Recent research has uncovered that a child’s brain may harbor cells containing the mother’s DNA, which can persist for decades.
According to survey results shared on the preprint database BioRxiv, a June 10 paper—yet to undergo peer review—adds to the accumulating evidence that mothers and fetuses exchange cells during pregnancy, a phenomenon termed “microchimerism.” Prior studies have indicated that mothers also possess cells containing their child’s DNA in their brains.
This discovery is significant for several reasons, as noted by Amy Boddy, co-director of the Microchimerism, Human Health and Evolution Project at UC Santa Barbara, who was not part of the study. Previous research primarily detected maternal microchimerism in infancy blood samples, she stated in an email to Live Science. “What’s intriguing is that this is based on tissue rather than blood, using real human data instead of animal models, and employs cutting-edge methodology.”
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More broadly, Boddy stated, the study reinforces that microchimerism is a “normal process in mammalian biology.”
Investigating Maternal Cells in the Brain
Prior to this research, limited evidence was available regarding microchimeric cells in mothers’ brains due to challenges in obtaining human brain tissue and DNA samples from both parents and children.
To address this issue, Sami Kanaan and his team at Fred Hutchinson Cancer Center in Seattle examined brain tissue surgically removed from children with severe epilepsy as part of their treatment. The study included patients aged from 28 days post-birth to 19 years old at the time of surgery, with mothers providing DNA samples via cheek swabs.
Kanaan’s group employed quantitative PCR to locate and quantify maternal cells amidst the millions of cells present in each child’s brain.
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Of the 37 mother-child pairs examined, 26 children (approx. 70%) exhibited maternal cells in their brains. These cells were present in various brain regions, namely the frontal, temporal, and parietal lobes, as well as the hippocampus. Each brain sample contained roughly 2.2 maternal cells per 100,000, with one hippocampal sample revealing 459 maternal cells per 100,000. Notably, 11 children’s brains showed no evidence of maternal DNA.
Professor Boddy remarked, “This method has limitations in detecting rare cells at low frequencies, so the actual prevalence is likely underestimated.”
Interestingly, firstborn children seem to have a higher likelihood of possessing maternal cells in their brains. Of those with maternal cells, 14 were firstborns, whereas of the children lacking these cells, only one was a firstborn.
Utilizing single-nuclear RNA sequencing, which helps reveal cellular functions by identifying active genes, researchers found that the maternal cells were differentiating into multiple brain cell types. These cells may have originated as white blood cells and stem cells, potentially transmitted via the placenta during pregnancy or breastfeeding.
The transformed cells included neurons, oligodendrocytes producing protective sheaths around neurons, astrocytes supporting various brain functions, microglia acting as the brain’s immune cells, and endothelial cells lining blood vessels.
“Leveraging single-nuclear RNA sequencing to identify the types of maternal microchimeric cells is remarkable,” Boddy noted. “Our understanding of these cells’ functions has been quite limited until now, but studies like this, using novel techniques, are enhancing our insights.”
During pregnancy, the mother and fetus exchange cells—a phenomenon known as “microchimerism.”
(Image credit: Rhenizara S, via Getty Images)
Examining Healthy Brains
To assess if these findings extend to individuals without epilepsy, the researchers analyzed brain anatomical data from 29 individuals with unknown neurodevelopmental status, spanning from 22 weeks of gestation to age 40. They also evaluated brain tissue from three elderly men in their late 80s to early 90s, originally collected for Alzheimer’s research.
Ultimately, the study found foreign cells in 25 of the 32 participants, approximately 78%, including in the brains of elderly men in their 90s.
While researchers suspect these cells originated from the mother, confirmation was not possible due to the absence of maternal DNA. The foreign cells might have come from a twin, older sibling, past pregnancy, miscarriage, or in rare instances, a maternal grandmother.
Similar to epilepsy patients, these cells had differentiated into various functional brain cell types. In younger brains, they predominantly manifested as specific neurons, whereas in older brains, maternal cells were more likely to become microglia.
Considering the distinct roles of these microchimeric cells, understanding their diversity and origins—whether maternal, from an older biological sibling, or maternal grandmother—could yield intriguing insights, according to Dr. Sing Sing Way, a microchimerism researcher at Cincinnati Children’s Hospital Medical Center, who did not participate in the study.
The research uncovered that maternal cells diminish with age, yet they never completely vanish.
Boddy articulated that most of these findings prompt new inquiries. “Could microchimeric cells be necessary to ‘assist’?” she wondered. “Does diversity among brain cells hold significance, or is it merely a byproduct of being a placental mammal?”
Given the commonality of microchimeric cells, Boddy speculates they “might play vital roles in the brain, and understanding their function could be crucial for grasping healthy brain development.”
Through the application of new analytical methods to identify microchimeric cells, this study “has pushed the boundaries” of previous research. However, future studies would benefit from larger, more homogeneous datasets, suggested Wei. This entails gathering more brain biopsies, analyzing a greater number of cells in each sample, capturing specimens across a range of ages, and sampling similar brain regions among individuals to enhance comparative results.
This article is intended for informational purposes only and does not constitute medical advice.
Kanaan, S. B., McDonough, A., Gentil, C., Ojeman, J., Haynes, H., Beboudi, R., Eisenberg, D. T. A., Furlan, S. N. D., Rutledge, J., Urselli, F., Weinstein, J. R., and Nelson, J. L. (2026). Microchimerism, quantitative assessment, and mononuclear profiling establish cell type and diversity in the human brain. BioRxiv.
Source: www.livescience.com