intellectual disability

Intellectual disability (ID) becomes apparent during childhood, and involves deficits in mental abilities, social skills, and core activities of daily living (ADLs) when compared to peers of the same age.{{citation|title=Intellectual disability|website=MedlinePlus|first=Neil K.|last=Kaneshiro|date=April 21, 2015|publisher=U.S. National Library of Medicine|url=https://medlineplus.gov/ency/article/001523.htm|access-date=October 27, 2016|url-status=live|archive-url=https://web.archive.org/web/20161028153231/https://medlineplus.gov/ency/article/001523.htm|archive-date=October 28, 2016}} There are often no physical signs of mild forms of ID, although there may be characteristic physical traits when it is associated with a genetic disorder (e.g. Down syndrome).{{Cite book |author=American Psychiatric Association |title=Diagnostic and Statistical Manual of Mental Disorders |publisher=American Psychiatric Publishing |year=2013 |isbn=978-0-89042-555-8 |edition=Fifth |location=Arlington, VA |page=[https://archive.org/details/diagnosticstatis0005unse/page/809 809] |chapter=Highlights of Changes from DSM-IV to DSM-5 |doi=10.1176/appi.books.9780890425596 |hdl=2027.42/138395 |chapter-url=https://archive.org/details/diagnosticstatis0005unse/page/809 }}

The level of impairment ranges in severity for each person. Some of the early signs can include:

• Delays in reaching, or failure to achieve milestones in motor skills development (sitting, crawling, walking)
• Slowness learning to talk, or continued difficulties with speech and language skills after starting to talk
• Difficulty with self-help and self-care skills (e.g., getting dressed, washing, and feeding themselves)
• Poor planning or problem-solving abilities
• Behavioral and social problems{{citation|title=Intellectual disability|author=Queensland Government|date=July 30, 2015|website=qld.gov.au|url=https://www.qld.gov.au/disability/community/intellectual-disability/|access-date=October 27, 2016|archive-url=https://web.archive.org/web/20161028153057/https://www.qld.gov.au/disability/community/intellectual-disability/|archive-date=October 28, 2016}}
• Failure to grow intellectually, or continued infant childlike behavior
• Problems keeping up in school
• Failure to adapt or adjust to new situations
• Difficulty understanding and following social rules

In early childhood, mild ID (IQ 50–69) may not be obvious or identified until children begin school.{{Cite web |date=2016-05-17 |title=Intellectual Disability: Signs and Symptoms |url=https://psychcentral.com/disorders/intellectual-disability-symptoms |access-date=2025-05-08 |website=Psych Central |language=en}}{{cite journal |last1=Siegel |first1=Matthew |title=Practice Parameter for the Assessment and Treatment of Psychiatric Disorders in Children and Adolescents With Intellectual Disability (Intellectual Developmental Disorder) |journal=Journal of the American Academy of Child and Adolescent Psychiatry |date=1 April 2020 |volume=59 |issue=4 |pages=468–96 |doi=10.1016/j.jaac.2019.11.018 |eissn=1527-5418 |publisher=Elsevier on behalf of the American Academy of Child and Adolescent Psychiatry |pmid=33928910 |s2cid=212947591 |issn=0890-8567 |oclc=14404226 |lccn=87640752}}{{Cite journal |last1=Tafla |first1=Tally Lichtensztejn |last2=Brunoni |first2=Decio |last3=Carreiro |first3=Luiz Renato Rodrigues |last4=Seabra |first4=Alessandra Gotuzo |last5=Silva |first5=Leandro Augusto da |last6=Bastos |first6=Daiane Cristina de Souza |last7=Rossi |first7=Ana Claudia |last8=Santos |first8=Pedro Henrique Araujo dos |last9=Teixeira |first9=Maria Cristina Triguero Veloz |date=2021-03-08 |title=DIagnosys: An Analytical Framework for the Identification of Elementary School Students with Intellectual Disability |journal=Frontiers in Education |language=English |volume=6 |doi=10.3389/feduc.2021.609523 |doi-access=free |issn=2504-284X}}{{Cite web |last=Byrd |first=Florence |title=Intellectual Disability in Children |url=https://www.webmd.com/parenting/baby/child-intellectual-disability |access-date=2025-05-08 |website=WebMD |language=en}} Even when poor academic performance is recognized, it may take expert assessment to distinguish mild intellectual disability from specific learning disability or emotional/behavioral disorders. People with mild ID are capable of learning reading and mathematics skills to approximately the level of a typical child aged nine to twelve. They can learn self-care and practical skills, such as cooking or using the local transit system. As individuals with intellectual disabilities reach adulthood, many learn to live independently and maintain gainful employment.{{Cite web |last=Butrymowicz |first=Sarah |date=2017-11-04 |title=Almost all students with disabilities are capable of graduating on time. Here's why they're not. |url=http://hechingerreport.org/high-schools-fail-provide-legally-required-education-students-disabilities/ |access-date=2022-07-07 |website=The Hechinger Report |language=en-US|archiveurl=https://web.archive.org/web/20230420153514/https://hechingerreport.org/high-schools-fail-provide-legally-required-education-students-disabilities/|archive-date= April 20, 2023}} About 85% of people with ID are likely to have mild ID.

Moderate ID (IQ 35–49) is almost always apparent within the first years of life. Speech delays are particularly common signs of moderate ID. People with moderate intellectual disabilities need considerable support in school, at home, and in the community in order to fully participate. While their academic potential is limited, they can learn simple health and safety skills and to participate in simple activities. As adults, they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, to manage their finances. As adults, they may work in a sheltered workshop. About 10% of people with ID are likely to have moderate ID.

People with Severe ID (IQ 20–34), accounting for 3.5% of persons with ID, or Profound ID (IQ 19 or below), accounting for 1.5% of people with ID, need more intensive support and supervision for their entire lives. They may learn some ADLs, but an intellectual disability is considered severe or profound when individuals are unable to independently care for themselves without ongoing significant assistance from a caregiver throughout adulthood. Individuals with profound ID are completely dependent on others for all ADLs and to maintain their physical health and safety. They may be able to learn to participate in some of these activities to a limited degree.

Intellectual disability and autism spectrum disorder (ASD) share clinical characteristics which can result in confusion while diagnosing. Overlapping these two disorders, while common, can be detrimental to a person's well-being. Differentiating between these two disorders will allow clinicians to deliver or prescribe the appropriate treatments, though comorbidity between ID and ASD is very common; roughly 30% of those with ASD also have ID.{{Cite journal |last1=Polyak |first1=Andrew |last2=Kubina |first2=Richard M. |last3=Girirajan |first3=Santhosh |date=2015-07-22 |title=Comorbidity of intellectual disability confounds ascertainment of autism: implications for genetic diagnosis |url=https://onlinelibrary.wiley.com/doi/10.1002/ajmg.b.32338 |journal=American Journal of Medical Genetics Part B: Neuropsychiatric Genetics |language=en |volume=168 |issue=7 |pages=600–608 |doi=10.1002/ajmg.b.32338|pmid=26198689 |s2cid=7635120 }}{{Cite journal |last1=Katusic |first1=Maja Z. |last2=Myers |first2=Scott M. |last3=Weaver |first3=Amy L. |last4=Voigt |first4=Robert G. |date=2021-12-01 |title=IQ in Autism Spectrum Disorder: A Population-Based Birth Cohort Study |url=https://publications.aap.org/pediatrics/article/148/6/e2020049899/183390/IQ-in-Autism-Spectrum-Disorder-A-Population-Based |journal=Pediatrics |language=en |volume=148 |issue=6 |pages=e2020049899 |doi=10.1542/peds.2020-049899 |pmid=34851412 |s2cid=243762735 |issn=0031-4005|url-access=subscription }}{{Cite journal |last1=Shenouda |first1=Josephine |last2=Barrett |first2=Emily |last3=Davidow |first3=Amy L. |last4=Sidwell |first4=Kate |last5=Lescott |first5=Cara |last6=Halperin |first6=William |last7=Silenzio |first7=Vincent M. B. |last8=Zahorodny |first8=Walter |date=2023-02-01 |title=Prevalence and Disparities in the Detection of Autism Without Intellectual Disability |url=https://publications.aap.org/pediatrics/article/151/2/e2022056594/190525/Prevalence-and-Disparities-in-the-Detection-of |journal=Pediatrics |language=en |volume=151 |issue=2 |pages=e2022056594 |doi=10.1542/peds.2022-056594 |pmid=36700335 |s2cid=256273971 |issn=0031-4005|url-access=subscription }}{{primary source inline|date=December 2024}} Both ASD and ID require shortfalls in communication and social awareness as defining criteria.{{cite journal | vauthors = Pedersen AL, Pettygrove S, Lu Z, Andrews J, Meaney FJ, Kurzius-Spencer M, Lee LC, Durkin MS, Cunniff C | display-authors = 6 | title = DSM Criteria that Best Differentiate Intellectual Disability from Autism Spectrum Disorder | journal = Child Psychiatry and Human Development | volume = 48 | issue = 4 | pages = 537–545 | date = August 2017 | pmid = 27558812 | doi = 10.1007/s10578-016-0681-0 | s2cid = 4377173 }}

In a study conducted in 2016 surveying 2816 cases, it was found that the top subsets that help differentiate between those with ID and ASD are, "impaired non-verbal social behavior and lack of social reciprocity, [...] restricted interests, strict adherence to routines, stereotyped and repetitive motor mannerisms, and preoccupation with parts of objects". Those with ASD tend to show more deficits in non-verbal social behavior such as body language and understanding social cues. In a study done in 2008 of 336 individuals with varying levels of ID, it was found that those with ID display fewer instances of repetitive or ritualistic behaviors. It also recognized that those with ASD, when compared to those with ID, were more likely to isolate themselves and make less eye contact.{{cite journal |vauthors=Matson JL, Dempsey T |year=2008 |title=Stereotypy in Adults with Autism Spectrum Disorders: Relationship and Diagnostic Fidelity |journal=Journal of Developmental and Physical Disabilities |volume=20 |issue=2 |pages=155–165 |doi=10.1007/s10882-007-9086-0 |s2cid=143874013}} When it comes to classification ID and ASD have very different guidelines. ID has a standardized assessment called the Supports Intensity Scale (SIS); this measures severity on a system built around how much support an individual will need. While ASD also classifies severity by support needed, there is no standard assessment; clinicians are free to diagnose severity at their own judgment.{{cite book |url=https://www.ncbi.nlm.nih.gov/books/NBK332877/ |title=Mental Disorders and Disabilities Among Low-Income Children |vauthors=Boat TF, Wu JT |publisher=National Academies Press (US) |year=2015 |pages=169–176) |chapter=Clinical Characteristics of Intellectual Disabilities}}

