Cognitive-Behavioral Differences in Children with Autism Spectrum Disorder Predicted by Sex-Age

Background:  There is a male-predominance in autism spectrum disorder (ASD), supporting the hypothesis that sex-linked factors may be associated with neural risk that could be reflected in performance differences in cognitive-behavioral measures, with age-related divergence.  Results of previous studies examining sex differences have been inconsistent and age effects on potential sex differences have not been established.

Objectives: The purpose of this study was to investigate potential sex-linked cognitive-behavioral differences in younger (2-5 years) and older (6-19 years) children with ASD by examining cognitive abilities and autism symptoms in a large clinical cohort (N=505).

Methods:  Two groups (Younger, n=300, Older, n=205), evaluated at the Autism Clinic at Children’s Hospital between 2005 and 2012, were compared on estimated full-scale IQ (Mullen Scales of Early Learning in Young; Wechsler Scale, Leiter, or Mullen in Older group).  The ADOS and parent report measures (Behavior Assessment System for Children; BASC and Adaptive Behavior Assessment System; ABAS) were also examined.

Results:  In both age groups, there were more males (Young n=250, Older n=164) than females (Young n=50, Older n=41) with ASD (Male-to-Female Ratio=5:1 Young; 4:1 Older).  The younger group tended to be more impaired than the older group.  ASD subtypes by age-sex groups were as follows:  young girls – 76% autism, 24% PDD-NOS; young boys – 64% autism, 34% PDD-NOS, 2% Asperger; older girls – 44% autism, 41% PDD-NOS, 15% Asperger; older boys – 45% autism, 40% PDD-NOS, 15% Asperger.  The young group had fewer verbal individuals (Girls=18%; Boys=29%) than the older group (Girls=78%; Boys=84%). A different profile of sex differences in cognitive abilities was found for young compared to older children.  In 2-5 year olds, there were no significant sex differences in visual reception (p=.069) or receptive or expressive language (p=.159), but there was a trend for lower expressive language scores (p=.055) in females compared to males.  In older children, there were no sex effects for verbal IQ (p=.249), but a significant sex difference in performance IQ (p=.036), with females having lower scores than males.  There were no sex differences in ADOS social or communication scores in either age group.  When sensory interests, hand mannerisms, and repetitive behaviors were examined, there was a sex effect (p=.044) in the young group, with girls having higher scores (more impairments) than boys.  Parent report measures of communication, social, and motor functioning revealed no sex differences in either age group.

Conclusions:  These results suggest some subtle sex differences in cognitive and clinical measures in children with ASD, which vary with age.  Specifically, girls in the younger group tended to have more language and motor impairments (slightly more nonverbal individuals, trend for lower expressive language, more sensory interests/hand mannerisms/repetitive behaviors) than boys, whereas in the older group differences emerged in nonverbal abilities, with males outperforming females on performance IQ.  Further study is warranted to examine these trends in a longitudinal cohort.