London - Men delaying fatherhood have been told to consider freezing their sperm after a study showed they also have a rapidly ticking biological clock.
Researchers found older fathers pass down the majority of the faulty genes linked to conditions such as autism and schizophrenia.
Scientists in Iceland discovered 97 percent of genetic mutations were caused by the age of the father, while the mother’s age had no effect at all.
The child of a 40-year-old father had two-and-a-half times as many potentially damaging mutations as that of a 20-year-old, and the gap increased with every passing year.
Reacting to the study, Alexey Kondrashov, a professor of evolutionary biology at Michigan University, said if the findings were confirmed, “collecting the sperm of young adult men and cool-storing it for later use could be a wise individual decision”.
While it was suspected that the trend towards late fatherhood may be related to rising rates of autism, this was the first large-scale test.
Experts say the study raises the possibility that men in their thirties should freeze their sperm if they are planning to have children late in life like Rod Stewart or Sir Paul McCartney.
Genetic screening was carried out on 78 families with children who were either on the autistic spectrum or had been diagnosed with schizophrenia.
This information was compared with data from hundreds more families with no link to either condition.
Everyone has some genetic mutations, but on average children had an additional two for every year of the father’s life. A 20-year-old father transmitted on average 25 mutations to his child, while 40-year-old fathers, the oldest in the study, transmitted around 65.
The mother transmitted around 15, regardless of her age.
Lead author Dr Kari Stefansson, of deCODE, a leading genetics firm in Reykjavik, said the father’s age was “an extraordinarily important force in evolution”, adding: “The number of mutations coming from the mother is constant, which makes sense as her eggs are formed before she is born, whereas men constantly generate sperm through to old age.
“The very important conclusion we can draw from this is that the concern focused on the increasing age of mothers is probably misplaced.
“They may be off the hook, and men are on it – as disorders from these mutations are much more common than the risks associated with older mothers.”
The researchers, writing in the journal Nature, say the father’s age seems to increase problems with brain function – such as autism, schizophrenia and possibly dyslexia and low intelligence.
However, while there is no increase in genetic mutations, older mothers are known to increase their child’s risk of more serious chromosome abnormalities, which make them more likely to miscarry or have children with Down’s syndrome.
Dr Allan Pacey, fertility expert at the University of Sheffield, said the study “should remind us that nature designed us to have our children at a young age and if at all possible men and women should not delay parenthood if they are in a position not to”.
Darren Griffin, genetics professor at the University of Kent, said older fathers should not panic as the risk is still small – there are three billion letters in the human DNA code and the number of mutations found was only in the dozens – while the risk from older mothers was “far more potent and measurable”. - Daily Mail