The gap between IQ and adaptive functioning in autism spectrum disorder: Disentangling diagnostic and sex differences
Authors: McQuaid Goldie A , Pelphrey Kevin A , Bookheimer Susan Y , Dapretto Mirella , Webb Sara J , Bernier Raphael A , McPartland James C , Van Horn John D , Wallace Gregory L 
Published: March 2021

Adaptive functioning, or the suite of skills essential for real-world, day-to-day functioning, includes daily living, communication, and socialization abilities. Even in the absence of co-occurring intellectual disability (IQ < 70), difficulties in adaptive functioning are prominent in autism spectrum disorder (ASD). Further, ASD individuals without co-occurring intellectual disability (ID) demonstrate a gap between IQ and adaptive functioning, which widens with age. Existing studies of IQ-adaptive functioning discrepancies have characterized predominantly male ASD samples; thus, whether the gap is demonstrated in ASD females is unknown. To probe sex- versus diagnosis-specific differences in adaptive functioning in ASD, we characterized adaptive functioning using the Vineland Adaptive Behavior Scales, Second Edition in 177 non-ID (IQ > 70) ASD (females = 75, males = 102), and 178 typically developing (TD) (females = 87, males = 91) youth, aged 8–17 years. We examined whether each group evidenced a gap between full-scale IQ and adaptive skills and its associations with age. ASD youth evinced significantly lower adaptive skills and a significantly greater IQ-adaptive functioning gap than their same-sex TD peers. In this cross-sectional sample, the increase in the IQ-adaptive functioning gap with age was of similar magnitude for ASD males and females, but only reached statistical significance in males. We discuss unique implications the profound IQ-socialization skills gap in particular may have for ASD females. Lay abstract Adaptive functioning refers to skills that are vital to success in day-to-day life, including daily living (e.g. grocery shopping, food preparation, transportation use), communication (e.g. verbal expression of needs), and socialization skills (e.g. interpersonal skills, including expressing and recognizing emotions, and understanding turn-taking in conversation). Among autistic individuals without intellectual disability, adaptive functioning is not commensurate with intellectual ability (IQ), and instead a gap exists between these individuals’ intellectual ability and their adaptive skills. Further, these autistic individuals show a widening of this gap with increasing age. Existing studies of the gap between IQ and adaptive functioning have studied predominantly male samples. Thus, we do not know if the gap also exists in autistic females. We therefore looked at adaptive functioning and the gap between IQ and adaptive functioning in a large sample of autistic girls and boys without intellectual disability. To disentangle effects of group (autistic vs typically developing) from effects of sex (girls vs boys), we compared autistic girls and boys to one another as well as to their same-sex typically developing peers. Analyses took into consideration differences in IQ between autistic and typically developing youth. We found autistic girls, like autistic boys, show lower adaptive functioning than their same-sex typically developing peers. Results underscore the need to evaluate adaptive functioning in autistic individuals without intellectual disability and to provide necessary supports. The large gap between intellectual ability and socialization skills, in particular, may be of critical importance in improving our understanding of outcomes and mental health difficulties among autistic females.