Dad’s age links to child’s mental disorders
Researchers are surprised to find that children with middle-aged or elderly fathers are 25 times more likely to become bipolar as children who have younger fathers.
Men are increasingly likely to father children at a later age. A new study by Sweden’s Karolinska Institute in cooperation with Indiana University in the USA shows this raises the risks significantly of fathering children who will be diagnosed with a mental disorder.
The researchers have crunched the numbers for all Swedes born from 1973 to 2001 – over 2.6 million people – and looked for a link between advanced paternal age and psychological diagnoses and learning disorders among their offspring.
The diagnoses seen by the researchers included autism, attention deficit hyperactivity disorder (ADHD), bipolar disorder, schizophrenia, suicidality and drug abuse.
Compared to children with 24-year-old fathers, kids whose dads were 45 and up were 3.5 times more at risk of autism, 13 times more at risk of ADHD and 25 times more likely to develop bipolar disorder.
These are some of the unexpectedly strong findings published by the Swedish and American researchers in the journal JAMA Psychiatry.
Risk rises with advancing paternal age
“We are surprised by the results,” says one of the researchers behind the study, Brian D’Onofrio of the Department of Psychological and Brain Sciences at Indiana University in a press release.
“We find elevated risks that are much greater than any discovered previously,” says a co-author, Paul Lichtenstein of Karolinska Institute.
The scientists reason that previous studies have failed to detect such large risks because disparate effects of advancing paternal ages have pulled in different directions, partially counteracting each other.
“The reason is that older fathers probably tend to provide a better social environment, in part because the children of older fathers get better educations. So you have two opposing effects: older fathers provide a better social environment but [the fathers’ sperm] is more prone to genetic mutations. When we control against family environments, the effects are thus greater than we have previously seen,” says Lichtenstein.
For most of these disorders the risk rose steadily along with the age of the fathers, and the researchers found no theshold age above which the numbers of disorders spiked dramatically.
Gene mutations believed to be the cause
The researchers think the problem is associated with mutations in spermatogenesis – genetic changes that crop up when sperm cells are produced.
“The main hypothesis is that each time a sperm is produced a cell division occurs that increases the probability of new mutations. The older you are, the more cell divisions have occurred,” says Lichtenstein.
Although these risks increase when viewed from a population level, Lichtenstein warns against thinking that older fathers automatically encounter such problems.
“Instead we should look at this knowledge as support for individuals in making medical and social decisions,” he says.
“These days, families make decisions based on the mother’s age. We see a tendency to wait to have children until the mother is nearing 40 and her biological clock is ticking. The couple then begins thinking about starting a family. Perhaps we should now factor the father’s age into the equation, too,” says Lichtenstein.
Considerable rise in risks
Professor Pål Richard Romundstad of the Department of Public Health and General Practice at the Faculty of Medicine of the Norwegian University of Science and Technology (NTNU) is fascinated by the study. He says the researchers have eliminated most of the factors that could be caused by other genetic or environmental differences among families.
He says the study makes it clear that an elevated risk of mental disorders is linked to advanced age of the father, rather than due to alternative explanations, such as the personality types of men who choose to father children so late in life.
“But the potential for preventive measures on a social level is not very great,” says Romundstad.
“Twenty-five times the normal risk of developing bipolar disorder is a considerable increase in risks. It’s almost beyond belief. This is nothing to be scoffed at. But this is hard to prevent. It means you need to try and have children when you are younger,” says Romundstad.
Prevention would otherwise be possible if there were prevailing factors in the environment of families with older fathers – issues that could be changed.
Nevertheless, Romundstad thinks the study has not totally eliminated all environmental factors as part of the explanation.
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling