Depressive disorders represent a prevalent (1 to 2%) and major illness characterized by episodes of dysphoria that are associated with somatic symptoms. It may have a manic-depressive (bipolar) or purely depressive (unipolar) course. The most characteristic features of bipolar affective disorder (BPAD) are episodes of mania (bipolar I, BP I) or hypomania (bipolar II, BP II) interspersed with periods of depression. If untreated, manic-depressive illness is associated with a suicide rate of approximately 20%. [From OMIM]