Morbid Risk of Schizophrenia in First-Degree Relatives of White and African–Caribbean Patients with Psychosis

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Abstract
Background: The high rate of schizophrenia among the second-generation African–Caribbean population in Britain has prompted much concern and speculation. Sugarman and Craufurd have reported that the morbid risk in the siblings of second-generation African–Caribbean schizophrenic patients was unusually high compared with that of the siblings of White patients.Method: We sought to replicate these findings by comparing the morbid risk for schizophrenia in the first-degree relatives of 111 White and 73 African–Caribbean psychotic probands. The latter comprised 35 first-generation (bom in the Caribbean) and 38 second-generation (born in Britain) probands.Results: The morbid risk for schizophrenia was similar for the parents and siblings of White and first-generation African–Caribbean patients, and for the parents of the second-generation African–Caribbean probands. However, the siblings of second-generation African–Caribbean psychotic probands had a morbid risk for schizophrenia that was seven times that of their White counterparts (P=0.007); similarly, the siblings of second-generation African–Caribbean schizophrenic probands had a morbid risk for schizophrenia that was four times that of their White counterparts (P=0.05).Conclusions: These findings replicate those of the earlier report of Sugarman and Craufurd, and suggest either that the second-generation African–Caribbean population in Britain is particularly vulnerable to some environmental risk factors for schizophrenia, or that some environmental factors act selectively on this population in Britain.