New research findings may explain the high incidence of fertility problems among men
One of the principles of the theory of evolution states that natural selection gradually "cleanses" harmful mutations from the population. Still, certain genetic diseases that originate from harmful mutations not only have not disappeared, but are sometimes quite common. The question of how harmful mutations survive becomes more valid when it comes to mutations that cause infertility and fertility problems, which significantly impair the ability to produce offspring, and therefore should not spread in the population. However, paradoxically, fertility problems are extremely common among humans (about 15% of the adult population), and many of them have a genetic background.
A study by Weizmann Institute of Science scientists, which was recently published in the journal Nature Communications., came up with an explanation for the mystery. The findings may explain the high incidence of fertility problems among men, and open up new lines of thought regarding the causes of genetic diseases and the methods of treating them.
Dr. Moran Gershoni, a post-doctoral researcher in the group of Prof. Shmuel Pitrokovsky, in the department of molecular genetics, wanted to examine an explanation for the survival of harmful mutations, based on the fact that in nature there are two species, males and females, belonging to the same biological species, and sharing an almost identical genetic load. Most of the differences between them lie in the way they use their genes and activate them, so natural selection acts on them differently. For example, a mutation that impairs the function of a gene for milk production will lead to negative selection among women only. In the most extreme situation, some mutation - beneficial for females but disastrous for males - could spread through the population because it tests positive in half of the population. The hypothesis is that as a result of such situations, harmful mutations in certain genes tend to accumulate in the population: a mathematical model created by Dr. Gershoni and Prof. Pitrokowski showed that the expected frequency of such mutations is twice as great as mutations in genes that are activated in both males and females.
To test the hypothesis, the scientists looked for genes that are found in both males and females, but are activated only in tissues exclusive to one of the sexes: the testicles, ovaries and uterus. In a computer analysis, 95 such genes were found, all of which are active only in the testicles. Most of these genes are essential for a man's successful reproductive ability, and damage to them leads to infertility in many cases. Later, the scientists scanned a database containing genomic information of over a thousand people, and checked the frequency of mutations, distinguishing between harmful mutations and mutations that do not affect the bearer. The findings showed that the genes active only in the testes contain double the amount of harmful mutations, and twice as often, compared to the genes active in both sexes - in accordance with the prediction of the theoretical model.
The scientists hypothesize that this phenomenon can explain the high incidence of fertility problems among men: mutations that impair fertility can accumulate in the population to relatively high frequencies because they are inherited unhindered by women - where no selection is applied to them. In follow-up experiments, they examine whether the mutations they discovered actually play a role in men who suffer from fertility problems.
In a broader aspect, the approach proposed by the researchers can help in the study of common genetic diseases, and in particular diseases that affect women and men "asymmetrically" (such as schizophrenia and Parkinson's in men, and depression and autoimmune diseases in women). The new findings show that the potential suspects in causing this type of disease may be genes that work differently in males and females. In addition, because of the different activity of genes in the two sexes, and the different effect of mutations on them, the findings also emphasize the need to provide sex-tailored medical treatment.
More information can be obtained from the Weizmann Institute of Science spokesperson's office: 08-934-3856
One response
The reason is much simpler
For 40 years now, people with fertility problems have been able to have children with help
In order to do an accurate survey, fertility should only be tested in children of people who have not had fertility problems