study on the Timing of Aneurysm Surgery. Part 1: overall management results. J Neurosurg 73: 18–36. Kawata, Y., Suzuki, T., Kagaya, H., Omi ,R., Shiroto, H. and Ebina, K. (1996). An MRI analysis of brain-stem and cerebellar lesions and olivary hypertrophy. Neuroradiology 38: 441–3. Keidel, M. and Miller, J.D. (1996). Head trauma. In Neurological Disorders, ed. T. Brandt, L.R. Caplan, J. Dichgans, H.C. Diener and C. Kennard, pp. 531–44. San Diego: Academic Press. Kim, S.E., Choi, C.W., Yoon, B.W. et al. (1997). Crossed-cerebellar diaschisis in cerebral infarction: technetium-99m-HMPAO SPECT and MRI. J Nucl Med 38: 14–19. Klintworth, G.K. (1968). Paratentorial grooving of human brains with particular reference to transtentorial herniation and the pathogenesis of secondary brainstem hemorrhages. Am J Pathol 53: 391–408. Knuckey, N.W., Gelbard, B. and Epstein, M.H. (1989). The management of ‘asymptomatic’ epidural hematomas: a prospective study. J Neurosurg 70: 392–6. Kraus, J.F., Morgenstern, H., Fife, D., Conroy, C. and Nourjah, P. (1989). Blood alcohol test, prevalence of involvement and outcomes following brain injury. Am J Public Health 79: 294–9. Laitt, R.D., Lewis, T.T. and Bradshaw, J.R. (1996). Blunt carotid arterial trauma. Clin Radiol 51: 117–22. Larochelle, L., Bedard, P., Boucher, R. and Poirier, L.J. (1970). The rubro-olivo-cerebello-rubral loop and postural tremor in the monkey. J Neurol Sci 11: 53–64. Lee, C., Woodring, J.H. and Walsh, J.W. (1991). Carotid and verte-

bral artery injury in survivors of atlanto-occipital dislocation: case reports and literature review. J Trauma 31: 401–7. Levin, B.E., Brown, K.L., Pawar, G. and Dunn-Meynell, A. (1995). Widespread and lateralized effects of acute traumatic brain injury on norepinephrine turnover in the rat brain. Brain Res 674: 307–13. Levin, H.S., Mattis, S., Ruff, R.M. et al. (1987). Neurobehavorial outcome following minor head injury. J Neurosurg 66: 234–43. Leys, D., Lucas, C., Gobert, M., Deklunder, G. and Pruvo, J-P. (1997). Cervical artery dissections. Eur Neurol 37: 3–12. Lippoldt, A., Bunnemann, B., Ueki, A. et al. (1994). On the plasticity of the cerebellar renin–angiotensin system: localization of components and effects of mechanical perturbation. Brain Res 668: 144–59. Louis, E.D., Lynch, T., Ford, B., Greene, P., Bressman, S.B. and Fahn, S. (1996). Delayed-onset cerebellar syndrome. Arch Neurol 53: 450–4. Luna, G., Maier, R., Sowder, L., Copass, M. and Oreskovich, M. (1984). The influence of ethanol intoxication on outcome of injured motorcyclists. J Trauma 24: 695–700. Marchi, V. (1891). Sull’Origine e Decorso dei Peduncoli e sui loro Rapporti cogli altri Centri Nervosi. Florence: Le Monnier. Marshall, L.F. (1990). Surgical treatment of extracerebral lesions in head injury. In Craniospinal Trauma, ed. L.H. Pitts and F.C. Wagner, pp. 37–48. New York: Thieme. Martinez-Murillo, R., Fernandez, A.P., Bentura, M.L. and Rodrigo, J. (1998). Subcellular localization of low-affinity nerve growth factor receptor–immunoreactive protein in adult rat Purkinje cells following traumatic injury. Exp Brain Res 119: 47–57. Mautes, A.E.M., Fukuda, K. and Noble, L.J. (1996). Cellular response in the cerebellum after midline traumatic brain injury in the rat. Neurosci Lett 214: 95–8. McGowan, J.C., McCormack, T.M., Grossman, R.I. et al. (1999). Diffuse axonal pathology detected with magnetization transfer imaging following brain injury in the pig. Magn Reson Med 41: 727–33. Menkes, J.H. (1985). Textbook of Child Neurology. Philadelphia: Lea and Febiger. Miles, J. and Medlery, A.V. (1974). Posterior fossa subdural haematomas. J Neurol Neurosurg Psychiatry 37: 1373–7. Miller, J.D. (1986). Minor, moderate and severe head injury. Neurosurg Rev 9: 135–9. Miller, J.D. (1993). Head injury. J Neurol Neurosurg Psychiatry 56: 440–7. Miller, J.D. (1997). Head injury. In Neurological Emergencies, ed. R.A.C. Hughes, pp. 29–49. London: British Medical Group. Morard, M. and de Tribolet, N. (1991). Traumatic aneurysm of the posterior inferior cerebellar artery: case report. Neurosurgery 3: 438–41. Noetzel, H. (1940). Diffusion von Blutfarbstoff in der inneren Randzone und äusseren Oberfläche des Zentralnervensystems bei subarachnoidaler Blutung. Arch Psychiatr 111: 120–38. Ommaya, A.K. and Gennarelli, T.A. (1974). Cerebral concussion and traumatic unconsciousness. Correlation of experimental and clinical observations on blunt head injuries. Brain 97: 633–54.

303

304

M. Maschke, U. Dietrich, and D. Timmann-Braun

Parizel, P.M., Ozsarlak, G., Van Goethem, J.W. et al. (1998). Imaging findings in diffuse axonal injury after closed head trauma. Eur Radiol 8: 960–5. Peyster, R.G. and Hoover, E.D. (1982). CT in head trauma. J Trauma 22: 25–38. Piatt, J.H. and Schiff, S.J. (1984). High dose barbiturate therapy in neurosurgery and intensive care. Neurosurgery 15: 427–44. Pickard, J.D. and Czosnyka, M. (1993). Management of raised intracranial pressure. J Neurol Neurosurg Psychiatry 56: 845–58. Pozzati, E., Tognetti, F., Cavallo, M. and Acciarri, N. (1989). Extradural hematomas of the posterior cranial fossa. Observations on a series of 32 consecutive cases treated after the introduction of computed tomography scanning. Surg Neurol 32: 300–3. Reid, J.D. and Weigelt, J.A. (1988). Forty-three cases of vertebral artery trauma. J Trauma 28: 1007–12. Rivara, F.P., Dicker, B.G., Bergman, A.B., Dacey, R. and Herman, C. (1988). The public cost of motorcycle trauma. J Am Med Assoc 260: 221–3. Ruff, R.M., Crouch, J.A., Troster, A.I. et al. (1994). Selected cases of poor outcome following a minor brain trauma: comparing neuropsychological and positron emission tomography assessment. Brain Inj 8: 297–308. Sato, M. and Noble, L.J. (1998). Involvement of the endothelin receptor subtype A in neural pathogenesis after traumatic brain injury. Brain Res 809: 39–49. Soloniuk, D.S., Aldrich, E.F. and Eisenberg, H.M. (1990). Traumatic intra-cerebral hematomas. In Craniospinal Trauma, ed. L.H. Pitts and F.C. Wagner, pp. 49–58. New York: Thieme. Sutton, R.L. and Feeney, D.M. (1992). Alpha-noradrenergic ago-

nists and antagonists affect recovery and maintenance of beamwalking ability after sensorimotor cortex ablation in the rat. Restor Neurol Neurosci 4: 1–11. Tanaka, T., Sakai, T., Uemura, K., Teramura, A., Fujishima, I. and Yamamoto, T. (1988). MR imaging as predictor of delayed posttraumatic cerebral hemorrhage. J Neurosurg 69: 203–9. Teasdale, G. and Jennett, B. (1974). Assessment of coma and impaired consciousness. A practical scale. Lancet 2: 81–4. Tien, R.D. and Ashdown, B.C. (1992). Crossed cerebellar diaschisis and crossed cerebellar atrophy: correlation of MR findings, clinical symptoms, and supratentorial diseases in 26 patients. Am J Roentgenol 158: 1155–9. Tsai, F.Y., Teal, J.S., Itabashi, H.H., Huprich, J.E., Hieshima, G.B. and Segall, H.D. (1980). Computed tomography of posterior fossa trauma. J Comp Assist Tomogr 4: 291–305. Vaughan, V.C. (1983). History of pediatrics. In Nelson Textbook of Pediatrics, 12th edn., ed. R.E. Behrman and V.C. Vaughan, pp. 1–4. Philadelphia: W.B. Saunders. Verstichel, P., Servan, J. and Cohen, L. (1993). Post-traumatic crossed cerebellar atrophy. Rev Neurol (Paris) 149: 491–3. Von Rosen, F. and Guazzo, E.P. (1996). Increased intracranial pressure. In Neurological Disorders, ed. T. Brandt, L.R. Caplan, J. Dichgans, H.C. Diener and C. Kennard, pp. 521–9. San Diego: Academic Press. Willer, B., Button, J. and Rempel, R. (1999). Residential and homebased rehabilitation of individuals with traumatic brain injury: a case control study. Arch Phys Med Rehabil 80: 399–406. Zimmerman, R.A. (1991). Head injury. Curr Opin Neurol Neurosurg 4: 864–6.

19

Thyroid hormone and cerebellar development Noriyuki Koibuchi Department of Physiology, Gunma University School of Medicine, Maebashi, Japan

The important role of thyroid hormone (-triiodothyronine, T3; -tetraiodothyronine, T4) in the growth and differentiation of many organs, including the central nervous system, is well known (Legrand, 1986; Oppenheimer and Schwartz, 1997). In particular, the development of the rodent cerebellum is severely affected by perinatal hypothyroidism (Legrand, 1979; Koibuchi and Chin, 1999). Although the mechanism of thyroid hormone action on cerebellar development is not fully understood, recent studies have provided new insights into its molecular mechanisms in this process.

Molecular mechanisms of thyroid hormone action: a general overview Thyroid hormone exerts its major effect by binding to the nuclear thyroid hormone receptor, a ligand-regulated transcription factor (Chin and Yen, 1997), although thyroid hormone action at non-genomic sites such as mitochondria, plasma membrane, and cytoplasm has also been reported (Davis and Davis, 1997). Figure 19.1 shows the mechanism of thyroid hormone action at the nuclear level. Thyroid hormone receptor is bound to specific DNA sequences known as thyroid hormone-response elements. When thyroid hormone receptor binds to thyroid hormone response element, it interacts with retinoid X receptors to form heterodimers, which, in turn, bind to a number of coregulators such as corepressors and coactivators. The liganded thyroid hormone receptor/retinoid X receptor/coregulator complex ultimately determines nuclear thyroid hormone action (Chin and Yen, 1997). Nuclear thyroid hormone receptors are encoded by two genomic loci (alpha and beta). Each thyroid hormone receptor gene produces two variants as a result of alternative splicing and different promoter usage (Lazar, 1993).

Thyroid hormone receptor alpha gene produces thyroid hormone receptor alpha1 and c-erbA alpha2, whereas thyroid hormone receptor beta gene produces thyroid hormone receptor beta1, and beta2 (Fig. 19.2). Thyroid hormone receptor alpha1, beta1, and beta2 act as authentic thyroid hormone receptors because they bind thyroid hormone and transactivate transcription. In contrast, c-erbA alpha2 and related variants do not bind thyroid hormone, cannot activate transcription, and might act as antagonists of the thyroid hormone receptors. T3, an active compound of thyroid hormone, is produced locally in the brain by the 5-deiodination from T4, which enters the developing brain more easily than T3 (Calvo et al., 1990). Type II iodothyronine 5-deiodinase (D2), which is abundant in the brain (Croteau et al., 1996), plays a major role in its conversion (Leonard et al., 1981). Recent data showing a high expression of D2 in glial cells (Guadaño-Ferraz et al., 1997) have indicated the possibility that T4 is taken up from capillaries by astrocytes, deiodinated to T3, and transferred to neurons by direct cell–cell interactions to associate with neuronal thyroid hormone receptor. Although thyroid hormone receptor is highly expressed in many brain regions, including the cerebellum, during development in many species (Bernal and Pekonen, 1984; Polk et al., 1989; Mellström et al., 1991; Bradley et al., 1992), the target genes of thyroid hormone that play critical roles in brain development are not yet fully clarified.

Anatomical alterations induced by perinatal hypothyroidism in the developing cerebellum Because neuronal development of the rodent cerebellum is largely postnatal (Altman, 1982), perinatal hypothyroidism dramatically affects the morphogenesis of cerebellar

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Fig. 19.1 Thyroid hormone action at the nucleus. Thyroid hormone (TH) exerts its major effect by regulating gene expression through nuclear thyroid hormone receptor (TR). The receptor forms a heterodimer complex with retinoid X receptor (RXR) on thyroid hormoneresponse elements (TRE) located at the promoter region of target genes. Coregulators then bind to TR/RXR complex in a liganddependent manner to regulate transcription through basal transcriptional factors (TFs).

Fig. 19.2 Isoforms of thyroid hormone receptor (TR). The amino acid sequences are deduced from rat cDNAs. Numbering of the amino acid residues is shown above each isoform. The amino acid homology (%) in each domain is also indicated. TR is encoded by two genomic loci ( and ), each of which produces two isoforms (TR1 and c-erbA2, or TR1 and TR2) as a result of different promoter usage and alternative splicing. Note that c-erbA2 does not bind T3 to induce transactivation.

Thyroid hormone and cerebellar development

cells (Legrand, 1979; Koibuchi and Chin, 1999). These abnormalities cannot be corrected unless thyroid hormone is replaced within two weeks after birth (Legrand, 1967). Cerebellar weight, RNA, DNA and protein contents, as well as total body weight are retarded in the hypothyroid rat during postnatal development (Patel et al., 1976). After this critical period, these cerebellar parameters return to the normal range in the hypothyroid animal in spite of the morphological alterations of cerebellar cells. The only evident macroanatomical difference seen in the hypothyroid animal after this period is the increase in the number of cerebellar fissures with decreased depth, probably due to the prolonged cellular proliferation (Lauder et al., 1974). It should be noted that thyroid hormone receptors are expressed in all cerebellar neurons during development (Mellström et al., 1991; Strait et al., 1991; Bradley et al., 1992). Figure 19.3 summarizes the anatomical alterations in the hypothyroid cerebellum, as discussed below.

Alteration of Purkinje cell development In the perinatal hypothyroid rat, growth and branching of dendritic arborization of Purkinje cells as well as the ontogenesis of their dendritic spines are markedly reduced (Legrand, 1967, 1979; Geloso et al., 1968; Nicholson and Altman, 1972a; Hajós et al., 1973). On the other hand, the number of Purkinje cells is not altered by perinatal hypothyroidism because Purkinje cells are generated early during the gestational period (Nicholson and Altman, 1972a). Synaptogenesis between Purkinje cells and granule cell axons in the molecular layer is also greatly reduced as a result of hypoplasia of Purkinje cell dendritic spines (Nicholson and Altman, 1972a, 1972b) and decrease in the number of presynaptic terminals per parallel fiber (Lauder, 1978).

Delayed proliferation and migration, and transient increase in apoptosis of granule cells Both neurogenesis and differentiation of granule cells are retarded in hypothyroid animals. The external granule cell layer persists longer (Nicholson and Altman, 1972c), but the rate of proliferation is reduced (Lauder, 1977). The rate of migration into the internal granule cell layer is also decreased (Lauder, 1979). However, the change in the rate of proliferation may not be the direct effect of thyroid hormone, because thyroid hormone treatment in the cultured granule cell does not increase proliferation (Messer at al., 1984). Because proliferation of granule cells is known to be regulated by the interaction with Purkinje cells (Messer, 1980), the prolonged proliferation could be

Fig. 19.3 Effect of perinatal hypothyroidism on neurogenesis and development in the cerebellar cortex. In the hypothyroid cerebellum, disappearance of the external granule cell layer (EGL) is retarded as a result of delayed proliferation and migration of granule cells (G) to the internal granule cell layer (IGL). In the molecular layer (ML), the dendritic arborization of Purkinje cells (P) is decreased. Synaptic connections between Purkinje cell dendrites and parallel fibers (pf) from granule cells (shown by closed circles on Purkinje cell dendrites) are also decreased. Synaptic connections between Purkinje cells and climbing fibers are shown by open circles. Note that the disappearance of axosomatic synapses between climbing fibers and Purkinje cells is retarded in the hypothyroid animal. Also note that synaptic connections between mossy fibers (mf) and granule cells (shown by closed circle on mf) are decreased. (Adapted and reprinted from Brain Research, Vol. 50, F. Hajós, A.J. Patel and R. Balázs, Effect of thyroid deficiency on the synaptic organization of the rat cerebellar cortex, pp. 387–401, © 1973, with permission from Elsevier Science.)

caused by abnormal Purkinje cells in the hypothyroid animal. In the internal granule cell layer, the transient increase in granule cell death has been initially reported as pyknotic cells (Rabié et al., 1979). A recent study has shown a marked increase and prolongation of apoptosis in the hypothyroid animal (Xiao and Nikodem, 1998). The increase in granule cell apoptosis is probably due to the decreased synaptic connection to Purkinje cell dendrites, which is required for granule cell survival (Messer, 1980). However, the decrease in the number of granule cells is seen only during the critical period (Lewis et al., 1976). The number of granule cells becomes identical to that of the euthyroid animal thereafter (Nicholson and Altman, 1972c). Several mechanisms of restoration of cell number in the hypothyroid cerebellum

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have been considered. In the hypothyroid animal, synaptogenesis is low but is maintained to retain survival of some granule cells (Nicholson and Altman, 1972a, 1972b). Furthermore, the external granule cell layer persists beyond the critical period of thyroid hormone action, during which the rate of proliferation is higher (Lewis et al., 1976). Thus, the prolonged period of proliferation results in ‘catch-up’ in cell numbers.

Morphological alterations in other cerebellar cells In addition to Purkinje and granule cells, the abnormal development of other subsets of cerebellar neurons such as basket and stellate cells has been reported (Nicholson and Altman, 1972c; Clos and Legrand, 1973; Gravel and Hawkes, 1987). However, because fewer data are available concerning the effect of thyroid hormone on neurogenesis and development of these subsets of cells compared to those for Purkinje and granule cells, further study is required to clarify the thyroid hormone action on these cell types. Glial cells have also been considered to be the target of thyroid hormone (Legrand, 1980). Delayed myelination induced by perinatal hypothyroidism is one of the most well-known abnormalities seen in the hypothyroid brain (Hamburgh, 1966; Balázs et al., 1969, 1971). A recent study has shown that thyroid hormone independently regulates the development of oligodendrocytes at multiple levels, such as the proliferation of progenitor cells and differentiation (Baas et al., 1997). Delayed maturation and increase in the number of astrocytes in hypothyroid animal have also been reported (Pesetsky, 1973). In particular, retardation of differentiation of Bergmann’s glia, which plays a critical role in granule cell migration, has been reported (Pesetsky, 1973). This may contribute to the decrease in the rate of migration of granule cells into the external granule cell layer. However, the effect of thyroid hormone on astrocytes may not be direct in as much as thyroid hormone receptors are exclusively expressed in oligodendrocytes (Carlson et al., 1994; Leonard et al., 1994).

Changes in synaptic connections between cerebellar cells and afferent fibers from extracerebellar regions The synaptic connections between cerebellar cells and neuronal fibers from extracerebellar cells are also greatly affected by thyroid hormone status. The formation of somatic synapses between Purkinje cells and climbing fibers starts around postnatal day (P) 3, reaches its peak at around P7, and gradually disappears by P15 (Altman, 1972). In the hypothyroid animal, the axosomatic synapses

Fig. 19.4 Diagram showing the change in thyroid hormoneregulated gene expression. In many cases, thyroid hormone alters the timing of thyroid hormone-regulated gene expression during cerebellar development. Such genes include genes coding for calbindin, IP3 receptor, PCP-2 and myelin basic protein. (Adapted and reprinted with permission from K.A. Strait, L. Zou and J.H. Oppenheimer, Beta1 isoform-specific regulation of triiodo-thyronine-induced gene during cerebellar development, Molecular Endocrinology, Vol. 6, pp. 1874–80, 1992, © The Endocrine Society.) Note that the mRNA levels become identical after the critical period.

between climbing fibers and Purkinje cells persist for approximately ten days longer than those in the euthyroid animal (Hajós et al., 1973). On the other hand, when granule cells migrate into internal granule cell layer, they attract mossy fibers to form glomeruli (Altman, 1973). This synaptogenesis is also retarded in the hypothyroid animal (Hajós et al., 1973).

Current progress in the understanding of the molecular mechanisms of thyroid hormone action in cerebellar development As mentioned above, thyroid hormone exerts its effect largely by binding to nuclear thyroid hormone receptor, a ligand-regulated transcription factor. Therefore, it is reasonable to hypothesize that the thyroid hormone action on brain development is mostly exerted through regulation of transcription of genes, which, in turn, play critical roles in the developmental process. At present, the expression of many genes is known to be altered by perinatal hypothyroidism (Wills et al., 1991; Strait et al., 1992; Figueiredo et al., 1993; Neveu and Arenas, 1996; Koibuchi et al., 1996; Thompson, 1996; Koibuchi and Chin, 1998). Figure 19.4 shows a typical pattern of the change in expression of thyroid hormone-regulated genes during cerebellar development. Interestingly, after the critical period (the first two weeks of postnatal life), the activities of many genes that are altered by perinatal hypothyroidism return to the same

Thyroid hormone and cerebellar development

Fig. 19.5 Effect of daily T4 replacement on neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) mRNA content in the hypothyroid newborn rat cerebellum. Mothers of the pups received 0.05% propylthiouracyl in their drinking water. T4 (2 g/100 g body weight) was injected subcutaneously every day. *: p0.01 compared to hypothyroid rat. (NT-3; from Koibuchi and Chin, 1999, with permission. BDNF: reproduced with permission from N. Koibuchi, H. Fukuda and W.W. Chin, Promoter-specific regulation of the brainderived neurotrophic factor (BDNF) gene by thyroid hormone in the developing rat cerebellum, Endocrinology, Vol. 140, pp. 3955–61, 1999a, © The Endocrine Society.)

levels as those of the euthyroid animal, despite morphological alterations, although some of these genes are known to be directly regulated by thyroid hormone receptor (Farsetti et al., 1992; Zou et al., 1994). The changes in expression of these genes do not reflect those of thyroid hormone receptors, since the pattern of change in thyroid hormone receptor expression by altered thyroid status is different from those of other genes known to be altered in hypothyroid animals (Wills et al., 1991; Koibuchi and Chin, 1998). Despite the finding of many thyroid hormoneregulated genes, the genes that are critical for normal development and are regulated directly by thyroid hormone are not well known. Several potent candidates that may play ‘key’ roles in thyroid hormone-mediated cerebellar development are discussed below.

Possible roles of neurotrophic factors in thyroid hormone-mediated cerebellar development The only genes known to be directly regulated by thyroid hormone receptor in the cerebellum at the transcriptional level are pcp-2 and myelin basic protein (MBP) genes (Farsetti et al., 1992; Zou et al., 1994). The change in expression of the MBP gene in oligodendrocytes may affect the change in myelination in altered thyroid status. However, this cannot fully explain the abnormal development seen in hypothyroid animals. Current studies have raised the

possibility that neurotrophins, such as brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3, may be directly regulated by thyroid hormone receptor. These belong to a group of proteins called neurotrophic factors or neurotrophins, which include nerve growth factor and NT-4/5, and which play critical roles in neuronal differentiation, neurite growth, and synaptogenesis (Lewin and Barde, 1996). In the developing cerebellum, BDNF and NT-3 serve important functions. NT-3 secreted from granule cells promotes Purkinje cell development such as neurite sprouting (Lindholm et al., 1993). Mature granule cells also repond to NT-3 to promote branching of the axon (Segal et al., 1995). BDNF secreted from Purkinje and granule cells promotes axonal elongation and enhances the survival of granule cells (Segal et al., 1992, 1995). BDNF also increases the expression of NT-3, and thyroid hormone additively enhances the augmentation (Leingärtner et al., 1994). Another recent study using BDNF-knockout mice shows that BDNF may regulate Purkinje cell dendrite arborization (Schwartz , P.M. et al., 1997). As shown in Fig. 19.3, in the hypothyroid rat, Purkinje cell dendrite arborization, and synaptogenesis between Purkinje and granule cells are suppressed. Such events are associated with decreased levels of NT-3 and BDNF mRNA (Lindholm et al., 1993; Neveu and Arenas, 1996; Koibuchi and Chin, 1999; Koibuchi et al., 1999a; Fig. 19.5). Grafting cell lines expressing NT-3 or BDNF into the

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fourth ventricle in part prevents hypothyroidism-induced abnormal cerebellar neurogenesis (Neveu and Arenas, 1996), indicating that the thyroid hormone effect on neurogenesis is partially exerted through these neurotrophins. These results indicate that BDNF and NT-3 may play a critical role in thyroid hormone-mediated cerebellar development.

Other candidate genes that may play key roles in thyroid hormone-mediated cerebellar development. Recently, several interesting reports have been published regarding factors that may modify thyroid hormone receptor action in cerebellar development. In particular, the involvement of ROR alpha (an orphan nuclear hormone receptor strongly expressed in Purkinje cells) on thyroid hormone-mediated cerebellar development has been proposed (see below). Furthermore, Thompson and Bottcher (1997) have shown that hairless, a gene that is expressed in perinatal cerebellum and is directly regulated by thyroid hormone receptor (Thompson, 1996), encodes a protein that interacts with thyroid hormone receptor to repress transactivation by thyroid hormone receptor. Another orphan nuclear receptor, chicken ovalbumin upstream promoter-transcription factor (COUP-TF), which is also strongly expressed in fetal and early neonatal cerebellum, represses thyroid hormone receptor-mediated transactivation (Anderson et al., 1998). During the prenatal period when COUP-TF is strongly expressed in the prenatal Purkinje cell, thyroid hormone-regulated gene expression is relatively unresponsive to thyroid hormone (Schwartz, H.L. et al., 1997), indicating that this factor may in part govern the responsiveness of thyroid hormone-responsive genes to thyroid hormone by modulating thyroid hormone receptor action during brain development. Another potential target gene of thyroid hormone is the neural cell adhesion molecule (N-CAM), which could be a critical gene regulated by thyroid hormone (Iglesias et al., 1996). As discussed above, the rate of granule cell migration is reduced in the hypothyroid animal (Lauder, 1979), indicating that the cellular adhesion between granule cell and Bergmann glia may be altered by thyroid hormone. The expression of N-CAM is up-regulated in hypothyroid animals (Iglesias et al., 1996). Because N-CAM is an important molecule in the regulation of neuronal migration, the altered expression of N-CAM may play a role in abnormal granule cell migration. It is likely that the genes described above do not represent all of the genes that are regulated by thyroid hormone and play critical roles in cerebellar development. Studies to

identify such genes are currently underway by many investigators.

Animal models to study thyroid hormone action in cerebellar development In order to examine further the mechanisms of thyroid hormone action in cerebellar development in vivo, animal models may serve as important tools. Indeed, in addition to experimentally induced hypothyroid animals, there are several models that have been used to study the mechanisms of thyroid hormone action.

Congenital hypothyroid hyt/hyt mouse The most intensively studied animal model of congenital hypothyroidism is the hyt/hyt mouse, an autosomal recessive mutant of the thyrotropin (TSH) receptor gene (Biesiada et al., 1996). Although this mouse exhibits several phenotypes that are characteristic of congenital hypothyroidism, including cerebral neuroanatomical abnormalities (Stein et al., 1991) and abnormal motor behavior (Adams et al., 1989), it may not be very useful for the study of thyroid hormone action on cerebellar development. While this mouse model shows altered cerebellar enzyme activities, such as Na, K-ATPase, carbonic anhydrase and glycerol-3-phosphate dehydrogenase, which are also seen in hypothyroid animals (Sugisaki et al., 1991; Li and Chow, 1994), the developmental increase in their body weights is not dramatically different from that of normal mice (Li and Chow, 1994). Moreover, the Purkinje cell morphology appeared to be normal (Sugisaki et al., 1991), indicating that some compensatory mechanisms may be acquired to survive under severe hypothyroidism.

Transgenic animal models Another possible model for the study of the molecular mechanisms of thyroid hormone action in cerebellar development is the thyroid hormone receptor-knockout mouse. The thyroid hormone receptor beta knockout mouse, however, shows no abnormalities in cerebellar morphogenesis (Forrest et al., 1996) and expression of pcp2 and MBP genes (thyroid hormone-regulated) is normal (Sandhofer et al., 1998). On the other hand, the thyroid hormone receptor alpha-knockout study shows an abnormal phenotype, i.e., growth arrest, incomplete maturation of the intestine, impaired ossification, bone marrow hypoplasia, and smaller brain, but no evident cellular and morphological differences are observed only postnatally

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Fig. 19.6 Alteration of Purkinje cell morphology in normal, hypothyroid and, staggerer animals. (Adapted and reproduced from J. Legrand, Thyroid hormone effect on growth and development. In G. Hennemann, Thyroid Hormone Metabolism, pp. 503–34, Marcel Dekker, Inc. N.Y., 1986, by courtesy of Marcel Dekker, Inc.; and Brain Research, Vol. 142, D.J. Bradley and M. Berry, The Purkinje cell dendritic tree in mutant mouse cerebellum. A quantitative Golgi study of weaver and staggerer mice, pp. 135–41, © 1978, with permission from Elsevier Science.)

(Fraichard et al., 1997). To study the thyroid hormone receptor effect on neuronal development, therefore, targeting of the thyroid hormone receptor gene within a specific subset of neurons may be essential.

Staggerer mouse and the possible involvement of ROR alpha in thyroid hormone-mediated cerebellar development An animal model called the staggerer (sg) mouse exhibits morphological and neurological abnormalities of the cerebellum similar to those seen in the hypothyroid animals (Sidman et al., 1962). As shown in Fig. 19.6, Purkinje cells have extremely atrophic dendrites and synaptic connections from granule cell axons are greatly disturbed in this mouse (Sotelo and Changeux, 1974; Bradley and Berry, 1978). Similar abnormalities are also seen in the hypothyroid animal, as discussed above. The abnormal neurogenesis seen in the sg mouse has been considered to be caused by the abnormal Purkinje cells that fail to form synaptic connections with axons of the granule cells, which then leads to granule cell death (Herrup, 1983). On the other hand, the decrease in the number of granule cells is seen only during the critical period in perinatal hypothyroid animal (Lewis et al., 1976); the number of granule cells becomes identical to that of the euthyroid animal thereafter, because of a probable ‘catch-up’ mechanism, as discussed above. Interestingly, sg

Purkinje cells completely lack the ability to form synaptic connections, which leads to granule cell death. It has recently been reported that the orphan nuclear hormone receptor ROR alpha gene is disrupted in this mouse (Hamilton et al., 1996). ROR alpha is a novel member of the steroid hormone nuclear receptor superfamily, and is related to the retinoic acid receptors. Four isoforms (ROR alpha 1–4) are generated by alternative RNA processing (Giguère et al., 1994; Matsui et al., 1995; Hamilton et al., 1996). ROR alpha transcripts are highly expressed in the brain, especially in the Purkinje cells of the cerebellar cortex. The abnormal neurogenesis of sg mice, which is similar to that of the hypothyroid animal, may suggest a disorder of thyroid function in this mouse strain. Although the thyroid hormone level in blood remains within the normal range (Messer and Hatch, 1984), thyroid hormone effect on cerebellar development is partly impaired. Although thyroid hormone receptor is normally expressed in sg mice, the expression of the pcp-2 gene, which is directly regulated by thyroid hormone receptor (Zou et al. 1994), is low (Hamilton et al., 1996). Also, thyroid hormone treatment does not induce thymidine kinase activity, which is stimulated in proliferating granule cells by interaction with Purkinje cells (Messer, 1988). These results suggest that ROR alpha may be involved in the regulation of gene expression by thyroid hormone receptors. At least two possibilities can be considered regarding the interplay of thyroid hormone receptor and ROR alpha in this model. In one, thyroid hormone may regulate the expression of the ROR alpha gene, which then regulates a gene(s) essential for normal cerebellar development. In another, thyroid hormone receptor and ROR alpha competitively or cooperatively bind to their respective hormone-responsive elements to regulate transcription of target genes. As shown in Fig. 19.7A, daily T4 treatment significantly accelerates the increase in cerebellar ROR alpha gene expression compared to that of the hypothyroid animal (Koibuchi and Chin, 1998). However, ROR alpha mRNA levels become identical by P30, with or without thyroid hormone treatment. These results suggest that thyroid hormone may exert its effect, as least in part, by regulation of the expression of ROR alpha, which, in turn, may regulate gene expression essential for normal Purkinje cell development. Further, ROR alpha augments liganded thyroid hormone receptor action on various thyroid hormone response elements without affecting basal repression by unliganded thyroid hormone receptor in a transient transfection assay (Fig. 19.7B; Koibuchi et al., 1999b). Although further studies are required to identify genes regulated by ROR alpha or thyroid hormone receptor/ROR alpha complexes, ROR alpha may play a critical

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Fig. 19.7 (A) The effect of daily T4 replacement on ROR alpha mRNA content in the hypothyroid newborn rat cerebellum. Mothers of the pups received 0.05% propylthiouracyl in their drinking water. T4 (2 g/100 g body weight) was injected subcutaneously every day. *: p 0.01 compared to hypothyroid rat on postnatal day 15 (P15). (Reprinted with permission from N. Koibuchi and W.W. Chin, ROR alpha gene expression in the perinatal rat cerebellum: ontogeny and thyroid hormone regulation, Endocrinology, Vol. 139, pp. 2335–41, 1998, © The Endocrine Society.) (B) Interaction of TR and ROR alpha1 on TRE. TR and/or ROR alpha1 were cotransfected in CV-1 cells along with a reporter plasmid containing a TRE coupled with the luciferase reporter gene, and cultured with or without T3. Luciferase activity in the cell extract was measured. Unliganded TR alpha1 and TR beta1 repressed basal transcription. In the presence of T3, liganded TRs enhanced transcriptional activity above basal levels. Addition of ROR alpha1 further augmented the transactivation by T3 but basal repression was unaffected. *: p0.01 compared to TR-transfected and T3-treated group. (Reprinted with permission from N. Koibuchi, Y. Liu, H. Fukuda, A. Takeshita, P.M. Yen and W.W. Chin, ROR alpha augments thyroid hormone receptor-mediated transcriptional activation, Endocrinology, Vol. 140, pp. 1356–60, 1999b, © The Endocrine Society.)

TH-regulated Transcriptional Factors ROR α etc.

Other Transcriptional Factors COUP-TF etc.

Thyroid Hormone T4

TR

Type 2 Deiodinase

T3

Critical Genes Neutrophines Myelin Basic Protein N–CAM etc.

Non-genomic Action? Cerebellar Development Fig. 19.8 Diagram showing the potential factors involved in thyroid hormone actions in cerebellar development.

role in the full expression of thyroid hormone action in cerebellar development.

Conclusion Figure 19.8 summarizes the possible molecular interactions mediating the thyroid hormone action in cerebellar development. T4 is first taken up by astrocytes to be converted to T3 by type II 5-deiodinase. Then T3 is transferred to neurons by direct cell–cell interactions to associate with nuclear thyroid hormone receptor in order to regulate gene expression, although non-genomic actions of thyroid hormone have also been proposed. thyroid hormone may in part exert its effect by directly regulating genes critical for cerebellar development such as genes of MBP, N-CAM, and neurotrophins. Furthermore, thyroid hormone may regulate the expression of other transcription factor genes, which may in turn regulate critical genes. Such thyroid hormone-regulated transcription factors may also interact with thyroid hormone receptor to modulate its action. Examples of such genes are ROR alpha and

Thyroid hormone and cerebellar development

hairless. There are other transcription factors which may not be regulated by thyroid hormone but are developmentally regulated to modulate thyroid hormone receptor action, such as COUP-TF. However, additional factors must be involved in this process. State-of-the-art techniques such as gene chip technology (Marshall and Hodgson, 1998) and serial analysis of gene expression (SAGE) (Velculescu et al., 1995) will undoubtedly help to determine such thyroid hormone-regulated critical factors. Such studies of the mechanisms of thyroid hormone action in cerebellar development will provide useful information for further understanding of the molecular mechanism of cerebellar development. On the other hand, because the rodent cerebellum develops postnatally, the effect of thyroid status is relatively easily investigated compared to other brain regions. Therefore, the rodent cerebellum is a useful model to study the mechanism of thyroid hormone action on brain development, which may have clinical importance in cretinism and infantile hypothyroidism.

Acknowledgments I thank Dr William W. Chin, Division of Genetics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, for his advise during the preparation of this manuscript, and Drs Harumi Fukuda and Momoyo Kuno-Murata for their technical assistance.

xReferencesx Adams, P.M., Stein, S.A., Palnitkar, M., Anthony, A., Gerrity, L. and Sanklin, D.R. (1989). Evaluation and characterization of hypothyroid hyt/hyt mouse. I: Somatic and behavioral studies. Neuroendocrinology 49: 138–43. Altman, J. (1972). Postnatal development of cerebellar cortex in the rat. II. Phases in the maturation of Purkinje cells and of the molecular layer. J Comp Neurol 145: 399–464. Altman, J. (1973). Experimental reorganization of the cerebellar cortex. III. Regeneration of the external germinal layer and granule cell ectopia. J Comp Neurol 149: 153–80. Altman, J. (1982). Morphological development of the rat cerebellum and some of its mechanisms. Exp Brain Res 6: 8–49. Anderson, G.W., Larson, R.J., Oas, D.R., et al. (1998). Chicken ovalbumin upstream promoter-transcription factor (COUP-TF) modulates expression of the Purkinje cell protein-2 gene. J Biol Chem 273: 16391–9. Baas, D., Bourbeau, D., Sarlieve, L.L., Ittel, M.E., Dussault, J.H. and Puymirat, J. (1997). Oligodendrocyte maturation and progenitor cell proliferation are independently regulated by thyroid hormone. Glia 19: 324–32.

Balázs, R., Brooksbank, B.W.L., Davison, A.N., Eayrs, J.T. and Wilson, D.A. (1969). The effect of neonatal thyroidectomy on myelination in the rat brain. Brain Res 15: 219–32. Balázs, R., Brooksbank, B.W.L., Patel, A.J., Johnson, A.L. and Wilson, D.A. (1971). Incorporation of [35S] sulphate into brain constituents during development and the effect of thyroid hormone on myelination. Brain Res 30: 273–93. Bernal, J., Pekonen, F. (1984). Ontogenesis of the nuclear 3,5,3-triiodothyronine receptor in the human fetal brain. Endocrinology 114: 677–9. Biesiada, E., Adams, P.M., Shanklin, D.R., Bloom, G.S. and Stein, S.A. (1996). Biology of congenital hypothyroid hyt/hyt mouse. Adv Neuroimmunol 6: 309–46. Bradley, D.J., Towle, H.C. and Young, W.S. (1992). Spatial and temporal expression of alpha- and beta-thyroid hormone receptor mRNAs, including the beta2-subtype, in the developing mammalian nervous system. J Neurosci 12: 2288–302. Bradley, P. and Berry, M. (1978). The Purkinje cell dendritic tree in mutant mouse cerebellum. A quantitative Golgi study of weaver and staggerer mice. Brain Res 142: 135–41. Calvo, R., Obregón, M.J., Ruiz de Oña, C., Escobar del Rey, F. and Morreale de Escobar, G. (1990). Congenital hypothyroidism, as studied in rats. J Clin Invest 86: 889–99. Carlson, D.J., Strait, K.A., Schwartz, H.L. and Oppenheimer, J.H. (1994). Immunofluorescent localization of thyroid hormone receptor isoforms in glial cells of rat brain. Endocrinology 135: 1831–6. Chin, W.W. and Yen, P.M. (1997). Molecular mechanisms of nuclear thyroid hormone action. In Diseases of the Thyroid, ed. L.E. Braverman, pp. 1–15. Totowa, NJ: Humana Press. Clos, J. and Legrand, J. (1973). Effects of thyroid deficiency of the different cell populations of the cerebellum in the young rat. Brain Res 63: 450–5. Croteau, W., Davey, J., Galton, V. and St Germain, D.L. (1996). Cloning of the mammalian type II iodothyronine deiodinase. A selenoprotein differentially expressed and regulated in human and rat brain and other tissues. J Clin Invest 98: 405–417. Davis, P.J. and Davis, F.B. Nongenomic actions of thyroid hormone. In Diseases of the Thyroid, ed. L.E. Braverman, pp. 17–34. Totowa, NJ: Humana Press. Farsetti, A., Desvergne, B., Hallenbeck, P., Robbins, J. and Nikodem, V.M. (1992). Characterization of myelin basic protein thyroid hormone response element and its function in the context of native heterologous promoter. J Biol Chem 267: 15784–8. Figueiredo, B.C., Almazan, G., Ma, Y., Tetzlaff, W., Miller, F.D. and Cuello, A.C. (1993). Gene expression in the developing cerebellum during perinatal hypo- and hyperthyroidism. Mol Brain Res 17: 258–68 Forrest, D., Hanebuth, E., Smeyne, R.J. et al. (1996). Recessive resistance to thyroid hormone in mice lacking thyroid hormone receptor beta: evidence for tissue-specific modulation of receptor function. EMBO J 15: 3006–15. Fraichard, A., Chassande, O., Plateroti, M. et al. (1997). The T3R alpha gene encoding a thyroid hormone receptor is essential for post-natal development and thyroid hormone production. EMBO J 16: 4412–20.

313

314

N. Koibuchi

Geloso, J.P., Hemon, P., Legrand, J., Legrand, C. and Jost, A. (1968). Some aspects of thyroid physiology during the perinatal period. Gen Comp Endocrinol 10: 191–7. Giguère, V., Tini, M., Flock, G., Ong, E., Evans, R.M. and Otulakowski, G. (1994). Isoform-specific amino-terminal domains dictate DNA-binding properties of ROR alpha, a novel family of orphan hormone nuclear receptors. Genes Dev 8: 538–53. Gravel, C. and Hawkes, R. (1987). Thyroid hormone modulates the expression of a neurofilament antigen in the cerebellar cortex: premature induction and overexpression by basket cells in hyperthyroidism and a critical period for the correction of hypothyroidism. Brain Res 422: 327–35. Guadaño-Ferraz, A., Obregón, M.J., St Germain, D.L. and Bernal, J. (1997). The type 2 iodothyronine deiodinase is expressed primarily in glial cells in the neonatal rat brain. Proc Natl Acad Sci USA 94: 10391–6. Hajós, F., Patel, A.J. and Balázs, R. (1973). Effect of thyroid deficiency on the synaptic organization of the rat cerebellar cortex. Brain Res 50: 387–401. Hamburgh, M. (1966). Evidence for a direct effect of temperature and thyroid hormone on myelinogenesis in vitro. Dev Biol 13: 15–30. Hamilton, B.A., Frankel, W.N., Kerrebrock, A.W. et al. (1996). Disruption of the nuclear hormone receptor ROR alpha in staggerer mice. Nature 379: 736–9. Herrup, K. (1983). Role of staggerer gene in determining cell number in cerebellar cortex. I. Granule cell death is an indirect consequence of staggerer gene action. Brain Res 313: 267–74. Iglesias, T., Caubin, J., Stunnenberg, H.G., Zaballos, A., Bernal, J. and Muñoz, A. (1996). Thyroid hormone-dependent transcriptional repression of neural cell adhesion molecule during brain maturation. EMBO J 15: 4307–16. Koibuchi, N. and Chin, W.W. (1998). ROR alpha gene expression in the perinatal rat cerebellum: ontogeny and thyroid hormone regulation. Endocrinology 139: 2335–41. Koibuchi, N. and Chin, W.W. (1999). Mechanisms underlying neurological abnormalities resulting from developmental hypothyroidism. Curr Opin Endocrinol Diabet 6: 26–32. Koibuchi, N., Fukuda, H. and Chin, W.W. (1999a). Promoterspecific regulation of the brain-derived neurotrophic factor (BDNF) gene by thyroid hormone in the developing rat cerebellum. Endocrinology 140: 3955–61. Koibuchi, N., Liu, Y., Fukuda, H., Takeshita, A., Yen, P.M. and Chin, W.W. (1999b). ROR alpha augments thyroid hormone receptormediated transcriptional activation. Endocrinology 140: 1356–60. Koibuchi, N., Matsuzaki, S., Ichimura, K., Ohtake, H. and Yamaoka, S. (1996). Ontogenic changes in the expression of cytochrome c oxidase subunit I gene in the cerebellar cortex of the perinatal hypothyroid rat. Endocrinology 137: 5096–108. Lauder, J.M. (1977). The effects of early hypo- and hyperthyroidism on development of rat cerebellar cortex. III. Kinetics of cell proliferation in the external granule cell layer. Brain Res 126: 31–51. Lauder, J.M. (1978). Effects of early hypo- and hyperthyroidism on

development of rat cerebellar cortex. IV. The parallel fibers. Brain Res 142: 25–39. Lauder, J.M. (1979). Granule cell migration in developing rat cerebellum. Influence of neonatal hypo- and hyperthyroidism. Dev Biol 70: 105–15. Lauder, J.M., Altman, J. and Krebs, H. (1974). Some mechanisms of cerebellar foliation: effects of early hypo- and hyperthyroidism. Brain Res 76: 33–40. Lazar, M.A. (1993). Thyroid hormone receptors: multiple forms, multiple possibilities. Endocrine Rev 14: 184–93. Legrand, J. (1967). Variations, en fonction de l’âge, de la réponse du cervelet à l’action morphogénétique de la thyroïde chez le rat. Arch Anat Microsc Morphol Exp 56: 291–308. Legrand, J. (1979). Morphogenetic actions of thyroid hormones. Trends Neurosci 2: 234–6. Legrand, J. (1980). Effects of thyroid hormone on brain development, with particular emphasis on glial cells and myelination. In Multidisciplinary Approach to Brain Development, ed. C. Di Benedetta, R. Balázs, G. Gombos and G. Porcellati, pp. 279–92. Amsterdam: Elsevier. Legrand, J. (1986). Thyroid hormone effect on growth and development. In Thyroid Hormone Metabolism, ed. G. Hennemann, pp. 503–34. New York: Marcel Dekker. Leingärtner, A., Heisenberg, C.P., Kolbeck, R., Thoenen, H. and Lindholm, D. (1994). Brain-derived neurotrophic factor increases neurotrophin-3 expression in cerebellar granule neurons. J Biol Chem 269: 828–30. Leonard, J.L., Farwell, A.P., Yen, P.M., Chin, W.W. and Stula, M. (1994). Differential expression of thyroid hormone receptor isoforms in neurons and astroglial cells. Endocrinology 135: 548–55. Leonard, J.L., Kaplan, M.M., Visser, T.J., Silva, J.E. and Larsen, P.R. (1981). Cerebral cortex responds rapidly to thyroid hormones. Science 214: 571–3. Lewin, G.R. and Barde, Y-A. (1996). Physiology of the neurotrophins. Ann Rev Neurosci 19: 289–317. Lewis, P.D., Patel, A.J., Johnson, A.L. and Balázs, R. (1976). Effect of thyroid deficiency on cell acquisition in the postnatal rat brain: a quantitative histological study. Brain Res 104: 49–62. Li, J. and Chow, S.Y. (1994). Subcellular distribution of carbonic anhydrase and Na, KATPase in the brain of the hyt/hyt hypothyroid mice. Neurochem Res 19: 83–8. Lindholm, D., Castrén, E., Tsoulfas, P. et al. (1993). Neurotrophin-3 induced by triiodothyronine in cerebellar granule cells promotes Purkinje cell differentiation. J Cell Biol 122: 443–50. Marshall, A. and Hodgson, J. (1998). DNA chips: an array of possibilities. Nature Biotech 16: 27–31. Matsui, T., Sashihara, S., Oh, Y. and Waxman, S.G. (1995). An orphan nuclear receptor, mROR alpha, and its spatial expression in adult mouse brain. Mol Brain Res 33: 217–26. Mellström, B., Naranjo, J.R., Santos, A., Gonzales, A.M. and Bernal, J. (1991). Independent expression of the alpha and beta c-erbA genes in developing rat brain. Mol Endocrinol 5: 1339–50. Messer, A. (1980). Cerebellar granule cells in normal and neurological mutant mice. In Advances in Cellular Neurobiology, ed. S. Federoff and l. Hertz, pp. 180–207. New York: Academic Press.

Thyroid hormone and cerebellar development

Messer, A. (1988). Thyroxine injections do not cause premature induction of thymidine kinase in sg/sg mice. J Neurochem 51: 888–91. Messer, A. and Hatch, K. (1984). Persistence of cerebellar thymidine kinase in staggerer and hypothyroid mutants. J Neurogenet 1: 239–48. Messer, A., Maskin, P. and Snodgrass, G.L. (1984). Effects of triiodothyronine (T3) on the development of rat cerebellar cells in culture. Int J Dev Neurosci 2: 277–85. Neveu, I. and Arenas, E. (1996). Neurotrophins promote the survival and development of neurons in the cerebellum of hypothyroid rats in vivo. J Cell Biol 133: 631–46. Nicholson, J.L. and Altman, J. (1972a). The effects of early hypoand hyperthyroidism on the development of the rat cerebellar cortex. II. Synaptogenesis in the molecular layer. Brain Res 44: 25–36. Nicholson, J.L. and Altman, J. (1972b). Synaptogenesis in the rat cerebellum: effects of early hypo- and hyperthyroidism. Science 176: 530–2. Nicholson, J.L. and Altman, J. (1972c). The effects of early hypoand hyperthyroidism on development of rat cerebellar cortex. I. Cell proliferation and differentiation. Brain Res 44: 13–23. Oppenheimer, J.H. and Schwartz, H.L. (1997). Molecular basis of thyroid hormone-dependent brain development. Endocrine Rev 18: 462–75. Patel, A.J., Rabié, A., Lewis, P.D. and Balázs, R. (1976). Effect of thyroid deficiency on postnatal cell formation in the rat brain: a biochemical investigation. Brain Res 104: 33–48. Pesetsky, I. (1973). The development of abnormal cerebellar astrocytes in young hypothyroid rats. Brain Res 63: 456–60. Polk, D., Cheromcha, D., Riviczky, A. and Fisher, D.A. (1989). Nuclear thyroid hormone receptors: ontogeny and thyroid hormone effects in sheep. Am J Physiol 256: E543–9. Rabié, A., Favre, C., Clavel, M.C. and Legrand, J. (1979). Sequential effects of thyroxine on the developing cerebellum of rats made hypothyroid by propylthiouracil. Brain Res 161: 469–79. Sandhofer, C., Schwartz, H.L., Mariash, C.N., Forrest, D. and Oppenheimer, J.H. (1998). Beta receptor isoforms are not essential for thyroid hormone-dependent acceleration of PCP-2 and myelin basic protein gene expression in the developing brains of neonatal mice. Mol Cell Endocrinol 137: 109–15. Schwartz, H.L., Ross, M.E. and Oppenheimer, J.H. (1997). Lack of effect of thyroid hormone on late fetal rat brain development. Endocrinology 138: 3119–24. Schwartz, P.M., Borghesani, P.R., Levy, R.L., Pormeroy, S.L. and Segal, R.A. (1997). Abnormal cerebellar development and foliation in BDNF/ mice reveals a role for neurotrophins in CNS patterning. Neuron 19: 269–81. Segal, R.A., Pomeroy, S.L. and Stiles, C.D. (1995). Axonal growth and

fasciculation linked to differential expression of BDNF and NT3 receptors in developing cerebellar granule cells. J Neurosci 15: 4970–81. Segal, R.A., Takahashi, H. and McKay, R.D.G. (1992). Changes in neurotrophin responsiveness during the development of cerebellar granule neurons. Neuron 9: 1041–52. Sidman, R.L., Lane, P.W. and Dickie, M.M. (1962). Staggerer, a new mutation in the mouse affecting the cerebellum. Science 137: 610–12. Sotelo, C. and Changeux, J-P. (1974). Transsynaptic degeneration ‘en cascade’ in the cerebellar cortex of staggerer mutant mice. Brain Res 67: 519–26. Stein, S.A., Adams, P.M., Shanklin, D.R. and Palnitkar, M.B. (1991). Thyroid hormone control of brain and motor development: molecular, neuroanatomical, and behavioral studies. In Advances in Perinatal Thyroidology, ed. B. Bercu and D. Shulamn, pp. 47–101. New York: Plenum Press. Strait, K.A., Schwartz, H.L., Seybold, V.S., Ling, N.C. and Oppenheimer, J.H. (1991). Immunofluorescence localization of thyroid hormone receptor protein beta1 and variant alpha2 in selected tissues: cerebellar Purkinje cells as a model for beta1 receptor-mediated developmental effects of thyroid hormone in brain. Proc Natl Acad Sci USA 88: 3887–91. Strait, K.A., Zou, L. and Oppenheimer, J.H. (1992). Beta1 isoformspecific regulation of a triiodo-thyronine-induced gene during cerebellar development. Mol Endocrinol 6: 1874–80. Sugisaki, T., Noguchi, T., Beamer, W. and Kozak, L.P. (1991). Genetic hypothyroid mice: normal cerebellar morphology but altered glycerol-3-phosphate dehydrogenase in Bergmann glia. J Neurosci 11: 2614–21. Thompson, C.C. (1996). Thyroid hormone-responsive genes in developing cerebellum include a novel synaptotagmin and hairless homolog. J Neurosci 16: 7832–40. Thompson, C.C. and Bottcher, M. (1997). The product of a thyroid hormone-responsive gene interacts with thyroid hormone receptors. Proc Natl Acad Sci USA 94: 8527–32. Velculescu, V.E., Zhang, L., Vogelstein, B. and Kinzler, K.W. (1995). Serial analysis of gene expression. Science 270: 484–7. Wills, K.N., Zhang, X-K. and Pfahl, M. (1991). Coordinate expression of functionally distinct thyroid hormone receptor alpha isoforms during neonatal brain development. Mol Endocrinol 5: 1109–19. Xiao, Q. and Nikodem, V.M. (1998). Apoptosis in the developing cerebellum of the thyroid hormone deficient rat. Front Biosci 3: A52–7. Zou, L., Hagen, S.G., Strait, K.A. and Oppenheimer, J.H. (1994). Identification of thyroid hormone response elements in rodent pcp-2, a developmentally regulated gene of cerebellar Purkinje cells. J Biol Chem 269: 13346–52.

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Endocrine disorders: clinical aspects Mario-Ubaldo Manto1 and Henryk Zulewski2 1 2

Cerebellar Ataxias Unit, Free University of Brussels, Belgium Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Harvard Medical School, Boston, USA

Introduction The main endocrine cause of cerebellar ataxia is hypothyroidism. The incidence of the sporadic congenital form of hypothyroidism is about 1 per 4000 births (Delange, 1996), but the percentage of patients presenting cerebellar deficits associated with congenital hypothyroidism has not been determined. In adults, the reported percentages of hypothyroid patients with ataxic gait vary according to series (Kudrjavcev, 1978), varying from 0.3% to 5%. Subclinical hypothyroidism has a high prevalence in the general population, reaching a level of 5–10% (Cooper, 1991; Wiersinga, 1995; Samuels, 1998). Elderly women are particularly at risk (Samuels, 1998). The incidence of progression to clinical hypothyroidism has been estimated to be 5–15% per year. For subclinical hyperthyroidism, the prevalence is estimated to be 0.7–6.0% (Ross, 1996). Studies on the natural history of endogenous subclinical hyperthyroidism are limited to patients presenting autonomously functioning adenomas. Between 8.8% and 18% of patients develop thyrotoxicosis over a follow-up period of six to seven years. There are no epidemiological data concerning the incidence of cerebellar ataxia in subclinical hypothyroidism and subclinical hyperthyroidism. Recently, there have been several descriptions of cerebellar ataxia associated with Hashimoto’s thyroiditis, but its incidence is also undetermined, partly because assessment of the prevalence of Hashimoto’s thyroiditis is difficult. Indeed, laboratory signs are found in 5–11% of the general population, but are not necessarily associated with clinical signs of thyroid dysfunction (Flynn et al., 1988; Kothbauer-Margreiter et al., 1996). In addition, studies reporting this association have included only small numbers of patients.

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Endocrine diseases associated with cerebellar ataxia The consequences of endocrine disorders on cerebellar function will depend on several factors, mainly the stage of development of the cerebellum and the severity of endocrine dysfunction (Gilman et al., 1981). In daily practice, cerebellar ataxia resulting from endocrine diseases is usually related to a disturbance of thyroid function, as stated previously, or, less commonly, to a disturbance of calcium metabolism (Table 20.1).

Thyroid dysfunction Clinical presentation Hypothyroidism The general signs and the neurological deficits observed in cases of congenital hypothyroidism, endemic cretinism, and adult-onset hypothyroidism are given in Table 20.2 (Müller et al., 1995; Delange, 1996; Zulewski et al., 1997). Soederbergh was the first to focus attention on unsteady Table 20.1 Endocrine diseases associated with cerebellar ataxia Thyroid dysfunction Hypothyroidism Hyperthyroidism Drug-induced thyroid dysfunction (amiodarone) Parathyroid dysfunction Primary and secondary hypoparathyroidism Pseudohypoparathyroidism Pseudo-pseudohypoparathyroidism Primary and secondary hyperparathyroidism

Endocrine disorders: clinical aspects

Table 20.2 General signs and neurological deficits in hypothyroidism General signs

Neurological signs

Congenital hypothyroidism Endemic cretinism

Deficient growth Retardation of skeletal maturation Constipation Skin mottling

Mental deficiency Lethargy Deaf mutism Spastic diplegia Cerebellar ataxia

Adult-onset hypothyroidism

Dry skin, coarse skin Cold intolerance Diminished sweating Periorbital puffiness Constipation Bradycardia

Impairment of hearing Dementia Depression Coma Myoclonus Myopathy and polymyositis-like syndrome Delayed relaxation phase of tendon reflexes Entrapment neuropathy Polyneuropathy Cerebellar ataxia

gait associated with hypothyroidism as a genuine cerebellar sign (Soederbergh, 1910). In most cases, ataxia is associated with extracerebellar signs: cognitive deficits, seizures, myoclonus, and prolonged relaxation time of tendon reflexes – all well-described neurological complications of hypothyroidism (Jellinek, 1962; Sanders, 1962; Pinelli et al., 1990; Dugbartey, 1998). When present, tendinous hyporeflexia mainly reflects a muscular involvement. In adults, cerebellar ataxia may be the first manifestation of hypothyroidism (Gilman et al., 1981). Usually, the cerebellar syndrome generates subtle manifestations initially and develops gradually over a period of several months. Patients often complain of slowly increasing unsteadiness and gait difficulties (Harayama et al., 1983), and may present concomitant general symptoms. Ataxia predominates for trunk and limb movements and is usually more marked for the lower limbs. A 3-Hz body oscillation has been reported (Harayama et al. 1983; see also Chapter 7). Intention tremor, dysmetria, and dysdiadochokinesia are also observed. Dysmetria of saccades is absent or moderate, and ocular pursuit is often saccadic. Cerebellar dysarthria is rare. In some cases, cochleo-vestibular dysfunction generates sensorineural deafness with lack of recruitment and vestibular signs, which may confound cerebellar ataxia. Patients with subclinical hypothyroidism are free of ataxic symptoms in the large majority of cases.

Hyperthyroidism In thyrotoxicosis, various combinations of the following general symptoms are always noted: sweating, restless-

ness, palpitations, intolerance to heat, and diarrhea. Patients present endocrine ophthalmopathy, palpable thyroid, wet skin, and weight loss (Crooks et al., 1959). Hyperthyroidism produces exaggerated physiological tremor affecting essentially the hands, myopathy, seizures, choreoathetosis, pyramidal signs, and multiple psychiatric symptoms (Tonner and Schlechte, 1993). Ataxia involves gait and may have a recurrent character (Aberg et al., 1976).

Cerebellar ataxia associated with Hashimoto’s thyroiditis There are two main neurological presentations: the encephalopathy type and the vasculitic type (KothbauerMargreiter et al., 1996). The first and usual presentation is an encephalopathy affecting middle-aged women, which may be misdiagnosed as a primary psychiatric disorder due to agitation, confusion, sleep disturbances or hallucinations. Patients complain of headaches in up to 50% of cases. Epileptic seizures are present in the large majority of the patients, whereas ataxic signs occur as myoclonic jerks in about one to two patients in ten. The second possible presentation is characterized by stroke-like episodes, with focal neurological deficits, including cerebellar signs, and with a variable degree of confusion. The cerebellar syndrome may be subacute and may even take the form of a relapsing and remitting ataxia if untreated. The association of focal cerebellar signs such as dysmetria or dysdiadochokinesia in a patient with acute confusional state should raise the possibility of Hashimoto’s encephalopathy.

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Drug-induced thyroid dysfunction: amiodarone and lithium salts Amiodarone is a benzofuran derivative with a thyroxinelike structure. Its half-life is between 28 and 100 days and the drug has an exceptionally long half-life of elimination. A daily dose of 400 mg yields about 8–9 mg of iodine/day, which is 100 times the normal daily intake. Patients who develop a thyroid disorder secondary to amiodarone treatment have a cumulative risk of (a) hypothyroidisminduced or hyperthyroidism-induced ataxia, and (b) a direct toxic effect of the drug on cerebellar function, but also on basal ganglia, brainstem and peripheral nervous system. A similar risk is associated with lithium salts, which may give rise to hypothyroidism and goiter.

Pathophysiology Experimental studies have demonstrated that thyroid hormones exert a determinant trophic action not only during growth of the cerebellum, but also during an individual’s lifespan, mature neurons keeping the cellular machinery to respond to hormones. Thyroid hormones act through a nuclear receptor and the interaction modulates gene transcription. In the prenatal period, thyroid hormones modulate proliferation, migration, and differentiation of cerebellar neurons. In the postnatal period, they promote myelination and gliogenesis. Hormones participate in the following major phenomena: proliferation of cells, neurite outgrowth, cell migration, myelin synthesis, organization of cytoskeleton (glial fibrillary acidic protein (GFAP) filaments) and extracellular matrix (fibronectin) (Trentin and Moura Neto, 1995). There are also synergistic effects between thyroid hormones and neuromodulators such as insulin-like growth factors (IGFs), which are involved in the development of climbing fiber topography, regulate synapses activity, and exert a trophic action on cerebellar glioblasts and Purkinje cells through activation of protein kinases. For details about the effects of thyroid hormones on the development of neurons in the cerebellum, see Chapter 19.

Hypothyroidism In humans, the clinical predominance of cerebellar ataxia in the lower limbs is explained by the fact that pathological modifications predominate in the superior vermis. In a post-mortem study of a 57-year-old hypothyroid patient who had had cerebellar ataxia affecting, in particular, the lower limbs, there was a cerebellar atrophy predominating in the anterosuperior vermis, atrophy of middle and superior cerebellar peduncles, of pons and transverse pontine fibers (Barnard et al., 1971). The topography of these

lesions was remarkably similar to that of lesions seen in alcoholic patients. Cerebellar involvement is not the only factor explaining unsteadiness. Slowness of the muscle contractions also plays a role in the irregular character of stance and gait, as does involvement of peripheral nerves.

Hyperthyroidism The mechanisms of clumsiness in hyperthyroidism are unknown. They may include the overstimulation of cerebellar pathways by thyroid hormones. In addition, reduced vitamin E concentrations could contribute to cerebellar ataxia. Indeed, vitamin E levels tend to be low in hyperthyroidism, mainly because of the reduction of low-density lipoprotein (LDL) levels (Asayama et al., 1989).

Cerebellar ataxia associated with Hashimoto’s thyroiditis Autoimmune disturbances probably play a determinant role in the pathophysiology of cerebellar ataxia associated with Hashimoto’s thyroiditis. Indeed, women are predominantly affected, and up to 25–30% of the patients with cerebellar ataxia and Hashimoto’s thyroiditis have other autoimmune disorders: myasthenia gravis, Guillain–Barré syndrome, glomerulonephritis, primary biliary cirrhosis, pernicious anemia, and splenic atrophy (Brain et al., 1966; Jellinek and Ball, 1976; Behar et al. 1986; Claussman et al., 1994; Susuki et al., 1994; Takahashi et al., 1994). Moreover, laboratory investigations show inflammatory signs in cerebrospinal fluid (CSF), and clinical deficits respond to steroid administration. A process of acute disseminated encephalitis has been proposed (Henderson et al., 1987), while others have considered the possibility of an immune cerebral vasculitis (Shein et al., 1986). However, hypothyroidism is unlikely to be the direct cause of the neurological deficits, because normalization of thyroid dysfunction may not improve the neurological status.

Diagnosis Table 20.3 lists the main investigations to be performed when a thyroid dysfunction is suspected to be the cause of the cerebellar ataxia. In all ataxic patients, thyrotropin hormone (TSH) and free T4 levels should be determined in order to exclude a treatable cause. If hyperthyroidism is suspected, diagnostic procedures involving iodinated contrast agents should be avoided. In cerebellar ataxia associated with Hashimoto’s thyroiditis, the following results are found. (a) Blood studies: high titers of autoantibodies against thyroglobulin and thyroid peroxidase are highly

Endocrine disorders: clinical aspects

Table 20.3 Thyroid tests Blood studies: Free T4, thyroid stimulating hormone, thyroglobulin antibody, thyroid peroxidase antibody (formerly called microsomal antibody) Thyroid sonography Thyroid scintigraphy

(b)

(c)

(d)

(e)

(f)

suggestive of the disease. About one-third of patients are hypothyroid at the time of neurological presentation. Thyroid sonography: hypoechoic thyroid ultrasonogram is a typical feature (Seipelt et al., 1999). Some authors require the presence of a goitre for the diagnosis of Hashimoto’s thyroiditis, but others argue that the inflammatory mechanism will often lead to atrophy of thyroid tissue at a latter stage (Kothbauer-Margreiter et al., 1996). Cerebrospinal fluid studies: CSF studies are abnormal in 80% of patients. A normal count or predominantly mononuclear pleocytosis (from 31 to 169 cells/mm3), increased protein level (up to 298 mg/dl), and oligoclonal bands may be found. Increase of the CSF: serum albumin ratio occurs in half of the cases. A normal glucose level is the rule. Brain computed tomography (CT)/magnetic resonance imaging (MRI): hypodense area(s) on CT are found in 30% of patients. Subcortical hypersignal lesion(s) in T2-weighted image without gadolinium enhancement may be revealed. These areas of increased signal may be restricted to the cerebellum. In addition, MRI may also demonstrate atrophy of gray matter in the absence of infarction (Takahashi et al., 1994). However, both CT and MRI are strictly normal in some patients. Single-photon emission computed tomography/ positron emission tomography: SPECT shows a decreased tracer uptake with a patchy pattern. In some patients exhibiting cognitive deficits, a global hypoperfusion is observed (Forchetti et al., 1997). Electroencephalography (EEG): recording demonstrates slowing of the background rhythm in about 50% of the patients and epileptic activity in about 15% of the patients.

Differential diagnosis In the case of encephalopathy, appropriate tests should be performed to exclude metabolic, infectious, vascular, and toxic causes. Seilpelt et al. have reported seven cases of

Hashimoto’s thyroiditis presenting an association of dementia, cerebellar ataxia, and myoclonus (Seipelt et al., 1999). Six patients were euthyroid and one was hyperthyroid. The main differential diagnosis was Creutzfeldt–Jakob disease (CJD), which presents with ataxia in about 85% of cases. Whereas symptoms have a fluctuating course in Hashimoto’s encephalopathy, they have a progressive and fatal course in CJD. Moreover, visual symptoms, startle reactions, and akinetic mutism are observed in CJD, but not in Hashimoto’s encephalopathy. Both blood studies and EEG recordings are useful in this differential diagnosis, because protein 14-3-3 and periodic sharp wave complexes are found in CJD, but not in Hashimoto’s encephalopathy (Otto et al., 1997; Seipelt et al., 1999). Steroid-responsiveness of encephalopathy associated with thyroiditis is another distinguishing feature (see below).

Treatment Hypothyroidism Levothyroxine is the treatment of choice for the management of hypothyroidism. The aim is to reach both clinical and biological euthyroid status. The initial dose of levothyroxine is 50 g/day. The dose is increased by steps of 25 g every six weeks according to basal TSH. The mean daily dose of levothyroxine is 100 g/day (Brent and Larsen, 1996). Once treatment is established, monitoring after six months is useful.

Hyperthyroidism There are three methods to treat hyperthyroidism: (1) antithyroid drug therapy, e.g., propylthiouracil and methimazole, (2) radioactive iodine therapy, and (3) surgical thyroid ablation. Propranolol is often added to the regimen. Overall, beta-blockers are well tolerated by thyrotoxic patients (Feely and Peden, 1984).

Cerebellar ataxia associated with Hashimoto’s thyroiditis Neurological deficits show a favorable response to immunosuppressive treatment. The cerebral complications of Hashimoto’s thyroiditis, including cerebellar ataxia, are considered as steroid-responsive disorders (Shaw et al., 1991). Therefore, they should be recognized and not misdiagnosed as CJD. Trials of high-dose steroid treatment (methylprednisolone 1 g/day for three to five days) are recommended in case of suspicion, eventually with the concomitant administration of levothyroxine. Typically, there is a rapid and good clinical response to steroids. For some patients, it has been reported that the

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addition of immunosuppressive therapy, such as azathioprine or methotrexate, is required for clinical improvement (Shaw et al., 1991). Epileptic seizures and myoclonus respond to anticonvulsant drugs. Clonazepam and valproate are among the drugs of choice. There is often a decrease of antiperoxisomal and antithyroglobulin antibodies and a trend towards normalization of other tests after steroid administration: CSF investigations, EEG, and MRI lesions (Bohnen et al., 1997). The steroids are progressively tapered thereafter.

Prognosis/outcome

Table 20.4 Neurological signs of hypoparathyroidism Tetany Paresthesias Muscle cramps Muscle spasms Seizures Choreoathetosis Parkinsonism Cerebellar ataxia Paroxysmal dystonia Paroxysmal hemiballism Mental retardation

Hypothyroidism As a rule, cerebellar ataxia resulting from congenital hypothyroidism carries a poor prognosis when thyroid treatment is not started immediately after birth. Delay in the administration of thyroxine in newborns with congenital hypothyroidism leads to irreversible brain sequelae, including in the cerebellum, although biochemical abnormalities might improve (Jagannathan et al., 1998). Indeed, using in-vivo proton magnetic resonance spectroscopy (MRS), reversible biochemical deficits have been shown recently in the cerebellum of three patients with congenital hypothyroidism after thyroid hormone administration (Jagannathan et al., 1998). Reversibility of biochemical abnormalities was documented even though thyroxine therapy was given at ages beyond which deficits of myelinogenesis are thought to be irreversible. However, clinical deficits were not improved. In adult-onset hypothyroidism, ataxia usually decreases after replacement therapy with levothyroxine. Regression of ataxia associated with hypothyroidism may be complete and may take only a few weeks (Hammar and Regli, 1975). Rarely, achievement of an euthyroid state does not ameliorate cerebellar dysfunction (Bonuccelli et al., 1991).

Cerebellar ataxia associated with Hashimoto’s thyroiditis The encephalopathy or the ataxic syndrome associated with Hashimoto’s thyroiditis responds to treatment in most cases, provided the treatment is initiated early enough in the course of the disease. Indeed, irreversible brain sequelae may occur if the neurological signs persist for years. Rise of antibody titers after withdrawal of steroids is not indicative of a relapse, but these patients are probably at risk. It has been noted that patients with encephalopathy exhibit a quicker response to steroids than patients with stroke-like deficits. Unlike younger patients with thyroid disease, elderly people often have concomitant illnesses which interfere with brain functions or with general status (Shetty and

Duthie, 1995). These factors slow down rehabilitation, which is recommended during corrections of neurological deficits associated with hormonal defects like hypothyroidism.

Parathyroid disorders Patients with disorders of parathyroid hormone signaling may exhibit cerebellar ataxia. Some rare examples are described below.

Clinical presentation Hypoparathyroidism This endocrine dysfunction is mostly idiopathic or acquired, due to resection of glands during thyroidectomy. Signs of neuromuscular hyperexcitability predominate (Table 20.4) as a consequence of hypocalcemia: tetany, paresthesias, muscle cramps, and spasms. Ertas et al. (1997) have reported two cases of hypoparathyroidism presenting a bilateral cerebellar syndrome, in the absence of extrapyramidal signs. Both patients had seizures and exhibited Chvostek and Trousseau signs. Although one patient presented the idiopathic form of hypoparathyroidism and the other had a secondary form due to prior surgery, the two patients had similar ataxic syndrome: dysarthria, dysmetria, dysdiadochokinesia, and ataxia of gait.

Pseudohypoparathyroidism and pseudopseudohypoparathyroidism Pseudohypoparathyroidism is a genetic disease presenting with short stature, round face, short metacarpals, obesity, and hypertension. Some individuals in families with pseudohypoparathyroidism inherit the phenotype of Albright’s osteodystrophy, but have no disorder of calcium metabolism: this state is called pseudohypoparathyroid-

Endocrine disorders: clinical aspects

ism. Patients with this rare familial disorder present cerebellar ataxia as part of a late-onset syndrome including mental deterioration and extrapyramidal signs (Nyland and Skre, 1977).

Hyperparathyroidism Hyperparathyroidism is primary (adenoma), secondary to hypocalcemia (malabsorption, pancreatic failure, vitamin D deficiency), or tertiary (renal failure). Hyperparathyroidism is responsible for cognitive signs, psychiatric manifestations, internuclear ophthalmoplegia, pyramidal signs, fasciculations, myopathy, and cerebellar ataxia. Nevertheless, cerebellar signs are usually minimal. A slight kinetic tremor may be the only manifestation of involvement of cerebellar pathways. An association of primary hyperparathyroidism with cerebellar hemangioblastomas has been reported (Gaymard et al., 1989; see also Chapter 17).

Pathophysiology Hypoparathyroidism Parathyroid hormone increases calcemia via hormonal binding to a membrane receptor. Several types of receptors have been identified; some of them are expressed in the brain (Mannstadt and Drueke, 1997). It is established that calcium plays a major function in the brain, and maintenance of calcium homeostasis is crucial to the Purkinje cells (Bezprozvanny et al., 1991; Gruol et al., 1996; Atluri and Regehr, 1998). However, the consequences of disturbed calcium metabolism upon cerebellar function are not fully understood. In chronic cases of hypoparathyroidism, deposits of calcium very often occur in dentate nuclei, cerebellar white matter, and the granular layer of the cerebellar cortex, as a result of a slowly progressive metabolic process. A similar pathogenesis is suspected for idiopathic calcifications in the brain, which may be extensive (Fahr syndrome), involving not only cerebellum but also thalami, lentiform nuclei and white matter in the cerebral lobes (Araki et al., 1990; Dragasevic et al., 1997). In this case, histochemical studies have shown that idiopathic calcifications are composed of glycoproteins, mucopolysaccharides, calcium salts, and iron and seem to accumulate initially in perivascular areas (Kobayashi et al., 1987). However, there is no correlation between the presence of deposits in the cerebellum and ataxia, either for hypoparathyroidism or for idiopathic calcifications (Kazis, 1985; Ertas et al., 1997). Bilateral calcifications are a common, aspecific, and often incidental finding after the age of 55 years, though predominating in globus pallidus. Therefore, mechanisms other than calcium deposits are likely to play a role in ataxia associated with abnormal calcium metabolism.

Table 20.5 Differential diagnosis in cerebellar patients presenting diabetes mellitus Friedreich’s ataxia (see Chapter 36) Mitochondrial diseases: GH deficiency, hypogonadism, hypoparathyroidism Stiffman syndrome: anti-GAD antibodies Cerebellar atrophy with anti-GAD antibodies Hereditary ceruloplasmin deficiency Hemochromatosis Cytomegalovirus infection Von Hippel–Lindau disease

Pseudohypoparathyroidism and pseudopseudohypoparathyroidism Pseudohypoparathyroidism is a parathyroid resistance syndrome caused by a defect in the hormone receptor. The parathyroids are present, and even often show a variable level of hyperplasia. Renal tubules fail to respond to parathyroid hormone. Pseudo-pseudohypoparathyroidism is explained by an insufficient intracellular response to cyclic adenosine monophosphate (cAMP) (Nyland and Skre, 1977). The mechanisms of cerebellar dysfunction associated with these rare endocrine disorders remain to be elucidated.

Treatment and prognosis In the case of idiopathic hypoparathyroidism, cerebellar syndrome may be reversible following calcium administration, even in the case of calcifications in the cerebellar dentate nuclei (Ertas et al., 1997; Dragasevic et al., 1997). In patients exhibiting ataxia associated with hyperparathyroidism, residual neurological sequelae are often noted after treatment (Patten and Pages, 1984).

Cerebellar ataxia and diabetes mellitus Not exceptionally, cerebellar patients are found to present a diabetes mellitus during diagnostic work-up, or have a previous history of diabetes mellitus (see also Chapter 13 for diabetes mellitus as a risk factor of stroke). In this latter case, patients are usually examined initially within the department of internal medicine and are referred subsequently to a neurologist. Table 20.5 lists the diseases causing both diabetes mellitus and cerebellar ataxia. Hyperglycemia has also been reported in the case of phenytoin intoxication, which typically includes ataxic signs.

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Cerebellar ataxia and diabetes insipidus

xReferencesx

The association of diabetes insipidus and cerebellar ataxia is encountered in Langerhans’ cell histiocytosis and in Erdheim–Chester disease, two diseases characterized by proliferation of histiocytic granulomas. Neurological involvement occurs in about 20% of patients with Erdheim–Chester disease (Wright et al., 1999). In addition to diabetes insipidus and cerebellar ataxia, the most frequent neurological manifestations are related to orbital lesions and development of extra-axial lesions along the dura. Brain MRI shows increased signal intensity in peridentatal regions on T2-weighted sequences (Pautas et al., 1998). The involvement of the pons and the middle cerebellar peduncles may be prominent (Evidente et al., 1998). Symmetric sclerosis of the metaphysis and diaphysis of long bones is very suggestive. Neurological deficits may improve with steroid therapy in some patients (Pautas et al., 1998). Cerebellar ataxia and diabetes insipidus have also been described concomitantly in the De Morsier syndrome (septo-optic dysplasia) (Grois et al., 1993; Willnow et al., 1996) and in some families (Robinson et al., 1988). In addition, cerebellar ataxia, diabetes mellitus, and diabetes insipidus may coexist in the DIDMOAD syndrome (Wolfram syndrome), an autosomal recessive disease including optic atrophy, deafness, ataxia, and peripheral neuropathy (Strom et al., 1998).

Aberg, H.E., Herbai, G.L. and Westerberg, C.E. (1976). Recurrent and reversible cerebellar ataxia with concomitant episodes of hyperthyroidism: a new autoimmune syndrome. Acta Med Scand 199: 331–4. Araki, Y., Furukawa, T., Tsuda, K., Yamamoto, T. and Tsukaguchi, I. (1990). High field MR imaging of the brain in pseudohypoparathyroidism. Neuroradiology 32: 325–7. Asayama, K., Dobashi, K., Hayashibe, H. and Kato, K. (1989). Vitamin E protects against thyroxine-induced acceleration of lipid peroxidation in cardiac and skeletal muscles in rats. J Nutr Sci Vitaminol 35: 407–18. Atluri, P.P. and Regehr, W.G. (1998). Delayed release of neurotransmitter from cerebellar granule cells. J Neurosci, 18: 8214–27. Barnard, R.O., Campbell, M.J. and McDonald, W.I. (1971). Pathological findings in a case of hypothyroidism with ataxia. J Neurol Neurosurg Psychiatry 34: 755–60. Behar, R., Penny, R. and Powell, H.C. (1986). Guillain–Barre syndrome associated with Hashimoto’s thyroiditis. J Neurol 233: 233–6. Berciano, J., Amado, J.A., Freijanes, J., Rebollo, M. and Vaquero, A. (1982). Familial cerebellar ataxia and hypogonadotrophic hypogonadism: evidence for hypothalamic LHRH deficiency. J Neurol Neurosurg Psychiatry 45: 747–51. Bezprozvanny, I., Watras, J. and Ehrlich, B.E. (1991). Bell-shaped calcium-response curves of Ins(1,4,5)P3- and calcium-gated channels from endoplasmic reticulum of cerebellum. Nature 351: 751–4. Bohnen, N.I., Parnell, K.J. and Harper, C.M. (1997). Reversible MRI findings in a patient with Hashimoto’s encephalopathy. Neurology 49: 246–7. Bonuccelli, U., Nuti, A., Monzani, F., De Negri, F. and Muratorio, A. (1991). Familial occurrence of hypothyroidism and cerebellar ataxia. Funct Neurol 6: 171–5. Brain L., Jellinek, E.H. and Ball, K. (1966). Hashimoto’s disease and encephalopathy. Lancet ii: 512–14. Brent, G.A. and Larsen, P.R. (1996). Treatment of hypothyroidism. In Werner and Ingbar’s The Thyroid, 7th edn., ed. L.E. Braverman and R.D. Utiger, pp. 883–7. Philadelphia: Lippincott-Raven Publishers. Claussman, C., Offner, C., Chevalier, Y., Sellal, F. and Collard, M. (1994). Encephalopathie et thyroidite de Hashimoto. Rev Neurol (Paris) 150: 166–8. Cooper, D.S. (1991). Subclinical hypothyroidism. In Advances in Endocrinology and Netabolism, ed. E.L. Mazzaferri, St Louis, Baltimore: Boston. Crooks, J., Murray, I.P.C. and Wayne, E.J. (1959). Statistical methods applied to the diagnosis of thyrotoxicosis. Q J Med 28: 211–34. Delange, F.M. (1996). Endemic cretinism. In Werner and Ingbar’s The Thyroid, 7th edn., ed. L.E. Braverman and R.D. Utiger, pp. 756–67. Philadelphia: Lippincott-Raven Publishers. Dragasevic, N., Petkovic-Medved, B., Svetel, M. and Filipovic, S.R., Kostic, V.S. (1997). Paroxysmal hemiballism in idiopathic hypoparathyroidism. J Neurol 244: 389–90.

Other associations Other associations of endocrine disorders and cerebellar deficits have also been reported (Berciano et al., 1982): Cerebellar ataxia and hypogonadotrophic hypogonadism (Holmes’ ataxia) Boucher–Neuhauser syndrome: ataxia, hypogonadism, retinochoroidal degeneration. Cowden syndrome/Lhermitte–Duclos hamartoma. Cerebellar ataxia with growth hormone deficiency. Carbohydrate-deficient glycoprotein syndrome.

Acknowledgments M-U. Manto is supported by a grant from the Belgian National Research Foundation and the Belgian American Educational Foundation (BAEF). M-U. Manto is David and Alice van Buuren Fellow of the BAEF.

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Dugbartey, A.T. (1998). Neurocognitive aspects of hypothyroidism. Arch Intern Med 158: 1413–18. Ertas, N.K., Hanoglu, L., Kirbas, D. and Hatemi, H. (1997). Cerebellar syndrome due to hypoparathyroidism. J Neurol 244: 338–9. Evidente, V.G., Adler, C.H., Giannini, C., Conley, C.R., Parisi, J.E. and Fletcher, G.P. (1998). Erdheim–Chester disease with extensive intraaxial brain stem lesions presenting as a progressive cerebellar syndrome. Mov Disord 13: 576–81. Feely, J. and Peden, N. (1984). Use of beta-adrenoceptor blocking drugs in hyperthyroidism. Drugs 27: 425–46. Flynn, S.D., Nishiyama, R.H. and Bigos, S.T. (1988). Autoimmune thyroid disease: immunological, pathological, and clinical aspects. Crit Rev Clin Lab Sci 26: 43–95. Forchetti, C.M., Katsamakis, G. and Garron, D.C. (1997). Autoimmune thyroiditis and a rapidly progressive dementia: global hypoperfusion on SPECT scanning suggests a possible mechanism. Neurology 49: 623–6. Gaymard, B., Jan, M., Gouase, M.D., Ozoux, P., Autret, A. and Bacq, Y. (1989). Cerebellar hemangioblastoma and primary hyperparathyroidism. Surg Neurol 31: 369–75. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadelphia: F.A. Davis. Grois, N., Barkovich, A.J., Rosenau, W. and Ablin, A.R. (1993). Central nervous system disease associated with Langerhans’ cell histiocytosis. Am J Pediatr Hematol Oncol 15: 245–54. Gruol, D.L., Netzeband, J.G. and Parsons, K.L. (1996). Ca2 signaling pathways linked to glutamate receptor activation in the somatic and dendritic regions of cultured cerebellar Purkinje neurons. J Neurophysiol 76: 3325–40. Hammar, C.H. and Regli, F. (1975). Cerebellar ataxia due to hypothyroidism in adults. Dtsch Med Wochenschr 100: 1504–6. Harayama, H., Ohno, T. and Miyatake, T. (1983). Quantitative analysis of stance in ataxic myxoedema. J Neurol Neurosurg Psychiatry 46: 579–81. Henderson, L.M., Behan, P.O., Aarli, J., Hadley, D. and Draper, I.T. (1987). Hashimoto’s encephalopathy: a new neuroimmunological syndrome. Ann Neurol 22: 140–1. Jagannathan, N.R., Tandon, N., Raghunathan, P. and Kochupillai, N. (1998). Reversal of abnormalities of myelination by thyroxine therapy in congenital hypothyroidism: localized in vivo proton magnetic resonance spectroscopy (MRS) study. Brain Res Dev Brain Res 109: 179–86. Jellinek, E.H. (1962). Fits, faints, coma, and dementia in myxoedema. Lancet, ii: 1010–12. Jellinek, E.H. and Ball, K. (1976). Hashimoto’s disease, encephalopathy and splenic atrophy. Lancet i: 1248. Kazis, A.D. (1985). Contribution of CT to the diagnosis of Fahr’s syndrome. Acta Neurol Scand 71: 206–11. Kobayashi, S., Yamadori, I., Miki, H. and Ohmori, M. (1987). Idiopathic nonarteriosclerotic cerebral calcification (Fahr’s disease): an electron microscopic study. Acta Neuropathol 73: 62–6. Kothbauer-Margreiter, I., Sturzenegger, M., Komor, J.,

Baumgartner, R. and Hess, C.W. (1996). Encephalopathy associated with Hashimoto’s thyroiditis: diagnosis and treatment. J Neurol 243: 585–93. Kudrjavcev, T. (1978). Neurologic complications of thyroid dysfunction. Adv Neurol 19: 619–36. Mannstadt, M. and Drueke, T.B. (1997). Parathyroid hormone receptors: from cloning to physiological, physiopathological and clinical implications. Nephrologie 18: 5–10. Müller, B., Zulewski, H., Huber, P., Ratcliffe, J.G. and Staub, J.J. (1995). Impaired action of thyroid hormone associated with smoking in women with hypothyroidism. N Engl J Med 333: 964–9. Nyland, H. and Skre, H. (1977). Cerebral calcinosis with late onset encephalopathy. Unusual type of pseudo-pseudohypoparathyroidism. Acta Neurol Scand 56: 309–25. Otto, M., Wiltfang, J., Tumani, H. et al. (1997). Elevated levels of tauprotein in cerebrospinal fluid of patients with Creutzfeldt–Jakob disease. Neurosci Lett 225: 210–12. Patten, B.M. and Pages, M. (1984). Severe neurological diseases associated with hyperparathyroidism. Ann Neurol 15: 453–6. Pautas, E., Cherin, P., Pelletier, S., Vidailhet, M. and Herson, S. (1998). Cerebral Erdheim–Chester disease: report of two cases with progressive cerebellar syndrome with dentate abnormalities on magnetic resonance imaging. J Neurol Neurosurg Psychiatry 65: 597–9. Pinelli, P., Pisano, F. and Miscio, G. (1990). Ataxia in myxoedema: a neurophysiological reassessment. J Neurol 237: 405–9. Robinson, I.C., O’Malley, B.P. and Young, I.D. (1988). Familial cerebellar ataxia and diabetes insipidus. J Neurol Neurosurg Psychiatry 51: 1576–7. Ross, D.S. (1996). Subclinical thyrotoxicosis. In Werner and Ingbar’s The Thyroid. 7th edn., ed. L.E. Braverman and R.D. Utiger, pp. 1016–20. Philadelphia: Lippincott-Raven Publishers. Samuels, M.H. (1998). Subclinical thyroid disease in the elderly. Thyroid 8: 803–13. Sanders, V. (1962). Neurologic manifestations of myxoedema. N Engl J Med 266: 547–52. Seipelt, M., Zerr, I., Nau, R. et al. (1999). Hashimoto’s encephalitis as a differential diagnosis of Creutzfeldt–Jakob disease. J Neurol Neurosurg Psychiatry 66: 172–6. Shaw P.J., Walls, T.J., Newman, P.K., Cleland, P.G. and Cartlidge, N.E.F. (1991). Hashimoto’s encephalopathy: a steroid-responsive disorder associated with high anti-thyroid antibody titers. Neurology 41: 228–33. Shein, M., Apter, A., Dickerman, Z., Tyano, S. and Gadoth, N. (1986). Encephalopathy in compensated Hashimoto’s thyroiditis: a clinical expression of autoimmune cerebral vasculitis. Brain Dev 8: 60–6. Shetty K.R. and Duthie, E.H. Jr (1995). Thyroid disease and associated illness in the elderly. Clin Geriatr Med 11: 311–25. Soederbergh, G. (1910). Faut-il attribuer à une perturbation des fonctions cérébelleuses certains troubles moteurs du myxoedème? Rev Neurol (Paris) 2: 487–91. Strom, T.M., Hortnagel, K., Hofmann, S. et al. (1998). Diabetes insipidus, diabetes mellitus, optic atrophy and deafness

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(DIDMOAD) caused by mutations in a novel gene (wolframin) coding for a predicted transmembrane protein. Hum Mol Genet 7: 2021–8. Susuki, N., Mitamura, R., Ohmi, H. and Itoh, Y. (1994). Hashimoto’s thyroiditis, distal renal tubular acidosis, pernicious anemia, and encephalopathy: a rare combination of auto-immune disorders in a 12 year old girl. Eur J Pediatr 153: 78–9. Takahashi, S., Mitamura, R., Itoh, Y., Suzuki, N. and Okuno, A. (1994). Hashimoto encephalopathy: etiologic considerations. Pediatr Neurol 11: 328–31. Tonner, D.R. and Schlechte, J.A. (1993). Neurologic complications of thyroid and parathyroid disease. Med Clin North Am 77: 251–63. Trentin, A.G. and Moura Neto, V. (1995). T3 affects cerebellar astrocyte proliferation, GFAP and fibronectin organization. Neuroreport 6: 293–6.

Wiersinga, W.M. (1995). Subclinical hypothyroidism and hyperthyroidism. I. Prevalence and clinical relevance. Neth J Med 46: 197–204. Willnow, S., Kiess, W., Butenandt, O. et al. (1996). Endocrine disorders in septo-optic dysplasia (De Morsier syndrome) – evaluation and follow up of 18 patients. Eur J Pediatr 155: 179–84. Wright, R.A., Hermann, R.C. and Parisi, J.E. (1999). Neurological manifestations of Erdheim–Chester disease. J Neurol Neurosurg Psychiatry 66: 72–5. Zulewski, H., Müller, B., Exer, P., Miserez, A.R. and Staub, J.J. (1997). Estimation of tissue hypothyroidism by a new clinical score: evaluation of patients with various grades of hypothyroidism and controls. J Clin Endocrinol Metab 82: 771–6.

Part V

Toxic Agents

21

Alcohol toxicity in the cerebellum: fundamental aspects Roberta Pentney Department of Anatomy and Cell Biology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, USA

Introduction Abuse of alcohol and alcoholism are associated with a risk of toxic damage to the central nervous system (CNS), frequently accompanied by modified behavioral patterns, such as ataxia of the lower extremities associated with alcohol-induced cerebellar degeneration in humans. Most of what is known about alcohol toxicity has been inferred from the study of autopsied human tissues and of in-vitro and in-vivo tissue and animal models. A major advantage of well-characterized animal models is that in them the progress of particular diseases and associated behavioral dysfunction can be documented. The discussion in this chapter focuses primarily on the toxic actions of ethanol in an animal model and on our current understanding of the functional consequences of those actions. The rodent cerebellum is illustrated schematically in Fig. 21.1. Basic similarities in the organization and synaptic circuitry of the cerebellum in all mammals make nonprimate mammalian species, especially rodents, excellent subjects for experimental studies of cerebellar structure and function. Toxic effects of ethanol on cerebellar structure and function have been studied extensively in rodents, and results from studies not considered here have been reviewed previously (see Hunt and Nixon, 1993).

Neuronal targets of ethanol As illustrated in Fig. 21.1C–F, there are five major types of resident cerebellar neurons, but only two of these have figured prominently in studies of the effects of ethanol: the granule neurons, the most numerous neurons in the cerebellum, and the Purkinje neurons, the most spectacular neurons in the cerebellum. The discussion that follows focuses on these two cell types. The experimental effects of

alcohol on the morphometry and function of these cerebellar cortical cells are summarized in Table 21.1.

Toxic effects of ethanol on cerebellar granule neurons Morphometry Chronic ethanol intake by adult Sprague Dawley rats induces major morphometric changes in cerebellar granule neurons. After three months of ethanol treatment, the microtubular density in granule cell axons of the ethanol-treated rats was higher (70/m2) than in control rats (45/m2). By 12 months of ethanol treatment, the microtubular density reached a new plateau (90/m2) that persisted through 18 months of treatment (PaulaBarbosa and Tavares, 1985). In contrast, the numerical density of the granule neurons declined significantly during ethanol treatment (Tavares and Paula-Barbosa, 1982), suggesting that the increase in the microtubular density in the parallel fibers of surviving granule cells might reflect a plasticity that served to re-establish synaptic contacts vacated by other ethanol-damaged granule neurons. Additional measurements of the volumes of the cerebellar layers permitted conversion of the numerical densities of granule neurons to total numbers of cells, and a significant decrease in the total number of granule neurons of approximately 25% after six months of chronic ethanol intake was shown (Tavares et al., 1987). An equivalent loss of granule neurons was also reported in Long–Evans hooded rats after five months of ethanol treatment (Walker et al., 1980), but interpretation of this latter result was complicated by the fact that the neurons were counted only after a period of recovery. The effect of ethanol intake on total numbers of granule neurons was recently studied anew in Fischer 344 (F344) rats when it appeared that a loss of granule neurons might

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Fig. 21.1 (A) External view of the rodent cerebellum. (B) Schematic drawing of a parasagittal view of the layering and lobular folding of the cerebellar cortex, exposed by a cut along the shaded plane in (A). (C–F) Repeated views of the shaded block of tissue in (B), illustrating separately the major afferent fibers and the major types of cerebellar cortical neurons. 1, monoaminergic fiber; 2, climbing fiber; 3, Golgi neuron; 4, Purkinje neuron; 5, mossy fiber; 6, basket neuron (Purkinje cell body is shaded for orientation); 7, stellate neuron; 8, granule neurons with ascending axons and parallel fibers in the molecular layer. (Modified and reproduced from Pentney, 1993.)

Alcohol toxicity in the cerebellum: fundamental aspects

Table 21.1 Effects of alcohol on cerebellum: experimental evidence Morphometry

Function

Granule cells

Change in microtubular density in axons Loss of granule cells (?)

Inhibition of calcium uptake Reduction in the expression of BDNF Inhibition of IGF-1 signaling Reduction in cGMP Inactivation of cerebellar NOS Impairment of adenosine A1 neurotransmission

Purkinje cells

Dendritic damage Loss of Purkinje neurons

Impairment of protein functions via conformational changes Impairment of GABA neurotransmission ↑ Volume of SER Alteration in Purkinje cell firing behavior

Notes: BDNF: brain-derived neurotrophic factor; IGF-1: insulin-like growth factor 1; cGMP: cyclic guanosine monophosphate; NOS: nitric oxide synthase; GABA: gamma-aminobutyric acid; SER: smooth endoplasmic reticulum.

be the cause of ethanol-related dendritic degeneration in Purkinje neurons of aging F344 rats. The experiments conducted to verify that hypothesis provided quite unexpected results. Ten months of chronic ethanol intake by aging F344 rats did not produce significant decreases in the total numbers of cerebellar granule neurons (Tabbaa et al., 1999). Several studies were initiated to determine whether major methodological differences, such as the animals’ age during treatment, the strain of rat used, and the type of diet selected for ethanol administration, as well as the dose of ethanol consumed might underlie this discrepancy. These studies have been completed recently or are near completion. One of these, a comparative study of the effects of chronic ethanol intake by F344 rats during the first half of the lifespan, showed that younger F344 rats had significantly more granule neurons than aging F344 rats, an agerelated difference. There were, nonetheless, no significant ethanol-related differences in the total numbers of granule neurons in F344 rats of either age (Pentney et al., submitted). Results from a companion study using young and aging Wistar-Kyoto (Wky) rats, treated identically to the F344 rats, are also now available. The Wky rats consumed larger volumes of the ethanol-containing diet than the F344 rats, and they developed higher blood ethanol levels. Nonetheless, there were no losses of granule neurons in the Wky rats at either age, confirming results obtained with the F344 rats (Pentney et al., submitted). These data, currently being considered for publication, revive questions concerning the actions of ethanol on cerebellar granule neurons that need to be resolved.

Function of granule neurons Granule neurons are activated by glutamate, and their specific glutamate receptor subtype is the N-methyl-aspartate (NMDA) receptor linked to a membrane calcium channel (Iorio et al., 1992). NMDA has an anti-apoptotic effect on cerebellar granule cells in vitro, associated with increased levels of brain-derived neurotrophic factor (BDNF) protein that potentially mimics the effects of glutamatergic innervation of granule neurons in vivo. BDNF acts as a protective autocrine agent, and the mechanism by which NMDA promotes BDNF expression is assumed to involve calcium ion influx through activated NMDA receptors. The initial actions of ethanol on NMDA receptors inhibit calcium uptake, thereby inhibiting the expression of BDNF (Bhave et al., 1999; Fig. 21.2). Ethanol does not inhibit the protective effects of BDNF protein directly (Fig. 21.3), however, whereas it does reduce the protective effects of insulin-like growth factor-1 (IGF-1), another important neurotrophin for cerebellum (Zhang et al., 1998). These results suggest (1) that ethanol does not act downstream of the NMDA receptor, and (2) that the NMDA receptor may be one of a number of ‘receptive targets’ for toxic actions of ethanol in the brain (Bhave et al.,1999). With prolonged exposure to ethanol, NMDA receptor function becomes upregulated, presumably to overcome the initial inhibition of NMDA receptor function. It is postulated that the upregulation of receptor function produces subsequent imbalances in intracellular calcium levels that contribute to withdrawal seizures once chronic ethanol consumption is discontinued (Iorio et al., 1992). Recently, Freund and Anderson (1999) tested the hypothesis that the cumulative effects of chronic alcohol in

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*

Control

*, **

Ethanol

50

25

0

Apoptotic cell death (% of total)

Control

75

BDNF (pg)

330

Ethanol

60

*

50

**

40 30

* *

20 10 0 5 mM KCl

5 mM KCl

NMDA

Fig. 21.2 Ethanol reduces NMDA-induced BDNF expression. Cerebellar granule cells are grown in medium containing 5 mM of KCl, which induces apoptosis. On day 4, ethanol (100 mM) is administered five minutes before addition of 100 M NMDA; 24 hours later, BDNF levels (expressed in pg) are determined. Values are mean SEM of 4–19 observations in two experiments. *: p 0.001 compared to physiological concentration of KCl (5 mM); **: p0.001 compared with NMDA group in absence of ethanol. (Reproduced with permission from S.V. Bhave, L. Ghoda and P.L. Hoffman (1999). Journal of Neuroscience, Vol. 19, pp. 3277–86.)

human alcoholics alter glutamate receptors. They compared samples of the vermis from autopsied cerebella of alcoholics and controls for differences in NMDA receptor densities and receptor binding and found no significant differences. There are currently no other published data concerning the effects of chronic alcohol toxicity on NMDA subunits in humans. Calcium imbalance within neurons may also alter synaptic relationships between neurons. The regulation of synaptic transmission and the development of long-term depression associated with cerebellar learning involve coordinated actions of the NMDA receptor, nitric oxide synthase, and guanylate cyclase (Boxall and Garthwaite, 1996). Under normal conditions, nitric oxide and cyclic guanosine monophosphate (cGMP) levels are elevated following NMDA-activated calcium uptake. Intoxicating doses of ethanol cause reductions in cerebellar cGMP levels, presumably through induced functional changes in NMDA receptors. Physiologically relevant levels of ethanol also inactivate cerebellar nitric oxide synthase (Fataccioli et al., 1997). The adenosine A1 receptors are found in high concentrations in granule neurons. They are also involved in the appearance of ethanol-related ataxia. It has been shown in rats that the dose–response effect between alcohol concentration and ataxic behavior is potentiated if a pretreatment with dilazep, an adenosine reuptake blocker, is

*

BDNF

IGF-1

Fig. 21.3 Ethanol increases apoptosis of granule cells, reduces the protective effect of IGF-1 but not of BDNF. Cerebellar granule cells are grown in medium containing 5 mM of KCl, which has an apoptotic effect. On day 4, granule cells are treated with 100 mM ethanol, before addition of BDNF or IGF-1. Apoptosis is assessed 24 hours later. Apoptotic cell death is expressed as a percentage of total cells (% of total). Values are mean SEM of a series of eight observations in three different experiments. *: p0.001 compared with control group in absence of ethanol; **: p0.05 compared with IGF-1 group in absence of ethanol. (Reproduced with permission from S.V. Bhave, L. Ghoda and P.L. Hoffman (1999). Journal of Neuroscience, Vol. 19, pp. 3277–86.)

administered (Clark and Dar, 1988). Moreover, the level of incoordination diminishes with administration of antagonists of adenosine, such as theophylline.

Toxic effects of ethanol on cerebellar Purkinje neurons Morphometry Early post-mortem studies of the cerebella of human alcoholics reported extensive loss of Purkinje neurons, but without supporting quantitative data (Neubuerger, 1957; Victor et al., 1959; Lynch, 1960; Allsop and Turner, 1966). Several newer studies have now increased our understanding of alcohol toxicity in the human cerebellum by providing important quantitative information. Torvik and Torp (1986) found that the prevalence of reductions in densities of Purkinje neurons and in the thickness of the molecular and granular layers in alcoholics was over 40%. Lobules I–IV rostrally and lobules IX–X caudally were the most severely atrophied regions of the cerebellar vermis, with marked reductions in the area of the molecular layer (Phillips et al., 1987). The precise duration of chronic alcohol abuse by each alcoholic subject was generally not known in these studies, but Karhunen et al. (1994) did attempt to estimate the daily consumption of each subject in their study. They found that a moderate intake of 41–80 g

Alcohol toxicity in the cerebellum: fundamental aspects

Fig. 21.4 Camera lucida drawings (left column) and corresponding photographic montages (right column) of Purkinje cells from a 6-month control rat (1, 2), 6-month alcoholfed rat (3, 4), and a 12-month alcohol-fed rat (5, 6). Note the disruption of the dendritic domains. Magnification 500. (Modified and reproduced from M.A. Tavares, M.M. PaulaBarbosa and E.G. Gray (1983). A morphometric Golgi analysis of the Purkinje cell dendritic tree after long-term alcohol consumption in the adult rat. Journal of Neurocytology, Vol. 12, pp. 939–48, with permission from Kluwer Academic/Plenum Publishers.)

daily for 20–30 years resulted in a significant loss of Purkinje neurons within a sagittal section of the cerebellum in advance of apparent macroscopic atrophy (Karhunen et al., 1994). To what extent episodes of withdrawal from alcohol during binge drinking contribute to cerebellar damage in human subjects remains unknown, however. Some alcohol-induced atrophic changes described in human alcoholics have been verified in animal models. For example, an ethanol-induced loss of Purkinje neurons in adult Sprague Dawley rats was reported by Tavares et al. (1987), but consumption of ethanol during 80% of the rats’ lifespan was required. Phillips and Cragg (1982, 1984) did not find significant atrophy of the cerebellar vermis or significant loss of Purkinje neurons in C57/Bl/6J mice after chronic ethanol intake for four months. Their results suggested, however, that even this short period of ethanol intake had disturbed Purkinje neuron homeostasis, because after four months of recovery there was a significant loss of Purkinje neurons in the treated mice. Neonatal animals were most vulnerable to alcohol, with the overall shape of the vermal cerebellum being grossly altered, appearing ‘short and squat’ (Pierce and West, 1987). Cell death is an accepted endpoint of ethanol toxicity, but neuronal damage antecedent to cell death also provides important clues concerning the cellular mechanisms activated by ethanol. A neuron as expansive as the Purkinje cell may sustain extensive dendritic damage and resultant dysfunction before cell death occurs. Thus, morphometric evidence of dendritic damage in Purkinje neurons of rats is present after 3 to 12 months of chronic ethanol intake, long before significant death of Purkinje neurons occurs. Examples of such damage in dendritic arbors include: decreases in total branch length and total number of spines (Tavares et al., 1983), decreases in dendritic field area (Walker et al., 1980), decreases in the total number of branches (Pentney, 1982), and decreases in branch density and spine density (Tavares et al., 1983; Fig. 21.4). Extensive follow-up studies have provided important details that

Fig. 21.4

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define the ethanol-induced dendritic damage. As a result, it is now known that the mean lengths of terminal dendritic segments (segments with free tips) increase significantly (Pentney et al., 1989; Pentney and Quackenbush, 1991), the median path lengths of dendritic arbors decreases significantly (Pentney, 1995), and the total number of synapses on dendritic arbors decreases significantly (Dlugos and Pentney, 1997). The one model of dendritic degeneration that is consistent with the above data is based on a hypothesized vulnerability of the branch points (junctions) of terminal segments to the actions of ethanol. Branch points involve a minimum of three segments, commonly two terminal segments and one parent internal segment or one terminal segment and two internal segments, one of which is the parent of the terminal segment. In either case, if one terminal segment is deleted at the branch point, the remaining two segments form a continuous longer segment, in the first case a longer terminal segment and in the second case a longer internal segment. In this model, then, dendritic segments lengthen by confluence of two sequential dendritic segments. Multiple deletion events of this type were shown to occur at random throughout the dendritic arbor, with no particular region of the tree being more sensitive to ethanol than other regions (Pentney, 1995). Deletion events led to a thinning of the dendritic arbor and, indirectly, to a loss of synapses. It was shown further that granule cell numbers and spine densities on the Purkinje neurons did not change in the ethanol-treated rats (Tabbaa et al., 1999) and were not responsible, therefore, for the deletion of terminal segments. Significant decreases in dendritic arborization of Purkinje neurons have also been shown in human alcoholics (Ferrer et al., 1984). The major difference between ethanol-induced dendritic damage in human cerebella and that in rat cerebella was that dendritic damage was restricted to the rostral cerebellum in human alcoholics, whereas it was distributed throughout all lobules of the vermis in the rat cerebellum (Pentney and Dlugos, 2000).

Function of cerebellar Purkinje neurons Current information suggests that the mechanism(s) underlying the toxic effects of ethanol on Purkinje neurons involves specific actions of ethanol on membrane and cytoplasmic proteins. In a recent review, Fadda and Rossetti (1998) discussed the wealth of evidence that points to selective effects of ethanol that produce conformational changes that can alter protein functions. Of great importance are the facts that the selectivity of ethanol for proteins is evident at pharmacologically and physiologically relevant levels of ethanol and that the actions of

ethanol on membrane proteins commonly involve a disruption of the membrane regulation of calcium levels. Purkinje neurons are not responsive to NMDA. Nonetheless, their somatic and dendritic membranes contain at least two other neurotransmitter receptors that are implicated in ethanol’s actions on neurons. One of these is the -amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptor lining a ligand-gated calcium channel that mediates glutamate-activated currents in Purkinje neurons and participates in ethanolinduced excitotoxicity (Lovinger, 1993). The AMPA/kainate channels are distributed in the dendritic and somatic membranes of the Purkinje neuron (Häusser and Roth, 1997). The other is the -aminobutyric acid (GABAA) receptor linked to a chloride channel. This receptor is directly inhibited by low concentrations of ethanol (5–50 mM). Particular combinations of GABAA subunits are required for receptor sensitivity to ethanol, but the exact subunits involved have not yet been identified (Grant and Lovinger, 1995). The function of the GABAA receptor is to regulate glutamate transmission, and it is likely that ethanol inhibition of the GABAA receptor contributes to the potential for excitotoxic levels of calcium to enter the cell through glutamate-activated channels (Lovinger, 1993). Moreover, GABAA receptors modulate the activity of immature neurons during embryonic and early postnatal development. The observation that early postnatal exposure to alcohol inhibits the maturation of GABAA receptors suggests that these receptors may be a key factor in the fetal alcohol syndrome (Hsiao et al., 1999). The smooth endoplasmic reticulum is of great interest in the context of ethanol’s actions in the Purkinje neuron. The average relative volume of smooth endoplasmic reticulum in the dendrites of Purkinje neurons increased almost fivefold in young Wistar rats after three months of ethanol intake (Lewandowska et al.,1994). Many smooth endoplasmic reticulum profiles in the dendrites of Purkinje neurons of aging, ethanol-treated rats were also found to be significantly dilated (Dlugos and Pentney, 2000; Fig. 21.5). It has been noted that excessive calcium influx is often associated with expansion of the endoplasmic lumen (Garthwaite et al., 1992), and receptors in the smooth endoplasmic receptors membranes of Purkinje neurons may be important targets of the actions of ethanol. Visualization of the smooth endoplasmic reticulum in Purkinje neurons by quick-freezing techniques recently revealed membrane projections on the smooth endoplasmic reticulum membranes that are likely to be tetramers of IP3 receptor molecules associated with a central channel, presumably a calcium channel (Kanaseki et al., 1998). A study of the effects of ethanol on mRNA levels of inositol

Alcohol toxicity in the cerebellum: fundamental aspects

reported a relatively transient effect of acute alcohol application on Purkinje cell firing, lasting 30–60 minutes. Low doses have an excitatory effect, evidenced by an increase in simple spike discharges, whereas high doses exert an inhibitory action (Chu, 1983), except that doses higher than 1g/kg produce an increase in the complex spikes. By contrast, chronic exposure does not seem to modify Purkinje cell firing behavior. Nonetheless, withdrawal of animals from chronic alcohol treatment results in a decrease in frequency of climbing fiber bursts and depression of spontaneous rates of Purkinje neuron discharges.

Ethanol and cytochrome P450 P450 IIE1 is a specific form of cytochrome P450 that is active in ethanol oxidation. With polyclonal antisera against P450 IIE1, immunoreactivity has been demonstrated in all cell layers in the rat cerebellum (Hansson et al., 1990). Prominent reactivity was observed in glial cells, including astrocytes and oligodendrocytes. Staining of blood vessels was also observed throughout the cerebellum, particularly in the white matter where the end-feet of immunoreactive glial cells surrounded the vessels. By contrast, staining did not occur in Purkinje cells. Although these findings seem interesting, their potential implications have not been established.

Fig. 21.5 Electron micrographs illustrating the smooth endoplasmic reticulum (SER) in Purkinje neuron dendrites in a pair-fed control rat and an ethanol-fed rat treated for ten months. (A) Pair-fed rat. Profiles of hypolemmal cisternae of the SER (surrounded by three arrows) just beneath the dendritic membrane at a branch point of a dendritic shaft (dsh). Profile of a tubular portion of the SER (indicated by single arrow). (B) Ethanol-fed rat. Profile of a dilated tubular portion of the SER (surrounded by three arrows) located centrally in a dendritic shaft (dsh).

1,4,5-trisphosphate receptor 1 (IP3R1) suggested that ethanol decreased mRNA levels for IP3R1 and for the IP3linked metabotropic glutamate receptor 1, but not for IP3kinase (Simonyi et al., 1996). Data relative to ethanol targeting of specific smooth endoplasmic reticulumlinked proteins are not yet available, but specific actions of ethanol on the mRNA levels of these proteins may figure prominently in the toxicity of ethanol-induced dendritic degeneration in Purkinje neurons. Ethanol is known to impair Purkinje cell firing in rats (Bloom and Siggins, 1987; Worner, 1993). Most studies have

Conclusion CNS impairment is a major complication of alcohol intake. Animal studies, especially with rodent models, demonstrate that ethanol modifies the morphometry and the function of cerebellar neurons, chiefly granule cells and Purkinje cells. These new insights into the mechanisms of alcohol-related cerebellar damage have direct implications for our understanding of ataxia in humans.

xReferencesx Allsop, J. and Turner, B. (1966). Cerebellar degeneration associated with chronic alcoholism. J Neurol Sci 3: 238–58. Bhave, S.V., Ghoda, L. and Hoffman, P.L. (1999). Brain-derived neurotrophic factor mediates the anti-apoptotic effect of NMDA in cerebellar granule neurons: signal transduction cascades and site of ethanol action. J Neurosci 19: 3277–86. Bloom, F.E. and Siggins, G.R. (1987). Electrophysiological action of ethanol at the cellular level. Alcohol 4: 331–7.

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Boxall, A.R. and Garthwaite, J. (1996). Long-term depression in rat cerebellum requires both NO synthase and NO-sensitive guanylyl cyclase. Euro J Neurosci 8: 2209–12. Chu, N.S. (1983). Effects of alcohol on rat cerebellar Purkinje cells. Int J Neurosci 21: 265–78. Clark, M. and Dar, M.S. (1988). Mediation of acute ethanolinduced motor disturbances by cerebellar adenosine in rats. Pharmacol Biochem Behav 30: 155–61. Dlugos, C.A. and Pentney, R.J. (1997). Morphometric evidence that the total number of synapses on Purkinje neurons of old F344 rats is reduced after long-term ethanol treatment and restored to control levels after recovery. Alcohol Alcohol 32: 161–72. Dlugos, C.A. and Pentney, R.J. (2000). Effects of chronic ethanol consumption on SER of Purkinje neurons in old F344 rats. Alcohol 20: 125–32. Fadda, F. and Rossetti, Z.L. (1998). Chronic ethanol consumption: from neuroadaptation to neurodegeneration. Prog Neurobiol 56: 385–431. Fataccioli, V., Gentil, M., Nordmann, R. and Rouach, H. (1997). Inactivation of cerebellar nitric oxide synthase by ethanol in vitro. Alcohol Alcohol 32: 683–91. Ferrer, I., Fabregues, I., Pineda, M., Gracia, I. and Ribalta, T. (1984). A Golgi study of cerebellar atrophy in human chronic alcoholism. Neuropathol Appl Neurobiol 10: 245–53. Freund, G. and Anderson, K.J. (1999). Glutamate receptors in the cingulate cortex, hippocampus, and cerebellar vermis of alcoholics. Alcohol Clin Exp Res 23: 1–6. Garthwaite, G., Hajos, F. and Garthwaite, J. (1992). Morphological response of endoplasmic reticulum in cerebellar Purkinje cells to calcium deprivation. Neuroscience 48: 681–8. Grant, K.A. and Lovinger, D.M. (1995). Cellular and behavioral neurobiology of alcohol: receptor-mediated neuronal processes. Clin Neurosci 3: 155–64. Hansson, T., Tindberg, N., Ingelman-Sundberg, M. and Köhler, C. (1990). Regional distribution of ethanol-inducible cytochrome P450 IIE1 in the rat central nervous system. Neuroscience 34: 451–63. Häusser, M. and Roth, A. (1997). Dendritic and somatic glutamate receptor channels in rat cerebellar Purkinje cells. J Physiol 501.1: 77–95. Hsiao, S-H., West, J.R., Mahoney, J.C. and Frye, G.D. (1999). Postnatal ethanol exposure blunts upregulation of GABAA receptor currents in Purkinje neurons. Brain Res 832: 124–35. Hunt, W.A. and Nixon, S.J. (eds.) (1993). Alcohol-induced Brain Damage. NIH Publication No. 93–3549. National Institute on Alcohol Abuse and Alcoholism, US Department of Health and Human Services. Iorio, K.R., Reinlib, L., Tabakoff, B. and Hoffman, P.L. (1992). Chronic exposure of cerebellar granule cells to ethanol results in increased N-methyl--aspartate receptor function. Mol Pharmacol 41: 1142–8. Kanaseki, T., Ikeuchi, Y. and Tashiro, Y. (1998). Rough surfaced smooth endoplasmic reticulum in rat and mouse cerebellar Purkinje cells visualized by quick-freezing techniques. Cell Struct Funct 23: 373–87. Karhunen, P.J., Erkinjuntti, T. and Laippala, P. (1994). Moderate

alcohol consumption and loss of cerebellar Purkinje cells. Br Med J 308: 1663–7. Lewandowska, E., Kujawa, M. and Jedrzejewska, A. (1994). Ethanol-induced changes in Purkinje cells of rat cerebellum. II. The ultrastructural changes after chronic ethanol intoxication (morphometric evaluation). Folia Neuropathol 32: 61–4. Lovinger, D.M. (1993). Excitotoxicity and alcohol-related brain damage. Alcohol Clin Exp Res 17: 19–27. Lynch, M.J.G. (1960). Brain lesion in chronic alcoholism. Arch Pathol (Chicago) 69: 342–53. Neubuerger, K.T. (1957). The changing neuropathologic picture of chronic alcoholism. Arch Pathol (Chicago) 63: 1–6. Paula-Barbosa, M.M. and Tavares, M.A. (1985). Long term alcohol consumption induces microtubular changes in the adult rat cerebellar cortex. Brain Res 339: 195–9. Pentney, R.J. (1982). Quantitative analysis of ethanol effects on Purkinje cell dendritic tree. Brain Res 249: 397–401. Pentney, R.J. (1993). Alterations in the structure of the cerebellum after long-term ethanol consumption. In Alcohol-induced Brain Damage, ed. W.A. Hunt and S.J. Nixon, NIH Publication No. 93–3549. pp. 249–76. National Institute on Alcohol Abuse and Alcoholism, US Department of Health and Human Services. Pentney, R.J. (1995). Measurements of dendritic path lengths provide evidence that ethanol-induced lengthening of terminal dendritic segments may result from dendritic regression. Alcohol Alcohol 30: 87–96. Pentney, R.J. and Dlugos, C.A. (2000). Cerebellar Purkinje neurons with altered terminal dendritic segments are present in all lobules of the cerebellar vermis of aging, ethanol-treated F344 rats. Alcohol Alcohol 35: 35–43. Pentney, R.J., Mullan, B.A., Felong, A.M. and Dlugos, C.A. (Submitted). The total numbers of cerebellar granule neurons in young and aged Fischer 344 and Wistar–Kyoto rats do not change as a result of lengthy ethanol treatment. Pentney, R.J. and Quackenbush, L.J. (1991). Effects of long durations of ethanol treatment during aging on dendritic plasticity in Fischer 344 rats. Alcohol Clin Exp Res 15: 1024–30. Pentney, R.J., Quackenbush, L.J. and O’Neill, M. (1989). Length changes in dendritic networks of cerebellar Purkinje cells of old rats after chronic ethanol treatment. Alcohol Clin Exp Res 13: 413–19. Phillips, S.C. and Cragg, B.G. (1982). A change in susceptibility of the cerebellar Purkinje cells to damage by alcohol during fetal, neonatal or adult life. Neuropathol Appl Neurobiol 8: 441–54. Phillips, S.C. and Cragg, B.G. (1984). Alcohol withdrawal causes a loss of cerebellar Purkinje cells in mice. J Stud Alcohol 45: 475–80. Phillips, S.C., Harper, C.G. and Kril, J. (1987). A quantitative histological study of the cerebellar vermis in alcoholic patients. Brain 110: 301–14. Pierce, D.R. and West, J.R. (1987). Differential deficits in regional brain growth induced by postnatal alcohol. Neurotoxicol Teratol 9: 129–41. Simonyi, A., Zhang, J-P., Sun, A.Y. and Sun, G.Y. (1996). Chronic ethanol on mRNA levels of IP3R1, IP3-kinases and mGluR1 in mouse Purkinje neurons. NeuroReport 7: 2115–18. Tabbaa, S., Dlugos, C. and Pentney, R. (1999). The number of

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granule cells and spine density on Purkinje cells in aged, ethanol-fed rats. Alcohol 17: 253–60. Tavares, M.A. and Paula-Barbosa, M.M. (1982). Alcohol-induced granule cell loss in the cerebellar cortex of the adult rat. Exp Neurol 178: 574–82. Tavares, M.A., Paula-Barbosa, M.M. and Cadete-Leite, A. (1987). Chronic alcohol consumption reduces the cortical layer volumes and the number of neurons of the rat cerebellar cortex. Alcohol Clin Exp Res 11: 315–19. Tavares, M.A., Paula-Barbosa, M.M. and Gray, E.G. (1983). A morphometric Golgi analysis of the Purkinje cell dendritic tree after long-term alcohol consumption in the adult rat. J Neurocytol 12: 939–48. Torvik, A. and Torp, S. (1986). The prevalence of alcoholic cerebellar atrophy. J Neurol Sci 75: 43–51.

Victor, M., Adams, R.D. and Mancall, E.L. (1959). A restricted form of cerebellar cortical degeneration occurring in alcoholic patients. Arch Neurol 1: 579–608. Walker, D.W., Barnes, D.E., Riley, J.N., Hunter, B.E. and Zornetzer, F. (1980). Neurotoxicity of chronic alcohol consumption: an animal model. In Psychopharmacology of Alcohol, ed. M. Sandler, pp.17–31. New York: Raven Press. Worner, T.M. (1993). Effects of alcohol. In Handbook of Cerebellar Diseases, ed. R. Klechtenberg, pp. 547–66. Marcel Dekker. Zhang, F.X., Rubin, R. and Rooney, T.A. (1998). Ethanol induces apoptosis in cerebellar granule neurons by inhibiting insulinlike growth factor 1 signaling. J Neurochem 71: 196–204.

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Alcohol toxicity in the cerebellum: clinical aspects Mario-Ubaldo Manto1 and Jean Jacquy2 1

Cerebellar Ataxias Unit, 2 Department of Neurology, Free University of Brussels, Belgium

Introduction

Table 22.1 Neurological features in alcoholic patients

Alcohol consumption is a mattern of concern world-wide and a major problem of public health in many countries. The estimated overall prevalence of alcohol dependence is 0.5–3% of the population in Europe or in the USA. The central and peripheral nervous systems are the two principal targets. Chronic alcohol ingestion can impair the function and morphology of most, if not all, brain structures (Fadda and Rossetti, 1998). In particular, alcohol is an important toxic agent for the cerebellum (see also Chapter 21). This chapter describes the effects of alcohol consumption in humans, focusing on cerebellar function.

Cerebellar signs Gaze-evoked nystagmus () Ocular dysmetria () Slurred speech () Kinetic tremor () 3 Hz postural leg tremor () Ataxic gait () Titubation () Hypotonia () Decreased tendon reflexes Amyotrophy Wernicke’s encephalopathy: mental confusion, ophthalmoparesia, ataxic gait Korsakoff’s psychosis, dementia Alcohol withdrawal syndrome: hallucinations, agitation, autonomic overactivity Asterixis Myoclonus Seizures Extensor plantar reflexes

Clinical findings Both acute and chronic ingestion of alcohol result in cerebellar dysfunction (Gilman et al., 1981). The main complaint in patients presenting alcohol-induced cerebellar dysfunction is difficulty in standing and walking. The majority of patients report a lack of coordination in the lower extremities (Gilman et al., 1990). Table 22.1 summarizes the neurological signs, both cerebellar and extracerebellar, which are observed in adult alcoholic patients. During acute alcohol intoxication, patients exhibit slurred speech, gaze-evoked nystagmus, anterior–posterior oscillations in Romberg’s test, and broad-based ataxic gait. These ataxic signs tend to become chronic features with chronic alcohol abuse (Gilman et al., 1981). Gait difficulties either worsen progressively over weeks or months, or may rapidly turn to a debilitating deficit, particularly in the case of malnutrition. A third pattern of progression is encountered rarely and comprises relatively unpredictable exacerbations. In alcoholic patients, legs appear stiff during gait but not when the patient is in a lying position. This ‘stiff

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appearance’ was well observed in the syndrome of ‘alcoholinduced cerebellar degeneration’, described by Victor and colleagues in 1959. The patients had not only consumed alcohol every day for several years, but also had clinical evidence of malnutrition. More than half of them had concomitant polyneuropathy and half of them suffered from liver disease. The clinical deficits included moderate to severe ataxia of stance and gait, contrasting with relative sparing of upper limbs. Nystagmus and dysarthria were less prominent than in degenerative diseases. Nearly 30% of the patients presenting cerebellar degeneration had a prior history of delirium tremens. Nowadays, with the improvements in the prevention and treatment of alcohol-

Alcohol toxicity in the cerebellum: clinical aspects

Table 22.2 Conditions associated with the Wernicke–Korsakoff syndrome

Table 22.3 Factors apparent on brain MRI in alcoholic patients

Alcoholism Hyperemesis gravidarum Dialysis: peritoneal dialysis, hemodialysis Gastroplasty for obesity, intestinal surgery (Whipple’s procedure) Psychogenic food refusal, beriberi Patients in critical care units who do not receive nourishment by mouth Induced by therapy Acquired immunodeficiency syndrome (AIDS) Chemotherapy for malignancies Immunosuppressants after bone marrow transplantation Thyrotoxicosis

Widening of cerebral sulci Dilatation of ventricles and aqueduct Symmetric lesions in the periventricular areas and dorsal thalamus Atrophy of mamillary bodies Mamillary body enhancement following gadolinium injection Cerebellar atrophy predominating in anterior lobe

withdrawal syndrome, the incidence of delirium tremens has decreased, so that only 5–12% of the patients showing alcohol-induced cerebellar degeneration have a history of delirium tremens. In Wernicke’s encephalopathy, some of the most severely afftected patients exhibit a combination of mental confusion, oculomotor signs, and ataxic gait (Zubaran et al., 1997). Oculomotor signs include a nystagmus and paralysis of the external rectus muscles generating a diplopia. The onset of Wernicke’s encephalopathy is usually abrupt. The patients may also present a cerebellar ataxia associated with severely restricted memory and confabulation suggestive of Korsakoff’s syndrome. Characteristically, immediate memory is preserved, but short-term memory is defective. The term Wernicke–Korsakoff syndrome is often applied in this case. Table 22.2 lists the conditions associated with the Wernicke–Korsakoff syndrome. Due to the rigid traditional diagnostic criteria and to the subclinical forms of Wernicke’s encephalopathy, the diagnosis may be overlooked (Zubaran et al., 1997). For example, in a neuropathological series of 131 cases, the diagnosis was made in only 20% of the cases (Harper, 1983). Neuropsychological studies have confirmed cognitive deficits in patients with alcoholic cerebellar degeneration (Johnson-Greene et al., 1997). In particular, executive skills are impaired, such as the Category Test. However, alcoholic patients without cerebellar degeneration have similar cognitive deficits, suggesting that alcoholic cerebellar degeneration is not accompanied by more severe deficits in higher cerebral functions.

Incidence and demonstration of cerebellar atrophy It is estimated that between 27% and 42% of patients presenting alcoholism have a cerebellar degeneration (Torvik et al., 1982; Torvik 1987; Worner, 1993). Approximately a quarter of these patients have severe hepatic disease. However, more than 20% of patients with hepatic cirrhosis have no cerebellar signs. Other studies have estimated that a daily consumption of 150 g of alcohol for ten years was associated with a significant cerebellar atrophy as demonstrated by brain computed tomography (CT) in 30% of patients (Haubek and Lee, 1979). With such consumption, concomitant widening of fissures and sulci over the cerebral hemispheres is often found, particularly in the frontal lobes. In Wernicke’s encephalopathy, brain CT shows in 10–20% of cases a non-enhancing hypodense area around the aqueduct during the acute phase (Gallucci et al., 1990), usually in association with superior vermian atrophy. It should be emphasized that it is not exceptional to observe a severe cerebellar atrophy on brain CT in young chronic alcohol-dependent patients without cerebellar signs on neurological examination. However, follow-up of these patients will often reveal the appearance of cerebellar deficits later. Brain magnetic resonance imaging (MRI) is a very useful tool to demonstrate atrophy of the cerebellum and to demonstrate extracerebellar lesions in adults and in children (Table 22.3). For instance, Sowell et al. have demonstrated in a group of nine children and in young adults with a prenatal alcohol exposure, atrophy of the anterior region of the vermis (lobules I to V), whereas the remaining lobules (VI to X) had a normal development (Sowell et al., 1996). Six of the children met the criteria of the fetal alcohol syndrome.

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Blood studies Blood investigations may show the following abnormalities: moderate to marked macrocytic anemia, platelet reduction, impaired liver function tests, sideropenia, and reduction of the levels of the blood transketolase. However, there is no direct correlation between these laboratory findings and the development of cerebellar ataxia.

Neuropathological findings The main sites of the deleterious effects of alcohol in the brain are the diencephalon/mesencephalon, medial temporal lobe structures, cortex in frontal lobes and cerebellum (Fadda and Rossetti, 1998). Microscopic changes in the mamillary bodies are the most common findings in autopsied cases (Cravioto et al., 1961; Harper, 1983). In the series of Victor et al. (1959), the major neuropathological abnormality was a widening of sulci in the cerebellar anterior lobe, with loss of cells in all layers of the cortex. Purkinje cells seem to be one of the most vulnerable neuronal populations in the cerebellum, as was pointed out by Thomas in 1905. Other structures in the cerebellar pathways are often affected; particularly, the deep cerebellar nuclei and the inferior olivary nuclei are not spared. In patients with a prior history of Wernicke’s encephalopathy, punctate hemorrhages affecting the gray matter around the third and fourth ventricles are usually found (‘polioencephalitis hemorrhagica superioris’), along with lesions in the medial portions of the thalami, dilatation of the third ventricle, and atrophic mamillary bodies. In addition, when death occurs following a deterioration of hepatic function, various degrees of diffuse degeneration of neurons are observed in the whole brain, in association with patchy loss of myelin.

Pathophysiology of cerebellar toxicity in humans During acute and chronic intoxication, alcohol interferes with neurotransmission and brain metabolism. Many neurotransmitter systems are affected, including the glutamatergic pathways, the gamma-aminobutyric acid (GABA)ergic pathways, the serotoninergic and noradrenergic systems (Gilman et al., 1996; Fadda and Rossetti, 1998). Alterations in benzodiazepine receptor density have been documented in post-mortem and in vivo studies of alcoholic patients with single-photon emission computed tomography (SPECT) method. With the benzo-

diazepine receptor radiotracer 123I-iomazenil, it has been shown recently that frontal, anterior cingulate, and cerebellar cortices were the principal zones affected (AbiDargham et al., 1998). Using 11C-flumazenil, Gilman et al. have demonstrated that severe chronic alcoholism damages neurons containing GABA-A/benzodiazepine receptors in the superior cerebellar vermis in patients showing clinical signs of alcoholic cerebellar degeneration (Gilman et al., 1996). The same authors also demonstrated a glucose hypometabolism in the anterior and superior portions of the cerebellar vermis in alcoholic patients with a previous history of malnutrition and exhibiting cerebellar ataxia (Gilman et al., 1990). Moreover, such effects of alcohol on the cerebellar glucose metabolic rate have been observed following acute ethanol administration of 1 g/kg (Volkow et al., 1990). The hypometabolism in the superior portions of the cerebellar vermis probably results from decreased cellular and synaptic activity because of neuronal loss (Gilman et al., 1990). Nutritional deficiencies are frequently observed in alcoholic patients and may contribute to the cerebellar degeneration (Gilman et al., 1981). Thiamine deficit seems to be a determinant factor of neuronal injury in the case of chronic consumption. Thiamin-deficient membranes are unable to maintain osmotic gradients, resulting in intracellular edema with swelling of oligodendrocytes, myelin sheaths, and neuronal dendrites. The periventricular regions would be preferentially injured because of the high rate of thiamine-related glucose and oxidative metabolism (Witt and Goldman-Rakic, 1983; Witt, 1985). Experimental studies not only support the hypothesis that thiamine deficiency can be the consequence of alcohol consumption, but also suggest that thiamine deficiency might be a predisposing factor in increased alcohol ingestion (Zimatkin and Zimatkina, 1996). Besides thiamine deficiency, electrolyte disorders have also been implicated in the pathogenesis of alcoholic cerebellar degeneration (Kleinschmidt-De Masters and Norenberg, 1981; Gilman et al., 1990). A personal susceptibility is a key factor in cerebellar alcohol toxicity and its metabolites (Setta et al., 1998). Some patients prove to be highly sensitive to low doses of alcohol even in the absence of cerebellar atrophy (Setta et al., 1998). Ingestion of 5 g of alcohol may be sufficient to induce a disabling cerebellar syndrome (Fig. 22.1). In chronic alcohol intake, cerebellar degeneration is not dependent on the dose ingested (Estrin, 1987). It has been suggested that personal neurological vulnerability may be related to individual differences in thiamine enzyme systems, because different levels of affinity have been found between thiamine pyrophosphate and transketolase (Greenwood et al., 1984). However, it is still not clear why

Alcohol toxicity in the cerebellum: clinical aspects

Fig. 22.1 High vulnerability to a small dose of alcohol. This patient exhibited a normal neurological examination in the basal condition and a cerebellar syndrome following intake of small doses of alcohol. Cerebellar deficits were a gaze-evoked nystagmus, scanning speech, increased body sway, and postural leg tremor. This figure illustrates the fast wrist flexion movements towards a fixed target before and after intake of 5 gr of alcohol. In the basal condition, voluntary movements are normometric; they become hypermetric after alcohol ingestion. EMG, electromyographic activity; AGO, agonist muscle; ANTA, antagonist muscle. (Reproduced from F. Setta, J. Jacquy, J. Hildebrand and M. Manto (1998). Ataxia induced by small amounts of alcohol. Journal of Neurology, Neurosurgery and Psychiatry, Vol. 65, pp. 370–3, with permission from BMJ Publishing Group.)

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Table 22.4 Treatment in alcoholism Thiamine parenterally 100–200 mg for the Wernicke–Korsakoff syndrome Maintenance with oral thiamine 100 mg daily Replacement therapy for ion deficits Alcohol abstinence Balanced diet Clonidine/fluvoxamine; benzodiazepines Disulfiram Acamptosate Naltrexone Rehabilitation of stance/gait; assistive devices Clinical–psychological follow-up

the spinocerebellum is particularly vulnerable (Setta et al., 1998). The hypothesis has been raised of an anatomical compartmentalization of cerebrospinal fluid flow within meninges, resulting in an increasing exposure of the vermis and paravermis to the toxic effects of alcohol (Cavanagh et al., 1997). Advanced liver disease is likely to contribute to the neuronal degeneration in the cerebellum, partly because liver dysfunction leads to impaired metabolism of thiamine and generates an imbalance in amino acid metabolism (Acker et al., 1982; Thomson et al., 1987; Zubaran et al., 1997).

Treatment The recommended treatment is given in Table 22.4. There should be no delay in the administration of thiamine in patients presenting Wernicke–Korsakoff encephalopathy, because thiamine may prevent the progression of the disease and even reverse some brain abnormalities. The intravenous route should be used because impaired intestinal absorption is common in alcoholics (Hoyumpa, 1986). It is important to note that electrolyte disorders such as hypomagnesemia can reduce the clinical response, particularly for cerebellar signs. Clonidine and fluvoxamine have been shown to improve moderately the amnesic disorders in alcoholism (McEntee and Mair, 1980; Martin et al., 1989). Nevertheless, their role in the improvement of ataxic gait is negligible.

Prognosis of cerebellar ataxia There is evidence that ataxia of stance and gait may improve in patients becoming abstinent. This has been

demonstrated using posture studies (Diener et al., 1984). In patients less than 40 years of age with a good nutritional status, the reduction in body sway can be evident after a period of abstinence of five to eight months, whereas body oscillations often worsen in patients who continue to drink. Furthermore, generalized cerebral cortical atrophy has been shown to be partially reversible with abstinence (Carlen et al., 1986). Recovery of ataxia is often incomplete in patients with a previous history of Wernicke–Korsakoff syndrome, even with abstinence and appropriate thiamine replacement. Approximately 60–70% of patients will exhibit irreversible nystagmus and ataxic gait. The reason seems to be irreversible neuronal damage (Butterworth, 1993).

xReferencesx Abi-Dargham, A., Krystal, J.H., Anjilvel, S. et al. (1998). Alterations of benzodiazepine receptors in type II alcoholic subjects measured with SPECT and 123I-iomazenil. Am J Psychiatry 155: 1550–5. Acker, W., Aps, E.J., Majumdar, S.K., Shaw, G.K. and Thomson, A.D. (1982). The relationship between brain and liver damage in chronic alcoholic patients. J Neurol Neurosurg Psychiatry 45: 984–7. Butterworth, R.F. (1993). Pathophysiology of cerebellar dysfunction in the Wernicke–Korsakoff syndrome. Can J Neurol Sci 20: 123–6. Carlen, P.L., Penn, R.D., Fornazzari, L. et al. (1986). Computerized tomographic scan assessment of alcoholic brain damage and its potential reversibility. Alcohol Clin Exp Res 10: 226–32. Cavanagh, J.B., Holton, J.L. and Nolan, C.C. (1997). Selective damage to the cerebellar vermis in chronic alcoholism: a contribution from neurotoxicology to an old problem of selective vulnerability. Neuropathol Appl Neurobiol 23: 355–63. Cravioto, H., Korein, J. and Silberman, J. (1961). Wernicke’s encephalopathy: a clinical and pathological study of 28 autopsied cases. Arch Neurol 4: 510–19. Diener, H.C., Dichgans, J., Bacher, M. and Guschlbauer, B. (1984). Improvement of ataxia in alcoholic cerebellar atrophy through alcohol abstinence. J Neurol 231: 258–62. Estrin, W.J. (1987). Alcoholic cerebellar degeneration is not a dosedependent phenomenon. Alcohol Clin Exp Res 11: 372–5. Fadda, F. and Rossetti, Z.L. (1998). Chronic ethanol consumption: from neuroadaptation to neurodegeneration. Prog Neurobiol 56: 385–431. Gallucci, M., Bozzao, A., Splendiani, A., Masciocchi, C. and Passariello, R. (1990). Wernicke encephalopathy: MR findings in 5 patients. Am J Neuroradiol 11: 887–92. Gilman, S., Adams, K., Koeppe, R.A. et al. (1990). Cerebellar and frontal hypometabolism in alcoholic cerebellar degeneration studied with positron emission tomography. Ann Neurol 28: 775–85.

