Depression, one of the most prevalent and life-threatening forms of mental illness affecting about 21% of the world's population, is believed to be related to individual alterations of a complex signaling network including the hypothalamic-pituitary-adrenal axis; the production of neurotrophins and proinflammatory cytokines and these alterations may be intimately involved in major mood changes. The gene discussed is BDNF; the disease is psychiatric disorder.