the genotyped proxy SNPs in the CYP2A6 locus confirmed our analysis on imputed SNPs with respect to lifetime average CPD. The lack of convincing association for the proxy SNP rs7251418 with current CPD may be explained by the relatively smaller sample size in this analysis, and incomplete LD between the target and the proxy SNPs. Previous GWAS suggested that other genes may be associated with CPD in the 19q13 region, yet we observed no nominally significant associations for EGLN2, RAB4B and CY2B6.
