Sex Differences in Young Children Referred for Autism Spectrum Disorder

Background:  Research has consistently found a sex difference in Autism Spectrum Disorder (ASD), such that boys are 2-5 times more likely to be diagnosed with ASD than girls. Previous studies have suggested that girls, particularly those without comorbid behavior problems or developmental delays, may be less likely to be diagnosed with ASD compared to boys with similar levels of ASD-related symptoms, although this relationship is less clear in toddler and preschool-aged children referred for ASD.

Objectives: (1) To evaluate sex differences in age of referral and age of diagnosis for children under 6 years of age referred due to concerns for ASD; (2) To examine sex differences in cognitive, developmental, and adaptive functioning for young children referred for concerns for ASD and those ultimately diagnosed with ASD; (3) To compare the severity of ASD-symptomology and behavior problems in males and females referred for and diagnosed with ASD.

Methods:  Data for the present study comes from a multisite study examining the sensitivity and specificity of a novel smartphone screening tool for ASD. Participants included 230 children between the ages of 18 and 72 months who were referred for evaluation due to concerns for ASD (mean = 40.34 months; SD = 14.88 months). All participants received thorough ASD diagnostic evaluations including clinical interview, demographics, and measures of cognitive/developmental abilities (Mullen or DAS-II), adaptive functioning (Vineland-2), behavior problems (CBCL/TRF), and ASD symptomology via the SRS-2 and ADOS-2. Participants were 80% male, 77% White, 17% Black, 6% Other/Unknown, and 4% Hispanic. Seventy-one percent of participants (164/230) were diagnosed with ASD following the evaluation.

Results:  Of the 230 children referred for concerns for ASD, 20% (n = 47) were female. Sixty four percent met DSM-5 criteria for ASD (n = 31), compared to 73% of referred boys who received an ASD diagnosis. Among the full sample of those referred for ASD concerns, girls had equal concerns for ASD on ASD-screening instruments (M-CHAT or SCQ). On average, girls were older at the time of referral than boys (43.18 vs. 39.46 months) and this difference was more pronounced among those subsequently diagnosed with ASD (44.19 vs 38.01 months; p < 0.05). Among those who met criteria for ASD, girls had less cognitive impairment (p < 0.05), but poorer average adaptive functioning when compared to boys. Among those diagnosed with ASD, boys and girls had similar rates of restricted repetitive behaviors, although there was a non-significant trend for girls to be less likely to have difficulty with transitions and changes in routine (p = 0.07).

Conclusions:  Few studies have evaluated sex differences in young children referred for concerns of ASD. Although girls and boys presented with similar ASD-related concerns at referral, girls in this study were both referred and diagnosed at later ages compared to boys. There also appear to be a number of differences with respect to cognitive and adaptive behaviors between girls and boys diagnosed with ASD and additional analyses focused on clarifying the differences between boys and girls meeting DSM-5 criteria for ASD are ongoing.