READING DISABILITIES NEUROPSYCHOLOGY AND COGNITION VOLUME 4 Series Editor: R. Malatesha Joshi, Oklahoma State University, U.S.A. Advisory Board: Alfonso Caramazza, The Johns Hopkins University, U.S.A. George Hynd, University of Georgia, U.S.A. C.K. Leong, The University of Victoria, Canada John Marshall, University of Oxford, U.K. Gabriele Miceli, Universita Cattolica Del Sacro Cuore, Italy Loraine Obler, City University ofN ew York, U.S.A. Sandra Witelson, McMaster University, Canada The purpose of the Neuropsychology and Cognition series is to bring out volumes that promote understanding in topics relating brain and behavior. It is intended for use by both clinicians and research scientists in the fields of neuropsychology, cognitive psychology, psycholinguistics, speech and hearing, as well as education. Examples of topics to be covered in the series would relate to memory, language acquisition and breakdown, reading, attention, developing and aging brain. By addressing the theoretical, empirical, and applied aspects of brain-behavior relationships, this series will try to present the information in the fields of neuro psychology and cognition in a coherent manner. The titles published in this series are listed at the end o/this volume. Reading Disabilities Genetic and Neurological Influences Edited by BRUCE F. PENNINGTON University of Denver, U.S.A. Reprinted from Reading and Writing, Volume 3, Nos. 3-4 (1991) SPRINGER-SCIENCE+BUSINESS MEDIA, B.V ISBN 978-94-010-5081-4 ISBN 978-94-011-2450-8 (eBook) DOl 10.1007/978-94-011-2450-8 All Rights Reserved © 1991 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 1991 Softcover reprint ofthe hardcover 1s t edition 1991 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. (on acid-free paper) Contents BRUCE F. PENNINGTON I Genetic and Neurological Influences on Reading Disability: An Overview [3] PART ONE: Genetics JEFFREY W. GILGER, BRUCE F. PENNINGTON and J. C. DEFRIES I Risk for Reading Disability as a Function of Parental History in Three Family Studies [17] HOLLIS S. SCARBOROUGH I Antecedents to Reading Disability: Preschool Language Development and Literacy Experiences of Children from Dyslexic Families [31] R. K. OLSON, J. J. GILLIS, J. P. RACK, J. C. DEFRIES and D. W. FULKER I Confirmatory Factor Analysis of Word Recognition and Process Measures in the Colorado Reading Project [47] JIM STEVENSON I Which Aspects of Processing Text Mediate Genetic Effects? [61] J. C. DEFRIES, JIM STEVENSON, JACQUELYN J. GILLIS and SALLY J. WADSWORTH I Genetic Etiology of Spelling Deficits in the Colorado and London Twin Studies of Reading Disability [83] SHELLEY D. SMITH, WILLIAM J. KIMBERLING and BRUCE F. PENNINGTON I Screening for Multiple Genes Influencing Dyslexia [97] D. W. FULKER, L. R. CARDON, J. C. DEFRIES, W. J. KIMBERLING, B. F. PENNINGTON and S. D. SMITH I Multiple Regression Analysis of Sib-Pair Data on Reading to Detect Quantitative Trait Loci [111] BRUCE G. BENDER, MARY LINDEN and ARTHUR ROBINSON I Cognitive and Academic Skills in Children with Sex Chromosome Abnormalities [127] PART TWO: Neurology / Neuropsychology HELMUTH STEINMETZ and ALBERT M. GALABURDA / Planum Temporale Asymmetry: In-Vivo Morphometry Affords a New Perspective for Neuro-Behavioral Research [143] GEORGE W. HYND, RICHARD M. MARSHALL and MARGARET SEMRUD-CLIKEMAN I Developmental Dyslexia, Neurolinguistic Theory and Deviations in Brain Morphology [157] PAULA TALLAL, ROBERT L. SAINBURG and TERRY JERNIGAN I The Neuropathology of Developmental Dysphasia: Behavioral, Morphological, and Physiological Evidence for a Pervasive Temporal Processing Disorder [175] FRANK WOOD, LYNN FLOWERS, MONTE BUCHSBAUM and PAULA T ALLAL I Investigation of Abnormal Left Temporal Function ing in Dyslexia Through rCBF, Auditory Evoked Potentials, and Positron Emisson Tomography [191] JOHN KERSHNER and JOHN MICALLEF I Cerebral Laterality in Dyslexic Children: Implications for Phonological Word Decoding Deficits [207] LINDA AGUIAR and SUSAN BRADY I Vocabulary Acquisition and Reading Ability [225] PART THREE: Discussion A. M. LmERMAN I Observations from the Sidelines [241] J. F. STEIN I Hemispheric Specialisation and Dyslexia [247] Overview Genetic and Neurological Influences on Reading Disability: An Overview BRUCE F. PENNINGTON University ofD enver, U.S.A. ORIGINS This special issue grew out of the XVI International Rodin Remediation Scientific Conference held in Boulder, Colorado in September, 1990 which was devoted to the topic of genetic and neurological influences on dyslexia, or reading disability (RD). This conference would not have been possible without the vision and generosity of Per Udden and the Rodin Remediation Foundation, who have been unique catalysts in fostering an interdisciplinary understanding of dyslexia or RD. This conference was special both scientifically and personally. Scien tifically, this was the first time that most of the world's experts on the genetics and neurology of RD all gathered at the same meeting, although subsets of these research communities have met at previous meetings. Moreover, because of recent advances in both fields, the outlines of a complete neuroscientific understanding of this prevalent, complex behav ioral disorder was finally within our grasp; the proof of this perhaps bold assertion is contained in the papers that follow. The 1990s had been dubbed "The Decade of the Brain" and this meeting was one of several fitting inaugurals of this decade. Personally, this was a poignant occasion because one of the world's pioneers in reading research, Isabelle Liberman, had died unexpectedly a few months before. The conference included a tribute to her. Her close collaborators, Don Shankweiler and Susan Brady, both delivered moving reminiscences about her life and work. Alvin Liberman, her husband and fellow scientist, was there to be part of that tribute. As Isabelle certainly would have wished, he also attended the conference and served as a stimulating, ad hoc discussant, presenting the views on reading that Isabelle, he and other co-workers have so impressively developed. He also contributed a formal discussion to this volume. Sadly, another loss followed the conference. Karen Gross-Glenn, a cognitive scientist working on visual and neuroanatomical differences in RD in collaboration with Herbert Lubs, died in November, 1990. She was one of the presenters at the conference, and will be sorely missed. [3J Reading and Writing: An Interdisciplinary Journal 3: 191-201, 1991. © 1991 Kluwer Academic Publishers. Printed in the Netherlands. 