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The variant in a woman's genome, which causes errors in the cell replication process, is strongly associated with risk of aneuploidy -- an abnormal number of chromosomes in a cell, the researchers said. But they did not prove that the variant causes pregnancy problems.
"Early in human development, this [cell replication] process is particularly error-prone, affecting as many as 75 percent of embryos and often causing pregnancy loss as soon as five days after fertilization -- before the mother even knows she is pregnant," study first author Rajiv McCoy, a postdoctoral researcher at the University of Washington in Seattle, said in a news release from the American Society of Human Genetics.
Healthy human cells contain a total of 46 chromosomes, or 23 pairs. Aneuploidy results when chromosomes distribute unevenly. This condition is believed to be a major cause of early pregnancy loss. It may also prevent successful IVF treatments. A woman's age affects the risk for aneuploidy, but the study authors theorized that genetics also played a role.
In order to test their theory, McCoy and colleagues from Stanford University analyzed more than 46,000 embryos from about 2,400 IVF patients. The investigators found the gene variant known as rs2305957 was strongly associated with risk of aneuploidy. They also discovered that embryos with this uneven distribution of chromosomes were more likely to have come from patients who had a failed IVF treatment in the past, suggesting treatment failure may have been due to aneuploidy.
"Surprisingly, about half of women had this genetic variant, and that rate is fairly consistent across populations," McCoy said. "If it's so damaging to reproduction, why does it appear so often? Why isn't it selected against?"
One possible explanation is that having lower odds for a successful pregnancy may have promoted long-term bonding between ancient men and women, increasing their investment in the health and safety of each child. These children would also be more likely to survive and have their own children, the researchers said.
A nearby gene may also hold clues that could help scientists determine what causes aneuploidy. The study authors suspect PLK4, which governs the distribution of chromosomes as cells divide, may be involved.
"It would be great if we could positively identify the gene, the causal variant, and the molecular mechanism that the variant affects," McCoy said in the news release.
The researchers plan to investigate PLK4's role in development and why this gene variant linked to chromosome errors and early pregnancy loss remains common today.
The findings were to be presented Thursday at the American Society of Human Genetics annual meeting in Baltimore. Research presented at meetings should be viewed as preliminary until published in a peer-reviewed journal.
-- Mary Elizabeth Dallas
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