A rare genetic flaw that occurs spontaneously near or during conception may sharply increase the risk that a child will develop autism, researchers reported Wednesday.

The new study, released online by the , is based on the most comprehensive DNA scan ever performed of families with autistic children. Experts said it illustrated both the promise and the challenges inherent in the search for genetic explanations of the disorder.

Although the researchers found strong evidence that the genetic alteration could cause autism, they said it turned up in less than 1 percent of about 1,500 children with the disorder.

The finding is not likely to improve diagnosis or treatment for most children struggling with autism or related problems anytime soon, experts said, but it points to a specific chunk of DNA where some developmental problems could originate. Up to one in 150 children born in the United States show some evidence of the social and learning difficulties that characterize autism, and scientists understand very little about how or why those problems develop.

“This is a fantastic study, in that it points us toward a path, gives us an idea of where to look,” said Thomas Lehner, chief of the genomics research branch at the National Institute of Mental Health, who was not involved in the research. “However, it also shows we have a long way to go to understand what is a very complex disorder.”

The study involved more than a dozen researchers from several institutions, most associated with the Autism Consortium, a nonprofit research organization in Boston. The investigators analyzed DNA from 751 families with autistic children and found that five of the youngsters had a region on Chromosome 16 that had been deleted. Further analysis, in 512 children with autism at Children’s Hospital Boston, and a group of 299 Icelandic people, turned up eight more such cases.

The rate of the chromosome alteration in a group of normally developing people was one in 10,000. “The analysis tells us that this is a very strong risk factor for autism, increasing the risk by ten- to a hundred-fold,” said the study’s senior author, Mark J. Daly, an assistant professor of medicine at Harvard and .

The rarity of chromosome alteration in people without developmental problems, Dr. Daly said, suggests that natural selection has worked against it — most likely because its effects on development can be disabling.

In the past year, several research groups have linked spontaneous alterations in this or nearby areas on Chromosome 16 to a variety of developmental problems, including autism. It will take more research to determine which precise alterations lead to autism or other neurological problems, they say.

“We want to be careful that we understand these alterations before assuming that any one of them caused a child’s problem,” said Lisa G. Shaffer, who is chief executive of Signature Genomic Laboratories in Spokane, Wash. “Because if it’s not the cause, we need to keep searching; the child may have a problem that’s treatable.”


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