Alcohol toxicity in the cerebellum: clinical aspects

Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadephia: F.A. Davis. Gilman, S., Koeppe, R.A., Adams, K. et al. (1996). Positron emission tomographic studies of cerebral benzodiazepine-receptor binding in chronic alcoholics. Ann Neurol 40: 163–71. Greenwood, J., Jeyasingham, M., Pratt, O.E., Ryle, T.R., Shaw, G.K. and Thomson, O.D. (1984). Heterogeneity of human erythrocyte transketolase: a preliminary report. Alcohol Alcohol 19: 123–9. Harper, C.G. (1983). The incidence of Wernicke’s encephalopathy in Australia – a neuropathological study of 131 cases. J Neurol Neurosurg Psychiatry 46: 593–8. Haubek, A. and Lee, K. (1979). Computed tomography in alcoholic cerebellar atrophy. Neuroradiology 18: 77–9. Hoyumpa, A.M. (1986). Mechanism of vitamin deficiencies in alcoholism. Alcohol Clin Exp Res 10: 572–81. Johnson-Greene, D., Adams, K.M., Gilman, S. et al. (1997). Impaired upper limb coordination in alcoholic cerebellar degeneration. Ann Neurol 54: 436–9. Kleinschmidt-De Masters, B.K. and Norenberg, M.D. (1981). Cerebellar degeneration in the rat following rapid correction of hyponatremia. Ann Neurol 10: 561–5. Martin, P.R., Adinoff, B., Eckardt, M.J. et al. (1989). Effective pharmacotherapy of alcoholic amnesic disorder with fluvoxamine: preliminary findings. Arch Gen Psychiatry 46: 617–21. McEntee, W.J. and Mair, R.J. (1980). Memory enhancement in Korsakoff’s psychosis by clonidine: further evidence for a noradrenergic deficit. Ann Neurol 7: 466–70. Setta, F., Jacquy, J., Hildebrand, J. and Manto, M. (1998). Ataxia induced by small amounts of alcohol. J Neurol Neurosurg Psychiatry 65: 370–3. Sowell, E.R., Jernigan, T.L., Mattson, S.N., Riley, E.P., Sobel, D.F. and

Jones, K.L. (1996). Abnormal development of the cerebellar vermis in children prenatally exposed to alcohol: size reduction in lobules I–V. Alcohol Clin Exp Res 20: 31–4. Thomas, A. (1905). Atrophie lamellaire des cellules de Purkinje. Rev Neurol (Paris) 13: 917–24. Thomson, A.D., Jeyasingham, M.D., Pratt, O.E. and Shaw, G.K. (1987). Nutrition and alcoholic encephalopathies. Acta Med Scand 717: 55–65. Torvik, A. (1987). Brain lesions in alcoholics: neuropathological observations. Acta Med Scand (Suppl.)717: 47–54. Torvik, A., Lindboe, C.F. and Rogde, S. (1982). Brain lesions in alcoholics. J Neurol Sci 56: 233–48. Victor, M., Adams, R.D. and Mancall, E.L. (1959). A restricted form of cerebellar cortical degeneration occurring in alcoholic patients. Arch Neurol 1: 579–688. Volkow, N.D., Hitzemann, R., Wolf, A.P. et al. (1990). Acute effects of ethanol on regional brain glucose metabolism and transport. Psychiatr Res: Neuroimaging 35: 39–48. Witt, E.D. (1985). Neuroanatomical consequences of thiamine deficiency: a comparative analysis. Alcohol Alcohol 2: 201–21. Witt, E.D. and Goldman-Rakic, P.S. (1983). Intermittent thiamine deficiency in the rhesus monkey. I. Progression of neurological signs and neuroanatomical lesions. Ann Neurol 13: 376–95. Worner, T.M. (1993). Effects of alcohol. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 547–66. New York: Marcel Dekker. Zimatkin, S.M. and Zimatkina, T.I. (1996). Thiamine deficiency as predisposition to, and consequence of, increased alcohol consumption. Alcohol Alcohol 31: 421–7. Zubaran, C., Fernandes, J.G. and Rodnight, R. (1997). Wernicke–Korsakoff syndrome. Postgrad Med J 73: 27–31.

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Other cerebellotoxic agents Mario-Ubaldo Manto1 and Jean Jacquy2 1

Cerebellar Ataxias Unit, 2 Department of Neurology, Free University of Brussels, Belgium

D RU G S

Indeed, pontocerebellar hypoplasia has been described following intrauterine exposure in humans (Gadisseaux et al., 1984; Squier et al., 1990).

Anticonvulsants Interactions Phenytoin Clinical findings Phenytoin is the anticonvulsant drug which is the most frequently implicated in drug-induced cerebellar ataxia. Toxicity develops either during chronic treatment or as a consequence of an acute overdose. Patients exhibit cerebellar signs ranging from a mild vestibulo-ocular cerebellar syndrome including nystagmus and ataxic gait, to a marked pancerebellar syndrome comprising nystagmus, ocular dysmetria, slurred speech, limb ataxia, and broadbased ataxic gait (Utterbock, 1958; Selhorst et al., 1972). In the case of chronic administration for epilepsy, the delay between initiation of treatment and onset of ataxic signs varies from several days to several years. The cerebellar syndrome may be completely reversible after reduction of doses or withdrawal of the drug, or can be irreversible. Most clinicians agree that patients exhibiting irreversible signs have a higher phenytoin serum level and a longer history of epilepsy than those with reversible signs (Munoz-Garcia et al., 1982). In addition, these patients were usually taking a greater number of drugs. In rare conditions, phenytoin-induced cerebellar ataxia may be associated with a peripheral neuropathy or a slight cognitive deterioration. In the case of overt or silent cerebellar disease, patients are at risk of developing marked ataxia when phenytoin is administered. For instance, in hereditary myoclonus epilepsy, phenytoin worsens myoclonic jerks and generates severe ataxia. Phenytoin is also toxic during the prenatal period.

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Ataxic signs may also appear as a result of the interaction between phenytoin and drugs increasing its half-life. One of these is ticlopidine, which inhibits the clearance of phenytoin by acting at the level of cytochrome P450, thus increasing plasma levels of diphantoin. This association is not uncommon, due to the incidence of epileptic crises of vascular origin in adults (Lopez-Ariztegui et al., 1998), hence the advice that blood levels of phenytoin should be monitored when treatment with ticlopidine is initiated or when its dose is increased.

Radiological and neuropathological findings In patients developing irreversible cerebellar signs in the course of chronic treatment, brain computed tomography (CT) and brain magnetic resonance imaging (MRI) show various degrees of cerebellar atrophy. Moreover, several cases of acute intoxication with subsequent development of cerebellar atrophy have been reported. For instance, severe cerebellar atrophy has been demonstrated as a result of a suicidal attempt with 7 g (Masur et al., 1989). Similar atrophy also occurs as a result of accidental acute overdose (Kuruvilla and Bharucha, 1997). Furthermore, the cerebellar atrophy associated with phenytoin intake has also been observed in the absence of cerebellar signs, raising the possibility of presymptomatic detection of cerebellar vulnerability (Koller et al., 1981). Koller et al. (1981) have shown that atrophy includes enlargement of the cisterna magna, of the cerebellopontine angle, and of the superior cerebellar cisterns. The fourth ventricle may be particularly dilated in some patients. The prevalence of cerebellar atrophy is high in patients

Other cerebellotoxic agents

with chronic epilepsy, varying from 18% to 61% in studies based upon CT or MRI (Botez et al., 1988; Ney et al., 1994; Specht et al., 1997). A toxic effect of hypoxia related to seizures has been suggested as the cause of cerebellar degeneration, but cerebellar atrophy has been described in the absence of episodes of hypoxia (Rapport and Shaw, 1977; Lindvall and Nilsson, 1984; Johnson et al., 1993) and the correlation between cerebellar atrophy and duration of epilepsy is a matter of debate. In humans who developed a cerebellar syndrome during maintenance therapy or as a result of acute overdose, neuropathological studies have shown diffuse loss of Purkinje neurons, reduction in the number of granule cells, and Bergmann gliosis (Utterbock, 1958; Chatak et al., 1976). Basket cell axons are relatively spared (Gilman et al., 1981). Electron microscopic studies have revealed swelling in the axons of granule cells and Purkinje cells (see below).

Experimental models The question of the minimal dose inducing a deficit in the developing cerebellum has been addressed recently by Ohmori and colleagues (1997). Newborn mice (the neonatal period of cerebellar development in mice corresponds to the last trimester in humans) were given 10, 17.5, 25 or 35 mg/kg of phenytoin once daily during postnatal days two to four. These dose levels result in plasma levels corresponding to therapeutic ranges in humans. When a dose of 10 or 17.5 mg/kg was administered, the size and weight of the cerebellum did not differ from those of a control group on postnatal day 21. By contrast, for a dose of 25 or 35 mg/kg of phenytoin, the size and weight of the cerebellum were significantly lower. The same authors have demonstrated that Purkinje cells had poor and immature arbors, and that some Purkinje neurons were aligned irregularly (Fig. 23.1; Ohmori et al., 1999). These data emphasize the phenomenon of phenytoin-induced developmental toxicity in animals. Studies in adult mice have shown that administration of phenytoin generates focal swellings along the axons of Purkinje cells. In murine cerebellar slice cultures with postnatal Purkinje cells, administration of phenytoin induces not only swellings along axons, but also aberrant axon collaterals and dendritic degeneration (Tauer et al., 1998). These alterations in Purkinje cell axon morphology and in targeting to deep cerebellar nuclei seem to be related to the dosage of the drug. Experimentally, the neurotoxicity of diphantoin is not limited to Purkinje cells. Yan et al. have demonstrated in cultured rat cerebellar granule neurons that diphantoin causes cytoplasmic and nuclear changes (Yan et al., 1995; Ohmori et al., 1999). The neurotoxicity is associated with

biochemical and morphological features of apoptotic cell death. In addition, electron microscopic studies have revealed an accumulation of tubular structures corresponding to smooth endoplasmic reticulum following chronic administration (Volk et al., 1986; see also Chapter 21 concerning effects of ethanol on SER). Interestingly, these structures are also observed in hepatocytes. Because of the accumulation of tubular structures in the axon terminals of parallel fibers, swelling would occur and would lead finally to pyknosis of the granule cell through a dyingback process. Acute non-toxic administration of phenytoin in rats is associated with an increase in the firing rate of Purkinje cells (Mameli et al., 1982). This increase is correlated not only with the plasma level of phenytoin, but also with the cerebellar level of the drug, and is explained by a direct effect on Purkinje cells combined with higher activity of climbing fibers. Overactivity of the inferior olive nucleus may be a key pathophysiological mechanism of the cerebellar toxicity of the drug (see also section on the cerebellar toxicity of phencyclidine, below).

Management At the initial phase of severe intoxication, monitoring in an intensive care unit is recommended. Phenytoin is inappropriate and should be replaced by valproic acid in patients with progressive myoclonic epilepsy or other patients at risk of developing cerebellar deficits (Eldridge et al., 1983).

Carbamazepine Clinical findings Carbamazepine is currently a drug of choice to treat focal epilepsy. The ataxic effects of the drug are dose dependent, and typically include dizziness, gaze-evoked nystagmus, action tremor, and ataxia of stance/gait (Masland, 1982). They may be overlooked because of a diminished conscious state in the case of intoxication (Table 23.1; Seymour, 1993). It is estimated that ataxic signs occur in up to 50% of acute, acute-on-chronic or chronic overdose (Bridge et al., 1994). The ataxic signs are not due to genuine cerebellar disturbances only, but are also related to involvement of afferent and efferent cerebellar pathways, in particular at the brainstem level.

Predisposing factors There is a high interindividual variation in the tolerance of high serum concentrations of carbamazepine (Tomson, 1984; Specht et al., 1997). Elderly patients seem more susceptible. As for other anticonvulsants, pre-existing structural damage in the cerebellum is a predisposing factor for

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A

B

C

D

Fig. 23.1 Developmental expression pattern of IP3R1 (inositol 1,4,5-triphosphate receptor type 1, which is particularly enriched in Purkinje neurons) in the vermis of newborn mice. (A)–(D) control mice; (E)–(H) group treated by phenytoin 35 mg/kg of body weight once a day during postnatal days 2–4. (A) and (E): postnatal day 7; (B) and (F): postnatal day 10; (C) and (G): postnatal day 14; (D) and (H): postnatal day 21. In the control group, cell bodies and dendrites including arbors of Purkinje cells are immunostained with IP3R1. In the treated group, dendritic arbors appear as immature. Some Purkinje neurons show an irregular arrangement (arrows). (Reproduced with permission from H. Ohmori et al. (1997). Effects of low-dose phenytoin administered to newborn mice on developing cerebellum. Neurotoxicology and Teratology, Vol. 19, pp. 205–11.)

intolerance. In a prospective series of 26 patients presenting a chronic focal epilepsy treated with high-dose monotherapy, it has been shown that cerebellar atrophy increases the susceptibility for cerebellar adverse events (Specht et al., 1997). Patients with moderate or severe cerebellar atrophy demonstrated by brain MRI exhibit cerebellar signs at significantly lower serum levels than patients without cerebellar atrophy (Fig. 23.2). In the group of nine patients presenting cerebellar atrophy, ataxia of

stance first occurred for a mean serum level of 51 3 mol/l, whereas in the group of 17 patients without cerebellar atrophy, ataxia of stance first appeared for a mean serum level of 63 3 mg/l (p 0.02). A similar observation was made for the occurrence of gaze-evoked nystagmus (Fig. 23.3). The description of Hori et al. (1987) strengthens the hypothesis that the neurotoxicity of carbamazepine is influenced by structural lesions in the cerebellum. These authors have described two brothers with Lennox–Gastaut

Other cerebellotoxic agents

E

F

G

H

Fig. 23.1 (cont.)

Table 23.1 Frequency of neurological signs in carbamazepine intoxication

syndrome. One had a Dandy–Walker malformation and showed toxic signs, including ataxia, at much lower doses of carbamazepine and of other antiepileptic drugs. Patients developing cerebellar toxicity with carbamazepine should be investigated for an underlying cerebellar pathology.

Signs

Frequency (%)

Interactions

Diminished conscious state Reduced muscle tone Ataxia of stance/gait Nystagmus Increased/decreased tendon reflexes Ophthalmoparesia Seizures

85–100 50 50 50 50 40 25

Carbamazepine also possesses antimanic properties and is used in association with lithium salts to treat manic–depressive disorders. When both drugs are combined, there is an increased risk of neurotoxic effects (Table 23.2; Shukla et al., 1984; Rittmannsberger et al., 1991; Rittmannsberger and Leblhuler, 1992). Toxic effects occur either at therapeutic levels or at toxic levels, and consist mainly of confusion, drowsiness, nystagmus, dysarthria, hyperreflexia, coarse tremor, and ataxia of limbs and trunk. Cerebellar ataxia restricted to the upper arms in the absence of extracerebellar signs may be triggered by the addition of carbamazepine in patients presenting a bipolar affective disorder treated by lithium salts, even if serum

levels of both drugs remain in the normal range. The ataxia is reversible after withdrawal of carbamazepine. Carbamazepine and lithium salts may interact by modifying the metabolism of the following brain monoamines: norepinephrine, dopamine, and serotonin (Hassan et al., 1987; Baf et al., 1994). Carbamazepine also interacts with sodium valproate, resulting in an intermittent syndrome of nausea, vomiting, lethargy, and ataxia (Rothner et al., 1987). In this case, total levels of carbamazepine are within the therapeutic range, but free levels are increased.

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Fig. 23.2 Brain MRI in the coronal plane in a 17-year-old patient (left) and in a 36-year-old patient (right). These patients suffered from complex partial epilepsy and generalized tonic-clonic seizures. Note the absence of cerebellar atrophy in the first patient (left) and the clear widening of the cerebellar sulci in the second patient (right). (Reproduced with permission from U. Specht et al., Archives of Neurology, Vol. 54, pp. 427–31, © 1997, American Medical Association.)

Table 23.2 Drugs interacting with carbamazepine

1.0 Probability of Nystagmus

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p < 0.001

0.8 0.6 With CA

Without CA

0.4

Lithium Valproic acid Erythromycin, clarythromycin Verapamil Viloxazine

0.2 0 42(10) 47(11) 51(12) 55(13) 59(14) 63(15) 68(16) 72(17) 76(18)

Carbamazepine Concentration, µmol/l (mg/l) Fig. 23.3 The probability of the appearance of gaze-evoked nystagmus as a function of carbamazepine concentration in two groups of patients with chronic focal epilepsy: one group (n 9) with cerebellar atrophy (CA) and the other group (n 17) without cerebellar atrophy. Gaze-evoked nystagmus occurred at a significantly lower serum concentration in the group with cerebellar atrophy. See also the legend of Fig. 23.2. (Reproduced with permission from U. Specht et al., Archives of Neurology, Vol. 54, pp. 427–31, © 1997, American Medical Association.)

Another clinically relevant interaction is the association of carbamazepine with erythromycin. Indeed, erythromycin alters cytochrome P450 function, and can induce an increase of more than 100% in the basal serum concentration of carbamazepine (Zitelli et al., 1987).

Experimental models Several experimental studies have suggested that cerebellar granule cells are particularly vulnerable to high doses of carbamazepine. Carbamazepine inhibits the increase in intracellular free calcium concentration that normally occurs in cerebellar granule cells as a result of N-methyl--aspartate (NMDA) effect (Hough et al., 1996). This inhibitory action is concentration dependent and may contribute to the cerebellar toxicity of the antiepileptic drug in the case of overdose. A mechanism of apoptosis has also been observed in cultured cerebellar granule cells (Gao et al., 1995).

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Nevertheless, its occurrence in humans remains to be established.

Management Due to the possibility of coma and the need for intubation in the case of high serum levels of carbamazepine, patients should be monitored, preferably in intensive care units. Patients with acute and acute-to-chronic overdoses are more at risk of developing coma than the chronic intoxication group. Activated charcoal is still used in the management of carbamazepine overdose. Because of the possible hepatic dysfunction and ion disturbances (Seymour, 1993), routine blood studies should always be performed, and electrolyte disorders should be corrected promptly. In addition, the possibility of concomitant intoxication with another drug or toxic agent such as alcohol should always be kept in mind.

Other antiepileptic agents Barbiturates Transient cerebellar ataxia may be observed with phenobarbital administration, especially via the intravenous route and when there is underlying structural damage in the cerebellum such as alcohol-induced atrophy. Patients exhibit gaze-evoked nystagmus, slight intention tremor, and ataxia of stance and gait. They usually present with oversedation, which evidently masks the ataxic signs. Ataxia is observed in about 5% of epileptic patients treated with barbiturates and is exacerbated by concurrent phenytoin administration (Young et al., 1987). However, there is no evidence that barbiturates generate any neuronal loss in the cerebellum of adult patients. Primidone is an anticonvulsant which is in large part metabolized in phenobarbital, and which causes ataxic signs that remit with discontinuation of the drug. In rats, low levels of phenobarbital impair Purkinje cell growth patterns (Hannah et al., 1988). Dendritic trees show morphologic alterations, confirming a vulnerability of the growth and remodeling processes when the drug is administered. Other studies have shown that acute or chronic phenobarbital administration to mice increased the density of benzodiazepine binding sites in the cerebellum (Miller et al., 1988; Weizman et al., 1989). The consequences of this effect upon cerebellar function remain unclear.

Vigabatrin Vigabatrin (gamma-vinyl-gamma-aminobutyric acid), an inhibitor of gamma-aminobutyric acid (GABA) transaminase, is usually well tolerated in patients with a

cerebellar disease. Mild ataxic posture occurs in about 5–10% of adults with poorly controlled epilepsy following the addition of vigabatrin. Drowsiness and ataxic gait show a dose-related increase with vigabatrin treatment.

Gabapentin Gabapentin is a new antiepileptic agent used in the treatment of partial and generalized seizures. It interacts with glutamate synthesis and enhances GABAergic inhibition. The neuronal binding site has a high density in the cerebellum. In a large population of patients with partial epilepsy treated with gabapentin in add-on therapy, ataxia was reported in 7.7% of cases (Baulac et al., 1998). Rarely, isolated severe ataxia can develop with low doses of gabapentin (Steinhoff et al., 1997). The ataxia is reversible after discontinuation of the drug. A mechanism of idiosyncratic adverse reaction has been proposed.

Topiramate and lamotrigine Except in the case of overdose, these drugs have a very safe profile in cerebellar patients. In epileptic patients without overt cerebellar disease, ataxia occurs when these drugs are used in association with other antiepileptic drugs. In particular, as a result of a pharmacodynamic interaction, addition of lamotrigine to carbamazepine may induce ataxic signs. A slow dosage titration schedule is thus recommended. There is no evidence that the dizziness and ataxic signs that have been described with lamotrigine in monotherapy are due to a direct toxic effect on the cerebellum. Experimentally, both topiramate and lamotrigine attenuate voltage-gated sodium currents in rat cerebellar granule cells (Zona et al., 1997; Zona and Avoli, 1997). This mechanism may contribute to control the sustained depolarizations with repetitive firing of action potentials which occur in neuronal networks during seizures.

Antineoplastics The toxic effects of 5-fluorouracil (5-FU), cytosine arabinoside (Ara-C), and methotrexate are discussed in Chapter 17.

Other drugs Lithium salts Lithium salts are used for the treatment of acute mania and as a prophylactic agent for recurrent bipolar and unipolar

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affective disorders, usually in combination with other psychotropic agents such as neuroleptics (Davis et al., 1973). Lithium carbonate may induce toxic effects either during a chronic treatment or as a result of acute intoxication. During maintenance therapy, the most common sideeffect is a tremor of the hands, which is an enhanced physiological tremor, but development of permanent neurological signs is rare. When sequelae appear, the cerebellum is a major target (Donaldson and Cuningham, 1983). Acute overdose is potentially harmful, affecting the cardiovascular, renal, and nervous systems (Simard et al., 1989). Neurological signs include coma, seizures, coarse tremor, hypokinesia, rigidity, and hyperreflexia. Because a concomitant high fever is often associated, neuroleptic malignant syndrome is a differential diagnosis of lithium poisoning in some patients. Neurotoxic signs are reversible in most cases, although severe neurological damage may develop after the acute episode. In this case, patients typically exhibit a marked cerebellar syndrome with scanning speech and ataxic gait (Manto et al., 1996a). Autopsies have revealed prominent spongy lesions in cerebellar white matter, associated with neuronal loss in the internal granule and Purkinje cell layers and in deep nuclei (Schneider and Mirra, 1994). Bergmann gliosis is a common finding. Neuropathological sequelae in humans probably have a multifactorial origin, resulting mainly from lithium overdosage, concomitant neuroleptic treatment, and hyperthermia (Grignon and Bruguerolle, 1996). An animal model of acute lithium-induced cerebellar degeneration has been proposed (Dethy et al., 1997). Following the intraperitoneal administration of lithium chloride in rats, extensive spongiform lesions are observed in cerebellar white matter (Fig. 23.4), reminiscent of the lesions observed in humans. Several studies have shown that lithium modulates phosphoinositide turnover in the cerebellum (del Rio et al., 1998) and it has been hypothesized that lithium, cytokines, and neuroleptics synergize to disrupt calcium homeostasis in Purkinje cells and to trigger calcium-mediated neurotoxic effects. Rapid hemodialysis may prevent the development of cerebellar sequelae and is thus recommended in lithium poisoning, as well as hydration with normal saline and intensive care monitoring.

Amiodarone Amiodarone is a widely used anti-arrhythmic drug. The most frequent neurological manifestations of toxicity are postural tremor, predominantly demyelinating peripheral neuropathy, and cerebellar signs (see also Chapter 20). Advanced age, renal failure, diabetes mellitus, and alcohol-

Fig. 23.4 Cerebellum of a lithium-intoxicated rat showing widespread vacuolization in the cerebellar white matter. Calbindin-D28K fixation revealed no loss of Purkinje cells. Magnification:  350. (From Dethy et al., 1997, with permission obtained).

ism may be risk factors for neurotoxicity (Arnaud et al., 1992). Cerebellar involvement has an incidence of about 5–7% and is characterized by vertigo, nystagmus, disturbed vestibulo-ocular reflex (VOR), abnormal finger-to-nose and heel-to-shin tests, ataxia of stance and gait, and titubation (Lhuillier and Gorin, 1972; Charness et al., 1984; Palakurthy et al., 1987; Garretto et al., 1994). A brainstem dysfunction including downbeat nystagmus has been described. Patients often experience intermittent episodes of diplopia. Moreover, encephalopathy, rest tremor, dyskinesia, myoclonus and proximal myopathy have been reported (Palakurthy et al., 1987, Werner and Olanow, 1989; Arnaud et al., 1992). Involvement of cerebellar structures, of brainstem connections, and of peripheral nerves contributes to the feeling of instability during walking. Cerebellar syndrome tends to vanish progressively several

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weeks to months after drug withdrawal. Rarely, cerebellar ataxia will persist for more than two years. Patients treated with amiodarone and developing ataxia should be investigated for a thyroid dysfunction (Raeder et al., 1985), which is among the most frequent untoward reactions and which can decompensate cerebellar signs.

Cyclosporin Cyclosporin A is a potent immunosuppressive drug administered in organ transplantation and in immunological diseases. The most common sign of neurotoxicity is a fine tremor. Behavioral disorders, episodes of aphasia, seizures, cerebellar ataxia, vestibular signs, motor spinal cord syndrome, and paresthesia are the other neurological side-effects (Palmer and Toto, 1991). The cerebellar toxicity of cyclosporin does not seem to be related to plasma levels of the drug. Administration of cyclosporin may unravel a silent cerebellar lesion in the elderly, such as a silent cerebellar infarction. By contrast with extracerebellar neurological complications occurring generally within the first month of administration, cerebellar toxicity may develop after several months. The ataxic signs may take the course of recurrent subacute episodes in the case of hypomagnesemia (Thompson et al., 1984), an important point to look for. Nystagmus, kinetic tremor in the upper limbs, and postural instability are the main cerebellar deficits. In addition, a leukoencephalopathy manifested by dysarthria and cerebellar ataxia has been reported after liver transplantation (Belli et al., 1993) and should be distinguished from progressive multifocal leukoencephalopathy (see Chapter 15). Lesions may be consistent in some circumstances with watershed zones (Bartynski et al., 1997). Exceptionally, cyclosporin toxicity will present with generalized seizures and cerebellar edema requiring posterior fossa decompression because of brainstem compression (Nussbaum et al., 1995). Any transplant recipient developing cerebellar ataxia under cyclosporin treatment should be investigated for magnesium deficit before considering withdrawal of the drug.

are particularly at risk (Playford et al., 1990). Clinically, bismuth intoxication is a differential diagnosis of Creutzfeldt–Jakob disease and thyroiditis encephalopathy (see also Chapter 20). The toxicity is usually reversible after several months when bismuth intake is stopped, although fatal cases have been reported (Liessens et al., 1978). CT studies have revealed patchy areas of increased density in the cerebellum, basal ganglia, and cerebral cortex, and hypodense zones in the centrum semi-ovale. Neuropathological observations have disclosed widespread loss of Purkinje cells in the cerebellum (Fig. 23.5; Liessens et al., 1978). An experimental model of single or multiple intraperitoneal injections of bismuth subnitrate in mice has been proposed (Ross et al., 1988). The signs are similar to those observed in human intoxication. In the cerebellum, bismuth deposits are observed in Purkinje and granule cell layers with the densest concentration in folia adjacent to the fourth ventricle (Ross et al., 1996). The chelator 2–3 dimercapto-1 propane sulphonic acid (DMPS) may be used to increase the renal clearance of the drug (Playford et al., 1990).

Bromides/bromvalerylurea Historically, bromism has been reported in patients receiving bromide salts as sleep medication. The intoxication with bromvalerylurea (BVU) has been described primarily in Japan. BVU is contained in some non-steroidal antiinflammatory drugs. Patients show cerebellar signs, pyramidal, and extrapyramidal features such as neck dystonia (Kawakami et al., 1998). The main cerebellar signs are slurred speech and gait ataxia. Alteration of consciousness and peripheral neuropathy have been associated (Arai et al., 1997). Blood studies may reveal a factitious hyperchloremia because of an interference of bromide with the dosage of chloride ion (Bonnotte et al., 1997). Brain MRI discloses cerebellar atrophy, sometimes with concomitant atrophy of the tegmentum pontine. Patients presenting cerebellar signs and elevated serum chloride levels of unknown origin should be evaluated to exclude bromide intoxication. Hemoperfusion is effective to remove BVU from the circulation (Ishiguro et al., 1982).

Bismuth Bismuth used to be administered in skin creams and orally for gastrointestinal complaints (Goetz and Cohen, 1989). It is a cause of encephalopathy with seizures, delirium, and multifocal myoclonic jerks (Gordon et al., 1995). Cerebellar signs consist of a coarse tremor in the limbs and ataxia of stance and gait. Patients presenting chronic renal failure

Mefloquine There have been several reports of neurological sideeffects of mefloquine, an antimalarial drug which has been used extensively for prophylaxis (Phillips-Howard and ter Kuile, 1995). An acute brain syndrome consisting of fever, nausea, headache, and dizziness has been reported.

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Fig. 23.5 Pathological findings in a fatal case of toxic encephalopathy due to ingestion of bismuth salts, showing loss of Purkinje neurons with proliferation of Bergmann cells . A glial shrubbery is found in the molecular layer, indicating a destruction of the dendritic trees of Purkinje cells ( 260). (Reproduced with permission from J.L. Liessens et al. (1978). Bismuth encephalopathy. A clinical and anatomopathological report of one case. Acta Neurologica Belgica, Vol. 78, pp. 301–8.)

Patients complain of clumsiness and may present gait instability. However, the drug’s actions on the cerebellum do not seem to be the main cause of this instability. Drug discontinuation and future avoidance of the drug are recommended.

Isoniazid Isoniazid (INH) is one of the most effective drugs against tuberculosis. The dose given is from 3–5 mg/kg up to 30 mg/kg per day in the case of meningitis. INH has also been suggested as a possible treatment of cerebellar tremor, due to its effects on GABA metabolism. Most of the toxic effects of INH are due to interference with vitamin B6. The occurrence of toxic side-effects is clearly related to the dose used, and also to the acetylation process of the subject. Nervous system and liver sideeffects are the most common (Spencer and Schaumburg,

1980). Peripheral neuropathy occurs in up to one in six subjects receiving 6 mg/kg of INH daily. With higher doses, seizures, dizziness, ataxia, slurred speech or even psychotic symptoms have been reported. However, clinical descriptions are incomplete and neuropathological details are lacking with regard to cerebellar toxicity.

Lindane Lindane (gamma-benzene hexachloride) is widely used to treat scabies and lice. Accidental ocular exposure causes conjunctivitis. Excessive use of the powder may result in central nervous system toxicity: hyperreflexia, hypertonia, limb and truncal ataxia, choreoathetosis, and seizures (Spencer and Schaumburg, 1980). Experimental studies show that lindane exerts a cytotoxic effect on the cerebellum mainly by acting on GABA(B) receptors. Rats administered lindane chronically show a significant increase in GABA levels in the cerebellum (Anand et al., 1998).

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Perhexiline maleate There have been many descriptions of perhexilineinduced peripheral neuropathy, which is of mixed sensorimotor type. The polyneuropathy occurs with or without cranial neuropathy or autonomic dysfunction. Cerebellar deficits have also been described in association with the toxic neuropathy (Turpin et al., 1983). Biochemical analysis of lipids has disclosed low values of cerebrosides and sulfatides in the cerebellum (Nick et al., 1978).

Cimetidine Cimetidine administration has been associated with mental confusion and postural tremor. A brainstem dysfunction including limb weakness, deafness, dysarthria, and ataxic gait has been reported in a 54-year-old man receiving 1 g/day (Cumming and Foster, 1978). There have also been several descriptions of ‘iatrogenic ataxia’ occurring during combined therapy with benzodiazepines in the elderly. However, many factors, such as concomitant renal failure, surgical operation, and electrolyte disorders, may be contributory and in many cases no certain cause is ascertainable. Because episodes are self-limiting, the recovery after drug withdrawal may be a coincidence. Most observations are not sufficiently consistent to establish a cause-and-effect relationship.

H E AV Y M E TA L S

Mercury Mercury was used as a treatment for syphilis in the sixteenth century, leading to increased mining activities (Manyam, 1996; Chang, 1980). Miners used to develop episodes of vertigo and tremor after several hours of work. Currently, the major physical forms of mercury to which humans are exposed are methylmercury and mercury vapor (Clarkson, 1997). Methylmercury compounds are found in seafood and freshwater fish, whereas exposure to mercury vapor is related to various industries. Release and spread of mercury from gold mining remain an important problem in the Amazon area (Lodenius and Malm, 1998). Mercury is still used for the amalgamation of gold and is released by evaporation. The metal also contaminates rivers and lakes. It is estimated that several hundred thousand workers are involved in mining-related activities and are at risk of mercury intoxication. However, as a rule applying also for other neurotoxic syndromes, the estima-

tion of cerebellar signs resulting from occupational exposure remains a challenge for the following reasons: (1) workers at risk are probably not screened well enough, (2) physicians lack the appropriate training to diagnose early intoxication, and (3) data are not transmitted quickly from manufacturers. In Japan, an epidemic occurred in 1953 related to industrial pollution in Minamata Bay. Patients have been affected after daily eating large quantities of seafood contaminated by methylmercury (Ninomiya et al., 1995; Korogi et al., 1998). The heavy metal was dispersed from Minamata to the Shiranui Sea until 1968 (Ninomiya et al., 1995). Patients typically exhibit constriction of visual fields, sensory impairment of the extremities, and cerebellar signs. In adults, alteration of consciousness and peripheral neuropathy may be clues for the diagnosis of mercury intoxication. Fetuses can present severe cerebral and cerebellar damage, even if the mother is asymptomatic (Matsumoto et al., 1965). Besides the chronic intoxication in Japan, there was also an acute intoxication described in 1971–2 in Iraq, resulting from the consumption of bread prepared from methylmercury-treated grain (Bakir et al., 1980). Congenital methylmercury poisoning has also been observed in the Faroe Islands, where intoxication has been related to the ingestion of pilot whale meat. MRI studies have demonstrated that the visual cortex, postcentral cortex and cerebellum are atrophic following intoxication (Korogi et al., 1998). In a quantitative image study with MR, it was shown that the inferior and middle parts of the vermis and cerebellar hemispheres are significantly atrophic, contrasting with the normal size of the middle cerebellar peduncles (Korogi et al., 1994). Neuropathologic changes mainly affect the calcarine cortex and cerebellum, with a predominant depletion of cerebellar granule cells (Hunter and Russel, 1954). Rats have commonly been used to investigate the mechanism of mercury neurotoxicity in humans, due to the resemblance of the pathologic lesions in the two species. Rats experimentally exposed to methylmercury exhibit ataxic behavior (Nagashima, 1997). Neuropathological studies show degeneration of spinal dorsal root ganglia, of the posterior funiculus of the spinal cord, and of cerebellar granule cells, with relative preservation of Purkinje cells. Loss of granule cells might evolve through a mechanism of apoptosis (Nagashima, 1997; Fig. 23.6). In addition, nitric oxide may play an important role in the degeneration of granular layer cells, because a rise in nitric oxide synthase activity is observed between the administration of methylmercury and the degenerative process (Yamashita et al., 1997). The other hypotheses of methylmercury cerebellar

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(a)

(b)

Fig. 23.6 Ultrastructure of cerebellar granule cells in rats experimentally exposed to methylmercury chloride. (a) In the early stage of degeneration, most granule cells remained ultrastructurally intact. Only a few pyknotic nuclei, smaller than intact nuclei, are observed. (b) At a later stage, numerous nuclei become pyknotic. In some cases, some of the electron-dense material protruded from the nuclei, taking the aspect of a teardrop, which is a typical feature of an apoptotic body. Magnification  6400. (Reproduced with permission from K. Nagashima (1997). A review of experimental methylmercury toxicity in rats: neuropathology and evidence of apoptosis. Toxicologic Pathology, Vol. 25, pp. 624–31.)

toxicity are an excess of oxidative stress (Sarafian et al. 1989) and the impairment of calcium homeostasis in granule cells (Marty and Atchison, 1997). Patients with mercury poisoning are treated with the chelators BAL and/or penicillamine.

Lead Lead intoxication can occur as a consequence of several circumstances, which are listed in Table 23.3. The neurotoxicity of lead exposure has a particular relevance in children, not only because they are at risk of ingesting paints containing lead, but also because the toxicity of lead is far greater in children (Finkelstein et al., 1998). In many cases, patients complain of abdominal pain, and blood studies show various degrees of anemia. The

three regions of the brain preferentially injured are the prefrontal cortex, hippocampus, and cerebellum. Clinically, patients exhibit a predominant encephalopathy with irritability, insomnia, memory loss, and hallucinations. Peripheral motor neuropathy is relatively common. Cerebellar involvement consists of ocular dysmetria and nystagmus, slurred speech, and ataxia of stance and gait. Romberg’s test is positive in most advanced cases. Cerebellar ataxia may be the prominent feature in adults (Mani et al., 1998). Because of edema, lead poisoning can mimic a cerebellar tumor, generating mass effect in posterior fossa and obstructive hydrocephalus (Pappas et al., 1986; Perelman et al., 1993). It is important to recognize this presentation to avoid the removal of a pseudotumor. In a posturography study in lead workers, Yokoyama et al. (1997a) provided evidence of subclinical dysfunction of the vestibulocerebellum and spinocerebellar pathways.

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Table 23.3 Causes of lead intoxication Ingestion of lead contained in paints Leaded gasoline sniffing Flour contamination Exposure to lead stearate (lead workers) Contamination from discarded automobile batteries

Postural sway was significantly greater than in controls not exposed to lead. In adults with chronic lead exposure and raised serum levels, CT may disclose calcifications in the subcortical areas, basal ganglia, and cerebellum (Reyes et al., 1986). Calcification patterns are punctiform, curvilinear, speck-like, and often diffuse. Moreover, MRI shows hyperintense lesions (T2) in periventricular white matter, basal ganglia, insula, and pons. High signal intensities in both thalami have been reported in cases with prominent ataxia (Mani et al., 1998). Although magnetic resonance spectroscopy (MRS) in a lead-exposed boy has shown impaired brain metabolism, with reduction of the Nacetylaspartate:creatine ratio for frontal gray and white matter (Troppe et al., 1998), the effects on metabolism in the cerebellum remain to be established. Neuropathologic evaluations have demonstrated a pattern of vascular edema with endothelial cell swelling, followed by brain edema (Johnson et al., 1993). The cerebellum is particularly affected by this vascular edema. Loss of Purkinje cells and neurons in dentate nuclei is observed, as well as gliosis. The mechanisms of lead neurotoxicity are numerous. The two mechanisms most frequently cited in cerebellar toxicity are raised intracranial pressure and alteration of mitochondrial metabolism. Indeed, the cerebellum is particularly affected by the raised intracranial pressure which follows lead intoxication. The metal disrupts the main components of the blood–brain barrier, causing primary injury to astrocytes and secondary lesions to the endothelial microvasculature (Finkelstein et al., 1998). In chronically exposed rats, astrocytes become hypertrophic, in particular in the cerebellum and hippocampus. Another cause of cellular injury is inhibition of mitochondrial function. The relative resistance of adults to lead intoxication might be due to the capacity of the mature brain to sequestrate lead away from its mitochondrial site of action in neurons (Holtzman et al., 1984; Mani et al., 1998). This hypothesis is based upon the following observations: (1) the in-vitro effects of lead are similar in immature and mature cerebellar mitochondria; (2) the cerebral and cerebellar lead concentrations are similar in immature encephalopathic and mature encephalopathy-resistant

lead-fed animals; and (3) cerebellar mitochondria from animals fed lead from 14 days of age contain higher levels of lead than cerebral mitochondria from non-lead-fed animals and cerebellar mitochondria from lead-fed adults (Holtzman et al., 1984). In models of postnatal lead intoxication in rat pups, lead decreases molecular layer width, reduces granule cell density, and alters dendritic arborization of Purkinje cells (Lorton and Anderson, 1986) When lead intoxication is suspected, the following blood studies should be performed: lead concentration measurement, red blood cell count, free erythrocyte protoporphyrin level, and search for basophilic stippling of red blood cells, which is found in 40–90% of cases. In addition, urinary concentrations of gamma-aminolevulinic acid (ALA) or coproporphyrin are useful indexes of intoxication. EDTA is administered to treat lead intoxication. Recently, whole-bowel irrigation associated with triple chelation therapy (BAL, EDTA, oral succimer) has been proposed in a child with massive lead intoxication (Gordon et al., 1998). Further evaluation of this treatment is required.

Manganese Manganese intoxication was described initially in the nineteenth century. Manganese poisoning is reported in miners and industrial workers exposed to the metal in the form of fumes or dust, in the case of exposure to herbicides or fungicides and soil, and has been observed recently during long-term total parenteral nutrition (Milla, 1996; Nagamoto et al., 1999). The main clinical signs are extrapyramidal: tremor, rigidity, bradykinesia, and postural instability. The clinical picture has to be distinguished from Parkinson’s disease. Other much less frequent features are psychiatric disturbances (‘manganese madness’ of the miners), dystonia, and ataxic signs. Dysdiadochokinesia, kinetic tremor, and ataxia of stance have been described, and may be related to involvement of cerebellar connections rather than to impairment of the cerebellum itself (Rodier, 1955). A motor neuron disease has been described at Angurugu in Northern Australia, in an environment including low calcium and iron but high levels of manganese (Cawte et al., 1989). This ‘Angurugu syndrome’ consists of motor neuron, cerebellar, extrapyramidal, and oculomotor signs. In patients developing manganese toxicity following parenteral nutrition, liver function is often impaired (Fell et al., 1994). Moreover, because manganese is primarily cleared by the liver, deficient elimination of the metal from the normal diet may cause manganese poisoning in

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patients with cirrhosis (Fell et al., 1994). MRI demonstrates symmetrical high-intensity lesions (T1 sequence) in the globus pallidus, in subthalamic nuclei, in the periventricular white matter, and in the cerebellum (Fell et al., 1994; Nagamoto et al., 1999; Komaki et al., 1999). MRI abnormalities may disappear after withdrawal of manganese administration (Komaki et al., 1999). A model of manganese intoxication has been described in rhesus monkeys (Olanow et al., 1996). Monkeys develop bradykinesia, rigidity, and dystonia, with no response to levodopa. Neuropathological studies show gliosis in the globus pallidus and substantia nigra pars reticularis, with relative sparing of the nigrostriatal dopaminergic system, in contrast to Parkinson’s disease and MPTP monkeys. Positron emission tomography (PET) studies with 18Ffluorodopa, 11C-raclopride or 18F-fluorodeoxyglucose support this view. One of the primary causes of the neurotoxicity of manganese is oxidative stress. Manganese may enhance catechol autoxidation in catecholaminergic neurons, with the formation of peroxides, superoxides, and free radicals (Vescovi et al., 1989). In monkeys intoxicated with manganese, the findings of mineral deposits made of iron and aluminium suggest an iron/aluminium-induced oxidant stress (Olanow et al., 1996). Chronic treatment in mice impairs binding of glutamate to total glutamate receptors, NMDA, and quisqualate receptors. Decrease of glutamate binding is observed in the cortex, hippocampus, basal ganglia, and cerebellum (Cano et al., 1997). In addition, binding to the quisqualate receptor subtype is reduced in the same brain regions. The decrease of glutamate binding sites has been interpreted as a down-regulation mechanism against excitotoxicity. While GABA contents increase in the striatum and substantia nigra after administration of the metal, cerebellar GABA is unaffected (Gianutsos and Murray, 1982). In frog cerebellum, parallel fiber–Purkinje cell synaptic transmission as well as climbing fiber–Purkinje cell synaptic transmission are blocked by the manganese ion, probably as a consequence of the interaction with calcium (Hackett, 1976). Intoxication can be confirmed with analysis of blood, urine or hair (Johnson et al., 1993). Extrapyramidal signs do not usually respond to antiparkinsonian treatment, but exceptions have been reported (Huang et al., 1989). Intravenous administration of sodium para-aminosalicylic acid has been proposed to treat chronic poisoning (Ky et al., 1992).

Thallium Thallium is a toxic heavy metal discovered in 1861 by William Crookes. It is used as a rodenticide and in the manufacture of optical lenses, semiconductors, scintillation counters, low-temperature thermometers, switching devices, green-colored fireworks, imitation jewelry, and as a chemical catalyst (Moore et al., 1993). Intoxication is favored by the fact that thallium salts are colorless, odorless, and tasteless. The poisoning occurs following oral ingestion, after inhalation of contaminated dust, after snorting, or via dermal absorption. Cases of thallium poisoning still occur, though rarely, as a result of homicide attempts (Meggs et al., 1997). Patients with acute intoxication exhibit loss of consciousness, convulsions, blurring of vision and field defects, tremor, ataxia, and paresthesia associated with sensorimotor polyneuropathy (Sabbioni and Manzo, 1980; Gilman et al., 1981). Immediate cardiovascular complications include hypertension and arrhythmias, in addition to the risk of respiratory failure (Wainwright et al., 1988). Severe vomiting and diarrhea occur after oral ingestion of large doses. Alopecia typically develops after a few days. Examination of hair roots under polarized light shows dark zones suggestive of thallium poisoning. In the case of polyneuropathy, electrophysiological studies reveal evidence of a distal axonopathy, sometimes prominent in the plantar nerves of the foot during the early course of poisoning (Dumitru and Kalantri, 1990). The main neurological sequelae of acute poisoning are mental impairment, paraparesis, and ataxia, which has a mixed cerebellar and peripheral origin. In the case of chronic intoxication with small doses, headaches, sleep disorders, painful neuropathy, psychosis, and ataxia are the principal features. Murine models of thallium poisoning have shown that thallium binds sulfhydryl groups and leads to altered Purkinje cells in the cerebellum (Meggs et al., 1997). Electron microscopic studies have disclosed multilamellar cytoplasmic bodies, and abnormal mitochondria have been observed in the cerebellar cortex of intoxicated rats (Hasan et al., 1978). Because of the possibility of respiratory failure due to muscle paralysis, intensive care monitoring is required in severe intoxication (Vergauwe et al., 1990). Oral Prussian blue, hemodialysis, and forced diuresis have been recommended for treatment (Wainwright et al., 1988). High blood flow and intravenous potassium chloride supplements contribute to the clearance of thallium from tissues (Malbrain et al., 1997). Combined antidotal treatment of penicillamine with Prussian blue has also been shown to

Other cerebellotoxic agents

be efficacious in experimental studies (Barroso-Moguel et al.,1994).

Germanium Patients affected by germanium intoxication develop peripheral neuropathy causing sensory ataxia, and myopathy. Autopsy studies have shown degeneration of dorsal root ganglion cells and of the dorsal column of the spinal cord (Asaka et al., 1995). A vacuolar myopathy has been depicted (Higuchi et al., 1989). Cerebellar involvement is extremely rare (Fujimoto et al., 1992).

TO LU E N E / B E N Z E N E D E R I VAT I V E S Toluene is a very useful chemical, but also potentially harmful (Saito and Wada, 1993). Solvents are well known to cause peripheral nervous system disturbances and there is growing evidence that the central nervous system may be the main target in some patients (Boor and Hurtig, 1977). Toluene intoxication is very common in glue-sniffing and also occurs after occupational exposure to toluene vapor in poorly ventilated areas. Children manifest an acute encephalopathy, with coma, seizures, cerebellar ataxia, and behavior abnormalities (King, 1982). In adults, headaches, hyperactivity, memory deficits, insomnia, and cerebellar ataxia have been reported (Boor and Hurtig, 1977; Saito and Wada, 1993). Cerebellar signs are prominent in some patients (Damasceno and de Capitani, 1994); dysarthria, kinetic tremor, and ataxic gait are the most common. In addition, downbeat nystagmus has been observed in patients exhibiting a predominant cerebellar syndrome. Cerebellar dysfunction may be reversible after several months (Malm and Lying-Tunell, 1980), but permanent and disabling neurological damage may develop. Brain CT and brain MRI have demonstrated severe pancerebellar atrophy after chronic intoxication of several years, usually associated with atrophy of the cerebral cortex and brainstem (Ikeda and Tsukagoshi, 1990). In an earlier stage of intoxication, MRI demonstrates white matter hyperintensities in the cerebrum, brainstem, and cerebellum on T2weighted images or using FLAIR sequence (Yamanouchi et al., 1995; Fig. 23.7). Yokoyama et al. (1997b) analyzed the postural sway in 29 factory workers exposed to hexane, xylene, and toluene. In the anterior–posterior direction, postural sway with a frequency of 2–4 Hz was significantly larger in solvent workers than in a control group of 22 non-exposed subjects. With the eyes closed, sway with a frequency of 0–1

Fig. 23.7 Axial brain MRI (FLAIR sequence) in a patient chronically exposed to benzene. Note the hypersignal in the white matter of the cerebellum (arrow).

Hz was significantly larger in the medio-lateral and anterior–posterior directions. These patterns were suggestive of a dysfunction of the vestibulocerebellar and spinocerebellar afferent pathways. In a model of chronic toluene inhalation in cats, various degrees of neuronal loss in the brain have been described (Saavedra et al., 1996). In the cerebellum, lesions were time related and mainly involved the Purkinje cells. Using microdialysis in the cerebellum of rats, an increase in extracellular GABA levels during and after exposure to toluene has been shown (Stengard et al., 1993). Experiments with tetrodotoxin suggest a sodiumdependent increase of GABA levels. Furthermore, a deleterious effect of toluene on the afferent mossy fibers system has been proposed.

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H Y PE RT H E R M I A

D RU G A BU S E

The cerebellum is particularly vulnerable to prolonged episodes of high fever. The typical example is heat stroke, which leads to a steady rise in body temperature to more than 40 °C, disorders of sweating, and severe central nervous system disturbances (Yaqub and Al Deeb, 1998). The clinical presentation includes coma, abnormal behavior, seizures, and acute cerebellar ataxia. An isolated cerebellar dysarthria may be the sole neurological sign. In some instances, a neuroleptic malignant syndrome – a serious complication usually associated with neuroleptic usage – will be the cause of cerebellar injury (Manto et al., 1996b). Cerebellar ataxia, parkinsonism, and limb paresia have been described as permanent sequelae following high-fever episodes. Enduring cerebellar signs are oculomotor deficits, dysarthria, limb incoordination, and ataxic gait, and may involve mainly gait (Manto et al., 1996b). Repeated brain CT and brain MRI demonstrate a progressive cerebellar atrophy beginning in the weeks or months after hyperthermia (Albukrek et al., 1997). Patchy areas of increased signal intensity in the white matter of the cerebral hemispheres and in basal ganglia are detected in some patients. In addition, brain CT may show lesions suggestive of cerebellar infarction, probably due to coagulation disorders associated with hyperthermia. Autopsy studies have disclosed marked loss of Purkinje cells, mild rarefaction of granule cells, and gliosis in the deep cerebellar nuclei (Lee et al., 1989; Pelletier et al., 1991). Studies in rats have revealed that high temperature is associated with a significant increase of nitric oxide production in the cerebellum (Canini et al., 1997). The large amounts of nitric oxide may participate in the pathogenesis of the neuronal insult. Other studies have demonstrated a marked increase in the expression of mRNA encoding heat shock protein (hsp) in the cerebellum (Quraishi et al., 1996; D’Souza et al., 1998). In the rabbit brain, an increase in temperature of 2.5 °C generates a major upregulation in the in-vivo transcription rate of hsp70 in the cerebellum (D’Souza et al., 1998). It has been hypothesized that expression of hsp attenuates neuronal damage in hyperpyrexia (Yang et al., 1998; see also toxicity of phencyclidine, below). Heat stroke is an emergency. Cooling of the body and support of vital functions should be performed in an intensive care unit. The key factors of prevention of heat stroke are: limiting exposure to the sun, use of sunscreens, adequate fluid and ion replacement, and acclimatization (Yaqub and Al Deeb, 1998). Attention should be given to patients receiving drugs impairing sweating function, especially in the elderly.

There is a very high number of drug abusers, although the patients seen because of medical complications represent only a small percentage of them (Becker, 1979). Cocaine, heroin, and phencyclidine (PCP) intoxication are all potential causes of cerebellar ataxia which may be encountered in daily practice.

Cocaine Cocaine poisoning is due to active consumption or passive intoxication in a room in which ‘crack’ (the alkaloid form of cocaine) is smoked (Mott et al., 1994). The neurological signs associated with acute cocaine exposure are focal or generalized seizures, drowsiness or lethargy, delirium, cerebellar ataxia, or features reminiscent of neuroleptic malignant syndrome (Daras et al., 1995). Cerebellar involvement may be the consequence of an infarction, which is massive in some cases (Aggarwal and Byrne, 1991), although small asymptomatic cerebellar infarcts have been described. Cocaine-induced hemorrhage within an unsuspected tumor of the posterior fossa is an exceptional complication (Yapor and Gutierrez, 1992). In cocaine abusers, concomitant intoxication with another neurotoxic agent should always be suspected. For instance, in patients exhibiting impaired mental status, ataxic gait, and nystagmus, phenytoin has been found to be added to crack cocaine (Katz et al., 1993). In some of these patients, phenytoin levels were in accordance with intoxication. In neonates who had been exposed to cocaine during pregnancy, cranial ultrasonography has revealed a significantly higher incidence of foci of necrosis or cavitary lesions in the basal ganglia, frontal lobes or posterior fossa (Dixon and Bejar, 1989). These lesions were not suspected on the basis of clinical examination. Their mechanism remains elusive. These lesions might share pathophysiological similarities with stroke observed in adults.

Heroin Heroin ingestion has been associated with toxic spongiform leukoencephalopathy (Weber et al., 1998). Wolters et al. (1982) described a series of 47 patients in whom inhalation of poisoned heroin vapors (pyrolysate) was probably the cause of the intoxication. Patients exhibit a cerebellar syndrome, usually beginning several days after last consumption (Weber et al., 1998). Brain CT shows hypodense lesions and T2-weighted brain MRI reveals hyperintense

Other cerebellotoxic agents

areas in the cerebellar hemispheres, cerebellar peduncles, and pyramidal tract. Lesions are typically symmetrical (Tan et al., 1994). In addition to spongiform demyelination, neuronal loss has been demonstrated in the Purkinje cell layer in chronic drug abusers (Oehmichen et al.,1996).

Phencyclidine Phencyclidine is a non-competitive NMDA receptor antagonist (Deutsch et al., 1998). It is a neurostimulant heightening sensory perception. Abuse was very popular in the 1970s and 1980s (Tong et al., 1975). The most common neurological features of PCP intoxication are disorders of behavior, hallucinations, lethargy, coma, catatonia, seizures, constricted pupils, dystonia, and athetosis. In addition, ataxia of stance/gait and nystagmus may be prominent features, especially in children (Schwartz and Einhorn, 1986). Elevations of blood pressure and body temperature have been noted, as well as hypersalivation, bronchospasm, and urinary retention (McCarron et al., 1981; Barton et al., 1981). Rhabdomyolysis is a serious complication requiring intensive therapy. NMDA receptors are involved in differentiation and trophic processes during development.Therefore, PCP abuse is a matter of concern for potential fetal developmental deficits following exposure in pregnant women, although the teratogenic effects require very high doses in animals (Marks et al., 1980; Deutsch et al., 1998). In adult animals, there is evidence that PCP is toxic for the posterior cingulate cortex, retrosplenial cortex, and Purkinje cells. In rats injected with PCP, activated microglia is found in the molecular layer of the vermis, as demonstrated by Nakki and colleagues (1995). In addition, PCP induces hsp70 and mRNA expression in Purkinje cells (Fig. 23.8), with mRNA detected in many Purkinje cells in the hemispheres and vermis. Heat shock proteins probably play a determinant role in cellular repair and protective mechanisms. Moreover, it has also been shown that PCP induces expression of immediate early genes in the inferior olive, granule cell layer, deep cerebellar nuclei, and vestibular nuclei (Nakki et al., 1996). The microglial reaction, the hsp induction, and the expression of immediate early genes are not specific to PCP intoxication. For instance, hsp70 synthesis is induced by ischemia or prolonged seizures (Nakki et al., 1995). Another mechanism of the cerebellar toxicity of PCP might be the activation of climbing fibers emerging from the inferior olive, a potent triggering factor in Purkinje cell toxicity. It has also been suggested that cerebellar toxicity of PCP might involve cerebellar noradrenergic pathways at a presynaptic level (Marwaha et al., 1980).

Fig. 23.8 Immunostaining of a rat Purkinje cell for the inducible heat shock protein 70 (hsp70), a marker for cell injury, showing immunoreaction 24 hours after injection with phencyclidine 50 mg/kg intraperitoneally. Scale bar: 50 m. (Reproduced with permission from R. Nakki et al. (1995). Cerebellar toxicity of phencyclidine. Journal of Neuroscience, Vol. 15, pp. 2097–108.)

Although levels of PCP in urine are determined as a routine procedure when intoxication is likely in a patient, they do not correlate with the intensity of the clinical signs. Routine blood studies should include the following tests when PCP abuse is suspected: glycemia, creatine kinase (CK) level, liver function tests, and renal function tests. Moreover, blood alcohol level, hypnotic screen, and urine tests for alkaloids should be evaluated (Barton et al., 1981).

C A R B O N M O N OX I D E Carbon monoxide, a colorless and odorless gas, is a neurotoxic and accounts for a large number of deaths and

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notable morbidity. Each year, thousands of people are poisoned (Tomaszewski, 1999). About 2–26% of patients die from acute intoxication (Pahwa, 1997). Clinical signs include coma, seizures, brainstem signs, and cerebellar ataxia (Pasquier et al., 1993). Memory disorders, neuropsychiatric signs, parkinsonian and cerebellar signs may be persistent sequelae, either appearing immediately after intoxication (progressive type) or occurring after a free interval (delayed relapsing type). In a series of 2360 patients with intoxication, Choi (1983) identified delayed neurological sequelae in 65 of them (2.75%). In two patients, the authors have observed a selective memory deficit and a broad-based ataxic gait as permanent sequelae after a severe intoxication which was followed by a free interval of about three weeks. In the acute phase of intoxication, brain CT shows hypodense areas in the cerebral white matter and globus pallidus, and usually sparing of the cerebellum (Silver et al., 1996). Electroencephalogram (EEG) recordings reveal either diffuse slowing or lateralized abnormal activities, such as sharp waves with focal seizure discharges (Neufeld et al., 1981). Using MRI, Mascalchi et al. (1996) have reported an extensive bilateral cerebellar white matter involvement in a 12-year-old boy with a history of intoxication six years previously. In other cases showing sequelae, MRI demonstrates cerebellar atrophy with high-intensity signals in white cerebellar matter, often in association with cerebral cortical atrophy. Single-photon emission computed tomography (SPECT) studies have disclosed reduction of cerebellar blood flow in patients exhibiting residual ataxia. Carbon monoxide has much higher affinity for hemoglobin oxygen-binding sites than oxygen, leading to anoxic injury. The gas is responsible for cerebral edema, inhibition of cytochrome oxidase of the mitochondrial chain, and central nervous system peroxidation. Experimentally, carbon monoxide-exposed rats exhibit learning and memory deficits associated with neuronal loss in the cerebral cortex, globus pallidus, and cerebellum (Piantadosi et al., 1997). Ultrastructural changes suggestive of both neuronal necrosis and apoptosis have been found. In mice exposed to acute intoxication, a marked induction of mRNA of NGFI-B and c-fos, two immediate early genes, has been demonstrated 30 minutes after exposure in various regions of the brain, but particularly in the brainstem and cerebellum (Tang et al., 1997). The expression of immediate early genes might be due to a direct hypoxic insult. Prenatal exposure of rats at moderate levels induces marked neurotoxic effects, and chronic perinatal exposure disrupts neuronal plasticity in the cerebellum and striatum (Fechter, 1987). There is a correlation between the reduction of cerebellar weights of carbon monoxide-

exposed offspring and the increase of carbon monoxide exposure concentrations (Storm and Fechter, 1985). However, when pregnant cats are exposed, the cerebella of their fetuses seem relatively resistant when compared with cerebral white matter or brainstem (Okeda et al., 1986). Immediate hyperbaric oxygen therapy is highly recommended to prevent irreversible cerebral damage, particularly in the case of blood levels of carbon monoxide higher than 15%, coma, cardiac disease, and in pregnant women. It greatly reduces the carboxyhemoglobin half-life and accelerates the clearance of carbon monoxide (Dean et al., 1993).

INSECTICIDES AND HERBICIDES

Chlordecone Chlordecone is an organochlorine insecticide. In workers chronically exposed, chlordecone is absorbed through the oral, respiratory, and dermal routes (Taylor et al., 1978). Patients complain of pleural pain and arthralgias. The main neurological manifestations of intoxication are postural and kinetic tremor, gait unsteadiness, and opsoclonus (Taylor, 1982, 1985). Pseudotumor cerebri has also been reported (Sanborn et al., 1979). In addition, chlordecone has shown toxicity for peripheral nerves. The insecticide might induce tremor by acting at the brainstem level, possibly disturbing the cerebellar afferent pathways, and at the striatal level. However, the olivocerebellar tract does not seem to be involved, because destruction of climbing fibers with 3-acetylpyridine does not modify the chlordecone-induced tremor (Gerhart et al., 1985).

Phosphin Phosphin is a toxic fumigant. Intoxication has been described aboard a grain freighter after inhalation (Wilson et al., 1980). The symptoms of intoxication are headache, nausea and vomiting, cough, paresthesias, and diplopia. Neurological examination shows kinetic tremor and gait difficulties.

Carbon disulfide Carbon disulfide is a volatile liquid used in industries for the production of cellophan, as a solvent, for carbon

Other cerebellotoxic agents

tetrachloride production, for pesticides, or as a fumigant (Pahwa, 1997). Outbreaks in viscose rayon workers have been reported. The central nervous system is the main target of carbon disulfide intoxication. The three main neurological manifestations are encephalopathy, movement disorders, and peripheral neuropathy. Patients present a combination of confusion, pyramidal and extrapyramidal signs, ataxia, and axonal and demyelinating polyneuropathy (Peters et al., 1988; Chu et al., 1996). It has been suggested recently that olivo-ponto-cerebellar atrophy may occur after a long exposure to carbon disulfide (Frumkin, 1998). Pathological studies in humans have shown diffuse neuronal degeneration in the cerebral cortex and basal ganglia, and a loss in Purkinje cells (Alpers and Lewey, 1940). The mechanism of the neurotoxicity is still undetermined. There may be a spontaneous reaction with amino or thiol groups, generating dithiocarbamates and inhibiting enzymes in the central and peripheral nervous systems (Dalvi, 1988). Indeed, dithiocarbamate complexes inactivate metalloenzymes by chelating metal ions such as copper or zinc (Pahwa, 1997). In addition, carbon disulfide may induce covalent cross-linking of proteins, though this phenomenon seems to be observed essentially outside the nervous system (Dalvi, 1988; Valentine et al., 1995).

STX binds to voltage-sensitive sodium channels. Autoradiographic studies in mice have demonstrated that the highest densities of STX-sensitive sodium channels are found in the Purkinje cell layer, in parallel fibers, and in axons of basket cells (Mourre et al., 1990). Only very low densities are observed in cerebellar white matter.

Nicotine

Eucalyptus oil poisoning occurs in children after ingestion or following application of a home remedy for a skin allergy. Patients exhibit alteration of conscious state, vomiting, ataxic signs, and signs of pulmonary dysfunction (Tibballs, 1995; Darben et al., 1998). Speech is slurred and gait is broad-based. The ataxic signs are reversible.

Nicotine may be a toxic factor for the cerebellum. Johnsen and Miller (1986) have described a patient with multiple system atrophy and exacerbation of ataxia by cigarette smoking. In another patient with spinocerebellar degeneration, dysarthria as well as ataxia of the trunk and limbs worsened 15 minutes after nicotine gum chewing (Houi et al., 1993). SPECT revealed accumulation of 123I-IMP in the cerebellum after nicotine intake. This accumulation of 123IIMP was not observed in a control patient presenting spinocerebellar degeneration whose ataxic signs were unaffected by nicotine. Experimentally, exposure to nicotine during the brain growth spurt period in rats has been associated with significant reduction of the Purkinje cell numbers in the cerebellar vermis, providing clear support for the hypothesis of a deleterious effect on brain development in animals and raising the issue of potential effects in human fetuses (Chen et al., 1998). Other studies have shown that nicotine given in lobule X (nodula) results mainly in prostration and atonia (Maiti et al., 1986). Preliminary administration of kainic acid (which destroys large neurons) prevented the nicotine-induced disturbances. However, the correlation in humans has not been established. Another interesting observation is that nicotine administered subcutaneously to mice at a dose of 1 mg/kg causes an ataxic-like behavior (Kita et al., 1988). Extrapolation from these results obtained in animal studies has potential pitfalls. Further studies are warranted.

Saxitoxin (shellfish poisoning)

Cyanide

Saxitoxin (STX) is a potent neurotoxin contaminating a mollusc called Mytilus. The intoxication is characterized by gastrointestinal (nausea, vomiting, diarrhea) and neurological signs. Axial and appendicular cerebellar signs are salient, leading some authors to suggest the name of ataxic shellfish poisoning (Rhodes et al., 1975). Paresthesias are also common. Recently, De Carvalho et al. (1998) reported nine Portuguese patients with a clinical course of benign cerebellar ataxia.

Acute cyanide poisoning results from accidental or suicidal intoxication or from asphyxiation due to hydrocyanic fumes (Pahwa, 1997). Patients exhibit headache, coma, and seizures. The mortality rate is very high. In those patients who survive, neurological sequelae may develop: parkinsonian signs, postural tremor, dystonia or dementia (Carella et al., 1988). Rosenow et al. (1995) have delineated a clinical syndrome characterized by extrapyramidal and cerebellar signs in two patients who ingested potassium

OT H E R TOX I C AG E N TS

Eucalyptus oil

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cyanide in a suicide attempt. MRI disclosed lesions in the basal ganglia and cerebellum in both patients. In one patient, symmetrical hemorrhages were seen in the cerebellar cortex. PET study with 18F-fluorodeoxyglucose showed hypometabolism in the putamen, temporoparieto-occipital cortex, and cerebellum in the two cases. Neuropathological studies have shown that the globus pallidus is particularly vulnerable to cyanide. Moreover, atrophy of the cerebellum has been reported in an 18year-old man who ingested 975–1300 mg of potassium cyanide in a suicide attempt (Uitti et al., 1985). Cyanide acts by inactivating oxidative enzymes. In the cerebellum of rats, sodium cyanide disturbs GABAergic metabolism and increases levels of cyclic guanosine monophosphate (Persson et al., 1985). In mice, cyanide intoxication is antagonized by dihydroxyacetone (a physiological agent) and sodium thiosulfate (Niknahad and O’Brien, 1996). Moreover, preadministration of dihydroxyacetone prevents the inhibition of cytochrome oxidase activity by cyanide. Other antidotes have been tested successfully in animals, including 4-dimethylaminophenol combined with sodium nitrite (Bhattacharya, 1995). In humans, mild poisoning is treated by rest, oxygen, and amylnitrite (Beasley and Glass, 1998). In moderate and severe poisoning, sodium nitrite and sodium thiosulfate are used. Hydroxycobalamin is an alternative.

xReferencesx Aggarwal, S.and Byrne, B.D. (1991). Massive ischemic cerebellar infarction due to cocaine use. Neuroradiology 33: 449–50. Albukrek, D., Bakon, M., Moran, D.S., Faibel, M. and Epstein, Y. (1997). Heatstroke-induced cerebellar atrophy: clinical course, CT and MRI findings. Neuroradiology 39: 195–7. Alpers, B.J. and Lewey, F.H. (1940). Changes in the nervous system following carbon disulfide poisoning in animals and in man. Arch Neurol Psychiatry 44: 725–39. Anand, M., Agrawal, A.K., Rehmani, B.N., Gupta, G.S., Rana, M.D. and Seth, P.K. (1998). Role of GABA receptor complex in low dose lindane (HCH) induced neurotoxicity: neurobehavioural, neurochemical and electrophysiological studies. Drug Chem Toxicol 21: 35–46. Arai, A., Sato, M., Hozumi, I. et al. (1997). Cerebellar ataxia and peripheral neuropathy due to chronic bromvalerylurea poisoning. Intern Med 36: 742–6. Arnaud, A., Neau, J.P., Rivasseau-Jonveaux, T., Marechaud, R. and Gil, R. (1992). Neurological toxicity of amiodarone. 5 case reports. Rev Med Interne 13: 419–22. Asaka, T., Nitta, E., Makifuchi, T. et al. (1995). Germanium intoxication with sensory ataxia. J Neurol Sci 130: 220–3.

Baf, M.H., Subhash, M.N., Lakshmana, K.M. and Rao, B.S. (1994). Alterations in monoamine levels in discrete regions of rat brain after chronic administration of carbamazepine. Neurochem Res 19: 1139–43. Bakir, F., Rustam, H., Tikriti, S., Al-Damluji, S.F. and Shihristani, H. (1980). Clinical and epidemiological aspects of methylmercury poisoning. Postgrad Med J 56: 1–10. Barroso-Moguel, R., Villeda-Hernandez, J., Mendez-Armenta, M., Rios, C. and Monroy-Noyola, A. (1994). Combined -penicillamine and prussian blue as antidotal treatment against thallotoxicosis in rats: evaluation of cerebellar lesions. Toxicology 89: 15–24. Barton, C.H., Sterling, M.L. and Vaziri, N.D. (1981). Phencyclidine intoxication: clinical experience in 27 cases confirmed by urine assay. Ann Emerg Med 10: 243–6. Bartynski, W.S., Grabb, B.C., Zeigler, Z., Lin, L. and Andrews, D.F. (1997). Watershed imaging features and clinical vascular injury in cyclosporin A neurotoxicity. J Comput Assist Tomogr 21: 872–80. Baulac, M., Cavalcanti, D., Semah, F., Arzimanoglou, A. and Portal, J.J. (1998). Gabapentin add-on therapy with adaptable dosages in 610 patients with partial epilespy: an open, observational study. The French Gabapentin Collaborative Group. Seizure 7: 55–62. Beasley, D.M. and Glass, W.I. (1998). Cyanide poisoning: pathophysiology and treatment recommendations. Occup Med 48: 427–31. Becker, C.E. (1979). Medical complications of drug abuse. Adv Intern Med 24: 183–202. Belli, L.S., De Carlis, L., Romani, F., et al. (1993). Dysarthria and cerebellar ataxia: late occurrence of severe neurotoxicity in a liver transplant recipient. Transpl Int 6: 176–8. Bhattacharya, R. (1995). Therapeutic efficacy of sodium nitrite and 4-dimethylaminophenol or hydroxylamine co-administration against cyanide poisoning in rats. Hum Exp Toxicol 14: 29–33. Bonnotte, B., Jolimoy, C., Pacaud, A., Belleville, Y., Allain, P. and Chevet, D. (1997). Factitious hyperchloremia disclosing bromide poisoning. 4 cases. Presse Med 26: 852–4. Boor, J.W. and Hurtig, H.I. (1977). Persistent cerebellar ataxia after exposure to toluene. Ann Neurol 2: 440–2. Botez, M.I., Attig, E. and Vezina, J.L. (1988). Cerebellar atrophy in epileptic patients. Can J Neurol Sci 15: 299–303. Bridge, T.A., Norton, R.L. and Robertson, W.O. (1994). Pediatric carbamazepine overdoses. Pediatr Emerg Care 10: 260–3. Canini, F., Bourdon, L., Cespuglio, R. and Buguet, A. (1997). Voltametric assessment of brain nitric oxide during heatstroke in rats. Neurosci Lett 231: 67–70. Cano, G., Suarez-Roca, H. and Bonilla, E. (1997). Alterations of excitatory amino acid receptors in the brain of manganesetreated mice. Mol Chem Neuropathol 30: 41–52. Carella, F., Grassi, M.P., Savoiardo, M., Contri, P., Rapuzzi, B. and Mangoni, A. (1988). Dystonic–Parkinsonian syndrome after cyanide poisoning: clinical and MRI findings. J Neurol Neurosurg Psychiatry 51: 1345–8. Cawte, J., Kilburn, C. and Florence, M. (1989). Motor neurone

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disease of the western Pacific: do the foci extend to Australia? Neurotoxicology 10: 263–70. Chang, L.W. (1980). Mercury. In Experimental and Clinical Neurotoxicology, ed. P.S. Spencer and H.H. Schaumburg, pp. 508–26. Baltimore: Williams & Wilkins. Charness, M.E., Morady, F. and Scheinman, M.M. (1984). Frequent neurologic toxicity associated with amiodarone therapy. Neurology 34: 669–71. Chatak, N.R., Santoso, R.A. and McKinney, W.N. (1976). Cerebellar degeneration following long-term phenytoin therapy. Neurology 26: 818–20. Chen, W.J., Parnell, S.E. and West, J.R. (1998). Neonatal alcohol and nicotine exposure limits brain growth and depletes cerebellar Purkinje cells. Alcohol 15: 33–41. Choi, I.S. (1983). Delayed neurologic sequelae in carbon monoxide intoxication. Arch Neurol 40: 433–5. Chu, C.C., Huang, C.C., Chu, N.S. and Wu, T.N. (1996). Carbon disulfide induced polyneuropathy: sural nerve pathophysiology, electrophysiology and clinical correlation. Acta Neurol Scand 94: 258–63. Clarkson, T.W. (1997). The toxicology of mercury. Crit Rev Clin Lab Sci 34: 369–403. Cumming, W.J. and Foster, J.B. (1978). Cimetidine-induced brainstem dysfunction. Lancet i: 1096. Dalvi, R.R. (1988). Mechanism of the neurotoxic and hepatotoxic effects of carbon disulfide. Drug Metabol Drug Interact 6: 275–84. Damasceno, B.P. and de Capitani, E.M. (1994). Cerebellar atrophy related to chronic exposure to toluene. Case report. Arq Neuropsiquiatr 52: 90–2. Daras, M., Kakkouras, L., Tuchman, A.J. and Koppel, B.S. (1995). Rhabdomyolysis and hyperthermia after cocaine abuse: a variant of the neuroleptic malignant syndrome? Acta Neurol Scand 92: 161–5. Darben, T., Cominos, B. and Lee, C.T. (1998). Topical eucalyptus oil poisoning. Australas J Dermatol 39: 265–7. Davis, J.M., Janowsky, D.S. and Khaled, E.M. (1973). The use of lithium in clinical psychiatry. Psychiatry Ann 3: 78–99. Dean, B.S., Verdile, V.P. and Krenzelok, E.P. (1993). Coma reversal with cerebral dysfunction recovery after repetitive hyperbaric oxygen therapy for severe carbon monoxide poisoning. Am J Emerg Med 11: 616–18. De Carvalho, M., Jacinto, J., Ramos, N., de Oliveira, V., Pinho e Melo, T. and de Sa, J. (1998). Paralytic shellfish poisoning: clinical and electrophysiological observations. J Neurol 245: 551–4. del Rio, E., Shinomura, T., van der Kaay, J., Nicholls, D.G. and Downes, C.P. (1998). Disruption by lithium of phosphoinositide signalling in cerebellar granule cells in primary culture. J Neurochem 70: 1662–9. Dethy, S., Manto, M., Bastianelli, E. et al. (1997). Cerebellar spongiform degeneration induced by acute lithium intoxication in the rat. Neurosci Lett 224: 25–8. Deutsch, S.I., Mastropaolo, J. and Rosse, R.B. (1998). Neurodevelopmental consequences of early exposure to phencyclidine and related drugs. Clin Neuropharmacol 21: 320–32. Dixon, S.D. and Bejar, R. (1989). Echoencephalographic findings in

neonates associated with maternal cocaine and methamphetamine use: incidence and clinical correlates. J Pediatr 115: 770–8. Donaldson, I.M. and Cuningham, J. (1983). Persisting neurologic sequelae of lithium carbonate therapy. Arch Neurol 40: 747–51. D’Souza, C.A., Rush, S.J. and Brown, I.R. (1998). Effect of hyperthermia on the transcription rate of heat-shock genes in the rabbit cerebellum and retina assayed by nuclear run-ons. J Neurosci Res 52: 538–48. Dumitru, D. and Kalantri, A. (1990). Electrophysiologic investigation of thallium poisoning. Muscle Nerve 13: 433–7. Eldridge, R., Iivanainen, M., Stern, R., Koerber, T. and Wilder, B.J. (1983). ‘Baltic’ myoclonus epilepsy: hereditary disorder of childhood made worse by phenytoin. Lancet ii: 838–42. Fechter, L.D. (1987). Neurotoxicity of prenatal carbon monoxide exposure. Res Rep Health Eff Inst 12: 3–22. Fell, J.M., Reynolds, A.P., Meadows, N. et al. (1994). Manganese intoxication and chronic liver failure. Ann Neurol 36: 871–5. Finkelstein, Y., Markowitz, M.E. and Rosen, J.F. (1998). Low-level lead-induced neurotoxicity in children: an update on central nervous system effects. Brain Res Brain Res Rev 27: 168–76. Frumkin, H. (1998). Multiple system atrophy following chronic carbon disulfide exposure. Environ Health Perspect 106: 611–13. Fujimoto, M., Ishibashi, H., Shimamura, R. et al. (1992). A patient with liver cirrhosis manifesting various symptoms including cerebellar ataxia due to germanium intoxication. Fukuoka Igaku Zasshi 83: 139–43. Gadisseaux, J.F., Rodriguez, J. and Lyon, G. (1984). Pontoneocerebellar hypoplasia – a probable consequence of prenatal destruction of the pontine nuclei and a possible role of phenytoin intoxication. Clin Neuropathol 3: 160–7. Gao, X.M., Margolis, R.L., Leeds, P., Hough, C., Post, R.M. and Chuang, D.M. (1995). Carbamazepine induction of apoptosis in cultured cerebellar neurons: effects of N-methyl--aspartate, aurintricarboxylic acid and cycloheximide. Brain Res 703: 63–71. Garretto, N.S., Rey, R.D., Kohler, G., et al. (1994). Cerebellar syndrome caused by amiodarone. Arq Neuropsiquiatr 52: 575–7. Gerhart, J.M., Hong, J.S. and Tilson, H.A.. (1985). Studies on the mechanism of chlordecone-induced tremor in rats. Neurotoxicology 6: 211–29. Gianutsos, G. and Murray, M.T. (1982). Alterations in brain dopamine and GABA following inorganic or organic manganese administration. Neurotoxicology 3: 75–81. Gilman, S., Bloedel, J.R. and Lechtenberg, R. (1981). Disorders of the Cerebellum. Contemporary Neurology Series. Philadephia: F.A. Davis. Goetz, C.G. and Cohen, M.M. (1989). Neurotoxic agents. In Clinical Neurology, Vol. 2, ed. R.J. Joynt, pp. 1–84. Philadelphia: Lippincott. Gordon, M.F., Abrams, R.I., Rubin, D.B., Barr, W.B. and Correa, D.D. (1995). Bismuth subsalicylate toxicity as a cause of prolonged encephalopathy with myoclonus. Mov Disord 10: 220–2. Gordon, R.A., Roberts, G., Amin, Z., Williams, R.H. and Paloucek, F.P. (1998). Aggressive approach in the treatment of acute lead encephalopathy with an extraordinarily high concentration of lead. Arch Pediatr Adolesc Med 152: 1100–4.

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362

M-U. Manto and J. Jacquy

Grignon, S. and Bruguerolle, B. (1996). Cerebellar lithium toxicity: a review of recent literature and tentative pathophysiology. Therapie 51: 101–6. Hackett, J.T. (1976). Selective antagonism of frog cerebellar synaptic transmission by manganese and cobalt ions. Brain Res 114: 47–52. Hannah, R.S., Roth, S.H. and Spira, A.W. (1988). Effect of phenobarbital on Purkinje cell growth patterns in the rat cerebellum. Exp Neurol 100: 354–64. Hasan, M., Ashraf, I. and Bajpai, V.K. (1978). Electron microscopic study of the effects of thallium poisoning on the rat cerebellum. Forensic Sci 11: 139–46. Hassan, N.H., Thakar, J., Weinberg, A.L. and Grimes, J.D. (1987). Lithium-carbamazepine interaction: clinical and laboratory investigations. Neurology 37(Suppl. 1): 172. Higuchi, I., Izumo, S., Kuriyama, M. et al. (1989). Germanium myopathy: clinical and experimental pathological studies. Acta Neuropathol (Berl) 79: 300–4. Holtzman, D., DeVries, C., Nguyen, H., Olson, J. and Bensch, K. (1984). Maturation of resistance to lead encephalopathy: cellular and subcellular mechanisms. Neurotoxicology 5: 97–124. Hori, A., Kazukawa, S., Fujii, T. and Kurachi, M. (1987). Lennox–Gastaut syndrome with and without Dandy–Walker malformation. Epilepsy Res 1: 258–61. Hough, C.J., Irwin, R.P., Gao, X.M., Rogawski, M.A. and Chuang, D.M. (1996). Carbamazepine inhibition of N-methyl--aspartate-evoked calcium influx in rat cerebellar granule cells. J Pharmacol Exp Ther 276: 143–9. Houi, K., Oka, H. and Mochio, S. (1993). The effects of nicotine on a patient with spinocerebellar degeneration whose symptoms were temporarily exacerbated by cigarette smoking. Rinsho Shinkeigaku 33: 774–6. Huang, C.C., Chu, N.S., Lu, C.S. et al. (1989). Chronic manganese intoxication. Arch Neurol 46: 1104–6. Hunter, D. and Russel, D.S. (1954). Focal cerebral and cerebellar atrophy in a human subject due to organic mercury compounds. J Neurol Neurosurg Psychiatry 17: 235–41. Ikeda, M. and Tsukagoshi, H. (1990). Encephalopathy due to toluene sniffing. Report of a case with magnetic resonance imaging. Eur Neurol 30: 347–9. Ishiguro, M., Yasue, T., Watanabe, S., Umemura, A., Okamoto, M and Yamada, F. (1982). Efficacy of hemoperfusion in the therapy of bromvalerylurea (bromural) intoxication. J Toxicol Clin Toxicol 19: 273–9. Johnsen, J.A. and Miller, V.T. (1986). Tobacco intolerance in multiple system atrophy. Neurology 36: 986–8. Johnson, L.M., Hubble, J.P. and Koller, W.C. (1993). Effect of medications and toxins on cerebellar function. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg. New York: Marcel Dekker. Katz, A.A., Hoffman, R.S. and Silverman, R.A. (1993). Phenytoin toxicity from smoking crack cocaine adulterated with phenytoin. Ann Emerg Med 22: 1485–7. Kawakami, T., Takiyama, Y., Yanaka, I. et al. (1998). Chronic bromvalerylurea intoxication: dystonic posture and cerebellar ataxia

due to nonsteroidal anti-inflammatory drug abuse. Intern Med 37: 788–91. King, M.D. (1982). Neurological sequelae of toluene abuse. Hum Toxicol 1: 281–7. Kita, T., Nakashima, T., Shirase, M., Asahina, M. and Kurogochi, Y. (1988). Effects of nicotine on ambulatory activity in mice. Jpn J Pharmacol 46: 141–6. Koller, W.C., Perlik, S., Glatt, S.L., Huckman, M.S. and Fox, J.H. (1981). Cerebellar atrophy demonstrated by computed tomography. Neurology 31: 405–12. Komaki, H., Maisawa, S., Sugai, K., Kobayashi, Y. and Hashimoto, T. (1999). Tremor and seizures associated with chronic manganese intoxication. Brain Dev 21: 122–4. Korogi, Y., Takahashi, M., Okajima, T. and Eto, K. (1998). MR findings of Minamata disease. J Magn Reson Imaging 8: 308–16. Korogi, Y., Takahashi, M., Sumi, M. et al. (1994). MR imaging of Minamata disease: qualitative and quantitative analysis. Radiat Med 12: 249–53. Kuruvilla, T. and Bharucha, N.E. (1997). Cerebellar atrophy after acute phenytoin intoxication. Epilepsia 38: 500–2. Ky, S.Q., Deng, H.S., Xie, P.Y. and Hu, W. (1992). A report of two cases of chronic serious manganese poisoning treated with sodium para-aminosalicylic acid. Br J Ind Med 49: 66–9. Lee, S., Merriam, A., Kim, T.S., Liebling, M., Dickson, D.W. and Moore, G.R. (1989). Cerebellar degeneration in neuroleptic malignant syndrome: neuropathologic findings and review of the literature concerning heat-related nervous system injury. J Neurol Neurosurg Psychiatry 52: 387–91. Lhuillier, M. and Gorin, B. (1972). Amiodarone et tremblement. Nouv Presse Med 1: 1844. Liessens, J.L., Monstrey, J., Vanden Eeckhout, E., Djudzman, R. and Martin, J.J. (1978). Bismuth encephalopathy. A clinical and anatomo-pathological report of one case. Acta Neurol Belg 78: 301–9. Lindvall, O. and Nilsson, B. (1984). Cerebellar atrophy following phenytoin intoxication. Ann Neurol 16: 258–60. Lodenius, M. and Malm, O. (1998). Mercury in the Amazon. Rev Environ Contam Toxicol 157: 25–52. Lopez-Ariztegui, N., Ochoa, M., Sanchez-Migallon, M.J., Nevado, C. and Martin, M. (1998). Acute phenytoin poisoning secondary to an interaction with ticlopidine. Rev Neurol (Spain) 26: 1017–18. Lorton, D. and Anderson, W.J. (1986). The effects of postnatal lead toxicity on the development of cerebellum in rats. Neurobehav Toxicol Teratol 8: 51–9. Maiti, A., Shahid Salles, K., Grassi, S. and Abood, L.G. (1986). Barrel rotation and prostration by vasopressin and nicotine in the vestibular cerebellum. Pharmacol Biochem Behav 25: 583–8. Malbrain, M.L., Lambrecht, G.L., Zandijk, E. et al. (1997). Treatment of severe thallium intoxication. J Toxicol Clin Toxicol 35: 97–100. Malm, G. and Lying-Tunell, U. (1980). Cerebellar dysfunction related to toluene sniffing. Acta Neurol Scand 62: 188–90. Mameli, O., Tolu, E., Piredda, S., Monaco, F. and Mutani, R. (1982). Cerebellar impairment following acute nontoxic administration of phenytoin in rat. Epilepsia 23: 683–91.

Other cerebellotoxic agents

Mani, J., Chaudhary, N., Kanjalkar, M. and Shah, P.U. (1998). Cerebellar ataxia due to lead encephalopathy in an adult. J Neurol Neurosurg Psychiatry 65: 797. Manto, M., Godaux, E., Jacquy, J. and Hildebrand, J. (1996a). Analysis of cerebellar dysmetria associated with lithium intoxication. Neurol Res 18: 416–24. Manto, M., Goldman, S. and Hildebrand, J. (1996b). Cerebellar gait ataxia following neuroleptic malignant syndrome. J Neurol 243: 101–2. Manyam, B.V. (1996). Uncommon forms of tremor. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 387–403. New York: McGraw Hill. Marks, T.A., Worthy, W.C. and Staples, R.E. (1980). Teratogenic potential of phencyclidine in the mouse. Teratology 21: 541–6. Marty, M.S. and Atchison, W.D. (1997). Pathways mediating Ca2 entry in rat cerebellar granule cells following in vitro exposure to methyl mercury. Toxicol Appl Pharmacol 147: 319–30. Marwaha, J., Palmer, M.R., Woodward, D.J., Hoffer, B.J. and Freedman, R. (1980). Electrophysiological evidence for presynaptic actions of phencyclidine on noradrenergic transmission in rat cerebellum. J Pharmacol Exp Ther 215: 606–13. Mascalchi, M., Petruzzi, P. and Zampa, V. (1996). MRI of cerebellar white matter damage due to carbon monoxide poisoning: case report. Neuroradiology 38 (Suppl. 1): 73–4. Masland, R.L. (1982). Carbamazepine neurotoxicity. In Antiepileptic Drugs, 2nd edn., ed. D.M. Woodbury, J.K. Penry and C.E. Pippenger, pp. 521–31. New York: Raven Press. Masur, H., Elger, C.E., Ludolph, A.C. and Galanski, M. (1989). Cerebellar atrophy following acute intoxication with phenytoin. Neurology 39: 432–33. Matsumoto, H., Koya, G. and Takeuchi, T. (1965). Fetal Minamata disease. J Neuropathol Exp Neurol 24: 563–74. McCarron, M.M., Schulze, B.W., Thompson, G.A., Conder, M.C. and Goetz, W.A. (1981). Acute phencyclidine intoxication: incidence of clinical findings in 1000 cases. Ann Emerg Med 10: 237–42. Meggs, W.J., Cahill-Morasco, R., Shih, R.D., Goldfrank, L.R. and Hoffman, R.S. (1997). Effects of Prussian blue and N-acetylcysteine on thallium toxicity in mice. J Toxicol Clin Toxicol 35: 163–6. Milla, P.J. (1996). Manganese toxicity in children receiving longterm parenteral nutrition. Lancet 347: 1218–21. Miller, L.G., Deutsch, S.I., Greenblatt, D.J., Paul, S.M. and Shader, R.I. (1988). Acute barbiturate administration increases benzodiazepine receptor binding in vivo. Psychopharmacology 96: 385–90. Moore, D., House, I. and Dixon, A. (1993). Thallium poisoning. Diagnosis may be elusive but alopecia is the clue. Br Med J 306: 1527–9. Mott, S.H., Packer, R.J. and Soldin, S.J. (1994). Neurologic manifestations of cocaine exposure in childhood. Pediatrics 93: 557–60. Mourre, C., Widmann, C. and Lazdunski, M. (1990). Saxitoxinsensitive Na channels: presynaptic localization in cerebellum and hippocampus of neurological mutant mice. Brain Res 533: 196–202.

Munoz-Garcia, D., Del Ser, T., Bermejo, F. and Portera, A. (1982). Truncal ataxia in chronic anticonvulsant treatment. Association with drug-induced folate deficiency. J Neurol Sci 55: 305–11. Nagamoto, S., Umehara, F., Hanada, K. et al. (1999). Manganese intoxication during total parenteral nutrition: report of two cases and review of the literature. J Neurol Sci 162: 102–5. Nagashima, K. (1997). A review of experimental methylmercury toxicity in rats: neuropathology and evidence for apoptosis. Toxicol Pathol 25: 624–31. Nakki, R., Koistinaho, J., Sharp, F.R. and Sagar, S.M. (1995). Cerebellar toxicity of phencyclidine. J Neurosci 15: 2097–108. Nakki, R., Sharp, F.R., Sagar, S.M. and Honkaniemi, J. (1996). Effects of phencyclidine on immediate early gene expression in the brain. J Neurosci Res 45: 13–27. Neufeld, M.Y., Swanson, J.W. and Klass, D.W. (1981). Localized EEG abnormalities in acute carbon monoxide poisoning. Arch Neurol 38: 524–7. Ney, G.C., Lantos, G., Barr, W.B. and Schaul, N. (1994). Cerebellar atrophy in patients with long-term phenytoin exposure and epilepsy. Arch Neurol 51: 767–71. Nick, J., Dudognon, P., Escourolle, R. et al. (1978). Neurological disorders and perhexiline maleate therapy. Clinical study of 10 cases. Neuropathological, pharmacokinetic and biochemical studies. Rev Neurol (Paris) 134: 103–14. Niknahad, H., and O’Brien, P.J. (1996). Antidotal effect of dihydroxyacetone against cyanide toxicity in vivo. Toxicol Appl Pharmacol 138: 186–91. Ninomiya, T., Ohmori, H., Hashimoto, K., Tsuruta, K. and Ekino, S. (1995). Expansion of methylmercury poisoning outside of Minamata: an epidemiological study on chronic methylmercury poisoning outside of Minamata. Environ Res 70: 47–50. Nussbaum, E.S., Maxwell, R.E., Bitterman, P.B., Hertz, M.I., Bula, W. and Latchaw, R.E. (1995). Cyclosporine A toxicity presenting with acute cerebellar edema and brainstem compression. Case report. J Neurosurg 82: 1068–70. Oehmichen, M., Meissner, C., Reiter, A. and Birkholz, M. (1996). Neuropathology in non-human immunodeficiency virusinfected drug addicts: hypoxic brain damage after chronic intravenous drug abuse. Acta Neuropathol 91: 642–6. Ohmori, H., Ogura, H., Yasuda, M. et al. (1999). Developmental neurotoxicity of phenytoin on granule cells and Purkinje cells in mouse cerebellum. J Neurochem 72: 1497–506. Ohmori, H., Yamashita, K., Hatta, T. et al. (1997). Effects of low-dose phenytoin administered to newborn mice on developing cerebellum. Neurotoxicol Teratol 19: 205–11. Okeda, R., Matsuo, T., Kuroiwa, T., Tajima, T. and Takahashi, H. (1986). Experimental study on pathogenesis of the fetal brain damage by acute carbon monoxide intoxication of the pregnant mother. Acta Neuropathol 69: 244–52. Olanow, C.W., Good, P.F., Shinotoh, H. et al. (1996). Manganese intoxication in the rhesus monkey: a clinical, imaging, pathologic, and biochemical study. Neurology 46: 492–8. Pahwa, R. (1997). Toxin-induced parkinsonian syndromes. In Movement Disorders, ed. R.L. Watts and W.C. Koller, pp. 315–23. New York: McGraw Hill.

363

364

M-U. Manto and J. Jacquy

Palakurthy, P.R., Iyer, V. and Meckler, R.J. (1987). Unusual neurotoxicity associated with amiodarone therapy. Arch Intern Med 147: 881–4. Palmer, B.F. and Toto, R.D. (1991). Severe neurologic toxicity induced by cyclosporine A in three renal transplant patients. Am J Kidney Dis 1: 116–21. Pappas, C.L., Quisling, R.G., Ballinger, W.E. and Love, L.C. (1986). Lead encephalopathy: symptoms of a cerebellar mass lesion and obstructive hydrocephalus. Surg Neurol 26: 391–4. Pasquier, F., De Poorter, M.C., Jacquemotte, N., Adnet-Bonte, C. and Petit, H. (1993). Cerebellar syndrome after carbon monoxide poisoning. Magnetic resonance imaging and single photon emission tomography. Rev Neurol (Paris) 149: 805–6. Pelletier, J., Habib, M., Pellissier, J.F., Crevat, A. and Khalil, R. (1991). Neurologic sequelae of the neuroleptics–lithium combination: role of hyperthermia. Rev Med Interne 12: 187–91. Perelman, S., Hertz-Pannier, L., Hassan, M. and Bourrillon, A. (1993). Lead encephalopathy mimicking a cerebellar tumor. Acta Paediatr 82: 423–5. Persson, S.A., Cassel, G. and Sellstrom, A. (1985). Acute cyanide intoxication and central transmitter systems. Fundam Appl Toxicol 5: S150–9. Peters, H.A., Levine, R.L., Matthews, C.G. and Chapman, L.J. (1988). Extrapyramidal and other neurologic manifestations associated with carbon disulfide fumigant exposure. Arch Neurol 45: 537–40. Phillips-Howard, P.A. and ter Kuile, F.O. (1995). CNS adverse events associated with antimalarial agents. Fact or fiction? Drug Saf 12: 370–83. Piantadosi, C.A., Zhang, J., Levin, E.D., Folz, R.J. and Schmechel, D.E. (1997). Apoptosis and delayed neuronal damage after carbon monoxide poisoning in the rat. Exp Neurol 147: 103–14. Playford, R.J., Matthews, C.H., Campbell, M.J. et al. (1990). Bismuth induced encephalopathy caused by tri-potassium dicitrato bismuthate in a patient with chronic renal failure. Gut 31: 359–60. Quraishi, H., Rush, S.J. and Brown, I.R. (1996). Expression of mRNA species encoding heat shock protein 90 (hsp90) in control and hyperthermic rabbit brain. J Neurosci Res 43: 335–45. Raeder, E.A., Podrid, P.J. and Lown, B. (1985). Side effects and complications of amiodarone therapy. Am Heart J 109: 975–83. Rapport, L.R. and Shaw, C.M. (1977). Phenytoin-related cerebellar degeneration without seizures. Ann Neurol 2: 437–9. Reyes, P.F., Gonzales, C.F., Zalewska, M.K. and Besarab, A. (1986). Intracranial calcification in adults with chronic lead exposure. Am J Roentgenol 146: 267–70. Rhodes, F.A., Mills, C.G. and Popei, K. (1975). Paralytic shellfish poisoning in Papua New Guinea. P N G Med J 18: 197–202. Rittmannsberger, H. and Leblhuler, F. (1992). Asterixis induced by carbamazepine. Biol Psychiatry 32: 364–8. Rittmannsberger, H., Leblhuler, F. and Sommer, R. (1991). Asterixis as a side effect of carbamazepine therapy. Klin Wochenschr 69: 279–81. Rodier, J. (1955). Manganese poisoning in Moroccan miners. Br J Ind Med 12: 21–35. Rosenow, F., Herholz, K., Lanfermann, H. et al. (1995). Neurological

sequelae of cyanide intoxication – the patterns of clinical, magnetic resonance imaging, and positron emission tomography findings. Ann Neurol 38: 825–8. Ross, J.F., Sahenk, Z., Hyser, C., Mendell, J.R. and Alden, C.L. (1988). Characterization of a murine model for human bismuth encephalopathy. Neurotoxicology 9: 581–6. Ross, J.F., Switzer, R.C., Poston, M.R. and Lawhorn, G.T. (1996). Distribution of bismuth in the brain after intraperitoneal dosing of bismuth subnitrate in mice: implications for routes of entry of xenobiotic metals into the brain. Brain Res 725: 137–54. Rothner, A.D., Pippenger, C., Cruse, R.P., Erenberg, G., Wyllie, E. and Zabukovec, M. (1987). Carbamazepine toxicity with therapeutic total levels and elevated free levels. Ann Neurol 22: 413–14. Saavedra, H., De Marinis, A. and Palestini, M. (1996). Neuronal changes induced by chronic toluene exposure in the cat. Arch Ital Biol 134: 217–25. Sabbioni, E. and Manzo, L. (1980). Metabolism and toxicity of thallium. In Advances in Neurotoxicology, ed. L. Manzo, pp. 249–70. Oxford: Pergamon Press. Saito, K. and Wada, H. (1993). Behavioral approaches to toluene intoxication. Environ Res 62: 53–62. Sanborn, G.E., Selhorst, J.B., Calabrese, V.P. and Taylor, J.R. (1979). Pseudotumor cerebri and insecticide intoxication. Neurology 29: 1222–7. Sarafian, T., Hagler, J., Vartavarian, L. and Verity, M.A. (1989). Rapid cell death induced by methyl mercury in suspension of cerebellar granule neurons. J Neuropathol Exp Neurol 48: 1–10. Schneider, J.A. and Mirra, S.S. (1994). Neuropathologic correlates of persistent neurologic deficit in lithium intoxication. Ann Neurol 36: 928–31. Schwartz, R.H. and Einhorn, A. (1986). PCP intoxication in seven young children. Pediatr Emerg Care 2: 238–41. Selhorst, J.B., Kaufman, B. and Horwitz, S.J. (1972). Diphenylhydantoin-induced cerebellar degeneration. Arch Neurol 27: 452–5. Seymour, J.F. (1993). Carbamazepine overdose. Features of 33 cases. Drug Saf 8: 81–8. Shukla, S., Godwin, C., Long, L.E. and Miller, M.G. (1984). Lithium–carbamazepine neurotoxicity and risk factors. Am J Psychiatry 141: 1604–6. Silver, D.A., Cross, M., Fox, B. and Paxton, R.M. (1996). Computed tomography of the brain in acute carbon monoxide poisoning. Clin Radiol 51: 480–3. Simard, M., Gumbiner, B., Lee, A., Lewis, H. and Norman, D. (1989). Lithium carbonate intoxication. A case report and review of the literature. Arch Intern Med 149: 36–46. Specht, U., May, T.W., Rohde, M. et al. (1997). Cerebellar atrophy decreases the threshold of carbamazepine toxicity in patients with chronic focal epilepsy. Arch Neurol 54: 427–31. Spencer, P.S. and Schaumburg, H.H. (eds.) (1980). Experimental and Clinical Neurotoxicology. Baltimore: Williams & Wilkins. Squier, W., Hope, P.L. and Lindenbaum, R.H. (1990). Neocerebellar hypoplasia in a neonate following intra-uterine exposure to anticonvulsants. Dev Med Child Neurol 32: 737–42. Steinhoff, B.J., Herrendorf, G., Bittermann, H.J. and Kurth, C.

Other cerebellotoxic agents

(1997). Isolated ataxia as an idiosyncratic side-effect under gabapentin. Seizure,6: 503–5. Stengard, K., Tham, R., O’Connor, W.T., Hoglund, G. and Ungerstedt, U. (1993). Acute toluene exposure increases extracellular GABA in the cerebellum of rat: a microdialysis study. Pharmacol Toxicol 73: 315–18. Storm, J.E. and Fechter, L.D. (1985). Prenatal carbon monoxide exposure differentially affects postnatal weight and monoamine concentration of rat brain regions. Toxicol Appl Pharmacol 81: 139–46. Tan, T.P., Algra, P.R., Valk, J. and Wolters, E.C. (1994). Toxic leukoencephalopathy after inhalation of poisoned heroin: MR findings. Am J Neuroradiol 15: 175–8. Tang, Y.P., Murata, Y., Nagaya, T., Noda, Y., Seo, H. and Nabeshima, T. (1997). NGFI-B, c-fos, and c-jun mRNA expression in mouse brain after acute carbon monoxide intoxication. J Cereb Blood Flow Metab 17: 771–80. Tauer, U., Knoth, R. and Volk, B. (1998). Phenytoin alters Purkinje cell axon morphology and targeting in vitro. Acta Neuropathol 95: 583–91. Taylor, J.R. (1982). Neurological manifestations in humans exposed to chlordecone and follow-up results. Neurotoxicology 3: 9–16. Taylor, J.R. (1985). Neurological manifestations in humans exposed to chlordecone: follow-up results. Neurotoxicology 6: 231–6. Taylor, J.R., Selhorst, J.B., Houff, S.A. and Martinez, A.J. (1978). Chlordecone intoxication in man. I. Clinical observations. Neurology 28: 626–30. Thompson, C.B., June, C.H., Sullivan, K.M. and Thomas, E.D. (1984). Association between cyclosporin neurotoxicity and hypomagnesemia. Lancet ii: 1116–20. Tibballs, J. (1995). Clinical effects and management of eucalyptus oil ingestion in infants and young children. Med J Aust 163: 177–80. Tomaszewski, C. (1999). Carbon monoxide poisoning. Early awareness and intervention can save lives. Postgrad Med 105: 39–40. Tomson, T. (1984). Interdosage fluctuations in plasma carbamazepine concentrations determine intermittent side effects. Arch Neurol 41: 830–4. Tong, T.G., Benowitz, N.L., Becker, C.E., Forni, P.J. and Boerner, U. (1975). Phencyclidine poisoning. J Am Med Assoc 234: 512–13. Troppe, I., Lopez-Villegas, D. and Lenkinski, R.E. (1998). Magnetic resonance imaging and spectroscopy of regional brain structure in a 10-year-old boy with elevated blood lead levels. Pediatrics 101: E7. Turpin, J.C., Pluot, M., Albouz, S., Bajolet, A., Caulet, T. and Baumann, N. (1983). Study of thesaurismosis induced by perhexiline maleate. Confirmation of experimental data. Sem Hop 59: 58–61. Uitti, R.J., Rajput, A.H., Ashenhurst, E.M. and Rozdilsky, B. (1985). Cyanide-induced parkinsonism: a clinicopathologic report. Neurology 35: 921–5. Utterbock, R.A. (1958). Parenchymatous cerebellar degeneration complicating diphenylhydantoin (Dilantin) therapy. Arch Neurol 80: 180–1. Valentine, W.M., Amarnath, V., Amarnath, K., Rimmele, F. and

Graham, D.G. (1995). Carbon disulfide mediated protein crosslinking by N,N-diethyldithiocarbamate. Chem Res Toxicol 8: 96–102. Vergauwe, P.L., Knockaert, D.C. and Van Tittelbaum, T.J. (1990). Near fatal subacute thallium poisoning necessitating prolonged mechanical ventilation. Am J Emerg Med 8: 548–50. Vescovi, A., Gebbia, M., Cappelletti, G., Parati, E.A. and Santagostino, A. (1989). Interactions of manganese with human brain glutathione-S-transferase. Toxicology 57: 183–91. Volk, B., Kirchgassner, N. and Detmar, M. (1986). Degeneration of granule cells following chronic phenytoin administration: an electron microscopic investigation of the mouse cerebellum. Exp Neurol 91: 60–70. Wainwright, A.P., Kox, W.J., House, I.M., Henry, J.A., Heaton, R. and Seed, W.A. (1988). Clinical features and therapy of acute thallium poisoning. Q J Med 69: 939–44. Weber, W., Henkes, H., Moller, P., Bade, K. and Kuhne, D. (1998). Toxic spongiform leucoencephalopathy after inhaling heroin vapour. Eur Radiol 8: 749–55. Weizman, A., Fares, F., Pick, C.G., Yanai, J. and Gavish, M. (1989). Chronic phenobarbital administration affects GABA and benzodiazepine receptors in the brain and periphery. Eur J Pharmacol 169: 235–40. Werner, E.G. and Olanow, C.W. (1989). Parkinsonism and amiodarone therapy. Ann Neurol 25: 630–2. Wilson, R., Lovejoy, F.H., Jaeger, R.J. and Landrigan, P.L. (1980). Acute phosphine poisoning aboard a grain freighter. Epidemiologic, clinical, and pathological findings. J Am Med Assoc 244: 148–50. Wolters, E.C., van Wijngaarden, G.K., Stam, F.C. et al. (1982). Leucoencephalopathy after inhaling ‘heroin’ pyrolysate. Lancet ii: 1233–7. Yamanouchi, N., Okada, S., Kodama, K. et al. (1995). White matter changes caused by chronic solvent abuse. Am J Neuroradiol 16: 1643–9. Yamashita, T., Ando, Y., Sakashita, N. et al. (1997). Role of nitric oxide in the cerebellar degeneration during methylmercury intoxication. Biochim Biophys Acta 1334: 303–11. Yan, G.M., Irwin, R.P., Lin, S.Z., Weller, M., Wood, K.A. and Paul, S.M. (1995). Diphenylhydantoin induces apoptotic cell death of cultured rat cerebellar granule neurons. J Pharmacol Exp Ther 274: 983–90. Yang, Y.L., Lu, K.T., Tsay, H.J., Lin, C.H. and Lin, M.T. (1998). Heat shock protein expression protects against death following exposure to heatstroke in rats. Neurosci Lett 252: 9–12. Yapor, W.Y. and Gutierrez, F.A. (1992). Cocaine-induced intratumoral hemorrhage: case report and review of the literature. Neurosurgery 30: 288–91. Yaqub, B. and Al Deeb, S. (1998). Heat strokes: aetiopathogenesis, neurological characteristics, treatment and outcome. J Neurol Sci 156: 144–51. Yokoyama, K., Araki, S., Murata, K. et al. (1997a). Subclinical vestibulo-cerebellar, anterior cerebellar lobe and spinocerebellar effects in lead workers in relation to concurrent and past exposure. Neurotoxicology 18: 371–80.

365

366

M-U. Manto and J. Jacquy

Yokoyama, K., Araki, S., Murata, K. et al. (1997b). Postural sway frequency analysis in workers exposed to n-hexane, xylene, and toluene: assessment of subclinical cerebellar dysfunction. Environ Res 74: 110–15. Young, G.P., Rores C., Murphy, C. and Daily, R.H. (1987). Intravenous phenobarbital for alcohol withdrawal and convulsions. Ann Emerg Med 16: 847–50. Zitelli, B.J., Howrie, D.L., Altman, H. and Maroon, T.J. (1987).

Erythromycin-induced drug interactions. An illustrative case and review of the literature. Clin Pediatr 26: 117–19. Zona, C. and Avoli, M. (1997). Lamotrigine reduces voltage-gated sodium currents in rat central neurons in culture. Epilepsia 38: 522–5. Zona, C., Ciotti, M.T. and Avoli, M. (1997). Topiramate attenuates voltage-gated sodium currents in rat cerebellar granule cells. Neurosci Lett 231: 123–6.

Part VI

Advances in Grafts

24

Cerebellar grafts Lazaros C. Triarhou Formerly, Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, USA

Introduction The complex organization of the adult cerebellar network is a product of precisely timed and spatially coordinated developmental events (Miale and Sidman, 1961; Fujita, 1967; Larramendi, 1969; Altman, 1982; Goffinet, 1983; Altman and Bayer, 1985a,1985b). Cerebellar Purkinje cells are generated in the cerebellar primordium around embryonic day (E) 12 and migrate to the surface before birth in the mouse (Miale and Sidman, 1961). Around postnatal day (P) 3, Purkinje cells start to disperse in a monolayer and soon afterwards they receive synaptic contacts from afferent axons. The advent of the interaction with migrating granule cells accelerates a profuse synaptogenesis with Purkinje cell dendrites, which grow into the characteristic Purkinje dendritic trees by P12 (Larramendi, 1969; Altman, 1982). Neurons of the deep cerebellar nuclei are generated about a day before Purkinje cells, Golgi cells toward the end of gestation, whereas stellate and basket cells are produced during the first postnatal week, and granule cells during the first two weeks of postnatal life (Miale and Sidman, 1961; Fujita, 1967; Altman, 1982). Normally, only Purkinje cells project axons outside the cerebellar cortex toward the deep cerebellar nuclei (Eccles et al., 1967; Ito, 1984). All of the remaining cortical neurons are interneurons, functioning to modulate Purkinje cell activity. Purkinje cells are also modulated by afferent olivocerebellar climbing fibers (see also Chapter 2). Mossy fibers indirectly affect Purkinje cell activity through the mediation of the granule cell parallel fibers, which establish synapses on Purkinje dendrites. The axons of the deep nuclei neurons transmit impulses outside the cerebellum, toward postcerebellar targets that include the ventrolateral nucleus of the thalamus, the red nucleus, and the vestibular nuclei (Thach et al., 1992). A small proportion of Purkinje axons project directly to the dorsal part of the lateral vestibular nucleus of Deiters.

The degeneration of Purkinje cells as seen in human cerebellar cortical atrophy and in experimental models deprives climbing fibers and cortical interneurons of a major synaptic target. However, the associated interruption of the cortico-nuclear projection is a fundamental factor contributing to the pathophysiology of the ataxic syndrome. Purkinje cells utilize -aminobutyric acid (GABA) as a neurotransmitter (Obata, 1969), and thus exert a powerful inhibition on deep nuclei neurons (details are given in Chapter 4). In the atrophic cerebellum, the loss of Purkinje cells and their axons leads to a substantial reduction of the GABAergic input to the deep nuclei and therefore a decreased inhibition of the firing of deep nuclei neurons toward their post-cerebellar targets. A Purkinje cell innervation of the deep cerebellar nuclei of the host is a key element in reinstating the missing inhibitory corticonuclear projection associated with normal cerebellar function. In reconstructing an adult cerebellum from which Purkinje cells have been lost, one is faced with several initial problems, such as (i) a difference in water content and size of the extracellular space between the embryonic and adult cerebellum (del Cerro et al., 1968); (ii) a mismatch in the biological age of donor Purkinje cells and host cerebellar neurons and, consequently, a temporal mismatch in the expression of developmental chemical cues; and (iii) a mismatch in migratory properties between donor Purkinje cells, which are still at the peak of their migratory potential, and settled host cerebellar cells, which have long ceased migrating, as well as in interactive events between granule cell axonogenesis and the morphogenesis of the Purkinje dendritic tree (Altman, 1982). On the other hand, factors that favor graft integration include (i) the availability of vacated postsynaptic sites in the host deep cerebellar nuclei for synaptic investment by transplanted Purkinje cells; and (ii) the availability in the host molecular layer of parallel, climbing, and

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monoamine fiber terminals, deprived of their postsynaptic targets, for the synaptic investment of postsynaptic sites on implanted Purkinje cells. Detailed reviews of the structural and functional aspects of cerebellar grafting have been given elsewhere (Triarhou, 1996, 1997, 2000).

Fundamental aspects of cerebellar tissue transplantation Intracerebral grafting of developing neuroblasts into the adult pathological brain has been successfully used to replace degenerated neurons in several experimental instances (Björklund, 1993; Dunnett and Björklund, 1994). Primordial cerebellar tissue in particular has been shown to survive and grow after orthotopic or heterotopic implantation into the adult rodent brain. Cerebellar neuron grafting has also been applied to neurological mutant mice in order (a) to create appropriate confrontations between wild-type and mutant cells in elucidating gene effects on the involved lineage, and (b) to study the structural integration of transplanted Purkinje cells into the disrupted cerebellar loop.

Growth and histotypic differentiation of cerebellar grafts Das and Altman (1971) transplanted slabs of infant (P7) rat cerebellum into the cerebellum of age-matched rat hosts, after labeling donor tissue with (3H)thymidine to tag cells undergoing mitotic divisions. Transplanted, undifferentiated cells had migrated into the cerebellar cortex of the hosts, where they had differentiated into basket cells in the molecular layer and into granule cells in the internal granule cell layer. That study indicated that transplantation of neuronal precursors is possible in the maturing nervous system of mammals and its success was attributed to two important factors: the active migratory behavior of donor tissue, and the ongoing generative process in the host cerebellum. In a subsequent study (Das and Altman, 1972), pathological changes were also reported in grafts with short-term survival, along with the aggregation of surviving and proliferating cells into areas representing the viable portions in the external germinal layer of grafted tissue. The issue of poor viability of postmigratory elements such as Purkinje and Golgi cells of the transplants was raised, and the idea of using germinal cells of the neuroepithelium at embryonic stages was proposed (Das and Altman, 1972). Hine (1977) implanted E18 rat cerebellar primordia into the rostral forebrain of P7 rat hosts and examined histolog-

ically the growth and differentiation of the transplanted tissue. The grafts grew and acquired the trilaminar structure characteristic of the organotypic differentiation of normal cerebellum. Non-specific host afferents into the transplant were found in specimens using the Fink–Heimer method. Wells and McAllister (1982) transplanted E18 rat cerebellar primordia into the neocortex of P10–P12 rats and studied in great detail the histological development of the transplants. They found that transplants grown on the neocortical surface had normal orientation and foliation patterns; on the other hand, pieces of cerebellar cortex confined within the depths of either the graft or the host tissue were layered normally, but the layers were arranged in concentric cylinders around blood vessels. Overall, the transplantation procedure did not delay the normal time sequence of prominent features of cerebellar development, such as initial molecular layer formation, peak development of the external germinal layer, completion of neuroblast migration from the external germinal layer, and postmigratory changes within the transplants; however, subtle differences were noted in Purkinje cell differentiation, in particular involving processes of monolayer formation and foliation. Alvarado-Mallart and Sotelo (1982) transplanted pieces of E14–E15 rat cerebellum into a cortical cavity in the occipital lobe of adult rats. They then analyzed the cytoarchitectonic and synaptic organization of the transplants by light and electron microscopy, and described the growth and development of donor tissue into a cerebellar structure containing cortical and nuclear regions, with all five categories of neurons normally found in cerebellar cortex present in the former and with normal lamination and foliation pattern. Qualitatively normal synaptic connections were found among the various neuronal elements of the grafts with the exception of climbing fibers, which were obviously missing from donor cerebellar tissue. Heterologous (atypical) synaptic arrangements were also encountered in the grafts, consisting of pseudoglomerular formations of tightly packed small axon terminals of unestablished origin with granule cell dendrites in the neuropil of the granule cell layer. Reciprocal connections were seen between the cortical and nuclear regions of the transplants by means of horseradish peroxidase (HRP) tracing experiments, providing further evidence for the organotypic, histotypic, and synaptotypic differentiation of the cerebellar anlage after heterotopic transplantation in the adult rat brain. Kromer et al. (1979, 1983) implanted E12–E13 and E17–E19 rat cerebellar primordia into cavities prepared ahead of time in the occipital-retrosplenial cortex or in the

Cerebellar grafts

parietal cortex and septal pole of the hippocampus. They described subdivisions similar to deep cerebellar nuclei and a trilaminar cerebellar cortex in the heterotopic grafts, with development of cortical invagination. Nonetheless, earlygestation implants grew larger in size than late-gestation tissues. In Golgi-impregnated specimens, Purkinje cells were found to possess well-developed dendritic arbors with smooth primary branches and studded-with-spines secondary and tertiary branches. The three-dimensional orientation of Purkinje dendritic trees was atypical, while the properties of the remaining four classes of cerebellocortical interneurons possessed a morphology very similar to that of normal adult cerebellum. In a subsequent study, Ezerman and Kromer (1985) prepared dissociated cell suspensions of E13 rat cerebellar primordia and reaggregated them into tissue pellets by centrifugation. After implantation into cortical cavities in adult rats, they observed an initial sorting of macroneurons (i.e., Purkinje cells and deep nuclei neurons), followed by segregation of developing cortical cells into a trilaminar structure. Ezerman (1988) also described the survival and development of fetal and postnatal cerebellar grafts after growth in culture in the form of explants. The organotypic and histotypic differentiation of cerebellar grafts transplanted into the lateral ventricle or hemispheric cerebral parenchyma of adult Wistar rats was described by Alexandrova and Polezhaev (1984). Kikuchi (1989) transplanted E14–E20 rat cerebellar primordia into the cerebellum of adult Fischer 344 rats and described normal synaptic connections between neuronal elements in the graft by electron microscopy at survival times of one month to one year after transplantation. The morphological maturation of cerebellar grafts has also been studied after homologous transplantation into the anterior eye chamber in the form of either single grafts (Woodward et al., 1977; Takács et al., 1986) or cerebellar/cortical co-grafts (Hámori and Takács, 1988; Takács and Hámori, 1988). Observations in Golgi–Cox and toluidine blue histological preparations indicated that grafts of E15–E16 rat cerebellar tissue in oculo grow into structures with a trilaminar organization that contain all types of cerebellar neurons (Woodward et al., 1977). Differentiated cerebellar glomeruli are found by electron microscopy, containing mossy terminals that probably originate in the cerebellar nuclei portion of the graft (Takács et al., 1986). When cerebellar grafts are co-cultivated with cerebral cortical grafts in the anterior eye chamber, both GABAimmunoreactive and GABA-immunonegative mossy-like terminals, originating either in the cerebral cortical tissue or in the cerebellar nucleus in the absence of ‘natural’ mossy fibers, are seen forming asymmetric synapses with

granule cell dendritic digits within the graft (Takács and Hámori, 1988). Further, in the absence of ‘natural’ climbing fibers, Purkinje dendritic shafts receive symmetrical synapses from GABA-immunopositive ‘foreign’ climbinglike terminals, a phenomenon pointing to the plasticity of Purkinje cell dendrites in the absence of specific afferents (Hámori and Takács, 1988). Wiestler et al. (1992a, 1992b) and Snyder et al. (1992) used retrovirus-mediated oncogene transfer technology in combination with neural grafting to study issues of the commitment and differentiation of cerebellar progenitor cells. Wiestler et al. (1992a) introduced the v-Ha-ras and vmyc oncogenes into the developing rat brain; introduction of the same oncogenes into newborn cerebellar cultures was effected as well. Their data showed a powerful complementary transforming effect of the two oncogenes on neural progenitors both in-vivo and in-vitro, suggesting that co-expression of the ras and myc oncogenes may provide a highly efficient tool for transforming neural precursor cells in distinct segments of central nervous system (CNS) at different stages of development. Snyder et al. (1992) generated multipotent neural cell lines via v-myc transfer into mouse cerebellar progenitor cells and transplanted them back into the cerebella of newborn mice. Transformed cells became integrated into the host cerebellum in a non-tumorigenic and cytoarchitectonically appropriate manner, differentiating into neurons or glia depending on engraftment site. That study lent support to the idea that immortalized cell lines can be generated to repair or to deliver exogenous genes into the CNS. Finally, retrovirus-mediated gene transfer has been used to transfect mouse cerebellar primary cultures with recombinant retroviruses harboring the bacterial enzyme chloramphenicol acetyltransferase prior to transplantation into adult mouse cerebellum (Tsuda et al., 1990; Yuasa et al., 1993). Immunocytochemical analyses of the tissues with various antibodies indicated stable marking of labeled cells both in the grafts and in the host molecular layer.

Blood–brain barrier of cerebellar grafts All ultrastructural elements of a normal blood–brain barrier are seen in the capillary vessels formed within cerebellar grafts heterotopically transplanted into the rat striatum (Gerloff et al., 1993). The functional permeability to macromolecules in cerebellar grafts has been studied in solid grafts of fetal rat tissue implanted into the cerebral ventricles of young adult hosts (Rosenstein, 1991). Fenestrated vessels were not directly observed, even

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though vessels indigenous to the grafts retained blood–brain barrier properties. HRP, HRP–human serum albumin and HRP–human immunoglobulin G (IgG), given intravascularly 3–60 min before sacrifice, showed that younger grafts were filled with the macromolecules, whereas older grafts displayed a variability in permeation. HRP injections into the cerebrospinal fluid (CSF) suggested that solutes may flow at an increased rate (up to three-fold greater than normal) through the grafts (Rosenstein, 1991).

Histochemical phenotype of transplanted Purkinje cells Histochemical studies have shown that transplanted Purkinje cells express many structural, neurotransmitterrelated, and growth-factor system molecules that normal Purkinje cells contain in the intact cerebellum. In particular, Purkinje cells in cerebellar grafts selectively express 28kDa Ca2-binding protein (CaBP or calbindin) (Sotelo and Alvarado-Mallart, 1986; Triarhou et al. 1992a), guanosine 3,5-phosphate-dependent protein kinase (cGK) (Sotelo and Alvarado-Mallart, 1985) and polypeptide PEP-19 (Chang et al., 1989). Further, they express zebrin I in a topographic order that consists of immunopositively defined compartments of longitudinal bands in grafts placed into the cerebellum of rats that had previously been subjected to kainic acid lesions (Rouse and Sotelo, 1990) and in intraocular or intracortical grafts (Wassef et al., 1990). Transplanted Purkinje cells immunoreact with monoclonal antibodies mab-Q113 (Sotelo, 1988) and mab-1D10 (Tokunaga et al., 1991), anti-spot 35 antibody (Tsurushima et al., 1993a, 1993b) and anti-Leu-4 (CD3) (Gerloff et al., 1993). Purkinje cells in cerebellar grafts express immunoreactivity for neurofilament protein, synapsin (Hall et al., 1992) and non-phosphorylated neurofilament epitopes (nPNF) (Poltorak et al., 1988). Furthermore, transplanted Purkinje cells show motilin (Perlow et al., 1984) and GluR2/3 immunoreactivity (Wenthold et al., 1992), and express brain-derived neurotrophic factor (BDNF) mRNA (Tsurushima et al., 1993b), nerve-growth factor (NGF) receptor peptide (Tsurushima et al., 1993b), insulin-like growth factor (IGF)-I mRNA and peptide, and type I IGF receptor mRNA (Zhang et al., 1996).

Physiological activity of transplanted Purkinje cells The functional maturation of cerebellar grafts has been studied electrophysiologically in solid grafts of fetal rat cerebellum placed either into the anterior chamber of the rat eye (Hoffer et al., 1974) or into the cerebella of P5–P7 and

P13–P14 rat pups (Björklund et al., 1984, 1985). The spontaneous discharge rate of transplanted Purkinje cells was slightly slower than normal, a fact ascribable at least in part to the absence from the grafts of high-frequencey bursts normally caused by the excitatory input from climbing fibers. On the other hand, the fact that local stimulation of the graft surface causes both decreased and increased Purkinje cell discharges suggests a normally functioning neurotransmission from the inhibitory molecular interneurons and the excitatory granule cells to Purkinje cell dendrites, physiological characteristics quite similar to the normal cerebellum (Björklund et al., 1984, 1985). In a different study, fetal cerebellar tissue from E20–E25 rabbit brain implanted intraocularly into the anterior eye chamber of athymic nude rats grows and, at 15 weeks after transplantation in-vivo recording of single neuron activity reveals normal discharge rates of neurons (Hall et al., 1992).

Migratory phenomena and morphogenesis of transplanted Purkinje cells Purkinje cells from heterotopic rat cerebellar grafts migrate into the host brain over considerable distances into regions adjacent to the transplants (Perlow et al., 1984). Neuronal migration and cerebellar lamination in rat fetal cerebellar grafts placed into the cerebral ventricles, lateral hypothalamus or parietal cortex of adult rats are more frequent at earlier gestational periods among E16, E18, E20 and E22 donor tissues (Perlow et al., 1984). Kawamura et al. (1988) showed that both granule and Purkinje cells can migrate into the mature cerebellar cortex of normal adult rats. Solid grafts of fetal rat cerebellum transplanted into the fourth ventricle of normal rats develop into minicerebella that grow either toward the dorsal surface of the brainstem or to the overlying cerebellar cortex (Rossi et al., 1992). Grafted Purkinje cells may migrate out of the solid grafts to a certain extent into the normal cerebellar cortex of the host. A site that favors Purkinje cell survival and growth appears to be the dorsal cochlear nucleus (Rossi and Borsello, 1993), which shares structural homology with the cerebellum (Mugnaini and Morgan, 1987). By grafting solid fetal cerebellar tissue into the fourth ventricle in apposition to the dorsal cochlear nucleus, Rossi and Borsello (1993) found that large numbers of donor Purkinje cells migrate and develop in its superficial layers, passing through the various phases that characterize normal ontogeny. A chick/quail chimaeric model with partial cerebellar grafts has been employed to analyze the origin and migration of cerebellar cells (Alvarez Otero et al., 1993).

Cerebellar grafts

In intraparenchymal cerebellar grafts, the development of transplanted Purkinje cells can be monitored with CaBP immunocytochemistry. At short survival times (five days after grafting), grafts are confined to the site of the original injection. At longer survival times (seven days to one month after grafting), grafted Purkinje cells form a migratory stream that reaches the cerebellar cortex of the host (Triarhou et al., 1992a). The orientation of Purkinje dendritic trees is toward the pia, i.e., in the direction of their migration. In terms of morphogenesis, Purkinje cells appear elongated and spindle-shaped at early survival times, later becoming spherical, and increasing their dendritic arborization with time, and acquiring a monoplanar disposition flattened in the transverse plane when they reach the cerebellar cortex. Sotelo and Alvarado-Mallart (1987b) eloquently showed that the phases of Purkinje cell dendritogenesis in transplants correspond to those described by Ramón y Cajal (1926) during normal cerebellar ontogeny, namely, the phases of ‘fusiform cells’ (5–9 days after grafting), ‘stellate cells with disoriented dendrons’ (10–11 days after grafting), and ‘orientation and flattening of dendrites’ (11–14 days after grafting).

Graft–host interactions Sympathetic adrenergic fibers from the host iris grow and functionally innervate intraocular cerebellar grafts in the rat (Hoffer et al., 1975). Cerebellar grafts of E20–E25 fetal rabbit cerebellum, transplanted into the anterior eye chamber of athymic nude rats, receive excitatory cholinergic innervation from the host parasympathetic iris ground plexus, as well as sparse innervation of TyrOHasepositive fibers from the sympathetic plexus of the host iris (Hall et al., 1992). Serotonin-immunoreactive fibers grow from the adult host forebrain (fornix-fimbria, neocortex, and hippocampus) into heterotopic cerebellar transplants placed into the parietal neocortex (Sotelo and Alvarado-Mallart, 1985). Heterotopic grafts of rat fetal cerebellar tissue into the cerebral ventricles or lateral hypothalamus have also been reported to receive peptidergic input from the host brain, based on oxytocin and neurophysin fiber immunostaining (Perlow et al., 1984). Neural grafting studies in adult rats with kainic acid lesions of the cerebellum (Armengol et al., 1989) have shown that donor Purkinje cells preferentially invade regions of the host molecular layer that are devoid of host Purkinje cells; there, they receive organotypic climbing fiber afferents that are organized along normal projectional maps, based on the orthograde transport of

(3H)amino acids injected into the inferior olivary complex of the host. Adult climbing fibers of normal rat cerebellum, labeled by means of Phaseolus vulgaris leucoagglutinin (PHA-L), can be induced by fetal cerebellar grafts to sprout new collaterals that terminate on donor Purkinje cells (Rossi et al., 1994). The phenomenon seems to be specifically elicited by fetal cerebellar grafts, as neocortical tissue grafts have no such effect. On the other hand, transplants of medullary embryonic tissue containing the primordial inferior olivary complex into the cerebellum of rats previously subjected to 3-acetylpyridine lesions of the endogenous olivocerebellar projection lead to synaptic formation between donor climbing fiber terminals and host Purkinje cells (Kawamura et al., 1990). Efferent projections from axons of heterotopically transplanted Purkinje cells, immunocytochemically labeled with anti-Leu-4 (CD3) antibody, into the rat striatum have been reported over distances of at least 500 m at 2.5 months after grafting (Gerloff et al., 1993). In a different experimental setting, axons of tranplanted olfactory bulb neurons (marked by BALB/c strain of mouse allelic form of Thy-1.2 antibodies) invade the host cerebellum and elongate into the granule cell layer of the host (marked by the AKR strain of Thy-1.1), where they form asymmetrical synapses with local dendrites, probably of host granule cells (Fujii and Hayakashi, 1992). The granule cell layer is also able to receive novel ‘retinocerebellar’ synapses from regenerating retinal ganglion cell axons guided to the cerebellum of adult hamsters by means of a peripheral nerve graft (Zwimpfer et al., 1992).

Cerebellar grafts in ataxic mouse mutants There are several mutations in the laboratory mouse that interfere in various ways with the formation and maintenance of the cerebellar circuitry (Sidman et al., 1965; Sidman, 1982). The cerebellar lesion may consist in either defective positioning of specific neuronal populations or selective loss. Such mutations provide unique material for investigating developmental and degenerative events because (i) the background on the cellular architecture and synaptic connections of the cerebellum is strong; (ii) the cerebellum is a relatively simple neuronal circuit for studying phenomena with general implications for the CNS; and (iii) the molecular genetics and chromosomal structure of the laboratory mouse are better characterized than those of any other mammal.

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Staggerer mutant mice In the staggerer (sg) mutant, Purkinje cells are reduced in number and have abnormal dendritic branches that lack the peripheral components, i.e., the spiny branchlets, leading to an inability of synapse formation between parallel fiber nerve endings and Purkinje cell spines, and eventually causing progressive degeneration of granule cells (Sidman et al., 1962; Sotelo and Changeux, 1974). Pieces of E11 cerebellar anlagen from sg/  sg/ matings were transplanted into the anterior eye chamber of wild-type recipient mice, with the aim of studying the character of the sg mutation (Wille et al., 1983). Six weeks after transplantation in oculo, graft viability was 80%. About 35% of the surviving transplants contained Purkinje, Golgi, and deep nuclei macroneurons, but no or very few granule cells, a proportion within the range of the 1:2 :1 genetic probability of sg/sg: sg/: / donor tissue genotype, and consistent with an intrinsic action of the sg gene in determining the phenotype of the transplanted tissue. On the other hand, wild-type grafts maturing in the eye of wildtype hosts contained granule cells, as well as macroneurons, in 100% of the cases (Wille et al., 1983).

Weaver mutant mice The weaver (wv) mutation leads to a massive death of postmitotic granule cell precursors during the first 15 days of postnatal life and to a reduced number of Purkinje cells in the cerebellum of homozygotes. Solid grafts of E15 wildtype cerebellar tissue were transplanted into the cerebellomedullary cisterna of weaver hosts, between the uvula vermis and the dorsal surface of the brainstem, to study its survival, growth, and synaptic properties inside the CSF of the mutant environment (Triarhou, 1992; Triarhou et al., 1986, 1987). The grafts displayed a layered cellular organization reminiscent of the normal cerebellar cortex, with identifiable molecular, Purkinje cell, and granule cell layers. Parallel fiber terminals presynaptic to Purkinje cell dendritic spines were identified in the molecular layer of the grafts. However, the number of parallel fibers was reduced compared to normal cerebellar cortex, a phenomenon commonly seen in cerebellum in tissue culture or in cerebellar transplants into normal hosts. It was concluded that the weaver environment does not pose any apparent limitations beyond those inherent in the process of cerebellar growth and differentiation outside its normal anatomical context. In another study, pieces of E15 wild-type cerebellar tissue were transplanted into the cerebellum of weaver mutants (Takayama et al., 1987, 1988). Donor tissue

developed a trilaminar organization, which contrasted with the granuloprival cerebellar cortex of the hosts. Evidence for the migration of implanted granule cells into the host cerebellum was presented. Immunoreactivity for synapsin I (a synaptic vesicle membrane-specific phosphoprotein) was taken as an index of synapse formation by donor granule and Purkinje cells, possibly on host cerebellar neurons.

Nervous mutant mice In the nervous (nr) mutant, most Purkinje cells degenerate between three and six weeks of age (Sidman and Green, 1970; Landis, 1973). In two-month-old animals, 90% of Purkinje cells in the cerebellar hemispheres and 50% of Purkinje cells in the vermis have died off. In transplantation experiments, E12 cerebellar grafts were implanted into the intermediate cerebellar cortex of nervous mutants and allowed survival times of two to four months after grafting (Sotelo and Alvarado-Mallart, 1992). The general conclusion was that grafted Purkinje cells invade the host molecular layer with preference for regions of the host cerebellar cortex that are devoid of endogenous Purkinje cells, and stop their migration once they encounter the dendritic trees of surviving host Purkinje cells.

Lurcher mutant mice The Lurcher (Lc) mutation leads to extensive Purkinje cell death commencing around P8; by two months the Lurcher cerebellum is virtually devoid of Purkinje cells (Phillips, 1960; Caddy and Biscoe, 1979). In one study, E12 cerebellar cell suspensions were implanted into the cerebellum of both juvenile (17 days old) and adult (one to six months old) Lurcher mutants (Tomey and Heckroth, 1993). The rate of graft survival in that study was 50% for both age groups of recipient mice. Purkinje cells from the grafts, immunolabeled for CaBP, were found to infiltrate the atrophic cerebellar cortex of the host, occupying most frequently the molecular layer. The dendrites of the transplanted Purkinje cells failed to adopt the characteristic planar disposition inside the host cerebellum, an observation that was attributed to the severe depletion of granule cells and hence the parallel fibers in the Lurcher mutant (Caddy and Biscoe, 1979), elements that have a decisive role in the morphogenesis of the Purkinje dendritic tree during normal development (Altman, 1982). Grafted Purkinje cells supplied an axonal innervation to the deep cerebellar nuclei of the hosts in 30% of the cases (Tomey and Heckroth, 1993). In another study, E12–E14 solid cerebellar grafts were

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implanted into the cerebellum of two-month-old to sixmonth-old Lurcher recipients (Dumesnil-Bousez and Sotelo, 1993b). Donor Purkinje cells, immunoreactive for CaBP or cGK, were found to migrate into the granular and molecular layers of the host cerebellar cortex and occasionally to innervate the deep nuclear complex, but never in a massive fashion. A similar invasion by grafted Purkinje cells is seen into the molecular layer of the host dorsal cochlear nucleus (Dumesnil-Bousez and Sotelo, 1993a). The dendritic trees of grafted Purkinje cells extend in the sagittal plane to some degree, but are not completely flat, again probably owing to the marked parallel fiber deficit in the Lurcher cerebellum. An important finding of that study relates to the synaptic investment of grafted Purkinje cells, which is abnormal in both quantitative and qualitative terms. Synaptic inputs to both the perikaryon and dendrites of donor Purkinje cells are reduced; the compartmentation in proximal and distal dendritic segments is severely affected; climbing fiber afferents scarcely form synapses; and, finally, large perisomatic baskets as well as ‘pinceau’ formations around the axon initial segment are absent. Grafted Purkinje cells located in the host granule cell layer receive heterologous synapses from mossy fibers, a phenomenon previously described in granuloprival cerebella (Sotelo, 1980). In all, it seems that the restoration of the developmentally perturbed cerebellar circuit of the Lurcher mutant by means of neural transplantation poses some serious limitations.

