Previously, we had reported other SNPs in smoking-related genes as NRXN1, DRD4, HTR2A, CHRNA3, CHRNA5, and CYP2A6 in Mexican mestizo, focused on smokers enrolled in a smoking cessation program, mostly with high tobacco consumption and nicotine dependence [15,16,20]. The gene discussed is DRD4; the disease is nicotine dependence.