• In a family study of 1,254 adult relatives of patients and controls, lifetime prevalences of major affective disorder (including schizoaffective) were 37%, 24%, 25%, 20% and 7% in relatives of probands with schizoaffective, bipolar I, bipolar II, and unipolar disease, and normal controls. These data were compatible with the different affective disorders representing thresholds on a continuum of underlying multifactorial vulnerability. In this model, schizoaffective illness represents greatest vulnerability, followed by bipolar I and bipolar II, then unipolar illnesses. Alcoholism, drug abuse, and sociopathy were not more frequent in relatives of patients v relatives of controls. Sex-related transmission of morbid risk was not present. Morbid risk was 74% to offspring of two ill parents, and 27% to offspring of one ill parent. Nationality and age at time of interview seem to be nongenetic factors that affect frequency of diagnosis.
Gershon ES, Hamovit J, Guroff JJ, Dibble E, Leckman JF, Sceery W, Targum SD, Nurnberger JI, Goldin LR, Bunney WE. A Family Study of Schizoaffective, Bipolar I, Bipolar II, Unipolar, and Normal Control Probands. Arch Gen Psychiatry. 1982;39(10):1157–1167. doi:10.1001/archpsyc.1982.04290100031006