New University of Otago research into two sex hormones released by the testes of male fetuses and boys may help solve the enduring mystery of why autism is much more common in boys than girls.

The researchers studied blood samples from 82 boys with ASD and 16 control boys, all aged between 4.4 to 8.9 years. Measuring the levels of the two hormones, the researchers found that these were highly variable from boy to boy, but no different on average between the two groups of boys.

Professor McLennan says the findings indicate that male hormones are important for autism, but not because autistic boys have abnormal levels.

While it has been previously suggested that exposure in the womb to excessive levels of testosterone might be creating an ‘extreme male brain’, this does not explain why some females have autism, or why males with autism do not exhibit an extreme male physical form.

"Our data suggest that the still-elusive primary initiating cause of ASD is common to both males and females, with the condition being more frequent in males because normal levels of male hormones exacerbates the pathology,” he says.

The researchers say that their hypothesis now needs further testing through longitudinal studies of at-risk male babies to determine whether their levels of AMH and InhB early in development can predict the breadth of autistic traits later in life.

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