MESA, Ariz. — Researchers have identified a genetic cause for epilepsy, which could lead to the development of medicines to treat epilepsy and autism, the Translational Genomics Research Institute announced Thursday.

"This is the first step" in finding a cure for the childhood-onset diseases, said Dr. Dietrich Stephan, director of the neurogenomic division of TGen, the Phoenix-based research group that focuses on treatments and cures for genetically related illnesses.

"It allows us to better understand what causes the diseases," Stephan said of the discovery of a genetic mutation in Old Order Amish children in Pennsylvania.

Then and the Clinic for Special Children in Strasburg, Pa., made the finding together.

Currently, medications treating epilepsy don't work on about 40 percent of the varying types of the disease, Stephan said. And the only treatment for autism are behavioral therapies — working with kids extensively on a daily basis to teach them life skills, he said.

Most epileptic symptoms, including recurring seizures, have been traced to abnormalities of the brain structure or chemistry that alter the electrical activity in nerve cells.

Autistic traits also are believed to be caused by disrupted nerve networks.

An estimated 2 million Americans are affected by epilepsy, while autism occurs in about 1.5 million.