Why Are Autism Spectrum Conditions More Prevalent in Males?

Abstract

Autism Spectrum Conditions (ASC) are much more common in males, a bias that may offer clues to the etiology of this condition. Although the cause of this bias remains a mystery, we argue that it occurs because ASC is an extreme manifestation of the male brain. The extreme male brain (EMB) theory, first proposed in 1997, is an extension of the Empathizing-Systemizing (E-S) theory of typical sex differences that proposes that females on average have a stronger drive to empathize while males on average have a stronger drive to systemize. In this first major update since 2005, we describe some of the evidence relating to the EMB theory of ASC and consider how typical sex differences in brain structure may be relevant to ASC. One possible biological mechanism to account for the male bias is the effect of fetal testosterone (fT). We also consider alternative biological theories, the X and Y chromosome theories, and the reduced autosomal penetrance theory. None of these theories has yet been fully confirmed or refuted, though the weight of evidence in favor of the fT theory is growing from converging sources (longitudinal amniocentesis studies from pregnancy to age 10 years old, current hormone studies, and genetic association studies of SNPs in the sex steroid pathways). Ultimately, as these theories are not mutually exclusive and ASC is multi-factorial, they may help explain the male prevalence of ASC.

Psychometric properties of the Chinese version of the Psychoeducational Profile – Third Edition – Caregiver Report

“…Table 1 provides a summary of the characteristics of the sample in terms of age and gender. The ratio of boys to girls is 6:1, which reflects the gender bias evident in epidemiological studies of ASD (Baron-Cohen et al, 2011;Fombonne, 1999) and is consistent with the findings reported by Wong and Hui (2008) in which the male to female ratio was found to be 6.58:1 in Hong Kong children.…”

Gender Dysphoria and Autism Spectrum Disorder: A Systematic Review of the Literature

“…Within the general population, typical females are thought to display more empathising and less systemising traits compared to typical males. Studies assessing these brain domains in people (both males and females) with ASD have found an extreme version of the male brain, where systemising is above average and empathy is reduced [55,56]. It has been hypothesised that high levels of fetal testosterone are responsible for the EMB [57].…”

Mapping ecologically relevant social behaviours by gene knockout in wild mice

“…A major debate has recently emerged in the scientific community concerning the consistent neglect in the use of females as animal subjects in neuroscientific and biomedical studies related to mental disorders 40,41 , including sexually ARTICLE dimorphic disorders such as autism 42 and anxiety 43 . Gender biases in experimental cohorts have been reported to influence both the investigation of biological mechanisms underlying the diseases and the effectiveness of available drugs and treatments 40,41,44 .…”