In addition, chronic stress may also lead to decreased expression of brain derived neurotrophic factor (BDNF) in the hippocampus, which in turn may reduce its capability to inhibit the HPA axis (20, 21).These persistent alterations in the regulation of the HPA axis, such as the observed during chronic stress, has been associated with the origin and development of mood and anxiety disorders, where hyperactivity of the HPA axis, and the consequent hypercortisolism, represents one of the most consistent biological findings (6, 22, 23). The gene discussed is BDNF; the disease is anxiety disorder.