An update on the hypothesis that one cause of autism is high intrauterine levels of testosterone of maternal origin.

Baron-Cohen's hypothesis that autism is caused by exposure to high intrauterine testosterone levels is considered in the context of (1) my hormonal hypothesis of sex ratio and (2) the notion of multifactorial inheritance. This yields the suggestions that (1) female cases of autism may be the product of (high genetic loading+moderate environmental exposure) and male cases of (high environmental exposure+moderate genetic loading), (2) one environmental agent is intrauterine testosterone and (3) the mother is the major source of that testosterone. These suggestions may help to explain most of the major established epidemiological risk factors for autism. These include various forms of pathology associated with psychological and/or physical stress. Stress of many sorts promotes the secretion of adrenal androgens in women. The three suggestions above may also explain some recently described features of autism including the psychological, behavioural and neuroanatomical differences between male and female cases.