Age at migration and psychotic-like experiences: Clues in childhood to explain the increased risk for psychosis among ethnic minorities

The risk for psychotic disorders is increased among immigrants compared to native populations in several countries around the world. The exact nature of this environmental exposure remains unclear. In order to find an explanation for the excess risk, it is crucial to determine the relevant timing of exposure. Most research studied the period of onset of the disorder, but research should extend to early childhood and adolescence. Methods: Two studies were conducted. A 7-year first-contact incidence study identified and diagnosed all individuals aged 15-54with a first episode of psychosis in The Hague (N=618), and investigated the effect of age at the time of migration on the incidence of psychotic disorders among immigrants A comprehensive municipal registration system provided the denominator, including information on ethnicity and age at migration to the Netherlands. The second study assessed prevalence and correlates of psychotic-like experiences (PLEs) in a multi-ethnic cohort of 10-16 year-old schoolchildren (N=1563), using self-reportmeasures. Psychotic-like experiences were measured with 7 items from the Kiddie-Schedule for Affective Disorders and Schizophrenia. Additional questions explored frequency of the experiences, associated distress and cultural familiarity with the experiences. Emotional and behavioral problems were measured with the Strengths and Difficulties Questionnaire and the Social and Health Assessment. Results: Lower age at migration was associated with a higher incidence of psychotic disorders in immigrants. People who migrated between 0-4 years had the most elevated risk for psychotic disorders compared to Dutch (age- and sex-adjusted IRR= 2.96; 95% CI, 2.10-4.17) and the risk gradually decreased with older age at migration: adjusted IRR= 2.31 (1.61-3.29), 1.51 (1.02-2.25) to 1.00 (0.58-1.72) for age at migration categories 5-9, 10-14 and >29 respectively. Ethnic minority youth reported a higher rate of psychotic-like experiences with high impact (that is, high frequency or strong influence on their life) than Dutch youth (8.4% and 3.1% respectively, OR 2.8; 95% 1.7-4.6).Moroccan and Turkish youth more often knew a healthy person in their family or culture who had the same experiences, but after adjustment for this “cultural context”, differences with native Dutch youth in the impact of psychotic-like experiences remained substantial and statistically significant. Psychotic-like experiences were strongly correlated with emotional and behavioral problems. Conclusions: The adverse influence of migration on the risk of psychotic disorders is most prominent in early life. Psychotic-like experiences with high impact are more common in ethnic minority youth than in Dutch youth. These findings suggest that early childhood is the critical period for developing an increased vulnerability for psychotic disorders among immigrants, and that early, subclinical expression of this vulnerability can already be found in (pre-)adolescents from ethnic minority groups.