Sex Differences in Social Impairment in Preschool-Aged Children with Autism Spectrum Disorder

Background:  

Females are diagnosed with autism spectrum disorder (ASD) less frequently than males, and there is evidence of differing underlying genetic and neurobiological characteristics in females and males with ASD. However, detection of behavioral differences between the sexes within ASD has been inconsistent and controversial.

Objectives:  

We sought to explore sex differences in social impairment in young females and males with ASD.

Methods:  

Participants were part of the Autism Phenome Project, which includes a large sample of clinically diagnosed children with ASD (mean age 33.28 months) and age-matched typically developing (TD) control children (153 ASD males, 33 ASD females, 58 TD males, 31 TD females).  The Social Responsiveness Scale (SRS), a measurement of the presence and extent of social impairments was administered to parents of children with ASD and typical development.  Analysis of covariance was used to investigate interactions between sex and diagnosis. Pillai’s trace was used as a test statistic. As a post hoc analysis to further investigate sex by diagnosis interactions, we also examined deviation from typical development in a sex-specific manner.  We calculated a mean score for TD males and females on the SRS composite as well as each of the sub-scales. Then, for each participant with ASD, a deviation from typical development score was calculated by subtracting the individual score from the same-sex TD mean.

Results:  

There were significant sex by diagnosis interactions for the multivariate analysis of the SRS (p = 0.008) as well as on the univariate SRS total score (p < 0.001), suggesting that for children with ASD, the pattern of differences from typical development occurs in a sex-specific manner.  Follow-up univariate tests on the sub-scales also exhibited significant sex by diagnosis interactions. Post hoc analyses of deviation from typical development revealed significant sex differences in the deviation scores. Females with ASD always exhibited a larger deviation from TD females than males with ASD relative to TD males. 

Conclusions:  

A diagnosis of ASD places an individual into a small population defined by similar behavioral characteristics, making potential behavioral differences between subgroups of this population difficult to detect. Most studies evaluating behavioral sex differences in individuals with ASD directly compare males and females with the disorder. Our findings suggest that females with ASD have deviated more from typical development compared to males with the disorder in the degree of social impairment, as measured by the SRS. These findings suggest that females must diverge further from typical development to receive an autism diagnosis and could be considered more severely affected compared to males.