Application of polygenic threshold models in the etiology of affective disorders

Multiple studies show that familial transmission of affective disorders does not conform to the classical principles of Mendelian inheritance. With the purpose of testing polygenic threshold models of inheritance of affective disorders, a study was carried out on 1184 probands with affective disorders with secondary cases in their families (siblings and offspring). Nonparametric analysis (Chi square test) indicates that there is no statistically significant difference between the observed and expected frequencies of secondary cases, when the probands are divided into two subgroups--unipolar and bipolar. It is proved that the two forms have common etiologic factors and the clinical differences between them can be attributed to the threshold gene effects. The hypothesis that bipolar and unipolar disorders are respectively severe and mild forms of the same disorder and that the two-threshold multifactorial polygenic model most adequately predicts the familial transmission of affective disorders is accepted.