Psych · intellectual-disability
Intellectual disability: assessment and classification
Also known as Intellectual developmental disorder · IDD · Learning disability UK · Mental retardation historical · Disorders of intellectual development · Global developmental delay · Adaptive functioning assessment
Exam-exhaustive fellowship reference on intellectual disability assessment and classification — DSM-5-TR intellectual developmental disorder and ICD-11 disorders of intellectual development; dual intellectual-plus-adaptive criteria with developmental onset; severity by adaptive function; standardised assessment; aetiological workup (CMA, fragile X, exome, metabolic, imaging red flags); differentials; multiagency services, supported decision-making and premature mortality. FRANZCP-primary, globally tagged.
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Target exams
Red flags
- Diagnosing ID from IQ score alone without adaptive functioning assessment and developmental-onset history
- Developmental regression, seizures, focal neurology, or progressive micro/macrocephaly — urgent neurological and metabolic pathway, not watchful waiting
- Sudden behavioural change — exclude pain, constipation, dental disease, infection, epilepsy, medication toxicity before labelling behaviour as 'the disability'
- Diagnostic overshadowing — missing treatable mental or physical illness because the person has ID
- Assuming global incapacity — capacity is decision-specific; use supported decision-making
- Premature mortality risk from preventable physical disease — active health surveillance, not passive acceptance of early death
Meet the patient
A 9-year-old boy lands in your clinic because he is "not coping" in a mainstream classroom. He cannot follow multi-step instructions, misreads social cues, and still cannot manage money or tell the time. His mother recalls he sat late, spoke late, and still struggles with shoelaces. The school psychologist's report records a full-scale IQ of 62.[2][6]
Two questions are now live, and fellowship examiners ask both: is this intellectual disability — and by what three criteria? and what is the first-tier genetic test you must not omit? Everything below answers both at consultant depth.[2][3]
References18ShowHide
- [1]Maulik PK, Mascarenhas MN, Mathers CD, Dua T, Saxena S Prevalence of intellectual disability: a meta-analysis of population-based studies Res Dev Disabil, 2011.PMID 21236634
- [2]Moeschler JB, Shevell M; Committee on Genetics Comprehensive evaluation of the child with intellectual disability or global developmental delays Pediatrics, 2014.PMID 25157020
- [3]Miller DT, Adam MP, Aradhya S, et al. Consensus statement: chromosomal microarray is a first-tier clinical diagnostic test for individuals with developmental disabilities or congenital anomalies Am J Hum Genet, 2010.PMID 20466091
- [4]Shevell M, Ashwal S, Donley D, et al. Practice parameter: evaluation of the child with global developmental delay Neurology, 2003.PMID 12578916
- [5]Vissers LE, Gilissen C, Veltman JA Genetic studies in intellectual disability and related disorders Nat Rev Genet, 2016.PMID 26503795
- [6]Tassé MJ, Schalock RL, Balboni G, et al. The construct of adaptive behavior: its conceptualization, measurement, and use in the field of intellectual disability Am J Intellect Dev Disabil, 2012.PMID 22809075
- [7]Tassé MJ, Luckasson R, Schalock RL The Relation Between Intellectual Functioning and Adaptive Behavior in the Diagnosis of Intellectual Disability Intellect Dev Disabil, 2016.PMID 27893317
- [8]Schalock RL, Luckasson R, Tassé MJ An Overview of Intellectual Disability: Definition, Diagnosis, Classification, and Systems of Supports (12th ed.) Am J Intellect Dev Disabil, 2021.PMID 34700345
- [9]Salvador-Carulla L, Reed GM, Vaez-Azizi LM, et al. Intellectual developmental disorders: towards a new name, definition and framework for "mental retardation/intellectual disability" in ICD-11 World Psychiatry, 2011.PMID 21991267
- [10]de Ligt J, Willemsen MH, van Bon BW, et al. Diagnostic exome sequencing in persons with severe intellectual disability N Engl J Med, 2012.PMID 23033978
- [11]Vissers LE, de Ligt J, Gilissen C, et al. A de novo paradigm for mental retardation Nat Genet, 2010.PMID 21076407
- [12]Cooper SA, Smiley E, Morrison J, Williamson A, Allan L Mental ill-health in adults with intellectual disabilities: prevalence and associated factors Br J Psychiatry, 2007.PMID 17197653
- [13]Heslop P, Blair PS, Fleming P, Hoghton M, Marriott A, Russ L The Confidential Inquiry into premature deaths of people with intellectual disabilities in the UK: a population-based study Lancet, 2014.PMID 24332307
- [14]Moeschler JB; American Academy of Pediatrics Committee on Genetics Clinical genetic evaluation of the child with mental retardation or developmental delays Pediatrics, 2006.PMID 16740881
- [15]van Karnebeek CD, Shevell M, Zschocke J, Moeschler JB, Stockler S The metabolic evaluation of the child with an intellectual developmental disorder: diagnostic algorithm for identification of treatable causes and new digital resource Mol Genet Metab, 2014.PMID 24518794
- [16]Totsika V, Liew A, Absoud M, Adnams C, Emerson E Mental health problems in children with intellectual disability Lancet Child Adolesc Health, 2022.PMID 35421380
- [17]Reiss S, Szyszko J Diagnostic overshadowing and professional experience with mentally retarded persons Am J Ment Defic, 1983.PMID 6829617
- [18]Waggoner D, Wain KE, Dubuc AM, et al. Yield of additional genetic testing after chromosomal microarray for diagnosis of neurodevelopmental disability and congenital anomalies: a clinical practice resource of the American College of Medical Genetics and Genomics (ACMG) Genet Med, 2018.PMID 29915380