findings in these analyses may be the result of analyzing only variants in OPRM1, and not OPRD1. The 118G allele was found to be protective against opioid dependence in a cohort of Malaysians, but this finding was not replicated in subsequent research [53, 58]. A118G and rs9479757 were also not significant in Han Chinese populations and no associations were found across 24 SNPs in two African American case-control analyses [57, 59-61]. In aggregate, these findings suggest that genetic variation in OPRM1 may affect susceptibility to opioid dependence in an ethnicity-dependent manner. In most ethnic groups, however, there is little evidence supporting an association between OPRM1 polymorphisms and opioid dependence. The statistical power of each study to detect relatively small effect sizes may also play a role in the conflicting results.
