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Last Updated: Friday, 4 November 2005, 00:19 GMT
Autism 'extreme male brain' clue
Pregnant woman
Prenatal exposure to hormones may affect brain development
The brain structure of people with autism is an "exaggeration" of the normal male brain, researchers suggest.

It has long been suggested that autistic behaviour is an exaggeration of male habits such as making lists.

But Cambridge Autism Research Centre researchers say the actual development of the autistic brain also exaggerates what happens in male brains.

Writing in Science, they say investigating this theory further will aid understanding of autism.

Anything that adds to the body of knowledge on autism is clearly welcome
Eileen Hopkins, National Autistic Society

The team, led by Professor Simon Baron-Cohen, looked at research carried out into this "extreme male brain" explanation for autism.

They point to evidence that males generally have greater early growth of certain brain regions, and less hemispheric connectivity than females.

Ethical concerns

Boys' brains grow more quickly than girls'. In the brains of people with autism, this growth appears to occur to an even more extreme degree.

There are also specific differences seen in certain areas of the brain.

The amygdala, which plays a key role in emotional responses, is abnormally large in toddlers with autism; again an exaggeration of the typical development of the male brain.

The researchers say evidence points to exposure to male hormones, such as testosterone, before birth affecting these brain development patterns.

Male foetuses produce these hormones from their testes, and female foetuses from their adrenal glands.

So girls too could be exposed to higher than normal level of hormones.

Professor Baron-Cohen stressed researchers were interested in understanding autism.

"This is not about how we could intervene to prevent autism, or developing a pre-natal test.

"There are two ethical concerns; whether autism is a disease, which one would want to prevent or eradicate - a lot of people don't see it as a disease. These are simply children who develop differently.

"Secondly, there is the issue of pre-natal testing. Would a test be specific or sensitive enough?"

Eileen Hopkins, of the National Autistic Society, welcomed the Science paper: "Anything that adds to the body of knowledge on autism is clearly welcome," she said.

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