The brains of women contain male DNA, most likely derived from prior pregnancy with a male fetus, states recent research.

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.The study also does not provide an association between male microchimerism in the female brain and relative health versus disease. "Currently, the biological significance of harboring male DNA and male cells in the human brain requires further investigation," Chan said.However, other Hutchinson Center studies of male microchimerism in women have found it to impact a woman's risk of developing some types of cancer and autoimmune disease. In some conditions, such as breast cancer, cells of fetal origin are thought to confer protection; in others, such as colon cancer, they have been associated with increased risk. Hutchinson Center studies also have linked lower risk of rheumatoid arthritis to women who previously had given birth at least once as compared to nulliparous women.
Source-Eurekalert