Study: Having a Male Child Leaves Male DNA in Women's Brains

By James Hamblin

The presence of the DNA persisted into old age and correlated with a slightly decreased risk of Alzheimer's disease. No word on behavior changes, but there's a joke in there about football or another hilarious but not-too-sensitive gender normative topic.

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PROBLEM: We know of relationships between parity (bearing children) and likelihood of developing certain diseases later in life, but the mechanisms are unclear. Studies with mice had shown that DNA of a fetus can cross the blood-brain barrier and get into the brain (suggesting involvement in neurologic effects), but it hadn't been shown in humans. 


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METHODOLOGY: Researchers out of the University of Alberta looked at autopsy specimens of the brains of 59 women (ages 32 to 101). They used PCR to scan the brain tissue for a gene that's only found on the male Y chromosome. The women's histories of pregnancy weren't available to the reseachers.

RESULTS: Male DNA was present in 63% of the female brains. It was distributed throughout the brain, not just in a particular area, and across all ages.

CONCLUSION: Male DNA is often found in the brains of women -- reasoned by the researchers to be a remnant from pregnancy with a male fetus -- and remains present into old age. That would mean fetal DNA is able to cross the blood-brain barrier, which hadn't been demonstrated before in humans.

IMPLICATIONS: Largely speculative at this point, but the researchers did look at how the presence and concentration of male DNA in the brain related to the women's likelihood of Alzheimer's Disease, and found it was slightly lower in the women who had the male DNA. But the sample size was small and there are a lot of other variables. The simple fact that the male DNA is there in the female brain, though, invites multiple directions for larger follow-up studies on neurocognitive diseases. If a fetus of a certain gender was found to have health benefits for the mother, it would also further complicate future discussions of sex selection and genetic engineering of our kids. 

The study, "Male Microchimerism in the Human Female Brain," was published yesterday in the online journal PLOS ONE.

This article available online at:

http://www.theatlantic.com/health/archive/2012/09/study-having-a-male-child-leaves-male-dna-in-womens-brains/262921/