Around 22% of individuals with ID suffer from epilepsy.{{Cite journal |last1=Robertson |first1=Janet |last2=Hatton |first2=Chris |last3=Emerson |first3=Eric |last4=Baines |first4=Susannah |date=July 2015 |title=Prevalence of epilepsy among people with intellectual disabilities: A systematic review |url=https://linkinghub.elsevier.com/retrieve/pii/S1059131115000862 |journal=Seizure |language=en |volume=29 |pages=46–62 |doi=10.1016/j.seizure.2015.03.016|pmid=26076844 }} The incidence of epilepsy is associated with level of ID; epilepsy affects around half of individuals with profound ID.{{Cite journal |last1=Robertson |first1=Janet |last2=Hatton |first2=Chris |last3=Emerson |first3=Eric |last4=Baines |first4=Susannah |date=July 2015 |title=Prevalence of epilepsy among people with intellectual disabilities: A systematic review |url=https://linkinghub.elsevier.com/retrieve/pii/S1059131115000862 |journal=Seizure |language=en |volume=29 |pages=46–62 |doi=10.1016/j.seizure.2015.03.016|pmid=26076844 }} Proper epilepsy management is particularly crucial in this population, as individuals are at increased risk of sudden unexpected death in epilepsy.{{Cite journal |last1=Kiani |first1=R. |last2=Tyrer |first2=F. |last3=Jesu |first3=A. |last4=Bhaumik |first4=S. |last5=Gangavati |first5=S. |last6=Walker |first6=G. |last7=Kazmi |first7=S. |last8=Barrett |first8=M. |date=June 2014 |title=Mortality from sudden unexpected death in epilepsy ( SUDEP ) in a cohort of adults with intellectual disability |url=https://onlinelibrary.wiley.com/doi/10.1111/jir.12047 |journal=Journal of Intellectual Disability Research |language=en |volume=58 |issue=6 |pages=508–520 |doi=10.1111/jir.12047 |pmid=23647577 |issn=0964-2633|url-access=subscription }} Nonetheless, epilepsy management in the ID population can be challenging due to high levels of polypharmacy prescribing, drug interactions, and increased vulnerability to adverse effects.{{Cite journal |last1=Kinnear |first1=Deborah |last2=Morrison |first2=Jill |last3=Allan |first3=Linda |last4=Henderson |first4=Angela |last5=Smiley |first5=Elita |last6=Cooper |first6=Sally-Ann |date=2018-02-01 |title=Prevalence of physical conditions and multimorbidity in a cohort of adults with intellectual disabilities with and without Down syndrome: cross-sectional study |url=https://bmjopen.bmj.com/content/8/2/e018292 |journal=BMJ Open |language=en |volume=8 |issue=2 |pages=e018292 |doi=10.1136/bmjopen-2017-018292 |issn=2044-6055 |pmc=5829598 |pmid=29431619}}{{Cite journal |last1=Shankar |first1=Rohit |last2=Eyeoyibo |first2=Mogbeyiteren |last3=Scheepers |first3=Mark |last4=Dolman |first4=Jennifer |last5=Watkins |first5=Lance |last6=Attavar |first6=Rajnish |last7=Carmody |first7=Elizabeth |last8=Haut |first8=Fabian |last9=Kerr |first9=Michael |last10=Alexander |first10=Regi T. |last11=Devapriam |first11=J. |last12=Roy |first12=Ashok |date=2017-05-01 |title=Management of epilepsy in adults with intellectual disability |url=https://pearl.plymouth.ac.uk/pms-research/1090/ |journal=Peninsula Medical School}} It is thought that 70% of individuals with ID are pharmaco-resistant, however only around 10% of individuals are prescribed Anti-Seizure Medications (ASMs) licensed for pharmaco-resistant epilepsy.{{Cite journal |last1=Sun |first1=James J. |last2=Perera |first2=Bhathika |last3=Henley |first3=William |last4=Angus-Leppan |first4=Heather |last5=Sawhney |first5=Indermeet |last6=Watkins |first6=Lance |last7=Purandare |first7=Kiran N. |last8=Eyeoyibo |first8=Mogbeyiteren |last9=Scheepers |first9=Mark |last10=Lines |first10=Geraldine |last11=Winterhalder |first11=Robert |last12=Ashby |first12=Samantha |last13=De Silva |first13=Ravi |last14=Miller |first14=Jonjo |last15=Philpott |first15=David E. |date=2022-05-01 |title=Epilepsy related multimorbidity, polypharmacy and risks in adults with intellectual disabilities: a national study |url=https://link.springer.com/article/10.1007/s00415-021-10938-3 |journal=Journal of Neurology |language=en |volume=269 |issue=5 |pages=2750–2760 |doi=10.1007/s00415-021-10938-3 |pmid=35067759 |issn=1432-1459|hdl=10871/128802 |hdl-access=free }}{{Cite journal |last1=Sun |first1=James J. |last2=Watkins |first2=Lance |last3=Henley |first3=William |last4=Laugharne |first4=Richard |last5=Angus-Leppan |first5=Heather |last6=Sawhney |first6=Indermeet |last7=Shahidi |first7=Meissam Moghaddassian |last8=Purandare |first8=Kiran |last9=Eyeoyibo |first9=Mogbeyiteren |last10=Scheepers |first10=Mark |last11=Lines |first11=Geraldine |last12=Winterhalder |first12=Robert |last13=Perera |first13=Bhathika |last14=Hyams |first14=Benjamin |last15=Ashby |first15=Samantha |date=2023-07-01 |title=Mortality risk in adults with intellectual disabilities and epilepsy: an England and Wales case–control study |journal=Journal of Neurology |language=en |volume=270 |issue=7 |pages=3527–3536 |doi=10.1007/s00415-023-11701-6 |issn=1432-1459 |pmc=10078066 |pmid=37022478}}{{Cite journal |last1=Shankar |first1=Rohit |last2=Marston |first2=Xiaocong Li |last3=Danielson |first3=Vanessa |last4=Do Rego |first4=Bronwyn |last5=Lasagne |first5=Reginald |last6=Williams |first6=Oliver |last7=Groves |first7=Lara |date=2024-05-01 |title=Real-world evidence of epidemiology, patient characteristics, and mortality in people with drug-resistant epilepsy in the United Kingdom, 2011–2021 |journal=Journal of Neurology |language=en |volume=271 |issue=5 |pages=2473–2483 |doi=10.1007/s00415-023-12165-4 |issn=1432-1459 |pmc=11055725 |pmid=38240828}} Research shows that certain ASMs, including Levetiracetam and Brivaracetam, show similar efficacy and tolerability in individuals with ID as compared to those without.{{Cite journal |last1=Allard |first1=Jon |last2=Henley |first2=William |last3=Sellers |first3=Adrian |last4=O’Shaughnessy |first4=Emma |last5=Thomson |first5=Oliver |last6=McLean |first6=Brendan |last7=Parrett |first7=Mary |last8=Rajakulendran |first8=Sanjeev |last9=Watkins |first9=Lance |last10=Maguire |first10=Melissa |last11=Ellawela |first11=Shan |last12=Tittensor |first12=Phil |last13=Sen |first13=Arjune |last14=Mohanraj |first14=Rajiv |last15=Bagary |first15=Manny |date=September 2024 |title=Efficacy and tolerability of Brivaracetam in people with intellectual disability compared to those without intellectual disability |journal=Epilepsy & Behavior |volume=158 |pages=109906 |doi=10.1016/j.yebeh.2024.109906 |pmid=38936308 |issn=1525-5050|doi-access=free }}{{Cite journal |last1=Allard |first1=Jon |last2=Sellers |first2=Adrian |last3=Henley |first3=William |last4=McLean |first4=Brendan |last5=Parrett |first5=Mary |last6=Rajakulendran |first6=Sanjeev |last7=Watkins |first7=Lance |last8=Maguire |first8=Melissa |last9=Ellawela |first9=Shan |last10=Tittensor |first10=Phil |last11=Bransgrove |first11=Juliet |last12=Sen |first12=Arjune |last13=Mohanraj |first13=Rajiv |last14=Bagary |first14=Many |last15=Ram |first15=Sunil |date=August 2024 |title=Efficacy and tolerability of levetiracetam in people with and without intellectual disabilities: A naturalistic case control study |url=https://linkinghub.elsevier.com/retrieve/pii/S1059131124001419 |journal=Seizure: European Journal of Epilepsy |volume=120 |pages=25–32 |doi=10.1016/j.seizure.2024.05.010 |pmid=38897161 |issn=1059-1311|url-access=subscription }} There is much ongoing research into epilepsy management in the ID population.

{{further|X-linked intellectual disability}}

File:Boy with Down Syndrome.JPG is the most common genetic cause of intellectual disability.]]

