For example, in the serotonergic system, genetic variations in the regulatory region of 5-HT transporters (5-HTT) seem to influence the “harm avoidance” trait [1], [2] as assessed by the Tri-dimensional Personality Questionnaire [3] and susceptibility to depression [4] as assessed by NEO personality tests [5]. Here, SLC6A4 is linked to major depressive disorder.