Theory on autism challenged

University of Otago research is shedding new light on why autism is more common among boys, and challenges the view an "extreme male brain" is the cause.

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

Otago anatomy department researchers have discovered variations within normal-range levels of anti-Mullerian hormone (AMH) and inhibin B (InhB) are linked with the severity of symptoms in boys with autism spectrum disorders (ASDs).

ASDs are developmental disorders involving repetitive or stereotyped behaviours, as well as impairments to social interaction and communication.

The Otago study challenges current thinking that they reflect a testosterone-fuelled extreme of male biology.

The study by Dr Michael Pankhurst and Prof Ian McLennan has just been published in the journal Translational Psychiatry.

Dr Pankhurst said the findings were exciting and there was scope for much more research, including more hormone testing.

Researchers said the AMH Neurobiology Laboratory, headed by Prof McLennan, was the leading international facility for such research involving AMH's role as a hormone.

The researchers studied blood samples from 82 boys with an ASD and 16 control boys, all aged between 4.4 and 8.9 years. They found levels of the two hormones were highly variable among individual boys, but there was no difference in the average hormone levels of the two groups.

However, among boys with an ASD, those with high InhB levels tended to have worse symptoms than those with low levels.

ASD boys with high AMH levels tended to have fewer symptoms.

Prof McLennan said the findings indicated male hormones were important for autism, but not because autistic boys had abnormal levels.

It had been suggested that exposure in the womb to excessive levels of testosterone could be creating an "extreme male brain", but this did not explain why some females had autism.

The Otago data suggested the still-elusive primary cause of ASD was common to both sexes, but the condition was more frequent in males because normal levels of male hormones exacerbated the pathology, he said.

The research was funded from a New Economic Research Fund grant, and its origins were linked to earlier Marsden Fund support. The blood samples were provided by the Autism Genetic Resource Exchange in Los Angeles, California.

john.gibb@odt.co.nz