Among children, the cause of intellectual disability is unknown for one-third to one-half of cases. About 5% of cases are inherited.{{cite encyclopedia|url=http://medical-dictionary.thefreedictionary.com/mentally%20retarded|title=Definition of mentally retarded|encyclopedia=Gale Encyclopedia of Medicine}} Genetic defects that cause intellectual disability, but are not inherited, can be caused by accidents or mutations in genetic development. Examples of such accidents are development of an extra chromosome 18 (trisomy 18) and Down syndrome, which is the most common genetic cause. DiGeorge syndrome and fetal alcohol spectrum disorders are the next most common causes. Some other frequently observed causes include:

• Genetic conditions. Sometimes disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons like de novo mutations in genes associated with intellectual disability.{{Cite journal |last1=Maia |first1=Nuno |last2=Nabais Sá |first2=Maria João |last3=Melo-Pires |first3=Manuel |last4=de Brouwer |first4=Arjan P. M. |last5=Jorge |first5=Paula |date=2021-12-20 |title=Intellectual disability genomics: current state, pitfalls and future challenges |journal=BMC Genomics |volume=22 |issue=1 |pages=909 |doi=10.1186/s12864-021-08227-4 |doi-access=free |issn=1471-2164 |pmc=8686650 |pmid=34930158}}{{Cite journal |last1=Jansen |first1=Sandra |last2=Vissers |first2=Lisenka E. L. M. |last3=de Vries |first3=Bert B. A. |date=2023-01-30 |title=The Genetics of Intellectual Disability |journal=Brain Sciences |volume=13 |issue=2 |pages=231 |doi=10.3390/brainsci13020231 |doi-access=free |issn=2076-3425 |pmc=9953898 |pmid=36831774}}{{Cite web |author1=Natalie Wolchover |date=2012-10-01 |title=Many Low IQs Are Just Bad Luck |url=https://www.livescience.com/23620-mutations-intellectual-disability-cause.html |url-status=live |archiveurl=https://web.archive.org/web/20230404162739/https://www.livescience.com/23620-mutations-intellectual-disability-cause.html |archive-date=April 4, 2023 |access-date=2022-08-16 |website=livescience.com |language=en}} The most prevalent genetic conditions include Down syndrome, Klinefelter syndrome, Fragile X syndrome (common among boys), neurofibromatosis, congenital hypothyroidism, Williams syndrome, phenylketonuria (PKU), and Prader–Willi syndrome. Other genetic conditions include Phelan–McDermid syndrome (22q13del), Mowat–Wilson syndrome, genetic ciliopathy,{{cite journal | vauthors = Badano JL, Mitsuma N, Beales PL, Katsanis N | s2cid = 40223129 | title = The ciliopathies: an emerging class of human genetic disorders | journal = Annual Review of Genomics and Human Genetics | volume = 7 | pages = 125–48 | date = September 2006 | pmid = 16722803 | doi = 10.1146/annurev.genom.7.080505.115610 }} and Siderius type X-linked intellectual disability ({{OMIM|300263||shortlink}}) as caused by mutations in the PHF8 gene ({{OMIM|300560||shortlink}}).{{cite journal | vauthors = Siderius LE, Hamel BC, van Bokhoven H, de Jager F, van den Helm B, Kremer H, Heineman-de Boer JA, Ropers HH, Mariman EC | display-authors = 6 | title = X-linked mental retardation associated with cleft lip/palate maps to Xp11.3-q21.3 | journal = American Journal of Medical Genetics | volume = 85 | issue = 3 | pages = 216–20 | date = July 1999 | pmid = 10398231 | doi = 10.1002/(SICI)1096-8628(19990730)85:3<216::AID-AJMG6>3.0.CO;2-X | doi-access = free }}{{cite journal | vauthors = Laumonnier F, Holbert S, Ronce N, Faravelli F, Lenzner S, Schwartz CE, Lespinasse J, Van Esch H, Lacombe D, Goizet C, Phan-Dinh Tuy F, van Bokhoven H, Fryns JP, Chelly J, Ropers HH, Moraine C, Hamel BC, Briault S | display-authors = 6 | title = Mutations in PHF8 are associated with X linked mental retardation and cleft lip/cleft palate | journal = Journal of Medical Genetics | volume = 42 | issue = 10 | pages = 780–6 | date = October 2005 | pmid = 16199551 | pmc = 1735927 | doi = 10.1136/jmg.2004.029439 }} In the rarest of cases, abnormalities with the X or Y chromosome may also cause disability. Tetrasomy X and pentasomy X syndrome affect a small number of girls worldwide, while boys may be affected by 49, XXXXY (Fraccaro syndrome), or 49, XYYYY. Jacobs syndrome (47, XYY) is not associated with significantly lowered IQ though affected individuals may have slightly lower IQs than non-affected siblings on average.{{Cite book |title=Genetics and Learning Disabilities|last=Bender|first=Bruce G.|publisher=College Hill Press|year=1986|location=San Diego|pages=175–201 |quote=Figure 8-3. Estimated full-scale IQ distributions for SCA and control children: 47,XXX (mean ~83), 45,X & Variant (mean ~85), 47,XXY (mean ~95), 47,XYY (mean ~100), Controls and SCA Mosaics (mean ~104)}}{{cite journal | vauthors = Leggett V, Jacobs P, Nation K, Scerif G, Bishop DV | title = Neurocognitive outcomes of individuals with a sex chromosome trisomy: XXX, XYY, or XXY: a systematic review | journal = Developmental Medicine and Child Neurology | volume = 52 | issue = 2 | pages = 119–29 | date = February 2010 | pmid = 20059514 | pmc = 2820350 | doi = 10.1111/j.1469-8749.2009.03545.x }}
• Problems during pregnancy. Intellectual disability can result when the fetus does not develop properly. For example, there may be a problem with the way the fetus's cells divide as it grows. A pregnant woman who drinks alcohol {{xref|(see: Fetal alcohol spectrum disorder)}} or gets an infection like rubella during pregnancy may also have a baby with an intellectual disability.
• Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, they may have a developmental disability due to brain damage.
• The group of proteins known as histones have an essential part in gene regulation, and sometimes these proteins become modified and are prevented from working properly. When the genes responsible for the development of neurons are affected, it affects the brain and behavior in the individual.{{Cite web |title=Loss of epigenetic regulators causes mental retardation |url=https://www.sciencedaily.com/releases/2010/01/100114225326.htm |access-date=2022-08-16 |website=ScienceDaily |language=en}}
• Exposure to certain types of disease or toxins. Diseases like whooping cough, measles, or meningitis can cause intellectual disability if medical care is delayed or inadequate. Exposure to poisons like lead or mercury may also affect mental ability.
• Iodine deficiency, affecting approximately 2 billion people worldwide, is the leading preventable cause of intellectual disability in areas of the developing world where iodine deficiency is endemic. Iodine deficiency also causes goiter, an enlargement of the thyroid gland. More common than full-fledged congenital iodine deficiency syndrome (formerly cretinism), as intellectual disability caused by severe iodine deficiency is called, is mild impairment of intelligence. Residents of certain areas of the world, due to natural deficiency and governmental inaction, are severely affected by iodine deficiency. India has 500 million people with a deficiency, 54 million with goiter, and 2 million with congenital iodine deficiency. Among other nations affected by iodine deficiency, China and Kazakhstan have instituted widespread salt iodization programs. But, as of 2006, Russia had not.{{Cite news|url= https://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|work=The New York Times|title=In Raising the World's I.Q., the Secret's in the Salt|last=McNeil|first=Donald G. Jr.|date=2006-12-16|access-date=2009-07-21|url-status=live|archive-url= https://web.archive.org/web/20100712011551/http://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|archive-date=2010-07-12}}
• Malnutrition is a common cause of reduced intelligence in parts of the world affected by famine, such as Ethiopia and nations struggling with extended periods of warfare that disrupt agriculture production and distribution.{{Cite news|url= https://www.nytimes.com/2006/12/28/world/africa/28malnutrition.html|work=The New York Times|title=Malnutrition Is Cheating Its Survivors, and Africa's Future|last=Wines|first=Michael|date=2006-12-28|access-date=2009-07-21|url-status=live|archive-url= https://web.archive.org/web/20090417073800/http://www.nytimes.com/2006/12/28/world/africa/28malnutrition.html|archive-date=2009-04-17}}
• Absence of the arcuate fasciculus.{{cite journal | vauthors = Sundaram SK, Sivaswamy L, Makki MI, Behen ME, Chugani HT | title = Absence of arcuate fasciculus in children with global developmental delay of unknown etiology: a diffusion tensor imaging study | journal = The Journal of Pediatrics | volume = 152 | issue = 2 | pages = 250–5 | date = February 2008 | pmid = 18206698 | doi = 10.1016/j.jpeds.2007.06.037 }}
• Furthermore, lack of stimulation of sensory pathways in infants can also cause developmental and cognitive delays.{{Cite journal |last1=Ardiel |first1=Evan L |last2=Rankin |first2=Catharine H |date=March 2010 |title=The importance of touch in development |journal=Paediatrics & Child Health |language=en |volume=15 |issue=3 |pages=153–156 |doi=10.1093/pch/15.3.153 |pmid=21358895 |pmc=2865952 |issn=1205-7088}}

According to both the American Association on Intellectual and Developmental Disabilities{{cite web|url=http://aaidd.org/intellectual-disability/definition|title=Definition of Intellectual Disability|url-status=live|archive-url=https://web.archive.org/web/20170123212226/http://aaidd.org/intellectual-disability/definition|archive-date=2017-01-23}} and the American Psychiatric Association's{{Cite web|url=https://www.psychiatry.org/patients-families/intellectual-disability/what-is-intellectual-disability?_ga=1.127171085.1694806465.1485894944|title=What Is Intellectual Disability?|website=www.psychiatry.org}} Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), three criteria must be met for a diagnosis of intellectual disability: significant limitation in general mental abilities (intellectual functioning), significant limitations in one or more areas of adaptive behavior across multiple environments (as measured by an adaptive behavior rating scale, i.e. communication, self-help skills, interpersonal skills, and more), and evidence that the limitations became apparent in childhood or adolescence (onset during developmental phase).

In general, people with intellectual disabilities have an IQ below 70, but clinical discretion may be necessary for individuals who have a somewhat higher IQ but severe impairment in adaptive functioning.

It is formally diagnosed by an assessment of IQ and adaptive behavior. A third condition requiring onset during the developmental period is used to distinguish intellectual disability from other conditions, such as traumatic brain injuries and dementias (including Alzheimer's disease).

The first English-language IQ test, the Stanford–Binet Intelligence Scales, was adapted from a test battery designed for school placement by Alfred Binet in France. Lewis Terman adapted Binet's test and promoted it as a test measuring "general intelligence". Terman's test was the first widely used mental test to report scores in "intelligence quotient" form ("mental age" divided by chronological age, multiplied by 100). Current tests are scored in "deviation IQ" form, with a performance level by a test-taker two standard deviations below the median score for the test-takers age group defined as IQ 70. Until the most recent revision of diagnostic standards, an IQ of 70 or below was a primary factor for intellectual disability diagnosis, and IQ scores were used to categorize degrees of intellectual disability.

