beta-endorphin, dynorphin, leu-enkephalin, rimorphin, and leumorphin. These endogenous opioids are ligands for several different subtypes of opioid receptors; the proteolytic product, dynorphin, has been studied most extensively, which binds to the kappa opioid receptor (OPRK1). A recent paper reported an association of the PDYN gene with alcohol dependence and the propensity to drink in negative emotional states. Further an association of a PDYN variant with drinking to avoid emotional or somatic discomfort was also reported (Karpyak et al., 2013; Preuss et al., 2013).
