CHICAGO — Men who become fathers in their 40s or older are much more likely to have autistic children than younger dads, a new study released Monday shows, bolstering evidence that genetics contributes to the mental disorder.

The research involved about 130,000 Israeli Jews born in the 1980s. Those fathered by older men were almost six times more likely to have autism or related disorders than those fathered by men younger than 30, and more than 1 1/2 times more likely than children fathered by men ages 30-39.

The mothers' age at childbirth appeared to have little impact on autism, although the researchers said they couldn't rule out "a possible small effect" from the oldest mothers.

Autism experts called the study intriguing but not definitive, and the authors said the results need to be tested in a broader population to see if similar findings would occur in other ethnic groups.

It's not the first time fathers' age has been implicated in autism, but the new research stands out because "it's a strong effect in a carefully designed study," said Dr. Edwin Cook, an autism researcher at University of Illinois-Chicago who was not involved in the study.

The study was released Monday in September's Archives of General Psychiatry.

It is based on biographical information on Israeli boys and girls who at age 17 were being assessed for eligibility to serve in the Israeli military. Among them, 110 had been diagnosed earlier with autism or related disorders, which include a less severe condition called Asperger's syndrome. However, most of the affected children in the study had autism, and the researchers said their results may not apply to Asperger's or other autism-like disorders.

Lead author Abraham Reichenberg, a researcher at Mount Sinai School of Medicine in New York, called it the first rigorous population-based study to investigate whether a father's age affects the risk of a child developing autism. Researchers from Columbia University and Israeli institutions including Chaim Sheba Medical Center and Hebrew University participated in the research.

Previous research by some of the same authors linked advanced paternal age with lower intelligence scores and with schizophrenia.

Other studies have shown that sperm mutate more often in older men, potentially leading to increased risk for brain abnormalities in their children.

"It's a very interesting, strong study," said Dr. Fred Volkmar, an autism researcher at Yale University who was not involved in the research.

Volkmar said the study is consistent with a prevailing theory that genes are a cause of autism, but he said the results need to be tested to prove the fathers' age was a culprit. For example, the study lacked information on whether the fathers themselves had autism.