Many things affect the composition of breast milk: what a lactating woman eats, how long since she gave birth, even the time of day. Now, new research by Kelsey Johnson of the College of Biological Sciences, Ellen Demerath of the School of Public Health, and colleagues characterizes yet another important one—mom’s genetic makeup. The research, the first ever to analyze the genetic factors that influence gene expression in human milk cells, not only shines light on how genetics affect human milk, but also opens the door to new insights for ensuring babies get the best nutritional start possible in the early months of life.
“Our goal was to better understand the basic biology underlying variation in human milk and lactation, and how it may influence normal infant development,” says lead author Kelsey Johnson, a postdoctoral fellow in the Department of Genetics, Cell Biology and Development. “Our results show how an improved understanding of the genetics and genomics of human milk can connect lactation biology with maternal and infant health.”
In the study, published September 11 in Cell Genomics, Johnson, Demerath, and colleagues analyzed both genotype and gene expression differences in milk for hundreds of healthy mother-baby pairs. They looked at what genes are active in cells found in the milk and how that relates to maternal traits, the composition of the milk, and the baby’s gut bacteria.
“It reveals that hundreds of components of human milk are driven by genetic differences in women,” says Demerath, Distinguished McKnight University professor in the School of Public Health.
Importantly, the researchers discovered that the mother’s genetic makeup plays a big role in determining levels of key beneficial components of milk. In particular, they discovered many new genes involved in the synthesis of human milk oligosaccharides (HMOs), sugars the baby can’t digest but that contribute to the growth of beneficial bacteria in the baby’s digestive tract.
The team also found surprisingly strong gene expression signals that are not characteristic of the mammary epithelial cells that synthesize milk, but rather of immune cells, like macrophages and neutrophils. It isn’t clear exactly what those immune cells might be doing in the mammary gland, but the researchers found that their expression of pro-inflammatory proteins like IL-6 varied a great deal between women. Infants that consumed milk that was high in IL-6 had lower abundance of health-promoting “good” bacteria in their digestive tract. This shows that infant gut health can be impacted by the precise breast milk recipe they are receiving from their mother, and that the mother’s genetics are a big determinant of that—not only in terms of the level of different HMOs, but of many other milk components as well.
Next, the researchers aim to extend their findings to include larger numbers of mother-infant dyads and by conducting deeper milk composition analysis, including quantifying levels of lipids involved in healthy brain development. Ultimately, they hope that a deeper understanding of the complex biology of human milk and exactly what features are most important for infant health will yield better and more precise recommendations on its use as baby’s first food, especially for sick and preterm infants who need it most.
The University of Minnesota is a leader in understanding mother’s milk and how it affects mom’s and baby’s health. For more information, see the Human Milk and Nutrition Research Group.
This article was written by Mary Hoff and originally appeared on the College of Biological Sciences website
