CHRNA3 and nicotine dependence: Genetic factors, which are indicated in affecting nicotine dependence, include genetic variants of α3, α4 and α5 subunits of nicotinic receptors, which are encoded by CHRNA3, CHRNA4 and CHRNA5 genes, respectively (Saccone et al., 2007; Chenoweth and Tyndale, 2017).