Recent pathway- and network-based analyses of available candidate gene- and genome-wide- genetic association results of smoking and nicotine dependence indicated the importance of genes related to (1) drug metabolism (e.g., ADH1B, SULT1A1, ALDH2, CYP17A1, and CYP1A1); (2) synaptic transmission of cholinergic (e.g. CHRNB4, CHRNA1, CHRNA3, CHRNA5, and CHRNA7), glutaminergic (e.g., GRM7 and GRM8) and dopaminergic (e.g., DRD1, DRD2, DRD3, DRD4, and DRD5) systems, and (3) reuptake and vesicular packaging of neurotransmitters (e.g., SLC6A4, SLC18A2, and SLC9A9) related to learning and memory (Harari et al., 2012; Liu, Fan, Liu, Cheng, & Wang, 2015; Minica et al., 2017; Yang and Li, 2016; Begum et al., 2016). Consequently, genetic association studies of alcohol as well as nicotine dependence highlight the complex nature of addiction as an outcome with physiological aspects including drug metabolism and availability within the body and brain, as well as neurobiological mechanisms related to the development of addiction.
