Men planning to have babies later in life might want to re-consider after a major study found older dads' sperm has a higher rate of mutations that could increase their children's risk of schizophrenia and autism.
According to Icelandic researchers, sperm appears to develop two extra mutations per year, so the older a man gets, the more likely he is to pass on genetic mutations to his child.
The researchers undertook a large genome-sequencing study that found fathers pass on four times as many DNA mutations as mothers, which could contribute to an increased risk of autism and schizophrenia.
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"The older we are as fathers, the more likely we will pass on our mutations," says lead author Dr Kari Stefansson, whose study was published in Nature.
"The more mutations we pass on, the more likely that one of them is going to be deleterious."
Older mothers less to blame for difficulties
Dr Stefansson said this research could shift the blame for birth defects from older mothers.
"The very important conclusion we can draw from this is that the concern focused on the increasing age of mothers is probably misplaced," he said.
"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 from deCODE, a genetics firm in Reykjavik, studied "new mutations" –– mutations not inherited from the parents –– in 78 Icelandic parents and children. They found a father's age had the biggest impact on mutations in their child's DNA.
Past studies have found a link between a father's age and schizophrenia and autism, while other studies have found a link between new mutations and the diseases. This study provides a clearer link between the two.
According to Nature, the fact sperm is continually being generated by dividing cells makes it more likely to mutate. It's the opposite in women, who are born with all their eggs so they are less likely to mutate.
Professor Ravi Savarirayan, clinical geneticist at Murdoch Children’s Research Institute, told ninemsn this study adds to earlier research about the link between older dads and genetic mutations but
warned against concluding a definite link between older fathers and mental illness.
"We know that older fathers are associated with schizophrenia and autism but we don't know if that has anything to do with a causal link — it could be that older parents treat their kids differently," he said.
"It's not something we should focus on and it could be only one piece of a hundred-piece jigsaw puzzle. There is a lot of hysteria and bad information about autism and schizophrenia."
Don't rush to have babies earlier just yet
Professor Savarirayan said it would be unnecessary for experts to advise men to get their sperm frozen when they're younger.
"I still think people are going to wait until they are set up and able to afford their first house and that's now mid-thirties or even later," he said.
And that might not be a bad idea, anyway — a study from London has found babies born to older mothers appear to be healthier and experience faster language development and social interaction.
The researchers from University College London looked at 78,000 children born between 2000 and 2002 to mothers aged between 13 and 57.
When they analysed child weight, accidents, hospital admissions and language development, they found that the older mothers' children fared better.
For example, a nine-month-old baby born to a 20-year-old has a 9.5 percent chance of having an accident compared with 6.1 percent for a mother aged 40.
The authors hypothesised that this could be because older mothers are more likely to be married, educated and have higher incomes, which can contribute to better child wellbeing.