Multiple SNPs in the 15q25.1 region have been shown to be associated with CPD, nicotine dependence, or risk of lung cancer [44], [47], [49], [50], [59]. We directly genotyped some of these SNPs and could impute others using the observed genotypes in PLCO and NHS samples and the phased HapMap CEU samples (Release 21). Imputation, restricted to the region of chromosome 15q23, was performed for each study separately using the Hidden Markov Model implemented in Mach 1.0 [62]. All of the imputed genotypes had high quality scores (R-squares>0.8 for 95% of SNPs in the region).
