Twins, triplets and mom's genes
The probability of having twins depends on two genes
In Europe and North America, there are 9 to 16 twins per thousand births. In Latin America and South Asia, this level is lower (6-9 per thousand). And record-breaking twins are born to the African Yoruba people (45-50 per thousand). It has also been noticed for a long time that women born in families where there were twins among the children themselves have an increased chance of giving birth to twins. But until recently, it was not possible to identify genetic evidence of such a predisposition.
Now, having studied the genomes of almost two thousand mothers of fraternal twins from eight countries, scientists have identified two genes that increase a woman's chances of multiple pregnancies. A team led by molecular geneticist Hamdi Mbarek from the Free University of Amsterdam used the university's database of Dutch twins, which has been maintained since 1987, which now contains information about more than 75 thousand twins, triplets and other twins born in the country. Researchers also had access to similar registers of twins from Australia, Iceland and the state of Minnesota. Mothers whose twins were not born were also selected for comparison.
Geneticists were looking for SNP markers of single-nucleotide polymorphisms, that is, differences in one nucleotide at a specific point in the genome that can be inherited. They were looking for those polymorphisms that occur in mothers of fraternal twins, and are absent in other women. As a result, it was possible to detect two such markers, the presence of each of which increases the chances of having twins by 29%. The first SNP marker is located near a gene called FSHB, which is involved in the production of follicle-stimulating hormone (FSH). A higher level of this hormone promotes the production of more eggs, which can eventually lead to multiple pregnancies.
Another marker was seen in a gene called SMAD3. Studies in laboratory mice have shown that this gene regulates the ovarian response to follicle-stimulating hormone. Therefore, this variation of it, as scientists suggest, can not only increase the chances of having twins, but also increase the probability of success with artificial insemination.
The study by Hamdi Mbarek and his colleagues was published by The American Journal of Human Genetics (Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility).
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29.04.2016