For the first time, researchers have found that DNA from fetuses can migrate into a mother's brain and stay there for years, LiveScience reports. The process of mothers and fetuses exchanging cells, known as microchimerism, has been observed in the past, but until now scientists had only found evidence of fetal cells entering the actual brains of mice, not humans. Typically, a blood-brain barrier keeps things from entering the brain, but the barrier relaxes during pregnancy.
Scientists analyzed women's brains after death, and found that almost two-thirds had traces of male DNA, which must have come from their sons. And it can apparently stay there for a while, as one 94-year-old still had traces. It's not yet clear whether this phenomenon is helpful, harmful, or both. Investigators did find that women with Alzheimer's were less likely to have the male chromosomes in their brains, and previous research has suggested the disease is more common in women who had many pregnancies than in those with no children.