Genetic interactions that appear to create a risk for autism have been identified by researchers at Duke University.
The researchers determined that one so-called GABA-receptor gene -- which plays a critical role in stopping or slowing nerve impulses -- is involved in the origin of autism. Autism risk increases through that gene's interaction with another GABA gene, they found.
The finding adds to the likelihood there is no single "autism gene," unlike some other disorders in which one primary genetic defect has been identified.
"The fact that we find these two GABA genes that contribute to autism risk by interacting, I think it lets us say, yes, this is going to be a complex trait," Margaret Pericak-Vance, director of the Duke Center for Human Genetics, told United Press International.
"So far we haven't found that big (primary) gene in autism," she said. "Have we done a complete, exhaustive search? No, but we've done a lot of looking."
The findings are in the September issue of the American Journal of Human Genetics, available online.
GABA-receptor problems already have been implicated as a possible factor in autism, in part because people with the disorder have altered GABA levels. Also, GABA appears to play a key role in early neurological development, and autism is a disorder that manifests in the first three years of life.
Duke researchers earlier linked a portion of chromosome 15 to autism risk. That chromosome contains codes for GABA receptors. Because GABA stops nerve cells from firing, a flaw there could explain why some children with autism appear to be overwhelmed by stimulation.
Pericak-Vance said the findings don't rule out an environmental link to autism. Diagnoses have soared in the past decade, and some parents and researchers suspect that a mercury preservative in vaccines triggered the increase, although most medical experts dismiss that.
"We know autism is complex, and when I think of a complex trait I think of gene-gene and gene-environment interactions," she said. "And I am sure that's what's going on in autism if I had to bet -- a combination of both.
"I think there are going to be multiple different forms. Some forms have certain genes contributing to it and other forms have gene-environment type interactions."
She said current research "is going to make it possible for us to attack these more complex problems where we might not have 10 years ago. We have methods that can detect these things -- that's what's key."