Recently, extensive works of literature have investigated the relationships between 5-HTTLPR and depression, the serotonin transporter gene-linked promoter region (5-HTTLPR) is a variable number tandem repeats (VNTR) located in the promoter region of SLC6A4 (the human 5-HTT-encoding gene) (Iurescia et al., 2016). Here, SLC6A4 is linked to depressive disorder.