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

TLDR

Schizophrenia rates are markedly higher among second‑generation African‑Caribbean people in Britain, and prior work has shown that their siblings have an unusually high morbid risk compared with siblings of White patients. This study aimed to replicate that finding by comparing the schizophrenia morbid risk in first‑degree relatives of 111 White and 73 African‑Caribbean psychotic probands. The sample included 35 first‑generation Caribbean and 38 second‑generation British African‑Caribbean probands, with their parents and siblings assessed for schizophrenia incidence. Siblings of second‑generation African‑Caribbean probands exhibited a seven‑fold higher schizophrenia risk than White siblings (and a four‑fold increase for those with schizophrenic probands), whereas parents and siblings of White and first‑generation African‑Caribbean probands had comparable risks.

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.