We examined the sequence of the OPRM1 promoter region for genetic variants that may alter CpG sites, and, therefore, may influence our results. The dbSNP database (www.ncbi.nlm.nih.gov/SNP/index.html) was searched for SNPs (single-nucleotide polymorphisms) located in this region. We found nine SNPs (rs17174638, rs9282814, rs9282815, rs9282816, rs41292890, rs35174096, rs1799972, rs62436460, and rs1799973). Of these, three SNPs (rs41292890, rs1799973, and rs9282816) could alter CpG sites. rs41292890 is a C to a T transition at the −25 CpG, and rs1799973 is a G to A transition at the +23 CpG. Neither of these SNPs has been validated and they are extremely rare. rs9282816 is a G-T transversion at the −32 CpG site. This SNP is rare; it has not been found in Caucasians or Hispanics, and has a minor allele frequency of 0.021 in African-Americans. This SNP does not affect our findings, as we did not find any significant results with the −32 CpG site.
