The Rostrum Is Smaller in High Functioning Adolescents with Autism Spectrum Disorders and Associated with Subclinical Autistic Traits in Typically Developing Adolescents

Background: Autism spectrum disorders (ASDs) are associated with abnormal corpus callosum morphology.  However, (1) previous investigations of subregional callosal morphology in ASD provide inconsistent results, and (2) it remains unknown if, extending this line of inquiry beyond the ASD diagnosis, corpus callosum morphology is associated with subclinical autistic behavior.  

Objectives: The present study examined corpus callosum morphology in adolescents with high functioning ASDs versus typically developing adolescents and its relationship with subclinical autistic traits.
Methods: T1-weighted MP-RAGE MRI volumes were acquired at 3T from 30 adolescents (87% male), each diagnosed with a high functioning ASD and from 30 typically developing adolescents (90% male) matched group-wise on age (range=12-24) and IQ (>85).  ASD diagnoses (i.e., high functioning autism, Asperger’s syndrome, pervasive developmental disorder-not otherwise specified) were based upon DSM-IV criteria as well as scores from the Autism Diagnostic Interview and the Autism Diagnostic Observation Schedule.  The most medial saggital slice was used to measure the area of the corpus callosum.  Witelson’s method, providing metrics of seven subregions of the corpus callosum (the rostrum, genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium) was used.  Subclinical autistic traits were acquired through parent ratings from the Social Responsiveness Scale.

Results: Overall corpus callosum area was not different between groups; however, one subregion, the rostrum, was found to be smaller among adolescents with ASD.  Furthermore, among typically developing adolescents, parent ratings of subclinical autistic traits were negatively correlated with rostral area (uniquely among the seven corpus callosum subregions) such that higher autistic trait ratings were associated with smaller rostral area.
Conclusions: Smaller than average rostral area in adolescents with ASD may reflect abnormal connectivity in frontal (particularly ventral) regions.  Furthermore, this relationship may extend beyond an ASD diagnosis since rostral area was also associated with subclinical autistic traits among typically developing adolescents.