Why female fertility fades as you age: Researchers uncover the chromosome defect to blame?
A chromosomal defect could be the cause behind fertility problems in older women, a new study has found.
Scientists say that in older women’s eggs, a biological structure that separates chromosomes sends them all over the place instead of distributing them evenly to each egg. An egg typically has 46 chromosomes, and having more than 46 is the cause behind Down syndrome, while having too few will likely end in miscarriage.
Past studies have attributed the only reason to be that the glue keeping chromosomes together works poorly. Researchers tell Daily Mail Online that this theory is not incorrect but that there’s an additional problem – the eggs don’t have the right number of chromosomes to begin with. Women are born with a fixed number of eggs, which remain dormant in the ovaries until the release of a single egg per menstrual cycle. But fertility declines significantly at around age 35. When an egg has more than 46 chromosomes, it is called an aneuploid egg. Scientists previously believed that eggs were more likely to be aneuploid with age because the ‘glue’ that keeps the chromosomes together works poorly in older eggs.
Dr Greg FitzHarris, a professor at the Université de Montréal, told Daily Mail Online that microtubules, the biological structure that separates chromosomes, act differently in older eggs.‘Instead of sending an even number to each egg in a controlled fashion, the microtubules go in all directions,’ he said.
The study, conducted at the University of Montreal Hospital Research Center (CRCHUM), used both young and old mice in experiments. Researchers performed a series of micromanipulations on the eggs of mice between the ages of six- and 12-week-old mice and 60-week-old mice. They swapped the nuclei of young eggs with those of old eggs and observed problems in the old eggs containing a young nucleus. The researchers say this show that the age of the mother influences how microtubules behave.Dr FitzHarris says that these aneuploid eggs come with a few risks. ‘One is that they’re nonviable, which means a woman can’t carry a pregnancy to term and she has a miscarriage,’ he said.‘The other is they are viable, which means the egg can give rise to life. But these defected eggs can cause birth defects such as Down syndrome.’ While a women of any age can have a child born with Down syndrome, the age of the mother has been found in the past to increase the risk of baby born with the disorder.Dr FitzHarris says fertility treatments are still a long way off, but the ultimate goal is to find strategies in older females and try to stop eggs from having the defects. ‘The things that go wrong with eggs that cause them to be defected are complicated and multi-faceted,’ he said. ‘It’s still in its early stages but we’re currently using these findings to try and devise strategies that get old eggs to behave like young eggs.’