Alcohol dependence (AD) and nicotine dependence (ND) frequently co-occur in the same individuals. Alcohol and nicotine co-dependence may represent an independent phenotype. A large number of common risk genetic loci have been reported separately for AD and ND in the dopaminergic, serotoninergic, GABAergic, glutamatergic, cholinergic, opioid, and endocannabinoid systems by candidate gene approach; several genome-wide association studies (GWASs) on AD or ND reported other risk loci (summarized by [Zuo et al., 2011a; Zuo et al., In revision]). Only one study employed GWAS [Lind et al., 2010] to examine alcohol and nicotine co-dependence, and its results have yet to be replicated.
