SCIENTISTS made a major step towards understanding why older women are more likely to produce abnormal eggs, increasing the risk of infertility, miscarriage and birth defects such as Down’s Syndrome.
While researchers have long known that women having babies in their late 30s and 40s posed an increased risk of disability due to eggs containing the wrong number of chromosomes, the underlying cause has not been known.
Research published yesterday in the journal Current Biology, said the key is declining levels of proteins called Cohesins, which hold chromosomes together by entrapping them in a ring. This is essential for chromosomes to split evenly when cells divide.
All the cells, except for sperm and eggs, contain two copies of each chromosome. Sperm and eggs must lose exactly one copy in preparation for fertilisation.
This requires a complex form of cell division. In eggs the problem is compounded by the fact that the physical attachments that hold chromosomes together are established before birth and must be maintained by Cohesins until the egg divides just before ovulation. In humans this can take decades.
Researchers at Newcastle University and Newcastle Fertility Centre, used eggs from young and old mice to show that Cohesin levels decline as females get older.
This results in weakened cohesion between chromosomes and failure to divide equally during the halving of chromosome number in eggs of older females.
Dr Herbert said further research would be carried out. “If we can understand this, we will be in a better position to know if there is any possibility of developing interventions to help reduce Cohesin loss,” she said.
“Undoubtedly, the best way for women to avoid this problem is to have their children earlier.”
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