Pairwise LD estimates were listed in Table 3, with D' listed below the diagonal and r2 above the diagonal. These analyses indicated that there was only one LD block, covering markers 6–11. From markers 1 to 4, most pairwise LDs were low. However, several markers, i.e., 1, 3 and 5, or rs1799971, rs524731 and rs9479757, were in high LD with markers 6–11 individually. Based on this LD structure, we conducted multi-marker haplotype analyses using only the markers showing substantial pairwise LDs. The markers included in these analyses were markers 1, 3, 5, and 6 to 11. Of these analyses, several combinations reached or approached nominal significance. The most significant combination was combination 5-6-7 or rs9479757-rs2075527-rs10485057, with global P values of 0.0021 and 0.0514 for SI and ND respectively, Table 4. In this combination, there were two haplotypes contributing to elevated risks to tobacco smoking: Haplotype 1-2-1, or G-C-A, had a frequency of 0.363 in the regular smokers and that of 0.307 in the non-smokers (P = 0.0373), and haplotype 1-2-2, or G-C-G, was observed only in the regular smokers (frequency
