Genome wide association studies (GWAS) and candidate gene studies of nicotine dependence have identified several variants in the gene cluster encoding the α5, α3, and β4 nicotinic receptor subunits on chromosome 15 that alter risk for nicotine dependence, including an amino acid substitution (aspartic acid to asparagine at codon 398) in the α5 nicotinic receptor subunit gene (CHRNA5) and several non-coding variants [8]–[15]. This evidence concerns the gene CHRNA5 and nicotine dependence.