The march toward understanding the etiology of autism took a giant step foward today.

In a landmark genome-wide association study, published online today in Nature, researchers found that a variant on chromosome 5 was about 20 percent more common in autistic children.

Researchers examined DNA from more than 3,100 people in 780 families (with at least two autistic children), and then looked at an additional 1,200 individuals from families affected by autism, as well as nearly 6,500 healthy controls.

"The scientists evaluated the relationship of more than half a million gene variants to autism and consistently discovered six changes that occurred more frequently in autistic children than in the control group. These variants sat on chromosome 5 between two genes, CDH9 and CDH10," says the press release from UCLA.

Study author and UCLA Center for Autism Treatment and Research Director Daniel Geschwind said that a "major change like this in the genetic code is too common to be a simple mutation — it is a risk factor in the origin of the disease."

What do the two genes on chromosome 5 do? CDH9 didn't appear to do much at all, but CDH10 was most active in the fetal brain in key regions supporting language, speech and interpretation of social behavior. Geschwind hypothesized that "CDH10 is switched on at a very early stage and plays an important role in regulating the developing brain. This prenatal activity somehow makes the infant more susceptible to autism."

CHD10 is involved in production of neuronal cell adhesion molecules, which affect neuronal communication and structure. In a second study also published in Nature, looked at ubiquitins, enzymes that degrade neuronal connections made by the adhesion molecules.

Hakon Hakonarson, an author on the two studies, said, "Both studies implicated genes involved in synaptic generation and neuronal connectivity. This is highly consistent with previously published research." It also boosts a theory that autism is caused by abnormal connections between nerves in the brain, Hakonarson said.

So now we have genes and children born breech/first/to mothers older than 35 as possible risk factors for autism. Hopefully we can keep the research going and help more families touched by this disease.