Bruce F. Pennington
Professor, Clinical Child, Cognitive and DCN
I am interested in understanding atypical development. What causes it?
How do these causes change brain development? How do these changes in
brain development alter the development of psychological functions? Which
altered psychological functions underlie the patterns of abnormal behaviors
that distinguish different developmental disorders? What does atypical
development tell us about normal development?
Answering these questions about a disorder will provide an integrated
scientific explanation for that disorder. Achieving such explanations
will have profound consequences for both basic developmental science and
clinical practice. For instance, understanding the different ways that
language development goes wrong in dyslexia, autism, Down syndrome, and
fragile X syndrome will help us understand how it goes right in typical
language development. The same is true for other domains like executive
control, social cognition, and emotion regulation. As for clinical practice,
having an integrated scientific explanation of a disorder almost inevitably
leads to revolutionary changes in diagnosis, early identification, and
For over 25 years, my colleagues and I have been pursuing such integrated
explanations of several developmental disorders: dyslexia, ADHD, autism,
and mental retardation. Our lab includes a Child Neuropsychology Clinic,
and we have had clinical experience with all these disorders. To understand
the developmental pathways that lead to the different neuropsychological
phenotypes found in these disorders, my colleagues and I have pursued
two strategies: working forward from genotype to phenotype, and backward
from phenotype to genotype.
If the genetic etiology of a syndrome is known, one can work forward
from genotype to phenotype. This is the approach we have taken with phenylketonuria,
fragile X syndrome, and Down syndrome. In some of these disorders, we
have been able to demonstrate a dose-response relation between an aspect
of the disorder's biology and the severity of the neurocognitive phenotype.
In the Down syndrome work, we have collaborated with other scientists
who have developed mouse models of Down syndrome. Yet, even with a known
mutation, there is variability in the neuropsychological phenotype.
But most developmental disorders are behaviorally-defined and etiologically
complex: They are caused by the interaction of multiple genetic and environmental
risk factors. Because they are behaviorally-defined, one must work backward
from phenotype to etiology. This is the approach we have taken to understand
the development of several related, complex behavioral disorders: dyslexia,
other speech and language disorders, and ADHD. In addition, since these
disorders are comorbid with each other, we can use genetic and neuropsychological
methods to test hypotheses to explain their comorbidity. We now know that
each of these disorders is familial and heritable and that some pairs
of them are co-familial and co-heritable, which means that comorbidity
is due in part to shared genes. Because molecular work to identify genes
influencing these disorders is proceeding rapidly, we can perform molecular
tests of shared genetic influence. For instance, we have recently found
that the dyslexia locus on chromosome 6p also influences comorbid ADHD.
We are also testing the hypothesis that the comorbidity between dyslexia
and some speech and language disorders is due to shared genes, in this
case, ones that alter the development of implicit phonological representations.
Since our collaborators have identified several risk loci for dyslexia
(on chromosomes 2p, 3p-q, 6p, 15q, and 18p), we are testing whether some
of these loci also influence speech delay.
Another area of interest is understanding how the neuropsychological
phenotype develops in individuals with infantile autism. A wide range
of neuropsychological models have been proposed to account for the symptoms
that define autism. Sally Rogers and I are testing which of these models
is consistent with early development in autism. Specifically, we and our
collaborators are testing developmental relations among these candidate
deficits: in executive functions, imitation, emotion, and social cognition.
For instance, we have recently found executive deficits are much less
apparent in young children with autism and that such children appear to
understand intentionality. These findings challenge both the executive
and theory of mind theories of autism.
Our clinical experience with all of these disorders has helped focus
our research, and our research results have led to improvements in their
diagnosis and treatment. My research and clinical work informs the courses
I regularly teach on developmental psychopathology and developmental neuropsychology.
Aman, C.J., Roberts, Jr., R.J., & Pennington, B.F.
(1998). A neuropsychological examination of the underlying deficit in ADHD:
The frontal lobe vs. right parietal lobe theories. Developmental Psychology,
Cardon, L.R., DeFries, J.C., Fulker, D.W., Kimberling,
W.J., Pennington, B.F., & Smith, S.D. (1994). Quantitative trait locus
for reading disability on chromosome 6. Science, 265, 276-279.
Gayan, J., Smith, S.D., Cherny, S.S., Cardon, L.R.,
Fulker, D.W., Brower, A.M., Olson, R.K., Pennington, B.F., & DeFries,
J.C. (1999). Quantitative-trait locus for specific language and reading
deficits on chromosome 6p. American Journal of Human Genetics, 64, 157-164.
Griffith, E.M., Pennington, B.F., Wehner, E.A.,
& Rogers, S.J. (1999). Executive functions in young children with
autism. Child Development, 70, 817-832.
Pennington, B.F., & Ozonoff, S. (1996). Executive
functions and developmental psychopathology. Journal of Child Psychology
and Psychiatry, 37, 51-87.
Pennington, B.F., Filipek, P.A., Lefly, D., Churchwell,
J., Kennedy, D.N., Simon, J.H., Filley, C.M., Galaburda, A., Alarcon,
M., & DeFries, J.C. (1999). Brain morphometry in reading-disabled
twins. Neurology, 53, 723-729.
Bruce F. Pennington
Ph.D. 1977, Duke University
Professor, Clinical Child,
Cognitive and DCN
office: Frontier Hall,