OPRK1 and alcohol dependence: Allelic variations in the KOR (Oprk1) and prodynorphin (Pdyn) genes are associated with alcohol dependence (Flory, Pytte, Hurd, Ferrell, & Manuck, 2011; Karpyak et al., 2013; Xuei et al., 2006), and constitutive KOR knockout mice exhibit a decrease in ethanol preference compared to wild‐type mice (Kovacs et al., 2005).