Since genotype data was not available from the International HapMap Project public database[82] at the time this study was conceived (October 2004), seventeen single nucleotide polymorphisms (SNPs) in or near the OPRM1 locus were selected from the Applied Biosystems SNP database [83]. SNPs were initially chosen to be evenly distributed across OPRM1 with an average intermarker spacing of 5,133 bp. Assays for three SNPs (rs561720, hCV32237184, rs3798687) failed and were excluded from analyses. One SNP, rs12333298 in intron 1, showed significant (p = 0.018) deviations from Hardy-Weinberg equilibrium (HWE) at a p < 0.05 level and was also dropped from further analyses. The locations of the thirteen remaining SNPs typed in the study are shown in Figure 1 and SNP information, including the observed minor allele frequency (MAF), is described in Table 1.
