[Empirical risk of oligophrenia in siblings of proband-oligophrenics in populations with high levels of inbreeding].

An investigation is carried out on 214 patients with oligophreny with regard to the secondary risk of the same disease for their four sibs. All patients were divided into 4 groups according to etiological symptoms, and it was found that maximal risk of the secondary disease with oligophreny was for the sibs of probably genetic group, and minimal one--for the sibs of the exogenic group. Maximal resemblance in the degree of the defect in the pair of proband-sibs was found both in probably-genetic and presumably-genetic groups. The risk of secondary oligophreny was significantly higher in sibs-probands with relatively lower degree of weak-mindedness than in those with severe mental defects. The frequency of the secondary oligophreny amond sibs of the inbred origin (18.9%) was more than twice as high (P less than 0.001) as in those of outbred origin (8.3%).