Researchers have discovered that children's brains can contain cells with their mother's DNA and that these cells can persist for decades.

The findings, which were posted to the preprint database bioRxiv June 10 but have not been peer-reviewed yet, are part of a growing body of work showing that a mother and fetus exchange cells during pregnancy — a phenomenon known as "microchimerism." Previously, scientists had found that a mother's brain harbors cells with her children's DNA.

The findings are important for several reasons, said Amy Boddy, co-director of the Microchimerism, Human Health and Evolution Project at the University of California, Santa Barbara, who was not involved in the study. Past work mostly found evidence of maternal microchimerism in infancy, and in blood samples, she told Live Science in an email. "What's exciting here is that it's tissue, not blood; it's real human data, not an animal model; and the methods are cutting-edge."

More broadly, the work reinforces the idea that microchimerism is "a normal process of mammalian biology," Boddy said.

Hunting down maternal cells in the brain
Before this study, there was sparse evidence for maternal microchimeric cells in brains, mostly because it is hard for researchers to get samples of human brain tissue and DNA from both parents and their children.

To overcome this challenge, a team led by Sami Kanaan, a staff scientist at the Fred Hutchinson Cancer Center in Seattle, analyzed brain tissue that had been surgically removed from dozens of children with severe epilepsy as part of their treatment. The patients ranged in age from 28 days to 19 years at the time of their surgery, and their mothers provided DNA samples through cheek swabs.

Kanaan's team used a tool called quantitative PCR to identify and count maternal cells hiding among millions of cells in the children's brains.