Male 'biological clock' ticking

\By Leah Dunaief

March 11, 2009 03:36 PM

When an older man fathers a child, regardless of the age of the mother, there seems to be a small but increased risk that the child may score less well in intelligence tests. And although the risk is still quite small, such a child may also have an increased chance of birth defects and neuropsychiatric conditions like schizophrenia, autism and bipolar disorders. These results of a broad scientific study involving 33,500 children born in the United States between 1959 and 1965 are causing a sea change in medical perspective.Until now, the age of the mother has been considered of paramount importance, especially since the biological clock of women is limited while the ability of men to father children continues as they age. With these results, it would appear that men too have a "clock" that begins ticking in their mid-30s. Evidence suggests that the chance of a successful pregnancy falls slightly after the father turns 35 and more so, although the risk is still quite small, after 40 years of age. This information is of particular relevance today, when more men are delaying fatherhood until their 40s. For example, in 1993, in England and Wales, about 25 percent of births within marriage were to fathers ages 35-54, but by 2003, the number had risen to 40 percent. And according to the National Center for Health Statistics in the U.S., in 2004 about 24 in every 1,000 men aged 40-44 fathered a child — an increase of 18 percent from the previous decade.Further, the children of older mothers in the study tend to fare better in intelligence tests than the children of younger mothers.John McGrath of the University of Queensland in Brisbane, Australia, led the primary study. "We report, to our knowledge for the first time, that the offspring of older fathers show subtle impairments on a range of neurocognitive tasks during infancy and childhood. The patterns of these findings were relatively consistent across ages and across neurocognitive domains," according to McGrath. However, there was no further study to show if these children catch up with their peers later in life.So what's going on here?For starters, women are born with all the cells that will evolve into future eggs. These eggs undergo 22 divisions in the womb. Men, however, produce new sperm cells throughout their lives. By age 20, sperm cells have divided 150 times and by age 50 some 840 times. With division there can be "copy error mutations," or environmentally induced mutations, which in turn could lead to developmental problems. That could explain why the man's age at fatherhood is relevant to the outcome of the pregnancy.Further, children of older mothers, while less at risk from cell mutation, may perform better also because they receive the benefits of a more nurturing home environment. They are on the right side of the heredity/environment question on both counts.A study recently published in the Archives of General Psychiatry concludes that the offspring of older fathers have a higher risk of autism than that of younger fathers. If the father is over 40, the risk, though still small, is six times higher than if the father is under 30.Researchers at Columbia University found that men aged 50 and over are three times as likely to father a child with schizophrenia compared to men 25 and under. And men aged 45-49 are twice as likely to have a child with this illness. The researchers estimated that "as many as one in four cases of schizophrenia may be caused by the age of the father." This conclusion is based on a study of 88,000 people.And in Sweden, in a study at the Karolinska Institute, the conclusion was that the older a child's father, the more likely he or she was to have bipolar disorder. Children of men 55 years and up were 1.37 times more likely to be diagnosed with bipolar disorder than those of men 20-24. Please note that these are still small risks overall.The risk of preterm birth increases with paternal age, according to a March 2005 issue of Epidemiology. Because of increased risk of genetic abnormalities in the offspring of older fathers, the American Society for Reproductive Medicine has limited semen donors to 40 years or younger, and in the U.K., 39 is the top age.Men aged 50 and older are four times more likely to have a child with Down syndrome.Some famous older fathers include the likes of Michael Douglas, Mick Jagger and Rupert Murdoch.Perhaps society should look more kindly on older women who partner with younger men. It's an idea that tickles me.