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Possible culprit for down syndrome found
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In a recent study conducted by researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of Tennessee, Knoxville it was found that in mice, if a mother’s egg cell has a mutation in just one copy of a gene, called Bub1, then she is more likely to have fewer offspring that survive to birth. Normally, both copies of a gene in a chromosome must carry the same mutation in order for an organism to be adversely effected.
The importance of this discovery is underlined by the fact that it’s rare for humans to have mutations in both copies of a gene, while it is quite common to have a mutation in only one copy. Usually, the healthy gene overrides the mutated gene - but not in Bub1, at least in mice.
What this means is that having only one mutated Bub1 gene could be a significant predisposing factor for passing on an abnormal number of chromosomes to offspring causing such things as Down Syndrome and other genetic disorders.
The scientists also found that the harmful effects of this mutation increased with a mother’s age. The older the female mice got, the fewer offspring they had. The same is true in humans: the chance of having an aneuploid pregnancy increases with the age of the mother. In addition, the scientists found that the same mutation in sperm cells had no effect on the health of offspring.
Scientists have used mice to study the genetic causes of aneuploidy, a condition marked by having an abnormal number of chromosomes. The bub1 gene plays a role in a cell’s spindle assembly checkpoint, which is a control mechanism that ensures that chromosomes are properly divided during meiosis, the cell division process that enables a stem cell to become an egg. This checkpoint hiccups when Bub1 is mutated, sometimes producing an egg with an extra chromosome and sometimes producing an egg with a missing chromosome.
Researchers found that when a male with one bad copy of the gene mated with a normal female, their number of offspring was normal. But when a female with a bad copy of the gene mated with a normal male, very few babies were born. Further research revealed this is because aneuploidy was generated in the egg and passed on to the single-cell zygote that forms when a sperm fertilizes an egg. And this led to the loss of the embryo.
For more information on this study you can visit Yale University School of Medicine in Connecticut.
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