Congenital riskStudy finds genetic cause of miscarriages
23.01.2026, 06:21 Clock
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About one in seven detected pregnancies ends prematurely – a painful experience for many women. Researchers are now finding a cause in the mothers’ genetic makeup, which is present before they are born. A certain gene variant seems to be particularly crucial.
About 15 percent of all detected pregnancies end in miscarriage. And many other pregnancies end at a very early stage without even being noticed. A large study now provides a possible explanation for this high loss rate. Accordingly, common genetic variations in the mother’s genome that are present before she is born can increase the risk of a subsequent miscarriage.
The main cause of miscarriages is aneuploidy, a type of chromosomal abnormality. A cell has a number of chromosomes that deviates from the norm. It is estimated that only about half of all fertilized human eggs survive to birth, primarily due to the frequency of those with aneuploidies that are not viable in early pregnancy. This is what the team led by Rajiv McCoy from Johns Hopkins University in Baltimore (US state of Maryland) writes in the journal “Nature”.
If the number of chromosomes is less than the usual 46, embryos are rarely able to survive. With excess chromosomes, more combinations can result in viable embryos. Examples include Down syndrome (trisomy 21), Klinefelter syndrome (extra X chromosome in men) and Turner syndrome (only one X chromosome in women).
The gene SMC1B plays a special role
It was previously known that the number of embryos with a different number of chromosomes increases with the mother’s age during pregnancy. But studies also suggest that other factors can increase the likelihood of aneuploidy much earlier – during the formation of the eggs.
The team now tested this using data from almost 140,000 artificially fertilized embryos and almost 23,000 pairs of parents. The researchers discovered more than 92,000 aneuploid chromosomes. “This allowed us to discover, at this scale and at this resolution, some of the first well-characterized connections between maternal DNA and the risk of producing non-viable embryos,” McCoy is quoted as saying in a statement from his university.
“This finding is particularly convincing”
The connection is particularly strong for those genes that are responsible for the development of the structure of chromosomes during their creation. The SMC1B gene therefore plays a role. A variant of this results in the protein of the same name being produced less frequently than usual. The protein SMC1B is part of a ring-shaped protein complex that contributes to the formation of the three-dimensional structure when building chromosomes.
Mice lacking the SMC1B gene are unable to reproduce. Insufficient production of the SMC1B protein leads, among other things, to the development of aneuploidies in humans. Further investigations revealed that other genes may also be involved in the formation of abnormal chromosome numbers.
“This finding is particularly compelling because the genes that our human study identified are exactly those that experimental biologists have described for decades as crucial for recombination and chromosome cohesion in model organisms such as mice and worms,” emphasizes McCoy.
