Total Brain Volume and Corpus Callosum Size in Medication Naïve Adolescents and Young Adults with Autism Spectrum Disorder

Background: Increased total brain volume (TBV) has been reported for children with autism spectrum disorder (ASD), but studies in older ASD subjects have been contradictory. Similarly, studies of CC area in ASD differ with regard to inclusion criteria, age, and IQ, and functional correlates have rarely been assessed.

Objectives: To compare TBV, gray matter (GM), white matter (WM) volume and mid-sagittal CC area in ASD and typically developing subjects and explore correlations with visuo-motor coordination and imitation abilities.

Methods: TBV, gray matter (GM), and white matter (WM) volume as well as mid-sagittal CC area were compared between 15 medication-naïve high functioning adolescent and young adult ASD subjects and 15 healthy control individuals. In addition, computational surface-based methods were implemented to encode callosal thickness at high spatial resolution. Also, measures on visuo-motor coordination and imitation abilities were assessed. 

Results: TBV, GM, and WM were increased, and CC area was decreased in ASD subjects, a finding, which was prevailingly due to ASD subjects with lower IQ. Only in control subjects, positive correlations of IQ with volume measures were observed. In addition, ASD subjects showed reduced thickness in the posterior part of the CC. WM volume was negatively correlated with dynamic balance and imitation abilities across groups.

Conclusions: This study replicates and expands previous structural MRI findings in ASD and adds evidence for functional implications of these structural changes.