A whole-genome sequencing company in Iceland has discovered a direct link between the age of a father and the likelihood he is to pass on a genetic mutation to his offspring. The resultant study published in Nature shows that it's the father, and not the mother, who may be contributing to the onset of such conditions as autism and schizophrenia.
The finding also suggests that prospective fathers have a biological clock of sorts — and that they should seriously consider freezing their sperm if they want to put off having children until later in life.
Writing in Nature News, Ewen Callaway describes the details of the study:
Fathers passed on nearly four times as many new mutations as mothers: on average, 55 versus 14. The father's age also accounted for nearly all of the variation in the number of new mutations in a child's genome, with the number of new mutations being passed on rising exponentially with paternal age. A 36-year-old will pass on twice as many mutations to his child as a man of 20, and a 70-year-old eight times as many, [Kári] Stefánsson's team estimates.
The researchers estimate that an Icelandic child born in 2011 will harbour 70 new mutations, compared with 60 for a child born in 1980; the average age of fatherhood rose from 28 to 33 over that time.
Most such mutations are harmless, but Stefánsson's team identified some that studies have linked to conditions such as autism and schizophrenia. The study does not prove that older fathers are more likely than younger ones to pass on disease-associated or other deleterious genes, but that is the strong implication, Stefánsson and other geneticists say.
Previous studies have shown that a child's risk of being diagnosed with autism increases with the father's age. And a trio of papers published this year identified dozens of new mutations implicated in autism and found that the mutations were four times more likely to originate on the father's side than the mother's.
As Callaway correctly notes, the study has serious implications for scientists trying to determine why the prevalence of autism has increased so substantially in the last several years. Establishing a link between a father's age and the presence of autism in his children could change the way the condition is viewed — and potentially prevented.