Heritability of schizophrenia. A controlled family history investigation in Nigeria.

Thirty-six consecutively admitted patients with schizophrenia and 20 with mania were studied for the morbid risk of psychosis in their first-degree relatives. Using the family history method of ascertainment, the morbid risk for schizophrenia in the relatives of schizophrenic probands was 4.12% compared with 1.42% in the relatives of manic probands. While this difference was not statistically significant, that between the morbid risk for affective psychoses in the relatives of manic patients (7.81%) was significantly higher than for the relatives of schizophrenic patients (0%).