Which twins are hereditary

Genetics: Why Twin Births Stay in the Family

Scientists led by Hamdi Mbarek from the Free University of Amsterdam have discovered two genes that increase the chances of women having dizygoti twins. Researchers have been observing for a long time: If mothers-to-be already have dizygoti twins in the family, the probability is higher that they will also give birth to two children at the same time, although in this case they are not more closely related than other siblings. From this they concluded that there must be some kind of twin disposition that is passed on - so far, however, all attempts to track down a specific genetic mechanism have been unsuccessful.

Mbarek and his team therefore searched the genome of around 2000 such twin mothers from the Netherlands, Australia and the USA for similarities and differences compared to mothers who did not give birth to twins or identical twins. In the end, they actually came across two gene variants that seem to have an influence on the probability of twins. The first is near the geneFSHBwhich plays a role in the production of follicle stimulating hormone (FSH). The concentration of FSH fluctuates as the woman's egg cells mature. If it remains permanently elevated, several cells leave the ovaries at the same time, which ultimately paves the way for two egg cells to be fertilized and dizygoti twins to develop. The second variant of the gene affects the geneSMAD3, which affects how the ovaries react to the follicle-stimulating hormone, at least in mice. If a woman carries a copy of both gene variants, the probability of giving birth to dizygotic twins increases by almost 30 percent, the researchers calculate. Next, they want to test whether the geneSMAD3 this also increases the likelihood of becoming pregnant through artificial insemination. After such treatment, twin births are more common.