Purkinje cell degeneration mutant mice One of the most widely used models in cerebellar transplantation has been the‘Purkinje cell degeneration’ mutant mouse (pcd). The pcd mutation is responsible for a virtually complete degeneration of Purkinje cells between P17 and P45, i.e., after the maturation of the cerebellar circuitry (Mullen et al., 1976; Mullen, 1977; Landis and Mullen, 1978). Behaviourally, pcd homozygotes manifest an ataxic syndrome beginning at three and four weeks of age. The pcd mutant mouse has been used to address both issues of cerebellar cortical plasticity (Sotelo and Alvarado-Mallart, 1986, 1987a, 1987b, 1988, 1991, 1992; Gardette et al., 1988; 1990; Sotelo, 1988, 1991, 1993; Sotelo et al., 1990, 1992, 1994; Keep et al., 1992; Alvarado-Mallart and Sotelo, 1993) and the reconstruction of the corticonuclear projection and the recovery of function (Triarhou et al., 1986, 1987, 1989, 1992a, 1992b, 1995, 1996;Triarhou, 1995; Zhang et al., 1996). The fate of E14–E15 cerebellar implants was studied after grafting into the cerebellomedullary cisterna of adult pcd recipients (Triarhou et al., 1986, 1987). Grafts exhibited a layered cellular organization reminiscent of normal

cerebellum, and surviving Purkinje cells displayed typical cytological features (Fig. 24.1), indicating that the environment of the mutant hosts did not appear to pose any apparent limitations to the application of neural grafting techniques for the correction of the neurological deficiency. When E12 cerebellar grafts are implanted between two adjacent cerebellar cortical folia of pcd mutants in the form of either solid pieces or dissociated cell suspensions, donor Purkinje cells migrate along stereotyped pathways into the molecular layer of the deficient host cerebellum, where they develop flattened dendritic trees perpendicular to the host parallel fibers; donor Purkinje cell dendrites are composed of thick proximal branches and distal spiny branchlets that receive precisely segregated synaptic inputs from host neuronal elements (Sotelo and Alvarado-Mallart, 1986, 1987a, 1987b, 1987c). The timetable of these cellular interactions is remarkably similar to normal (Sotelo and Alvarado-Mallart, 1987b), with the essential difference that the phase of radial migration occurs in the opposite direction, whereas during normal development the migration proceeds from the ventricular primitive neuroepithelium toward the cerebellar surface (Sotelo and AlvaradoMallart, 1988). The developmental phases of Purkinje cell migration and dendritogenesis have been described in detail (Sotelo, 1988; Sotelo et al., 1990; Sotelo and AlvaradoMallart, 1991; 1992). A positive neurotropism has been theorized to attract the grafted embryonic Purkinje cells into the host molecular layer (Alvarado-Mallart and Sotelo, 1993). Transplanted Purkinje cells become synaptically integrated into the cerebellar circuitry of the deficient host brain by receiving afferent innervation from (i) parallel fibers, as determined by electron microscopy (Sotelo and Alvarado-Mallart, 1986, 1987c), (ii) climbing fibers, as determined by both electron microscopy and by electrophysiology of in-vitro cerebellar slice preparations after juxtafastigial stimulation and intracellular recording from Purkinje cells (Gardette et al., 1988, 1990; Sotelo et al., 1990), and (iii) serotoninergic axons, as determined by immunocytochemistry after selective neurotoxic removal of serotonin neurons from the grafts prior to transplantation (Triarhou et al., 1992b). The most serious limitation with intracerebellocortical grafts is that grafted Purkinje cells do not reach the host deep cerebellar nuclei, which is a key element in reinstating a Purkinje cell inhibitory input to the deep cerebellar nuclei. Such a failure has been attributed to a ‘physicochemical barrier’ imposed by the host granule cell layer and white matter (Keep et al., 1992; Sotelo et al., 1992). In an attempt to re-establish the missing Purkinje cell

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Fig. 24.1 (A) A solid wild-type cerebellar graft (asterisk) implanted into the cerebellomedullary cisterna of a pcd mouse. (B) View of the cerebellar cortices of the mutant pcd host (marked H) and of the wild-type graft (marked G) showing, respectively, the absence and presence of Purkinje cells; notice the cerebellar lamination in the graft. (C) Electron micrograph depicting the typical hypolemmal cisterna in association with a mitochondrion in a transplanted Purkinje cell. All tissues shown from a graft 39 days after transplantation. For more details, refer to Triarhou et al. (1987). (A) and (B) 10-m thick paraffin sections cut sagittally and stained with gallocyanin Nissl; (C) ultrathin section stained with uranyl acetate and lead citrate. Magnifications: (A)  63; (B)  250; (C)  32 000.

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cortico-nuclear inhibitory projection, Triarhou et al. (1989, 1992a) implanted cerebellar cell suspensions directly into the deep nuclei parenchyma of the pcd hosts. With this protocol, the denervated deep nuclei receive a new Purkinje axonal innervation; further, most of the transplanted Purkinje cells end up occupying cortical localities, and display a correct dendritic tree orientation toward the pia (Figs. 24.2 and 24.3), due to the recapitulation of a migratory course normally taken during cerebellar ontogeny from the ventricular neuroepithelium toward the cerebellar cortex, and to a crossing of trajectories that allows developing Purkinje cells to establish synaptic contacts with deep nuclei neurons on the way of their perikarya to the surface (Ramón y Cajal, 1929; Miale and Sidman, 1961; Altman, 1982; Altman and Bayer, 1985a). The functional effects of such intraparenchymal cerebellar grafts and some pathophysiological considerations are described in the sections that follow.

Functional graft effects on cerebellar amino acid receptors Quantitative autoradiography of (3H)CNQX, (3H)muscimol, and (3H)flunitrazepam binding has been used to study the distribution of non-N-methyl--aspartate (NMDA) and GABAA receptors in the cerebellum of pcd mutant mice with cerebellar grafts (Stasi et al., 1997). In pcd mutants, nonNMDA receptors are reduced by 38% in the molecular layer and by 47% in the granule cell layer. The reduction of nonNMDA receptors in the pcd cerebellar cortex supports their localization on Purkinje cells. (3H)CNQX binding sites were visualized at higher density in grafts that had migrated to the cerebellar cortex of the hosts than in grafts arrested intraparenchymally; such a pattern of expression of nonNMDA receptors in cortical versus parenchymal grafts suggests a possible regulation of their levels by transacting elements from host parallel fibers. Experiments were carried out using in-situ hybridization histochemistry to investigate the types of AMPA receptor subunits that are expressed by fetal cerebellar grafts in relationship to the subtypes of the same receptors that are expressed in various areas of the wild-type cerebellum (Mitsacos et al., 1999). Synthetic oligonucleotide probes for the four subunits of the AMPA receptor (GluRA, GluRB, GluRC and GluRD) were labelled by means of deoxynucleotidyltransferase with (35S)dATP and used to incubate cerebellar tissue sections. Hybridized sections were exposed to beta-max autoradiographic film, and optical densities of the radioactive signal were measured using image analysis. Non-specific binding was determined from parallel section

incubations with the corresponding non-radioactive probes at concentrations 100 times higher than the radioactive probes. The main result from these analyses is that cerebellar grafts express the same AMPA receptor subunit mRNAs as those that are normally expressed in the Purkinje cell layer of the wild-type cerebellum, namely, GluRB and GluRC. These findings add a further level of pharmacological dissection to the pattern of (3H)CNQX binding sites previously visualized in the grafts and suggest normal molecular functions of transplanted Purkinje cells. GABAA binding levels in the grafts for both ligands used were similar to those found in the cerebellar molecular layer of wild-type mice (Stasi et al., 1997). Binding was increased in the deep cerebellar nuclei of pcd mutants: the increase in (3H)muscimol binding over normal was 215% and the increase in (3H)flunitrazepam binding was 89%. Such increases in the pcd deep cerebellar nuclei reflect a denervation-induced supersensitivity subsequent to the loss of Purkinje axon terminal innervation. In the deep nuclei of pcd mutants with cerebellar grafts, (3H)muscimol binding was 31% lower in the grafted side than in the contralateral non-grafted side at 37 days after transplantation; (3H)flunitrazepam binding was also lower in the grafted side by 15% compared to the non-grafted side. Such changes in GABAA receptors suggest a significant, albeit partial, normalizing effect of cerebellar grafts on the state of postsynaptic supersensitive receptors in the host cerebellar nuclei.

Cerebellar grafts and the recovery of behavioral function Behaviorally, the ataxic syndrome of pcd mice begins at three to four weeks of age and includes a lowered, widened stance, with an inability to sustain the abdomen in a raised relief, and the hindlimbs being in an abducted and hyperextended position. Evidence for functional recovery after cerebellar transplantation has been obtained in the pcd mouse (Triarhou et al., 1995, 1996; Zhang et al., 1996). Grafts of E11–E12 cerebellar cell suspensions were placed bilaterally into the deep cerebellar nuclei of the mutants, according to the protocol that emphasizes the reconstruction of the corticonuclear GABAergic projection (Triarhou et al., 1992a). Animals were tested in a battery of motor tasks to determine the recovery of behavioral responses. Counts of CaBP-immunoreactive neurons in histochemical preparations of the transplanted cerebella, combined over both sides, yielded numbers in the range of 1000–6500 surviving Purkinje cells per animal, with a 2865 cell average (Triarhou et al., 1996).

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Fig. 24.2 Intraparenchymal grafts of cerebellar cell suspensions into the cerebellum of pcd mice. Immunohistochemical labeling with anti-calbindin antibodies reveals the distribution of donor Purkinje cells, since virtually all of the host Purkinje cells have degenerated. At 5 days after grafting (A), donor Purkinje cells are confined to a well-demarcated cluster. At 7 days after grafting (B), a migratory stream of calbindin-immunoreactive Purkinje cells is observed. One month after grafting (C and D), donor Purkinje cells occupy extensive areas of the host cerebellar cortex. Sagittal sections with unilateral grafts (A, B, D); coronal section with bilateral grafts (C); larger arrows in (C) point at the cerebellar grafts, and smaller arrows point at the two sides of the inferior olivary complex, which is also calbindin immunopositive. For more details, refer to Triarhou et al. (1992a). Freezing microtome sections, 50 m in thickness. Magnifications: (A) and (B)  350; (C)  12; (D)  40.

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Equilibrium As an index of equilibrium, the time was measured between placement on and falling off a still balance rod suspended 13 cm over the ground (Zhang et al., 1996). Wild-type mice generally remained on the rod for long periods of time. Sham-injected pcd mutants stayed on the rod for an average of less than 3 s; pcd mutant mice with bilateral cerebellar grafts stayed for an average 10 s before falling off the bar, indicating a more than three-fold improvement after transplantation.

Motor coordination and fatigue resistance

Fig. 24.3 (A) Transplanted Purkinje cells settled in the cortex of the host pcd cerebellum, with their dendrites oriented toward the pia. (B) Innervation of the host deep cerebellar nuclei by a calbindin-immunoreactive axonal plexus emanating from transplanted Purkinje cells. One month after transplantation, 50m thick parasagittal sections. For more details, refer to Triarhou et al. (1992a). Magnifications: (A)  290; (B)  250.

Spontaneous movement and stance Grafted pcd mice are able to keep their body in an upright posture, markedly contrasting with the lowered, widened stance of sham-operated mutants; furthermore, they are capable of sustaining their abdomen in a raised relief from the matrix floor and of moving about for relatively long periods of time with falling over; the hindlimbs are less abducted and less hyperextended in transplant-receiving animals than in mice with vehicle injections (Triarhou et al., 1996).

A rota-rod apparatus was used, designed for mice and rotating at 3 rpm. The rota-rod treadmill paradigm is widely used to assess motor coordination and fatigue resistance in brain abiotrophies (Jones and Roberts, 1968; Pellegrino and Altman, 1979). Animals were tested one week preoperatively and six weeks postoperatively. Three successive trials were given to each mouse. Bilateral injections of vehicle did not appreciably modify the performance of pcd mutant mice in the rota-rod tests, whereas bilateral cerebellar grafts led to a 3.5-fold increase in the time period that pcd mutants stayed on the rotating drum based on the comparison of the three-trial mean scores, and to a 5.5-fold increase based on the comparison of the maximum scores out of the three trials (Triarhou et al., 1995). In particular, postoperative times on the rota-rod were as follows: for the sham-injected group, the average of the three-trial means was 3 s, and the average of maximum scores was 4.2 s; for the graft-receiving group, the average of the three-trial means was 13.5 s, and the average of the maximum scores out of the three trials was 21.5 s (Triarhou et al., 1996).

Open-field activity Quantification of motor activity was effected in a 5  5 square open-field matrix (Bureˇs et al., 1976). The pattern of animal movement was traced over an observation period of 5 min and the number of square-crossing events registered. The tracking of movement paths showed wild-type mice to exhibit the most complex pattern of activity, shamoperated pcd mice the lowest activity, and graft-recipient pcd mice to be between the two (Zhang et al., 1996). Normal animals display levels of activity in the vicinity of 200–250 square-crossing events; overall activity is reduced to an average 21 square crossings in sham-operated mutants, and an increase to an average 69 events is brought about after bilateral cerebellar transplants, which

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represents an improvement of more than three-fold in motor performance (Triarhou et al., 1996).

Pathophysiological considerations The graft-induced improvement of motor performance in pcd mutant mice could be theoretically linked to two components: first, an increase in grip strength and muscle responsiveness to commands from higher brain centers, resulting from the restoration of a certain degree of physiological activity in the deep cerebellar nuclei and the associated cerebellothalamic and dentatorubral projections; second, an enhancement of balance functions due to the effects of reinstating a Purkinje cell innervation of deep cerebellar neurons on the functional state of the cerebellovestibular system. With the intraparenchymal transplantation protocol used, the denervated deep nuclei of pcd hosts receive a new Purkinje axonal innervation. Further, most of the transplanted Purkinje cells end up occupying cortical localities and displaying a correct dendritic tree orientation toward the pia. Such an effect is likely to be due to a recapitulation of the migratory course normally followed by Purkinje cells during ontogeny. The direction of migration from the ventricular neuroepithelium to the cerebellar cortex and the crossing of trajectories allow developing Purkinje cells to establish synaptic contacts with deep neurons on the way of their perikarya to the surface of the developing cerebellum (Altman and Bayer, 1985a, 1985b; Yuasa et al., 1991). The physiological advantage of placing the grafts intraparenchymally is two-fold: first, donor Purkinje axons are able to innervate the host deep cerebellar neurons; and, second, they then migrate stereotypically to colonize cerebellocortical areas, where they can be contacted and synaptically invested by host parallel and climbing fibers, as is the case for grafts placed into the cerebellar cortex (Sotelo and Alvarado-Mallart, 1986, 1987c; Gardette et al., 1988). In that context, one index of functional responsiveness of transplanted Purkinje cells to an afferent innervation by host parallel fibers, which utilize glutamate as their neurotransmitter (Hudson et al., 1976), is the expression of GluR2/3 immunoreactivity on their postsynaptic receptive fields (Triarhou et al., 1996). It has been estimated in the mouse that loss of up to 90% of Purkinje cells produces only minor effects on the functional capabilities of the animal, indicating that 10% of the Purkinje cell complement may sustain many normal motor skills (Wetts et al., 1985). While the grafting procedure leads to an improvement of motor activity in pcd

mutants, the performance of recipient animals is still poorer than that of wild-type mice. Such a difference could be attributed to several factors, such as: (i) Purkinje cell replacement is only partial, if one considers that the mouse cerebellum normally contains about 200 000 Purkinje cells (Caddy and Biscoe, 1979); (ii) quantitative aspects of the cerebellar reconstruction in terms of neuronal connectivity, neurotransmitter regulation mechanisms, and transmitter–receptor interactions remain largely unknown; and (iii) the extracerebellar components of the pcd mutant phenotype that include degeneration of retinal photoreceptors (Mullen and LaVail, 1975), mitral cells of the olfactory bulb (Greer and Shepherd, 1982), and thalamic neurons (O’Gorman and Sidman, 1985) may compromise overall animal performance and prevent a graft-induced 100% functional restoration.

Concluding remarks Neural transplantation has been successfully applied to replace degenerated neurons in several anatomical systems experimentally (Björklund, 1993; Dunnett and Björklund, 1994) and in clinical studies with Parkinson’s disease patients (Lindvall et al., 1990, 1994). A distinction has been made between ‘global’ or ‘paracrine’ systems (such as the mesostriatal dopamine projection), in which local release of neurotransmitter may suffice for recovery, and ‘point-to-point’ systems (such as the cerebellum), where a precise re-establishment of the missing circuitry is deemed necessary (Sotelo and Alvarado-Mallart, 1985), although synaptic formation is considered as one of the mechanisms underlying the recovery of function in global systems as well (Björklund et al., 1987). The functional effects of neural transplants on motor performance in ‘point-to-point’ systems had long remained unknown (Dunnett, 1987). The behavioral findings reviewed here provide evidence for motor enhancement in an ataxic mouse model after intracerebellar transplantation of fetal Purkinje neurons, lending credence to the idea that neural grafting is a viable approach in restoring function not only in diffuse ‘paracrine’ systems, but also in neural systems characterized by ‘point-to-point’ synaptic connectivity, and underscoring the theoretical potential for future cerebellar neuron implantation to treat certain forms of human cerebellar ataxias. The complexity and spatiotemporal precision of developmental events during cerebellar ontogeny may be two of the reasons why grafts only lead to partial improvement, a serious limitation being posed by the chronological discord at the graft–host interface. Specific aspects of

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transplant growth and integration in conjunction with functional effects still remain undeciphered. Such questions can be answered in animal studies before considering the application of cerebellar transplantation as a clinical treatment, and a successful outcome of experimental transplantation protocols may generate a valuable basis in guiding optimal cell replacement therapies for the human cerebellar ataxias.

xReferencesx Alexandrova, M.A. and Polezhaev, L.V. (1984). Transplantation of various regions of embryonic brain tissue into the brain of adult rats. J Hirnforsch 25: 89–98. Altman, J. (1982). Morphological development of the rat cerebellum and some of its mechanisms. Exp Brain Res (Suppl.) 6: 8–49. Altman, J. and Bayer, S.A. (1985a). Embryonic development of the rat cerebellum. II. Translocation and regional distribution of the deep neurons. J Comp Neurol 231: 27–41. Altman, J. and Bayer, S.A. (1985b). Embryonic development of the rat cerebellum. III. Regional differences in the time of origin, migration, and settling of Purkinje cells. J Comp Neurol 231: 42–65. Alvarado-Mallart, R.M. and Sotelo, C. (1982). Differentiation of cerebellar anlage heterotopically transplanted to adult rat brain: a light and electron microscopic study. J Comp Neurol 212: 247–67. Alvarado-Mallart, R.M. and Sotelo, C. (1993). Cerebellar grafting in murine heredodegenerative ataxia. Current limitations for a therapeutic approach. Adv Neurol 61: 181–92. Alvarez Otero, R., Sotelo, C. and Alvarado-Mallart, R.M. (1993). Chick/quail chimeras with partial cerebellar grafts: an analysis of the origin and migration of cerebellar cells. J Comp Neurol 333: 597–615. Armengol, J.A., Sotelo, C., Angaut, P. and Alvarado-Mallart, R.M. (1989). Organization of host afferents to cerebellar grafts implanted into kainate lesioned cerebellum of adult rats: hodological evidence for the specificity of host–graft interactions. Eur J Neurosci 1: 75–93. Björklund, A. (1993). Intracerebral transplantation: prospects for neuronal replacement in neurodegenerative diseases. Res Publ Assoc Res Nerv Ment Dis 71: 361–74. Björklund, A., Lindvall, O., Isacson, O. et al. (1987). Mechanisms of action of intracerebral neural implants: studies on nigral and striatal grafts to the lesioned striatum. Trends Neurosci 10: 509–16. Björklund, H., Bickford, P., Dahl, D., Hoffer, B. and Olson, L. (1984). Intracranial cerebellar grafts: intermediate filament immunohistochemistry and electrophysiology. Exp Brain Res 55: 372–85. Björklund, H., Bickford, P., Dahl, D., Elfman, L., Hoffer, B. and Olson, L. (1985). Morphological and functional properties of intracranial cerebellar grafts. In Neural Grafting in the Mammalian C.N.S., ed. A. Björklund and U. Stenevi, pp. 191–203. Amsterdam: Elsevier.

Buresˇ, J., Buresˇová, O. and Huston, J. (1976). Techniques and Basic Experiments for the Study of Brain and Behavior, pp. 37–89. Amsterdam: Elsevier Scientific. Caddy, K.W.T. and Biscoe, T.J. (1979). Structural and quantitative studies in the normal C3H and Lurcher mutant mouse. Philos Trans Roy Soc Lond (Biol) 287: 167–201. Chang, A.C., Triarhou, L.C., Alyea, C.J., Low, W.C. and Ghetti, B. (1989). Developmental expression of polypeptide PEP-19 in cerebellar suspensions transplanted into the cerebellum of pcd mutant mice. Exp Brain Res 76: 639–45. Das, G.D. and Altman, J. (1971). Transplanted precursors of nerve cells: their fate in the cerebellums of young rats. Science 173: 637–8. Das, G.D. and Altman, J. (1972). Studies on the transplantation of developing neural tissues in the mammalian brain. I. Transplantation of cerebellar slabs into the cerebellum of neonate rats. Brain Res 38: 233–49. del Cerro, M., Snider, R.S. and Oster, M.L. (1968). Evolution of the extracellular space in immature nervous tissue. Experientia (Basel) 24: 929–30. Dumesnil-Bousez, N. and Sotelo, C. (1993a). The dorsal cochlear nucleus of the adult Lurcher mouse is specifically invaded by embryonic grafted Purkinje cells. Brain Res 622: 343–7. Dumesnil-Bousez, N. and Sotelo, C. (1993b). Partial reconstruction of the adult Lurcher cerebellar circuitry by neural grafting. Neuroscience 55: 1–21. Dunnett, S.B. (1987). Specificity of cerebellar grafts. Nature 327: 366–7. Dunnett, S.B. and Björklund, A. (eds.) (1994). Functional Neural Transplantation. New York: Raven Press. Eccles, J.C., Ito, M. and Szentágothai, J. (1967). The Cerebellum as a Neuronal Machine. Berlin, Heidelberg: Springer Verlag. Ezerman, E.B. (1988). Survival and development of embryonic and postnatal cerebellum transplanted into adult rat hosts: effect of growth as explants in culture prior to transplantation. Dev Brain Res 41: 253–61. Ezerman, E.B. and Kromer, L.F. (1985). Development and neuronal organization of dissociated and reaggregated embryonic cerebellum after intracephalic transplantation to adult rodent recipients. Dev Brain Res 23: 287–92. Fujii, M. and Hayakashi, T. (1992). Axons from the olfactory bulb transplanted into the cerebellum form synapses with dendrites in the granular layer, as demonstrated by mouse allelic form of Thy-1 and electron microscopy. Neurosci Res 14: 73–8. Fujita, S. (1967). Quantitative analysis of cell proliferation and differentiation in the cortex of the postnatal mouse cerebellum. J Cell Biol 32: 277–88. Gardette, R., Alvarado-Mallart, R.M., Crepel, F. and Sotelo, C. (1988). Electrophysiological demonstration of a synaptic integration of transplanted Purkinje cells into the cerebellum of the adult Purkinje cell degeneration mutant mouse. Neuroscience 24: 777–89. Gardette, R., Crepel, F., Alvarado-Mallart, R.M. and Sotelo, C. (1990). Fate of grafted embryonic Purkinje cells in the cerebellum of the adult ‘Purkinje cell degeneration’ mutant mouse. II.

381

382

L.C. Triarhou

Development of synaptic responses: an in vitro study. J Comp Neurol 295: 188–96. Gerloff, C., Knappe, U.J.K., Hettmannsperger, U., Duffner, T.K. and Volk, B. (1993). Intrastriatal cerebellar grafts: differentiation of cerebellar anlage and sprouting of Purkinje cell axons. Dev Brain Res 74: 30–40. Goffinet, A.M. (1983). The embryonic development of the cerebellum in normal and reeler mutant mice. Anat Embryol 168: 73–86. Greer, C.A. and Shepherd, G.M. (1982). Mitral cell degeneration and sensory function in the neurological mutant mouse Purkinje cell degeneration. Brain Res 235: 156–61. Hall, M., Wang, Y., Granholm, A.C., Stevens, J.O., Young, D. and Hoffer, B.J. (1992). Comparison of fetal rabbit brain xenografts to three different strains of athymic nude rats: electrophysiological and immunohistochemical studies of intraocular grafts. Cell Transpl 1: 71–82. Hámori, J. and Takács, J. (1988). Morphological study of cerebellar transplant cocultivated with cerebral cortical graft in the anterior eye chamber. II. Purkinje cells and molecular layer. Anat Embryol 177: 557–69. Hine, R.J. (1977). Transplanted cerebellar tissue in the rat: its growth and its afferents. Anat Rec 187: 605. Hoffer, B.J., Olson, L., Seiger, Å. and Bloom, F.E. (1975). Formation of a functional adrenergic input to intraocular cerebellar grafts: ingrowth of sympathetic fibers and inhibition of Purkinje cell activity by adrenergic input. J Neurobiol 6: 565–86. Hoffer, B.J., Seiger, Å., Ljungberg, T. and Olson, L. (1974). Electrophysiological studies of brain homografts in the anterior chamber of the eye: maturation of cerebellar cortex in oculo. Brain Res 79: 165–84. Hudson, D.B., Valcana, T., Bean, G. and Timiras, P.A. (1976). Glutamic acid: a strong candidate as the neurotransmitter of the cerebellar granule cell. Neurochem Res 1: 73–81. Ito, M. (1984). The Cerebellum and Neural Control. New York: Plenum Press. Jones, B.J. and Roberts, D.J. (1968). The quantitative measurement of motor incoordination in naïve mice using an accelerating rotarod. J Pharm Pharmacol 20: 302–4. Kawamura, K., Murase, S., Yuasa, S. and Yoshida, K. (1990). Transplantation of embryonic olive in the climbing-fiberdeprived adult rat cerebellum: Synaptogenesis on host Purkinje dendritic spines by donor climbing fibers. Neurosci Res (Suppl.) 13: S61–4. Kawamura, K., Nanami, T., Kikuchi, Y. and Kitakami, A. (1988). Grafted granule and Purkinje cells can migrate into the mature cerebellum of normal adult rats. Exp Brain Res 70: 477–84. Keep, M., Alvarado-Mallart, R.M. and Sotelo, C. (1992). New insights on the factors orienting the axonal outgrowth of grafted Purkinje cells in the pcd cerebellum. Dev Neurosci 14: 153–65. Kikuchi, Y. (1989). Transplantation of embryonic cerebella into adult rat cerebella. Brain Nerve (Tokyo) 41: 45–53. Kromer, L.F., Björklund, A. and Stenevi, U. (1979). Intracephalic implants: a technique for studying neuronal interactions. Science 204: 1117–19.

Kromer, L.F., Björklund, A. and Stenevi, U. (1983). Intracephalic embryonic neural implants in the adult rat brain. I. Growth and mature organization of brainstem, cerebellar, and hippocampal implants. J Comp Neurol 218: 433–59. Landis, S.C. (1973). Ultrastructural changes in the mitochondria of cerebellar Purkinje cells of nervous mutant mice. J Cell Biol 57: 782–97. Landis, S.C. and Mullen, R.J. (1978). The development and degeneration of Purkinje cells in pcd mutant mice. J Comp Neurol 177: 125–44. Larramendi, L.M.H. (1969). Analysis of synaptogenesis in the cerebellum of the mouse. In Neurobiology of Cerebellar Evolution and Development, ed. R. Llinás, pp. 803–43. Chicago: AMA/ERF Institute for Biomedical Research. Lindvall, O., Brundin, P., Widner, H. et al. (1990). Grafts of fetal dopamine neurons survive and improve motor function in Parkinson’s disease. Science 247: 574–7. Lindvall, O., Sawle, G., Widner, et al. (1994). Evidence for long-term survival and function of dopaminergic grafts in progressive Parkinson’s disease. Ann Neurol 35: 172–80. Miale, I.L. and Sidman, R.L. (1961). An autoradiographic analysis of histogenesis in the mouse cerebellum. Exp Neurol 4: 277–96. Mitsacos, A., Fragioudaki, K., Kouvelas, E.D. and Triarhou, L.C. (1999). AMPA receptor subunit gene expression in cerebellar grafts: In situ hybridization histochemical studies. Abstr Am Soc Neural Transpl 6: 58. Mugnaini, E. and Morgan, J.I. (1987). The neuropeptide cerebellin is a marker for two similar neuronal circuits in rat brain. Proc Natl Acad Sci USA 84: 8692–6. Mullen, R.J. (1977). Site of pcd gene action and Purkinje cell mosaïcism in the cerebella of chimæric mice. Nature 270: 245–7. Mullen, R.J., Eicher, E.M. and Sidman, R.L. (1976). Purkinje cell degeneration, a new neurological mutation in the mouse. Proc Natl Acad Sci USA 73: 208–12. Mullen, R.J. and LaVail, M.M. (1975). Two new types of retinal degeneration in cerebellar mutant mice. Nature 258: 528–30. Obata, K. (1969). GABA in Purkinje cells and motoneurons. Experientia (Basel) 25: 1285. O’Gorman, S. and Sidman, R.L. (1985). Degeneration of thalamic neurons in ‘Purkinje cell degeneration’ mutant mice. I. Distribution of neuron loss. J Comp Neurol 234: 277–97. Pellegrino, L.J. and Altman, J. (1979). Effects of differential interference with postnatal cerebellar neurogenesis on motor performance, activity level, and maze learning of rats: a developmental study. J Comp Physiol Psychol 93: 1–33. Perlow, M.J., Nilaver, G., Beinfeld, M.C. and Zimmerman, E.A. (1984). Host–graft interactions following cerebellar transplantation in rat. Soc Neurosci Abstr 10: 663. Phillips, R.J.S. (1960). ‘Lurcher’, a new gene in linkage group XI of the house mouse. J Genet 57: 35–42. Poltorak, M., Freed, W.J., Sternberger, L.A. and Sternberger, N.H. (1988). A comparison of intraventricular and intraparenchymal cerebellar allografts in rat brain: evidence for normal phosphorylation of neurofilaments. J Neuroimmunol 20: 63–72. Ramón y Cajal, S. (1926). Sur les fibres moussues et quelques

Cerebellar grafts

points douteux de la texture de l’écorce cérébelleuse. Trab Lab Invest Biol Univ Madrid 24: 215–51. Ramón y Cajal, S. (1929/1960). Studies on Vertebrate Neurogenesis, translated by L. Guth, pp. 251–321. Springfield, IL: Charles C. Tromas. Rosenstein, J.M. (1991). Permeability to blood-borne protein and (3H)GABA in CNS tissue grafts. I. Intraventricular grafts. J Comp Neurol 305: 676–90. Rossi, F. and Borsello, T. (1993). Ectopic Purkinje cells in the adult rat: olivary innervation and different capabilities of migration and development after grafting. J Comp Neurol 337: 70–82. Rossi, F., Borsello, T. and Strata, P. (1992). Embryonic Purkinje cells grafted on the surface of the cerebellar cortex integrate in the adult unlesioned cerebellum. Eur J Neurosci 4: 589–94. Rossi, F., Borsello, T. and Strata, P. (1994). Embryonic Purkinje cells grafted on the surface of the adult uninjured rat cerebellum migrate in the host parenchyma and induce sprouting of intact climbing fibres. Eur J Neurosci 6: 121–36. Rouse, R.V. and Sotelo, C. (1990). Grafts of dissociated cerebellar cells containing Purkinje cell precursors organize into zebrin I defined compartments. Exp Brain Res 82: 401–7. Sidman, R.L. (1982). Mutations affecting the central nervous system in the mouse. In Molecular Genetic Neuroscience, ed. F.O. Schmitt, S.J. Bird and F.E. Bloom, pp. 389–400. New York: Raven Press. Sidman, R.L. and Green, M.C. (1970). ‘Nervous’, a new mutant mouse with cerebellar disease. In Les Mutants Pathologiques chez l’ Animal, ed. M. Sabourdy, pp. 69–79. Paris: Éditions du C.N.R.S. Sidman, R.L., Green, M.C. and Appel, S.H. (1965). Catalog of the Neurological Mutants of the Mouse. Cambridge, MA: Harvard University Press. Sidman, R.L., Lane, P.W. and Dickie, M.M. (1962). Staggerer, a new mutation in the mouse affecting the cerebellum. Science 137: 610–12. Snyder, E.Y., Deitcher, D.L., Walsh, C., Arnold-Aldea, S., Hartwieg, E.A. and Cepko, C.L. (1992). Multipotent neural cell lines can engraft and participate in development of mouse cerebellum. Cell 68: 33–51. Sotelo, C. (1980). Mutant mice and the formation of cerebellar circuitry. Trends Neurosci 3: 33–6. Sotelo, C. (1988). Transplantation de neurones embryonnaires dans le cervelet de souris: restauration de l’ intégrité cérébelleuse chez des souris avec ataxie hérédo-dégénérative. Méd Sci 8: 507–14. Sotelo, C. (1991). Cerebellar synaptogenesis: mutant mice – neuronal grafting. J Physiol (Paris) 85: 134–44. Sotelo, C. (1993). Cell interactions underlying Purkinje cell replacement by neural grafting in the pcd mutant cerebellum. Can J Neurol Sci 20 (Suppl. 3): S43–52. Sotelo, C. and Alvarado-Mallart, R.M. (1985). Cerebellar transplants: immunocytochemical study of the specificity of Purkinje cell inputs and outputs. In Neural Grafting in the Mammalian C.N.S., ed. A. Björklund and U. Stenevi U, pp. 205–215. Amsterdam: Elsevier.

Sotelo, C. and Alvarado-Mallart, R.M. (1986). Growth and differentiation of cerebellar suspensions transplanted into the adult cerebellum of mice with heredodegenerative ataxia. Proc Natl Acad Sci USA 83: 1135–9. Sotelo, C. and Alvarado-Mallart, R.M. (1987a). Cerebellar transplantations in adult mice with heredo-degenerative ataxia. Ann NY Acad Sci 495: 242–66. Sotelo, C. and Alvarado-Mallart, R.M. (1987b). Embryonic and adult neurons interact to allow Purkinje cell replacement in mutant cerebellum. Nature 327: 421–3. Sotelo, C. and Alvarado-Mallart, R.M. (1987c). Reconstruction of the defective cerebellar circuitry in adult Purkinje cell degeneration mutant mice by Purkinje cell replacement through transplantation of solid embryonic implants. Neuroscience 20: 1–22. Sotelo, C. and Alvarado-Mallart, R.M. (1988). Integration of grafted Purkinje cells into the host cerebellar ciruitry in Purkinje cell degeneration mutant mouse. Prog Brain Res 78: 141–54. Sotelo, C. and Alvarado-Mallart, R.M. (1991). The reconstruction of cerebellar circuits. Trends Neurosci 14: 350–5. Sotelo, C. and Alvarado-Mallart, R.M. (1992). Cerebellar grafting as a tool to analyze new aspects of cerebellar development and plasticity. In The Cerebellum Revisited, ed. R. Llinás and C. Sotelo, pp. 84–115. New York, Berlin, Heidelberg: Springer-Verlag. Sotelo, C., Alvarado-Mallart, R.M., Frain, M. and Vernet, M. (1994). Molecular plasticity of adult Bergmann fibers is associated with radial migration of grafted Purkinje cells. J Neurosci 14: 124–33. Sotelo, C., Alvarado-Mallart, R.M., Gardette, R. and Crepel, F. (1990). Fate of grafted embryonic Purkinje cells in the cerebellum of the adult ‘Purkinje cell degeneration’ mutant mouse. I. Development of reciprocal graft–host interactions. J Comp Neurol 295: 165–87. Sotelo, C., Alvarado-Mallart, R.M. and Keep, M. (1992). Fate of axons of embryonic Purkinje cells grafted in the adult cerebellum of the pcd mutant mouse. In The Nerve Growth Cone, ed. P.C. Letourneau, S.B. Kater and E.R. Macagno, pp. 505–17. New York: Raven Press. Sotelo, C. and Changeux, J-P. (1974). Transsynaptic degeneration ‘en cascade’ in the cerebellar cortex of staggerer mutant mice. Brain Res 67: 519–26. Stasi, K., Mitsacos, A., Triarhou, L.C. and Kouvelas, E.D. (1997). Cerebellar grafts partially reverse amino acid receptor changes observed in the cerebellum of mice with hereditary ataxia: quantitative autoradiographic studies. Cell Transpl 6: 347–59. Takács, J. and Hámori, J. (1988). Morphological study of cerebellar transplant cocultivated with cerebral cortical graft in the anterior eye chamber. I. Granular layer. Anat Embryol 177: 543–56. Takács, J., Tran Minh Nhon, T. and Hámori, J. (1986). Electron microscopical study of synaptic glomeruli in cerebellum transplanted to the anterior eye chamber. Acta Biol Hung (Budapest) 37: 259–76. Takayama, H., Kohsaka, S., Shinozaki, T. et al. (1987). Immunohistochemical studies on synapse formation by embryonic cerebellar tissue transplanted into the cerebellum of the weaver mutant mouse. Neurosci Lett 79: 246–50. Takayama, H., Toya, S., Shinozaki, T. et al. (1988). Possible synapse

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formation by embryonic cerebellar tissue grafted into the cerebellum of the weaver mutant mouse. Acta Neurochirurg (Suppl.) 43: 154–8. Thach, W.T., Kane, S.A., Mink, J.W. and Goodkin, H.P. (1992). Cerebellar output: Multiple maps and modes of control in movement coordination. In The Cerebellum Revisited, ed. R. Llinás and C. Sotelo, pp. 283–300. New York: Springer Verlag. Tokunaga, A., Ono, K., Date, I. and Arisawa, T. (1991). A monoclonal antibody that labels Purkinje cells in the rat cerebellum. Brain Res Bull 27: 669–74. Tomey, D.A. and Heckroth, J.A. (1993). Transplantation of normal embryonic cerebellar cell suspensions into the cerebellum of Lurcher mutant mice. Exp Neurol 122: 165–70. Triarhou, L.C. (1992). Weaver gene expression in central nervous system. In Gene Expression in Neural Tissues, ed. P.M. Conn, pp. 209–27. Methods in Neurosciences, Vol. 9. San Diego: Academic Press. Triarhou, L.C. (1995). Cerebellar transplantation in hereditary ataxia and the recovery of function: why do the deep cerebellar nuclei represent a better graft site than the cerebellar cortex. Abstr Am Soc Neural Transpl 2: 21. Triarhou, L.C. (1996). The cerebellar model of neural grafting: structural integration and functional recovery. Brain Res Bull 39: 127–38. Triarhou, L.C. (1997). Neural Transplantation in Cerebellar Ataxia. Austin: Landes Bioscience; Heidelberg: Springer-Verlag. Triarhou, L.C. (2000). Functional aspects of cerebellar transplantation. In Functional Neural Transplantation, 2nd edn. ed. S.B. Dunnett and A. Björklund A, eds. Amsterdam: Elsevier Science. Triarhou, L.C., Ghetti, B. and Low, W.C. (1986). Purkinje and granule cells survive in cerebellar grafts implanted into hosts with genetically-determined Purkinje or granule cell degeneration. Ann Neurol 20: 138. Triarhou, L.C., Low, W.C. and Ghetti, B. (1987). Transplantation of cerebellar anlagen to hosts with genetic cerebellocortical atrophy. Anat Embryol 176: 145–54. Triarhou, L.C., Low, W.C. and Ghetti, B. (1989). Intraparenchymal grafting of cerebellar cell suspensions to the deep cerebellar nuclei of pcd mutant mice: Rationale and histochemical organization. Soc Neurosci Abstr 15: 10. Triarhou, L.C., Low, W.C. and Ghetti, B. (1992a). Intraparenchymal grafting of cerebellar cell suspensions to the deep cerebellar nuclei of pcd mutant mice, with particular emphasis on reestablishment of a Purkinje cell cortico-nuclear projection. Anat Embryol 185: 409–20. Triarhou, L.C., Low, W.C. and Ghetti, B. (1992b). Serotonin fiber innervation of cerebellar cell suspensions intraparenchymally grafted to the cerebellum of pcd mutant mice. Neurochem Res 17: 475–82. Triarhou, L.C., Zhang, W. and Lee, W-H. (1995). Graft-induced restoration of function in hereditary cerebellar ataxia. Neuroreport 6: 1827–32. Triarhou, L.C., Zhang, W. and Lee, W-H. (1996). Amelioration of the behavioral phenotype in genetically ataxic mice through bilat-

eral intracerebellar grafting of fetal Purkinje cells. Cell Transpl 5: 269–77. Tsuda, M., Yuasa, S., Fujino, Y. et al. (1990). Retrovirus-mediated gene transfer into mouse cerebellar primary culture and its application to the neural transplantation. Brain Res Bull 24: 787–92. Tsurushima, H., Yuasa, S., Kawamura, K. and Nose, T. (1993a). Migration of donor Purkinje cells in the host adult rat cerebellum. Brain Nerve (Tokyo) 45: 255–62. Tsurushima, H., Yuasa, S., Kawamura, K. and Nose, T. (1993b). Expression of tenascin and BDNF during the migration and differentiation of grafted Purkinje and granule cells in the adult rat cerebellum. Neurosci Res 18: 109–20. Wassef, M., Sotelo, C., Thomasset, M. et al. (1990). Expression of compartmentation antigen zebrin I in cerebellar transplants. J Comp Neurol 294: 223–34. Wells, J. and McAllister, J.P. (1982). The development of cerebellar primordia transplanted to the neocortex of the rat. Dev Brain Res 4: 167–79. Wenthold, R.J., Yokotani, N., Doi, K. and Wada, K. (1992). Immunochemical characterization of the non-NMDA glutamate receptor using subunit-specific antibodies: evidence for a hetero-oligomeric structure in rat brain. J Biol Chem 267: 501–7. Wetts, R., Moran, T., Oster-Granite, M. and Gearhart, J. (1985). Effect of Purkinje cell loss on complex motor behavior. Soc Neurosci Abstr 11: 1037. Wiestler, O.D., Aguzzi, A., Schneemann, M., Eibl, R., von Deimling, A. and Kleihues, P. (1992a). Oncogene complementation in fetal brain transplants. Cancer Res 52: 3760–7. Wiestler, O.D., Brustle, O., Eibl, R.H., Radner, H., Aguzzi, A. and Kleihues, P. (1992b). Retrovirus-mediated oncogene transfer into neural transplants. Brain Pathol 2: 47–59. Wille, W., Goldowitz, D., Seiger, Å. and Olson, L. (1983). The neurological mutation staggerer is expressed in embryonic cerebellar transplants matured in the anterior eye chamber of normal mice. Neurosci Lett 42: 1–6. Woodward, D.J., Seiger, Å., Olson, L. and Hoffer, B.J. (1977). Intrinsic and extrinsic determinants of dendritic development as revealed by Golgi studies of cerebellar and hippocampal transplants in oculo. Exp Neurol 57: 984–98. Yuasa, S., Kawamura, K., Ono, K., Yamakuni, T. and Takahashi, Y. (1991). Development and migration of Purkinje cells in the mouse cerebellar primordium. Anat Embryol 184: 195–212. Yuasa, S., Tsuda, M. and Kawamura, K. (1993). Fate and behavior of genetically labeled cerebellar cells after transplantation into mouse cerebellum. Neurosci Res 17: 257–63. Zhang, W., Lee, W-H. and Triarhou, L.C. (1996). Grafted cerebellar cells in a mouse model of hereditary ataxia express IGF-I system genes and partially restore behavioral function. Nature Med 2: 65–71. Zwimpfer, T.J., Aguayo, A. and Bray, G.M. (1992). Synapse formation and preferential distribution in the granule cell layer by regenerating retinal ganglion cell axons guided to the cerebellum of adult hamsters. J Neurosci 12: 1144–59.

Part VII

Neuropathology

25

Neuropathology of the inherited ataxias Arnulf H. Koeppen Neurology Service, Veterans Affairs Medical Center, Albany, New York, USA

Introduction Numerous neuropathological studies of patients with hereditary ataxia have revealed heterogeneous lesions of the central and peripheral nervous systems, and clinicoanatomic correlation has been difficult. In light of recent progress in molecular genetics, it has become unnecessary to seek a classification on the basis of neuropathological observations. Nevertheless, traditional terms such as‘olivopontocerebellar atrophy’ or ‘cerebello-olivary atrophy’ will remain useful in anatomical descriptions. In the study of the hereditary ataxias, neuropathologists will have a new task. They must view their observations as a phenotype, similar to age at onset, disease duration, and age at death. They must also be familiar with the mutations that cause ataxia and correlate the complex structural abnormalities with data from molecular genetics. The findings include the length of the cytosine-adenine-guanine (CAG) trinucleotide repeats in various types of spinocerebellar ataxia (SCA), such as SCA1, SCA2, SCA3/Machado–Joseph disease, SCA6, and SCA7, the expanded GAA trinucleotide repeats in Friedreich’s ataxia, and the matching abnormal or missing gene products. New names have appeared for gene products, e.g., frataxin in Friedreich’s ataxia, and ataxin-1, ataxin-2, and ataxin-3 for SCA1, SCA2, and SCA3, respectively. Patients affected by SCA1, SCA2, and SCA3/Machado–Joseph disease biosynthesize normal and mutated ataxins, but the physiological roles of the unmutated polypeptides remain elusive. More is known about frataxin as an iron-carrying protein and the normal SCA6 gene product, an 1A-calcium channel protein. Qualitative and quantitative morphological analyses, and measurement of gene products will all be required to identify the true cause of ataxia. The illustrations in this neuropathological review derive from the examination of genetically defined types of

hereditary ataxia. In some cases, the genetic diagnosis was made by subsequent analysis of DNA in surviving relatives. Accordingly, the precise length of the repeats was not always available, and a correlation between the severity of the tissue abnormalities and the CAG or GAA expansions is still quite limited. Whenever possible, vibratome sections at 40 m thickness were prepared for immunocytochemical visualization of dendrites and axons with monoclonal antibodies to phosphorylated and non-phosphorylated neurofilament proteins (PNF, NPNF), the microtubuleassociated proteins 1 and 2 (MAP-1, MAP-2), and the synaptosome-associated protein 25 (SNAP-25). Only promptly fixed samples allowed successful detection of NPNF, MAP-1, and MAP-2. Sometimes, the dendritic expanse could be visualized in sufficient detail to match a successful Golgi impregnation. An effort was made to illustrate those lesions that are likely to cause clinical ataxia. Hence, the emphasis was on the cerebellar cortex, the dentate and inferior olivary nuclei, the gray matter of the basis pontis, the nucleus dorsalis of Clarke, and the dorsal and lateral columns of the spinal cord. Many authors have reported lesions in other regions of the brain and spinal cord, such as the diencephalon and basal ganglia, the substantia nigra and adjacent red nucleus, and the anterior horns of the spinal gray matter. Lesions in these regions are not considered in this review, though they may contribute in known and unknown ways to the overall clinical presentation.

Friedreich’s ataxia Most Friedreich’s ataxia patients have homozygous GAA trinucleotide expansions of the X25 gene on the ninth chromosome. Compound heterozygotes have one expansion and one point mutation (Cossée et al., 1999; De

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Fig. 25.1 The spinal lesions in Friedreich’s ataxia. (A) anterior aspect of the thoracic spinal cord; (B) dorsal aspect of the thoracic spinal cord; (C) transverse sections of the cervical, thoracic, and lumbar spinal cord; (D) thoracic spinal cord section stained for myelin by the Luxol Fast blue-periodic acid-Schiff method; (E) nucleus dorsalis of Clarke, stained for SNAP-25; (F) dorsal root ganglion (hematoxylin and eosin). The transverse diameter of the thoracic spinal cord is greatly reduced at all levels (A, B, C). The dorsal roots (arrows in B) are thin in comparison with the anterior roots (A). Atrophy and gray discoloration of the dorsal columns and the dorsal portions of the lateral funiculi are grossly visible at the level of the thoracic and cervical spinal cord (C ). The myelin stain (D) shows symmetrical fiber loss in the dorsal columns, the dorsal spinocerebellar tracts, and the lateral corticospinal tracts. The nucleus dorsalis of Clarke (E) shows subtotal loss of synaptic terminals. The arrows in (E) outline the junction of the dorsal columns and the spinal gray matter. The dorsal root ganglion in (F) shows paucity of nerve cells and several nodules of Nageotte (arrows). Markers: (A, B, C), 1cm; (D), 0.5 cm; (E) and (F), 100 m.

Michele et al., 2000). It is not known whether the neuropathological abnormalities in these allelic conditions differ substantially from each other, though they share the genetically determined frataxin deficiency. Although the lesions of the spinal cord in typical Friedreich’s ataxia are quite uniform, there is at least some indication that longer GAA repeats cause more serious morphological spinal cord disease (Koeppen, 1998).

Lesions of spinal cord, dorsal roots, dorsal root ganglia, peripheral nerves, and cerebellum in Friedreich’s ataxia The gross and microscopic abnormalities are illustrated in Figs. 25.1(A–F). Friedreich’s first descriptions in 1863 were properly entitled ‘on degenerative atrophy of the dorsal spinal columns’. The dorsal columns are invariably reduced in size and lack the white color of normal myelin (Fig. 25.1C). The gray discoloration of the spinocerebellar and corticospinal tracts may also be grossly visible (Fig. 25.1C). Transverse and anteroposterior diameters of the spinal cord, especially at thoracic level, are reduced (Fig.

25.1C), causing an overall diminution of the cross-sectional area to below 25 mm2 (Fig. 25.2). The small size holds equally true for early-onset and late-onset cases (Fig. 25.2), and it may be incorrect to speak of ‘atrophy,’ which would imply initially normal development and subsequent degeneration. Although the onset may be delayed to middle or later years of life (Dürr et al., 1996; Gellera et al., 1997; De Michele et al., 1998), it may be more appropriate to consider the lesion a form of genetically determined hypoplasia. Based on neuroanatomical considerations, Friedreich (1877; p. 147) argued persuasively that atrophy of the spinal cord was the likely result of inhibited development. Radiographic measurements of the cervical spinal canal (Vassilopoulos et al., 1977) also suggest that the skeleton fails to expand properly due to delayed growth of the spinal cord at that level. Magnetic resonance imaging (MRI) confirms an overall reduction in the dimensions of the spinal cord itself (Wessel et al., 1989; Mascalchi et al., 1994). Beyond the smallness of the spinal cord, there is often considerable thinning of the dorsal roots (Figs. 25.1A and B) and reduction in the size of the dorsal root ganglia.

Neuropathology of the inherited ataxias

Fig. 25.2 Age of onset and cross-sectional area of the thoracic spinal cord in Friedreich’s ataxia. The cross-sectional area of the midthoracic spinal cord in ten patients with Friedreich’s ataxia and four controls was determined after photography of stained sections and measurement of the area with a Zeiss MOP3 digital analyzer. Similar plots were obtained for age at death or disease duration. Average survival after onset was 30  12 years (range 19–52 years). The findings support the concept that the spinal cord does not reach normal bulk, even in mildly affected Friedreich’s ataxia patients.

Myelin stains are well suited to visualize the fiber depletion of the posterior and lateral funiculi (Fig. 25.1D). In the illustrated case, there is no obvious destruction of the anterior corticospinal tract, though it does not always escape the disease process (Greenfield, 1954). The dorsal spinocerebellar tracts are generally more seriously affected than the ventral spinocerebellar tracts. Cell stains, such as cresyl violet, show total or subtotal neuronal loss in the nucleus dorsalis of Clarke. Loss of synapses is commensurate to nerve cell depletion (Fig. 25.1E). Dorsal root ganglia reveal a great reduction in the number of nerve cells and proliferation of satellite cells. The nodules of Nageotte are always more numerous than in age-matched controls and often very abundant (Fig. 25.1F). The spinal roots have been examined by many authors, but studies of peripheral nerves are comparatively rare. The dorsal roots invariably show fiber depletion, whereas the anterior roots remain unaffected. In peripheral sensory nerves, such as the sural nerve, cross-sections of resin-embedded nerves are particularly convincing of the loss of large myelinated fibers. Hughes et al. (1968) provided the first electron microscopic study of a sural nerve in Friedreich’s ataxia, and several

other ultrastructural studies of this nerve and the dorsal spinal roots followed (see review in Midroni and Bilbao, 1995, pp. 376–7). Lamarche et al. (1982) studied a biopsied dorsal root ganglion from a patient with Friedreich’s ataxia. Teased-fiber preparations almost always revealed foreshortened internodes and, in some studies, segmental demyelination and remyelination (McLeod, 1971; Rizzuto et al., 1981; Caruso et al., 1983; Said et al., 1986; Santoro et al., 1990; Dyck, 1993; Jitpimolmard et al., 1993). Santoro et al. (1990) reported follow-up biopsies of the sural nerve in three patients with Friedreich’s ataxia. Morphometry of the myelinated fibers showed no progression of fiber loss. Others observed more serious fiber depletion in older patients, implying that worsening neuropathy after longer periods does occur (Ouvrier et al., 1982). Most authors reported and illustrated only minor axonal changes though all agreed that the underlying cause is a long-standing axonopathy, possibly even a developmental delay and a ‘hypotrophy.’ Onion bulb formation must be quite rare (Rizzuto et al., 1981; Lamarche et al., 1982). Electrophysiological studies also support a motor neuropathy, and it is of historical interest that the first study of skeletal muscle in Friedreich’s ataxia revealed group atrophy (Fig. 1 in Mott, 1907). The cerebellar cortex is generally normal, though, occasionally, Purkinje cell abnormalities are quite apparent (Fig. 25.3A and B). The dentate nucleus is more frequently involved (Fig. 25.3C) and, in severe lesions, the superior cerebellar peduncles are thinned (Fig. 25.4B and C). In contrast to SCA-3/Machado–Joseph disease, surviving neurons in the dentate nucleus show only little if any grumose degeneration (see below). In theory, preservation of the cerebellar cortex and neuronal loss in the dentate nucleus should cause transneuronal changes in the inferior olivary nuclei (Foix et al., 1926). However, the inferior olivary nuclei are regularly preserved (Urich et al., 1957; Oppenheimer, 1979), and palatal myoclonus is not a clinical feature of Friedreich’s ataxia. The normal dentate nucleus is rich in iron (Fig. 25.4A), and MRI readily reveals signal depression due to the paramagnetic effect on T2-weighted images. The combination of high iron concentration and frataxin deficiency may make this gray matter structure more vulnerable to ironcatalyzed oxidative damage. Waldvogel et al. (1999) used MR measurement to support the claim that iron in the dentate nucleus of Friedreich’s ataxia patients increases. However, other iron-rich regions, such as the globus pallidus, substantia nigra, red nucleus, and subthalamic nucleus, are not especially susceptible to destruction in Friedreich’s ataxia. The illustrations in Fig. 25.4 do not support iron accumulation in Friedreich’s ataxia. They

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Fig. 25.3 Cerebellar lesions in Friedreich’s ataxia. The number of Purkinje cells is approximately normal (A), but the dendritic arborization is abnormal (B). The Purkinje cell illustrated in (B) shows three primary, excessively thick, dendrites that do not branch correctly near the soma of the Purkinje cell. There is also a distinct lack of terminal arborization into spiny branchlets. (C) Dentate nucleus in Friedreich’s ataxia: The section reveals severe neuronal loss and reduced size of the remaining nerve cells. (A) and (B), vibratome sections (40 m) stained for NPNF; (C), paraffin section (6 m) stained with cresyl violet. Markers: 100 m.

Fig. 25.4 Iron in the dentate nucleus of patients with Friedreich’s ataxia. Fixed slices of the cerebellar hemispheres were reacted with Perls’s solution of 1% potassium ferrocyanide and 1% hydrochloric acid. (A) Normal; (B) and (C), Friedreich’s ataxia. The ribbon-like gray matter of the dentate nucleus in Friedreich’s ataxia has become indistinct (B, C), and the hilum is narrowed. Commensurate shrinkage of the superior cerebellar peduncles is apparent in (B) and (C). The macrostain for iron shows less reaction product in Friedreich’s ataxia (B and C).

show macro-stains of iron in the dentate nucleus of two Friedreich’s ataxia patients (Fig. 25.4B and C) and a neurologically normal control (Fig. 25.4A). The size of the nucleus is reduced (Fig. 25.4B and C), and iron reaction product in Friedreich’s ataxia is much less prominent than in the control specimen (Fig. 25.4A). On paraffin sections of human brain, plain (Perls, 1867) or enhanced iron stains (Nguyen-Legros et al., 1980) do not provide the cellular detail that is obtained with frozen or vibratome sections of perfusion-fixed animal tissues. However, immunocytochemical and immunofluorescent stains for ferritin on frozen or vibratome sections give information on the likely cellular location of brain iron, at least to the degree that it is associated with this protein (estimated as 40%). Figure 25.5 shows confocal images of holoferritin and its lightferritin subunits in normal and Friedreich’s ataxia dentate nuclei. The bulk of the normal reaction product is located

in the cytoplasm of perineuronal oligodendroglia. In contrast, ferritin in the cerebellar cortex is mainly localized in microglia (not illustrated). Due to neuronal death in the dentate nucleus of patients with Friedreich’s ataxia, the juxtaneuronal position of ferritin-reactive oligodendroglia is lost. Generally, immunofluorescent oligodendroglia are less abundant which is due to loss of the light-ferritin signal (Fig. 25.5D). Reduced immunofluorescence also applies to heavy-ferritin subunits (not illustrated). These observations on the main iron-carrying protein in the brain invite the interpretation that loss of dentate iron is a secondary phenomenon in the course of neuronal atrophy and that the decline in total iron may be unrelated to frataxin deficiency. The autopsy findings represent end-stage lesions and are not necessarily at variance with the reported increase of dentate iron detected by MR in living Friedreich’s ataxia patients (Waldvogel et al., 1999).

Neuropathology of the inherited ataxias

A common interpretation of the described lesions in the central and peripheral nervous systems of Friedreich’s ataxia patients has been ‘dying back’ neuropathy in sensory nerves, dorsal spinal roots, dorsal columns, and corticospinal tracts. However, the pathogenesis of the neuronal loss in the nucleus dorsalis may include transneuronal degeneration secondary to loss of afferent synaptic terminals (see Fig. 25.1E). In turn, the atrophy of the spinocerebellar tracts follows from the loss of neurons in the nucleus dorsalis. Deafferentation of the gracile and cuneate nuclei results from atrophy of the dorsal columns and has been shown by synaptophysin immunocytochemistry (Goto and Hirano, 1990). The destruction of the dentate nucleus is unexplained. It remains unknown how the complex combined lesions of dorsal root ganglia, spinal cord, and cerebellum related to a mutation in the frataxin gene. At this time, the metabolic basis of the shared vulnerability of the nerve cells that undergo primary degeneration remains elusive. The clinical phenotype of Friedreich’s ataxia can be caused by mutations that are unrelated to frataxin. One autopsy case of a patient with ‘Friedreich’s ataxia’ due to vitamin E deficiency has been reported (Larnaout et al., 1997), but the abnormalities differed greatly from those in frataxin-related Friedreich’s ataxia. A typical neurological Friedreich’s ataxia phenotype without cardiomyopathy may also occur in the absence of a frataxin mutation or vitamin E deficiency (Smeyers et al., 1996). The neuropathological lesions have not been reported.

The lesion of the heart in Friedreich’s ataxia In a post scriptum to his last paper, Friedreich (1877, p. 152) commented on the fatty degeneration of the myocardium in three of his six autopsied cases. He attributed the disease of the heart to typhoid fever that occurred in six of his nine patients. The febrile illness was the cause of death in five patients. The cardiac hypertrophy in one patient with Friedreich’s ataxia is illustrated in Fig. 25.6. In addition to a greatly thickened ventricular wall, the patient also had an asymptomatic mural thrombus in the apex of the left ventricle. Microscopically, the endomysial connective tissue is increased, and the myocardial fibers are widely separated from each other (restrictive cardiomyopathy). Cellular nuclei are large and often contain intranuclear inclusion bodies (Fig. 25.6B). Iron stains of paraffin sections often show fibers with granular reaction product near their nuclei. This observation was made years before the role of frataxin in cellular iron homeostasis was known (Lamarche et al., 1980, 1993). Biochemical analysis of myocardial tissue obtained by endocardial biopsy (Rötig et al., 1997)

strongly supports the concept that frataxin deficiency causes oxidative damage to mitochondrial enzymes. A mitochondrial localization of frataxin has been shown in cultured cells by immunochemical methods at the light and electron microscopic levels (Campuzano et al., 1997; Priller et al., 1997). The toxicity of iron on mitochondrial function is supported by investigations of the frataxinhomologue in yeast (Babcock et al., 1997; Koutnikova et al., 1997; Foury and Cazzalini, 1997; Wilson and Roof, 1997).

The dominant ataxias The dominant ataxias designated as SCA1, SCA2, SCA6, and SCA7 share cerebellar cortical atrophy and variable neuronal loss in the inferior olivary nuclei. The term ‘olivopontocerebellar atrophy,’ attributed to Menzel (1891), always applies to SCA2 and SCA7, and less frequently to SCA1. For cases with selective and occasionally ‘pure’ cerebellar atrophy, the term familial cortical cerebellar atrophy may be more appropriate. It remains enigmatic why pontine involvement does not always affect patients with SCA1. Robitaille et al. (1995) made a full comparative list of brain and spinal cord lesions in SCA1, SCA2, and SCA3/Machado–Joseph disease. In SCA3/Machado– Joseph disease, sparing of the cerebellar cortex and inferior olivary nuclei, and lesions of the dentate nuclei and the nucleus dorsalis of Clarke make distinction from SCA1 and SCA2 straightforward. The neuropathological distinction of SCA1 from SCA2 is less certain, especially if a case of SCA1 shows olivopontocerebellar atrophy. To overcome neuropathological uncertainties, fresh post mortem tissue should be extracted for gene analysis in all cases in which the diagnosis was not established during life, and presumably in all cases of seemingly sporadic ataxia. Experience with the tissue donation program of the National Ataxia Foundation, Minneapolis, MN (USA) indicates that many patients with sporadic ataxia and imaging evidence of olivopontocerebellar atrophy do not have hereditary ataxia but multiple system atrophy. In these cases, the presence of glial cytoplasmic inclusions is a valuable diagnostic observation (Papp et al., 1989).

Spinocerebellar ataxia type 1 Gross and microscopic observations are illustrated in Fig. 25.7(A–G). The midsagittal section (Fig. 25.7A) shows overall reduction in the size of the cerebellum and especially the vermis. The interfolial subarachnoid space is widened, and the fourth ventricle is dilated. There is no obvious gross atrophy of the pons, though microscopic

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Fig. 25.5

Neuropathology of the inherited ataxias

Fig. 25.6 Hypertrophic cardiomyopathy in Friedreich’s ataxia. (A) Apex and wall of the left ventricle. In addition to the greatly thickened ventricular wall (about 1.5 cm), the heart shows an apical thrombus (arrow). (B) Microscopic appearance of the myocardium. The myocardial fibers are spaced more widely due to excessive endomysial connective tissue. The fibers are of highly variable size and often contain bizarre nuclei and intranuclear inclusions. (C) and (D) Perls’s iron stain of longitudinal (C) and transverse (D) sections of Friedreich’s ataxia myocardium. Granular reaction product often lies immediately adjacent to sarcoplasmic nuclei. Markers: (A) 1 cm; (B)–(D), 100 m.

examination in this case confirms severe neuronal loss in the gray matter of the basis pontis (Fig. 25.7F). In addition to Purkinje cell depletion, the remaining stainable neurons show loss of dendrites (Fig. 25.7B), and occasional bizarre dendrites are present (Fig. 25.7C). The unusual dendrite in Fig. 25.7C reacted with a monoclonal antibody to PNF. Normal Purkinje cells stain readily with antibodies to NPNF but not to PNF. The accumulation of phosphorylated antigenic determinants may be attributed to axonal injury (Shiurba et al., 1987). A frequent observation is the preservation of parallel fibers (Fig. 25.7D). ‘Empty baskets’ and torpedoes in the granular layer are abundant, though they are not specific for hereditary cortical cerebellar atrophy (Fig. 25.7D). Neuronal loss is present in the dentate nucleus (Fig. 25.7E), the basis pontis (Fig. 25.7F), and the inferior olivary nuclei (Fig. 25.7G).

Spinocerebellar ataxia type 2 In a recent tally of autopsy specimens of olivopontocerebellar atrophy, SCA2 was the most common form (10/18) (Koeppen et al., 1999), and clinicians may gain the impression that it constitutes a more severe form of olivopontocerebellar atrophy than SCA1. Loss of saccadic eye movements is highly characteristic for SCA2 (Wadia and Swami, 1971; Koeppen and Hans, 1976), though it may also occur in other hereditary (Bürk et al., 1999) and sporadic ataxias (Maas and Scherer, 1933). The lesion giving rise to slowed or absent saccadic eye movements is probably located in the nucleus pontis centralis caudalis in the lower pontine tegmentum, though no formal morphometry of this region has been reported. Gross and microscopic observations in SCA2 are

Fig. 25.5 (left) Ferritin in the dentate nucleus of patients with Friedreich’s ataxia. Confocal images of the dentate nucleus were obtained by double-label immunofluorescence with antibodies to holoferritin (A and B, polyclonal antibody; fluorescein isothiocyanate) and the light (L)-ferritin subunit (C and D, monoclonal antibody, Quantum Red). (E) and (F) show superimposed images. Left panel (A, C, E), control tissue; right panel (B, D, F), Friedreich’s ataxia. The section of the normal dentate nucleus (A) shows intense holoferritin reaction product in cells that have the morphological characteristics of oligodendroglia. Most are located in the immediate vicinity of large dentate neurons. Light ferritin was detected in the same oligodendroglia (C), and the superimposed images produce an intense yellow color (E). The neuronal cell body in (A) is outlined by arrowheads. In Friedreich’s ataxia, the cellular localization of holoferritin is also oligodendroglial (B), though the immunoreactive cells are no longer adjacent to neurons (B). Light ferritin was no longer detectable by the monoclonal antibody (D). Superimposition of (B) and (D) fails to reveal the yellow color generated in normal perineuronal oligodendroglia (F). The images were obtained from 40 m-thick vibratome sections. The polyclonal antiserum to human holoferritin and the monoclonal antibody to its L-ferritin subunit were obtained from commercial sources. The images were processed to remove the autofluorescence of lipofuscin. Magnification marker for (A)–(F), 25 m.

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Fig. 25.7 Spinocerebellar ataxia type 1. (A) The midsagittal section of the brain reveals smallness of the cerebellar vermis and modest dilatation of the fourth ventricle. Gross pontine atrophy is absent, though microscopy reveals neuronal loss in the basis pontis. (B) The dendritic arbor of the remaining Purkinje cells is greatly simplified or totally lost (stain for NPNF). (C) An unusual dendrite in the molecular layer reacts strongly with anti-PNF as a possible indication of axonal interruption. (D) The internal third of the cerebellar molecular layer reveals abundant parallel fibers. Empty baskets and axonal torpedoes are present in the granular layer (stain for PNF). (E) The dentate nucleus reveals severe neuronal loss (cresyl violet). (F) The gray matter of the basis pontis shows neuronal depletion (cresyl violet). (G) The chief inferior olivary nucleus shows regional loss of nerve cells (hematoxylin and eosin). Markers: (B), 100 m; (C), 50 m; (D), 100 m; (E), 1 mm; (F), 100 m; (G), 100 m.

illustrated in Fig. 25.8. Some of the microphotographs derive from a previously published case in which rapid autopsy and fixation by perfusion allowed immunocytochemical visualization of most cell types in the cerebellar cortex including the stellate and basket neurons, and Golgi neurons (Koeppen et al., 1986). The gross appearance is often quite dramatic, with cerebellar and pontine atrophy. As in other hereditary and sporadic system degenerations, the uvula and nodulus of the cerebellar vermis and the cerebellar tonsil are not affected (Fig. 25.8A). The histopathology in SCA2 is quite similar to that in olivopontocerebellar

atrophy due to SCA1, though the lesions are generally more severe, especially in the inferior olivary nuclei (Fig. 25.8F) and the basis pontis (Fig. 25.8G). The severe lesions in SCA2 offer an opportunity to investigate retrograde and transneuronal atrophies in the pathogenesis. Despite the loss of Purkinje cells (Fig. 25.8B), nerve cells with afferent connections to Purkinje cells, such as the granular neurons and the stellate and basket cells, appear to survive. Stellate and basket cells undergo rounding of their cell bodies, but no obvious numerical reduction (Fig. 25.8C). Golgi neurons with their very long apical dendrites also survive (Fig. 25.8C). Immunostaining of the inferior olivary nuclei with monoclonal anti-MAP-2 shows depletion of nerve cells, whereas the remaining neurons retain their extremely elaborate spherical dendritic expanse (Fig. 25.8F). It is obvious that loss of their synaptic connections with Purkinje cells (via climbing fibers) causes extensive retrograde atrophy in the inferior olivary nuclei, while similarly ‘orphaned’ synaptic terminals arising from granule, stellate, and basket cells remain intact. This early observation was recently confirmed by direct staining of presynaptic membranes with anti-SNAP-25 (Koeppen et al., 1999). Despite collapse of the molecular layer in the course of Purkinje cell atrophy, intense immunoreaction for synaptic terminals remained in the atrophic cerebellar cortex. The disappearance of pontine neurons (Fig. 25.8G) should cause synaptic depletion in the granular layer of the cerebellar cortex. Loss of mossy fiber terminals was demonstrated by immunocytochemistry with anti-synaptophysin (Koeppen, 1991), but quantitative confocal immunofluorescence microscopy with anti-SNAP-25 did not confirm it (Koeppen et al., 1999). A possible reason for this discrepancy may be retention of presynaptic membranes (SNAP25) while synaptic vesicles (synaptophysin) are lost.

Neuropathology of the inherited ataxias

Fig. 25.8 Spinocerebellar ataxia type 2. (A) The midsagittal section of the brain shows severe cerebellar and pontine atrophy, wide interfolial spaces, and dilatation of the fourth ventricle and aqueduct. The uvula and nodulus of the vermis are not seriously affected. (B) The cerebellar cortex shows loss of Purkinje cells and impoverished dendritic arbors (immunostain for NPNF). (C) Stellate and basket cells (arrowheads) have lost their normal starshaped dendritic expansions and instead appear rounded. The highly reactive varicose processes (arrows) are the apical dendrites of Golgi neurons in the granular layer (MAP-2). (D) Parallel fibers in the depth of the molecular layer are preserved. However, there are numerous ‘empty baskets’ and scattered torpedoes in the granular layer (arrows) (PNF). (E) The dentate nucleus shows neuronal loss and dendritic atrophy (NPNF). (F) The inferior olivary nucleus reveals neuronal loss, but the few remaining cells appear normal. Immunocytochemistry with antiMAP-2 shows their typical elaborate spherical dendritic arbor. (G) Pontine neurons are greatly reduced in number, and the remaining nerve cells show rounding of their somata and dendritic atrophy (MAP-2). Markers: 100 m.

Sprouting from spinocerebellar fibers may also occur. In contrast to the granular layer, loss of synaptic terminals in the dentate nucleus of patients with SCA2 was readily apparent and presumably paralleled the degree of Purkinje cell loss (Koeppen et al., 1999).

Spinocerebellar ataxia type 3/Machado–Joseph disease The gross and microscopic observations in SCA3/ Machado–Joseph disease are represented in Figs. 25.9 and 25.10. The smallness of the cerebellum (Fig. 25.9A) must be attributed to atrophy of the dentate nucleus and its efferent fibers. It is a hallmark of SCA3/Machado– Joseph disease that the cerebellar cortex (Fig. 25.9B and C) and the inferior olivary nucleus are preserved (Fig. 25.9D), much in contrast to other autosomal dominant hereditary ataxias. The severe lesion of the dentate nucleus (Fig. 25.9E) does not cause transneuronal atrophy in the nerve cells of the inferior olivary nuclei (Foix et al., 1926). The remaining neurons of the dentate nucleus often show grumose degeneration which is a combination of dendritic expansion and overabundance of synaptic terminals (Fig. 25.9F and G). It is best known from the study of progressive supranuclear palsy, but also occurs in dentatorubropallidoluysian atrophy (Arai, 1989). Pontine involvement is variable, ranging from absent to severe (see reviews in Coutinho et al., 1982; and Yuasa et al., 1986). It remains uncertain whether spinopontine atrophy is a variant of SCA3/Machado–Joseph disease (Eto et al., 1990). SCA3/Machado–Joseph disease has a characteristic

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Fig. 25.9 Spinocerebellar ataxia type 3/Machado–Joseph disease. (A) Gross specimen. The photograph of the gross specimen reveals smallness of the cerebellum, though the cerebellar cortex (B and C) is normal. The reduction of cerebellar size must be attributed to atrophy of the dentate nucleus and its efferent fibers. (B) Cerebellar cortex. The molecular layer has normal overall thickness (400–440 m). Purkinje cells are abundant and have their normal primary, secondary, and terminal dendritic branches (NPNF). (C) Higher magnification of a Purkinje cell reveals preservation of the entire dendritic arbor (NPNF). (D) Inferior olivary nucleus. Neurons in the chief inferior olivary nucleus are preserved (cresyl violet). (E) Dentate nucleus. Only one nerve cell remains in this high-power field, and grumose degeneration is very prominent (arrows) (cresyl violet). (F) Dentate nucleus. A silver stain shows an isolated nerve cell and cloud-like reaction product (arrows) (Bielschowsky). (G) Dentate nucleus. Confocal immunofluorescence microscopy of SNAP-25 indicates that grumose degeneration is related to presynaptic membranes (SNAP-25). Markers: (B)–(E), 100 m; (F), 50 m; (G), 25 m.

spinal cord pathology that includes neuronal loss in the nucleus dorsalis, and degeneration of the spinocerebellar tracts and dorsal columns. In some ways, the spinal lesion is quite similar to that in Friedreich’s ataxia, but the following differences are apparent: The cross-sectional area of the thoracic cord is not reduced, and the atrophy of the dorsal and lateral funiculi is not as severe as in Friedreich’s ataxia (see also Fig. 25.1D). It is surprising that the

comparable loss of neurons in the dorsal nucleus in SCA3/Machado–Joseph disease (Fig. 25.10) does not cause a similar degeneration of the ascending spinocerebellar fibers. In the material available to the author, the ventral spinocerebellar tracts were more seriously affected than the dorsal spinocerebellar tracts. This observation is also contrary to the lesion in Friedreich’s ataxia. In SCA3/Machado–Joseph disease, the corticospinal tracts (Fig. 25.1D) and dorsal root ganglia are not seriously affected (Woods and Schaumburg, 1972; Coutinho et al., 1982). Loss of synaptic afferents does not fully explain neuronal atrophy in the nucleus dorsalis (Fig. 25.10B), and primary neuronal atrophy appears more likely. Neuropathy in SCA3/Machado–Joseph disease may be quite prominent, and biopsied peripheral nerves (Coutinho et al., 1986) and autopsy specimens of sensory, motor, cranial, and autonomic nerves have also been studied (Kinoshita et al., 1995). Loss of myelinated fibers in peripheral nerves varies with the severity of the neuropathy, and only the most severe neuropathy shows a somewhat selective loss of the larger myelinated fibers (Coutinho et al., 1986).The post-mortem study of the oculomotor nerve and the anterior roots of the first cervical and second thoracic spinal segments revealed fiber loss that matched the atrophy of the corresponding motor neurons (Kinoshita et al., 1995). Loss of large myelinated fibers in the dorsal roots followed a pattern seen in the sural nerve (Kinoshita et al., 1995). The phenomenon of a ‘dying back’ neuropathy is generally less convincing in SCA3/Machado–Joseph disease than in Friedreich’s ataxia (Kanda et al., 1989).

Neuropathology of the inherited ataxias

Fig. 25.10 Atrophy of the nucleus dorsalis of Clarke in spinocerebellar ataxia type 3/Machado–Joseph disease. (A) The nucleus dorsalis of Clarke at a high lumbar level stands out by its lack of immunocytochemical reaction product for SNAP 25 (arrow). (B) A confocal immunofluorescence image of presynaptic membranes shows depletion in the nucleus dorsalis. The arrow indicates a residual rim of reaction product about a small neuron (SNAP-25). (C) Normal nucleus dorsalis. Immunofluorescent reaction product outlines a large, round neuron and shows many other presynaptic terminals (SNAP-25). Markers: (A), 1 mm; (B) and (C), 25 m.

Independent neuropathological reports (Woods and Schaumburg, 1972; Sakai et al., 1983) appeared before the identity of Machado–Joseph disease and cases of dominant ataxias without Portuguese ancestry were known (Stevanin et al., 1995; Twist et al., 1995; Haberhausen et al., 1995). Discovery of the gene defect (SCA3) prompted a reexamination of the neuropathological findings. The author attributes the first pathological description to Becker et al. (1971), though the preservation of the dentate nucleus in the reported case is surprising. An autopsy of a patient in a later generation revealed the now characteristic lesion of the dentate and also permitted the clear identification of the SCA3 mutation. The neuropathology of SCA3/ Machado–Joseph disease is less uniform than that of Friedreich’s ataxia. However, on balance, gross and microscopic findings in most cases are sufficiently characteristic to allow assignment to the SCA3 gene locus even in the absence of prior confirmation by molecular techniques.

Spinocerebellar ataxia type 6 The gross and microscopic features of SCA6 are illustrated in Figs. 25.11 and 25.12. Whereas atrophy of the cerebellum is quite severe, sparing of the uvula and nodulus occurs in SCA6, as it does in other autosomal dominant ataxias. Purkinje cell loss and an impoverished dendritic arbor are illustrated in Fig. 25.11 (B and C). In SCA6, the granular layer is variably thinned. Even in the same case, some areas of the cerebellar cortex show severe loss of granule cells, while elsewhere they are better preserved. The persistence of parallel fibers depends on the relative abundance of

granule cells. Figure 25.11D shows empty baskets, and parallel fibers are very sparse. More abundant baskets and empty baskets can be visualized in a region with better retention of the granular layer (Fig. 25.11E). Neurons of the dentate nucleus are generally quite abundant, though the overall cellularity is increased due to small-cell gliosis (Fig. 25.11F). There is considerable disparity between the severity of the cerebellar cortical lesion and the degree of olivary atrophy. Many olivary nerve cells remain despite subtotal Purkinje cell loss (Fig. 25.12A). This preservation of the inferior olivary nucleus is also readily apparent by staining for synaptic membranes (Fig. 25.12B). Neuropathological experience with SCA6 is still quite limited (Subramony et al., 1996; Gomez et al., 1997; Koeppen, 1998; Takahashi et al., 1998). However, there is general agreement that SCA6 constitutes a form of ‘pure cerebellar ataxia.’ The term cerebello-olivary atrophy may apply when authors considered nerve cell loss in the inferior olivary nuclei significant (Subramony et al., 1996; Takahashi et al., 1998). The basis pontis and the spinal cord are entirely spared, and neuronal loss in the dentate nucleus is absent or minor. Gliosis in the dentate nucleus may be a response to the obvious deafferentation in the course of Purkinje cell loss. The author found no significant loss of SNAP-25 reaction product in one case of SCA6, which was surprising given the severe atrophy of the cerebellar cortex (Koeppen et al., 1999). In its causation, SCA6 differs in several important ways from other ataxias with CAG trinucleotide repeat expansions. The polyglutamine expansion in the human 1Acalcium channel protein is relatively short (Zhuchenko et

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Fig. 25.11 Spinocerebellar ataxia type 6. (A) Gross specimen. The cerebellum is greatly reduced in size. The folia of the superior vermis are narrowed and reveal wide spaces between them, whereas the uvula and nodulus are better preserved. (B)–(F) Microscopic findings. Purkinje cells are greatly reduced in number and show an impoverished dendritic arbor (B and C; NPNF). Their somata are small, with an estimated diameter of 25 m (C ). Parallel fibers in some regions of the cerebellar cortex are sparse, making the remaining ‘empty baskets’ more distinct (D). Elsewhere, parallel fibers are preserved (E). The section in (E) also reveals an axonal torpedo (arrow; PNF). The dentate nucleus shows abundant nerve cells (F; cresyl violet). Markers: 100 m.

due to functional loss affecting an established ion channel.

Spinocerebellar ataxia type 7 A characteristic feature of SCA7 is the pigmentary retinopathy that occurs in association with the ataxic condition. It is not known whether the retinal lesion is sufficiently specific to classify all previously published autopsy cases as SCA7, even though confirmation of the locus was not available. At the time of writing this chapter, only the autopsy cases of Gouw et al. (1994) and Holmberg et al. (1998) can be considered genetically confirmed as SCA7. The earlier descriptions by Jampel et al. (1961), Carpenter and Schumacher (1966), and Weiner et al. (1967) established the autosomal dominant transmission, anticipation, and the neuropathological phenotype of olivopontocerebellar atrophy. The severe retinal destruction was illustrated by several authors. It causes atrophy of the optic nerves and chiasm, and transneuronal changes in the lateral geniculate bodies. The microscopic examination discloses severe Purkinje cell loss, neuronal depletion of the inferior olivary nuclei, atrophy of the nerve cells in the basis pontis, and fiber loss in the spinocerebellar tracts and dorsal columns of the spinal cord. It would be of interest to achieve retrospective confirmation of the gene locus and the length of the CAG trinucleotide repeats (David et al., 1997) in the reported families by extracting DNA from archival paraffin-embedded tissues.

Inclusion bodies in the dominant ataxias al., 1997). Furthermore, familial hemiplegic migraine and episodic ataxia type 2 are allelic conditions; and murine mutations of the protein are known (see review in Zoghbi, 1997). Whereas in other CAG-related dominant ataxias the much larger polyglutamine expansions are thought to convey a ‘toxic gain of function,’ SCA6 is more likely to be

The discovery of intranuclear inclusion bodies in the neurons of patients with Huntington disease (DiFiglia et al., 1997) and transgenic Huntington disease mice (Davies et al., 1997) catalyzed a search for similar aggregates in other heritable diseases with expanded CAG trinucleotide repeats. Immunocytochemical studies supported

Neuropathology of the inherited ataxias

Fig. 25.12 Inferior olivary nucleus in spinocerebellar ataxia type 6. Numerous neurons in the chief inferior olivary nucleus remain (A; cresyl violet). Neuronal preservation is also shown by staining synaptic terminals (B). The granular reaction product for SNAP-25 shows a gray-matter ribbon with an approximate width of 250 m (normal). The cell bodies of inferior olivary neurons stand out as negative images. The arrow indicates one of the spaces occupied by an intact nerve cells. Markers: 100 m.

abnormal intranuclear inclusions as a shared phenomenon in some, though not all, dominant ataxias. Figures 25.13A–C shows the results of positive-contrast immunocytochemistry with anti-ataxin-3 in the neurons of the basis pontis in SCA3/Machado–Joseph disease. The nuclear inclusions are revealed by dense reaction product, are distinct from the nucleolus, and have slightly smaller diameters (1–3 m). Their distribution in the illustrated case is uneven, with clusters of three or four neurons giving a positive immunoreaction alternating with areas in which neurons are devoid of reaction product. This variability was observed previously (Paulson et al., 1997a, 1997b). Figure 25.13D shows intranuclear ubiquitin immunoreactivity. Figure 25.13E, taken from the cerebellar cortex of a SCA3/Machado–Joseph disease patient, shows normal punctate cytoplasmic reaction product in a Purkinje cell (Paulson et al., 1997a; Schmidt et al., 1998). Figure 25.13 (F–H) illustrates confocal immunofluorescent images obtained with anti-ataxin-3 (F and G) and anti-ubiquitin (H). Figure 25.13 (G and H) was derived by double-labeling of the same section with anti-ataxin-3 (G; fluorescein isothiocyanate) and ubiquitin (H; Quantum Red). In Huntington disease and SCA, results varied with the nature of the antibody (polyclonal or monoclonal) and the immunogens used to generate antibodies. An early study with anti-huntingtin actually revealed no intranuclear reaction product in nerve cells (Sapp et al., 1997). In SCA1, nuclear staining also depended on the antiserum. It was pan-nuclear rather than punctate with a polyclonal antibody to an ataxin-1 fusion protein (Servadio et al., 1995). With an anti-ataxin-1 peptide antiserum, paraffin sections from human SCA1 brains and vibratome sections from

SCA1 transgenic mice revealed a more restricted nuclear reaction product (Skinner et al., 1997; Cummings et al., 1998). Studies of SCA2 resulted in disparate observations. Huynh et al. (1999) saw no ubiquitinated intranuclear inclusions that were reactive with polyclonal antibodies raised against several ataxin-2-specific peptides. In contrast, the use of a monoclonal antibody caused intense fluorescence of intranuclear inclusions that were also ubiquitinated (Koyano et al., 1999). In sections from SCA3/Machado–Joseph disease patients, Schmidt et al. (1998) observed much better staining of intranuclear neuronal inclusion bodies with a monoclonal antibody recognizing the C-terminal portion of ataxin-3 than with those reacting with the N-terminal or middle portions of the molecule. A monoclonal antibody reactive against polyglutamine stretches (Trottier et al., 1995) revealed neuronal intranuclear inclusions in SCA7 (Holmberg et al., 1998). In all SCA types with documented intranuclear inclusions, their anatomical location and abundance do not fully correlate with other neuropathological observations. Most authors agree that their formation is not a prerequisite for nerve cell atrophy, though the mechanism of their formation may provide further insight into the pathogenesis of SCA. The appearance of inclusions is thought to occur in a complex process of protein misfolding, aggregation, and defective proteolysis in proteasomes (Chai et al., 1999; Cummings et al., 1999). Other proteins are likely participants in this pathological mechanism, and it is not surprising that aggregation of the mutated protein may cause loss of some epitopes that would otherwise be detectable by monoclonal antibodies. The confocal microscope has contributed considerable insight into the

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Fig. 25.13 Inclusion bodies in spinocerebellar ataxia type 3/Machado–Joseph disease. (A)–(C) Neuronal intranuclear inclusion bodies in the basis pontis (arrows in A and B) were visualized by immunocytochemistry with polyclonal anti-ataxin-3 (Paulson et al., 1997b). In (C), the darkly stained intranuclear inclusion is distinct from the adjacent nucleolus. (D) A neuronal intranuclear inclusion body (arrow) was detected by monoclonal anti-ubiquitin. (E) Punctate reaction product with anti-ataxin-3 occurs in a Purkinje cell. Tissue sections were processed by positive-contrast immunocytochemistry and counterstained with hematoxylin. Laser confocal immunofluorescence with anti-ataxin-3 (F and G) and with anti-ubiquitin (H). The inclusions show bright fluorescence and occasionally occur in pairs (arrows). (G) and (H) represent the same neuron to show the colocalization of ataxin-3 (G) and ubiquitin (H). In (F)–(H), the gray areas represent lipofuscin, whose yellow and red autofluorescence was attenuated by computer-assisted image analysis. (B) and (C), Nomarski optics; (F)–(H), computer-assisted differential interference contrast. Magnification markers: (A)–(D), 50 m; (E), 100 m; (F)–(H), 25 m.

Neuropathology of the inherited ataxias

pathogenesis of the inclusions, because it allows the visualization of two or more fluorophores attached to tissuebound antigens, such as the listed ataxins, ubiquitin, and the proteins of the nuclear matrix and proteasomes (Matilla et al., 1997; Paulson et al., 1997b; Skinner et al., 1997; Cummings et al., 1998; Holmberg et al., 1998; Chai et al., 1999; Koyano et al., 1999).

The neuropathological ‘severity’ of hereditary ataxia In SCA1, SCA2, SCA6, and SCA7, the ‘idiodendritic’ Purkinje cells may have been studied with greater intensity because of their visual appeal, whereas other cells in the cerebellar cortex, such as the stellate and basket neurons, granular cells, and Golgi neurons, were largely ignored. A relationship of Purkinje cell atrophy to onset, severity, and progression of ataxia has not been firmly established. In toxic lesions of the cerebellar cortex, such as caused by alcoholism or mercury exposure, removal of the toxin allows substantial clinical improvement, whereas destruction of the dentate nucleus causes more persistent ataxia. Neuronal loss in the inferior olivary nuclei has often been viewed as the pari passu result of Purkinje cell atrophy irrespective of etiology. The assumed shared process was the loss of targets for climbing fibers. However, retrograde atrophy of olivary neurons is not invariable. In experimental animals with selective ablation of Purkinje cells, climbing fibers have substantial ability to find new targets (see review in Strata and Rossi, 1998). The preservation of the inferior olivary neurons in SCA6, as shown by their afferent synapses (see Fig. 25.12B), may represent the human equivalent to climbing fiber plasticity in experimental animals (Strata and Rossi, 1998). The author has studied the afferent connections to the inferior olivary nucleus in hereditary ataxia and normal controls (Koeppen et al., 1999). It is a remarkable observation that the loss of inferior olivary neurons causes total loss of SNAP-25 reactive terminals. This observation is much in contrast to the preservation of synapses in the molecular layer of the cerebellar cortex despite subtotal loss of Purkinje cells. It may be justified to compare Purkinje cell and olivary lesions in their ability to generate ‘ataxia.’ The neurons of the inferior olivary nucleus have a dense spherical dendritic arbor (see Fig. 25.8F) and a complex microcircuitry that rivals that of Purkinje cells (see review in De Zeeuw et al., 1998). Olivary function may be viewed in several ways (De Zeeuw et al., 1998), though a role as a sentinel of motor control appears most attractive. It may be proposed that the great clinical severity of SCA2 is due to total or subtotal

loss of inferior olivary neurons rather than Purkinje cell depletion. In contrast, the milder ataxia in SCA6 may reflect the relative preservation of the inferior olivary nucleus. The propensity of lesions in the dentate nucleus to cause ataxia is quite variable. Synaptic terminals in the neuropil of the dentate nucleus are often better preserved than would be expected from the subtotal loss of Purkinje cells (Koeppen et al., 1999). It may be proposed that, in humans, the dentate nuclei receive extracerebellar afferents or that sprouting from adjacent surviving axons takes place. Acquired lesions of the dentate nucleus are associated with a spectrum of clinical manifestations ranging from mild dysmetria to action myoclonus. However, the severe dentate lesion in SCA3/Machado–Joseph disease does not translate into the expected flinging dysmetria. It is obvious that mitigating factors are present, and the grumose degeneration may constitute an elusive afferent fiber ‘plasticity.’ The role of the pontine gray matter in the generation of ataxia is similarly uncertain, though patients with ‘spinopontine atrophy’ are ataxic. It may be argued that lesions of the inferior olivary nuclei, the dentate nuclei, and the basis pontis by themselves cause ataxia, and that their combination in the same patient is associated with more severe clinical manifestations. Spinocerebellar ataxia type 2 lends support to this concept. The severe spinal lesion in Friedreich’s ataxia clearly explains the gross ataxia of the affected patient that reminded early observers of tabes dorsalis (e.g., Mott, 1907; Spiller, 1910; Lambrior, 1911). However, it is likely that the lesion of the dentate in Friedreich’s ataxia also contributes to ataxia. Though dentate lesions were described by early observers (see review in Greenfield, 1954), little attention was paid to this cerebellar nucleus as a symptom maker until 1957 (Urich et al., 1957). The reason for the apparent omission may again be the visual appeal that prominent lesions have, at the expense of a more precise pathophysiological interpretation. The dentate nucleus gives rise to dentato-olivary fibers that travel through the superior cerebellar peduncles and the central tegmental tracts to reach the contralateral inferior olivary nuclei. Destructive lesions of the dentate nucleus and the pontine tegmentum often give rise to olivary hypertrophy (Foix et al., 1926), with or without the clinical phenomenon of palatal myoclonus. It is a general requirement that the cerebellar cortex remain intact for this unique olivary lesion to occur. In a systematic study of progressive supranuclear palsy, dentatorubropallidoluysian atrophy, and SCA3/Machado–Joseph disease, Hanihara et al. (1998) observed olivary hypertrophy in five

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of 11 cases of progressive supranuclear palsy and one of six cases of dentatorubropallidoluysian atrophy. It did not occur in SCA3/Machado–Joseph disease. This exemption in SCA3/Machado–Joseph disease and the lack of olivary hypertrophy in Friedreich’s ataxia point to differential effects of neuronal loss in the dentate nucleus, and it is likely that this gray matter structure plays a much more complex role in the generation of ataxia than simple allor-none functional loss.

Correlation of neuropathology, mutation, and length of repeats Longer GAA or CAG repeats generally cause earlier onset and a more severe clinical phenotype in Friedreich’s ataxia and the dominant ataxias, respectively. However, it is uncertain how ‘onset’ or ‘severity’ can be measured in neuropathological terms. The variation in survival time complicates attempts to grade the severity of the disease from post-mortem tissues. Nevertheless, the lengths of the repeats have become known in numerous cases, and the task is to correlate it with morphometric parameters. The cross-sectional area of the spinal cord in Friedreich’s ataxia is smaller with longer GAA expansions (Koeppen, 1998), but the measurements are insufficient to plot a regression curve or extrapolate to the ‘normal’ state. ‘Onset’ of the disorder in neuropathological terms may occur prenatally and differs greatly from the time of the first clinical abnormality. In this context, it is of interest that homozygous offspring of Friedreich’s ataxia transgenic mice die in utero (Cossée et al., 2000). Olivopontocerebellar atrophy in SCA2 was more severe in a patient who died at 18 years (22 and 58 CAG trinucleotide repeats) than in his father (death at 42 years; 22 and 41 repeats) (Koeppen, 1998). This observation was based on macroscopic examination, and it remained uncertain which of the characteristic histopathological lesions should be studied by quantitative morphometry. In a systematic study of synapses in Friedreich’s ataxia and several types of dominant ataxia, the author and his collaborators examined SNAP-25 reaction product (revealing presynaptic membranes) as a function of age at onset, age at death, and disease duration (Koeppen et al., 1999). Relative quantitation of the reaction product by confocal immunofluorescence showed better synaptic retention in the dentate nucleus of long-surviving Friedreich’s ataxia patients, and in the inferior olivary nucleus of patients with protracted illness in the course of the dominant ataxias. Beyond knowledge of trinucleotide length, measurements of putative toxic gain of function and abnormal

function of mutated or deficient proteins will be needed in clinico-anatomic correlation. The physiological roles of the normal non-mutated proteins in SCA1, SCA2, SCA3/Machado–Joseph disease, and SCA7 have not yet been clarified. In two forms of hereditary ataxia, a better understanding of the pathogenesis seems at hand. Evidence is compelling that frataxin deficiency in Friedreich’s ataxia is related to iron dysmetabolism. In SCA6, functional impairment and neuronal death are probably related to impairment of calcium channels.

Acknowledgments This work was supported by generous donations of the Edith C. Brennan and Luís León families, and by the Department of Veterans Affairs. Dr Henry L. Paulson made available polyclonal anti-ataxin-3. The author expresses his appreciation to Mr Andrew C. Dickson for his expert technical assistance.

xReferencesx Arai, N. (1989). ‘Grumose degeneration’ of the dentate nucleus. A light and electron microscopic study in progressive supranuclear palsy and dentatorubropallidoluysian atrophy. J Neurol Sci 90: 131–45. Babcock, M., de Silva, D., Oaks R. et al. (1997). Regulation of mitochondrial iron accumulation of Yfh1p, a putative homolog of frataxin. Science 276: 1709–12. Becker, P.E., Sabuncu, N. and Hopf, H.C. (1971). Dominant erblicher Typ von ‘cerebellarer Ataxie’. Z Neurol 199: 116–39. Bürk, K., Fetter, M., Abele, M. et al. (1999). Autosomal dominant cerebellar ataxia type I: oculomotor abnormalities in families with SCA1, SCA2, and SCA3. J Neurol 246: 789–97. Campuzano, V., Montermini, L., Lutz, Y. et al. (1997). Frataxin is reduced in Friedreich ataxia patients and is associated with mitochondrial membranes. Hum Mol Genet 6: 1771–80. Carpenter, S. and Schumacher, G.A. (1996). Familial infantile cerebellar atrophy associated with retinal degeneration. Arch Neurol 14: 82–94. Caruso, G., Santoro, L., Perretti, A. et al. (1983). Friedreich’s ataxia: electrophysiological and histological findings. Acta Neurol Scand 67: 26–40. Chai, Y., Koppenhafer, S.L., Shoesmith, S.J., Perez, M.K. and Paulson, H.L. (1999). Evidence for proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro. Hum Mol Genet 8: 673–82. Cossée, M., Dürr, A., Schmitt, M. et al. (1999). Friedreich’s ataxia: point mutations and clinical presentation of compound heterozygotes. Ann Neurol 45: 200–6.

Neuropathology of the inherited ataxias

Cossée, M., Puccio, H., Gansmuller, A., et al. (2000). Inactivation of the Friedreich ataxia mouse gene leads to early embryonic lethality without iron accumulation. Hum Mol Genet 9: 1219–26. Coutinho, P., Guimarães, A., Melo Peres M. and Scaravilli, F. (1986). The peripheral neuropathy in Machado–Joseph disease. Acta Neuropathol (Berl) 71: 119–24. Coutinho, P., Guimarães, A. and Scaravilli, F. (1982). The pathology of Machado–Joseph disease. Acta Neuropathol (Berl) 58: 48–54. Cummings, C.J., Mancini, M.A, Antalffy, B., DeFranco, D.B. and Orr, H.T. and Zoghbi, H.Y. (1998). Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1. Nature Genet 19: 148–54. Cummings, C.J., Orr, H.T. and Zoghbi, H.Y. (1999). Progress in pathogenesis studies of spinocerebellar ataxia type 1. Philos Trans R Soc Lond B 354: 1079–81. David, G., Abbas, N., Stevanin, G. et al. (1997). Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nature Genet 17: 65–70. Davies, S.W., Turmaine, M., Cozens, B.A. et al. (1997). Formation of neuronal intranuclear inclusions underlies the neurological dysfunction in mice transgenic for the HD mutation. Cell 90: 537–48. De Michele, G., Filla, A., Cavalcanti, F. et al. (2000). Atypical Friedreich ataxia phenotype associated with a novel missense mutation in the X25 gene. Neurology 54: 496–9. De Michele, G., Filla, A., Crisuolo, B. et al. (1998). Determinants of onset age in Friedreich’s ataxia. J Neurol 245: 166–8. De Zeeuw, C.I., Simpson, J.I., Hoogenraad, C.C., Galjart, N., Koekkoek, S.K.E. and Ruigrok, T.J.H. (1998). Microcircuitry and function of the inferior olive. Trends Neurosci 21: 391–400. DiFiglia, M., Sapp, E., Chase, K.O. et al. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science 277: 1990–3. Dürr, A., Cossée, M., Agid, Y. et al. (1996). Clinical and genetic abnormalities in patients with Friedreich’s ataxia. N Engl J Med 335: 1169–75. Dyck, P.J. (1993). Neuronal atrophy and degeneration predominantly affecting peripheral sensory and autonomic neurons. In Peripheral Neuropathy, 3rd edn., ed. P.J. Dyck, P.K. Thomas, J.W. Griffin, P.A. Low and J.F. Poduslo, pp. 1065–93. Philadelphia: W.B. Saunders. Eto, K., Sumi, S.M., Bird, T.D., McEvoy-Bush, T., Boehnke, M. and Schellenberg, G. (1990). Family with dominantly inherited ataxia, amyotrophy, and peripheral sensory loss. Spinopontine atrophy or Machado–Azorean disease in another nonPortuguese family? Arch Neurol 47: 968–74. Foix, C., Chavany, J.-A. and Hillemand, P. (1926). Le syndrome myoclonique de la calotte: étude anatomo-clinique du nystagmus du voile et des myoclonies rythmiques associées, oculaires, faciales, etc. Rev Neurol 45: 942–56. Foury, F. and Cazzalini, O. (1997). Deletion of the yeast homologue of the human gene associated with Friedreich’s ataxia elicits iron accumulation in mitochondria. FEBS Lett 411: 373–7. Friedreich, N. (1863a). Ueber degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat Physiol Klin Med 26: 391–419.

Friedreich, N. (1863b). Ueber degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat Physiol Klin Med 26: 433–59. Friedreich, N. (1863c). Ueber degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat Physiol Klin Med 27: 1–26. Friedreich, N. (1876). Ueber Ataxie mit besonderer Berücksichtigung der hereditären Formen. Virchows Archiv Pathol Anat Physiol Klin Med 68: 145–245. Friedreich, N. (1877). Ueber Ataxie mit besonderer Berücksichtigung der hereditären Formen. Nachtrag. Virchows Arch Pathol Anat Physiol Klin Med 70: 140–52. Gellera, C., Pareyson, D., Castelloti, B. et al. (1997). Very late onset Friedreich’s ataxia without cardiomyopathy is associated with limited GAA expansion in the X25 gene. Neurology 49: 1153–5. Gomez, C.M., Thompson, R.M., Gammack, J.T. et al. (1997). Spinocerebellar ataxia type 6: gaze-evoked and vertical nystagmus, Purkinje cell degeneration, and variable age of onset. Ann Neurol 42: 933–50. Goto, S. and Hirano, A. (1990). Immunohistochemical evidence for the selective involvement of dorsal root fibres in Friedreich’s ataxia. Neuropathol Appl Neurobiol 16: 365–70. Gouw, L.G., Digre, K.B., Harris, C.P., Haines, J.H. and Ptacek, L.J. (1994). Autosomal dominant cerebellar ataxia with retinal degeneration. Clinical, neuropathological, and gene analysis of a large kindred. Neurology 44: 1441–7. Greenfield, J.G. (1954). The Spino-cerebellar Degenerations. Blackwell: Oxford. Haberhausen, G., Damian, M.S., Leweke, F. and Müller, U. (1995). Spinocerebellar ataxia, type 3 (SCA3) is genetically identical to Machado–Joseph disease (MJD). J Neurol Sci 132: 71–5. Hanihara, T., Amano, N., Takahashi, T., Itoh, Y. and Yagishita, S. (1998). Hypertrophy of the inferior olivary nucleus with progressive supranuclear palsy. Eur Neurol 39: 97–102. Holmberg, M., Duyckaerts, C., Dürr, A. et al. (1998). Spinocerebellar ataxia type 7 (SCA-7). A neurodegenerative disorder with neuronal intranuclear inclusions. Hum Mol Genet 7: 913–18. Hughes, J.T., Brownell, B. and Hewer, R.L. (1968). The peripheral sensory pathway in Friedreich’s ataxia. Brain 91: 803–18. Huynh, D.P., Del Bigio, M.R., Ho, D.H. and Pulst, S.-M. (1999). Expression of ataxin-2 in brains from normal individuals and patients with Alzheimer’s disease and spinocerebellar ataxia 2. Ann Neurol 45: 232–41. Jampel, R.S., Okazaki, H. and Bernstein, H. (1961). Ophthalmoplegia and retinal degeneration associated with spinocerebellar ataxia. Arch Ophthalmol 66: 247–59. Jitpimolmard, S., Small, J., King, R.H.M. et al. (1993). The sensory neuropathy of Friedreich’s ataxia: an autopsy study of a case with prolonged survival. Acta Neuropathol (Berl) 86: 29–35. Kanda, T., Isozaki, E., Kato, S., Tanabe, H. and Oda, M. (1989). Type III Machado–Joseph disease in a Japanese family: a clinicopathological study with special reference to the peripheral nervous system. Clin Neuropathol 8: 134–41. Kinoshita, A., Hayashi, M., Oda, M. and Tanabe, H. (1995).

403

404

A.H. Koeppen

Clinicopathological study of the peripheral nervous system in Machado–Joseph disease. J Neurol Sci 130: 48–58. Koeppen, A.H. (1991). The Purkinje cell and its afferents in human hereditary ataxia. J Neuropathol Exp Neurol 50: 505–14. Koeppen, A.H. (1998). The hereditary ataxias. J Neuropathol Exp Neurol 57: 531–43. Koeppen, A.H., Dickson, A.C., Lamarche, J.B. and Robitaille, Y. (1999). Synapses in the hereditary ataxias. J Neuropathol Exp Neurol 58: 748–64. Koeppen, A.H. and Hans, M.B. (1976). Supranuclear ophthalmoplegia in olivopontocerebellar degeneration. Neurology 26: 764–8. Koeppen, A.H., Mitzen, E.J., Hans, M.B. and Barron, K.D. (1986). Olivopontocerebellar atrophy: Immunocytochemical and Golgi observations. Neurology 36: 1478–88. Koutnikova, H., Campuzano, V., Foury, F., Dollé, P., Cazzalini, O. and Koenig, M. (1997). Studies of human, mouse and yeast homologues indicate a mitochondrial function for frataxin. Nature Genet 16: 345–51. Koyano, S., Uchihara, T., Fujigasaki, H., Nakamura, A., Yagishita, S. and Iwabuchi K. (1999). Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triple-labeling immunofluorescent study. Neurosci Lett 273: 117–20. Lamarche, J., Luneau, C. and Lemieux, B. (1982). Ultrastructural observations on spinal ganglion biopsy in Friedreich’s ataxia. Can J Neurol Sci 9: 137–9. Lamarche, J.B., Côté, M. and Lemieux, B. (1980). The cardiomyopathy of Friedreich’s ataxia. Morphological observations in 3 cases. Can J Neurol Sci 7: 389–96. Lamarche, J.B., Shapcott, D., Côté, M. and Lemieux, B. (1993). Cardiac iron deposits in Friedreich’s ataxia. In Handbook of Cerebellar Diseases, ed. R. Lechtenberg, pp. 453–7. New York: Marcel Dekker. Lambrior, A.A. (1911). Un cas de maladie de Friedreich avec autopsie. Rev Neurol 21: 525–40. Larnaout, A., Belal, S., Zouari, M. et al. (1997). Friedreich’s ataxia with isolated vitamin E deficiency: a neuropathological study of a Tunisian patient. Acta Neuropathol (Berl) 93: 633–7. Maas, O. and Scherer, H.-J. (1933). Zur Klinik und Anatomie einiger seltener Kleinhirnerkrankungen. Z Ges. Neurol Psychiat 145: 420–44. Mascalchi, M., Salvi, F., Piacentini, S. and Bartolozzi, C. (1994). Friedreich’s ataxia: MR findings involving the cervical portion of the spinal cord. Am J Roentgenol 163: 187–91. Matilla, A., Koshy, B.T., Cummings, C.J., Isobe, T., Orr, H.T. and Zoghbi, H.Y. (1997). The cerebellar leucine-rich acidic nuclear protein interacts with ataxin-1. Nature 389: 974–8. McLeod, J.G. (1971). An electrophysiological and pathological study of peripheral nerves in Friedreich’s ataxia. J Neurol Sci 12: 333–49. Menzel, P. (1891). Beitrag zur Kenntnis der hereditären Ataxie und Kleinhirnatrophie. Arch Psychiat Nervenkrankh 222: 160–90. Midroni, G. and Bilbao, J.M. (1995). Biopsy Diagnosis of Peripheral Neuropathy. Boston: Butterworth–Heinemann. Mott, F.W. (1907). Case of Friedreich’s disease, with autopsy and

systematic microscopical examination of the nervous system. Arch Neurol Psychiatry 3: 180–200. Nguyen-Legros, J., Bizot, J., Bolesse, M. amd Pulicani, J.-P. (1980). Noir de diaminobenzidine: une nouvelle méthode histochimique de révélation du fer exogène. Histochemistry 66: 239–44. Oppenheimer, D.R. (1979). Brain lesions in Friedreich’s ataxia. Can J Neurol Sci 6: 173–6. Ouvrier, R.A., McLeod, J.G. and Conchin, T.E. (1982). Friedreich’s ataxia. Early detection and progression of peripheral nerve abnormalities. J Neurol Sci 55: 137–45. Papp, M.I., Kahn, J.E. and Lantos, P.L. (1989). Glial cytoplasmic inclusions in the CNS of patients with multiple system atrophy (striatonigral degeneration, olivopontocerebellar atrophy and Shy–Drager syndrome). J Neurol Sci 94: 79–100. Paulson, H.L., Das, S.S., Crino, P.B. et al. (1997a). Machado–Joseph disease gene product is a cytoplasmic protein widely expressed in brain. Ann Neurol 41: 453–62. Paulson, H.L., Perez, M.K., Trottier, Y. et al. (1997b). Intranuclear inclusions of expanded polyglutamine protein in spinocerebellar ataxia type 3. Neuron 19: 333–44. Perls, M. (1867). Nachweis von Eisenoxyd in gewissen Pigmenten. Virchows Arch Pathol Anat Physiol Klin Med 39: 42–8. Priller, J., Scherzer, C.R., Faber, P.W., MacDonald, M.E. and Young, A.B. (1997). Frataxin gene of Friedreich’s ataxia is targeted to mitochondria. Ann Neurol 42: 265–9. Rizzuto, N., Monaco, S., Moretto, G. et al. (1981). Friedreich’s ataxia. A light- and electron microscopic study of peripheral nerve biopsies. Acta Neuropathol (Berl) 7(Suppl.): 344–7. Robitaille,Y., Schut, L. and Kish, S.J. (1995). Structural and immunocytochemical features of olivopontocerebellar atrophy caused by the spinocerebellar ataxia type 1 (SCA-1) mutation define a unique phenotype. Acta Neuropathol (Berlin) 90: 572–81. Rötig, A., de Lonlay, P., Chretien, D. et al. (1997). Aconitase and mitochondrial iron–sulphur protein deficiency in Friedreich ataxia. Nature Genet 17: 215–17. Said, G., Marion, M.-H., Selva, J. and Jamet, C. (1986). Hypotrophic and dying-back nerve fibers in Friedreich’s ataxia. Neurology 36: 1292–9. Sakai, T., Ohta, M. and Ishino, H. (1983). Joseph disease in a nonPortuguese family. Neurology 33: 74–80. Santoro, L., Perretti, A., Crisci, R. et al. (1990). Electrophysiological and histological follow-up in 15 Friedreich’s ataxia patients. Muscle Nerve 13: 536–40. Sapp, E., Schwarz, C., Chase, K. et al. (1997). Huntingtin localization in brains of normal and Huntington’s disease patients. Ann Neurol 42: 604–12. Schmidt, T., Landwehrmeyer, B., Schmitt, I. et al. (1998). An isoform of ataxin-3 accumulates in the nucleus of neuronal cells in affected brain regions of SCA3 patients. Brain Pathol 8: 669–79. Servadio, A., Koshy, B., Armstrong, D., Antalffy, B., Orr, H.T. and Zoghbi, H.Y. (1995). Expression analysis of the ataxin-1 protein in tissues from normal and spinocerebellar ataxia type 1 individuals. Nature Genet 10: 94–8.

Neuropathology of the inherited ataxias

Shiurba, R.A., Eng, L.F., Sternberger, N.H., Sternberger, L.A. and Urich, H. (1987). The cytoskeleton of the human cerebellar cortex: an immunohistochemical study of normal and pathological material. Brain Res 407: 205–11. Skinner, P.J., Koshy, B., Cummings, C.J. et al. (1997). Ataxin-1 with expanded glutamine tracts alters nuclear matrix-associated structures. Nature 389: 971–7. Smeyers, P., Monrós, E., Vílchez, J., Lopez-Arlandis, J., Prieto, F. and Palau. F. (1996). A family segregating a Friedreich ataxia phenotype that is not linked to the FRDA locus. Hum Genet 97: 824–8. Spiller, W.G. (1910). Friedreich’s ataxia. J Nerv Ment Dis 37: 411–35. Stevanin, G., Cancel, G., Dürr, A. et al. (1995). The gene for spinal cerebellar ataxia 3 (SCA3) is located in a region of 3 cM on chromosome 14q24.3–q32.2. Am J Hum Genet 56: 193–201. Strata, G. and Rossi, F. (1998). Plasticity in the olivocerebellar pathway. Trends Neurosci 21: 407–13. Subramony, S.H., Fratkin, J.D., Manyam, B.V. and Currier, R.D. (1996). Dominantly inherited cerebello-olivary atrophy is not due to a mutation at the spinocerebellar ataxia-I, Machado– Joseph, or dentato-rubro-pallido-luysian atrophy locus. Mov Disord 11: 174–80. Takahashi, H., Ikeuchi, T., Honma, Y., Hayashi, S. and Tsuji, S. (1998). Autosomal dominant cerebellar ataxia (SCA-6): clinical, genetic and neuropathological study in a family. Acta Neuropathol (Berl) 95: 333–7. Trottier, Y., Lutz, Y., Stevanin, G. et al. (1995). Polyglutamine expansion as a pathological epitope in Huntington’s disease and four dominant cerebellar ataxias. Nature 378: 403–5. Twist, E., Casaubon, L.K., Ruttledge, M.H. et al. (1995). Machado– Joseph disease maps to the same region of chromosome 14 as spinocerebellar ataxia type 3 locus. J Med Genet 32: 25–31. Urich, H., Norman, R.M. and Lloyd, O.C. (1957). Suprasegmental lesions in Friedreich’s ataxia. Confin Neurol 17: 360–71.

Vassilopoulos, D., Spengos, M. and Scarpalezos, S. (1977). Étude radiologique de la colonne vertébrale cervicale dans certaines maladies dégéneratives neurologiques. J Radiol Electrol 58: 183–6. Wadia, N.H. and Swami, R.K. (1971). A new form of heredo-familial spinocerebellar degeneration with slow eye movements (nine families). Brain 94: 359–74. Waldvogel, D., van Gelderen, P and, Hallett, M. (1999). Increased iron in the dentate nucleus of patients with Friedreich’s ataxia. Ann Neurol 46: 123–5. Weiner, L.P., Konigsmark, B.W., Stoll, J. and Magladery, J.W. (1967). Hereditary olivopontocerebellar atrophy with retinal degeneration. Arch Neurol 16: 364–76. Wessel, K., Schroth, G., Diener, H.C., Muller-Forell, W. and Dichgans, J. (1989). Significance of MRI-confirmed atrophy of the cranial spinal cord in Friedreich’s ataxia. Eur Arch Psychiatry Neurol Sci 238: 225–30. Wilson, R.B. and Roof, D.M. (1997). Respiratory deficiency due to loss of mitochondrial DNA in yeast lacking the frataxin homologue. Nature Genet 6: 352–7. Woods, B.T. and Schaumburg, H.H. (1972). Nigro-spino-dentatal degeneration with nuclear ophthalmoplegia. A unique and partially treatable clinico-pathological entity. J Neurol Sci 17: 149–66. Yuasa, T., Ohama, E., Harayama, H. et al. (1986). Joseph’s disease: clinical and pathological studies in a Japanese family. Ann Neurol 19: 152–7. Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the 1A-voltage-dependent calcium channel. Nature Genet 15: 62–9. Zoghbi, H.Y. (1997). CAG repeats in SCA6. Anticipating new clues. Neurology 49: 1196–9.

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Part VIII

Dominantly Inherited Progressive Ataxias

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Spinocerebellar ataxia type 1 Xi Lin1, Harry T. Orr2, and Huda Y. Zoghbi1 1

Departments of Pediatrics, Neurology, Neuroscience, and Molecular and Human Genetics, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, USA 2 Institute of Human Genetics, University of Minnesota, Minneapolis, USA

Introduction Spinocerebellar ataxia type 1 (SCA1) is one of a complex group of autosomal dominant ataxias, which were first recognized as distinct from the recessive Friedreich’s ataxia in 1893 by Marie. The clinicopathological presentations of these ataxias are extremely heterogeneous, with variable degrees of neurodegeneration in the cerebellum, spinal tracts, and brainstem. Thus, the classification of SCAs remained difficult and controversial until the 1990s, when the identification of distinct genes for several dominant ataxias allowed unequivocal genetic, if not clinical, differentiation (Orr and Zoghbi, 1996). SCA1 was one of the first neurogenetic diseases to be mapped to an autosome using classical linkage studies (Yakura et al., 1974; Jackson et al., 1977). The cloning of the SCA1 gene, the elucidation of a dynamic CAG trinucleotide repeat expansion as the mutational mechanism, and the establishment of cellular and animal models for this disorder have greatly advanced our understanding of the molecular and cellular mechanisms underlying SCA1 pathogenesis. These studies will undoubtedly provide the basis for developing effective therapeutics.

Clinical features SCA1 usually strikes during the third or fourth decade of life, typically progressing over 10 to 15 years. In SCA1 families, the affected individuals in successive generations tend to have an earlier onset and more severe manifestations of the disease, a phenomenom referred to as anticipitation. Early onset in the first decade has been documented in such families (Schut, 1950; Zoghbi et al., 1988). The most salient clinical features of SCA1 include ataxia, dysarthria, and bulbar palsies. Other neurological

abnormalities, such as extrapyramidal signs and peripheral neuropathy, often show extensive interfamilial and intrafamilial variability (Subramony and Vig, 1998; Zoghbi and Orr, 2000). The initial symptoms include slight gait and limb incoordination, which manifest only occasionally when stepping downstairs or turning abruptly. Upon physical examination, patients demonstrate impaired finger-tonose and heel-to-shin movements, indicating cerebellar dysfunction. Another early indication of SCA1 is slurred speech, which gradually evolves to the scanning and explosive speech typical of ataxia (dysarthria). As the disease progresses, hyperreflexia may be detected, the ataxia worsens, and other cerebellar signs such as dysmetria, dysdiadochokinesia, hypotonia, and the rebound phenomenon become apparent. Cerebellar problems are often accompanied by signs of bulbar dysfunction. Early in the disease, mild dysphagia characterized by coughing or choking may occur after eating and drinking. In the final stage of the disease, bulbar palsy sets in, with facial weakness, tongue atrophy and fasciculations, severe dysarthria, and dysphagia. Frequent choking spells occur as the patient loses the ability to cough effectively. This impairment often leads to pneumonia and respiratory failure, the most common cause of death. Oculomotor difficulties are frequent and can present as hypermetric saccades and nystagmus in the early stages. A number of other oculomotor signs, such as eyelid retraction, enlarged pupils, blepharospasm, impairment of the vestibulo-ocular reflex, and optokinetic nystagmus, can occur late in the disease (Sasaki et al., 1996). Other neurological signs are more variable. Extrapyramidal signs, including dystonic posturing and choreiform or athetoid movements, have been observed in the later stages of the disease. Signs of peripheral polyneuropathy

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may develop in some patients, with loss of proprioception or vibration sense and disappearance of deep tendon reflex. Amyotrophy and muscle fasciculation may be secondary to the peripheral neuropathy. Mild impairment of cognition, such as inappropriate laughing, emotional lability, decreased attention, and memory loss, has been documented in some SCA1 patients (Zoghbi et al., 1988; Dubourg et al., 1995; Schols et al., 1995). Other abnormalities, such as optic nerve atrophy, ophthalmoparesis, sphincter disturbances, and urinary urgency, have also been reported. Neuroimaging, neurophysiological and neuropathological studies have been carried out on patients with molecularly proven SCA1 diagnosis. Both computerized tomography and magnetic resonance imaging reveal pontocerebellar atrophy and enlargement of the fourth ventricle. Positron emission tomography shows reduced glucose metabolism in the cerebellar cortex, brain stem nuclei, and, surprisingly, other brain areas that are not typically affected in SCA1, such as the cerebral cortex, basal ganglia, and thalamus (Gilman et al., 1996). Some SCA1 patients have been reported to have abnormal motor nerve conduction and reduced amplitude of sensory response as measured by the brain stem, visual and somatosensory evoked potentials (Schols et al., 1995; Perretti et al., 1996). Pathologically, atrophy of the cerebellum and brainstem is consistently observed. There is severe loss of Purkinje cells, dentate nucleus neurons, and neurons in the inferior olive and cranial nerve nuclei III, IV, IX, X, and XII. Eosinophilic spheres, also known as torpedoes, are present in the internal granule cell layer and represent proximal axonal swelling of Purkinje cells. There is also mild neuronal loss in components of the extrapyramidal system, including the substantia nigra, subthalamic nuclei, caudate, and putamen. The dorsal and ventral spinocerebellar tracts and dorsal columns are demyelinated; gliosis of the molecular layer of the cerebellum is marked, whereas gliosis of the anterior horn of the spinal cord is milder (Currier et al., 1972; Nino et al., 1980; Bebin et al., 1990; Spadaro et al., 1992; Servadio et al., 1995).

The SCA1 gene The first clue to the locus of a gene for a dominantly inherited ataxia came from a report in 1974 by Yakura and colleagues, who suggested the linkage to the human leukocyte antigen (HLA) complex on the short arm of chromosome 6 based on the studies of a very small kindred (Yakura et al., 1974). This map location was subsequently established by Jackson et al. and confirmed by several independent

studies (Jackson et al., 1977; Rich et al., 1987; Zoghbi et al., 1988). Hence this locus was designated as spinocerebellar ataxia type 1 (SCA1). The mapping of the SCA1 locus was later refined based on genotyping of several kindreds using polymorphic DNA markers from 6p22–p23 (Ranum et al., 1991; Zoghbi et al., 1991; Kwiatkowski et al., 1993). Key recombination events further narrowed the mapping location of the SCA1 gene between DNA marker D6S89 and D6S274, which are estimated to be 1.2 Mb apart (Banfi et al., 1993). Because trinucleotide expansion had been elucidated as the molecular mechanism of anticipation in fragile X syndrome, myotonic dystrophy, and Huntington disease, a directed search for a trinucleotide repeat was carried out in the SCA1 candidate region. Specific hybridization was indeed discovered by using a CAG-containing oligonucleotide probe with cosmids from the region. This led to the identification of a CAG trinucleotide repeat, which is expanded in affected individuals (Orr et al., 1993). Polymerase chain reaction (PCR) primers flanking this repeat-containing region were therefore designed to characterize the length of the repeat and explore the genotype–phenotype correlation in SCA1 patients. The number of CAG repeats in SCA1 is highly polymorphic in the general population, ranging from six to 44. SCA1 patients typically have expansions between 39 and 82 repeats (Jodice et al., 1994; Ranum et al., 1994; Quan et al., 1995; Goldfarb et al., 1996). Normal alleles with 21 or more CAG repeats are interrupted with one to four CAT repeat units encoding histidine; in contrast, SCA1 alleles contain only uninterrupted CAG repeat tracts (Chung et al., 1993; Jodice et al., 1994; Chong et al., 1995; Quan et al., 1995). Importantly, there is a direct relationship between the length of repeat and the age of onset and the severity of disease: the longer the repeat length, the earlier the onset and the more severe the disease. Whereas normal alleles are stable during transmission, the dynamic nature of the mutation is revealed by the intergenerational instability of CAG repeat sizes in the expanded range. Both contraction and expansion of repeat size have been observed. A significant bias for expansion occurs in paternal transmission, which corroborates the higher mosaicism of repeat length observed in sperms (Chung et al., 1993; Jodice et al., 1994; Chong et al., 1995). These observations provide a genetic explanation for anticipitation, a salient feature of SCA1 that is more frequent upon paternal transmission. Thus, the earlier age of onset and the more severe clinical phenotypes in later generations result from larger repeat expansions. The CAG repeat in the SCA1 gene is located in the coding region and encodes a polyglutamine tract. The gene has nine exons transcribing a mRNA of 10 660 nucleotides (Banfi et al., 1994). Most of these exons contain

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untranslated sequences, including a 7277 bp 3 untranslated region (UTR) in exon 9, one of the longest 3 UTRs reported so far. The 5 UTR spreads over the first seven exons. The coding region, which spans 2448 bp, is in exons 8 and 9. Both SCA1 mRNA and protein, ataxin-1, are ubiquitously expressed. Ataxin-1 is a novel protein that shares no homology with other proteins. Wild-type ataxin-1 is predicted to encode 792–830 amino acids, the exact number of which is determined by the polymorphic CAG repeat size. The mutant protein with an expanded polyglutamine tract is translated in SCA1 patient tissues and accordingly has slow electrophoretic mobility (Servadio et al., 1995). Both normal and mutant ataxin-1 are localized to neuronal nuclei; in Purkinje cells and brainstem nuclei, the primary sites of SCA1 pathology, ataxin-1 is also present in the cytoplasm, albeit to a lesser extent. Immunoblot and immunohistochemical analyses using antibodies raised to different regions of ataxin-1 revealed that the level of the protein in the central nervous system is two to four times that found in peripheral tissues (Koshy et al., 1998). In peripheral tissues, ataxin-1 is predominantly localized to the cytoplasm (Servadio et al., 1995). The murine homolog of the SCA1 gene shares a similar genomic structure. The protein is highly homologous to the human protein (89% identity) and has a similar pattern of expression; a notable difference in the mouse is the presence of two glutamines and three prolines in place of the long glutamine repeat (Banfi et al., 1996).

Studies in SCA1 pathogenesis The identification of the SCA1 gene and the elucidation of the pathogenetic mutation opened the door for subsequent studies aimed at understanding SCA1 pathogenesis. A diverse array of approaches has been used in the establishment and analysis of several SCA1 mouse models, identification of ataxin-1 interacting proteins, investigation of the molecular properties of mutant ataxin-1 in cell culture, and gene expression analysis in the mouse models. Through these efforts, our understanding of the molecular mechanisms underlying SCA1 pathogenesis has been advanced. The following sections review these developments and end with an integrating model for SCA1 pathogenesis.

Animal models Gain-of-function mechanism established Extensive evidence has accumulated to indicate that SCA1 pathogenesis is caused by some toxic function gained by

the mutant protein as a result of the expanded polyglutamine tract. Clinical observations have indicated that SCA1 is an autosomal, dominantly inherited disorder. While several mechanisms may underlie this dominant inheritance, such as imprinting and haploinsufficiency, the most probable one is gain-of-function mutation. SCA1 develops only as a consequence of the expansion of a polyglutamine tract within the SCA1 gene (Orr et al., 1993), and the expression of the expanded protein has been clearly demonstrated (Servadio et al., 1995). Moreover, the age of onset and disease progression are influenced by the length of polyglutamine tract present in the mutant protein. To determine if ataxin-1 loss-of-function can cause the typical SCA1 phenotype and to explore the physiological roles of ataxin-1 in mice, Matilla et al. generated mice containing either heterozygous or homozygous Sca1 null mutation (Matilla et al., 1998). These mice develop no ataxia or Purkinje cell degeneration, suggesting that neither haploinsufficiency nor complete loss of murine Sca1 function causes any phenotypes related to cerebellar ataxia. Interestingly, Sca1 null mice have impairments in spatial and motor learning and decrease in paired-pulse facilitation in the CA1 area of the hippocampus, indicating that ataxin-1 might play a role in learning and memory mediated by the cerebellum and hippocampus (Matilla et al., 1998). Recently, Davies et al. reported that a heterozygous deletion of a genomic region encompassing the SCA1 gene in humans results in mental retardation and seizures, but not SCA1 (Davies et al., 1998, 1999). This observation further supports the studies of Sca1 null mice, effectively ruling out the possibility that SCA1 is caused by haploinsufficiency or loss of function of the SCA1 gene.

Mouse models of gain-of-function The first transgenic mouse model of a polyglutamine disease utilized a strong Purkinje cell-specific promoter from the Pcp2/L7 gene to direct expression of the human SCA1 cDNA encoding full-length ataxin-1 (Burright et al., 1995). These lines expressed high levels of either a wildtype SCA1 allele with 30 repeats (30Q) or an expanded allele with 82 repeats (82Q). The 82Q transgenic mice developed severe ataxia and progressive Purkinje cell pathology, whereas mice expressing wild-type ataxin-1 displayed no neurologic abnormalities and were indistinguishable from non-transgenic littermates (Clark et al., 1997). These studies demonstrated that pathological changes are induced by the expression of ataxin-1 with an expanded polyglutamine tract. Pathologically, the first abnormality in the 82Q transgenic mice is the development of cytoplasmic vacuoles

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within Purkinje cell bodies at postnatal day 25; by five weeks, loss of proximal dendritic branches and a decrease in the number of dendritic spines become apparent, indicating that mutant ataxin-1 may impair the maintenance of dendritic arborization. By 12–15 weeks, the complexity of the dendritic arborization of Purkinje cells is markedly reduced, the molecular layer atrophied, and there are several heterotopic Purkinje cells within the molecular layer. The heterotopia, not detected in young animals, is not a developmental abnormality, but is probably an attempt to preserve synapses in the face of severely reduced dendritic arborization. Cell loss was minimal at the time of progressive gait abnormality. Though it had long been assumed that the neurological phenotype in SCA1 patients results from neuronal death, these mice demonstrated that the neurological impairment is due instead to neuronal dysfunction. Neurobehavioral studies of SCA1 transgenic mice from the 82Q line reveal mild cerebellar impairment at five weeks of age, when there is no evidence of gait abnormalities or balance problems at that age (Clark et al., 1997). By 12 weeks, this slight motor skill impairment progresses to overt ataxia, which worsens over time. One important finding in SCA1 transgenic mice is the presence of nuclear aggregates in their Purkinje cells. In transgenic mice from a 30Q line, ataxin-1 localized to several 0.5 m nuclear inclusions. In contrast, in 82Q mice, ataxin-1 localized to a single 2 m ubiquitinated nuclear aggregate, as it does in patient tissue (Skinner et al., 1997). The appearance of these aggregates, which stain positive for the 20S proteasome and the HDJ-2/HSDJ (Hsp40) chaperone protein, precedes the onset of ataxia by approximately six weeks (Cummings et al., 1998). To ascertain whether ataxin-1 must be in the nucleus to cause disease, Klement et al. (1998) generated and characterized transgenic mice that express expanded ataxin-1 (82 glutamines) with a mutated nuclear localization sequence, ataxin-1K772T. Although these mice express high levels of ataxin-1 in Purkinje cells, similar to those observed in the original SCA1 (82Q) transgenic mice, they never develop Purkinje cell pathology or motor dysfunction. Ataxin-1 is diffusely distributed throughout the cytoplasm and forms no aggregates, even when the mice are a year old. Nuclear localization is clearly critical for pathogenesis and ataxin1 aggregation. Disruption of certain nuclear function(s) might mediate the toxicity of mutant ataxin-1. Neuronal nuclear inclusions are a hallmark of polyglutamine diseases. Two mechanisms have been proposed for polyglutamine aggregation: polar zipper formation through the hydrogen bonds between the side-chain amine group of glutamines, and transglutaminase-

catalyzed aggregation of polyglutamine-containing proteins. Whereas it remains to be resolved which mechanism is responsible for aggregate formation, nuclear aggregates have been consistently observed in patients and SCA1 mouse models. This observation raised the possibility that nuclear aggregation is itself pathogenic. A space-occupying lesion or abnormal interaction with nuclear proteins might perturb the ability of the nucleus to function properly. In transfected COS-1 cells, ataxin-1 has been found associated with the nuclear matrix (Skinner et al., 1997). Colocalization studies showed that mutant ataxin-1 causes a specific redistribution of the promyelocytic leukemia protein (PML), the major component of the nuclear matrix-associated domain, promyelocytic oncogenic domain (POD). These data further support the concept that nuclear aggregation of mutant ataxin-1 might be pathogenic. In order to evaluate the role of nuclear aggregates in causing disease, Klement et al. (1998) generated transgenic mice using ataxin-1 (77Q) with amino acids deleted from the self-association region found to be essential for ataxin-1 dimerization. These mice developed ataxia and Purkinje cell pathology similar to the original SCA1(82Q) mice, but without apparent nuclear ataxin-1 aggregation. Thus, although nuclear localization of ataxin-1 is necessary, nuclear aggregation of ataxin-1 is evidently not required to initiate pathogenesis in transgenic mice. It is likely that this protein with an expanded polyglutamine tract exerts similar pathogenicity to full-length expanded ataxin-1, in spite of the fact that it does not accumulate in visible aggregates.

Protein folding and degradation Another prominent pathological feature in SCA1 patients and transgenic mice is the positive ubiquitin immunoreactivity of the nuclear aggregates in the affected neurons, suggesting protein misfolding and/or faulty proteasomal degradation. An increasing number of cellular proteins has been recognized to be degraded, at least in part, by the ubiquitinationproteasomal machinery. Three distinct enzymes are known to be involved in successive steps in the polyubiquitination of proteins destined for degradation. The first step involves the activation of ubiquitin by the E1-ubiquitin-activating enzyme. An E2-ubiquitin-conjugating enzyme subsequently transfers the activated ubiquitin to the substrate protein, either directly or through E3, a substrate-specific ubiquitin ligase. It is generally believed that polyubiquitination serves as a molecular tag, targeting the conjugated proteins for degradation by the 26S proteasome, an ATP-dependent, multisubunit proteinase complex. The ubiquitination-

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proteasomal machinery plays important roles in many aspects of cell physiology, such as cellular protein quality control. Under stress or pathological insult, cellular proteins can adopt abnormally folded configurations. Molecular chaperones, an array of highly conserved cellular proteins, can either refold these proteins or direct them to the ubiquitination-proteasomal machinery for degradation. In SCA1, polyglutamine expansion in ataxin-1 might pose an insurmountable folding task for molecular chaperones. Unable to fold correctly, mutant ataxin-1 may be handed over to the ubiquitin-proteasome pathway. Consistent with this hypothesis are the observations in previous studies that ataxin-1 nuclear inclusions stain positive for the 20S proteasome, HSP40 and HSP70 in transfected Hela cells, the transgenic mice, and SCA1 patients. Recently, Cummings et al. (1999) provided the first evidence that ataxin-1 is ubiquitinated both in transfected cells and in vitro. However, in-vitro ubiquitin conjugation of expanded ataxin-1 does not seem to occur at a higher level than that of wild-type ataxin-1, indicating that polyglutamine expansion in mutant ataxin-1 does not lead to enhanced ubiquitination. However, specific inhibition of the proteasome causes significantly more aggregates in transfected cells, suggesting that proteasomal degradation might be the limiting factor in the clearance of mutant ataxin-1. Moreover, when ubiquitination was rendered limiting in mice by a null mutation in an E3 ligase, Ube3a, the frequency of aggregation was significantly decreased, whereas SCA1-induced Purkinje cell pathology was much more enhanced in transgenic mice, indicating that perturbation of the ubiquitination-proteasomal pathway may contribute to SCA1 pathogenesis, and proving that aggregation is not itself pathogenic (Cummings et al., 1999). Interestingly, overexpressing HSP40 in Hela cells decreases the frequency of ataxin-1 aggregation, indicating a possible titration of molecular chaperones by misfolded ataxin-1 (Cummings et al., 1998). Misfolded ataxin-1 might divert molecular chaperones from their normal task in chaperoning other cellular proteins, rendering the affected neurons more vulnerable to stressful conditions. It is also likely that polyglutamine expansion in the mutant ataxin1 directly affects proteasomal activity, resulting in the accumulation of ataxin-1 and alteration of the turnover of other cellular proteins. Better understanding of these issues will undoubtedly provide insight into pathogenesis and perhaps lead to effective treatment for SCA1 and other polyglutamine diseases as well.

Ataxin-1 interacting proteins One perplexing issue pertinent to all polyglutamine diseases is that of cell-specific degeneration. Why are Purkinje cells especially vulnerable in SCA1, when mutant ataxin-1 is ubiquitously expressed? One hypothesis is that abberant protein–protein interactions mediate selective neuronal vulnerability. To investigate this hypothesis, yeast twohybrid screening to identify ataxin-1 interactors was carried out. One protein has been identified to interact with ataxin-1 in a repeat length-dependent manner, the leucine-rich acidic nuclear protein (LANP). LANP was identified in a screening using a mouse brain cDNA library (Matilla et al., 1997). The portion of LANP interacting with ataxin-1 is the first 147 amino acids, containing the leucine-rich repeat (LRR), an amphipathic motif known to mediate protein–protein interactions. Two regions of ataxin-1 proteins can interact with LANP: the Nterminal encompassing the polyglutamine expansion, and the last 268 amino acids at the C-terminus. When the strength of this interaction was assessed in yeast, it was found that LANP interacts much more strongly with ataxin-1 containing 82Q than with ataxin-1 containing either 2Q or 32Q. Immunofluorescence studies revealed that in transfected COS cells, LANP localized to the nuclear aggregates containing either wild-type or mutant ataxin-1. More importantly, LANP is expressed predominantly in cerebellar Purkinje cells, suggesting that LANP is an excellent candidate for mediating selective neuronal degeneration in SCA1 (Matilla et al., 1997). Previously, LANP was identified as a developmentally regulated protein in rat cerebellum by two-dimensional polyacrylamide gel electrophoresis (Matsuoka et al., 1994). In cerebellum, LANP protein expression reaches the maximal level (about three-fold over the adult level) on postnatal day 12 (P12), at which time a peak of LANP mRNA is also observed. In-situ hybridization studies further indicated that this peak of LANP mRNA expression is largely due to the increased expression in Purkinje cells and granule cells during the second postnatal week, the same time as the transient burst of Sca1 expression in the mouse (Matsuoka et al., 1994; Banfi et al., 1996). Moreover, immunohistochemical analysis using a LANP polyclonal antibody revealed intense staining in Purkinje cell nuclei and much lower but detectable levels in Purkinje cell cytoplasm and granule cells (Matsuoka et al., 1994; Matilla et al., 1997). Therefore, LANP and ataxin-1 share the same subcellular localization in Purkinje cells, confirming the possibility of their interaction under physiological conditions. LANP has also been isolated from peripheral tissues using a variety of independent strategies (Vaesen et al.,

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1994; Li et al., 1995, 1996; Chen et al., 1996; Ulitzur et al., 1997a). A strong inhibitory activity to protein phosphatase 2A (PP2A) has been attributed to LANP purified from bovine kidney extract (Li et al., 1995, 1996). However, LANP purified from the cytosol of Chinese hamster ovary cells does not seem to have similar activity (Ulitzur et al., 1997b). It remains to be resolved whether this discrepency is due to different tissue and/or subcellular sources of purification (cytoplasm versus whole cell). It is important to establish whether LANP can function as a regulator of PP2A, because PP2A has been known to have extensive modulatory effects both in the nucleus and in the cytoplasm. It will be very interesting to find out if the nuclear PP2A activity in Purkinje cells can be perturbed by the interaction of mutant ataxin-1 with LANP. Another research group also independently isolated LANP and designated it mapmodulin (Ulitzur et al., 1997a, 1997b). These workers showed that LANP is a phosphoprotein that binds to microtubule-associated proteins (MAPs), such as MAP2, MAP4, and tau, and facilitates vesicular transport in a phosphorylation-dependent fashion. Interaction between LANP and mutant ataxin-1 might therefore affect vesicular transport in Purkinje cells, contributing to Purkinje cell degeneration. It is of note that certain morphological observations, such as the axonal dilatations in SCA1 patients and the cytoplasmic vacuoles in SCA1 transgenic mice, might indicate perturbed vesicular transport in Purkinje cells. However, this cytoplasmic interaction might be only a contributing factor and not an initiating one in SCA1 pathogenesis, because it has been clearly demonstrated in SCA1 transgenic mouse models that nuclear localization of mutant ataxin-1 is necessary for Purkinje cell degeneration (Klement et al., 1998). Another protein found to interact with ataxin-1 is glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This interaction is unusually strong and the binding can resist washes with 1 M NaCl, which normally disrupts most protein–protein interactions (Koshy et al., 1996). The GAPDH/ ataxin-1 interaction is mediated through the dehydrogenase dinucleotide binding domain of GAPDH and the N-terminal polyglutamine-containing domain of ataxin-1. Interestingly, GAPDH also interacts with androgen receptor, huntingtin and atrophin-1, which are mutated in three other polyglutamine diseases (Burke et al., 1996; Koshy et al., 1996). Because GAPDH is a regulatory enzyme in glycolysis, it is tempting to propose that the binding of mutant ataxin-1 to GAPDH may have deleterious effects on its glycolytic function, decreasing adenosine triphosphate (ATP) production and subsequently leading to neuronal degeneration. However, direct measurement of GAPDH activity in several morphologically affected and

unaffected brain regions in four different polyglutamine diseases (Huntington disease, SCA13) revealed no significant changes (Kish et al., 1998). In contrast, another study using fibroblasts from Huntington patients demonstrated reduced upregulation of GAPDH dehydrogenase activity when the cells were challenged with medium depletion, suggesting an impairment in the regulation of GAPDH dehydrogenase activity (Cooper et al., 1998). Further investigations are necessary to evaluate whether GAPDH binding with ataxin-1 attenuates upregulation of glycolytic activity under stressful conditions. Such perturbation could cause neuronal degeneration over time, because neurons are totally dependent on the glycolytic pathway for ATP production. Recently, Sawa et al. reported that lymphoblasts of Huntington disease patients showed markedly increased stress-induced mitochondria depolarization and apoptosis; but similar abnormalities are not found in lymphoblasts from SCA1 patients (Sawa et al., 1999). This observation suggests that distinct molecular events may underlie Huntington disease and SCA1 pathogenesis. Over the last decade, the results of numerous studies have accumulated to indicate that GAPDH is not simply a glycolytic protein. GAPDH has extremely diverse biological properties, including membrane transport and fusion, microtubule assembly, nuclear RNA transport, RNA binding, protein phosphotransferase and/or kinase reactions, translational control of gene expression, DNA replication, and DNA repair (Sirover, 1999). More recently, in addition to the evidence for its potential involvement in neurodegenerative diseases, nuclear translocation of GAPDH has been implicated as an essential component for neuronal apoptosis, which is independent of its glycolytic activity (Ishitani and Chuang, 1996; Sawa et al., 1997). Therefore, it is possible that the interaction between mutant ataxin-1 and GAPDH might affect these non-glycolytic functions, the perturbation of which could lead to neuronal degeneration.

