Have you ever heard of fetal microchimerism? It's where cells from a fetus cross over to the mother — and for the first time, it's been detected in the brain.
Researchers analyzed the brains 59 female autopsy specimens, and in 63% of them found Y-chromosome DNA. That's right, the DNA from male fetuses is migrating into the body, and passing the blood brain barrier to implant in the brain. Not only that, but the age of these women was between 32 and 101 — a 94-year-old had the male DNA, so it persists for a long time.
Since they don't have accurate birth records for all of the women analyzed, it's impossible to fully know if those 63% had male babies, but other examples of microchimerism are well documented, and the blood brain barrier is particularly permeable when pregnant.
What makes this research interesting beyond the obviously disturbing side of it (your baby is leaving DNA in your brain) is its link to disease. Microchimerism has previously been tied to a number of ailments, and has been associated with decreased rates of breast cancer and rheumatoid arthritis arthritis, but a boosted chance of colon cancer. This research also looked into a link with Alzheimer's disease — which has previously been linked to an increased risk with more pregnancies.
What they discovered is that the 33 women with Alzheimer's disease had a lower prevalence of the male microchimerism. The study is too small, and the pregnancy histories too vague, to form any sort of concrete connection, but it opens the doors for further research.
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