To scrutinize whether previously identified smoking‐related genes affect the transitions in the Finnish sample, we investigated common variants (MAF > 5%) surpassing our quality control thresholds from seven relevant gene regions (CHRNA5‐CHRNA3‐CHRNB4 gene cluster, CYP2A6, DRD2, DRD4, DBH, CHRNA4, and BDNF). Multiple SNPs in each gene region were nominally associated (P < 0.05) with at least one of the transitions (Table S3) although some well‐known SNPs, such as rs16969968 in CHRNA5, showed no association (P > 0.05) with the transitions, although suggestive association was detected with CPD (P = 0.012) and FTND (P = 0.0001). Furthermore, SNPs in DBH were involved in all four transitions, and rs6011794 in CHRNA4 was associated with initiation (P = 0.0469), tolerance (P = 0.0217), and cessation (P = 0.0331). Rs2086484 in CHRNB4, rs1611121 in DBH, and seven SNPs (rs144298540, rs62206942, rs117589312, rs59073906, rs58253278, rs112265183, and rs116920489) in CHRNA4 showed evidence of association with two transitions. Two SNPs (rs7260629 in CYP2A6 and rs75298795 in BDNF) associated with initiation (P = 2.45e‐03) and tolerance (P = 2.42e‐03), respectively, with P‐values surpassing the significance thresholds (P = 2.94e‐03 and P = 2.78e‐03, respectively) based on the modified Bonferroni correction.
