June 7, 2006 — -- Men don't typically worry about the ticking of their biological clocks, but perhaps they should -- new research suggests that as men get older they have a slow decline in fertility and are more likely to pass along genetic traits that could result in birth defects in their children.
Researchers checked sperm from about 100 healthy, nonsmoking men between the ages of 22 and 80 (the average age was 44) to look for DNA damage, chromosome flaws and gene mutations. Scientists at Lawrence Livermore National Laboratory and the University of California at Berkeley conducted the study.
They found that the genetic quality of sperm decreases as men age, which may lead to an increased risk of infertility, failed pregnancies and possibly even genetic disorders that result in birth defects.
Dr. Andrew Wyrobek, a researcher at Lawrence Livermore, studied specifically the links between older men's sperm and two known genetic defects: dwarfism and Apert syndrome, which causes facial and skull deformations.
Older men's sperm showed a higher risk of producing children with dwarfism. Yet the older men showed no increased risk of producing offspring with Apert syndrome.
Wyrobek plans to look at other possible genetic changes.
"We've just opened the door on gene mutations out there," said Wyrobek, an author of the study. Humans carry 30,000 genes in their DNA makeup; among those, Wyrobek said, several hundred are associated with "gross genetic defects," such as diseases and severe physical abnormalities.
Wyrobek's research also showed that a man's risk of infertility increases as he gets older and increases his wife's risk of miscarrying, regardless of her age. This results, Wyrobek said, from older men having a lower sperm count, loss of sperm mobility and sperm that are less able to swim in a straight line.
Wyrobek concluded that a man's biological time clock ticks down more gradually, while a woman's takes a steeper drop.
This may have important implications, as men have been waiting longer to start families. Since 1980, there has been a 40 percent increase in older men -- between the ages of 35 and 49 -- fathering children and a 20 percent dip in men under the age of 30 having children, according to Lawrence Livermore laboratory.
However, a man's age isn't that big of a difficulty, said Dr. Richard Paulson, a fertility expert and professor at the University of Southern California's Keck School of Medicine.
In his own testing, Paulson said, "We could not show an increase in infertility in men, but we did see a decrease in sperm count ... with age."
Paulson agreed with Wyrobek that men and women produce more chromosomal defects as they age. As women age, chromosomal defects are more common in their fetuses, resulting in congenital conditions like Down syndrome, characterized by mental deficiency and a broader-than-normal face.
Doctors tend to agree that Down syndrome isn't attributable to older men; however, as men age, their sperm can more often inaccurately transcribe a chromosome's letters, resulting in dwarfism, which occurs about one in every 25,000 births.
So, men and women produce chromosome mistakes in different ways as they age.
Survival of the fittest is the biological theory that Abe Morgenthaler, associate clinical professor at Harvard Medical School, still relies on when it comes to procreation.
"Men make 100 million sperm and only one of those is used to create a child," Morgenthaler said. "Take the healthiest 20-year-old man and about a quarter of his sperm isn't good -- it could have two heads or two tails. Only the best sperm gets there."
Morgenthaler does agree that as men age, their sperm may have more abnormalities. And if one of those "abnormal" sperm wins out, it could jeopardize the health of the family lineage..