Several early association studies (e.g, Franke et al. 1999) that focused on coding OPRD1 SNPs in small samples produced largely negative findings. A more recent examination (Zhang et al. 2008) of opioid and other substance dependence observed significant opioid dependence risk associated with rs1042114, a coding SNP in OPRD1, but not with other OPRD1 or OPRK1 SNPs. Another investigation (Levran et al. 2008) that had a larger sample (N=412) of heroin dependent cases and used Goldman’s “addiction chip” (Hodgkinson et al. 2008) reported putative association with three SNPs in OPRD1 and one in OPRK1.
