A rare genetic flaw that occurs spontaneously during development may sharply increase the risk that a child will develop autism, researchers reported Wednesday.
The new study, released early online by the New England Journal of Medicine, is based on the largest DNA scan ever 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 aberration 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 1 in 150 children born in this country 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 5 of the youngsters had a region on Chromosome 16 that had been deleted. Further analysis, in 512 children with autism at Children’s Hospital in Boston, and a group of 299 Icelandic children, turned up 8 more such cases.
The rate of the chromosome alteration in a group of normally developing people was 1 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 Massachusetts General Hospital. The rarity of chromosome alteration in people without developmental problems, he said, suggests that natural selection has worked to prevent it — most likely because its effects on development can be disabling.
In other studies, researchers have linked spontaneous alterations in this or nearby areas on Chromosome 16 to a variety of developmental problems. It will take more research to determine which precise alterations lead to autism or 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; child may have problem that’s treatable.”