The polymorphisms rs2486001 (SLC6A9) and rs2000959 (SLC6A5) showed no statistically significant difference in the genotype (rs2486001: p = 0.53; rs2000959: p = 0.71) and allele (rs2486001: p = 0.91; rs2000959: p = 0.69) distributions between the MDD and the control group (Table 3 and Table 4). This evidence concerns the gene SLC6A5 and major depressive disorder.