Abstract
Sex differences in typical development can provide context for understanding ASD. Baron-Cohen (Trends Cogn Sci 6(6):248–254, 2002) suggested ASD could be considered an extreme expression of normal male, compared to female, phenotypic profiles. In this paper, sex-specific M-CHAT scores from N = 53,728 18-month-old toddlers, including n = 185 (32 females) with ASD, were examined. Results suggest a nuanced view of the “extreme male brain theory of autism”. At an item level, almost every male versus female disadvantage in the broader population was consistent with M-CHAT vulnerabilities in ASD. However, controlling for total M-CHAT failures, this male disadvantage was more equivocal and many classically ASD-associated features were found more common in non-ASD. Within ASD, females showed relative strengths in joint attention, but impairments in imitation.
Highlights
Studies examining gender differences in typically developing infants and toddlers show sex-specific patterns in behavior and development
From the clinical records registered in the Norwegian Patient Registry (NPR), ASD-diagnosis registered at any-time from the first 1 year of age were used
There was an interaction effect between diagnosis and sex, showing that the relation between sex and severity of mean Modified Checklist for Autism in Toddlers (M-CHAT) score depended on the diagnostic status of the child [F(1,53724) = 123.374, p < 0.001, partial η2 = 0.002]
Summary
Studies examining gender differences in typically developing infants and toddlers show sex-specific patterns in behavior and development. One study found that infants as young as 1-day of age showed sex-specific looking preferences, with males preferring mechanical objects while females showed a greater degree of interest in faces (Connellan et al 2000). These findings are consistent with several studies suggesting that females in the general population outperform males in a variety of skills typically perceived as being deficits within ASD, e.g. sensitivity to facial expressions (McClure 2000; Montagne et al 2005), performance on questionnaires measuring empathy (Davis 1994), age when reaching developmental milestones e.g. theory of mind (Happé 1995), and language development (Halpern 1997; Zahn-Waxler et al 2006). The most frequently reported sex difference in ASD is the disproportionally higher male to female prevalence, consistently reported since the seminal studies by Kanner (1943) and Asperger (1944). Fombonne (2003, 2005, 2007) reported across studies male to female prevalence ratios
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