Many female brains contain male DNA

In the first study of its kind, researchers have discovered that male DNA is commonly found in the brains of women – a finding that could hold important implications for diseases like Alzheimer’s disease and cancer.

Male DNA is likely transferred to female brains during pregnancy, according to researchers from the Fred Hutchinson Cancer Research Center in Seattle.  During this time, mothers and fetuses exchange and harbor genetic material and cells in a phenomenon called microchimerism.

This means, if a mother is pregnant with a boy, she will end up with male DNA in her system – potentially for the rest of her life. If the fetus is female, the mother will end up with genetic material from her daughter, though it is difficult for researchers to distinguish between two sets of female DNA in microchimerism studies.

What this means for treating diseases

Prior studies have observed fetal DNA in many other of the mother’s tissues and organs, but this is the first to confirm fetal cells can cross the blood-brain barrier and reside in the mother’s brain beyond pregnancy.

“We were interested in looking at the human brain because it’s never been looked at before, and it was really unknown if the cells of fetal origin could reach the brain,” study senior author Dr. Lee Nelson, a member of the Fred Hutchinson Cancer Research Center and professor of medicine at the University of Washington, told  Nelson and her colleagues performed autopsies on 59 brains of deceased females and detected male microchimerism in 63 percent of them.

Male microchimerism was distributed across multiple regions of the female brain, including those affected by dementia, and could persist for decades – potentially even an entire human lifespan.  According to the study, the oldest female with microchimerism detected in her brain was 94.

“The question naturally arises what role might the cells have in benefiting health and what role they play in diseases,” Nelson added.

The researchers hope further studies on microchimerism might shed new light on various diseases that affect the brain, such as Alzheimer’s, Parkinson’s or even brain tumors.

“These cells have access to the brain could help us understand different treatment options for diseases that aren’t well treated,” Nelson said.  “It’s a very exciting new area that opens up different possibilities, such as, what if these cells have anti-tumor potential?  For example, glioblastomas are deadly tumors, (which) have poor treatment options.  We’re very much in need of new potential options.”

The researchers also examined rates of Alzheimer’s disease in women with and without male microchimerism in their brains.  In previous studies, it has been suggested that Alzheimer’s may be more prevalent in women who have had children.  However, data from this study found the women who had been diagnosed with Alzheimer’s had lower rates, or concentrations, of microchimerism in their brains than those without dementia.

Studies of other tissues and organs have suggested both protective benefits and risks associated with male microchimerism in mothers.  In a study of breast cancer, male microchimerism appeared to play a protective role: Women with male DNA had a lower rate of the disease than those without.

But –  a colon cancer study showed the opposite: Mothers with microchimerism had higher rates of the disease.

Researchers have a theory behind the protective benefits of microchimerism: They believe the ‘outsider’ DNA may boost the capacity of the mother’s immune system to seek out and destroy antigens.

“The theory is because the cells persisting after pregnancy are half-genetically different, they have another small window to recognize antigens, or cells that are either malignant or pre-malignant,” Nelson said.  “They can look at the cells with a slightly different perspective.”

The researchers said the next steps are to further define the role of microchimerism in health and disease, and see if the fetal cells are able to differentiate into other cells and perform other functions in the mother’s body.

The study was published in the journal PLOS ONE.