Genetic variation in nicotine metabolism also plays an important role in cigarette consumption (93, 116) and nicotine dependence (8). Conversion of nicotine to cotinine typically accounts for 70%–80% of nicotine metabolism, the majority of which is catalyzed by the cytochrome P450 2A6 (CYP2A6) enzyme (67). Recent GWAS meta-analyses using subjects of European descent identified SNPs in the region of CYP2A6 associated with CPD (124, 124a).
