However, recently it has been proposed the hypothesis about a role of the SLC6A4 gene not directly in the MDD susceptibility but rather in the some features of the pathology such as the response/resistance to antidepressant treatment [5-8], or the interaction with the stressful life events, given the robust correlation between these events and risk of developing depressive symptoms [9-11,90]. Here, SLC6A4 is linked to major depressive disorder.