In a study of Western Europeans, Gerra et al. [59] genotyped 106 heroin-dependent subjects and 70 healthy controls for a silent mutation on the OPRK1 gene. At the rs1051660 SNP, there was a significantly higher frequency of the G allele among controls compared to cases, and the T allele was present in higher frequencies among heroin-dependent subjects (Fisher’s exact = 0.044, Pearson χ2 = 4.2734, P = 0.039) [59]. Yuferov et al. [80] examined 12 SNPs in the OPRK1 gene in African American, Caucasian, Hispanic, Asian-American, and mixed ethnic groups and reported that the rs1051660 SNP displayed slightly higher frequencies in all of the subjects with opioid dependence combined (P=0.016). In the Hispanic group, haplotype analysis revealed two combinations of OPRK1 SNPs that were significantly associated with opioid dependence (AGCTCGTC and GGCGTGCC haplotypes) [80].
