Older men have an increased risk of fathering children who eventually develop bipolar disorder, according to new research. It’s the latest study to refute the earlier theory that men could father children into their old age with no ill effects; other recent studies have linked older fathers to an increased risk of miscarriages, and to children with schizophrenia or autism.
The theory linking paternal age with an offspring’s health rests on the genetics of aging sperm. Spontaneous mutations can accumulate in the genes of a man’s sperm cells as he ages. These cells divide as many as 660 times by the time a man reaches 40, by some estimates. Each division increases the risk of acquiring a harmful mutation from erroneous gene copying, the theory holds [Science News]. Women are born with their full complement of eggs already in place in the ovaries, and therefore don’t have to worry about increased genetic errors as they age.
A broad study of couples seeking fertility help has shown that men are not immune from the ticking of the biological clock: They become less fertile after the age of 35. Researchers at a French fertility clinic studied over 12,000 couples who sought treatment at the clinic, and found that older men were less likely to conceive a child with their partners, and were more likely to conceive a child that ultimately miscarried.
Yves Ménézo, an embryologist involved in the study, says the researchers didn’t look for the cause of the would-be fathers‘ declining fertility. But researchers believe that as men age, genetic defects build up in their sperm. In younger men, the damage is minor and can be repaired inside the fertilised egg. But in older men the amount of DNA damage can overwhelm the body’s natural repair mechanisms. “We think there’s a critical threshold of DNA damage and above that, the damage can no longer be repaired. When that happens, genetic mistakes get through to the embryo and you get an increase in miscarriages,” Ménézo said [The Guardian].