Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a neuropeptide that is presumed to play a role in disorders that are characterised by enhanced activity of the neuroendocrine stress systems, such as in major depressive disorder (MDD), bipolar disorder (BD), post-traumatic stress disorder and schizophrenia (Katayama, Hattori, Yamada, Matsuzaki, & Tohyama, 2009). The gene discussed is ADCYAP1; the disease is major depressive disorder.