Autism May Be More Genes Than Environment, Studies Say

Jan. 10, 2008 — -- When Ann Hotez's third child Rachel was diagnosed with autism at the age of 2, the mother's first reaction was to believe something she had done while pregnant had brought about the condition.

"I was blaming myself terribly, like it was something I did wrong during my pregnancy," Hotez said.

She began racking her brain for a possible explanation for possible causes of the condition. This was 1994 and comparatively little information was available about autism. Many doctors still believed the disorder was caused by environmental factors.

Hotez, desperate to find a reason for her daughter's disorder, landed upon the fish industry.

"For a while I was furious at all the fish companies for letting me eat tuna fish while I was pregnant with Rachel," she explained.

But as more research became available on the genetics of autism, Hotez reconciled her pain with the understanding that the disorder doesn't have one simple external cause. Indeed, for years now, scientists have suspected that autism is a complex genetic disorder, the development of which depends on a constellation of genes working together rather than the work of one single gene.

Now, three different laboratories across the country have identified the same gene abnormality as a possible cause of autism — adding to the growing body of evidence that the disorder is primarily genetic.

The gene — known to scientists as contactin-associated proteinlike 2 (CNTNAP2) — has been a prime autism suspect among scientists. The gene is a blueprint of sorts for an important protein involved in the ability of brain cells to communicate with each other properly.

Today, a group of studies published in the American Journal of Human Genetics not only confirmed the link between this gene and autism, but they begin to identify the specific role this gene plays in the development of the disorder.

While each of the studies found that this genetic variant increases the risk of developing autism, one of them also revealed that the gene variation is especially risky when inherited from mothers rather than fathers.

In the first part of the study, researchers analyzed data from 145 children with autism whose families had two or more children with the condition. They found by chance that the subjects had a higher rate of the abnormal gene.

To validate these findings, researchers studied a separate group of participants, which included 1,295 autistic children and their healthy parents. They found again that the subjects had higher rates of the variant gene than would have occurred by chance.

When researchers combined the data from the two studies, they found that children with autism were about 20 percent more likely to have inherited this genetic variant from their mothers than from their fathers.

According to Aravinda Chakravarti, primary investigator and a professor at Johns Hopkins School of Medicine, this research may take us one step closer to a better understanding of the genetic causes of autism and how large a role environmental factors truly play in the development in the disorder.

"Environmental factors might be important, but we don't know which or how much they affect the development of this disorder," Chakravarti said. "But I'm very confident that this is a first step in a series of steps we need to take to study autism with some measure of comprehensiveness before we can estimate the totality of meaning for the role of environmental factors."

In another lab across the country, researchers at UCLA landed upon the same gene — CNTNAP2 — as a possible candidate for autism. But the UCLA researchers identified the specific role this gene might play in affecting language, thought and behavior for people with autism.

Taking a different approach, these investigators used data from the Autism Genetic Resource Exchange and studied the DNA of 291 families nationwide who had at least one autistic child. They also found that an unusually high number of the autistic subjects had this gene variant.