Analyses in the individual cohorts were adjusted for sex and principal components for genetic ancestry. In total, meta-analysis included 3,397 subjects for the age at smoking initiation phenotype. Lambda inflation factors were between 0.986 and 1.019 for individual cohorts (table 1), and 1.002 for meta-analytic p values (see online supplementary figure 1 for a Q-Q plot of meta-analysis). No SNPs showed meta-analytic association p values below the genome-wide significance level. Numerous SNPs in the intergenic region on chromosome 2q21 and in the region between BCL2-antagonist/killer 1 (BAK1) and Zinc finger and BTB domain containing 9 (ZBTB9) on chromosome 6p21 were associated with age at smoking initiation at a suggestive significance level (figure 1 and online supplementary table 1). In total 24 SNPs were associated with age at smoking initiation with p<10−5 in the meta-analysis (online supplementary table 1).
