Scientists have discovered a “cloaking device” for human sperm that helps explain why many men are infertile and gives new hope that they will be able to produce children in the near future.

The breakthrough study shows that many infertile men lack a protein coating on their sperm that helps hide the tailed cells from antibodies in some women’s mucus that recognize the invading sperm as foreign bodies and attack them as they swim frantically towards a waiting egg.

“We’re hopeful that this can lead to therapies for some couples who are infertile,” says Scott Venners, an epidemiologist from British Columbia’s Simon Fraser University.

And Venners, a study co-author, says the research may also help solve a medical mystery that has long kept about 70 per cent of infertile men in the dark about their troubles producing children.

Until now, only about 30 per cent of male infertility could be explained with a microscope diagnosis of too few or malformed sperm.

For the rest, doctors could see no reason for the apparent sterility, only presuming there was an issue with the man’s sperm when his partner’s eggs and reproductive equipment were found to be functioning properly.

But the study shows that many of these inexplicably infertile men likely inherited defective genes for a protein known as DEFB126 that keeps their sperm safe on their journey through the female reproductive tract.

Venners says mucus that lines a woman’s cervix holds electrical charges that are opposite of those borne by the male sperm, naturally repulsing them like matched poles of two magnets.

That mucus may also hold the antibodies that perceive invading sperm as foreign bodies and attack them, he says.

But for most men, sperm are protected from these mucosal antagonists, with DEFB126 providing them a Harry Potter like invisibility cloak.

DEFB126 is pooled in the epididymis, a structure where sperm are stored after they’re churned out by the testis.

There the protein coats the sperm for their fraught journey to the uterus where female eggs are deposited during ovulation.

Venners says it’s possible that scientists could create quantities of DEFB126 in laboratories and use it to coat sperm through a variety of potential measures.

“Even a home kit where the protein would be concentrated in a vaginally applied cream or gel,” is possible, he says.“The sperm would ‘pick up’ the defensive coat as they advance into the cervix.”

More presently, researchers could develop a screen for the faulty gene, a defective copy of which must be inherited from both a man’s mother and father to produce the DEFB126 depletion.

“It could become part of the routine clinical (examination) for couples who are infertile,” Venners says.

Men found with the faulty gene pairing could have their otherwise healthy sperm harvested and directly inserted into an egg-bearing uterus, bypassing the guarding mucus on the cervix.

About one half of all men worldwide carry one copy of the defective DEFB126 gene, and about one quarter carry both.

But only about seven per cent of North American men have been diagnosed as being infertile, meaning that even without the protein protection many sperm are able to run the mucus gauntlet.

Venners’ global studies, however, showed that men who had the defective gene produced far fewer children than those who had a healthy version.

A portion of these would have been deemed infertile.

“We don’t think (the defective gene) would make a man sterile, we just think that it would just take longer for him and his partner to become pregnant,” Venners says.

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The research was released Wednesday by the journal Science Transitional Medicine.

Because evolution selects genetic traits that allow individuals to reproduce most successfully, it’s unclear why a gene that could decrease fertility was so common across the globe.

But Venners theorizes that men who have only one copy of the gene must gain a reproductive advantage of some sort.