Men: Your Clock is Ticking, Too
In the past, scientists knew that genetics plays a role in the development of autism, but it was uncertain which genes are involved, and to what extent new mutations play a role. It’s well known that females are born with their full complement of eggs. They’re carefully doled out throughout a woman’s reproductive lifetime. Once this finite supply is depleted, a woman’s reproductive capacity comes to a predictable close. In contrast, men produce new sperm capable of fertilizing eggs on an ongoing basis, throughout their lifetimes. There is no obvious expiration date on sperm, provided they retain the ability to swim.
And older fathers are increasingly common. In the past, men and women alike began families at much younger ages. These days many couples are choosing career and education first, delaying starting a family until much later in life. The mother’s age was often viewed as the limiting factor. The age of 35 is a commonly accepted reproductive deadline, after which the risk of a number of defects rises alarmingly. Down syndrome, for example, is clearly linked to
“advanced maternal age.” Now it appears that we may need to view men’s reproductive viability with a similar sense of “expiration date approaching”.
According to research published last year in Nature, new mutations in aging sperm are responsible for an alarming number of cases of autism (and schizophrenia, as it happens). To put it one way, a 40-year-old man is six times more likely to father an autistic child than a 30-year-old man. Another way to look at it: a 20 year old man is likely to pass along an average of 25 new errors in the genetic code, while a man twice his age is likely to pass on about 65 of these errors. Each passing year after the age of 20 results in an average of two new genetic errors.
Kenny LC, Lavender T, McNamee R, O'Neill SM, Mills T, Khashan AS. Advanced maternal age and adverse pregnancy outcome: evidence from a large contemporary cohort. PLoS One. 2013;8(2):e56583. doi: 10.1371/journal.pone.0056583. Epub 2013 Feb 20.
Kong A, Frigge ML, Masson G, Besenbacher S, Sulem P, Magnusson G, et al. Rate of de novo mutations and the importance of father's age to disease risk. Nature. 2012 Aug 23;488(7412):471-5. doi: 10.1038/nature11396.