Blind assessment of relatives of 200 schizophrenic probands and relatives of 325 affective disorder probands indicates that these illnesses run in families. Suicide is more frequently seen in relatives of affective disorder probands. These findings may be construed as data in favor of the concept of two independent illnesses.
Winokur G, Morrison J, Clancy J, Crowe R. The Iowa 500II. A Blind Family History Comparison of Mania, Depression, and Schizophrenia. Arch Gen Psychiatry. 1972;27(4):462-464. doi:10.1001/archpsyc.1972.01750280030006