What's That Doing in My Head?
Schaffer, Amanda, Newsweek
Byline: Amanda Schaffer
Scientists find male DNA lurking in women's brains.
In case any doubt remained that guys get into girls' heads, for the first time scientists have found male DNA in the human female brain. Researchers at the Fred Hutchinson Cancer Research Center in Seattle examined dozens of women's brains and discovered that the majority of them contained genetic material found only on the Y chromosome.
This material almost certainly isn't found in girls' genomes when they're born (except in cases of rare genetic abnormalities). So when material from the Y chromosome is found in women's bodies, a phenomenon more broadly called microchimerism, scientists suspect that it somehow got in later on. But how?
The most likely explanation is that during a pregnancy cells from a male fetus slipped across the placenta, circulated in the mother's body and lodged in her brain. In the new work, made public in September in the journal PLOS ONE, J. Lee Nelson, an immunogeneticist, and her colleagues examined autopsy specimens from 59 women and found that 63 percent of them had male genetic material in their brains. (Cells from a female fetus can also slip in, but they are harder to detect in the mother, hence the focus on sons.) Even for those who've never given birth to sons, a pregnancy that ended in abortion or miscarriage can also lead to microchimerism. (So can blood transfusions of nonirradiated blood, as trauma victims sometimes receive, and so can having a twin, including one that disappeared in utero.)
While microchimerism has been found in other parts of the body, the discovery extends the phenomenon to the human brain. And it energizes many questions about how this curious mix of self and other functions in our bodies--and how its presence in such a crucial and sensitive organ might differ. To start with, researchers are not sure how, exactly, fetal cells or genetic material is tolerated by the mother's immune system, which can go into attack mode when foreign or semiforeign material enters the body. Researchers also wonder how the new cells manage to stick around for so long and in what form: the oldest subject in the autopsy study was 94, meaning that male DNA that arrived during pregnancy could have been there for more than half a century.
Most importantly, they puzzle over whether this semiforeign material is detrimental or beneficial to the host mother. "The question," explains Diana Bianchi, a reproductive geneticist and professor at Tufts University School of Medicine, "is whether it is helping or hurting." And as the burgeoning literature on autoimmune diseases, cancer, and tissue injury and repair suggests, the answer is probably some of both.
On the negative side of the ledger, studies now suggest links to autoimmune diseases, like scleroderma, lupus, and in some cases rheumatoid arthritis, a disorder in which the joints become inflamed, causing pain and decreased mobility. Rheumatoid arthritis (like scleroderma and lupus) is known to affect more women than men. It also has a strong genetic basis. But there are women who suffer from this form of arthritis who do not have the most common genetic risk factors. …