All of these terms included the clusters of cholinergic receptors on chromosome 15 (CHRNA5-A3-B4) [5]–[10] and chromosome 8 (CHRNB3-A6) [8]–[10]. By virtue of the broad range of SNP significance analyzed, these genes were tagged in each of the 3 studies, whether or not the significant SNPs achieved genome-wide level (Figure 1; See Table S3 for the rs numbers of the SNPs tagging the genes in cholinergic receptor genes). In addition, several other cholinergic receptors were tagged by SNPs with more moderate p-values (<0.05) (Figure 1). CHRNA7 (chr. 15q14) [11] and CHRNA9 (chr. 4p14) were tagged in each of the three studies (Figure 1), suggesting that variants in these genes, are also implicated in the genetic susceptibility to smoking quantity. To determine whether the nicotinic receptor genes on chromosomes 15 and 8 drove the statistical significance of these terms we analyzed a reduced dataset that did not include these genes (i.e., we removed CHRNA5-A3-B4 and CHRNB3-A6 genes). Although there was a considerable difference in the significance, the terms GO:0005892, GO:0042166 and GO:0004889 showed p-values <0.05 for SAGE (i.e., 0.014, 0.02 and
