Definition and Diagnosis
Intellectual disability, historically termed mental retardation, is a neurodevelopmental disorder characterized by significant limitations in both intellectual functioning (reasoning, problem-solving, abstract thinking) and adaptive behavior across conceptual, social, and practical domains, with onset during the developmental period.
Epidemiology
Intellectual disability affects roughly 1-3% of the population globally, with mild forms far more common than severe or profound forms. It is somewhat more frequently diagnosed in males, and prevalence is higher in low-resource settings where perinatal care and nutrition may be limited.
Risk Factors
Risk factors include genetic conditions such as Down syndrome and fragile X syndrome, prenatal exposure to alcohol or other teratogens, perinatal complications including hypoxia and prematurity, childhood central nervous system infections or injury, and severe early childhood deprivation or malnutrition.
Symptoms and Subtypes
Presentation varies with severity, ranging from mild difficulties with academic skills and abstract reasoning in mild intellectual disability, to profound impairment requiring constant support for basic self-care and communication in the most severe forms. Adaptive impairments affect communication, social participation, and independent functioning in daily life.
Diagnosis
Diagnosis under DSM-5-TR requires deficits in intellectual functioning confirmed by clinical assessment and standardized IQ testing, deficits in adaptive functioning across multiple domains, and onset during the developmental period, with severity classified as mild, moderate, severe, or profound based on adaptive functioning rather than IQ score alone.
Treatment
Management is supportive and educational rather than curative, involving early intervention services, individualized special education, speech and occupational therapy, and family support and training. Co-occurring psychiatric or medical conditions are treated as they arise, and vocational and social support services help maximize independence in adulthood.
Prognosis
Outcomes vary widely with severity and access to early, sustained intervention; many individuals with mild intellectual disability achieve considerable independence in adulthood, while those with more severe forms typically require lifelong support. Early identification and intervention consistently improve long-term adaptive functioning.
Reference
American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders (5th ed., text rev.).