EPA-1403 – Testing Alternative Hypotheses for the Increased Rate of Psychotic Disorder in Immigrants

Abstract

Increased incidence rates of psychotic disorder have been consistently observed in immigrants with significant variability across ethnic groups. These findings have been attributed to cross-cultural biases, i.e. misinterpretation of culturally appropriate ideas leading to an overestimation of these disorders among ethnic minorities. Another alternative explanation constitutes the selection hypothesis positing that the increased rate is due to selective migration of predisposed people. We will present two studies that aimed at testing these hypotheses by examining (a) whether risk factors for psychosis are more prevalent among future emigrants, and (b) whether psychotic symptoms differ in severity and nature according to ethnic group. The first study was conducted among a cohort of 50 087 conscripts who were assessed at age 18 on cannabis use, IQ, psychiatric diagnosis, social adjustment, history of trauma and urbanicity of place of upbringing. Through data linkage we examined whether these exposures predicted emigration out of Sweden. The second study included 301 first episode psychosis (FEP) patients within a defined catchment area in Montreal, Canada. Patients were administered scales for the assessment of positive and negative symptoms, as well as general psychopathology. Symptom scores of the reference group were compared to those of patients with different ethnic backgrounds. The results of these studies will be discussed in light of candidate explanations for the increased risk of psychotic disorder among immigrants. Future avenues using data from the EUropean Gene-Environment Interaction (EU-GEI) project will be proposed.