Since the current diagnosis of intellectual disability is not based on IQ scores alone, but must also take into consideration a person's adaptive functioning, the diagnosis is not made rigidly. It encompasses intellectual scores, adaptive functioning scores from an adaptive behavior rating scale based on descriptions of known abilities provided by someone familiar with the person, and also the observations of the assessment examiner, who is able to find out directly from the person what they can understand, communicate, and such like. IQ assessment must be based on a current test. This enables a diagnosis to avoid the pitfall of the Flynn effect, which is a consequence of changes in population IQ test performance changing IQ test norms over time.

Clinically, intellectual disability is a subtype of cognitive deficit or disabilities affecting intellectual abilities, which is a broader concept and includes intellectual deficits that are too mild to properly qualify as intellectual disability, or too specific (as in specific learning disability), or acquired later in life through acquired brain injuries or neurodegenerative diseases like dementia. Cognitive deficits may appear at any age. Developmental disability is any disability that is due to problems with growth and development. This term encompasses many congenital medical conditions that have no mental or intellectual components, although it, too, is sometimes used as a euphemism for intellectual disability.{{Cite web |last=Lawyer |first=Liz |date=2010-11-26 |url=http://www.theithacajournal.com/article/20101126/NEWS01/11260346/Rosa+s+Law+to+remove+stigmatized+language+from+law+books |title=Rosa's Law to remove stigmatized language from law books |location=Ithaca, New York |publisher=The Ithaca Journal |access-date=2010-12-04 |quote=The resolution ... urges a change from the old term to "developmental disability" }}{{Dead link|date=October 2018 |bot=InternetArchiveBot |fix-attempted=yes }}

Adaptive behavior, or adaptive functioning, refers to the skills needed to live independently (or at the minimally acceptable level for age). To assess adaptive behavior, professionals compare the functional abilities of a child to those of other children of similar age. To measure adaptive behavior, professionals use structured interviews, with which they systematically elicit information about persons' functioning in the community from people who know them well. There are many adaptive behavior scales, and accurate assessment of the quality of someone's adaptive behavior requires clinical judgment as well. Certain skills are important to adaptive behavior, such as:

• Daily living skills, such as getting dressed, using the bathroom, and feeding oneself
• Communication skills, such as understanding what is said and being able to answer
• Social skills with peers, family members, spouses, adults, and others

Other specific skills can be critical to an individual's inclusion in the community and to develop appropriate social behaviors, as for example being aware of the different social expectations linked to the principal lifespan stages (i.e., childhood, adulthood, old age). The results of a Swiss study suggest that the performance of adults with ID in recognizing different lifespan stages is related to specific cognitive abilities and to the type of material used to test this performance.{{Cite journal| vauthors = Straccia C, Tessari Veyre A, Bernasconi F, Petitpierre G |date=2019-04-11|title=Examining lifespan stage recognition abilities among adults with intellectual disability|journal=Journal of Intellectual & Developmental Disability|language=en|pages=110–118|doi=10.3109/13668250.2019.1580116|issn=1366-8250|volume=45|issue=2|s2cid=151191181}}

By most definitions, intellectual disability is more accurately considered a disability rather than a disease. Intellectual disability can be distinguished in many ways from mental illness, such as schizophrenia or depression. Currently, there is no "cure" for an established disability, though with appropriate support and teaching, most individuals can learn to do many things. Causes, such as congenital hypothyroidism, if detected early may be treated to prevent the development of an intellectual disability.

There are thousands of agencies around the world that provide assistance for people with developmental disabilities. They include state-run, for-profit, and non-profit, privately run agencies. Within one agency there could be departments that include fully staffed residential homes, day rehabilitation programs that approximate schools, workshops wherein people with disabilities can obtain jobs, programs that assist people with developmental disabilities in obtaining jobs in the community, programs that provide support for people with developmental disabilities who have their own apartments, programs that assist them with raising their children, and many more. There are also many agencies and programs for parents of children with developmental disabilities.

Beyond that, there are specific programs that people with developmental disabilities can take part in wherein they learn basic life skills. These "goals" may take a much longer amount of time for them to accomplish, but the ultimate goal is independence. This may be anything from independence in tooth brushing to an independent residence. People with developmental disabilities learn throughout their lives and can obtain many new skills even late in life with the help of their families, caregivers, clinicians and the people who coordinate the efforts of all of these people.

There are four broad areas of intervention that allow for active participation from caregivers, community members, clinicians, and of course, the individual(s) with an intellectual disability. These include psychosocial treatments, behavioral treatments, cognitive-behavioral treatments, and family-oriented strategies.{{cite book |last1=Mash |first1=E. |last2=Wolfe |first2=D. |year=2013 |title=Abnormal child psychology |edition=5th |pages=308–313). Wadsworth Cengage Learning}} Psychosocial treatments are intended primarily for children before and during the preschool years as this is the optimum time for intervention.{{cite book |vauthors=Hodapp RM, Burack JA |title=Developmental Psychopathology |chapter=Developmental Approaches to Children with Mental Retardation: A Second Generation |date=2015 |editor=Cicchetti, Dante |editor2=Cohen, Donald J.|isbn=978-0-471-23738-9 |doi=10.1002/9780470939406.ch6 |volume=3: Risk, disorder, and adaptation |edition=2nd |pages=235–267 |place=Hoboken, NJ |publisher=Wiley}} This early intervention should include encouragement of exploration, mentoring in basic skills, celebration of developmental advances, guided rehearsal and extension of newly acquired skills, protection from harmful displays of disapproval, teasing, or punishment, and exposure to a rich and responsive language environment.{{cite journal |vauthors=Ramey SL, Ramey CT | year = 1992 | title = Early educational intervention with disadvantaged children—To what effect? | journal = Applied and Preventive Psychology | volume = 1 | issue = 3| pages = 131–140 | doi=10.1016/s0962-1849(05)80134-9}} A great example of a successful intervention is the Carolina Abecedarian Project that was conducted with over 100 children from low socioeconomic status families beginning in infancy through pre-school years. Results indicated that by age 2, the children provided the intervention had higher test scores than control group children, and they remained approximately 5 points higher 10 years after the end of the program. By young adulthood, children from the intervention group had better educational attainment, employment opportunities, and fewer behavioral problems than their control-group counterparts.{{cite journal |vauthors=Campbell FA, Ramey CT, Pungello E, Sparling J, Miller-Johnson S | year = 2002 | title = Early childhood education: Young adult outcomes from the Abecedarian Project | journal = Applied Developmental Science | volume = 6 | pages = 42–57 | doi=10.1207/s1532480xads0601_05| s2cid = 71602425 }}

Core components of behavioral treatments include language and social skills acquisition. Typically, one-to-one training is offered in which a therapist uses a shaping procedure in combination with positive reinforcements to help the child pronounce syllables until words are completed. Sometimes involving pictures and visual aids, therapists aim at improving speech capacity so that short sentences about important daily tasks (e.g. bathroom use, eating, etc.) can be effectively communicated by the child.{{cite journal | vauthors = Matson JL, Matson ML, Rivet TT | title = Social-skills treatments for children with autism spectrum disorders: an overview | journal = Behavior Modification | volume = 31 | issue = 5 | pages = 682–707 | date = September 2007 | pmid = 17699124 | doi = 10.1177/0145445507301650 | s2cid = 35318587 }}{{cite journal | vauthors = van der Schuit M, Segers E, van Balkom H, Verhoeven L | title = Early language intervention for children with intellectual disabilities: a neurocognitive perspective | journal = Research in Developmental Disabilities | volume = 32 | issue = 2 | pages = 705–12 | year = 2011 | pmid = 21159487 | doi = 10.1016/j.ridd.2010.11.010 }} In a similar fashion, older children benefit from this type of training as they learn to sharpen their social skills such as sharing, taking turns, following instruction, and smiling.{{cite journal |vauthors=Kemp C, Carter M | year = 2002 | title = The social skills and social status of mainstreamed students with intellectual disabilities | journal = Educational Psychology | volume = 22 | issue = 4| pages = 391–411 | doi=10.1080/0144341022000003097| s2cid = 143880400 }} At the same time, a movement known as social inclusion attempts to increase valuable interactions between children with an intellectual disability and their non-disabled peers.{{cite journal | vauthors = Siperstein GN, Glick GC, Parker RC | title = Social inclusion of children with intellectual disabilities in a recreational setting | journal = Intellectual and Developmental Disabilities |eissn = 1934-9556 |issn = 1934-9491 |publisher = American Association on Intellectual and Developmental Disabilities| volume = 47 | issue = 2 | pages = 97–107 | date = April 2009 | pmid = 19368488 | doi = 10.1352/1934-9556-47.2.97 }} Cognitive-behavioral treatments, a combination of the previous two treatment types, involves a strategical-metastrategical learning technique{{clarify|date=March 2014}} that teaches children math, language, and other basic skills pertaining to memory and learning.{{Cite web |last=Services |first=Department of Health & Human |title=Cognitive behaviour therapy |url=https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/cognitive-behaviour-therapy |access-date=2025-05-08 |website=www.betterhealth.vic.gov.au |language=en}} The first goal of the training is to teach the child to be a strategical thinker through making cognitive connections and plans. Then, the therapist teaches the child to be metastrategical by teaching them to discriminate among different tasks and determine which plan or strategy suits each task.{{cite journal | vauthors = Hay I, Elias G, Fielding-Barnsley R, Homel R, Freiberg K | title = Language delays, reading delays, and learning difficulties: interactive elements requiring multidimensional programming | journal = Journal of Learning Disabilities | volume = 40 | issue = 5 | pages = 400–9 | year = 2007 | pmid = 17915494 | doi = 10.1177/00222194070400050301 | s2cid = 21854907 }} Finally, family-oriented strategies delve into empowering the family with the skill set they need to support and encourage their child or children with an intellectual disability. In general, this includes teaching assertiveness skills or behavior management techniques as well as how to ask for help from neighbors, extended family, or day-care staff.{{cite journal | vauthors = Bagner DM, Eyberg SM | title = Parent-child interaction therapy for disruptive behavior in children with mental retardation: a randomized controlled trial | journal = Journal of Clinical Child and Adolescent Psychology | volume = 36 | issue = 3 | pages = 418–29 | year = 2007 | pmid = 17658985 | doi = 10.1080/15374410701448448 | s2cid = 18526396 }} As the child ages, parents are then taught how to approach topics such as housing/residential care, employment, and relationships. The ultimate goal for every intervention or technique is to give the child autonomy and a sense of independence using the acquired skills they have. In a 2019 Cochrane review on beginning reading interventions for children and adolescents with intellectual disability, small to moderate improvements in phonological awareness, word reading, decoding, expressive and receptive language skills, and reading fluency were noted when these elements were part of the teaching intervention.{{cite journal | vauthors = Reichow B, Lemons CJ, Maggin DM, Hill DR | title = Beginning reading interventions for children and adolescents with intellectual disability | journal = The Cochrane Database of Systematic Reviews | volume = 2019 | pages = CD011359 | date = December 2019 | issue = 12 | pmid = 31805208 | pmc = 6894923 | doi = 10.1002/14651858.CD011359.pub2 }} Overall, about a third of people with ID do not learn how to read, another third learn to recognize sight words and how to sound out words, and the other third learn to read fairly well.{{Cite journal |last1=Ratz |first1=Christoph |last2=Lenhard |first2=Wolfgang |date=2013-05-01 |title=Reading skills among students with intellectual disabilities |url=https://www.sciencedirect.com/science/article/abs/pii/S0891422213000346 |journal=Research in Developmental Disabilities |volume=34 |issue=5 |pages=1740–1748 |doi=10.1016/j.ridd.2013.01.021 |pmid=23500168 |issn=0891-4222|url-access=subscription }}

