Background: Studies in the UK compared psychosis risks for first-degree relatives of White and African-Caribbean patients and found "normal" risks for the parents of Caribbean patients, but very high risks for siblings of second-generation Caribbean patients.
Aim: To compare the risk of non-affective psychotic disorder (NAPD) for the parents and siblings of Moroccan-Dutch patients to that for the parents and siblings of Dutch patients. The "Moroccan-Dutch" are Dutch residents of Moroccan origin (first or second generation).
Method: Informants related to 29 Moroccan-Dutch and 63 Dutch patients were interviewed about the presence of psychiatric disorders in first-degree relatives (N=508), by means of the Family Interview for Genetic Studies.
Results: The risks for NAPD in both parent groups were similar (age and sex-adjusted odds ratio 1.0; 95% CI: 0.3-3.8). However, among the siblings, the risk for NAPD was significantly higher for the Moroccan-Dutch than for the Dutch (sex-adjusted hazard ratio 4.5; 95% Confidence Interval: 1.5-14.0). This was due to a large number of cases among the brothers of the Moroccan-Dutch patients (N=14), not among their sisters (N=1). Owing to small numbers separate hazard ratios for the first and the second generation were not calculated.
Conclusion: These preliminary results suggest that environmental factors in the Netherlands have a great impact on the psychosis risk for male immigrants from Morocco.