Men and women are equally likely to acquire the mutation that causes autism, but symptomatic autism is three times more likely to occur in men, making women the more likely carriers of the mutations, a new study says.

Researchers at Cold Spring Harbor Laboratory and Albert Einstein College analyzed data on autism incidence and found a previously unrecognized pattern, which points to spontaneous germ-line mutation as a significant cause of the disorder.

Spontaneous mutations are changes in a chromosome that alter genes. Germ-line mutations are newly acquired in a germ cell of a parent, and sometimes are transmitted to offspring at conception.

Parents, especially women, who acquire the mutation, but do not exhibit severe symptoms of the disorder, have a 50 percent chance of passing the mutation on to their children, according to the study.

The evidence also led researchers to believe that older parents are more likely to have autistic children.

“The fact that germ-line mutations increase with age places older parents at a higher risk of having children with autism, explaining a pattern that has been recently observed,” said CSHL co-author of the study Michael Wigler, Ph.D, in a news release.