Alteration of gene expression The study of Klement et al. (1998) firmly established that nuclear localization of mutant ataxin-1 is necessary for SCA1 pathogenesis in SCA1 transgenic mice. Thus, certain nuclear functions, such as gene transcription and mRNA metabolism, might be specifically impaired. Polyglutamine tracts of various lengths are also known to be present in a number of transcription factors and serve as transcription activation domains (Gerber et al., 1994; Karlin and Burge, 1996). The functions of these transcription factors in SCA1 might be perturbed either

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through direct interactions with mutant ataxin-1 (e.g., polar zipper formation between polyglutamine tracts) or through indirect competition if mutant ataxin-1 interacts with the basal transcriptional machinery. Another indication for potential alteration in gene expression came from the observation that mutant ataxin-1 redistributes PML, a coactivator for cAMP-response element binding protein (CREB)-binding protein (CBP), into nuclear aggregates in transfected COS cells (Skinner et al., 1997; Doucas et al., 1999). To evaluate how changes in gene expression might be involved in SCA1 pathogenesis, Lin and colleagues adopted a subtractive cDNA cloning approach to investigate alterations of gene expression in early SCA1 pathogenesis using SCA1 transgenic mice (Lin et al., 2000). Several genes whose expression is highly enriched in cerebellar Purkinje cells are specifically downregulated in SCA1 transgenic mice, including prenylcysteine carboxyl methyltransferase (PCCMT), inositol triphosphate receptor type 1 (IP3R1), sarcoplasmic and endoplasmic reticulum calcium ATPase type 2 (SERCA2), inositol polyphosphate 5phosphatase type 1 (Ins-5P1), mammalian homologue to Drosophila transient receptor potential type 3 (TRP3), and excitatory amino acid transporter type 4 (EAAT4). These genes are thought to be important in Purkinje cell signal transduction, neurotransmission, and calcium homoeostasis. Interestingly, all these genes are downregulated sequentially in early pathogenesis prior to any other pathologic changes. The SCA1 transgenic mice first express the expanded allele with 82 repeats at P10 (Clark et al., 1997). It is remarkable that, by P11, the steady state level of PCCMT mRNA in the transgenic mice is already significantly reduced in comparison with their wild-type littermates. Such a swift change is likely to represent a direct response to mutant ataxin-1 in the Purkinje cells. At P14, four days after the transgene is turned on, SERCA2 and IP3R1 are downregulated, indicating that mutant ataxin-1 could perturb Purkinje cell calcium homoeostasis through alteration of the expression of key regulators of calcium stores. Alterations in calcium homoeostasis are also indicated by the reduced expression of calbindin and parvalbumin (two major calcium-binding proteins in Purkinje cells) at six weeks of age by immunohistochemistry and Western blot analysis (Vig et al., 1998). Ins-5P1, TRP3, and EAAT4 are greatly downregulated between three and four weeks of age, when Purkinje cell cytoplasmic vacuoles are first identified in the transgenic mice. Furthermore, a careful comparison of the expression of these genes in different lines of SCA1 transgenic mice indicates that these changes are associated specifically with those forms of ataxin-1 that are

clearly pathogenic. For example, no change in the expression of these genes is observed in the non-symptomatic transgenic mice overexpressing either wild-type ataxin-1 or the expanded ataxin-1 crippled by a point mutation in the nuclear localization signal. However, downregulation of these genes occurs in the transgenic lines that develop the typical Purkinje cell pathology, such as the line expressing expanded ataxin-1 without the self-association domain (Lin et al., 2000). These observations strongly support the hypothesis that mutant ataxin-1 alters the expression of key neuronal genes early in SCA1 pathogenesis. Specific downregulation of key neuronal genes in Purkinje cells might mediate, at least in part, the pathogenetic effect of mutant ataxin-1. It is striking that all the genes whose expression is altered early in the pathogenesis are downregulated, which suggests that there may be a common mechanism operating at transcriptional and/or post-transcriptional levels.

A model of SCA1 pathogenesis The current model for SCA1 pathogenesis contends that polyglutamine expansion renders ataxin-1 neurotoxic. Selective degeneration of Purkinje cells and pontine neurons is presumably determined by the protein context in which the polyglutamine expansion resides, because expanded polyglutamine tracts in isolation cause widespread neuronal degeneration (Ikeda et al., 1996; Mangiarini et al., 1996). Ataxin-1 with polyglutamine expansion is believed to misfold and adopt abnormal conformations, which could overwhelm cellular protein folding/degradation machinery and lead to deleterious interactions with other proteins. The primary site of SCA1 polyglutamine toxicity is the nucleus. Perturbation of nuclear events, such as gene transcription and/or mRNA processing, could mediate polyglutamine toxicity in early SCA1 pathogenesis. Without doubt, this model is general and oversimplified. But several insights could be drawn for designing rational therapeutics and directing future research efforts in tackling SCA1 pathogenesis. For example, a better understanding of the cellular functions of GAPDH and LANP is needed to elucidate their roles in SCA1 pathogenesis. Further exploration of more interacting partners with both the wild-type and mutant ataxin-1 is going to be important for obtaining a fuller picture of ataxin-1’s function. The immediate changes in the expression of certain key neuronal genes reveal that alteration of gene expression is an integral component of early SCA1 pathogenesis. It is important to determine whether this change is due to altered transcription or altered post-transcriptional mRNA

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processing and stability. Perhaps the more exciting finding in SCA1 pathogenesis is the revelation that protein folding and/or degradation machinery plays a role in ataxin-1 metabolism. This finding suggests that enhancing the clearance of ataxin-1 might be a critical step for mitigating its neurotoxic effects. This opens the opportunity for studying the roles of molecular chaperones and proteasomes in a number of neurodegenerative conditions and possibly for deriving rational therapeutics that modulate their cellular activities.

Acknowledgments The authors thank V. Brandt for critical reading of the manuscript and editorial input. Their SCA1 research is supported by grants from the National Institutes of Health, NS27699 and NS22920 (to HYZ and HTO). X. Lin is an Associate, and H. Zoghbi an Investigator, with the Howard Hughes Medical Institute.

xReferencesx Banfi, S., Chung, M.Y., Kwiatkowski, T.J. J. et al. (1993). Mapping and cloning of the critical region for the spinocerebellar ataxia type 1 gene (SCA1) in a yeast artificial chromosome contig spanning 1.2 Mb. Genomics 18: 627–35. Banfi, S., Servadio, A., Chung, M.-Y. et al. (1996). Cloning and developmental expression analysis of the murine homolog of the spinocerebellar ataxia type 1 gene (Sca1). Hum Mol Genet 5: 33–40. Banfi, S., Servadio, A., Chung, M.-Y. et al. (1994). Identification and characterization of the gene causing type 1 spinocerebellar ataxia. Nat Genet 7: 513–19. Bebin, E.M., Bebin, J., Currier, R.D., Smith, E.E. and Perry, T.L. (1990). Morphometric studies in dominant olivopontocerebellar atrophy. Arch Neurol 47: 188–92. Burke, J.R., Enghild, J.J., Martin, M.E. et al. (1996). Huntingtin and DRPLA proteins selectively interact with the enzyme GAPDH. Nat Med 2: 347–50. Burright, E.N., Clark, H.B., Servadio, A. et al. (1995). SCA1 transgenic mice: a model for neurodegeneration caused by an expanded CAG trinucleotide repeat. Cell 82: 937–48. Chen, T.H., Brody, J.R., Romantsev, F.E. et al. (1996). Structure of pp32, an acidic nuclear protein which inhibits oncogeneinduced formation of transformed foci. Mol Biol Cell 7: 2045–56. Chong, S.S., McCall, A.E., Cota, J., Subramony, S.H., Orr, H.T. and Zoghbi, H.Y. (1995). Gametic and somatic tissue-specific heterogeneity of the expanded SCA1 CAG repeat in spinocerebellar ataxia type 1. Nat Genet 10: 344–50. Chung, M.Y., Ranum, L.P.W., Duvick, L., Servadio, A., Zoghbi, H.Y.

and Orr, H.T. (1993). Analysis of the CAG repeat expansion in spinocerebellar ataxia type I: evidence for a possible mechanism predisposing to instability. Nat Genet 5: 254–8. Clark, H.B., Burright, E.N., Yunis, W.S. et al. (1997). Purkinje cell expression of a mutant allele of SCA1 in transgenic mice leads to disparate effects on motor behaviors, followed by a progressive cerebellar dysfunction and histological alterations. J Neurosci 17: 7385–95. Cooper, A.J., Sheu, K.F., Burke, J.R., Strittmatter, W.J. and Blass, J.P. (1998). Glyceraldehyde 3-phosphate dehydrogenase abnormality in metabolically stressed Huntington disease fibroblasts. Dev Neurosci 20: 462–8. Cummings, C.J., Mancini, M.A., Antalffy, B., DeFranco, D.B., Orr, H.T. and Zoghbi, H.Y. (1998). Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1. Nat Genet 19: 148–54. Cummings, C.J., Reinstein, E., Sun, Y. et al. (1999). Mutation of the E6–AP ubiquitin ligase reduces nuclear inclusion frequency while accelerating polyglutamine-induced pathology in SCA1 mice. Neuron 24: 879–92 Currier, R.D., Glover, G., Jackson, J.F. and Tipton, A.C. (1972). Spinocerebellar ataxia: study of a large kindred. Neurology 22: 1040–3. Davies, A.F., Mirza, G., Sekhon, G., et al. (1999). Delineation of two distinct 6p deletion syndromes. Hum Genet 104: 64–72. Davies, S.W., Beardsall, K., Turmaine, M., DiFiglia, M., Aronin, N. and Bates, G.P. (1998). Are neuronal intranuclear inclusions the common neuropathology of triplet-repeat disorders with polyglutamine-repeat expansions? Lancet 351: 131–3. Doucas, V., Tini, M., Egan, D.A. and Evans, R.M. (1999). Modulation of CREB binding protein function by the promyelocytic (PML) oncoprotein suggests a role for nuclear bodies in hormone signaling. Proc Natl Acad Sci USA 96: 2627–32. Dubourg, O., Dürr, A., Cancel, G. et al. (1995). Analysis of the SCA1 CAG repeat in a large number of families with dominant ataxia: clinical and molecular correlations. Ann Neurol 37: 176–80. Gerber, H.-P., Seipel, K., Georgiev, O. et al. (1994). Transcriptional activation modulated by homopolymeric glutamine and proline stretches. Science 263: 808–11. Gilman, S., Sima, A.A., Junck, L. et al. (1996). Spinocerebellar ataxia type 1 with multiple system degeneration and glial cytoplasmic inclusions. Ann Neurol 39: 241–55. Goldfarb, L.G., Vasconcelos, O., Platonov, F.A. et al. (1996). Unstable triplet repeat and phenotypic variability of spinocerebellar ataxia type 1. Ann Neurol 39: 500–6. Ikeda, H., Yamaguchi, M., Sugai, S., Aze, Y., Narumiya, S. and Kakizuka, A. (1996). Expanded polyglutamine in the Machado–Joseph disease protein induces cell death in vitro and in vivo. Nat Genet 13: 196–202. Ishitani, R. and Chuang, D.M. (1996). Glyceraldehyde-3-phosphate dehydrogenase antisense oligodeoxynucleotides protect against cytosine arabinonucleoside- induced apoptosis in cultured cerebellar neurons. Proc Natl Acad Sci USA 93: 9937–41. Jackson, J.F., Currier, R.D., Terasaki, P.I. and Morton, N.E. (1977).

Spinocerebellar ataxia type 1

Spinocerebellar ataxia and HLA linkage: risk prediction by HLA typing. N Engl J Med 296: 1138–41. Jodice, C., Malaspina, P., Persichetti, F. et al. (1994). Effect of trinucleotide repeat length and parental sex on phenotypic variation in spinocerebellar ataxia 1. Am J Hum Genet 54: 959–65. Karlin, S. and Burge, C. (1996). Trinucleotide repeats and long homopeptides in genes and proteins associated with nervous system disease and development. Proc Natl Acad Sci USA 93: 1560–5. Kish, S.J., Lopes-Cendes, I., Guttman, M. et al. (1998). Brain glyceraldehyde-3-phosphate dehydrogenase activity in human trinucleotide repeat disorders. Arch Neurol 55: 1299–304. Klement, I.A., Skinner, P.J., Kaytor, M.D. et al. (1998). Ataxin-1 nuclear localization and aggregation: role in polyglutamineinduced disease in SCA1 transgenic mice. Cell 95: 41–53. Koshy, B., Matilla, T., Burright, E.N. et al. (1996). Spinocerebellar ataxia type-1 and spinobulbar muscular atrophy gene products interact with glyceraldehyde-3-phosphate dehydrogenase. Hum Mol Genet 5: 1311–18. Koshy, B.T., Matilla, A. and Zoghbi, H.Y. (1998). Clues about the pathogenesis of SCA1 from biochemical and molecular studies of ataxin-1. In Genetic Instabilities and Hereditary Neurological Disorders, ed. R.D. Wells and S.T. Warren, pp. 241–8. San Diego: Academic Press. Kwiatkowski, T. J. Jr, Orr, H.T., Banfi, S. et al. (1993). The gene for autosomal dominant spinocerebellar ataxia (SCA1) maps centromeric to D6S89 and shows no recombination, in nine large kindreds, with a dinucleotide repeat at the AM10 locus. Am J Hum Genet 53: 391–400. Li, M., Guo, H. and Damuni, Z. (1995). Purification and characterization of two potent heat-stable protein inhibitors of protein phosphatase 2A from bovine kidney. Biochemistry 34: 1988–96. Li, M., Makkinje, A. and Damuni, Z. (1996). Molecular identification of I1PP2A, a novel potent heat-stable inhibitor protein of protein phosphatase 2A. Biochemistry 35: 6998–7002. Lin, X., Antalffy, B., Kang, D., Orr, H.T. and Zoghbi, H.Y. (2000). Poluglutamine expansion downregulates specific neuronal genes before pathological changes in SCA1. Nat Neurosci 3: 157–63. Mangiarini, L., Sathasivam, K., Seller, M. et al. (1996). Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell 87: 493–506. Marie, P. (1893). Sur l’heredoataxie cerebelleuse. Semin Med (Paris) 13: 444–7. Matilla, A., Roberson, E.D., Banfi, S. et al. (1998). Mice lacking ataxin-1 display learning deficits and decreased hippocampal paired-pulse facilitation. J Neurosci 18: 5508–16. Matilla, T., Koshy, B., Cummings, C.J., Isobe, T., Orr, H.T. and Zoghbi, H.Y. (1997). The cerebellar leucine-rich acidic nuclear protein interacts with ataxin-1. Nature 389: 974–8. Matsuoka, K., Taoka, M., Satozawa, N. et al. (1994). A nuclear factor containing the leucine-rich repeats expresses in murine cerebellar neurons. Proc Natl Acad Sci USA 91: 9670–4.

Nino, H.E., Noreen, H.J. and Dubey, D.P. (1980). A family with hereditary ataxia: HLA typing. Neurology 30: 12–20. Orr, H., Chung, M.Y., Banfi, S. et al. (1993). Expansion of an unstable trinucleotide (CAG) repeat in spinocerebellar ataxia type 1. Nat Genet 4: 221–6. Orr, H.T. and Zoghbi, H.Y. (1996). Toward understanding polyglutamine-induced neurological disease in spinocerebellar ataxia type 1. Cold Spring Harb Symp Quant Biol 61: 649–57. Perretti, A., Santoro, L., Lanzillo, B. et al. (1996). Autosomal dominant cerebellar ataxia type I: multimodal electrophysiological study and comparison between SCA1 and SCA2 patients. J Neurol Sci 142: 45–53. Quan, F., Janas, J. and Popovich, B.W. (1995). A novel CAG repeat configuration in the SCA1 gene: implications for the molecular diagnostics of spinocerebellar ataxia type 1. Hum Mol Genet 4: 2411–13. Ranum, L.P.W., Chung, M.Y., Banfi, S. et al. (1994). Molecular and clinical correlations in spinocerebellar ataxia type 1 (SCA1): evidence for familial effects on the age of onset. Am J Hum Genet 55: 244–52. Ranum, L.P.W., Chung, M.Y., Duvick, L.A., Zoghbi, H.Y. and Orr, H.T. (1991). Dinucleotide repeat polymorphism at the D6S109 locus. Nucl Acids Res 19: 1171. Rich, S.S., Wilkie, P., Schut, L., Vance, G. and Orr, H.T. (1987). Spinocerebellar ataxia: localization of an autosomal dominant locus between two markers on human chromosome 6. Am J Hum Genet 41: 524–31. Sasaki, H., Fukazawa, T., Wakisaka, A. et al. (1996). Central phenotype and related varieties of spinocerebellar ataxia 2 (SCA2): a clinical and genetic study with a pedigree in the Japanese. J Neurol Sci 144: 176–81. Sawa, A., Khan, A.A., Hester, L.D. and Snyder, S.H. (1997). Glyceraldehyde-3-phosphate dehydrogenase: nuclear translocation participates in neuronal and nonneuronal cell death. Proc Natl Acad Sci USA 94: 11669–74. Sawa, A., Wiegand, G.W., Cooper, J. et al. (1999). Increased apoptosis of Huntington disease lymphoblasts associated with repeat length-dependent mitochondrial depolarization. Nat Med 5: 1194–8. Schols, L., Riess, O., Schols, S. et al. (1995). Spinocerebellar ataxia type 1: clinical and neurophysiological characteristics in German kindreds. Acta Neurol Scand 92: 478–85. Schut, J.W. (1950). Hereditary ataxia: clinical study through six generations. Arch Neurol Psychiatr 63: 535–68. Servadio, A., Koshy, B., Armstrong, D., Antalfy, B., Orr, H. T. and Zoghbi, H.Y. (1995). Expression analysis of the ataxin-1 protein in tissues from normal and spinocerebellar ataxia type 1 individuals. Nat Genet 10: 94–8. Sirover, M.A. (1999). New insights into an old protein: the functional diversity of mammalian glyceraldehyde-3-phosphate dehydrogenase. Biochim Biophys Acta 1432: 159–84. Skinner, P.J., Koshy, B., Cummings, C. et al. (1997). Ataxin-1 with extra glutamines induces alterations in nuclear matrix-associated structures. Nature 389: 971–4. Spadaro, M., Giunti, P., Lulli, P. et al. (1992). HLA-linked

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X. Lin, H.T. Orr, and H.Y. Zoghbi

spinocerebellar ataxia: a clinical and genetic study of large Italian kindreds. Acta Neurol Scand 85: 257–65. Subramony, S.H. and Vig, P.J.S. (1998). Clinical aspects of spinocerebellar ataxia 1. In Genetic Instabilities and Hereditary Neurological Diseases, ed. R.D. Wells and S.T. Warren, pp. 231–9. San Diego: Academic Press. Ulitzur, N., Humbert, M. and Pfeffer, S.R. (1997a). Mapmodulin: a possible modulator of the interaction of microtubule-associated proteins with microtubules. Proc Natl Acad Sci USA 94: 5084–9. Ulitzur, N., Rancaño, C. and Pfeffer, S.R. (1997b). Biochemical characterization of mapmodulin, a protein that binds microtubule-associated proteins. J Biol Chem 272: 30577–82. Vaesen, M., Barnikol-Watanabe, S., Gotz, H. et al. (1994). Purification and characterization of two putative HLA class II associated proteins: PHAPI and PHAPII. Biol Chem Hoppe Seyler 375: 113–26. Vig, P.J., Subramony, S.H., Burright, E.N. et al. (1998). Reduced

immunoreactivity to calcium-binding proteins in Purkinje cells precedes onset of ataxia in spinocerebellar ataxia-1 transgenic mice. Neurology 50: 106–13. Yakura, H., Wakisaka, A., Fujimoto, S. and Itakura, K. (1974). Hereditary ataxia and HLA genotypes. N Eng J Med 291: 154–5. Zoghbi, H.Y., Jodice, C., Sandkuijl, L.A. et al. (1991). The gene for autosomal dominant spinocerebellar ataxia (SCA1) maps telomeric to HLA complex and is closely linked to the D6S89 locus in three large kindreds. Am J Hum Genet 49: 23–30. Zoghbi, H.Y. and Orr, H.T. (2000). Glutamine repeats and neurodegeneration. Ann Rev Neurosci 23: 217–47. Zoghbi, H.Y., Pollack, M.S., Lyons, L.A., Ferell, R.E., Daiger, S.P. and Beaudet, A.L. (1988). Spinocerebellar ataxia: variable age of onset and linkage to human leukocyte antigen in a large kindred. Ann Neurol 23: 580–4.

27

Spinocerebellar ataxia type 2 Stefan-M. Pulst UCLA School of Medicine, Los Angeles, California, USA

Introduction Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease caused by expansion of an unstable CAG repeat in the SCA2 or ataxin-2 gene on human chromosome 12. Ataxin-2 is a member of a novel protein family of unknown function that is evolutionarily conserved. The wide separation between normal and pathological repeat ranges seen in other CAG repeat disorders is not present in SCA2.

Phenotype The first description of what is now genotypically confirmed as SCA2 occurred in several families in the province of Holguin in Cuba (Orozco et al., 1989, 1990; Santos et al., 1999). The majority were of Caucasian Spanish ancestry. In addition to ataxic gait and other cerebellar findings, many patients had slow saccadic eye movements. Tendon reflexes were brisk during the first years of life, but absent several years later. Independently, Wadia and Swami (1971) in India noticed a subset of patients with inherited ataxias who appeared to have greatly reduced saccadic eye movement velocities. However, subsequent genotyping of these families has indicated that this population was not genetically homogenous and some patients carried mutations in other ataxia genes (Wadia et al., 1998). Analysis of a large number of SCA2 pedigrees has indicated a wide range of phenotypic manifestations that make SCA2 indistinguishable from other SCAs in the individual patient (Table 27.1). However, when compared as a group, certain phenotypic features appear that are more common in SCA2 than in other ataxias, such as slow saccades, peripheral neuropathy, and dementia.

Ataxia Ataxia is universally present and usually a presenting sign, although some Cuban patients may present with muscle cramps. A subclinical neuropathy may be identified before any other clinical signs (Velazquez and Medina, 1998). Ataxia involves gait and stance, but is also prominent in appendicular functions. In the Cuban population, a prominent truncal oscillation was seen when patients were standing with their eyes open. Schols et al. (1997a) found SCA2 expansion in 6 of 64 autosomal dominant cerebellar ataxia (ADCA) families of German ancestry. Clinical features were highly variable within and between families. Although no specific single feature was sufficient to distinguish SCA2 from other SCAs, slowed saccades, postural and action tremors, myoclonus, and hyporeflexia were more common than in SCA1 and SCA3. In a retrospective study, the rate of progression was similar for SCA1, SCA2, and SCA3 (Klockgether et al., 1998a). Female gender was associated with shortened survival.

Eye movements Abnormal eye movements have been identified in all clinical studies of SCA2 (reviewed in Pulst and Perlman, 2000). Several studies have provided formal eye movement recordings (Burk et al., 1996, 1999a; Rivaud-Pechoux et al., 1998; Buttner et al., 1998). Burk et al. (1996) examined several SCA2 patients defined by linkage analysis and compared them with SCA1 and SCA3 patients. SCA2 patients had significantly slower saccadic speed (138°/s) than patients with SCA1 (244°/s) or SCA3 (347°/s). All eight SCA2 patients had saccadic velocities two standard deviations below the mean of a control group. Buttner et al. (1998)

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Table 27.1 SCA2 phenotype compared with SCA1, SCA3, and SCA6*

Cerebellar dysfunction Reduced saccadic velocity Myoclonus Dystonia or chorea Pyramidal involvement Peripheral neuropathy Intellectual impairment

SCA1

SCA2a

SCA2b

SCA3

SCA6c

SCA6d

100 50 0 20 70 100 20

100 71 40 0 29 94 31

100 92 0 38 31 44 37

100 10 4 8 70 80 5

100 6 0 0 44 44 0

100 0 0 25 33 16 0

Notes: * Percent of patients with a specific sign are indicated. Percentages for SCA1, SCA2,a SCA3, and SCA6c were modified from Schols et al. (1997a, 1997b), those for SCA2b and SCA6d from Geschwind et al. (1997a, 1997b). Source: Reproduced from Pulst and Perlman (2000).

compared patients with SCA1, SCA2, SCA3, and SCA6 identified by direct mutation analysis. Patients with SCA2 had the slowest peak saccadic velocity, ranging from 80°/s to 295o/s (normal >400o/s). Saccades were also slowed in SCA1 patients, but patients with SCA3 or SCA6 had normal saccades. In a recent follow-up study of 46 patients with ADCA, SCA2 patients were characterized by reduced saccadic velocity and the absence of square-wave jerks and gazeevoked nystagmus (Burk et al., 1999a). Rivaud-Pecheaux (1998) made the same observations, but also found that an increased saccade amplitude may help distinguish SCA1 from SCA2.

Movement disorders Belal et al. (1994) described a surprising 23% incidence of extrapyramidal signs in one family. Using direct analysis of the SCA2 repeat, Geschwind et al. (1997b) found a relatively high incidence of dystonia or chorea (38%). Dystonia or chorea was rare in the series reported by Schols et al. (1997b). In a series of 111 patients from 32 families of diverse origins, Cancel et al. (1997) found dystonia in 9%. The authors also examined which findings were correlated with disease duration and which were correlated with increasing CAG repeat length. The size of the repeat was significantly larger in patients with dystonia, myoclonus, and myokymia. Sasaki et al. (1998) point to the presence of choreiform movements in their patients in Japan. Parkinsonism was seen in a man homozygous for the SCA2 mutation. Myoclonus is prominent in Cuban SCA2 patients, especially in those with early onset (S.-M. Pulst, personal observation).

Neuropathy, fasciculations The incidence of neuropathy is high in all studies of SCA2 worldwide. In most studies, hyperreflexia due to upper motor neuron dysfunction is followed by hyporeflexia. Eighty percent of French SCA2 patients had a neuropathy (Kubis et al., 1999). Cancel et al. (1997) observed fasciculations in 25% of SCA2 patients. Both CAG length and duration influenced the frequency of decreased reflexes and vibration sense in the lower extremities, amyotrophy, and fasciculations (Cancel et al., 1997). In two Japanese SCA2 pedigrees, nerve conduction studies revealed a subclinical sensory neuropathy (Ueyama et al., 1998). In Cuban SCA2 patients, a decrease in the amplitude of sensory nerve potentials was seen early and frequently, and even in the absence of other clinical signs (Velazquez and Medina, 1998). Prolonged latencies of somatosensory and brainstem auditory potentials were also observed, but visual-evoked potentials remained normal.

Dementia Durr et al. (1995) recognized the prevalence of dementia in SCA2 in that 29% of their patients showed an abnormal mental status. Geschwind et al. (1997b) found an abnormal mental status in 37% of their patients. Formal mental status testing has indicated significant frontal executive dysfunction in SCA2. A quarter of SCA2 patients were demented in a study of German SCA2 patients and even in non-demented subjects, verbal and executive dysfunction could be detected (Burk et al., 1999b). Storey et al. (1999) studied a northern Italian SCA2 pedigree. Five of six individuals displayed frontal executive dysfunction despite a Mini-Mental Status score in the non-

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demented range. Gambardella et al. (1998) observed an early and selective impairment of conceptual reasoning ability as shown by the Wisconsin Card Sorting Test.

Neonatal onset A neonatal phenotype reminiscent of neonatal SCA7 was reported in an infant born to a father with 43 repeats and an age of onset at 22 years (Babovic-Vuksanovic et al., 1998). The infant had more than 200 repeats and presented with neonatal hypotonia, developmental delay, and dysphagia. Retinitis pigmentosa was noticed at 10 months of age.

slight reduction in Huntington’s disease caudate and Alzheimer temporal lobe (Kish et al., 1998).

Magnetic resonance imaging In a study of 20 Italian SCA2 patients, ponto-cerebellar atrophy did not appear to correlate with CAG repeat length or disease duration, but supratentorial atrophy did (Giuffrida et al., 1999b). Compared with SCA1 and SCA3, cerebellar and brainstem atrophy appear to be more severe in SCA2 (Klockgether et al., 1998b). Putaminal and caudate volume was reduced in SCA3, but not in SCA2. SCA1 morphometry overlapped with that of SCA2 and SCA3.

Neuropathology The SCA2 gene Post-mortem examinations have been reported in the Holguin population of Cuba, in Martinican pedigrees, and in Caucasian patients (Orozco et al., 1989; Durr et al., 1995; Adams et al., 1997; Huynh et al., 1999; Estrada et al., 1999). Cerebellar Purkinje cells were reduced in number in all autopsies. In silver preparations, Purkinje cell dendrites had poor arborization and torpedo-like formation of their axons as they passed through the granular layer. Parallel fibers were scanty. Granule cells were decreased in number, whereas Golgi and basket cells were well preserved, as were neurons in the dentate and other cerebellar nuclei. In the brainstem, there was marked neuronal loss in the inferior olive and pontocerebellar nuclei. The dentate nucleus was not (or only minimally) affected. Degeneration in the nigroluyso-pallidal system mainly involved the substantia nigra. Six of seven brains in the Cuban study had marked loss in the substantia nigra. In five spinal cords that were available for analysis, marked demyelination was present in the posterior columns and to a lesser degree in the spinocerebellar tracts. Motor neurons and neurons in Clarke’s column were reduced in size and number. Especially in lumbar and sacral segments, anterior and posterior roots were partially demyelinated. In some brains, severe gyral atrophy, most prominent in the frontotemporal lobes, has been noted. The cerebral cortex was thinned, but without neuronal rarefaction. The cerebral white matter was atrophic and gliotic. One brain showed patchy loss in parts of the third nerve nuclei. Adams et al. (1997) reported similar findings in one member of the FS pedigree. Nerve biopsy has shown moderate loss of large myelinated fibers (Filla et al., 1995). Biochemical analysis for activity in glyceraldehyde-3phosphate dehydrogenase (GAPDH) did not show regionspecific differences from normal controls, in contrast to a

Using a genome-wide screen, (Gispert et al., 1993) mapped SCA2 to a 20-cM interval on chromosome 12q24.1. Pulst et al. (1993) confirmed this location in a second pedigree of southern Italian descent and demonstrated that SCA2 showed marked anticipation of disease onset. Of 15 parent–child pairs, 14 showed earlier disease onset by at least one year. The observed anticipation was not due to biased ascertainment, because the use of linked genetic markers demonstrated that none of the asymptomatic individuals was a gene carrier with a potential for later onset of the disease (Pulst et al., 1993). This observation strongly suggested that SCA2 was caused by an unstable DNA repeat. Additional pedigrees from diverse ethnic and geographic groups (Belal et al., 1994; Lopes-Cendes et al. 1994; Ihara et al., 1994; Durr et al., 1995; Filla et al., 1995; Nechiporuk et al., 1996) showed linkage to the SCA2 locus on chromosome 12 as well. In 1996, the SCA2 gene was identified independently by three groups using different approaches. Pulst et al. (1996) constructed a physical map of the critical region using P1 artificial chromosomes (PACs) and bacterial artificial chromosomes (BACs) and then identified CAG repeatcontaining sequences. With a genomically based assay to detect expanded polyglutamines, Sanpei et al. (1996) detected a CAG-containing band on Southern blots hybridized under high-stringency conditions with a (CAG)55 oligonucleotide. The third approach made use of the 1C2 monoclonal antibody that recognizes long stretches of glutamines (Trottier et al., 1995). Imbert et al. (1996) identified clones in expression libraries generated from lymphoblastoid cDNAs generated from SCA2 and SCA7 patients. Interestingly, the clone, which was later shown to encode the SCA2 cDNA, was identified in the library made

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from patients with SCA7 and contained the normal alleles encoding 22 glutamines. The SCA2 gene contains 25 exons encompassing 130 kb of genomic DNA (Nechiporuk et al., 1997; Sahba et al., 1998).

Repeat range The SCA2 CAG trinucleotide repeat is unusual in several aspects. First, it is not highly polymorphic in normal individuals. Two alleles of 22 and 23 repeats account for more than 95% of alleles in most studies (Pulst et al., 1996; Sanpei et al., 1996; Riess et al., 1997; Cancel et al., 1997; Santos et al., 1999). Rare normal alleles ranging from 15 to 32 repeats have also been identified (Sanpei et al.,1996; Imbert et al., 1996; Riess et al., 1997). Second, normal alleles typically show one or two CAA interruptions. In contrast to the SCA1 gene, which contains CAT interruptions coding for histidine, the CAA interruptions do not interrupt the glutamine tract at the protein level. Thus, it may be more difficult to determine what biologic consequences are associated with intermediate alleles of 32 to 34 repeats containing CAA interruptions. Indeed, two patients carrying a 34 repeat allele containing one CAA interruption have been described (Costanzi-Porrini et al., 2000). Finally, the expansions on disease chromosomes are relatively small compared with those of SCA1 and SCA3. The most common disease alleles contain 37 to 39 repeats and are thus smaller than the longest normal alleles seen in the SCA3/MJD gene.

Pathologic alleles Although initial studies appeared to suggest a gap between normal and abnormal repeat sizes, it is now apparent that, similar to Huntington’s disease, alleles with reduced penetrance may exist. Initially, all symptomatic SCA2 patients had disease alleles of at least 36 repeats. In subsequent studies, several symptomatic individuals have been described carrying 34 or 35 repeat alleles (Malandrini et al., 1998). In the Holguin SCA2 population, the most common allele contained 37 repeats. A woman with a typical SCA2 phenotype and an age of onset of 48 years carried an SCA2 allele with 32 repeats (Santos et al., 1999). Recently, Fernandez et al. (2000) described a family segregating 33 CAG repeat alleles with very late onset.

Normal alleles In a study of 241 apparently healthy octagenarians, alleles longer than the most common alleles with 22 and 23 repeats were extremely rare. Four alleles contained 27 repeats, one allele had 29, and another one had 31 repeats (Riess et al., 1997). When 842 patients with sporadic

progressive ataxia were examined, 717 (85%) patients were homozygous for the 22 repeat allele. One patient had 30, four had 31, and two had 32 repeats (Riess et al., 1997). One of the patients with 32 repeats was homozygous for an expansion in the Friedreich’s ataxia gene. An allele of 34 repeats was seen in the asymptomatic mother of a woman with SCA2. An allele with 32 repeats has also been seen in an asymptomatic 19-year-old whose symptomatic father carried an allele of 40 repeats (Cancel et al., 1997). The contracted allele had no CAA interruptions. Thus, alleles with 32 and 33 repeats may be associated with very late onset or reduced penetrance.

Anticipation and meiotic instability of the SCA2 repeat As in other diseases caused by unstable CAG DNA repeats, there is a clear inverse correlation between age of onset and repeat length. However, this correlation is not linear and is best approximated by a negative exponential fit (Pulst et al., 1996). The widest range of age of onset is observed for fewer than 40 repeats (Fig. 27.1). For example, in one study the presence of 37 repeats was associated with ages of onset ranging from 20 to 60 years of age (Pulst et al., 1996). Even in the Cuban population, which is genetically more homogeneous, a repeat of 37 repeats was associated with an age of onset from 15 to 65 years of age (Fig. 27.1). For larger repeat sizes, the variability is less and repeat sizes of more than 45 are almost always associated with disease onset under 20 years of age (Pulst et al., 1996; Sanpei et al., 1996; Imbert et al., 1996; Riess et al., 1997; Cancel et al., 1997; Geschwind et al., 1997b). Homozygosity for an expanded SCA2 allele does not appear to influence age of onset (Sanpei et al., 1996), although the number of observations is small given the ranges observed with a specific repeat size. Animal studies, however, appear to suggest a clear dosage effect for mutant SCA2 alleles (Huynh et al., 2000). Initial observations in the FS pedigree from southern Italy (Pulst et al., 1993) did not point to consistent differences in the degree of anticipation depending on paternal or maternal inheritance. The lack of a paternal bias in expansion was also confirmed by Cancel et al. (1997). However, other studies have indicated that large expansions are almost exclusively observed when the repeat is passed through the paternal germline (Riess et al., 1997; Geschwind et al., 1997b). In addition to SCA2 CAG repeat length, CAG length in RAI1 alleles accounts for 4% of the variance in age of onset (Hayes et al., 2000). RAI1 is the human homologue of a mouse gene that encodes a protein of unknown function expressed during retinoic acid-induced differentiation of

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Expanded (CAG)n repeat length Fig. 27.1 Relationship between CAG repeat length and age of onset in 392 Cuban patients with SCA2. (Reproduced with permission from N. Santos et al., 1999, Biotecnologia Aplicada, Vol. 16, pp. 219–21.)

mouse embryonic carcinoma cells into neurons. An unknown sex-linked factor may also modify age of onset independent of CAG repeat length (Giuffrida et al., 1999a).

Frequency SCA2 is a frequent cause of ADCA. The identification of the SCA2 CAG repeat has now widened the scope of phenotypic analysis to smaller pedigrees and has provided an estimate of SCA2 frequency in different sets of ethnic and geographic populations. Geschwind et al. (1997b) found that, in an ethnically varied population in the ataxia clinic of the University of California at Los Angeles, SCA2 accounted for 13% of the ADCAs, compared with 6% for SCA1 and 23% for SCA3. No common haplotype was found on disease chromosomes. In a large series from several ataxia clinics in Germany, SCA2 represented 14% of ADCA pedigrees (Riess et al., 1997). A similar percentage (15%) was reported by Cancel et al. (1997) in a set of 184 families from an ethnically and geographically diverse population. In the Baylor Ataxia Clinic, SCA2 was actually the most common ADCA, with 18% (Lorenzetti et al., 1997). In

another clinic with samples from different ethnic groups, SCA2 accounted for 15.2% (Moseley et al., 1998). SCA2 is frequent in Italy, especially in southern Italy and Sicily (Giunti et al., 1998; Filla et al., 1999; Pareyson et al., 1999). In Spain, the frequency was 15% and similar to that of SCA3 (Pujana et al., 1999), whereas in Taiwan it was only 8.6% (Hsieh et al., 1999).

Haplotype Most studies indicate that SCA2 mutations have arisen on different founder chromosomes (Geschwind et al., 1997b). In Gunma prefecture, Japan, at least two founder haplotypes were identified (Mizushima et al., 1999). These authors also identified a CCG or CCGCCG interruption of the CAG repeat that can be useful for haplotype analysis. In contrast, Pang et al. reported an identical core haplotype established by alleles in the loci D12S1672 and D12S1333 in pedigrees of diverse ethnic origin from India, Japan, and England (Pang et al., 1999). This haplotype may, however, be common in these populations. In another study using samples from different ethnic and geographic groups, an analysis of 33 SCA2 pedigrees showed different

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D12S1332/S1333/S1672 haplotypes (Didierjean et al., 1999). German, Serbian, and some French families shared the same haplotype, suggesting a common founder or a recurrent mutation on an at-risk chromosome.

Sporadic patients Testing of DNA samples from patients with sporadic ataxia or without obvious family history of ataxia occasionally reveals SCA2 mutation. Only 2 of 842 sporadic ataxia patients in the series of Riess et al. (1997) had expansions of 41 and 49 repeats. In the series reported by Cancel et al. (1997), 2 out of 90 patients with sporadic olivo-ponto-cerebellar atrophy had alleles with 37 and 39 repeats. In a series by Moseley et al., a total of 5% of patients without obvious family history had a mutation in one of the known dominant ataxia genes. Of these, half were due to SCA2 mutation and half to SCA6 mutation (Moseley et al., 1998). In Italy, two of seven patients with late-onset ataxia had an SCA2 mutation (Giuffrida et al., 1999a). Two parent–child pairs in which the asymptomatic parent carries a premutation allele have been described (Riess et al., 1997; Futamura et al., 1998).

cDNA sequence, expression patterns The ataxin-2 cDNA sequence predicts a protein with 1312 amino acids with the CAG repeat coding for polyglutamine (Pulst et al., 1996; Sanpei et al.,1996). The 5 sequence of the SCA2 cDNA is extremely GC rich, and two potential ATG initiation codons can be identified. The most 5 ATG is located 78 bp downstream of an in-frame stop codon. Usage of this translation initiation site predicts a protein of 140.1 kD. The second ATG, which has a better Kozak consensus sequence, is located just 5 to the CAG repeat and would result in a protein with a relative molecular weight of 125 kD. Proteins observed by Western blot analysis and conservation of the 5 ATG in the mouse (Nechiporuk et al., 1998) suggest that the 5 ATG is the predominant site of translation initiation. Homology searches using the cDNA and amino acid sequences have not identified homologies with proteins of known function. However, significant sequence homology was detected with a protein designated ataxin-2-related protein (A2RP) and the mouse SCA2 protein (Pulst et al., 1996; Figueroa et al., submitted). Despite the significant homologies, the polyglutamine tract in human ataxin-2 is not present in A2RP or in mouse ataxin-2, suggesting that it may not be important for ataxin-2 function. However, all acidic amino acids comprising a highly acidic domain adjacent to the human polyglutamine domain are conserved in A2RP and mouse ataxin-2.

Despite a phenotype confined to dysfunction in the nervous system, the SCA2 gene is widely expressed in human and mouse tissues. On Northern blots, a 4.5-kb transcript is recognized in RNAs isolated from brain, heart, placenta, liver, skeletal muscle, and pancreas (Pulst et al., 1996; Sanpei et al., 1996; Imbert et al., 1996). Little or no expression is seen in lung or kidney. The transcript is expressed throughout the brain. In RNAs isolated from SCA2 lymphoblastoid cell lines, expression of both the normal and expanded alleles is seen using reversetranscribed polymerase chain reaction (Pulst et al., 1996). The SCA2 transcript in the mouse is of identical size (Nechiporuk et al.,1998). Expression during mouse embryonic development, with strong expression at days E11 and E12, suggests that ataxin-2 may have a role in normal embryogenesis. Interestingly, little protein expression is seen when mouse E11 embryos are stained with ataxin-2 antibodies, and at E12 the predominant organ staining is detected in the liver. Central nervous system staining is detected at later stages. The function of ataxin2 in development may not be essential, because mouse lines homozygously deleted for ataxin-2 have apparently normal development (A. Nechiporuk and S.-M. Pulst, personal communication). On the other hand, knock-out of ataxin-2 expression in Cenorhabditis elegans using RNA interference results in embryonic lethality (Kiehl et al., 2000).

Isoforms and genomic structure The SCA2 gene is transcribed from telomeric to centromeric and has 25 exons. The CAG repeat is contained in exon 1, which is also the largest exon, with 15 kb. The identification of exon–intron boundaries allowed the identification of alternatively spliced transcripts. A transcript deleted in frame for exon 10 appears to be enriched in the cerebellum, although the functional consequences of this splicing event are unknown at this point. Matsuura and colleagues (1999) described mosaicism in specific brain regions in a father–daughter pair. In the cerebellum, the repeat was three to eight repeats smaller than in other central nervous system regions.

Protein expression Antibodies to ataxin-2 recognize a 145-kD protein in mouse and human brains (Nechiporuk et al., 1998; Huynh et al., 1999). In addition, a larger protein of approximately 200 kD and several smaller proteins are recognized by these antibodies, suggesting that ataxin-2 may undergo post-translational processing and aggregation. In normal

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Day of testing Fig. 27.2 Progressive functional loss in SCA2[Q58] transgenic mouse lines. Rotarod analysis of mice from line Q58–11. The graph shows average performance on the rotarod apparatus of four trials each day on four consecutive days. Differences were significant for homozygous (hom) Q58–11 mice at 16 and at 26 weeks (two-way ANOVA compared with wild type, p0.0001), and for heterozygous (het) Q58–11 mice at 26 weeks (p0.0001). Numbers in parentheses indicate numbers of animals tested. (Reproduced with permission from D. Huynh, K. Figueroa, N. Hoang and S-M. Pulst (2000), Nature Genetics, Vol. 26, pp. 44–50.)

and SCA2 brains, ataxin-2 has a cytoplasmic localization. Antibodies to ataxin-2 or to expanded polyglutamine repeats did not detect intranuclear inclusions in Purkinje cells. The protein expression is not restricted to those neuronal populations that show the most severe degeneration. Ataxin-2 labeling is seen in a number of neuronal groups, including brainstem neurons, cranial nerve nuclei, and hippocampal neurons. Ataxin-2 interacts with a protein (A2BP) that is the human homolog of the C. elegans protein fox-1 (Shibata et al., 2000). Although Huynh et al. did not identify intranuclear inclusion bodies in three brains from SCA2 patients, Koyano et al. (1999) reported ubiquitinated intranuclear inclusions in a very small number of brainstem neurons. Purkinje neurons, however, did not show inclusions in Japanese patients, strongly suggesting that the formation of intranuclear inclusions is a late event and not necessary for pathogenesis.

(ataxin-2[Q58]), but not those with ataxin-2[Q22] showed a progressive motor deficit (Fig. 27.2). Similar to human SCA2 brains, ataxin-2 staining was increased in mouse Purkinje cells from Q[58] lines. Intranuclear inclusions were not seen, similar to results in human SCA2 Purkinje cells. Calbindin staining became abnormal at four weeks in homozygous animals and showed disruption of the dendritic arborization. There was a clear dosage effect. Homozygous animals showed functional impairment earlier than heterozygous animals. This was paralleled by more severe morphologic changes in homozygous animals.

Acknowledgments This work was supported by the Carmen and Louis Warschaw Endowment for Neurology, F.R.I.E.N.D.s of Neurology, the National Ataxia Foundation, and grant RO1–NS33123 (SMP).

Animal studies The generation of mouse models of human diseases has been instrumental in the understanding of neurodegeneration. Recently, Huynh et al. (2000) have expressed fulllength human ataxin-2 under the control of the Purkinje cell-specific Pcp2 promoter in C57BL/6JxDBA/2J mice. Only mice expressing ataxin-2 with 58 glutamine repeats

xReferencesx Adams, C.R., Starkman, S. and Pulst, S.M. (1997). Clinical and molecular analysis of a pedigree of southern Italian ancestry with spinocerebellar ataxia type 2. Neurology 49: 1163–6.

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Babovic-Vuksanovic, D., Snow, K., Patterson, M.C. et al. (1998). Spinocerebellar ataxia type 2 (SCA2) in an infant with extreme CAG repeat expansion. Am J Med Genet 79: 383–7. Belal, S., Cancel, G., Stevanin, G. et al. (1994). Clinical and genetic analysis of a Tunisian family with autosomal dominant cerebellar ataxia type 1 linked to the SCA2 locus. Neurology 44: 1423–6. Burk, K., Abele, M., Fetter, M. et al. (1996). Autosomal dominant cerebellar ataxia type 1: clinical features and MRI in families with SCA1, SCA2 and SCA3. Brain 119: 1497–505. Burk, K., Fetter, M., Abel, M. et al. (1999a). Autosomal dominant cerebellar ataxia type 1: oculomotor abnormalities in families with SCA1, SCA2, and SCA3. J Neurol Sci 246: 789–97. Burk, K., Globas, C., Bosch, S. et al . (1999b) Cognitive deficits in spinocerebellar ataxia 2. Brain 122: 769–77. Buttner, N., Geschwind, D., Jen, J.C. et al. (1998). Oculomotor phenotypes in autosomal dominant ataxias. Arch Neurology 55: 1353–7. Cancel, G., Dürr, A., Didierjean, O. et al. (1997). Molecular and clinical correlations in spinocerebellar ataxia 2: a study of 32 families. Hum Mol Genet 6: 709–15. Costanzi-Porrini, S., Tessarolo, D., Abbruzzese, C. et al. (2000). An interrupted 34-CAG repeat SCA-2 allele in patients with sporadic spinocerebellar ataxia. Neurology 54: 491–3. Didierjean, O., Cancel, G., Stevanin, G. et al. (1999). Linkage disequilibrium at the SCA2 locus. J Med Genet 36: 415–17. Durr, A., Smadja, D., Cancel, G. et al. (1995). Autosomal dominant cerebellar ataxia type 1 in Martinique (French West Indies). Clinical and neuropathological analysis of 53 patients from three unrelated SCA2 families. Brain 118: 1573–81. Estrada, R., Galarraga, J., Orozco, G. et al. (1999). Spinocerebellar ataxia 2 (SCA2): morphometric analyses in 11 autopsies. Acta Neuropathol (Berl) 97: 306–10. Fernandez, M., McClain, M.E., Martinez, R.A. et al. (2000) Lateonset SCA2: 33 CAG repeats are sufficient to cause disease. Neurology 55: 569–72. Filla, A., De Michele, G., Banfi, S. et al. (1995). Has spinocerebellar ataxia type 2 a distinct phenotype? Genetic and clinical study of an Italian family. Neurology 45: 793–6. Filla, A., De Michele, G., Santoro, L. et al. (1999). Spinocrebellar ataxia type 2 in southern Italy: a clinical and molecular study of 30 families. J Neurol 246: 467–71. Futamura, N., Matsumura, R., Fujimoto, Y. et al.(1998). CAG repeat expansions in patients with sporadic cerebellar ataxia. Acta Neurol Scand 98: 55–9. Gambardella, A., Annesi, G., Bono, F. et al. (1998). CAG repeat length and clinical features in three Italian families with spinocerebellar ataxia type 2 (SCA2): early impairment of Wisconsin Card Sorting Test and saccade velocity. J Neurol 245: 647–52. Geschwind, D.H., Perlman, S.B., Figueroa, K.P. et al. (1997a). Spinocerebellar ataxia type 6. Frequency of the mutation and genotype–phenotype correlations. Neurology 49: 1247–51. Geschwind, D.H., Perlman, S. B., Figueroa, K.P. et al. (1997b). The prevalence and wide clinical spectrum of the spinocerebellar ataxia type 2 trinucleotide repeat in patients with autosomal dominant cerebellar ataxia. Am J Hum Genet 60: 842–50.

Gispert, S., Twells, R., Orozco, G. et al. (1993). Chromosomal assignment of the second (Cuban) locus for autosomal dominant cerebellar ataxia (SCA2) to chromosome 12q23–24.1. Nat Genet 4: 295–9. Giuffrida, S., Lanza S., Restivo, D.A. et al. (1999a). Clinical and molecular analysis of 11 Sicilian SCA2 families: influence of gender on age at onset. Eur J Neurol 6: 301–7. Giuffrida, S., Saponara, R., Restivo, D.A. et al. (1999b). Supratentorial atrophy in spinocerebellar ataxia type 2: MRI study of 20 patients. J Neurol 246: 383–8. Giunti , P., Sabbadini, G., Sweeney, M.G. et al. (1998). The role of the SCA2 trinucleotide repeat expansion in 89 autosomal dominant cerebellar ataxia families. Frequency, clinical and genetic correlates. Brain 121: 459–67. Hayes, S., Turecki, G., Brisebois, K. et al. (2000). CAG repeat length in RAI1 is associated with age at onset variability in spinocerebellar ataxia type 2 (SCA2). Hum Mol Genet 9: 1753–8. Hsieh, M., Li, S.Y., Tsai, C.J. et al. (1999). Identification of five spinocerebellar ataxia type 2 pedigrees in patients with autosomal dominant cerebellar ataxia in Taiwan. Acta Neurol Scand 100: 189–94. Huynh, D.P., Del Bigio, M.R., Ho, D.H. et al. (1999). Expression of ataxin-2 in brains from normal individuals and patients with Alzheimer’s disease and spinocerebellar ataxia 2. Ann Neurol 45: 232–41. Huynh, D.P.; Figueroa, K.P., Hoang, N. and Pulst, S.M. (2000). Nuclear localization or inclusion body formation are not necessary for SCA2 pathogenesis in man or mouse. Nat Genet 26: 44–50. Ihara, T., Sasaki, H., Wakisaka, A. et al. (1994). Genetic heterogeneity of dominantly inherited olivopontocerebellar atrophy (OPCA) in the Japanese: linkage study of two pedigrees and evidence for the disease locus on chromosome 12q (SCA2). J J Hum Genet 39: 305–13. Imbert, G., Saudou, F., Yvert, G. et al. (1996). Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG glutamine repeats. Nat Genet 14: 285–91. Kiehl, T.R., Shibata, H. and Pulst, S.M. (2000). The ortholog of human ataxin-2 is essential for early embryonic patterning in C. elegans. J Mol Neurosci 00: 000–00. Kish, S.J., Lopes-Cendes, I., Guttman, M. et al. (1998). Brain glyceraldehyde-3-phosphate dehydrogenase activity in human trinucleotide repeat disorders. Arch Neurol 55: 1299–304. Klockgether, T., Ludtke, R., Kramer, B. et al. (1998a). The natural history of degenerative ataxia: a retrospective study in 466 patients. Brain 121: 589–600. Klockgether, T., Skalej, M., Wedekind, D. et al.. (1998b). Autosomal dominant cerebellar ataxia type 1. MRI-based volumetry of posterior fossa structures and basal ganglia in spinocerebellar ataxia types 1, 2, and 3. Brain 121: 1687–93. Koyano, S., Uchihara, T., Fujigasaki, H. et al. (1999). Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triplelabeling immunofluorescent study. Neurosci Lett 273: 117–20. Kubis, N., Durr, A., Gugenheim, M. et al. (1999). Polyneuropathy in autosomal dominant cerebellar ataxias: phenotype–genotype correlation. Muscle Nerve 22: 712–17.

Spinocerebellar ataxia type 2

Lopes-Cendes, I., Andermann, E., Attig, E. et al. (1994). Confirmation of the SCA-2 locus as an alternative locus for dominantly inherited spinocerebellar ataxias and refinement of the candidate region. Am J Hum Genet 54: 774–81. Lorenzetti, D., Bohlega, S. and Zoghbi, H.Y. (1997). The expansion of the CAG repeat in ataxin-2 is a frequent cause of autosomal dominant spinocerebellar ataxia. Neurology 49: 1009–13. Malandrini, A., Galli, L., Villanova, M. et al. (1998). CAG repeat expansion in an Italian family with spinocerebellar ataxia type 2 (SCA2): a clinical and genetic study. Eur Neurol 40: 164–8. Matsuura, T., Sasaki, H., Yabe, I. et al. (1999). Mosaicism of unstable CAG repeats in the brain of spinocerebellar ataxia type 2. J Neurol 246: 835–9. Mizushima, K., Watanabe, M., Kondo, I. et al. (1999). Analysis of spinocerebellar ataxia type 2 gene and haplotype analysis (CCG)1–2 polymorphism and contribution to founder effect. J Med Genet 36: 112–14. Moseley, M.L., Benzow, K.A., Schut, L.J. et al. (1998). Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 families. Neurology 51: 666–1671. Nechiporuk,T., Huynh, D.P., Figueroa, K. et al. (1998). The mouse SCA2 gene: cDNA sequence, alternative splicing and protein expression. Hum Mol Genet 8: 1301–9. Nechiporuk, A., Lopes-Cendes, I., Nechiporuk, T. et al. (1996). Genetic mapping of spinocerebellar ataxia type 2 gene on human chromosome 12. Neurology 46: 1731–5. Nechiporuk, T., Nechiporuk, A., Sahba, S. et al. (1997). A high-resolution PAC and BAC map of the SCA2 region. Genomics 44: 321–9. Orozco, G., Fleites, A., Cordoves Sagaz, R. et al. (1990). Autosomal dominant cerebellar ataxia: clinical analysis of 263 patients from a homogeneous population in Holguin, Cuba. Neurology 40: 1369–75. Orozco , G., Estrada, R., Perry, T.L. et al. (1989). Dominantly inherited olivopontocerebellar atrophy from eastern Cuba: clinical, neuropathological, and biochemical findings. J Neurol Sci 93: 37–50. Pang, J., Allotey, R.,Wadia, N. et al. (1999). A common disease haplotype segregating in spinocerebellar ataxia 2 (SCA2) pedigrees of diverse ethnic origin. Eur J Hum Genet 7: 841–5. Pareyson, D., Gellera, C., Castellotti, B. et al. (1999). Clinical and molecular studies of 73 Italian families with autosomal dominant cerebellar ataxia type I: SCA1 and SCA2 are the most common genotypes. J Neurol 246: 389–93. Pujana, M.A., Corral, J., Gratacos, M. et al. (1999). Spinocerebellar ataxias in Spanish patients: genetic analysis of familial and sporadic cases. The Ataxia Study Group. Hum Genet 104: 516–22. Pulst, S.-M. and Perlman, S. (2000). Hereditary ataxias. In Neurogenetics, ed. S.M. Pulst, pp. 231–63. New York: Oxford University Press. Pulst, S.-M., Nechiporuk, A., Nechiporuk, T. et al. (1996). Moderate

expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2. Nat Genet 14: 269–76. Pulst, S.-M., Nechiporuk, A. and Starkman, S. (1993). Anticipation in spinocerebellar ataxia type 2. Nat Genet 5: 8–10. Riess, O., Laccone, F., Gispert, S. et al. (1997). SCA2 trinucleotide expansion in German SCA patients. Neurogenetics 1: 59–64. Rivaud-Pechoux, S., Durr, A., Gaymard, B. et al. (1998). Eye movement abnormalities correlate with genotype in autosomal dominant cerebellar ataxia type 1. Ann Neurol 43: 297–302. Sahba, S., Nechiporuk, A., Figueroa, K.P., Nechiporuk, T. and Pulst S.-M. (1998). Genomic structure of the human gene for spinocerebellar ataxia type 2 (SCA2) on chromosome 12q24.1. Genomics 47: 359–64. Sanpei, K., Takano, H., Igarashi, S. et al. (1996). Identification of the spinocerebellar ataxia type 2 gene using a direct identification of repeat expansion and cloning technique, DIRECT. Nat Genet 14: 277–84. Santos, N., Aguiar, J., Fernandez, J. et al. (1999). Molecular diagnosis of a sample of the Cuban population with spinocerebellar ataxia type 2. Biotecnologia Aplicada 16: 219–21. Sasaki, H., Wakisaka, A., Sanpei, K. et al.. (1998). Phenotype variation correlates with CAG repeat length in SCA2 – a study of 28 Japanese patients. J Neurol Sci 159: 202–8. Schols, L., Amoiridis, G., Buttner T. et al. (1997a). Autosomal dominant cerebellar ataxia: phenotypic differences in genetically defined subtypes. Ann Neurol 42: 924–32 Schols, L., Gispert, S., Vorgerd, M. et al. (1997b). Spinocerebellar ataxia type 2: genotype and phenotype in German kindreds. Arch Neurol 54: 1073–80. Shibata, H., Huynh, D.P. and Pulst, S.-M. (2000). A novel protein with RNA binding motifs interacts with ataxin-2. Hum Mol Genet 9: 1303–13. Storey, E., Forrest, S.M., Shaw, J.H. et al. (1999). Spinocerebellar ataxia type 2: clinical features of a pedigree displaying prominent frontal-executive dysfunction. Arch Neurol 56: 43–50. Trottier, Y., Lutz, Y., Stevanin, G. et al. (1995). Polyglutamine expansion as a pathological epitope in Huntington’s disease and four dominant cerebellar ataxias. Nature 378: 403–6. Ueyama, H., Kumamoto, T., Nagao, S. et al. (1998). Clinical and genetic studies of spinocerebellar ataxia type 2 in Japanese kindreds. Acta Neurol Scand 98: 427–32. Velazquez, L. and Medina, E.E. (1998). Electrophysiological characteristics of asymptomatic relatives of patients with type 2 spinocerebellar ataxia. Rev Neurol 160: 955–63. Wadia, N., Pang, J., Desai, J. et al., (1998). A clinicogenetic analysis of six Indian spinocerebellar ataxia (SCA2) pedigrees. The significance of slow saccades in diagnosis. Brain 121: 2341–55. Wadia, N.H. and Swami, R.K. (1971). New form of heredo-familial spinocerebellar degeneration with slow eye movements (nine families). Brain 94: 359–74.

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Spinocerebellar ataxia type 3 S.H. Subramony and Paraminder J.S. Vig Department of Neurology, University of Mississippi Medical Center, USA

Historical introduction Spinocerebellar ataxia type 3 (SCA3) is a form of dominant ataxia which, prior to the recognition of its genotype, would have been labeled as Marie’s ataxia, olivoponto-cerebellar atrophy, or autosomal dominant cerebellar ataxia type 1. The occurrence of a dominant ataxia among the Azorean immigrants to the USA was first described by Nakano et al. (1972) in the family of William Machado from Massachusetts. A second family from the Azores, descended from Anton Joseph, with a dominantly inherited neurodegenerative disease that was primarily characterized by spasticity and rigidity, was described from California by Rosenberg et al. (1976). Neuropathologic examination in this family showed loss of nigral and spinal cord neurons. Other Azorean families with a similar disorder had members with a Parkinsonian phenotype (Romanul et al., 1977). Field trips to the Azores by Portuguese and American workers found a high prevalence of this dominantly inherited neurodegenerative disorder among the residents of the Azorean islands (Coutinho and Andrade, 1978). The disease was characterized by considerable intrafamilial variation in clinical phenotype; both the ataxic and the spastic-rigid phenotypes were found within the same families, and the disease was variously named Machado–Joseph disease and Azorean disease of the nervous system (Romanul et al., 1977; Dawson, 1977). Though the disorder shared many features with dominantly inherited cerebellar ataxia in nonPortuguese populations, its unique phenotypic variability was thought to reflect a disease prevalent only among the Portuguese Azoreans. A similar clinical disorder occurring in non-Portuguese families was thought to result from the introduction of Portuguese genes into these ethnic groups (Healton et al., 1980; Sakai et al., 1983; Subramony et al., 1993). Others, however, maintained that the clinical features of Machado–Joseph disease did not reliably distinguish it

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from other dominantly inherited ataxias (Harding, 1984). As the understanding of the genetic heterogeneity of the dominant ataxias grew in the early 1990s, it became apparent that the gene locus for Machado–Joseph disease was not identical to that of spinocerebellar ataxia type 1 (SCA1). The gene weas localized to chromosome 14q in Japanese families with Machado–Joseph disease and also in Portuguese families (Takiyama et al., 1993; St George-Hyslop et al., 1994; Sequeiros et al., 1994). The gene mutation was shown to involve an unstable expansion of a CAG repeat sequence in a gene coding for a novel protein, subsequently labeled as the MJD 1 gene (Kawaguchi et al., 1994) The same mutation was also shown to occur in many families with dominant ataxia worldwide. Many of these families had clinical features similar to those of other dominant ataxias such as SCA1 and SCA2, from which they could not be reliably distinguished based on phenotype alone. Stevanin et al. (1995b) suggested the term SCA3 for this phenotype. Thus, the identical CAG repeat expansion in the MJD 1 gene on chromosome 14q occurs in families with the clinical diagnosis of Machado–Joseph disease as well as SCA3. As with other genetic disorders, it is now possible to make a retrospective diagnosis for families whose details were published earlier in the literature. As an example, the Drew family of Walworth, described in 1929 by Ferguson and Critchley, is now known to result from the SCA3 mutation (Lazzarini et al., 1992; Giunti et al., 1995).

Prevalence of SCA3 Several workers have examined the prevalence of SCA3 among the dominant ataxias; Table 28.1 summarizes some of the data. In many series, SCA3 constitutes the major category among the molecularly defined ataxias, varying from about 20% in US series to close to 50% in German and

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Table 28.1 Prevalence of SCA3 among dominant ataxias

Table 28.2 Prevalence of neurological signs in SCA3*

Series

Ethnicity

SCA3 (%)

Schols et al. (1995) Durr et al. (1996) Inoue et al. (1996) Watanabe et al. (1996) Moseley et al. (1998) Takano et al. (1998)

German European, North African Japanese Japanese African American, German Caucasian Japanese

50 28 56 34 21 30 43

A/O (range) A/O (mean) Ataxia Dysarthria Dysphagia Ophthalmoparesis Nystagmus Upper motor neuron signs Lower motor neuron signs Sensory loss Basal ganglia signs: dystonia, akinesia

Japanese series (Schols et al., 1995; Durr et al., 1996; Inoue et al., 1996; Watanabe et al.,1998; Moseley et al., 1998). Takano et al. (1998), in a comparative study of Japanese and Caucasian dominant ataxia families, found a higher prevalence of SCA3 in Japan and speculated that this may be related to the higher prevalence of large normal alleles in the Japanese population compared to Caucasian populations. Interestingly, in a study of 29 families with autosomal dominant ataxia from Italy, no SCA3 was found (Filla et al., 1996). Also of interest, Ramesar et al. (1997) reported no SCA3 among 14 South African families with dominant ataxias: this is intriguing in view of the frequent occurrence of the disease among African Americans (Subramony, personal observations). The mutation is rarely detected in patients with the diagnosis of ‘sporadic ataxia’ (Schols et al., 1995; Moseley et al., 1998).

Clinical features The age of onset of SCA3/Machado–Joseph disease is variable and ranges from childhood to late adult life. Most patients have onset in the second to fourth decade; the mean age of onset in a large cohort of patients reported by Sequeiros and Coutinho (1993) was 37 years, and in many other series the mean age of onset is in the mid-thirties. The range of onset age reported in representative series varies from 5 to 70 years (Cancel et al., 1995; Schols et al., 1996; Watanabe et al., 1996; Zhou et al., 1997). Table 28.2 summarizes the prevalence of various clinical signs in some representative series of patients (Sequeiros and Coutinho, 1993; Takiyama et al., 1994; Cancel et al., 1995; Sasaki et al., 1995; Higgins et al., 1996; Matsamura et al., 1996a; Durr et al., 1996; Schols et al., 1996; Watanabe et al., 1996; Zhou et al., 1997). It is clear that, apart from the ataxia related to cerebellar dysfunction, there are numerous other signs related to the brainstem, oculomo-

5–70 years 30–38 years 95–100% 62–100% 29–77% 40–100% 67–100% 25–100% 11–67% 19–80% 7–80%

Other signs: bulging eyes and ocular stare, blepharospasm, perioral fasciculations, temporal atrophy, limb atrophy Notes: A/O  age at onset. Source: *References: Takiyama et al. (1994); Sasaki et al. (1995); Cancel et al. (1995); Durr et al. (1996); Higgins et al. (1996); Schols et al. (1996); Matsumura et al. (1996a); Watanabe et al. (1996); Zhou et al. (1997).

tor system, pyramidal system, extrapyramidal system, peripheral nervous system, and lower motor neuron. Typically, patients present with gait imbalance and slurring of speech. Visual blurring and diplopia may be early symptoms as well. There is gradual progression of neurological deficits, involving increasing motor dysfunction, bulbar symptoms and signs, and oculomotor deficits. Eventually, there is loss of ambulation. Death results from immobility, nutritional impairment, and respiratory compromise. Progressive ataxia, dysarthria, spasticity, hyperreflexia, and nystagmus characterize the early phase of the disease. As the disease evolves, there is slowing of saccades and ophthalmoplegia with early limitation of up-gaze and disconjugate eye movements. Ophthalmoplegia is supranuclear in its characteristics (Coutinho and Andrade, 1978). The temporal and facial muscles undergo atrophy; perioral muscle twitches, often induced by labial movement, are frequent. The tongue may appear mildly atrophic and may have fasciculations. Some impairment of cough is present, even early in the disease. Evidence of peripheral nerve involvement is present in the form of loss of distal sensation and ankle areflexia. Amyotrophy and fasciculations of the limb muscles may occur, usually later in the course of the disease, but profound atrophy and weakness are rare. Deep tendon reflexes that were previously brisk may become hypoactive. Late in the disease, patients are chairbound, have severe dysarthria and

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dysphagia, facial and temporal atrophy, ineffective cough, ophthalmoparesis, dystonic posturing, and amyotrophy. Schols et al. (1997) compared the phenotypes of different dominant ataxias and noted that diplopia, severe spasticity, and pronounced peripheral neuropathy were more frequently associated with SCA3. In our experience, prominent extrapyramidal signs, often responsive to -dopa, in some affected members of the family were clinical clues to the SCA3 mutation (Subramony et al., 1993). Many, but not all, families may exhibit startling phenotypic variability among affected persons that cannot be accounted for by duration of disease alone (Subramony and Currier, 1996). Based on this variability, Portuguese workers classified Machado–Joseph disease into several types (Sequeiros and Coutinho, 1993). Type 1 disease has a younger age of onset (mean about 25 years) and is characterized by prominent spasticity and rigidity, bradykinesia, and minimal ataxia (Rosenberg et al., 1976); it constitutes 10–13% of cases. Type 2 disease has an intermediate age of onset (mean about 38 years); it is characterized by progressive ataxia and upper motor neuron signs. This is the most common phenotype; comprising 57% in the series of Sequeiros and Coutinho (1993) and 76% in the series of Matsumura et al. (1996a). Type 3 phenotype has a mean age of onset of 48 and manifests with ataxia and more significant evidence for peripheral nerve involvement with amyotrophy and generalized areflexia. A type 4 phenotype with Parkinsonian features has also been described. Parkinsonian features are prominent in some families (Romanul et al., 1977; Cancel et al., 1995). Many of the clinical phenomena have received more detailed attention.

Cognitive dysfunction Disabling dementia is not a feature of SCA3, even in the late stages. Maruff et al. (1996) have examined visual memory, attention, and execution in a small sample of six patients with SCA3 using the Cambridge Neuropsychological Test Automated Battery (CANTAB). They found abnormalities of visual attention characterized by slow processing of complex visual information and an inability to shift attention. They proposed that this reflected a syndrome of frontal subcortical dysfunction.

Oculomotor involvement Patients with Machado–Joseph disease may exhibit many other ocular signs apart from those already described. Ptosis occurs in close to 20% cases (Watanabe et al., 1996). Lid retraction and apparent bulging of the eyes can be

seen, but are not early signs (Coutinho and Andrade, 1978; Watanabe et al., 1996; Zhou et al., 1997). Blepharospasm occurs in some patients, usually later in the disease. Buttner et al. (1998) performed electro-oculographic examination of eye movements in different types of SCAs. Gaze-evoked and rebound nystagmus was frequent in SCA3. Peak saccade velocity was relatively preserved in SCA3 in contrast to the slowing observed in SCA2. Moderate pursuit gain abnormalities were observed. A significant reduction in vestibulo-ocular reflex gain was observed in contrast to normal results in SCA1, SCA2, and SCA6. Burk et al. (1996) also found a relative preservation of saccade velocity in SCA3, especially in contrast to SCA2; in this study, saccade velocity was slow in SCA1 patients as well. Rivaud-Pechoux et al. (1998) noted that SCA3 patients had a high incidence of gaze nystagmus together with hypometria of visually guided saccades and abnormal smooth pursuit. Saccade velocity was relatively preserved.

Peripheral nerve involvement Klockgether et al. (1999) studied 58 patients with SCA3 and found the sural sensory response and tibial motor response to be of low amplitude compared to controls. Age of the patient at the time of the study best correlated with the degree of abnormality, suggesting that the normal agerelated attenuation of these responses was accentuated in Machado–Joseph disease. The CAG repeat number had no effect. An axonal neuropathy detected by nerve conduction studies was found in 60% of the patients by Durr et al. (1996). A sensory motor polyneuropathy was also found in four patients studied by Soong and Lin (1998); these authors also noted loss of large myelinated fibers in sural nerve biopsies; large repeat sizes correlated with loss of fiber density.

Sleep disturbances Among 51 patients with SCA3 studied using a questionnaire, 26 had restless legs syndrome; this was less common in SCA1, SCA2, and SCA6 (Schols et al. 1998). Though clinically evident polyneuropathy was more common among those with restless legs syndrome, electrophysiologic evidence for a neuropathy was found equally among those with and without it. SCA3 patients also had greater trouble falling asleep and more nocturnal awakening; sleep impairment was more common in older patients and in patients with greater impairment of brainstem function. Central sleep apnea has been documented in some patients (Kitamura et al., 1989).

Spinocerebellar ataxia type 3

Autonomic disturbances Sphincter disturbances occur in close to a third of the patients (Durr et al., 1996; Matsumura et al., 1996a). More prominent autonomic disturbance in the form of impotence and orthostatic hypotension has been occasionally seen, including in a patient with a short CAG expansion (56 repeats) (Takiyama et al., 1997).

Evoked potentials Increased latencies of visual and brainstem evoked responses have been noted in SCA3 patients by Durr et al. (1996).

Imaging studies A number of studies have examined the brain imaging abnormalities in patients with SCA3. Abe et al. (1998) studied magnetic resonance imaging (MRI) abnormalities in 30 patients with SCA3 and found significant brainstem and cerebellar atrophy, even when this was expressed in relation to skull size. When the degree of atrophy was related to the age at examination, the severity of atrophy was related to the CAG repeat size. On the other hand, the degree of atrophy had no relation to duration of disease alone. Also, atrophy expressed as per year of disease duration had no relation to CAG repeat size. This suggests that atrophy probably begins very early in life and is related to the expansion size of the CAG repeat. In planimetric and volumetric studies comparing brain MRIs in SCA1, SCA2, and SCA3, Burk et al. (1996) and Klockgether et al. (1998) have shown atrophy of the brainstem and cerebellum in all the types, but most prominent in SCA2. Significant decreases in caudate and putaminal volumes were found only in SCA3; perhaps this could relate to the more prominent basal ganglia signs often found in SCA3. Recent positron emission tomographic studies have shown hypometabolisn not only in the cerebellum and brainstem of these patients but also, unexpectedly, in the occipital cortex (Soong et al., 1997).

Neuropathology Sequeiros and Coutinho (1993) have reviewed the neuropathology of this disease. Though there was considerable variability in the neuropathologic phenotype, some findings were consistent enough for them to propose a set of neuropathologic criteria. They found the following structures to be consistently involved: substantia nigra and subthalamic nuclei; red nuclei; medial longitudinal fasciculus;

pontine nuclei and the middle cerebellar peduncles; dentate nuclei; Clarke’s column and spinocerebellar tracts; vestibular nuclei; anterior horn cells; motor cranial nerve nuclei; posterior root ganglia; and posterior columns. The cerebral cortex, striatum, cerebellar cortex, olivary nuclei, and corticospinal tract were found to be spared. The cerebellar signs appear to be related to pontine and dentate pathology; the akinetic-rigid syndrome occasionally seen in the disorder to substantia nigra pathology. The usual corticospinal tract signs found are not readily explained by this pathology.

Molecular genetics Takiyama et al. (1993) localized the gene for Machado– Joseph disease to chromosome 14q 24.3–q32, and Kawaguchi et al. (1994) described the unstable expansion of a repeated CAG sequence within the coding region of the MJD 1 gene in this area. The CAG repeat occurs near the Cterminus of the MJD 1 gene. The gene consists of a 1776base pair coding region with one, long, open reading frame. Variations in the (CAG)n sequence occur in normal alleles: the third, fourth, and sixth CAG may be replaced by CAA, AAG, and CAA, respectively (Kawaguchi et al., 1994; Limprasert et al., 1996). Such variant triplet repeats also occur in the expanded alleles. The CAG repeat is highly polymorphic in normal individuals, varying from 12 to 43 in number (Matilla et al., 1995; Ranum et al., 1995; Sasaki et al., 1995; Cancel et al., 1995; Maciel et al., 1995; Matsumura et al., 1996a). Over 90% of the alleles have fewer than 31 repeats (Takiyama et al., 1995; Limprasert et al., 1996). The number of (CAG)n in normal alleles often assumes a bimodal or trimodal distribution with peaks at 14, 22 to 24, and 27 repeats. Among 748 normal chromosomes examined by Rubinsztein et al. (1995), 14 and 21–23 repeat alleles were the most frequent in different populations, a finding similar to that reported by Limprasert et al. (1996). The nucleotide following the (CAG)n is usually guanine; however, when the repeat number is either 20 or 21 and in over half the alleles with repeat size over 27, the guanine is replaced by cytosine (Limprasert et al., 1996; Matsumura et al., 1996b). Cytosine also occurs at this region in all expanded alleles. This cytosine may play a role in the instability of the repeat.

Expanded repeat The mutation responsible for Machado–Joseph disease is an unstable expansion of the (CAG)n sequence in the MJD 1 gene. This expansion has now been documented in a

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considerable number of families with dominant ataxia from many ethnic groups (Kawaguchi et al., 1994; Matilla et al., 1995; Ranum et al., 1995; Maciel et al., 1995; Schols et al., 1996; Silveira et al., 1996). In many areas of the world, this is the most common mutation responsible for dominant ataxia. The mutated alleles have ranged from 56 to 86 repeats and can be clearly distinguished from normal alleles based on repeat size alone. DNA-based mutation analysis using polymerase chain reaction (PCR) or Southern blotting can unequivocally establish the diagnosis of SCA3.

years. Typically, anticipation is more prominent with paternal than with maternal inheritance of the disease. Very often, the observed anticipation cannot all be accounted for by the intergenerational expansion size. Some anticipation may reflect bias in the ascertainment of age of onset and the failure to include people with later ages of onset who may still be asymptomatic at the time of study. Takiyama et al. (1998) have reported significant anticipation with maternal transmission, with almost no change in CAG repeat size, suggesting genetic factors other than CAG repeat contributing to anticipation.

Somatic and gametic instability of the expanded repeat

Other issues

The number of CAG repeats in the normal alleles does not vary from tissue to tissue in autopsied individuals, nor does it change with intergenerational transmission (Limprasert et al., 1996). The expanded repeat, however, shows mosaicism as revealed by PCR products of several molecular weights in different tissues (Maciel et al., 1996). The cerebellar cortex typically has smaller repeat sizes compared to other areas of the central nervous system, including areas unaffected by disease, a finding that has also been observed in other CAG expansion diseases. Hashida et al. (1997) have speculated that this may be related to large numbers of granule cells, which may have smaller repeat sizes. Many workers have noted intergenerational instability of the repeat size (Takiyama et al., 1995; Maciel et al., 1995). In Maciel’s study, 55% of 58 parent–child transmissions were unstable. Over 75% of the instability resulted in an expansion. Though the number of contractions and expansions of the repeat was similar between paternal and maternal transmissions, paternal transmission caused greater volatility of the repeat with regard to both contractions and expansions. Sasaki et al. (1995) also noted greater instability of the repeat with paternal than with maternal transmission. Direct evidence for meiotic instability is provided by the occurrence of a larger number of PCR products in sperm than in leukocytes (Cancel et al., 1995; Watanabe et al., 1996), even though the major allele in sperm may have a smaller repeat size. Overall, the range of variation in repeat size from one generation to the next has varied from 8 to 9 repeats. Apart from paternal transmission, the presence of an intragenic CGG/GGG polymorphism has been linked to the intergenerational instability (Igarashi et al., 1996). The occurrence of anticipation in the age of onset is well documented in SCA3. Durr et al. (1996), for example, noted a mean anticipation of 12 years in the age of onset; Takiyama et al. (1994) noted a mean anticipation of 9.2

A non-Mendelian inheritance pattern of the disease has been reported by Ikeuchi et al. (1996), who noted that 73% of children from affected fathers were involved, significantly in excess of the expected 50%. This pattern was not found among offspring of affected mothers. Rubinsztein and Leggo (1997) have examined the transmission of normal-sized alleles of different repeat lengths and found that males transmitted larger and smaller alleles equally; however, females transmitted the smaller alleles preferentially. This observation is at variance with the paternal effect reported in the transmission of the expanded allele. The occurrence of linkage dysequilibrium at the SCA3 locus has been examined. Stevanin et al. (1995a) found several different haplotypes in patients from different geographic areas, suggesting multiple mutational origins for SCA3 worldwide. Gaspar et al. (1996) studied 64 unrelated patients, mostly from the Azores and Portugal, and nearly all shared a specific allele at locus D14S280, suggesting a founder effect in this population. However, Lima et al. (1998), studying 32 families from the Azores, could not establish a link between families from the island of Sao Miguel and families from the other islands in the Azores; even molecular studies revealed two distinct haplotypes in these families, suggesting more than one mutational event in the Azores. Takiyama et al. (1995) found at least some shared haplotypes between Japanese and Azorean patients with SCA3, again suggesting a common founder or a predisposing haplotype toward CAG expansion.

Phenotype–genotype correlation As in other CAG repeat disorders, there is an inverse correlation between age of onset and the number of CAG repeats in the expanded allele, with correlation coefficient varying from 0.67 to 0.92. The largest repeat sizes of 86 and 83 reported by Zhou et al. (1997) from China occurred in

Spinocerebellar ataxia type 3

children with ages of onset at 5 and 11 years, respectively. There is a loose correlation between the overall clinical phenotype and the expansion size. Patients with type 1 disease have larger repeat sizes than those with type 2 and 3 phenotypes. In Sasaki’s study (1995), patients with type 1, type 2, and type 3 phenotypes had mean repeat sizes of 80, 76, and 73, respectively. Maciel et al.’s study (1995) noted a mean repeat size of 76 5 in type 1 patients. Schols et al. (1996) reported repeat sizes of 79 and 81 in two type 1 patients; but four patients with repeat size of over 80 were classified as type 2, illustrating the less than optimal correlation between phenotype and CAG repeat size. These authors noted the rarity of peripheral neuropathy signs in patients with repeat size larger than 73. This is in keeping with the observations of Durr et al. (1996) that generalized areflexia and signs of peripheral polyneuropathy occurred mainly in patients with fewer than 71 repeats. In their study, Durr et al. (1996) found that many other clinical signs, such as amyotrophy, ophthalmoplegia, dysphagia, and sphincter difficulties, were correlated more with disease duration than with the CAG repeat size. The occurrence of pyramidal signs and bulging eyes has also been related to larger repeat sizes in one series (Takiyama et al., 1995). In a Yemenese family reported by Lerer et al. (1996), several homozygotes were reported to have an earlier onset and a more rapid progression than heterozygotes, similar to observations in Portugal (Rosenberg, 1984). The expansion size in this family was limited (66 to 72) and some heterozygotes remained asymptomatic well into their seventh decade. Other patients with small expansions and late adult onset may have a ‘pure cerebellar’ presentation.

Pathogenetic mechanisms The MJD gene codes for a novel protein, named ataxin-3, with a predicted molecular weight of 42 Kd. Because the CAG codes for glutamine, ataxin-3 has a polyglutamine stretch of variable length near its COOH terminal. Reverse transcriptase-PCR (RT-PCR) analysis of normal human and rat brain has revealed the MJD 1 transcript in many areas. In-situ hybridization revealed MJD 1 expression to be relatively high in the cerebellum, hippocampus, substantia nigra, striatum, and cerebral cortex. The mRNA content of different neurons appeared to be similar (Nishiyama et al., 1996). Western blot and immunohistochemical studies using ataxin-3-specific antibodies have revealed that ataxin-3 is widely distributed in neuronal as well as in non-neuronal tissues. In electrophoretic studies, ataxin-3 migrates more slowly than predicted from its molecular weight, a feature that it shares with other poly-

glutamine proteins. In the brain, samples from the cortex, striatum, brainstem, and cerebellum expressed a prominent doublet band immunoreactive to a polyclonal ataxin3 antibody and corresponding to the full-length ataxin-3 (Paulson et al., 1997a). Immunohistochemical examination of cells transfected with normal full-length ataxin-3 as well as normal central nervous tissue shows a predominantly cytoplasmic localization for ataxin-3 with at best faint nuclear staining. In studies on COS cells and neuroblastoma cells transfected with ataxin-3 with a 22 glutamine repeat, Tait et al. (1998) showed that ataxin-3 indeed has a nuclear localization. In fact, untransfected cells showed predominantly a nuclear localization of ataxin-3; transfected cells showed both a cytoplasmic and a nuclear localization. In the nucleus, Tait et al. (1998) showed that ataxin-3 was associated with the nuclear matrix. In neuronal cytoplasm, ataxin-3 has a somato-dendritic distribution with some extension into axonal processes (Paulson et al., 1997a). In different brain regions, only subpopulations of neurons were positive, staining being particularly pronounced in the pontine neurons and in the anterior horn cells, both targets of the disease. Schmidt et al. (1998) have suggested ataxin-3 may be expressed in a heterogeneous pattern and may have multiple isoforms. There is no significant information on the normal function of ataxin-3. It has a large coiled-coil domain just N-terminal to the glutamine repeat that may be important in protein–protein interactions (H. Paulson, personal communication). Ataxin-3 is small enough to get into the nucleus and may not require assisted transport by karyopterins, though a potential nuclear localization signal and two casein kinase II sites upstream from the polyglutamine repeats have been suggested by Tait et al. (1998). Perez et al. (1999) have proposed that ataxin-3 in the nucleus may assume a different conformation that makes the polyglutamine repeat more accessible, based on the fact that in the context of the nucleus, the 1C2 antibody tends to recognize ataxin-3 with a non-pathogenic glutamine repeat; in the cytoplasm, this antibody tends to bind preferentially to ataxin-3 with glutamine repeat in the pathologic range. The exact mechanism by which the inheritance of a single mutated copy of the MJD gene results in a progressive but selective neuronal degeneration is not yet clear. Because affected individuals also inherit a normal copy of the gene, several possible mechanisms have been considered in these dominant disorders, including a partial deficiency of the protein (due to inability of the mutated gene to encode the protein: haploinsufficiency), a dominant negative effect (interference of the function of the normal protein by the mutated protein), and the gain of a novel function by the mutated protein that is toxic to cells.

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Fig. 28.1 Intranuclear inclusions as seen in pontine neurons of a patient with SCA3 and identified by a polyclonal antibody to ataxin-3. (Antibody kindly provided by Dr H. Paulson.)

MJD 1 mRNA has been found in disease brain in a fashion comparable to that in normal brain tissue (Nishiyama et al., 1996). Immunoblot studies of brain tissue from affected individuals using a polyclonal ataxin3 antibody showed two distinct bands of reactivity corresponding to the protein products of both the normal and the mutated allele. The molecular weight of the heavier and slower migrating band, corresponding to the mutated allele with a larger number of CAG repeats, varied with the number of the CAG repeats in the mutated allele (Paulson et al., 1997b). Thus, both the normal and the expanded alleles are transcribed and translated. The expression of the mutant protein occurred in both the affected and nonaffected tissues of patients in approximately equal amounts, lending credence to the idea that a partial deficiency of the protein was not responsible for the disease. The subcellular distribution of ataxin-3 is altered in affected brain tissue. In those regions of the brain known to be the targets of the disease, many surviving neurons contained densely stained, rounded intranuclear inclusions

(NIs) recognized by both polyclonal and monoclonal antibodies to ataxin-3 (Paulson et al., 1997b). These inclusions were most abundant in the pontine neurons, but also occurred in the substantia nigra, globus pallidus, and inferior olive neurons; there were no inclusions in glial cells (Fig. 28.1). Cerebellar Purkinje cells have not been reported to have inclusions. The inclusions are recognized by the monoclonal antibody 1C2, which recognizes polyglutamine stretches in the context of different proteins; staining with the 1C2 antibody occurred at dilutions that tend to preferentially recognize expanded polyglutamine domains. These studies suggested that ataxin-3 with the expanded polyglutamine domain is a component of the nuclear inclusions and that the mutated protein may have acquired novel properties that allowed it to aggregate in the nucleus. Both the aggregation formation resulting from the mutated ataxin-3 and its possible pathogenic mechanisms have been modelled in transgenic and transfection systems. Ikeda et al. (1996) expressed the mutated MJD 1

Spinocerebellar ataxia type 3

gene with 79 repeats in a transgenic mouse model using a Purkinje cell-specific promoter. Transgenic mice, resulting from constructs expressing the full-length protein with the expanded repeat, did not develop an ataxic phenotype. Mice expressing various truncated constructs containing the expanded repeat developed ataxia and had cerebellar atrophy. Truncated constructs containing a normal number of repeats did not develop a neurologic phenotype either. A similar effect of truncated constructs has also been noted in a Drosophila model of SCA3 in which targeted expression of the mutated gene has been shown to cause neuronal loss (Warrick et al., 1998). In this model, neuronal degeneration is accompanied by formation of nuclear inclusions. Ikeda et al. (1996) also showed that expression of a truncated construct with the expanded repeat resulted in increased apoptotic cell death in COS cells. Paulson et al. (1997b) also noted that 293T cells expressing a truncated version of the MJD protein with an expanded CAG repeat suffered excessive apoptosis and formed perinuclear and intranuclear aggregates reminiscent of the aggregates found in diseased human brain. Thus, truncation of ataxin-3 resulting in fragments containing the expanded repeat appears essential for pathology in these model systems. Even more recently, Yoshizawa et al. (2000) again noted that truncated forms of ataxin-3 were more toxic to cultured BHK-21 cells. In this model, cell cycle arrest in the G0/G1 phase enhanced this toxic effect. However, high-level expression of full-length ataxin3 with an expanded repeat in a rat mesencephalic cell line resulted in nuclear inclusion formation (Evert et al., 1999). This model also resulted in decreased viability of the neurons, though the neuronal death bore no correlation to NI formation. Whether the NIs that occur in human neural tissue and model systems are essential for the pathogenesis of neuronal degeneration remains unsettled. In the case of SCA1, Klement et al. (1998) have provided evidence that preventing large aggregation of mutant ataxin by deleting a selfaggregation domain from the molecule does not prevent cell toxicity in a transfection model. However, preventing nuclear entry of ataxin-1 by knocking out the nuclear localization signal normally expressed by ataxin-1 results in loss of pathogenic effect. Thus, nuclear entry is essential for mutant ataxin-1 to cause cell death in such transfection systems. No similar study has been done in SCA3, but there is evidence that many cell types will suffer no excessive death despite the presence of aggregates in the nuclei, as shown in the wing and limbs of the Drosophila model. Similarly, we have never observed nuclear inclusions in the cerebellar Purkinje cells in many patients dying of SCA3 (Subramony and Vig, unpublished obervations), despite

the fact that quantitative studies have documented Purkinje cell loss in these patients (Bebin et al., 1990). However, the detailed biochemistry and protein composition of the NIs in SCA3 have been the focus of continued studies by Paulson, Pittman, and colleagues. These efforts have shown that the polyglutamine domain is important in mediating the recruitment of other proteins as well as for possible self-association of mutant ataxin-3 (Perez et al., 1998). Though truncated protein containing the expanded glutamine tract appears essential for initiating the NI formation, it has been shown to recruit full-length protein with the expanded repeat. Full-length ataxin that lacks the glutamine stretch cannot be recruited into the NI; on the other hand, large aggregations of mutant ataxin-1 can secondarily recruit full-length ataxin-3 into them as long as the glutamine tract of the latter has not been deleted. Similarly, green fluorescent protein (GFP) fused to stretches of 19 or 35 glutamine repeats will be recruited into ataxin-3 NIs, but GFP alone will not. Finally, endogenous proteins containing glutamine stretches can often be colocalized in NIs; examples include the eye absent protein (EYA) in the Drosophila model and TATA-binding protein in human tissue. These data suggest that the glutamine tract in the mutant protein, as well as possibly in other proteins, may be important for such protein to be recruited into the NIs. This is consistent with the polarzipper hypothesis put forward by Perutz et al. (1994). In addition, ubiquitin is an almost constant colocalizing protein in the NIs. The presence of ubiquitin suggests misfolding of the protein in the NIs. Ubiqitin-dependent protein degradation depends on a multicatalytic complex called the proteasome. Many components of the proteasome complex can be detected in the NIs. Proteasome colocalization appears to be a common phenomenon in the aggregates formed by several polyglutamine proteins. Proteasome may serve to eliminate the misfolded protein; consistent with this idea, inhibition of proteasome by lactastatin has been shown to increase aggregation formation in HeLa cells transfected with a truncated MJD construct with 49 repeats (Chai et al., 1999b). Interestingly enough, this increased aggregation did not result in increased cell toxicity. Components of the heat-shock protein (hsp) –chaperone system have also been shown to localize in the NIs in human brain as well as in the Drosophila model (Warrick et al., 1998; Chai et al., 1999a). This system is also involved in the handling of misfolded proteins and the formation of the appropriate tertiary structure of the protein. In transfected COS cells and PC12 cells, expression of an expanded polyglutamine protein elicits the colocalization of a number of the heat-shock protein components in the NIs, including Hsp 70 and 2

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Fig. 28.2 The intranuclear inclusions often stain positively for components of the heat-shock protein chaperone system, especially the Hsp-40 components, HDJ-1 and HDJ-2. Hsp 70 is found far less commonly, as shown in the right-hand panel. (Reproduced with permission from Chai et al. (1999a), Journal of Neuroscience, Vol. 19, pp. 10338–47.)

components of the Hsp 40 family, HDJ-1 and HDJ-2. In human brain tissue, HDJ-1 and HDJ-2 were found more commonly in NI than Hsp 70 (Fig. 28.2; Chai et al., 1999a). Overexpression of HDJ-1 and HDJ-2 using genetic technology in the COS cell model and of an Hsp 70 analogue (HSPAIL) in the Drosophila model resulted in a decrease in cell death (Chai et al., 1999a; Warrick et al., 1999). In the fly model, this effect was seen in the absence of a significant reduction in aggregate formation. In summary, considerable evidence has accumulated that mutant ataxin-3 acquires novel properties that are cell toxic. These properties include the possible acquisition of a susceptibility to truncation, to easier nuclear entry, and the formation of aggregates within the nuclear environment. Whether all or any of these are essential for pathology is as yet unclear. Manipulation of such potential pathogenic events may constitute useful treatments for this disease.

Acknowledgments The authors wish to thank Dr Henry Paulson for helpful comments on the manuscript. They also want to thank Mrs Triston Kelly for assistance with the manuscript preparation.

iReferencesi Abe, Y., Tanaka, F., Matsumoto, M. et al. (1998). CAG repeat number correlates with the rate of brainstem and cerebellar atrophy in Machado–Joseph disease. Neurology 51: 882–4.

Bebin, E.M., Bebin, J., Currier, R.D., Smith, E.E. and Perry, T.L. (1990). Morphometric studies in dominant olivopontocerebellar atrophy. Comparison of cell losses with amino acid decreases. Arch Neurol 47: 188–92. Burk, K., Abele, M., Fetter, M. et al. (1996). Autosomal dominant cerebellar ataxia type 1: clinical features and MRI in families with SCA1, SCA2 and SCA3. Brain 119: 1497–505. Buttner, N., Geschwind, D., Jen, J.C., Perlaman, S., Pulst, S.M. and Baloh, R.W. (1998). Oculomotor phenotypes in autosomal dominant ataxias. Arch Neurol 55: 1353–7. Cancel, G., Abbas, N., Stevanin, G. et al. (1995). Marked phenotypic heterogeneity associated with expansion of a CAG repeat sequence at the spinocerebellar ataxia 3/Machado–Joseph disease locus. Am J Hum Genet 57: 809–16. Chai, Y., Koppenhafer, S., Bonini, N. and Paulson, H.L. (1999a). Analysis of the role of heat shock protein chaperones in polyglutamine disease. J Neurosci 19: 10338–47. Chai, Y., Koppenhafer, S.L., Shoesmith, S.J., Perez, M.K. and Paulson, H.L. (1999b). Evidence of proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro. Hum Mol Genet 8(4): 673–82. Coutinho, P. and Andrade, C. (1978). Autosomal dominant system degeneration in Portuguese families of the Azores Islands. Neurology 28:703–9. Dawson, D.M. (1977). Ataxia in families from the Azores. N Engl J Med 296: 1529–30. Durr, A., Stevanin, G., Cancel, G. et al. (1996). Spinocerebellar ataxia 3 and Machado–Joseph disease: clinical, molecular and neuropathological features. Ann Neurol 39: 490–9. Evert, B.O., Wullner, U., Schulz, J.B. et al. (1999). High level expression of expanded full-length ataxin-3 in vitro causes cell death and formation of intranuclear inclusions in neuronal cells. Hum Mol Genet 8: 1169–76. Ferguson, F.R. and Critchley, M. (1929). A clinical study of an heredo-familial disease resembling disseminated sclerosis. Brain 52: 203–25.

Spinocerebellar ataxia type 3

Filla, A., De Michele, G., Campanella, G. et al. (1996). Autosomal dominant cerebellar ataxia type I. Clinical and molecular study in 36 Italian families including a comparison between SCA1 and SCA2 phenotypes. J Neurol Sci 142: 140–7. Gaspar, C., Lopes-Cendes, I., DeStefano, A.L. et al. (1996). Linkage disequilibrium analysis in Machado–Joseph disease patients of different ethnic origins. Hum Genet 98 (5): 620–4. Giunti, P., Sweeney, M.G. and Harding, A.E. (1995). Detection of the Machado–Joseph disease/spinocerebellar ataxia three trinucleotide repeat expansion in families with autosomal dominant motor disorders, including the Drew family of Walworth. Brain 118: 1077–85. Harding, A.E. (1984). The Hereditary Ataxias and Related Disorders. Edinburgh: Churchill Livingstone. Hashida, H., Goto, J., Kurisaki, H., Mizusawa, H. and Kanazawa, I. (1997). Brain regional differences in the expansion of a CAG repeat in the spinocerebellar ataxias: dentatorubralpallidoluysian atrophy, Machado–Joseph disease, and spinocerebellar ataxia type I. Ann Neurol 41: 505–11. Healton, E.B., Brust, J.C., Kerr, D.L., Resor, S. and Penn, A. (1980). Presumably Azorean disease in a presumably non-Portuguese family. Neurology 30: 1084–9. Higgins, J.J., Nee, L.E., Vasconcelos, O. et al. (1996). Mutations in American families with spinocerebellar ataxia (SCA) type 3: SCA3 is allelic to Machado–Joseph disease. Neurology 46: 208–13. Igarashi, S., Takiyama, Y., Cancel, G. et al. (1996). Intergenerational instability of the CAG repeat of the gene for Machado–Joseph disease (MJD1) is affected by the genotype of the normal chromosome: implications for the molecular mechanisms of the instability of the CAG repeat. Hum Mol Genet 5 (7): 923–32. Ikeda, H., Yamaguchi, M., Sugai, S., Aze, Y., Narumiya, S. and Kakizuka, A. (1996). Expanded polyglutamine in the Machado–Joseph disease protein induces cell death in vitro and in vivo. Nat Genet 13: 196–202. Ikeuchi, T., Igarashi, S., Takiyama, Y. et al. (1996). Non-mendelian transmission in dentatorubral-pallidoluysian atrophy and Machado–Joseph disease: the mutant allele is preferentially transmitted in male meiosis. Am J Hum Genet 57: 730–3. Inoue, K., Hanihara, T., Yamada, Y., Kosaka, K., Katsuragi, K. and Iwabuchi, K. (1996). Clinical and genetic evaluation of Japanese autosomal dominant cerebellar ataxias: is Machado–Joseph disease common in the Japanese? J Neurol Neurosurg Psychiatry 60: 697–8. Kawaguchi, Y., Okamoto, T., Taniwaki, M. et al. (1994). CAG expansions in a novel gene for Machado–Joseph disease at chromosome 14q32.1. Nat Genet 8: 221–8. Kitamura, J., Kuvuki, Y., Tsuruta, K., Kurihara, T. and Matsukura, S. (1989). A new family with Joseph disease in Japan. Homovanillic acid, magnetic resonance and sleep apnea studies. Arch Neurol 46: 425–8. Klement, I.A., Skinner, P.J., Kaytor, M.D. et al. (1998). Ataxin-1 nuclear localization and aggregation: role of polyglutamineinduced disease in SCA1 transgenic mice. Cell 95: 41–53. Klockgether, T., Schols, L., Abele, M. et al. (1999). Age related axonal

neuropathy in spinocerebellar ataxia type 3/Machado–Joseph disease (SCA3/MJD). J Neurol Neurosurg Psychiatry 66: 222–4. Klockgether, T., Skalej, M., Wedekind, D. et al. (1998). Autosomal dominant cerebellar ataxia type I. MRI based volumetry of posterior fossa structures and basal ganglia in spinocerebellar ataxia type 1, 2 and 3. Brain 121: 1687–93. Lazzarini, A., Zimmerman, T.A., Johnson, W.G. and Duvoisin, R.C. (1992). A 17th century founder gives rise to a large North American pedigree of autosomal dominant spinocerebellar ataxia not linked in the SCA 1 locus on chromosome 6. Neurology 42: 2118–24. Lerer, I., Merims, D., Abeliovich, D., Zlotogora, J. and Gadoth, N. (1996). Machado–Joseph disease: correlation between the clinical features, the CAG repeat length and homozygosity for the mutation. Eur J Hum Genet 4(1): 3–7. Lima, M., Mayer, F.M., Coutinho, P. and Abade, A. (1998). Origins of a mutation: population genetics of Machado–Joseph disease in the Azores (Portugal). Hum Biol 70: 1011–23. Limprasert, P., Nouri, N., Heyman, R.A. et al. (1996). Analysis of CAG repeat of the Machado–Joseph gene in human, chimpanzee and monkey populations: a variant nucleotide is associated with the number of CAG repeats. Hum Mol Genet 5(2): 207–13. Maciel, P., Gaspar, C., DeStefano, A.L. et al. (1995). Correlation between CAG repeat length and clinical features in Machado–Joseph disease. Am J Hum Genet 57: 54–61. Maciel, P., Lopes-Cendes, I., Gaspar, C. et al. (1996). Somatic mosaicism of the CAG repeat length in brain specimens of spinocerebellar ataxia type 1 and Machado–Joseph disease. Neurology 46 (Suppl.): A330. Maruff, P., Tyler, P., Burt, T., Currie, B., Burns, C. and Currie, J. (1996). Cognitive deficits in Machado–Joseph disease. Ann Neurol 40: 421–7. Matilla, T., McCall, A., Subramony, S.H. et al. (1995). Molecular clinical correlations in spinocerebellar ataxia type 3 and Machado–Joseph disease. Ann Neurol 38: 68–72. Matsumura, R., Takayanagi, T., Fujimoto, Y. et al. (1996a). The relationship between trinucleotide repeat length and phenotypic variation in Machado–Joseph disease. J Neurol Sci 139: 52–7. Matsumura, R., Takayanagi, T., Murata, K., Futamura, N., Hirano, M. and Ueno, S. (1996b). Relationship between (CAG)n C configuration to repeat instability of the Machado–Joseph disease gene. Hum Genet 98: 643–5. Moseley, M.L., Benzow, K.A., Schut, L.J. et al. (1998). Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families. Neurology 51: 1666–71. Nakano, K.K., Dawson, D.M. and Spence, A. (1972). Machado disease: a hereditary ataxia in Portuguese emigrants to Massachusetts. Neurology 22: 49–55. Nishiyama, K., Murayama, S., Goto, J. et al. (1996). Regional and cellular expression of the Machado–Joseph disease gene in brains of normal and affected individuals. Ann Neurol 40: 776–81. Paulson, H.L., Das, S.S., Crino, P.B. et al. (1997a). Machado–Joseph disease gene product is a cytoplasmic protein widely expressed in brain. Ann Neurol 41: 453–62.

437

438

S.H. Subramony and P.J.S. Vig

Paulson, H.L., Perez, M.K., Trottier, Y. et al. (1997b). Intranuclear inclusions of expanded polyglutamine protein in spinocerebellar ataxia type 3. Neuron 19: 333–44. Perez, K.P., Paulson, H.L. and Pittman, R.N. (1999). Ataxin-3 with an altered conformation that exposes the polyglutamine domain is associated with the nuclear matrix. Hum Mol Genet 8: 2377–85. Perez, M.K., Paulson, H.L., Pendse, S.J., Saionz, S.J., Bonini, N.M. and Pittman, R.N. (1998). Recruitment and the role of nuclear localization in polyglutamine-mediated aggregation. J Cell Biology 143(6): 1457–70. Perutz, M.F., Johnson, T., Suzuki, M. and Finch, J.T. (1994). Glutamine repeats as polar zippers: their possible role in inherited neurological diseases. Proc Natl Acad Sci USA 91: 5355–8. Ramesar, R.S., Bardlen, S., Beighton, P. and Bryer, A. (1997). Expanded CAG repeat in spinocerebellar ataxia (SCA1) segregates with distinct haplotypes in South African families. Hum Genet 100: 131–7. Ranum, L.P.W., Lundgren, J.K., Schut, L.J. et al. (1995). Spinocerebellar ataxia type 1 and Machado–Joseph disease: incidence of CAG expansions among adult-onset ataxia patients from 311 families with dominant, recessive or sporadic ataxia. Am J Hum Genet 57: 603–8. Rivaud-Pechoux, S., Durr, A., Gaymard, B. et al. (1998). Eye movement abnormalities correlate with genotype in autosomal dominant cerebellar ataxia type 1. Ann Neurol 43: 297–302. Romanul, F.C.A., Fowler, H.L., Radvany, J. et al. (1977). Azorean disease of the nervous system. N Engl J Med 296: 1505–8. Rosenberg, R.N. (1984). Joseph disease: an autosomal dominant motor system degeneration. In Advances in Neurology, Vol. 41 Olivopontocerebellar Atrophies, ed. R.C. Duvoisin and A. Plaitakis, pp. 179–94. New York: Raven Press. Rosenberg, R.N., Nyhan, W.L., Bau, C. and Shore, P. (1976). Autosomal dominant striatonigral degeneration. Neurology 26: 703–14. Rubinsztein, D.C. and Leggo, J. (1997). Non-mendelian transmission at the Machado–Joseph disease locus in normal females: preferential transmission of alleles with smaller CAG repeats. J Med Genet 34: 234–6. Rubinsztein, C., Leggo, J., Coetzee, G.A., Irvine, R.A, Buckley, M. and Ferguson-Smith, A. (1995). Sequence variation and size ranges of CAG repeats in the Machado–Joseph disease, spinocerebellar ataxia type 1 and androgen receptor genes. Hum Mol Genet 4(9): 1585–90. Sakai, T., Ohta, M. and Ishino, H. (1983). Joseph disease in a nonPortuguese family. Neurology (NY) 33: 74–80. Sasaki, H., Wakisaka, A., Fukazawa, T. et al. (1995). CAG repeat expansion of Machado–Joseph disease in the Japanese: analysis of the repeat instability for parental transmission, and correlation with disease phenotype. J Neurol Sci 133: 128–33. Schmidt, T., Landwehrmeyer, B., Schmitt, I. et al. (1998). An isoform of ataxin-3 accumulates in the nucleus of neuronal cells in affected brain regions of SCA3 patients. Brain Path 8: 669–79. Schols, L., Amoiridis, G., Langkafel, M. et al. (1995). Machado–Joseph disease mutation as the genetic basis of most

spinocerebellar ataxias in Germany. J Neurol Neurosurg Psychiatry 59: 449–50. Schols, L., Amoirides, G., Buttner, T., Przuntek, H., Epplen, J. and Riess, O. (1997). Autosomal dominant cerebellar ataxia: phenotypic differences in genetically determined subtypes? Ann Neurol 42: 924–32. Schols, L., Amoiridis, G., Epplen, J.T. et al. (1996). Relations between genotype and phenotype in German patients with the Machado–Joseph disease mutation. J Neurol Neurosurg Psychiatry 61: 466–70. Schols, L., Haan, J., Riess, O., Amoiridis, G. and Przuntek, H. (1998). Sleep disturbance in spinocerebellar ataxias. Is the SCA3 mutation a cause of restless legs syndrome? Neurology 51: 1603–7. Sequeiros, J. and Coutinho, P. (1993). Epidemiology and clinical aspects of Machado–Joseph disease. In Advances in Neurology, Vol. 61, Inherited Ataxias, ed. A.E. Harding and T. Duefel, pp. 139–53. New York: Raven Press. Sequeiros, J., Silviera, I., Maciel, P. et al. (1994). Genetic linkage studies of Machado–Joseph disease with chromosome 14q STRP’s in 16 Portuguese-Azorean kindreds. Genomics 21: 645–8. Silveira, I., Lopes-Cendes, I., Kish, S. et al. (1996). Frequency of spinocerebellar ataxia type I, dentatorubrual-pallidoluysian atrophy and Machado–Joseph disease mutations in a large group of spinocerebellar ataxia patients. Neurology 46: 214–18. Soong, B.-W., Cheng, C.-H., Liu, R.-S. and Shan, D.-E. (1997). Machado–Joseph disease: clinical, molecular, and metabolic characterization in Chinese kindreds. Ann Neurol 41: 446–52. Soong, B.-W. and Lin, K.-P. (1998). An electrophysiologic and pathologic study of peripheral nerves in individuals with Machado–Joseph disease. Chin Med (Taipei) 61: 181–7. St George-Hyslop, P., Rogaeva, E., Huterer, J. et al. (1994). Machado–Joseph disease in pedigrees of Azorean descent is linked to chromosome 14. Am J Hum Genet 55: 120–5. Stevanin, G., Cancel, G., Didierjean, O. et al. (1995a). Linkage disequilibrium at the Maschado–Joseph disease/spinal cerebellar ataxia 3 losus: evidence for a common founder effect in French and Portuguese–Brazilian families as well as a second ancestral Portuguese–Azorean mutation. Am J Hum Genet 57: 1247–9. Stevanin, G., Cancel, G., Durr, A. et al. (1995b). The gene for spinal cerebellar ataxia 3 (SCA3) is located in a region of 3 cM on chromosome 14q24.3–q32.2. Am J Hum Genet 56: 193–201. Subramony, S.H., Bock, H.G., Smith, S.C., Currier, R.D. and Smith, E.E. (1993). Presumed Machado–Joseph disease: four kindreds from Mississippi. In Handbook of Cerebellar Disease, ed. R. Lechentenberg, pp. 353–62. New York: Marcel Dekker. Subramony, S.H. and Currier, R.D. (1996). Intrafamilial variability in Machado–Joseph disease. Mov Disord 11: 741–3. Tait, D., Riccio, M., Sittler, A. et al. (1998). Ataxin-3 is transported into the nucleus and associates with the nuclear matrix. Hum Mol Genet 7: 991–7. Takano, H., Cancel, G., Ikeuchi, T. et al. (1998). Close association between prevalence of dominantly inherited spinocerebellar ataxias with CAG-repeat expansions and frequencies of large normal CAG alleles in Japanese and Caucasian populations. Amer J Hum Genet 63: 1060–6.

Spinocerebellar ataxia type 3

Takiyama, Y., Igarashi, S., Rogaeva, E.A. et al. (1995). Evidence for intergenerational istability in the CAG repeat in the MJD1 gene and for conserved haplotypes at flanking markers amongst Japanese and Caucasian subjects with Machado–Joseph disease. Hum Mol Genet 4(7): 1137–46. Takiyama,Y., Nishizawa, S., Tanaka, H. et al. (1993). The gene for Machado–Joseph disease maps to human chromosome 14q. Nat Genet 4: 300–5. Takiyama, Y., Okynagi, S., Kawashima, S. et al. (1994). A clinical and pathologic study of a large Japanese family with Machado–Joseph disease tightly linked to the DNA markers on chromosome 14q. Neurology 44: 1302–8. Takiyama, Y., Sakoe, K., Nakano, I. and Nishizawa, M. (1997). Machado–Joseph disease: cerebellar ataxia and autonomic dysfunction in a patient with the shortest known expanded allele (56 CAG repeat units) of the MJD1 gene. Neurology 49: 604–6. Takiyama, Y., Shimazaki, H., Morita, M. et al. (1998). Maternal anticipation in Machado–Joseph disease (MJD); some maternal factors independent of the number of CAG repeat units may play a role in genetic anticipation in a Japanese MJD family. J Neurol Sci 155: 141–5.

Warrick, J.M., Chan, E., Gray-Board, G.L. et al. (1999). Suppression of polyglutamine-mediated neurodegeneration in Drosophila by the molecular chaperone Hsp70. Nat Genet 23: 425–8. Warrick, J.M., Paulson, H.L., Gray-Board, G.L. et al. (1998). Expanded polyglutamine protein forms nuclear inclusions and causes neural degeneration in drosophila. Cell 93: 939–49. Watanabe, H., Tanaka, F., Matsumoto, M. et al. (1998). Frequency analysis of autosomal dominant cerebellar ataxias in Japanese patients and clinical characterization of spinocerebellar ataxia 6. Clin Genet 53: 13–19. Watanabe, M., Abe, K., Aoki, M. et al. (1996). Analysis of CAG trinucleotide expansion associated with Machado–Joseph disease. J Neurol Sci 136: 101–7. Yoshizawa, T., Yamagishi, Y., Koseki, N. et al. (2000). Cell cycle arrest enhances the in vitro cellular toxicity of the truncated Machado–Joseph disease gene product with an expanded polyglutamine stretch. Hum Mol Genet 9: 69–78. Zhou, X.Y., Takiyama, Y., Igarashi, S. et al. (1997). Machado–Joseph disease in four Chinese pedigrees: molecular analysis of 15 patients including two juvenile cases and clinical correlations. Neurology 48: 482–5.

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Spinocerebellar ataxia type 4 Ying-Hui Fu1 and Louis J. Ptacek2 1

Department of Neurobiology and Anatomy, 2 Department of Neurology and Human Genetics, Howard Hughes Medical Institute, University of Utah, Salt Lake City, USA

Introduction The autosomal dominant cerebellar ataxias are a heterogeneous group of dominantly inherited disorders which have been divided into several types with different predominant clinical features. Collectively, these disorders are called the spinocerebellar ataxias (SCAs) and are known to be genetically heterogeneous. For example, clinically similar (or identical) SCA, characterized by ataxia, nystagmus, and long tract signs, can be caused by a number of different SCA genes. In addition to this heterogeneity, there is also prominent pleiotropy with a single gene giving rise to considerable variation in phenotypic expression. SCA7 stands out as a unique form given the dramatic additional feature of retinal degeneration (Gouw et al., 1994). A third group of the SCAs is characterized by a purely cerebellar syndrome. More recent genetic studies have defined numerous loci for the SCAs. Disease loci were assigned to chromosomes 6p (SCA1: Zoghbi et al., 1991), 12q (SCA2: Gispert et al., 1993), 14q (SCA3: Stevanin et al., 1994), 16q (SCA4: Gardner et al., 1994), 11cen (SCA5: Ranum et al., 1994), 19p (SCA6: Zhuchenko et al., 1997), 3p (SCA7: Gouw et al., 1995; Benomar et al., 1995), 10q24 (SCA8: Nikali et al., 1997), and 22q13 (SCA10: Zu et al., 1999). An interesting feature of many of these diseases is the clinical phenomenon of anticipation, where disease severity often worsens on transmission of a disease allele through families. Individuals in subsequent generations are affected at earlier ages and with more severe disease. Among the spinocerebellar ataxias, this is most notable in SCA7 (Gouw et al., 1994, 1998). It was the cloning of the fragile-X mental retardation and myotonic dystrophy genes that led to the recognition that expanded trinucleotide repeats are the molecular basis for anticipation (Fu et al., 1991, 1992). These studies demonstrated the dynamic nature of these mutations – they may expand (or, rarely,

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contract) on passage through meiosis; expansion of the mutation leads to a worsening of the phenotype as these disorders are transmitted through families. Insight into this mutational mechanism allowed efficient cloning of genes responsible for a number of neurodegenerative disorders, including the SCAs. The disease-causing genes for SCA1, SCA2, SCA3, SCA6, and SCA7 have been cloned and the mutations have been shown to be unstable trinucleotide (CAG) repeat expansions within coding regions of the respective genes (Orr et al., 1993; Kawaguchi et al., 1994; Pulst et al., 1996; Imbert et al., 1996; Sanpei et al., 1996; David et al., 1997; Zhuchenko et al., 1997; Gouw et al., 1998). In addition, the mutations that are responsible for SCA8 and SCA12 were found in the 3 and 5 untranslated region (UTR) of their respective genes (Koob et al., 1999; Holmes et al., 1999). The different SCA mutations cause phenotypes with similar clinical, electrophysiological and magnetic resonance imaging features (Gouw et al., 1994; Ranum et al., 1994; Ptacek, 1995; Burk et al., 1996). However, there is considerable overlap of these syndromes and reliable diagnosis on the basis of clinical features is only possible for SCA7 (Gouw et al., 1994; Ptacek, 1995). SCA1–3 and SCA5–8 are described in detail in the other chapters of this book. The description of the SCA4 locus as a distinct genotype dates back to 1994 when we reported linkage to chromosome 16q22.1 in a five-generation family with an autosomal dominant, late-onset spinocerebellar ataxia associated with sensory axonal neuropathy (Gardner et al., 1994). This large family had been followed for many years and was said to have an autosomal dominant form of Friedreich’s ataxia, because of the prominent posterior column findings on clinical examination. However, these patients do not have other findings that are characteristic of Friedreich’s ataxia. Subsequent evaluation of additional branches of the family led to more precise mapping of the

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SCA4 locus (Flanigan et al., 1996). There have been several reports in the past about families with similar clinical features (Singh et al., 1973; Bennett et al., 1984; Marbini et al., 1994; van Dijk et al., 1995; Gemignani et al., 1997; Nachmanoff et al., 1997). Since Biemond reported clinical and neuropathological features in 1954, this type of ataxia has been referred to as ‘Biemond’s ataxia’ (Biemond and Daniels, 1954). SCA4 seems to be an extremely rare disorder. To date, our Utah/Wyoming pedigree of Scandinavian origin is the only SCA4 family confirmed by linkage analysis (Flanigan et al., 1996). However, a definite statement on the prevalence is difficult, because the gene has not yet been isolated and routine screening of patients with degenerative cerebellar ataxia is not possible. We have also identified a number of additional families that appear clinically to be very similar to our large SCA4 family. The ethnic backgrounds of these additional small families include Scandinavian, Spanish, and Italian origins. These additional families are of insufficient size to prove linkage to the SCA4 locus, but may provide a valuable resource in our attempts to clone this gene.

Table 29.1 Clinical and electrophysiological characteristics of 20 SCA4 patients Median age of onset Fourth generation Fifth generation

39.3 years 41.9 years 36.7 years

Gait ataxia Limb dysmetria Decreased sensation Vibration / joint position Pinprick Reflex abnormalities Absent ankle jerks Absent knee jerks Complete areflexia Dysarthria Distal Proximal and distal Extensor plantar response Oculomotor signs Saccadic visual pursuit Square wave jerks Abnormal SNAP (13 patients) Absent sural nerve response Absent radial nerve response

95% 95% 100% 100% 95% 100% 100% 85% 25% 50% 20% 10% 20% 15% 10% 5% 100% 92% 23%

Clinical features The following description of clinical features refers to our previous report (Flanigan et al., 1996). Of the 38 individuals examined, 20 were clinically affected. Although disease onset was most frequent in the fourth or fifth decade, age of onset ranged from 19 to 59 years. The median age of onset was 39.3 years. The first symptom noted by the patients was usually gait disturbance, followed by clumsiness of hands and often dysarthria. At presentation, most patients did not complain of neuropathic symptoms, although evidence of a length-dependent neuropathy could invariably be demonstrated on examination: all had vibratory and joint position sense loss, and 95% had at least a minimal pinprick sensation loss. Because neuropathy can be seen in all of the SCAs, it is impossible to classify patients as having SCA4 without performing linkage analysis. However, we believe that SCA families in which a very prominent sensory axonal neuropathy is present in all affected individuals are likely to have SCA4. Loss of proprioception and absent ankle-jerk reflexes were found in all patients. Pinprick sensation was impaired in all but one and dysarthria was present in 50% of the patients. Less frequent findings were extensor plantar response (20%) and distal limb weakness (20%). Oculomotor disturbances were present in only 15% of the patients, including saccadic smooth pursuit and occasional square wave jerks.

Notes: SNAP, sensory nerve action potential.

Two patients denied any neurological symptoms despite clear evidence of clinical and electrophysiological affection. The clinical findings in SCA4 are summarized in Table 29.1. In the families resembling SCA4, some additional clinical features have been reported. These include vertical gaze-evoked nystagmus, sensory loss in the distribution of the trigeminal nerve, and hearing loss (Biemond and Daniels, 1934; Gemignani et al., 1997; Nachmanoff et al., 1997). It remains to be seen whether these are truly manifestations of the SCA4 phenotype. The course of the disease is slowly progressive over decades, often leading to wheelchair dependence. As in other dominantly inherited spinocerebellar ataxias, there is a suggestion of anticipation in SCA4, at least in some branches of the family (Flanigan et al., 1996). Several members of the fifth generation of our pedigree denied neurologic symptoms but had clear signs of neuropathy and ataxia or dysmetria on examination. The age of symptom onset was self-reported in all members of the fourth generation and, therefore, intergenerational comparisons of reported age of onset are problematic. Reliable ages of onset could be ascertained for nine individuals in

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each of the fourth and fifth generations. For this data set, the median age of onset was 41.9 years for the fourth generation, and 36.7 years for the fifth generation. Anticipation is suggested within some individual branches. One woman first noted gait difficulty at the age of 62, whereas her children noted difficulty walking at the ages of 25 and 45 years. Similarly, one individual noted symptoms at the age of 45, while the reported age of symptom onset ranged from 19 to 39 years in his children. In contrast, another individual reported symptoms at the age of 35, whereas his children denied symptoms but had demonstrable signs at the ages of 46 and 49 years. It remains to be seen whether SCA4, like the other cloned SCA genes, results from a trinucleotide repeat expansion.

Laboratory tests Sensory nerve conduction studies in the reported SCA4 family revealed sensory axonal neuropathy in all 13 patients examined (Flanigan et al., 1996). Sensory nerve action potentials of the sural nerve were absent in 12 out of 13 patients; the one patient with preserved sural nerve response had a decreased amplitude of the radial sensory nerve action potential (Table 29.1). Despite clinical and electrophysiological evidence of sensory neuropathy in all patients, most of them did not complain of symptoms of neuropathy. In the families with disease resembling SCA4, possible electrophysiological features included abnormal somatosensory, visual or brainstem auditory evoked potentials (van Dijk et al., 1995; Gemignani et al., 1997; Nachmanoff et al., 1997). The reported computerized tomography/ magnetic resonance imaging scans in these families were normal (van Dijk et al., 1995; Gemignani et al., 1997). In patients with an autosomal dominant inherited ataxia, molecular genetic testing is possible to exclude SCA1–3, SCA6, and SCA7. SCA4 can be assumed if patients present with ataxia and predominant sensory axonal neuropathy, which might be confirmed by nerve conduction studies. However, diagnosis of definite SCA4 is only possible by means of linkage analysis.

Treatment The molecular defect underlying SCA4 is unknown and there is no rational treatment for slowing or preventing disease progression. All patients with a progressive hereditary ataxia should receive physical and occupational therapy and, if necessary, speech therapy. Such treatment

can often allow patients to remain ambulatory longer, with improved quality of life. General healthy behavior should always be encouraged – healthy diet, daily moderate exercise, adequate sleep, and stress reduction. As with all genetically transmitted diseases, patients should be informed and counseled concerning the hereditary character of the disease and possible implications for family planning.

Neuropathology There are no neuropathological data for the SCA4 family that we reported (Gardner et al., 1994; Flanigan et al., 1996). Neuropathological abnormalities in the families with disease clinically resembling SCA4 include degeneration of the posterior columns and roots as well as demyelination of the trigeminal roots. In addition, mild atrophy of the cerebral cortex and severe atrophy of the cerebellar hemispheres with slight Purkinje cell loss are reported (Biemond and Daniel, 1934; Nachmanoff et al., 1997). Sural nerve biopsy revealed a severe loss of myelinated fibers (van Dijk et al., 1995; Gemignani et al., 1997).

Genetic mapping of SCA4 The SCA4 gene was mapped to chromosome 16q22.1 (Flanigan et al., 1996), with a maximum likelihood of odds (LOD) score of 5.93 (  0) at marker D16S397. Flanking markers from obligate recombinants are D16S514 at the centromeric side and D16S512 on the telomeric side. The genetic distance between these two markers is approximately 6 cM based on available genetic maps. We have used the information from the Genethon chromosome 16 map and have screened the CEPH YAC library with new markers to identify yeast artificial chromosomes (YAC) clones in order to build a physical representation for the region. A total of 36 YAC clones has been identified in the region. Thirty-two markers from this general region have been used to screen these YACs and to begin ordering them in a physical map. Deleted YACs and those containing short inserts were not characterized further. Fifteen YACs were selected for further characterization and more precise mapping. Eleven of these 15 clones have now been ordered into a contig with approximately 1X to 3X coverage (Fig. 29.1). We are currently identifying additional YACs from the region and obtaining end sequence to identify chimeric clones. Based on our minimal tiling set of YACs, the distance between the two flanking markers D16S514 and D16S512 is estimated to be 7–12 Mb.

Spinocerebellar ataxia type 4

Fig. 29.1 A preliminary physical map of the SCA4 region.Screening of the CEPH YAC library with markers spanning the SCA4 locus has allowed identification of 11 YAC clones that form a contiguous physical map across the region. Recovery of the YAC ends is underway and will allow testing to see whether these clones are chimeric. Additional YACs from the region are being isolated to give denser coverage of this region. The physical distance between the two flanking markers D16S514 and D16S512 is estimated to be 7–12 Mb.

We have recently used more markers from this region and typed additional family collections that we have obtained since the original linkage analysis. One of the new families shows a shared haplotype with the large SCA4 family in a smaller region of the original defined locus. These new data suggest that the two families are distantly related and that the SCA4 gene is more likely to reside in a narrower (6 Mb) region of chromosome 16q. In addition to the original YAC contig, we have started to build BAC contigs for the subregions. These BAC contigs will be useful for the purpose of cloning the SCA4 gene.

Acknowledgments This investigation was supported by Public Health Service research grant M01–RR00064 from the National Center for Research Resources.

xReferencesx Biemond, A. and Daniels, A.P. (1954). Familial periodic paralysis and its transition into spinal muscular atrophy. Brain 57: 90–108. Bennett, R.H., Ludvigson, P., DeLeon, G. and Berry, G. (1984). Large-fiber sensory neuronopathy in autosomal dominant spinocerebellar degeneration. Arch Neurol 41: 175–8. Benomar, A., Krols, L., Stevanin, G. et al. (1995). The gene for autosomal dominant cerebellar ataxia with pigmentary macular dystrophy maps to chromosome 3p12–p21.1. Nat Genet 10: 84–8. Burk, K., Abele, M., Fetter, M. et al. (1996). Autosomal dominant cerebellar ataxia type I clinical features and MRI in families with SCA1, SCA2 and SCA3. Brain 119: 1497–505. David, G., Abbas, N., Stevanin, G. et al. (1997). Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nat Genet 17: 65–70. Flanigan, K., Gardner, K., Alderson, K. et al. (1996). Autosomal dominant spinocerebellar ataxia with sensory axonal neuropathy (SCA4): clinical description and genetic localization to chromosome 16q22.1. Am J Hum Genet 59: 392–9. Fu, Y.H., Kuhl, D.P., Pizzuti, A. et al. (1991). Variation of the CGG

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repeat at the fragile X site results in genetic instability: resolution of the Sherman paradox. Cell 67: 1047–58. Fu, Y.H., Pizzuti, A., Fenwick, R.G., Jr et al. (1992). An unstable triplet repeat in a gene related to myotonic muscular dystrophy. Science 255: 1256–8. Gardner, K., Alderson, K., Galster, B., Kaplan, C., Leppert, M. and Ptacek, L.J. (1994). Autosomal dominant spinocerebellar ataxia: clinical description of a distinct hereditary ataxia and genetic localization to chromosome 16 (SCA4) in a Utah kindred. Neurology 44: A361. Gemignani, F., Pavesi, G. and Marbini, A. (1997). A new variant of sensory ataxic neuropathy with autosomal dominant inheritance [letter; comment]. Brain 120: 379–80. Gispert, S., Twells, R., Orozco, G. et al. (1993). Chromosomal assignment of the second locus for autosomal dominant cerebellar ataxia (SCA2) to chromosome 12q23–24.1. Nat Genet 4: 295–9. Gouw, L.G., Castaneda, M.A., McKenna, C.K. et al. (1998). Analysis of the dynamic mutation in the SCA7 gene shows marked parental effects on CAG repeat transmission. Hum Mol Genet 7: 525–32. Gouw, L.G., Digre, K.B., Harris, C.P., Haines, J.H. and Ptacek, L.J. (1994). Autosomal dominant cerebellar ataxia with retinal degeneration: clinical, neuropathologic, and genetic analysis of a large kindred. Neurology 44: 1441–7. Gouw, L.G., Kaplan, C.D., Haines, J.H. et al. (1995). Retinal degeneration characterizes a spinocerebellar ataxia mapping to chromosome 3p. Nat Genet 10: 89–93. Holmes, S.E., O’Hearn, E.E., McInnis, M.G. et al. (1999). Expansion of a novel CAG trinucleotide repeat in the 5 region of PPP2R2B is associated with SCA12 [letter]. Nat Genet 23: 391–2. Imbert, G., Saudou, F., Yvert, G. et al. (1996). Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats [see comments]. Nat Genet 14: 285–91. Kawaguchi, Y., Okamoto, T., Taniwaki, M. et al. (1994). CAG expansions in a novel gene for Machado–Joseph disease at chromosome 14q32.1. Nat Genet 8: 221–8. Koob, M.D., Moseley, M.L., Schut, L.J. et al. (1999). An untranslated CTG expansion causes a novel form of spinocerebellar ataxia (SCA8). Nat Genet 21: 379–84. Marbini, A., Pavesi, G., Cenacchi, G., Mazzucchi, A., Preda, P. and Gemignani, F. (1994). Hereditary sensory and autonomic neuropathy with ataxia and late onset. Clin Neurol Neurosurg 96: 191–6.

Nachmanoff, D.B., Segal, R.A., Dawson, D.M., Brown, R.B. and De Girolami, U. (1997). Hereditary ataxia with sensory neuronopathy: Biemond’s ataxia. Neurology 48: 273–5. Nikali, K., Isosomppi, J., Lonnqvist, T., Mao, J.I., Suomalainen, A. and Peltonen, L. (1997). Toward cloning of a novel ataxia gene: refined assignment and physical map of the IOSCA locus (SCA8) on 10q24. Genomics 39: 185–91. Orr, H.T., Chung, M.Y., Banfi, S. et al. (1993). Expansion of an unstable trinucleotide CAG repeat in spinocerebellar ataxia type 1. Nat Genet 4: 221–6. Ptacek, L.J. (1995). Autosomal dominant spinocerebellar atrophy with retinal degeneration. Clin Neurosci 3: 28–32. Pulst, S.-M., Nechiporuk, A., Nechiporuk, T. et al. (1996). Moderate expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2. Nat Genet 14: 269–76. Ranum, L.P., Schut, L.J., Lundgren, J.K., Orr, H.T. and Livingston, D.M. (1994). Spinocerebellar ataxia type 5 in a family descended from the grandparents of President Lincoln maps to chromosome 11. Nat Genet 8: 280–4. Sanpei, K., Takano, H., Igarashi, S. et al. (1996). Identification of the spinocerebellar ataxia type 2 gene using a direct identification of repeat expansion and cloning technique, DIRECT [see comments]. Nat Genet 14: 277–84. Singh, N., Mehta, M. and Roy, S. (1973). Familial posterior column ataxia (Biemond’s) with scoliosis. Eur Neurol 10: 160–7. Stevanin, G., Le Guern, E., Ravise, N. et al. (1994). A third locus for autosomal dominant cerebellar ataxia type I maps to chromosome 14q24.3–qter: evidence for the existence of a fourth locus. Am J Hum Genet 54: 11–20. van Dijk, G.W., Wokke, J.H., Oey, P.L., Franssen, H., Ippel, P.F. and Veldman, H. (1995). A new variant of sensory ataxic neuropathy with autosomal dominant inheritance [see comments]. Brain 118: 1557–63. Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1A-voltage-dependent calcium channel. Nat Genet 15: 62–9. Zoghbi, H.Y., Jodice, C., Sandkuijl, L.A., et al. (1991). The gene for autosomal dominant spinocerebellar ataxia (SCA1) maps telomeric to the HLA complex and is closely linked to the D6S89 locus in three large kindreds. Am J Hum Genet 49: 23–30. Zu, L., Figueroa, K.P., Grewal, R. and Pulst, S.-M. (1999). Mapping of a new autosomal dominant spinocerebellar ataxia to chromosome 22. Am J Hum Genet 64: 594–9.

30

Spinocerebellar ataxia type 5 Christina L. Liquori1, Lawrence J. Schut2, H. Brent Clark3, John W. Day4, and Laura P.W. Ranum1 1

Department of Genetics, Cell Biology, and Development, 2 Department of Neurology, CentraCare Clinic, St Cloud, Minnesota, USA 3 Department of Laboratory Medicine/Pathology, 4 Department of Neurology, Institute of Human Genetics, University of Minnesota, USA

Introduction A ten-generation family with a clinically mild autosomal dominant form of spinocerebellar ataxia (SCA) was identified in 1992 (Ranum et al., 1994). This Caucasian kindred has two major branches that both trace their ancestries to the paternal grandparents of President Lincoln (Fig. 30.1). Abbreviated versions of the two branches of the family are shown in Fig. 30.2. DNA has been obtained from 215 members (60 affected) of this kindred. After excluding linkage to the known ataxia loci, a genome wide screen mapped the disease locus, spinocerebellar ataxia type 5 (SCA5), to chromosome 11q13 (Ranum et al., 1994). Although disease onset is typically in the third or fourth decade, it can range from 10 to 68 years. Signs and symptoms progress over several decades, beginning with a mild disturbance of gait, incoordination of upper extremities, and slurred speech. SCA5 primarily affects the cerebellum and is clinically more benign (Ranum et al., 1994) than other SCAs (Gouw et al., 1994; Yagishita and Iouue, 1997). In general, the adult-onset cases appear similar to patients with SCA6 (Zhuchenko et al., 1997) and to previously described families with relatively ‘pure’ forms of cerebellar ataxia (Holmes, 1907; Harding, 1983). Whereas adult-onset SCA5 is disabling, the most striking clinical distinctions from SCA1, SCA2, SCA3, SCA4, and SCA7 are that SCA5 progresses more slowly and generally does not shorten life (Ranum et al., 1994). This clinical difference is probably due to the lack of bulbar paralysis in all of the adult-onset SCA5 patients examined. Bulbar paralysis in other forms of dominant ataxia often leads to a weakened ability to combat recurrent pneumonia (Zoghbi, 1991). Two relatively young individuals with juvenile onset of SCA5 have some bulbar involvement that may lead to early death. A second SCA5 family of French origin with similar

Fig. 30.1 The common ancestry of the two branches of the family. The solid square and circle indicate President Lincoln’s uncle Josiah and aunt Mary, who passed the ataxia gene to their descendants. (Reproduced with permission from Ranum et al. (1994), Nature Genetics, Vol. 8, pp. 280–4.)

clinical features was recently reported (Stevanin et al., 1999).

Clinical features The clinical features of affected family members are summarized in Table 30.1. The core clinical feature of the disease in the Lincoln family is progressive ataxia of gait with truncal instability. Of the 58 affected individuals examined, only six had normal gait. Early in the disease process, patients complain of excessive stumbling, uncertainty negotiating stairs, or unsteadiness standing on one foot in the shower. There is a gradual progression of symptoms over many years, which only sometimes progresses to wheelchair dependence. Ataxia of the upper limbs occurred in more than 90% of affected individuals in this family, but the coordination disturbances of the upper limbs are not as marked as those of the lower limbs and gait. In fact, the upper limb incoordination in many subjects may only be detectable during

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Fig. 30.2 Abbreviated pedigrees of two branches of the family. To preserve confidentiality, the identities of the branches are not given, generations three and four have been omitted, and changes have been made in the pedigree structure. Whereas more than 800 family members have been identified to date, only 275 individuals are represented. Family members who are not at first-degree risk and some younger family members who are at first-degree risk have been omitted. Furthermore, the number of siblings and the sex of some individuals have been changed. The portions of the two branches shown represent individuals from whom most of the blood samples were obtained (black dot beneath symbol). Solid circles (females) and squares (males) represent affected individuals. Generations for both branches are numbered with reference to their common ancestors, Captain Abraham Lincoln and Bathsheba Herring, of generation I. (Reproduced with permission from Ranum et al. (1994), Nature Genetics, Vol. 8, pp. 280–4.)

