Three association studies of OPRL1 and drug addiction were reported. In the first study, 10 SNPs covering OPRL1 (and RGS19) were analyzed and no association was found with alcohol addiction or illicit drug dependence. Two intronic SNPs in high LD (rs6512305 and rs6090043) were marginally associated with OD in a small subsample of 83 affected subjects (Xuei et al. 2008). In the second study, 15 SNPs were analyzed and one SNP (rs6010718) showed an association with AD (Huang et al. 2008). A haplotype of five tag SNPs TTTGC (rs6090043, rs6010718, rs7271530, rs2295448, and rs6089789) was significantly more common in cases than in controls (Huang et al. 2008). In the third study of five SNPs in three ethnicities (EA, AA and His), association of two SNPs in the 5′ flanking region (rs6090041 and rs6090043) with vulnerability to develop heroin addiction was reported in EA only, and a haplotype was associated with heroin addiction in AA and EA (Briant et al. 2010). No association with heroin addiction was detected for six SNPs (including rs6512305, rs6090041 and rs6090043) in a larger cohort of
