Organizational Effects of Fetal Testosterone On Human Corpus Callosum Size and Asymmetry: Potential Implications for Autism Spectrum Conditions

Background: Previous theory and research in animals has identified the critical role that foetal testosterone (FT) plays in organizing sexually dimorphic brain development. Foetal exposure to elevated levels of testosterone has been implicated as a possible contributory influence in the development of to Autism Spectrum Conditions (ASC) (Baron-Cohen et al., 2004). FT is positively correlated to number of autistic traits in typically developing children (Auyeung et al, 2009) and SNPs in genes related to sex steroid hormones show association with autistic traits and Asperger Syndrome (Chakrabarti et al, 2009). However there are no studies in humans directly testing the organizational effects of FT on structural brain development. Objectives: Here we selected the corpus callosum and neural assymetry because both show sexual dimorphism in the typical brain (Hines, 2003). Aim To investigate the effects of FT on corpus callosum size and asymmetry. Methods: High-resolution structural magnetic resonance images (MRI) of the brain were obtained on n = 28 8—11-year-old boys whose exposure to FT had been measured in utero via amniocentesis. Results: Although there was no relationship between FT and midsaggital corpus callosum size, increasing FT was significantly related to increasing rightward asymmetry (e.g., Right > Left) of a posterior subsection of the callosum, the isthmus (Chura et al., 2009). Conclusions: Organizational effects of FT on callosal asymmetry may also shape sexual dimorphism in functional and structural brain development, cognition, and behaviour. Ongoing work employing the same technique for callosal measurements is investigating samples of individuals with ASC, their unaffected siblings and unrelated typically developing controls.