OPRK1 contains four exons and is located on chromosome 8q11.2 (Yuferov et al. 2004). Twenty-seven SNPs are described in the coding sequence, out of which twelve are rare non-synonymous SNPs that alter an amino acid in the protein. Four synonymous SNPs that do not modify an amino acid but may have other functions (rs1051660 (36G>T), rs702764, rs16918875 and rs7815824) are common in at least one population. An indel of net insertion of 830 bp (rs35566036) was described at the 5′ flanking region (-1986 bp) and was shown to reduce transcription in transient transfection assays, in vitro (Edenberg et al. 2008).
