[Problem of the etiology of undifferentiated oligophrenia].

On the basis of examination of 150 families with clinically and etiologically undifferentiated oligophrenias the authors have studied a possible contribution of genetic and psychosocial factors to the formation of mental retardation. The examined families present a high and approximately equal frequency of mild forms of oligophrenia among parents and siblings which confirms a polygenic model of heredity. Familial and psychological factors appear to be involved in the formation of mental retardation. The data obtained may be used for predicting the status of the progeny and for developing therapeutic and corrective measures in cases of oligophrenia.