Scientists have discovered a genetic mutation that helps explains male infertility.
It involves the gene that codes for a protein called beta-Defensin 126, which coats the surface of sperm and helps to penetrate the female’s mucus on the way to her egg.
Infertility – the inability to conceive after a year of unprotected sex – affects up to 15% of couples around the world. Male infertility, in particular, often can't be explained by sperm count and quality. This study though, might.
Men who have a variant of a gene called DEFB126 lack that protein coating, making it harder for their sperm to swim through cervical mucus and avoid the female’s immune system.
"It has always been an enigma in biology why sperm cells in the female tract are not recognized as foreign cells and subsequently destroyed," says study researcher Gary Cherr at the University of California, Davis. "We now know this protein coat helps the sperm cells evade the female's natural surveillance mechanisms."
Like a "Klingon cloaking device," he adds.
About 25% of men have 2 copies of the mutant gene, and about half of all men on earth have one mutant gene. (Why evolution has allowed that, scientists don’t know.)
Their sperm (pictured) look normal under a microscope and swim around like normal sperm. But they’re far less able to swim through an artificial gel made to resemble human cervical mucus. So it doesn’t mean these men can’t impregnate their partner… it means that it’ll be that much harder if they have lower sperm counts and less mobile sperm too.
Cherr and his colleagues examined 500 newly married Chinese couples. Wives of the men with 2 copies of the DEFB126 mutation were 30% less likely to give birth.
According to the researchers, it should be easy to create a test to diagnose the problem so that couples could try treatments to bypass it:
- Such as having sperm placed directly into the woman's uterus.
- Or, because when the normal protein is added to the sperm, they recover their normal abilities, there could be a vaginal gel to let sperm pick up the protein coating as it travels into the cervix.
The work was published in Science Translational Medicine today.
Images: Theodore L. Tollner
This post was originally published on Smartplanet.com