The current study focuses on the opioid receptor, mu 1 (OPRM1) gene, the most widely studied candidate gene (17), which encodes a predominant target for heroin and other opioid molecules. The OPRM1 missense polymorphism rs1799971 has been widely studied for its functional consequences, including reduced signaling efficiency and reduced expression of the receptor (21-25). However, rs1799971 associations with heroin and other drug addictions (13-17) have been modest and often inconsistent. Additional OPRM1 single nucleotide polymorphisms (SNPs) have been tested for association with heroin/opioid addiction (10, 12, 13, 18, 19), but none of the findings have been independently replicated.
