Sons can permanently alter their mothers’ brain chemistry and may help defend against Alzheimer’s disease, a new study shows.
DNA received from a male fetus during pregnancy can remain in a woman’s brain throughout her life. Previous studies have discovered a condition called microchimerism, in which fetal cells persist in a mother’s blood and bones for decades. The residual DNA can help repair tissue and improve immune health, but may also cause autoimmune reactions.
At this time it is unclear whether male DNA helps prevent diseases like Alzheimer’s or some other factor is the cause. But studies on autopsied brain matter have found that women with Alzheimer’s were significantly less likely to have male DNA in their brains.
One question is how leftover fetal cells affect the brain. Researchers have shown that fetal microchimerism occurs in mouse brains, but they had not shown this in humans. So a team led by autoimmunity researcher and rheumatologist J. Lee Nelson of the Fred Hutchinson Cancer Research Center in Seattle, Washington, took samples from autopsied brains of 59 women who died between the ages of 32 and 101. By testing for a gene specific to the Y chromosome, they found evidence of male DNA in the brains of 63% of the women. (The researchers did not have the history of the women’s pregnancies.) The male DNA was scattered across multiple brain regions, the team reports online today in PLoS ONE.
Because some studies have suggested that the risk of Alzheimer’s disease (AD) increases with an increasing number of pregnancies, the team also examined the brains for signs of the disease, allowing them to determine whether AD correlated with the observed microchimerism. Of the 59 women, 33 had AD—but contrary to the team’s expectation, the women with AD had significantly less male DNA in their brains than did the 26 women who did not have AD.