OPRD1 contains 3 exons and is located on chromosome 1p36. Nine polymorphisms were identified in the coding region (four non-synonymous, three synonymous and one insertion), out of which only one SNP (921T>C, rs2234918) is common in several ethnicities. SNP rs1042114 (80G>T, Phe27Cys) is common mainly in Europeans, and the synonymous SNP rs118175398 was described in Asians. In addition, two SNPs were described in the 3′ UTR, out of which SNP rs4654327 is common in several ethnicities.
