Narrative review of intellectual disability: definitions, evaluation and principles of treatment

Background and Objective: Intellectual disability is clinically recognized in childhood and adolescence by deficits in cognitive and adaptive abilities. The prevalence of intellectual disability is 1% in the general population. With early recognition and appropriate support systems, most persons with intellectual disability can live healthy and productive life. Our objective is to provide practice relevant narrative review of definitions, evaluation and principles of treatment for persons with intellectual disability. Methods: We conducted a literature search (2005-2020) using online database PubMed, specifically for studies related to the clinical aspects of intellectual disability as they apply to practice, with specific relevant to children and adolescents. Our search was limited to English language publications. In addition to PubMed, we also consulted standard textbooks. We included original research as well as systematic reviews and meta-analysis type of articles. The key search terms included intellectual disability, neurodevelopmental disability, tests for cognitive function, tests for adaptive function, genetics of intellectual disability, and treatment of intellectual disability. Key Content and Findings: While most individuals have mild intellectual disability, 6 per 1,000 individuals have severe intellectual disability. In persons with mild intellectual disability a specific underlying etiology is generally not recognized; whereas, a specific genetic or biologic etiology is more likely to be recognized in persons who have severe intellectual disability. The diagnosis of intellectual disability requires clinical evaluation and judgment as well as a formal testing of the cognitive and adaptive functions. Such formal testing is done by individually administered standardized tests. The treatment of persons with intellectual disability at an individual level depends on the identified underlying cause, if any, and appropriate support to allow optimal functioning and independent living. Conclusions: Persons who have severe intellectual disability require life-long intensive supports. In addition to general medical care, persons who have intellectual disability also need interventions in the educational settings, provision of educational remediation and accommodations, and appropriate level of community based support. The management, quality of life and longevity vary depending up on the severity of intellectual disability and adequacy of community based support systems.