Bioinformatics resources and results from the International HapMap Project were used to identify tag SNPs (tSNPs) for the OPRK1 and OPRD1 genes. Specifically, Haploview v4.1 (Barrett et al., 2005) was used to conduct a search with the following parameters: (a) haplotype r2 cutoff = 0.8 and (b) minor allele frequency (MAF) of 0.2. Results of this search suggested two tSNPs for the kappa opioid receptor gene (rs997917, rs6985606) and eight tSNPs for the delta opioid receptor gene (rs760588, rs529520, rs2236856, rs499062, rs678849, rs4654327, rs508448, rs581111). Based on this search and the available resources, the following SNPs were assayed in addition to the A118G SNP of the OPRM1 and will be named in the manuscript as follows: OPRK1^1 (rs6985606), OPRK1^2 (rs997917), OPRD1^1 (rs2236856), OPRD1^2 (rs499062), OPRD1^3 (rs678849), OPRD1^4 (rs4654327), and OPRD1^5 (rs508448). For statistical power and data analytic purposes, participants were grouped into two genotype categories where the heterozygote group was combined with the homozygote cell with the lowest frequency (Table 1).
