Behavioral and cognitive characteristics of females and males with autism in the Simons Simplex Collection

Abstract

Objective: To examine differences in behavioral symptoms and cognitive functioning between males and females with autism spectrum disorder (ASD).

Method: We analyzed data from 2,418 probands with autism (304 females and 2,114 males) included in the Simons Simplex Collection. Sex differences were evaluated across measures of autism symptoms, cognitive and motor functioning, adaptive behavior, and associated behavior problems. Measurement bias was examined using latent variable models of symptoms. Unadjusted and propensity-adjusted analyses were computed to ensure that sex differences were not due to unbalanced sampling. Moderator and mediator analyses evaluated whether sex differences were modified by clinical characteristics or were driven by cognitive ability.

Results: Females with ASD had greater social communication impairment, lower levels of restricted interests, lower cognitive ability, weaker adaptive skills, and greater externalizing problems relative to males. Symptom differences could not be accounted for by measurement differences, indicating that diagnostic instruments captured autism similarly in males and females. IQ reductions mediated greater social impairment and reduced adaptive behavior in females with ASD, but did not mediate reductions in restricted interests or increases in irritability.

Conclusions: A specific female ASD phenotype is emerging that cannot be accounted for by differential symptom measurement. The present data suggest that the relatively low proportion of high-functioning females may reflect the effect of protective biological factors or may be due to under-identification. Additional carefully accrued samples are needed to confirm the present pattern and to evaluate whether observed sex ratios in high-functioning cases are reduced if female-specific indicators of restricted interests are included.

Keywords: autism spectrum disorder (ASD); behavior problems; cognitive; females; restricted interests.

Figure 1

Full scale IQ as a mediator of greater social communication/interaction symptoms, lower restricted interests, poorer adaptive function, and increased irritability in females with autism spectrum disorder. Note: Lower IQ drove greater social communication/interaction symptoms and lower adaptive function. Lower restricted interests and greater irritability in females with autism spectrum disorder were largely independent of IQ. All coefficients are unstandardized with standard errors in parentheses. Social communication symptoms were measured using Social Responsiveness Scale: Social Communication subscale and restricted interests were measured using the Repetitive Behavior Scale–Revised: Restricted Interests subscale. Adaptive function was measured using the Vineland composite score and Irritability was measured using the Aberrant Behavior Checklist: Irritability subscale.