Second, most previous association studies of the CHRNA5/A3/B4 cluster were focusing on ND or related measures [14], [15], [19], [24], [25], although a few studies were focused on SI [23], [27] or SC [26], [46], [47]. Given the significant overlap of genetic underpinnings among these three smoking-related phenotypes [48], [49], it is of great interest to investigate these phenotypes systemically in one sample. This is especially true for the CHRNA5/A3/B4 cluster, as it has been associated with ND in several reports, especially in samples of European origin [14], [18], [19], [20], [21], [22], [23], [24], [25]. However, association of the variants of this cluster with SI and SC has not been well established. By analyzing the three major smoking-related phenotypes together in the Korean sample, we found significant associations of some variants in this cluster with the three smoking-related phenotypes at both the individual SNP and the haplotype levels.