Although there is no specific medication for intellectual disability, many people with developmental disabilities have further medical complications and may be prescribed several medications. Use of psychotropic medications such as benzodiazepines in people with intellectual disability requires monitoring and vigilance, as side effects occur commonly and are often misdiagnosed as behavioral and psychiatric problems.{{cite journal | vauthors = Kalachnik JE, Hanzel TE, Sevenich R, Harder SR | title = Benzodiazepine behavioral side effects: review and implications for individuals with mental retardation | journal = American Journal on Mental Retardation| volume = 107 | issue = 5 | pages = 376–410 | date = September 2002 | pmid = 12186578 | doi = 10.1352/0895-8017(2002)107<0376:BBSERA>2.0.CO;2 | issn = 0895-8017 }}

Intellectual disability affects about 2–3% of the general population. 75–90% of the affected people have mild intellectual disability. Non-syndromic or idiopathic ID accounts for 30–50% of cases. About a quarter of cases are caused by a genetic disorder. Cases of unknown cause affect about 95 million people {{as of|2013|lc=y}}. It is more common in males and in low to middle income countries.{{cite book|title=IACAPAP Textbook of Child and Adolescent Mental Health|date=2015|isbn=978-0-646-57440-0|url=http://iacapap.org/iacapap-textbook-of-child-and-adolescent-mental-health|url-status=live|archive-url=https://web.archive.org/web/20150813132641/http://iacapap.org/iacapap-textbook-of-child-and-adolescent-mental-health|archive-date=2015-08-13}}

{{anchor|History}}

Intellectual disability has been documented under a variety of names throughout history. Throughout much of human history, society was incredibly discriminatory towards those with any type of disability, and people with intellectual disability were commonly viewed as burdens on their families.

Greek and Roman philosophers, who valued reasoning abilities, disparaged people with intellectual disability as barely human. The oldest physiological view of intellectual disability is in the writings of Hippocrates in the late fifth century BCE, who believed that it was caused by an imbalance in the four humors in the brain. In ancient Rome people with intellectual disabilities had limited rights and were generally looked down upon.Louhiala, Pekka (2004). Preventing Intellectual Disability: Ethical and Clinical Issues. Cambridge University Press. p. 33. {{ISBN|978-0-521-53371-3}}. They were considered property and could be kept slaves by their father.Albrecht, Gary; Seelman, Katherine; Bury, Michael (2001). Handbook of Disability Studies. SAGE Publications. p. 269. {{ISBN|978-0-7619-2874-4}}. These people could also not marry, hold office, or raise children. Many of them were killed early in the childhood, and then dumped into the Tiber in order to avoid them burdening society.Hersen, Michael (2013). Handbook of Child Psychopathology. Springer US. p. 6. {{ISBN|978-1-4615-7136-0}}. However, they were exempt from their crimes under Roman law,Laes, Christian (2018). Disabilities and the Disabled in the Roman World: A Social and Cultural History. Cambridge: Cambridge University Press. pp. 46–54, 65–66. {{ISBN|978-1-107-16290-7}}.Noll, Richard (2009). The Encyclopedia of Schizophrenia and Other Psychotic Disorders. Facts on File, Incorporated. pp. 179, 330. {{ISBN|978-0-8160-7508-9}}. and they were also used to perform menial labor.{{cite book|url=http://www.faqs.org/childhood/Re-So/Retardation.html| last = Wickham | first = Parnell | name-list-style = vanc |title=Encyclopedia of Children and Childhood in History and Society|access-date=8 October 2010|url-status=live|archive-url=https://web.archive.org/web/20100928233511/http://www.faqs.org/childhood/Re-So/Retardation.html|archive-date=28 September 2010}}Yong, Amos (2007). Theology and Down Syndrome: Reimagining Disability in Late Modernity. Baylor University Press. p. 28. {{ISBN|978-1-60258-006-0}}.

Caliph Al-Walid (r. 705–715) built one of the first care homes for individuals with intellectual disabilities and built the first hospital which accommodated intellectually disabled individuals as part of its services. In addition, Al-Walid assigned each intellectually disabled individual a caregiver.{{cite journal | vauthors = Abedi H, Javadi A, Naji S | title = An exploration of health, family and economic experiences of leprosy patients, Iran | journal = Pakistan Journal of Biological Sciences | volume = 16 | issue = 18 | pages = 927–32 | date = September 2013 | pmid = 24502149 | doi = 10.1080/02673843.2011.649565 | s2cid = 43528098 | doi-access = free }}

Until the Enlightenment in Europe, care and asylum was provided by families and the church (in monasteries and other religious communities), focusing on the provision of basic physical needs such as food, shelter, and clothing. Negative stereotypes were prominent in social attitudes of the time.

In the 13th century, England declared people with intellectual disabilities to be incapable of making decisions or managing their affairs. Guardianships were created to take over their financial affairs.

In the 17th century, Thomas Willis provided the first description of intellectual disability as a disease. He believed that it was caused by structural problems in the brain. According to Willis, the anatomical problems could be either an inborn condition or acquired later in life.

The first known person in the British colonies with an intellectual disability was Benoni Buck, son of Richard Buck, whose life and guardianship battles provide significant insight into the early legal and social treatment of people with disabilities in what is now the United States.{{Citation needed|date=December 2024}}

In the 18th and 19th centuries, housing and care moved away from families and towards an asylum model. People were placed by, or removed from, their families (usually in infancy) and housed in large professional institutions, many of which were self-sufficient through the labor of the residents. Some of these institutions provided a very basic level of education (such as differentiation between colors and basic word recognition and numeracy), but most continued to focus solely on the provision of basic needs of food, clothing, and shelter. Conditions in such institutions varied widely, but the support provided was generally non-individualized, with aberrant behavior and low levels of economic productivity regarded as a burden to society. Individuals of higher wealth were often able to afford higher degrees of care such as home care or private asylums.{{cite book| first1 = Roy | last1 = Porter| first2 = David | last2 = Wright | name-list-style = vanc |title=The Confinement of the Insane: International Perspectives, 1800–1965|url=https://books.google.com/books?id=i7ktMJZC_HsC|access-date=11 August 2012|date=7 August 2003|publisher=Cambridge University Press|isbn=978-0-521-80206-2}} Heavy tranquilization and assembly-line methods of support were the norm, and the medical model of disability prevailed. Services were provided based on the relative ease to the provider, not based on the needs of the individual. A survey taken in 1891 in Cape Town, South Africa shows the distribution between different facilities. Out of 2,046 persons surveyed, 1,281 were in private dwellings, 120 in jails, and 645 in asylums, with men representing nearly two-thirds of the number surveyed. In situations of scarcity of accommodation, preference was given to white men and Black men (whose insanity threatened white society by disrupting employment relations and the taboo sexual contact with white women).

In the late 19th century, in response to Charles Darwin's On the Origin of Species, Francis Galton proposed selective breeding of humans to reduce intellectual disability. Early in the 20th century, the eugenics movement became popular throughout the world. This led to forced sterilization and prohibition of marriage in most of the developed world and was later used by Adolf Hitler as a rationale for the mass murder of people with intellectual disability during the Holocaust. Eugenics was later abandoned as a violation of human rights, and the practice of forced sterilization and prohibition from marriage was discontinued by most of the developed world by the mid-20th century.

In 1905, Alfred Binet produced the first standardized test for measuring intelligence in children.

Although ancient Roman law had declared people with intellectual disability to be incapable of the deliberate intent to harm that was necessary for a person to commit a crime, during the 1920s, Western society believed they were morally degenerate.

Ignoring the prevailing attitude, U.S.-based Civitans adopted service to people with developmental disabilities as a major organizational emphasis in 1952. Their earliest efforts included workshops for special education teachers and day camps for children with disabilities, all at a time when such training and programs were almost nonexistent.{{Cite book|last=Armbrester |first=Margaret E. |title=The Civitan Story |year=1992 |publisher=Ebsco Media |location=Birmingham, AL |pages=74–75}} The segregation of people with developmental disabilities was not widely questioned by academics or policy-makers until the 1969 publication of Wolf Wolfensberger's seminal work "The Origin and Nature of Our Institutional Models",{{Cite web | first = Wolf | last = Wolfensberger | name-list-style = vanc |title=The Origin and Nature of Our Institutional Models |url=http://www.disabilitymuseum.org/lib/docs/1909.htm?page=print |date=January 10, 1969 |publisher=President's Committee on Mental Retardation, Washington, D.C. |work=Changing Patterns in Residential Services for the Mentally Retarded |url-status=live |archive-url=https://web.archive.org/web/20060512185841/http://www.disabilitymuseum.org/lib/docs/1909.htm?page=print |archive-date=May 12, 2006 }} drawing on some of the ideas proposed by S. G. Howe 100 years earlier. This study posited that society characterizes people with disabilities as deviant, sub-human and burdens of charity, resulting in the adoption of that "deviant" role. Wolfensberger argued that this dehumanization, and the segregated institutions that result from it, ignored the potential productive contributions that all people can make to society. He pushed for a shift in policy and practice that recognized the human needs of those with intellectual disability and provided the same basic human rights as for the rest of the population.{{Citation needed|date=February 2025}}

This publication may be regarded as the first move towards the widespread adoption of the social model of disability in regard to these types of disabilities, and was the impetus for the development of government strategies for desegregation. Successful lawsuits against governments and increasing awareness of human rights and self-advocacy also contributed to this process, resulting in the passing in the U.S. of the Civil Rights of Institutionalized Persons Act in 1980.