192 BRUCE F. PENNINGTON INTRODUCTION TO THE ISSUE: CONVERGENCES AND DIVERGENCES I have tried to organize the papers in this volume to emphasize both convergences and divergences in our emerging understanding of the neuroscience of RD, and I will sketch out my sense of these here. Hopefully, this introduction will make the volume more accessible to readers not versed in the technical complexities of behavior genetics and neuroimaging. Despite these complexities, the overall significance of the genetic results presented here are straightforward: RD runs in families (familiality); this familiarlity is partly due to genetic influence (heritability); these heritable influences act more on the phonological than the orthographic aspect of word recognition (differential heritability), both in RD and normal sub jects; and we are beginning to locate some of the genes that may be influencing RD (gene locations). While these genes ultimately influence RD, it would be misleading to say there are genes specifically for either normal or abnormal reading ability, since reading per se was never subject to natural selection in evolution. Instead, spoken language and other behavioral skills that proved adaptive were selected for in human evolution. Only behavioral variations that were genetically based could be selected and maintained by natural selection, so human, species-typical cognitive characteristics, such as spoken language, must have a genetic and therefore physical basis, most likely in the brain. It could be that variations within our species in spoken language facility and other cognitive skills are entirely environmental, in contrast to the clear genetic basis for differences in these skills between species. However, it is quite plausible that there would be genetically based, within-species variation, especially for recently evolved skills such as spoken language. Variations in some of these spoken language and possibly other cognitive skills could in turn have effects on reading skill; hence there would, indirectly, be genetic influences on reading skill. As the reader will see, there is both convergence and controversy about the precise nature of the cognitive and neurological phenotype that is geneti cally influenced in RD. Before proceeding further, it is important to address another frequent but mistaken inference about the implications of genetic influence on RD, this time in the domain of treatment. Genetic influence on a disorder is a separate issue from whether or how the disorder can be treated. Many practitioners resist genetic interpretations because they fear they neces sarily imply either untreatability or a biological (e.g., drug) treatment. But that is hardly the case. Some genetic disorders (e.g., phenylketonuria) are readily treatable, whereas some environmentally caused disorders (e.g., some effects of parental maltreatment) are not. Moreover, despite genetic [4] OVERVIEW 193 influence on RD, the most efficacious available treatment is still behavioral (see Clark, 1988). Returning to our main theme, the genetic influences on RD have implications for neuroimaging studies of RD. As indicated above, genetic influence on RD implies there is a physical basis for the trait, most likely in the brain and most likely in a specific part of the brain. Thus it makes sense to look for the neurological phenotype in RD (as well as in other genetically influenced behavior disorders). Obviously environmental influ ences also affect the physical structure of the brain, (unless one is a dualist), but likely in a different way than genetic ones. For instance, cultural influences on literacy would affect synapse strengths and dendritic branching, which are parameters of brain structure associated with learn ing (Greenough, Black and Wallace, 1987). If the genetic effects act early in development (as they must in an early appearing developmental disorder like RD), then the parameters of brain structure affected would be ones such as neuronal number, neuronal migration and axonal connec tivity, which are determined with few exceptions before birth. Neuroimaging is a newer specialty than behavior genetics, and there are naturally more technical issues and complexities. Nonetheless, the papers in this volume indicate an encouraging degree of convergence on what the neurological phenotype in RD may be. Several independent studies have found alterations in the size and symmetry of the planum temporale, a posterior structure in the neocortex which contributes to the processing of phonology in speech. The planum thus makes theoretical sense as being part of the neurological phenotype in RD. There are other reasons discussed below why it is unlikely to be the necessary and sufficient neurological phenotype in RD. So much for the "big picture," which at this point is very exciting - so exciting that we may be tempted to gloss over discrepancies and gaps in our knowledge. What I will do next is introduce each paper in each section in turn, highlighting both its relation to others and the empirical and theoretical issues that it raises. Genetics These papers are arranged in order of the series of linked questions we can ask of a behavioral phenotype like RD. First, is it familial? The paper by Gilger, Pennington, and DeFries provides clear evidence of familiality from four samples, replicating earlier results from several studies. Al though risk to first degree relatives varies understandably with the defini tion of RD and how the sample was ascertained, this familial risk is clearly significant and substantial in all samples studied. As every clinician knows, many RD children have RD parents. So the fact of familiality in RD is a [51