International Meeting for Autism Research (May 7 - 9, 2009): Early Brain Development in Toddlers with Fragile X Syndrome Compared to Toddlers with Autism
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Early Brain Development in Toddlers with Fragile X Syndrome Compared to Toddlers with Autism

Thursday, May 7, 2009: 1:30 PM
Northwest Hall Room 2 (Chicago Hilton)
H. C. Hazlett , Psychiatry, University of NC, Chapel Hill, NC
A. A. Lightbody , Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA
M. D. Poe , FPG Child Development Institute, University of NC, Chapel Hill, NC
A. Reiss , Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA
J. Piven , Carolina Institute for Developmental Disabilities, University of North Carolina, Chapel Hill, NC
Background: While the genetic basis of autism is not yet known, the genetics of fragile X syndrome (FXS) is well characterized.  Both disorders share a number of behavioral characteristics, suggesting common neuropathology.  Neuroanatomical evidence suggests that brain enlargement may be a characteristic of both disorders.

Objectives: In this structural MRI study, we examined brain volumes in 52 young males (aged 18-42 months) with FXS (subdivided into those with and without autism), 63 males with autism, and 50 comparison cases (31 typically developing children and 19 children with developmental-delay). 

Methods: We obtained total and regional gray and white matter tissue volumes for the subjects with FXS and compared them to the brain volumes of the children with autism and our comparison cases.  Additionally, we measured the volumes of selected subcortical structures, such as the caudate nucleus and amygdala.  As a secondary analysis, we also examined the brain volumes of boys with FXS who also met criteria for autism (FXS+Autism).

Results: Boys with FXS were observed to have enlarged total brain volume, and significantly enlarged cerebellar gray matter volume, compared to the controls. Volume of  the basal ganglia structures, such as the caudate, globus pallidus and putamen, were enlarged in the boys with FXS compared to boys with autism or controls.  No significant differences in hippocampal volume was observed.  Children with FXS+Autism were observed to have a different profile of brain volume enlargement compared to children with autism.  Specifically, children with FXS+Autism had significantly enlarged caudate volumes, but significantly smaller amygdala volumes.  

Conclusions: The ability to distinguish the neurobiological phenotypes of FXS and autism may provide important clues to the pathogenesis of autism.  Clearly the study of biological mechanisms underlying autistic behavior in etiologically-defined subgroups such as those with fragile X syndrome, is an important and probably under-employed strategy for dealing with the heterogeneity of autism.

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