Foetal DNA in Mum's Brain

Male DNA, almost certainly left over from a male foetus, has been found lurking in women's brains, according to research published in PLoS ONE this week. It's unclear what effect this may have on maternal health.

Foetal Microchimerism is the process by which foetal cells and DNA can escape the womb and get into the tissues and blood stream of a pregnant woman, but this work, carried out by William Chan of Fred Hutchinson Cancer Research Center and his colleagues, is the first to show that these cells can reach and persist in her brain.

The team looked at brain samples taken from the autopsies of 59 women and tested for the presence of Y chromosome DNA, which can only have come from a male.  63% of their samples were positive for male DNA, showing not just that it's very common, but also that it's very long lasting - the oldest female positive for male DNA was 94 years old.

Generally, the blood brain barrier should keep foreign cells like these out, but changes during pregnancy can cause the barrier to become more porous, giving chimeric cells a window of opportunity.

This is a small study, so any potential effect on maternal health is unclear.  Foetal microchimerism has previously been shown to be a double edged sword.  These cells may aid tissue repair and protect against breast cancer, but may also increase the risk of autoimmune diseases and other cancers.

Women who have had more children also seem to be at greater risk of developing Alzheimer's disease, so the researchers were very surprised to see that women with Alzheimer's had a lower prevalence of male cells in the brain and in particular in brain regions most affected by the disease.  This finding raises more questions than it answers, but does suggest that microchimerism may have some protective effect on the brain.