Intellectual disability

Kimon Bekelis MD (Dr. Bekelis of Dartmouth-Hitchcock Medical Center has no relevant financial relationships to disclose.)
Robert J Singer MD (Dr. Singer of Dartmouth-Hitchcock Medical Center/Geisel School of Medicine at Dartmouth has no relevant financial relationships to disclose.)
Bernard L Maria MD, editor. (Dr. Maria of Thomas Jefferson University has no relevant financial relationships to disclose.)
Originally released May 3, 1994; last updated September 12, 2016; expires September 12, 2019
Notice: This article has expired and is therefore not available for CME credit.

This article includes discussion of intellectual disability, global developmental delay, intellectual challenge, intellectual handicap, learning disability (United Kingdom), mental deficiency, mental handicap, mental retardation, and mental subnormality. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


Over the past decade, important changes have been made in disability terminology, resulting in the renaming of mental retardation to intellectual disability. Newly published DSM-5 from the American Psychiatric Association has made revision to its diagnostic criteria for intellectual disability. Medical science has also developed a better understanding of the causes of this disability with major impact on a patient's life. The authors review the updated terminology and definitions, the most recent guidelines for the diagnostic evaluation of intellectual disability, and its ongoing management in this update of this article, formerly named mental retardation.

Historical note and terminology

Clear examples of people with intellectual disability have been recorded since biblical times. During the medieval period there was legal and medical interest in differentiating between idiots and lunatics. A 13th-century law distinguished between those who were unfit to inherit because of innate incapacity from those who could be temporarily deprived of their inheritance while they were judged "out of their mind." During the 15th and 16th centuries, courts evaluated idiocy by competence in numeracy and social skills. Labels used were "idiot," "fool," "non compos mentis," or "an innocent." The evidence was that they could not perform everyday tasks such as count to 20, name their parents or neighbors, clothe themselves, or go out unaided. They were not generally considered a social threat, as opposed to lunatics, where a danger to self or others was a factor in judging insanity. In addition, lunacy was considered a possible temporary condition, whereas idiots were said to be "incurably and naturally damaged" (Rushton 1988). In 1614, Montalto in Florence published a major medical textbook called Archipathologia. His chapter entitled "on Loss of Mental Faculties and Simple Mindedness" (translation from Latin), distinguishes between intellectual disability, mental illness, dementia, and delirium. He stated that these conditions originated in the brain. He also recognized that intellectual disability could arise from birth defects and postnatal causes including brain damage at birth.

By the late 19th and 20th centuries, with the coming of universal school education, recognition and assessment of intellectual disability was required for educational purposes and more formal testing of individuals began. Categories used professionally at 1 time included idiocy, imbecility, feeble-mindedness, simpleton, and moron. The terms used most commonly to describe intellectual disability in the twentieth century included mental retardation, mental deficiency, mental subnormality, amentia, and oligophrenia.

Intellectual disability is currently defined by the American Association on Intellectual and Developmental Disabilities (formerly American Association on Mental Retardation [AAMR]) as “a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18” (American Association on Intellectual and Developmental Disabilities 2009). In 2007, this organization renamed itself, as well as renaming this disability from the prior term “mental retardation” (Schalock et al 2007), in order to better conform to current constructs of disability. This disability is also defined similarly by the American Psychiatric Association in its Diagnostic and Statistical Manual 5 as “a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains”. Additionally, newly published DSM-5 uses the term “intellectual developmental disorder” as the equivalent term for “intellectual disability” because upcoming ICD-11 will likely use the term “intellectual developmental disorder” to indicate involvement of impaired brain functioning early in life.

Moreover, a federal statute in the United States (Public Law 111-256, Rosa's Law) replaces the term mental retardation with intellectual disability; thus intellectual disability is the term used in law and public policy in the United States, whereas “learning disability” is used in the United Kingdom.

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