Fertility and pregnancy * Women's health

Scientists unravel secret of infertility in older women

Scientists unravel secret of infertility in older women Low levels of cohesin proteins may be to blame

Scientists say they are closer to 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.

Although past research has shown that the increase risk of abnormalities in older women is due to eggs containing the wrong number of chromosomes, the reason for this has been something of a mystery.

However, new research suggests that levels of proteins called cohesins declines as women age.

Cohesins hold chromosomes together by entrapping them in a ring, an essential role which ensures chromosomes are split evenly between cells when they divide.

In the study, led by Dr Mary Herbert, a team of researchers at Newcastle University and Newcastle Fertility Centre used eggs from young and old mice to show that cohesin levels decline gradually as females get older.

By tracking chromosomes during cell division in the egg, the researchers found that the lower levels of cohesin in eggs from older females led to some chromosomes becoming trapped and being unable to divide properly.

Eggs such as these may fail to develop properly leading to infertility, or they may give rise to a pregnancy with a high risk of miscarriage, or to the birth of a baby with Down’s Syndrome.

“Reproductive fitness in women declines dramatically from the mid-thirties onwards. Our findings point to cohesin being a major culprit in this," said Dr Mary Herbert, a Reader in Reproductive Biology at the university's Institute of Ageing and Health.

“The aged mice we used are equivalent to a woman in her early forties. Cohesin levels were very much reduced in eggs from older mice and the chromosomes underwent a very messy division resulting in the wrong number of chromosomes being retained in the egg.

The finding are published in the journal Current Biology.

“The next step in this research will be to see if the same problem exists in human eggs and to work out why cohesin is lost during female reproductive ageing. 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."

Dr Herbert stressed: "Undoubtedly, the best way for women to avoid this problem is to have their children earlier.”

This article was published on Thu 2 September 2010

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