(10-19) in humans have implicated genes encoding opioid receptors (OPRM1, OPRD1, and OPRK1), potassium channels (KCNG1 and KCNG2), and others as contributing to heroin/opioid addiction phenotypes. In supporting the biological plausibility of the candidate genes, particularly genes in the opioid system (20), knockout mouse models have been used to study behavioral effects resulting from genetic perturbations. However, conclusively identified associations of specific genetic variants remain elusive.
