Prior studies in humans have supported CHRNA4 as a susceptibility gene for nicotine dependence and other smoking behaviors. Genome-wide significant linkage signals have been observed in the chromosome 20q13 region containing CHRNA4 for maximum number of cigarettes smoked in a 24-h period74 and in the nearby chromosome 20q11 region for DSM-IV-defined nicotine dependence.75 Several candidate gene association studies have focused on CHRNA4.76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 Among the common SNPs with reported associations, only rs2236196 was associated in our study (P=0.027, Table 3): its minor allele (frequency=0.28) conferring increased risk for nicotine dependence, consistent with prior reports.76, 82, 83, 85, 86, 87 rs2236196 shows some linkage disequilibrium with rs2273500 (D′=0.86 and r2=0.50, Supplementary Figure 3). However, in a model including both SNPs, the association remained for rs2273500 (P=2.4 × 10−5) but not rs2236196 (P=0.79) in meta-analysis across our GWAS samples, indicating that our signal is distinct from the previously reported SNP association. rs2273500 was presented in one of our prior reports as having a suggestive, but nonsignificant, association with nicotine dependence
