Children born to middle-aged men are more likely than their older siblings to develop a range of mental difficulties, according to a new study.
The new report, authored by a research team led by Dr. Brian M. D’Onofrio of Indiana University, looked at many mental disorders in Sweden, including attention deficits, bipolar disorder, autism and schizophrenia. The report suggests that men have a biological clock of sorts because of random mutations in sperm over time and that the risks associated with later fatherhood may be higher than previously thought.
The findings were published on Wednesday in the journal JAMA Psychiatry.
Lead researcher Dr. Brian M. D’Onofrio of Indiana University.
Compared with the children of young fathers, aged 20 to 24, those born to the same men age 45 and older had about twice the risk of developing psychosis, the signature symptom of schizophrenia; more than three times the likelihood of receiving a diagnosis of autism; and about 13 times the chance of having a diagnosis of attention deficit disorder. Children born to older fathers also tended to struggle more with academics and substance abuse.
The researchers say that any increased risk due solely to paternal age is most likely a result of the accumulation of genetic mutations in sperm cells. Unlike women, who age with a limited number of eggs, men have to replenish their supply of sperm cells. Studies suggest that the cells’ repeated reproductions lead to the accumulation of random errors over time, called de novo mutations.
Experts say the numbers in the study look more alarming than they probably are in particular areas, such autism and psychosis. However, the researchers found much larger increases in risk for attention deficits (13-fold) and bipolar disorder (25-fold) associated with late fatherhood.
Paternal age correlations with child mental illnesses.
In recent years, scientists have debated based on mixed evidence whether a father’s age is linked to his child’s vulnerability to individual disorders like autism and schizophrenia. Some studies have found strong associations, while others have found weak associations or none at all.
The strengths of the new report are size and rigor. D’Onofrio’s research team analyzed medical and public records of about 2.6 million people born in Sweden from 1973 to 2001.
Like many European countries, Sweden has centralized medical care and keeps detailed records, so the scientists knew the father’s age for each birth and were able to track each child’s medical history over time, as well as that of siblings and other relatives. Among other things, the analysis compared the mental health of siblings born to the same father and found a clear pattern of increased risk with increasing paternal age.
“This is the best paper I’ve seen on this topic, and it suggests several lines of inquiry into mental illness,” said Dr. Patrick F. Sullivan, a professor of genetics at the University of North Carolina, who was not involved in the research. “But the last thing people should do is read this and say, ‘Oh no, I had a kid at 43, the kid’s doomed.’ The vast majority of kids born to older dads will be just fine.”
The Karolinska Institute in Sweden.
The researchers controlled for every factor they could think of, including parents’ education and income. Older couples tend to be more stable and have more income — both protective factors that help to temper mental problems — and this was the case in the study. But much of the risk associated with paternal age remained.
“We spent months trying to make the findings go away, looking at the mother’s age, at psychiatric history, doing sub-analyses,” Dr. D’Onofrio said. “They wouldn’t go away.”
Dr. D’Onofrio had seven co-authors, including Paul Lichtenstein of the Karolinska Institute in Stockholm and Dr. Catarina Almqvist of the Karolinska Institute and Astrid Lindgren Children’s Hospital in nearby Solna.
“The question we now need to ask,” said Dr. Kenneth S. Kendler, a professor of psychiatry and human molecular genetics at Virginia Commonwealth University, “is what else is going on with respect to older and younger siblings that could cause these differences.”
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(Modified by Geoffrey Babbitt. Benedict Carey’s original article can be found here.)