Concomitantly, most of these molecular alterations are represented by genetic signatures, which have been reported in a variety of studies relating the prevalence of genetic polymorphisms on monoamine- and interleukin- related pathways with the development of IFN-induced depression (i.e., IDO1, serotonin receptor and transporter polymorphisms [24]–[27], and IL-6 polymorphisms [24], reviewed in [28]). Here, IL6 is linked to major depressive disorder.