Male DNA discovered inside female brain
Researchers also find that women with Alzheimer's possess less nucleic acid from opposite sex
Male DNA has been found inside the female brain and researchers say it most likely got there from cells from a pregnancy with a baby boy. Male DNA had earlier been discovered in women's blood, bone marrow, liver and other tissues from male fetal cells, but this is the first time it has been found in the brain.
Photograph by: Matt Cardy, Getty Images Files , Postmedia News
Male DNA has for the first time been found inside the female brain, according to new research led by a Canadian scientist.
No, the finding doesn't explain why women sometimes know what their husbands are thinking.
But it could lead to refining what "the self," biologically speaking at least, really means.
Plus, in an unexpected finding, the researchers found women with Alzheimer's disease had less male DNA in their brains - and in lower concentrations in the brain regions most affected by the memory-robbing disease - than women without Alzheimer's.
Observers said the finding also raises the hypothesis that, if male DNA can infiltrate a woman's brain, it might have some "masculinizing" effect on the female brain.
And, if that's so, "what consequences does this have on how the brain functions - in other words, thinking and behaviour?" said neuroscientist Dr. Sandra Witelson, a professor in the department of psychiatry and behavioural neurosciences at the Michael G. DeGroote School of Medicine at McMaster University in Hamilton.
Appearing in the latest edition of the journal PLOS ONE, the study is the first to describe the presence of male "microchimerism" in women's brains.
Microchimerism is the "intermingling" of small numbers of cells or portions of DNA in a person or animal from a genetically different individual.
In this case, the male DNA found in women's brains most likely came from cells from a pregnancy with a baby boy.
But women can acquire male DNA without ever having a son. In women without boys, male DNA can come from sharing her mother's womb with a male twin, from a non-irradiated blood transfusion and possibly even from an older sibling.
During pregnancy, cells are exchanged in both directions, from mother to fetus, and fetus to mother. After birth, women retain a small number of fetal cells. Although it hasn't yet been reported, the cells from an earlier pregnancy might be passed along with the maternal cells that reach a fetus in a later pregnancy.
Other scientists had already found evidence of male microchimerism in the blood, bone marrow, liver and other tissues of women from fetal cells exchanged between mother and baby via the placenta.
But until now, no one had ever looked at whether the cells could cross the blood-brain barrier, and live in the human brain, potentially for decades.
According to the researchers, "male microchimerism is frequent and widely distributed in the human female brain."
Whether this is a good thing or bad isn't yet clear. "Currently, the biological significance of harbouring male DNA and male cells in the human brain requires further investigation," lead author Dr. William Chan, of the department of biochemistry at the University of Alberta, said in a statement.
Nevertheless, "this is the first evidence that microchimerism can cross the blood-brain barrier to establish male fetal cells in the human female brain," he said.
For their study, the scientists examined brain autopsy specimens from 59 women who had died when they were between the ages of 32 and 101. Thirty-three women had Alzheimer's disease; 26 were free of Alzheimer's.
In all, 63 per cent of the women tested - 37 of 59 - harboured male DNA in multiple brain regions, and the cells appear to persist "across the human lifespan," according to the researchers.
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