The analysis of the total sample identified 4 SNPs: 1 for SI-1, 1 for SI-2, and 2 for ND, with p values < 10 −5 (Table 3). The analysis of the male sample identified 10 SNPs: 1 for SI-1, 5 for SI-2, and 4 for ND with p values < 10 −5 (Table 3). Among the total 14 SNPs identified, two overlapped. For these 12 SNPs brought to replication, the quality of genotyping was investigated through cluster plots, which revealed no evidence of genotyping error. Figure 1 shows the chromosomal plots and quantile-quantile (QQ) plots of the association signals for three smoking-related phenotypes. The values of genomic inflation factor λ (ranging from 0.97 to 1.01) and QQ plot of signals showed no evidence of the presence of population stratification in our discovery sample.