Spinocerebellar ataxia type 5

Table 30.1 Clinical features of SCA5 Limb ataxia Gait ataxia Truncal ataxia Muscle weakness Muscle atrophy Deep tendon reflexes Hypoactive Hyperactive Bulbar abnormalities Abnormal eye movements Sensory Dysarthria Abnormal three-cough sequence Babinski sign Abnormal Romberg

  / / 

Notes: , 90%; , 50–89%; , 25–49%; , 10–24%; /, 2–9%, , 2%.

clinical testing. Most affected family members ultimately complain of deterioration in handwriting or other activities requiring fine finger dexterity. Only four individuals, all of whom were in their seventh to ninth decades of life, were severely disabled by their upper extremity ataxia. The dysarthria observed in the Lincoln family is of a cerebellar type without significant bulbar or spastic components. Over 75% of affected individuals have articulation problems. However, only one affected member has severe dysarthria that interferes with verbal communication. No one in the family has dysarthria as the sole abnormal finding. Sensory deficits are inconsistent, with approximately one-third having mild sensory changes. Approximately half of the affected individuals have some eye movement abnormalities, including mild gaze-evoked nystagmus, square wave jerks, and saccadic intrusions during smooth pursuit. No one has definite tongue atrophy, although two individuals may have shown fasciculations, one of whom developed symptoms of the disease at the age of ten. The presence of brisk reflexes suggests pyramidal tract involvement in approximately one-third of affected people, with only one individual having extensor plantar reflexes. The mean age of onset was 33.013.1 years, with five family members having disease onset before the age of 20. In addition to the usual cerebellar findings, these patients also demonstrated signs of mild bulbar or pyramidal tract involvement. It remains to be seen whether family members with early onset will eventually develop a more

Fig. 30.3 Sagittal MRI scan from an affected individual at the age of 64. There is marked cerebellar atrophy, minimal brainstem atrophy, and no evidence of cerebral involvement. The relative preservation of the posterior vermis, posterior hemisphere, and tonsillar cortex is evident.

severe life-threatening disease due to bulbar atrophy, pyramidal tract degeneration, or basal ganglia disease.

Neuroimaging and neuropathology Brain magnetic resonance imaging (MRI) scans have been performed on 12 members of the large SCA5 family. These have shown dramatic cerebellar cortical atrophy, with greater involvement of the superior hemispheres and anterior vermis, and selective sparing of the inferior vermis and tonsils. The brainstem is only minimally atrophic late in the course of the disease, and there are no changes seen in the basal ganglia, cerebral white matter, or cerebral cortex. Figure 30.3 shows these findings in a sagittal MRI section of an affected 64-year-old woman who had onset of disease symptoms at the age of 57. The brain of one individual affected with SCA5 has been examined at autopsy. This woman had been evaluated clinically five years prior to her death, at which time she had slight ataxia in the upper extremities, moderate ataxia in the lower extremities, and minimal dysarthria. Her sensory examination was normal, and there was no abnormality of tone or movement other than the ataxia. The combination of her ataxia and severe arthritis made her unable to walk for the last ten years of her life. Atypical for SCA5, this woman was also demented due to superimposed, pathologically confirmed Alzheimer’s disease. Her brain was examined after she died at the age of 89

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years. The brain weighed 940 g and showed frontal and temporal atrophy. The cerebellum was grossly shrunken (88 g), with accentuated folial atrophy in the anterior vermis and the anterior–superior portions of the hemispheres. There was severe loss of Purkinje cells in most areas of cortex, with shrinkage of the molecular layer, variable mild loss of granular neurons, and frequent empty basket fibers. There was relative sparing of the tonsillar cortex. The deep cerebellar nuclei were gliotic, without obvious neuronal loss, suggesting loss of afferents from Purkinje cells. Although the inferior olivary nuclei had mild-to-moderate neuronal loss, the basis pontis, red nuclei, cranial nerve nuclei, dorsal columns, Clarke’s nuclei, and spinocerebellar tracts were intact. Widespread neuropathological changes indicative of superimposed Alzheimer’s disease were present in the cerebral hemispheres. Pathologically, SCA5 appears to be principally a cerebellar cortical degeneration with predominant effects on Purkinje cells, in contrast to the majority of the dominantly inherited SCAs, in which there are often degenerative changes in the afferent and efferent cerebellar connections as well as in other brainstem nuclei.

Evidence of anticipation Because anticipation is common in various SCAs (Brice, 1998; Klockgether and Evert, 1998) we examined the SCA5 family for evidence that succeeding generations had earlier ages of onset. The ages of onset for parent–offspring pairs for maternally and paternally inherited ataxia are shown in Table 30.2. The mean ages at onset for the older (43.3 years) versus younger (29.9 years) generations are significantly different (p0.001). Although the average decrease in age at onset for maternally (15.7 years) and paternally (9.3 years) inherited ataxia do not significantly differ from one another, the most dramatic examples of decreasing ages of onset were for maternal transmissions. All five cases of juvenile-onset (10–18 years) SCA5 were maternally inherited. Also, there are several three-generation examples of anticipation in which grandmothers have onsets 10–20 years later in life than their daughters, who in turn have onsets 10–20 years later in life than their children. Although anticipation due to an unstable trinucleotide repeat expansion is an attractive explanation for these data, the decrease in age at onset among the parent– offspring pairs could also be explained by an ascertainment bias. For example, the age at onset difference for the older versus the younger generations will be lessened when the currently unaffected offspring develop signs of

Table 30.2 Age at onset for maternal versus paternal transmission Mother

Child

Age change

Father

Child

Age change

68 68 68 40 22 59 59 36 55 26 39 39 29 29 28 28

50 28 40 30 25 20 36 18 33 24 25 30 28 32 13 10

18 40 28 10 1 3 39 23 18 22 12 14 19 11 1 3 15 18

50 50 50 40 40 50 27 38 45

32 37 20 42 29 30 38 28 50

18 13 30 1 2 11 20 11 10 1 5

Average change 9.3 years

Average change 15.7 years Notes: Table reproduced with permission from Ranum et al. (1994), Nature Genetics 8: 280–4.

the disease later in life and are included in the calculation. Anticipation was not observed in the French SCA5 family; however, given the small size of the family, anticipation may not have been readily apparent (Stevanin et al., 1999).

Repeat expansion detection and RAPID cloning Because the anticipation observed in the Lincoln family is consistent with the presence of a trinucleotide repeat expansion, experiments have been performed to determine whether or not a CAG/CTG repeat expansion is involved in the disease. Repeat expansion detection (RED) assays (Schalling et al., 1993) were performed on genomic DNA from affected members of the SCA5 family with juvenile-onset ataxia. In the RED assay, human genomic DNA is used as a template for a two-step ligation cycling process that generates sequence specific [(CAG)n] oligonucleotide multimers when expanded trinucleotide sequences are present in the genome. It is an elegant technique that detects potentially pathological trinucleotide repeat expansions without knowledge of chromosomal location (Schalling et al., 1993) . Using genomic DNA from SCA1, SCA3, Huntington disease, and myotonic dystrophy type 1 patients with CAG/CTG repeat expansions of known

Spinocerebellar ataxia type 5

sizes, the RED assay has been painstakingly optimized in our laboratory so that the RED products from control samples are of the predicted size and the results are highly reproducible. To investigate further whether or not the CAG repeat expansions that were detected by RED analysis in the SCA5 family were pathogenic, we developed a procedure that isolates flanking sequence surrounding specific CAG repeat expansions that are detected by RED analysis. Our method, called repeat analysis pooled isolation and detection (RAPID) of expanded trinucleotide repeats (Koob et al., 1998), uses an optimized RED protocol to follow the repeat through a series of enrichment steps until a single, isolated clone is obtained. The nucleotide sequence flanking the repeat is then determined and used to design a polymerase chain reaction (PCR) assay to determine if a particular repeat cosegregates with a given disease. The power of RAPID cloning was demonstrated by independently isolating the expanded CAG repeat involved in SCA7 (Koob et al., 1998) and, most recently, by isolating an untranslated CTG expansion that causes another novel form of ataxia (SCA8: Koob et al., 1999). RAPID cloning was also used to isolate the SCA12 expansion (Stevanin et al., 1998). Our RED and RAPID analyses indicate that SCA5 is not caused by a CAG/CTG expansion of 40 or more repeats. However, it is possible that a short CAG/CTG tract (40 repeats) or another trinucleotide motif may cause this disease.

Genetic and physical mapping After mapping the SCA5 gene to the centromeric region of chromosome 11 (Ranum et al., 1994), a high-resolution genetic map of the region was constructed, positioning SCA5 on the long arm of chromosome 11 (11q13). Haplotype analyses using 27 microsatellite markers from the region now localizes SCA5 to a 3 cM region on 11q13. Table 30.3 shows a summary of the pairwise LOD scores for selected markers. A yeast artificial chromosome (YAC) contig covering approximately 90% of the SCA5 region was constructed as a first step towards physically isolating the SCA5 gene. Because of the marked anticipation observed for this kindred, clones from this contig were used to identify and isolate trinucleotide repeats. Five candidate CAG repeats and their corresponding flanking sequence were isolated from YACs in the region, but subsequent PCR analyses showed those repeats were not involved in the SCA5 disease process. A positional cloning approach to identify the gene is still being used.

Table 30.3 Pairwise lod scores Lod scores AT 

Marker

GATA2A01 D11S913 INT2

0.00

0.01

0.05

0.10

0.20

0.30

0.40

 14.66 

8.76 14.39 12.60

10.25 13.28 14.40

10.09 11.85 14.07

8.30 8.83 11.66

5.68 5.64 8.18

2.69 2.48 4.05

Conclusions In contrast to many of the ataxias, SCA5 is clinically milder, because it primarily affects the cerebellum and usually spares the brainstem. Although marked anticipation has been observed, we have not detected a CAG/CTG repeat expansion by RED/RAPID analysis. The eventual characterization of the SCA5 gene will lead to a better understanding of the interdependence and functioning of the neuronal systems that degenerate during the SCA processes.

xReferencesx Brice A. (1998).Unstable mutations and neurodegenerative disorders. J Neurol 245: 505–10. Gouw, L.G,. Digre, K.B., Harris, C.P,, Kaplan, C.D., Haines, J.H. and Ptacek, L.J. (1994). Autosomal dominant cerebellar ataxia with retinal degeneration: clinical, neuropathologic and genetic analysis of a large kindred. Neurology 44: 1441–7. Harding, A. (1983). Classification of the hereditary ataxias and paraplegias. Lancet 1: 1151–5. Holmes G. (1907). A form of familial degeneration of the cerebellum. Brain 30: 466–89. Klockgether, T. and Evert, B. (1998). Genes involved in hereditary ataxias. Trends Neurosci 21: 413–18. Koob, M.D., Benzow, K.A., Bird, T.D., Day, J.W., Moseley, M.L and Ranum, L.P.W. (1998). Rapid cloning of expanded trinucleotide repeat sequences from genomic DNA. Nat Genet 18: 72–5. Koob, M.D., Moseley, M.L., Schut, L.J. et al. (1999). An untranslated CTG expansion causes a novel form of spinocerebellar ataxia (SCA8). Nat Genet 21: 379–84. Ranum, L.P.W., Schut, L.J., Lundgren, J.K., Orr, H.T. and Livingston, D.M. (1994). Spinocerebellar ataxia type 5 in a family descended from the grandparents of President Lincoln maps to chromosome 11. Nat Genet 8: 280–4. Schalling, M., Hudson, T.J., Buetow, K.H. and Housman, D.E. (1993). Direct detection of novel expanded trinucleotide repeats in the human genome. Nat Genet 4: 135–9. Stevanin, G., Herman, A., Brice, A. and Durr, A. (1999). Clinical and

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MRI findings in spinocerebellar ataxia type 5. Neurology 53: 1355–1357. Yagishita, S. and Inoue, M. (1997). Clinicopathology of spinocerebellar degeneration – its correlation to the unstable CAG repeat of the affected gene. Pathol Int 47: 1–15. Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dom-

inant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha-1A-voltage-dependent calcium channel. Nat Genet 15: 62–9. Zoghbi, H.Y. (1991). The spinocerebellar degenerations. Curr Neurol 11: 121–44.

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Spinocerebellar ataxia type 6 Marina Frontali1 and Carla Jodice2 2

Introduction Spinocerebellar ataxia type 6 (SCA6) belongs to the group of autosomal dominant cerebellar ataxias (ADCAs) as well as to that of channelopathies (Ptacek, 1997). Its highly variable phenotype defies a clear-cut classification in any of the three major types of ADCAs, as defined by Harding (1982), though sharing the type of mutation (expansion of a CAG repeat stretch) with SCA1, SCA2, SCA3, and SCA7. The expandable sequence is embedded in a calcium channel gene, CACNA1A, on chromosome 19p13, coding for the 1A subunit of voltage-gated calcium channels type P/Q, expressed predominantly in cerebellar Purkinje and granule cells. In many respects, SCA6 differs from ADCAs with the same type of mutation, and is unique among channelopathies for being due to the expansion of a repeat sequence. Point mutations at the CACNA1A gene are known to cause episodic ataxia type 2 (EA2) and familial hemiplegic migraine (Ophoff et al., 1996). These disorders, and particularly EA2, share some features with SCA6, raising the problem of the relationship among the three allelic diseases.

Clinical features SCA6 exhibits a highly variable clinical picture. In some studies (e.g., Zhuchenko et al., 1997 ; Geschwind et al., 1997; Filla et al., 1999) the phenotype includes a multisystem in addition to a cerebellar involvement, as observed in ADCA type I; in others (Ishikawa et al., 1997; Nagai et al., 1998; Watanabe et al., 1998; Garcia-Planells et al., 1999) the disease has been classified as a pure cerebellar ataxia (ADCA type III); and in others (Jodice et al., 1997; Jen et al., 1998; Yabe et al., 1998) it showed the features of

1 Istituto di Medicina Sperimentale del CNR, Department of Biology, TorVergata University, Rome, Italy

EA2, with ataxia/vertigo episodes and interictal cerebellar deficits with variable degree of severity. The clinical picture was first described by Zhuchenko et al. (1997) as a late-onset, slowly progressive cerebellar ataxia with nystagmus and dysarthria, brainstem involvement, vibratory and proprioceptive sensory loss, and an insidious onset characterized by ‘wooziness’ and momentary imbalance. The permanent and progressive character of the cerebellar deficit, the coexisting brainstem, and sensory involvement led these authors to consider SCA6 as a disorder distinct from EA2. However, a more complex picture emerged from the subsequent studies. Patients may initially experience episodes of ataxia and dysarthria, and/or of vertigo and nausea, accompanied by visual disturbance (such as dyplopia or blurred vision), and tinnitus, lasting from minutes to days and triggered by movements and physical or emotional stress. Episodes have a variable frequency (from yearly to daily) and duration (from seconds to days). Interictally, patients may be neurologically normal or show mild cerebellar signs such as gaze-evoked nystagmus and/or saccadic pursuit, mild dysarthria and dysmetria, but no overt limb or trunk ataxia (Calandriello et al., 1996; Geschwindt et al., 1997; Jodice et al., 1997) . This early phase may have a variable duration. It commonly lasts a few years before the onset of a permanent and progressive ataxia, but in some cases the disease may not progress towards a full-blown disorder (Calandriello et al., 1996; Jodice et al., 1997, Takiyama et al., 1998). Other studies, on the contrary, do not report an episodic phase (Ikeuchi et al., 1997; Matsumura et al., 1997; Stevanin et al., 1997). However, one should bear in mind that episodes may be overlooked or attributed to other causes such as low blood pressure. Patients tend to seek a neurologist’s advice when ataxia becomes permanent, and the preceding episodic phase often emerges only after a prolonged and specific enquiry about it.

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Unbalance and gait difficulties usually herald the transition to a permanent and slowly progressive ataxia. The neurological examination commonly shows trunk and limb ataxia, dysmetria, dysarthria, hypotonia, and a pattern of ocular movement abnormalities, similar to that described for EA2: gaze-evoked nystagmus with or without a downbeat component, dysmetric saccades, saccadic pursuit, and hyperactive vestibulo-ocular reflex (Gomez et al., 1997). Vertigo episodes may continue during this second phase (Gomez et al., 1997) and periodic exacerbations of the cerebellar signs can be present (Yabe et al., 1998). The clinical picture is often limited to a pure cerebellar deficit, but deep sensory deficits, ophthalmoplegia, hyperreflexia or hyporeflexia, dysphagia, and extrapyramidal signs are sometimes also reported (Geschwind et al., 1997 ; Stevanin et al., 1997; Zhuchenko et al., 1997). These latter features, however, are found more frequently in old subjects (Ikeuchi et al., 1997; Ishikawa et al., 1997; Stevanin et al., 1997) or in patients with other coexisting disorders, such as diabetes mellitus (Takiyama et al., 1998). Neuroimaging reveals a cerebellar vermis atrophy, with or without the involvement of cerebellar hemispheres, with preservation of brainstem (Calandriello et al., 1996; Gomez et al., 1997; Jodice et al., 1997; Nagai et al., 1998; Satoh et al., 1998; Shizuka et al., 1998a; Takiyama et al., 1998). Occasionally, a size reduction of the pons has been reported (Murata et al., 1998; Arpa et al., 1999; Nakagawa et al., 1999). When treatment with acetazolamide was tried, by analogy with EA2, patients showed a reduced frequency, duration, and severity of episodes, with little effect on permanent symptoms (Calandriello et al., 1996; Jen et al., 1998).

Neuropathology Macroscopically, the brains of autopsied patients show a marked atrophy of the cerebellar vermis and, to a lesser extent, of the hemispheres. Microscopically, the cerebellar cortex is characterized by a remarkable loss of Purkinje cells. Granule cells are also affected, although less severely. Loss of neurons is sometimes found in the dentate and inferior olivary nuclei (Subramony et al., 1996; Gomez et al., 1997; Sasaki et al., 1998; Ishikawa et al., 1999b; Tashiro et al., 1999). Atrophy of brainstem has occasionally been described (Zhuchenko et al., 1997). No ubiquitin immunoreactive nuclear inclusions, similar to those observed in other CAG repeat expansion disorders, have been found. However, non-ubiquitinated cytoplasmic protein aggregates, detected by anti-1A

subunit antibodies, have been described in Purkinje cells (Ishikawa et al., 1999a, 1999b)

Natural history It may be difficult to define age at onset when, as in this case, early signs are insidious and often overlooked by patients and general practitioners. In most studies, age at onset refers to the beginning of permanent gait imbalance and is, on average, around 50, with a range from 19 to 73 years (Gomez et al., 1997; Matsumura et al., 1997; Watanabe et al., 1998). As in other CAG expansion disorders, a significant inverse correlation between age at onset and size of expanded alleles has been reported in several studies (e.g., Ikeuchi et al., 1997; Ishikawa et al., 1997; Riess et al., 1997; Zhuchenko et al., 1997). Anticipation of age at onset over successive generations has been observed (e.g., Ikeuchi et al., 1997; Matsumura et al., 1997; Matsuyama et al., 1997; Watanabe et al., 1998), although in the absence of an intergenerational variation of the expanded allele size (see below). This phenomenon might be due to ascertainment biases, as pointed out by Penrose (1948). An offspring with an earlier onset than the parent is, in fact, more likely to be encountered in clinical practice, than the reverse situation. In addition, an accurate assessment of older generations might be more difficult, as a consequence of less strict diagnostic criteria in the past, or of fading memories about the exact period in which the first symptoms arose. The disease usually progresses very slowly towards inability: autonomous walking has been observed even after 18–20 years from the onset (Geschwind et al., 1997). However, a very rapid course has also been reported (Watanabe et al., 1998). The lifespan appears to be normal, although no statistical analysis is available.

Inheritance and mutation SCA6 is an autosomal dominant disorder, due to the expansion of a small polymorphic CAG repeat stretch at the 3 end of the CACNA1A gene. Normal alleles range from 4 to 18 units (Zhuchenko et al., 1997; Shizuka et al., 1998a, 1998b). Expanded alleles range from 20 to 30 repeats (Jodice et al., 1997; Matsuyama et al., 1997 ; Shizuka et al., 1998a, 1998b), i.e., a size well within the normal range for other CAG expansion disorders. A complete sequence analysis of the gene coding region in a SCA6 patient showed that the expansion was the only detectable mutation (Jodice et al., 1997).

Spinocerebellar ataxia type 6

Homozygous patients do not differ substantially from heterozygous ones, showing a slightly earlier onset and a more rapid course (Geschwind et al., 1997; Matsumura et al., 1997; Takiyama et al., 1998). The size of SCA6 expanded alleles is more stable than that of other repeat expansion disorders, as expected on the basis of its relatively low number of units. No variation is usually observed in families over successive generations, and no mosaicism is apparent in cells from different parts of the brain (Ishikawa et al., 1999b) or in sperm (Shizuka et al., 1998b). However, some degree of meiotic instability should be assumed, because in two families an intergenerational jump of the expanded allele size has been reported (Jodice et al., 1997; Matsuyama et al., 1997). SCA6 expanded alleles have been found in a number of sporadic ataxia cases (Ikeuchi et al., 1997; Matsumura et al., 1997; Riess et al., 1997; Zhuchenko et al., 1997; Shizuka et al., 1998b), but a new mutation has been documented in one patient only (Shizuka et al., 1998a). Should all these cases be new mutations, the mutability of normal alleles would be very high, particularly if compared to that of SCA1, SCA2, or SCA3 alleles, for which an expansion has never (SCA1 and SCA2) or rarely (SCA3) been found among sporadic cases (Andrew et al., 1999). In addition, if a mutation/selection equilibrium is assumed, a high frequency of SCA6 de-novo mutations would be in contrast with the (presumably) small or absent selection against a disease, such as this one, with a very late onset and a long lifespan of patients. Incomplete penetrance or the presence of neglected mild episodic symptoms in relatives appears to be a more likely explanation for the high number of sporadic cases.

brain (Ophoff et al., 1996), more abundantly in the cerebellum than in other cerebral areas, and particularly in Purkinje cells. The transcript undergoes a considerable variety of alternative splicing, producing at least six isoforms (Mori et al., 1991; Zhuchenko et al., 1997). These differ from each other (Fig. 31.2A) according to three main variations: (1) the presence of exon 37a or of the alternative exon 37b (Trettel et al., 1999); (2) the presence or absence of exon 44; (c) the presence or absence of a five-nucleotide stretch, GGCAG, at the 3 end of the gene between exons 46 and 47. The latter variation is critical for the expression of the CAG repeat stretch (Fig. 31.2B): when the five nucleotides are left in place, the CAG repeat is translated and expressed as a polyglutamine sequence at the protein level; when they are spliced out, a stop codon is encountered upstream of the CAGn stretch, and the protein does not include the glutamine repeat. Isoforms both with and without the GGCAG insertion, i.e., expressing or not expressing the polyglutamine tract, have been found in the cerebellar cortex, with a predominance of the first type in SCA6 brains (Ishikawa et al., 1999a). The distinct properties of the various isoforms are unknown, but they are thought to have regulatory and/or modulatory functions. It has been suggested, for instance, that they can modulate the binding sites for the presynaptic plasma membrane proteins, syntaxin and SNAP-25 (synaptosome-associated protein of 25 kDa), implying that a neuron could adjust the efficiency of synaptic transmission (synaptic vesicle fusion) by regulating the expression of different isoforms of the Ca2 channel gene (Sheng et al., 1994; Rettig et al., 1996).

SCA6 as compared with other ADCAs The gene and the protein The CACNA1A gene encodes for the 1A subunit of the voltage-gated calcium channel type P/Q, a pore-forming membrane protein. The gene maps on chromosome 19p13.1–p13.2 (Diriong et al., 1995) and covers about 300 kb with 47 exons (Ophoff et al., 1996). The cDNA clones predict large peptides with molecular masses of 200 to 275 kDa with four homologous domains (I–IV), each containing six hydrophobic transmembrane segments, S1–S6 (Fig. 31.1). This primary structure gives a four-fold symmetry to the voltage-gated channels, with the pore formed at the central line of contact of four channelforming domains. The short N-terminal and the long Cterminal tails of the protein are located in the cytoplasm. The CACNA1A gene, well conserved during evolution, is expressed as a transcript of approximately 9.8 kb in the

SCA6 differs from other disorders due to the expansion of a CAG repeat (SCA1–3 and SCA7, Huntington disease, dentato-rubro-pallido-luysian atrophy, and spino-bulbar muscular atrophy) in many respects. In the latter diseases, the unstable expanded CAG stretch, located within the coding regions of their genes, typically has a number of units that ranges from 35 to over 100. The gene products are nuclear or cytoplasmic rather than membrane proteins, to which the expanded polyglutamine stretch confers a gain of function, as shown, for example, by the absence of ataxia or neurodegeneration in knock-out mice (e.g., Matilla et al., 1998). Although the pathogenic role of elongated polyglutamine stretches is far from clear, intracellular ubiquitinated insoluble polyglutamine aggregates appear to be a common feature of cells specifically affected in each of these disorders (for a review, see Paulson, 1999).

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Fig. 31.1 (A) Schematic structure of the 1A subunit of the voltage-gated calcium channel type P/Q. Each of the four domains (I–IV) has six -helix transmembrane segments (S1–S6). The carboxyl terminus of the protein contains, in some of the isoforms (see text), a stretch of polyglutamines (gln). (B) Top view of the protein according to the molecular model proposed by Guy and Conti (1990), showing its four-fold symmetry and the central pore formed by the P segments.

These nuclear aggregations are found to be ubiquitinated and, as in SCA1, associated to the proteasome and nuclear matrix (Cummings et al., 1998). In addition, observations deriving from transgenic SCA1 mice and cellular models of Huntington disease suggest that the nuclear translocation of the mutant proteins has a critical pathogenic role (Klement et al., 1998; Saudou et al., 1998). These common features of polyglutamine disorders are not shared with SCA6. The number of triplets in SCA6 expanded alleles is much shorter and stable, falling within the distribution of the normal alleles in the other diseases. The CAG repeat is not expressed in all isoforms, and recent evidence suggests that it confers to the protein a loss rather than a gain of function. Cultured cells transfected with 1A subunit cDNAs, engineered to translate the poly-CAGs in 4, 24, 30, and 40 glutamine residues, showed that expansions of 30 and 40 polyglutamines induce a hyperpolarizing shift

in the voltage dependence of channel inactivation (Matsuyama et al., 1999). This shift can be predicted to exert a considerable effect on channel availability, by halving the Ca2 influx, which may, in turn, lead directly or indirectly to neuronal cell death (Matsuyama et al., 1999). In addition, current density of Ca2 channels in transfected cells is not reduced, implying that the mutated protein is normally transported to the membrane and is not sequestered into aggregates (Matsuyama et al., 1999). Histologically, however, cytoplasmic aggregation, immunoreactive with the 1A subunit antibodies, has indeed been observed in Purkinje cells of SCA6 brains (Ishikawa et al., 1999a). These aggregates, unlike those found in other polyglutamine diseases, are not ubiquitinated and are localized in the cytoplasm. Their nature and implications with the disease should be further investigated. The available evidence shows striking analogies

Spinocerebellar ataxia type 6

Fig. 31.2 Isoforms of the CACNA1A gene (modified from Zhuchenko et al., 1997). (A) The six different isoforms described by Zhuchenko et al. (1997), produced by various combinations of alternative splicing (see text). (B) Alternative splicing between exons 46 and 47. If exon 46 is joined to exon 47 downstream of the GGCAG segment, a stop codon is encountered and the poly-CAG stretch is not expressed. However, if exon 46 is joined to exon 47 upstream of the GGCAG segment, the translation continues beyond the poly-CAG, until a stop codon is encountered, thus producing a protein containing a polyglutamine stretch.

between SCA6 and EA2. The vast majority of EA2 mutations lead to a premature stop codon (Ophoff et al., 1996; Denier et al., 1999), probably producing a non-functional protein, acting either through a mechanism of haploinsufficiency or through a dominant negative effect, e.g., by interfering with the subunit assembly. Carriers of EA2 point mutations share with SCA6 patients: (a) a similar, highly variable phenotype, ranging from vertigo/ataxia episodes with interictal nystagmus and mild cerebellar signs with no overt ataxia (Denier et al., 1999) to a severe progressive pure cerebellar ataxia preceded or not by episodes (Yue et al., 1997); (b) a predominant atrophy of the cerebellar vermis (Denier et al., 1999); and (c) a sensitivity of episodes to acetazolamide treatment (Calandriello et al., 1996; Jen et al., 1998). Furthermore, a continuity between SCA6 and EA2 phenotypes has been observed in the same kindred segregating for an unstable allele with 20 or 25 CAG repeats in different family branches (Jodice et al., 1997). Patients with 25 repeats had a severe progressive ataxia similar to that described as SCA6, while those with 20 repeats had the typical features of EA2, with short vertigo episodes and interictal nystagmus.

Conclusions SCA6 is one of the three allelic disorders due to CACNA1A gene mutations. The other two, familial hemiplegic migraine and EA2, display a predominantly episodic phenotype, typical of channelopathies, mainly associated with point mutations. Missense mutations are found in familial hemiplegic migraine families, suggesting that, in these cases, structural anomalies of the protein may alter the channel activity (Ophoff et al., 1996; Ducros et al., 1999), possibly by a gain of function (Hans et al., 1999). Mutations involving a premature stop codon and a truncated protein are carried by most EA2 families, indicating that a haploinsufficiency mechanism or a dominant negative effect could be responsible for this disorder (Ophoff et al.,1996; Denier et al., 1999). Expansion mutation, instead, is predominantly associated with a pure, permanent and progressive ataxia, for which a pathogenic mechanism similar to that of polyglutamine disorders could be hypothesized (Zhuchenko et al., 1997). However, several lines of evidence appear to blur this hypothetical phenotype–genotype correlation. First of all, the three allelic disorders show a considerable amount of phenotypic overlap. This holds true not only for EA2 and SCA6 (see above), but also for familial hemiplegic migraine, as shown by some families in which hemiplegic migraine is associated with a

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permanent cerebellar ataxia (Ducros et al., 1999). It is interesting to note that the missense mutations in these type of families were found to confer a loss of function to the protein, as hypothesized also for EA2 (Hans et al., 1999), and for SCA6 (Matsuyama et al., 1999). In addition, a truncating mutation was reported in patients with ataxic as well as hemiplegic episodes (Jen et al., 1999). Second, different mutations can be associated with similar phenotypes: expansion mutations are also found in patients with an EA2 phenotype (Jodice et al., 1997; Jen et al., 1998), whereas a permanent and progressive cerebellar deficit, similar to that of SCA6, was reported in subjects carrying a missense mutation (Yue et al., 1997). In this situation, more work is needed to delineate the clinical and pathological spectrum associated with the CACNA1A expansion mutation and the extent of its overlap with the other allelic diseases, on the one hand, and the group of disorders due to CAGn expansions, on the other. A study of expression regulation and function of different 1A subunit isoforms, particularly of those with or without the polyglutamine tract, as well as an analysis of their biophysical properties with different kind of mutations would be highly relevant to understanding the homologies and differences between SCA6 and the other allelic disorders at a cellular level. Finally, animal models could greatly contribute to the understanding of the pathogenic mechanisms involved in SCA6, namely, whether the mutation acts by altering the channel function, as in channelopathies, leading, in turn, to Purkinje cell death, or through a toxic effect of the mutated protein per se, as envisaged for other polyglutamine disorders.

Acknowledgments This work was supported by Telethon grant E847.

xReferencesx Andrew, S.E., Goldberg, Y.P. and Hayden, M.R. (1999). Rethinking genotype and phenotype correlations in polyglutamine expansion disorders. Hum Mol Genet 6: 2005–10. Arpa, J., Cuesta, A., Cruz-Martinez, A., Santiago, S., Sarrià, J. and Palau, F. (1999). Clinical features and genetic analysis of a Spanish family with spinocerebellar ataxia 6. Acta Neurol Scand 99: 43–7. Calandriello, L., Veneziano, L., Francia, A. et al. (1996). Acetazolamide-responsive episodic ataxia in an Italian family refines gene mapping on chromosome 19p13. Brain 120: 805–12.

Cummings, C.J., Mancini, M.A., Antalffy, B., DeFranco, D.B., Orr, H.T. and Zoghbi, H.Y. (1998). Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1. Nat Genet 19: 148–54. Denier, C., Ducros, A., Vahedi, K. et al. (1999). High prevalence of CACNA1A truncations and broader clinical spectrum in episodic ataxia type 2. Neurology 52: 1816–21. Diriong, S., Lory, P., Williams, M.E., Ellis, S.B., Harpold, M.M. and Taviaux, S. (1995). Chromosomal localization of the human genes for 1A, 1B, and 1E voltage-dependent Ca2 channel subunits. Genomics 30: 605–9. Ducros, A., Denier, C., Joutel, A. et al. (1999). Recurrence of the T666M calcium channel CACNA1A gene mutation in familial hemiplegic migraine with progressive cerebellar ataxia. Am J Hum Genet 64: 89–98. Filla, A., De Michele, G., Santoro, L. et al.(1999). Spinocerebellar ataxia type 2 in Southern Italy: a clinical and molecular study of 30 families. Neurology 246: 467–71. Garcia-Planells, J., Cuesta, A., Vilchez, J.J., Martinez, F., Prieto, F. and Palau, F. (1999). Genetics of the SCA6 gene in a large family segregating an autosomal dominant ‘pure’ cerebellar ataxia. J Med Genet 36: 148–51. Geschwind, D.H., Perlman, S., Figueroa, B.S., Karrim, B.S., Baloh, R.W. and Pulst, S.-M. (1997). Spinocerebellar ataxia type 6. Frequency of the mutation and genotype–phenotype correlations. Neurology 49: 1247–51. Gomez, C.M., Thompson, R.M., Gammack, J.T. et al. (1997). Spinocerebellar ataxia type 6: gaze-evoked and vertical nystagmus, Purkinje cell degeneration, and variable age of onset. Ann Neurol 42: 933–50. Guy, H.R. and Conti, F. (1990). Pursuing the structure and function of voltage-gated channels. Trends Neurosci 13: 201–6. Hans, M., Luvisetto, S., Williams, M.E. et al. (1999). Functional consequences of mutations in the human 1A calcium channel subunit linked to familial hemiplegic migraine. J Neurosci 19: 1610–19. Harding, A.E. (1982). The clinical features and classification of the late onset autosomal dominant cerebellar ataxias: a study of 11 families, including descendants of the Drew family of Walworth. Brain 105: 1–28 Ikeuchi, T., Takano, H., Koide, R. et al. (1997). Spinocerebellar ataxia type 6: CAG repeat expansion in 1A voltage-dependent calcium channel gene and clinical variations in Japanese population. Ann Neurol 42: 879–84. Ishikawa, K., Fujigasaki, H., Saegusa, H. et al. (1999a). Abundant expression and cytoplasmic aggregations of 1A voltagedependent calcium channel protein associated with neurodegeneration in spinocerebellar ataxia type 6. Hum Mol Genet 8: 1185–93. Ishikawa, K., Tanaka, H., Saito, M. et al. (1997). Japanese families with autosomal dominant pure cerebellar ataxia map to chromosome 19p13.1–p13.2 and are strongly associated with mild CAG expansions in the spinocerebellar ataxia type 6 gene in chromosome 19p13.1. Am J Hum Genet 61: 336–46

Spinocerebellar ataxia type 6

Ishikawa, K., Watanabe, M., Yoshizawa, K. et al. (1999b). Clinical, neuropathological, and molecular study in two families with spinocerebellar ataxia type 6 (SCA6). J Neurol Neurosurg Psychiatry 67: 86–9. Jen, J.C., Yue, Q., Karrim, J., Nelson, S.F. and Baloh, R.W. (1998). Spinocerebellar ataxia type 6 with positional vertigo and acetazolamide responsive episodic ataxia. J Neurol Neurosurg Psychiatry 65: 565–8. Jen, J.C., Yue, Q, Nelson, S.F. et al. (1999) A novel nonsense mutation in CACNA1A causes episodic ataxia and hemiplegia. Neurology 53: 34–7 Jodice, C., Mantuano, E., Veneziano, L. et al. (1997). Episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6) due to CAG repeat expansion in the CACNA1A gene on chromosome 19p. Hum Mol Genet 6: 1973–8. Klement, I.A., Skinner, P.J., Kayton, M.D. et al. (1998). Ataxin-1 nuclear localization and aggregation: role in polyglutamineinduced disease in SCA1 transgenic mice. Cell 95: 41–53. Matilla, A., Roberson, E.D., Banfi, S. et al. (1998). Mice lacking ataxin-1 display learning deficits and decrease hippocampal paired-pulse facilitation. J Neurosci 18: 5508–16. Matsumura, R., Futamura, N., Fujimoto, Y. et al. (1997). Spinocerebellar ataxia type 6. Molecular and clinical features of 35 Japanese patients including one homozygous for the CAG repeat expansion. Neurology 49: 1238–43. Matsuyama, Z., Kawakami, H., Maruyama, H. et al. (1997). Molecular features of the CAG repeats of spinocerebellar ataxia 6 (SCA6). Hum Mol Genet 6: 1283–7. Matsuyama, Z., Wakamori, M., Mori, Y., Kawakami, H., Nakamura, S. and Imoto, K. (1999). Direct alteration of the P/Q-type Ca2 channel property by polyglutamine expansion in spinocerebellar ataxia 6. J Neurosci 19: RC14 (1–5). Mori, Y., Friedrich, T., Kim, M.S. et al. (1991). Primary structure of functional expression from complementary DNA of a brain calcium channel. Nature 350: 398–402. Murata, Y., Kawakami, H., Yamaguchi, S. et al. (1998). Characteristic magnetic resonance imaging findings in spinocerebellar ataxia 6. Arch Neurol 55: 1348–52. Nagai, Y., Azuma, T., Unauchi, M. et al. (1998). Clinical and molecular genetic study in seven Japanese families with spinocerebellar ataxia type 6. J Neurol Sci 157: 52–9. Nakagawa, N., Katayama, T., Makita, Y., Kuroda, K., Aizawa, H. and Kikuchi, K. (1999). A case of spinocerebellar ataxia type 6 mimicking olivopontocerebellar atrophy. Neuroradiology 41: 501–3. Ophoff, R.A., Terwindt, G.M., Vergouwe, M.N. et al. (1996). Familial hemiplegic migraine and episodic ataxia type-2 are caused by mutations in the Ca2 channel gene CACNL1A4. Cell 87: 543–52. Paulson, H.L. (1999). Protein fate in neurodegenerative proteinopathies: polyglutamine diseases join the (mis)fold. Am J Hum Genet 64: 339–45. Penrose, L.S. (1948). The problem of anticipation in pedigrees of dystonia myotonica. Ann Eugenics 14: 125–32. Ptacek, L.J. (1997). Channelopathies: ion channel disorders of

muscle as a paradigm for paroxysmal disorders of the nervous system. Neuromuscul Disord 7: 250–5. Rettig, J, Sheng, Z.H., Kim, D.K., Hodson, C.D., Snutch, T.P. and Catterall, W.A. (1996). Isoform-specific interaction of the 1A subunits of brain Ca2 channels with the presynaptic proteins syntaxin and SNAP-25. Proc Natl Acad Sci USA 93: 7363–8. Riess, O., Schols, L., Bottger, H. et al. (1997). SCA6 is caused by moderate CAG expansion in the 1A-voltage-dependent calcium channel gene. Hum Mol Genet 6: 1289–93. Saudou, F., Finkbeiner, S., Devys, D. and Greenberg, M.E. (1998). Hungtintin acts in the nucleus to induce apoptosis but death does not correlate with formation of intranuclear inclusions. Cell 95: 55–66. Sasaki, H., Kojima, H., Yabe, I. et al. (1998) Neuropathological and molecular studies of spinocerebellar ataxia type 6 (SCA6). Acta Neuropathol 95: 199–204. Satoh, J.I., Tokumoto, H., Yukitake, M. et al. (1998). Spinocerebellar ataxia type 6: MRI of three Japanese patients. Neuroradiology 40: 222–7. Sheng, Z.H., Rettig, J., Takahashi, M. and Catteral, W.A. (1994). Identification of a syntaxin-binding site on N-type calcium channels. Neuron 13: 1303–13. Shizuka, M., Watanabe, H., Ikeda, Y., Mizushima, K., Okamoto, K. and Shoji, M. (1998a). Molecular analysis of a de novo mutation for spinocerebellar ataxia type 6 and (CAG)n repeat units in normal elder controls. J Neurol Sci 161: 85–7. Shizuka, M., Watanabe, H., Ikeda, Y. et al. (1998b). Spinocerebellar ataxia type 6: CAG trinucleotide expansion, clinical characteristics and sperm analysis. Eur J Neurol 5: 381–7. Stevanin, G., Durr, A., David, G. et al. (1997). Clinical and molecular features of spinocerebellar ataxia type 6. Neurology 49: 1243–6. Subramony, S.H., Fratkin, J.D., Manyam, B.V. and Currier, R.D. (1996). Dominantly inherited cerebello-olivary atrophy is not due to a mutation at the spinocerebellar ataxia 1, Machado–Joseph disease, or dentato-rubro-pallido-luysian atrophy locus. Mov Disord 11: 174–80. Takiyama, Y., Sakoe, K., Nemekawa, M. et al. (1998). A Japanese family with spinocerebellar ataxia type 6 which includes three individuals homozygous for an expanded CAG repeat in the SCA6/CACNL1A4 gene. J Neurol Sci 158: 141–7. Tashiro, H., Suzuki, S.O., Hitotsumatsu, T. and Iwaki, T. (1999). An autopsy case of spinocerebellar ataxia type 6 with mental symptoms of schizophrenia and dementia. Clin Neuropathol 18: 198–204. Trettel, F., Mantuano, E., Calabresi, V. et al. (1999). A fine physical map of the CACNA1A gene region on 19p13.1–p13.2 chromosome. Gene 241: 45–50. Watanabe, H., Tanaka, F., Matsumoto, M. et al. (1998). Frequency analysis of autosomal dominant ataxias in Japanese patients and clinical characterization of spinocerebellar ataxia type 6. Clin Genet 53: 13–19. Yabe, I., Sasaki, H., Yamashita, I. et al. (1998). Initial symptoms and

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mode of neurological progression in spinocerebellar ataxia type 6. Rinsho Shinkeigaku 38: 489–94. Yue, Q., Jen, C.J., Nelson, S.F. and Baloh, R.W. (1997). Progressive ataxia due to a missense mutation in a calcium-channel gene. Am J Hum Genet 61: 1078–87.

Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansion in the 1a-voltage-dependent calcium channel. Nat Genet 15: 62–9.

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Autosomal dominant cerebellar ataxia with progressive pigmentary macular dystrophy Giovanni Stevanin, Anne-Sophie Lebre, Cecilia Zander, Géraldine Cancel, Alexandra Dürr, and Alexis Brice Neurogenetics Group, l’Hôpital de la Saltpêtrière, Paris, France

History Autosomal dominant cerebellar ataxia (ADCA) associated with progressive macular degeneration, also designated olivo-ponto-cerebellar-atrophy type III (Konigsmark and Weiner, 1970) or ADCA type II (Harding, 1982, 1993), was initially described by Froment et al. (1937) and is characterized by heterogeneous clinical presentation, disease severity, and age at onset (Benomar et al., 1994; Enevoldson et al., 1994). Because of the retinopathy observed in most patients, this form of ADCA was considered to be a separate entity (OMIM database entry: 164500).

Identification of the SCA7 gene and the responsible mutation Three independent groups mapped the responsible gene, designated SCA7 (spinocerebellar ataxia 7), to chromosome 3p and postulated that a trinucleotide CAG repeat expansion might be involved in this disease, because the phenomenon of anticipation is particularly marked in SCA7 (20 years per generation; Gouw et al., 1995; Benomar et al., 1995; Holmberg et al., 1995). A pure (CAG)10 repeat, located between markers D3S1600 and D3S1287, was found in a subclone of yeast artificial chromosome (YAC) 88-d-9 (David et al., 1997; Del-Favero et al., 1998). Polymerase chain reaction (PCR) analysis with primers flanking this CAG repeat showed the presence of an expansion in SCA7 patients (David et al., 1997; Del-Favero et al., 1998) that was confirmed by a strategy derived from the rapid expansion detection (RED) technique (Koob et al., 1998). Large series of controls and patients have now been analyzed and it has been shown that the SCA7 CAG repeat is polymorphic, with sizes ranging from 4 to 35 units in

control, and from 36 to 306 in SCA7 and at-risk carrier chromosomes (Del-Favero et al., 1998; Johansson et al., 1998; Koob et al., 1998; Lyoo et al., 1998; Gouw et al., 1998; Benton et al., 1998; Stevanin et al., 1998; David et al., 1998b; Giunti et al., 1999; Nardacchione et al., 1999). The largest expansions (between 114 and 306 CAG repeats) were found in juvenile or infantile cases (Johansson et al., 1998; Benton et al., 1998; David et al., 1998b; Giunti et al., 1999).

Instability of the CAG repeat in SCA7 families Somatic mosaicism is observed in DNA extracted from patients’ leukocytes but not from lymphoblastoid cell lines (David et al., 1997). In a 67-year-old patient, a bimodal distribution of the expanded allele in leukocytes with mean values of 45 and 350 repeats was reported (Matsuura et al., 1999). The mean size of the expansion and the degree of gonadal instability in SCA7 are greater than those observed in any of the other neurodegenerative diseases known to be caused by translated CAG repeat expansions (Table 32.1). In 84% of the parent–child transmissions, the number of CAG repeats increases on the pathological chromosome. Contractions are very rare (8%). The mean variation in the reported series of patients is 12 and ranges from 13 to 263 CAG repeats (Table 32.1). The largest increases in CAG repeat size, which result in juvenile cases, always occur during transmission by affected fathers, and are correlated with the size of the repeat in the parent (Johansson et al., 1998; David et al., 1998b). Instability is greater (p0.001) in paternal ( 2145, n 72) than in maternal transmissions ( 69, n97) and remains significantly different (p0.05) even if juvenile cases are omitted, resulting in a mean variation of 1010 CAGs in paternal transmissions (n67).

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Table 32.1 Instability of CAG repeats during transmission as a function of the sex of the transmitting parent Male

Female

References

SCA1

2.2 (0 to 8, n16)

0.4 (0 to 4, n10)

Unpublished data

SCA2

3.5 (8 to 17, n33)

1.7 (4 to 8, n23)

(Sanpei et al. (1996); Cancel et al. (1997)

SCA3/MJD

0.9 (3 to 5, n26)

0.6 (8 to 3, n34)

Unpublished data

SCA7

21.0 (6 to 263, n72)

6.0 (13 to 56, n97)

(Del-Favero et al. (1998); Johansson et al. (1998); Koob et al. (1998); Lyoo et al. (1998); Gouw et al. (1998); Benton et al. (1998); Stevanin et al. (1998); David et al. (1998b); Giunti et al. (1999)

DRPLA

7.0 (0 to 28, n33)

0.3 (4 to 4, n9)

(Ikeuchi et al. (1995); Komure et al. (1995)

SBMA

1.8 (2 to 5, n11)

0.2 (4 to 2, n20)

(Biancalana et al. (1992); Watanabe et al. (1996)

HD

6.1 (4 to 74, n156)

0.6 (4 to 16, n160)

(Duyao et al. (1993); Kremer et al. (1995)

Notes: MJDMachado–Joseph disease; DRPLAdentatorubropallidoluysian atrophy; SBMAspinal and bulbar muscular atrophy; HDHuntington’s disease.

Gonadal mosaicism estimated on sperm DNA is much greater than in leukocytes, with a strong tendency to massive expansion (David et al., 1998b; Monckton et al., 1999). It has been hypothesized that the excess of affected women as transmitting parents in this disease (Gouw et al., 1998) might result from embryonic lethality of very large alleles transmitted by affected fathers (Monckton et al., 1999). The marked instability of the SCA7 mutation compared to other polyglutamine diseases suggests that factors other than the length of the repeat, such as upstream or downstream sequences in cis or trans (Igarashi et al., 1996), location with respect to the origin of replication (Kang et al., 1995), or genetic background, may affect the stability of CAG repeats. It should be noted that the SCA7 region is characterized by a large discrepancy between the estimated genetic and physical distances (David et al., 1997), although the significance of this observation with respect to gonadal instability of the expanded repeat remains to be determined.

Epidemiology and origin of the mutation Frequency and origin of the SCA7 mutation The relative frequency of the SCA7 mutation in large series of ADCA kindreds ranges from 1.4% to 12% (Koob et al.,

1998; Moseley et al., 1998; Benton et al., 1998; Stevanin et al., 1999; Pujana et al., 1999; Hsieh et al., 1999). The SCA7 mutation has been found in all but one of the ADCA II kindreds tested (Giunti et al., 1999), but not in the ADCA type I or III. The frequency can vary greatly according to geographic origin, from 0% of kindreds in Eastern India (Basu et al., 2000) to 35% in those from North Africa. ADCA II is detected is patients from various ethnic and geographical origins. Most reported families were either North African or continental European (France, Belgium, Sweden, Finland, the Netherlands, Italy, Portugal, Germany, Spain). Several were Latin American (Ecuador, Peru), African American, Asian (Korea, Philippines, Taiwan), Middle Eastern, and Anglo-Saxon. Single families also originated from Australia, Israel, and Liberia. Flanking and intragenic markers were used in linkage disequilibrium studies and showed that several ancestral mutations probably account for the SCA7 kindreds in Scandinavia, Korea, North-Africa, continental Europe, and Anglo-Saxon countries (UK and USA) (Stevanin et al., 1999; Jonasson et al., 2000). The haplotypes segregating in Jamaican, Filipino, Brazilian, and German families are different, which suggests that independent regional founders introduced the SCA7 mutation in each population (Stevanin et al., 1999).

Cerebellar ataxia with progressive pigmentary macular dystrophy

De novo mutations from intermediate alleles The strong anticipation in SCA7 and the rarity of contractions should have led to its extinction within a few generations. However, de novo SCA7 expansions occur (Stevanin et al., 1998) from intermediate alleles (IAs) with 28 to 35 repeats. De novo events have only been observed so far at the SCA7 and Huntington’s disease loci (Myers et al., 1993), composed of pure CAG repeats on normal alleles. They have not yet been observed, however, in other polyglutamine diseases, for which a lesser degree of instability – for both expansion and contraction – may explain their persistence.

Consequences for molecular diagnosis Care should be taken to detect both intermediate-sized and large alleles. The latter are difficult to amplify, but should be suspected in juvenile or infantile forms of the disease (Johansson et al., 1998; Benton et al., 1998; David et al., 1998b). Individuals carrying 34 (Gouw et al., 1998) and 35 (Koob et al., 1998) CAG repeats have been reported, but their clinical status and ages at onset were not described. However, several individuals with 35 CAG repeats were reported to be unaffected at ages 50 to 84 (Stevanin et al., 1998). If several of these cases prove to be true patients in the future, these intermediate-sized alleles may result in incomplete penetrance, as is the case for small expansions carrying 36 to 41 repeats at the Huntington’s disease locus (Rubinsztein et al., 1996; Andrew et al., 1997). Isolated cases with a phenotype compatible with SCA7 should systematically be tested for the mutation, because de novo mutations are possible (Stevanin et al., 1998) and because anticipation can result in much earlier onset in the affected child than in the transmitting parent, usually the father.

Clinical and neuro-anatomical features Visual impairment SCA7, unlike other ADCAs, is characterized by a progressive macular degeneration that can be visualized in most patients as a pigmented central core in the macula that can extend, in latter stages, into the periphery. Visual failure is progressive, bilateral, and symmetrical, and leads irreversibly to blindness (Gouw et al., 1994; Enevoldson et al., 1994). Central vision is affected first. Peripheral vision is preserved at early stages, explaining why patients do not complain of symptoms until failure is

Table 32.2 Major phenotypic characteristics of 69 SCA7 patients with a mean age at onset of 2916 years (1–70) and carrying 5113 CAG repeats (38–130) Clinical signs

%

Cerebellar ataxia Dysarthria Decreased visual acuity Brisk reflexes Diminished or abolished reflexes Babinski sign Ophthalmoplegia Slow saccades Deep sensory loss Sphincter disturbances Amyotrophy Auditory impairment Axonal neuropathy Facial myokimia Dementia Extrapyramidal rigidity Dystonia Bulging eyes Nystagmus

100 98.5 81 80 3 55 54 63 60 55 25 24 18 13 12 14 9 6 2

well advanced, and why night vision is not impaired. Interestingly, dyschromatoptia in the blue–yellow axis is found years before visual failure becomes symptomatic (Gouw et al., 1994). In contrast, fundoscopic abnormalities, consisting of a loss of the foveal reflex and progressive molting of pigment at the macula, are often delayed. Secondary optic atrophy can often be detected in later stages. Electroretinograms show abnormal photopic responses, but scotopic responses are preserved late. Visual-evoked potentials are not discriminative for diagnostic purposes (Enevoldson et al., 1994).

Neurological signs The neurological signs of the ADCAs clearly overlap (Stevanin et al., 2000). Studies of large groups of patients have, however, revealed a constellation of signs that are frequently found in SCA7 patients (Table 32.2). Cerebellar ataxia is always associated with dysarthria, but patients present variably with pyramidal signs (increased reflexes and/or extensor plantar reflexes and/or lower limb spasticity), decreased vibration sense, dysphagia, sphincter disturbances, and oculomotor abnormalities (supranuclear ophthalmoplegia and/or viscosity of eye movements). Extrapyramidal features (dystonia), myokymia, peripheral

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neuropathy, and mental impairment are rare. The frequency of swallowing and sphincter disturbances significantly increases with disease duration (David et al., 1998b). The association of cerebellar ataxia and dysarthria with pyramidal signs, supranuclear ophthalmoplegia, slow saccades, and decreased visual acuity is highly suggestive of SCA7.

Neuropathology and brain imaging Brain imaging shows marked atrophy in the cerebellum, particularly in the superior part of the vermis, and the brainstem, which may be associated with moderate atrophy of the cerebral cortex. The neuropathology differs from olivopontocerebellar atrophy, however, because pontocerebellar pathways are normal on post-mortem brain samples (Gouw et al., 1994; Martin et al., 1994; Enevoldson et al., 1994). Spinocerebellar, olivocerebellar, and efferent cerebellar tracts are severely affected. In the cerebellum, the vermis is more affected than hemispheres, where Purkinje cells and, to a lesser extent, granule cells degenerate. Mild cell loss also occurs in the dentate nucleus, which, as the result of Purkinje cell degeneration, has a reduced mantel. Extensive neuronal loss is observed in the inferior olive, with marked astrocytic gliosis. Mild cell loss is also observed in the substantia nigra and the basis pontis, whereas the thalamus and the striatum are spared. The distinctive neuropathological features of ADCA type II are degeneration of optic pathways and of the retina. The pregeniculate visual pathways and the optic nerve are affected, probably as a consequence of retinal degeneration. In juvenile cases presenting with blindness, those systems may not be altered, probably due to the rapid course of the disease. Pathological examination of the retina shows early degeneration of photoreceptors and of bipolar and granular cells, particularly in the foveal and parafoveal regions. Later, patchy loss of epithelial pigment cells and their ectopic migration into the retinal layers are observed (Martin et al., 1994).

Genotype–phenotype correlations First sign at onset Cerebellar ataxia is usually the presenting symptom in adults with onset over the age of 30. In patients with earlier onset, however, decreased visual acuity, alone or associated with cerebellar ataxia, is the initial symptom (Benomar et al., 1994; Enevoldson et al., 1994), although some infantile cases may result in early death without detectable retinal alteration (Martin et al., 1999). More

than 45 years can elapse between the appearance of cerebellar symptoms and visual failure, whereas, in the reverse situation, the latency never exceeds nine years (David et al., 1998b; Giunti et al., 1999). In some patients with late onset, visual acuity may never decrease.

Age at onset, anticipation, and disease duration The clinical manifestations typically begin in the third or fourth decade, with mean age at onset close to 30, but a range of three months or less to over 70 years (Martin et al., 1994; Holmberg et al., 1995; Jöbsis et al., 1997; Gouw et al., 1998; Benton et al., 1998; David et al., 1998b; Giunti et al., 1999). Analysis of parent–child couples has revealed striking anticipation (20 years/generation). Previous studies reported significantly greater anticipation in paternal than in maternal transmissions (Benomar et al., 1994;, 1995; David et al., 1996). This was not confirmed by recent reports (Del-Favero et al., 1998; Johansson et al., 1998; Benton et al., 1998; David et al., 1998b; Giunti et al., 1999), although all juvenile cases are paternally transmitted. There is a strong negative correlation between the size of the CAG expansion and age at onset. The former accounts for 75% of the variability of the latter, suggesting that other genetic and/or environmental factors play only a minor role in determining the SCA7 phenotype, unlike other disorders involving polyglutamine expansions (Gouw et al., 1998; David et al., 1998b; Giunti et al., 1999). The CAG length/age at onset correlation, together with the increase in expansion size in successive generations, is consistent with the marked anticipation observed in ADCA II families (David et al., 1998b). In SCA7, anticipation is characterized by earlier onset, but also by more rapid disease progression and increased severity in successive generations. Disease duration until death is negatively correlated with the number of CAG repeats on the expanded allele and is limited to a few month or years in early-onset patients (David et al., 1998b). The mean value for subjects carrying fewer than 49 repeats is 15 years and differs significantly from the 11-year duration when the number of repeats is at least 49 (Giunti et al., 1999). Longer disease durations, up to 30 years or more, are observed only in late-onset patients (Neetens et al., 1990). Anticipation is also associated with increasing severity of symptoms in successive generations. The frequency of decreased visual acuity, ophthalmoplegia, scoliosis, and extensor plantar reflexes significantly increases with the size of the expansion (David et al., 1998b). The SCA7 phenotype of a given patient partly depends on both the size of the mutation and the disease duration at examination. In some infantile cases with very large repeat

Cerebellar ataxia with progressive pigmentary macular dystrophy

expansions, progression is extremely rapid and the heart can be affected (Neetens et al., 1990; Benton et al., 1998). It is surprising that the retina may also be affected in juvenile SCA2 patients (Babovic-Vuksanovic et al., 1998). It may be that the retina and the cardiac muscle are sensitive only to large and very large expansions, respectively. The pathological threshold of the polyglutamine expansion may therefore be tissue dependent.

Normal and pathological functions of SCA7 The SCA7 cDNA and its expression The 2727 bp open reading frame of the SCA7 cDNA (David et al., 1997; Del-Favero et al., 1998), encodes a protein of 892 amino acids of unknown function, designated ataxin7. It contains an N-terminal polyglutamine tract at codons 30–39, present in exon 3, and a functional nuclear localization signal at amino acids 378–394 (Kaytor et al., 1999). The polyglutamine region is preceded by an alanine-rich region and followed by a proline-rich sequence that contains four SH3 binding domains. There is no significant homology with known gene or protein sequences, except the polyglutamine and polyproline tracts observed in huntingtin, atrophin, and several homeodomain-containing proteins and other transcription factors (Gerber et al., 1994). Ataxin-7 also shares a short and functional motif homologous to the phosphate-binding site of arrestin (Mushegian et al., 2000). Serine residues are abundant in the 3-end of the cDNA sequence. Polymorphisms in the number of GCN and CCG repeats, upstream and downstream, respectively, of the CAG repeat have also been observed (Stevanin et al., 1998). A A/G3145 polymorphism resulting in a Met→Val substitution without functional effect has been reported (Stevanin et al., 1999). Putative caspase cleavage sites exist at amino acid positions 149, 534, and 770. A 7.5 kb transcript is detected by Northern-blot analysis and is expressed ubiquitously in adult and fetal tissues (David et al., 1997; Del-Favero et al., 1998). The level of expression is higher in heart, placenta, skeletal muscle, and pancreas, than in brain, liver, and kidney, but similar in the retina (unpublished data) and all other central nervous system structures tested, except for the cerebellum, where expression is higher. In testis, a second transcript 7 Kb is expressed at the same level (M. Holmberg, unpublished data). Homologous genes are also present in monkey, mouse, rat, and cow (David et al., 1998a). Polyclonal and monoclonal antibodies have been produced against the N-terminal domain of ataxin-7, overlapping, in one of them, the polyglutamine tract (Cancel et al.,

Fig. 32.1 Intranuclear inclusions in the inferior olive of a SCA7 patient carrying 85 CAG repeats ( 250). The inclusion has been labeled with the 1C2 antibody (Trottier et al., 1995) and revealed by the peroxidase/antiperoxidase technique, with diaminobenzidine as the chromogen. Staining of the nucleus by Harris haematoxylin. These nuclear inclusions are also detected with an anti-ubiquitine antibody (data not shown).

2000). Whereas the mutated protein has been reported in the nucleus of lymphoblasts of SCA7 patients (Trottier et al., 1995), wild-type ataxin-7 localizes in the cytoplasm of all the populations of neurons analyzed in control brains. Nuclear labeling has been observed in some neurons and its frequency and intensity vary greatly and are not correlated with the topography of lesions in patients. For example, only 5% of neurons showed nuclear staining in the inferior olives, a structure that is severely affected in patients. In patients, however, the nuclear labeling was higher in regions with neuronal loss.

Pathological consequences of the expansion in ataxin-7 In agreement with Trottier et al. (1995), who detected the pathological protein in the cell nuclei, Holmberg et al. (1998; Mauger et al., 1999) reported intranuclear inclusions in neurons of several brain regions in a juvenile SCA7 patient, including the cerebellum, the inferior olive, and the retina, which severely degenerate (Fig. 32.1), as well as the cerebral cortex, which is much less affected. These aggregates were labelled with 1C2, an antibody which selectively recognizes large polyglutamine stretches, as well as with an antibody directed against ubiquitin. The degree of ubiquitination varied according to the structure (ranging from 1% in the cerebral cortex to 60% in the inferior olive) and might be related to the progression of the disease in each structure at the time of death. In addition, the 1C2 antibody stained the cytoplasm of neurons in

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the supramarginal gyrus, hippocampus, thalamus, lateral geniculate body and pontine nuclei. Similar nuclear inclusions, restricted to neurons, were detected in patients and in animal and cellular models of other polyglutamine diseases (Lunkes and Mandel, 1997; Kim and Tanzi, 1998), and appear to constitute a common feature of these disorders. However, whether they are the cause or a consequence of the degenerative process remains a matter of debate. They are predominantly found in affected tissues and can be detected before the phenotype in a mouse model of Huntington’s disease (Mangiarini et al., 1996; Davies et al., 1997), suggesting that they may be deleterious. Their presence, however, is not sufficient to initiate the degenerative process in epithelial cells of a SCA3 drosophila model with no phenotype or degeneration (Warrick et al., 1998), and in unaffected tissues in SCA7 patients (Holmberg et al., 1998). Klement et al. (1998) demonstrated that, although nuclear translocation of mutated ataxin-1 is necessary, as also shown in cellular models with Huntington’s disease constructs (Saudou et al., 1998), aggregation is not required to initiate pathogenesis. Furthermore, cell dysfunctions exist before detectable pathology (Lin et al., 2000). The inclusions may, therefore, only represent a pathological hallmark of the diseases and/or a cellular defence mechanism. If the inclusions are not responsible for the initiation of the disease, they may be implicated in disease progression and severity by sequestration of proteins and RNA. The presence of several caspase-mediated cleavage sites in ataxin-7 is reminiscent of huntingtin, atrophin, ataxin3, and androgen receptor, which are suspected to be truncated by such proteases (Wellington et al., 1998) and, as a consequence, can have a toxic effect (Ikeda et al., 1996; Ellerby et al., 1999), and/or can more easily enter the nucleus (Igarashi et al., 1998; Hackam et al., 1999), and/or aggregate (Cooper et al., 1998; Martindale et al., 1998). Inhibition of caspases should, as in Huntington’s disease (Ona et al., 1999), be promising in animal and cellular SCA7 models. Abnormal processing of mutant proteins is confirmed by colocalization of chaperones in inclusions and inhibition of aggregation by overexpression of heat-shock protein HDJ-2 in cellular models (Cummings et al., 1998; Stenoinen et al., 1999; Wyttenbach et al., 2000). Because the specificity of neuronal death cannot be explained solely by the expression pattern of the SCA7 gene, its level of expression and/or the presence of other proteins with which ataxin-7 interacts might also be implicated.

Models Immunocytochemical studies have been carried out on COS-1 (Kaytor et al., 1999) and COS-7 (Lebre et al., 1999)

A

B

Fig. 32.2 COS-7 cells expressing full-length ataxin-7/myc-tag fusion protein with 10 (A) or 100 (B) glutamines. Transient transfections were performed by electroporation. Forty-eight hours post-transfection, cells were fixed with paraformaldehyde, permeabilized in detergents, then incubated subsequently with anti myc antibody 9E10 (Santa Cruz Biotechnology, CA) and antimouse secondary antibody conjugated to TRITC (Dako). Cells were mounted in Mowiol (Sigma) and examined with a microscope (Zeiss, objective 63) coupled to a CDD camera allowing digital capture. Diffuse staining, except a few nuclear domains, was noted in both experiments. After 48 hours culture, however, strong labeling accumulates as a few spots in cells transfected with pathological ataxin-7 (B).

cells expressing both wild-type and mutated ataxin-7. In both cases, intense labeling was observed almost exclusively in the nucleus (Fig. 32.2). Nuclear transport was blocked by disruption of the nuclear localization signal (Kaytor et al., 1999). Aggregation and ubiquitination were

Cerebellar ataxia with progressive pigmentary macular dystrophy

not observed in cells transfected with mutant ataxin-7 (52 repeats), which was associated with the nuclear matrix, promyelocytic leukemia protein (PML) bodies, and nucleoli (Kaytor et al., 1999). The presence of mutant ataxin-7 in the nucleoli might alter rRNA synthesis and processing. Interestingly, mutant ataxin-1 is responsible for a redistribution of PML from the PML oncogenic domains (PODs) to the nucleoplasm (Skinner et al., 1997). Similarly, mutant ataxin-1 causes redistribution of ataxin-7 in the nucleolus, therefore demonstrating that PML and mutant ataxin-7 colocalize to PODs (Kaytor et al., 1999). Recently, directed expression of ataxin-7 with a pathological expansion to photoreceptors or Purkinje cells mimicked the human disease in mouse (Yvert et al., 2000).

Conclusion and perspectives SCA7 shares common features with other diseases of the growing group of neurodegenerative disorders with polyglutamine expansions: (i) the appearance of clinical symptoms above a threshold number of CAG repeats (>35); (ii) a strong negative correlation between the CAG repeat size and both age at onset and disease progression; (iii) instability of the repeat sequence (12 CAG/transmission) that accounts for the marked anticipation of 20 years/generation; (iv) ubiquitous expression of the gene; and (v) accumulation of the pathological protein in ubiquitinated nuclear inclusions, predominantly in severely affected brain structures. However, SCA7 is the first such disorder in which the degenerative process affects the retina in addition to other brain structures. The CAG repeat sequence is particularly unstable and de novo mutations can occur during paternal transmissions of intermediate alleles (28 to 35 CAG repeats). This can explain the persistence of the disease despite the anticipation that should have resulted in its extinction. The considerable clinical heterogeneity, which greatly complicated the establishment of classifications of ADCAs in the past, can now be explained by the variable size of the CAG repeat tract that influences not only the age at onset but also disease severity and clinical presentation (Stevanin et al., 2000). Disease duration, as demonstrated in ADCA type I (Durr et al., 1993), can also alter the clinical phenotype. Molecular analysis can therefore be used to confirm the clinical diagnosis and to identify gene carriers amongst at-risk individuals, according to the classical guidelines in use for Huntington’s disease (World Federation of Neurology Research Group on Huntington’s Chorea, 1994). ADCA II is not genetically homogeneous. Another locus could be responsible for the disease in a small proportion of families

(Giunti et al., 1999). However, whether maculopathy is similar in both cases remains to be investigated. Immunocytochemical studies have revealed differences in the intensity and site of labeling of wild-type ataxin-7. The mutated protein, however, always accumulates in the nucleus and processes. Because of its marked instability, the strong effect of CAG repeat size on phenotype and the wide variety of tissues affected, including retina, SCA7 cell, and animal models, promise to increase our understanding of the physiopathology of polyglutamine diseases.

Acknowledgments The authors’ studies on SCA7 were supported financially by the Association Française contre les Myopathies, the VERUM Foundation, the Association pour le Développement de la Recherche sur les Maladies Génétiques Neurologiques et Psychiatriques, the Biomed concerted action No. BMH4 CT96 0244, and the Association Française Retinitis Pigmentosa/Retina France. We are grateful to M. Abada-Bendib, N. Abbas, S. Belal, A. Benomar, J. Bou, A. Camuzat, H. Chneiweiss, S. Cunha, G. David, C. Duyckaerts, P. Giunti, D. Grid, D.B. Hanna, A.E. Harding, M. Holmberg, W. Horta, S.G. Jacobson, J. Julien, J.M. Kwon, C.H. Lyoo, C. Penet, Y. Pothin, M. Ruberg, N. Wood, M. Yahyaoui, J. Zlotogora, J-L. Mandel and his collaborators for their contribution. G.S. and C.Z. were recipients of fellowships from the Société de Secours des Amis des Sciences and France Huntington, respectively.

xReferencesx Andrew, S.E., Goldberg, Y.P. and Hayden, M.R. (1997). Rethinking genotype and phenotype correlations in polyglutamine expansion disorders. Hum Mol Genet 6: 2005–10. Babovic-Vuksanovic, D., Snow, K., Patterson, M.C. and Michels, V.V. (1998). Spinocerebellar ataxia type 2 (SCA 2) in an infant with extreme CAG repeat expansion. Am J Med Genet 79: 383–7. Basu, P., Chattopadhyay, B., Gangopadhaya, P.K. et al. (2000). Analysis of CAG repeats in SCA1, SCA2, SCA3, SCA6, SCA7 and DRPLA loci in spinocerebellar ataxia patients and distribution of CAG repeats at the SCA1, SCA2 and SCA6 loci in nine ethnic populations of eastern India. Hum Genet 106: 597–604. Benomar, A., Krols, L., Stevanin, G. et al. (1995). The gene for autosomal dominant cerebellar ataxia with pigmentary macular dystrophy maps to chromosome 3p12–p21.1. Nat Genet 10, 84–8. Benomar, A., Le Guern, E., Dürr, A. et al. (1994). Autosomal-dominant cerebellar ataxia with retinal degeneration (ADCA type II) is genetically different from ADCA type I. Ann Neurol 35: 439–44.

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Benton, C.S., de Silva, R., Rutledge, S.L., Bohlega, S., Ashizawa, T. and Zoghbi, H.Y. (1998). Molecular and clinical studies in SCA-7 define a broad clinical spectrum and the infantile phenotype. Neurology 51: 1081–6. Biancalana, V., Serville, F., Pommier, J., Julien, J., Hanauer, A. and Mandel, J.L. (1992). Moderate instability of the trinucleotide repeat in spino bulbar muscular atrophy. Hum Mol Genet 1: 255–8. Cancel, G., Dürr, A., Didierjean, O. et al. (1997). Molecular and clinical correlations in spinocerebellar ataxia 2: a study of 32 families. Hum Mol Genet 6: 709–15. Cancel, G., Duyckarets, C., Holmberg, M. et al. (2000). Distribution of ataxin-7 in normal human brain and retina. Brain 123: 2519–30. Cooper, J.K., Schilling, G., Peters, M.F. et al. (1998). Truncated Nterminal fragments of huntingtin with expanded glutamine repeats form nuclear and cytoplasmic aggregates in cell culture. Hum Mol Genet 7: 783–90. Cummings, C.J., Mancini, M.A., Antalffy, B., De Franco, D.B., Orr, H.T. and Zoghbi, H.Y. (1998). Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1. Nat Genet 19: 148–54. David, G., Abbas, N., Durr, A. et al. (1998a). Autosomal dominant cerebellar ataxia with macular dystrophy (SCA7) is caused by a highly unstable CAG repeat expansion. In Genetic Instabilities and Hereditary Neurological Diseases, ed. R.D. Wells and S.T. Warren, pp. 273–82. San Diego: Academic Press. David, G., Dürr, A., Stevanin, G. et al. (1998b). Molecular and clinical correlations in autosomal dominant cerebellar ataxia with progressive macular dystrophy (SCA7). Hum Mol Genet 7: 165–70. David, G., Abbas, N., Stevanin, G. et al. (1997). Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nat Genet 17: 65–70. David, G., Giunti, P., Abbas, N. et al. (1996). The gene for autosomal dominant cerebellar ataxia type II is located in a 5-cM region in 3p12–p13: genetic and physical mapping of the SCA7 locus. Am J Hum Genet 59: 1328–36. Davies, S.W., Turmaine, M., Cozens, B.A. et al. (1997). Formation of neuronal intranuclear inclusions (NII) underlies the neurological dysfunction in mice transgenic for the HD mutation. Cell 90: 537–48. Del-Favero, J., Krols, L., Michalik, A. et al. (1998). Molecular genetic analysis of autosomal dominant cerebellar ataxia with retinal degeneration (ADCA type II) caused by CAG triplet repeat expansion. Hum Mol Genet 7: 177–86. Durr, A., Chneiweiss, H., Khati, C. et al. (1993). Phenotypic variability in autosomal dominant cerebellar ataxia type I is unrelated to genetic heterogeneity. Brain 116: 1497–508. Duyao, M., Ambrose, C., Myers, R. et al. (1993). Trinucleotide repeat length instability and age of onset in Huntington’s disease. Nat Genet 4: 387–92. Ellerby, L.M., Andrusiak, R.L., Wellington, C.L. et al. (1999). Cleavage of atrophin-1 at caspase site aspartic acid 109 modulates cytotoxicity. J Biol Chem 274: 8730–6. Enevoldson, T.P., Sanders, M.D. and Harding, A.E. (1994).

Autosomal dominant cerebellar ataxia with pigmentary macular dystrophy. A clinical and genetic study of eight families. Brain 117: 445–60. Froment, J., Bonnet, P. and Colrat, A. (1937). Heredo-dégénérations rétinienne et spino-cérébelleuses: variantes ophtalmoscopiques et neurologiques présentées par trois générations successives. J Méd Lyon 22: 153–63. Gerber, H.P., Seipel, K., Georgiev, O. et al. (1994). Transcriptional activation modulated by homopolymeric glutamine and proline stretches. Science 263: 808–11. Giunti, P., Stevanin, G., Worth, P., David, G., Brice, A. and Wood, N.W. (1999). Molecular and clinical study of 18 families with ADCA type II: evidence for genetic heterogeneity and de novo mutation. Am J Hum Genet 64: 1594–603. Gouw, L.G., Castaneda, M.A., McKenna, C.K. et al. (1998). Analysis of the dynamic mutation in the SCA7 gene shows marked parental effects on CAG repeat transmission. Hum Mol Genet 7: 525–32. Gouw, L.G., Digre, K.B., Harris, C.P., Haines, J.H. and Ptacek, L.J. (1994). Autosomal dominant cerebellar ataxia with retinal degeneration: clinical, neuropathologic, and genetic analysis of a large kindred. Neurology 44: 1441–7. Gouw, L.G., Kaplan, C.D., Haines, J.H. et al. (1995). Retinal degeneration characterizes a spinocerebellar ataxia mapping to chromosome 3p. Nat Genet 10: 89–93. Hackam, A.S., Singaraja, R., Zhang, T., Gan, L. and Hayden, M.R. (1999). In vitro evidence for both the nucleus and cytoplasm as subcellular sites of pathogenesis in Huntington’s disease. Hum Mol Genet 8: 25–33. Harding, A.E. (1982). The clinical features and classification of the late onset autosomal dominant cerebellar ataxias. A study of 11 families, including descendants of the ‘the Drew family of Walworth’. Brain 105: 1–28. Harding, A.E. (1993). Clinical features and classification of inherited ataxias. Adv Neurol 61: 1–14. Holmberg, M., Duyckaerts, C., Durr, A. et al. (1998). Spinocerebellar ataxia type 7 (SCA7): a neurodegenerative disorder with neuronal intranuclear inclusions. Hum Mol Genet 7: 913–18. Holmberg, M., Johansson, J., Forsgren, L., Heijbel, J., Sandgren, O. and Holmgren, G. (1995). Localization of autosomal dominant cerebellar ataxia associated with retinal degeneration and anticipation to chromosome 3p12– p21.1. Hum Mol Genet 4: 1441–5. Hsieh, M., Lin, S.J., Chen, J.F. et al. (1999). Studies of the CAG repeat in the spinocerebellar ataxia type 7 gene in Taiwan. Am J Hum Genet 65 (Suppl.): 1535. Igarashi, S., Koide, R., Shimohata, T. et al. (1998). Suppression of aggregate formation and apoptosis by transglutaminase inhibitors in cells expressing truncated DRPLA protein with an expanded polyglutamine stretch. Nat Genet 18: 111–7. Igarashi, S., Takiyama, Y., Cancel, G. et al. (1996). Intergenerational instability of the CAG repeat of the Machado–Joseph disease (MJD1) is affected by the genotype of the normal chromosome: implications for the molecular mechanisms of the instability of the CAG repeat. Hum Mol Genet 5: 923–32.

Cerebellar ataxia with progressive pigmentary macular dystrophy

Ikeda, H., Yamaguchi, M., Sugai, S., Aze, Y., Narumiya, S. and Kakizuka, A. (1996). Expanded polyglutamine in the Machado–Joseph disease protein induces cell death in vitro and in vivo. Nat Genet 13: 196–202. Ikeuchi, T., Onodera, O., Oyake, M., Koide, R., Tanaka, H. and Tsuji, S. (1995). Dentatorubral-pallidoluysian atrophy (DRPLA): close correlation of CAG repeat expansions with the wide spectrum of clinical presentations and prominent anticipation. Semin Cell Biol 6: 37–44. Jöbsis, G.J., Weber, J.W., Barth, P.G. et al. (1997). Autosomal dominant cerebellar ataxia with retinal degeneration (ADCA II): clinical and neuropathological findings in two pedigrees and genetic linkage to 3p12–p21.1. J Neurol Neurosurg Psychiatry 62: 367–71. Johansson, J., Forsgren, L., Sandgren, O., Brice, A., Holmgren, G. and Holmberg, M. (1998). Expanded CAG repeat in Swedish spinocerebellar ataxia type 7 (SCA7) patients: effect of CAG repeat length on the clinical manifestation. Hum Mol Genet 7: 171–6. Jonasson, J., Juvonen, V., Sistonen, P. et al. (2000). Evidence for a common spinocerebellar ataxia type type 7 (SCA7) founder mutation in Scandinavia. Eur J Hum Genet 8: 918–22. Kang, S., Jaworski, A., Ohshima, K. and Wells, R.D. (1995). Expansion and deletion of CTG repeats from human disease genes are determined by the direction of replication in E. coli. Nat Genet 10: 213–18. Kaytor, M.D., Duvick, L.A., Skinner, P.J., Koob, M.D., Ranum, L.P. and Orr, H.T. (1999). Nuclear localization of the spinocerebellar ataxia type 7 protein, ataxin-7. Hum Mol Genet 8: 1657–64. Kim, T.W. and Tanzi, R.E. (1998). Neuronal intranuclear inclusions in polyglutamine diseases: nuclear weapons or nuclear fallout? Neuron 21: 657–9. Klement, I.A., Skinner, P.J., Kaytor, M.D. et al. (1998). Ataxin-1 nuclear localization and aggregation: role in polyglutamineinduced disease in SCA1 transgenic mice. Cell 95: 41–53. Komure, O., Sano, A., Nishino, N. et al. (1995). DNA analysis in hereditary dentatorubral-pallidoluysian atrophy: correlation between CAG repeat length and phenotypic variation and the molecular basis of anticipation. Neurology 45: 143–9. Konigsmark, B.W. and Weiner, L.P. (1970). The olivopontocerebellar atrophies: a review. Medicine (Baltimore) 49: 227–41. Koob, M.D., Benzow, K.A., Bird, T.D., Day, J.W., Moseley, M.L. and Ranum, L.P.W. (1998). Rapid cloning of expanded trinucleotide repeat sequences from genomic DNA. Nat Genet 18: 72–5. Kremer, B., Almqvist, E., Theilmann, J. et al. (1995). Sex-dependent mechanisms for expansions and contractions of the CAG repeat on affected Huntington disease chromosomes. Am J Hum Genet 57: 343–50. Lebre, A.-S., Cancel, G., Zander, C. et al. (1999). Spinocerebellar ataxia 7 (SCA7): cellular localization and search for partners of ataxin-7. Am J Hum Genet 65 (Suppl.): 2592. Lin, X., Antalffy, B., Kang, D., Orr, H.T. and Zoghbi, H.Y. (2000). Polyglutamine expansion down-regulates specific neuronal genes before pathologic changes in SCA1. Nat Neurosci 3: 157–63.

Lunkes, A. and Mandel, J.-L. (1997). Polyglutamines, nuclear inclusions and neurodegeneration. Nat Med 3: 1201–2. Lyoo, C.H., Hun, K., Choi, Y.C. et al. (1998). CAG repeat expansion in the SCA7 gene in Korean families presenting with ADCA type II. J Korean Neurol Assoc 16: 341–52. Mangiarini, L., Sathasivam, K., Seller, M. et al. (1996). Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell 87: 493–506. Martin, J., Van Regemorter, N., Del-Favero, J., Lofgren, A. and Van Broeckhoven, C. (1999). Spinocerebellar ataxia type 7 (SCA7) – correlations between phenotype and genotype in one large belgian family. J Neurol Sci 168: 37–46. Martin, J.J., Van Regemorter, N., Krols, L. et al. (1994). On an autosomal dominant form of retinal-cerebellar degeneration: an autopsy study of five patients in one family. Acta Neuropathol (Berl) 88: 277–86. Martindale, D., Hackam, A., Wieczorek, A. et al. (1998). Length of huntingtin and its polyglutamine tract influences localization and frequency of intracellular aggregates. Nat Genet 18: 150–4. Matsuura, T., Khajavi, M., de Silva, R. and Ashizawa, T. (1999). A very large SCA7 CAG expansion is compatible with cell viability in somatic mosaicism. Am J Hum Genet 65 (Suppl): 2611. Mauger, C., Del-Favero, J., Ceuterick, C., Lofgren, A., Van Broeckhoven, C. and Martin, J. (1999). Identification and localization of ataxin-7 in brain and retina of a patient with cerebellar ataxia type II using anti-peptide antibody. Brain Res Mol Brain Res 74: 35–43. Michalik, A., Del-Favero, J., Mauger, C., Lofgren, A. and Van Broeckhoven, C. (1999). Genomic organisation of the spinocerebellar ataxia type 7 (SCA7) gene responsible for autonomal dominant cerebellar ataxia with retinal degeneration. Hum Genet 105: 410–17. Monckton, D.G., Cayuela, M.L., Gould, F.K., Brock, G.J., Silva, R. and Ashizawa, T. (1999). Very large (CAG)(n) DNA repeat expansions in the sperm of two spinocerebellar ataxia type 7 males. Hum Mol Genet 8: 2473–8. Moseley, M.L., Benzow, K.A., Schut, L.J. et al. (1998). Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families. Neurology 51: 1666–71. Mushegian, A.R., Vishnivetski, S.A. and Gurevich, V.V. (2000). Conserved phosphoprotein interaction motif is functionally interchangeable between ataxin-7 and arrestins. Biochemistry 39: 6809–13. Myers, R.H., MacDonald, M.E., Koroshetz, W.J. et al. (1993). De novo expansion of a (CAG)n repeat in sporadic Huntington’s disease. Nat Genet 5: 168–73. Nardacchione, A., Orsi, L., Brusco, A. et al. (1999). Definition of the smallest pathological CAG expansion in SCA7. Clin Genet 56: 232–4. Neetens, A., Martin, J.J., Libert, J. and Van Den Ende, P. (1990). Autosomal dominant cone-dystrophy-cerebellar atrophy (ADCoCA) (modified ADCA Harding II). Neuro-ophthalmology, 10: 261–75. Ona, V.O., Li, M., Vonsattel, J.P. et al. (1999). Inhibition of caspase-1

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slows disease progression in a mouse model of Huntington’s disease. Nature 399: 263–7. Pujana, M.A., Corral, J., Gratacos, M. et al. (1999). Spinocerebellar ataxias in Spanish patients: genetic analysis of familial and sporadic cases. The Ataxia Study Group. Hum Genet 104: 516–22. Rubinsztein, D.C., Leggo, J., Coles, R. et al. (1996). Phenotypic characterization of individuals with 30–40 CAG repeats in the Huntington disease (HD) gene reveals HD cases with 36 repeats and apparently normal elderly individuals with 36–39 repeats. Am J Hum Genet 59: 16–22. Sanpei, K., Takano, H., Igarashi, S. et al. (1996). Identification of the spinocerebellar ataxia type 2 gene using a direct identification of repeat expansion and cloning technique, DIRECT. Nat Genet 14: 277–84. Saudou, F., Finkbeiner, S., Devys, D. and Greenberg, M.E. (1998). Huntington acts in the nucleus to induce apoptosis but death does not correlate with the formation of intranuclear inclusions. Cell 95: 55–66. Skinner, P.J., Koshy, B.T., Cummings, C.J. et al. (1997). Ataxin-1 with an expanded glutamine tract alters nuclear matrix-associated structures. Nature 389: 971–4. Stenoien, D.I., Cummings, C.J., Adams, H.P. et al. (1999). Polyglutamine-expanded androgen receptors form aggregates that sequester heat shock proteins, proteasome components and SRC-1, and are suppressed by the HDJ-2 chaperone. Hum Mol Genet 8: 731–41. Stevanin, G., David, G., Durr, A. et al. (1999). Multiple origins of the spinocerebellar ataxia 7 (SCA7) mutation revealed by linkage disequilibrium studies with closely flanking markers, including an intragenic polymorphism (G3145TG/A3145TG). Eur J Hum Genet 7: 889–96. Stevanin, G., Dürr, A. and Brice, A. (2000). Clinical and molecular

advances in autosomal dominant cerebellar ataxias: from genotype to phenotype and physiopathology. Eur J Hum Genet 8: 418. Stevanin, G., Giunti, P., Belal, G.D.S. et al. (1998). De novo expansion of intermediate alleles in spinocerebellar ataxia 7. Hum Mol Genet 7: 1809–13. Trottier, Y., Lutz, Y., Stevanin, G. et al. (1995). Polyglutamine expansion as a pathological epitope in Huntington’s disease and four dominant cerebellar ataxias. Nature 378: 403–6. Warrick, J.M., Paulson, H.L., Gray-Board, G.L. et al. (1998). Expanded polyglutamine protein forms nuclear inclusions and causes neural degeneration in Drosophila. Cell 93: 939–49. Watanabe, M., Abe, K., Aoki, M. et al. (1996). Mitotic and meiotic stability of the CAG repeat in the X-linked spinal and bulbar muscular atrophy gene. Clin Genet 50: 133–7. Wellington, C.L., Ellerby, L.M., Hackam, A.S. et al. (1998). Caspase cleavage of gene products associated with triplet expansion disorders generates truncated fragments containing the polyglutamine tract. J Biol Chem 273: 9158–67. World Federation of Neurology Research Group on Huntington’s Chorea. (1994). International Huntington Association and the World Federation of Neurology Research Group on Huntington’s Chorea. Guidelines for the molecular genetics predictive test in Huntington’s disease. J Med Genet 31: 555–9. Wyttenbach, A., Carmichael, J., Swartz, J. et al. (2000). Effects of heat shock, heat shock protein 40 (HDJ-2), and proteasome inhibition on protein aggregation in cellular models of Huntington’s disease. Proc Natl Acad Sci USA 97: 2898–903. Yvert, G., Lindenberg, K.S., Picaud, S. et al. (2000). Expanded polyglutamines induce neurodegeneration and trans-neuronal alterations in cerebellum and retina of SCA7 transgenic mice. Hum Mol Genet 9: 2491–506.

33

Spinocerebellar ataxia type 8 Melinda L. Moseley1, Lawrence J. Schut3, John W. Day2, and Laura P.W. Ranum1 1

Department of Genetics, Cell Biology, and Development, Institute of Human Genetics, University of Minnesota, Minneapolis, USA 2 Department of Neurology, Institute of Human Genetics 3 Department of Neurology, CentraCare Clinic, St Cloud, Minnesota, USA

Introduction

Table 33.1 Ataxia family collection

It was recently demonstrated that an untranslated CTG expansion causes a novel form of ataxia – spinocerebellar ataxia type 8 (SCA8: Koob et al., 1999a). In addition to being the first example of a dominant SCA that is not caused by the expansion of a CAG repeat translated into a polyglutamine tract, the mutation underlying SCA8 shows marked intergenerational changes that are probably responsible for dramatically variable disease penetrance. The RAPID cloning method used to isolate the SCA8 CTG expansion and the clinical and genetic features of the disease are discussed below.

Inheritance pattern

Number of families

%

Dominant Apparently recessive Apparently sporadic Unknown Total

188 48 152 26 414

45 12 37 6

RAPID cloning As part of a broader goal to understand better the various genetic causes of ataxia and to develop a resource to clone novel ataxia genes, an ataxia DNA collection has been established that now represents over 380 different ataxia kindreds with dominant, recessive, and sporadic forms of adult-onset ataxia (Moseley et al., 1998). Table 33.1 summarizes the inheritance patterns of the various families represented in the collection. Although direct gene tests are now available for eight of the ataxia loci, a large portion of the dominant ataxia families in our collection (35%) do not harbor expansions at the known loci, and thus remain genetically undefined. To determine whether or not CAG repeat expansions are the pathogenic mechanism involved for some of these genetically undefined forms of ataxia, the repeat expansion detection (RED) assay was performed on affected family representatives. The RED assay, developed by Schalling et al. (1993), is an elegant technique that allows for the detection of potentially pathogenic trinucleotide

repeat expansions without prior knowledge of chromosomal location. Human genomic DNA is used as a template for a two-step ligation cycling process that generates sequence specific (CAG)n oligonucleotide multimers when expanded trinucleotide sequences are present in the genome. The RED assay was optimized in our laboratory using genomic DNA from SCA1, SCA3, Huntington disease and myotonic dystrophy type 1 (DM1) patients with CAG/CTG repeat expansions of known sizes. To investigate further whether or not specific CAG repeat expansions were pathogenic, a procedure was developed to isolate the sequence flanking the CAG repeat expansions detected by RED. Our method is called repeat analysis pooled isolation and detection (RAPID) cloning of expanded trinucleotide repeats (Koob et al., 1998). In general, this technique uses an optimized RED protocol to follow the repeat through a series of powerful enrichment steps until a single, isolated clone is obtained. The sequence flanking the repeat is then used to design a polymerase chain reaction (PCR) assay to determine whether the repeat cosegregates with disease. A schematic overview of the RAPID cloning method is presented in Fig. 33.1. Genomic DNA is digested with a restriction enzyme and size-separated on an agarose gel. The lane containing the DNA is excised and uniformly cut every 2 mm along its length using a gel-slicing device. DNA

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Digested genomic DNA

Separate gel into fractions

Agarose gel

RED assay size fractions

Clone DNA from RED+ fraction

Convert RED+ dsDNA library to ssDNA containing uracil

RED assay clone pools

RAPID cloning of an expanded CTG repeat from an ataxia patient

u u

u

u

u u

u

u

u

u u

Extend from a (CAG)10 oligo at high temperature

u

u u

u

u

u

u

u

schemes established by Kunkel and coworkers (1987). Plasmid DNA (0.1 g) representing a RED-positive pool of clones was electroporated into Escherichia coli strain CJ236 (dut-, ung-, BioRad, Hercules, CA) to generate uracilsubstituted DNA (Kunkel et al., 1987). The doublestranded plasmid DNA was converted to single-stranded DNA with M13K07 helper phage. The CTG repeat containing ssDNA was then converted to dsDNA by primer extension using a (CAG)10 primer. Uracil DNA glycosylase (UDG) is added to remove the uracil residues from the original DNA strand. Transformation of this mixture into E. coli results in the repair and replication of CAG-containing dsDNA clones and in the degradation and elimination of the ssDNA background. Clones from the enriched library are assayed, either individually or in small pools of approximately 20 clones each, to determine which clones contain the CAG expansion.

u

Add uracil-DNA glycosylate

Transform, RED assay to find individual clones Fig. 33.1 Schematic overview of RAPID cloning of expanded trinucleotide repeats from genomic DNA. (Reproduced with permission from Koob et al. (1998), Nature Genetics, Vol. 18, pp. 72–5.)

from each individual size-fractionated slice is purified, and RED analysis is then performed separately on each size fraction. DNA from the RED-positive fraction is cloned and pools consisting of approximately 5 104 clones each are assayed by RED. A RED-positive clone pool is then subjected to a post-cloning CAG-enrichment procedure. The enrichment of CAG-containing clones is an adaptation of the general approach described by Duyk and colleagues (Ostrander et al., 1992), which is based on the selection

RED analysis performed on DNA samples from an affected mother and an affected daughter with a genetically undefined form of ataxia generated RED products with 80 CAG repeats (RED80) for both DNA samples. Two-dimensional RED analysis (Koob et al., 1998) of EcoRI-digested genomic DNA from the daughter was subsequently performed and it was determined that the RED80 product was not generated by a previously isolated CAG expansion of known molecular weight (Fig. 33.2A). To characterize this CAG expansion futher, the 1.15 kb EcoRI fragment containing the expansion (Fig. 33.2B) was cloned using the RAPID cloning procedure (Koob et al., 1998) and the genomic insert in the resulting clone was sequenced. Sequencing revealed that the expansion consisted of 80 uninterrupted CAG repeats followed by a stretch of 11 TAG repeats (Fig. 33.2C). There are no significant open reading frames that extend through this expansion. Most notably, in the reading frame that would produce a polyglutamine expansion, 17 of the 31 codons immediately flanking the expansion are stop codons. In addition, detailed analysis of this sequence did not reveal any possible splice donor or acceptor signals that would allow an open reading frame to extend through the expansion in a spliced transcript of this genomic sequence. These data made it appear unlikely that the expansion could be translated into a polyglutamine tract. PCR primers were designed from the genomic sequence to amplify across the repeat, and PCR analysis of a chromosome hybrid panel and the CEPH YAC library physically

Spinocerebellar ataxia type 8

A

B

C

Fig. 33.2 RAPID cloning of the SCA8 expanded CTG repeat. (A) Two-dimensional RED analysis of EcoRI-digested genomic DNA isolated from an individual with a dominantly inherited ataxia. The number of CAG repeats in the RED products generated are indicated at the side of the panel, and the four fractions that generate RED products are indicated below the panel. The genomic DNA size fractions that generate the RED30, RED70, and RED40 products contain large, non-pathogenic ‘background’ CTG repeats present in many unaffected individuals. The size fraction containing the RED80 CTG expansion (indicated by an asterisk) was unique to this ataxia patient and was cloned as described. (B) RED analysis of CTG-enriched clone pools derived from a RED-positive primary clone pool. Each pool contains DNA from 36 individual clones. RED analysis of plasmid DNA from the individual clones in pool 9 identified two clones containing the expanded CTG repeat. Sequence analysis of these clones revealed an expanded CTG tract with 80 uninterrupted repeats. (C) Genomic sequence flanking the expansion and the predicted translation products in the polyglutamine (polyQ) reading frame. The sequence is shown for the DNA strand encoding the CAG expansion. Stop codons in the polyQ reading frame are underlined with a solid line, and the stop codons in the other reading frames are underlined with a dashed line. Predicted amino acids are indicated by their single letter code, and translation stop sites are indicated by a crossed circle. The multiple stop codons present in the glutamine reading frame and the absence of splice donor or acceptor sites in the sequences shown indicate that the SCA8 CTG expansion is unlikely to encode a polyQ-containing protein. (Reproduced with permission from Koob et al. (1999b), Nature Genetics, Vol. 21, pp. 379–84.)

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I

II

III

IV

V 118

91 88

86

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100

101

74

75

94

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107

127

117 124

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VI:20

90

86

94

VI:24 VI:26 94 89

90 111

81 111

VI:25

112

VII 85 97

118

119140 123 91

80

96 87

Fig. 33.3 The large SCA8 kindred. Filled symbols indicate individuals with ataxia, symbols with a dot indicate individuals who have inherited the CTG expansion but are not clinically affected by ataxia. The CTG repeat lengths of expanded alleles are indicated below the symbols. Haplotype analyses using five short tandem repeat markers confirm that both branches of the family inherited the expanded repeat from a common founder. The family members who are homozygous for the SCA8 expansion and their affected heterozygous siblings (individuals VI: 24–26) had similar clinical features, with comparable ages of onset and rates of disease progression. (Reproduced with permission from Koob et al. (1999b), Nature Genetics, Vol. 21, pp. 379–84.)

mapped the expansion to chromosome 13q21 near the polymorphic markers D13S275 and D13S135. No ataxia genes had previously been mapped to this locus (Koob et al., 1999b). PCR analysis of the CAG/CTG repeat was performed on genomic samples from the kindred from which it was isolated. Both of the affected individuals (each with 80 CTG repeats) and two at-risk individuals (87 and 113 CTG repeats, ages 38 and 35 years, respectively) were found to have an expansion in one of their alleles. Our ataxia family collection was then screened (Moseley et al., 1998) and seven additional probands were identified, representing unrelated kindreds with dominant ataxia. To investigate whether or not this triplet expansion was pathogenic, we collected blood from and examined additional members of these kindreds. The largest of these families (the MN-A family in Fig. 33.3) is a seven-generation kindred from which 84 members were clinically evaluated and tested for expansions. PCR analyses showed that all of the affected individuals in the family had an expanded allele. Linkage analyses between ataxia and the expansion in this kindred gave a maximum lod score of 6.8 at 0.00, indicating that the expansion is tightly linked to a novel dominant SCA locus (SCA8) (Koob et al., 1999b).

Within the MN-A family there were 17 individuals who carried an expanded repeat but were not clinically affected at the time of evaluation. The ages at the time of evaluation of these asymptomatic carriers ranged between 14 and 74 years, with a mean (4317 years) that was comparable to the mean age at examination of the affected family members. However, the repeat lengths among these asymptomatic carriers are significantly (p108) shorter than those found among the affected individuals (means 91.9 and 116.6 repeats, respectively), suggesting that disease penetrance is affected by the length of the CTG repeat. All but one of the individuals with a CTG repeat tract  107 repeats is clinically affected. The exception is a 42-year-old individual with 140 CTG repeats. Although this person’s repeat length is larger than the apparent pathogenic threshold, a currently asymptomatic status is not surprising given that SCA8 is an adult-onset disease with a documented age of onset as late as 65 years of age. Because the penetrance of the disease depends on both age and repeat length, affected individuals within the large SCA8 family did not always have an obviously dominant family history of ataxia (Fig 34.3: individuals IV24–26; Day et al., 2000)

Spinocerebellar ataxia type 8

4 Maternal Transmissions

2

600

375

250

30 to 34

25 to 29

20 to 24

15 to 19

10 to 14

5 to 9

0 to 4

–5 to –1

–10 to –6

–15 to –11

–20 to –16

–25 to –21

–30 to –26

–35 to –31

– 40 to –36

– 45 to –41

–50 to –46

0

–80

1

–86

Number of chromosomes

Paternal Transmissions 3

Change in CTG repeat length Fig. 33.4 Intergenerational variation in repeat number for maternal and paternal transmissions. Repeat variation is shown as a decrease or an increase of CTG repeat units. Maternal and paternal transmissions are represented by gray and black bars, respectively.

Instability and maternal penetrance of the SCA8 CTG repeat The intergenerational changes in CTG repeat number are typically larger for SCA8 than for the other dominant SCAs (Chung et al., 1993; Maciel et al., 1995; Maruyama et al., 1995; Cancel et al., 1997; David et al., 1997; Jodice et al., 1997; Zhuchenko et al., 1997), but are generally not as large as for DM1. A histogram of the change in CTG repeat number in maternal and paternal transmissions of the SCA8 expansion is shown in Fig. 33.4. Among the ataxia families, paternal transmissions resulted in contractions in the CTG repeat (86 to 7), and most maternal transmissions resulted in expansions (11 to 600). Three very large increases in repeat length ( 250, 375, 600), similar in size to those seen in myotonic dystrophy, all resulted from maternal transmissions. A maternal bias toward expansions has not been reported for the other SCAs (Koob et al., 1999b). Nineteen of the 21 documented transmissions of ataxia in the MN-A family resulted from maternal transmissions. The remaining two individuals inherited expanded alleles from both parents (see Fig. 34.3). In contrast, of the 19 asymptomatic individuals with repeat expansions, three

were maternally transmitted and 16 were paternally transmitted. Among all of the families with long SCA8 alleles, 26 of the 30 affected individuals inherited the repeat expansion from their mother. This maternal penetrance bias for disease transmission is consistent with the higher frequency of expansions into the pathogenic range for female transmissions and contractions below the pathogenic threshold for paternal transmissions (Koob et al., 1999b). In two families, unaffected men (73 and 79 years) with 260 and 300 CTG repeats transmitted shorter pathogenic alleles to four affected offspring. In addition, three offspring in another ataxia family inherited expanded alleles of 400, 500, and 700 repeats (ages 24, 17, and 15, respectively) but are not clinically affected. Although we cannot be sure that these individuals will not develop ataxia in the future, these very large alleles did not lead to a congenital form of the disease. The only affected individual that we have seen with a repeat larger than 250 CTGs is an individual with 800 repeats. Because this patient’s 54-year-old mother (who carries an expanded SCA8 allele of 230 repeats) is asymptomatic and his father (who does not carry an expanded SCA8 allele) is affected by a disease similar to that of his son, it is not clear that this patient’s very large SCA8 allele causes his ataxia. These large expansions, not detectable by PCR, were

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identified by Southern analysis. After finding several large, apparently non-penetrant expansions by Southern analysis among the ataxia families, the control panel was rescreened. Out of 1200 control chromosomes, one allele of 800 repeats was found in a CEPH grandmother. Medical histories indicate that neither this woman nor her son (54 years, 800 repeats) is affected by ataxia. These observations indicate that very large alleles (>250 repeats) may not be pathogenic, or are not always pathogenic, possibly because they are not expressed or because of altered RNA processing or stability (Ranum et al., 1999). Very large, apparently non-pathogenic expansions (>500 repeats) have also been reported by Kennedy et al. (1999). In the CEPH family, four children inherited an expanded allele from their father, but in each case the alleles had undergone massive deletions (700 repeats), resulting in 85, 93, 116 and 118 combined CTA/CTG repeats (Ranum et al., 1999). Because our PCR assay measures the overall size of the combined CTA/CTG repeat tract, and the CTA tract can vary in size (3–17 repeats), it is not clear if these alleles contain CTG tracts below the pathogenic range or if these young people are at risk for ataxia. To investigate further the instability of very large alleles, Southern analysis was performed on sperm DNA from two unrelated men with 500 and 800 repeats. In both cases, all or nearly all of the expanded alleles underwent massive deletions into size ranges (90 and 110 combined repeats) typically at or below the pathogenic threshold. These massive paternal deletions may contribute to the reduced penetrance of SCA8. Histograms summarizing the allele sizes found among affected individuals from the large SCA8 kindred and those found among 1200 control chromosomes are compared in Fig. 33.5a. Repeat sizes for the combined CTA/CTG lengths are presented because both the CTG and the CTA repeats are polymorphic and our PCR assay determines the combined size of these two repeats. Although SCA8 alleles ranging in size from 16 to 91 were found, as well as an allele containing approximately 800 combined CTA/CTG triplet repeats in the general population, more than 99% of the alleles in the general population had from 16 to 34 combined repeats. Among ataxia patients from the large SCA8 kindred, alleles ranged in size from 110 to 130 combined CTA/CTG repeats (107–127 CTG repeats alone), but alleles less than 100 repeats within the family were not pathogenic. The potential overlap between the large normal and affected alleles makes it important to establish the pathogenic range using only families that are large enough to link independently to the SCA8 locus. Although we cannot use families that are too small for linkage analysis to define the affected CTA/CTG repeat range, 11 of the ataxia families in

our family collection have ‘potentially pathogenic’ alleles with repeat lengths longer than 91 combined CTA/CTG repeats. The sizes of potentially pathogenic alleles in these families ranged from 93 to 250 combined repeats (Fig. 33.5b; Koob et al., 1999b; Ranum et al., 1999).

Ancestral origins of SCA8 expansions Although the frequency of expansions greater than 91 combined repeats among the unrelated ataxia probands (15/408) is significantly higher than the 1/1200 observed in the general population (p1 10125) the relative frequency of rare large alleles (600–800 repeats) in the general population appears to occur at a higher frequency (1/1200) than does ataxia (1/10 000). These data suggest that either (a) the SCA8 expansion is not pathogenic, but is simply a polymorphism in linkage disequilibrium with an ataxia locus, or (b) that the CTG repeat can cause ataxia, but other factors in addition to repeat length also affect disease penetrance. To test whether or not the CTG expansion could be a non-pathogenic polymorphism that by chance lies close enough to be in linkage disequilibrium with an ataxia locus, haplotype analysis was performed on: 24 SCA8 ataxia families, 14 SCA8 expansion samples from Athena Diagnostics, 12 expansion families with psychiatric diseases, and 5 control individuals with SCA8 expansions. Although initial studies with markers 100–200 kb from the CTG expansion did not detect a common haplotype, subsequent analysis with eight flanking STR markers we developed (at 72, 56, 52, 24, 9, 13, 17, and 20 kb) detected a highly conserved haplotype among the Caucasian ataxia and psychiatric patients as well as the controls, indicating that the region closely linked to the SCA8 expansion originates from a common ancestor (Moseley et al., 2000a). These data suggest that a separate mutation found only in the ataxia families that is in linkage disequilibrium with the repeat is unlikely to account for the reduced penetrance of the disease. Further evidence supporting a pathogenic role of the CTG expansion is indicated by the fact that second independently arising SCA8 expansion was found among four Japanese ataxia families and one of the Athena samples. The fact that the SCA8 expansion has arisen at least twice and in both cases these expansions are associated with ataxia supports the conclusion that expansions at the SCA8 locus can cause a progressive adult-onset ataxia, but that other factors, such as the length of the CTA or CTG repeart tracts, interruptions within the CTG repeat (Moseley et al., 2000b), or other unlinked genetic or environmental factors, also affect penetrance.

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Fig. 33.5 (a) Distributions of composite CTA/CTG repeat lengths among control chromosomes (n1200) and SCA8 alleles. A polymorphic (CTA)n3–17 repeat that is stable upon transmission is located at the 5 end of the unstable CTG stretch. The range of sizes for the composite repeats in control samples varies from 16 to 92 combined CTA/CTG repeats, although >99% of the normal alleles have from 19 to 34 repeats. In contrast, there is a range of 110–130 combined CTA/CTG repeats among affected individuals from the large family confirmed by linkage analysis to have SCA8. The length of the CTG repeat tracts alone among affected individuals from the SCA8 family varies from 107 to 127 CTG repeats. (b) Potentially pathogenic allele sizes found among affected individuals from small ataxia families. Because the affected range for SCA8 must be established using families that are definitively linked to the SCA8 locus, these potentially pathogenic alleles are shown separately. The sizing of alleles >150 repeats is approximate. (Reproduced with permission from Koob et al. (1999b), Nature Genetics, Vol. 21, pp. 379–84.)

Sequence variations at the SCA8 locus In contrast to other triplet repeat diseases, pathogenic SCA8 expansions often have triplet interruptions within the repeat tracts. The SCA8 CTG repeat is preceded by a poly-

morphic but stable CTA tract, with the configuration (CTA)3–29(CTG)n (Moseley et al., 2000b). The CTG portion of the repeat tract is elongated on pathogenic alleles and nearly always changes in size when transmitted from one generation to the next. Sequence interruptions observed

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within expanded CTG tracts among 11 ataxia families include CCG, CTA, CTC, CCA, and CTT. These interruptions are clustered at the 5 end of the CTG portion of the repeat tract. Surprisingly, these interruptions can duplicate when transmitted, resulting in a variety of alleles that vary both in overall CTG tract length and sequence configuration. Although both interrupted and pure repeat tracts are found among affected individuals in the various SCA8 families, the possible role that interruptions within the CTG repeat tract may play in disease pathogenesis is unclear (Moseley et al., 2000b).

Clinical features Affected individuals have gait, limb, speech, and oculomotor incoordination, spasticity, and sensory loss. A common finding of mild truncal involvement was the inability to hop on one foot without support. The onset of gait abnormalities in the MN-A family ranged from 13 to 60 years, and the age at which affected individuals needed a cane or a walker ranged from 35 to 50 years, with no one requiring a wheelchair prior to the age of 45. No affected MN-A family member with disease duration less than 20 years required mobility aids, while those requiring aids needed the support after 20–36 years of disease progression. Mild athetotic movements of extended fingers and intermittent, low-amplitude myoclonic jerks in the fingers and arms are sometimes present. Signs of oculomotor involvement are common in moderately and severely affected individuals. Speech is dysarthric, with both ataxic and spastic components. Hyperreflexia is common, with Babinski signs occasionally elicitable. Mild sensory loss, primarily affecting vibratory perception, is occasionally observed. Unaffected family members have no clinical findings of ataxia or other nervous system disease (Day et al., 2000).

Magnetic resonance imaging Magnetic resonance imaging (MRI) scans of the brains of three affected family members showed atrophy of the cerebellar hemispheres and vermis. The image in Fig. 33.6 shows dramatic vermian atrophy, which was also marked in superior and inferior aspects of the cerebellum. As is typical of other SCA8 patients, the cerebrum shows no definite abnormalities, with no atrophy, white matter abnormalities, or basal ganglia involvement, and there is minimal brainstem atrophy.

Fig. 33.6 Sagittal MRI of a 35-year-old woman with SCA8, showing profound cerebellar and minimal brainstem atrophy.

SCA8 gene organization and expression The maternal penetrance bias seen in the MN-A family raised the possibility of imprinting. To address this issue, strand-specific reverse transcriptase PCR (RT-PCR) analysis of polyA cerebellar RNA was performed to determine which, if either, strand of the SCA8 repeat is transcribed in the tissue affected by the SCA8 form of ataxia. This analysis confirmed that repeat is transcribed in the CTG orientation as is seen for DM1, and not in the CAG orientation, as seen with the other dominant SCAs (Fig. 33.7a; Koob et al., 1999b). As was expected from the genomic sequence, rapid amplification of cDNA ends (RACE) analysis confirmed that the CTG repeat is present in the 3 terminal exon that begins at the predicted splice-acceptor site. The longest transcripts identified are comprised of four exons. A shorter variant that does not have exon B was also identified. These transcripts have no extended open reading frames and have no significant homology to known genes. The genomic and cDNA organizations of the SCA8 gene are summarized in Fig 33.7b (Koob et al., 1999b).

Both SCA8 alleles are expressed An RT-PCR reaction using a primer pair (C24/F4) designed to amplify from the 3 end of exon C to 3’ of the CTG repeat

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C24R/F4 RT-PCR Fig. 33.7 (a) The SCA8 repeat is transcribed exclusively in the CTG orientation and is present in the 3 terminal exon of a fully processed transcript. Strand-specific reverse transcriptase-PCR (RT-PCR) assay of SCA8 transcripts. cDNA was synthesized from polyA cerebellar RNA using RT and either a primer that will anneal to RNA transcribed in the CUG-encoding orientation (primer F4) or a primer that will anneal to RNA transcribed in the CAG-encoding orientation (primer R4), as shown schematically to the left. Subsequent PCR amplification of these RT products using both primers F4 and R4 detected an RNA transcribed in the CUG-orientation ( F4), but failed to detect an RNA transcribed in the CAG orientation ( R4). A cDNA reaction using both primers but without RT served as a negative control for the experiment (RT). (b) The genomic and mRNA contexts of the SCA8 CTG expansion. A splice acceptor site is present in the genomic sequence 5 of the CTG expansion, and a consensus polyadenylation signal is present in the sequence 3 of the repeat. The SCA8 transcript is shown with four exons (A–D), but splice variants were also isolated that only contained exons D, C, and A. (c) Both SCA8 alleles are expressed in the cerebellum. An RT-PCR reaction using primers C24R and F4 was performed on cerebellar RNA isolated from two individuals heterozygous for the SCA8 CTG marker, and the 33P-labeled PCR products were separated on a denaturing polyacrylamide gel (lanes 2 and 3). Both SCA8 alleles were clearly detected in both individuals. The shorter products from transcripts that did not contain exon B were also detected in this reaction (not shown). A negative control using genomic DNA isolated from one of these individuals is shown in lane 1. (Reproduced with permission from Koob et al. (1999b), Nature Genetics, Vol. 21, pp. 379–84.)

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in exon A was performed on cerebellar RNA isolated from two unaffected individuals heterozygous for the SCA8 CTG marker. Both of the SCA8 alleles were detected in each of the RNA samples, clearly indicating that both SCA8 alleles are expressed in the cerebellum (Fig 33.7c; Koob et al., 1999b). To characterize the expression of the SCA8 transcript, a multiple-tissue dot blot was probed with a probe specific for the SCA8 transcript. A very weak signal was detected from most of the tissues represented on the dot blot, but, due to the low level of this signal, it was not possible to differentiate rigorously between hybridization to SCA8 transcripts and background hybridization with other transcripts. Similarly, no transcript was convincingly detected on a Northern blot made from the mRNA of various brain tissues. These results indicate that the SCA8 transcript is present at a fairly low level, even in brain. Therefore, SCA8 PCR analysis was performed of normalized amounts of first-strand cDNA made from mRNA extracted from eight human tissues (MTC Panel I, Clontech, Palo Alto, CA). SCA8 PCR product was generated from whole-brain cDNA and a small amount of SCA8 PCR product from lung cDNA, but no product was detected using the cDNAs from heart, placenta, liver, skeletal muscle, kidney, and pancreas as PCR templates. These results demonstrate that the SCA8 transcript is clearly expressed in brain tissue, and is absent, or present at much lower levels, in the other tissues examined (Koob et al., 1999b).

The SCA8 transcript may be a naturally occurring antisense transcript A novel transcript separate from the SCA8 transcript was unexpectedly identified when Marathon RACE procedures were performed using primers from the 5 exon D of the SCA8 transcript. Sequencing revealed that these polyadenylated cDNAs contain a long open reading frame, but were derived from mRNA transcribed in an orientation opposite to that of the SCA8 transcript. These data suggest that the SCA8 transcript is a naturally occurring antisense RNA. Antisense transcripts have been shown to regulate complementary sense transcripts through a number of different mechanisms. It is possible that the role of the normal SCA8 transcript may, in fact, be to regulate this sense transcript (Koob et al., 1999b). In its processed form, the SCA8 transcript has an approximately 1100 bp overlap with a 3.5 kb sense mRNA. The 5 end of the sense transcript lies within exon D of the SCA8 transcript, very near the exon D/C junction. The putative 5 end of the SCA8 antisense transcript begins approximately

1 kb into the first intron of the sense transcript and crosses the splice-donor site of this intron. The SCA8 CTG repeat is present in the antisense but not in the sense transcript. The open reading frame in the sense mRNA is predicted to encode a protein that is 748 amino acids in length and is highly homologous to the Drosophila kelch protein (Robinson and Coolley, 1997). The kelch protein is an actin-binding component of ring canals (Robinson and Coolley, 1997), which are required for cytoplasm transport from nurse cells to the oocyte during oogenesis. This gene has been named Kelch-like1 (KLHL1). KLHL1 is primarily expressed in brain (Koob et al., 1999a).

Pathogenic models for SCA8 The size, orientation, and general location of the pathogenic SCA8 CTG expansions within the SCA8 transcript are strikingly similar to those of the 3 untranslated CTG expansions that cause myotonic dystrophy type 1. Given these similarities, the molecular mechanisms ultimately responsible for the pathology associated with SCA8 may also prove to be similar to those responsible for DM1. However, the mechanism by which the DM1 CTG expansion causes disease remains controversial. Mouse models indicate that the molecular mechanism in DM1 may not simply be a lack or excess of the myotonic dystrophy protein kinase (DMPK) protein (Jansen et al., 1996; Reddy et al., 1996). A possible explanation for the complex phenotype of DM1 is that the CTG expansion, by altering the adjacent chromatin structure (Wang et al., 1994; Otten and Tapscott, 1995; Wang and Griffith, 1995), affects the expression of neighboring genes (Shaw et al., 1993; Boucher et al., 1995). Alternatively, DM1 may be caused by abnormal interactions between RNA containing the CUG expansion and other cellular factors (Shaw et al., 1993; Boucher et al., 1995). Alternatively, SCA8 may be caused by antisense interactions with the KLHL1 gene. Because the SCA8 transcript is processed, it is presumably present in the cytoplasm together with the KLHL1 mRNA, where it could potentially affect either the translation or stability of this complementary transcript. Alteration of the regulation of the SCA8 transcript may exert an affect on the KLHL1 transcript, which may play a role in the pathology of SCA8. For instance, if the SCA8 transcripts with large CUG expansions accumulate in the nucleus, as is the case with DMPK RNA (Taneja, 1998), these accumulated nuclear antisense transcripts could potentially interfere with the expression, maturation, or transport of the complementary KLHL1 transcripts in a manner that the normal SCA8 transcript does not. Although the KLHL1 transcript appears to be

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largely localized to specific brain tissues, we do not know enough about KLHL1 at this time to determine if altered levels of this protein in these tissues could plausibly contribute to cerebellar degeneration and ataxia.

Conclusion The linkage analysis (lod6.8, 0.00) and the strong correlation between CTG repeat size (107–127 CTGs) and affected status in the MN-A family, as well as the high prevalence of independently arising expanded alleles among ataxia patients, demonstrate that the SCA8 CTG expansion underlies SCA8 pathogenesis. However, the reduced penetrance and unusual patterns of repeat instability seen for SCA8 complicate diagnostic testing. Whereas large families with clearly dominant disease were used to localize and isolate the SCA1, SCA2, SCA3, SCA6, and SCA7 genes, the SCA8 expansion was identified from the DNA of a single affected individual. Given that the RAPID method used to isolate the SCA8 CTG expansion did not depend on the genetic bias needed for positional cloning, it is not surprising that the ataxia gene found has so many distinctions from the other genes. RAPID cloning provides a useful tool to identify genes for diseases with reduced penetrance and complex patterns of inheritance. A variation of the RAPID cloning method was recently used to identify a novel CAG expansion involved in yet another form of ataxia (SCA12; Holmes et al., 1999). SCA8 holds promise for further defining the diversity of molecular mechanisms that cause ataxia and for better defining trinucleotide repeat disorders in general. The molecular similarities between SCA8 and myotonic dystrophy type 1 provide an opportunity to define further the pathogenic mechanisms mediated by the untranslated CTG expansions found in both diseases. Understanding how these untranslated CTG expansions can cause diseases as different as ataxia and myotonic dystrophy should further our understanding of the diversity of molecular mechanisms involved in neurodegenerative disease.

xReferencesx Boucher, C.A., King, S.K., Carey, N. et al. (1995). A novel homeodomain-encoding gene is associated with a large CpG island interrupted by the myotonic dystrophy unstable (CTG)n repeat. Hum Mol Genet 4: 1919–25. Cancel, G., Durr, A., Didierjean, O. et al. (1997). Molecular and clinical correlations in spinocerebellar ataxia 2 – a study of 32 families. Hum Mol Genet 6: p. 709–15.

Chung, M.-y., Ranum, L.P.W., Duvick, L.A. et al. (1993). Evidence for a mechanism predisposing to intergenerational CAG repeat instability in spinocerebellar ataxia type 1. Nat Genet 5: 254–8. David, G., Durr, A., Stevanin, G. and Cancel, G. (1997). Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nat Genet 17: 65–70. Day, J.W., Schut, L.J., Moseley, M.L., Durand, A.C. and W. Ranum, L.P. (2000). Spinocerebellar ataxia type 8: clinical features in a large family. Neurology 55: 649–57. Holmes, S.E., O’Hearn, E.E., McInnis, M.G. et al. (1999). Expansion of a novel CAG trinucleotide repeat in the 5 region of PPP2R2B is associated with SCA12. Nat Genet 23: p. 391–2. Jansen, J., Groenen, P.J.T.A., Bachner, D. et al. (1996). Abnormal myotonic dystrophy protein kinase levels produce only mild myopathy in mice. Nat Genet 13: 316–24. Jodice, C., Mantuano, E., Veneziano, L. et al. (1997). Episodic ataxia type 2 (EA2) and spinocerebellar atxia type 6 (SCA6) due to CAG repeat expansion in the CACNA1A gene on chromosome 19p. Hum Mol Genet 6: 1973–8. Kennedy, J.L., Neves-Pereira, M.L., Paterson, A.D. et al. (1999). Trinucleotide repeat for SCA8 on 13q21: super expansion in psychosis individuals unaffected by ataxia. Am J Hum Genet 65: A278. Koob, M.D., Benzow, K.A., Bird, T.D. et al. (1998). Rapid cloning of expanded trinucleotide repeat sequences from genomic DNA. Nat Genet 18: 72–5. Koob, M.D., Moseley, M.L., Benzow, K.A. et al. (1999a). The SCA8 transcript is an antisense RNA to a brain-specific transcript encoding a novel actin-binding protein (KLHL1). Am J Hum Genet 65: A30. Koob, M.D., Moseley, M.L., Schut, L.J. et al. (1999b). An untranslated CTG expansion causes a novel form of spinocerebellar ataxia (SCA8). Nat Genet 21: 379–84. Kunkel, T.A., Roberts, J.D. and Zakour, R.A. (1987). Rapid and efficient site-specific mutagenesis without phenotypic selection. Methods Enzymol 154: 367–82. Maciel, P., Gaspar, C., DeStefano, A. et al. (1995). Correlation between CAG repeat length and clinical features in Machado–Joseph disease. Am J Hum Genet 57: 54–61. Maruyama, H., Nakamura, S., Matsuyama, Z. et al. (1995). Molecular features of the CAG repeats and clinical manifestation of Machado–Joseph disease. Hum Mol Genet 4: 807–12. Moseley, M.L., Benzow, K.A., Schut, L.J. et al. (1998). Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families. Neurology 51: 1666–71. Moseley, M., Jacobsen, J., Liquori, C. et al. (2000a). SCA8 CTG expansion: evidence for a common haplotype and highly mutable region on both ataxia and non-ataxia chromosomes. Am J Hum Genet 67: S2, 363. Moseley, M.L., Schut, L.J., Bird, T.D. et al. (2000b). SCA8 CTG repeat: en masse contractions in sperm and intergenerational sequence changes may play a role in reduced penetrance. Hum Mol Genet 9: 2125–30. Ostrander, E.O., Jong, P.M., Rine, J. and Duyk, G. (1992). Construction of small-insert genomic DNA libraries highly

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enriched for microsatellite repeat sequences. Proc Natl Acad Sci USA 89: 3419–23. Otten, A.D. and Tapscott, S.J. (1995). Triplet repeat expansion in myotonic dystrophy alters the adjacent chromatin structure. Proc Natl Acad Sci USA 92: 5465–9. Ranum, L.P.W., Moseley, M.L., Leppert, M.F. et al. (1999). Massive CTG expansions and deletions may reduce penetrance of spinocerebellar ataxia type 8. Am J Hum Genet 65: A466. Reddy, S., Smith, D.B.J., Rich, M.N. et al. (1996). Mice lacking the myotonic dystrophy protein develop a late onset progressive myopathy. Nat Genet 13: 325–35. Robinson, D.N. and Coolley, L. (1997). Drosophila kelch is an oligomeric ring canal actin organizer. J Cell Biol 138: 799–810. Schalling, M., Hudson, T.J., Buetow, K.H. and Housman, D.E. (1993). Direct detection of novel expanded trinucleotide repeats in the human genome. Nat Genet 4: 135–9. Shaw, D.J., McCurrach, M., Rundle, S.A. et al. (1993). Genomic organization and transcriptional units at the myotonic dystrophy locus. Genomics 18: 673–9.

Taneja, K.L. (1998). Localization of trinucleotide repeat sequences in myotonic dystrophy cells using a single fluorochrome-labeled PNA probe. Biotechniques 24: 472–6. Tsilfidis, C., MacKenzie, A.E., Mettler, G. et al. (1992). Correlation between CTG trinucleotide repeat length and frequency of severe congenital myotonic dystrophy. Nat Genet 1: 192–5. Wang, Y.-H., Amirhaeri, S., Kang, S., Wells, R.D. and Griffith, J.D. (1994). Preferential nucleosome assembly at DNA triplet repeats from the myotonic dystrophy gene. Science 265: 669–71. Wang, Y.-H. and Griffith, J. (1995). Expanded CTG triplet blocks from the myotonic dystrophy gene create the strongest known natural nucleosome positioning elements. Genomics 25: 570–3. Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha-1A-voltage-dependent calcium channel. Nat Genet 15: 62–9.

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Dentatorubral-pallidoluysian atrophy Shoji Tsuji Department of Neurology, Brain Research Institute, Niigata University, Japan

Introduction Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare, autosomal dominant, neurodegenerative disorder clinically characterized by various combinations of cerebellar ataxia, choreoathetosis, myoclonus, epilepsy, dementia, and psychiatric symptoms (MIM# 125370) (Naito and Oyanagi, 1982). The term DRPLA was originally used by Smith et al. to describe a neuropathological condition associated with severe neuronal loss, particularly in the dentatorubral and pallidoluysian systems of the central nervous system, in a sporadic case without a family history (Smith et al., 1958; Smith, 1975). The hereditary form of DRPLA was first described in 1972 by Naito and his colleagues. Since then, several reports on Japanese pedigrees with similar clinical presentations have been published (Oyanagi and Naito, 1977; Tanaka et al., 1977; Hirayama et al., 1981; Iizuka et al., 1984; Suzuki et al., 1985; Iizuka and Hirayama, 1986; Akashi et al., 1987; Iwabuchi, 1987; Iwabuchi et al., 1987; Naito et al., 1987), and DRPLA has been established as a distinct disease entity. The gene for DRPLA was discovered by two independent Japanese groups in 1994, and an unstable CAG trinucleotide repeat expansion in the protein-coding region of this gene was found to be the causative mutation for DRPLA (Koide et al., 1994; Nagafuchi et al., 1994a). To date, at least eight diseases have been found to be caused by expansion of CAG repeats coding for polyglutamine stretches, which include spinal and bulbar muscular atrophy (SBMA) (La Spada et al., 1991), Huntington’s disease (The Huntington’s Disease Collaborative Research Group, 1993), spinocerebellar ataxia type 1 (SCA1) (Orr et al., 1993), DRPLA (Koide et al., 1994; Nagafuchi et al., 1994a), Machado–Joseph disease (Kawakami et al., 1995), SCA2 (Imbert et al., 1996; Pulst et al., 1996; Sanpei et al., 1996), SCA6 (Zhuchenko et al., 1997), and SCA7 (David et al., 1997).

In this chapter, the clinical and molecular genetic aspects of DRPLA are described. Recent progress in the study of the molecular mechanisms of neurodegeneration caused by expanded polyglutamine stretches is also discussed.

Clinical features: genotype–phenotype correlations The most notable clinical characteristic of DRPLA is the considerable heterogeneity in clinical presentation, depending on the age of onset and the prominent genetic anticipation. Naito and Oyanagi reported that juvenileonset patients (onset before the age of 20) frequently exhibit a phenotype of progressive myoclonus epilepsy, characterized by myoclonus, seizures, and progressive intellectual deterioration. Epileptic seizures are a feature in all patients with onset before the age of 20, and the frequency of seizures decreases in patients with onset between the ages of 20 and 40. The occurrence of seizures in patients with onset after the age of 40 is rare. Various forms of generalized seizures, including tonic, clonic, or tonic–clonic seizures, are observed in DRPLA. Myoclonic epilepsy and absent or atonic seizures are occasionally observed in patients with onset before the age of 20. In contrast, patients with onset after the age of 20 tend to develop cerebellar ataxia, choreoathetosis, and dementia, thereby occasionally making this disease difficult to differentiate from Huntington’s disease and other spinocerebellar degenerations (Naito and Oyanagi, 1982). Some patients were diagnosed as having Huntington’s disease because their main clinical features were involuntary movements and dementia, which masked the presence of ataxia. The evaluation of preceding ataxia as well as atrophy of the cerebellum and brainstem, in particular the

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CAG repeat Fig. 34.1 Correlation of the age of onset of DRPLA and the size of expanded CAG repeats. PME: progressive myoclonus epilepsy.

pontine tegmentum, is crucial for the differential diagnosis. It would be beneficial to analyze the CAG repeat size in the DRPLA and HD genes in patients with involuntary movements and dementia. It should also be noted that these variable phenotypes of DRPLA may often appear within the same family as a result of prominent anticipation. The mode of inheritance of DRPLA is autosomal dominant with a high penetrance. The prevalence rate of DRPLA in the Japanese population has been estimated to be 0.2–0.7 per 100 000, which is comparable with that of Huntington’s disease in the Japanese population (Inazuki et al., 1990). Although DRPLA has been reported to occur predominantly in Japanese individuals, several cases with similar clinical features have been described in other ethnic groups (Titica and van Bogaert, 1946; De Barsy et al., 1968; Farmer et al., 1989). Since the discovery of the gene for DRPLA (Koide et al., 1994; Nagafuchi et al., 1994a), CAG repeat expansion of the DRPLA gene has been demonstrated by molecular analysis in several European and North American families (Warner et al., 1994a, 1994b; Burke et al., 1994b; Norremolle et al., 1995; Connarty et al., 1996; Potter, 1996). The discovery of the gene for DRPLA has made it possible to analyze the diverse clinical presentations based on the size of expanded CAG repeats. There is an inverse correlation between the age at onset and the size of expanded CAG repeats (Fig. 34.1). To clarify the clinical presentations of DRPLA, we analyzed the relationship between the common clinical features of DRPLA (ataxia, dementia or mental retardation, myoclonus, epilepsy, choreoathetosis,

and psychiatric changes, including character changes, delusions, or hallucinations) and the age at onset (Ikeuchi et al., 1995) (Ikeuchi et al., 1995a, 1995b, 1995c). Ataxia and dementia were found to be cardinal features, irrespective of the age at onset. Patients with onset before the age of 20 frequently exhibit myoclonus and epilepsy in addition to ataxia and dementia. The combination of these clinical features corresponds to the progressive myoclonus epilepsy phenotype. On the other hand, patients with onset after the age of 20 frequently exhibit choreoathetosis and psychiatric disturbances in addition to ataxia and dementia. Because the age at onset is inversely correlated with the size of expanded CAG repeats, the above observations imply that the clinical presentation is strongly correlated with the expanded CAG repeat size. A similar correlation between the clinical features and the expanded CAG repeat size has been demonstrated in other diseases caused by CAG repeat expansions. A clear genotype–phenotype correlation was also observed in magnetic resonance imaging (MRI) findings of DRPLA patients (Koide et al., 1997). To clarify the relationship between the size of expanded CAG repeat of the DRPLA gene and the atrophic changes of the brainstem and cerebellum, we quantitatively analyzed the MRI findings of 26 patients with DRPLA whose diagnosis was confirmed by molecular analysis of the DRPLA gene. When the DRPLA patients were classified into two groups based on the size of the expanded CAG repeat of the DRPLA gene (group 1, number of CAG repeat units  66; group 2, number of CAG repeat unit 65), strong inverse correlations were found between the age at MRI and the areas of

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midsagittal structures of the cerebellum and brainstem in group 1 but not in group 2, suggesting a clear genotype–phenotype correlation in patients with largely expanded CAG repeats. Furthermore, multiple regression analysis of the overall groups revealed that both the patient’s age at MRI and the size of the expanded CAG repeat correlated with the areas of the midsagittal structures. Taken together, these results suggest that both the age and the size of expanded CAG repeats independently affect the atrophic changes in the midsagittal structures of the cerebellum and brainstem. Involvement of the cerebral white matter, detected as areas with high-intensity signals on T2–weighted images, was occasionally observed in DRPLA patients. It was found that the involvement of cerebral white matter is more frequently observed in patients belonging to group 2 than in group 1 patients, suggesting that the disease duration is a major determinant for the white matter involvement.

Molecular genetics DRPLA is characterized by prominent anticipation (Koide et al., 1994; Nagafuchi et al., 1994a,b; Ikeuchi et al., 1995a,b; Naito, 1995; Ueno et al., 1995). Paternal transmission results in more prominent anticipation (26–29 years/generation) than does maternal transmission (14–15 years/generation). Given the strong parental bias on the degree of anticipation observed in Huntington’s disease (The Huntington’s Disease Collaborative Research Group, 1993) and SCA1 (Orr et al., 1993), we speculated that DRPLA must be a disease caused by unstable CAG repeat expansion of an as yet unidentified gene. Using cDNA clones known to carry CAG repeats as candidate genes, our own and another study group independently discovered that the CAG repeat of a gene on chromosome 12, which had been reported as CTG-B37, was expanded in patients with DRPLA (Koide et al., 1994; Nagafuchi et al., 1994). The CAG repeats in patients with DRPLA were expanded to 54–79 repeat units, as compared to 6–35 repeat units in normal individuals (Koide et al., 1994; Ikeuchi et al., 1995a, 1995b, 1995c). The detailed structure of the full-length cDNA of the human DRPLA gene has been determined (Nagafuchi et al., 1994a,b; Onodera et al., 1995). The DRPLA cDNA is predicted to code for 1185 amino acids. The CAG repeat expansion in the DRPLA gene is located 1462 bp downstream from the putative methionine initiation codon and is predicted to code for a polyglutamine stretch. Interestingly, polyserine and polyproline stretches exist near the CAG repeat. In contrast to the length of the

polyglutamine stretch, the lengths of these polyserine and polyproline stretches are not highly polymorphic (Onodera et al., 1995). Putative nuclear localizing signals have been identified near the amino-terminus of DRPLA protein (Miyashita et al., 1998), which is compatible with recent observations that DRPLA protein is translocated into nucleus preferentially in neuronal cells (Sato et al., 1999a). However, the physiological functions of DRPLA protein remain to be elucidated. The gene for DRPLA was mapped to 12p13.31 by in-situ hybridization (Takano et al., 1996b). The human DRPLA gene spans approximately 20 kb and consists of ten exons, with the CAG repeats located in exon 5 (Nagafuchi et al., 1994a,b). Northern blot analysis revealed that a 4.7-kb transcript is widely expressed in various tissues, including the heart, lung, kidney, placenta, skeletal muscle, and brain, without predilection for regions exhibiting neurodegeneration (Nagafuchi et al., 1994a,b; Onodera et al., 1995). Reverse transcription-polymerase chain reaction (RT-PCR) analysis of mRNA extracted from various regions of autopsied brains of patients with DRPLA demonstrated that DRPLA mRNA from a mutant DRPLA gene with expanded CAG repeats is expressed at levels comparable to the wild-type DRPLA gene, suggesting that CAG repeat expansion does not alter the transcriptional efficiency of the DRPLA gene (Onodera et al., 1995). The expression levels of the mutant DRPLA proteins were also analyzed by Western blot analysis, which indicated that mutant DRPLA proteins are expressed at levels similar to those of wild-type DRPLA proteins (Yazawa et al., 1995). These studies strongly indicate that CAG repeat expansion does not alter the transcription or translation efficiency of the mutant DRPLA gene. Therefore, it seems likely that mutant DRPLA proteins with expanded polyglutamine stretches are toxic to neuronal cells, suggesting ‘gain of toxic functions.’

Population genetics of DRPLA and dominant ataxias Recent studies suggest that the prevalence rates of dominant SCAs including DRPLA are considerably different among different populations (Illarioshkin et al., 1996; Cancel et al., 1997; Geschwind et al., 1997a, 1997b; Lorenzetti et al., 1997). On the other hand, strong linkage disequilibria have been demonstrated in expanded alleles of SCA1 (Wakisaka et al., 1995), SCA2 (Hernandez et al., 1995), Machado–Joseph disease/SCA3 (Stevanin et al., 1995; Takiyama et al., 1995; Endo et al., 1996), and DRPLA (Yanagisawa et al., 1996) in particular populations.

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Japanese (n = 202)

Caucasian (n = 177) Others 18%

SCA1 (3%) SCA2 (5%)

SCA1 15%

Others 36% SCA2 14%

SCA6 11% MJD/SCA3 43%

SCA6 5%

DRPLA 20%

MJD/SCA3 30%

Fig. 34.2 Relative prevalence rate of dominant SCAs. MJD: Machado–Joseph disease.

Haplotype analyses have also demonstrated that founder chromosomes are present in Huntington’s disease (Squitieri et al., 1994; Kremer et al., 1995; Rubinsztein and Leggo, 1997), Machado–Joseph disease (Takiyama et al., 1995; Stevanin et al., 1995; Endo et al., 1996), DRPLA (Yanagisawa et al., 1996), and SCA7 (Johansson et al., 1998) chromosomes. These observations raise the possibility that cis-elements in the genomic structure are associated with CAG repeat instability. Furthermore, in French Machado–Joseph disease/SCA3 families, a close association was observed between expanded alleles and a particular haplotype that was also found in all normal alleles with larger than 33 repeats (Stevanin et al., 1997). In Japanese DRPLA patients, a particular haplotype has been found to be associated with expanded alleles, which was also exclusively associated with normal alleles with larger than 17 CAG repeats (Yanagisawa et al., 1996). These results raise the possibility that expanded alleles of the dominant SCAs are also generated from intermediate alleles associated with particular haplotypes, and that the prevalence rates of the dominant SCAs in individual populations correlate with the frequencies of intermediate alleles of the corresponding genes. Initial analysis on the distribution of CAG repeats of the DRPLA gene demonstrated that normal alleles with larger than 17 repeats were overrepresented in Japanese populations in comparison to observations in Caucasian (Burke et al., 1994). Furthermore, we have recently analyzed the relative prevalence rates of the dominant SCAs in large population-based data sets from Japanese (n202) and Caucasian (n177) pedigrees with dominant SCAs and the distribu-

tion of the sizes of normal alleles of the corresponding genes in both populations (Takano et al., 1998). The relative prevalence rates of SCA1 and SCA2 were higher in Caucasian pedigrees (15% and 14%, respectively) than in Japanese pedigrees (3% and 5%, respectively), and the differences were statistically significant (SCA1: 2 13.58, df1, p 0.0002; SCA2: 2 8.41, df1, p0.0037). The relative prevalence rates of Machado–Joseph disease/SCA3, SCA6, and DRPLA were higher in Japanese pedigrees (43%, 11%, and 20%, respectively) than in Caucasian pedigrees (30%, 5%, and 0%, respectively), and the differences were also statistically significant (Machado–Joseph disease/SCA3: 2 5.05, df1, p0.024; SCA6: 2 5.05, df1, p0.015; DRPLA: 2 38.21, df1, p 0.0001) (Fig. 34.2) The frequencies of large normal alleles in SCA1 (larger than 30 repeats) and SCA2 (larger than 22 repeats) were significantly higher in Caucasian compared to Japanese patients (SCA1: 2 22.23, df1, p0.0001; SCA2: 2  14.84, df1, p0.0001). Cut-off value of 31 or 32 repeats for SCA1 and of 23 or 24 repeats for SCA2 also gave significantly higher frequencies of large normal alleles of SCA1 and SCA2 genes in Caucasian than in Japanese population. These results were in good accordance with the relatively higher prevalence rates of SCA1 and SCA2 in Caucasians than in Japanese. The frequencies of large normal alleles in Machado–Joseph disease/SCA3 (larger than 27 repeats), SCA6 (larger than 13 repeats), and DRPLA (larger than 17 repeats) genes were significantly higher in Japanese than in Caucasians (Machado–Joseph disease/SCA3: 2 24.16, df 1, p0.0001; SCA6: 2 38.64, df1, p0.0001; DRPLA: 2 11.80, df1, p0.0006) (Fig. 34.3). These results are

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0.3

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Caucasian (n = 156)

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10

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20

25

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CAG repeat size

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Japanese (n = 307)

0.1

10

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CAG repeat size Fig. 34.3 Distributions of the size of CAG repeats of the DRPLA gene in normal alleles in Caucasians and Japanese.

also in accordance with the relatively higher prevalence rates of Machado–Joseph disease/SCA3, SCA6, and DRPLA in Japanese than in Caucasian populations. Thus, a close association was found between the relative prevalence rates of the dominant SCAs in Japanese and Caucasian pedigrees and the frequencies of large normal alleles of the corresponding genes. The results suggest that the relative prevalence rates of these dominant SCAs are determined by the balance between continuous generation of new expanded alleles and loss of expanded alleles due to the impaired reproductive fitness of severely affected patients. Recent observations that particular haplotypes of large normal alleles of Machado–Joseph disease/SCA3 and DRPLA genes are commonly shared with Machado–Joseph disease/SCA3 (Stevanin et al., 1997) and DRPLA (Yanagisawa et al., 1996), respectively, strongly suggest that large normal alleles with particular haplotypes are prone to further expansion to the disease range of CAG repeats.

