Moreover, in some cases, the same biomarker showed to play a role also in other psychiatric disorders than ADs (e.g., BDNF in depression [269] or OCD [267], and OXT in depression or schizophrenia [270]), emphasizing how psychiatric disorders exist in a continuum expression of symptomatology and that the common genes and pathological mechanisms are underpinned. This evidence concerns the gene BDNF and major depressive disorder.