Purpose: There is a paucity of data on heritability of psychotic disorders in Africa. The study aimed to investigate morbid risk of schizophrenia and mood disorder among first-degree relatives of schizophrenia probands, compared with mood disorder and healthy controls.
Methods: The study examined 330 first-degree relatives of probands with schizophrenia (n = 50), 350 first-degree relatives of probands with mood disorder (n = 50) and 387 first-degree relatives of healthy control (n = 50). The Schedules for Clinical Assessment in Neuropsychiatry, SCAN was used to ascertain diagnosis in ill subjects. To each subject, a socio-demographic questionnaire was administered. Family history was obtained using the Family History Schedule. Morbid risk estimates were calculated using the Weinberg shorter method.
Results: There was a significant difference between the mean age of relatives of schizophrenia probands compared to mood disorder (p = 0.01, 95 % CI 1.34-9.61) and healthy control (p < 0.01, 95 % CI 1.53-9.84). There were also significant differences between the number of children of schizophrenia probands and the number of children of normal control (p < 0.01, 95 % CI -2.0 to -3.9), as well as the number of deceased first-degree relatives of schizophrenia probands compared to normal control (p = 0.04, 95 % CI 0.01-0.94). Finally, there was a significant difference between the number of first-degree relatives of schizophrenia probands compared to the number of first-degree relatives of healthy control who were below the age of risk for schizophrenia (p = 0.01, 95 % CI -0.12 to -1.27). Morbid risks of 4.38 and 0.39 were obtained for schizophrenia among first-degree relatives of probands with schizophrenia and mood disorder, while first-degree relatives of probands with schizophrenia, mood disorder and healthy control had morbid risks for mood disorder of 0.42, 3.82 and 0.35, respectively.
Conclusion: The study revealed excess mortality among first-degree relatives of schizophrenia patients. First-degree relatives of probands with schizophrenia and mood disorder also had higher morbid risks for these psychotic conditions than healthy control with some measure of overlap between the two diagnostic categories.