Association of the Lactose Intolerance–Related Variant MCM6 rs4988235 With Breastfeeding Duration in Individuals From the Volga–Ural Region

Primary lactose non-persistence (LNP, hypolactasia) represents an autosomal-recessive condition, which is mainly attributed to the presence of the ancestral C-allele in the MCM6 -13910C>T (rs4988235) variant regulating the expression of the lactase (LCT) gene in individuals of European ancestry. Since the studies linking lactose intolerance C-allele and caloric accumulation, as well as gastrointestinal symptoms remain ambiguous to date, we decided to examine for a possible relation between the rs4988235 lactose intolerance allele and certain health parameters (body mass index, waist circumference, breastfeeding duration, and existing gastrointestinal tract diseases) in individuals (N = 2912) from four regions of the Volga-Ural region (VUR), i.e., Sverdlovsk Oblast, Republic of Bashkortostan, Chelaybinsk Oblast, and Udmurt Republic. In addition, we sought to clarify the genotype and allele frequencies of the MCM6 rs4988235 in the large sample from the VUR based on territorial and ethnic specificity. While examining a relation between several health conditions and the MCM6 variant, we determined a link between the rs4988235 CC genotype and prolonged breastfeeding duration (more than 1 year) in the total sample (OR = 1.63, 95%CI 2.32–5.88, p = 0.005) and in Russians (OR = 1.75, 95%CI 2.85–4.16, p = 0.024), which became more significant in individuals with a full-term period of gestation (more than 36 weeks) (OR = 1.67, 95%CI 1.13–2.45, p = 0.009) and was positively associated with higher birth weight (β = 3.11, p = 1.8x10^-3). Findings obtained point to a compensatory effect of prolonged breastfeeding on diminishing manifestation of genetically predisposed primary hypolactasia.