For a long time prospective fathers could wile away the years without much worry about when to have kids, while prospective moms were constantly checking their ticking biological clocks.A recent study may turn the tables a bit, pushing men to think a little more about how long they wait to start a family.
The study by DeCODE in Iceland shows that each year a man delays fatherhood he increases the number of new genetic mutations that he passes on to his children. These “de novo” mutations are not ones that the father was born with, and therefore unrelated to any previous family history or condition. They occur spontaneously in the father’s sperm cells.
Using the data from the study, 23andMe’s Emily Chang lead the team that created a simple tool that uses a man’s age to calculate the number of mutations he might pass on to his children.
So what does the number mean? The implication from the study is that the longer a man waits the more he increases the chances his child might develop certain kinds of conditions, such as autism. Yet while the risk may increase, it is still very low.
Also, keep in mind that despite the name, mutations are not necessarily bad. In fact, these different spellings within a person’s genetic code are largely benign while some may even be beneficial and lead to long term genetic diversity among people. Science writer Alok Jha pointed out in a piece in the Guardian that a single mutation in the APP gene actually protects against Alzheimer’s disease and helps people live longer. At the same time, some preliminary studies suggest that the more de novo mutations passed onto a child the higher the risk that child could develop certain types of conditions, such as autism and schizophrenia.
Or as lead author Kári Stefánsson, deCODE’s chief executive, told Ewen Callaway at Nature:
“The older we are as fathers, the more likely we will pass on our mutations. The more mutations we pass on, the more likely that one of them is going to be deleterious.”
For women, who pass on other risks to their children with age, the number of de novo mutations a mom passes on to a child is constant at about 14. The number of new mutations a father passes to a child goes up by two each year, so that a 50-year-old new father might pass on about 65 new mutations to his child, while a father half his age would pass on about 35 mutations. The reason the number of de novo mutations women and men pass on to their children is so different is because women are born with all their eggs, while men produce sperm throughout their lifetime, offering more opportunities for mutations to occur.
This doesn’t necessarily mean that men should start having kids or having their sperm frozen right out of college, but it does add more information for prospective fathers to consider. It also gives us a little more understanding about complex conditions like autism.