Psychotic experiences and disorders in adolescents and young adults with intellectual disabilities: Evidence from a population-based birth cohort in the United Kingdom.

Summary Background Evidence suggests that individuals with intellectual disabilities may be at increased risk of affective and non-affective psychotic disorders. However, studies so far have been limited by small and selected samples. Moreover, the role of early life trauma, a key environmental risk factor for psychosis, in the potential associations is unknown. Methods Using data from Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort, we investigated the associations between ID, psychotic disorders, and psychotic experiences in adulthood, and assessed the potential mediating role of trauma in childhood. Individuals with intellectual disabilities were identified using a multisource measure utilising cognitive, functional, and diagnostic indicators from ALSPAC combined with health and administrative records. Psychotic disorder clinical diagnoses were extracted through linkage to primary care records. Psychotic experiences were assessed at ages 18 and 24 using the semi-structured Psychosis-Like Symptoms interview (PLIKSi). Traumatic experiences between ages 5 and 11 were assessed with questionnaires and interviews administered to children and parents at multiple ages. Multiple imputation was performed across all analyses to mitigate potential bias due to missing data. Findings The maximum sample after multiple imputation was 9,407. We found evidence of associations between intellectual disabilities and psychotic disorders (OR= 4.57; 95%CI: 1.56-13.39). Evidence was weaker in the case of psychotic experiences (OR=1.63; 95%CI: 0.93-2.84). There was some evidence suggesting a potential mediating role of traumatic experiences in the associations between ID and psychotic experiences (OR= 1.09; 95%CI: 1.03-1.15). Evidence was less consistent in the case of psychotic disorders. Complete records analyses yielded comparable estimates. Interpretation Intellectual disabilities are associated with psychotic disorders and experiences in young adulthood. Further research into the contribution of trauma could shape current intervention strategies for psychotic disorders in this population. Funding The Baily Thomas Charitable Fund