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WASHINGTON (Reuters) -- U.S. researchers said Monday that they had identified a genetic mutation that raises the risk of autism and could also explain some of the other symptoms seen in children with autism.
Although autism and similar disorders can clearly run in families, theirs is the first study to find a definitive genetic link to the disorder, which affects as many as 1 in 175 U.S. children.
Dr. Pat Levitt and colleagues at Vanderbilt University in Nashville, Tennessee, studied 743 families in which 1,200 family members were affected by autism spectrum disorders, which range from fully disabling autism to Asperger's syndrome.
They found a single mutation in a gene called MET, which is known to be involved in brain development, regulation of the immune system and repair of the gastrointestinal system. All of these systems can be affected in children with autism.
"This is a vulnerability gene," Levitt said in a telephone interview. "There are not genes that actually cause autism. It raises the risk."
People with two copies of the mutated gene have 2 to 2.5 times the normal risk of autism and people with one mutated copy have 1.7 times the risk, he said.
The findings, published in the Proceedings of the National Academy of Sciences, offer a way to start looking for the actual causes of autism, Levitt said.
Autism can cause a range of symptoms, from fairly mild social dysfunction to severe and disabling learning and social impairments.
Researchers knew it could run in families, but the cause has been unknown. Autism is usually diagnosed in toddlers, with parents often describing a sudden regression in abilities and behavior. There is no known cure.
Levitt said the mutation does not change the function of the gene, but changes gene expression -- how active the gene is.
Levitt says his team will now try to make a rat or a mouse with the same genetic mutation and use it to study what in the environment might cause autism in people with the mutation.
"It may be more than one thing," Levitt said.
"Let's say it is exposure to some chemical. It is a long list of everything from food additives to mercury to fertilizers. This will help."
Levitt said his study may help answer questions about links between vaccines and autism.
Experts virtually all agree that vaccines do not cause autism but some parents remain mistrustful. The U.S. Centers for Disease Control and Prevention has launched a series of studies into the potential causes of autism.
In a second study, a team at Cornell University and Indiana University-Purdue University found that television viewing may be a factor among American children.
Michael Waldman of Cornell University and colleagues found that children from rainy U.S. counties watch more television and autism rates corresponded with this pattern.
"The analysis shows that early childhood television viewing could be an environmental trigger for the onset of autism and strongly points to the need for more research by experts in the field of autism," said Waldman, who will present his findings on Friday to a conference of the National Bureau of Economic Research.
A third team of researchers found that the brain regions of adults with autism may not communicate with each other as efficiently as they do in other people.
Michael Murias and colleagues at the University of Washington used high-resolution electroencephalography or EEG to find patterns of abnormal connectivity between brain regions in 36 people with autism.
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