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.
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As for the age related mutation rate: that may actually be an evolutionary advantage. Nature does not care about the occasional child with developmental problems, it does, however, care about the survival of the species by keeping the gene pool diverse... at whatever cost that comes to the individual.
We haven't had fairness in reproduction in my lifetime with my youngest sibling and half-sibling fathering children first for one. Another issue is whether we forget about all the men who gave their lives in our wars and the few children they left, how they should have society's respect and support to begin families. The Baby Boom should be called the Forget About Those Left Behind Boom in my book.
Genetic counseling usually operates under the assumption that genetic deviations are a bad thing, which is a value judgement based on the individual medical outcome. Genetics, however, is a group property of a species (actually, it is even more than that, since the human genome strongly interacts with the genomes of all our parasites and disease carriers, as well as our food sources and the general changes in our environment!). The only thing that actually counts, in nature, is the gene pool, not the individual genome. Genetic counseling is therefor, a short sighted reaction to something that is not even a problem, when viewed on the proper scale.
Having said that, the reduction of the human genome to a "normal" expectation value with little variability is, at this point, culturally almost inevitable. We are already losing enormous amounts of genetic variability simply by interbreeding of originally isolated population groups. It may take active genetic engineering to counteract the resulting consequences for our species.