Group differences in relative regional white matter (WM) volume between the autism spectrum disorder (ASD) and typically developing control (TDC) groups. (A) In model 1 (only controlling for age effects), individuals with ASD, relative to TDC, had larger regional WM volumes in the splenium of corpus callosum. (B) In model 2 (additionally considering diagnosis-by-age interaction effects), there were larger WM volumes in the splenium and external capsule/anterior corona radiata (Ext. capsule/ant. CR), in ASD relative to TDC groups; (C) the left forceps minor showed significant diagnosis-by-age interaction in model 2, and its associated scatterplots for relationships between age and relative volumes of the region. (D) In model 3, adolescents with ASD had larger WM volumes in ant. CR, compared with TDC adolescents.