Becoming a father at age 40 or older linked to offspring at a higher risk of schizophrenia, autism and syndromes that cause facial and skull abnormali
Father's age may affect child's IQ level
Becoming a father at age 40 or older linked to offspring at a higher risk of schizophrenia, autism and syndromes that cause facial and skull abnormalities
From Tuesday's Globe and Mail
March 10, 2009 at 9:09 AM EDT
While it's nowhere near as deafening as the female biological clock, the male timepiece is poised to start ticking just a little bit louder. Despite many famous examples of men fathering children into their 50s, 60s and 70s - Pierre Trudeau, Mick Jagger, Jack Nicholson - a new study adds to a growing body of evidence that those children may face a number of health problems.
Becoming a father at age 40 or older has been linked repeatedly to offspring at a significantly higher risk of schizophrenia, autism and rare syndromes that cause facial and skull abnormalities. Now, Australian researchers have found a correlation between "advanced paternal age" and lower intelligence scores in children 7 and under. The findings were published yesterday in the journal PLoS Medicine.
Researchers studied data collected from about 33,000 American children and their parents as part of the U.S. Collaborative Perinatal Project between 1959 and 1965. Fathers in the study ranged in age from 14 to 66. Their children were tested using standard intelligence scales at eight months, four years and seven years of age.
Lead author John McGrath, a psychiatrist and epidemiologist at the Queensland Brain Institute at the University of Queensland in Brisbane, acknowledges his finding is small and preliminary.
The difference between the child of a 20-year-old and that of a 50-year-old is about two IQ points, for instance.
But as Western populations delay childbearing, it could have a significant impact, he says. "If you shift the whole population slightly one way or the other, that can translate into a whole range of health and educational outcomes."
After controlling their results for the effects of the mothers' ages and socio-economic factors such as income and education, researchers found that older moms tended to be of a better socio-economic status than young moms, with better health care and health literacy. Their children tended to score better on cognitive testing.
But these factors don't appear to help the children of older dads in the same way. Instead, something biological seems to be at work. As men age, the sperm they produce appears to acquire genetic mutations, Dr. McGrath says.
While men's fertility declines with age, the number of damaged sperm - which are still able to fertilize a woman's egg - increases.
"It was all very clear: If your mother was older you were doing better, but it went the other way for the dad," Dr. McGrath says. Researchers cannot yet predict the ideal maternal and paternal age that might result in a healthy, intelligent child.
There was no single age threshold at which the risk increases, as is the case with women and Down syndrome after age 35; for men, it was a continual decline, he says.
"We as a society need to worry about the age of fatherhood a little bit more than in the past," Dr. McGrath says. While everyone is aware of a decline in fertility as we age, "maybe the general public needs to be aware that there may be something else happening."
However, other research suggests being a very young dad can have its drawbacks, too. A recent Canadian study found that children of teenaged fathers were 15 per cent more likely to be born premature and 13 per cent more likely to be of low birth weight. They also had a 22 per cent greater risk of dying within four weeks.
These problems were associated with socio-economic factors, says lead researcher Shi-Wu Wen, a senior scientist in clinical epidemiology at the Ottawa Health Research Institute and a professor at the University of Ottawa. "Teenaged boys often don't have stable income, don't know how to care for the baby. They sometimes smoke and use drugs more frequently," he says.
While his work did not find a link with advanced paternal age, he says the Australian research focused more on the biological underpinnings of advanced paternal age and its results appeared "reasonable" and "common sense."
"The chance of mutation is increasing with paternal age," he says.
Researchers are also trying to look at possible epigenetic effects of older dads: How these findings play out in future generations.
"Future generations will still be bearing the age-related mutations their fathers, grandfathers or great-grandfathers accumulated," Dr. McGrath says. "It's a non-trivial issue."