Previous studies suggest a strong association between increased head circumference (HC) in ASD and more severe autism symptoms and lower IQ (Chaste et al., 2013; Chawarska et al., 2011; Lainhart et al., 2006). Given the small sample size (n=4) and limited range of severity scores in the probands we were not able to evaluate these associations directly. However, in a supplementary analysis we obtained the correlations of interest after adding 5 participants who did not all meet the stringent criteria for macrocephaly that we required for deriving iPSCs (see “Participant” section in Extended Experimental Procedures) and thus display a wider spectrum of head circumference sizes. Correlation analysis in this enriched sample (n=9) indicated strong associations between HC and autism symptom severity (Spearman r = 0.79, p=0.01) (data not shown).
