mu-opioid receptor, such as stress responsivity and pain perception. Processes related to abnormal stress responsivity, such as alcohol and opioid addictions, were found to be associated with genetic variation at the mu-opioid receptor even though these are very distinct disorders (reviewed in (44, 45), Supplementary Table 1, 3). Several studies, including those in the relatively non-admixed populations of central Sweden and the Han Chinese, have shown that the Asn40Asp variant is associated with opiate addiction, and one study has shown that it is also associated with alcoholism, although negative studies have also been reported ((44), Supplementary Table 1, 3). Of particular pharmacogenetic and clinical significance is that the presence of one or two copies of this variant predicts favorable outcome to treatment of alcoholism with naltrexone, a selective opioid antagonist (47).
