The most studied OPRM1 variant is the non-synonymous (changing an amino acid) variant rs1799971 (118A>G, Asn40Asp) that was shown to remove a potential N-glycosylation site in the extracellular domain, to be more potent in beta-endorphin binding, and to reduce receptor signaling efficacy (Bond et al. 1998). The 118G allele is common in persons of European (15–30%) and Asian ancestry (40–50%), and has lower prevalence in African Americans (AA) (1-3%) (Deb et al. 2010; Gelernter et al. 1999). The variant 118G allele is not found in the African HapMap population (Yoruba, Nigeria), suggesting that it arose after the ‘out-of-Africa’ migration (Cavalli-Sforza and Feldman. 2003).
