Ethnic origin and increased risk for schizophrenia in immigrants to countries of recent and longstanding immigration

Objectives: Compare the risk for schizophrenia in immigrants to countries of recent and longstanding immigration. Compare prevalence and incidence rates in black subjects under different conditions. Method: An electronic literature search was complemented by review articles and cross-references. Studies reporting standard diagnosis and incidence or prevalence rates were included. Results: Immigrants had an increased risk for schizophrenia in countries of longstanding immigration, but with lower risk ratios than in those of recent immigration. The risk was higher in black immigrants and the black population living in the United States. But incidence and prevalence rates in Africa and the Caribbean were similar to those of international studies. Conclusion: Comparing the most recent generation of immigrants with descendants of previous ones may account for the lower risk ratios observed in countries of longstanding vs. recent immigration. Two neurobiological hypotheses are proposed to explain the epidemiological findings in black populations and in immigrants.