Depression and endogenicity

There is evidence from genetic and clinical studies, especially from therapeutic response to biological treatments, that endogenous or constitutional factors are important in some types of depressive illnesses. Unipolar depression is inherited differently from bipolar depression; monozygotic twins have a higher concordance rate than dizygotic twins. Endogenous depressions are cyclic in nature: the length of phases as well as the length of cycles are log-normally distributed. The effectiveness of antidepressants and ECT in endogenous depression points to a biochemical disorder. The author discusses the distinction between endogenous and exogenous depressions or between psychotic and neurotic depressions by reporting the work of Brown and others on "significant vs. stressful" events and on increased vulnerability.