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Mothers always have their children in the back of their minds – now it seems that this is quite literally true. Fetal DNA can enter a mother’s brain and remain there for decades, according to autopsies of female brains.

During a pregnancy, cells from mother and fetus can cross the placenta and survive for decades in the skin, liver and spleen – a phenomenon called fetal microchimerism.

Fetal DNA can also cross the blood-brain barrier and enter the brain of pregnant mice (Stem Cells, doi.org/ctfj7v). But it’s unclear whether the same happens in humans, says Lee Nelson of the Fred Hutchinson Cancer Research Center in Seattle.


If it does, having foreign DNA in your brain may be one possible explanation for why certain neurological disorders, such as Alzheimer’s disease, are more common in women who have had children (European Journal of Neurology, doi.org/dwwz99).

To investigate this, Nelson and her colleagues autopsied 59 brains of deceased women – 33 of whom had Alzheimer’s disease. They amplified the DNA that they found, creating many more copies, and looked for the presence of a male Y chromosome.

They found it in 63 per cent of the brains. This male DNA showed up in many different brain regions and some of it had been there for a very long time: one brain that contained the male DNA was from a 94-year-old woman.

Way in

Nelson says that pregnancy is the most likely explanation for the presence of male DNA, but having an organ transplant or an older brother, for example, could also explain it. Unfortunately, the pregnancy history was unknown for most of the people in the study.

Brains from people with Alzheimer’s seemed slightly less likely to contain male DNA – the opposite of what the researchers expected. The authors say this might be due to the small number of brains analysed, or to unknown factors in the life history of the women.

The presence of fetal cells in a mother’s body might allow her immune system to recognise her child’s cells, to prevent them from seeming like foreign bodies that need to be attacked, says Edward Scott of the Department of Molecular Genetics and Microbiology at the University of Florida in Gainesville.

That might one day make it possible for a mother and child to accept transplants from one another without the need for immunosuppressant drugs, although he believes that the number of foreign cells may need to be artificially boosted to make this happen.

The next step, Scott says, is to determine what the fetal cells do when they reach the mother’s brain.

Journal reference: PLoS One, doi:10.1371/journal.pone.0045592