If you want to be a father...

Two horror stories about the causes of male infertility. It is unclear how, with all these mutations in spermatozoa, the number of mankind continues to grow...

Horror story No. 1
The secret cause of male infertility has been discovered
Kirill Stasevich, Compulenta

To get to the egg, the spermatozoa must be covered with a special protein that helps them pass through the mucus that is secreted by the walls of the uterus. Without this protein, male germ cells, not inferior to normal ones either in quantity or mobility, are unable to fertilize an egg.

Even in our enlightened age, many men perceive male infertility as an absurdity and fiction, or even as a direct insult. Meanwhile, the ability to leave offspring does not depend in any way on the "bravery" of the cavalier: even with exceptional sexual activity, spermatozoa can form in negligible quantities, and the germ cells themselves may not be active enough to effectively fertilize an egg. At the same time, it is believed that human sperm is generally less active and carries a higher percentage of defective cells than in the same primates and other mammals, since long monogamous relationships eventually allow us to achieve our goals – not this time, but the next.

But male infertility has one mystery... In 70% of cases, it is impossible to say what its cause is, because, at first glance, "infertile" sperm is no different from normal: there are many cells, and they are also active.

Scientists from the University of California at Davis (USA) managed to get much closer to solving this phenomenon. Apparently, the answer is hidden at the molecular level, inaccessible even to the armed eye. At the last stages of maturation, spermatozoa pass into the appendage of the testes, the epididymis, where they are covered with a special protein from the defensin class, DEF126. Proteins of this class are designed to attack foreign microorganisms, but DEF126 also serves as a kind of camouflage robe for spermatozoa: due to this protein, male germ cells pass through the mucus in the cervix. Protein protects spermatozoa from attacks by the female immune system. Without it, male germ cells, not inferior to normal ones either in quantity or mobility, still cannot reach the egg.

In collaboration with colleagues from other universities and research centers, the researchers undertook a search for mutant variants of the DEF126 protein gene in residents of the UK, USA, Africa, Japan and China. As the authors write in the journal Science (Tollner et al., A Common Mutation in the Defensin DEFB126 Causes Impaired Sperm Function and Subfertility), about half of the men had one of the two copies of this gene defective, a quarter had both; in the latter case, the chances of spermatozoa breaking through to the egg are almost zero. Statistics confirmed the researchers' correctness: the number of pregnancies among couples in which a man possessed both defective copies of the DEF126 gene was negligible.

In this regard, however, another question arises: why is this literally "infertile" mutation so common? Scientists believe that the presence of one defective copy of the DEF126 gene, without damaging sperm cells, may have some additional advantages for men. Nevertheless, researchers are ready to link the sharp drop in the fertility of the male population in recent decades with this mutation that has escaped.

Prepared based on the materials of the University of California at Davis: Sperm coat protein may be key to male infertility 

Passive smoking can lead to genetic mutations in spermatozoa and, possibly, to congenital genetic defects in offspring, American and Canadian scientists have established during experiments on mice.

The results of the study conducted by Carole Yauk from the Research Bureau of the Ministry of Health of Canada and her colleagues were published in the journal Proceedings of the National Academy of Sciences (Marchetti et al., Sidestream tobacco smoke is a male germ cell mutagen – VM).

The authors note that there is a large amount of evidence of the negative impact of smoking on reproductive abilities. "Men who smoke have a high risk of certain abnormalities in sperm, including decreased motility, DNA damage to sperm cells, such as DNA strand breaks and chromosomal damage," the article says.

Although about 40% of non-smokers are exposed to tobacco smoke as passive smokers, much less is known about the indirect effects of tobacco.

The smoke entering the human body during passive smoking is a mixture of four thousand different substances, of which at least 50 are carcinogenic. Although the differences in the composition of "passive" and "active" tobacco smoke are small, some of the toxic and carcinogenic substances have different concentrations.

Scientists conducted experiments on male mice, exposing them to tobacco smoke for two weeks in special chambers, at a level corresponding to active or passive smoking. The researchers then studied the sperm of mice, analyzing the resulting genetic mutations.

As it turned out, both active and passive "smokers" had an increased frequency of a certain type of genetic mutations – tandem repeats, when individual DNA fragments repeat one after another. At the same time, passive smoking, unlike active smoking, did not lead to damage to bone marrow cells and blood cells.

Scientists note that the relationship between tandem repeats and mutations in functional segments of the genome is unclear, but the data they obtained may become another argument in favor of considering passive smoking as one of the factors affecting reproductive abilities and the health of offspring.

"Our data suggest that passive smoking can have far–reaching consequences for the reproductive sphere," the article says.

Portal "Eternal youth" http://vechnayamolodost.ru21.07.2011