Genetic subtypes of unipolar primary depressive illness distinguished by hypothalamic-pituitary-adrenal axis activity.

Serum-cortisol response to the 1 mg overnight dexamethasone suppression test was investigated in 86 patients with unipolar primary depressive illness and 80 non-depressed controls (45 with mania and 35 with schizophrenia). The depressed patients were assigned to one of three genetic subtypes according to the family psychiatric history. Resistance to suppression of serum-cortisol by dexamethasone was found in 37 of 86 (43%) depressives and none of the 80 controls. Non-suppression distinguished the three genetic subtypes of depression, being found in 23 of 28 (82%) patients with familial pure depressive disease (F.P.D.D.), 13 of 35 (37%) patients with sporadic depressive disease (S.D.D.), and 1 of 23 (4%) patients with depression spectrum disease (D.S.D.). The three genetic subtypes were further distinguished by the age of onset, with S.D.D. the oldest, and by the number of previous depressive episodes, with F.P.D.D. the most. Severity of depression did not separate the three subtypes. This is the first report of a distinct neuroendocrine abnormality which supports an objectively defined classification of unipolar primary depressive illness. It is suggested that unipolar primary depressive illness is three or more separate illnesses, each with a potentially distinctive mode of inheritance, pathophysiology, neurochemistry, clinical course, and treatment response.