From the 1960s to the present, most states have moved towards the elimination of segregated institutions. Normalization and deinstitutionalization are common. Along with the work of Wolfensberger and others including Gunnar and Rosemary Dybwad,{{Cite web |url=http://www.disabilitymuseum.org/beyond-affliction/ba_shows.dir/revoluti.dir/highlights/subject/ng0002tx.html |title=The ARC Highlights — Beyond Affliction: Beyond Affliction Document |publisher=Disabilitymuseum.org |access-date=2010-06-29 |archive-url=https://web.archive.org/web/20100711075247/http://www.disabilitymuseum.org/beyond-affliction/ba_shows.dir/revoluti.dir/highlights/subject/ng0002tx.html |archive-date=2010-07-11 }} a number of scandalous revelations around the horrific conditions within state institutions created public outrage that led to change to a more community-based method of providing services.{{Cite web |url=http://www.arcmass.org/StateHousePolicy/RegulationandPolicyDebates/FernaldSchoolClosingandRICCIClass/FernaldNews/WhyTheFernaldCenterShouldClose/ChristmasinPurgatoryWillowbrook/tabid/692/Default.aspx |title=Christmas in Purgatory & Willowbrook |publisher=Arcmass.org |access-date=2010-06-29 |archive-url=https://web.archive.org/web/20100711170039/http://www.arcmass.org/StateHousePolicy/RegulationandPolicyDebates/FernaldSchoolClosingandRICCIClass/FernaldNews/WhyTheFernaldCenterShouldClose/ChristmasinPurgatoryWillowbrook/tabid/692/Default.aspx |archive-date=2010-07-11 }}

By the mid-1970s, most governments had committed to de-institutionalization and had started preparing for the wholesale movement of people into the general community, in line with the principles of normalization. In most countries, this was essentially complete by the late 1990s, although the debate over whether or not to close institutions persists in some states, including Massachusetts.{{Cite web |url=http://www.arcmass.org/StateHousePolicy/RegulationandPolicyDebates/FernaldSchoolClosingandRICCIClass/tabid/175/Default.aspx |title=Fernald School Closing and RICCI Class |publisher=Arcmass.org |access-date=2010-06-29 |archive-url=https://web.archive.org/web/20100530082416/http://www.arcmass.org/StateHousePolicy/RegulationandPolicyDebates/FernaldSchoolClosingandRICCIClass/tabid/175/Default.aspx |archive-date=2010-05-30 }}

In the past, lead poisoning and infectious diseases were significant causes of intellectual disability. Some causes of intellectual disability are decreasing, as medical advances, such as vaccination, increase. Other causes are increasing as a proportion of cases, perhaps due to rising maternal age, which is associated with several syndromic forms of intellectual disability.{{citation needed|date=October 2013}}

Along with the changes in terminology, and the downward drift in acceptability of the old terms, institutions of all kinds have had to repeatedly change their names. This affects the names of schools, hospitals, societies, government departments, and academic journals. For example, the Midlands Institute of Mental Sub-normality became the British Institute of Mental Handicap and is now the British Institute of Learning Disability. This phenomenon is shared with mental health and motor disabilities, and seen to a lesser degree in sensory disabilities.{{Citation needed|date=April 2010}}

{{anchor|Archaic terms|Alternative terms}}

Over the past two decades,{{when|date=August 2024}} the term intellectual disability has become preferred by most advocates and researchers in most English-speaking countries. In a 2012 survey of 101 Canadian healthcare professionals, 78% said they would use the term developmental delay with parents over intellectual disability (8%). Expressions like developmentally disabled,[http://encyclopedia2.thefreedictionary.com/mentally+retarded Columbia Electronic Encyclopedia], 2013 special, special needs, or challenged are sometimes used, but have been criticized for "reinforc[ing] the idea that people cannot deal honestly with their disabilities".{{Cite journal |last1=Gernsbacher |first1=Morton Ann |last2=Raimond |first2=Adam R. |last3=Balinghasay |first3=M. Theresa |last4=Boston |first4=Jilana S. |date=2016-12-19 |title="Special needs" is an ineffective euphemism |journal=Cognitive Research: Principles and Implications |volume=1 |issue=1 |pages=29 |doi=10.1186/s41235-016-0025-4 |issn=2365-7464 |pmc=5256467 |pmid=28133625 |doi-access=free }}{{Cite web |date=2015 |title=Disability Style Guide |url=https://ncdj.org/wp-content/uploads/2012/08/NCDJStyleGuide2015.pdf |access-date=30 April 2022 |website=National Center on Disability and Journalism|archiveurl=https://web.archive.org/web/20230404111734/https://ncdj.org/wp-content/uploads/2012/08/NCDJStyleGuide2015.pdf|archive-date=April 4, 2023}}

The term mental retardation, which stemmed from the understanding that such conditions arose as a result of delays or retardation of a child's natural development,{{cite book |last1=Smith |first1=J. D. |last2=Wehmeyer |first2=M. L. |title=Mental Retardation in the 21st Century |date=1999 |publisher=Pro-ED |location=Austin, TX |isbn=978-0-89079-819-5 |pages=380–381 |url=https://mn.gov/mnddc/parallels2/pdf/90s/99/99-MRI-MLW.pdf |access-date=16 June 2022 |archive-url=https://web.archive.org/web/20201112005230/https://mn.gov/mnddc/parallels2/pdf/90s/99/99-MRI-MLW.pdf |archive-date=12 November 2020 |chapter=TWENTIETH-CENTURY DEFINITIONS OF MENTAL RETARDATION}} was used in the American Psychiatric Association's DSM-IV (1994) and in the World Health Organization's ICD-10 (codes F70–F79). In the next revision, ICD-11, it was replaced by the term "disorders of intellectual development" (codes 6A00–6A04; 6A00.Z for the "unspecified" diagnosis code).{{cite web |url=https://icd.who.int/browse11/l-m/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f605267007 |title=ICD-11 for Mortality and Morbidity Statistics (2018): 6A00 Disorders of intellectual development |author=World Health Organization |year=2018 |access-date=26 August 2018}}{{cite journal | vauthors = Salvador-Carulla L, Reed GM, Vaez-Azizi LM, Cooper SA, Martinez-Leal R, Bertelli M, Adnams C, Cooray S, Deb S, Akoury-Dirani L, Girimaji SC, Katz G, Kwok H, Luckasson R, Simeonsson R, Walsh C, Munir K, Saxena S | display-authors = 6 | title = Intellectual developmental disorders: towards a new name, definition and framework for "mental retardation/intellectual disability" in ICD-11 | journal = World Psychiatry | volume = 10 | issue = 3 | pages = 175–80 | date = October 2011 | pmid = 21991267 | pmc = 3188762 | doi = 10.1002/j.2051-5545.2011.tb00045.x }} The term "intellectual disability (intellectual developmental disorder)" is used in the DSM-5 (2013). The term "mental retardation" is still used in some professional settings such as governmental aid programs or health insurance paperwork, where "mental retardation" is specifically covered but "intellectual disability" is not.{{cite news|url=http://www.slate.com/id/111355/|title=The "R" Word| first = John | last = Cook | name-list-style = vanc |date=5 July 2001|work=Slate|url-status=live|archive-url=https://web.archive.org/web/20110908223756/http://www.slate.com/id/111355/|archive-date=8 September 2011}}

Historical terms for intellectual disability eventually become perceived as an insult, in a process commonly known as the euphemism treadmill.{{Cite journal |last1=Nash |first1=Chris |last2=Hawkins |first2=Ann |last3=Kawchuk |first3=Janet |last4=Shea |first4=Sarah E |date=February 2012 |title=What's in a name? Attitudes surrounding the use of the term 'mental retardation' |journal=Paediatrics & Child Health |volume=17 |issue=2 |pages=71–74 |doi=10.1093/pch/17.2.71 |issn=1205-7088 |pmc=3299349 |pmid=23372396}} The terms mental retardation and mentally retarded became popular in the middle of the 20th century to replace the previous set of terms, which included "imbecile",Fernald, Walter E. (1912). The imbecile with criminal instincts. Fourth edition. Boston: Ellis. {{oclc|543795982}}.{{cite book |last1=Duncan |first1=P. Martin |last2=Millard |first2=William |year=1866 |title=A manual for the classification, training, and education of the feeble-minded, imbecile, and idiotic |publisher=Longmans, Green, and Co.}} "idiot", "feeble-minded", and "moron",{{cite book | last=Rafter | first=Nicole Hahn | title=Creating born criminals | publication-place=Urbana | date=1997 | isbn=0-252-02237-8 | oclc=35548813 | publisher=University of Illinois Press}} among others, and are now considered offensive. By the end of the 20th century, retardation and retard become widely seen as disparaging, politically incorrect, and in need of replacement.{{cite book|last1=Cummings|first1=Nicholas A.|first2=Rogers H.|last2=Wright | name-list-style = vanc |title=Destructive trends in mental health: the well-intentioned path to harm|publisher=Routledge|location=New York|year=2005|chapter=Chapter 1, Psychology's surrender to political correctness|isbn=978-0-415-95086-2 }}

Usage has changed over the years and differed from country to country. For example, mental retardation in some contexts covers the whole field, but it previously applied to people with milder impairments. Feeble-minded used to mean mild impairments in the UK, and once applied in the US to the whole field. "Borderline intellectual functioning" is not currently defined, but the term may be used to apply to people with IQs in the 70s. People with IQs of 70 to 85 used to be eligible for special consideration in the US public education system on grounds of intellectual disability.{{Citation needed|date=April 2010}}

File:President Trump Meets with Members of Team USA for the 2019 Special Olympics World Games (48317653106).jpg USA team in July 2019]]

• In North America, intellectual disability is subsumed into the broader term developmental disability, which also includes epilepsy, autism, cerebral palsy, and other disorders that develop during the developmental period (birth to age 18). Because service provision is tied to the designation "developmental disability", it is used by many parents, direct support professionals, and physicians. In the United States, however, in school-based settings, the more specific term mental retardation or, more recently (and preferably), intellectual disability, is still typically used, and is one of 13 categories of disability under which children may be identified for special education services under Public Law 108–446.
• The phrase intellectual disability is increasingly being used as a synonym for people with significantly below-average cognitive ability. These terms are sometimes used as a means of separating general intellectual limitations from specific, limited deficits as well as indicating that it is not an emotional or psychological disability. It is not specific to congenital disorders such as Down syndrome.

