Rare coding variants in OPRM1 were assessed for their contribution to risk for addiction to heroin and cocaine. Our findings show that rs62638690 is associated with drug addiction in EAs, as the minor allele is found at a higher frequency in controls (0.38% vs 0.79%). Therefore, the common allele of rs62638690 may increase risk for drug addiction (OR=0.47). However, the finding needs to be replicated in an independent cohort in order to confirm its association with addiction. The function of rs62638690 has previously been determined by stably expressing MOR carrying the rs62638690 (192F) variant in HEK293 cells. When expressed on a MOR-1A (lacking the 12 amino acids encoded by exon 4) background, a reduced potency for [D-Ala2,N-MePhe4,Gly5-ol]enkephalin (DAMGO) and morphine was observed [31].
