Sex Differences in the Expression of Autism Spectrum Disorders in Children

Background: Epidemiologic studies consistently show that males are disproportionately affected by Autism Spectrum Disorder (ASD) and that girls with ASD are more likely than boys to be cognitively impaired.  Sex differences in the clinical expression of ASD have not been elucidated, however.

Objectives: The purpose of this study was to examine sex-based differences in the clinical expression of ASD in a large, population-based, sample. 

Methods: Data from three successive cycles (2000, 2002, 2006) of ASD surveillance in New Jersey, according to the Centers for Disease Control and Prevention (CDC) multiple source ascertainment method were analyzed to understand the expression of core ASD (social, communication and behavioral) dysfunctions (parsed according to DSM-IV-stipulated criteria) in boys and girls, and 2) to assess the effect of cognitive functioning, as indicated by intelligence quotient (IQ) scores, on the expression of ASD.  Group differences were compared by Chi-square tests.

Results: 1,012 eight-year old children with ASD were identified and their data was analyzed. The sample was predominately male (males = 805, 79.5%; females = 207, 20.5%). Overall, there was no significant difference by race/ethnicity or SES between males and females. However, several sex-based differences in expression of core ASD characteristics were identified. In comparison to boys, girls were more likely to lack social or emotional reciprocity (72% vs. 62%, p<.001) and to lack spontaneous seeking to share enjoyment, interests and achievement (38% vs. 28%, p<.01).  Girls showed more stereotypic language (73% compared to 60%, p<.001) and had a higher frequency of impaired imaginative/symbolic play (48% vs. 33%, p<.001). Girls were more likely to exhibit inflexible adherence to specific, nonfunctional routines or rituals (66% vs. 54%, p<.01), to have stereotyped and repetitive motor mannerisms (62% vs. 47%, p<.001) and, also, to have persistent preoccupation with parts of objects (34% vs. 20%, p<.001).   Furthermore, when we analyzed the population according to whether the ASD cases had cognitive impairment (IQ below 70) or not (IQ above 70), many of the sex-based differences in the expression of core ASD indicators were evident in the children with IQ above 70, but not in the children with IQ below 70.  

Conclusions: Consistent with other epidemiologic studies, males with ASD outnumbered females by a ratio of 4.1:1.  While boys and girls with ASD were equally likely to show deficits in non-verbal social behavior, peer relations, expressive and receptive language operations and to have equivalent levels of restricted interest, contrary to expectation, girls in our population had documented indication of all other core ASD indicators more frequently than boys.  Understanding sex-based differences in the expression of ASD is important for the specification of autism phenotypes and for development of effective interventions.  Additional research is needed to further investigate sex-based differences in the expression of ASD and to assess the influence of cognitive level on the expression of ASD.