Researchers this week identified two separate genetic defects linked to autism, one that directly causes the disorder in about 1 percent of all cases and a second that may play a role in a larger percentage of patients by increasing their susceptibility to environmental or other genetic influences.
The findings offer hope that it may be possible to identify vulnerable children early in life and begin treatment to mitigate the effects of the disabling disorder, which is marked by poor language ability and strong social isolation. Autism now affects 1 in every 150 U.S. children.
In the first study, headed by geneticist Mark J. Daly of Massachusetts General Hospital, a team called the Autism Consortium reported Thursday in New England Journal of Medicine that deletions or duplications of a specific small segment of chromosome 16 increases the risk of autism one-hundredfold.
The genetic defect was found in children with autism but not in their parents, indicating a spontaneous mutation that occurred after fertilization. The location, called 16p11.2, is what is known as a genetic "hot spot," meaning it is unusually susceptible to such mutations.
The deletions or repetitions were found in 24 of 2,252 people in families with at least one autistic member but in only two out of 18,834 people without the disorder.
The team is now trying to identify the specific gene involved.
The second defect was originally identified in 2006 in four Amish children. Three groups of researchers independently reported Friday in the American Journal of Human Genetics that they had identified the same defect in much larger groups of subjects.
The gene they found is called contactin-associated protein-like 2,or CNTNAP2, which produces a protein that allows brain cells to communicate with one another.
"This gene not only may predispose children to autism," said Dr. Daniel Geschwind, "it may also influence the development of brain structures involved in language, providing a tangible link between genes, the brain and behavior."
Geschwind, of David Geffen School of Medicine at the University of California, Los Angeles, is one of the researchers involved in the study.