More than 100 SNPs in the human OPRM1 gene have been identified, some of which have been tested for associations with a range of substance dependence [14-19]. Most studies focus on analyzing the variants in coding regions or 5' UTRs. The Asn40Asp variant or rs1799971 is one of the most studied polymorphisms in the gene. However, the results are not consistent. Of the studies conducted for the gene, many do not have comprehensive coverage. In this study, we use haplotype-tagging approach to select SNPs and carry out association analyses for both individual markers and haplotypes. Our results indicate that a major haplotype may be involved in tobacco smoking.
