Table Of ContentREADING 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
