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A new study suggests that men, as well as women, should keep an eye on their biological clocks.

Children born of fathers aged 45 and older are at greater risk for autism, attention deficit hyperactivity disorder and other psychiatric problems, according to research published Wednesday in JAMA Psychiatry.

Compared with the offspring of fathers in their early 20s, children born of older fathers are also more likely to have academic problems, including failing grades and failure to graduate from secondary school, the study found.

Researchers looked at data from more than 2.6 million people born in Sweden between 1973 and 2001. They excluded individuals born of older mothers to isolate the effects of delayed fatherhood, said Dr. Brian D'Onofrio, lead author of the study and associate professor of psychological and brain sciences at Indiana University.

The greater risk of psychiatric and educational problems in children were not limited to those with much older fathers, but increased in tandem with the fathers' age, the researchers found.

"The older the fathers, the more pronounced the effects of the risks," D'Onofrio said.

Because of the large sample size, "we were able to look at fathers who were teenagers all the way through to fathers who were over the age of 45," he added.

Previous research has linked advanced paternal age at childbirth with genetic mutations in sperm, which may affect the child's mental and intellectual health, D'Onofrio said. But he noted that the science of predicting psychiatric disorders based on DNA is in the early stages. Mutations that might affect a child's mental well being would not necessarily be detected in a sperm analysis at a fertility clinic, he said.

"If these [disorders] are actually due to random genetic mutations, then you would find [mutations] in some sperm, but not others," he pointed out.

Previous studies into the psychiatric risks associated with advanced paternal age have compared the children of younger dads with completely unrelated individuals born of older fathers. But this study is unique, D'Onofrio said, because it compared the offspring of older dads with earlier children of the same fathers, as well as with the children's cousins and first cousins.

This allowed the researchers to rule out other factors that might affect the children's well being, including the family's psychiatric history, socioeconomic status and the impact of birth order.

"We were actually shocked when we got these findings from the sibling comparisons," D'Onofrio said. The researchers challenged their own findings by altering the study designs, he added, "but we kept getting the same results, which suggest that these findings are pretty robust."

The researchers used statistical analysis to account for the ways in which advanced paternal age may have a protective effect on children's well being. Compared with men who become fathers in their 20s, older dads tend to have less criminality, less substance abuse, more income and greater education, D'Onofrio said.

But even after controlling for the advantages associated with delayed fatherhood, the researchers found that compared with the offspring of fathers in their 20s, children of fathers aged 45 and older had more than triple the risk of autism and 13 times the risk of being diagnosed with attention deficit hyperactivity disorder.

D'Onofrio noted that although the increased risks are significant, the rates of psychiatric disorders in children of older fathers are relatively low. Nevertheless, the study "adds to a growing body of literature that suggests that parents need to weigh both the pros and cons of delaying childbearing," he said.

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