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Early studies (21, 22, 25, 12) have pointed to a genetic component in the aetiology of manic-depressive disorders. More recently, careful clinical observation has suggested the division of the affective disorders into two distinct groups: the so-called bipolar or manic-depressive group and the unipolar type with recurrent depressions only (14, 27, 1). Although genetic differences in terms of family risk have been demonstrated between the so-called bipolar and unipolar psychoses, it is not yet evident whether each group constitutes a homogeneous entity. Moreover, the diagnosis of unipolar depressive disease for the authors cited above includes such syndromes as involutional psychotic reactions, psychotic depressive reactions, and probably also psychoneurotic depressions.
Mendlewicz et al. (Mon,) studied this question.