WASHINGTON Scientists revealed the most extensive findings to date on the genetics of autism on Sunday, pinpointing two new genetic links that may predispose children to develop the complex brain disorder.
The five-year study, led by an international consortium of researchers from 19 nations, indicated autism had numerous genetic origins rather than a single or a few primary causes.
The researchers scoured DNA samples from 1,168 families with two or more children with autism, and used "gene chip" technology to detect genetic similarities. They also looked for tiny insertions and deletions of genetic material that could play a role in autism.
The scientists hope that nailing down the genetics of autism will lead to better ways to diagnose it and focus efforts on developing drugs to treat it. They announced they are launching a new phase in the research to map genes responsible for autism.
The study incriminated a gene called neurexin 1 involved with glutamate, a brain chemical previously implicated in autism that plays a role in early brain development, as a possible susceptibility gene for autism. A previously unidentified region of chromosome 11 also was implicated.
Autism is a spectrum of disorders apparently stemming from genetic and environmental causes. Geneticist Stephen Scherer of the University of Toronto and the Hospital for Sick Children in Toronto said 90 percent of autism may have a genetic basis.
"What we have now that we didn't really have before is a pretty decent understanding of what the genetic architecture is looking like in the autism genome," said Scherer, who worked on the study published in the journal Nature Genetics.
Autistic children have problems with social interaction and verbal and nonverbal communication, as well as repetitive behaviors such as rocking and twirling or narrow and obsessive interests. These behaviors can vary in severity from mild to disabling.
Autism appears in early childhood, often as young as age 2 or 3, and affects four times as many boys as girls.
"It's such a perplexing issue and it's so serious for the children," said University of Pittsburgh researcher Bernie Devlin, who helped lead the study.
Some advocacy groups believe too little attention is given to environmental factors they believe may contribute to autism, like mercury.
A problem in autism research has been that some studies have been based on data from relatively few people. In this study, more than 120 researchers from Europe and North America pooled efforts and expanded the number of people studied.
"Most researchers tend to work in their own world, collect their own set of families to study genetic disorders, and not share," said Rita Cantor, a University of California-Los Angeles geneticist involved in the study.
U.S. federal health experts this month called autism an urgent public health concern that is more common than previously estimated. They said it affects about one in 150 U.S. children.
The research was funded by the nonprofit group Autism Speaks and the U.S. National Institutes of Health.
"I think the most important thing that the study shows is that the genetic causes of autism are likely to be varied," said Andy Shih, chief science officer for Autism Speaks. "The genetic mechanism involved is probably not uniform."