Genetic markers in cycloid psychosis.

Frequencies of HLA antigens, blood groups, serum groups and red cell enzyme types in patients with cycloid psychosis were compared with those in patients with bipolar psychosis and in normal controls. Patients with cycloid psychosis showed (1) an increased frequency of the Rh-negative type compared to controls, (2) an increased frequency of the K(+) phenotype compared to both bipolar patients and controls, and (3) an increased frequency of the serum group Gc2--1.