Genetical analysis of unipolar and bipolar endogenous affective psychoses.
The mode of inheritance of affective psychoses was studied in 800 first degree and 582 second degree relatives of 122 probands. Morbidity risk for unipolar depression was 12.0+/-3.2 and 11.4+/-2.7 per cent respectively for parents and siblings of probands suffering from unipolar depression. Morbidity risk for manic-depressive psychosis for the respective groups of first degree relatives of manic-depressive probands was 15.1+/-3.2 and 16.9+/-3.2 per cent. In second degree relatives the morbidity risk was 3.4+/-1.0 and 5.3+/-1.4 per cent for unipolar depression and manic-depressive psychosis respectively. The results indicate the role of genetical factors in the etiology of both types of affective disorder and show that unipolar depression and manic-depressive psychosis are distinct entities. The hypothesis of X-linked dominant transmission was not confirmed in either of these affective disorders. By means of the computational model of Slater, no results compatible with a polygenic inheritance of unipolar depression or manic-depressive psychosis were found.