Prevalence of mental disorders in people with intellectual disabilities across the lifespan: an umbrella review

BackgroundPeople with intellectual disabilities (ID) experience higher rates of mental disorders, contributing to restrictive practices and premature mortality. Prevalence data are essential to inform support and policy decisions. AimsTo examine the prevalence of mental disorders in people with ID across the lifespan. MethodsWe systematically searched six databases and conducted a manual search up to December 15th, 2024, to identify systematic reviews on the prevalence of mental disorders in people with ID of any aetiology with or without other neurodevelopmental conditions. We summarised prevalence data from systematic reviews with meta-analyses and from systematic reviews with a narrative synthesis of results, including subgroup analyses (ID level, sex, age, autism), where possible. We compared these results with published prevalence rates of mental disorders in people without ID. PROSPERO: CRD42024610611. ResultsWe included twenty-six systematic reviews: seven with meta-analyses, and nineteen with subgroup or narrative synthesis. Compared to the general population, people with ID showed higher prevalence of schizophrenia (3.55%-4.8%), anxiety (5.4%-5.5%), and obsessive-compulsive (2.4%) disorders, while mood disorders (6%-7%), personality and post-traumatic stress disorders were less frequent, though data were limited. Study quality was moderate to critically low (AMSTAR-2). An emerging picture of mental disorders is evident in syndromic ID, with high anxiety rates in fragile X, Williams, and 22q11.2 deletion syndromes, and in co-occurring autism. This umbrella review revealed gaps in research on other mental disorders (i.e., dementia, bipolar, substance use, and eating disorders) and a lack of prevalence data stratified by age, sex, and ID level. This is compounded by the absence of dependable diagnostic criteria suitable for people with ID. ConclusionsThis umbrella review confirms the high prevalence of mental disorders among people with intellectual disabilities, and highlights limited evidence for several conditions and population subgroups. Standardised, high-quality epidemiological research is needed to guide clinical practice and policy.