If you're a woman who has been pregnant with a male fetus, you may have male DNA permanently in your body, according to a study that found such genetic material in the brains of women.

The study, published in PLoS ONE, is the first description of male

microchimerism in the female human brain. Microchimerism is when someone harbors cells that came from a genetically distinct individual. Or, in the immortal words of the Monkees (singing a Neil Diamond penned song), a person can be A Little Bit Me, A Little Bit You.

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The serious side of this is that scientists working at the Fred Hutchinson Cancer Research

Center  have linked the phenomenon to

autoimmune diseases and cancer, sometimes for better and other times for


Lead author William Chan, who is in the Department of

Biochemistry at the University of Alberta, conducted the research while

working in the lab of J. Lee Nelson, a

member of the Center’s Clinical Research Division and a leading

international authority on microchimerism.

The scientists believe it is likely that fetal cells frequently cross the human blood-brain

barrier and that microchimerism in the brain is relatively common. Until

this study, it was not known whether these cells could cross the

barrier in humans.

According to a press release issued by the cancer center:

The researchers examined brain autopsy specimens from 59 women who had died between the ages of 32 and 101. Male microchimerism was detected in 63 percent of subjects, was distributed in multiple brain regions and was potentially persistent throughout the human lifespan; the oldest female in whom male fetal DNA was detected in the brain was 94.
Twenty six of the women had no neurological disease and 33 had Alzheimer’s disease. The brains of women with Alzheimer’s had a somewhat lower prevalence of male microchimerism, which appeared in lower concentrations in regions of the brain most affected by the disease. However, the authors noted that the small number of subjects and largely unknown pregnancy history of the women means a link between Alzheimer’s disease and level of male cells of fetal origin cannot be established.

"Currently, the biological

significance of harboring male DNA and male cells in the human brain

requires further investigation," Chan was quoted as saying in the release.

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Prior research does, however, suggest that women who harbor male DNA might be protected against some types of cancer, such as breast cancer, and

autoimmune disease, like rheumatoid arthritis. It may, though, increase the risk of other cancers, such as colon cancer.

Many studies suggest that just having a child affects the future health of the mother, and not just because the kid could drive her crazy or, conversely, help to improve her lot in life. At least mothers now know that their sons might not ever fully leave them, even after they move out of the nest.

(Image: Taylor Schlades)