Older fathers may be at higher risk for passing on genetic mutations that could increase the odds of their children having schizophrenia, autism, and other disorders.
Although recent studies have found a link between older fathers and an increased autism risk among their children, for years it was believed that the mother’s age was the driving factor in children being at greater danger of having genetic defects, such as Down syndrome.
But not anymore. A study published online today in the journal Nature compared whole-genome sequences in 78 mother-father-child trios to see how parents passed along mutations to their children. Researchers were focused on de novo mutations, or new mutations that appear in the child but are not seen in the parents.
In each family the child had developed autism or schizophrenia, while the parents had no evidence of mental disorders.
Researchers discovered that on average, fathers passed along 55 new mutations, while mothers averaged 14. They also found that as the father’s age increased, the number of mutations he passed along increased exponentially.
For example, a 36-year-old dad would pass on double the mutations as would a 20-year-old father, and a 70-year-old would pass along eight times the number of mutations.
“The older we are as fathers, the more likely we will pass on our mutations,” lead author Kari Stefansson, chief executive of a Reykjavik-based genetics company, said in a story on the Nature Web site. Although most of the mutations are thought to be benign, Stefansson added, “The more mutations we pass on, the more likely that one of them is going to be deleterious.”
They key to the genetic discrepancies between mothers and fathers might lie in their reproductive cells. Sperm cells are renewed throughout a man’s life, while the number of eggs a woman has is fixed and determined at birth. With more cell copying comes a greater risk of mutations.
But can advanced paternal age alone account for the steep rise in autism diagnoses in recent years? Probably not—the New York Times reports that the birth rate among older fathers hasn’t kept pace with the autism diagnosis rate. According to the Centers for Disease Control and Prevention, one in 88 children in the U.S. has been diagnosed with some form of autism, an increase of 78 percent since 2007.
But men may not need to worry unduly about starting a family late in life. Darren Griffin, a genetics professor at the University of Kent who was not involved with the study, told Reuters, “There are three billion of letters in the DNA code of humans and the numbers of mutations detected in this study are in the dozens.”
Do you think that having kids later in life is worth the risk of passing on genetic mutations? Let us know in the comments.