08/24/2012 04:10 pm ET Updated Oct 24, 2012

Older Fathers: Now We Know More About the Risks Their Children Face

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An important study appearing today in the journal Nature sharply advances what's known about the risks faced by the children of older fathers.

The idea that the children of older fathers face special risks is not new. As I wrote in 2009:

A study of the children of older fathers has found subtle impairments of intelligence and other mental abilities during infancy and childhood... The risks faced by the children of older fathers are similar to those faced by the children of older mothers. But while we all know about the risks of Down syndrome in older mothers, most of us are ignorant of the risks in the children of older fathers.

And the risks for older fathers are comparable to those for older mothers.

What's new in today's study is that researchers have quantified the risks -- they have actually measured the increase in mutations in fathers' sperm as fathers age. And they found that the number of mutations -- and, hence, the risk to children -- doubles every 16-1/2 years.

A 20-year-old father had, on average, 25 mutations in his sperm, while 40-year-old fathers had 65 mutations.

The findings could go a long way to explaining the apparent rise in autism. The average age at which fathers have children is rising, and so are the number of autism cases. Better diagnosis could also be a factor, but this study provides a potential scientific explanation for at least some of the increase -- perhaps a lot of it.

I won't repeat what you can read in a story in The New York Times by behavior writer Benedict Carey. The researchers reported that finding more than two mutations a year, or a doubling of mutations every 16 1/2 years, "is striking." In any future study of children's risks, "it is crucial to take the father's age into account," they wrote.

This is an important study -- should I repeat that? It's time we stopped focusing on women's biological clocks, and started thinking about everyone's.

This post also appeared in Psychology Today on Aug. 23, 2012.