Researchers from the Technion Institute have identified a zinc transporter mutation that causes zinc deficiency in the milk of breastfeeding mothers. The deficiency can lead to serious health problems and the study is paving the way for a genetic test that will identify mothers who will need to provide their babies with supplements.
The belief that breast milk is always the healthier option for infants is widespread. The World Health Organization suggests that “the vast majority of mothers can and should breastfeed, just as the vast majority of infants can and should be breastfed.” Even Gisele Bundchen has declared that there should be a “worldwide law” that requires new mothers to breastfeed for at least six months. But, as the researchers discovered, a certain mutation in some breastfeeding mothers could cause serious health problems in exclusively breastfed infants.
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Zinc: helping infants grow and develop
“Zinc is a mineral that plays an essential role in growth and development process, including the development of cognitive and motor functions of the brain as well as the proper function of the immune system and the skin. Thus, zinc is a highly essential mineral, particularly for infants as they undergo accelerated growth and development process,” explained Prof. Yehuda G. Assaraf who headed the research.
Many proteins in our body rely on zinc to function normally. Low levels can lead to rashes and dermatitis that have the appearance of severe burns. It can also lead to diarrhea, hair loss, loss of appetite and impaired functioning of the immune and nervous systems.
Inability to transport zinc
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During the breastfeeding period it is the zinc transporter-2 (ZnT-2) protein that delivers zinc from the mother’s blood to her breast milk. The researchers discovered that a mutation in the genetic code –the set of rules that determines how DNA and mRNA are translated into proteins– prevents the ZnT-2 protein from delivering zinc. “As a result, an infant who is exclusively breastfed, and who does not receive any food supplement, does not receive the appropriate zinc levels, which in turn leads to disease,” said Prof. Assaraf.
The research began with a referral to Sheba Medical Center of two infants who suffered from a variety of symptoms that included a severe, burn-like rash. Blood tests and breast milk analysis pointed to zinc deficiency. This led the researchers to examine each mother’s ZnT-2 gene sequence. “Every gene has two genetic components known as alleles – one originates from the father and the other from the mother,” described Prof. Assaraf. In both mothers one of the alleles was defective. Normally the second, healthy allele should have been enough for regular functioning, but in this case the transporter stopped working.
The study shed light on the issue with the discovery that the ZnT-2 transporter operates as a couple. This means that two identical ZnT-2 proteins couple together to create the active zinc transporter. When one of the proteins is impaired the transporter becomes inactive. That is, a single mutation, in either the paternal or maternal allele, is enough to hinder one of the proteins and shut down the zinc transporter.
This discovery paves the way for pre-pregnancy genetic screening in women to check for the defective gene. Those breastfeeding mothers who do will have to provide their baby with zinc-containing food supplements to avoid health problems. The researchers are currently examining the prevalence of ZnT-2 gene mutations.
Prof. Yehuda G. Assaraf is head of the Fred Wyszkowski Cancer Research Laboratory in the Department of Biology at the Technion. He headed the study along with a biology doctoral student, Inbal Lasry. They worked in collaboration with researchers from the Sheba Medical Center, headed by Dr. Yair Anikster, and with Prof. Shannon L. Kelleher of Pennsylvania State University. The findings were published in the Journal of Biological Chemistry.