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 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
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.