Depression Research: A Review with Special Emphasis Etiology

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Abstract
In this review of depression research the author has focused the attention on twin and adoption studies, although problems of classification, epidemiology, and biological and environmental factors related to depression are also touched upon.It is being noted that the available studies in the area are few, the number of twins in the various samples is small and the diagnostic classificationsvary. Of particular interest are the results presented by Bertelsen et al. (l), because of the large systematic sample. A summary of the studies that are based upon sampling through twin registers, i.e. the Scandinavian investigations, employing a relatively strict concept of manic depressive psychosis (bipolar disorder), gives a mean concordance of 50% in MZ twins and 15% in DZ twins. (1, 2, 3) Whereas genetical factors seem to play a significant role in the etiology of severely depressed subjects, there is no evidence that hereditary factors are of importance in the neurotic or reactive depressions, since concordance is low in both MZ and DZ (4).The available adoption studies are also few and replications are definitely necessary before one can arrive at firm conclusions. Mendlewicz & Rainer (5) reported more psychopathology of an affective nature in the biological parents of the adoptees with bipolar illnes than in the social parents. In contrast, von Knorring et al. (6) did not observe an increase in affective psychopathology in the biological parents of adoptees with affective disorder. Noteworthy is the excess of affective psychoses in the social parents.The author holds the view that any speculation with regard to genetic transmission is premature.Although the findings from the various investigations are not unambiguous, twin and adoption studies support the notion that genetic factors play a considerable role in bipolar disorder, whereas non‐bipolar depression is basically environmentally determined.