Seppo AE, et al. - Researchers investigated the association of maternal probiotic supplementation with human milk oligosaccharides (HMOs) concentrations. HMOs are a major substrate for infants’ gut microbiota and affect the maturation of the intestinal mucosal immune system. Throughout lactation, changes in HMO abundance were noted. Depending on the mother’s Secretor and Lewis blood groups, the synthesis of HMOs involve the fucosyltransferases FUT2 (the Secretor gene) and/or FUT3 (the Lewis gene). This heterogeneity suggests nonexposure of some breastfed infants to certain structures, which may affect their microbiome composition and thereby disease risk for illnesses in which gut microbiome plays a role. Infants fed by mothers who lack a Secretor gene, lack a functional FUT2 enzyme and all α-1-2-fucosylated oligosaccharides and thus have delayed development of bifidobacteria-laden microbiota. Also, a higher risk to manifest IgE-associated eczema was noted among these infants if are born via cesarean delivery. Certain HMOs are noted to be associated with protection against cow-milk allergy in infants.