Analysis of familial factors in bipolar affective illness.

Familial transmission of affective illness was studied using a family interview and family history method in a group of 35 bipolar manic-depressive patients. Morbidity risk for bipolar and unipolar affective illness in first-degree relatives is approximately 30% in this population. Probands with a positive family history for bipolar illness have a significantly greater risk for alcoholism in first-degree relatives. Four cases of father-to-son transmission are reported. Linkage of color vision deficiency or Xga blood group and affective illness within families could not be substantiated in our sample. We discuss evidence regarding the mode of transmission of affective illness.