Molecular basis of genetic anticipation and molecular mechanisms of instability of CAG repeats As described above, DRPLA is characterized by a prominent genetic anticipation with a mean acceleration of age at onset of 25.6  2.4 years in paternal transmission and 14.0  4.0 years in maternal transmission (Koide et al., 1994; Nagafuchi et al., 1994a,b; Ikeuchi et al., 1995a, 1995b, 1995c). In accordance with the strong parental bias for genetic anticipation, a much larger intergenerational increase was observed for paternal transmission (5.80.9 repeat units/generation, n16) compared to maternal transmission (1.31.6 repeat units/generation, n4) (Koide et al., 1994; Ikeuchi et al., 1995a, 1995b, 1995c). This phenomenon has also been described for Huntington’s disease (The Huntington’s Disease Collaborative Research Group, 1993; Duyao et al., 1993; Snell et al., 1993; Andrew et al., 1993), SCA1 (Orr et al., 1993; Chung et al., 1993), and SCA7 (David et al., 1997). These results strongly indicate that similar mechanisms must underlie the intergenerational instability of the expanded CAG repeats during male

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gametogenesis. In fact, it has been demonstrated that DNA from the sperm of patients with Huntington’s disease show considerable variations in the size of expanded CAG repeats compared to DNA from somatic cells (Telenius et al., 1994). With this background, we considered that transgenic mice harboring an entire mutant gene including flanking regions derived from a mutant allele would be required to investigate the molecular mechanisms of CAG repeat instability. The DRPLA gene spans only 20 kb (Nagafuchi et al., 1994a,b), and the disease is among those characterized by large intergenerational changes, including SCA7 (Koide et al., 1994; Ikeuchi et al., 1995a,b; David et al., 1997, 1998; Gouw et al., 1998), suggesting that the DRPLA gene is quite suitable for investigating the molecular mechanisms of CAG repeat instability. We generated transgenic mice harboring a single copy of a mutant DRPLA gene (Sato et al., 1999b). The transgenic mice, in fact, exhibited an agedependent increase ( 0.31 per year) in male transmission and an age-dependent contraction (1.21 per year) in female transmission. Such an age-dependent increase in the intergenerational changes in the sizes of expanded CAG repeats in paternal transmission and an age-dependent contraction in maternal transmission were also observed in 83 parent–offspring pairs of DRPLA patients (56 paternal and 27 maternal transmissions). Based on a linear regression model and the continuous cell divisions required for spermatogenesis throughout adult life, the mean increase in the size of CAG repeats in male transmission in mice was calculated to be 0.31 per year and 0.0073 per spermatogenesis cycle. These values were comparable to those observed in DRPLA patients, which were calculated to be 0.27 and 0.012, respectively. These results strongly indicate that the difference in the actual intergenerational changes between humans and mice is due to the reproductive lifespan variations, and that a common mechanism underlies the age-dependent increase in the sizes of CAG repeats both in humans and in mice. In contrast to spermatogenesis, oogenesis occurs only during fetal life, and ceases at the diploten stage of the first meiotic prophase by five days after birth, suggesting that age-dependent contraction of CAG repeats occurs after the cessation of meiotic DNA replication. Similar observations have been made in transgenic mice for SCA1 and SBMA (Kaytor et al., 1997; La Spada et al., 1998). These results strongly suggest that contraction of the CAG repeats occurs during the prolonged resting stage, and mechanisms such as repair of damaged DNA or selective degeneration of the primary oocyte with larger CAG repeats might be involved in the contraction process.

The transgenic mice also exhibited somatic instabilities of CAG repeats, similar to those observed in DRPLA patients (Sato et al., 1999b). The size range of the CAG repeats was smallest in the cerebellum compared to that in the cerebrum and various somatic tissues. This observation has been well documented in Huntington’s disease, SCA1, Machado–Joseph disease, and DRPLA (Telenius et al., 1994; Chong et al., 1995; Ueno et al., 1995; Takano et al., 1996b; Hashida et al., 1997). Because the cerebellum contains a dense population of granule cells which are neuronal cells, it is assumed that neuronal cells exhibit the least instability, because they do not undergo cell divisions, and that cell divisions are required for the development of somatic instabilities of CAG repeats (Takano et al., 1996a). Similar phenomena were observed in the granular layers of the cerebellar cortex and hippocampal formation in autopsied DRPLA brains (Hashida et al., 1997). Another interesting finding of this study is the age-dependent increase in the degree of somatic mosaicism. The size ranges of CAG repeats were much larger at 64 weeks compared to those at three weeks. These data strongly support an increase in the degree of somatic mosaicism with age. However, it remains to be elucidated how the age-dependent increase in the degree of somatic mosaicism is involved in the pathogenesis of DRPLA.

Mechanisms of neurodegeneration caused by CAG repeat expansion There is increasing evidence suggesting ‘gain of toxic functions’ of mutant proteins with expanded polyglutamine stretches, in particular, truncated mutant proteins containing expanded polyglutamine stretches. Such toxicities have been demonstrated not only in transient expression systems (Ikeda et al., 1996; Skinner et al., 1997; Paulson et al., 1997; Igarashi et al., 1998; Martindale et al., 1998; Cooper et al., 1998), but also in transgenic mice (Ikeda et al., 1996; Mangiarini et al., 1996; Hodgson et al., 1999). To investigate whether full-length or truncated mutant DRPLA proteins with expanded polyglutamine stretches are toxic to cells, we created deletions with various lengths either upstream or downstream of the expanded CAG repeats, and expressed these mutant DRPLA proteins in COS7 cells (Igarashi et al., 1998). Formation of perinuclear and intranuclear aggregates was observed in COS7 cells expressing truncated mutant DRPLA proteins with an expanded polyglutamine stretch (Q82), but not in COS7 cells expressing truncated wild-type DRPLA protein (Q19). The cells with the aggregate bodies were shown to undergo apoptotic cell death as assayed by TUNEL. Electron

Dentatorubral-pallidoluysian atrophy

microscopic observation demonstrated that the aggregate bodies were composed of fibrous structures, 10–12 nm in diameter. Furthermore, these aggregates were not observed either in cells expressing full-length mutant DRPLA protein or in cells expressing full-length wild-type DRPLA protein, raising the possibility that the processing of mutant proteins carrying expanded polyglutamine stretches is important for the toxicity caused by expanded polyglutamine stretches. The recent discovery of neuronal intranuclear inclusions containing mutant proteins has given rise to new controversial issues concerning the mechanisms of neurodegeneration caused by expanded polyglutamine stretches. Although neuronal intranuclear inclusions were first identified in Huntington’s disease and SCA1 transgenic mice (Skinner et al., 1997; Davies et al., 1997; Hodgson et al., 1999), subsequent intensive studies revealed them in postmortem human brains, including cases of Huntington’s disease (Davies et al., 1997; Difiglia et al., 1997), SCA1 (Skinner et al., 1997), Machado–Joseph disease/SCA3 (Paulson et al., 1997), DRPLA (Igarashi et al., 1998; Hayashi et al., 1998), SCA7 (Holmberg et al., 1998), and SBMA (Li et al., 1998). Although formation of neuronal intranuclear inclusions seem to be fundamental processes, it is still controversial whether they are toxic to neuronal cells (Sisodia, 1998; Zoghbi and Orr, 1999). Various hypotheses have been put forward as to the mechanisms of aggregate formation of proteins containing expanded polyglutamine stretches. Perutz and colleagues proposed that polyglutamine stretches may function as polar zippers by joining complementary proteins through hydrogen bonding, and that extensions of the polyglutamine stretches may result in tight joining and aggregation of the affected proteins (Perutz et al., 1994; Perutz, 1995, 1996). Another intriguing hypothesis has recently been proposed by Kahlem et al. (1996). They proposed that proteins with expanded polyglutamine stretches may serve as better substrates for transglutaminase than wildtype proteins, and that expanded polyglutamine stretches preferentially become cross-linked with polypeptides containing lysyl groups to form covalently bonded aggregates. We have demonstrated that the aggregate formation and apoptosis are partially suppressed by transglutaminase inhibitors such as cystamine and monodansylcadaverine (Igarashi et al., 1998). The results opened new prospects for developing therapeutic measures for the polyglutamine diseases. Although the physiological functions remain unclear, full-length wild-type DRPLA protein has recently been demonstrated to be localized predominantly in the nuclei of cultured cells (Miyashita et al., 1998; Sato et al., 1999b).

Such nuclear localization is presumably mediated by putative nuclear localization signals. In fact, we found that fulllength DRPLA protein is expressed predominantly in the nucleus of neuronally differentiated PC12 cells using an adenovirus expression system. It was further demonstrated that intranuclear aggregate bodies are preferentially formed in neuronally differentiated PC12 cells and that these cells are more vulnerable than fibroblasts to the toxic effects of expanded polyglutamine stretches of the DRPLA protein (Sato et al., 1999b). These observations emphasize the importance of nuclear translocation of fulllength or truncated DRPLA proteins with expanded polyglutamine stretches. The observations that transgenic mice expressing mutant ataxin-1 with a mutated nuclear localization signal did not develop ataxia (Klement et al., 1998), and that addition of a nuclear export signal to mutant huntingtin suppressed the formation of neuronal intranuclear inclusions and apoptosis (Saudou et al., 1998), further emphasize the role of nuclear translocation of mutant proteins with expanded polyglutamine stretches. Interaction of polyglutamine stretches and some nuclear proteins may be involved in the cytotoxicity caused by expanded polyglutamine stretches.

Acknowledgments This study was supported in part by the Research for the Future Program from the Japan Society for the Promotion of Science (JSPS-RFTF96L00103); a Grant-in-Aid for Scientific Research on Priority Areas (Human Genome Program) from the Ministry of Education, Science, Sports and Culture, Japan; a grant from the Research Committee for Ataxic Diseases, the Ministry of Health and Welfare, Japan; a grant for Surveys and Research on Specific Diseases, the Ministry of Health and Welfare, Japan; and special coordination funds from the Japanese Science and Technology Agency.

iReferencesi Akashi, T., Ando, S., Inose, T. et al. (1987). Dentato-rubro-pallidoluysian atrophy: A clinicopathological study. (in Japanese). Rinsho Seishin Igaku 29: 523–31. Andrew, S.E., Goldberg, Y.P., Kremer, B. et al. (1993). The relationship between trinucleotide (CAG) repeat length and clinical features of Huntington’s disease. Nat Genet 4: 398–403. Burke, J.R., Ikeuchi, T., Koide, R. et al. (1994a). Dentatorubral-pallidoluysian atrophy and Haw River syndrome. Lancet 344: 1711–12.

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S. Tsuji

Burke, J.R., Wingfield, M.S., Lewis, K.E. et al. (1994b). The Haw River syndrome: dentatorubropallidoluysian atrophy (DRPLA) in an African–American family. Nat Genet 7: 521–5. Cancel, G., Durr, A., Didierjean, O. et al. (1997). Molecular and clinical correlations in spinocerebellar ataxia 2 – a study of 32 families. Hum Mol Genet 6: 709–15. Chong, S.S., McCall, A.E., Cota, J. et al. (1995). Gametic and somatic tissue-specific heterogeneity of the expanded SCA1 CAG repeat in spinocerebellar ataxia type 1. Nat Genet 10: 344–50. Chung, M.Y., Ranum, L.P., Duvick, L.A. et al. (1993). Evidence for a mechanism predisposing to intergenerational CAG repeat instability in spinocerebellar ataxia type 1. Nat Genet 5: 254–8. Connarty, M., Dennis, N.R., Patch, C. et al. (1996). Molecular reinvestigation of patients with Huntington’s disease in Wessex reveals a family with dentatorubral and pallidoluysian atrophy. Hum Genet 97: 76–8. Cooper, J.K., Schilling, G., Peters, M.F. et al. (1998). Truncated Nterminal fragments of huntingtin with expanded glutamine repeats form nuclear and cytoplasmic aggregates in cell culture. Hum Mol Genet 7: 783–90. David, G., Abbas, N., Stevanin, G. et al. (1997). Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion. Nat Genet 17: 65–70. David, G., Durr, A., Stevanin, G. et al. (1998). Molecular and clinical correlations in autosomal dominant cerebellar ataxia with progressive macular dystrophy (SCA7). Hum Mol Genet 7: 165–70. Davies, S.W., Turmaine, M., Cozens, B.A. et al. (1997). Formation of neuronal intranuclear inclusions underlies the neurological dysfunction in mice transgenic for the HD mutation. Cell 90: 537–48. De Barsy, T.H., Myle, G., Troch, C. et al. (1968). La dyssynergie cerebelleuse myoclonique (R. Hunt): affection autonome ou rariante du type degeneratif de l’epilepsie-myoclonie progressive (Unvericht–Lundborg) appoche anatomo-alinique. J Neurol Sci 8: 111–27. Difiglia, M., Sapp, E., Chase, K.O. et al. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science 277: 1990–3. Duyao, M., Ambrose, C., Myers, R. et al. (1993). Trinucleotide repeat length instability and age of onset in Huntington’s disease. Nat Genet 4: 387–92. Endo, K., Sasaki, H., Wakisaka, A. et al. (1996). Strong linkage disequilibrium and haplotype analysis in Japanese pedigrees with Machado–Joseph disease. Am J Med Genet 67: 437–44. Farmer, T.W., Wingfield, M.S., Lynch, S.A. et al. (1989). Ataxia, chorea, seizures, and dementia. Pathologic features of a newly defined familial disorder. Arch Neurol 46: 774–9. Geschwind, D.H., Perlman, S., Figueroa, C.P. et al. (1997a). The prevalence and wide clinical spectrum of the spinocerebellar ataxia type 2 trinucleotide repeat in patients with autosomal dominant cerebellar ataxia. Am J Hum Genet 60: 842–50. Geschwind, D.H., Perlman, S., Figueroa, K.P. et al. (1997b). Spinocerebellar ataxia type 6. Frequency of the mutation and genotype–phenotype correlations. Neurology 49: 1247–51.

Gouw, L.G., Castaneda, M.A., McKenna, C.K. et al. (1998). Analysis of the dynamic mutation in the SCA7 gene shows marked parental effects on CAG repeat transmission. Hum Mol Genet 7: 525–32. Hashida, H., Goto, J., Kurisaki, H. et al. (1997). Brain regional differences in the expansion of a CAG repeat in the spinocerebellar ataxias: dentatorubral-pallidoluysian atrophy, Machado–Joseph disease, and spinocerebellar ataxia type 1. Ann Neurol 41: 505–11. Hayashi, Y., Kakita, A., Yamada, M. et al. (1998). Hereditary dentatorubral-pallidoluysian atrophy – ubiquitinated filamentous inclusions in the cerebellar dentate nucleus neurons. Acta Neuropathol (Berl) 95: 479–82. Hernandez, A., Magarino, C., Gispert, S. et al. (1995). Genetic mapping of the spinocerebellar ataxia 2 (SCA2) locus on chromosome 12q23–q24.1. Genomics 25: 433–5. Hirayama, K., Iizuka, R., Maehara, K. et al. (1981). Clinicopathological study of dentatorubropallidoluysian atrophy. Part I – Its clinical form and analysis of symptomatology (in Japanese). Adv Neurol 25: 725–36. Hodgson, J.G., Agopyan, N., Gutekunst, C.A. et al. (1999). A YAC mouse model for Huntington’s disease with full-length mutant huntingtin, cytoplasmic toxicity, and selective striatal neurodegeneration. Neuron 23: 181–92. Holmberg, M., Duyckaerts, C., Durr, A. et al. (1998). Spinocerebellar ataxia type 7 (SCA7): a neurodegenerative disorder with neuronal intranuclear inclusions. Hum Mol Genet 7: 913–18. Igarashi, S., Koide, R., Shimohata, T. et al. (1998). Suppression of aggregate formation and apoptosis by transglutaminase inhibitors in cells expressing truncated DRPLA protein with an expanded polyglutamine stretch. Nat Genet 18: 111–17. Iizuka, R. and Hirayama, K. (1986). Dentato-rubro-pallido-luysian atrophy. In Handbook of Clinical Neurology, Vol. 5, ed. P.J. Vinken, G.W. Bruyn and H.L. Klawans, pp. 437–43, Amsterdam: North-Holland. Iizuka, R., Hirayama, K. and Maehara, K.A. (1984). Dentato-rubropallido-luysian atrophy: a clinico-pathological study. J Neurol Neurosurg Psychiatry 47: 1288–98. Ikeda, H., Yamaguchi, M., Sugai, S. et al. (1996). Expanded polyglutamine in the Machado–Joseph disease protein induces cell death in vitro and in vivo. Nat Genet 13: 196–202. Ikeuchi, T., Koide, R., Onodera, O. et al. (1995a). Dentatorubralpallidoluysian atrophy (DRPLA). Molecular basis for wide clinical features of DRPLA. Clin Neurosci 3: 23–7. Ikeuchi, T., Koide, R., Tanaka, H. et al. (1995b). Dentatorubralpallidoluysian atrophy (DRPLA): clinical features are closely related to unstable expansions of trinucleotide (CAG) repeat. Ann Neurol 37: 769–75. Ikeuchi, T., Onodera, O., Oyake, M. et al. (1995c). Dentatorubralpallidoluysian atrophy (DRPLA): close correlation of CAG repeat expansions with the wide spectrum of clinical presentations and prominent anticipation. Semin Cell Biol 6: 37–44. Illarioshkin, S.N., Slominsky, P.A., Ovchinnikov, I.V. et al. (1996). Spinocerebellar ataxia type 1 in Russia. J Neurol 243: 506–10. Imbert, G., Saudou, F., Yvert, G. et al. (1996). Cloning of the gene for

Dentatorubral-pallidoluysian atrophy

spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats. Nat Genet 14: 285–91. Inazuki, G., Kumagai, K. and Naito, H. (1990). Dentatorubralpallidoluysian atrophy (DRPLA): its distribution in Japan and prevalence rate in Niigata. Seishin Igaku 32: 1135–8. Iwabuchi, K. (1987). Clinico-pathological studies on dentato-rubropallido-luysian atrophy (DRPLA). Yokohama Igaku 38: 291–301. Iwabuchi, K., Amano, N., Yagishita, S. et al. (1987). A clinicopathological study on familial cases of dentatorubro-pallidoluysian atrophy (DRPLA). Clin Neurol 27: 1002–12. Johansson, J., Forsgren, L., Sandgren, O. et al. (1998). Expanded CAG repeats in Swedish spinocerebellar ataxia type 7 (SCA7) patients: effect of CAG repeat length on the clinical manifestation. Hum Mol Genet 7: 171–6. Kahlem, P., Terre, C., Green, H. et al. (1996). Peptides containing glutamine repeats as substrates for transglutaminase-catalyzed cross-linking: relevance to diseases of the nervous system. Proc Natl Acad Sci USA 93: 14580–5. Kawakami, H., Maruyama, H., Nakamura, S. et al. (1995). Unique features of the CAG repeats in Machado–Joseph disease. Nat Genet 9: 344–5. Kaytor, M.D., Burright, E.N., Duvick, L.A. et al. (1997). Increased trinucleotide repeat instability with advanced maternal age. Hum Mol Genet 6: 2135–9. Klement, I.A., Skinner, P.J., Kaytor, M.D. et al. (1998). Ataxin-1 nuclear localization and aggregation: role in polyglutamineinduced disease in SCA1 transgenic mice. Cell 95: 41–53. Koide, R., Ikeuchi, T., Onodera, O. et al. (1994). Unstable expansion of CAG repeat in hereditary dentatorubral-pallidoluysian atrophy (DRPLA). Nat Genet 6: 9–13. Koide, R., Onodera, O., Ikeuchi, T. et al. (1997). Atrophy of the cerebellum and brainstem in dentatorubral pallidoluysian atrophy. Influence of CAG repeat size on MRI findings. Neurology 49: 1605–12. Kremer, B., Almqvist, E., Theilmann, J. et al. (1995). Sex-dependent mechanisms for expansions and contractions of the CAG repeat on affected huntington disease chromosomes. Am J Hum Genet 57: 343–30. La Spada, A.R., Peterson, K.R., Meadows, S.A. et al. (1998). Androgen receptor YAC transgenic mice carrying CAG 45 alleles show trinucleotide repeat instability. Hum Mol Genet 7: 959–67. La Spada, A.R., Wilson, E.M., Lubahn, D.B. et al. (1991). Androgen receptor gene mutations in X-linked spinal and bulbar muscular atrophy. Nature 352: 77–9. Li, M., Miwa, S., Kobayashi, Y. et al. (1998). Nuclear inclusions of the androgen receptor protein in spinal and bulbar muscular atrophy. Ann Neurol 44: 249–54. Lorenzetti, D., Bohlega, S. and Zoghbi, H.Y. (1997). The expansion of the CAG repeat in ataxin-2 is a frequent cause of autosomal dominant spinocerebellar ataxia. Neurology 49: 1009–13. Mangiarini, L., Sathasivam, K., Seller, M. et al. (1996). Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell 87: 493–506. Martindale, D., Hackam, A., Wieczorek, A. et al. (1998). Length of

huntingtin and its polyglutamine tract influences localization and frequency of intracellular aggregates. Nat Genet 18: 150–4. Miyashita, T., Nagao, K., Ohmi, K. et al. (1998). Intracellular aggregate formation of dentatorubral-pallidoluysian atrophy (DRPLA) protein with the extended polyglutamine. Biochem Biophys Res Commun 249: 96–102. Nagafuchi, S., Yanagisawa, H., Ohsaki, E. et al. (1994a). Structure and expression of the gene responsible for the triplet repeat disorder, dentatorubral and pallidoluysian atrophy (DRPLA). Nat Genet 8: 177–82. Nagafuchi, S., Yanagisawa, H., Sato, K. et al. (1994b). Expansion of an unstable CAG trinucleotide on chromosome 12p in dentatorubral and pallidoluysian atrophy. Nat Genet 6: 14–18. Naito, H. (1995). Clinical picture of DRPLA. [Review in Japanese.] No To Shinkei 47: 931–8. Naito, H., Izawa, K., Kurosaki, T. et al. (1972). Two families of progressive myoclonus epilepsy with Mendelian dominant heredity. (in Japanese). Psychiatr Neurol Jpn 74: 871–97. Naito, H., Ohama, E., Nagai, H. et al. (1987). A family of dentatorubropallidoluysian atrophy (DRPLA) including two cases with schizophrenic symptoms (in Japanese). Psychiatr Neurol Jpn 89: 144–58. Naito, N. and Oyanagi, S. (1982). Familial myoclonus epilepsy and choreoathetosis; hereditary dentatorubral-pallidoluysian atrophy. Neurology 32: 789–817. Norremolle, A., Nielsen, J.E., Sorensen, S.A. et al. (1995). Elongated CAG repeats of the B37 gene in a Danish family with dentatorubro-pallido-luysian atrophy. Hum Genet 95: 313–18. Onodera, O., Oyake, M., Takano, H. et al. (1995). Molecular cloning of a full-length cDNA for dentatorubral-pallidoluysian atrophy and regional expressions of the expanded alleles in the CNS. Am J Hum Genet 57: 1050–60. Orr, H.T., Chung, M.Y., Banfi, S. et al. (1993). Expansion of an unstable trinucleotide CAG repeat in spinocerebellar ataxia type 1. Nat Genet 4: 221–6. Oyanagi, S. and Naito, H. (1977). A clinico-neuropathological study on four autopsy cases of degenerative type of myoclonus epilepsy with Mendelian dominant heredity (in Japanese). Psychiatr Neurol Jpn 79: 113–29. Paulson, H.L., Perez, M.K., Trottier, Y. et al. (1997). Intranuclear inclusions of expanded polyglutamine protein in spinocerebellar ataxia type 3. Neuron 19: 333–44. Perutz, M.F. (1995). Glutamine repeats as polar zippers: their role in inherited neurodegenerative disease. Mol Med 1: 718–21. Perutz, M.F. (1996). Blood. Taking the pressure off [news]. Nature 380: 205–6. Perutz, M.F., Johnson, T., Suzuki, M. et al. (1994). Glutamine repeats as polar zippers: their possible role in inherited neurodegenerative diseases. Proc Natl Acad Sci USA 91: 5355–8. Potter, N.T. (1996). The relationship between (CAG)n repeat number and age of onset in a family with dentatorubral-pallidoluysian atrophy (DRPLA): diagnostic implications of confirmatory and predictive testing. J Med Genet 33: 168–70. Pulst, S.M., Nechiporuk, A., Nechiporuk, T. et al. (1996). Moderate expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2. Nat Genet 14: 269–76.

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Rubinsztein, D.C. and Leggo, J. (1997). Non-mendelian transmission at the Machado–Joseph disease locus in normal females: preferential transmission of alleles with smaller CAG repeats. J Med Genet 34: 234–6. Sanpei, K., Takano, H., Igarashi, S. et al. (1996). Identification of the spinocerebellar ataxia type 2 gene using a direct identification of repeat expansion and cloning technique, DIRECT. Nat Genet 14: 277–84. Sato, A., Shimohata, T., Koide, R. et al. (1999a). Adenovirus-mediated expression of mutant DRPLA proteins with expanded polyglutamine stretches in neuronally differentiated PC12 cells. Preferential intranuclear aggregate formation and apoptosis. Hum Mol Genet 8: 997–1006. Sato, T., Oyake, M., Nakamura, K. et al. (1999b). Transgenic mice harboring a full-length human mutant DRPLA gene reveal CAG repeat instability. Hum Mol Genet 8: 99–106. Saudou, F., Finkbeiner, S., Devys, D. et al. (1998). Huntingtin acts in the nucleus to induce apoptosis but death does not correlate with the formation of intranuclear inclusions. Cell 95: 55–66. Sisodia, S.S. (1998). Nuclear inclusions in glutamine repeat disorders: are they pernicious, coincidental, or beneficial? [comment]. Cell 95: 1–4. Skinner, P.J., Koshy, B.T., Cummings, C.J. et al. (1997). Ataxin-1 with an expanded glutamine tract alters nuclear matrix-associated structures. Nature 389: 971–4. Smith, J.K. (1975). Dentatorubropallidoluysian atrophy. In Handbook of Clinical Neurology, Vol. 21, ed. P.J. Vinken and G.W. Bruyn, pp. 519–34. Amsterdam: North-Holland. Smith, J.K., Gonda, V.E. and Malamud, N. (1958). Unusual form of cerebellar ataxia: combined dentato-rubral and pallido-luysian degeneration. Neurology 8: 205–9. Snell, R.G., MacMillan, J.C., Cheadle, J.P. et al. (1993). Relationship between trinucleotide repeat expansion and phenotypic variation in Huntington’s disease. Nat Genet 4: 393–7. Squitieri, F., Andrew, S.E., Goldberg, Y.P. et al. (1994). DNA haplotype analysis of Huntington disease reveals clues to the origins and mechanisms of CAG expansion and reasons for geographic variations of prevalence. Hum Mol Genet 3: 2103–14. Stevanin, G., Cancel, G., Didierjean, O. et al. (1995). Linkage disequilibrium at the Machado–Joseph disease/spinal cerebellar ataxia 3 locus: evidence for a common founder effect in French and Portuguese–Brazilian families as well as a second ancestral Portuguese–Azorean mutation. Am J Hum Genet 57: 1247–50. Stevanin, G., Lebre, A.S., Mathieux, C. et al. (1997). Linkage disequilibrium between the spinocerebellar ataxia 3/Machado–Joseph disease mutation and two intragenic polymorphisms, one of which, x359y, affects the stop codon [letter]. Am J Hum Genet 60: 1548–52. Suzuki, S., Kamoshita, S. and Ninomura, S. (1985). Ramsay Hunt syndrome in dentatorubral-pallidoluysian atrophy. Pediatr Neurol 1: 298–301. Takano, H., Cancel, G., Ikeuchi, T. et al. (1998). Close associations between the prevalence rates of dominantly inherited spinocerebellar ataxias with CAG repeat expansions and the frequen-

cies of large normal CAG alleles in Japanese and Caucasian populations. Am J Hum Genet 63: 1060–6. Takano, H., Onodera, O., Takahashi, H. et al. (1996a). Somatic mosaicism of expanded CAG repeats in brains of patients with dentatorubral-pallidoluysian atrophy – cellular populationdependent dynamics of mitotic instability. Am J Hum Genet 58: 1212–22. Takano, T., Yamanouchi, Y., Nagafuchi, S. et al. (1996b). Assignment of the dentatorubral and pallidoluysian atrophy (DRPLA) gene to 12p 13.31 by fluorescence in situ hybridization. Genomics 32: 171–2. Takiyama, Y., Igarashi, S., Rogaeva, E.A. et al. (1995). Evidence for inter-generational instability in the CAG repeat in the MJD1 gene and for conserved haplotypes at flanking markers amongst Japanese and Caucasian subjects with Machado–Joseph disease. Hum Mol Genet 4: 1137–46. Tanaka, Y., Murobushi, K., Ando, S. et al. (1977). Combined degeneration of the globus pallidus and the cerebellar nuclei and their efferent systems in two siblings of one family – primary system degeneration of the globus pallidus and the cerebellar nuclei. (in Japanese). Brain Nerve 29: 95–104. Telenius, H., Kremer, B., Goldberg, Y.P. et al. (1994). Somatic and gonadal mosaicism of the Huntington disease gene CAG repeat in brain and sperm. Nat Genet 6: 409–14. The Huntington’s Disease Collaborative Research Group (1993). A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington’s disease chromosomes. Cell 72: 971–83. Titica, J. and van Bogaert, L. (1946). Heredo-degenerative hemiballismus: a contribution to the question of primary atrophy of the corpus Luysii. Brain 69: 251–63. Ueno, S., Kondoh, K., Kotani, Y. et al. (1995). Somatic mosaicism of CAG repeat in dentatorubral-pallidoluysian atrophy (DRPLA). Hum Mol Genet 4: 663–6. Wakisaka, A., Sasaki, H., Takada, A. et al. (1995). Spinocerebellar ataxia 1 (SCA1) in the Japanese in Hokkaido may derive from a single common ancestry. J Med Genet 32: 590–2. Warner, T.T., Lennox, G.G., Janota, I. et al. (1994a). Autosomaldominant dentatorubropallidoluysian atrophy in the United Kingdom. Mov Disord 9: 289–96. Warner, T.T., Williams, L. and Harding, A.E. (1994b). DRPLA in Europe. Nat Genet 6: 225. Yanagisawa, H., Fujii, K., Nagafuchi, S. et al. (1996). A unique origin and multistep process for the generation of expanded DRPLA triplet repeats. Hum Mol Genet 5: 373–9. Yazawa, I., Nukina, N., Hashida, H. et al. (1995). Abnormal gene product identified in hereditary dentatorubral-pallidoluysian atrophy (DRPLA) brain. Nat Genet 10: 99–103. Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1a-voltage-dependent calcium channel. Nat Genet 15: 62–9. Zoghbi, H.Y. and Orr, H.T. (1999). Polyglutamine diseases: protein cleavage and aggregation. Curr Opin Neurobiol 9: 566–70.

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Molecular mechanisms of triplet repeat expansions in ataxias Robert D. Wells Center for Genome Research, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, USA

Introduction Expansions of specific DNA triplet repeats are an initial step in the etiology of a number of ataxias in humans. In some diseases, such as spinocerebellar ataxia 1 (SCA1), SCA2, SCA3, and Machado–Joseph disease, the repetitive DNA sequences are translated into long tracts of polyglutamine, which alters the interactions of the target protein with cellular constituents and leads to the development of disease. For other disorders, including SCA8, the DNA repeat is located in a non-coding region of transcribed sequences and disease is probably caused by altered gene expression. In studies in lower organisms, mammalian cells, and transgenic mice, high frequencies of length changes (increases and decreases) occur in long DNA triplet repeats. A variety of processes acting on DNA influences the genetic stability of DNA triplet repeats, including replication, recombination, repair, and transcription. It is not yet known how these different multi-enzyme systems interact to produce the genetic mutation of expanded repeats. In-vitro studies have shown that DNA triplet repeats can adopt several unusual DNA structures, including hairpins, triplexes, sticky DNA, quadruplexes, slippedstructures, and highly flexible and writhed helices. The formation of stable, unusual structures within the cell is likely to disturb DNA metabolism and be a critical factor in the molecular mechanism(s) leading to genetic instabilities of DNA repeats and, hence, to disease pathogenesis. During the 1990s, unusual mutation events that produce expansion of DNA triplet repeats were identified as the cause of several hereditary neurological disorders. The association of length changes within repetitive DNA tracts in human diseases has stimulated interest in these sequences, as illustrated by recent authoritative books (Wells and Warren, 1998; Oostra, 1998; Rubinsztein and Hayden, 1998). The review in this chapter discusses how

biochemical and genetic studies from a variety of experimental systems are improving our understanding of these mutations and disease pathologies at the molecular level. Other excellent chapters in this book describe the human genetics, molecular biology, and pathology of several ataxias, including SCA1–8, Machado–Joseph disease, and Friedreich’s ataxia. This chapter will focuses on the molecular mechanisms of the expansions of the triplet repeat sequences (TRS) as related to pathology. Most of the triplet repeat diseases, except Friedreich’s ataxia, display the clinical features of anticipation, defined as a more severe form or earlier age of onset of disease with successive family generations. For all triplet repeat diseases there is a direct correlation between TRS length and disease severity. Detailed analysis of TRS has identified that anticipation occurs because genetic instabilities within TRS produce longer repeats upon transmission to offspring. Notably, the genetic instability of a specific TRS is dependent on its locus, and expansions of TRS are not due to a destabilization of the whole genome (Sutherland and Richards, 1995; McMurray, 1999). In general, this review discusses the mechanisms of expansion at the DNA level and does not focus on the relationship of expanded sequences to lengthened glutamine tracts or to other downstream molecular events.

Genetic instabilities General features When expansions of TRS were first shown to occur in several different diseases, it was thought possible that all expansion events may occur via the same biochemical mechanism. In fact, this is unlikely to be the case. Even in simple organisms, experiments have shown that mutation

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mechanisms producing repeat tract instability are complex (Bowater et al., 1997; Sarkar et al., 1998; Jakupciak and Wells, 1999). This chapter discusses a wide variety of experimental studies that have confirmed the potential for different biochemical processes to cause length changes to repeat sequences.

Replication Replication of the DNA molecule is a prime candidate for the process that generates repeat tract instability, and simple models to explain its involvement in both expansions and deletions of repeats have been proposed (Wells, 1996; Pearson and Sinden, 1998; Sinden, 1999). It should be noted that many mechanisms invoking DNA synthesis to generate repeat tract instabilities are common to DNA replication and repair. In this chapter, these processes are discussed separately. A variety of studies have shown that replication has a dramatic impact on the genetic stability of TRS in-vivo. For both expansions and deletions, the stability of repeat tracts is highly dependent on the orientation of the repeat with respect to the direction of replication. This orientation dependence has been studied in most detail for (CTG•CAG) tracts and, at least in bacteria and yeast, deletions to the repeat occur more readily when the (CTG)n tract is found on the lagging template strand of the replication fork (Wells, 1996; Pearson and Sinden, 1998; Sinden, 1999). Conversely, the frequency of expansions in (CTG•CAG) repeats is increased when the (CTG)n tract is the newly synthesized strand. These observations fit well with the hypothesis proposed to explain repeat tract instability shown in Fig. 35.1. The effects of orientation on deletions and expansions suggest that hairpins are favored on the CTG strand, consistent with thermodynamic studies of unusual DNA structures for the two complementary DNA strands of (CTG•CAG) repeats (Wells, 1996; Mitas, 1997; Pearson and Sinden, 1998; Sinden, 1999). Similar effects on the replication fork can be postulated for other unusual DNA structures within other repeat sequences. The orientation effect on repeat tract stability has been observed by electrophoretic analysis of (CTG•CAG) repeats contained on plasmids in Escherichia coli (Kang et al., 1995; Shimizu et al., 1996; Hirst and White, 1998; Sarkar et al., 1998) and in chromosomal locations in Saccharomyces cerevisiae (Maurer et al., 1996; Schweitzer and Livingston, 1997; Freudenreich et al., 1997; White et al., 1999; Balakumaran et al., 2000). Using a similar biochemical assay, (GAA•TTC) repeats also exhibit differential genetic

stability depending on their orientation, when propagated on plasmids in E. coli or in primate cell culture (Ohshima et al., 1998). A genetic assay in S. cerevisiae also detected orientation dependence of expansions of (CTG•CAG) repeats (Miret et al., 1998). A different genetic assay in yeast did not detect orientation dependence of deletions to (CTG•CAG)50 located on the chromosome (Miret et al., 1997), although the relationship of the repeat tract to replication origins was unknown. The observed orientation dependence of repeat tract stability is consistent with known biochemical properties of replication forks. Because the lagging-strand has more single-stranded character than the leading-strand, it has more opportunity to fold into unusual structures that can be bypassed during DNA synthesis (Sinden, 1999). Indeed, single-stranded binding protein (SSB) normally binds to Okazaki fragments in E. coli to prevent their association into unwanted configurations. Notably, deletion of SSB in E. coli increases the frequency of deletions in (CTG•CAG) repeats (Rosche et al., 1996). Slippage of DNA polymerase during in-vitro synthesis of oligonucleotides containing repetitive DNA was observed many years ago and was, in fact, used as an early method to prepare long polymers of DNA (Wells et al., 1965; Tautz and Schlotterer, 1994). A wide range of studies support the proposal that different lengths of repeat sequences are formed due to slippage of the polymerase at sites of DNA synthesis (Streisinger and Owen, 1985). The association of simple DNA repeats with human diseases has led to further examination of the effects of repetitive sequences on in-vitro DNA synthesis. Expansions resulting from slippage were observed during DNA synthesis using all ten TRS with several different DNA polymerases (Schlötterer and Tautz, 1992; Ji et al., 1996; Petruska et al., 1998; Lyons-Darden and Topal, 1999a, 1999b). A variety of factors altered the extent of repeat tract expansions during in-vitro DNA synthesis, including the type of DNA polymerase (Ji et al., 1996), ionic conditions and temperature of the reaction (Lyons-Darden and Topal, 1999b) and the presence of incorrect base-pairs (Lyons-Darden and Topal, 1999a, 1999b). In these experiments, DNA synthesis was initiated with small oligonucleotides consisting only of repetitive DNA. This arrangement is likely to give more slippage of complementary DNA strands compared to systems in which part of the newly synthesized DNA is held in place within non-repetitive, flanking DNA sequences. However, these results may be pertinent if synthesis of the lagging-strand of DNA is important for generating expansions of TRS. Because the size of some TRS is greater than the length of Okazaki fragments, it is possible that

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Fig. 35.1 Expansions and deletions may occur at sites of DNA synthesis. Note that deletions occur when hairpins form on the template strand and expansions occur when hairpins form on the nascent strand. Original DNA is shown in black and newly synthesized DNA is shown in gray. Thicker lines indicate regions of triplet repeat DNA and arrows show the direction of DNA synthesis. (Reproduced from Bowater and Wells, 2000, with permission.)

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particularly large expansions occur when the complete Okazaki fragment can slip at both ends (Richards and Sutherland, 1994). These in-vitro studies confirm that unusual structures within the TRS influence the fidelity of DNA polymerases and support the proposal that these factors may be important for mechanisms generating length changes to DNA repeats.

Involvement of repair functions DNA repair pathways have a particularly intriguing role in relation to genetic instabilities of TRS. Genomic integrity is normally maintained by repair pathways, such as mismatch repair, nucleotide and base excision repair, SOS repair, and the repair of double-stranded and singlestranded breaks (Friedberg et al., 1995; Lindahl et al., 1997). However, the observed length changes within TRS indicate that modifications to the genome are not always repaired. Possibly, specific cells may not be able to repair some types of length changes to TRS, due to non-recognition of certain structures or inaccessibility of DNA processed by some events; this could explain the tissue-specificity of some of the triplet repeat disorders. Alternatively, mutations in repair proteins may induce length alterations to repeats. As discussed below, numerous studies show that the impact of DNA repair pathways on repeat tract stability is complex (McMurray, 1999). Several DNA repair pathways have been demonstrated to have profound influences on the genetic instabilities of TRS related to ataxias. A detailed discussion of these processes is beyond the scope of this review. However, the reader is referred to other excellent reviews for further information on this topic (Wells and Warren, 1998; Bowater and Wells, 2000). These processes include the following: nucleotide excision repair (Hanawalt, 1994; Friedberg et al., 1995; Sancar, 1996; Lindahl et al., 1997; Wood, 1997), methyl-directed mismatch repair (Modrich, 1994, 1997; Kramer et al., 1996; Modrich and Lahue, 1996; Umar and Kunkel, 1996; Goellner et al., 1997; Pearson et al., 1997; Prolla, 1998; Schumacher et al., 1998; Wells et al., 1998), SOS pathways (Friedberg et al., 1995; Friedberg and Gerlach , 1999), SbcCD proteins (Sarkar et al., 1998), and DNA polymerase III proofreading (Iyer et al., 2000).

Recombination (gene conversion)-mediated expansions Homologous recombination was considered an unlikely cause of TRS expansion because DNA sequences flanking the repeat in disease genes are usually unaltered (Sinden

and Wells, 1992). However, other types of recombination pathways occur in all organisms and are particularly utilized in DNA repair. Furthermore, because recombination events were known to alter the lengths of direct repeats of DNA, the influence of various recombination proteins on the genetic stability of TRS has been considered. Analysis of the genetic stability of large TRS in E. coli identified that large deletions and expansions could occur in the absence of RecA protein (Jaworski et al., 1995; Kang et al., 1995; Bi and Liu, 1996; Bowater et al., 1996). However, recent experiments have demonstrated that recombination events effect large expansions of (CTG•CAG) repeats in E. coli (Jakupciak and Wells, 1999). This study established a two-plasmid system for evaluating the potential role of homologous recombination in the expansion of TRS in E. coli. One family of plasmids comprised derivatives of pUC19 that contained the unidirectional ColE1 origin of replication and harbored the ampicillin-resistance gene. The other family of plasmids was derived from pACYC184 and harbored the tetracycline-resistance gene. The nonidentical sequences of these two vectors allowed examination of the potential effects of cloned tracts of different TRS on recombination (Jakupciak and Wells, 1999). Recombination was proven genetically and biochemically by the following: (a) the presence of both ampicillin and tetracycline resistance in the recombinant products; (b) the formation of long cointegrant DNAs; (c) the expansion of (CTG•CAG) tracts by DNA sequencing and by restriction mapping for the longest tracts; (d) the transfer of a G-to-A polymorphism from the TRS in the pACYC184 derivative to the TRS in the pUC19 derivatives; and (e) inserts with strand inversions. This work established relationships between (CTG•CAG) sequences, multiple-fold expansions, genetic recombination-gene conversion, formation of new recombinant products, and the presence of two drug resistances from the two plasmids. It was proposed that expansions in hereditary neurological syndromes could occur via recombination mechanisms that include gene conversion/repair (right side of Fig. 35.2) or unequal crossing-over (left side of Fig. 35.2). The flanking sequences are exchanged in the unequal crossing-over mechanism, whereas they are not exchanged in the gene conversion mechanism. Preliminary recent investigations indicate that both mechanisms take place but that the gene conversion pathway is predominant (Jakupciak and Wells, unpublished data). Further work is required to determine the mechanism of these events and to evaluate their behaviors in chromosomes as well as human cells.

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80 + k Fig. 35.2 Model system to identify expansion of (CTG•CAG) repeats mediated by recombination in E. coli. Utilization of two compatible plasmids, pACYC184 and pUC19, harboring different lengths of (CTG•CAG) repeats identified that recombination leads to expansion of the repeats (Jakupciak and Wells, 1999). The heavy solid lines represent the pUC19 vector and the shaded region represents pACYC184. Each strand of the (CTG•CAG) repeat participating in recombination is shown, with the dots in the insert in pACYC184 representing interruptions that are used as markers to follow strand-exchange. Expansion may occur via distinct mechanisms of recombination: homologous recombination between the two repeats (left side) or recombinational repair of a double-strand break within the repeat (right side). These mechanisms can be differentiated because homologous recombination leads to exchange of sequence between the plasmids, but double-strand break repair leads to formation of an extra interruption in the pUC19 repeat without exchange of flanking vector sequences. Note that two Holliday-like junctions separated by the distance k (in repeat units) are formed during double-strand break repair. Depending on the extent of branch-migration of the junctions, different sizes of expansions may be formed. Intermediates involving single-stranded loops or misalignment of exchanging strands could lead to new expanded products. (Reproduced from Jakupciak and Wells, 1999, with permission.)

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Small slipped-register instabilities As described above, E. coli has proved to be a valuable system for the study of basic mechanisms underlying triplet repeat instabilities. The sizes of these replicationdependent expansions and contractions are substantial, ranging from 20 to >100 repeats. In addition to these large expansions and deletions, small 1 to 7 repeat units were observed in the position of (CTA•TAG) marker interruptions when (CTG•CAG)n tracts were sequenced following subculturing in E. coli (Wells et al., 1998). Thus, these occasional sequence polymorphisms, which were the result of cloning of human sequences into plasmid DNA, provided a valuable means for following small slippedregister expansions and deletions (SSED). Several observations suggest that SSED is the consequence of small slippages occurring along the duplex DNA rather than at the replication fork, and, therefore, that this instability involves mechanisms different from those associated with errors of replication. For consideration of the non-replication-based slippage (Fig. 35.3), it is assumed that the complementary DNA strands are not nicked and, hence, are not free to rotate around each other, as in closed, circular, or genomic DNA. However, because nicks exist at the replication fork in Fig. 35.3, free rotation is possible in this case. Because small expansions can be achieved by this replication-independent instability mechanism, we propose that the expansions observed in SCA1–7 and Machado– Joseph disease occur by this repair process.

Friedreich’s ataxia Molecular mechanisms of expansion of GAA•TTC Very few studies have been reported on the molecular mechanisms of the expansion process involved in the very long GAA•TTC tracts involved in the majority of the cases of Friedreich’s ataxia (Ohshima et al., 1998). Hence, most researchers presume that the mechanism is similar to the processes described above (see Figs. 35.1 and 35.2). However, this mechanism is currently under active investigation (R.R. Iyer and R.D. Wells, unpublished work).

Triplexes, sticky DNA, and Friedreich’s ataxia Other chapters in this book describe the human genetics and pathology of Friedreich’s ataxia. During investigations of the properties of long tracts of GAA•TTC, we discovered a novel DNA structure, sticky DNA (Fig. 35.4), for the lengths of this TRS found in intron 1 of the frataxin gene of

Friedreich’s ataxia patients. Sticky DNA is formed by the association of two purine•purine•pyrimidine (R•R•Y) triplexes in negatively supercoiled plasmids at neutral pH (Sakamoto et al., 1999). An excellent correlation was found between the lengths of GAA•TTC (>59 repeats); first, in Friedreich’s ataxia patients, second, required to inhibit transcription in-vivo and in-vitro, and third, required to adopt the sticky conformation. Additionally, (GAAGGA•TCCTTC)65, also found in intron 1, does not form sticky DNA, inhibit transcription, or associate with the disease. Hence, R•R•Y triplexes and/or sticky DNA may be involved in the etiology of Friedreich’s ataxia (Sakamoto et al., 1999). Current evidence suggests a role for sticky DNA in human Friedreich’s ataxia. Normal individuals have less than 38 (GAA•TTC) repeats, whereas Friedreich’s ataxia patients have 66 or more triplets (Campuzano et al., 1996; Durr et al., 1996; Montermini et al., 1997). First, no retarded band (sticky DNA) was found for repeat lengths up to 33, but the retarded bands appeared for 59 repeats and longer. Second, the level of in-vivo transcription of a reporter gene containing (GAA•TTC) repeats in the intron was inversely proportional to the number of repeats (Ohshima et al., 1998) and the inhibition was significant when the repeat lengths reached the range found for Friedreich’s ataxia patients. These results were confirmed in-vitro (Bidichandani et al., 1998). Thus, the range of TRS lengths responsible for the transcriptional inhibition was similar to that required for the formation of the retarded band (RB), in these investigations. Third, plasmids containing the (GAAGGA•TCCTTC)65 hexamer repeat did not form RB, whereas plasmids with the same length of (GAA•TTC) repeats did form sticky DNA. Other investigations (Ohshima and Pandolfo, in preparation) revealed that the hexamer repeat is not associated with Friedreich’s ataxia, is stably transmitted from parent to child for three sibs, and did not inhibit transcription of a reporter gene in transfected cells, whereas the same length of the (GAA•TTC) repeat caused a large extent of inhibition. Fourth, sticky DNA is formed under physiological conditions. Hence, we propose that the sticky dimeric-associated conformation and/or the R•R•Y triplex are important, perhaps critical, factors in the hereditary disease. The two long (GAA•TTC) tracts in the daughter strands behind the replication fork could associate to form the strandexchanged sticky complex which would inhibit transcription. The relatively high level of negative supercoil density (Liu and Wang, 1987) behind the replication fork would enhance the triplex–sticky DNA formation. Hence, the formation of sticky DNA in a Friedreich’s ataxia patient would result in reduced levels of frataxin.

Molecular mechanisms of triplet repeat expansions in ataxias

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Fig. 35.3 Mechanisms for small, slipped register-mediated expansions and deletions (SSED). For further details on this mechanism, see Wells et al. (1998). (Reproduced from Wells et al., 1998, with permission.)

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A(a) B-DNA

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Molecular mechanisms of triplet repeat expansions in ataxias

Non-B DNA structures DNA is a dynamic molecule which has a variety of unorthodox conformations at certain specific loci depending on the sequence and conditions in the test tube and in the cell. Fig. 35.4 shows a right-handed duplex B-DNA structure along with slipped DNA, which is a conformation found at direct repeat sequences. Because the complementary strands can slip relative to each other, slipped DNA is a pronounced feature of repetitive DNA. Furthermore, triplexes are formed intramolecularly at tracts of purine•pyrimidine sequences. The structure show in Fig. 35.4A is a purine•purine•pyrimidine intramolecular triplex (reviewed in Wells and Warren, 1998). Long tracts of CTG•CAG and CGG•CCG responsible for hereditary neurological diseases (Wells and Warren, 1998) adopt flexible and writhed conformations which are probably responsible for the formation of slipped structures and their genetically unstable behaviors (Bacolla et al., 1997; Gellibolian et al., 1997).

Prospects for the future Expansions in TRS were discovered to be associated with human hereditary disorders at the beginning of the 1990s (reviewed in Wells and Warren, 1998). The marriage of a wide range of scientific disciplines, including basic biochemistry, genetics, and molecular and cellular biology, has produced remarkable insights into these unusual mutations during the past decade. Neither the pathogenesis of the triplet repeat diseases nor the molecular basis of the mutations is understood fully, but a variety of experimental systems are now in place that should yield direct evidence in both areas. Much experimental evidence suggests that DNA polymerases play a central role in molecular mechanisms generating genetic instabilities of TRS. However, it is not clear if this occurs only through the functions of DNA poly-

merases in DNA replication, or also through their interactions with other processes occurring on DNA. It is now apparent that the genetic instabilities of TRS may be mediated by many biochemical processes, including DNA replication-based slipped-strand mispairing, small slipped-register DNA synthesis, tandem duplications, and gene conversion-recombination processes. These processes may occur independently or in concert with each other and/or other DNA metabolic processes such as MMR, nucleotide excision repair (NER), DNA polymerase proofreading, SOS repair, transcription, etc. Experimental systems now in place should allow determination of the precise roles of these various events in generating the genetic instabilities of TRS in-vivo. This, in turn, will allow identification of their role in the molecular mechanisms to initiate disease pathogenesis. It is also clear that structural properties of the TRS (hairpin loop formation, slipped structures, triplexes, and flexible and writhed conformations) play an important role in their genetic instabilities. Unusual DNA structures may be involved because they are inherent within long TRS inside cells, or because enzymes manipulating DNA may promote their formation. Either way, the presence of unusual structures within TRS will influence the interaction of the DNA with proteins, which, in turn, facilitates the genetic instability of TRS. A comprehension of the molecular processes that elicit genetic instabilities of TRS is critical for developing diagnostic and therapeutic tools for these diseases. We anticipate that the information gained from basic experimental studies will be translated into direct benefit to patients who suffer from these devastating disorders and their families.

Acknowledgments This work was supported by grants from the National Institutes of Health (GM52982 and NS37544), the

Fig. 35.4 Unusual DNA structures implicated in processes leading to genetic instabilities of TRS. (A) TRS associated with human diseases form a variety of well-characterized non-B-DNA structures, including triplexes, tetraplexes and slipped DNA (containing hairpins and/or unpaired regions). (B) TRS have increased flexibility and writhing compared to random sequence DNA. In this representation, a circular, double-stranded DNA molecule is shown as a closed ribbon. The winding of the DNA helix is ignored and the direction in space of the helix axis (corresponding to the ribbon axis), or writhe of the DNA, is emphasized. In this diagram, TRS sequences are placed at the top of the DNA molecule and, due to their greater flexibility compared to random sequence DNA, a relatively large amount of the molecule’s writhe is associated with the TRS. Negative supercoiling of the DNA molecule introduces additional writhing (right side of figure), with a greater proportion of this localizing to the TRS. Two possibilities for the three-dimensional structure of highly flexible TRS are shown because the conformation of the TRS remains to be elucidated. (C) (GAA•TTC) repeats can adopt a novel, unusual DNA structure, ‘sticky DNA’ (Sakamoto et al., 1999). (The diagrams are reproduced with permission from Gellibolian et al., 1997, and Sakamoto et al., 1999.)

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Polycystic Kidney Research Foundation, and the Robert A. Welch Foundation. The author thanks his colleagues from the Center for Genome Research for stimulating discussions about many of the ideas outlined in this chapter. Note that the reference list is not an exhaustive review of all literature associated with this field. In many cases the most recent reference (up to February 2000) from a series of papers from a given laboratory is cited to enable the reader to trace back to earlier contributions. A portion of this work has been reviewed previously (Bowater and Wells, 2000) and is republished with permission.

xReferencesx Bacolla, A., Gellibolian, R., Shimizu, M. et al. (1997). Flexible DNA: genetically unstable CTG•CAG and CGG•CCG from human hereditary neuromuscular disease genes. J Biol Chem 272: 16783–92. Balakumaran, B.S., Freudenreich, C.H. and Zakian, V.A. (2000). CGG/CCG repeats exhibit orientation dependent stability and orientation independent fragility in Saccharomyces cerevisiae. Hum Mol Genet 19: 93–100. Bi, X. and Liu, L.F. (1996). DNA rearrangement mediated by inverted repeats. Proc Natl Acad Sci USA 93: 819–23. Bidichandani, S.I., Ashizawa, T. and Patel, P.I. (1998). The GAA triplet-repeat expansion in Friedreich ataxia interferes with transcription and may be associated with an unusual DNA structure. Am J Hum Genet 62: 111–21. Bowater, R.P., Jaworski, A., Larson, J.E., Parniewski, P. and Wells, R.D. (1997). Transcription increases the deletion frequency of long CTG•CAG triplet repeats from plasmids in Escherichia coli. Nucl Acids Res 25: 2861–8. Bowater, R.P., Rosche, W.A., Jaworski, A., Sinden, R.R. and Wells, R.D. (1996). Relationship between Escherichia coli growth and deletions of CTG•CAG triplet repeats from human neuromuscular disease genes in plasmids. J Mol Biol 264: 82–96. Bowater, R.P. and Wells, R.D. (2000). The intrinsically unstable life of DNA triplet repeats associated with human hereditary disorders. Proc Nucl Acids Res Mol Biol in press Campuzano, V., Montermini, L., Moltò, M.D. et al. (1996). Friedreich’s ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science 271: 1423–7. Durr, M., Cossee, Y., Agid, V. et al. (1996). Clinical and genetic abnormalities in patients with Friedreich’s ataxia. N Engl J Med 335: 1169–75. Freudenreich, C.H., Stavenhagen, J.B. and Zakian, V.A. (1997). Stability of a CTG/CAG trinucleotide repeat in yeast is dependent on its orientation in the genome. Mol Cell Biol 17: 2090–8. Friedberg, E.C. and Gerlach, V.L. (1999). Novel DNA polymerases offer clues to the molecular basis of mutagenesis. Cell 98: 413–16. Friedberg, E.C., Walker, G.C. and Siede, W. (1995). DNA Repair and

Mutagenesis. Washington, DC: American Society for Microbiology. Gellibolian, R., Bacolla, A. and Wells, R.D. (1997). Triplet repeat instability and DNA topology: an expansion model based on statistical mechanics. J Biol Chem 272: 16793–7. Goellner, G.M., Tester, D., Thibodeau, S. et al. (1997). Different mechanisms underlie DNA instability in Huntington disease and colorectal cancer. Am J Hum Genet 60: 879–90. Hanawalt, P.C. (1994). Transcription-coupled repair and human disease. Science 266: 1957–8. Hirst, M.C. and White, P.J. (1998). Cloned human FMR1 trinucleotide repeats exhibit a length- and orientation-dependent instability suggestive of in vivo lagging strand secondary structure. Nucl Acid Res 26: 2353–61. Iyer, R.R., Pluciennik, A., Rosche, W.A., Sinden, R.R. and Wells, R.D. (2000). DNA polymerase III proofreading mutants enhance the expansion and deletion of triplet repeat sequences in Escherichia coli. J Biol Chem 275: 2174–84. Jakupciak, J.P. and Wells, R.D. (1999). Genetic instabilities in (CTG•CAG) repeats occur by recombination. J Biol Chem 274: 23468–79. Jaworski, A., Rosche, W.A., Gellibolian, R. et al. (1995). Mismatch repair in Escherichia coli enhances instability of (CTG)n triplet repeats from human hereditary diseases. Proc Natl Acad Sci USA 92: 11019–23. Ji, J., Clegg, N.J., Peterson, K.R., Jackson, A.L., Laird, C.D. and Loeb, L.A. (1996). In vitro expansion of GGC: GCC repeats: identification of the preferred strand of expansion. Nucl Acids Res 24: 2835–40. Kang, S., Jaworski, A., Ohshima, K. and Wells, R.D. (1995). Expansion and deletion of CTG repeats from human disease genes are determined by the direction of replication in E. coli. Nature Genet 10: 213–18. Kramer, P.R., Pearson, C.E. and Sinden, R.R. (1996). Stability of triplet repeats of myotonic dystrophy and Fragile X loci in human mutator mismatch repair cell lines. Human Genet 98: 151–7. Lindahl, T., Karran, P. and Wood, R.D. (1997). DNA excision repair pathways. Curr Opin Genet Dev 7: 158–69. Liu, L.F. and Wang, J.C. (1987). Supercoiling of the DNA template during transcription. Proc Natl Acad Sci USA 84: 7024–7. Lyons-Darden, T. and Topal, M.D. (1999a). Abasic sites induce triplet-repeat expansion during DNA replication in vitro. J Biol Chem 274: 25975–8. Lyons-Darden, T. and Topal, M.D. (1999b). Effects of temperature, Mg2 concentration and mismatches on triplet-repeat expansion during DNA replication in vitro. Nucl Acids Res 27: 2235–40. Maurer, D.J., O’Callaghan, B. and Livingston, D.M. (1996). Orientation dependence of trinucleotide CAG repeat instability in Saccharomyces cerevisiae. Mol Cell Biol 16: 6617–22. McMurray, C.T. (1999). DNA secondary structure: a common causative factor for expansion in human disease. Proc Natl Acad Sci USA 96: 1823–5. Miret, J.J., Pessoa-Brandão, L. and Lahue, R.S. (1997). Instability of CAG and CTG trinucleotide repeats in Saccharomyces cerevisiae. Mol Cell Biol 17: 3382–7.

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Miret, J.J., Pessoa-Brandao, L. and Lahue, R.S. (1998). Orientationdependent and sequence-specific expansions of CTG/CAG trinucleotide repeats in Saccharomyces cerevisiae. Proc Natl Acad Sci USA 95: 12438–43. Mitas, M. (1997). Trinucleotide repeats associated with human disease. Nucl Acid Res 25: 2245–51. Modrich, P. (1994). Mismatch repair, genetic stability, and cancer. Science 266: 1959–60. Modrich, P. (1997). Strand-specific mismatch repair in mammalian cells. J Biol Chem 272: 24727–30. Modrich, P. and Lahue, R. (1996). Mismatch repair in replication fidelity, genetic recombination and cancer biology. Annu Rev Biochem 65: 101–33. Montermini, L., Richter, A., Morgan, K. et al. (1997). Phenotypic variability in Friedreich ataxia: role of the associated GAA triplet repeat expansion. Ann Neurol 41: 675–82. Ohshima, K., Montermini, L., Wells, R.D. and Pandolfo, M.(1998). Inhibitory effects of expanded GAA•TTC triplet repeats from intron 1 of the Friedreich’s ataxia gene on transcription and replication in vivo. J Biol Chem 273: 14588–95. Oostra, B.A. (1998). Trinucleotide Diseases and Instability. New York: Springer-Verlag. Pearson, C.E., Ewel, A., Acharya, S., Fishel, R.A. and Sinden, R.R. (1997). Human MSH2 binds to trinucleotide repeat DNA structures associated with neurodegenerative diseases. Hum Mol Genet 6: 1117–23. Pearson, C.E. and Sinden, R.R. (1998). Trinucleotide repeat DNA structures: dynamic mutations from dynamic DNA. Curr Opin Struct Biol 8: 321–30. Petruska, J., Hartenstine, M.J. and Goodman, M.F. (1998). Analysis of strand slippage in DNA polymerase expansions of CAG/CTG triplet repeats associated with neurodegenerative diseases. J Biol Chem 273: 5204–10. Prolla, T.A. (1998). DNA mismatch repair and cancer. Curr Opin Cell Biol 10: 311–16. Richards, R.I. and Sutherland, G.R. (1994). Simple repeat DNA is not replicated simply. Nature Genet 6: 114–16. Rosche, W.A., Jaworski, A., Kang, S. et al. (1996). Single-stranded DNA-binding protein enhances the stability of CTG triplet repeats in Escherichia coli. J Bacteriol 178: 5042–4. Rubinsztein, D. and Hayden, M. (1998). Analysis of Triplet Repeat Disorders. Oxford: Human Molecular Genetics BIOS Scientific Publishers Ltd. Sakamoto, N., Chastain, P.D., Parniewski, P. et al. (1999). Sticky DNA: self-association properties of long GAA•TTC repeats in R•R•Y triplex structures from Friedreich’s ataxia. Mol Cell 3: 465–75. Sancar, A.(1996). DNA excision repair. Annu Rev Biochem 65: 43–81. Sarkar, P.S., Chang, H.-C., Boudi, F.B. and Reddy, S. (1998). CTG repeats show bimodal amplification in E. coli. Cell 95: 531–40.

Schlötterer, C. and Tautz, D. (1992). Slippage synthesis of simple sequence DNA. Nucl Acids Res 20: 211–15. Schumacher, S., Fuchs, R.P.P. and Bichara, M. (1998). Expansion of CTG repeats from human disease genes is dependent upon replication mechanisms in Escherichia coli: the effect of long patch mismatch repair revisited. J Mol Biol 279: 1101–10. Schweitzer, J.K. and Livingston, D.M. (1997). Destabilization of CAG trinucleotide repeat tracts by mismatch repair mutations in yeast. Hum Mol Genet 6: 349–55. Shimizu, M., Gellibolian, R., Oostra, B.A. and Wells, R.D. (1996). Cloning, characterization, and properties of plasmids containing CGG triplet repeats from the FMR-1 gene. J Mol Biol 258: 614–26. Sinden, R.R. (1999). Biological implications of the DNA structures associated with disease-causing triplet repeats. Am J Hum Genet 64: 346–53. Sinden, R.R. and Wells, R.D. (1992). DNA structure, mutations, and human genetic disease. Curr Opin Biotechnol 3: 612–22. Streisinger, G. and Owen, J. (1985). Mechanisms of spontaneous and induced frameshift mutation in bacteriophage T4. Genetics 109: 633–59. Sutherland, G.R. and Richards, R.I. (1995). Simple tandem DNA repeats and human genetic disease. Proc Natl Acad Sci USA 92: 3636–41. Tautz, D. and Schlotterer, C. (1994). Simple sequences. Curr Opin Genet Dev 4: 832–7. Umar, A.and Kunkel, T.A. (1996). DNA-replication fidelity, mismatch repair and genome instability in cancer cells. Eur J Biochem 238: 297–307. Wells, R.D. (1996). Molecular basis of genetic instability of triplet repeats. J Biol Chem 271: 2875–8. Wells, R.D., Ohtsuka, E. and Khorana, H.G. (1965). Studies on polynucleotides. L. Synthetic deoxyribopolynucleotides as templates for the DNA polymerase of Escherichia coli: a new doublestranded DNA-like polymer containing repeating dinucleotide sequences. J Mol Biol 14: 221–40. Wells, R.D., Parniewski, P., Pluciennik, A., Bacolla, A., Gellibolian, R. and Jaworski, A. (1998). Small slipped register genetic instabilities in Escherichia coli in triplet repeat sequences associated with hereditary neurological diseases. J Biol Chem 273: 19532–41. Wells, R.D. and Warren, S.T. (1998). Genetic Instabilities and Hereditary Neurological Diseases. San Diego: Academic Press. White, P.J., Borts, R.H. and Hirst, M.C. (1999). Stability of the human fragile X (CGG)n triplet repeat array in Saccharomyces cerevisiae deficient in aspects of DNA metabolism. Mol Cell Biol 19: 5675–84. Wood, R.D. (1997). Nucleotide excision repair in mammalian cells. J Biol Chem 272: 23465–8.

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Part IX

Recessive Ataxias

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Friedreich’s ataxia Massimo Pandolfo Service de Neurologie, l’Hôpital Erasme, Free University of Brussels, Belgium

Introduction In 1863, Nicholaus Friedreich, Professor of Medicine in Heidelberg, Germany, wrote three articles about a ‘degenerative atrophy of the posterior columns of the spinal cord’ causing progressive ataxia, sensory loss, and muscle weakness (Friedreich, 1863a, 1863b, 1863c). It could strike several siblings with normal, unaffected parents. Friedreich reported additional cases in 1876 and 1877. Charcot suspected for some time that Friedreich had described a form of tabes, but eventually he recognized that it was a new disease entity. Brousse (1882) was the first to use the name ‘Friedreich ataxia.’ After a few years, Ladame (1890) reported more than 100 cases. In the years that followed, more and more descriptions of inherited degenerative diseases causing ataxia were published. Many of these cases were noted to have some characteristics resembling Friedreich’s ataxia, eventually blurring the definition of the disease (Bell and Carmichael, 1939). Only in the late 1970s did landmark studies establish the autosomal recessive pattern of inheritance (Geoffroy et al., 1976; Harding, 1981; Harding and Zilkha, 1981) and define rigorous diagnostic criteria (Geoffroy et al., 1976; Harding, 1981). It was realized that the disease shows variability in the clinical picture, sometimes with atypical presentations coexisting in the same family with typical cases (Winter et al., 1981; Filla et al., 1990, 1991; Muller-Felber et al., 1993). Specific variants, such as the so-called Acadian ataxia (Barbeau et al., 1984; Richter et al., 1996), were recognized in some ethnic groups. The very atypical variants lateonset Friedreich’s ataxia (LOFA) (Klockgether et al., 1993; De Michele et al., 1994) and Friedreich’s ataxia with retained reflexes (FARR) (Palau et al., 1997) were described only much later, after the chromosomal localization of the gene became known (Chamberlain et al., 1988). The Friedrech’s ataxia gene (FRDA) was identified in 1996 (Campuzano et al., 1996). Its most common mutation was

found to be the unstable hyperexpansion of a GAA triplet repeat in the first intron, but point mutations were also identified. Thanks to this discovery, genetic testing, genotype–phenotype correlations, pathophysiological studies, and new approaches to treatment became possible.

Epidemiology Friedreich’s ataxia has been reported to account for almost half of the overall hereditary ataxia cases in Caucasians, up to three-quarters of those with onset before age 25 (Harding, 1983). Its prevalence is estimated to be around 2 105 (Skre, 1975; Harding, 1983; Romeo et al., 1983; Leone et al., 1990; Lopez-Arlandis et al., 1995). Local clusters due to a founder effect have been reported in Rimouski, Québec (Bouchard et al., 1979) and in KathikasArodhes, Cyprus (Dean et al., 1988). The disease seems to be limited to people of European, North African and Middle Eastern descent, reflecting a unique origin of the long alleles at the GAA triplet repeat from which pathogenic expansions derive (Labuda et al., 2000).

Pathology The pathology of Friedreich’s ataxia is described in detail in Chapter 25.

Clinical aspects Onset Most commonly, the onset of Friedreich’s ataxia is around puberty (Table 36.1; Geoffroy et al., 1976; Campanella et al., 1980; D’Angelo et al., 1980; Harding, 1981; Filla et al., 1990;

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Table 36.1 Diagnostic criteria for Friedreich’s ataxia Québec Cooperative Study on Friedreich’s Ataxiaa 1. Onset before age 20 2. Progressive, unremitting ataxia 3. Absent deep tendon reflexes in lower limbs 4. Decreased vibration sense 5. Weakness 6. Dysarthria Harding (1981) 1. Onset before age 25 2. Progressive, unremitting ataxia 3. Absent deep tendon reflexes in lower limbs 4. Babinski sign 5. Neurophysiological evidence of axonal sensory neuropathy (small or absent sensory action potentials, motor nerve conduction velocities 40 m/s) Within five years from onset: 6. Dysarthria Notes: a

Geoffroy et al. (1976).

Muller-Felber et al., 1993), but it may be earlier (Ulku et al., 1988; De Michele et al., 1994), or later, in adult life (Klockgether et al., 1993; De Michele et al., 1994). The Québec Collaborative Group proposed onset before the age of 20 as a diagnostic criterion (Geoffroy et al., 1976); Harding (1981) extended the limit to age 25. When the molecular defect was identified, it became clear that lateonset patients (LOFA) carry mutations in the same gene as typical Friedreich’s ataxia cases. Large variations of age of onset within a sibship may be observed, and are explained in part by the dynamic nature of the mutation (Campuzano et al., 1996). Gait instability (65%) and generalized clumsiness (25%) are the most common initial symptoms, but nonneurological manifestations such as scoliosis (5%) or cardiomyopathy (5%) may precede the onset of ataxia (Geoffroy et al., 1976; Harding, 1981; Filla et al., 1990; Muller-Felber et al., 1993).

Neurological signs and symptoms Ataxia is progressive, unremitting, with mixed cerebellar and sensory features. It is caused by the degeneration of the dorsal columns, the spinocerebellar tracts, and the dentate nucleus. Onset is usually with truncal ataxia, followed by limb incoordination, dysmetria, and intention tremor. Eventually, most patients lose the ability to

perform fine motor activities, walk, stand, and sit without support. A progressive dysarthria with slow, jerky speech and sudden utterances (Gentil, 1990; Cisneros and Braun, 1995) appears shortly after onset in typical cases (Geoffroy et al., 1976; Harding, 1981; Filla et al., 1990; Muller-Felber et al., 1993). Progressive muscular weakness is common, thought to derive from the degeneration of the corticospinal tracts. However, when patients become wheelchair bound, they still have on average 70% of their normal strength in their lower limbs, indicating that ataxia and not weakness is the primary cause of loss of ambulation (Beauchamp et al., 1995). Muscle tone is not altered in any typical manner. Distal amyotrophy in the lower limbs and in the hands is frequent, even early in the course of the disease (Harding, 1981). When patients are wheelchair bound, disuse atrophy occurs. The axonal sensory neuropathy results in loss of position and vibration sense and in areflexia. Perception of light touch, pain, and temperature is initially normal, but decreases with advancing disease. Loss of tendon reflexes in the lower limbs was considered essential for the diagnosis both by the Québec Collaborative Group and by Harding. It is now known that a minority of patients with Friedreich’s ataxia have elicitable tendon reflexes, sometimes even exaggerated reflexes with spasticity, for several years after diagnosis (FARR). Pyramidal involvement causes extensor plantar responses, another obligatory sign for the Québec Collaborative Group and for Harding. Again, exceptions to this rule are now well known. Probably, the relative weight of sensory neuropathy and of pyramidal tract degeneration varies from patient to patient, resulting most often in a typical mixed picture, but sometimes in one component obscuring the other. Such partial pictures are usually observed in milder cases of the disease. Fixation instability with square-wave jerks is the typical oculomotor abnormality of Friedreich’s ataxia (Spieker et al., 1995). Various combinations of cerebellar, vestibular, and brainstem oculomotor signs may sometimes be observed, but nystagmus is uncommon and ophthalmoparesis does not occur. Optic atrophy, with or without visual impairment, can be detected in about 30% of the patients (Geoffroy et al., 1976; Harding, 1981; Kirkham and Coupland, 1981; Livingstone et al., 1981; Muller-Felber et al., 1993; Rabiah et al., 1997). Sensorineural hearing loss affects about 20% of patients (Ell et al., 1984; Cassandro et al., 1986). Optic atrophy and sensorineural hearing loss tend to be associated with each other and with diabetes (Harding, 1981; Montermini et al., 1997c).

Friedreich’s ataxia

507

CIII CIII

CI CII CI –

O2

mtDNA OH •

Aconitase

MnSOD H2O2 F Iron

Heme

Iron Sulfur Protein F

Frataxin

mitochondrion

Fig. 36.1 Model scheme of the role of frataxin in mitochondrial iron metabolism and free radical production. Iron is shown to enter the cell via the transferrin-TfR system and to be transported in and out of mitochondria by as yet unidentified carriers. The picture shows the hypothetical function of frataxin as an intra-mitochondrial chaperone that protects iron from free radicals and makes it available for biosynthetic and transport pathways. Transport of iron for heme synthesis and heme export are shown as an independent pathway, probably non-frataxin dependent. When frataxin is deficient redox-active iron accumulates, triggering the Fenton reaction with production of toxic OH• radicals. Free radical damage and decreased bioavailability of iron for mitochondrial metalloprotein assembly result in multiple enzyme deficiencies. Free radicals also damage membrane lipids and nucleic acids.

Non-neurological involvement Heart disease is almost universal in Friedreich’s ataxia, but it remains asymptomatic in about half of the patients. However, particularly in patients with early onset, cardiomyopathy may be a cause of disability and shortened life expectancy because of heart disease (Hartman and Booth, 1960; Boyer et al., 1962; Geoffroy et al., 1976; Harding, 1981; Harding and Hewer, 1983; Pentland and Fox, 1983; Alboliras et al., 1986; Child et al., 1986; Leone et al., 1988; Filla et al., 1990; Muller-Felber et al., 1993; Maione et al., 1997). The most common symptoms of cardiomyopathy are shortness of breath (40%) and palpitations (11%) (Harding, 1981). The electrocardiogram (ECG) shows T-wave inversions, signs of ventricular hypertrophy, occasionally (about 10% of patients) conduction disturbances, supraventricular ectopic beats, and atrial fibrillation (Alboliras et al., 1986; Child et al., 1986; Filla et al., 1990; Muller-Felber et al., 1993). Atrial fibrillation is a negative prognostic sign (Harding, 1984). ECG changes may vary in time, with occasional normal recordings: this has led to underestimation of

their frequency. Repeated ECG recordings are the most sensitive test for Friedreich’s ataxia cardiomyopathy. Echocardiography and Doppler-echocardiography demonstrate concentric hypertrophy of the ventricles (62%) or asymmetric septal hypertrophy (29%), with diastolic function abnormalities (Harding, 1981; Morvan et al., 1992). About 10% of Friedreich’s ataxia patients develop diabetes mellitus and 20% have carbohydrate intolerance. Beta-cell dysfunction (Finocchiaro et al., 1988) and atrophy (Schoenle et al., 1989), as well as peripheral insulin resistance (Fantus et al., 1993), are thought to play a role. Although some cases may be initially controlled by oral hypoglycemic drugs, insulin dependence is eventually the rule. It is important to check Friedreich’s ataxia patients regularly for the development of diabetes, as it may increase the burden of disease, complicate the neurological picture, and even promote potentially fatal complications. Kyphoscoliosis may cause pain and cardiorespiratory problems. Pes cavus and pes equinovarus may render gait even more difficult. Autonomic disturbances, most commonly cold and cyanotic legs and feet, are increasingly

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frequent as the disease advances (Margalith et al., 1984). Parasympathetic abnormalities such as decreased heart rate variability parameters have been reported (Pousset et al., 1996). Urgency of micturition is rare.

Biochemical investigations Lipoproteins, vitamin E, lactate, pyruvate, urinary organic acids, serum very long chain fatty acids (VLCFA), serum phytanic acid, and leukocyte and/or fibroblast lysosomal enzymes are all normal in Friedreich’s ataxia. These tests are done to exclude the diagnoses of abetalipoproteinemia or ipobetalipoproteinemia, isolated vitamin E deficiency, mitochondrial disorders, adrenoleukodystrophy, or adrenomyeloneuropathy, Refsum disease, and a number of lysosomal storage diseases can be differential diagnoses, particularly at the early stage of the disease. Current attention is focused on iron metabolism (Babcock et al., 1997). Blood iron, iron-binding capacity and ferritin are normal (Wilson et al., 1998), but circulating transferrin receptors are increased (Wilson et al., 2000). Erythrocyte protoporphyrin IX has been reported to be increased (Morgan et al., 1979). Increased plasma malondialdehyde (MDA) was recently observed in children with Friedreich’s ataxia, which may reflect oxidative damage to lipids (M. Pandolfo and M. Vanasse, unpublished data).

Neuroimaging Almost all Friedreich’s ataxia patients show thinning of the cervical spinal cord with signal abnormalities in the posterior and lateral columns on sagittal and axial magnetic resonance images (MRI) (Wessel et al., 1989; Wullner et al., 1993; Junck et al., 1994; Mascalchi et al., 1994; Riva and Bradac, 1995). Brainstem, cerebellum, and cerebrum are less severely affected, but are all smaller in Friedreich’s ataxia patients compared to healthy controls, at an extent that correlates with clinical severity (Junck et al., 1994). Mild vermian and lobar cerebellar atrophy occurs in more severe and more advanced cases (Wullner et al., 1993; Giroud et al., 1994). Blood flow in the cerebellum, as assessed by TC-HMPAO single positron emission computerized tomography (SPECT), appears to be markedly decreased, more than expected for the degree of atrophy (Giroud et al., 1994). Positron emission tomography (PET) scans reveal an increased glucose metabolism in the brain of Friedreich’s ataxia patients who are still ambulatory (Gilman et al., 1990). As disease progresses and the patients lose their ability to walk, brain glucose metabolism decreases and eventually becomes subnormal (Gilman et al., 1990; Junck et al., 1994). Although not yet fully

explained, this abnormality may relate to mitochondrial dysfunction (Babcock et al., 1997).

Neurophysiological investigations Electromyographic and electroneurographic studies reveal the sensory neuronopathy, with severe reduction or loss of sensory action potentials (SAPs) (McLeod, 1971; Peyronnard et al., 1976; Ackroyd et al., 1984), whereas motor and sensory nerve conduction velocities (NCVs) remain within or just below the normal range. These findings clearly distinguish an early case of Friedreich’s ataxia from a case of demyelinating hereditary sensorimotor neuropathy, such as Charcot–Marie–Tooth disease. Loss of both peripheral and central sensory fibers results in dispersion and delay of somatosensory evoked potentials (SEPs) (Muller-Felber et al., 1993). The severity of the neurophysiological abnormalities consequent to the axonal sensory neuropathy does not correlate with disease duration, indicating that the atrophy of sensory neurons is non-progressive (Santoro et al., 1999). Conversely, central motor conduction, measured after magnetic stimulation, shows progressive slowing with increasing disease duration (Mondelli et al., 1995; Santoro et al., 1999). These findings may reflect different patterns of involvement of the somatosensory versus the motor system, the former being ‘hypoplasic’ (Chapter 25; Friedreich, 1877), the latter being actually progressively degenerating. As far as special sensory modalities are concerned, brainstem auditory evoked potentials (BAEPs), beginning from the most rostral component, wave V, progressively deteriorate in all patients (Vanasse et al., 1988; Muller-Felber et al., 1993). Visual evoked potentials (VEPs) are commonly (50–90%) reduced in amplitude with a normal P 100 latency (Kirkham and Coupland, 1981; Livingstone et al., 1981; Vanasse et al., 1988; Muller-Felber et al., 1993; Rabiah et al., 1997).

Variant phenotypes Up to 10% of patients with recessive or sporadic ataxia who do not fulfill the diagnostic criteria for Friedreich’s ataxia nevertheless have a positive molecular test for Friedreich’s ataxia (Moseley et al., 1998). No clinical finding or combination exclusively characterizes or is necessarily present in these individuals. Even neurophysiological evidence of axonal sensory neuropathy may be absent in rare patients with a proven molecular diagnosis and a very mild, lateonset disease. Overall, presence of the ‘classical’ features of Friedreich’s ataxia, including cardiomyopathy, is highly predictive of a positive test, though a few negative cases are

Friedreich’s ataxia

reported. Absence of cardiomyopathy and moderate or severe cerebellar cortical atrophy, demonstrated by MRI shortly after the onset of the clinical symptoms, appear the best predictors of a negative test (Pandolfo, 1998; Table 36.2). In general, a molecular test for Friedreich’s ataxia may be recommended in the initial work-up for all cases of sporadic or recessive degenerative ataxia, regardless of whether or not they fulfill the diagnostic criteria, unless an alternative diagnosis is strongly suggested by some clinical feature (e.g., marked cerebellar atrophy, oculomotor apraxia). More complex investigations of metabolic defects, such as those listed above, are better postponed after a negative Friedreich’s ataxia test result. Specific variant phenotypes due to the same genetic mutation that causes typical Friedreich’s ataxia (GAA repeat expansion) include LOFA, FARR, and Acadian ataxia. LOFA patients have onset after the age of 25 and an overall milder, slowly evolving disease with fewer skeletal abnormalities. The frequency of cardiomyopathy in LOFA was found to be similar to that of typical Friedreich’s ataxia in some studies (De Michele et al., 1994; Montermini et al., 1997c), lower in others (Maione et al., 1997). FARR patients have retained deep tendon reflexes in the lower limbs after the onset of neurological symptoms. They also tend to be mild cases with later onset and a slower course than typical Friedreich’s ataxia patients (Palau et al., 1997; Montermini et al., 1997c). Acadian ataxia is found among the descendants of French colonizers who settled in eastern Canada during the seventeenth century and were expelled by the British in the eighteenth century. Many moved to Louisiana, where they became known as ‘Cajuns’ (a corruption of Acadians); some later returned to the Canadian Atlantic provinces. The disease was introduced into this population by very few individuals, possibly a single couple, a so-called ‘founder effect.’ Acadian ataxia is milder and evolves more slowly than typical Friedreich’s ataxia, with less severe cardiomyopathy (Barbeau et al., 1984; Montermini et al., 1997c).

Prognosis and treatment Loss of gait occurs in almost all cases of Friedreich’s ataxia. On average, patients need a wheelchair 15 years after onset, but variability is very large (Harding, 1981; De Michele et al., 1996a). Early onset and left ventricular hypertrophy appear to be predictors of a faster rate of progression of the disease (De Michele et al., 1996b; Montermini et al., 1997c). The burden of neurological impairment, cardiomyopathy, and, when present, diabetes, shortens life expectancy (De Michele et al., 1996b). Accordingly, survival may be significantly prolonged by

Table 36.2 Clinical signs and symptoms in a series of patients with recessive or sporadic degenerative ataxia, no detectable metabolic abnormality, and either a positive (GAA positive) or a negative (GAA negative) molecular test for Friedreich’s ataxia

Signs and symptoms Ataxia Deep sensory loss in lower limbs Dysarthria Cardiomyopathy Lower limb areflexia Abnormal eye movements Upper limb areflexia Babinski Scoliosis Pes cavus Weakness of lower limbs Distal amyotrophy Decreased tone in lower limbs Carbohydrate intolerance Optic atrophy Cerebellar atrophy on MRI Increased tone in lower limbs Hearing loss Mental retardation

GAA positive (%)

GAA negative (%)

p

100 89

100 67

n.s. 0.06

83 79 75 75 72 62 68 58 46 26 22 18 13 11 7 6 0

65 5 36 70 27 63 11 17 40 13 0 7 0 67 25 0 27

n.s. 104 0.003 n.s. 0.001 n.s. 0.0002 0.01 n.s. n.s. n.s. n.s. n.s. 0.03 n.s. n.s. 0.001

Notes: Signs and symptoms found with a significantly different frequency in the two groups are in bold.

adequate treatment of cardiac symptoms, particularly arrhythmias, by antidiabetic treatment, and by preventing and controlling complications resulting from prolonged disability. Carefully assisted patients may live much longer that the 30–40 years previously indicated as the life expectancy of Friedreich’s ataxia patients. There are currently no treatments that affect the degenerative process, but new knowledge derived from the characterization of the Friedreich’s ataxia gene product may be changing this situation. Attempts at symptomatic treatment have been made with drugs affecting neurotransmitters involved in the cerebellar circuitry. Tested compounds include cholinergic agonists, such as physostigmine (Kark et al., 1981) and choline, neuropeptides, such as thyrotropin releasing hormone (Le Witt and Ehrenkranz, 1982; Filla et al., 1989), serotoninergic agonists, such as 5-OH tryptophan (Wessel et al., 1995; Trouillas et al., 1995) and buspirone, and the

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dopaminergic drug amantadine (Peterson et al., 1988; Filla et al., 1993; Botez et al., 1996). Overall, despite some positive reports, results have not been encouraging. Rehabilitation programs should include exercises aimed at maximizing the residual capacity of motor control. Orthopedic interventions are sometimes necessary, including surgical correction of severe scoliosis and, in patients who can still walk, of foot deformity.

Molecular genetics The Friedreich’s ataxia gene The Friedreich’s ataxia gene (FRDA, according to the Human Genome Organization nomenclature) is localized on the long arm of chromosome 9 (Chamberlain et al., 1988; Fujita et al., 1989), just below the pericentromeric heterochromatic region. Its seven exons are spread over 95 kb of genomic DNA. Transcription is in the centromere to telomere direction. The most abundant, and probably only functionally relevant, transcript contains the first five exons, 1–5a, with a size of 1.3 kb. Rare isoforms contain exon 5b instead of 5a, followed or not by the non-coding exon 6. The first exon harbors an unmethylated CpG island, containing several rare restriction sites, which is a common finding at the 5 end of many genes. The open reading frame begins within exon 1 and terminates in exon 5a (or 5b). The encoded protein, predicted to contain 210 amino acids, is called frataxin (Campuzano et al., 1996). The gene is transcribed in every cell type, but its level of expression varies widely in different tissues and during development (Campuzano et al., 1996; Jiralerspong et al., 1997; Koutnikova et al., 1997). Frataxin mRNA is most abundant in adult human heart and spinal cord, followed by liver, skeletal muscle, and pancreas. Northern blot and RNA in-situ hybridization analyses of mouse embryos (Jiralerspong et al., 1997; Koutnikova et al., 1997) revealed expression starting at embryonic day 10.5 (E10.5) in the neuroepithelium, reaching its highest level at E14.5 and into the postnatal period. Maximum expression was observed in the spinal cord, particularly at the thoracolumbar level, and in the dorsal root ganglia. Significant levels of transcript could also be detected in the proliferating neural cells in the periventricular zone, in the cortical plates, in the ganglionic eminence, in the heart, in the axial skeleton, and in some epithelial and mesenchymal tissues. In the adult brain, the level of frataxin mRNA is reduced and mostly confined to the ependyma, but remains high in the spinal cord and dorsal root ganglia (Koutnikova et al., 1997). Interestingly, protein levels (estimated by Western

blot analysis) remain high in the adult brain and cerebellum (Campuzano et al., 1997; L. Montermini and M. Pandolfo, unpublished observation).

The GAA triplet repeat expansion The most common mutation causing Friedreich’s ataxia (98%) is the hyperexpansion of a GAA triplet repeat within an Alu sequence in the first intron of the frataxin gene (Campuzano et al., 1996). Repeats on normal chromosomes contain less than about 40 GAA triplets, diseaseassociated repeats contain from approximately 70 to more than 1000 triplets, most commonly 600–900. Expanded repeats show meiotic (Pianese et al., 1997; Montermini et al., 1997a; Cossée et al., 1997b) and mitotic (Montermini et al., 1997a) instability. The GAA expansion changes in size in parent–child transmission, to affected as well as to carrier offspring. Paternal transmission is most often accompanied by a contraction of the repeat. Accordingly, in male carriers smaller repeats are found in sperm than in leukocytes (Pianese et al., 1997). Maternal transmission may result in further expansion or in contraction, with about equal probability (Pianese et al., 1997; Monros et al., 1997). Somatic mosaicism for expansion sizes, resulting from mitotic instability, has been observed in leukocytes, fibroblasts, and brain of Friedreich’s ataxia patients (Montermini et al., 1997b, 1997c). The Friedreich’s ataxia-associated GAA repeat expansion is probably the most common disease-causing triplet repeat expansion, as it was found in 1 in 90 chromosomes in a French population sample (Cossée et al., 1997b). In normal chromosomes, two classes of alleles of the GAA repeat can be distinguished. Short normal (SN) alleles contain 6–10 GAA triplets and account for 83% of chromosomes in Caucasians; long normal (LN) alleles contain more than 12 triplets and account for 17% of chromosomes in Caucasians (Montermini et al., 1997a; Cossée et al., 1997b). LN alleles constitute a reservoir of ‘at-risk’ alleles that may eventually expand into the disease range. Such an origin for expansions was indicated by linkage disequilibrium analysis (Cossée et al., 1997b), which revealed the same marker haplotypes on chromosomes containing LN alleles and expanded repeats, as well as by the direct observation of catastrophic expansions of LN alleles to hundreds of triplets in a single generation (Montermini et al., 1997a; Cossée et al., 1997b). A few LN alleles are interrupted by a hexanucleotide repeat (GAGGAA), which probably has a stabilizing role (Montermini et al., 1997a; Cossée et al., 1997b). The GAA triplet repeat expansion that causes Friedreich’s ataxia is only found in individuals of European,

Friedreich’s ataxia

North African, Middle Eastern, or Indian origin (IndoEuropean and Afro-Asiatic speakers). LN alleles are found in these populations as well as in subSaharan Africans. Analysis of closely linked markers suggests that expansions arose through a unique two-step process, the first leading to the appearance of LN alleles in Africa, the second to larger LN alleles and expansions in ancestors of IndoEuropean and Afro-Asiatic speakers. A major implication of these findings is that Friedreich’s ataxia may not exist among subSaharan Africans, Amerindians, and people from China, Japan, and south-east Asia (Labuda et al., 2000). The expanded GAA repeat inhibits the expression of the frataxin gene. Severely reduced levels of frataxin mRNA and protein have been demonstrated in tissue samples and cultured cells from Friedreich’s ataxia patients. The reduction is proportional to the size of the expanded GAA repeats, particularly of the smaller one (Cossée et al., 1997a; Campuzano et al., 1997). The mechanism causing reduced gene expression is probably inhibition of transcription mediated by an unusual DNA structure adopted by the expanded repeat. GAA repeats containing up to 270 triplets cloned into plasmids and transfected into mammalian cells have been shown to inhibit transcription in a length-dependent and orientation-dependent manner, i.e., long repeats that transcribe rGAA cause the strongest inhibition (Ohshima et al., 1998). A GAA triplet repeat is a long DNA segment containing only purines (R) on one strand and pyrimidines (Y) on the complementary strand. Such R•Y sequences are known to form triple helical structures. Lengths of GAA triplet repeats such as those associated with Friedreich’s ataxia have been shown to form triple helical structures in physiological conditions and to associate in bimolecular complexes (sticky DNA) (Sakamoto et al., 1999). Triplexes are known to block transcription (Duval-Valentin et al., 1992), providing a mechanism for inhibited gene expression in Friedreich’s ataxia.

Correlation between GAA expansions and phenotype As expected following the experimental finding that smaller expansions allow a higher residual gene expression (Cossée et al., 1997a; Campuzano et al., 1997; Ohshima et al., 1998), expansion sizes have an influence on the severity of the phenotype. Several studies (Filla et al., 1996; Dürr et al., 1996; Montermini et al., 1997c; Monros et al., 1997; Lamont et al., 1997; Schols et al., 1997) have shown a direct correlation between the size of GAA repeats and earlier age of onset; earlier age when confined in a wheelchair, more rapid rate of disease progression, and presence of non-

obligatory disease manifestations indicative of more widespread degeneration. However, differences in GAA expansions account for only about 50% of the variability in age of onset. Other factors that influence the phenotype may include somatic mosaicism for expansion sizes, variations in the frataxin gene itself, modifier genes, and environmental factors.

Point mutations in the frataxin gene About 2% of the Friedreich’s ataxia chromosomes have a normal GAA repeat but carry missense, nonsense, or splice site mutations ultimately affecting the frataxin coding sequence (Campuzano et al., 1996; Cossée et al., 1997a; Bidichandani et al., 1997). All affected individuals with a point mutation so far identified are heterozygous for an expanded GAA repeat on the other homolog of chromosome 9. Homozygotes for point mutations may not be found just because point mutations are rare, but it is possible that homozygosity for frataxin point mutations would cause a very severe or lethal phenotype. Frataxin knockout mice and mice homozygous for a frataxin missense mutation die during embryonic development (Cossée et al., 2000; P. Ioannou, personal communication). Mutations have frequently been found to affect the initiation ATG codon in exon 1, where changes involving each of the nucleotides were identified. A stretch of four Cs near the end of exon 1 is another hot spot for mutations, with insertions or deletions detected in several unrelated families (Cossée et al., 1999). Missense mutations have so far been identified only in the C-terminal portion of the protein corresponding to the mature intramitochondrial form of frataxin (see below). Nonsense and most missense mutations result in a complete loss of function, determining a typical Friedreich’s ataxia phenotype. A few missense mutations are associated with milder atypical phenotypes with slow progression, suggesting that the mutated proteins preserve some residual function. Patients carrying the G130V mutation have early onset but slow progression, no dysarthria, mild limb ataxia, and retained reflexes (Bidichandani et al., 1997; Cossée et al., 1999). A similar phenotype occurs in individuals with the mutations D122Y (Cossée et al., 1999) and R165P (De Michele et al., 2000). For unclear reasons, optic atrophy is more frequent in patients with point mutations of any kind (50%) (Cossée et al., 1999).

The function of frataxin and pathogenesis Frataxin does not resemble any protein of known function. It is highly conserved during evolution (Campuzano et al.,

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1996), with homologs in mammals, invertebrates, yeast, and plants.

Subcellular localization Frataxin is targeted to the mitochondria, as determined by the intracellular localization of frataxin–green fluorescent protein (GFP) fusion proteins (Babcock et al., 1997; Campuzano et al., 1997). The mitochondrial localization of endogenous frataxin was then demonstrated by immunocytofluorescence, Western blot analysis of cellular fractions obtained by differential centrifugation, and immunoelectron microscopy (EM). Frataxin has an N-terminal mitochondrial targeting sequence, which is proteolytically removed after the protein is imported into mitochondria. First, the mitochondrial processing peptidase (MPP) removes the first 40 amino acids (Koutnikova et al., 1998), then about 20 more amino acids are removed in a second proteolytic step, also carried out by MPP (Branda et al., 1999).The yeast homologous gene, YFH1, also encodes a mitochondrial protein (Babcock et al., 1997). In yeast, the second proteolytic step that generates the mature intramitochondrial form of frataxin may be promoted by a specific mitochondrial heatshock protein of the hsp70 class, ssq1p. Yeast mutants with a defect of ssq1p process frataxin slowly and accumulate iron in mitochondria as frataxin knock-out mutants do (see below; Knight et al., 1998).

Knock-out of the yeast frataxin homolog A YFH1 knock-out yeast strain, YFH1 (yfh1:: HIS3), loses the ability to carry out oxidative phosphorylation, forming petite colonies with defects or loss of mitochondrial DNA that cannot grow on non-fermentable substrates (Babcock et al., 1997; Wilson and Roof, 1997). YFH1 accumulates iron in mitochondria (more than ten-fold in excess of wildtype yeast) at the expense of cytosolic iron. Loss of respiratory competence requires the presence of iron and occurs more rapidly as iron concentration in the medium is increased. Iron in mitochondria amplifies the toxicity of reactive oxygen species leaking from the respiratory chain, where electrons from reduced ubiquinone (or probably its semiquinone form) may directly reduce molecular oxygen to superoxide (O2). Mitochondrial manganesedependent superoxide dismutase (SOD2) usually takes care of O2, generating H2O2, which in turn, in a reaction catalyzed by glutathione peroxidase, reacts with reduced glutathione (GSH), generating oxidized glutathione (GSSG) and H2O (Harding, 1981). Iron may intervene in this process and be engaged in a cycle with O2 and H2O2 as follows:

Fe(III) O2 2H → Fe(II) H2O2 Fe(II) H2O2 → Fe(III) OH• OH (Fenton reaction) Whether the free hydroxyl radical (OH•) or the similarly reactive ferryl radical is produced by the Fenton reaction, as some authors suggest (Linseman et al., 1993), the result is lipid peroxidation, protein and nucleic acid damage. Occurrence of the Fenton reaction in YFH1 yeast cells is suggested by their highly enhanced sensitivity to H2O2 (Babcock et al., 1997). Several mitochondrial enzymes are impaired in YFH1 yeast cells, including respiratory chain complexes I, II, and III, and aconitase (Rötig et al., 1997). These enzymes have in common that they contain iron–sulfur (Fe–S) clusters in their active sites. Fe-S proteins are remarkably sensitive to free radicals (Gardner et al., 1995). Whether Fe–S clusters are damaged by free radicals or lack of yfh1p affects their synthesis is not known. Heme synthesis takes place in mitochondria, where the enzyme ferrochelatase inserts iron into the protoporphyrin IX ring. Interestingly, heme synthesis is normal in YFH1 yeast, suggesting that the transport of iron into mitochondria, its utilization by ferrochelatase, and the transport of heme out of mitochondria are not affected by frataxin deficiency. A model scheme is shown in Fig. 36.1. Disruption of frataxin causes a general dysregulation of iron metabolism in yeast cells. The reason for mitochondrial iron accumulation in YFH1 cells may in principle involve increased iron uptake, altered utilization or decreased export from these organelles. Experiments involving induction of frataxin expression from a plasmid transformed into YFH1 yeast cells indicate that the protein stimulates a flux of non-heme iron out of mitochondria (Radisky et al., 1999), but this can again be compatible with different functional roles for frataxin. As iron is trapped in the mitochondrial fraction, cytosolic iron decreases, resulting in a marked induction (10-fold to 50fold) of the high-affinity iron transport system, consisting of a ferroxidase (Fet3p) and permease (Ftr1p) normally not expressed in yeast cells that are iron replete (Babcock et al., 1997). As a consequence, iron crosses the plasma membrane in large amounts and further accumulates in mitochondria, engaging the cell in a vicious cycle.

Biochemical and structural studies The yeast frataxin homolog yfh1p (the protein product of the YFH1 gene) may be an iron-binding protein (Isaya et al., 1999). Monomers of yfh1p are not capable of binding iron, but experiments using gel filtration and analytical ultracentrifugation have shown that a high molecular

Friedreich’s ataxia

weight yfh1p–iron complex forms when ferrous iron is added to the protein at a 40 :1 molar ratio. Small amounts of intermediates containing two, three, or more molecules of yfh1p complexed with iron form at lower iron: protein ratios. The high molecular weight complex is estimated to contain about 60 molecules of frataxin and 4000 atoms of iron. Western blot analysis of gel filtration fractions of yeast extracts suggests that high molecular weight complexes containing yfh1p may exist in-vivo. These data may suggest a role for yfh1p in protecting iron in mitochondria from contacts with free radicals. Because iron in the complexes seems to be readily accessible to chelators, so probably bioavailable, yfh1p could be a sort of mitochondrial iron chaperone, in the absence of which several biosynthesis and transport processes are impaired while iron accumulates in a toxic, redox-active form. The structure of frataxin is the object of intensive analysis. Preliminary data indicate that mature frataxin is a globular protein containing an N-terminal  helix, a middle  sheet region, and a C-terminal  helix. Hydrophobic amino acids are buried inside the structure, with several charged residues on the surface. It is to be hoped that a correlation between structural data and biochemical findings will soon be available.

Hypotheses for the pathogenesis of the human disease Normal human frataxin is able to complement the defect in YFH1 cells, whereas human frataxin carrying a point mutation found in Friedreich’s ataxia patients is unable to complement it (Wilson and Roof, 1997). These findings strongly suggest that the function of yfh1p is conserved in human frataxin. Involvement of iron in Friedreich’s ataxia was previously suggested by the finding of deposits of this metal in myocardial cells from Friedreich’s ataxia patients (Lamarche et al., 1980). Iron accumulation has been demonstrated by MRI in the dentate nucleus, a severely affected structure in the central nervous system (Waldvogel et al., 1999). Atomic absorption spectroscopy analysis of pathological samples from three Friedreich’s ataxia patients also showed increased iron in the dentate nucleus (J. Kaplan and M. Pandolfo, unpublished data). Very importantly, mitochondrial iron concentrations were found to be moderately but significantly increased in Friedreich’s ataxia fibroblasts (Delatycki et al., 1999) and in a single sample of mitochondria from a Friedreich heart (unpublished data). A hint of a possible role of free radicals came from the observation that vitamin E deficiency produces a phenotype resembling that of Friedreich’s ataxia (Ben Hamida

et al., 1993). Vitamin E localizes in mitochondrial membranes where it acts as a free-radical scavenger (Di Mascio et al., 1991). Friedreich’s ataxia fibroblasts are sensitive to low doses of H2O2, that induce cell shrinkage, nuclear condensation, and apoptotic cell death at lower doses than in control fibroblasts (Wong et al., 1999; unpublished observations). This finding suggests that even non-affected cells are in an ‘at-risk’ status for oxidative stress as a consequence of the primary genetic defect. Mitochondrial dysfunction has been proven to occur invivo in Friedreich’s ataxia patients. Magnetic resonance spectroscopy analysis of skeletal muscle shows a reduced rate of adenosine triphosphate (ATP) synthesis after exercise, which is inversely correlated to GAA expansion sizes (Lodi et al., 1999). In addition, Rötig et al. demonstrated the same multiple enzyme dysfunctions found in YFH1 yeast (deficit of respiratory complexes I, II, and III, and of aconitase) in endomyocardial biopsies from two Friedreich’s ataxia patients (Rötig et al., 1997). A general abnormality of iron metabolism may also be occurring in Friedreich’s ataxia patients, as suggested by the high level of circulating transferrin receptor (Wilson et al., 2000). As YFH1 yeast increases iron uptake because of low cytosolic iron, a similar process may occur in human patients. In higher eukaryotes, cytosolic iron is sensed by two iron-responsive element-binding proteins (IRP-1 and IRP-2), which regulate the expression of several genes at the post-transcriptional level. When activated by low iron, they bind to specific sequence elements (iron-responsive elements, IREs) present in some mRNAs, stabilizing those encoding proteins that enhance iron uptake, such as the transferrin receptor (TfR), while blocking the translation of those encoding proteins that utilize or store iron, such as ferritin (Hentze and Kühn, 1996). IRP-1 is a cytosolic aconitase containing an Fe-S cluster. It is activated in response not only to low cytosolic iron, but also to oxidative radicals and to signaling molecules such as nitric oxide and carbon monoxide (Hentze and Kühn, 1996). If the loss of aconitase activity observed by Rötig et al. (1997) involves the cytosolic enzyme, it might result in changes in the abundance of IRP1-regulated proteins (Rötig et al., 1997), including the observed increase in transferrin receptor. It should be noted that the expression of frataxin does not seem to be regulated by iron (J. Kaplan and M. Pandolfo, unpublished observation) and its mRNA does not contain an IRE.

Possible approaches for treatment Removal of excess mitochondrial iron and/or antioxidant treatment may in principle be attempted. However,

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removal of excess mitochondrial iron is problematic with the currently available drugs. Desferioxamine is effective in chelating iron in the extracellular fluid and cytosol, not directly in mitochondria. Furthermore, desferioxamine toxicity may be higher when there is no overall iron overload. Thus, chelation therapy has a number of unknowns: it is probably better tested in pilot trials involving a small number of closely monitored patients. Iron depletion by phlebotomy, though less risky, presents the same uncertainties concerning possible efficacy. As far as antioxidants are concerned, these include a long list of molecules with specific mechanisms of action and pharmacokinetic properties. To have the potential to be effective in Friedreich’s ataxia, an antioxidant must protect against the damage caused by the free radicals involved in this disease, in particular OH•, act in the mitochondrial compartment, and be able to cross the blood–brain barrier. At this time, coenzyme Q derivatives, like their short chain analog idebenone, appear to be interesting molecules and are the object of pilot studies (Rustin et al., 1999) However, there is a basic reason to think that neither approach has the potential to cure the disease. Mitochondrial iron accumulation and oxidative stress are downstream consequences of frataxin deficiency. The early embryonic lethality caused by knocking out the mouse frataxin gene further suggests that this protein has a still undetermined function that may go beyond protection from reactive oxygen species damage. Frataxin deficiency may directly affect some specific mitochondrial process independently of oxidative stress. New knowledge in this regard may suggest new pharmacological options to treat the disease. Gene replacement, protein replacement, or reactivation of the expression of endogenous frataxin could in principle be cures. All patients so far identified have at least a normal copy of the coding sequence of the frataxin gene, most have two, so no immune response is expected to complicate these treatments. However, many years of research are likely to be needed before any of these approaches becomes reality. In general, treatment should be started as early as possible, ideally before any symptom has developed. Although there is evidence that sensory nerve damage is established very early, possibly during development, patients start to show symptoms when motor and cerebellar dysfunctions develop. So, treating the progressive component of the disease should suffice to restore acceptable neurological function. Furthermore, heart disease and diabetes are also progressive and of later onset, and therefore potentially treatable and even preventable. Recent progress in Friedreich’s ataxia research has been

substantial. Progress in understanding this disease may represent an example of how molecular genetic studies aimed at the identification of a disease gene eventually result both in increased knowledge about basic cellular processes and in improvements in patient care.

Acknowledgments Work in the author’s laboratory was supported by grants from the Medical Research Council of Canada, the National Institute of Neurological Diseases and Stroke (NINDS), and the Muscular Dystrophy Association (MDA), USA.

xReferencesx Ackroyd, R.S., Finnegan, J.A. and Green, S.H. (1984). Friedreich ataxia. A clinical review with neurophysiological and echocardiographic findings. Arch Dis Child 59: 217–21. Alboliras, E.T., Shub, C., Gomez, M.R. et al. (1986). Spectrum of cardiac involvement in Friedreich ataxia: clinical, electrocardiographic and echocardiographic observations. Am J Cardiol 58: 518–24. Babcock, M., de Silva, D., Oaks, R. et al. (1997). Regulation of mitochondrial iron accumulation by Yfh1, a putative homolog of frataxin. Science 276: 1709–12. Barbeau, A., Roy, M., Sadibelouiz, M. and Wilensky, M.A. (1984). Recessive ataxia in Acadians and ‘Cajuns’. Can J Neurol Sci 11: 526–33. Beauchamp, M., Labelle, H., Duhaime, M. and Joncas, J. (1995). Natural history of muscle weakness in Friedreich ataxia and its relation to loss of ambulation. Clin Orthop 311: 270–5. Bell, J. and Carmichael, E.A. (1939). On hereditary ataxia and spastic paraplegia. Treas Hum Inherit 4: 141–281. Ben Hamida, M., Belal, S., Sirugo, G. et al. (1993). Friedreich ataxia phenotype not linked to chromosome 9 and associated with selective autosomal recessive vitamin E deficiency in two inbred Tunisian families. Neurology 43: 2179–83. Bidichandani, S.I., Ashizawa, T. and Patel, P.I. (1997). Atypical Friedreich ataxia caused by compound heterozygosity for a novel missense mutation and the GAA triplet-repeat expansion. Am J Hum Genet 60: 1251–6. Botez, M.I., Botez-Marquard, T., Elie, R., Pedraza, O.L., Goyette, K. and Lalonde, R. (1996). Amantadine hydrochloride treatment in heredodegenerative ataxias: a double blind study. J Neurol Neurosurg Psychiatry 61: 259–64. Bouchard, J.P., Barbeau, A., Bouchard, R., Paquet, M. and Bouchard, R.W. (1979). A cluster of Friedreich ataxia in Rimouski, Quebec. Can J Neurol Sci 6: 205–8. Boyer, S.H., Chisholm, A.W. and McKusick, V.A. (1962). Cardiac aspects of Friedreich ataxia. Circulation 25: 493–505.

Friedreich’s ataxia

Branda, S.S., Cavadini, P., Adamec, J. et al. (1999). Yeast and human frataxin are processed to mature form in two sequential steps by the mitochondrial processing peptidase. J Biol Chem 274: 22763–9. Brousse, M. (1882). De l’ataxie héréditaire. Thesis, University of Montpellier, France. Campanella, G., Filla, A., De Falco, F., Mansi, D., Durivage, A. and Barbeau, A. (1980). Friedreich ataxia in the south of Italy: a clinical and biochemical survey of 23 patients. Can J Neurol Sci 7: 351–7. Campuzano, V., Montermini, L., Lutz, Y. et al. (1997). Frataxin is reduced in Friedreich ataxia patients and is associated with mitochondrial membranes. Hum Mol Genet 6: 1771–80. Campuzano, V., Montermini, L., Moltó, M.D. et al. (1996). Friedreich ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science 271: 1423–7. Cassandro, E., Mosca, F., Sequino, L., De Falco, F.A. and Campanella, G. (1986). Otoneurological findings in Friedreich ataxia and other inherited neuropathies. Audiology 25: 84–91. Chamberlain, S., Shaw, J., Rowland, A. et al. (1988). Mapping of mutation causing Friedreich’s ataxia to human chromosome 9. Nature 334: 248–50. Child, J.S., Perloff, J.K., Bach, P.M., Wolfe, A.D., Perlman, S. and Kark, R.A. (1986). Cardiac involvement in Friedreich ataxia: a clinical study of 75 patients. J Am Coll Cardiol 7: 1370–8. Cisneros, E. and Braun, C.M. (1995). Vocal and respiratory diadochokinesia in Friedreich ataxia. Neuropathological correlations. Rev Neurol (Paris) 151: 113–23. Cossée, M., Campuzano, V., Koutnikova, H. et al. (1997a). Frataxin fracas. Nat Genet 15: 337–8. Cossée, M., Dürr, A., Schmitt, M. et al. (1999). Frataxin point mutations and clinical presentation of compound heterozygous Friedreich ataxia patients. Ann Neurol 45: 200–6. Cossée, M., Puccio, H., Gansmuller, A. et al. (2000). Inactivation of the Friedreich ataxia mouse gene leads to early embryonic lethality without iron accumulation. Hum Mol Genet 9: 1219–26. Cossée, M., Schmitt, M., Campuzano, V. et al. (1997b). Evolution of the Friedreich ataxia trinucleotide repeat expansion: founder effect and premutations. Proc Natl Acad Sci USA 94: 7452–7. D’Angelo, A., Di Donato, S., Negri, G., Beulche, F., Uziel, G. and Boeri, R. (1980). Friedreich ataxia in northern Italy: I. Clinical, neurophysiological and in vivo biochemical studies. Can J Neurol Sci 7: 359–65. De Michele, G., Di Maio, L., Filla, A. et al. (1996a). Childhood onset of Friedreich ataxia: a clinical and genetic study of 36 cases. Neuropediatrics 27: 3–7. De Michele, G., Filla, A., Cavalcanti, F. et al. (1994). Late onset Friedreich’s disease: clinical features and mapping of mutation to the FRDA locus. J Neurol Neurosurg Psychiatry 57: 977–9. De Michele, G., Filla, A., Cavalcanti, F. et al. (2000). Atypical Friedreich ataxia phenotype associated with a novel missense mutation in the X25 gene. Neurology 54: 496–9. De Michele, G., Perrone, F., Filla, A. et al. (1996b). Age of onset, sex, and cardiomyopathy as predictors of disability and survival in Friedreich’s disease: a retrospective study on 119 patients. Neurology 47: 1260–4.

Dean, G., Chamberlain, S. and Middleton, L. (1988). Friedreich ataxia in Kathikas-Arodhes, Cyprus. Lancet 1: 587. Delatycki, M.B., Camakaris, J., Brooks, H. et al. (1999). Direct evidence that mitochondrial iron accumulation occurs in Friedreich ataxia. Ann Neurol 45: 673–5. Di Mascio, P., Murphy, M.E. and Sies, H. (1991). Antioxidant defense systems: the role of carotenoids, tocopherols, and thiols. Am J Clin Nutr 53: 194S–200S. Dürr, A., Cossée, M., Agid, Y. et al. (1996). Clinical and genetic abnormalities in patients with Friedreich ataxia. N Engl J Med 335: 1169–75. Duval-Valentin, G., Thuong, N.G. and Hélène, C. (1992). Specific inhibition of transcription by triple-helix forming oligonucleotides. Proc Natl Acad Sci USA 89: 504–8. Ell, J., Prasher, D. and Rudge, P. (1984). Neuro-otological abnormalities in Friedreich ataxia. J Neurol Neurosurg Psychiatry 47: 26–32. Fantus, I.G., Seni, M.H. and Andermann, E. (1993). Evidence for abnormal regulation of insulin receptors in Friedreich ataxia. J Clin Endocrinol Metab 76: 60–3. Filla, A., De Michele, G., Caruso, G., Marconi, R. and Campanella, G. (1990). Genetic data and natural history of Friedreich’s disease: a study of 80 Italian patients. J Neurol 237: 345–51. Filla, A., De Michele, G., Cavalcanti, F., Santorelli, F., Santoro, L. and Campanella, G. (1991). Intrafamilial phenotype variation in Friedreich’s disease: possible exceptions to diagnostic criteria. J Neurol 238: 147–50. Filla, A., De Michele, G., Cavalcanti, F. et al. (1996). The relationship between trinucleotide (GAA) repeat length and clinical features in Friedreich ataxia. Am J Hum Genet 59: 554–60. Filla, A., De Michele, G., Di Martino, L. et al. (1989). Chronic experimentation with TRH administered intramuscularly in spinocerebellar degeneration. Double-blind cross-over study in 30 subjects. Riv Neurol 59: 83–8. Filla, A., De Michele, G., Orefice, G. et al. (1993). A double-blind cross-over trial of amantadine hydrochloride in Friedreich ataxia. Can J Neurol Sci 20: 52–5. Finocchiaro, G., Baio, G., Micossi, P., Pozza, G. and Di Donato, S. (1988). Glucose metabolism alterations in Friedreich ataxia. Neurology 38: 1292–6. Friedreich, N. (1863a). Uber degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat 26: 391–419. Friedreich, N. (1863b). Über degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat 27: 1–26. Friedreich, N. (1863c). Über degenerative Atrophie der spinalen Hinterstränge. Virchows Arch Pathol Anat 26: 433–59. Friedreich, N. (1876). Über ataxie mit besonderer berücksichtigung der hereditären formen. Virchows Arch Pathol Anat 68: 145–245. Friedreich, N. (1877). Über ataxie mit besonderer berücksichtigung der hereditären formen. Virchows Arch Pathol Anat 70: 140–2. Fujita, R., Agid, Y., Trouillas, P. et al. (1989). Confirmation of linkage of Friedreich ataxia to chromosome 9 and identification of a new closely linked marker. Genomics 4: 110–11. Gardner, P.R., Rainieri, I., Epstein, L.B. and White, C.W. (1995).

515

516

M. Pandolfo

Superoxide radical and iron modulate aconitase activity in mammalian cells. J Biol Chem 270: 13399–405. Gentil, M. (1990). Dysarthria in Friedreich disease. Brain Lang 38: 438–48. Geoffroy, G., Barbeau, A., Breton, G. et al. (1976). Clinical description and roentgenologic evaluation of patients with Friedreich ataxia. Can J Neurol Sci 3: 279–86. Gilman, S., Junck, L., Markel, D.S., Koeppe, R.A. and Kluin, K.J. (1990). Cerebral glucose hypermetabolism in Friedreich ataxia detected with positron emission tomography. Ann Neurol 28: 750–7. Giroud, M., Septien, L., Pelletier, J.L., Dueret, N. and Dumas, R. (1994). Decrease in cerebellar blood flow in patients with Friedreich ataxia: A TC-HMPAO SPECT study of three cases. Neurol Res 16: 342–4. Harding, A.E. (1981). Friedreich ataxia: a clinical and genetic study of 90 families with an analysis of early diagnosis criteria and intrafamilial clustering of clinical features. Brain 104: 589–620. Harding, A.E. (1983). Classification of the hereditary ataxias and paraplegias. Lancet 1: 1151–5. Harding, A.E. (1984). The Hereditary Ataxias and Related Disorders. New York: Churchill Livingstone. Harding, A.E. and Hewer, R.L. (1983). The heart disease of Friedreich ataxia. A clinical and electrocardiographic study of 115 patients, with an analysis of serial electrocardiographic changes in 30 cases. Q J Med 208: 489–502. Harding, A.E. and Zilkha, K.J. (1981). ‘Pseudo-dominant’ inheritance in Friedreich ataxia. J Med Genet 18: 285–7. Hartman, J.M. and Booth, R.W. (1960). Friedreich ataxia: a neurocardiac disease. Am Heart J 60: 716–20. Hentze, M.W. and Kühn, L.C. (1996). Molecular control of vertebrate iron metabolism: mRNA-based regulatory circuits operated by iron, nitric oxide, and oxidative stress. Proc Natl Acad Sci USA 93: 8175–82. Isaya, G., Adamec, J., Rusnak, F. et al. (1999). Frataxin is an ironstorage protein. Am J Hum Genet 65 (Suppl.): A33 (abstract). Jiralerspong, S., Liu, Y., Montermini, L., Stifani, S. and Pandolfo, M. (1997). Frataxin shows developmentally regulated tissue-specific expression in the mouse embryo. Neurobiol Dis 4: 103–13. Junck, L., Gilman, S., Gebarski, S.S., Koeppe, R.A., Kluin, K.J. and Markel, D.S. (1994). Structural and functional brain imaging in Friedreich ataxia. Arch Neurol 51: 349–55. Kark, R.A., Budelli, M.M. and Wachsner, R. (1981). Double-blind, triple-crossover trial of low doses of oral physostigmine in inherited ataxias. Neurology 31: 288–92. Kirkham, T.H. and Coupland, S.G. (1981). An electroretinal and visual evoked potential study in Friedreich ataxia. Can J Neurol Sci 8: 289–94. Klockgether, T., Chamberlain, S., Wullner, U. et al. (1993). Lateonset Friedreich ataxia. Molecular genetics, clinical neurophysiology, and magnetic resonance imaging. Arch Neurol 50: 803–6. Knight, S.A., Sepuri, N.B., Pain, D. and Dancis, A. (1998). Mt-Hsp70 homolog, Ssc2p, required for maturation of yeast frataxin and mitochondrial iron homeostasis. J Biol Chem 273: 18389–93.

Koutnikova, H., Campuzano, V., Foury, F., Dollé, P., Cazzalini, O. and Koenig, M. (1997). Studies of human, mouse and yeast homologues indicate a mitochondrial function for frataxin. Nat Genet 16: 345–51. Koutnikova, H., Campuzano, V. and Koenig, M. (1998). Maturation of wild-type and mutated frataxin by the mitochondrial processing peptidase. Hum Mol Genet 7: 1485–9. Labuda, M., Labuda, D., Miranda, C. et al. (2000). Unique origin and specific ethnic distribution of the Friedreich ataxia GAA expansion. Neurology 54: 2322–5. Ladame, P. (1890). Friedreich’s disease. Brain 13: 467–537. Lamarche, J.B., Côté, M. and Lemieux, B. (1980). The cardiomyopathy of Friedreich ataxia morphological observations in 3 cases. Can J Neurol Sci 7: 389–96. Lamont, P.J., Davis, M.B. and Wood, N.W. (1997). Identification and sizing of the GAA trinucleotide repeat expansion of Friedreich ataxia in 56 patients – clinical and genetic correlates. Brain 120: 673–80. Le Witt, P.A. and Ehrenkranz, J.R. (1982). TRH and spinocerebellar degeneration [letter]. Lancet 2: 981. Leone, M., Brignolio, F., Rosso, M.G. et al. (1990). Friedreich ataxia: a descriptive epidemiological study in an Italian population. Clin Genet 38: 161–9. Leone, M., Rocca, W.A., Rosso, M.G., Mantel, N., Schoenberg, B.S. and Schiffer, D. (1988). Friedreich’s disease: survival analysis in an Italian population. Neurology 38: 1433–8. Linseman, K.L., Larson, P., Braughler, M. and McCall, J.M. (1993). Iron-initiated tissue oxidation: lipid peroxidation, vitamin E destruction and protein thiol oxidation. Biochem Pharmacol 45: 1477–82. Livingstone, I.R., Mastaglia, F.L., Edis, R. and Howe, J.W. (1981). Visual involvement in Friedreich ataxia and hereditary spastic ataxia. A clinical and visual evoked response study. Arch Neurol 38: 75–9. Lodi, R., Cooper, J.M., Bradley, J.L. et al. (1999). Deficit of in vivo mitochondrial ATP production in patients with Friedreich ataxia. Proc Natl Acad Sci U S A 96: 11492–5. Lopez-Arlandis, J.M., Vilchez, J.J., Palau, F. and Sevilla, T. (1995). Friedreich ataxia: an epidemiological study in Valencia, Spain, based on consanguinity analysis. Neuroepidemiology 14: 14–19. Maione, S., Giunta, A., Filla, A. et al. (1997). May age onset be relevant in the occurrence of left ventricular hypertrophy in Friedreich ataxia? Clin Cardiol 20: 141–5. Margalith, D., Dunn, H.G., Carter, J.E. and Wright, J.M. (1984). Friedreich ataxia with dysautonomia and labile hypertension. Can J Neurol Sci 11: 73–7. Mascalchi, M., Salvi, F., Piacentini, S. and Bartolozzi, C. (1994). Friedreich ataxia: MR findings involving the cervical portion of the spinal cord. Am J Roentgenol 163: 187–91. McLeod, J.G. (1971). An electrophysiological and pathological study of peripheral nerves in Friedreich ataxia. J Neurol Sci 12: 333–49. Mondelli, M., Rossi, A., Scarpini, C. and Guazzi, G.C. (1995). Motor evoked potentials by magnetic stimulation in hereditary and sporadic ataxia. Electromyogr Clin Neurophysiol 35: 415–24. Monros, E., Moltó, M.D., Martinez, F. et al. (1997). Phenotype

Friedreich’s ataxia

correlation and intergenerational dynamics of the Friedreich ataxia GAA trinucleotide repeat. Am J Hum Genet 61: 101–10. Montermini, L., Andermann, E., Richter, A. et al. (1997a). The Friedreich ataxia GAA triplet repeat: premutation and normal alleles. Hum Mol Genet 6: 1261–6. Montermini, L., Kish, S.J., Jiralerspong, S., Lamarche, J.B. and Pandolfo, M. (1997b). Somatic mosaicism for the Friedreich ataxia GAA triplet repeat expansions in the central nervous system. Neurology 49: 606–10. Montermini, L., Richter, A., Morgan, K. et al. (1997c). Phenotypic variability in Friedreich ataxia: role of the associated GAA triplet repeat expansion. Ann Neurol 41: 675–82. Morgan, R.O., Naglie, G., Horrobin, D.F. and Barbeau, A. (1979). Erythrocyte protoporphyrin levels in patients with Friedreich’s and other ataxias. Can J Neurol Sci 6: 227–32. Morvan, D., Komajda, M., Doan, L.D. et al. (1992). Cardiomyopathy in Friedreich ataxia: a Doppler-echocardiographic study. Eur Heart J 13: 1393–8. Moseley, M.L., Benzow, K.A., Schut, L.J. et al. (1998). Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families. Neurology 51: 1666–71. Muller-Felber, W., Rossmanith, T., Spes, C., Chamberlain, S., Pongratz, D. and Deufel, T. (1993). The clinical spectrum of Friedreich ataxia in German families showing linkage to the FRDA locus on chromosome 9. Clin Invest 71: 109–14. Ohshima, K., Montermini, L., Wells, R.D. and Pandolfo, M. (1998). Inhibitory effects of expanded GAA•TTC triplet repeats from intron I of the Friedreich ataxia gene on transcription and replication in vivo. J Biol Chem 273: 14588–95. Palau, F., De Michele, G., Vilchez, J.J. et al. (1997). Early-onset ataxia with cardiomyopathy and retained tendon reflexes maps to Friedreich ataxia locus on chromosome 9q. Ann Neurol 37: 359–62. Pandolfo, M. (1998). A reappraisal of the clinical features of Friedreich ataxia: which indications for a molecular test? Neurology 52 (Suppl. 2): A260. Pentland, B. and Fox, K.A. (1983). The heart in Friedreich ataxia. J Neurol Neurosurg Psychiatry 46: 1138–42. Peterson, P.L., Saad, J. and Nigro, M.A. (1988). The treatment of Friedreich ataxia with amantadine hydrochloride [see comments]. Neurology 38: 1478–80. Peyronnard, J.M., Bouchard, J.P. and Lapointe, M. (1976). Nerve conduction studies and electromyography in Friedreich ataxia. Can J Neurol Sci 3: 313–17. Pianese, L., Cavalcanti, F., De Michele, G. et al. (1997). The effect of parental gender on the GAA dynamic mutation in the FRDA gene. Am J Hum Genet 60: 463–6. Pousset, F., Kalotka, H., Durr, A. et al. (1996). Parasympathetic activity in Friedrich’s ataxia. Am J Cardiol 78: 847–50. Rabiah, P.K., Bateman, J.B., Demer, J.L. and Perlman, S. (1997). Ophthalmologic findings in patients with ataxia. Am J Ophthalmol 123: 108–17. Radisky, D.C., Babcock, M.C. and Kaplan, J. (1999). The yeast frataxin homologue mediates mitochondrial iron efflux. Evidence for a mitochondrial iron cycle. J Biol Chem 274: 4497–9. Richter, A., Poirier, J., Mercier, J. et al. (1996). Friedreich ataxia in

Acadian families from eastern Canada: clinical diversity with conserved haplotypes. Am J Med Genet 64: 594–601. Riva, A. and Bradac, G.B. (1995). Primary cerebellar and spinocerebellar ataxia an MRI study on 63 cases. J Neuroradiol 22: 71–6. Romeo, G., Menozzi, P., Ferlini, A. et al. (1983). Incidence of Friedreich ataxia in Italy estimated from consanguinous marriages. Am J Hum Genet 35: 523–9. Rötig, A., deLonlay, P., Chretien, D. et al. (1997). Frataxin gene expansion causes aconitase and mitochondrial iron-sulfur protein deficiency in Friedreich ataxia. Nat Genet 17: 215–17. Rustin, P., von Kleist-Retzow, J.C., Chantrel-Groussard, K. et al. (1999). Effect of idebenone on cardiomyopathy in Friedreich’s ataxia: a preliminary study. Lancet 354: 477–9. Sakamoto, N., Chastain, P.D., Parniewski, P. et al. (1999). Sticky DNA: self-association properties of long GAA•TTC repeats in R•R•Y triplex structures from Friedreich ataxia. Mol Cell 3: 465–75. Santoro, L., De Michele, G., Perretti, A. et al. (1999). Relation between trinucleotide GAA repeat length and sensory neuropathy in Friedreich ataxia. J Neurol Neurosurg Psychiatry 66: 93–6. Schoenle, E.J., Boltshauser, E.J., Baekkeskov, S., Landin Olsson, M., Torresani, T. and von Felten, A. (1989). Preclinical and manifest diabetes mellitus in young patients with Friedreich ataxia: no evidence of immune process behind the islet cell destruction. Diabetologia 32: 378–81. Schols, L., Amoiridis, G., Przuntek, H., Frank, G., Epplen, J.T. and Epplen, C. (1997). Friedreich ataxia. Revision of the phenotype according to molecular genetics. Brain 120: 2131–40. Skre, H. (1975). Friedreich ataxia in western Norway. Clin Genet 7: 287–98. Spieker, S., Schulz, J.B., Petersen, D., Fetter, M., Klockgether, T. and Dichgans, J. (1995). Fixation instability and oculomotor abnormalities in Friedreich ataxia. J Neurol 242: 517–21. Trouillas, P., Serratrice, G., Laplane, D. et al. (1995). Levorotatory form of 5-hydroxytryptophan in Friedreich ataxia. Results of a double-blind drug–placebo cooperative study. Arch Neurol 52: 456–60. Ulku, A., Arac, N. and Ozeren, A. (1988). Friedreich ataxia: a clinical review of 20 childhood cases. Acta Neurol Scand 77: 493–7. Vanasse, M., Garcia-Larrea, L., Neuschwander, P., Trouillas, P. and Mauguiere, F. (1988). Evoked potential studies in Friedreich ataxia and progressive early onset cerebellar ataxia. Can J Neurol Sci 15: 292–8. Waldvogel, D., van Gelderen, P. and Hallett, M. (1999). Increased iron in the dentate nucleus of patients with Friedreich ataxia. Ann Neurol 46: 123–5. Wessel, K., Hermsdorfer, J., Deger, K. et al. (1995). Double-blind crossover study with levorotatory form of hydroxytryptophan in patients with degenerative cerebellar diseases. Arch Neurol 52: 451–5. Wessel, K., Schroth, G., Diener, H.C., Muller-Forell, W. and Dichgans, J. (1989). Significance of MRI-confirmed atrophy of the cranial spinal cord in Friedreich ataxia. Eur Arch Psychiatry Neurol Sci 238: 225–30. Wilson, R.B., Lynch, D.R., Farmer, J.M. et al. (2000). Increased

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serum transferrin receptor concentrations in Friedreich ataxia. Ann Neurol 47: 659–61. Wilson, R.B., Lynch, D.R. and Fischbeck, K.H. (1998). Normal serum iron and ferritin concentrations in patients with Friedreich ataxia. Ann Neurol 44: 132–4. Wilson, R.B. and Roof, D.M. (1997). Respiratory deficiency due to loss of mitochondrial DNA in yeast lacking the frataxin homologue. Nature Genet 16: 352–7. Winter, R.M., Harding, A.E., Baraitser, M. and Bravery, M.B. (1981).

Intrafamilial correlation in Friedreich ataxia. Clin Genet 20: 419–27. Wong, A., Yang, J., Cavadini, P. et al. (1999). The Friedreich ataxia mutation confers cellular sensitivity to oxidant stress which is rescued by chelators of iron and calcium and inhibitors of apoptosis. Hum Mol Genet 8: 425–30. Wullner, U., Klockgether, T., Petersen, D., Naegele, T. and Dichgans, J. (1993). Magnetic resonance imaging in hereditary and idiopathic ataxia [see comments]. Neurology 43: 318–25.

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Early-onset inherited ataxias Giuseppe De Michele and Alessandro Filla Department of Neurological Sciences, Medical School, Federico II University, Naples, Italy

Congenital cerebellar ataxias Congenital ataxic syndromes are rare and probably underdiagnosed. Clinical presentation is often non-specific, with motor and mental retardation, sometimes associated with spasticity and microcephaly. Nystagmus and intention tremor can be observed before ataxia becomes evident. Ataxia is usually not progressive and improvement has been observed in some cases during the course of the disease. Many individuals with cerebellum agenesis never develop symptoms of cerebellar dysfunction. Inheritance is autosomal recessive in most cases, but dominant and Xlinked transmission has also been reported. Sporadic cases are often misdiagnosed as cerebral palsy. Ataxia is present in 15% of the patients with cerebral palsy and a large proportion of those with no history of perinatal asphyxia may have a genetic disorder.

Granule cell layer hypoplasia (OMIM 213200) This is an autosomal recessive, congenital cerebellar ataxia also characterized by mental deficiency and delayed motor milestones. The disorder is not progressive and long survival has been described. The cerebellum is small, with severe loss of granule cells and heterotopic Purkinje cells.

Pontocerebellar hypoplasia Two forms of autosomal recessive pontocerebellar hypoplasia have been described. Type 1 is associated with neuromuscular weakness, hypoventilation, and death during the first year of life. Type 2 (OMIM 277470) is characterized by microcephaly, severely impaired mental and motor development, chorea or dystonia, and seizures. Some patients die during childhood, but survival to adulthood is possible. In the latter form, computed tomography

(CT) scan and magnetic resonance imaging (MRI) show marked hypoplasia of the pons, the vermis, and the cerebellar hemispheres, and progressive cerebral atrophy. Autopsy of two cases revealed loss of neurons affecting the olivopontoneocerebellar structures and accounting for the macroscopic pontocerebellar hypoplasia. A cortical biopsy from another patient showed that the pathological process also involves the neocortex.

Dysequilibrium syndrome (OMIM 224050) The dysequilibrium syndrome is an autosomal recessive disorder which includes disturbed equilibrium, broadly based gait and stance, motor and mental retardation in most cases, muscular hypotonia, and increased tendon reflexes. Motor milestones are delayed and the age of unsupported walking varies from 5 to 21 years. Postnatal cataract has been described and a differential diagnosis with the Marinesco–Sjögren syndrome has to be considered. CT scan shows cerebellar atrophy.

Gillespie syndrome (OMIM 206700) Peculiar clinical and pathological features are present in Gillespie syndrome (see below) and Joubert syndrome. Inheritance of Gillespie syndrome is autosomal recessive, but apparent autosomal dominant transmission has been reported in two families. The syndrome is characterized by bilateral partial aniridia at birth, delayed developmental milestones, hypotonia with normal tendon reflexes and sensation, cerebellar ataxia, and mental retardation. The diagnosis is suggested by the presence of dilated, unreactive pupils in a hypotonic infant. In one case, MRI scan showed cerebral and cerebellar atrophy with white matter changes, suggesting a more extensive central nervous system (CNS) involvement.

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Joubert syndrome (OMIM 213300) This is an autosomal recessive condition characterized by early episodes of hyperpnea and apnea, abnormal eye movements with oculomotor apraxia, hypotonia, developmental delay with psychomotor retardation, truncal ataxia, and dysmorphic features with large head, prominent forehead, high, rounded eyebrows, epicanthal folds, upturned nose, and open mouth with protruded tongue. Retinal dystrophy, chorioretinal and optic nerve coloboma, and renal cysts may be also found. Most patients die in the first years of life. Autopsy shows complete or partial absence of the cerebellar vermis. Other abnormalities may be present, including Dandy–Walker malformation, hypoplasia of the corpus callosum, and occipital meningoencephalocele. Neuroimaging demonstrates deep posterior interpeduncular fossa, thick and elongated superior cerebellar peduncles, and hypoplastic or aplastic superior cerebellar vermis. The combination of these features characterizes a ‘molar tooth’ appearance on axial MRI. Prenatal diagnosis is now possible by ultrasound. Linkage to chromosome 9q34.3 has been shown in a few Arabian families (Saar et al., 1999).

X-linked congenital cerebellar hypoplasia X-linked congenital cerebellar hypoplasia has been described in a large family from eastern Russia. The main features are severe developmental delay, cerebellar ataxia, dysarthria, external ophthalmoplegia, and increased tendon reflexes. The course is not progressive. Neuroimaging shows marked hypoplasia of the vermis and cerebellar hemispheres. The locus has been localized to chromosome Xq23 (Illarioshkin et al., 1996).

Paine syndrome (OMIM 311400) The inheritance is also X-linked in Paine syndrome, characterized by microcephaly, severe developmental delay, myoclonic jerks, generalized seizures, optic atrophy, and spasticity. Death may occur in the first decade of life, or later. Necropsy shows hypoplasia of the cerebellum, inferior olives, and pons.

