Ancestral secondary cases on paternal and maternal sides in bipolar affective illness

An analysis of the distribution of ancestral secondary cases of affective illness in families of patients with bipolar manicdepressive disorder was undertaken. Twenty probands with at least two affectively ill second degree relatives were available for study. Probands with both parents affected were excluded. The distribution of unilateral to bilateral pairs of all affected relatives, both excluding and including parents, of probands showed no significant differences from that expected in polygenic inheritance. However, separation into bipolar family history, positive or negative, showed significant differences from the expected ratio of unilateral to bilateral pairs in a bipolar family history positive group consistent with a single dominant gene inheritance.