As shown in Table S1, the allele frequencies of an array of genetic variants (e.g., rs7168796, rs16969922, and rs1979906, to name a few) located in CHRNA5/A3/B4 differ dramatically across ethnic and geographical populations (i.e., the Caucasian [CEU], African [YRI], and Asian [CHB, JPT, and Korean] samples). Therefore, this study provides an essential basis for genetic association analysis by comparing different frequencies of SNPs of this region between smoking and non-smoking populations to examine whether such associations are consistent in different ethnicities. Indeed, different genotype frequencies have been compared in smoking and non-smoking populations in different ethnic groups for several polymorphisms of CYP2A6 [51] as well as a 44-bp insertion/deletion polymorphism of the serotonin transporter (5-HTT) gene [52], and such studies may shed new light on what molecular variants have diverging effects, and what molecular variants have converging effects in populations of different ancestries. This approach is termed “cross-population contrast mapping” based on the hypothesis that important biological mechanisms underlying a disease of interest are shared by various human populations, although differences in allele frequencies at risk loci could result in
