Could a genetic mutation make breastfeeding harder?

Zinc, an essential trace element, plays an important role in a woman’s ability to successfully breastfeed her child.

While studying that link, researchers have found that a genetic mutation in a specific zinc-related protein could cause some breastfeeding problems in certain women.
Biology behind some breastfeeding issues?

It has long been known that zinc is passed to infants through mother’s breastmilk. The levels of zinc in mother’s milk and the effects of zinc deficiency in infants have been previously studied, but the role of zinc in breast development and function in lactating mothers is a relatively new area of research.

baby breastfeeding“It is believed that ‘breast is best,’ but breastfeeding is hard to do,” says Shannon L Kelleher, associate professor of cellular and molecular physiology, Penn State College of Medicine. “We believe that there is biology behind some breastfeeding issues. If we can identify women who will have trouble with breastfeeding while they’re still pregnant [by identifying genetic mutations in their ZnT2 proteins], then maybe we can help them better prepare before the baby comes.”

If zinc is not transported by ZnT2, its absence impacts milk composition and volume. The researchers found that along with insufficient zinc levels in breastmilk, mice without ZnT2 had significantly reduced beta-casein, fat and lactose in their milk. All are important for sustaining infant health. These mice were also unable to produce an adequate volume of milk for their offspring.

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“We really need to better understand the biological factors of lactation,” says Kelleher. “Seventy-five percent of mothers intend to breastfeed when they leave the hospital. Six months later, only 14 percent are still exclusively breastfeeding.”

Zinc and breastmilk: The genetic mutation

The protein ZnT2 transports zinc in specific tissues in the body, including the mammary glands. Kelleher and colleagues have previously found that some women have mutations in ZnT2, and that when the protein does not function correctly, breastmilk will have very low amounts of zinc, which can cause severe zinc deficiency in exclusively breastfed infants. Their recent research on mice suggests that ZnT2 mutations may also cause other deficiencies in breastmilk and may create difficulty for breastfeeding in general.

“This finding changes the paradigm,” says Kelleher. “It is no longer only about transporting zinc into milk, but now it’s also about milk composition and milk production.”

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The researchers studied the function of ZnT2 by observing the development of mammary glands in mice — both with and without functioning ZnT2 — reporting their results in the Journal of Biological Chemistry. The group of mice lacking ZnT2 showed reduced mammary gland development and severe defects in function during lactation.

ZnT2 transports zinc by importing it into vesicles — small organelles within the cell — that then secrete zinc into the breastmilk. Zinc is also necessary to trigger the growth of mammary glands, mammary epithelial cells and secretion pathways. Kelleher and colleagues found that without functional ZnT2, zinc accumulates in the cytoplasm, becoming toxic to the cell.

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In the future, Kelleher hopes to sequence the gene that codes for ZnT2 in women to figure out how lactation is affected, and how to help pregnant and lactating women who have ZnT2 mutations.



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