*Gene could explain 15 percent of cases

*Affects nerve connections in the brain

By Maggie Fox, Health and Science Editor

WASHINGTON, April 28 (Reuters) - Researchers have found the first common genetic link to autism and said on Tuesday it could potentially account for 15 percent of the disease's cases.

Three studies, two in the journal Nature and one in Molecular Psychiatry, suggest changes in brain connections could underlie some cases.

While the findings do not immediately offer hope for a treatment, they do help explain the underlying causes of the condition, which affects as many as one in 150 children, according to the U.S. Centers for Disease Control and Prevention.

"These findings establish that genetic factors play a strong role in autism spectrum disorder," National Institutes of Health acting director Dr. Raynard Kington said in a statement.

"Detailed analysis of the genes and how they affect brain development is likely to yield better strategies for diagnosing and treating children with autism."

Autism refers to a spectrum of diseases, from severe and profound inability to communicate and mental retardation, to relatively mild symptoms called Asperger's syndrome.