Intellectual Disability is Definitively Classified as a Developmental Disability
Yes, intellectual disability (formerly termed mental retardation) is explicitly classified as an intellectual developmental disorder, which is a type of developmental disability characterized by onset during the developmental period with significant impairments in cognitive functions and adaptive behavior. 1
Official Classification Framework
Intellectual disability is formally recognized as a neurodevelopmental disorder by major psychiatric and medical organizations, placing it squarely within the developmental disability category. 2
The American Psychiatric Association defines intellectual disability (intellectual developmental disorder) as both a psychiatric disorder and a developmental condition that manifests during the developmental period. 1
The World Health Organization adopted "intellectual developmental disorders" as the preferred terminology, explicitly recognizing these as disorders of neurodevelopment occurring during the developmental period. 3, 2
The condition is incorporated within the larger parent category of neurodevelopmental disorders, which definitively establishes it as a developmental disability. 2
Defining Characteristics That Establish Developmental Disability Status
The classification as a developmental disability is based on three critical features:
Timing of onset: The condition must begin during the developmental period (before age 18), which distinguishes it from later-onset neurocognitive disorders. 4
Impairment domains: Significant limitations must be present in cognitive functions associated with learning, adaptive behavior, and skills across three domains: conceptual (reading, writing, mathematics, problem-solving), social (interpersonal communication, social judgment), and practical (self-management, personal care, daily activities). 4, 2
Developmental trajectory: The condition affects 2% of the population and represents an unusual developmental trajectory that requires early identification and sustained support during formative years. 5, 6
Terminology Evolution Reinforcing Developmental Framework
The shift from "mental retardation" to "intellectual disability (intellectual developmental disorder)" or ID/IDD in 2013 was specifically designed to emphasize the developmental disability construct rather than a fixed deficit. 3
The American Association on Intellectual and Developmental Disabilities initiated this paradigm shift in 1992 to emphasize the disability construct. 3
This terminology change reflects the understanding that intellectual disability results from complex interactions between genetic abnormalities, environmental insults, and developmental vulnerability that disrupt brain development during critical developmental periods. 4
Clinical Implications of Developmental Disability Classification
The classification as a developmental disability has significant implications for health policy and access to services. 2
Defining intellectual disability as a health condition within the developmental disability framework is central to retaining it in the International Classification of Diseases, with direct implications for health policy and access to health services. 2
The majority of youth with intellectual disability can live independent or semi-independent lives as adults if they receive appropriate personalized support over a sustained period during their formative years. 7
Age-Specific Diagnostic Terminology Within Developmental Framework
The developmental disability classification includes age-appropriate diagnostic terms:
"Global Developmental Delay" should be used when clinical severity cannot be reliably assessed in children under age 5. 1, 3
"Unspecified Intellectual Disability (Intellectual Developmental Disorder)" applies to children over age 5 when other impairments make assessment difficult. 1, 3
Common Pitfall to Avoid
A critical distinction exists between intellectual disability (a developmental condition with onset during the developmental period) and acquired brain injury or later-onset neurocognitive disorders. 4 The timing of onset during the developmental period is the key differentiating factor that establishes intellectual disability as a developmental disability rather than an acquired condition.