Morbid risk of schizophrenia in first-degree relatives of White and African-Caribbean patients with psychosis

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 (born 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.