LOS ANGELES Autism is not caused by one or two gene defects but probably by hundreds of different mutations, many of which arise spontaneously, according to research that examined the genetic underpinnings of the disorder in more than 1,000 families.

The findings, reported in three studies published Wednesday in the journal Neuron, cast autism disorders as genetically very complex, involving many potential changes in that may produce, essentially, different forms of autism.

The affected genes, however, appear to be part of a large network involved in controlling the development of synapses, the critical junctions between nerve cells that allow them to communicate, according to one of the three studies.

Although the work will have no immediate value to patients or their families, the insights provide a wealth of targets to pursue in developing treatments for the disorder, scientists said. Understanding the genetic causes of autism spectrum disorders may promote more accurate diagnoses, and research on synapse formation and function could yield treatments that address the flow of signals between nerve cells.

"For the first time we're getting a sense of how many areas of the genome are likely to contribute to autism," said Dr. Matthew W. State, associate professor of psychiatry and of genetics at Yale University and the lead investigator of one of the reports. "We know there are multiple, different ways to get autism."

Autism spectrum disorders are a group of conditions, ranging from severe to mild, that are characterized by problems with social interactions. Those with autism may exhibit repetitive behaviors and narrow, obsessive interests; some may have low IQs or problems with language development. About one in 110 U.S. children has an autism spectrum disorder, according to the Centers for Disease Control and Prevention.

About 25 percent of autism spectrum disorder cases are linked to inherited gene mutations. Some of these high-risk genes already have been identified. But researchers have been puzzled by the cause of the disorder in families with no history of autism.