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Scientists Highlight the X Factor in Autism

Tue Sep 9, 2003

By Jeremy Lovell

MANCHESTER (Reuters) - X may mark the spot in the search for the cause of autism, a brain disorder affecting millions of people across the globe, a leading research scientist said on Tuesday.

A part of the brain that is key to reading expressions in people's faces and which is affected by the X chromosome could give a new insight into the causes of the disease, says Professor David Skuse of the Britain's Institute of Child Health.

"We have not discovered the cause of autism, but in the X chromosome we may have discovered a mechanism that could lead to a cause," he told reporters at the British Association for the Advancement of Science's annual conference.

Recent U.S. figures showed that one in 150 people there suffered from autism -- a disease that effectively cuts the victim off from their social surroundings -- and the incidence of the illness has been rising at over 10 percent a year.

Skuse noted that 10 times more males than females suffered from autism, and that males have an X and a Y chromosome while females have two Xs.

Women suffering from Turner Syndrome in which they have only one X chromosome had also been found to suffer far higher rates of autism than their double X counterparts, he said.

Skuse said the key lay in the amygdala, a part of the brain directly involved in processing emotional expressions seen on another's face.

In most people the facial expression was immediately put in context with the aid of the amygdala, with the widely opened eyes that accompanied both fear and joy being correctly interpreted for what they actually represented.

But in autistics the amygdala appeared not to function properly and meant all such expressions were interpreted as fear.

This in turn could explain why autistics rarely made eye contact, Skuse added.

He said women with both Xs functioning normally had a fully operational amygdala, while those with only one X or with only one functioning as it should had poor expression recognition.

In males the Y chromosome probably compensated for the key section of the missing X. Where it did not, the amygdala did not function properly.

"We now have evidence of a plausible neural mechanism that puts boys at risk," Skuse said.

But while the general area of the X chromosome that influenced the amygdala had been isolated, it was so large that it would take many years more work to find exactly what gene or genes were the culprits, Skuse said.

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