Carbohydrate-deficient glycoprotein syndrome type I (OMIM 212065) Olivopontocerebellar atrophy of neonatal onset may be due to the carbohydrate-deficient glycoprotein syndrome type I, a multisystem autosomal recessive disorder caused by mutations in the gene for phosphomannomutase-2

(type Ia) or in the gene for phosphomannose isomerase-1 (type Ib). Main clinical features are psychomotor and growth retardation, non-progressive ataxia, stroke-like episodes, demyelinating neuropathy, and hepatopathy. The disease is associated with abnormalities of multiple secretory glycoproteins which are partially deficient in sialic acid, galactose, and N-acetylglucosamine. Isoelectric focusing of transferrin shows increases in disialo and asialo fractions and decrease in the tetrasialo fraction.

Early-onset cerebellar ataxia with retained tendon reflexes Friedreich’s ataxia is the most common form of earlyonset, autosomal recessive cerebellar ataxia. The next most common form is early-onset cerebellar ataxia with retained tendon reflexes (OMIM 212895). Loss of tendon jerks was reported by Friedreich in his later paper (1876), after these reflexes were described by Erb in 1875. Ladame (1890) felt that the retained knee and ankle reflexes excluded the diagnosis of Friedreich’s ataxia. Tyrer (1975) considered that, in the presence of exaggerated reflexes, most neurologists would hesitate to diagnose Friedreich’s ataxia. Geoffroy et al. (1976) and Harding (1981a) considered lower limb areflexia to be an essential criterion for the diagnosis. After Friedreich’s report, several familial cases of earlyonset cerebellar ataxia with recessive inheritance and retained or increased knee jerks were described. Fraser’s (1880) and Nonne’s (1891) families are both included in Marie’s series (1893), which is traditionally considered the first report of hereditary spastic ataxia. Fraser (1880) described two sibs, whose ataxia started in childhood, and Nonne (1891) described three brothers with onset in the second–third decade. Additional features were optic atrophy in both and mental impairment in Nonne’s family. The autopsy of one of the two patients reported by Fraser (1880) showed a small cerebellum and normal spinal cord. The autopsy of one among the three patients reported by Nonne (1891) showed a small brain and spinal cord, with the cerebellum and brainstem disproportionately small. Hodge (1897) described three sibs with progressive cerebellar ataxia with increased tendon reflexes, developing around puberty. None was able to walk unsupported by the age of 40 years. Two had moderate wasting of the small hand muscles. Similar families were described by Sinkler (1906), Harris (1908), Söderbergh (1910), and Fickler (1911). The autopsy of one of the two patients reported by Fickler (1911) showed atrophy of the cerebellum, affecting mainly the hemispheres, and more upper than lower

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surface. Microscopy showed loss of Purkinje cells, thinning of the granular layer, atrophy of the dentate nucleus, thinned nuclei of the pons, and loss of transverse fibers. In the medulla, olives were small. No tract degeneration was observed in the spinal cord. In 1981, Harding described a personal series of 20 patients with progressive cerebellar ataxia, developing in the first two decades, associated with dysarthria, pyramidal weakness, and retained or increased knee jerks and upper limb reflexes (Harding, 1981b). Inheritance was consistent with an autosomal recessive transmission of the disease. Other important differences compared with Friedreich’s ataxia were absence of cardiomyopathy, optic atrophy, diabetes mellitus, and severe skeletal deformity. These patients also had a better prognosis and remained ambulant, on average, for more than ten years longer than Friedreich’s ataxia patients. Harding proposed the label of early-onset cerebellar ataxia with retained tendon reflexes for this entity. Early-onset cerebellar ataxia patients have been shown to be genetically and phenotypically heterogeneous (Filla et al., 1990; Klockgether et al., 1991). In a personal series of hereditary ataxias, early-onset cerebellar ataxia with retained tendon reflexes represents 9% of all patients and 18% of the patients with early onset. The ratio of early-onset cerebellar ataxia families to those with Friedreich’s ataxia is 1:4. This ratio is probably underestimated, because referral bias favors Friedreich’s ataxia. Indeed, the few epidemiological studies available in Europe give prevalence ratios ranging from 0.8–1.5 105 (Polo et al., 1991; Filla et al., 1992; Chiò et al., 1993a), which is about half that of Friedreich’s ataxia. Four out of the five studies available in the literature on early-onset cerebellar ataxia reported a high consanguinity rate (15–40%), suggesting an autosomal recessive inheritance (Harding, 1981b; Serlenga et al., 1987; Özeren et al., 1989; Filla et al., 1990; Klockgether et al., 1991). Three of them reported the segregation ratio (0.11–0.16), which was below that expected in an autosomal recessive disorder (Harding, 1981b; Filla et al., 1990; Klockgether et al., 1991). This finding together with the predominance of males in four studies (Harding, 1981b; Özeren et al., 1989; Filla et al., 1990; Klockgether et al., 1991), suggested that some forms may be X-linked, new dominant mutations, or non-genetic phenocopies. We reviewed a personal series of 43 earlyonset cerebellar ataxia patients from 38 families, and found consanguinity in 24% of marriages and a segregation ratio of 0.25, which fits with an autosomal recessive disorder. The molecular advances in recent years have improved the classification of hereditary ataxias, but have only partially solved early-onset cerebellar ataxia heterogeneity. Fourteen percent of our patients with early-onset cerebel-

lar ataxia phenotype received a molecular diagnosis of Friedreich’s ataxia. Two loci have been identified in the Finnish and French–Canadian populations, which have remained genetically isolated for many generations. Mutations causing recessive disorders, generally very rare throughout the world, are enriched in such populations. Finns originate from a limited founder population (about 2000 individuals) that settled in Finland about 20 centuries ago. An infantile-onset spinocerebellar ataxia (OMIM 271245), which comprises, besides ataxia, epilepsy, athetosis, optic atrophy, ophthalmoplegia, hearing loss, sensory neuropathy, and primary hypogonadism in females, has been mapped to a 4 cM region on 10q23.3–24.1 in a few Finnish families. French–Canadians originate from about 8000 people, who migrated from France to Quebec, mainly in the seventeenth century. In the second half of the seventeenth century, 40 families moved from Quebec City to Charlevoix county on the north shore of the St Laurence River. After about a century, the descendants established themselves in the Saguenay territory. More than 300 patients with autosomal recessive spastic ataxia of Charlevoix–Saguenay (OMIM 270550) have been described in Northeastern Quebec. This ataxia has a birth incidence of 1/1932 in the Saguenay area, giving a carrier frequency of 1/21. It is characterized by onset in childhood, ataxia, saccadic horizontal pursuit, marked spasticity, distal amyotrophy, and prominent nerve fiber layer in the optic fundi. Its locus has been localized on 13q11 and the gene has recently been cloned (Engert et al., 2000). Because the molecular genetic advances led to a definite classification for only a small percentage of these patients, the clinical category of early-onset cerebellar ataxia still remains useful.

Clinical features and laboratory findings The diagnostic criteria for early-onset cerebellar ataxia are early onset (within 25 years) progressive ataxia, retained knee jerks, and exclusion of a known etiology (metabolic or defective DNA repair), or associated features as hypogonadism and myoclonus. In our personal series, 20 patients were singletons, seven couples, and three triplets. Half of the patients presented as sporadic cases and half have an affected sib. No instance of a similar disease was found in either the parents or the offspring of the patients. Mean onset ageSD is 10.48.1 years (range 2–25 years). A major peak was evident at 1–4 years and two smaller peaks at 9–12 and 17–20 years. This finding, together with that of higher variability of onset age between families than within families, suggests genetic heterogeneity.

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Gait ataxia is usually the first symptom, but, rarely, the disease may manifest with dysarthria, intention tremor, lower limb weakness, or clumsiness. Gait and stance ataxia is constant. Gait is ataxic or ataxic–spastic. Dysarthria, which is very frequent, is usually mild to moderate and, exceptionally, leads to explosive voice. Nystagmus in lateral gaze affects threequarters of the patients. Jerky smooth pursuit is present in almost all. Saccades are usually dysmetric, with normal velocity. Gaze paralysis is absent. Dysphagia, usually for liquids, affects one-third of the patients. Knee jerks are increased in 60% of the patients, weak in 18%, and normal in the remainder. Ankle jerks are brisk in one-third, and weak or absent in another third. The association of brisk knee jerks and absent ankle jerks occurs in 11%. Lower limb tone is increased in half of the patients and decreased in one-third. Proximal weakness at the lower limbs is present in half. Plantar responses are extensor in one-third. Two-thirds of the patients have decreased vibration sense at the external malleolus. Skeletal deformity is relatively frequent. Two-thirds of the patients have scoliosis or pes cavus, which is usually mild. Urinary symptoms (the most common being urgency), non-progressive mental deficiency, and slight distal amyotrophy may occur. Very few patients present head titubation, seizures, psychosis, hypoacusia, dystonia, and perioral fasciculations. The overall clinical picture is that of a cerebellar syndrome, associated with signs of corticospinal impairment (extensor plantar response and/or brisk tendon jerks associated with increased tone) in two-thirds of the patients. Both cerebellar and corticospinal signs affect the lower limbs more severely than the upper limbs. Clinical signs of peripheral neuropathy (decreased vibration sense and decreased/absent ankle jerks) are present in one-third of the patients. No patient has diabetes or echocardiographic findings of hypertrophic cardiomyopathy. Progression is usually slow. The mean age at the time of the study is 27.89.3 years and mean disease duration is 17.49.8 years in our series. Only five patients (12%) were wheelchair bound, 8 patients (19%) needed constant support, and 30 (70%) walked independently. Klockgether et al. (1998) calculated a median time of 22 years from disease onset to wheelchair. Chiò et al. (1993b) reported a death rate four times higher in earlyonset cerebellar ataxia than in the general population, and a 77% survival rate after 20 years from onset. Neurophysiological investigations show peripheral neuropathy in half of the patients (Klockgether et al., 1991; Santoro et al., 1992). The abnormalities consist of a marked amplitude reduction of the sensory potentials with a slight

slowing of distal sensory and motor conduction. These findings are consistent with a mainly sensory axonal neuropathy. The presence of peripheral neuropathy is not related to disease duration and severity (Santoro et al., 1992). The pathological findings of sural nerve biopsy are consistent with neurophysiology and vary from normality to a marked loss of large myelinated fibers with unimodal distribution of the axon diameters (Fig. 37.1). Shortlatency, central, somatosensory-evoked potentials are abnormal after stimulation of the tibial nerve in 80% of the patients. They are more frequently abnormal than after stimulation of the median nerve, indicating a more severe impairment of the longest pathways (Klockgether et al., 1991). Brainstem auditory-evoked potentials are abnormal in about three-quarters of the patients, and central motorevoked potentials in half of them (Santoro et al., 1992). Most, but not all, patients have cerebellar atrophy, the cerebellar vermis being the most frequently and severely affected structure at MRI. Cerebellar atrophy, which is usually slight, may be severe in some instances. Among patients showing cerebellar atrophy, two-thirds have a pure cerebellar atrophy and the remainder have an associated atrophy of the brainstem and/or cervical cord (Fig. 37.2). Cortical atrophy may be rarely observed. Altogether, MRI findings are heterogeneous and a pattern of olivopontocerebellar atrophy is unusual (Wüllner et al., 1993; Ormerod et al., 1994; De Michele et al., 1995). 99mTcHMPAO single photon emission tomography (SPET) shows cerebellar hypoperfusion in two-thirds of the patients, cerebral cortical hypoperfusion (usually parietal) in half of them, and normal perfusion of the brainstem. There is no correlation between SPET and MRI findings (De Michele et al., 1998).

Differential diagnosis Most early-onset cerebellar ataxia patients have been diagnosed as suffering from atypical Friedreich’s ataxia at some stage of their illness. This is the most relevant differential diagnosis to keep in mind. Preservation of knee jerks is the clinical hallmark that separates early-onset cerebellar ataxia from typical Friedreich’s ataxia. In Friedreich’s ataxia, distal reflexes are absent at the upper limbs, whereas the tricipital and sometimes the bicipital reflexes are retained in 27% of the patients. Fixation instability, finger-to-nose dysmetria, lower limb weakness and wasting, extensor plantar response, and skeletal deformities are more frequent in Friedreich’ ataxia than in earlyonset cerebellar ataxia (Harding 1981b; Filla et al., 1990; Klockgether et al., 1991). Abnormal peripheral nerve conduction studies and somatosensory-evoked potentials are

Early-onset inherited ataxias

Fig. 37.1 Semi-thin transverse sections of the sural nerves in two patients with early-onset cerebellar ataxia with retained tendon reflexes (upper), one with Friedreich’s ataxia (lower left) and one control (lower right). Note that the loss of large myelinated fibers, which occurs in all patients, is more marked in the Friedreich’s ataxia patient, who also shows a decreased number of small fibers. Toluidine blue stain. Original magnification 360. Bar30 m. (Courtesy of Professor F. Barbieri and the Department of Neurological Sciences, Federico II University, Naples, Italy.)

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Fig. 37.2 T1-weighted brain sagittal (upper left), axial (upper right), and coronal (lower left) MR images of a 20-year-old early-onset cerebellar ataxia patient showing atrophy of the vermis, enlargement of the fourth ventricle, and normal pons. Sagittal section showing normal cervical cord (lower right).

constant in Friedreich’s ataxia, because involvement of the dorsal root ganglia is the pathological hallmark of the disease. Absent peripheral neuropathy and normal central conduction of the somatosensory pathway suggest earlyonset cerebellar ataxia. Moreover, echocardiographic signs of hypertrophic cardiomyopathy are absent in this ataxia. Severe cerebellar atrophy may be found only in early-onset cerebellar ataxia. Cervical cord atrophy at MRI, which is

very frequent in Friedreich’s ataxia, may also occur in earlyonset cerebellar ataxia. The differential diagnosis is more difficult with the Friedreich’s ataxia variants. About 10% of Friedreich’s ataxia patients have retained tendon reflexes (Palau et al., 1995; Coppola et al., 1999). The molecular test can easily differentiate early-onset cerebellar ataxia from Friedreich’s ataxia, showing in the latter the GAA expansion in homozygous or heterozygous state.

Early-onset inherited ataxias

Progressive metabolic ataxias are rare. They are usually transmitted in an autosomal, recessive fashion, may present with early-onset cerebellar ataxia phenotype, and should be considered in differential diagnosis. Patients with ataxia and isolated vitamin E deficiency (OMIM 277460) may retain lower limb reflexes. Head titubation, cardiomyopathy, and dystonia point to the diagnosis of ataxia and isolated vitamin E deficiency. Peripheral nerve conduction studies may be normal. Somatosensoryevoked potentials show normal peripheral and delayed central conduction. Serum vitamin E levels are markedly reduced in all patients and represent the diagnostic test. The disease is caused by mutations in the alphatocopherol transfer protein gene. In Niemann–Pick type C (OMIM 257220), also called DAF (down gaze paralysis, ataxia, foam cell) syndrome, the onset age varies from 6 months to 18 years and the clinical picture comprises ataxia, mental impairment, supranuclear vertical gaze paralysis, dystonia, seizures, pyramidal signs, organomegaly, and pulmonary involvement. Lipid-laden macrophages (foam cells) are present in the bone marrow aspiration and liver biopsy specimen. Sphyngomyelinase is not deficient, but impaired esterification of exogenous cholesterol is present in cultured fibroblasts. The disease is genetically heterogeneous. Mutations in the NPC1 gene, which is a member of a family of genes encoding membrane-bound proteins containing putative sterol-sensing domain, are found in 95% of the patients. Onset occurs by the age of ten years in most patients with Krabbe disease (OMIM 245200), rarely later. Mental retardation, psychomotor deterioration, impaired vision, progressive spasticity, ataxia, and a demyelinating peripheral neuropathy may be present. Most patients show rapid deterioration initially, followed by a more gradual progression lasting for years. Assays for galactosylceramidase (galactocerebroside -galactosidase) in peripheral leukocytes or cultured fibroblasts offer the most reliable tool for the diagnosis. The most frequent mutation appears to be a large deletion of exons 11–17 associated with a C-to-T transition at position 502 of the coding sequence of the GALC gene. A few patients, mainly of Jewish descent, have been described with hexosaminidase A deficiency (OMIM 272800) and early-onset cerebellar ataxia, followed by development of upper and lower motor neuron signs. Dementia, psychosis, and ophthalmoplegia are also present. Lamellar cytoplasmic inclusions are found in rectal biopsy specimens. Loss of serum and leukocyte enzyme activities varies from partial to complete. Elevated levels of serum lactate dehydrogenase are present in several patients and may point to the diagnosis. The most

frequent mutation in the Askenazi Jewish population is a 4bp insertion in exon 11 of the HEXA gene in 79% of the pathological alleles. Onset age ranges from adolescence to the fifth decade, with clusters around the age of 30 in the adult variety of neuronal ceroid lipofuscinosis (Kufs’ disease; OMIM 204300). The clinical manifestation includes psychiatric, cognitive, extrapyramidal, and cerebellar features, myoclonus, and seizures. Two main clinical presentations have been defined, one characterized by progressive myoclonic epilepsy and the other by dementia and orofacial dyskinesia. Visual problems are usually absent. Diagnosis requires the demonstration of the characteristic inclusions by electron microscopy. Fingerprint profiles or granular osmiophilic deposits are found in eccrine secretory cells, rectal biopsy, and usually in skeletal muscle. Onset is in childhood in cerebrotendinous xanthomatosis (cholestanolosis; OMIM 213700). Xanthomata, especially of the Achilles tendon, and cataracts appear early, and neurological impairment develops later. The most prominent clinical feature is spastic ataxia, associated with pseudobulbar palsy, dementia, palatal myoclonus, and peripheral neuropathy. Serum cholestanol (a metabolite of cholesterol) is increased. Lack of the sterol 27-hydroxylase can be shown in fibroblast cultures. Mutations in the CYP27 gene are responsible for the disease. Metabolic screening includes determination of urinary bile alcohol excretion and serum cholestanol level. Both are increased. Atrophy and parenchymal abnormalities can be found on brain MRI. Symmetrical lesions in the cerebellum are observed in up to 80% of the patients (Fig. 37.3). Treatment includes chenodeoxycholic acid and simvastatine. The ‘pseudosclerotic’ form of Wilson disease (OMIM 277900) presents with ataxia, dysarthria, and intention tremor. Onset usually occurs in the second decade. Signs of hepatic dysfunction, greatly reduced serum ceruloplasmin, and increased urinary copper excretion point to the diagnosis. Liver copper is greatly increased and its measurement represents the most sensitive and accurate test for the disease. Mutations occur in the ATP7B gene, encoding for a copper-transporting P-type ATPase. Spastic paraplegia complicated by cerebellar ataxia has to be considered in differential diagnosis. Autosomal recessive spastic paraplegia type 7 (OMIM 602783), whose gene, paraplegin, has been recently identified, presents as a pure form or may be associated with optic and cerebellar atrophy. X-linked spastic paraplegia type 2 (OMIM 312920), which is caused by mutations in the proteolipid protein gene, may also present as a pure form or as a complicated one with nystagmus, dysarthria, mild ataxia, mental retardation, and optic atrophy.

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A

B

Fig. 37.3 (A) T1-weighted cerebral MR image showing cerebellar low-signal lesions in a patient with cerebrotendinous xanthomatosis. (B) T2-weighted MR image showing high-signal lesions bilaterally. (Courtesy of Dr Aad Verrips.)

The possibility of X-linked recessive spinocerebellar degeneration should be raised in sibships in which only males are affected. Adrenomyeloneuropathy (OMIM 300100) presents with spastic paraplegia and distal sensory loss in affected males, but cerebellar signs may be prominent. Hypoadrenalism and MRI findings of diffuse demyelination may lead to the diagnosis, which is confirmed by measurement of very long-chain fatty acids showing elevated C 26:0 levels in plasma and fibroblasts. A single peroxisomal enzyme defect of an ATP-binding cassette transporter reduces the capacity to form the coenzyme derivatives of very long-chain fatty acids. Mutation analysis has revealed that a deletion of 2 bp in exon 5 of the ALD gene is responsible for 20% of the cases. Some autosomal dominant ataxic syndromes may present in the first two decades of life. Patients with autosomal dominant cerebellar ataxia with macular degeneration (SCA7; OMIM 164500) often develop symptoms in their teens and occasionally earlier, in rare instances before their affected parents, simulating a sporadic occurrence. Ataxia is a common feature in mitochondrial disorders. Kearns–Sayre syndrome (OMIM 530000) is a form of sporadic, chronic, progressive ophthalmoplegia that begins before the age of 20 years; it is characterized by pigmentary retinopathy, elevated levels of cerebrospinal fluid protein, ataxia, and heart block. Almost all patients have large, single deletions in mitochondrial DNA. Myoclonic

epilepsy with ragged-red fibers (OMIM 545000) is characterized by action myoclonus, myoclonic epilepsy, cerebellar ataxia, weakness, and short stature. Dementia and hearing loss may be present. Onset varies from the first to the fifth decade. Maternal inheritance may be evident. Plasma pyruvate, lactate, alanine, and creatine phosphokinase are increased and muscle biopsy shows accumulation of abnormal subsarcolemmal and intermyofibrillar mitochondria (ragged-red fibers). Pathogenic point mutations have been shown in the lysine tRNA gene of the mitochondrial DNA, resulting in defective translation of all mtDNA-encoded genes. Neuropathy, ataxia, and retinitis pigmentosa (OMIM 551500) is a maternally inherited, multisystem disorder characterized by developmental delay, retinitis pigmentosa, dementia, seizures, ataxia, and sensory neuropathy. It is associated with a point mutation in the ATPase 6 gene of mtDNA. Diseases other than hereditary ataxias can mimic earlyonset cerebellar ataxia phenotype. MRI is useful in demonstrating platybasia and basilar impression, conditions in which spastic quadriparesis and cerebellar signs may occur, and in diagnosing ataxic paraparesis caused by progressive multiple sclerosis. The detection of antigliadin and antiendomysial antibodies points to a diagnosis of gluten sensitivity, which may cause a progressive and treatable cerebellar syndrome (Hadjivassiliou et al., 1998; Pellecchia et al., 1999). Gastrointestinal symptoms and signs of malabsorption are usually absent. The duodenal biopsy

Early-onset inherited ataxias

Fig. 37.4 Cerebellar autopsy specimen from a 70-year-old male with gluten ataxia showing perivascular cuffing with lymphocytes. (Courtesy of Dr M. Hadjivassiliou.)

changes in keeping with the diagnosis of celiac disease are not always present. Ninety percent of patients have HLA DQ2 genotype. The available post-mortem studies show lymphocytic infiltration of the cerebellum (Fig. 37.4) and of the posterior columns.

Cerebellar ataxia with hypogonadism The association of cerebellar ataxia and hypogonadism (OMIM 212840) was first reported in 1907 by Holmes, who described a family in which three brothers and one sister developed progressive ataxia in the fourth decade. The three brothers also had hypogonadism. The post-mortem examination of a case showed a very small cerebellum, with atrophy greatest in the superior part of the vermis and hemispheres and atrophy of the inferior olives. Inheritance appeared to be autosomal recessive. Since then, there has been a tendency to apply the label of ‘Holmes’ type’ of cere-

bello-olivary degeneration to dominant ataxias in the absence of genital abnormalities, only because of similar pathological findings at autopsy. The onset age and clinical picture are extremely variable. Both hypergonadotrophic and hypogonadotrophic hypogonadism have been reported. Hypogonadotrophic hypogonadism may arise from either hypothalamic or pituitary dysfunction. We observed five unrelated patients with cerebellar ataxia and hypogonadism. Onset ranged from the first to the third decade and, in addition to cerebellar ataxia and dysarthria, which were constant, the most frequent features were nystagmus, abnormal eye movements, dysmetria, and brisk tendon reflexes, present in four cases; and mental impairment, tremor, urinary incontinence, and skeletal deformity, present in three cases. Hypogonadism was primary in four cases and secondary to decreased secretion of gonadotrophins in one. Neuroimaging studies showed cerebellar atrophy and, in one instance, cerebral white matter abnormalities.

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Peripheral nerve studies demonstrated an axonal neuropathy in three patients. In one case a muscle biopsy showed deficiency of cytochrome c oxidase (De Michele et al., 1993). Variable onset age, neurological picture, and endocrine findings favor the hypothesis that cerebellar ataxia with hypogonadism is a heterogeneous syndrome. Boucher–Neuhäuser syndrome (OMIM 215470) is a rare autosomal recessive disorder characterized by the triad of spinocerebellar ataxia, chorioretinal dystrophy, and hypogonadotrophic hypogonadism. Ataxia begins during adolescence or early adulthood, whereas ophthalmological signs usually appear later. Mitochondrial respiratory chain complex I deficiency and a 5.5 kb mtDNA single deletion in skeletal muscle have been reported in one case (Barrientos et al., 1997). The Richards–Rundle syndrome (OMIM 245100) is characterized by autosomal recessive ataxia, hearing loss, mental deterioration, ketoaciduria, and hypergonadotrophic hypogonadism.

Cerebellar ataxia with ocular features Retinitis pigmentosa and optic atrophy are relatively nonspecific manifestations, which have been found associated with cerebellar ataxia in a number of families (Harding, 1984). Mental retardation or dementia, deafness, pyramidal signs, peripheral neuropathy, and seizures may be also present in a variable combination. Inheritance is autosomal recessive in the majority of patients. Wolfram syndrome (OMIM 222300), also known by the acronym DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness), is an autosomal recessive disorder characterized by a number of neurological symptoms, including ataxia, myoclonus, peripheral neuropathy, mental retardation, and psychiatric illnesses. A locus has been mapped to 4p16 by linkage analysis, and loss-of-function mutations of wolframin gene, which encodes for a predicted transmembrane protein, have been described. Behr’s syndrome is inherited in an autosomal recessive fashion and it is probably a heterogeneous entity. It is characterized by optic atrophy, spasticity, ataxia, and mental retardation. Optic atrophy is also a feature of infantile-onset spinocerebellar ataxia (OMIM 271245) which has been previously treated. All the above syndromes with optic atrophy are characterized by autosomal recessive inheritance. Optic atrophy has also been described in an X-linked ataxia with onset in early childhood and death usually before the age of five years (Arts et al., 1993). The clinical spectrum comprises hypotonia, areflexia, weakness, nystagmus, pale optic disk, hearing loss, and recurrent respiratory infections. Autopsy

showed no myelinated axons in the dorsal columns. A possibly similar syndrome has been previously reported by Schmidley et al. (1987). Posterior column ataxia with retinitis pigmentosa is a neurodegenerative, childhood-onset disorder with autosomal recessive transmission, visual impairment, sensory ataxia, areflexia, and proprioceptive loss. The disease locus has been assigned to chromosome 1q31–q32 (Higgins et al., 1999). Ataxia and retinitis pigmentosa are also found in metabolic diseases as abetalipoproteinemia (OMIM 200100), ataxia and isolated vitamin E deficiency (OMIM 277460), Refsum’s disease (OMIM 266500), neuropathy, ataxia and retinitis pigmentosa (OMIM 551500), and Kearns–Sayre syndrome (OMIM 530000). Ophthalmological examination in neuronal ceroid lipofuscinoses with infantile (OMIM 256730) and juvenile onset (OMIM 204200) reveals optic atrophy and retinal and macular degeneration. Marinesco–Sjögren syndrome (OMIM 248800) is an autosomal recessive disorder which comprises mental retardation, cerebellar ataxia with cerebellar atrophy, congenital cataracts, short stature, and delayed sexual development due to hypergonadotrophic hypogonadism. Most patients have elevated serum creatine kinase levels and myopathic changes at muscle biopsy. Multiple skeletal abnormalities may be found.

Cerebellar ataxia with deafness There are many reports of autosomal recessive ataxia associated with cochleovestibular degeneration, mostly associated with other anomalies (Konigsmark, 1975). Some of them are mentioned in the above section. The Lichtenstein–Knorr syndrome is characterized by progressive hearing loss, unsteady gait, and dysarthria. According to Harding, the originally described patients might have been affected by Friedreich’s ataxia. Additional features in the Berman syndrome (OMIM 208850) are mental deficiency and signs of upper and lower motor neuron involvement. Mental retardation and skin pigmentary changes are present in Jeune–Tommasi disease.

Cerebellar ataxias with parkinsonism The association of cerebellar ataxia and parkinsonism (not unusual in late-onset degenerative diseases as multiple system atrophy, Machado–Joseph disease, and prion disorders) is rare in early-onset cases. Cerebellar ataxia has been described in association with tremor and other

Early-onset inherited ataxias

parkinsonian features only in a few families, mostly from consanguineous marriages. Improvement after levodopa administration has been reported in a patient by Harding (1984). Autopsy of one case showed degeneration of basal nuclei and pyramidal tracts and loss of Purkinje cells in the cerebellum.

Acknowledgments This work has been partially supported by grants from MURST 1/CO4 Biomedicina and from Ministry of Health to A.F. The authors thank Dr G. Coppola for reviewing the clinical data of early-onset cerebellar ataxia patients.

xReferencesx Arts, W.F., Loonen, M.C., Sengers, R.C. and Slooff, J.L. (1993). Xlinked ataxia, weakness, deafness, and loss of vision in early childhood with a fatal course. Ann Neurol 33: 535–9. Barrientos, A., Casademont, J., Genís, D. et al. (1997). Sporadic heteroplasmic single 5.5 kb mitochondrial DNA deletion associated with cerebellar ataxia, hypogonadotropic hypogonadism, choroidal dystrophy, and mitochondrial respiratory chain complex I deficiency. Hum Mutat 10: 212–16. Chiò, A., Orsi, L., Mortara, P. and Schiffer, D. (1993a). Early onset cerebellar ataxia with retained tendon reflexes: prevalence and gene frequency in an Italian population. Clin Genet 43: 207–11. Chiò, A., Orsi, L., Mortara, P. and Schiffer, D. (1993b). Reduced life expectancy in 40 cases of early onset cerebellar ataxia with retained tendon reflexes: a population-based study. Acta Neurol Scand 88: 358–62. Coppola, G., De Michele, G., Cavalcanti, F. et al. (1999). Why do some Friedreich’s ataxia patients retain tendon reflexes? A clinical, neurophysiological and molecular study. J Neurol 246: 353–7. De Michele, G., Di Salle, F., Filla, A. et al. (1995). Magnetic resonance imaging in ‘typical’ and ‘late onset’ Friedreich’s disease and early onset cerebellar ataxia with retained tendon reflexes. Ital J Neurol Sci 16: 303–8. De Michele, G., Filla, A., Striano, S., Rimoldi, M. and Campanella, G. (1993). Heterogeneous findings in four cases of cerebellar ataxia associated with hypogonadism (Holmes’ type ataxia). Clin Neurol Neurosurg 95: 23–8. De Michele, G., Mainenti, P.P., Soricelli, A. et al. (1998). Single photon emission tomography in spinocerebellar degeneration. J Neurol 245: 603–8. Engert, J.C., Bérubé, P., Mercier, J. et al. (2000). ARSACS, a spastic ataxia common in northeastern Québec, is caused by mutations in a new gene encoding an 11.5-kb ORF. Nat Genet 24: 120–5. Erb, W.H. (1875). Über Sehnenreflexe bei gesunden und bei

Rückenmarkskranken. Arch Psychiatrie Nervenkrankenheiten 5: 792–802. Fickler, A. (1911). Klinische und pathologisch-anatomische Beitrëge zu den erkrankungen des Kleinhirns. Dtsch Z Nervenheilkunde 41: 306–75. Filla, A., De Michele, G., Cavalcanti, F. et al. (1990). Clinical and genetic heterogeneity in early onset cerebellar ataxia with retained tendon reflexes. J Neurol Neurosurg Psychiatry 53: 667–70. Filla, A., De Michele, G., Marconi, L. et al. (1992). Prevalence of hereditary ataxias and spastic paraplegias in Molise, a region of Italy. J Neurol 239: 351–3. Fraser, D. (1880). Defect of the cerebellum occurring in a brother and sister. Glasgow Med J 13: 199–210. Friedreich, N. (1876). Über Ataxie mit besonderer berücksichtigung der hereditären Formen. Virchows Archiv Patolog Anat Physiol 68: 145–245. Geoffroy, G., Barbeau, A., Breton, et al. (1976). Clinical description and roentgenologic evaluation of patients with Friedreich’s ataxia. Can J Neurol Sci 3: 279–86. Hadjivassiliou, M., Grünewald, R.A., Chattopadhyay, A.K. et al. (1998). Clinical, radiological, neurophysiological, and neuropathological characteristics of gluten ataxia. Lancet 352: 1582–5. Harding, A.E. (1981a). Friedreich’s ataxia: a clinical and genetic study of 90 families with an analysis of early diagnostic criteria and intrafamilial clustering of clinical features. Brain 104: 589–620. Harding, A.E. (1981b). Early onset cerebellar ataxia with retained tendon reflexes: a clinical and genetic study of a disorder distinct from Friedreich’s ataxia. J Neurol Neurosurg Psychiatry 44: 503–8. Harding, A.E. (1984). The Hereditary Ataxias and Related Disorders. Edinburgh: Churchill Livingstone. Harris, W. (1908). Two cases of cerebellar ataxy. Proc R Soc Med 1: 52–4. Higgins, J.J., Morton, D.H. and Loveless, J.M. (1999). Posterior column ataxia with retinitis pigmentosa (AXPC1) maps to chromosome 1q31–q32. Neurology 52: 146–50. Hodge, G. (1897). Three cases of Friedreich’s disease all presenting marked increase of knee jerks. Br Med J 1: 1405–6. Holmes, G. (1907). A form of familial degeneration of the cerebellum. Brain 30: 466–85. Illarioshkin, S.N., Tanaka, H., Markova, E.D., Nikolskaya, N.N., Ivanova-Smolenskaya, I.A. and Tsuji, S. (1996). X-linked non progressive congenital cerebellar hypoplasia: clinical description and mapping to chromosome Xq. Ann Neurol 40: 75–83. Klockgether, T., Lüdtke, R., Kramer, B. et al. (1998). The natural history of degenerative ataxia: a retrospective study in 466 patients. Brain 121: 589–600. Klockgether, T., Petersen, D., Grodd, W. and Dichgans, J. (1991). Early onset cerebellar ataxia with retained tendon reflexes. Clinical, electrophysiological and MRI observations in comparison with Friedreich’s ataxia. Brain 114: 1559–73. Konigsmark, B.W. (1975). Hereditary diseases of the nervous system with hearing loss. In Handbook of Clinical Neurology, Vol. 22, ed. P.J. Vinken and G.W. Bruyn, pp. 499–526. Amsterdam: North-Holland Publishing Company.

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Ladame, P. (1890). Friedreich’s disease. Brain 13: 467–537. Marie, P. (1893). Sur l’hérédoataxie cérébellouse. Semaines Méd (Paris) 13: 444–7. Nonne, M. (1891). Über eine eigenthümliche familiäre Erkrankungskfrom des Centralnervensystem. Archiv Psychiatrie Nervenkrankheiten 22: 283–316. Online Mendelian Inheritance in Man, OMIM (TM). Center for Medical Genetics, Johns Hopkins University (Baltimore, MD) and National Center for Biotechnology Information, National Library of Medicine (Bethesda, MD), 1996. World Wide Web URL: http://www3.ncbi.nlm.nih.gov/omim/ Ormerod, I.E., Harding, A.E., Miller, D.H. et al. (1994). Magnetic resonance imaging in degenerative ataxic disorders. J Neurol Neurosurg Psychiatry 57: 51–7. Özeren, A., Araç, N. and Ülkü, A. (1989). Early-onset cerebellar ataxia with retained tendon reflexes. Acta Neurol Scand 80: 593–7. Palau, F., De Michele, G., Vilchez, J.J. et al. (1995). Early onset ataxia with cardiomyopathy and retained tendon reflexes maps to the Friedreich’s ataxia locus on chromosome 9q. Ann Neurol 37: 359–62. Pellecchia, M.T., Scala, R., Filla, A., De Michele, G., Ciacci, C. and Barone, P. (1999). Idiopathic cerebellar ataxia associated with celiac disease: lack of distinctive neurological features. J Neurol Neurosurg Psychiatry 66: 32–5. Polo, G.M., Calleia, J., Combarros, O. and Berciano, J. (1991).

Hereditary ataxias and paraplegias in Cantabria, Spain. An epidemiological and clinical study. Brain 114: 855–66. Saar, K., Al-Gazali, L., Sztriha, L. et al. (1999). Homozygosity mapping in families with Joubert syndrome identifies a locus on chromosome 9q34.3 and evidence for genetic heterogeneity. Am J Hum Genet 65: 1666–71. Santoro, L., Perretti, A., Filla, A. et al. (1992). Is early onset cerebellar ataxia with retained tendon reflexes identifiable by electrophysiologic and histologic profile? A comparison with Friedreich’s ataxia. J Neurol Sci 113: 43–9. Schmidley, J.W., Levinsohn, M.W. and Manetto, V. (1987). Infantile X-linked ataxia and deafness: a new clinicopathologic entity? Neurology 37: 1344–9 Serlenga, L., Trizio, M., Pozio, G., Oteri, G. and Caldarazzo, M. (1987). Le eredoatassie recessive ad esordio precoce. Studio clinico di 27 casi. Riv Neurol 57: 285–9. Sinkler, W. (1906). Friedreich’s ataxia, with a report of thirteen cases. N Y J Med 83: 65–72. Söderbergh, G. (1910). Un cas de maladie familiale. Rev Neurol 20: 7–12. Tyrer, J.H. (1975). Friedreich’s ataxia. In Handbook of Clinical Neurology, Vol. 21, ed. P.J. Vinken and G.W. Bruyn, pp. 319–64. Amsterdam: North-Holland Publishing Company. Wüllner, U., Klockgether, T., Petersen, D., Naegele, T. and Dichgans, J. (1993). Magnetic resonance imaging in hereditary and idiopathic ataxia. Neurology 43: 318–25.

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Ataxia-telangiectasia and variants Susan Perlman1, Jacques-Olivier Bay2, Nancy Uhrhammer2, and Richard A. Gatti3 1

Department of Neurology, 3 Department of Pathology, VCLA School of Medicine, Los Angeles, California, USA 2 Centre Jean Perrin, Department d’Oncologie Moléculaire, Clermont-Ferrand, France

Introduction Ataxia-telangiectasia (A-T) is an autosomal recessive, multisystem disorder with early-onset cerebellar ataxia as its most common defining neurologic feature. The constellation of accompanying extraneural features aids in its clinical diagnosis and includes conjunctival and cutaneous telangiectases, elevated levels of serum alphafetoprotein (AFP), chromosome aberrations, immunodeficiency with recurrent sinopulmonary infection, cancer susceptibility, and radiation hypersensitivity. Since identification of the causative gene, ATM (for ataxia-telangiectasia mutated), on chromosome 11q22-q23 (Gatti et al., 1988; Uhrhammer et al., 1995; Lange et al., 1995; Savitsky et al., 1995), the molecular basis of certain aspects of the disease have become clearer, although others remain to be elucidated (Gatti et al., 1991; Gatti, 2001).

Clinicopathologic syndrome The earliest reports of an early-onset, familial, progressive choreoathetosis with ocular telangiectases (Syllaba and Henner, 1926) and of an early-onset, progressive cerebellar degeneration with cutaneous telangiectasia (thought to be a variant neurocutaneous syndrome) (Louis-Bar, 1941) did not recognize this as a distinct entity until the seminal clinicopathological studies of Boder and Sedgwick (1957) and of Biemond (1957), calling attention to the absence of the thymus gland and the prominence of severe recurrent sinopulmonary infections, the main cause of death (47% in one series: Sedgwick and Boder, 1991). A rapid succession of case reports confirmed the clinical syndrome of ‘ataxia-telangiectasia’ and also the presence of lymphoreticular malignancy as the second most frequent cause of death (22% malignancy alone, 26%

malignancy with infection) (Boder and Sedgwick, 1963). It has proven to be the most common recessively inherited cerebellar ataxia in children under five years of age, with a prevalence of 1/40 000–1/100 000 live births (Swift, 1985; Swift et al., 1986).

Neurologic features Progressive cerebellar ataxia is almost always the presenting symptom and becomes apparent as early as the first year of life, when the child is learning to walk. The truncal and gait ataxia is slowly and steadily progressive, although between the ages of two and five years normal development of motor skills may temporarily mask this decline. Slowed and slurred speech is also seen in the early stages, followed by appendicular dyssynergia, decreased tone, and slowed movements. Nearly 90% show facial hypotonia and drooling, as well as depressed deep tendon reflexes. Just over 80% manifest characteristic eye movement abnormalities: fixation instability and a delayed initiation of voluntary saccades and smooth pursuit, termed oculomotor apraxia. Compensatory head thrusting and overshoot are used to look at objects. About 25% of patients develop intention tremor and myoclonic jerking of the limbs (Sedgwick and Boder, 1991). These signs of parenchymal cerebellar degeneration typically lead to wheelchair dependence by the second decade and the need for assistance in activities of daily living and personal care. Pathologically, prenatal Purkinje cell migration abnormalities and postnatal Purkinje cell degeneration have been seen (Gatti and Vinters, 1985; Vinters et al., 1985), with thinning of the molecular and granular cell layers and minor changes in dentate (outflow) and olivary (inflow) nuclei and medullary tracts. Neural imaging confirms the early presence of severe cerebellar atrophy. Extrapyramidal involvement with choreoathetosis and

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dystonia is seen in about 90% of patients, occasionally preceding and masking the ataxia, but usually presenting in older children. Pathological correlates have been minimal in younger children, but in older patients include degeneration of the substantia nigra and neurofibrillary tangles, lipofuscin granules, and gliosis in and around the basal ganglia (Sedgwick and Boder, 1991). Intact deep and superficial sensation, a negative Romberg’s sign, and flexor or equivocal plantar responses reflect minimal early spinal long tract involvement, confirmed by pathological studies. The typical patient with A-T is of normal intelligence and often described as having an unusually pleasant disposition. The motor abnormalities make formal psychometric testing and standard learning programs difficult. With adaptive learning resources, some patients complete high school and go on to earn college-level degrees, and even to live alone. Early neuropathology shows no cerebral abnormalities, although late studies (into the fourth decade) have shown white matter gliovascular malformations and neuronal neurofibrillary tangles, lipofuscin granules, and gliosis, possibly correlating with an accelerated aging of the brain and a more generalized ‘progeria’ (Kamoshita et al., 1975). Later neurological features have been observed in patients surviving into the late second decade and beyond. They may develop more spinal cord features – with posterior column sensory loss and upgoing toes, reflecting diffuse spinal long tract demyelination – or more neuromuscular features, with diffuse weakness, muscle atrophy, fasciculations, and absent deep tendon reflexes, consistent with anterior horn cell loss and peripheral nerve axonal degeneration. Denervation of muscle is seen on biopsy. Denervation changes and reduced motor velocities and sensory potentials on electromyographic and nerve conduction testing may be present before the peripheral neuropathy is clinically evident. Associated skeletal deformities are not a primary feature of A-T, but secondary kyphoscoliosis and lower limb contractures may develop late in non-ambulatory patients (Sedgwick and Boder, 1991).

Non-neurologic features There are several areas of non-neurologic involvement: ocular and cutaneous telangiectases (95%), serum AFP elevations (90%), serum and cellular immunodeficiencies with accompanying primarily sinopulmonary infections (60–80%), cancer (40%), hypersensitivity to ionizing radiation (probably universal and diagnostic in A-T), chromosomal instability (about 40%), endocrine, and progeric changes (variable).

Telangiectases appear on average of two to four years after onset of the neurologic syndrome and are progressive. They are composed of dilated capillaries in the conjunctive and, later, on the ears, over the bridge of the nose, in the antecubital fossae, behind the knees, or more diffusely. They may represent altered angiogenesis, sensitivity to ultraviolet light, or a progeric change similar to that reported with respect to gliovascular changes in the white matter of the brain. They are a hallmark of A-T and aid in diagnosis when and if they are present. They do not occur in internal organs and are not generally associated with bleeding problems. AFP levels are usually elevated, but are not a reliable clinical marker until after the age of two, due to normal persistence of elevated levels of AFP into late infancy. Although elevated even in the fetus, AFP does not appear in the amniotic fluid, as it would in cases of neural tube defect or Down syndrome. The high levels of AFP are felt to be of hepatic origin (Ishiguro et al., 1986) and may be accompanied by elevations of other liver enzymes (serum glutamicpyruvic transaminase, SGPT; serum glutamic-oxalacetic transaminase, SGOT; alkaline phosphatase, and carcinoembryonic antigen, CEA), with no evidence of liver disease at post mortem (McFarlin et al., 1972; Gatti and Walford, 1981). AFP may have a suppressor effect on the developing immune system or on immune function (Yamashita et al., 1994; Regueiro et al., 2000). Virtually all A-T homozygotes who have come to post mortem examination have a small, embryonic thymus, but the resulting immunodeficiencies can be quite variable, even within the same family suggesting a problem with maturation of B and T cell precursors (Gatti and Walford, 1981). IgA, IgE, and IgG2 deficiencies are most common, with the accompanying risk of recurrent sinopulmonary infection (Roifman and Gelfand, 1985; Regueiro et al., 2000). Elevated, possibly compensatory, serum IgM levels may occasionally progress to a high blood viscosity syndrome, with splenomegaly, lymphoadenopathy, neutropenia, thrombocytopenia, and congestive heart failure (Thiele et al., 1994; Regueiro et al., 2000). Gammopathies of other Ig classes are also seen in approximately 2% of patients. T-cell deficiencies occur in half the patients, with abnormal skin test antigen and phytohemagglutinin responses (Gatti et al., 1982; Paganelli et al., 1992). Natural killer cells may be increased; however, some reports do not confirm this. In a British study of 70 patients (Woods and Taylor, 1992), 10% had severe immunodeficiencies and nearly 40% had normal immunologic function. Over the course of their lives, nearly 40% of A-T patients will develop a malignancy (Morrell et al., 1986). Approximately 85% of these malignancies will be either

Ataxia-telangiectasia and variants

leukemia or lymphoma, which in younger patients may occasionally precede the onset of ataxia. Children will usually develop acute lymphocytic leukemia (ALL) of T-cell origin, rather than the pre-B-cell form seen in common childhood ALL. Leukemia in older A-T patients is usually an aggressive T-cell process with morphology similar to a chronic lymphoblastic leukemia (T-CLL, or T-cell prolymphocytic leukemia, T-PLL) (Taylor et al., 1996). Lymphomas are more often non-Hodgkin’s, extranodal, infiltrative, B-cell types, and harder to diagnose in their early stages (Murphy et al., 1999). Solid tumors of other tissues (breast, stomach, ovary, uterus, skin, including melanoma, brain, thyroid, liver, and kidney) occur more commonly as the A-T patient matures, and are being seen in greater numbers as these patients are living longer (Morrell et al., 1986). Radiation therapists have observed that when A-T patients with cancer are treated with conventional doses of ionizing radiation, they develop life-threatening sequelae characteristic of much higher doses (Gotoff et al., 1967; Morgan et al., 1968; Cunliffe et al., 1975; Abadir et al., 1983; Hart et al., 1987). This radiosensitivity could be demonstrated in vitro, using fibroblasts from A-T homozygotes, which showed sensitivity to a number of radiomimetic and free-radical-producing agents (Taylor et al., 1975, Shiloh et al., 1982). This finding led to the development of the highly sensitive and reasonably specific diagnostic test, the colony survival assay, which is performed on transformed lymphocytes obtained from a heparinized blood sample of suspected A-T patients (Huo et al., 1994). The occurrence of DNA damage in the natural pathobiology of A-T may reflect the accumulation of the effects of oxidative stress and free-radical products of metabolism. The original postulated mechanism of defective DNA repair in A-T has given way to the theory that A-T cells are defective rather in their ability to sense this damage, not in their ability to repair it, leading to non-repair of DNA double-strand breaks, altered cell cycle checkpoints (G1, S, and G2/M), defective DNA replication, and apoptosis or malignant transformation of particularly sensitive cells (neurons, thymocytes) (Rotman and Shiloh, 1999). All cells show nucleomegaly, with no evidence of viral particles contributing (Sedgwick and Boder, 1991). Polyploidy (4n and 8n) of lymphoblastoid cell lines from A-T patients has been demonstrated by flow cytometric cell cycle analysis (Naeim et al., 1994). Fusion of fibroblasts from unrelated AT patients was noted to correct or ‘complement’ their radiosensitivity, but this phenomenon is not well explained by the current level of understanding of the A-T gene, its mutations, and its purported functions (Jaspers et al., 1988; Gatti, 2001).

Karyotyping of peripheral lymphocytes from A-T homozygotes – if successful despite decreased PHA responsiveness – shows non-random chromosomal aberrations in lymphocytes, such as translocations and inversions, which preferentially involve chromosomal breakpoints at 14q11, 14q32, 7q35, 7p14, 2p11 and 22q11 and correlate with the regions of the T-cell and B-cell receptor gene complexes. A-T fibroblasts do not show these translocations, but show an increased frequency of random aberrations. Chromosomal instability has been reported, with homozygotes showing t(7; 14) translocations in lymphocytes in 1–2% of metaphases (Hecht and Hecht, 1985; Kojis et al., 1992). Somatic influences and cell cycle checkpoint abnormalities may affect the ultimate evolution of certain defective lymphocyte clones in some A-T patients, leading to the development of T-CLL/T-PLL (Taylor et al., 1975; Johnson et al., 1986; Russo et al., 1989; Madani et al., 1995, 1996; Narducci et al., 1995; Thick et al., 1996; Croce, 1998). Telomere shortening and fusions, with normal telomerase activity (Pandita et al., 1995), have been observed in peripheral blood lymphocytes of A-T patients, especially in preleukemic T-cell clones (Metcalfe et al., 1996). Accelerated telomere shortening is also seen in aging cells of normal persons and in tumor cells, as well as being associated with senescence of CD28/CD8 T cells in patients with autoimmune deficiency syndrome (AIDS) and centenarians, both conditions with waning T-cell immunity (Effros et al., 1996). This suggests a third mechanism for cellular immunodeficiency in A-T. Endocrine defects may result in gonadal abnormalities (gonadal streaks, absent or hypoplastic ovaries, dysgerminomas, and undeveloped fallopian tubes in females; erectile and ejaculatory difficulties and spermatogenesis problems in males) (Sedgwick and Boder, 1991). Most female patients will ultimately begin regular menstrual cycles, but may enter menopause prematurely. Osteoporosis may then become a clinical concern. Most male patients will develop normal secondary sexual characteristics. An associated retardation in somatic growth is seen in some. Pituitary function studies show no consistent abnormalities. Some patients will develop an insulin-resistant diabetes in their late teens, with hyperglycemia without glycosuria or ketosis, possibly due to a particular IgM antibody directed against insulin receptors (Barlow et al., 1965). A-T, as other chromosomal instability syndromes (e.g., Fanconi’s anaemia, xeroderma pigmentosum, Bloom’s syndrome), shows progeroid features (Gatti andWalford, 1981). Young A-T patients may have strands of gray hair or keratoses and basal cell carcinomas. These signs may be related to the accelerated telomeric shortening mentioned above, to increased tissue turnover, and/or to the exaggerated

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effects of oxidative damage. Autoantibody formation is found in both the aging population and A-T patients (Herndon, 1985). Other features of apparent premature aging (thymic dystrophy and lymphoid depletion) may alternatively be explained by intrinsic immune system defects during T-cell maturation. Post-mortem findings in older A-T patients show neuronal pathology (neurofibrillary tangles, lipofuscin granules, and Marinesco bodies) associated with an aging brain (Kamoshita et al., 1975), although presenile dementia has not been described.

Clinicopathology of the A-T heterozygote The carrier frequency for ATM is estimated at 1%. Carriers are normal neurologically, although some may have telangiectases. As detailed below, the major effect of ATM heterozygosity is a modestly increased risk of cancer. Idiopathic scoliosis and vertebral abnormalities have been reported in excess in A-T relatives. Swift also found a fourfold increase of ischemic heart disease among female A-T carriers, contributing to a 3.2-fold increased mortality risk. Juvenile-onset diabetes and late-onset diabetes may be quite frequently observed among non-affected members of A-T families, although this pattern has not been explained. Male heterozygotes may show premature graying of hair or baldness, and cataracts are seen at higher frequencies among carriers (Forrer et al., 1999). ATM heterozygotes have in-vitro radiosensitivity values that are intermediate between homozygotes and normals (Chen et al., 1978; Paterson et al., 1985). It remains unclear whether this translates to any greater risk during exposure to ionizing radiation clinically (diagnostic X-rays, radiation therapy). Excessive numbers of ATM heterozygotes have not been identified among patients over-reacting to radiotherapy, and ATM heterozygotes diagnosed with cancer have not been noted to have unusual reactions to irradiation, suggesting that their radiosensitivity in vivo is not great (Clarke et al., 1998; Hall et al., 1989). Routine, nonessential X-ray exposure is discouraged, although essential studies (age-dependent mammography) should not be avoided.

Cancer risk of AT carriers Even before the ATM gene was cloned, several authors reported that the incidence of cancer in A-T heterozygotes was higher than that in the general population, most notably breast cancer in female heterozygotes less than 60 years of age (Pippard et al., 1988; Borreson et al., 1990; Swift

et al., 1991). Other cancers were also mentioned, such as stomach and liver cancer (Swift et al., 1991; Chessa et al., 1994). Swift estimated the relative risks of cancer in general to be 3.7 in males and 3.5 in females, and the relative risk of breast cancer in females to be 5.1, although with large confidence intervals. Since then, estimates of cancer risk in A-T heterozygotes have been revised downward. Easton’s meta-analysis estimated the relative risk of breast cancer as 3.9 for all ages, with a greater relative risk at younger ages and no significantly increased risk above the age of 60, whereas the relative risk for other types of cancer was not elevated. A more recent analysis of mothers of A-T patients again estimated the relative risk of breast cancer as 3.37 (Inskip et al., 1999). The families studied by Swift in 1991 were re-analyzed by Athma et al. in 1996, with the confirmation of A-T heterozygote status through the determination of genetic haplotypes. This study found a relative risk of breast cancer of 3.8, in agreement with Easton. A study of confirmed French A-T heterozygotes also found relative risk of 3.32, regardless of age (Janin et al., 1999). Despite these studies of A-T families, the magnitude of the risk of breast cancer in female A-T heterozygotes is still imprecise, due to the small populations studied and thus the large confidence intervals (Table 38.1). This modest risk, however, may correspond to a significant percentage of breast cancer in the population at large being attributable to heterozygosity at ATM: if 1% of the population is heterozygous at ATM, and the relative risk of breast cancer is about 3, then 2–4% of new breast cancer cases may be due to defects in ATM. If this is true, then ATM is responsible for more breast cancers than BRCA1 and BRCA2 (0.11% and 0.12% of breast cancers, respectively: (Peto et al., 1999). Given the described increased incidence of cancer in A-T families, heterozygosity for ATM might contribute to the familial clustering of cancer. Among 88 breast cancer families, three patients in three families were found to be A-T heterozygotes, although the mutant ATM allele did not segregate with the presence of cancer (Vorechovsky et al., 1996a, 1996b). Similar results were found among 18 families affected with breast and gastric cancer: two ATM heterozygotes with breast cancer were found in one family (Bay et al., 1998). A third study identified one ATM heterozygote among 100 women with early-onset breast cancer and a family history of breast cancer (Chen et al., 1998). Two groups have searched for constitutional ATM mutations in circulating lymphocytes from sporadic breast cancer cases, using protein truncation testing (PTT). FitzGerald et al. (1997) identified two mutations among 401 cases (and two among 202 controls), whereas Spacey et

Ataxia-telangiectasia and variants

Table 38.1 Evaluation of the relative risk of breast cancer in female A-T heterozygotes by epidemiologic analysis

Study

Cases of breast cancer

Relative risk (95% CI)

Cases of other cancers

Relative risk (95% CI)

Number of families

Swift et al. (1987)

27

(6.8 (2–22.7) (1.3 (0.33–5.2) (3.9 (1.26–12.09) (5.1 (1.5–16.9) (3.9 (2.1–7.2) (3.37 (0.69–9.84)

44 men 67 women 25

(2.9 (1.5–5.5) (2.3 (1.3–3.9) (1 (0.59–1.7) (0.77 (0.32–1.85) (3.5 (2–6.1) (1.9 (1.5–2.5) (1.26 (0.34–3.21)

110

Pippard et al. (1988)

2

Borreson et al. (1990)

6

Swift et al. (1991)

23a

Easton (1994) meta-analysis Inskip et al. (1999)

58 3

14 68a 218 1

15 8 161

95

Notes: These numbers concern the cases of cancer observed in new A-T families plus the new cases observed in the 110 families already described in Swift et al. (1987). CI: confidence interval.

a

al. (2000) found no mutations among 47 cases. Thus, at first glance, it seems that heterozygosity for ATM is not associated with breast cancer susceptibility, even though family studies indicate increased risk. There may be several reasons for this discrepancy. First, PTT only identifies 60–70% of mutations in A-T homozygotes, and these are not necessarily representative of those associated with breast cancer (Telatar et al., 1996; Gatti et al., 1999). Second, the frequency of A-T heterozygotes in the population is not well defined, although 1% is often cited (Swift et al., 1986; Easton, 1994). Therefore, the low numbers of constitutional mutations found in the above studies do not exclude a role for ATM in breast cancer. Third, it now seems that two distinct populations of ATM carriers may exist within the population, i.e., those with truncating mutations, which induce the neurological syndrome of A-T and perhaps a slight increase in breast cancer susceptibility, and those with missense mutations, which do not generally cause A-T but are associated with breast and other cancers (Gatti et al., 1999; (Table 38.2)). Loss of heterozygosity at the ATM locus has been found in 60% of ovarian cancers, 44% of uterine cancers, 40% of breast cancers, and 30% of colon cancers. These results suggest that ATM may have a role in the development of these tumors, although it is difficult to interpret this type of study due to the large region of chromosome 11q that is often involved in loss of heterozygosity and the fact that genes near to ATM may also be involved. In addition, in breast and colon cancer, non-specific chromosomal loss is

Table 38.2 ATM missense mutations in cancer patientsa % Breast cancer Hall – meta-analysis Broeks et al. Angele et al. Yahalom et al.

150/333 7/82 4/27 15/51

45 9 15 29

Hodgkin disease followed by breast cancer Gilad et al.

17/63

27

B-Chronic Lymphocytic Leukaemia Stankovic et al.

14/40

35

Acute Lymphocytic Leukaemia Avigad et al.

10/25

40b

Notes: a Abstracts from A-T Workshop held at Citerno, Italy, March 17–19, 2000. b All types of ATM mutations  60%.

frequent and the incidence of loss of heterozygosity at the ATM locus is not very much higher than this background. Demonstrating the inactivation of the ATM protein in tumors would more precisely define its importance. A few cases have been described in which the wild-type allele of ATM is inactivated in the tumor tissue of a heterozygote, but the loss of ATM has not been described generally in breast oncogenesis (Vorechovsky et al., 1996a, 1996b; Chen

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et al., 1998; Bay et al., 1999). More definitive studies using antibodies against ATM on tumor tissue sections are underway in several laboratories. Somatic mutations of both alleles of ATM have been found in T-prolymphocytic leukemia, in chronic Blymphoid leukemias, and in mantel cell lymphoma, suggesting that, in these types of malignancy, ATM does play a tumor-suppressor role. This is an interesting finding, because although A-T homozygotes are prone to these types of cancer, they have not been described in A-T heterozygotes. This would again suggest that different types of mutations are involved in A-T and cancer.

Molecular basis of cancer risk in A-T heterozygotes DNA repair anomalies Even though ATM heterozygotes do not exhibit any hypersensitivity in vivo to ionizing radiation, studies of primary and transformed lymphocytes as well as transformed fibroblastoid cell lines show they are more sensitive to this type of DNA damage than normal controls, though less sensitive than A-T homozygotes (Chen et al., 1978; Paterson et al., 1985; Scott et al., 1994; Tchirkov et al., 1997; Pernin et al., 1999). Irradiated ATM heterozygous cells exhibit more G2 phase chromosomal anomalies, and this reduced efficiency of DNA repair could lead to transformation and explain the higher incidence of cancer in heterozygotes. ATM heterozygote cells also exhibit elevated apoptosis in response to irradiation, probably reflecting the elimination of cells with chromosomal anomalies.

Interaction with BRCA1 As described below, recent results have shown that ATM phosphorylates BRCA1 in response to irradiation, and that this phosphorylation is necessary for the normal function of BRCA1 (Cortez et al., 1999). BRCA1 is a transcriptional activator that responds to a variety of different types of DNA damage, and constitutional heterozygosity for BRCA1 leads to a very high risk of breast cancer. If ATM is necessary for BRCA1 to respond to a specific subset of DNA damage, namely double-strand breaks, then the breast cancer risk to ATM heterozygotes may be explained by the suboptimal activation of BRCA1. One may expect that a general deficit in DNA repair would lead to a general risk of cancer, and yet the relative risk of cancers other than breast cancer is not significant in ATM heterozygotes, making the interaction of ATM with BRCA1 an attractive explanation for the tissue specificity of their cancer risk. In further support of this hypothesis, a huge DNA repair/surveillance complex has recently been identified by immunoprecipitating with various antibodies to BRCA1; this BASC

(BRCA1-associated surveillance complex) includes ATM, ATR, Rad50, Rad51, Mrell, nibrin, BLM, MLH1, MSH2, MSH6, RPC, and about 30 other as yet unidentified proteins (Wang et al., 2000).

Structure and function of the ATM protein The ATM gene encompasses approximately 150 kb of 11q22.3-q23.1 (Platzer et al., 1997). ATM is transcribed from a bidirectional promotor that also drives expression of the gene NPAT/Cand3/E14 (Byrd et al., 1996; Imai et al., 1997; Chen et al., 1997); the significance of this physical feature is unknown, but implies coordinated regulation. There are two alternative exons 1, although differential expression of the mRNA isoforms in different tissues or in response to different stimuli has not been described, and there is no change in the amino acid sequence of the resulting protein, because translation is initiated in exon 4. The 13 kb ATM mRNA, with its 9168 bp of coding sequence, appears to be expressed in most tissues and stages of development (Savitsky et al., 1997; Soares et al., 1998). Notably, expression levels do not vary with the cell cycle phase or in response to irradiation (Brown et al., 1997). However, ATM kinase activity does increase following irradiation. Homologs of ATM have been identified in other mammals and in fish and amphibians, although no true yeast ortholog has been identified. Several proteins with homology to ATM have been found, including the catalytic subunit of DNA-PK and ATR. The greatest similarity between these proteins is in the kinase domain, and together they form a subfamily of high molecular weight PI3-kinase-related proteins. The 370 kD ATM protein contains a leucine zipper, a domain with homology to the Schizosaccharomyces pombe Rad3 protein, c-abl-binding and p53-binding domains, and a protein kinase domain homologous to the P13K family (Chen and Lee, 1996; Smith et al., 1999). ATM is localized mostly to the nucleus, but is also found in cytoplasmic vesicles (Watters et al., 1997; Chen et al., 1998; Gately et al., 1998). In the presence of DNA double strand break (DSB) damage, ATM phosphorylates a variety of protein targets and activates several different signaling cascades (Fig. 38.1).

G1 cell cycle arrest ATM induces G1 phase arrest through the action of several intermediates. One of the most important targets is the phosphorylation of p53 on ser15, and a concomitant

Ataxia-telangiectasia and variants

Fig. 38.1 The ATM pathways of phosphorylation.

dephosphorylation of ser376 (Watters et al., 1997; Canman et al., 1998; Khanna et al., 1998). This first modification allows p53 to dissociate from its negative regulator, MDM2, which in turn increases the half-life of p53 and allows it to function as a transcriptional regulator. The phosphorylation of MDM2 is also ATM dependent. The dephosphorylation of ser376 probably enhances the site-specific affinity of p53 for DNA. Among the genes whose transcription is induced by p53 is the cdk-inhibitor p21 Waf1/Clif1, which plays a key role in inhibiting the transition from G1 to S phase. ATM also induces G1 arrest through the phosphorylation of cAbI (Shafman et al., 1997; Baskaran et al., 1997), which in turn activates both the p53 homolog p73 and the SAPK pathway to block progression to S phase (Yuan et al., 1997; 1998). The G1 checkpoint serves to prevent a cell from attempting to replicate damaged DNA. If the cell were to enter synthesis, a DSB would lead to a chromosome break, which could be mistakenly resected to form a translocation or other chromosomal rearrangement, or to be left to create an acentric fragment. These anomalies would prove disastrous in the following mitosis.

S phase arrest The phosphorylation of cAbI also serves to halt progression within S phase by inhibiting Rad51, a single-stranded DNA-binding protein essential for replication. Replication

protein A (RPA), another protein essential for the progression of DNA replication, is inhibited by ATM through phosphorylation of its 34-kD subunit. Arrest in S phase serves the same function as G1 arrest in preventing the replication of damaged DNA templates. Replication seems to be halted at two levels, by prohibiting the initiation of new replicons and by inhibiting the elongation of replicons that have already been initiated. A-T cells are particularly deficient in inhibiting replicon initiation following radiation damage to DNA. This leads to the quantifiable phenotype known as ‘radiation-resistant DNA synthesis’ (Painter, 1993).

G2 cell cycle arrest ATM inhibits cells from entering mitosis after irradiation through the phosphorylation of Chk2 (Flaggs et al., 1997; Chaturvedi et al., 1999; Hirao et al., 2000; Carr, 2000). The literature is occasionally indistinct on the subject of G2 arrest in A-T cells, probably because there are two arrest points, and only one is defective in A-T. Immediately after DNA damage, the defective cell cycle checkpoint can be measured as a failure to diminish the numbers of cells that enter mitosis in the hours that follow irradiation. In contrast, at later times there is clearly an increase in G2 cells which is readily detectable by fluorescence-activated cell sorter (FACS) analysis. This late G2 accumulation is due to

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cells that were in G1 or S at the time of irradiation, which replicated their DNA despite the presence of DSBs, and which have now triggered a distinct G2 checkpoint.

ATM and radiation-induced apoptosis Radiosensitivity is a constant feature of A-T. The sensitivity of tissues to a given dose of irradiation, however, depends more on the initiation of programmed cell death than on the actual level of DNA damage experienced. Tissues with high proliferation potential, such as bone marrow and intestinal epithelia, are more sensitive than tissue with low or no replicative capacity, such as neurons. Studies performed on SV40 virus-transformed fibroblasts and Epstein–Barr virus (EBV)-transformed lymphoblastoid cell lines show that radiosensitivity is correlated with excessive apoptosis. Similarly, studies of Atm knockout mice (atm/) show more apoptosis in situ, both spontaneously and after irradiation. In contrast, irradiated primary A-T fibroblasts do not undergo apoptosis, but simply fail to replicate. Furthermore, the developing nervous system of atm/ shows a resistance to apoptosis following in-vivo irradiation (Herzog et al., 1998). How ATM inhibits apoptosis is not completely understood, and may be different according to the type of tissue studied. One route is through the phosphorylation of LB (Jung et al., 1997). IB is an inhibitor of NFB, and its phosphorylation leads to the release of NFB sequestered in the cytoplasm. NFB now translocates to the nucleus, where it acts as a transcriptional regulator or anti-apoptotic. A second level of apoptosis control acts through p53, though the mechanism is likely to be indirect. Cultured A-T fibroblasts undergo apoptosis in response to irradiation, and this process may be inhibited by the inactivation of p53. As we have seen, ATM activates the cell cycle arrest functions of p53, but it is as yet unknown how the inhibition of p53’s pro-apoptotic functions works. It is possible that ATM/ cells allow replication of damaged DNA templates, which in turn trigger p53 through independent mechanisms. A third pathway through which ATM inhibits apoptosis might be the ceramide synthesis cascade. This signaling cascade is initiated at the cell membrane in response to irradiation, and is dysregulated in A-T cells. It is not yet known how ATM is involved, and whether the detection of DNA damage is necessary or if ATM might detect some other damage signal. ATM apparently functions both in the nucleus and in the cytoplasm. In the nucleus, ATM surveys the DNA for DSBs, and phosphorylates nuclear substrates when necessary. The phosphorylation of IB (and possibly of c-AbI) occurs in the cytoplasm. The proteins of the ceramide signaling

pathway are located on membranes accessible from the cytoplasm. Some authors have proposed that the pool of ATM associated with cytoplasmic vesicles performs functions distinct from genomic surveillance. ATM has been shown to associate with •-adaptin in the cytoplasm and may be involved in vesicle trafficking and intercellular communication, and it is this aspect which may eventually explain the specific degeneration of cerebellar Purkinje cells (Lim et al., 1998). It is unknown whether there is any communication from the nucleus, where DNA damage occurs, and extranuclear ATM, or whether cytoplasmic ATM is responding to a signal other than DNA doublestrand breaks.

ATM and DSB repair A-T cells exhibit subtle defects in DSB repair: they take longer to repair DSBs and the repair of plasmid substrates is often inexact. While ATM itself does not seem to play a direct role in the rejoining of DSBs, it is involved in the control of this process. As we have seen, ATM activates GADD45 indirectly though p53. In addition, BRCA1 and CIIP have been shown to be phosphorylated by ATM in response to DSBs and this phosphorylation is essential to relieve the radiation sensitivity of BRCA1-mutant cells. BRCA1 has been described as being necessary for the aggregation of Rad51 or Rad50/Mre11/nibrin at DSB sites, in addition to being a transcriptional activator. Rad50 and Rad51 are both required for the repair of DSBs, and BRCA1 may provide a link in the signaling cascade that activates repair. Finally, ATM probably activates DSB repair through Rad50/Mre11/nibrin independently from BRCA1. However, all of the above molecules appear to cooperate as part of the BASC super complex (Wang et al., 2000). Cells experiencing DSB damage in G1 or G0 repair this damage through non-homologous end joining, a process controlled by DNA-PK. The relationship between ATM and DNA-PK is as yet unclear. The abundant Ku subunits of DNA-PK can bind to DNA ends on their own and recruit DNA-PKcs to the sites for repair. Ku70 has recently been shown to be essential for the binding of the Rad50/Mre11/nibrin complex at DSB sites. The similarities of the cellular phenotypes of A-T and NBS (nibrindeficient) cells suggest that this may also provide a link between ATM and DNA-PK. Cells experiencing DSB damage in G2 favor homologous recombination between sister chromatids for repair.

Ataxia-telangiectasia and variants

ATM mutant mouse models Atm/ mice were created in the hope that this animal model would allow the development of new treatments for the progressive ataxias. Several independently derived knockout mice have been made and most aspects of the AT phenotype are reproduced in the animals, except for the cerebellar degeneration (Barlow et al., 1996; Xu et al., 1996; Borghesani et al., 2000). Atm/ mice have radiosensitivity, meiotic failure, immune deficiency, a cancer risk approaching 100%, and small size. Upon close examination, Atm/ mice also show mild cerebellar abnormalities. Tests of coordination show a modest but significant deficit, even though the mice are not flagrantly ataxic. Sections of Atm/ mouse cerebellums show some disorganization, with misplaced and reduced numbers of Purkinje cells. This phenotype, in contrast to human patients, does not seem to be progressive, with older mice fareing no worse than younger mice. These findings suggest that, rather than a purely degenerative defect, whereby Purkinje cells are lost due to accumulated DNA damage, there is a developmental defect in A-T. Degenerative disorders can be especially difficult to reproduce in small animal models, both because their physiology is different and because the lifespan of the animal may be too short for significant defects to develop. An example of this phenomenon is the dystrophic mouse, which fails to replicate Duchenne muscular dystrophy largely because the affected muscle cells do not reach the limit of their capacity for replication before the mouse dies of old age. The lifespan of Atm/ mice is usually less than six months, because of the incidence of thymomas. If this malignancy is avoided by thymectomy or deletion of one of the RAG genes (which prevents the maturation of lymphocytes by eliminating V(D)J recombination), the mice live longer, but still do not develop progressive ataxia. Atm/ mice have been most useful in elucidating DNA repair signaling defects.

Genotype/phenotype correlations With over 400 mutations identified, extending over each of the 66 exons, and patients from non-consanguineous families typically being compound heterozygotes (especially in heterogeneous populations such as the USA), determining how specific allelic mutations affect phenotypes has been quite difficult (Concannon and Gatti, 1997; http:/www.vmresearch.org/atm.htm). Although founder effect mutations account for significant proportions of various ethnic populations (Telatar et al., 1998a) Table 38.3

these groups of patients who share common mutations do not share any common phenotypes thus far with just a few exceptions: (1) IVS40 1126AG from the British Midlands is associated with a later onset of ataxia, a slower rate of neurological deterioration, and lower incidence of cancer (McConville et al., 1996); (2) 7271TG has been described in two families with late-onset ataxia, minimal telangiectasia, normal AFP, a 12-fold increase in breast cancer, and even a homozygous individual who bore a child (Stankovic et al., 1998); (3) missense mutations in A-T patients are often associated with expression of ATM protein (Gilad et al., 1998), in contrast to most patients not expressing ATM protein (Becker-Catania et al., 2000). These mutations are often associated with cancer as well (Stankovic et al., 1998). Carriers of missense mutations also appear to be susceptible to various types of cancer (see Table 38.2). As discussed above, A-T patients who do not meet all the clinical criteria for A-T (i.e., relatively late onset of ataxia or chorea, unusually long survival – even to the sixth decade – absence of telangiectases, normal AFP elevations, normal immune status, intermediate levels of radiosensitivity) have been shown for the most part to have ATM mutations. Thus, while the A-T syndrome is fairly homogeneous and can be diagnosed at the clinical level in older patients, a fringe group of patients will need genetic studies to confirm the diagnosis. Because the gene is so large and time consuming to analyze, radiation sensitivity is usually tested before attempts are made to identify ATM mutations. Other regional-based A-T phenotypes are less well understood, for example the 40% incidence of clubbing of the fingertips in Costa Rican A-T (Porras et al., 1993). Despite the identification of the six most common mutations in Costa Rica (Telatar et al., 1998b) with rapid assays for each of these, fingertip clubbing has not been limited to just one of these mutations. Many other patients with phenotypes typical of A-T (Di Rocco et al., 1999) have not been shown to have mutations in the ATM gene, and may represent mutations in other genes that interact with the ATM protein. Of course, because present methods of mutation detection are only about 80% efficient (Table 38.3), some of the patients may still have ATM mutations (Concannon and Gatti, 1997; Gatti et al., 1999). As a general rule, patients manifesting all but one or two of the classic A-T signs will be found to have ATM mutations. Patients manifesting ataxia with just one of the non-neurologic signs will usually not have an ATM mutation. Aicardi et al. (1988) described 14 patients from ten families with neurologic findings resembling A-T who had none of the other features, including essentially normal radiosensitivity (Hannan et al., 1994). They were probably not patients with ATM mutations.

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Table 38.3 ATM mutation detection rates (A-T homozygotes)a % www.vmresearch.org/atm.htm Laake et al. Broeks et al. Doerk et al. Angele et al. Brusco et al. Sanal

254/382 67/82 14/19 81/102 72/116 45/70 59/90

66b 82 74 79 62 64 66

Notes: a Abstracts from A-T Workshop held at Citerno, Italy, March 17–19, 2000. b 70% truncating mutations; 15% missense mutations.

Some patients with classical symptoms of A-T radiosensitivity but without defined ATM mutations have to be considered as A-T in any case. ATM mutations in such patients may remain undetected, primarily for four technical reasons. 1. Introns may contain mutations that effect splicing; untested portions of ATM introns comprise 90% of the gene. The IVS40 1126AG mutation discussed above is an example of such a mutation, which is not detected by any routine detection strategies because it lies deep inside intron 40. 2. Large deletions in a second allele are routinely missed because they are masked by the polymerase chain reaction (PCR) product of the first allele. They are only detected easily in consanguineous patients who are homozygous for such mutations. 3. mRNA/cDNA-based assays will miss mutations that result in a decreased expression of the defective mRNA. Despite this, both mutations have been detected by mRNA-based assays in over 200 A-T patients. 4. In general, 5UT and 3UT (untranslated) regions of the ATM gene (5000 bp) are not screened for mutations. Sequencing the entire cDNA of a patients missing one or both mutations may identify additional mutations; however, we have not found this to be a high-yield approach. Similarly, when we screened the ATM promoter region of 30 patients lacking one or both mutations, we identified only one new mutation (Castellvi-Bel et al., 1999).

Nijmegan breakage syndrome (Weemaes et al., 1981) Nijmegan breakage syndrome (NBS) and Berlin breakage syndrome (BSS) are both due to mutations in the NBS1

gene, coding for nibrin (also called p95) (Varon et al., 1998). They should no longer be viewed as A-T variants; they themselves represent variants of a separate and distinct disease, nibrin deficiency, that shares some overlapping signs and symptoms with A-T – much as hypoglycemia can result from different genetic causes. These patients do not have ataxia, telangiectasia, or elevated AFP, but do manifest the 7;14 translocations, radiosensitivity, cancer susceptibility, and immunodeficiency, as seen in A-T. Conversely, the clinical features of NBS, i.e., microcephaly, mental retardation, and birdlike facies, are not seen in classic A-T. BBS patients may have the additional features of syndactyly, anal atresia, and hypospadias. In Eastern Europe, almost all NBS and BBS patients are homozygous for a Slavic mutation, 657del5. In the Western hemisphere, this mutation is less prominent. When this mutation was sought among 96 anonomyzed DNAs from mentally retarded patients who were negative for fragile X testing, it was not found (R.A. Gatti, unpublished data). The Seckel syndrome (bird-like dwarfism) also overlaps with NBS in some respects; however, neither radiosensitivity nor NBS1 mutations have been reported to date.

A-TFresno (Curry et al., 1989) A-TFresno represents a combination of both A-T and NBS features. The ataxia is often severe, with very young onset. Microcephaly and mental retardation are present. The AFP is usually elevated. ATM mutations have been found in several such patients. To date, no NBS1 mutations have been found.

Mre11 deficiency (Stewart et al., 1999) Since the cloning of ATM, the vast majority of recessive ataxia patients have been found to carry mutations in the ATM gene. There are a few cases, however, where no mutation was detectable in the ATM gene, and an intact ATM protein was present in cellular extracts (Hernandez et al., 1993). Stewart et al. (1999) have recently described mutations in the hMre11 gene in four such patients from two families. The hMre11 gene is located about 30 cM proximal to ATM on the long arm of chromosome 11, at band q22.1, and, therefore, these families linked to the general ‘A-T region’ at 11q22-q23. The phenotypes of patients with ATM and Mre11 mutations are very similar. Mre11-deficient patients have a milder phenotype than A-T patients. The phenotypic differences are also apparent at the cellular level: the induction of p53 is nearly normal, and clonogenic survival and radioresistant DNA synthesis curves are intermediate

Ataxia-telangiectasia and variants

between those of A-T patients and normal subjects. Intriguingly, the cellular phenotype of Mre11 deficiency is more similar to that of NBS patients, even though the neural phenotypes are different (i.e., no microcephaly or mental retardation in Mre11 deficiency, and no cerebellar ataxia in NBS). Mre11 deficiency patients have normal levels of ATM protein in cell lysates. However, the levels of nibrin and Rad50 are low; this is thought to reflect the critical role of Mre11 in maintaining the integrity of the Rad50/Mre11/nibrin protein complex. The four patients described with hMre11 mutations are two homozygotes for a nonsense mutation at codon 633, and two compound heterozygotes for a null mutation and a substitution of serine for asparagine at amino acid 117. Both the nonsense and missense mutated proteins produce stable products that are able to associate with Rad50 and nibrin, although the aggregation of this complex at DSB sites is abnormal. Data from mMre11 knockout mice indicate that these human mutations are most likely to be partially functional, because a null allele of mMre11 is lethal during embryogenesis, as are null alleles for mRad50. Mice with Nbs1 mutations have not yet been described.

An explanation for the overlapping symptoms of A-T, NBS/BBS, ATF and Mre11 deficiency (Fig. 38.2) It has recently become apparent that ATM lies upstream of the Rad50/Mre11/nibrin DNA repair complex and phosphorylates nibrin (Gatei et al., 2000; Zhao et al., 2000). Thus, NBS, BBS and Mre11 deficiency can be viewed as incomplete A-T syndromes. Because NBS/BBS patients do not have progressive ataxia, it can be surmised that nibrin does not play a major role in the ataxia of A-T. Conversely, the 7 and 14 translocations seen in each of these disorders suggest that a DNA-processing error involves the Rad50/Mre11/nibrin complex. Similarly, the fact that patients with defects in all three genes have endocrine problems suggests that these protein products are important to endocrinological development. A similar argument can be made for the high cancer incidence in NBS and A-T patients. No explanation presently exists to explain why certain patients with ATM mutations develop ATFresno, instead of A-T. Further, ATM, Mre11, nibrin, and BRCA1 are all required for the accumulation of Rad50 at doublestrand break sites, probably via the BASC complex (Wang et al., 2000). In the absence of nibrin, Mre11 does not become phosphorylated. Nibrin itself has no known kinase domain, and it is an attractive hypothesis that ATM phosphorylates Mre11 exclusively in the presence of fully functional nibrin. Rad50, Mre11, and the yeast analog of nibrin,

NBS Mental retardation Microcephaly Limb defects Anal stenosis

541

A-T RADIOSENSITIVITY 7;14 translocations immunodeficiency cancer risk

Progressive ataxia Telangiectasia Elevated serum AFP

Mild ataxia Mre11 deficiency Fig. 38.2 Phenotypic relationships between NBS, Mre11 deficiency and A-T.

xrs5, all perform essential repair functions and their loss is lethal. The loss of regulatory proteins such as ATM or BRCA1, or the reduced function of nibrin or Mre11 is tolerated, but decreases the efficiency of repair and leads to chromosomal instability.

Diagnosis and differential diagnosis The presence of early-onset ataxia with oculocutaneous telangiectases is strong clinical evidence for A-T. Oculomotor apraxia is a useful confirmatory sign. However, the clinical diagnosis of A-T can be problematic before the appearance of the telangiectases, as these early neurologic features can be misdiagnosed as cerebral palsy or a postviral syndrome and may be shared by other early-onset cerebellar syndromes (X-linked Pelizaeus–Merzbacher disease and Joubert syndrome). Neuroimaging (preferably nonradiologic, such as magnetic resonance imaging, MRI) can help distinguish these syndromes by the presence of leukoencephalopathy in the former and severe cerebellar hypoplasia in the latter. MRI will also rule out many non-genetic causes of late infantile ataxia–Arnold–Chiari malformation, Dandy–Walker syndrome, birth trauma, and posterior fossa neoplasms. The presence of parental consanguinity or another affected sibling will reinforce the recessive genetic underpinnings of the disease. Occasionally, early-onset Friedreich’s ataxia (FRDA) might be mistaken for A-T, but it can usually be distinguished on clinical grounds (early arreflexia and extensor plantar responses, early posterior column sensory loss with a positive Romberg sign, early peripheral motor–sensory neuropathy, fixation instability of eye movements rather than ocular apraxia, associated scoliosis, and cardiomyopathy). Direct testing of the FRDA gene is available to identify the intronic GAA repeat expansions that are responsible for the disease (Campuzano et al., 1996; Geschwind et al., 1997). Other inborn errors of metabolism, with progressive ataxia from an early age, can

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be ruled out by appropriate blood and urine studies or biopsy studies (muscle, nerve, conjunctiva, brain, bone marrow (Gatti, 2001). Colony survival assay for radiosensitivity is normal in Friedreich’s ataxia (R.A. Gatti, unpublished data). In various ethnic populations, founder effect mutations allow confirmation of a specific A-T mutation by rapid assays. For example, in the Amish/Mennonite community, two mutations account for essentially all A-T families. In Moroccan Jews, only one mutation is seen (Gilad et al., 1996). For heterogeneous populations, the numbers of different mutations make such assays impractical. At the present time, a clinically suspected diagnosis of A-T is best established by sequential testing, with false-negative results in less than 1% of bonafide A-T patients (Gatti et al., 1999). 1. Serum AFP levels will be elevated in about 85%. 2. Mega-protein truncation testing (mega-PTT) will identify at least one protein-terminating defect in about 91% (Telatar et al., 1996). 3. Western blotting will show little or no ATM protein in more than 85% (Becker-Catania et al., 2000). 4. Colony survival assay demonstrates radiosensitivity in more than 95% (Sun et al., personal communication). 5. Mega-SSCP identifies at least one mutation in 91% (Castellvi-Bel et al., 1999). Taken together, AFP levels, colony survival assay values, and Western blotting may serve as sensitive and reliable tests to confirm the diagnosis of A-T.

Prenatal diagnosis The presence of five highly polymorphic microsatellite markers in and around the ATM gene makes haplotyping very accurate, with virtually no risk of recombination (Gatti et al., 1993; Udar et al., 1999). This allows the diseaseaffected haplotypes to be identified in any family in which DNA from a prior affected sibling or close relative is available. It should be stressed, however, that a firm diagnosis for the prior affected relative is an absolute prerequisite for prenatal diagnosis. If this diagnosis is inaccurate or not firmly established, haplotyping for prenatal diagnosis is contraindicated and can actually result in misleading information being given to the family about the fetus in question. In young families in which an affected child is under the age of three and the mother is pregnant and requesting prenatal diagnosis, confirming a clinical diagnosis of A-T for the affected child becomes especially important. Our laboratory uses the colony survival assay to test for radiosensitivity for this purpose (Huo et al., 1994;

Sun et al., personal communication). Haplotyping in the 11q22.3-q23.1 region will only provide information relevant to the A-T gene (and any nearby genes). We also encourage preconceptual prenatal testing, whereby the diagnosis of the affected individual is confirmed and DNAs are haplotyped for parents and sibs before the mother becomes pregnant. The haplotyping is then repeated for everyone when the fetal sample arrives in the laboratory.

Treatment of ataxia-telangiectasia At present, there is no definitive gene-based therapy or neural-restorative therapy to halt progression of the neurologic symptoms of A-T. However, research in these areas continues at a rapid pace. The extraneural symptoms have many conventional treatment options, especially in the important areas of pulmonary infection and malignancy. Infection is usually with common microbes, not opportunistic organisms (despite the combined immunodeficiency), so prompt treatment with appropriate antibiotics and attention to aggressive pulmonary hygiene can prevent future complications (resistant infections, bronchiectasis, chronic respiratory failure, and aspiration). Pulmonary rehabilitation exercises for posture and muscle strength help maintain normal ventilation. For infection-prone patients, intravenous gamma globulin every three to four weeks may reduce the frequency of infections. Periodic pulmonary function studies may be a helpful monitor. Immunizations should preferentially be with killed vaccines, although many A-T children have inadvertently received live vaccines for varicella, smallpox, or polio before A-T was diagnosed and tolerated these well. Because varicella can be quite severe in A-T patients, the vaccine is now recommended for any A-T patients with an intact immune response. Regular physical examinations with blood cell counts and blood chemistries can serve as an early screen for leukemia/lymphoma and other cancers. Routine pelvic examinations and breast examination in young women should be instituted (Gatti et al., 1989). Non-radiologic imaging studies can be used, when any area of concern is raised (MRI, ultrasound). Radiologic studies should be used sparingly (chest X-ray, mammography). Should a malignancy occur, treatment protocols utilizing lower doses of radiation therapy and alternatives to radiomimetic and neurotoxic agents should be sought, and chemotherapy protocols with a high risk of developing a second malignancy (topoisomerase inhibitors) should be modified. (John Sandlund and Michael Kastan of St Jude’s Children’s

Ataxia-telangiectasia and variants

Hospital in Memphis, Tennessee, maintain a consulting service for such cases.) Young children presenting with leukemia or lymphoma, or any other malignancy, should be screened for the presence of A-T before a treatment regimen is begun. Bone marrow and hematopoietic stem cell transplantations have not been reliably evaluated, primarily because of the difficult and dangerous issue of ablation therapy. A-T patients should be encouraged to avoid excess sun exposure. Neurorestorative strategies and symptomatic medication can improve neurologic performance and reduce the risk of long-term complications from increasing immobility (deconditioning, contractures, decubiti, pneumonia, bladder infections, constipation). Physical therapy can help the patient maintain independence, continue in school, and enjoy leisure pursuits with family and friends. Gentle stretching, strengthening, and coordination exercises performed under guidance are of value. Swimming exercise, speech therapy, remedial learning programs, and appropriate adaptive equipment also reduce the ultimate handicaps of these patients. Drooling can be diminished by use of various anticholinergic agents (scopolomine, methyl-scopolomine, propantheline bromide) or ligation of the salivary glands. Postural tremors may respond to treatment with betablockers, and cerebellar tremor and myoclonus can be controlled with low doses of clonazepam or valproic acid (however, these agents may increase ataxia and cause sedation). Ataxia may improve with modest doses of buspirone or amantadine, brain monoamine stimulants (Trouillas et al., 1997; Peterson et al., 1998). Dopaminergic, dopamine-blocking, and anticholingergic agents can be tried for basal ganglia symptoms, should they interfere with functioning. Selective serotonin reuptake inhibitors (fluoxitine and others) have had some empirical efficacy for speech and swallowing, but could make chorea worse. N-acetylcysteine, and antioxidant/free radical scavenger, has been studied in small clinical trials, and myoinositol, which plays an important role in the synthesis of signaltransducing phosphoinositides, is currently in treatment trials. Most A-T patients in the USA live well beyond 20 years, thanks to improved health maintenance and rehabilitation options. This is a major change from just a few years ago, when it was unusual for patients to live past their teens, but much work still needs to be done. In view of studies implicating faulty oxidative stress responses in A-T patients, the use of dietary supplements of free radical scavengers is recommended, such as vitamin E, vitamin C, and alpha-lipoic acid. Mitochondrial

metabolism may be aided by coenzyme Q10. Folic acid supplementation may improve chromosomal stability. However, none of these dietary supplements has been formally tested for efficacy in A-T patients.

iReferencesi Abadir, R. and Hakami, N. (1983). Ataxia telangiectasia with cancer: an indication for reduced radiotherapy and chemotherapy dose. Br J Radiol 56: 343–5. Aicardi, J., Barbosas, C., Andermann, E. et al. (1988). Ataxia–ocular motor apraxia: a syndrome mimicking ataxia-telangiectasia. Ann Neurol 24: 297–502. Athma, P., Rappaport, R. and Swift, M. (1996). Molecular genotyping shows that ataxia-telangiectasia heterozygotes are predisposed to breast cancer. Can Genet Cytogenet 92: 130–4. Barlow, C., Hirotsune, S., Paylor, R. et al. (1996). Atm-deficient mice: a paradigm of ataxia telangiectasia. Cell 86: 159–71. Barlow, M.H., McFarlin, E.D. and Schalch, D.S. (1965). An unusual type of diabetes mellitus with marked hyperinsulinism in patients with ataxia telangiectasia. Clin Res 13: 530. Baskaran, R., Wood, L.D., Whitaker, L.L. et al. (1997). Ataxia-telangiectasia mutant protein activates c-AbI tyrosine kinase in response to ionizing radiation. Nature 387: 516–19. Bay, J-O., Grancho, M., Pernin, D. et al. (1998). No evidence for heterozygous ATM mutation using protein truncation test in breast/gastric cancer families. Int J Oncol 12(6): 1385–90. Bay, J-O., Uhrhammer, N., Pernin, D. et al. (1999). High incidence of cancer in a family segregating a mutation of the ATM gene: possible role of a ATM heterozygosity in cancer. Hum Mut 14: 485–92. Becker-Catania, S., Chen, G., Hwang, M.J. et al. (2000). Ataxiatelangiectasia: phenotype/genotype studies of ATM protein expression, mutations, and radiosensitivity. Mol Genet Metal 70: 122–33. Biemond, A. (1957). Palaeocerebellar atrophy with extrapyramidal manifestations in association with bronchoectasis and telangiectasis of the conjunctive bulbi as a familial syndrome. In Proceedings of the First International Congress of Neurological Sciences, Brussels, July 1957, ed. L. van Bogaert and J. Radermecker, pp. 206. London, Pergamon Press. Boder, E. and Sedgwick, R.P. (1957). Ataxia-telangiectasia; a familial syndrome of progressive cerebellar ataxia, oculocutaneous telangiectasia and frequent pulmonary infection. A preliminary report on seven children, an autopsy and a case history. Univ South California Med Bull 9: 15. Boder, E. and Sedgwick, R.P. (1963). Ataxia-telangiectasia: a review of 101 cases. In Little Club Clinics in Developmental Medicine, No. 8, ed. G. Walsh, pp. 110–18. London, Heinemann Medical Books. Borghesani, P.R., Alt, F.A., Bottaro, A. et al. (2000). Abnormal development of Purkinje cells and lymphocytes in Atm mutant mice. Proc Natl Acad Sci USA 97: 3336–41.

543

544

S. Perlman, J-O. Bay, N. Uhrhammer, and R.A. Gatti

Borresen, A.L., Anderson, T.I., Tretli, S., Heiberg, A. and Moller, P. (1990). Breast cancer and other cancers in Norwegian families with ataxia-telangiectasia. Genes, Chromosomes, and Cancer 2: 339–40. Brown, K.D., Ziv, Y., Sadanandan, S.N. et al. (1997). The ataxiatelangiectasia gene product, a constitutively expressed nuclear protein that is not up-regulated following genome damage. Proc Natl Acad Sci USA 94: 1840–5. Byrd, P.J., McConville, C.M., Cooper, P. et al. (1996). Mutations revealed by sequencing the 5 half of the gene for ataxia telangiectasia. Hum Mol Genet 5: 145–9. Campuzano, V., Montermini, L., Molto, M.D. et al. (1996). Friedreich’s ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science 271: 1423–7. Canman, C.E., Lim, D.S., Cimprich, K.A. et al. (1998). Activation of the ATM kinase by ionizing radiation and phosphorylation of p53. Science 281: 1677–9. Carr, A.M. (2000). Piecing together the p53 puzzle. Science 287: 1765–6. Castellvi-Bel, S., Sheikhavandi, S., Telatar, M. et al. (1999). New mutations, polymorphisms, and rare variants in the ATM gene detected by a novel strategy. Hum Mutat 14: 156–62. Chaturvedi, P., Eng, W.K., Zhu, Y. et al. (1999). Mammalian Chk2 is a downstream effector of the ATM-dependent DNA damage checkpoint pathway. Oncogene 18: 4047–54. Chen, G. and Lee, Y.-H.P. (1996). The product of the ATM gene is a 370–kD nuclear phosphoprotein. J Biol Chem 271: 33693–7. Chen, J., Birkholtz, G.G., Lindblom, P., Rubio, C. and Lindblom, A. (1998). The role of ataxia-telangiectasia heterozygotes in familial breast cancer. Cancer Res 58: 1376–9. Chen, P.C., Lavin, M.F., Kidson, C. and Moss, D. (1978). Identification of ataxia-telangiectasia heterozygotes; a cancer prone population. Nature 274: 484–6. Chen, X., Yang, L., Udar, N. et al. (1997). CAND3: a ubiquitouslyexpressed gene immediately adjacent and in opposite transcriptional orientation to the ATM gene at 11q23.1 Mamm Genome 8: 129–33. Chessa, L., Lisa, A., Fiorani, O. and Zei, G. (1994). Ataxia-telangiectasia in Italy: genetic analysis. Int J Radiat Biol 66: S31–3. Clarke, R.A., Goozee, G.R., Birrell, G. et al. (1998). Absence of ATM truncations in patients with severe acute radiation reactions. Int J Radiat Oncol Biol Phys 41: 1021–7. Concannon, P. and Gatti, R.A. (1997). Diversity of ATM gene mutations detected in patients with ataxia-telangiectasia. Hum Mutat 10: 100–7. Cortez, D., Wang, Y., Qin, J. and Elledge, S.J. (1999). Requirement of ATM-dependent phosphorylation of Brca1 in the DNA damage response to double-strand breaks. Science 286: 1162–6. Croce, C.M. (1998). Role of TCL1 and ALL1 in human leukemias and development. Canc Res 59: 177s–8s. Cunliffe, P.N., Mann, J.R., Cameron, A.H., Roberts, K.D. and Ward, H.W.C. (1975). Radiosensitivity in ataxia-telangiectasia. Br J Radiol 48: 374–6. Curry, C.J.R., O’Lague, P., Tsai, J. et al. (1989). ATFresno: a phenotype linking ataxia-telangiectasia with the Nijmegen breakage syndrome. Am J Hum Genet 45: 270–5.

Di Rocco, M., Arslanian, A., Romanengo, M., Dagna-Bricarelli, F. and Borrone, C. (1999). Ataxia, ocular telangiectasia, chromosome instability, and Langerhans cell histiocytosis in a patient with an unknown breakage syndrome. J Med Genet 36: 159–60. Easton, D.F. (1994). Cancer risks in A-T heterozygotes. Int J Radiat Biol 66: S177–82. Effros, R.B., Allsopp, R., Chiu, C-P. et al. (1996). Shortened telomeres in the expanded CD28CD8 cell subset in HIV disease implicate replicative senescence in HIV pathogenesis. AIDS 10: F17–F22. FitzGerald, M.G., Bean, J.M., Hegde, S.R. et al. (1997). Heterozygous ATM mutations do not contribute to early onset of breast cancer. Nat Genet 15: 307–10. Flaggs, G., Plug, A.W., Dunks, K.M. et al. (1997). Atm-dependent interactions of a mammalian chk1 homolog with meiotic chromosomes. Curr Biol 7: 977–86. Forrer, R., Chetrit, A., Luxenberg, O., Shiloh, Y. and Modan, B. (1999). Health status of A-T carriers. Eighth International Workshop on Ataxia-Telangiectasia, Las Vegas. USA, Feb 14–17. Gatei, M., Young, D., Cerosaletti, K.M. et al. (2000). ATM-dependent phosphorylation of nibrin in response to radiation exposure. Nat Genet 25: 115–19. Gately, D.P., Hittle, J.C., Chan, G.K.T. and Yen, T.J. (1998). Characterization of ATM expression, localization, and associated DNA-dependent protein kinase activity. Mol Biol Cell 9: 2361–74. Gatti, R.A. (2001). Ataxia-telangiectasia. In Metabolic and Molecular Basis of Inherited Disease, 8th edn, ed. C.R. Scriver, A.L. Beaudet, W.S. Sly and D. Valle, New York, McGraw-Hill. Gatti, R.A., Berkel, I., Boder, E. et al. (1988). Localization of an ataxia-telangiectasia gene to chromosome 11q22–23. Nature 336: 577–80. Gatti, R.A., Bick, M.B., Tam, C.F. et al. (1982). Ataxia-telangiectasia: a multiparameter analysis of eight families. Clin Immunol Immunopathol 23: 501–16. Gatti, R.A., Boder, E., Vinters, H.V., Sparkes, R.S., Normal, A. and Lange, K. (1991). Ataxia-telangiectasia: an interdisciplinary approach to pathogenesis. Medicine 70: 99–117. Gatti, R.A., Nieberg, R. and Boder, E. (1989). Uterine tumors in ataxia-telangiectasia. Gyn Oncol 32: 257–60. Gatti, R.A., Peterson, K.L., Novak, J. et al. (1993). Prenatal genotyping of ataxia-telangiectasia. Lancet 342: 376. Gatti, R.A., Tward, A. and Concannon, P. (1999). Cancer risk in ATM heterozygotes: a model of phenotypic and mechanistic differences between missense and truncating mutations. Mol Genet Metab 69: 419–23. Gatti, R.A. and Vinters, H.V. (1985). Cerebellar pathology in ataxiatelangiectasia. In: Ataxia-Telangiectasia: Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 225–32. New York, Alan R. Liss. Gatti, R.A. and Walford, R.L. (1981). Immune function and features of aging in chromosomal instability syndromes. In Immunologic Aspects of Aging, ed. D. Segre and L. Smith, pp. 449–65. New York: Marcel Dekker Inc. Geschwind, D.H., Perlman, S., Grody, W. et al. (1997). Friedreich’s

Ataxia-telangiectasia and variants

ataxia GAA repeat expansion in patients with recessive or sporadic ataxia. Neurology 49: 1004–9. Gilad, S., Bar-Shira, A., Harnik, R. et al. (1996). Ataxia-telangiectasia: founder effect among North African Jews. Hum Mol Genet 5: 2033–7. Gilad, S., Chessa, L., Khosravi, R. et al. (1998). Genotype– phenotype relationships in ataxia-telangiectasia and variants. Am J Hum Genet 62: 551–61. Gotoff, S.P., Amirmokri, E. and Liebner, E.J. (1967). Ataxia telangiectasia. Neoplasia, untoward response to x-irradiation, and tuberous sclerosis. Am J Dis Child 114: 617–25. Hall, E.J., Schiff, P.B., Hanks, G.E., et al. (1989). A preliminary report: frequency of A-T heterozygotes among prostate cancer patients with severe late responses to radiation therapy. Cancer J Sci Am 4, 385–9. Hannan, M.A., Sigut, D., Waghray, M. and Gascon, G.G. (1994). Ataxia-ocular motor apraxia syndrome: an investigation of cellular radiosensitivity of patients and their families. J Med Genet 31: 953–6. Hart, R.M., Kimler, B.F., Evans, R.G. and Park, C.H. (1987). Radiotherapeutic management of medulloblastoma in a pediatric patient with ataxia telangiectasia. Int J Radiat Oncol Biol Phys 13: 1237–40. Hecht, F. and Hecht, B.K. (1985). Ataxia-telangiectasia breakpoints in chromosome rearrangements reflect genes important to T and B lymphocytes. In Ataxia-Telangiectasia: Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 189–95. New York, Alan R. Liss, Inc. Hernandez, D., McConville, C.M., Stacey, M. et al. (1993). A family showing no evidence of linkage between the ataxia telaphigectasia gene and chromosome 11q22-23. J Med Genet 30: 135–40. Herndon, R.M. (1985). Selective vulnerability in the nervous system. In Ataxia-Telangiectasia: Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 257–67. New York, Alan R. Liss, Inc. Herzog, K-H., Chong, M.J., Kapsetaki, M., Morgan, J.I. and McKinnon, P.J. (1998). Requirement for Atm in ionizing radiation-induced cell death in the developing central nervous system. Science 280: 1089–91. Hirao, A., Kong, Y-Y., Matsuoka, S. et al. (2000). DNA damageinduced activation of p53 by the checkpoint kinase Chk2. Science 287: 1824–7. Huo, Y.K., Wang, Z., Hong, J-H. et al. (1994). Radiosensitivity of ataxia-telangiectasia, X-linked agammaglobulinemia and related syndromes. Cancer Res 54: 2544–7. Imai, T., Sugawara, T., Nishiyama, A. et al. (1997). The structure and organization of the human NPAT gene. Genomics 42(3): 388–92. Inskip, H.M., Kinlen, L.J., Taylor, A.M.R., Woods, C.G. and Arlett, C.F. (1999). Risk of breast cancer and other cancers in heterozygotes for ataxia-telangiectasia. Br J Cancer 79: 1304–7. Ishiguro, T., Taketa, K. and Gatti, R.A. (1986). Tissue of origin of elevated alphafetoprotein in ataxia-telangiectasia. Dis Markers 4: 293–7. Janin, N., Andrieu, N., Ossian, K. et al. (1999). Breast cancer risk in

ataxia telangiectasia (AT) heterozygotes: haplotype study in French AT families. Br J Cancer 80(7): 1042–5. Jaspers, N.G., Gatti, R.A., Baan, C., Linssen, P.C. and Bootsma, D. (1988). Genetic complementation analysis of ataxia telangiectasia and Nijmegen breakage syndrome: a survey of 50 patients. Cytogenet Cell Genet 49: 259–63. Johnson, J.P., Gatti, R.A., Sears, T.S., and White, R.L. (1986). Inverted duplication of the JH region in a patient with ataxia-telangiectasia. Am J Human Genet 39: 787–96. Jung, M., Kondratyev, A., Lee, S.A., Dimtchev, A. and Dritschilo, A. (1997). ATM gene product phosphorylates IB. Cancer Res 57: 24–7. Kamoshita, S., Aguilar, M.J. and Landing, B.H. (1975). Precocious aging in ataxia-telangiectasia: pathological evidence in the central nervous system. In Proceedings of the First International Congress of Child Neurology, Toronto. Khanna, K.K., Keating, K.E., Kozlov, S. et al. (1998). ATM associates with and phosphorylates p53: mapping the region of interaction. Nat Genet 20(4): 398–400. Kojis, T.L., Gatti, R.A. and Sparkes, R.S. (1992). The cytogenetics of ataxia-telangiectasia. Cancer Genet Cytogenet 56: 143–56. Lange, E., Borresen, A-L., Chen, X. et al. (1995). Localization of an ataxia-telangiectasia gene to a 500 kb interval on chromosome 11q23.1: linkage analysis of 176 families in an international consortium. Am J Hum Genet 57: 112–19. Lim, D-S., Kirsch, D.G., Canman, C.E. et al. (1998). ATM binds to beta-adaptin in cytoplasmic vesicles. Proc Natl Acad Sci USA 95: 10146–51. Louise-Bar, D. (1941). Sur un syndrome progressif comprenant des télangiectasies capillaires cutanees et conjonctivales symetriques, a disposition naevoide et de troubles cerebelleux. Confin Neurol (Basel) 4: 32–42. Madani, A., Choukroun, V., Soulier, J. et al. (1996). Expression of p13 MTCP1 is restricted to mature T-cell proliferations with t(X; 14) translocations. Blood 87: 1923–7. Madani, A., Soulier, J., Schmid, M. et al. (1995). The 8 kd protein of the putative oncogene MTCP-1 is a mitochondrial protein. Oncogene 10: 2259. McConville, C.M., Stankovic, T., Byrd, P.J. et al. (1996). Mutations associated with variant phenotypes in ataxia-telangiectasia. Am J Hum Genet 59: 320–30. McFarlin, D.E., Strober, W. and Waldmann, T.A. (1972). Ataxiatelangiectasia. Medicine 51: 281–314. Metcalfe, J.A., Parkhill, J., Campbell, L. et al. (1996). Accelerated telomere shortening in ataxia telangiectasia. Nat Genet 13: 350–3. Morgan, J.L., Holcomb, T.M. and Morrissey, R.W. (1968). Radiation reaction in ataxia telangiectasia. Am J Dis Child 116: 557–8. Morrell, D., Cromartie, E. and Swift, M. (1986). Mortality and cancer incidence in 263 patients with ataxia-telangiectasia. J Natl Cancer Inst 77: 89–92. Murphy, R.C., Berdon, W.E., Ruzal-Shapiro, C. et al. (1999). Malignancies in pediatric patients with ataxia telangiectasia. Pediatr Radiol 29: 225–30. Naeim, A., Repinski, C., Huo, Y. et al. (1994). Ataxia-telangiectasia: flow cytometric cell-cycle analysis of lymphoblastoid cell lines in G2/M before and after gamma-irradiation. Mod Path 7: 587–92.

545

546

S. Perlman, J-O. Bay, N. Uhrhammer, and R.A. Gatti

Narducci, M.G., Virgilio, L. and Isobe, M. (1995). TCL1 oncogene activation in preleukemic T cells from a case of ataxiatelangiectasia. Blood 86: 2358–64. Paganelli, R., Scala, E., Scarselli, E. et al. (1992). Selective deficiency of CD4 /CD45A lymphocytes in patients with ataxiatelangiectasia. J Clin Immunol 12: 84–91. Painter, R.B. (1993). Radiobiology of ataxia-telangiectasia. In Ataxia-Telangiectasia, NATO ASI Series, ed. R.A. Gatti and R.B. Painter, pp. 257–68. Heidelberg, Springer-Verlag. Pandita, T.K., Pathak, S. and Geard, C.R. (1995). Chromosome end associations, telomeres and telomerase activity in ataxia telangiectasia cells. Cytogenet Cell Genet 71: 86–93. Paterson, M.C., MacFarlane, S.J., Gentner, N.E. and Smith, B.P. (1985). Cellular hypersensitivity to chronic •-radiation in cultured fibroblasts from ataxia-telangiectasia heterozygotes. In Ataxia-Telangiectasia: Genetics, Neuropathology and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 73–87. New York, Alan R. Liss. Pernin, D., Bay, J-O., Uhrhammer, N. and Bignon, Y-J. (1999). ATM heterozygote cells exhibit intermediate levels of apoptosis in response to streptonigrin and etoposide. Eur J Cancer 35: 1130–5. Peterson, P.L., Saad, J. and Nigro, J. (1998). The treatment of Friedreich’s ataxia with amantidine hydrochloride. Neurology 38: 1478–80. Peto, J., Collins, N., Barfoot, R. et al. (1999). Prevalence of BRCA1 and BRCA2 gene mutations in patients with early-onset breast cancer. J Natl Cancer Inst 91: 943–9. Pippard, E.C., Hall, A.J., Barker, D.J.P. and Bridges, B.A. (1988). Cancer in homozygotes and heterozygotes of ataxia-telangiectasia and xeroderma pigmentosum in Britain. Cancer Res 118: 2929–32. Platzer, M., Rotman, G., Bauer, D. et al. (1997). Ataxia-telangiectasia locus: sequence analysis of 184 kb of human genomic DNA containing the entire ATM gene. Genome Res 7(6): 592–605. Porras, O., Arguendas, O., Arata, M., Barrantes, M., Gonzalez, L. and Saenz, E. (1993). Epidemiology of ataxia-telangiectasia in Costa Rica. In Ataxia-Telangiectasia, ed. R.A. Gatti and R.B. Painter, pp. 199–208. Heidelberg, Springer-Verlag. Regueiro, J.R., Porras, O., Lavin, M. and Gatti, R.A. (2000). Ataxiatelangiectasia. A primary immunodeficiency revisited. Immunol Allergy Clin N Am 20: 177–206. Roifman, C.M. and Gelfand, E.W. (1985). Heterogeneity of the immunological deficiency in ataxia-telangiectasia: absence of a clinical–pathological correlation. In Ataxia-Telangiectasia: Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 273–85. New York, Alan R. Liss, Inc. Rotman, G. and Shiloh, Y. (1999). ATM: a mediator of multiple responses to genotoxic stress. Oncogene 18: 6135–44. Russo, G., Isobe, M., Gatti, R.A. (1989). Molecular analysis of a t(14;14) translocation in leukemic T-cells of an ataxia-telangiectasia patient. Proc Natl Acad Sci USA 86: 602–6. Savitsky, K., Bar-Shira, A., Gilad, S. et al. (1995). A single ataxiatelangiectasia gene with a product similar to PI3 kinase. Science 268: 1749–53.

Savitsky, K., Platzer, M., Uziel, T. et al. (1997). Ataxia-telangiectasia: structural diversity of untranslated sequences suggests complex post-transcriptional regulation of ATM gene expression. Nucl Acids Res 25: 1678–84. Scott, D., Spreadborough, A.R. and Roberts, S.A. (1994). Radiationinduced G2 delay and spontaneous chromosomes aberrations in ataxia-telangiectasia homozygotes and heterozygotes. Int J Radiat Biol 66: S157–63. Sedgwick, R.P. and Boder, E. (1991). Ataxia-telangiectasia. In Handbook of Clinical Neurology, Vol. 16: Hereditary Neuropathies and Spinocerebellar Atrophies, ed. J.M.B.V. de Jong, pp. 347–423. Amsterdam, Elsevier Science. Shafman, T., Khanna, K.K., Kedar, P. et al. (1997). Interaction between ATM protein and c-AbI in response to DNA damage. Nature 387: 520–3. Shiloh, Y., Tabor, E. and Becker, Y. (1982). The response of ataxiatelangiectasia homozygous and heterozygous skin fibroblasts to neocarzinostatin. Carcinogenesis 3: 815–20. Smith, G.C., Cary, R.B. and Lakin, N.D. (1999). Purification and DNA binding properties of the ataxia-telangiectasia gene product ATM. Proc Natl Acad Sci USA 96: 11134–9. Soares, H.D., Morgan, J.I. and McKinnon, P.J. (1998). Atm expression patterns suggest a contribution from the peripheral nervous system to the phenotype of ataxia-telangiectasia. Neuroscience 86: 1045–54. Spacey, S.D., Gatti, R.A. and Bebb, G. (2000). The molecular basis and clinical management of ataxia-telangiectasia. Can J Neurol Sciences 27: 184–91. Stankovic, T., Kidd, A.M.J., Sutcliffe, A. et al. (1998). ATM mutations and phenotypes in ataxia-telangiectasia families in the British Isles: expression of mutant ATM and the risk of leukemia, lymphoma, and breast cancer. Am J Hum Genet 62: 334–5. Stewart, G.S., Maser, R.S., Stankovic, T. et al. (1999). The DNA double-strand break repair gene hMRE11 is mutated in individuals with an ataxia-telangiectasia-like disorder. Cell 99: 577–87. Swift, M. (1985). Genetics and epidemiology of ataxia-telangiectasia. In Ataxia-Telangiectasia. Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 133–44. New York, Alan R. Liss, Inc. Swift, M., Morrell, D., Cromartie, E., Chamberlin, A.R., Skolnick, M.H. and Bishop, D.T. (1986). The incidence and gene frequency of ataxia-telangiectasia in the United States. Am J Hum Genet 39: 573–83. Swift, M., Morrell, D., Massey, R.B. and Chase, C.L. (1991). Incidence of cancer in 161 families affected by ataxia-telangiectasia. N Engl J Med 325: 1831–6. Swift, M., Reitnauer, P.J., Morrell, D. and Chase, C.L. (1987). Breast and other cancers in families with ataxia-telangiectasia. N Engl J Med 316: 1289–94. Syllaba, L. and Henner, K. (1926). Contribution a l’independence de l’athetose double idiopathique et congenitale. Rev Neurol 1: 541–62. Taylor, A.M.R., Harnden, D.G., Arlett, C.F. et al. (1975). Ataxiatelangiectasia: a human mutation with abnormal radiation sensitivity. Nature 258: 427–9.

Ataxia-telangiectasia and variants

Taylor, A.M.R., Metcalfe, J.A., Thick, J. and Mak, Y-F. (1996). Leukemia and lymphoma in ataxia-telangiectasia. Blood 87: 423–38. Tchirkov, A., Bay, J-O., Pernin, D. et al. (1997). Detection of heterozygous carriers of the ataxia-telangiectasia (ATM) gene by G2 phase chromosomal radiosensitivity of peripheral blood lymphocytes. Hum Genet 101: 312–16. Telatar, M., Teraoka, S., Wang, Z. et al. (1998a). Ataxia-telangiectasia: identification and detection of founder-effect mutations in the ATM gene in ethnic populations. Am J Hum Genet 62: 86–97. Telatar, M., Wang, Z., Castellvi-Bel, S. et al. (1986b). A model for ATM heterozygote identification in a large population: four founder-effect ATM mutations identify most of Costa Rican patients with ataxia-telangiectasia. Mol Genet Metabol 64: 36–43. Telatar, M., Wang, Z., Udar, N. et al. (1996). Ataxia-telangiectasia: mutations in ATM cDNA detected by protein-truncation screening. Am J Hum Genet 59: 40–4. Thick, J., Metcalfe, J.A., Mak, Y-F. et al. (1996). Expression of either the TCL1 oncogene, or transcripts from its homologue MTCP1/c6. 1B, in leukaemic and non-leukaemic T cells from ataxia telangiectasia patients. Oncogene 12: 379–86. Thiele, E.A., Bonilla, F., Rosen, F. and Riviello, J.I. (1994). Ataxia telangiectasia associated with the hyper-IgM syndrome. International Neurology Conference, San Francisco, September 9–11. Trouillas, P., Xie, J., Adeleine, P. et al. (1997). Buspirone, 5-hydroxytryptamine 1A agonist, is active in cerebellar ataxia. Results of a double-blind drug placebo study in patients with cerebellar cortical atrophy. Arch Neurol 54: 49–52. Udar, N., Xu, S., Bay, J-O. et al. (1999). Physical map of the region surrounding the ataxia-telangiectasia gene on human chromosome 11q22-23. Neuropediatrics 30: 176–80. Uhrhammer, N., Lange, E., Porras, O. et al. (1995). Sublocalization of an ataxia-telangiectasia gene distal to D11S384 by ancestral haplotyping in Costa Rican families. Am J Hum Genet 57: 103–11. Varon, R., Vissinga, C., Platzer, M. et al. (1998). Nibrin, a novel DNA double-strand break repair protein, is mutated in Nijmegen breakage syndrome. Cell 93: 467–76. Vinters, H.V., Gatti, R.A. and Rakic, P. (1985). Sequence of cellular events in cerebellar ontogeny relevant to expression of neuronal abnormalities in ataxia-telangiectasia. In Ataxia-Telangiectasia:

Genetics, Neuropathology, and Immunology of a Degenerative Disease of Childhood, ed. R.A. Gatti and M. Swift, pp. 233–55. New York, Alan R. Liss, Inc. Vorechovsky, I., Luo, L., Lindblom, A. et al. (1996a). ATM mutations in cancer families. Cancer Res 56: 4130–3. Vorechovsky, I., Rasio, D., Luo, L. et al. (1996b). The ATM gene and susceptibility to breast cancer: analysis of 38 breast tumors reveals no evidence for mutation. Cancer Res 56: 2726–32. Wang, Y., Cortez, D., Yazdi, P., Neff, N., Elledge, S.J. and Qin, J. (2000). BASC, a super complex of BRCA-1-associated proteins involved in the recognition and repair of aberrant DNA structures. Genes Develop 14: 927–39. Watters, D., Khanna, K.K., Beamish, H. et al. (1997). Cellular localization of the ataxia-telangiectasia gene product and discrimination between mutated and normal forms. Oncogene 14: 1911–21. Weemaes, C.M.R., Hustinx, T.W.J., Scheres, J.M.J.C., Van Munster, P.J.J., Bakkeren, J.A.J.M. and Taalman, R.D.F.M. (1981). A new chromosomal instability disorder: the Nijmegen breakage syndrome. Acta Paediatr Scand 70: 557–62. Woods, C.G. and Taylor, A.M. (1992). Ataxia telangiectasia in the British Isles: the clinical and laboratory features of 20 affected individuals. Q J Med 82: 169–79. Xu, Y., Ashley, T., Brainerd, E.E., Bronson, R.T., Meyn, M.S. and Baltimore, D. (1996). Targeted disruption of ATM leads to growth retardation, chromosomal fragmentation during meiosis, immune defects, and thymic lymphoma. Genes Develop 10: 2411–22. Yamashita, T., Nakane, A., Watanabe, T., Miyoshi, I. and Kasai, M. (1994). Evidence that alpha-fetoprotein suppresses the immunological function in transgenic mice. Biochem Biophys Res Commun 201: 1154–9. Yuan, Z.M., Huang, Y. and Ishiko, T. (1997). Regulation of DNA damage-induced apoptosis by the c-AbI tyrosine kinase. Proc Natl Acad Sci USA, 94: 1437–40. Yuan, Z.M., Huang, Y., Ishiko, T. (1998). Regulation of Rad51 function by c-AbI in response to DNA damage. J Biol Chem 273(7): 3799–802. Zhao, S., Yuan, F.S-S., Weng, Y-C. et al. (2000). A functional link between ATM kinase and NBS1 in the DNA damage response. Nature 405: 473–6.

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Ataxia in mitochondrial disorders Massimo Zeviani1, Carlo Antozzi2, Mario Savoiardo3, and Enrico Bertini4 1

Division of Biochemistry and Genetics, 2 Neuromuscular Research Department, 3 Division of Neuroradiology, National Neurological Institute Carlo Besta, Milan, Italy, 4 Department of Neurosciences, Bambino Gesù Hospital, Rome, Italy

Definition and classification Neurological syndromes are the most frequent clinical presentations of mitochondrial disorders, a group of human diseases characterized by defects of the mitochondrial energy output. Mitochondrial energy metabolism is composed of several pathways, including the pyruvate dehydrogenase complex, the Krebs’ cycle, the mitochondrial beta-oxidation of fatty acids, etc., along with specialized transport systems specific to adenosine triphosphate/ adenosine diphosphate (ATP/ADP), metabolites, substrates, etc. However, the term ‘mitochondrial disorders’ is, to a large extent, applied to the clinical syndromes associated with abnormalities of the common final pathway of the mitochondrial energy metabolism, i.e., the oxidative phosphorylation (OXPHOS). OXPHOS is carried out in the inner mitochondrial membrane by the five enzymatic complexes of the respiratory chain (Zeviani and Antozzi, 1997). From a genetic standpoint, the respiratory chain is unique, because it is formed through the complementation of two separate genetic systems, the nuclear and the mitochondrial genomes. Nuclear genes provide most of the protein subunits of the respiratory complexes, the factors that control their intramitochondrial transport, assembly, and turnover, as well as the enzymes for the synthesis of prosthetic groups. In addition, most of the components of the mitochondrial DNA (mtDNA)-replication and mtDNA-expression systems are encoded by genes localized in the nucleus. In turn, human mtDNA, a maternally transmitted circular minichromosome, present in two to ten copies per organelle, is composed of mRNAgenes encoding 13 subunits of respiratory complexes I, III, IV, and V, as well as of tRNA-genes and rRNA-genes that are part of the RNA apparatus deputed to intra-organellar mtDNA translation (Anderson et al., 1981).

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The complexity of the biochemical and genetic features of the respiratory chain accounts for the extraordinarily wide range of clinical presentations of the mitochondrial disorders (DiMauro and Moraes, 1993). In general, organs with the highest aerobic demand, such as skeletal muscle, brain, and heart, are the most severely involved, although many exceptions are reported. In addition, because these organs are composed of highly specialized, postmitotic cells, negative selection against cells containing faulty mitochondria is impossible. As a result, abnormal organelles proliferate in these organs, often at an accelerated rate, probably as a compensatory, but ineffective, mechanism against OXPHOS impairment. In the case of skeletal muscle, mitochondria of larger size and/or bizarre shape can ultimately fill discrete portions of the sarcoplasm, producing the well-known morphological hallmark of many mitochondrial myopathies, i.e., the ragged-red transformation of the muscle fibers. Each tissue can be affected alone (‘pure’ mitochondrial myopathies, encephalopathies, or cardiomyopathies) or, more often, in combination with each other (mitochondrial encephalomyopathies and encephalocardiomyopathies). Hence, limb weakness with or without exercise intolerance may be the sole clinical feature of mitochondrial disease, or it may be associated with chronic progressive external ophthalmoplegia and ptosis, pigmentary retinopathy, and encephalopathic features including dementia, seizures, myoclonus, ataxia, and stroke-like episodes. Cardiac conduction defects are common in mitochondrial disorders, and symptomatic mitochondrial cardiomyopathy, with or without skeletal myopathy, has been reported at increasing frequency in the recent past (Antozzi and Zeviani, 1997; Bruno et al., 1999). However, virtually any organ or tissue in the body can be affected, including gastrointestinal tract (Bardosi et al., 1987), liver (Mazziotta et al., 1992), kidney, and the endocrine systems.

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Although some mitochondrial syndromes are wellestablished and nosologically defined entities, clinical data are not sufficient to provide a systematic classification of mitochondrial diseases, because overlap syndromes or aspecific phenotypes are possible. Likewise, identical biochemical (e.g., lactic acidosis) and morphological (e.g., ragged-red fibers) abnormalities can be found in different clinical presentations, or can be absent in patients with otherwise-proven mitochondrial diseases. Until the discovery of the first mutations of mtDNA, the diagnosis of mitochondrial (encephalo)myopathies was largely based on the detection of ragged red fibers in the muscle biopsy (Rowland et al., 1991). An important advancement towards the identification and characterization of these disorders was the set-up of methods to measure spectrophotometrically the activities of individual respiratory enzymes, as well as the respiration rate in intact mitochondria, or whole cells, by polarography. With the identification of mtDNA mutations, genetic studies have been providing further pathogenetic insights and new diagnostic clues about mitochondrial disorders. The recent discovery of the first mutations in nuclear genes responsible for OXPHOS abnormalities has ushered in a ‘fourth era’ of research. However, in several cases, mitochondrial disorders, defined on the basis of morphological or biochemical findings, still lack a molecular–genetic definition. More rarely, OXPHOS defects identified biochemically have no morphological counterpart in muscle, e.g., the neurogenic muscle weakness, ataxia, retinitis pigmentosa (NARP) syndrome: see below. In a few clinical syndromes, such as Leber’s hereditary optic atrophy, the diagnosis is based on the identification of mtDNA mutations only, and morphological and biochemical analyses are uninformative (Riordan-Eva and Harding, 1995). Therefore, an approach based on multiple diagnostic strategies is necessary and recommended. A widely accepted classification of mitochondrial disorders links the clinical and biochemical features to the genetic abnormalities allegedly or provenly associated with these disorders (Table 39.1). Accordingly, mitochondrial diseases can be divided into three main groups: (1) genetically defined defects of the mitochondrial genome; (2) disorders of the nuclear–mitochondrial cross-talk; and (3) OXPHOS defects due to abnormalities of nuclear genes. Given the scope of the present review, only the clinical presentations including ataxia as a prominent and consistent feature will be considered.

Mutations of mtDNA In normal conditions, the mitochondrial genotype of an individual is composed of a single mtDNA species, a condition known as homoplasmy. Mutations of mtDNA can produce a transitory condition known as heteroplasmy, in which the wild-type and the mutant genomes coexist intracellularly. Because of mitochondrial polyploidy, during mitosis the two mtDNA species are stochastically distributed to subsequent cell generations. By a genetic drift called ‘mitotic segregation’ (Marchington et al., 1998), the relative proportion between mutant and wild-type genomes can vary widely among cells and, consequently, among tissues and individuals. This phenomenon can explain the extreme variability of the phenotypic expression of a given mtDNA mutation, as often observed in mitochondrial disorders. Deleterious mutations may arise frequently, but are rapidly eliminated by negative selection; therefore, they do not become fixed in any specific mitochondrial haplogroup, but are rather found in different haplogroups, and are often heteroplasmic. Heteroplasmy, distribution among different human populations, and, of course, specific segregation with the disease are distinctive features of pathogenic mutations. As for heteroplasmic mutations, only when mutated gene copies accumulate over a certain threshold will the deleterious effects of the mutation no longer be complemented by the coexisting wild-type mtDNA, and will be expressed phenotypically as a cellular dysfunction leading to disease. In addition, phenotypic expression will depend upon the nature of the mutation, i.e., its intrinsic pathogenicity, its tissue distribution, and the relative reliance of each organ system on the mitochondrial energy supply.

Molecular features From a molecular genetic standpoint, two categories of mtDNA mutations have been identified: large-scale mtDNA rearrangements and mtDNA point mutations.

Large-scale rearrangements Large-scale rearrangements consist of single partial mtDNA deletions (mtDNA) or, more rarely, partial duplications (Holt et al., 1988; Zeviani et al., 1988; Moraes et al., 1989; Poulton, 1992). Both types of mutation are heteroplasmic, because they coexist with variable amounts of wild-type mtDNA (mtDNAwt). These mutations are associated with sporadic disorders (see below). Because deleted mtDNA species have been detected in human oocytes (Chen et al., 1995), an unknown mechanism must prevent the vertical transmission or the expansion of

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Table 39.1 Classification of mitochondrial disorders Phenotype

mtDNA mutation

1) Defects of mtDNA KSS/PEO/PS PEO/PEO multisystem

Single deletion/duplication Point mutation

MELAS

Point mutation

MERRF MERRF/MELAS

Point mutation Point mutation

NARP/MILS Bilateral striatal necrosis Mitochondrial myopathy

Point mutation Point mutation Point mutation

MIMyCa

260 bp tandem duplication Point mutation

Hypertrophic cardiomyopathy

Point mutation

Cardiomyopathy, multisystem Fatal multisystem disease Multisystem disease, sudden death LHON

Point mutation Point mutation Point mutation Point mutation

LHON–dystonia Dementia–chorea Diabetes–deafness

Point mutation Point mutation Point mutation Large-scale duplication/deletion duplication Point mutation Large-scale duplication Large-scale deletion Point mutation Point mutation Single insertion Point mutation Point mutation Point mutation Microdeletion Point mutation Point mutation Point mutation

Diabetes–ataxia–PEO Tubulopathy, diabetes, ataxia Ataxia–leukodystrophy Hearing loss, ataxia, myoclonus Encephalomyopathy

Myoglobinuria Aminoglycoside-induced deafness Sensorineural deafness Sideroblastic anemia

Gene location

tRNA-Leu(UUR) tRNA-Ile tRNA-Asn tRNA-Leu(CUN) tRNA-Leu(UUR) tRNA-Val tRNA-Phe tRNA-Cys COX III ND5 tRNA-Lys tRNA-Ser-UCN tRNA-Lys ATPase 6 ATPase 6 tRNA-Leu(UUR) tRNA-Leu(CUN) tRNA-Phe tRNA-Trp tRNA-Met tRNA-Pro Cyt b tRNA-Leu(UUR) 12sRNA tRNA-Ile tRNA-Gly tRNA-Ile, tRNA-Lys tRNA-Thr tRNA-Gly NDI, ND2, ND4, ND5, ND6, COXI, COXIII, Cyt b, ATPase 6 ND4, ND6 tRNA-Trp tRNA-Leu(UUR), tRNA-Lys tRNA-Leu(UUR)

tRNA-Ser4(UCN) tRNA-Leu(UUR) tRNA-Trp COXIII tRNA-Thr tRNA-Phe, Cyt b COXIII 12S rRNA tRNA-Ser(UCN) tRNA-Leu(CUN), COXI

Ataxia in mitochondrial disorders

Table 39.1 (cont.) Phenotype

mtDNA mutation

Gene location

2) Defects of neucleo-mitochondrial signalling a) Qualitative alterations of mtDNA Autosomal dominant PEO Autosomal recessive PEO, cardiomyopathy Myopathy–encephalomyopathy Familial myoglobinuria Familial cardiomyopathy PEO–cardiomyopathy Sensory ataxic neuropathy–PEO MERRF

Multiple deletions Multiple deletions Multiple deletions Multiple deletions Multiple deletions Multiple deletions Multiple deletions Multiple deletions

b) Quantitative alterations of mtDNA Fatal infantile hepatopathy Fatal infantile myopathy Myopathy of childhood Encephalomyopathy

mtDNA depletion mtDNA depletion mtDNA depletion mtDNA depletion

3) OXPHOS defects due to abnormalities of nuclear genes Biochemically defined defects Myopathy, encephalomyopathy, fatal/benign infantile myopathy, histiocytoid cardiomyopathy of infancy Leigh syndrome

Complex I, II, III, IV, V

Genetically defined defects Leigh syndrome Leigh syndrome Leigh syndrome

fp subunit, complex II NDUFS7, complex I NDUFS8, complex I

Assembly factors of the respiratory chain Leigh syndrome

Surf 1, 9q

Mitochondrial factors indirectly related to OXPHOS Friedreich’s ataxia X-linked sideroblastic anemia and ataxia X-linked deafness–dystonia syndrome Hereditary spastic paraplegia

GAA expansion Mutation Deletion Deletion, mutation

9q13 (frataxin) Xq13 (ABC7) Xq22 (DDP) 16q (paraplegin)

Notes: KSS: Kearns–Sayre syndrome; PEO: progressive external ophthalmoplegia; PS: Pearson’s syndrome; MELAS: mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes; MERRF: Myoclonic epilepsy with ragged red fibres; NARP: neuropathy, ataxia, retinitis pigmentosa; MILS: maternally inherited Leigh syndrome; MIMyCa: mitochondrial myopathy and cardiopathy; MNGIE: myo-neuro-gastrointestinal encephalopathy; LHON: Leber’s hereditary optic neuropathy; ND: NADH-ubiquinone oxidoreductase, complex 1; COX: cytochrome c oxidase, complex IV; UUR: codon UUR (coding for leucine); CUN: codon CUN (coding for leucine); NDUFS: NADH-ubiquinone oxidoreductase subunit; GAA: guanine–adenine–adenine triplet repeat (expanded in Friedreich’s ataxia); chr.: chromosome. For a detailed list and references see the appendix in each issue of the journal Neuromuscular Disorders and the website: http://www.gen.emory.edu/mitomap.html.

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mtDNA-genomes. The presence of a single mtDNA deletion (or partial duplication) in each patient is explained by the clonal amplification of a single mutational event. As for other mtDNA mutations, mitotic segregation can increase the variability of the tissue distribution of mtDNA, hence influencing the clinical phenotype. Deletions are usually flanked by direct repeats of variable length (Schon et al., 1989), suggesting that they are generated by a mechanism of slipped-mispairing of the single mtDNA strands during replication (Shoffner et al., 1989). All of the mtDNA deletions described so far encompassed more than one gene, including both mRNA and tRNA genes. The loss of tRNA genes contained in the deletion makes the mtDNA species translationally incompetent. Therefore, translation of these genomes can take place only through the complementation by mtDNAwt contained in the same organelle. The mtDNA/mtDNAwt ratio can thus influence dramatically the functional consequence of the mutation (Mita et al., 1989; Hayashi et al., 1991).

Of the very many mtDNA-related syndromes associated with ataxia, four are relatively frequent and well characterized both clinically and genetically. These are Kearns–Sayre syndrome; mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS); myoclonus-epilepsy with ragged-red fibers (MERRF); and neurogenic weakness, ataxia and retinitis pigmentosa (NARP). Kearns–Sayre syndrome is almost invariably associated with a heteroplasmic mtDNA deletion or duplication, whereas MELAS, MERRF, and NARP are due to different point mutations.

Point mutations

Kearns–Sayre syndrome

In contrast to large-scale rearrangements, mtDNA point mutations are usually maternally inherited, and can occur in mRNA, tRNA, or rRNA genes. Given the very high mutational rate of mtDNA and the presence of numerous ‘private’ or population-specific polymorphisms, it is essential to distinguish non-deleterious from pathogenic mutations. The latter are usually characterized by the following features: (1) high conservation; (2) segregation with phenotype; (3) quantitative correlation between phenotype and heteroplasmy, if present; and (4) identification of the mutation in affected families from ethnically distinct human populations. Point mutations involving tRNA genes cause a reduced availability of functional tRNAs that impairs the overall mitochondrial protein synthesis. Both mitochondrial protein synthesis and respiration are markedly reduced above a threshold of 80–90% of mutant mtDNA (Chomyn et al., 1992; King et al., 1992; Yoneda et al., 1994; Mariotti et al., 1994). Mutations involving protein-encoding genes affect specifically the function of the respiratory complex, to which the corresponding protein belongs. The clinical and biochemical variability of many mtDNA mutations may be due to different mitochondrial and/or nuclear ‘gene backgrounds.’ For instance, the fate and expression of mutations in cultures appear to be strongly influenced by the different nuclear backgrounds of the cell types (Dunbar et al., 1995). It has also been proposed that nucleotide changes in mtDNA that are not intrinsically pathogenic may predispose to, modulate the effects of, or reflect a propensity for the occurrence of deleterious muta-

Kearns–Sayre syndrome is a sporadic, severe disorder characterized by the invariant triad of (1) progressive external ophthalmoplegia, (2) pigmentary retinopathy, and (3) onset before age 20. Frequent additional symptoms are poor growth, a progressive cerebellar syndrome, heart block, and increased protein content in the cerebrospinal fluid (CSF). Cerebellar ataxia can be the only sign of CNS involvement for some time in Kearns–Sayre syndrome. A partial and milder variant of Kearns–Sayre syndrome, sporadic progressive external ophthalmoplegia, is an adult-onset disease characterized by bilateral ptosis and ophthalmoplegia, frequently associated with variable degrees of proximal muscle weakness and wasting, and exercise intolerance. Progressive external ophthalmoplegia is variably associated with signs of central nervous system (CNS) involvement, among which mild ataxia is frequent. Pearson’s bone marrow–pancreas syndrome is a rare disorder of early infancy characterized by sideroblastic anemia with pancytopenia and exocrine pancreatic insufficiency. It should not be mentioned here for any reason but for the observation that infants surviving into childhood may develop the clinical features of Kearns–Sayre syndrome (Rotig et al., 1990; McShane et al., 1991). Kearns–Sayre syndrome is characterized by distinctive neuroradiological abnormalities in the cerebellum and brainstem, but also in supratentorial structures including the basal ganglia, thalami, and subcortical white matter (Barkovich et al., 1993; Fig. 39.1). In the brainstem, the mesencephalon can be affected diffusely, but occasionally

tions. In turn, deleterious mutations may promote the accumulation of somatic changes, through the generation of OXPHOS-related mutagens (Luft, 1994). This phenomenon could trigger a positive feedback loop contributing to the progression of the mitochondrial dysfunction.

Ataxias associated with mtDNA mutations

Ataxia in mitochondrial disorders

A

B

C

D

Fig. 39.1 Kearns–Sayre syndrome. MRI T2-weighted coronal sections show hyperintensities involving the dentate nuclei (A) and the subcortical white matter of the cerebral hemispheres (B). Axial FLAIR images show more extensive signal abnormalities of the dentate nuclei and surrounding white matter (C), extending to the superior cerebellar peduncles (D).

the red nuclei are selectively involved. In the cerebellum, the most severely affected structures are the dentate nuclei and the dentate-rubral fibers in the superior cerebellar peduncle. Light microscopy examination can reveal neuronal degeneration and gliosis of the basal ganglia and spongy degeneration of the white matter, including the cerebellum (Oldfors et al., 1990; McKelvie et al., 1991). Loss

of Purkinje cells has been reported in Kearns–Sayre syndrome, along with severely reduced expression of mtDNAencoded proteins in neurons of the dentate nucleus (Tanji et al., 1999). These findings are quite specific to Kearns–Sayre syndrome, and contribute to explaining why cerebellar ataxia is a prominent, and occasionally the only, CNS symptom.

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A

B

Fig. 39.2. MELAS. (A) MRI axial T2-weighted sections of the cerebral hemispheres show multiple lesions, mostly involving the posterior regions of the cerebral hemispheres. Basal ganglia are also affected. (B) Coronal T2-weighted image on the cerebellum from a different patient shows hyperintensities mostly involving the lateral part of the cerebellar hemispheres.

Kearns–Sayre syndrome, progressive external ophthalmoplegia, and Pearson’s syndrome are all associated with large-scale heteroplasmic rearrangements of mtDNA. Usually, deletions are easily detected by Southern blot analysis of muscle DNA, whereas they can be absent in lymphocyte or fibroblast DNA, especially in the milder cases (e.g., progressive external ophthalmoplegia).

