Researchers have found a new cause of infertility that could allow millions of infertile couples around the world to have a child. The team found a common gene mutation that causes sperm to be far less able to swim through the mucus of the cervix and reach the egg.
The authors of the study at the University of California, Davis explain that the gene causes the production of a protein called beta-Defensin 126 or DEFB126, which coats the surface of sperm. When the gene is mutated, the protein is missing, and the sperm have that problem in transit. Wives of men with the genetic variation were less likely to become pregnant than other couples and 30 percent less likely to give birth, the researchers said.
Charles Bevins, the study author and a microbiologist at the University of California, Davis, said, “This is the kind of discovery that makes scientists almost giddy with excitement. When scientists tried to clone the cloaking protein from the sperm in lab studies, they noticed the mutation”, Bevins said. The mutation was so significant that no protein was made. Also, it was a gene involved in reproductive success, where mutations usually aren't seen.
About 10 percent of women of childbearing age have difficulty getting pregnant, and one in three cases involves male infertility, according to the National Institutes of Health. In another third of cases, the cause of infertility isn't known. Many cases of unexplained infertility are likely connected to this genetic variation, the researchers suggested. It appears that about one in every 250 men has this genetic mutation.
One reason this discovery is important is that the normal tests of the quality of sperm, such as examining them under a microscope and watching how quickly they move, do not detect the mutation. But with this new information a simple genetic test should soon allow doctors to find it easily. For couples who have the genetic mutation doctors can use insemination to get the sperm right next to the eggs and overcome the handicap.
The work was carried out by doctors and scientists from UC Davis; Simon Fraser University in Burnaby, BC, Canada; the University of Leicester I, UK; Anhui Medical University in Hefei, China; and the University of Illinois, Chicago. It was published in the journal Science Translational Medicine.
Gary Cherr, the paper's senior author and a professor at the University of California, Davis said, “We envision a clinical or home kit for detecting the presence or absence.” About 50 percent of men worldwide carry one defective copy of the gene, called DEFB126, according to the report. These men can still form normal sperm. Another 25 percent carry two defective copies and produce sperm that are poor at swimming through mucus.
In a study cited by the report, 500 couples in China showed that birth rates were 30 percent lower among those in which the husband had two copies of the gene than among those with men who had one or no mutations. “The mutated gene reduced the rate of contraception, so it took them longer to achieve a pregnancy,” said Scott Venners, another study author, and epidemiologist at Simon Fraser University in Burnaby, Canada. Further research may include seeing if the mutation changes anything in women.
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