Researchers have identified a common genetic variant strongly associated with chromosome gains and losses during the early stages of human embryonic development. These errors in cell division, which are almost always fatal to the embryo, are thought to be a major cause of early pregnancy loss in humans and contribute to failure of in vitro fertilization (IVF) treatments. The findings were presented on Thursday, October 8, at the American Society of Human Genetics (ASHG) 2015 Annual Meeting in Baltimore, Maryland. Healthy human somatic cells contain 23 pairs of chromosomes, for a total of 46. However, errors during the cell replication process can cause the chromosomes to distribute unevenly, a condition known as aneuploidy. “Early in human development, this 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,” explained Rajiv McCoy, Ph.D., a postdoctoral researcher at the University of Washington and first author on the study. The title of the presented abstract is “Complex Mitotic-Origin Aneuploidy in Human Embryos: Genetic Risk Factors and Fertility Consequences.” Previous research has found a correlation between the age of the mother (but not the father) and the likelihood of aneuploidy. In fact, it is the mother’s genes that govern cell replication during the first few days of embryonic development. “However,” Dr. McCoy said, “this relationship did not fully account for the variation in aneuploidy we found within each maternal age group, so we guessed a genetic factor was also involved.” Using data collected by collaborators at Natera, Inc., Dr.
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