Dad's biological clock is ticking too

Older dads have an increased risk of having children with psychiatric problems, according to the largest study of its type reported last week in JAMA Psychiatry, an American Medical Association journal. The number of children with bipolar disorder, autism, and attention deficit disorders gradually increased for fathers after age 24, but accelerated after age 46.

Compared to the child of a man in his early twenties, the child of a 46-year-old man has three times the risk for autism, 13 times the risk for ADHD, and 24 times the risk for bipolar disorder. The risk continues to rise as men get older.

A 2012 study from Iceland had previously shown a connection between older fathers and mental illness in their offspring, but it compared the children of different fathers. The much larger new study––2.6 million children in Sweden between 1973 and 2001––was able to compare children born to the same father at different times in his life. Surprised by their findings, the researchers tried to find some mistake in their methodology, but could not.

This latest American and Swedish research challenges the popular opinion that men’s sperm have no shelf life. Maternal eggs have long been known to be vulnerable to the ravages of time––all of a woman’s eggs are present in her ovaries at birth and they age with her, increasing the chance of genetic problems like Down’s syndrome. Because sperm are continuously being produced, they had been considered relatively immune to aging.

While lead author Brian D’Onofrio, associate professor of psychological and brain sciences at Indiana University, is unsure exactly why the risks increase, he and other scientists speculate that the continual production of sperm allows for DNA mutations to occur each time cells divide to make new sperm. These mutations could be cumulative over time.

Duke molecular geneticist Simon Gregory was impressed by the size and depth of the study but said father’s shouldn’t panic yet. “There is no reason to ring the alarm bells that older men shouldn’t have kids” unless the results are replicated in additional research and molecular evidence is found, he said.

Even if the study is proven correct, the actual number of children affected is not as great as might be expected. Parents in their twenties have a 1-in-300 chance of having an autistic baby. The 46-year-old father’s three-fold increased risk brings that up to 1 in 100 –– a significant increase, but still a relatively small number.