Rare diseases · Sign or symptom
Profound intellectual disability
IQ less than 20
HP:0002187
What it means
Profound intellectual disability (ID) is defined as a type of ID characterized by profoundly sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) below 20.
Persons with profound mental retardation generally require constant care.
Rare diseases that can present with this37
Very common80–99%
14- Aicardi-Goutières syndrome
- Autosomal recessive cutis laxa type 2, classic type
- Christianson syndrome
- Fallot complex-intellectual disability-growth delay syndrome
- Microcephaly-brachydactyly-kyphoscoliosis syndrome
- Oliver syndrome
- Progressive microcephaly-seizures-cortical blindness-developmental delay syndrome
- Richieri Costa-da Silva syndrome
- Severe oculo-renal-cerebellar syndrome
- SLC39A8-CDG
- Thanatophoric dysplasia
- Thanatophoric dysplasia type 1
- X-linked intellectual disability-hypotonia-facial dysmorphism-aggressive behavior syndrome
- X-linked intellectual disability-limb spasticity-retinal dystrophy-arginine vasopressin deficiency
Common30–79%
16- Alacrimia-choreoathetosis-liver dysfunction syndrome
- Bainbridge-Ropers syndrome
- Bohring-Opitz syndrome
- Childhood-onset motor and cognitive regression syndrome with extrapyramidal movement disorder
- DPM3-CDG
- Early-onset progressive diffuse brain atrophy-microcephaly-muscle weakness-optic atrophy syndrome
- Global developmental delay-visual anomalies-progressive cerebellar atrophy-truncal hypotonia syndrome
- Isolated lissencephaly type 1 without known genetic defects
- Keppen-Lubinsky syndrome
- Pyruvate dehydrogenase E1-alpha deficiency
- RNF13-related severe early-onset epileptic encephalopathy
- Severe growth deficiency-strabismus-extensive dermal melanocytosis-intellectual disability syndrome
- Severe neurodevelopmental disorder with feeding difficulties-stereotypic hand movement-bilateral cataract
- Spastic tetraplegia-retinitis pigmentosa-intellectual disability syndrome
- X-linked intellectual disability-acromegaly-hyperactivity syndrome
- X-linked intellectual disability-cardiomegaly-congestive heart failure syndrome
Sometimes5–29%
6The 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, profound · Mental retardation, profound · Profound 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.