DRD4 and nicotine dependence: In addition to CHRNA5-CHRNA3-CHRNB4 loci, which is the international validated loci for smoking quantity and nicotine dependence, [3, 4, 5] the most widely studied gene in the dopaminergic pathway is the dopamine receptor D4, which is encoded by the DRD4 gene; among the most explored genetic variants are the variable number tandem repeat (VNTR), located in exon III of this gene, however, studies that evaluated single nucleotide polymorphisms (SNPs) are scarce [6, 7].