The American Association on Mental Retardation changed its name to the American Association on Intellectual and Developmental Disabilities (AAIDD) in 2007, and soon thereafter changed the names of its scholarly journals{{cite web|url=http://aaidd.org/publications/journals|title=Journals|url-status=live|archive-url=http://archive.wikiwix.com/cache/20140821135338/http://aaidd.org/publications/journals|archive-date=2014-08-21}} to reflect the term "intellectual disability". In 2010, the AAIDD released its 11th edition of its terminology and classification manual, which also used the term intellectual disability.{{cite web |url=http://aaidd.org/publications/bookstore-home/product-listing/intellectual-disability-definition-classification-and-systems-of-supports-(11th-edition) |title=Intellectual Disability: Definition, Classification, and Systems of Supports (11th Edition) |url-status=live |archive-url=https://web.archive.org/web/20161202185316/http://aaidd.org/publications/bookstore-home/product-listing/intellectual-disability-definition-classification-and-systems-of-supports-(11th-edition) |archive-date=2016-12-02}}{{Cite web |url=http://aaidd.org/intellectual-disability/definition/faqs-on-intellectual-disability |title=Frequently Asked Questions on Intellectual Disability |publisher=American Association on Intellectual and Developmental Disabilities (AAIDD) |access-date=12 September 2013 |quote=The term intellectual disability covers the same population of individuals who were diagnosed previously with mental retardation in number, kind, level, type, duration of disability, and the need of people with this disability for individualized services and supports. |url-status=live |archive-url=http://archive.wikiwix.com/cache/20130914061929/http://aaidd.org/intellectual-disability/definition/faqs-on-intellectual-disability |archive-date=14 September 2013}}

In the UK, mental handicap had become the common medical term, replacing mental subnormality in Scotland and mental deficiency in England and Wales, until Stephen Dorrell, Secretary of State for Health for the United Kingdom from 1995 to 1997, changed the NHS's designation to learning disability.{{cite web |title=mencap |url=http://www.mencap.org.uk/ |access-date=2010-12-07 |url-status=live |archive-url=https://web.archive.org/web/20101215195240/http://www.mencap.org.uk/ |archive-date=2010-12-15 }} Website of the UK's leading learning disability charity, which uses that term throughout. The new term is not yet widely understood, and is often taken to refer to problems affecting schoolwork (the American usage), which are known in the UK as "learning difficulties". British social workers may use "learning difficulty" to refer to both people with intellectual disability and those with conditions such as dyslexia.{{cite web |title=Learning Disabilities: Prevalence |work=Social Work, Alcohol & Drugs |url=http://www.beds.ac.uk/swad/health/learning/prevalence |publisher=University of Bedfordshire |access-date=2014-10-18 |archive-url=https://web.archive.org/web/20141026181220/http://www.beds.ac.uk/swad/health/learning/prevalence |archive-date=2014-10-26 }} In education, "learning difficulties" is applied to a wide range of conditions: "specific learning difficulty" may refer to dyslexia, dyscalculia or developmental coordination disorder, while "moderate learning difficulties", "severe learning difficulties" and "profound learning difficulties" refer to more significant impairments.{{cite web |title=Special Educational Needs and Disability: A. Cognition and Learning Needs |url=http://www.teachernet.gov.uk/wholeschool/sen/datatypes/Cognitionlearningneeds/ |publisher=teachernet |archive-url=https://web.archive.org/web/20100501151033/http://www.teachernet.gov.uk/wholeschool/sen/datatypes/Cognitionlearningneeds/ |archive-date=2010-05-01 |access-date=2010-12-08}}{{cite web |last=Vickerman |first=Philip |date=2009-07-08 |title=Severe Learning Difficulties |work=Teacher Training Resource Bank |url=http://www.ttrb3.org.uk/severe-learning-difficulties/ |access-date=2014-10-19 |archive-url=https://web.archive.org/web/20141026171730/http://www.ttrb3.org.uk/severe-learning-difficulties/ |archive-date=2014-10-26 }} Extensive further references. The term "Profound and Multiple Learning Disability/ies" (PMLD) is used: the NHS describes PMLD as "when a person has a severe learning disability and other disabilities that significantly affect their ability to communicate and be independent".{{cite web |title=Learning disabilities |url=https://www.nhs.uk/conditions/learning-disabilities/ |website=nhs.uk |access-date=25 October 2023 |language=en |date=9 April 2018}}{{cite web |title=Profound and multiple learning disabilities (PMLD) |url=https://www.mencap.org.uk/learning-disability-explained/profound-and-multiple-learning-disabilities-pmld |website=Mencap |access-date=25 October 2023 |language=en}}

In England and Wales between 1983 and 2008, the Mental Health Act 1983 defined "mental impairment" and "severe mental impairment" as "a state of arrested or incomplete development of mind which includes significant/severe impairment of intelligence and social functioning and is associated with abnormally aggressive or seriously irresponsible conduct on the part of the person concerned."{{cite web |url=http://www.rcpsych.ac.uk/PDF/Draft%20Illustrative%20Code%20of%20Practice%20July%202007.pdf |title=Draft Illustrative Code of Practice |access-date=2007-08-23 |url-status=live |archive-url=https://web.archive.org/web/20070926115046/http://www.rcpsych.ac.uk/PDF/Draft%20Illustrative%20Code%20of%20Practice%20July%202007.pdf |archive-date=2007-09-26 }} As behavior was involved, these were not necessarily permanent conditions: they were defined for the purpose of authorizing detention in hospital or guardianship. The term mental impairment was removed from the Act in November 2008, but the grounds for detention remained. However, English statute law uses mental impairment elsewhere in a less well-defined manner—e.g. to allow exemption from taxes—implying that intellectual disability without any behavioral problems is what is meant.

A 2008 BBC poll conducted in the United Kingdom came to the conclusion that 'retard' was the most offensive disability-related word.{{cite news |last=Rohrer |first=Finlo |url=http://news.bbc.co.uk/1/hi/magazine/7629376.stm |title=The path from cinema to playground |publisher=BBC News |date=2008-09-22 |access-date=2010-06-29 |url-status=live |archive-url=https://web.archive.org/web/20080925044035/http://news.bbc.co.uk/1/hi/magazine/7629376.stm |archive-date=2008-09-25 }} On the reverse side of that, when a contestant on Celebrity Big Brother live used the phrase "walking like a retard", despite complaints from the public and the charity Mencap, the communications regulator Ofcom did not uphold the complaint saying "it was not used in an offensive context [...] and had been used light-heartedly". It was, however, noted that two previous similar complaints from other shows were upheld.{{cite news |last=Beckford |first=Martin |url=https://www.telegraph.co.uk/culture/tvandradio/7415425/Ofcom-says-TV-channels-have-human-right-to-broadcast-offensive-material.html |title=Ofcom says TV channels have 'human right' to broadcast offensive material |work=Telegraph |date=2010-03-11 |access-date=2010-06-29 |url-status=live |archive-url=https://web.archive.org/web/20100711102657/http://www.telegraph.co.uk/culture/tvandradio/7415425/Ofcom-says-TV-channels-have-human-right-to-broadcast-offensive-material.html |archive-date=2010-07-11 }}

In the past, Australia has used British and American terms interchangeably, including "mental retardation" and "mental handicap". Today, "intellectual disability" is the preferred and more commonly used descriptor.{{Cite web |url=http://www.psychology.org.au/publications/inpsych/disability/ |title=Australian Psychological Society: Psychologists and intellectual disability |publisher=Psychology.org.au |access-date=2010-06-29 |url-status=live |archive-url=https://archive.today/20120908235847/http://www.psychology.org.au/publications/inpsych/disability/ |archive-date=2012-09-08 }}

File:Cretin Child (1).jpg]]

People with intellectual disabilities are often not seen as full citizens of society. Person-centered planning and approaches are seen as methods of addressing the continued labeling and exclusion of socially devalued people, such as people with disabilities, encouraging a focus on the person as someone with capacities and gifts as well as support needs. The self-advocacy movement promotes the right of self-determination and self-direction by people with intellectual disabilities, which means allowing them to make decisions about their own lives.

Until the middle of the 20th century, people with intellectual disabilities were routinely excluded from public education, or educated away from other typically developing children. Compared to peers who were segregated in special schools, students who are mainstreamed or included in regular classrooms report similar levels of stigma and social self-conception, but more ambitious plans for employment.{{cite journal | vauthors = Cooney G, Jahoda A, Gumley A, Knott F | title = Young people with intellectual disabilities attending mainstream and segregated schooling: perceived stigma, social comparison and future aspirations | journal = Journal of Intellectual Disability Research | volume = 50 | issue = Pt 6 | pages = 432–44 | date = June 2006 | pmid = 16672037 | doi = 10.1111/j.1365-2788.2006.00789.x }} As adults, they may live independently, with family members, or in different types of institutions organized to support people with disabilities. About 8% currently live in an institution or a group home.

