From the female point of view, one of nature's seeming inequities is that men can father children well into their senior years, while women's child-bearing window slams shut decades earlier. Well, it turns out that becoming a dad later in life may not be such a hot idea after all, researchers say.
In a study of sperm from almost 100 healthy, non-smoking men aged 22 to 80, U.S. scientists found that the prevalence of certain genetic damage appears to increase with age -- and that can lead to infertility, unsuccessful pregnancies for their partners and the risk of passing on such genetic diseases as dwarfism to their offspring.
"There is consequence to delaying fatherhood," said principal investigator Andrew Wyrobek, a biophysicist at the Lawrence Livermore National Laboratory in California. The researchers found that the more birthdays a man had seen come and go, the higher the prevalence of DNA breakage in their sperm, a condition that can lead to infertility or pregnancies that end in miscarriage. Also more common with age was a gene mutation that causes dwarfism, an inherited defect that occurs in about one in every 25,000 births. Affected individuals have shortened arms and legs and reach a full adult height of about only four feet.
Compared with men in their 20s, a 50-year-old has a 34-per-cent higher risk of producing a child who is a dwarf, while an 80-year-old's risk is 85 per cent higher. Put another way, "one-third of men will have double the risk of having a child with dwarfism," Dr. Wyrobek said.
However, the multicentre study found no correlation between male aging and an increased risk of Down syndrome or other forms of birth defects associated with too few or two many chromosomes, including Turner syndrome and triple X syndrome. The risk of producing a child with Down syndrome, for instance, appears to rest primarily with the mother and rises dramatically after she reaches age 35.
"We know that women have a biological time clock with an increase in risk of miscarriage and producing children with trisomy (an extra chromosome) as women age, and with a seemingly abrupt end of fertility around perimenopause," said co-lead author Brenda Eskenazi of the School of Public Health at the University of California, Berkeley.
"Our research suggests that men, too, have a biological time clock -- only it is different," Dr. Eskenazi said.
The study appears this week in the Proceedings of the National Academy of Sciences.