Other genetic loci implicated by GWAS in smoking behavior include the cyto chrome P450, family 2, subfamily A, polypeptide 6 (CYP2A6). The CYP2A6 enzyme converts nicotine to cotinine and accounts for 70% of initial nicotine metabolism. Functional polymorphisms within CYP2A6 have been associated with number of cigarette smoked per day. Variation within the dopamine β-hydroxylase (DBH) gene has been associated with smoking cessation.111
