A report in the journal Nature stated that researchers also discovered that the increase in mutations is due to a precise form of natural selection.
Some mutations have a competitive advantage during sperm production in the testes, along with the constant accumulation of random changes in DNA as men age.
The researchers found that in 81 healthy volunteers, about two percent of sperm in men in their early 30s carried disease-causing mutations, compared with three to five percent of sperm in men aged 43 to 74 years, and 4.5 percent of sperm in men aged 75 years.
The researchers pointed out that some mutations have previously been associated with cell growth and development, while others are associated with severe neurodevelopmental disorders in children and the risk of hereditary cancer.
Others may impair fertilization and embryo development or lead to pregnancy loss, they said.
“Some changes in the DNA not only persist, but grow inside the testicles, meaning that fathers who give birth later in life may be unknowingly more likely to pass on a harmful mutation to their children,” Matt Hurles, a professor at the Wellcome Sanger Institute in Hinxton, England, said in a statement.
In a complementary study that included more than 54,000 parents and their children and 800,000 healthy people, also published in Nature, some researchers analyzed mutations that were actually transmitted to children, rather than those that were measured directly in sperm.
They identified more than 30 genetic factors where mutations give sperm cells a competitive advantage through natural selection, including many linked to rare developmental disorders and cancer.
Many of these mutations overlap with the array of genetic factors detected directly in sperm.
The researchers explained that this research work highlights how natural selection within sperm is directly observed in children’s DNA, which increases the possibility of them inheriting some genetic disorders.
According to Hurls, who participated in preparing the two studies, “Our findings reveal the presence of a hidden genetic risk that increases with the father’s age.”
