Sperm face steep odds when set free to fertilize an egg. A slightly faulty tail, a miscalibrated electrical charge on their cell membrane or some other subtle defect can keep these genetic couriers from becoming the lucky, lone swimmer that sires offspring.
According to a study published online July 20 in Science Translational Medicine, roughly a fifth of the male population may suffer lower fertility because of this mutation, and half of all men may be carriers of the trait. The frequency of the variation is surprising because natural selection quickly removes most genetic traits that limit sexual success from the gene pool.
In the team’s investigations, having just one of the mutant alleles did not seem to decrease a man’s likelihood of fathering a child. But about 20 percent of men in the study samples had two copies of the gene mutation, which, especially when combined with other factors—such as low sperm count or decreased sperm swimming ability—diminished chances for conception.
The gene DEFB126, helps to manufacture a protein that coats sperm in a sugary carbohydrate. Without that protective coating, sperm seemingly have trouble evading the immune defenses inside the female reproductive tract and are typically rapidly dispatched.
The recent research followed hundreds of couples in China who were trying to have their first child and had no known fertility issues. Couples in which the man had two copies of the genetic mutation were about 30 percent less likely to become pregnant or have a child within two years.
About 13 to 14 percent of all couples in their reproductive years experience infertility, which is defined as being unable to conceive after one year of trying. The roots of infertility are split fairly evenly between the sexes, but about 17 percent of cases have no apparent biological basis. Men with the newly discovered genetic mutation often have sperm that appear perfectly normal to standard evaluations. Thus this genetic variation potentially clouds interpretation of male fertility.
If all the sperm need is the protein coating, an answer to the problem could be as simple as a vaginal gel that could deliver the missing layer to sperm. So if the new link is supported by future research, it might help doctors and couples get to the bottom of their conception conundrum sooner—and recommend the appropriate remedy, whether that might be artificial insertion of sperm or in vitro fertilization (IVF).