Whose Biological Clock is Ticking?

For years the pressure has been on women to worry about how their age will affect the health of their child. But surprise, surprise, it just may be that men’s age matters, too.

According to the results of a new study published in the September issue of the Archives of General Psychiatry, children of men 40 years or older were almost six times more likely to develop autism “compared with offspring of men younger than 30 years, after controlling for year of birth, socioeconomic status, and maternal age.” The mother’s age made no difference.

The number of children diagnosed with autism has been on the rise. The L.A. Times notes that according to a recent government study, about one in 175 children is diagnosed with the disorder, up from about one in 1,000 two decades ago.

“Although some of the increase is due to better diagnosis of autism, researchers are at a loss to explain the bulk of the increase,” writes Thomas H. Maugh II in the Times. “Most researchers now believe that genetics plays a role in the onset of autism, said Dr. Fred Volkmar of Yale University, who was not involved in the study. So far, however, it has not been possible to implicate specific genes.”

The newest study looked at more than 300,000 children born in Israel in the 1980s and compared records showing whether a child was diagnosed with autism with government records that showed the age of the father and usually the mother. Another surprising twist: While autism generally affects many more boys than girls, when the fathers are over 40, the gender ratio is one to one.

The reasons why a father’s age would play a role are unclear, though Craig Newschaffer, professor and chairman of epidemiology and biostatistics at the Drexel University School of Public Health, told NPR’s All Things Considered on Tuesday that it could have to do with new mutations in the sperm as men age, or that older men are more likely to pass along genes associated with autism. From NPR:

It is tempting to ask whether the apparent rise in the number of children with autism is partly the result of a growing number of older fathers. But there’s no ready answer. The study doesn’t give a reliable indication of exactly how much the risk rises with age.

“If the magnitude of that effect truly were large,” Newschaffer says, “I might be more inclined to say, perhaps the aging of dads in general could explain a piece of that trend.”

The study also isn’t clear enough to help parents decide whether it’s too risky to have children based on the father’s age, Newschaffer says. But he believes that this study and other studies of older fathers do offer a message: “Probably like females, males have a reproductive age.” And that’s how “we should start thinking about it.”