In contrast to Bond et al’s study which did not detect the rs1799972 SNP in a Caucasian population [73], a prospective study of 282 opioid-dependent subjects of Indian origin found the minor allele frequencies of the rs1799971 and rs1799972 polymorphisms to be 31% and 17% respectively [72]. This study by Kapur et al [72] found an increased frequency of the rs1799971 variant in subjects with opioid dependence compared to controls (χ2 = 32.495, P < 0.0001; OR: 3.50; CI (95%) = 2.21-5.56), and there was no significant difference between the two groups with respect to the rs1799972 SNP (χ2 = 0.18, P < 0.67; OR: 0.79; CI (95%) = 0.35–1.79). A haplotype analysis found no association between the rs1799971 and rs1799972 SNPs and opioid dependence, therefore only the rs1799971 minor allele variant was associated with opioid dependence in the sample of Indian subjects [72]. The contrasting association of the rs1799971 SNP with opioid dependence in various ethnic groups is an important factor to consider in genetic association studies of multiethnic cohorts.
