Five SNPs (rs2236196, rs3787138, rs1044396, rs1044394 and rs6010918) across CHRNA4 were selected for genotyping. This included the 2 SNPs (rs2236196, rs1044396) that were associated with smoking behavior in previous studies (Feng et al., 2004; Li et al., 2005; Hutchison et al., 2007; Breitling et al., 2009). The proportions of HapMap Phase II common SNPs (MAF > 0.05) of CHRNA4 tagged using an r2 of 0.6 by the five SNPs are 0.83 and 0.80 for CEU and YRI, respectively. SNPs were genotyped with a fluorogenic 5’ nuclease assay method, i.e., the TaqMan technique, using the ABI PRISM 7900 Sequence Detection System (ABI, Foster City, CA, USA). For genotyping quality control, 8% of samples were re-genotyped with 100% concordance.