MELAS MELAS is defined by the presence of (1) stroke-like episodes due to focal brain lesions, often localized in the parieto-occipital lobes, and (2) lactic acidosis and/or ragged-red fibers. Other signs of CNS involvement include dementia, recurrent headache and vomiting, focal or generalized seizures, and deafness. Ataxia can be observed in some patients (Hirano et al., 1992). Infarct-like lesions widespread in the cerebral cortex are associated with diffuse fibrillary gliosis in the cerebral and cerebellar white matter. Multiple focal lesions with demyelination and numerous spheroids have been reported in the pontocerebellar fibers, together with marked degeneration of the posterior columns and spinocerebellar tracts (Mizukami et al., 1992). Electron microscopic examination shows accumulations of abnormal mitochondria in smooth muscle cells and endothelium of the cerebral and cerebellar blood vessels, suggesting a ‘mitochondrial angiopathy.’ However, the presence of diffuse, prominent white matter gliosis of the CNS and cerebellar cortical degeneration of granular cell type may

indicate morphologically widespread cellular dysfunction, not restricted to either neuronal or vascular derangement (Tsuchiya et al., 1999). Magnetic resonance imaging (MRI) examination typically shows that the signal abnormalities in the cerebellum, as well as in supratentorial structures, do not correspond to well-defined vascular territories. However, the lesions are usually located in the distal part of the areas supplied by the three major arteries of the cerebellum (superior, anterior-inferior, and posterior-inferior cerebellar arteries: Fig. 39.2). Cerebellar involvement can be detected by MRI several years before the development of strokes, and can be associated with increased signal intensity in T2-weighted images of the cerebellar hemispheres (Savoiardo et al., 1999). MELAS was first associated with a heteroplasmic point mutation in the tRNA Leu(UUR), an A→G transition at position 3243 (Goto et al., 1990). Other MELASassociated point mutations were later reported (http://www.gen.emory.edu/mitomap.html), although the A3243G remains by far the most frequent. The genotype–phenotype correlation of the A3243G mutation is rather loose, because the observed clinical manifestations are not limited to the full-blown MELAS syndrome. For instance, the A3243G mutation has been detected in several patients (and families) with maternally inherited progressive external ophthalmoplegia, isolated myopathy alone, cardiomyopathy, or in pedigrees with maternally inherited diabetes mellitus and deafness.

Ataxia in mitochondrial disorders

MERRF MERRF is a maternally inherited neuromuscular disorder characterized by myoclonus, epilepsy, muscle weakness and wasting, cerebellar ataxia, deafness, and dementia (Fukuhara et al., 1980; Wallace et al., 1988; Berkovic et al., 1989). Cerebellar lesions are prominent neuropathological features of MERRF syndrome, as originally described by Fukuhara in 1991. Neurodegenerative changes involve the dentate nuclei and the posterior columns and spinocerebellar tracts of the spinal cord. Neuronal loss and gliosis of the cerebellar dentate nuclei and inferior olives have been reported in patients carrying the 8344 mtDNA mutation in association with MERRF (Lombes et al., 1989; Oldorfs et al., 1995) or Leigh syndrome (Nijtmans et al., 1994). These neuropathological findings have been confirmed by a few neuroimaging studies on MERRF cases. Diffuse cerebral and cerebellar atrophy and calcifications in the basal ganglia can be associated with signal abnormalities in the dentate nuclei, superior cerebellar peduncles, and inferior olives (Barkovich et al., 1993). The most commonly observed mutation of mtDNA associated with MERRF is an A→G transition at nt 8344 in the tRNALys gene (Shoffner et al., 1990). A second mutation has been reported in the same gene, at position 8356 (Silvestri et al., 1992; Zeviani et al., 1993). Clinical, biochemical, and molecular investigation of large pedigrees showed a positive correlation between the severity of the disease, age at onset, mtDNA heteroplasmy, and reduced activity of respiratory chain complexes I and IV in skeletal muscle. However, even though the genotype–phenotype correlation between MERRF syndrome and the A8344G mutation is tighter than that of other mutations, the A8344G transition has also been reported in phenotypes as different as Leigh’s syndrome, isolated myoclonus, familial lipomatosis, and isolated myopathy (Silvestri et al., 1993; Hammans et al., 1993). MERRF must be considered in the differential diagnosis of progressive myoclonus epilepsies, including Ramsay–Hunt syndrome and Unverricht–Lundborg disease, in which cerebellar signs are prominent (Berkovic et al., 1993). The 8344 A→G mutation has been reported in association with other phenotypes, including MELAS, Leigh syndrome, and a variant neurologic syndrome characterized by ataxia, myopathy, hearing loss, and neuropathy (Austin et al., 1999).

NARP NARP is a maternally inherited syndrome in which ataxia is the cardinal manifestation of CNS involvement. MRI examination of NARP patients has revealed the

presence of moderate, diffuse cerebral and cerebellar atrophy and, in the most severely affected patients, symmetric lesions of the basal ganglia (Uziel et al., 1997). NARP is associated with a heteroplasmic T→G transversion at position 8993 in the ATPase 6 subunit gene (Holt et al., 1990). A transition in the same position (T8993C) was later described in other NARP patients (De Vries et al., 1993). Ragged-red fibers are consistently absent in the muscle biopsy. The degree of heteroplasmy is correlated with the severity of the disease. For instance, when the percentage of mutant mtDNA is more than 95%, patients show the clinical, neuroradiologic, and neuropathologic findings of maternally inherited Leigh syndrome (hence called MILS) (Tatuch et al., 1992). NARP/MILS phenotypes have been described in association with other mutations of the ATPase 6 gene, e.g., mutation 9176T→C (Thagarajan et al., 1995; Dionisi-Vici et al., 1998). NARP and MILS may coexist in the same family. Impairment of ATP synthesis has been reported in cell cultures harboring the T8993G mutation, possibly because of defective assembly of the enzyme complex (Houstek et al., 1995).

Other phenotypes Finally, brief mention should be made of a syndrome characterized by hearing loss, ataxia, and myoclonus, originally found in a large Italian pedigree (Tiranti et al., 1995). The responsible mutation, 7472insC, affects the tRNASer(UCN) gene. This mutation has subsequently been reported in several families, in which affected members showed a wide range of clinical manifestations, from isolated hearing loss (Verhoeven et al., 1999), to epilepsia partialis continua and ataxia (Schuelke et al., 1998), to overt MERRF (Jaksch et al., 1998). Given the increasing frequency at which the 7472insC has been found, the search for this mutation should become part of the routine screening of mitochondrial ataxias.

Defects of nucleo-mitochondrial signaling The presence of mtDNA abnormalities inherited as mendelian traits indicates the existence of mutations in nuclear genes affecting the integrity of the mitochondrial genome (Zeviani et al., 1995). Alternative hypotheses postulate that the responsible genes are involved in the nuclear control on biogenesis of the mitochondrial genome, or in the elimination of abnormal mtDNA species. Two groups of nucleus-driven abnormalities have been described: qualitative alterations of mtDNA, i.e., multiple, large-scale deletions of mtDNA, and quantitative decrease of the mtDNA copy number, i.e., tissue-specific depletion of mtDNA.

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Qualitative abnormalities: multiple familial mtDNA deletions Autosomal dominant progressive external ophthalmoplegia is characterized by adult-onset progressive external ophthalmoplegia, muscle weakness and wasting, vestibular areflexia, ataxia, cataracts, and sensori-motor peripheral neuropathy (Zeviani et al., 1989; Servidei et al., 1991; Suomalainen et al., 1992). Autosomal recessive progressive external ophthalmoplegia (Bohlega et al., 1996) is an earlyonset disease of childhood, often including severe cardiomyopathy, requiring cardiac transplantation. Both are associated with the coexistence of wild-type mtDNA with several deletion-containing mtDNA species. Linkage analysis has revealed the existence of different autosomal dominant progressive external ophthalmoplegia (adPEO) disease loci (Suomalainen et al., 1997; Kaukonen et al., 1999). Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a complex syndrome characterized by ophthalmoparesis, leukoencephalopathy, peripheral neuropathy, and gastrointestinal symptoms including intestinal dysmotility. Ataxia has been reported in approximately 13% of the cases. Southern blot analysis of mitochondrial DNA disclosed multiple deletions in some of the reported patients (Hirano et al., 1994). MNGIE is associated with mutations in the gene encoding thymidine phosphorylase, a key enzyme in the formation of the pyrimidine nucleoside pool necessary for the synthesis of nucleic acids (Nishino et al., 1999). However, it is still unclear how the loss of the enzymatic function produces the mitochondrial abnormalities observed in MNGIE and the peculiar clinical features of this disease.

Quantitative abnormalities: mtDNA depletion Depletion of mtDNA is a mendelian (autosomal recessive?) inherited disorder, possibly caused by a nuclear gene involved in the control of the mtDNA copy number. The clinical manifestations fall into three groups: (1) a fatal infantile congenital myopathy with or without a DeToni–Fanconi renal syndrome; (2) a fatal infantile hepatopathy leading to rapidly progressive liver failure; and (3) a late infantile or childhood myopathy, with onset after one year of age, characterized by a progressive myopathy causing respiratory failure and death by three years of age (Moraes et al., 1991; Tritschler et al., 1992). Ataxia is infrequent and can be masked by the profound muscle hypotonia of the patients.

Nuclear gene defects Nuclear genes encode hundreds of proteins related to mitochondrial metabolism and OXPHOS. Nevertheless, the identification of the nuclear genes responsible for OXPHOS-related disorders has proceeded at a much slower pace, compared with the discovery and characterization of mtDNA mutations. The reasons for such a gap are numerous, including the rarity of the syndromes, their genetic heterogeneity, and our ignorance about the nuclear gene repertoire encoding proteins that are part of, or regulate, the respiratory chain in humans. Thus, until recently, the attribution of mitochondrial syndromes to nuclear gene defects was completely circumstantial. In most of the cases it was based on the observation of familial syndromes with mendelian inheritance and severe isolated defects of the respiratory-chain complexes, not associated with mtDNA lesions. However, this scenario is rapidly changing, thanks to the discovery of several OXPHOS-related genes in humans, and to the identification in some of them of mutations responsible for different clinical syndromes. These achievements make it possible to propose three groups of nuclear gene defects related to mitochondrial disorders. The first group includes defects of genes encoding factors indirectly related to mitochondrial OXPHOS. The second group includes defects of factors that control the structural integrity of the respiratory chain. The third group includes genes encoding structural components of the mitochondrial respiratory chain. Examples of the first group include mutations of frataxin (Campuzano et al., 1996) and ABC7 (Allikmets et al., 1999). Both proteins are involved in the mitochondrial handling of iron, and are responsible for Friedreich’s ataxia and X-linked sideroblastic anemia and ataxia, respectively. Another example is paraplegin, an ATPbinding metalloprotease involved in the ‘quality control’ of mitochondrial membrane-bound protein, in autosomal recessive hereditary spastic paraplegia (Casari et al., 1998). Finally, X-linked deafness-dystonia syndrome results from the mutation of deafness–dystonia protein (Jin et al., 1996), a transporter protein involved in the insertion of metabolite carriers into the inner mitochondrial membrane (Koehler et al., 1999). As far as the second and third groups of nuclear gene defects are concerned, the most relevant recent contribution has been the (partial) elucidation of the molecular basis of Leigh syndrome.

Leigh syndrome Leigh syndrome is one of the most common mitochondrial disorders of the respiratory chain in infancy and child-

Ataxia in mitochondrial disorders

Fig. 39.3 Leigh syndrome. MRI: coronal spin echo proton density image shows hyperintensity involving the dentate nuclei. Signal abnormalities were also present in the pontine tegmentum, midbrain, periaqueductal area, and subthalamic nuclei (not shown).

hood. Affected infants show severe psychomotor delay, cerebellar and pyramidal signs, dystonia, respiratory abnormalities, incoordination of ocular movements, and recurrent vomiting. Ragged-red fibers are absent. The MRI picture reflects the typical neuropathological findings which define this condition (Medina et al., 1990; Savoiardo et al., 1991; Valanne et al., 1998). Symmetric lesions usually involve the medulla, the pontine tegmentum, and the periaqueductal region, and, in the cerebellum, the dentate nuclei and the deep white matter surrounding these nuclei (Fig. 39.3). Basal ganglia and posterior fossa structures may be involved simultaneously. Rarely, however, one group of structures or nuclei may improve while another becomes involved. Occasionally, the signal changes may completely spare the brainstem and cerebellum, being confined to basal ganglia, particularly the putamina and subthalamic nuclei. Leigh syndrome is clearly a genetically heterogeneous entity. In some cases, it is attributable to mtDNA mutations, as in the case of NARP/MILS (see above); in others, the defect is X-linked or sporadic, as in the case of the defect of the E1 subunit of pyruvate dehydrogenase. In still other cases it is attributable to an autosomal recessive defect of a nuclear gene. Defects of complex I, IV, or, more rarely, complex II, have been reported in autosomal recessive Leigh syndrome. However, with the exception of a

single report of a defect of complex II due to a point mutation in the gene encoding the flavoprotein subunit of succinate dehydrogenase (Bourgeron et al., 1995), the attribution of these disorders to nuclear gene defects has for long remained speculative, because it was based on biochemical findings only. Two recent discoveries have contributed to a rapid progress in our understanding of Leigh syndrome. One was the identification of mutations in genes encoding different subunits of complex I in Leigh syndrome associated with complex I deficiency (Loeffen et al., 1998; Triepels et al., 1999). A variant syndrome characterized by leukodystrophy and myoclonic epilepsy has been associated with a mutation in the NDUFV1 subunit of complex I (Schuelke et al., 1999). The molecular dissection of the structural components of complex I in Leigh syndrome is still ongoing, and is likely to contribute further to the elucidation of the genetic basis of complex I deficiency in Leigh syndrome. The second important contribution has been the discovery of SURF-1, a gene already well known in humans, as the gene responsible for most of the cases of Leigh syndrome due to a defect of complex IV (cytochrome c oxidase). Interestingly, the product of SURF-1 is not a subunit of cytochrome c oxidase, but, like its yeast homolog, is an integral component of the mitochondrial inner membrane, probably involved in the assembly of the complex (Tiranti et al., 1998; Zhu et al., 1998). Other phenotypes associated with ataxia still lack a molecular genetic definition, and are classified on the basis of biochemical and/or morphological findings only. For instance, a peculiar autosomal recessive syndrome characterized by severe sensory neuropathy, progressive external ophthalmoplegia, ataxia, and myoclonus epilepsy has been described in six adult patients from three separate families. The presence of ragged-red fibers in muscle biopsies, and elevation of CSF lactate, suggest a mitochondrial etiology of the multisystem degeneration in these patients (van Domburg et al., 1996). Another example of this broad category of defects is coenzyme Q10 muscle deficiency (Boitier et al., 1998), which is the cause of a progressive encephalopathy associated with muscular weakness, myoglobinuria, and lactic acidosis (Sobreira et al., 1997).

Ataxia as a symptom of mitochondriopathy Ataxia is one of the most frequent symptoms of CNS involvement found in mitochondrial disorders (Zeviani et al., 1996). However, it is seldom present as the only neurological abnormality. In most of the cases, it is part of a

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constellation of neurological and non-neurological signs that, as already mentioned, should alert the clinician to a mitochondrial etiology. However, in early infancy, overt ataxia may not be evident, or may be difficult to detect, because of the profound hypotonia that is frequently associated with infantile mitochondrial encephalopathies (e.g., Leigh syndrome). Progressive or intermittent ataxia may also be a frequent symptom in pyruvate dehydrogenase E1 deficiency (Bindoff et al., 1989). Occasionally, ataxia can be the first or an early symptom, and for some time the clinical picture can be confused with that of spinocerebellar ataxias (Klockgether and Evert, 1998). More rarely, ataxia has been reported as the most prominent neurological symptom in conditions that include one or a few additional features. For instance, combined ataxia and deafness (May and White syndrome) or ataxia and retinopathy have been reported in association with different mtDNA point mutations, including the 7472insC mutation, and both the mutations leading to the ‘NARP’ phenotype. In general, the diagnosis is not difficult once the typical morphological and laboratory clues of mitochondriopathy are found. A possible source of misdiagnosis is the similarity of some mitochondrial disorders with syndromes of different etiology and pathogenesis, which can be considered to some extent their ‘phenocopies.’ For instance, it has long been debated as to whether the so-called Ramsay–Hunt syndrome (or dyssynergia cerebellaris myoclonica) and MERRF were distinct nosological entities, or different clinical expressions of the same disease. Analysis of a large series of MERRF, dyssynergia cerebellaris myoclonica, and ‘progressive myoclonic epilepsy’ cases has shown that most of the MERRF patients carried the MERRF-associated A8344G mutation in the tRNALys gene, whereas none of the dyssynergia cerebellaris myoclonica or progressive myoclonic epilepsy cases showed the mutation. These findings confirm the different etiology of these disorders, and the importance of the molecular investigation in the differential diagnosis (Franceschetti et al., 1993). Likewise, the NARP syndrome shares several clinical features with a number of inherited disorders characterized by ataxia and visual impairment, in particular with spinocerebellar ataxia type 7 (SCA7) (MIM 164500) and Usher’s syndrome (MIM 276900). The similarity between NARP and SCA7 or Usher’s syndrome is made stronger by the lack of ragged-red-fibers or other histological ‘mitochondrial’ hallmarks in NARP (Holt et al., 1990). Lactic acidosis may be absent as well. Muscle weakness is frequently mild and masked by the cerebellar abnormalities, and the biochemical defect associated with NARP, a partial reduction of mitochondrial ATPase

(complex V) (Tatuch and Robinson, 1993; Tatuch et al., 1994), may be absent or very mild (Uziel et al., 1997).

Acknowledgments The financial support of Fondazione Telethon-Italy (grant n. 1180 to M.Z.) and the Italian Ministry of Health (grant ‘Ricerca Finalizzata’ ICS 030.3/RF98.37) is gratefully acknowledged.

iReferencesi Allikments, R., Raskind, W.H., Hutchinson, A. et al. (1999). Mutation of a putative mitochondrial iron transporter gene (ABC7) in X-linked sideroblastic anemia and ataxia (KLSA/A). Hum Mol Genet 8: 743–9. Anderson, S., Bankier, A.T., Barrel, B.G. et al. (1981). Sequence and organization of the human mitochondrial genome. Nature 290: 457–65. Antozzi, C. and Zeviani, M. (1997). Cardiomyopathies in disorders of oxidative metabolism. Cardiovasc Res 35: 184–99. Austin, S.A., Vriesendorp, F.J., Thandroyen, F.T. et al. (1999). Expanding the phenotype of the 8344 transfer RNAlysine mitochondrial DNA mutation. Neurology 51: 1447–50. Bardosi, A., Creutzfeld, W., DiMauro, S. et al. (1987). Myo-neurogastrointestinal encephalopathy (MNGIE syndrome) due to partial deficiency of cytochrome c oxidase: a new mitochondrial multisystem disorder. Acta Neuropathol (Berl) 74: 248–58. Barkovich, A., Good, W., Koch, T. and Berg, B. (1993). Mitochondrial disorders: analysis of their clinical and imaging characteristics. Am J Neuroradiol 14: 1119–37. Berkovic, S.F., Carpenter, S., Evans, A. et al. (1989). Myoclonus epilepsy and ragged-red fibres (MERRF) 1. A clinical, pathological, biochemical, magnetic resonance spectrographic and positron emission tomographic study. Brain 112: 1231–60. Berkovic, S.F., Cochius, J., Andermann, E. and Andermann, F. (1993). Progressive myoclonus epilepsies: clinical and genetic aspects. Epilepsia 34 (Suppl. 3): S19–30. Bindoff, L.A., Birch-Machin, M.A., Farnsworth, L. et al. (1989). Familial intermittent ataxia due to a defect of the E1 component of pyruvate dehydrogenase complex. J Neurol Sci 93: 311–18. Bohlega, S., Tanji, K., Santorelli, F.M. et al. (1996). Multiple mitochondrial DNA deletions associated with autosomal recessive ophthalmoplegia and severe cardiomyopathy. Neurology 46: 1329–34. Boitier, E., Degoul, F., Desguerre, I. et al. (1998). A case of mitochondrial encephalomyopathy associated with a muscle coenzyme Q10 deficiency. J Neurol Sci 156: 41–6. Bourgeron, T., Rustin, P., Chretien, D. et al. (1995). Mutation of a nuclear succinate dehydrogenase gene results in mitochondrial respiratory chain deficiency. Nat Genet 11: 144–9.

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Bruno, C., Kirby, D.M., Koga, Y. et al. (1999). The mitochondrial DNA C3303T mutation can cause cardiomyopathy and/or skeletal myopathy. J Pediatr 135: 197–202. Campuzano, V., Montermini, L., Molto, M.D. et al. (1996). Friedreich’s ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science 271: 1426–7. Casari, G., De Fusco, M., Ciarmatori, S. et al. (1998). Spastic paraplegia and OXPHOS impairment caused by mutations in paraplegin, a nuclear-encoded mitochondrial metalloproteinase. Cell 93: 973–83. Chen, X., Prosser, R., Simonetti, S. et al. (1995). Rearranged mitochondrial genomes are present in human oocytes. Am J Hum Genet 57: 239–47. Chomyn, A., Martinuzzi, A., Yoneda, M. et al. (1992). The MELASassociated mutations in the mtDNA binding site for the transcription termination factor cause protein synthesis and respiration defects, but do not affect the levels of upstream and downstream mature transcripts. Proc Natl Acad Sci USA 89: 4221–5. De Vries, D.D., van Engelen, B.G., Gabreels, F.J. et al. (1993). A second missense mutation in the mitochondrial ATPase 6 gene in Leigh’s syndrome. Ann Neurol 34: 410–12. DiMauro, S. and Moraes, C. (1993). Mitochondrial encephalomyopathies. Ann Neurol 50: 1197–208. Dionisi-Vici, C., Seneca, S., Zeviani, M. et al. (1998) Fulminant Leigh syndrome and sudden unexpected death in the family with the T9176C mutation of the mitochondrial ATPase 6 gene. J Inherit Metab Dis 21: 2–8. Dunbar, D.R., Moonie, P.A., Jacobs, H.T. and Holt, I.J. (1995). Different cellular backgrounds confer a marked advantage to either mutant or wild-type mitochondrial genomes. Proc Natl Acad Sci USA 92: 6562–6. Franceschetti, S., Antozzi, C., Binelli, S. et al. (1993). Progressive myoclonus epilepsies: an electroclinical, biochemical, morphological and molecular genetic study of 17 cases. Acta Neurol Scand 87: 219–23. Fukuhara, N. (1991). MERRF: a clinicopathological study. Relationships between myoclonus epilepsies and mitochondrial myopathies. Rev Neurol (Paris) 147: 476–9. Fukuhara, N., Tokiguchi, S., Shirakawa, K. and Tsubaki, T. (1980). Myoclonus epilepsy associated with ragged red fibres (mitochondrial abnormalities): disease entity or a syndrome? J Neurol Sci 47: 117–33. Goto, Y., Nonaka, I. and Horai, S. (1990). A mutation in tRNALeu(UUR) gene associated with MELAS subgroup of mitochondrial encephalomyopathies. Nature 348: 651–3. Hammans, S.R. Sweeney, M.G., Brockington, M. et al. (1993). The mitochondrial DNA transfer RNA(Lys)A→G(8344) mutation and the syndrome of myoclonic epilepsy with ragged red fibres (MERRF). Relationship of clinical phenotype to proportion of mutant mitochondrial DNA. Brain 116: 617–32. Hayashi, J.I., Ohta, S., Kikuchi, A. et al. (1991). Introduction of disease-related mitochondrial DNA deletions into HeLa cells lacking mitochondrial DNA results in mitochondrial dysfunction. Proc Natl Acad Sci USA 88: 10614–18.

Hirano, M., Ricci, E., Koenigsberger, R. et al. (1992). MELAS: an original case and clinical criteria for diagnosis. Neuromusc Disord 2: 125–35. Hirano, M., Silvestri, G., Blake, D.M. et al. (1994). Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE): clinical; biochemical, and genetic features of an autosomal recessive mitochondrial disorder. Neurology 44: 721–7. Holt, I.J., Harding, A.E. and Morgan-Hughes, J.A. (1988). Deletions of mitochondrial DNA in patients with mitochondrial myopathies. Nature 331: 717–19. Holt, I.J., Harding, A.E., Petty, R.H.K. and Morgan-Hughes, J.A. (1990). A new mitochondrial disease associated with mitochondrial DNA heteroplasmy. Am J Hum Genet 46: 428–33. Houstek, J., Klement, P., Hermanska, J. et al. (1995). Altered properties of mitochondrial ATP-synthase in patients with a T-G mutation in the ATPase (subunit 6) gene at position 8993. Biochim Biophys Acta 1271: 349–57. Jaksch, M., Klopstock, T., Kurlemann, G. et al. (1998). Progressive myoclonus epilepsy and mitochondrial myopathy associated with mutations in the tRNA(Ser(UCN)) gene. Ann Neurol 44: 635–40. Jin, H., May, M., Tranebjaerg, L. et al. (1996). A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness. Nat Genet 14: 177–80. Kaukonen, J., Amati, P., Suomalainen, A. et al. (1996). An autosomal locus predisposing to multiple deletions of mtDNA on chromosome 3p. Am J Hum Genet 58: 763–9. Kaukonen, J., Zeviani, M., Comi, G. et al. (1999). A third locus predisposing to multiple deletions of mtDNA in autosomal dominant progressive external ophthalmoplegia. Am J Hum Genet 65: 256–61. King, M.P., Koga, Y., Davidson, M. and Schon, E.A. (1992). Defects in mitochondrial protein synthesis and respiratory chain activity segregate with the tRNALeu(UUR) mutation associated with mitochondrial myopathy, lactic acidosis and stroke-like episodes. Mol Cell Biol 12: 480–90. Klockgether, T. and Evert, B. (1998). Genes involved in hereditary ataxias. Trends Neurosci 21: 413–18. Koehler, C.M., Leuenberger, D., Merchant, S. et al. (1999). Human deafness dystonia syndrome is a mitochondrial disease. Proc Natl Acad Sci USA 96: 2141–6. Loeffen, J., Smeitink, J., Triepels, R. et al. (1998). The first nuclear encoded complex I mutation in a patient with Leigh syndrome. Am J Hum Genet 63: 1598–608. Lombes, A., Mendell, J.R., Nakase, H. et al. (1989). Myoclonic epilepsy and ragged-red fibers with cytochrome oxidase deficiency: neuropathology, biochemistry, and molecular genetics. Ann Neurol 26: 20–33. Luft, R. (1994). The development of mitochondrial medicine. Proc Natl Acad Sci USA 91: 8731–8. Marchington, D.R., Macaulay, V., Hartshorne, G.M. et al. (1998). Evidence from human oocytes for a genetic bottleneck in an mtDNA disease. Am J Hum Genet 63: 769–75. Mariotti, C., Tiranti, V., Carrara, F. et al. (1994). Defective respiratory capacity and mitochondrial protein synthesis in transformants

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M. Zeviani, C. Antozzi, M. Savoiardo, and E. Bertini

cybrids harboring the tRNALeu(UUR) mutation associated with maternally inherited myopathy and cardiopathy. J Clin Invest 93: 1102–7. Mazziotta, M.R., Ricci, E., Bertini, E. et al. (1992). Fatal infantile liver failure associated with mitochondrial DNA depletion. J Pediatr 121: 896–901. McKelvie, P.A., Morley, J.B., Byrne, E. and Marzuki, S. (1991). Mitochondrial encephalomyopathies: a correlation between neuropathological findings and defects in mitochondrial DNA. J Neurol Sci 102: 51–60. McShane, M.A., Hammans, S.R., Sweeney, M.G. et al. (1991). Pearson syndrome and mitochondrial encephalomyopathy in a patient with a deletion of mtDNA. Am J Hum Genet 48: 39–42. Medina, L., Chi, T.L., DeVivo, D.C. and Hilal, S.K. (1990). MR findings in patients with subacute necrotizing encephalomyopathy (Leigh syndrome): correlation with biochemical defect. Am J Neuroradiol 11: 379–84. Mita, S., Schmidt, B., Schon, E.A. et al. (1989). Detection of deleted mitochondrial genomes in cytochrome c oxidase-deficient muscle fibers of a patient with Kearns–Sayre syndrome. Proc Natl Acad Sci USA 86: 9509–13. Mizukami, K., Sasaki, M., Suzuki, T. et al. (1992). Central nervous system changes in mitochondrial encephalomyopathy: a light and electron microscopic study. Acta Neuropathol (Berl) 83: 449–52. Moraes, C.T., DiMauro, S., Zeviani, M. et al. (1989). Mitochondrial DNA deletions in progressive external ophthalmoplegia and Kearns–Sayre syndrome. N Engl J Med 320: 1293–9. Moraes, C.T., Shanske, S., Tritschler, H.J. et al. (1991). MtDNA depletion with variable tissue expression: a novel genetic abnormality in mitochondrial diseases. Am J Hum Genet 48: 492–501. Nijtmans, M.G., Hammans, S.R., Duchen, L.W. et al. (1994). Mitochondrial DNA mutation underlying Leigh’s syndrome: clinical, pathological, biochemical, and genetic studies of a patient presenting with progressive myoclonic epilepsy. J Neurol Sci 121: 57–65. Nishino, I., Spinazzola, A. and Hirano, M. (1999). Thymidine phosphorylation gene mutations in MNGIE, a human mitochondrial disorder. Science 283: 689–92. Oldfors, A., Fyhr, I.M., Holme, E. et al. (1990). Neuropathology in Kearns–Sayre syndrome. Acta Neuropathol (Berl) 80(5): 541–6. Oldfors, A., Holme, E., Tulinius, M. and Larsson, N.G. (1995). Tissue distribution and disease manifestations of the tRNA(Lys) A→G(8344) mitochondrial DNA mutation in a case of myoclonus epilepsy and ragged red fibres. Acta Neuropathol (Berl) 90: 328–33. Poulton, J. (1992). Duplications of mitochondrial DNA: implications for pathogenesis. J Inher Metab Dis 15: 487–98. Riordan-Eva, P. and Harding, A.E. (1995). Leber’s hereditary optic neuropathy: the clinical relevance of different mitochondrial DNA mutations. J Med Genet 32: 81–7. Rotig, A., Cormier, C., Blache, S. et al. (1990). Pearson’s marrow–pancreas syndrome. A multisystem mitochondrial disorder of infancy. J Clin Invest 86: 1601–8. Rowland, L.P., Blake, D.M., Hirano, M. et al. (1991). Clinical syn-

dromes associated with ragged red fibres. Rev Neurol 147: 467–73. Savoiardo, M., Bruzzone, M.G., D’Incerti, L. et al. (1999). Metabolic and genetic diseases of the brain. Riv Neuroradiol 12: 73–86. Savoiardo, M., Ciceri, E., D’Incerti, L. et al. (1995). Symmetric lesions of the subthalamic nuclei in mitochondrial encephalomyopathies: an almost distinctive mark of Leigh disease with COX deficiency. Am J Neuroradiol 16: 1746–7. Savoiardo, M., Uziel, G., Strada, L. et al. (1991). MRI findings in Leigh’s disease with cytochrome-c-oxidase deficiency. Neuroradiology 33(Suppl.): 507–8. Schon, E.A., Rizzuto, R., Moraes, C.T. et al. (1989). A direct repeat is a hotspot for large-scale deletions of human mitochondrial DNA. Science 244: 346–9. Schuelke, M., Bakker, M., Stoltenburg, G. et al. (1998). Epilepsia partialis continua associated with a homoplasmic mitochondrial tRNA(Ser(UCN)) mutation. Ann Neurol 44: 700–4. Schuelke, M., Smeitink, J., Mariman, E. et al. (1999). Mutant NDUFV1 subunit of mitochondrial complex I causes leukodystrophy and myoclonic epilepsy. Nat Genet 21: 260–1. Servidei, S., Zeviani, M., Manfredi, G. et al. (1991). Dominantly inherited mitochondrial myopathy with multiple deletions of mitochondrial DNA: clinical, morphologic and biochemical studies. Neurology 41: 1053–9. Shoffner, J.M., Lott, M.T., Lezza, A.M.S. et al. (1990). Myoclonic epilepsy and ragged-red fiber disease (MERRF) is associated with a mitochondrial DNA tRNALys mutation. Cell 61: 931–7. Shoffner, J.M., Lott, M.T., Voliiavec, A.S. et al. (1989). Spontaneous Kearns–Sayre/chronic external ophthalmoplegia plus syndrome associated with a mitochondrial DNA deletion: a slip replication model and metabolic therapy. Proc Natl Acad Sci USA 86: 7952–6. Silvestri, G., Ciafaloni, E., Santorelli, F.M. et al. (1993). Clinical features associated with the A→G transition at nucleotide 8344 of mtDNA (‘MERRF’ mutation). Neurology 43: 1200–6. Silvestri, G., Moraes, C.T., Shanske, S. et al. (1992). A new mtDNA mutation of the tRNALys gene associated with myoclonic epilepsy and ragged-red fibers (MERRF). Am J Hum Genet 51: 1213–17. Sobreira, C., Hirano, M., Shanske, S. et al. (1997). Mitochondrial encephalomyopathy with coenzyme Q10 deficiency. Neurology 48: 1238–43. Suomalainen, A., Majander, A., Haltia, M. et al. (1992). Multiple deletions of mitochondrial DNA in several tissues of a patient with severe retarded depression and familial progressive external ophthalmoplegia. J Clin Invest 90: 9061–6. Suomalainen, A., Majander, A., Wallin, M. et al. (1997). Autosomal dominant progressive external ophthalmoplegia with multiple deletions of mtDNA: clinical, biochemical, and molecular genetic features of the 10q-linked disease. Neurology 48: 1244–53. Tanji, K., Vu, T.H., Schon, E.A., DiMauro, S. and Bonilla, E. (1999). Kearns–Sayre syndrome: unusual pattern of expression of subunits of the respiratory chain in the cerebellar system. Ann Neurol 45: 377–83. Tatuch, Y., Christodoulou, J., Feigenbaum, A. et al. (1992).

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Heteroplasmic mtDNA mutation (T→G) at 8993 can cause Leigh disease when the percentage of abnormal mtDNA is high. Am J Hum Genet 50: 852–8. Tatuch, Y., Pagon, R.A., Vlcek, B. et al. (1994). The 8993 mtDNA mutation: heteroplasmy and clinical presentation in three families. Euro J Hum Genet 2: 35–43. Tatuch, Y. and Robinson, B.H. (1993). The mitochondrial DNA mutation at 8993 associated with NARP slows the rate of ATP synthesis in isolated lymphoblast mitochondria. Biochem Biophys Res Commun 192: 124–8. Thagarajan, D., Shanske, S., Vazquez-Memije, M. et al. (1995). A novel mitochondrial ATPase 6 point mutation in familial bilateral striatal necrosis. Ann Neurol 38: 468–72. Tirani, V., Chariot, P., Carella, F. et al. (1995). Maternally inherited hearing loss, ataxia and myoclonus associated with a novel point mutation in mitochondrial tRNASer(UCN) gene. Hum Molec Genet 4: 1421–7. Tiranti, V., Hoertnagel, K., Carrozzo, R. et al. (1998). Mutations in SURF-1 in Leigh disease associated with cytochrome c oxidase deficiency. Am J Hum Genet 63: 1609–21. Triepels, R.H., van den Heuvel, L.P., Loeffen, J.L.C.M. et al. (1999). Leigh syndrome associated with a mutation in the NDUFS7 (PSST) nuclear encoded subunit of complex I. Ann Neurol 45: 787–90. Tritschler, H.J., Andreetta, F., Moraes, C.T. et al. (1992). Mitochondrial myopathy of childhood associated with depletion of mitochondrial DNA. Neurology 42: 209–17. Tsuchiya, K., Miyazaki, H., Akabane, H. et al. (1999). MELAS with prominent white matter gliosis and atrophy of the cerebellar granular layer: a clinical, genetic, and pathological study. Acta Neuropathol (Berl) 97: 520–4. Uziel, G., Moroni, I., Lamantea, A. et al. (1997). Mitochondrial disease associated with the T8993G mutation of the mitochondrial ATPase 6 gene: a clinical, biochemical and molecular study in six families. J Neurol Neurosurg Psychiatry 63: 16–22. Valanne, L., Ketonen, L., Majander, A. et al. (1998). Neuroradiologic findings in children with mitochondrial disorders. Am J Neuroradiol 19: 369–77.

van Domburg, P.H., Gabreels-Festen, A.A., Gabreels, F.J. et al. (1996). Mitochondrial cytopathy presenting as hereditary sensory neuropathy with progressive external ophthalmoplegia, ataxia and fatal myoclonic epileptic status. Brain 119: 997–1010. Verhoeven, K., Ensink, R.J., Tiranti, V. et al. (1999). Hearing impairment and neurological dysfunction associated with a mutation in the mitochondrial tRNASer(UCN) gene. Eur J Hum Genet 7: 45–51. Wallace, D.C., Zheng, X., Lott, M. et al. (1988). Familial mitochondrial encephalomyopathy (MERRF): genetic, pathophysiological, and biochemical characterization of a mitochondrial DNA disease. Cell 55: 601–10. Yoneda, M., Miyatake, T. and Attardi, G. (1994). Complementation of mutant and wild-type human mitochondrial DNAs coexisting since the mutation event and lack of complementation of DNAs introduced separately into a cell within distinct organelles. Mol Cell Biol 14: 2699–712. Zeviani, M., Amati, P., Comi, G. et al. (1995). Searching for genes affecting the structural integrity of the mitochondrial genome. Biochim Biophys Acta 1271: 153–8. Zeviani, M. and Antozzi, C. (1997). Mitochondrial disorders. Mol Hum Reprod 3: 133–48. Zeviani, M., Bertagnolio, B. and Uziel, G. (1996). Neurological presentations of mitochondrial diseases. J Inher Metab Dis 19: 504–20. Zeviani, M., Muntoni, F., Savarese, N. et al. (1993). A MERRF/MELAS overlap syndrome associated with a new point mutation in the mitochondrial DNA tRNALys gene. Eur J Hum Genet 1: 80–7. Zeviani, M., Moraes, C.T., DiMauro, S. et al. (1988). Deletions of mitochondrial DNA in Kearns–Sayre syndrome. Neurology 38: 1339–46. Zeviani, M., Servidei, S., Gellera, C. et al. (1989). An autosomal dominant disorder with multiple deletions of mitochondrial DNA starting at the D-loop region. Nature 339: 309–11. Zhu, Z., Yao, J., Johns, T. et al. (1998). Surf 1, a factor involved in the biogenesis of cytochrome c oxidase, is mutated in Leigh syndrome. Nat Genet 20: 337–43.

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Episodic ataxias as ion channel diseases Maria Cristina D’Adamo, Paola Imbrici, and Mauro Pessia Department of Vascular Medicine and Pharmacology, Istituto di Ricerche Farmacologiche ‘Mario Negri’, Chieti, Italy

Introduction Ion channels are membrane proteins that regulate the flow of specific ions in different cellular districts (Hille, 1992). The electrical signals flowing through the central and peripheral nervous systems are finely tuned by a number of different ion channels. Many of these channels have now been cloned and their activity has been characterized through various electrophysiological methods, including patch-clamp recordings. The involvement of defective ion channels in the pathophysiology of several neurological disorders had been postulated for years. Genetic linkage studies and mutation analysis have now demonstrated that a variety of inherited diseases are indeed ion channel diseases, named also ‘channelopathies’ (Ashcroft, 1999). This chapter focuses on episodic ataxia type 1 and type 2, two inherited diseases that have been associated with genetic mutations in specific potassium and calcium channel genes.

Episodic ataxia type 1 Clinical aspects Episodic ataxia type 1 (EA-1) is an autosomal, dominant disorder affecting both the central and peripheral nervous systems (Brunt and van Weerden, 1990). The first unambiguous description of this human neurological syndrome was reported in 1975 by Van Dyke and co-workers (Van Dyke et al., 1975). It can be classified as a rare disease, though its prevalence is unknown. The initial symptoms occur during infancy or early childhood. The hallmark of the disease is continuous myokymia (constant muscle rippling) and episodic attacks of spastic contractions of skeletal muscles, which often result in loss of balance. Attacks

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of ataxia are characterized by incoordination, impaired speech, and jerking movements of the head, arms, and legs. They may be brought on by fever, startle, vestibulogenic stimulation, emotional stress, exercise, or fatigue. Therefore, EA-1 patients tend to avoid abrupt movements or sport activity. It has been reported that the sound of a car horn may trigger an attack in affected individuals and cause a traffic accident. During the attacks, some patients also experience diplopia, blurred vision, headache, and diaphoresis. Alcohol and coffee do not increase the probability of undergoing an attack. EA-1-affected patients also show myokymia associated with continuous muscle unit activity. Myokymia can be detected as fine rippling in hand, periorbital or perioral musculature and by a rhythmic electromyography (EMG) pattern of repeated duplets and multiplets (Brunt and van Weerden, 1990). The myokymic activity may become more severe during an attack or after intense muscle activity. The EA-1 clinical signs may vary from severe to non-detectable neurological abnormalities. Some patients undergo more than 20 attacks a day of severe ataxia, lasting from minutes to hours; by contrast, other individuals show attack frequencies of less than one per month (Van Dyke et al., 1975; Brunt and van Weerden, 1990). In some cases, mild cognitive symptoms during attacks or an altered gain of vestibulo-ocular reflex have been described (Gancher and Nutt, 1986). Cerebellar dysfunction appears to be partially responsible for the abnormal movements in EA-1 syndrome. Thus, it has been proposed that EA-1 patients may have altered cerebellar neurotransmission. The electroencephalographic recordings (EEGs) from EA-1-affected individuals are usually normal; brain imaging studies also show no obvious abnormalities (Brunt and van Weerden, 1990). The chronic treatment of EA-1 patients with acetazolamide or sulthiame, two carbonic anhydrase inhibitors, may relieve an attack. However, acetazolamide may not be effective in

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some cases and may have notable side-effects (Bouchard et al., 1984). The mechanism of action of these drugs is not well understood. Patients may also be treated with carbamazepine or phenytoin.

Molecular determinants Genetic linkage studies of several EA-1-affected families led in 1994 to the localization of the disease gene on chromosome 12p13, in a region encoding voltage-dependent potassium channels (Litt et al., 1994). The subsequent screen of the KCNA1 gene for mutations resulted in the discovery of a number of point mutations in the Shakerrelated potassium channel hKv 1.1 (Browne et al., 1994). To date, 11 point mutations have been identified in 15 affected families: Val174Phe, Ile177Asn, Phe184Cys, Thr226Ala, Thr226Met, Arg239Ser, Phe249Ile, Gly311Ser, Glu325Asp, Val404Ile, Val408Ala (Browne et al., 1995; Comu et al., 1996; Scheffer et al., 1998; Fig. 40.1). Voltage-gated potassium channels (Kv) are composed of four subunits, each of which contains six transmembrane domains, S1 through S6. The H5 region (P loop) between S5 and S6 forms part of the ion-conducting pore and includes the selectivity filter. The S4 motif contains a cluster of positively charged residues (arginines and lysines) that form most of the voltage-sensing region of the channel. Both the N-terminal and C-terminal regions reside in the cytoplasm. The N-terminal of the Shaker protein confers the N-

type inactivation properties to the channel, generated by a ‘ball-and-chain’ occlusion mechanism (Armstrong and Bezanilla, 1977; Hoshi et al., 1990; Zagotta et al., 1990). However, the N-type inactivation features of the human homolog hKv1.1 are conferred by auxiliary -subunits. Kv channels also show a much slower C-type inactivation generated by conformational modifications of the extracellular mouth of the pore (Grissmer and Cahalan, 1989; Stühmer et al., 1989; Hoshi et al., 1991; Pardo et al., 1992; López-Barneo et al., 1993; Baukrowitz and Yellen, 1995; Molina et al., 1997). The molecular pathophysiology of EA-1 syndrome has been investigated by determining the biophysical properties of wild-type and several mutant channels in Xenopus oocytes or in mammalian cell lines. Valine 408 resides in the C-terminal region of transmembrane domain 6 (S6), which is thought to comprise part of the cytoplasmic vestibule of the pore (Choi et al., 1993; Lopez et al., 1994; Fig. 40.1). Moreover, this region appears to comprise part of an intracellular gate which hypothetically opens and closes Shaker K channels (Liu et al., 1997). Channels bearing V408A mutation show a normal voltage dependence of activation. However, the rates of activation, deactivation, and C-type inactivation of V408A channels were much faster compared to wild type (Adelman et al., 1995; D’Adamo et al., 1998). Moreover, the V408A mutation markedly reduces the mean open duration of the channel, suggesting that this mutation alters the open-state stability of the channel (D’Adamo et al., 1999). Another EA-1 mutation occurs at the highly conserved position 325. This glutamate residue is located within the loop linking S4 to S5, which also comprise part of the cytoplasmic mouth of the ion-conducting pore (Fig. 40.1; Slesinger et al., 1993). The E325D mutation accelerates the activation, deactivation, and C-type inactivation kinetics of the channel (D’Adamo et al., 1998, 1999; Fig. 40.2). These effects are similar to those described above for V408A channels. Voltage-dependent potassium channels are formed by the assembly of four subunits, each an independent polypeptide. EA-1-affected individuals are heterozygous at the Kv1.1 locus, possessing a normal and a mutant allele, which may be equally expressed (Browne et al., 1994). Therefore, channels composed of wild-type and mutated subunits might be formed in-vivo. Indeed, channels composed of two wild-type and two E325D subunits, linked as dimers, showed gating properties intermediate between those of channels formed from four normal or four mutated subunits (D’Adamo et al., 1998, 1999; Fig. 40.2). This evidence demonstrates that the degree of impairment of the delayed rectifier function of the channel is related to

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Fig. 40.2 The E325D mutation associated with EA-1 alters the kinetics of activation, deactivation, and voltage-dependence of the channels. (A) Representative current traces recorded form Xenopus oocytes expressing wild-type (WT), E325D and heterozygous WT-E325D (middle trace) channels. (B) The time constants of activation (closed circles) and deactivation (triangles) for E325D channels are plotted and the WT values are reported as solid lines for comparison. The current traces and the values of the time constants clearly show that E325D mutation markedly accelerates the kinetics of activation and deactivation of the channel. From D’Adamo et al., 1998; Reproduced with permission. (C) Current–voltage relationships showing that E325D mutant channels (open circles) display a voltage dependence of activation shifted 52.4 mV to more positive potentials compared to WT (closed circles). However, heterozygous WT-E325D channels (closed triangles) show intermediate voltage-gating properties. (Reproduced from D’Adamo et al. (1998). Episodic ataxia type-1 mutations in the hKV1.1 cytoplasmic pore region after the gating properties of the channel, Embo Journal, Vol. 17, pp. 1200–7, with permission from Oxford University Press.)

the number of mutated subunits which make up the tetrameric hKv1.1 channels. In addition, the E325D mutation provoked (a) a marked positive shift in the voltage dependence of activation (Fig. 40.2), (b) a dramatic reduction of the open probability of the channel (Fig. 40.3); and (c) several-fold reduction in current amplitude and protein expression (D’Adamo et al., 1998; Zerr et al., 1998a, 1998b). Other mutations associated with EA-1, such as V174F, F184C, T226A, T226M, and G311S, alter the voltage dependence of channel activation (Adelman et al., 1995; Zerr et al., 1998a, 1998b); R239S and F249I reduced the amount of protein synthesized (Zerr et al., 1998a); and most of the mutant channels tested yielded a variable reduction of the current amplitude. Potassium channel diversity is greatly enhanced by the ability of different types of -subunits to heteropolymerize and to form channels with properties different from those of the parental homomeric channels. Biochemical and biophysical studies have shown that mammalian Kv1.1 and Kv1.2 subunits are co-localized in several subcellular brain regions important for the control of movement and heteropolymerize to form channels (Ruppersberg et al., 1990; Isacoff et al., 1990; Christie et al., 1990; Beckh and Pongs, 1990; Po et al., 1993; McNamara et al., 1993; Wang et al., 1993, 1994; Hopkins et al., 1994; Laube et al., 1996). The human Kv1.2 and Kv1.1 subunits may also co-assemble to form a distinct channel, and EA-1 mutations profoundly impair the properties of this heteromeric K channel (Fig. 40.4). By using tandemly linked subunits, it has been demonstrated that hKv1.1 subunits bearing the EA-1 mutations V408A or E325D combine with hKv1.2 to produce channels with altered kinetics of activation, deactivation, C-type inactivation, and voltage dependence (D’Adamo et al., 1999). The heteropolymerization of mammalian voltagedependent potassium channel subunits appears to be confined to members of the same subfamily (Covarrubias et al., 1991). This evidence suggests that whenever EA-1 subunits form a heteromeric complex with any of the other subunits comprised in the Kv1 subfamily, they alter the delayed rectifier function of the resulting channel. Therefore, such phenomena may markedly broaden the electrophysiological alterations caused by the EA-1 mutations in the central and peripheral nervous systems of affected patients.

Pathophysiological mechanisms Immunocytochemical studies have shown that Kv1.1 channel proteins are present in the node of Ranvier of myelinated axons, on dendrites, synaptic zones, and soma

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Membrane potential (mV) Fig. 40.3 E325D mutation alters the open probability of the channel. Representative inside-out patch recordings from oocytes expressing (A) wild-type and (B) E325D channels. Channel openings were evoked by depolarizations at the indicated potentials. (C) The open probabilities as a function of voltage for WT (circles) and E325D (triangles) were computed from the shown patches and fitted with Boltzmann functions. (Reproduced from D’Adamo et al. (1998). Episodic ataxia type-1 mutations in the hKV1.1 cytoplasmic pore region after the gating properties of the channel, Embo Journal, Vol. 17, pp. 1200–7, with permission from Oxford University Press.)

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Fig. 40.4 Episodic ataxia type 1 mutations affect the C-type inactivation kinetics of heteromeric channels. (A) Schematic representation of the linked hKv1.2 and hKv1.1 subunits. Beside it is shown the proposed representation of a tetrameric channel in which two hKv1.2 and two hKv1.1 subunits are tandemly assembled. (B) Normalized current traces showing the C-type inactivation time course for the indicated channels. E325D and V408A mutations clearly accelerate the inactivation rate of heteromeric channels. (Reproduced with permission from D’Adamo et al. (1999), FASEB Journal, Vol. 13, pp. 1335–45.)

of cerebellar neurons, and in other mouse brain areas (Wang et al., 1993, 1994; Veh et al., 1995). In the peripheral nervous system, RCK1 channels (a rat homolog) have been localized in the dorsal root ganglia, sciatic nerves, and cranial nerves (Beckh and Pongs, 1990). A similar expression pattern is expected in humans. Kv1.1 channels have a role in the saltatory conduction of impulses, repolarizing phase of action potentials, release of neurotransmitters from the terminals, and firing pattern of central and peripheral neurons located in regions important for the control of movements. The information obtained from the structure–function studies implies that several possible EA-1 pathophysiological mechanisms may be involved. The overall effect of EA1 mutations is a reduction of the outward flow of potassium ions, which becomes insufficient to repolarize the membrane potential. Therefore, the neurons expressing mutated hKv1.1 channels might be hyperexcitable and have prolonged action potentials. During intense neuronal

activity, C-type inactivation can accumulate, modifying both the firing rate and shape of action potentials (Aldrich et al., 1979). Some EA-1 mutant channels undergo C-type inactivation with faster time courses. These findings suggest a mechanism by which a faster accumulation of Ctype inactivation, during the repetitive firings caused by physical or emotional stress, would be responsible, at least in part, for triggering the attacks of EA-1. Moreover, the degree of impairment of the delayed rectifier function of affected neurons and the severity of the symptoms may be related to the type and number of mutated subunits which make up the tetrameric hKv1.1 channels (D’Adamo et al., 1998). Particularly intriguing is the presence of both Kv1.1 and Kv1.2 subunits in Ranvier’s nodes of myelinated axons and at the level of the cerebellar Pinceau, a structure composed of several basket cell terminals which embrace the Purkinje cell axon hillock and proximal axon segment (Fig. 40.5; Wang et al., 1993, 1994; Laube et al., 1996). Purkinje cell axons represent the only output system of the cerebellar cortex and the Pinceau appear passively to hyperpolarize these axons by generating fast inhibitory electrical fields (Korn and Axelrad, 1980). Moreover, patch-clamp recordings from Purkinje cells have revealed that -dendrotoxin selectively blocks the Kv1.1 and Kv1.2 potassium channels from basket cell presynaptic terminals and increases both the amplitude and frequency of spontaneous inhibitory postsynaptic currents mediated by gamma-aminobutyric acid A (GABAA) receptor activation (Southan and Robertson, 1998). These findings suggest that Kv1.1 and Kv1.2 heteromeric channels may contribute to the excitability and rapid repolarization phase of action potentials in myelinated axons and basket cell terminals, where they modulate the release of the neurotransmitter GABA onto Purkinje cells. The human Kv1.2 and Kv1.1 subunits co-assemble to form a novel channel with distinct gating properties, which are profoundly altered by EA-1 mutations (D’Adamo et al., 1999). Therefore, it is conceivable that, in EA-1-affected patients, the prolongation of the action potential duration and the increased excitability of the presynaptic basket cell membranes may markedly increase the release of GABA from such terminals onto Purkinje cells (Fig. 40.5). Moreover, a basket cell makes contacts with a number of Purkinje cells. Consequently, a single EA-1-affected basket cell may at the same time alter the output of several Purkinje cells. As a result, the output of the entire cerebellum to the rest of the brain may be markedly altered, leading to the attacks of generalized spastic muscle contractions characteristic of EA-1 syndrome. Similar scenarios may be also envisaged in other districts of the

Episodic ataxias as ion channel diseases

Fig. 40.5 Proposed effects of genetic mutations associated with episodic ataxia type 1 on basket cell and Purkinje cell inhibitory outputs. The diagram shows a basket cell which has synapses on the initial segment and soma of a number of Purkinje cells from the cerebellar cortex of healthy subjects (left) compared to EA-1-affected patients (right). hKv1.1 and hKv1.2 subunits are located at the presynaptic membrane of basket cells. Thus, the reduced delayed rectifier function of both homomeric and heteromeric EA-1 channels may prolong their action potential duration, and increase the membrane excitability and Ca ion influx. The release of larger amounts of aminobutyric acid may result both from action potentials and from the release of single transmitter vesicles (miniature synaptic events), reducing the inhibitory outputs of the relevant Purkinje cells. (Reproduced with permission from D’Adamo et al. (1999), FASEB Journal, Vol. 13, pp. 1335–45.)

central and peripheral nervous systems where Kv1.1 channels are expressed.

Episodic ataxia type 2 Episodic ataxia type 2 (EA-2) is an autosomal, dominant, neurological disorder characterized by attacks of generalized ataxia accompanied by nausea and vertigo. The attacks, which may last for hours or days, manifest occasionally and may be brought on by emotional stress and exercise, but not by startle. Anxiety, alcohol, and coffee may increase the probability of undergoing an attack. The onset of the disease occurs in childhood, as in EA-1. However, the symptoms that clearly distinguish EA-2 from EA-1 are migraine, interictal nystagmus, and progressive cerebellar vermian atrophy, which causes permanent motor disability. The attacks of EA-2 may be effectively prevented by treatment with acetazolamide.

The locus for EA-2 was mapped to chromosome 19p13 by linkage studies (Kramer et al., 1995; Von Brederlow et al., 1995; Teh et al., 1995). Successively, mutation analysis of EA-2 families revealed two mutations in the CACNL1A4 gene, which encodes for the 1A-subunit of P/Q-type Ca channels (Ophoff et al., 1996): a basepair deletion, which results in a frame-shift and in the formation of a premature stop codon, and a splice-site mutation, which also results in a truncated protein. Therefore, it is expected that the calcium channel formed would be non-functional (Ophoff et al., 1996; Fig. 40.6). The pore-forming -subunit of a P/Q-type Ca channel is composed of four domains (I through IV), each of which contains six transmembrane segments (S1 through S6). The predicted topology and structural features of each domain are similar to those of a voltage-gated potassium channel subunit, as the S4 segment represents the voltagesensing region and the H5 loop comprises part of the channel pore (Fig. 40.6).

567

I

II R192Q

S1 S2 S3 S4 S5

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C4073 deletion

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+ + + + + + +

+ + + + + + +

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S6

+ + + + + + +

I1811L +

NH3

D715E

V714A Splice site (tgIa)

Splice site mutation

Poly-Q

COO

–

Fig. 40.6 Predicted membrane topology of a voltage-gated P/Q-type Ca channel. The diagram indicates the position of the mutations identified in patients affected by episodic ataxia type 2 (open squares), spinocerebellar ataxia type 6 (SCA6, Poly-Q) and familial hemiplegic migraine (FHM, closed circles). The tottering mice (diamond) and leaner mice tgla mutations are also shown.

Episodic ataxias as ion channel diseases

Voltage-gated P/Q-type Ca channels are abundantly and broadly expressed throughout the central nervous system. In particular, they are present in brainstem, cerebellar Purkinje and granule cells, and at the neuromuscular junction (Ludwig et al., 1997). These ion channels are located within the release site and close to the docked vesicle and play a pivotal role in the neurotransmitter release mechanisms from presynaptic terminals (Wu et al., 1999). P/Q-type Ca channels also control nerve cell survival, excitability, gene expression, and plasticity. Although the evidence may predict an altered cerebellar neurotransmission in EA-2 syndrome, the intimate pathophysiological mechanisms of this neurologic disease remain poorly understood. Two other neurologic diseases result from mutations in the same CACNL1A4 gene. Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominant disorder characterized by ataxia, nystagmus, and cerebellar degeneration. Affected individuals are eventually confined to a wheelchair. The genotypic analysis of a number of SCA6 patients revealed an expansion of CAG repeats in the CACNL1A4 gene. The resulting Poly-Q repeat is located within the Cterminal region of the 1A-subunit of P/Q-type Ca channel (Fig. 40.6; Zhuchenko et al., 1997). Familial hemiplegic migraine is also a rare, autosomal, dominant syndrome of childhood onset. It is characterized by migraine with aura, ictal hemiparesis lasting for hours or days, and progressive cerebellar atrophy. Mutation analysis of patients with familial hemiplegic migraine resulted in the identification of several missense mutations in the CACNL1A4 gene (Fig. 40.6; Ophoff et al., 1996; Ducros et al., 1999). Functional studies have shown that point mutations associated with familial hemiplegic migraine may cause both a gain and loss-of-function of P/Q-type Ca channel (Hans et al., 1999).

A mouse strain lacking the entire Kv1.1 gene has also been generated (Smart et al., 1998). These animals display spontaneous seizure, altered axonal action potential conduction in sciatic nerve, and an increased GABAergic inhibition of Purkinje cells. Some, but not all, of the neurologic alterations reported are consistent with the predictions made by the molecular studies on EA-1 channels. In fact, the Kv1.1 knock-out phenotype is behaviorally distinct from the episodic attacks of imbalance and incoordination inducible by stress characteristic of the EA-1 syndrome. To date, animals harboring both homozygous and heterozygous EA-1 mutations have not been constructed, although they may display a more specific EA-1 phenotype. Two strains of mutant mice, the tottering (tg) and the leaner (tgla) mice, are characterized by ataxia, stiffness, retarded motor activity, and cerebellar neurodegeneration (Fletcher et al., 1996; Ophoff et al., 1998). Recently, several mutations have been found in the 1A calcium channel gene of these mutant animals (Ophoff et al., 1998). In particular, a splice-site mutation has been found in leaner mice resulting in 1A-subunit with an altered C-terminal region (Fig. 40.6). This mutation is thought to cause loss-of-function or haploinsufficiency (Ophoff et al., 1998). Interestingly, the nature of the leaner mutation resembles the mutations described in EA-2 patients, suggesting that common pathogenetic mechanisms may be involved. Recently, 1A-deficient mice have been also generated (Jun et al., 1999). These animals lack P/Q-type Ca currents and show severe neurologic alterations such as progressive ataxia, dystonia, and imbalance. Thus, the leaner mouse and the null mutant mouse represent two interesting animal models to study the pathophysiological role of P/Q-type Ca channels in EA-2 syndrome.

Concluding remarks Animal models of episodic ataxia The similarities between the neurological symptoms of EA1 and the abnormalities found in Shaker Drosophila melanogaster are remarkable. The Shaker phenotype is characterized by jerking movements when anaesthetized with ether (Kaplan and Trout, 1969). The A-type potassium currents of these fruit flies are abolished in the homozygous phenotype and reduced in the heterozygous phenotype. The neurologic abnormalities displayed by the mutant flies are caused by prolonged action potentials in axons, by multiple firings, and by an increased neurotransmitter release from the terminals (Jan et al., 1977; Salkoff and Wyman, 1981; Tanouye and Ferrus, 1985; Kamb et al., 1987).

Although important advancement has been made in understanding the pathophysiology of episodic ataxia diseases, some pivotal information remains elusive. Which are the central and peripheral neurologic alterations responsible for the myokymia and for the attacks of ataxia? What determines its episodic nature? How do stress and fatigue trigger the attacks? What is the incidence of these diseases? What is the mechanism(s) of action of acetazolamide? Is there a more appropriate pharmacological treatment for these patients? Is there a possible gene therapy approach for EA syndrome? The detailed knowledge of the regulation, function, and physiological role of Kv1.1 and of P/Q-type Ca channels

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is of fundamental importance in this regard. Moreover, invitro expression studies as well as transgenic animal models may certainly make a significant contribution to answering the many questions that remain and to the development of specific therapies leading to treatment and prevention of ataxia.

Acknowledgments The financial support of Telethon – Italy (Grant no. 1083) and of the Compagnia di San Paolo (Torino) is gratefully acknowledged. Paola Imbrici is the recipient of a fellowship from M.U.R.S.T. ‘Corso Biennale per Esperto in Biotecnologie Applicate alla Ricerca Scientifica Biomedica,’ programma operativo 94–98, obbiettivo 1, asse 7.1b cod.1245/134.

xReferencesx Adelman, J.P., Bond, C.T., Pessia, M. and Maylie, J. (1995). Episodic ataxia results from voltage-dependent potassium channels with altered functions. Neuron 15: 1449–54. Aldrich, R.W. Jr, Getting, P.A. and Thompson, S.H. (1979). Mechanism of frequency-dependent broadening of molluscan neurone soma spikes. J Physiol 291: 531–44. Armstrong, C.M. and Bezanilla, F. (1977). Inactivation of the sodium channel. II. Gating current experiments. J Gen Physiol 70: 567–50. Ashcroft, F.M. (1999). Ion Channels and Diseases. San Diego: Academic Press. Baukrowitz, T. and Yellen, G. (1995). Modulation of K current by frequency and external [K ]: a tale of two inactivation mechanisms. Neuron 15: 951–60. Beckh, S. and Pongs, O. (1990). Members of the RCK potassium channel family are differentially expressed in the rat nervous system. EMBO J 9: 777–82. Bouchard, J.P., Roberge, C., van Gelder, N.M. and Barbeau, A. (1984). Familial periodic ataxia responsive to acetazolamide. Can J Neurol Sci 11: 550–3. Browne, D.L., Brunt, E.R.P., Griggs, R.C. et al. (1995). Identification of two new KCNA1 mutations in episodic ataxia/myokymia families. Hum Mol Genet 4: 1671–2. Browne, D.L., Gancher, S.T., Mutt, J.G. et al. (1994). Episodic ataxia/myokymia syndrome is associated with point mutations in the human potassium channel gene, KCNA1. Nat Genet 8: 136–40. Brunt, E.R.P. and van Weerden, T.W. (1990). Familial paroxysmal kinesigenic ataxia and continuous myokymia. Brain 113: 1361–82. Choi, K.L., Mossman, C., Aube, J. and Yellen, G. (1993). The internal

quaternary ammonium receptor site of Shaker potassium channels. Neuron 10: 533–41. Christie, M.J., North, R.A., Osborne, P.B., Douglass, J. and Adelman, J.P. (1990). Heteropolymeric potassium channels expressed in Xenopus oocytes from cloned subunits. Neuron 2: 405–11. Comu, S., Giuliani, M. and Narayanan, V. (1996). Episodic ataxia and myokymia syndrome: a new mutation of potassium channel gene Kv1.1. Ann Neurol 40: 684–7. Covarrubias, M., Wei, A.A. and Salkoff, L. (1991). Shaker, Shal, Shab, and Shaw express independent K current systems. Neuron 7: 763–73. D’Adamo, M.C., Imbrici, P., Sponcichetti, F. and Pessia, M. (1999). Mutations in the KCNA1 gene associated with episodic ataxia type-1 syndrome impair heteromeric voltage-gated K channel function. FASEB J 13: 1335–45. D’Adamo, M.C., Liu, Z., Adelman, J.P., Maylie, J. and Pessia, M. (1998) Episodic ataxia type-1 mutations in the hKv1.1 cytoplasmic pore region alter the gating properties of the channel. EMBO J 17: 1200–7. Ducros, A., Denier, C., Joutel, A. et al. (1999). Recurrence of the T666M calcium channel CACNA1A gene mutation in familial hemiplegic migraine with progressive cerebellar ataxia. Am J Hum Genet 64: 89–98. Fletcher, C.F., Lutz, C.M., O’Sullivan, T.N. et al. (1996). Absence epilepsy in tottering mutant mice is associated with calcium channel defects. Cell 87: 607–17. Gancher, S.T. and Nutt, J.G. (1986). Autosomal dominant episodic ataxia: a heterogeneous syndrome. Mov Disord 1: 239–53. Grissmer, S. and Cahalan, M. (1989). TEA prevents inactivation while blocking open K channels in human T lymphocytes. Biophys J 55: 203–6. Hans, M., Luvisetto, S., Williams, M.E. et al. (1999). Functional consequences of mutations in the human alpha1A calcium channel subunit linked to familial hemiplegic migraine. J Neurosci 19: 1610–19. Hille, B. (1992). Ionic Channels of Excitable Membranes, 2nd edn. Sunderland, MA: Sinauer. Hopkins, W.F., Allen, M.L., Houamed, K.M. and Tempel, B.L. (1994). Properties of voltage-gated K currents expressed in Xenopus oocytes by mKv1.1, mKv1.2 and their heteromultimers as revealed by mutagenesis of the dendrotoxin-binding site in mKv1.1. Pflugers Arch 428: 382–90. Hoshi, T., Zagotta, W.N. and Aldrich, R.W. (1990). Biophysical and molecular mechanisms of Shaker potassium channels inactivation. Science 250: 533–8. Hoshi, T., Zagotta, W.N. and Aldrich, R.W. (1991). Two types of inactivation in Shaker K channels: effects of alterations in the carboxy-terminal region. Neuron 7: 547–56. Isacoff, E.Y., Jan N.Y. and Jan, L.Y. (1990). Evidence for the formation of heteromultimeric potassium channels in Xenopus oocytes. Nature 345: 530–54. Jan, Y.N., Jan, L.Y. and Dennis, M.J. (1977). Two mutations of synaptic transmission in Drosophila. Proc R Soc Lond B Biol Sci 198: 87–108. Jun, K., Piedras-Renteria, E.S., Smith, S.M. et al. (1999). Ablation of

Episodic ataxias as ion channel diseases

P/Q-type Ca(2 ) channel currents, altered synaptic transmission, and progressive ataxia in mice lacking the alpha(1A)subunit. Proc Natl Acad Sci USA 96: 15245–50. Kamb, A., Iverson, L.E. and Tanouye, M.A. (1987). Molecular characterization of Shaker, a drosophila gene that encodes a potassium channel. Cell 50: 405–13. Kaplan, W.D. and Trout, W.E. III (1969). The behaviour of four neurological mutants of Drosophila. Genetics 61: 399–409. Korn, H. and Axelrad, H. (1980). Electrical inhibition of Purkinje cells in the cerebellum of the rat. Proc Natl Acad Sci USA 77: 6244–7. Kramer, P.L., Yue, Q., Gancher, S.T. et al. (1995). A locus for the nystagmus-associated form of episodic ataxia maps to an 11cM region on chromosome 19p. Am J Hum Genet 57: 182–5 Laube, G., Roper, J., Pitt, J.C. et al. (1996). Ultrastructural localization of Shaker-related potassium channel subunits and synapseassociated protein 90 to separate-like junctions in rat cerebellar Pinceaux. Brain Res Mol Brain Res 42: 51–61. Litt, M., Kramer, P., Browne, D. et al. (1994). A gene for episodic ataxia/myokymia maps to chromosome 12p13. Am J Hum Genet 55: 702–9. Liu, Y., Holmgren, M., Jurman, M.E. and Yellen, G. (1997). Gated access to the pore of a voltage-dependent K channel. Neuron 19: 175–84. Lopez, G.A., Jan, J.N. and Jan, L.Y. (1994). Evidence that the S6 segment of the voltage-gated K channel comprises part of the pore. Nature 367: 179–82. López-Barneo, J., Hoshi, T., Heinemann, S.H. and Aldrich, R.W. (1993). Effects of external cations and mutations in the pore region on C-type inactivation of Shaker potassium channels Receptors Channels 1: 61–71. Ludwig, A., Flockerzi, V. and Hofmann, F. (1997). Regional expression and cellular localization of the alpha1 and beta subunit of high voltage-activated calcium channels in rat brain. J Neurosci 15: 1339–49. McNamara, N.M., Muniz, Z.M., Wilkin, G.P. and Dolly, J.O. (1993). Prominent location of a K channel containing the  subunit Kv1.2 in the basket cell nerve terminals of rat cerebellum. Neuroscience 57: 1039–45. Molina, A., Castellano, A.G. and López-Barneo, J. (1997). Pore mutations in Shaker K channels distinguish between the sites of tetraethylammonium blockade and C-type inactivation. J Physiol 499: 361–7. Ophoff, R.A., Terwindt, G.M., Frants, R.R. and Ferrari, M.D. (1998). P/Q-type Ca2 channel defects in migraine, ataxia and epilepsy. Trends Pharmacol Sci 19: 121–7. Ophoff, R.A., Terwindt, G.M., Vergouwe, M.N. et al. (1996). Familial hemiplegic migraine and episodic ataxia type-2 are caused by mutations in the Ca2 channel gene CACNL1A4. Cell 87: 543–52. Pardo, L.A., Heinemann, S.H., Terlau, H. et al. (1992). Extracellular K specifically modulates a rat brain K channel. Proc Natl Acad Sci USA 89: 2466–70. Po, S., Roberds, S., Snyders, D.J., Tamkun, M.M. and Bennett, P.B. (1993). Heteromultimeric assembly of human potassium chan-

nels. Molecular basis of a transient outward current? Circ Res 72: 1326–36. Ruppersberg, J.P., Schroter, K.H., Sakmann, B., Stocker, M., Sewing, S. and Pongs, O. (1990). Heteromultimeric channels formed by rat brain potassium-channel proteins. Nature 345: 535–7. Salkoff, L. and Wyman, R. (1981). Genetic modification of potassium channels in Drosophila Shaker mutants. Nature 293: 228–30. Scheffer, H., Brunt, E.R., Mol, G.J. et al. (1998). Three novel KCNA1 mutations in episodic ataxia type I families. Hum Genet 102: 464–6. Slesinger, P.A., Jan, Y.N. and Jan, L.Y. (1993). The S4–S5 loop contributes to the ion-selective pore of potassium channels. Neuron 11: 739–49. Smart, S.L., Lopantsev, V., Zhang, C.L. et al. (1998). Deletion of the Kv1.1 potassium channel causes epilepsy in mice. Neuron 20: 809–19. Southan, A.P. and Robertson, B. (1998). Patch-clamp recordings form cerebellar basket cell bodies and their presynaptic terminals reveal an asymmetric distribution of voltage-gated potassium channels. J Neurosci 18: 948–55. Stühmer, W., Ruppersberg, J.P., Schörter, K.H. et al. (1989). Molecular basis of functional diversity of voltage-gated potassium channel in mammalian brain. EMBO J 8: 3235–44. Tanouye, M.A. and Ferrus, A. (1985). Action potentials in normal and Shaker mutant Drosophila. J Neurogenet 2: 253–71. Teh, B.T., Silburn, P., Lindblad, K. et al. (1995). Familial periodic cerebellar ataxia without myokymia maps to a 19-cM region on 19p13. Am J Hum Genet 56: 1443–9. Van Dyke, D.H., Griggs, R.C., Murphy, M.J. and Goldstein, M.N. (1975). Hereditary myokymia and periodic ataxia. J Neurol Sci 25: 109–18. Veh, R.W., Lichtinghagen, R., Sewing, S., Wunder, F., Grumbach, I.M. and Pongs, O. (1995). Immunohistochemical localization of five members of the Kv1 channel subunits: contrasting subcellular locations and neuron-specific co-localizations in rat brain. Eur J Neurosci 7: 2189–205. Von Brederlow, B., Hahn, A.F., Koopman, W.J., Ebers, G.C. and Bulman, D.E. (1995). Mapping the gene for acetazolamide responsive hereditary paroxysmal cerebellar ataxia to chromosome 19p. Hum Mol Genet 2: 279–84. Wang, H., Kunkel, D.D., Martin, T.M., Schwartzkroin, P.A. and Tempel, B.L. (1993). Heteromultimeric K channels in terminal and juxtaparanodal regions of neurons. Nature 365: 75–9. Wang, H., Kunkel, D.D., Schwartzkroin, P.A. and Tempel, B.L. (1994). Localization of Kv1.1 and Kv1.2, two K channel proteins, to synaptic terminals, somata, and dendrites in the mouse brain. J Neurosci 14: 4588–99. Wu, L.G., Westenbroek, R.E., Borst, J.G.G., Catterall, W.A. and Sakmann, B. (1999). Calcium channel types with distinct presynaptic localization couple differentially to transmitter release in single calyx-type synapses. J Neurosci. 15: 726–36. Zagotta, W.N., Hoshi, T. and Aldrich, R.W. (1990). Restoration of inactivation in mutants of Shaker potassium channels by a peptide derived from Sh.B. Science 250: 568–71.

571

572

M.C. D’Adamo, P. Imbrici, and M. Pessia

Zerr, P., Adelman, J.P. and Maylie, J. (1998a). Episodic ataxia mutations in Kv1.1 alter potassium channel function by dominant negative effects or haploinsufficiency. J Neurosci 18: 2842–8. Zerr, P., Adelman, J.P. and Maylie, J. (1998b). Characterization of three episodic ataxia mutations in the human Kv1.1 potassium channel. FEBS Lett. 431: 461–4.

Zhuchenko, O., Bailey, J., Bonnen, P. et al. (1997). Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1A-voltage-dependent calcium channel. Nat Genet 15: 62–9.

Index

Numbers in italics indicate tables or figures. Acadian ataxia 509 acetazolamide 567 acetlycholine 39 3-acetyl pyridine 7 acoustic afferents 19 action tremor 108, 109, 110 acute diffuse encephalomyelitis (ADEM) 248, 252, 253 acyclovir 254–5 adaptive control function 69–71 Ito’s model 85–6 adaptive timer/linear filter model 85 adenosine A1 receptors 330 adjustable pattern generator model 83 adjuvant chemotherapy 269, 271 adjuvant radiation therapy 271, 273 adrenocorticotrophic hormone 255 adrenomyeloneuropathy 526 adult Chiari malformation 163–5 affect and psychosis 136–57 affect and emotion 136–7 anatomic substrates: cerebellar connections with associative/neocortical systems 141–4 hypothalamus 139–40 limbic system 141 reticular system 139 behavioral observations 137–9 clinical observations (contemporary) 144–6 psychosis 147 early accounts 137 neuroimaging observations 147, 149 depression 150 mood 149–50 pain 148–9 schizophrenia 150–1 smell 149 thirst and hunger 149 synthesis and hypothesis 151–3 afferent systems 7 climbing fiber 22 neurotransmitters 39, 40

573

574

Index

afferent systems (cont.) mossy fiber acoustic, visual and trigeminal afferents 19 neurotransmitters 38, 39–40 overview 17 pontine nuclei 20–2 reticular precerebellar nuclei 19–20 spinocerebellar tracts 17–19 vestibular afferents 19 aggression 138, 141 AICA, see anterior inferior cerebellar artery AIDS 257–8, 260, 276 Albright’s osteodystrophy 320, 321 Albus models 54, 60, 61, 80–2 alcohol toxicity clinical aspects blood studies 338 cerebellar atrophy 337 clinical findings 336–7 neuropathology 338 pathophysiology 338–40 prognosis of cerebellar ataxia 340 treatment 340 fundamental aspects 327, 328 cytochrome P450 333 granule cells 327, 329–30 Purkinje cells 329, 330–3, 338 alien hand sign 198, 200 alphafetoprotein (AFP) 532 -aminobutyric acid (GABA), see gamma-aminobutyric acid amiodarone toxicity 318, 348–9 AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors AMPA/kainate 332 grafted pcd mice 377 amphibians 6, 7, 14 anatomic reference system establishment 33–4 anatomic substrates, see affect and psychosis: anatomic substrates anatomy, see high-resolution cerebellar anatomy; neuroanatomy of the cerebellum aneurysms 219, 220, 224 angiography 221, 295, 298 angiotensin II 299 Angurugu syndrome 353 animals cerebellar nuclei 14 evolution of the cerebellum 6, 7 nomenclature of cerebellar subdivisions 6, 9 see also specific animals anterior inferior cerebellar artery (AICA) 203, 204, 206–8 infarctions 212, 213–14, 215, 217, 218 antibiotic treatment cerebellar abscesses 243, 244 Whipple’s disease 263 anticancer chemotherapy astrocytomas 271 cerebellar injury from 278, 279 cerebellar metastases 278, 280 ependymomas 273 medulloblastomas 269

anticipation 440 DRPLA 481, 483, 485 SCA1 410 SCA2 421, 422–3 SCA3/Machado–Joseph disease 432 SCA4 441, 442 SCA5 448 SCA6 452 SCA7 459, 462 anticoagulants 223, 300 anticonvulsants, see drug toxicity: anticonvulsants anti-CV2; -Hu; -Mal; -Ri; -Tr; -Yo syndromes, see cerebellar disorders in cancer: paraneoplastic cerebellar degeneration antioxidants 514 antiplatelet agents 223 antisense RNA 478 antiviral agents 260 apoptosis, radiation induced 538 arachnoid cysts 172 archicerebellum 97, 98 arm movement model 87–8 arousal 137 arteries, see specific arteries; vascularization of the cerebellum: arterial supply -aspartate transmitter 40 aspergillosis 219 aspiration, cerebellar abscesses 243–4, 245 aspirin 223 associative/neocortical systems – cerebellar connections 141–4 astasia 100 astrocytes 308 astrocytomas 269–71 asynergia 100 A-T, see ataxia-telangiectasia ataxia defined 99–100 DNA collection 469 see also specific disorders ataxia and isolated vitamin E deficiency disorder 525 ataxia-telangiectasia (A-T) 531–47 ATM mutant mouse models 539 clinicopathologic syndrome 531 neurologic features 531–2 non-neurologic features 532–4 clinicopathology of the A-T heterozygote 534 cancer risk 534–6 diagnosis 541–2 prenatal 542 genotype/phenotype correlations 539–40 A-TFresno 540 Mre 11 deficiency 540–1 Nijmegan breakage syndrome 540 overlapping symptoms explained 541 structure and function of the ATM protein 536 double-strand break repair 538 G1 phase arrest 536–7 G2 phase arrest 537–8 radiation-induced apoptosis inhibition 538 S phase arrest 537 treatment 542–3

Index

ataxins 387 ataxin-1 411–16 ataxin-2 419, 424–5 ataxin-3 433–5 ataxin-7 463–5 A-TFresno 540, 541 atherosclerosis 218 atlases, see brain atlases ATM gene 534, 535, 536, 539–40, 541, 542 atonia 100 atrophy, see cerebellar atrophy; multiple system atrophy autism 147 autonomic failure multiple system atrophy 189, 190, 193 Shy–Drager syndrome 185, 186 autonomic functions hypothalamus–cerebellar connections 139 influence of cerebellum 27, 137 autonomic signs 117 autosomal dominant cerebellar ataxia with progressive pigmentary macular dystrophy, see spinocerebellar ataxia type 7 (SCA7) autosomal recessive spastic ataxia of Charlevoix–Saguenay 521 autosomal recessive spastic paraplegia type 7 525 axonal injury, diffuse, see diffuse axonal injury Babinski’s hypothesis 100, 108 bacteria associated with cerebellitis 249, 250 in cerebellar abscesses 241, 242, 243 see also specific bacteria ballistic movements 122 Barany’s test 106, 114, 115 barbiturate toxicity 347 basal ganglia 151–2 basilar artery 202, 204, 207–9, 218 basket cells 4, 11, 12, 13, 328 episodic ataxia type 1 566–7 beaded fibers 43 behavior changes 145 Behçet’s disease 234 Behr’s syndrome 528 benzene toxicity 355 benzodiazepine receptor densities, alcoholic patients 338 Berlin breakage syndrome (BBS) 540, 541 Berman syndrome 528 beta-interferons (IFN) 232, 233 bilateral ventral flexor reflex tract (bVFRT) 18, 19–20 biopsy 262, 284 birds 6, 7, 14 bismuth toxicity 349, 350 Blake’s pouch cyst 171, 172 blood–brain barrier of cerebellar grafts 371–2 blood studies alcohol toxicity 338 cerebellar stroke 221 cerebellitis 251, 252 Hashimoto’s thyroidosis 318–19 lead toxicity 353 phencyclidine abuse 357 body dynamics 71, 78–9, 93

body state estimation/prediction 78, 80 body sway 113, 115 border zone infarctions 216, 217, 218 Bordetella pertussis 251 botulinum toxin 200, 301 Boucher–Neuhäuser syndrome 528 boxing injuries 289 brain atlases 30, 32, 34–5 brain biopsy 262, 284 brain-derived neurotrophic factor (BDNF) 329, 330 brain mapping 33–4 brainstem compression 223 gliomas 271, 272 input to the inferior olive 22 signs, cerebellitis 248, 249 trauma, see posterior fossa trauma BRCA1 interaction with ATM 536, 538 breast cancer, A-T heterozygotes 534–5 bromide/bromvalerylurea toxicity 349 Brun’s ataxia 116 CACNA1A gene 451, 453, 455, 567, 569 CAG repeat expansions, see repeat expansions, CAG calcifications 321 calcium channels 12, 454, 567–9 calcium uptake inhibition, alcohol toxicity 329, 330 cancer ataxia-telangiectasia heterozygotes 534–6 homozygotes 532–3, 542–3 supportive therapy and cerebellar injury 279 see also cerebellar disorders in cancer capsule imaging, cerebellar abscesses 238, 239, 240, 241 carbamazepine toxicity 343, 344, 345–7 carbohydrate-deficient glycoprotein syndrome type 1 520 carbon disulphide toxicity 358–9 carbon monoxide poisoning 357–8 cardiac hypertrophy in Friedreich’s ataxia 391, 393, 507 cardiac studies, cerebellar stroke 221, 222 cardioembolism 218–19 catalepsy 100 catecholamines 298, 299 cats 26 experimental observations, behavior and affect 137 fastigius nuclei 49 inferior olive 15 toluene inhalation model 355 caudate nuclei 183, 184 CCNU (1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea) 269, 271 ceftriaxone 255 celiac disease 234 ceramide synthesis cascade 538 cerebellar abscesses 237–47 histology 242 overview 237–8 radiology computed tomography scans 238–9, 240 magnetic resonance imaging 239–41

575

576

Index

cerebellar abscesses (cont.) magnetic resonance spectroscopy 241 nuclear medicine imaging 241–2 treatment medical 242–3 outcome 244–5 surgical 243–4 cerebellar atrophy alcoholism 337 crossed 300 phenytoin toxicity 342–3 predisposes for carbamazepine toxicity 344, 345, 346 see also specific disorders cerebellar cognitive affective syndrome 62, 117, 145, 146–7, 148 cerebellar cortex neuronal activity in 50–2, 54–5 vascularization 202–303 see also neurotransmitters in the cerebellum: afferents to the cerebellar cortex; olivo-cerebellar system: cerebellar cortex cerebellar disorders in cancer 265–87 causes summarized 266 cerebrovascular diseases 280 clinical presentation 265 diagnosis 284–5 infections 280 metastases 276, 278, 280 neoplastic lesions 266 astrocytomas 269–71 brainstem gliomas 271, 272 ependymomas 273, 275, 276 epidermoid and dermoid tumors 273, 274, 278 hemangioblastomas 271, 272, 273, 274 Lhermitte–Duclos disease 276, 279 medulloblastomas 266–9 meningiomas 273, 277 primary malignant lymphoma 274, 276 schwannomas 273 paraneoplastic cerebellar degeneration syndromes 280–1 anti-CV2 283 anti-Hu 282 anti-Mal 283 anti-Ri 282, 283 anti-Tr 283 anti-Yo 281, 282 therapy 283, 284 treatment-related lesions anticancer chemotherapy 278, 279 superficial siderosis 280 supportive therapy 279 cerebellar hemorrhage 219–20, 280 cerebellar hemorrhagic infarction 220 cerebellar nuclei 14, 15 see also deep cerebellar nuclei; specific nuclei cerebellar-plus syndrome 181, 182, 185 cerebellar stroke, see stroke cerebellar system functions adaptive control cognitive control 71 motor control 69–70 sensory (sensorimotor) control 70–1

signal processing, unique aspects 71–2, 93 see also models of cerebellar system function cerebellar trauma, see posterior fossa trauma cerebellar vein thrombosis 224 cerebellitis agents implicated 249–50 clinical presentation 248–9 diagnosis 251–4 pathogenesis 250–1 prognosis/outcome 255–6 treatment 254–5 cerebral cortex 151–2 cerebral cortex–cerebellar connections 141–4 cerebral perfusion pressure 299 cerebro-cerebellar loops 26 cerebrospinal fluid (CSF) studies brain abscesses 238 cerebellitis 251, 252 Hashimoto’s thyroiditis 319 PML 258 Whipple’s disease 262 cerebrotendinous xanthomatosis 525, 526 cerebrovascular diseases in cancer patients 280 cGMP, see cyclic guanosine monophosphate channelopathies, see episodic ataxias as ion channel diseases; spinocerebellar ataxia type 6 (SCA6) check 112 chemical integration 11 Chiari I malformation 163–5 Chiari II malformation 165–8 Chiari III and IV malformations 168, 169 chicken ovalbumin upstream promoter-transcription factor (COUPTF) 310 chlordecone toxicity 358 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) 269, 271 cholestanolosis 525 choline acetyl transferase (ChAT) 39, 42 cholinergic afferents 7 cimetidine toxicity 351 cingulate gyrus 137, 141 cisplatin 269 CJD (Creutzfeldt–Jacob disease) 319 Clarke’s cells 17 climbing fibers 7, 11, 74, 328 afferent system 22 input to cerebellar nuclei 14 neurotransmitters 39, 40 Purkinje cell connections 10 clinical signs of cerebellar disorders 97–120 according to sagittal zone affected 101 ataxia defined 99–100 cognitive deficits 117 dysarthria 105–6 historical aspects 100 limb movement deficits 106–12 check and rebound 112 decomposition of movements 110, 111 dysdiadochokinesia 111, 112 dysmetria 107–8 dysrhythmokinesia 111, 112

Index

examination of limb movements 106–7 isometraxia 112, 113 muscle tone disorders 110, 111 sensitivity and specificity of upper limb tests 112, 114, 115 tremor 108–10, 111 non-cerebellar signs 117 oculomotor disturbances 103 correlation with lesion location 101, 102 extracerebellar disease 105 eye movement examination 101, 102 fixation disorders 102 nystagmus 102, 103–5 ocular tilt reaction 102 persuit disorders 102 saccade deficits 102, 103 skew deviation 102 stance and gait abnormalities 112–16 gait ataxia 114, 116 psychogenic ataxic gait 116 stance ataxia 113, 115, 116 tilted or rotated posture 116 symptoms 97, 99 visceral function 117 see also neuroanatomy of the cerebellum; pathophysiology of clinical cerebellar signs; specific disorders clock functions, see motor clock hypothesis clonazepam 200, 300, 320, 543 cocaine 356 cochlear nucleus, dorsal 372 Cogan’s syndrome 234 cognition contributions of the cerebellum 61–2 deficits in cerebellar patients 117 and emotion 139 see also cerebellar cognitive affective syndrome cognitive cerebellum 62, 148, 151 cognitive dysmetria, see dysmetria of thought colony survival assay 533 combiner–coordinator theory 58–60 command–feedback comparator theory 58 complex spikes, Purkinje cells 10, 12, 50–2, 53, 54–5 computed tomography 162 alcoholism 337 cerebellar abscesses 238–9, 240 corticobasal degeneration 198, 199 Hashimoto’s thyroiditis 319 multiple system atrophy 191 PML 258, 259 posterior fossa trauma 292, 293, 294, 295, 296 spiral 222 concussion 289 congenital hypothyroid hyt/hyt mice 310 congenital malformations of the cerebellum and posterior fossa 161–77 Chiari I 163–5 Chiari II 165–8 Chiari III and IV 168, 169 cystic posterior fossa and hindbrain malformations 168–9 Blake’s pouch cyst 171, 172 Dandy–Walker malformation and variant 169–71

megacisterna magna 171, 172 surgical treatment 172–3 imaging 161–2 normal embryology and development 161 other cerebellar developmental abnormalities global cerebellar hypoplasia 175 Joubert’s syndrome 173–4, 520 Lhermitte–Duclos syndrome 175 macrocerebellum 175 rhomboencephalosynapsis 175 tectocerebellar dysraphia 174–5 vermis hypoplasia 174 context–response linkages, storage 80–2 contigs, SCA4 442–3 contusion 289, 292–3 cooling of deep nuclei 55, 56, 57 core imaging, cerebellar abscesses 238, 239, 240, 241 cortical input to the inferior olive 22 corticobasal degeneration 198–201 clinical features 198 diagnostic studies 198–9 differential diagnosis 199–200 pathogenesis of cerebellar ataxia 199 treatment and prognosis 200 corticonuclear microcomplexes 72–3, 85, 93, 153 corticopontine fibers 20, 21 COUP-TF (chicken ovalbumin upstream promoter-transcription factor) 310 Coxiella burnetii 249, 253, 255 Creutzfeldt–Jacob disease (CJD) 319 crossed cerebellar atrophy 300 crossed cerebellar diaschisis 296, 297 cryosectioning 31, 32, 34 CSF, see cerebrospinal fluid CTG repeat expansions, see spinocerebellar ataxia type 8 (SCA8): CTG repeat expansions CT scans, see computed tomography scans cuneocerebellar tract 19 CV2 antigen 281, 283 cyanide poisoning 359–60 cyclic guanosine monophosphate (cGMP) 12, 43, 251, 330 cyclosporin toxicity 349 cytochrome P450 333, 346 cytomegalovirus (CMV) encephalitis 254 cytosine arabinoside 278 dab 1 5 DAF syndrome 525 Dandy–Walker malformation and variant 169–71 deafness 528 deafness–dystonia protein 556 decomposition of movements 110, 111, 122 decompressive surgery 223 deep cerebellar nuclei 8, 98 cerebellar grafts 375, 377, 379 genesis 4–5 linked by parallel fiber beams 61 three-dimensional histological reconstructions 30–1 see also specific nuclei; structure and function of the cerebellum deformable brain atlases 34–5

577

578

Index

delayed-onset cerebellar syndrome 300 delayed-onset intention tremor 300 delay settings 71, 72 deletions, mitochondrial DNA 549, 552, 556 delirium tremens 336, 337 2-receptors 41 dementia 420–1 demyelination cerebellitis 250 PML 258 dendrites basket cells 12 granule cells 10 Purkinje cells 10, 11, 12 alcohol-induced damage 331–2 Friedreich’s ataxia 390 phenytoin toxicity 343, 344, 345 SCA1 393, 394, 412 transplant dendritogenesis 373, 374, 375 dentate nuclei 5, 8, 14, 25, 142 ablation 56–7 Friedreich’s ataxia 389–90, 393 lesions and ataxia generation 401, 402 neuronal activity 50, 52, 53 SCA3/Machado–Joseph disease 395, 396 SCA6 397, 398 visualization 33, 34 dentatorubral-pallidoluysian atrophy (DRPLA) 481–90 clinical features 481–2 genotype–phenotype correlations 482–3 molecular genetics 483, 485–6 neurodegeneration mechanisms 486–7 population genetics 483–5 depression, neuroimaging observations 150 dermoid tumors 273, 274 desferioxamine 514 development of the cerebellum 3–5, 161, 369 see also congenital malformations of the cerebellum and posterior fossa diabetes insipidus 322 diabetes mellitus 321, 507 DIDMOAD syndrome 322, 528, 551 differentiation of signals 71, 73, 74 diffuse axonal injury 289, 293, 294, 295 digital image capture of cryosections 31 direct adaptive control 79 discontinuous control 79–80, 94 dissections, artery 218 DM1 (myotonic dystrophy type 1) 478 DNA non-B structures 498–9 repair, A-T heterozygotes 536, 538 sticky 496, 498–9 see also molecular mechanisms of triplet repeat expansions: genetic instability generation DNA polymerases 492, 494, 499 dog model, cerebellar abscesses 242 dominant ataxias 391, 483–5 see also specific disorders -dopa, see levodopa

dopamine D2 receptors 192, 194 dopaminergic fibers 27, 43 dorsal cochlear nucleus 372 dorsal roots/dorsal root ganglia, Friedreich’s ataxia 388, 389 dorsal spinocerebellar tract (Flechsig’s tract) 17 downbeat nystagmus 104, 105 Drosophila melanogaster models episodic ataxia type 1 (EA-1) 569 SCA3/Machado–Joseph disease 435 DRPLA, see dentatorubral-pallidoluysian atrophy drug-induced thyroid dysfunction 318 drug toxicity amiodarone 348–9 anticonvulsants barbiturates 347 carbamazepine 343, 344, 345–7 gabapentin 347 lamotrigine 347 phenytoin 342–3, 344, 345 topiramate 347 vigabatrin 347 bismuth 349, 350 bromides/bromvalerylurea 349 cimetidine 351 cyclosporin 349 isoniazid 350 lindane 350 lithium salts 347–8 mefloquine 349, 350 perhexiline maleate 351 dynamic interaction forces 124, 125, 126, 127, 131 dysarthria 105–6, 130 dyscoordination of movement, pathophysiology 123–7 dysdiadochokinesia 111, 112, 122, 127 dysequilibrium syndrome 519 dysmetria 100, 107–8, 122–3 dysmetria of thought 117, 150, 152, 153 dysplastic cerebellar gangliocytoma, see Lhermitte–Duclos disease dysrhythmokinesia 111, 112 dyssynergia 122 EA1/2, see episodic ataxias as ion channel diseases early-onset inherited ataxias 519–30 congenital 519 carbohydrate-deficient glycoprotein syndrome type 1 520 dysequilibrium syndrome 519 Gillespie syndrome 519 granule cell layer hypoplasia 519 Joubert syndrome 173–4, 520 Paine syndrome 520 pontocerebellar hypoplasia 519 X-linked congenital cerebellar hypoplasia 520 with deafness 528 with hypogonadism 527–8 with ocular features 528 with parkinsonism 528–9 with retained tendon reflexes 520–1 clinical features 521–2

Index

differential diagnosis 522, 524–7 laboratory findings 522, 523, 524 see also ataxia-telangiectasia (A-T); Friedreich’s ataxia EDTA 353 efferent systems 7 cerebro-cerebellar loops 26 fastigial nucleus 24, 25 interpositus nucleus 24, 25 lateral-dentate nucleus 25 overview 22, 24 thalamo-cortical relay 25–6 electrocardiography (ECG) 221 electroencephalography (EEG) 252, 319, 358 electromyography (EMG) 122, 123 embedding media 32 embolic stroke 218–19 emboliform nuclei 8, 14 embryology of the cerebellum 3–5, 161, 369 emotion 136–7, 139 endocrine disorders associated with cerebellar ataxia 316–24 diabetes insipidus 322 diabetes mellitus 321 other associations 322 parathyroid disorders hyperparathyroidism 321 hypoparathyroidism 320 pathophysiology 321 pseudohypoparathyroidism 320–1 treatment and prognosis 321 thyroid dysfunction diagnosis 318–19 drug-induced 318 Hashimoto’s thyroiditis 317 hyperthyroidism 317 hypothyroidism 316–17 pathophysiology 318 prognosis/outcome 320 treatment 319 endoscopy 262 endothelin 298 enkephalin 40 ependymomas 273, 275, 276 epidermoid tumors 273, 278 epidural hematomas 289, 291, 294, 296, 299 epilepsy 138, 481 episodic ataxias as ion channel diseases 562–72 animal models 569 episodic ataxia type 1 (EA-1) clinical aspects 562–3 molecular determinants 563–4, 565, 566 pathophysiological mechanisms 564, 566–7 episodic ataxia type 2 (EA-2) 451, 455, 456, 567–9 equilibrium point hypothesis 131 Erdheim–Chester disease 322 error signals 81, 82, 85, 87, 153 essential tremor 108 eucalyptus oil poisoning 359 excitatory amino acid transporters 40 executive functions 136, 145

exteroceptive cells 17, 19 eye movement control 82–3, 85–6, 94, 129–30, 131 see also specific disorders eye movement examination 101, 102 falciparum malaria 250, 255 famial hemiplegic migraine 455–6, 568, 569 fast excitation 38 fastigial nuclei 8, 14, 27, 102 ablation 55, 56 efferences 24, 25 neuronal activity 49, 50 stimulation, influence on behavior and affect 137–8, 141 feedback control 75, 76–7, 93 feedforward control 75–6, 93 ferritin 390, 392–3 fever 251, 356 firing rates 49, 54, 333, 343 fish 6, 7, 14 fissures 4, 8, 9, 97, 161 fits 110 Flechsig’s tract (dorsal spinocerebellar tract) 17 flexor reflex afferents 17, 18 flocculus 4, 8, 15, 83–4, 102 Flourens, P. 137 5-fluorouracil 278 flutter 102, 103 fractured somatotopy 21 frataxin, see Friedreich’s ataxia: frataxin function and pathogenesis; Friedreich’s ataxia: molecular genetics free radicals 507, 512, 513 Friedreich’s ataxia 505–18 clinical aspects biochemical investigations 508 neuroimaging 508 neurological signs and symptoms 506 neurophysiological investigations 508 non-neurological involvement 507–8 onset 505, 506 prognosis 509 treatment 509–10, 513–14 variant phenotypes 508–9 epidemiology 505 frataxin function and pathogenesis 391, 507, 511 biochemical and structural studies 512–13 pathogenesis hypotheses 513 subcellular localization 512 yeast knock-out 512 molecular genetics FRDA gene 510 GAA repeat expansions 510–11 point mutations 511 triplexes and sticky DNA 496, 498–9 neuropathology 387–91, 392, 393 see also early-onset inherited ataxias: with retained tendon reflexes frontal ataxia 116 functional microcomplexes 72–3, 85, 153 functions of the cerebellum, see models of cerebellar system function; structure and function of the cerebellum

579

580

Index

G1/G2 phase arrest 536, 537–8 GAA repeat expansions, see repeat expansions, GAA GABA, see gamma-aminobutyric acid gabapentin 347 gain-of-function mechanism 411–12 gain settings 71, 72 gait abnormalities 99, 114, 116, 127–8 see also specific disorders Galenic group of veins 211 gamma-aminobutyric acid (GABA) inhibitory interneuron transmitter 42 Purkinje cell transmitter 41 alcohol inhibition of receptor 332 receptor distribution in grafts 377 ganglionic layer 8 GAPDH (glyceraldehyde-3-phosphate dehydrogenase) 414 gaze-evoked nystagmus 103–4, 129 genetic mapping SCA4 442–3 SCA5 449 genetics of multiple sclerosis 231, 232 geographical distribution of multiple sclerosis 228 germanium toxicity 355 Gillespie syndrome 519 Glasgow Coma Scale 291 GLAST glial glutamate transporter 41 glial cells 43, 44, 308, 333 glial cytoplasmic inclusions, multiple system atrophy 187–8 global cerebellar hypoplasia 175 globosus nuclei 8, 14 glomerulus 10, 12 glucose hypometabolism 338 glutamate 38–9, 40, 40–1, 43, 354 glutamic acid decarboxylase 41 antibodies in cerebellar ataxia 234–5 gluten ataxia 234, 526–7 glyceraldehyde-3-phosphate dehydrogenase (GAPDH) 414 glycine 42 cGMP, see cyclic guanosine monophosphate Golgi cells 11, 12, 13, 14, 39, 42 Gomi, H. 87 Gower’s tract (ventral spinocerebellar tract) 17, 19 grafts 369–84 in ataxic mouse mutants Lurcher (Lc) 374–5 nervous (nr) 374 Purkinje cell degeneration (pcd) 375–80 staggerer (sg) 374 weaver (wv) 374 blood–brain barrier 371–2 graft–host interactions 373 growth and histiotypic differentiation 370–1 initial problems 369–70 transplanted Purkinje cells 372–3 histochemical phenotype 372 migration and morphogenesis 372–3 physiological activity 372 grammar formation 130

granular layer 11, 13–14, 328 granule cell layer hypoplasia 519 granule cells 10–11, 12, 13, 328 alcohol toxicity 327, 329–30 carbamazepine toxicity 346 glutamate transmitter 39, 40–1 mercury toxicity 351, 352 neurotrophins 309 PACAP action on 42 perinatal hypothyroidism 307–8, 310 phenytoin toxicity 343 staggerer mice 311 hairless 310 harmaline 16, 27, 55, 251 Hashimoto’s thyroiditis 316, 317, 318, 319–20 headache 99 head tilt/rotation 116 heart disease, Friedreich’s ataxia 391, 393, 507 heat shock proteins 356, 357, 435–6, 464 heat stroke 356 hemangioblastomas 271, 272, 273, 274 hemiplegic migraine, familial 455–6 heroin 356–7 3-Hertz leg tremor 108, 110 heteroplasmic mutations 549 hexosaminidase A deficiency 525 high-dimensional warping algorithms 34–5 high-resolution cerebellar anatomy 30–7 current challenges 30 deformable brain atlases 34–5 informatics and brain mapping 33–4 in-vivo 32–3 post-mortem 30–2 hindbrain 3 histochemistry of transplanted Purkinje cells 372 histological studies, limitations 30–1 hMre11 gene 540–1 Holmes, G. 100 homocysteic acid 40 horizontal pointing maneuver 106, 107, 114, 115 Hu antigen 281, 282 human immunodeficiency virus (HIV) 251, 252, 254, 260 hunger, neuroimaging observations 149 hydrocephalus, value of ventricular drainage 223, 245 hydroxyurea 273 hyperbaric oxygen therapy 358 hypermetria 107–8 hyperparathyroidism 321 hyperthermia 356 hyperthyroidism 316, 317, 318, 319 hypogonadism 527–8 hypometria 107, 108 hypoparathyroidism 320, 321 hypothalamus 27, 43, 137 hypothalamus–cerebellar connnections 139–40 hypothyroidism 316, 317, 318, 319, 320 hypotonia 110, 111, 129 hyt/hyt mice 310

Index

idiopathic late-onset cerebellar ataxia (ILOCA) 180–2 IFN (beta-interferons) 232, 233 imaging techniques 161–2 see also specific techniques immune diseases 228–36 Behçet’s disease 234 celiac disease 234 Cogan’s syndrome 234 glutamic acid decarboxylase antibody effects 234–5 Miller Fisher syndrome 233, 255 multiple sclerosis, see multiple sclerosis systemic lupus erythematosus 235 immunodeficiency, A-T patients 532 immunogold electron microscopy 38, 40, 41, 42 immunological hypothesis, cerebellitis 250–1 inclusion bodies, dominant ataxias 398–401, 412, 434–6, 463–4, 487 individual susceptibilities alcohol 338, 339 carbamazepine 343, 344, 345 indomethacin 194 inertia 100 infantile autism 147 infantile-onset spinocerebellar ataxia 521 infarctions, see MELAS; stroke: infarctions, territory of cerebellar arteries infections in cancer patients 280 infectious diseases, see cerebellar abscesses; cerebellitis; progressive multifocal leukoencephalopathy; Whipple’s disease inferior olive 10, 13, 15–16, 22, 401 inferior vermian veins 211 inhibitory interneurons granular layer 13–14 molecular layer 12, 13 neurotransmitters 42–3 insulin-like growth factor-1 (IGF-1) 329, 330 integration of signals 71–2, 89 intention tremor 100, 108, 109, 128 -interferons (IFN) 232, 233 interleukin-4 262 intermediate cerebellar model 87–8 internal dynamic models 78–9, 85–9 interpositus nuclei 24, 25, 98 ablation 55–6, 57 neuronal activity 50, 51, 52, 53 intracortical vessels 202 intracranial pressure control, trauma victims 299 lead intoxication 353 intranuclear inclusions, see inclusion bodies inverse dynamics 75, 76, 87, 93, 124 in-vivo anatomy 32–3 iodothyronine 5′-deiodinase (type II) 305 ion channel diseases, see episodic ataxias as ion channel diseases ion channels 562 see also calcium channels; potassium channels ipsilateral forelimb tract 20 iron, Friedreich’s ataxia 389, 390, 507, 512, 513 isometraxia 112, 113 isoniazid toxicity 350 Ito model 85–6

JC virus 258, 259 Jeune–Tommasi disease 528 Joubert syndrome 173–4, 520 Kalman filters 86, 87 Kawato et al. models 86, 87 KCNA1 gene 563 Kearns–Sayre syndrome 526, 552–3, 554 kinetic tremor 108, 128, 198 Kinsbourne syndrome (opsoclonus–myoclonus) 254 KLHL1 gene 478 knockout mice A-T 539 Kv1.1 569 Math 1 5 thyroid hormone receptor 310, 311 see also mouse models knock-out yeast, frataxin 512 Korsakoff’s syndrome 337 Krabbe disease 525 Kufs’ disease 525 Kv1.1 563, 564, 565 heteropolymerization with Kv1.2 564, 566 labyrinthitis 253 lacunar infarctions 216, 217 lamotrigine 347 Langerhans’ cell histiocytosis 322 LANP (leucine-rich acidic nuclear protein) 413–14 Larsell–Voogd’s nomenclature 6, 7, 9 lateral medullary infarctions (Wallenberg’s syndrome) 212, 291 lateral reticular nuclei (LRN) 18, 19–20, 140 lead toxicity 352–3 ‘leaky’ integrators 83–4 Leigh syndrome 556–7 leucine-rich acidic nuclear protein (LANP) 413–14 leukocyte scintigraphy 241–2 levodopa 187, 191, 192, 193, 194 levothyroxine 319 Lhermitte–Duclos disease 175, 276, 279 Lhermitte’s symptom 228 Lichtenstein–Knorr syndrome 528 limbic cerebellum 148, 151 limbic system 139, 141 limb movement tests 106–7, 112, 114, 115 lindane toxicity 350 linear filters 85 lipohyalinosis 219 Listeria monocytogenes 254 lithium 279, 318, 347–8 liver disease 340 lobes 97, 98 lobules 98 long-term depression (LTD) 43, 44, 61, 74, 330 long-term potentiation (LTP) 74 lookup table-based control 79, 82, 94 low-flow 219 Luciani’s triad of signs 100 Lugaro cells 13–14, 42 lumbar puncture 222 lupus ataxia 235

581

582

Index

Lurcher mutant mice 374–5 lymphocytosis-promoting factor 251 Machado–Joseph disease, see spinocerebellar ataxia type 3/Machado–Joseph disease macrocerebellum 175 macrosaccidic oscillations 102 macular degeneration 461 magnetic resonance angiography (MRA) 221 magnetic resonance imaging (MRI) alcoholism 337 astrocytomas 270 benzene/toluene toxicity 355 brainstem gliomas 272 carbon monoxide poisoning 358 cerebellar abscesses 239–41 cerebellar cancer 284, 285 cerebellar stroke 220–1 cerebellitis 252, 253, 254, 255 congenital malformations 162 corticobasal degeneration 198, 199 DRPLA 482–3 ependymomas 275, 276 epidermoid tumors 278 Hashimoto’s thyroiditis 319 hemangioblastomas 272, 274 Leigh syndrome 557 Lhermitte–Duclos disease 279 limbic cerebellum activation 148, 149 medulloblastomas 267–8 MELAS 554 meningiomas 277 mercury toxicity 351 multiple sclerosis 233 multiple system atrophy 191–2 multi-scan averaging 32–3 PML 259 posterior fossa trauma 292–3, 294, 295, 297, 298 primary malignant lymphoma 276 SCA2 421 SCA3/Machado–Joseph disease 431 SCA5 447 SCA8 476 striatonigral degeneration 184, 185 superficial siderosis 301 Whipple’s disease 262–3 magnetic resonance spectroscopy 192, 241, 259 Mal antigen 281, 283 manganese toxicity 353–4 mapmodulin (LANP) 413–14 Marinesco–Sjögren syndrome 528 Marr–Albus cerebellar system models 80–2 Marr–Albus–Ito Motor Learning Theory 54, 60, 61 Math 1 5 medulloblastomas 266–9 mefloquine toxicity 349, 350 megacisterna magna 171, 172 MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes) 554 meningiomas 273, 277 mercury toxicity 351–2 MERRF (myoclonic epilepsy with ragged red fibers) 555

mesodiencephalic input to the inferior olive 22 metastases 276, 278, 280 metencephalon 3, 4 methotrexate 279 N-methyl--aspartate (NMDA) receptors 329, 357, 377 methylmercury toxicity 351–2 Miall et al. model 87 microcircuitry adaptation of circuit behavior 74 functional microcomplexes 72–3, 85, 153 linear signal processing (possible) 73–4 see also neuroanatomy of the cerebellum migration primitive cells 4–5 transplanted Purkinje cells 372–3 Miller Fisher syndrome 233, 255 minocycline 255 mitochondrial disorders with ataxia 548–61 ataxia as a symptom 557–8 classification 549, 550–1 mtDNA defects Kearns–Sayre syndrome 552–3, 554 mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS) 554 myoclonic epilepsy with ragged red fibers (MERRF) 555 neuropathy, ataxia and retinitis pigmentosa (NARP) 555 other phenotypes 555 mutations of mtDNA 549 large-scale rearrangements 549, 552 point mutations 552 nuclear gene defects 556 Leigh syndrome 556–7 nucleo-mitochondrial signaling defects 555–6 mitochondrial metabolism of iron, role of frataxin 507, 512, 513 lead intoxication 353 mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) 556 mitotic segregation 549 MJD 1 gene 428, 431–2, 433, 434 models of cerebellar system function 69–94 adaptive timer/adaptive linear filter 85 adjustable pattern generator 83 internal dynamic model-based observer/controller adaptive control model 85–6, 94 intermediate cerebellar model 87–8 other related models 86–7 wave-variable control model 88–9 oculomotor predictive tracking model 82–3 regulator of temporal integration 83–4 repository for programmed motor responses (Marr–Albus models) 80–2 sensorimotor coordinate transformer and predictor 84 theoretical considerations discontinuous control 79–80, 94 feedback control 75, 76–7, 93 feedforward control 75–6, 93 internal model-based vs non-model-based control 74, 75, 78–9, 93 sensory features of servo controllers 77–8 see also cerebellar system functions; microcircuitry molecular chaperones 413

Index

molecular layer 11, 12, 13, 328 molecular mechanisms of triplet repeat expansions 491–501 Friedreich’s ataxia 496, 498–9 future prospects 499 genetic instability generation 491–2 recombination 494–5 repair 494 replication 492–4 small slipped-register instabilities 496, 497 non-B DNA structures 498–9, 511 see also repeat expansions monkeys cerebellocerebral projections 26, 142, 143, 144 corticopontine mossy fiber input 21 deficits on nuclear ablations 55, 56, 57 elbow movement simulation 88 emotional behavior 138 manganese toxicity model 354 Purkinje cell spike activity 55 visual tracking compared with model 82, 83 monoaminergic afferents 7, 43, 328 mood, see affect and psychosis mormyrid fish 6, 7 morphological maturation of cerebellar grafts 371 mossy fibers 7, 10, 11, 13, 14 in eye movement control 82 in Marr–Albus models 80–1 neurotransmitters 38, 39–40 Purkinje cell simple spikes 54 see also afferent systems: mossy fiber motor cerebellum 62 motor clock hypothesis 55, 58 motor control function 69–70, 130 motor learning theory of cerebellar operation 54, 60, 61 mouse ataxin-2 424 mouse models A-T 539 DRPLA 486 episodic ataxias types 1 and 2 (EA-1; EA-2) 569 myotonic dystrophy type 1 (DM1) 478 SCA1 411–12, 415 SCA2 425 SCA3/Machado–Joseph disease 434–5 thyroid hormone in cerebellar development, see thyroid hormone and cerebellar development: mouse models toxicity studies bismuth 349 carbon monoxide 358 cyanide 360 phenytoin 343 thallium 354 mouse mutants, grafts, see grafts: ataxic mouse mutants Mre 11 deficiency 540–1 MRI, see magnetic resonance imaging multijoint coordination 123–7 multiple cerebellar infarctions 217, 218 multiple sclerosis 228 clinical manifestations 228–9 course 229 diagnosis 232, 253 epidemiology 228

etiology 229–31, 232 genetics 231, 232 pathology 229 treatment 232, 233 multiple system atrophy general 178 clinical picture 188–90 definition and terminology 186 diagnosis 190–3 epidemiology 186 etiology 188 pathology and pathophysiology 187–8 prognosis 193 treatment 193–4 idiopathic late-onset cerebellar ataxia 180–2 olivo-ponto-cerebellar atrophy classification 179 clinical picture 179–80 historical review 178–9 pathology 180 Shy–Drager syndrome clinical picture 186 historical review 185 pathology 186 striatonigral degeneration clinical picture 183 historical review 182–3 neuroimaging studies 184–5 pathology 183–4 muscimol 55, 56 muscle tone disorders 110, 111 mutations of mitochondrial DNA 549, 552 mutism 106, 145 myelin attack in multiple sclerosis 229, 230 myelin basic protein 309 myelomeningoceles 165, 167 myoclonic epilepsy with ragged red fibers (MERRF) 526, 555 myotonic dystrophy type 1 (DM1) 478 NARP (neuropathy, ataxia and retinitis pigmentosa) 555 neocerebellum 97, 98 nerve growth factor 298, 299 nervous mutant mice, grafts 374 neural cell adhesion molecule (N-CAM) 310 neurinomas 273 neuroanatomy of the cerebellum 6–29 aminergic and cholinergic inputs 27 connections with autonomic centers 27 evolution 6, 7 macroscopic 8, 9 afferences and efferences 7, 98 clinically relevant 97, 98 nomenclature 6, 7 microscopic afferent systems, see afferent systems efferent systems, see efferent systems olivo-cerebellar system, see olivo-cerebellar system see also functional microcomplexes; high-resolution cerebellar anatomy neuroimaging studies, see specific methods neuronal ceroid lipofuscinosis 525

583

584

Index

neuropathology of the inherited ataxias 387–405 and clinical severity 401–2 correlated with mutations and repeat lengths 402 inclusion bodies, dominant ataxias 398–401, 412, 434–6, 463–4, 487 see also Friedreich’s ataxia: neuropathology; spinocerebellar ataxias types 1-7: neuropathology neuropathy, ataxia and retinitis pigmentosa (NARP) 526, 555 neuroprotective therapy, acute ischemic stroke 224 neuropsychological tests 146–7 neurotransmitters in the cerebellum 38–48 afferents to the cerebellar cortex climbing fibers 40 mossy fibers 38, 39–40 hypothalamic input 43 inhibitory interneurons 42–3 monoaminergic input 43 nitric oxide 43–4 outstanding questions 44 parallel fibers 40–1 Purkinje cells 41–2 summary 39, 44 neurotrophins 309–10 nibrin deficiency diseases 540, 541 nicotine toxicity 359 Niemann–Pick type C syndrome 525 Nijmegan breakage syndrome (NBS) 540, 541 nitric oxide 12, 43–4, 251, 356 NMDA (N-methyl--aspartate) receptors 329, 357, 377 noise in feedback signals 77 noradrenergic fibers 27, 43 nuclear medicine imaging, cerebellar abscesses 241–2 nuclear thyroid hormone receptors 305, 306, 307, 309, 312 nucleo-mitochondrial signaling defects 555–6 nucleus dorsalis of Clarke 388, 389, 391, 396, 397 nucleus prepositus hypoglossi 20 nucleus reticularis tegmenti pontis 20 nystagmus 83, 84, 102, 103–5 oculomasticatory myorhythmia 262 oculomotor disturbances, see clinical signs of cerebellar disorders: oculomotor disturbances oculomotor predictive tracking model 82–3 olfaction, neuroimaging observations 149 oligodendroglia damage in multiple sclerosis 230, 231 JC virus tropism 258 thyroid hormone and development 308 olivary cells 15, 16 olivary hypertrophy 300 olivo-cerebellar system cerebellar cortex granule cells 10–11 inhibitory interneurons 12–14 overview 8, 10, 11 Purkinje cells 8, 10 synapses, parallel fibers and Purkinje cells 12 cerebellar nuclei 14, 15 inferior olive 10, 15, 16 organization 16 summarized 13 see also specific system components

olivo-ponto-cerebellar atrophy, see multiple system atrophy: olivoponto-cerebellar atrophy oncogenes 371 opsoclonus 102 opsoclonus–myoclonus (Kinsbourne syndrome) 254 optic atrophy 528 optokinetic nystagmus 130 orientation dependence of repeat tract stability 492, 493 orthostatic hypotension 178, 185, 189, 194 oscillation dampener 152 otogenic infections and cerebellar abscesses 237 oxidative phosphorylation (OXPHOS) 548, 549, 551, 556 oxidative stress in manganese toxicity 354 PACAP (pituitary adenylate cyclase-activating polypeptide) 42 Paine syndrome 520 pain, neuroimaging observations 148–9 palatal tremor 108, 110, 300 paleocerebellum 97, 98, 161 parallel fibers 11, 12 coordination of linked nuclear cells 61 in eye movement control 82, 83 in functional microcomplexes 72, 73, 74, 93 glutamate transmitter 40–1 in long-term depression 43, 74 in Marr–Albus models 80, 81 tapped delay lines 85 paramedian reticular nucleus 20 paraneoplastic cerebellopathies, see cerebellar disorders in cancer: paraneoplastic cerebellar degeneration paraneoplastic oligodendrocyte protein 283 paraplegin 556 parathyroid disorders, see endocrine disorders associated with cerebellar ataxia: parathyroid disorders parkinsonism multiple system atrophy and 186, 187, 190 rare in early-onset inherited ataxias 528–9 Parkinson’s disease, differential diagnosis corticobasal degeneration 199–200 multiple system atrophy 191, 192, 193 striatonigral degeneration 183, 184 pathophysiology of clinical cerebellar signs 121–35 dysarthria 130 dyscoordination of movement 123–7 dysmetria 122–3 eye movement control 129–30 gait and posture ataxias 127–8 hypotonia 129 roles of the cerebellum questioned 130–2 terminology of clinical signs 121–2 tremors 128–9 see also clinical signs of cerebellar disorders; models of cerebellar system function Paulin model 86, 132 pcd mice, see Purkinje cell degeneration (pcd) mutant mice PCR, see polymerase chain reaction Pearson’s syndrome 552, 554 peduncles 4, 7, 8 perhexiline maleate toxicity 351 perihypoglossal nuclei 20 periodic alternating nystagmus 104, 105

Index

peripheral nerves Friedreich’s ataxia 388, 389 SCA3/Machado–Joseph disease 396 peripheral vestibular nystagmus 104, 105 personality changes and cerebellar lesions 145 PET, see positron emission topography petrosal group of veins 211 phencyclidine 357 phenobarbital toxicity 347 phenytoin toxicity 279, 342–3, 344, 345 phosphate-activated glutaminase (PAG) 41 phosphin toxicity 358 physiological activity, transplanted Purkinje cells 372 pial vessels 202 PICA, see posterior inferior cerebellar artery pilocytic astrocytomas 269, 271 pituitary adenylate cyclase-activating polypeptide (PACAP) 42 plaques, multiple sclerosis 228, 229 Plasmodium falciparum 250 PML, see progressive multifocal leukoencephalopathy point mutations frataxin gene 511 mitochondrial DNA 552, 554, 555 point-to-point transplant systems 380 polyglutamine diseases, see repeat expansions: CAG; specific dominant ataxias polymerase chain reaction diagnosis cerebellitis 252 PML 259–60 Whipple’s disease 262 in RAPID cloning 449, 469, 470, 472 pontine nuclei 20–2, 140, 395 pontocerebellar hypoplasia 519 pontocerebellum 97, 98 population genetics, dominant ataxias 483–5 positron emission tomography (PET) affect and psychosis 148, 149, 150 Friedreich’s ataxia 508 multiple system atrophy 192 posterior fossa trauma 296, 297 striatonigral degeneration 184 posterior column ataxia with retinitis pigmentosa disorder 528 posterior fossa congenital malformations, see congenital malformations of the cerebellum and posterior fossa posterior fossa trauma 288–304 clinical presentation 290–2 epidemiology 288 imaging 292–7 long-term complications 300–1 management 299–300 pathophysiology 297–9 rehabilitation 301 types 289–90 posterior inferior cerebellar artery (PICA) 61, 203, 204–8 infarctions 212, 213, 214, 217, 218 posterior vermal split syndrome 114 post-mortem anatomy 30–2 post-traumatic-delayed cerebellar syndrome 300 posture, see stance ataxias

potassium channels 563–7 P/Q-type Ca channels 567–9 prednisolone 255, 269 premature aging, A-T patients 533–4 primary malignant lymphoma 274, 276 primates 6, 7 primidone 347 primitive neuroectodermal tumors 266 primordial cerebellar tissue grafts 370, 371 progesterone receptor antagonist therapy 273 programmed motor response repository 80–2 progressive external ophthalmoplegias 552, 554, 556 progressive multifocal leukoencephalopathy (PML) 257 clinical presentation 258 diagnosis 258–60 pathophysiology 258 prognosis/outcome 260 treatment 260 progressive supranuclear palsy 193 proprioceptive cells 17, 19 proteasomes 435 protein functions, effects of ethanol 332 protein homology, A-T protein 536 proton magnetic resonance spectroscopy (MRS), see magnetic resonance spectroscopy pseudohypertrophy 300 pseudohypoparathyroidism/pseudo-pseudohypoparathyroidism 320, 321 pseudotumoral infarction 217 psychogenic ataxic gait 116 psychosis, see affect and psychosis psychosocial support 194, 200 Purkinje cell degeneration (pcd) mutant mice 375–80 Purkinje cells 8, 10, 11, 12, 369–70 in adjustable pattern generators 83 alcohol toxicity 329, 330–3, 338 anti-Tr syndrome 283 anti-Yo syndrome 281 in ataxic mouse mutants 311, 374, 375 bismuth toxicity 349, 350 episodic ataxia type 1 566–7 in eye movement control 82 in functional microcomplexes 72–3, 74, 93 inhibitory interneurons 12, 13, 14 in Marr–Albus models 81 migration 4, 5 neurotransmitters 39, 41–2 neurotrophins 309 parallel fiber synapse 11, 12 perinatal hypothyroidism 307, 308 phenytoin toxicity 343, 344, 345 posterior fossa trauma and 298 SCA5 448 SCA6 452 spikes 10, 12, 50–2, 53, 54–5 transplanted, see grafts: transplanted Purkinje cells vascularization 202–3 see also dendrites: Purkinje cells pursuit disorders 102, 103, 129 putamen 183, 184, 185, 187 pyramidal tract 20

585

586

Index

radiation sensitivity, A-T 533, 534, 536, 538, 542 radiation therapy astrocytomas 271 cerebellar metastases 278, 280 ependymomas 273 medulloblastomas 266, 269 schwannomas 273 radiosurgery 273, 278 ragged red muscle fibers 548, 549, 558 RAI1 422, 423 RAPID cloning 449, 469–72, 479 rats, cerebellar graft studies 370, 371, 372, 373 rat toxicity studies alcohol 327, 329, 331, 332, 333 barbiturates 347 carbon monoxide 358 cyanide 360 lead 353 lithium 348 mercury 351, 352 phencyclidine 357 rearrangements, mitochondrial DNA 549, 552, 554 rebound nystagmus 103, 104 reconstructions of cryosectioned cerebellum 32, 34 red nucleus 22 RED (repeat expansion detection) assays 448–9, 469–70, 471 reelin 5 rehabilitation, head trauma patients 301 relapsing–remitting pattern Behçet’s disease 234 multiple sclerosis 228, 229 remyelination 229 renin–angiotensin system and injury repair 299 repeat analysis pooled isolation and detection, see RAPID cloning repeat expansion detection (RED) assays 448–9, 469–70, 471 repeat expansions CAG DRPLA 482–3, 484, 485, 486, 487 SCA1 410 SCA2 420, 421, 422, 423, 424 SCA3/Machado–Joseph disease 431–2, 432–3 SCA5 448–9 SCA6 397, 398, 452, 453 SCA7 459–60, 461, 462 sporadic ataxia 182 CTG, see spinocerebellar ataxia type 8 (SCA8): CTG repeat expansions GAA, Friedreich’s ataxia 387, 388, 402, 510–11 see also molecular mechanisms of triplet repeat expansions reptiles 6, 7, 14 reticular precerebellar nuclei 18, 19–20 reticular system–cerebellar connections 139 retinal lesions, SCA7 398, 461 retinitis pigmentosa 528 retinoid X receptor 305, 306 retrocerebellar arachnoid cyst 171, 172 retrovirus-mediated gene transfer 371 rhombencephalon 3 rhomboencephalosynapsis 175 rhythmic palatal myoclonus 108, 110 Ri antigens 281, 282

Richards–Rundle syndrome 528 ROR alpha 310, 311, 312 rosettes, mossy fiber 10, 11, 12 rostral spinocerebellar tract 19 rubella infection 254 rubral tremor 300 rubrospinal tract 20 rudiment 3 saccade deficits 102, 103 saggital areas 97, 98, 101 saxitonin intoxication 359 SCA1-8, see spinocerebellar ataxia types 1–8 SCA, see superior cerebellar artery scaling of neuronal signals 71, 73, 74 schizophrenia, neuroimaging observations 150–1 schwannomas 273 Schweighofer et al. model 87–8 secondary traumatic lesions 289 self-stimulation 138 sensorimotor cerebellum 148 sensorimotor coordinate transformation/prediction 84 sensorimotor optimization 58 sensory processing function 60, 70–1, 132 serotonin fibers 27, 43 servo control systems 75, 76–8 Shaker Drosophila melanogaster 569 sham rage 137, 138, 141 shellfish poisoning 359 shunting, Dandy–Walker malformations 173 Shy–Drager syndrome, see multiple system atrophy: Shy–Drager syndrome signal processing, aspects unique to the cerebellar system 71–2 sign of the piano 111 signs, see clinical signs of cerebellar disorders simple spikes, Purkinje cells 50–2, 53, 54, 333 single photon emission computed tomography (SPECT) cerebellar stroke 221 cerebellitis 253, 254 Hashimoto’s thyroiditis 319 posterior fossa trauma 296, 297 skew deviation 102 small artery disease 219 smell, neuroimaging observations 149 Smith predictors 86, 87 smooth endoplasmic reticulum 332–3, 343 sniff volume 149 SPECT, see single photon emission computed tomography speech disturbance 105–6, 130 S phase arrest 537 spikes, see complex spikes; simple spikes spinal cord Friedreich’s ataxia 388, 389 SCA3/Machado–Joseph disease 395, 397 spinal olivo-cerebellar tracts 22, 23 spinocerebellar ataxia type 1 (SCA1) 409–18 clinical features 409–10, 420 neuropathology 391, 393, 394, 410 pathogenesis studies alteration of gene expression 414–15 ataxin-1 interacting proteins 413–14

Index

gain-of-function mechanism 411–12 model 415–16 protein folding and degradation 412–13 SCA1 gene 410–11 see also dominant ataxias spinocerebellar ataxia type 2 (SCA2) 419–27 magnetic resonance imaging 421 mouse models 425 neuropathology 393, 394, 395, 421 phenotype 419, 420 ataxia 419 dementia 420–1 eye movements 419, 420 movement disorders 420 neonatal onset 421 neuropathy 420 SCA2 gene 421–2 alleles 422 cDNA sequence, expression patterns 424 frequency 423 haplotype 423–4 isoforms and genomic structure 424 protein expression 424, 425 repeat length and age of onset 422–3 repeat range 422 sporadic patients 424 see also dominant ataxias spinocerebellar ataxia type 3 (SCA3)/Machado–Joseph disease 428–39 clinical features 429–30 autonomic disturbances 431 cognitive dysfunction 430 oculomotor involvement 430 peripheral nerve involvement 430 sleep disturbances 430 history 428 imaging studies 431 molecular genetics 431–2 neuropathology 395–7, 400, 431 pathogenic mechanisms 433–6 phenotype comparisons 420 phenotype–genotype correlation 432–3 prevalence 428–9 see also dominant ataxias spinocerebellar ataxia type 4 (SCA4) 440–1 clinical features 441–2 genetic mapping of SCA4 442–3 laboratory tests 442 neuropathology 442 treatment 442 spinocerebellar ataxia type 5 (SCA5) 445 anticipation 448 clinical features 445, 447 family ancestry 445, 446 genetic and physical mapping 449 neuroimaging and neuropathology 447–8 repeat expansion detection 448–9 spinocerebellar ataxia type 6 (SCA6) 451–8 clinical features 420, 451–2 compared with other cerebellar ataxias 453, 454, 455 gene and protein 453

inheritance and mutation 452–3 natural history 452 neuropathology 397–8, 399, 452 see also dominant ataxias; episodic ataxias as ion channel diseases: episodic ataxia type 2 (EA-2) spinocerebellar ataxia type 7 (SCA7) 459–68 CAG repeat instability 459–60 clinical features neurological signs 461–2 visual impairment 461 de novo mutations 461 frequency and origin of the SCA7 mutation 460 genotype–phenotype correlations 462–3 history 459 identification of the SCA7 gene and mutation 459 molecular diagnosis 461 neuropathology 398, 462 SCA7, normal and pathological functions ataxin-7 expansion, pathological consequences 463–4 cDNA and its expression 463 cellular models 464–5 spinocerebellar ataxia type 8 (SCA8) 469–80 clinical features 476 CTG repeat expansions independent origin 474 instability and maternal penetrance 473–4, 475 RAPID cloning 470–2, 479 sequence interruptions 474, 475, 476 magnetic resonance imaging 476 pathogenic models 478 SCA8 gene organization and expression 476–8 spinocerebellar tracts 17–19 spiral computed tomography scans 222 staggerer mutant mice 311, 312, 374 stance ataxias 113, 115, 116, 127–8 stellate cells 11, 13, 39, 42, 328 steroid therapy cerebellar abscesses 242–3 cerebellar metastases 278 cerebellitis 255 Hashimoto’s thyroiditis 319, 320 Stewart–Holmes maneuver 106, 107, 114, 115 sticky DNA 496, 498–9 striatal D2 receptors 192 striatonigral degeneration, see multiple system atrophy: striatonigral degeneration stroke 202–27 in cancer patients 280 cerebellar hemorrhage 219–20 cerebellar vein thrombosis 224 diagnostic studies 220–2 infarctions anterior inferior cerebellar artery (AICA) 212, 213, 214, 215 border zone 216, 217 course/outcome 217 lacunar 216, 217 multiple cerebellar 217 posterior inferior cerebellar artery (PICA) 212, 213, 214 superior cerebellar artery (SCA) 212, 213, 214, 215, 216 pathophysiology 218–19 treatments 222–4

587

588

Index

stroke (cont.) vascularization of the cerebellum, see vascularization of the cerebellum see also MELAS structure and function of the cerebellum 49–66 ablations of the nuclei 56 dentate 56, 57 fastigius 55 interpositus 55, 56, 57 cognition 61–2 mechanism of operation, theories combiner–coordinator 58–60 command–feedback comparator 58 coordination of linked nuclear cells 61 motor learning 60 sensory processor 60 timer 58 tonic reinforcer 57–8 neuronal activity in the nuclei 49 dentate 50, 52, 53 fastigius 49, 50 interpositus 50, 51, 52 Purkinje cell discharge and limb movements 51, 52, 54–5 see also models of cerebellar system function subarachnoid hemorrhage 290, 295 subdural hematomas 290, 291, 294–5, 297, 299 substantia nigra 183, 199, 421 superficial siderosis 280, 301 superior cerebellar artery (SCA) 203, 204, 207–8 infarctions 212, 213, 214–16, 217, 218 SURF-1 gene 557 surgery astrocytomas 271 cerebellar abscesses 243–4 cerebellar metastases 278, 280 Chiari I malformation 163, 164–5 Chiari II malformation 167, 168 Dandy–Walker malformations 172–3 ependymomas 273 fetal 168 medulloblastomas 266 meningiomas 273 multiple sclerosis 233 posterior fossa trauma lesions 299, 300 schwannomas 273 stroke 223–4 symptoms of cerebellar disorders 97, 99 see also specific disorders synapses 10, 11 parallel fibers–Purkinje cells 11, 12, 43, 54, 61 on spines of olivary cell dendrites 16 and thyroid hormone 308 alpha-synuclein 187, 188 systemic lupus erythematosus 235 T3, see -triiodothyronine T4, see -tetraiodothyronine tapped delay lines 85, 94 taurine 41–2 TCD (transcranial Doppler) 221 tectocerebellar dysraphia 174–5

telangiectases 532 telomere shortening 533 temporal integration 83–4 tendon reflexes, see early-onset inherited ataxias: with retained tendon reflexes tentorial group of veins 211 L-tetraiodothyronine (T4) 305, 311, 312, 318 thalamo-cortical relay 25–6 thallium toxicity 354–5 thiamine deficiency in alcoholism 338, 340 thirst, neuroimaging observations 149 three-dimensional warping algorithms 35 thrombolysis 222–3 thyroid dysfunction, see endocrine disorders associated with cerebellar ataxia: thyroid dysfunction thyroid hormone and cerebellar development 305–15 anatomical alterations induced by perinatal hypothyroidism 305, 307–8 molecular mechanisms of hormone action 305, 306 in cerebellar development 308–10, 312–13 mouse models congenital hypothyroid hyt/hyt 310 knockouts 310, 311 staggerer 311, 312 thyroid sonography 319 thyrotoxicosis, see hyperthyroidism TIA (transient ischemic attack) 212 ticlopidine 342 timing functions 55, 58, 80, 131–2 titubation 113, 129 toluene toxicity 355 tonic reinforcer theory 57–8 tonsillar herniation 265 tonsils (cerebellar) 163, 165 topiramate 347 topography of function 148, 149 toxic agents 254 alcohol, see alcohol toxicity carbon monoxide 357–8 cyanide 359–60 drug abuse cocaine 356 heroin 356–7 phencyclidine 357 drugs, see drug toxicity eucalyptus oil 359 heavy metals germanium 355 lead 352–3 manganese 353–4 mercury 351–2 thallium 354–5 insecticides and herbicides carbon disulfide 358–9 chlordecone 358 phosphin 358 nicotine 359 saxitonin 359 toluene/benzene derivatives 355 see also hyperthermia tracking function 60, 69, 82–3

Index

transcranial color-coded sonography 221 transcranial Doppler (TCD) 221 transesophageal echocardiography 221 transglutaminase inhibitors 487 transient ischemic attack (TIA) 212 transplantation of cerebellar tissue, see grafts transthoracic echocardiography 222 Tr antigens 281 traumatic injuries, see posterior fossa trauma tremors 108–10, 111, 128–9 see also specific disorders trigeminal afferents 19 -triiodothyronine (T3) 305, 306, 312 triple helices (triplexes) 496, 498–9, 511 triplet repeat expansions, see molecular mechanisms of triplet repeat expansions; repeat expansions Tropheryma whippelii 262 ubiquitin 187, 188, 399, 400, 412–13 Uhthoff’s sign 229 ultrasonography 162, 221, 356 unipolar brush cells 11, 39, 43 universal cerebellar transforms/impairments 152 upbeat nystagmus 104 vaccinations A-T patients 542 implicated in cerebellitis 249–50 vascularization of the cerebellum arterial supply brainstem and cerebellum, serial sections 204–10 cerebellar cortex 202–3 main cerebellar arteries 203 venous system 211 vertebrobasilar system 202 see also cerebellar stroke vascular lesions, traumatic 290 vein of Galen, thrombosis 224 venous system 211 ventral spinocerebellar tract (Gower’s tract) 17, 19 ventricular drainage cerebellar abscesses 245 cerebellitis 255 stroke 223 vermis in affect and psychosis 145, 150, 151 development 3, 161

hypoplasia 174 in oculomotor disorders 102 vertebral arteries 202, 204 atherosclerosis 218 dissections 218, 291, 295, 298, 300 vertebrobasilar system 202 vestibular afferents 19 vestibular input to the inferior olive 22, 24 vestibulo-ocular reflex 84, 85–6, 94, 105, 129–30 vigabatrin 347 vincristine 269, 271 viruses associated with cerebellitis 249, 250, 251, 252, 254 implicated in multiple sclerosis 230, 231 see also specific viruses visceral function 117 visual afferents 19 visual input to the inferior olive 22, 24 vitamin E deficiency 318, 391, 513, 525 voltage-gated potassium channels (Kv) 563–7 voltage-gated P/Q-type calcium channels 12, 454, 567–9 von Hippel–Lindau disease 271, 272, 273, 274 Wallenberg’s syndrome (lateral medullary infarctions) 212, 291 warping algorithms 34–5 wave-variable processing 88–9 weaver mutant mice, grafts 374 Wernicke–Korsakoff syndrome 337, 340 Wernicke’s encephalopathy 337, 338 Whipple’s disease clinical presentation 261–2 diagnosis 262–3 outcome/prognosis 263 pathophysiology 262 treatment 263 white matter 6, 7, 11, 15, 328 whooping cough 249, 251, 255 Wilson disease 525 Wolfram syndrome 322, 528, 551 X-linked congenital cerebellar hypoplasia 520 X-linked spastic paraplegia type 2 525 yeast artificial chromosome (YAC) contigs 442–3, 449 yeast frataxin homolog 512–13 Yo antigens 281

589