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Researchers have identified a genetic defect responsible for 1 per cent of the various forms of autism, and other experts say the DNA region involved could cause many more autism cases.
Identifying the genetic defect also gives another way to screen early for the disease, and perhaps to
help children with treatments that can reduce some effects of the developmental disorder, researchers said.
A test for such genetic defects already helps to inform parents with a child who has just been diagnosed with autism whether siblings might be at risk and whether future children might develop some form of autism, said Dr Mark Daly of Massachusetts General Hospital, who led the study.
Autism includes a range of disorders, from the mild Asperger's syndrome to profound mental retardation and lack of ability to socialise.
It affects as many as 1 in 150 children in the United States - up to 1.5 million children and adults.
Because "early intervention such as behavioural and educational therapy can have a positive effect on children who develop autism and other forms of developmental delay, any tool that can help give an earlier diagnosis at ages well before the formal diagnostic criteria kick in can be very useful", Daly said.
The genetic defect identified in the study "may be the tip of an iceberg" as a cause of autism, Dr Evan Eichler of the University of Washington, Seattle, and Dr Andrew Zimmerman of John Hopkins University in Baltimore wrote in the New England Journal of Medicine, where the study appears.
About 150 similar "hot spots" which are vulnerable to such jumbling of the human genetic code have been identified, Eichler and Zimmerman said.
Daly and colleagues of the Autism Consortium in Boston found deletions or duplications in chromosome 16 among 24 out of 2252 people from families with autism problems in the United States and Iceland, compared to two out of 18,000 people chosen randomly.
Earlier results linked autism to a duplication of a chunk of genetic material on chromosome 15, which may account for another 1 or 2 per cent of cases.
The researchers said most of the mutations did not appear to have been inherited. Genetic mutations can arise spontaneously, as often seen in cancer, or they can be inherited from one or both parents. The cause of most cases of autism remains a mystery.
A California study has found new evidence that an apparent rise in autism has not been caused by the mercury preservative formerly found in childhood vaccines, as some parents have believed.
"We're still a long way from understanding how this chromosomal deletion or duplication increases the risk for autism," said Daly. "This is only one piece of a very complex puzzle."
"It is interesting that most of the duplicated sequences on chromosome 16 also carry copies of one of the most rapidly evolving gene families in the human species," Eichler and Zimmerman wrote. That means that "from an evolutionary standpoint, autism may be a relatively 'young' disease".
- Reuters