Oct. 21 (HealthDay News) -- A new genetic signature that's strongly associated with autism has been identified by U.S. researchers, who said the finding may lead to new ways to diagnose and treat the disorder.

This genetic signature doesn't involve changes to DNA sequence itself, but rather to the way that genes are switched on and off, said the team from Duke University Medical Center in Durham, N.C. They found that people with autism have a higher-than-normal number of gene-regulating molecules called methyl groups in a region of the genome that regulates oxytocin receptor expression.

"In both blood samples and brain tissue, the methylation status of specific nucleotides in the oxytocin receptor gene is significantly higher in someone with autism, about 70 percent, compared to the control population, where it is about 40 percent," study co-lead author Simon G. Gregory, an assistant professor in the Duke department of medicine, said in a university news release.

Oxytocin is a hormone that affects social interaction. Previous research found that giving oxytocin to people with autism can improve their ability to socialize. The hormone is being investigated as a possible treatment for autism, the study authors noted.

In their report, published in the Oct. 21 online edition of the journal BMC Medicine, the researchers noted that higher methylation of the oxytocin receptor gene may result in less sensitivity to the hormone. The authors suggested that their research may lead to ways to identify people who will respond better to treatment with oxytocin.

"We are excited about our findings because they represent one of the few occasions in which a mechanism other than genetic susceptibility or genome instability is implicated in the development of autism," Gregory explained in the news release.

"These results provide a possible explanation of why social isolation forms part of the autism spectrum -- because an autistic individual's ability to respond to oxytocin may be limited. Oxytocin has been tied to levels of trust and ability to read social cues," Gregory added.

SOURCE: Duke University, news release, Oct. 21, 2009