Mental disorders are common in people with intellectual disability, with a reported point prevalence of 36% in children and young people (including challenging behaviours), and 40.9% in adults (or 28.3% excluding challenging behaviours). People with intellectual disability experience all types of mental disorders, some more commonly than the general population, e.g. autism, attention-deficit hyperactivity disorder, schizophrenia, bipolar affective disorder, and dementia. Challenging behaviours are also common, and have no clear general population equivalent. Multi-morbidity of mental and physical disorders is typical. Mental disorder assessments are complex due to multi-morbidity and polypharmacy, in addition to impairments in communication, understanding, vision, and hearing, and the need to work with family and paid carers as well as the person with intellectual disability. Mental disorder classificatory systems have been developed for people with intellectual disability, in view of under-reporting when using general population manuals: DC-LD was designed to complement ICD-10, and DM-ID 2 to interpret DSM-5.
Towards ICD-11 for alcohol dependence: Diagnostic agreement with ICD-10, DSM-5, DSM-IV, DSM-III-R and DSM-III diagnoses in a Swedish general population of women