A collaborative study has found that hundreds of small genetic variations are associated with autism spectrum disorders.

The study buttresses the theory that autism is not caused by one or two major genetic defects, but by many small variations, each associated with a small percentage of cases.

Matthew State, M.D., Ph.D., led the research team in their review of more than 1,000 families in which there was a single child with an autism spectrum disorder, an unaffected sibling and unaffected parents.

The team compared individuals with autism to their siblings to determine what types of genetic changes distinguished the affected child from the unaffected child.

“Thanks to an ambitious collaboration among a large group of autism researchers from around the country, supported by the Simons Foundation, we were able to focus on an ideal study population,” said State, co-director of the Yale Program on Neurogenetics. “It made all the difference in our ability to identify several regions of the genome clearly contributing to autism.”

The study is published in the journal Neuron.

One of the most intriguing of these findings points to the same small section of the genome that causes Williams syndrome—a developmental disorder marked by high sociability and an unusual aptitude for music.

“In autism, there is an increase in the chromosomal material, an extra copy of this region, and in Williams syndrome, there’s a loss of that same material,” said State.

“What makes this observation particularly interesting is that Williams syndrome is known for a personality type that is highly empathetic, social, and sensitive to the emotional state of others. Individuals with autism often have difficulties in the opposite direction.

“This suggests that there is an important key in that region to understanding the nature of the social brain.”

State and his team also found about 30 other regions in the genome that are very likely contributing to autism; a half-dozen of those regions showed the strongest evidence.

“We’re now moving on to a second phase of the study looking at an additional 1,600 families and should be able to identify multiple new regions that are strongly implicated in autism,” he said.

The researchers are optimistic about the new findings, pointing out that genetics is the first step to understanding what’s really going on at the molecular and cellular level of the brain.

“We can use these genetic findings to begin unraveling the underlying biology of autism,” said Sanders. “This will help tremendously in the effort to identify new and better approaches to treatment.”

Source: Yale University

Numerous Genetic Factors Tied to Autism