risk (DeMeo et al, 2009). Indeed, evidence points to the presence of multiple independent polymorphisms associated with nicotine dependence (Saccone et al, 2010a, 2010b). GWAS meta-analyses have identified four additional loci associated with nicotine dependence (The Tobacco and Genetics Consortium, 2010; Thorgeirsson et al, 2010). Two of these loci map close to additional nicotinic receptor subunits (CHRNA6 and CHRNB3) and to enzymes important for the metabolism of nicotine (CYP2A6 and CYP2B6).