In the United States, the average lifetime cost of a person with an intellectual disability amounts to $223,000 per person, in 2003 US dollars, for direct costs such as medical and educational expenses. The indirect costs were estimated at $771,000, due to shorter lifespans and lower than average economic productivity. The total direct and indirect costs, which amount to a little more than a million dollars, are slightly more than the economic costs associated with cerebral palsy, and double that associated with serious vision or hearing impairments. Of the costs, about 14% is due to increased medical expenses (not including what is normally incurred by the typical person), and 10% is due to direct non-medical expenses, such as the excess cost of special education compared to standard schooling. The largest amount, 76%, is indirect costs accounting for reduced productivity and shortened lifespans. Some expenses, such as ongoing costs to family caregivers or the extra costs associated with living in a group home, were excluded from this calculation.{{cite journal | title = Economic costs associated with mental retardation, cerebral palsy, hearing loss, and vision impairment--United States, 2003 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 53 | issue = 3 | pages = 57–9 | date = January 2004 | pmid = 14749614 | author-link = Centers for Disease Control and Prevention | jstor = 23315317 | author1 = Centers for Disease Control Prevention (CDC) }}

The law treats person with intellectual disabilities differently than those without intellectual disabilities. Their human rights and freedoms, including the right to vote, the right to conduct business, enter into a contract, enter into marriage, right to education, are often limited. The courts have upheld some of these limitations and found discrimination in others. The UN Convention on the Rights of Persons with Disabilities, which sets minimum standards for the rights of persons with disabilities, has been ratified by more than 180 countries. In several U.S. states, and several European Union states, persons with intellectual disabilities are disenfranchised.{{Cite web|last=Toplak|first=Jurij|date=2020-09-07|title=Voting is every EU citizen's right, regardless of disability|url=https://www.euractiv.com/section/eu-elections-2019/opinion/voting-is-every-eu-citizens-right-regardless-of-disability/|access-date=2020-11-29|website=euractiv.com|language=en-GB}}{{Cite web|date=2019-05-15|title=5 reasons why people with intellectual disabilities should get the right to vote|url=http://www.inclusion-europe.eu/why-people-with-intellectual-disabilities-should-get-the-right-to-vote/|access-date=2020-11-29|website=Inclusion Europe|language=en-US}} The European Court of Human Rights ruled in Alajos Kiss v. Hungary (2010) that Hungary cannot restrict voting rights only on the basis of guardianship due to a psychosocial disability.{{Cite web|title=Election Access|url=http://electionaccess.org/en/resources/publications/174/|access-date=2020-11-29|website=electionaccess.org}}

People with intellectual disabilities are usually at a higher risk of complex health conditions such as epilepsy and neurological disorders, gastrointestinal disorders, and behavioral and psychiatric problems compared to people without disabilities.{{cite journal | vauthors = Krahn GL, Fox MH | title = Health disparities of adults with intellectual disabilities: what do we know? What do we do? | journal = Journal of Applied Research in Intellectual Disabilities | volume = 27 | issue = 5 | pages = 431–46 | date = September 2014 | pmid = 23913632 | pmc = 4475843 | doi = 10.1111/jar.12067 }} Adults also have a higher prevalence of poor social determinants of health, behavioral risk factors, depression, diabetes, and poor or fair health status than adults without intellectual disability.

Studies from the United Kingdom show people there with intellectual disability live on average 16 years less than the general population. Some of the barriers that exist for people with ID accessing quality healthcare include: communication challenges, service eligibility, lack of training for healthcare providers, diagnostic overshadowing, and absence of targeted health promotion services.{{cite journal | vauthors = Ali A, Scior K, Ratti V, Strydom A, King M, Hassiotis A | title = Discrimination and other barriers to accessing health care: perspectives of patients with mild and moderate intellectual disability and their carers | journal = PLOS ONE | volume = 8 | issue = 8 | pages = e70855 | date = 2013-08-12 | pmid = 23951026 | pmc = 3741324 | doi = 10.1371/journal.pone.0070855 | bibcode = 2013PLoSO...870855A | doi-access = free }}{{cite journal | vauthors = Ervin DA, Hennen B, Merrick J, Morad M | title = Healthcare for persons with intellectual and developmental disability in the community | journal = Frontiers in Public Health | volume = 2 | pages = 83 | date = 2014-07-15 | pmid = 25077139 | pmc = 4098023 | doi = 10.3389/fpubh.2014.00083 | doi-access = free | bibcode = 2014FrPH....2...83E }} Key recommendations from the CDC for improving the health status for people with intellectual disabilities include: improve access to health care, improve data collection, strengthen the workforce, include people with ID in public health programs, and prepare for emergencies with people with disabilities in mind.{{Cite web|url=https://www.cdc.gov/ncbddd/disabilityandhealth/features/unrecognizedpopulation.html|title=Unrecognized Health Disparity Population {{!}} CDC| date=2019-10-28|website=Centers for Disease Control and Prevention|language=en-us|access-date=2020-04-06}}

• Future planning
• History of psychiatric institutions
• IQ classification
• Intermediate Care Facilities for Individuals with Intellectual Disabilities
• Secondary handicap
• Severe mental impairment
• Intellectual disability and higher education in the United States

{{Reflist|30em}}

• Adkins, B.; Summerville, J.; Knox, M.; Brown, A. R.; Dillon, S. (2012). "Digital technologies and musical participation for people with intellectual disabilities". New Media & Society. 15 (4): 501–518. {{doi|10.1177/1461444812457338}}. {{hdl|10072/47764}}. {{OCLC|829241491}}.
• Carey C. Allison (2010). On the Margins of Citizenship: Intellectual Disability and Civil Rights in Twentieth-Century America. Temple University Press.
• [http://www.eumap.org/topics/inteldis/reports Rights of People with Intellectual Disabilities: Access to Education and Employment], bilingual reports on 14 European countries
• Dalton, A. J.; Janicki, Matthew P., editors (1999). [https://archive.org/details/dementiaagingint0000unse/page/n7/mode/2up Dementia, aging, and intellectual disabilities: a handbook]. Philadelphia: Brunner/Mazel. p. 12. {{ISBN|0-87630-916-3}}. {{OCLC|39223703}}.
• [https://web.archive.org/web/20081223221747/http://www.aihw.gov.au/publications/welfare/dpida/dpida-c00.html The Definition and Prevalence of Intellectual Disability in Australia]. Australian Institute of Health and Welfare paper.
• Harris, James C. (2010). Intellectual Disability: A Guide for Families and Professionals. Oxford University Press.
• [https://web.archive.org/web/20131113152733/http://www2.stats.govt.nz/domino/external/pasfull/pasfull.nsf/web/Media+Release+2001+New+Zealand+Disability+Survey:+Snapshot+8+Intellectual+Disabilities?open 2001 New Zealand Snapshot of Intellectual Disability]
• Kovago, Emese (2003). [https://www.opensocietyfoundations.org/uploads/532ca033-ce53-4fe3-bc48-55d4c9059768/eu-mental-disabilities-20030624.pdf People with Intellectual Disabilities: from Invisible to Visible Citizens of the EU Accession Countries]; [https://web.archive.org/web/20190816095354/https://www.opensocietyfoundations.org/uploads/532ca033-ce53-4fe3-bc48-55d4c9059768/eu-mental-disabilities-20030624.pdf archived copy].
• {{cite book |last1=Endicott |first1=Orville |title=Persons with intellectual disability who are incarcerated for criminal offences: A literature review |date=1991 |publisher=Correctional Service of Canada |department=Communications and Corporate Development, Research Branch |url=https://www.csc-scc.gc.ca/research/092/r14e_e.pdf |access-date=30 June 2022 |archive-url=https://web.archive.org/web/20130701143732/https://www.csc-scc.gc.ca/research/092/r14e_e.pdf |archive-date=1 July 2013}}
• {{Cite web|title=John F. Kennedy and people with intellectual disabilities |date=15 December 2021 |url=https://www.jfklibrary.org/learn/about-jfk/jfk-in-history/john-f-kennedy-and-people-with-intellectual-disabilities |archive-url = https://web.archive.org/web/20220121030950/https://www.jfklibrary.org/learn/about-jfk/jfk-in-history/john-f-kennedy-and-people-with-intellectual-disabilities |archive-date = 21 January 2022 |publisher=Kennedy Presidential Library and Museum}}
• {{cite journal |last1=Jones |first1=Jessica |title=Persons with intellectual disabilities in the criminal justice system: Review of issues |journal=International Journal of Offender Therapy and Comparative Criminology |date=December 2007 |volume=51 |issue=6 |pages=723–733 |doi=10.1177/0306624X07299343 |pmid=17636203 |url=https://www.researchgate.net/publication/6202672|publisher=Sage |s2cid=27995011 |issn=0306-624X | eissn = 1552-6933}}
• {{cite journal |last1=Petersilia |first1=Joan |title=Invisible Victims Violence against persons with developmental disabilities |journal=Human Rights |date=2000 |volume=27 |issue=1 |pages=9–12 |url=http://www.abanet.org/irr/hr/winter00humanrights/petersilia.html |access-date=12 July 2022 |publisher=American Bar Association |archive-date=1 September 2000 |archive-url=https://web.archive.org/web/20000901075103/http://www.abanet.org/irr/hr/winter00humanrights/petersilia.html}}
• Smith, Philip (2010). [https://archive.org/details/whateverhappened0000unse_z7p9 Whatever Happened to Inclusion?: The Place of Students with Intellectual Disabilities in Education]. New York: Peter Lang Publishing. {{ISBN|978-1433104343}}. {{LCCN|2009044580}}. {{OCLC|460711867}}.
• {{cite journal |last1=Søndenaa |first1=Erik |last2=Linaker |first2=Olav Martin |last3=Nøttestad |first3=Jim Aage |title=Effects of the changes in legislation governing offenders with intellectual disabilities in Norway: A descriptive study |journal=Journal of Policy and Practice in Intellectual Disabilities |date=September 2009 |volume=6 |issue=3 |pages=229–235 |doi=10.1111/j.1741-1130.2009.00206.x |publisher=International Association for the Scientific Study of Intellectual Disabilities |issn=1741-1130|doi-access=free }}
• Wehmeyer, Michael L. (2013). The Story of Intellectual Disability: An Evolution of Meaning, Understanding, and Public Perception. Brookes Publishing.

• {{Wiktionary-inline|intellectual disability}}

{{commons category}}

• [https://www.cdc.gov/ncbddd/childdevelopment/facts-about-intellectual-disability.html Facts about intellectual disabilities] from the US Centers for Disease Control's National Center on Birth Defects and Developmental Disabilities

• [https://www.youtube.com/watch?v=Jgl-tfUkhsQ Let's Work!] A documentary about eight young people with IDD in California and their experiences with competitive integrated employment. Funded by the California State Council on Developmental Disabilities

{{Medical condition classification and resources

|DiseasesDB = 4509

|ICD10 = {{ICD10|F70-F79}}

|ICD9 = {{ICD9|317}}–{{ICD9|319}}

|ICDO =

|OMIM =

|MedlinePlus = 001523

|eMedicineSubj = med

|eMedicineTopic = 3095

|eMedicine_mult = {{eMedicine2|neuro|605}}

|MeshID = D008607

}}

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