Heritable factors in the severity of affective illness.

A review of clinical experience with 163 patients with primary affective disorder indicates that patients with a history characterized by recurrent depression interspersed with periods of hypomania (bipolar II) may have clinical courses that are distinguishable from bipolar I (depression with histories of mania) or unipolar patients. A prior history of suicide attempt and suicide after discharge from the research unit were most frequent among bipolar II patients. The family histories of bipolar I and bipolar II patients revealed similarly increased morbid risks for bipolar illness, whereas no bipolar illness was found in the first-degree relatives of unipolar patients. The suggestion that patients classified as bipolar II be separately considered in future studies of affective disorder is discussed.