Comorbidities in People With Intellectual Disability With and Without Schizophrenia and Schizophrenia Without Intellectual Disability: A Swedish Register Study (IDcare).

BACKGROUND: Intellectual disability (ID) and schizophrenia are known to separately carry a high risk of comorbidity of mental health and physical conditions. However, the prevalence and risk of comorbidities among people diagnosed with concurrent ID and schizophrenia have to date not been studied. METHODS: From a cohort including all people in Skåne, Sweden, the following three groups were established: (1) people with ID and concurrent schizophrenia, (2) people with ID without schizophrenia and (3) people with schizophrenia without ID. Diagnoses were determined using the Region Skåne healthcare database. Poisson regression was used to estimate relative risks (RRs) with 95% confidence intervals (CIs) of having at least one diagnosis in each ICD-10 chapter or block for group 1 versus groups 2 and 3, respectively. All analyses were adjusted for age at inclusion (i.e., 2014, continuous variable), sex and ethnicity. RESULTS: For several diagnostic chapters, there were higher risks among people with ID and schizophrenia, compared to both those with ID without schizophrenia and those with schizophrenia but without ID. These chapters included the following: I (parasites), III (blood and immunity), IV (endocrine), VII (eye), XII (skin and tissue) and XIV (genitourinary). The blocks with the highest risks compared to the other two groups were diabetes mellitus, disorders of other endocrine glands, obesity and other hyperalimentation, organic-including symptomatic and mental health conditions, extrapyramidal and movement and other respiratory diseases principally affecting the interstitium. CONCLUSIONS: People with the combination of ID and schizophrenia had an increased risk of both physical and mental health conditions that could not be explained by either ID or schizophrenia alone. A correct diagnosis for people with the combination of ID and schizophrenia is important for the provision of adequate treatment. Future research should investigate pathways and explanatory factors, as well as the provision of services for people with ID and schizophrenia.