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The ticking of the biological clock may have just gotten a lot louder for men.
Older dads have a much higher risk of having kids with mental health issues and learning disabilities, according to a report published Tuesday in JAMA Psychiatry.
After poring through data from 2.6 million Swedish-born children, an international team of researchers found the older a father got, the greater the risk that his child would have conditions such as autism, bipolar disorder or Attention Deficit and Hyperactivity Disorder.
Compared to dads in their early 20s, for example, a man who became a father at 45 would run a 13-fold increased risk of having a child with ADHD, a 25-fold increased risk of a child with bipolar disorder, and a 3.5-fold increased risk of having a child with an autism spectrum disorder.
"We were surprised by the magnitude of the association. But let me be clear. This study does not suggest that all children born to an older father will have psychological or academic problems."
Children born to older dads were also more challenged academically. They were 59 percent more likely to get failing grades in school and 70 percent more likely to drop out. And they were more than twice as likely to have suicidal behavior or a substance abuse problem.
"We were surprised by the magnitude of the association," said Brian D'Onofrio, the study's lead author and an associate professor of psychological and brain sciences at Indiana University. "But let me be clear. This study does not suggest that all children born to an older father will have psychological or academic problems. Our study shows that the overwhelming majority won't."
Nevertheless, D'Onofrio said, the study "suggests that couples — and society at large — need to weigh the pros and cons associated with delayed child bearing."
The differences found in the new study seem dramatic compared to earlier research. And the reason may be that D'Onofrio and his colleagues looked at their data in a new way: To get a better handle on the impact of age alone, they compared siblings born to the same parents.
When researchers look at children across the board, the biological effects may be obscured by the advantages older fathers bring to the equation, D'Onofrio said. "We do know that delaying childbearing gives parents more opportunities to get education," he explained. "It also leads to more financial security."
There have been hints all along that men might also have a ticking biological clock, experts said.
"We've known for a generation that paternal age has an effect on babies," said Dr. Harry Fisch, a urologist at New York-Presbyterian/Weill Cornell Medical Center. "For example, dwarfism is more common in children with older fathers."
But it's only been in recent years that researchers have started to look for a paternal age effect on some serious psychiatric disorders, such as schizophrenia, Fisch said.
"I consider this to be a public health concern," he added. "We're always trying to blame external forces for problems in our children. Now we're realizing that the longer we wait to have a baby, the higher the chance of having one with genetic problems."
With all the focus on women's age related decline in fertility the public isn't used to thinking about issues in men.
"What used to be thought of as a women's problem we now know is also a men's problem," Fisch said. "It's a parental age effect."
Scientists have long known that women are born with all their eggs, which deteriorate with age leading to chromosomal abnormalities such as Down syndrome.
But it was thought that men's reproductive abilities escaped the ravages of age because sperm are constantly being renewed. Scientists now are beginning to understand that genetic glitches can be the result of that renewal process.
Sperm created later in life may be like a Xerox of a Xerox of a Xerox. Or multiple generations of an audiotape.
"The more copying you do, the more chance there is for error," Fisch said. "It's incredible that people think that testicles don't age."
Another factor may be the decline with age in the number of stem cells whose job it is to make sperm, said Kyle Orwig, a specialist in male fertility and an associate professor at the University of Pittsburgh Medical Center.
"Sometimes the surviving ones are able to persist because they have an advantage that might be linked to a genetic defect that can lead to a developmental disorder," Orwig said.
Fisch suspects researchers will find more and more disorders linked to paternal age.
"This could be the tip of the iceberg," he said.