Twin study underscores role of genes in autism

NEW YORK (Reuters Health) - When one identical twin develops the developmental disorder autism, the risk of the other developing it is high -- substantially higher than it is for fraternal twins, a new study confirms.

The study, which gathered information from 277 twin pairs in which at least one had an autistic disorder, found that when one identical twin developed an autistic disorder, the other one also did 88 percent of the time.

That compared with 31 percent among fraternal twins. Unlike identical twins, fraternal twins are no more genetically similar than non-twin siblings.

What's more, researchers found, identical twins also had greater similarities in the form of autism that they developed, their level of day-to-day functioning and the risk of intellectual impairment.

The findings, reported in the Archives of Pediatrics & Adolescent Medicine, confirm the importance of genes in autism development.

Autism spectrum disorders (ASDs) include several developmental brain disorders that hinder a person's ability to communicate and interact socially. ASDs range from the more-severe cases of "classic" autism to Asperger's syndrome -- where a person has normal intelligence and verbal skills, but difficulty socializing and understanding subtler forms of communication, like body language and vocal tone.

"Autism research has been guided by one important observation for the past several decades - that autism has a large genetic component," Dr. Paul Law, of the Kennedy Krieger Institute in Baltimore, told Reuters Health in an email. "That observation was made through twin studies."

This new study confirms those findings using a much larger sample of twins, according to Law. The data come from an online registry called the Interactive Autism Network, which Kennedy Krieger set up two years ago to connect parents of children with autism with researchers.

Of the twin pairs in the current study, 67 were identical and 210 were fraternal. Among identical twins, all females had been diagnosed with an ASD, whereas the "concordance" was 86 percent among males.