The older a father is, the more genetic mutations he passes on to his offspring, says a study published in the journal Nature. The research indicates a man’s age can determine how many mutations children inherit, and men starting families in their 30s or later on can pass on traits which increase their children’s risk for autism, schizophrenia and debilitating diseases.
“The older we are as fathers, the more likely we will pass on our mutations,” said lead author Kári Stefánsson, chief executive of deCODE Genetics in Reykjavik. “The more mutations we pass on, the more likely that one of them is going to be deleterious.”
The theory that men are responsible for passing on more genetic mutations than women originated in the 1930s, when geneticist J.B.S Haldane found that families with a history of the clotting disorder haemophilia had more instances of the condition being passed down on the male X chromosome.
At the time, there was no way to prove Haldane’s theory. The current research, however, proves the geneticist was correct in his assumption, and he was also correct in his theory on why men pass on more mutations than women. The current study proves because sperm is being constantly produced by the male body, gene mutations increase with each cell division. Women, on the other hand, have their lifelong supply of eggs present at birth, eliminating the possibility for mutations due to continued production.
Stefánsson’s study, which looked at the genomes of 78 groups including mother, father and child, found fathers passed on approximately 4 times as many mutations as mothers (an average of 55 versus 14 mutations). The evidence also revealed the number of mutations rose exponentially with age; the team estimated a 36-year-old man would pass on twice as many mutations as a 20-year-old, and a 70-year-old would pass on 8 times as many.
The majority of mutations passed on were harmless, said the research team; however, the study did find mutations previously linked to increased risks for autism and similar disorders. The findings may account for the drastic rise in reported autism cases, which the Centers for Disease Control report have increased by 78 percent since 2007.
“I think we will find, in places where there are really old dads, higher prevalence of autism,” said Daniel Geschwind, a neurobiologist at the University of California, Los Angeles, who added that better diagnostic methods for the disease also account for the increase of cases.
Autism expert, Mark Daly, a geneticist at Massachusetts General Hospital in Boston, agrees that age of the father is not likely the only contributing factor to rising autism cases. According to Daly, while autism is highly heritable, there is no single mutation responsible for the condition, therefore parents must somehow provide predisposing factors which determine the disease.