Gender Differences in Autism Spectrum Disorder: Early Markers, Autism Manifestations and Cognitive Development From Birth to Preschool Age

Background:  Few studies to date have investigated gender differences in core deficits in social interaction (SI) and vocal communication (VC) in infants and toddlers later diagnosed with an Autism Spectrum Disorder (ASD) nor have they combined observational measures with clinical reports to understand the development of any gender differences in these children. Thus, to date, little is known about how ASD develops and manifests in girls.

Objectives:  Two complementary follow-up studies were conducted. The aim in the first study was to investigate gender differences in early markers of autism during the first two years of life in children later diagnosed with an ASD. A secondary aim was to explore the relationship between these early markers and the severity of ASD at 24-months. The aim in the second study was to investigate gender differences in early cognitive development and autism manifestations from 24- to 48-months of age in the same children.

Methods:  The sample comprised children from the SACS study (Barbaro & Dissanayake, 2010) which prospectively identified infants in the community who were at risk of an ASD through the Victorian Maternal and Child Health (MCH) system. The first study analysed observational data on the early development of SI and VC collected by MCH nurses across three time points: Time 1 (0- to-12-months); Time 2 (13- to-18-months); and Time 3 (19- to-24-months), for a cohort of 66 boys and 17 girls with an ASD. The second study included a subset of 45 boys and 13 girls to investigate gender differences across time (Time 1: 24-months; Time 2: 48-months) on their cognitive abilities as assessed using the Mullen Scales of Early Learning (MSEL; Mullen, 1995), and their autism severity as assessed with the Autism Diagnostic Observation Schedule (ADOS; Lord et al., 1999).  

Results:  Two 2 (Gender) x 3 (Time) ANOVAs assessed gender differences in SI and VC in Study 1, with no significant gender differences or Gender X Time interaction effects. Furthermore, there were no correlations between early SI and VC scores and ASD severity scores at 24-months. Similarly, no gender differences were found in  Study 2 as revealed in the two 2 (Gender) x 2 (Time) MANOVAs for the MSEL and ADOS assessments.

Conclusions:  The combined results from both studies indicate a similar developmental trajectory in boys and girls later diagnosed with an ASD in both, early signs during the first two years of life, and from ages 2- to 4-years on cognitive ability and autism manifestations. These findings contrast with those from recent gender studies on toddlers with ASD. The cohort is unique in providing relevant data from birth to four years of age as, to date, no such prospective community-based sample has been examined in relation to gender differences. Such studies are needed to understand similarities and differences in the early progression of ASDs in girls and boys.