Rare diseases · Sign or symptom
Severe intellectual disability
Early and severe mental retardation
HP:0010864
What it means
Severe intellectual disability (ID) is defined as a type of ID characterized by severely sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 20-34.
Persons with severe mental retardation can be taught basic life skills and simple tasks with supervision.
Rare diseases that can present with this197
Very common80–99%
79- 16p13.11microdeletion syndrome
- 1q44microdeletion syndrome
- 2q23.1microdeletion syndrome
- 2q32q33deletion syndrome
- 3-methylglutaconic aciduria type 9
- 4q21microdeletion syndrome
- 5q14.3microdeletion syndrome
- 8p inverted duplication/deletion syndrome
- 9q33.3q34.11microdeletion syndrome
- Acrocallosal syndrome
- Acrofrontofacionasal dysostosis
- Aicardi syndrome
- AICA-ribosiduria
- Alazami syndrome
- Alpha-N-acetylgalactosaminidase deficiency type 1
- Alport syndrome-intellectual disability-midface hypoplasia-elliptocytosis syndrome
- Amelocerebrohypohidrotic syndrome
- Angelman syndrome
- Argininemia
- Autosomal recessive primary microcephaly
- BRESEK syndrome
- Congenital muscular dystrophy, Fukuyama type
- Cono-spondylar dysplasia
- Cornelia de Lange syndrome
- Corpus callosum agenesis-abnormal genitalia syndrome
- Deafness-intellectual disability syndrome, Martin-Probst type
- Distal duplication 17q syndrome
- Duplication of the pituitary gland
- Early-onset seizures-distal limb anomalies-facial dysmorphism-global developmental delay syndrome
- Ectodermal dysplasia-intellectual disability-central nervous system malformation syndrome
- Encephalopathy due to sulfite oxidase deficiency
- Facial dysmorphism-macrocephaly-myopia-Dandy-Walker malformation syndrome
- FOXG1 syndrome due to 14q12 microdeletion
- Fucosidosis
- Hall-Riggs syndrome
- Hydrocephalus with stenosis of the aqueduct of Sylvius
- Hypotonia-speech impairment-severe cognitive delay syndrome
- Infantile choroidocerebral calcification syndrome
- Intellectual disability-balding-patella luxation-acromicria syndrome
- Intellectual disability-coarse face-macrocephaly-cerebellar hypotrophy syndrome
- Intellectual disability-hypoplastic corpus callosum-preauricular tag syndrome
- Intellectual disability-myopathy-short stature-endocrine defect syndrome
- Intellectual disability-obesity-brain malformations-facial dysmorphism syndrome
- Intellectual disability-seizures-hypophosphatasia-ophthalmic-skeletal anomalies syndrome
- Intellectual disability, Wolff type
- KAT6-related intellectual disability-craniofacial anomalies-cardiac defects syndrome
- KDM5C-related syndromic X-linked intellectual disability
- Kleefstra syndrome
- L-2-hydroxyglutaric aciduria
- Megalencephaly-severe kyphoscoliosis-overgrowth syndrome
- MEHMO syndrome
- Microcephaly-microcornea syndrome, Seemanova type
- Microlissencephaly
- Micro syndrome
- Monosomy 5p syndrome
- MPDU1-CDG
- Mucopolysaccharidosis type 3
- Pachygyria-intellectual disability-epilepsy syndrome
- Pallister-Killian syndrome
- PEHO syndrome
- Pelizaeus-Merzbacher disease, connatal form
- Peroxisomal acyl-CoA oxidase deficiency
- Posterior-predominant lissencephaly-broad flat pons and medulla-midline crossing defects syndrome
- Proximal Xq28 duplication syndrome
- PRUNE1-related neurological syndrome
- Pseudoleprechaunism syndrome, Patterson type
- Recessive intellectual disability-motor dysfunction-multiple joint contractures syndrome
- Ring chromosome 13 syndrome
- Severe achondroplasia-developmental delay-acanthosis nigricans syndrome
- Severe intellectual disability and progressive spastic paraplegia
- Severe intellectual disability-epilepsy-anal anomalies-distal phalangeal hypoplasia
- Severe intellectual disability-short stature-behavioral abnormalities-facial dysmorphism syndrome
- Sporadic fetal brain disruption sequence
- Stimmler syndrome
- TELO2-related intellectual disability-neurodevelopmental disorder
- Trisomy 13 syndrome
- Trisomy 18 syndrome
- Trisomy 5p syndrome
- Wolf-Hirschhorn syndrome
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Intellectual disability, severe · Mental retardation, severe · Severe mental retardation
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.