Rare diseases · Sign or symptom
Intellectual disability
Mental deficiency
HP:0001249
What it means
The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.
This term should be used for children who are at least five years old. For younger children, consider using the term Global developmental delay (HP:0001263). According to the WHO classification, Disorders of intellectual development are a group of etiologically diverse conditions originating during the developmental period characterized by significantly below average intellectual functioning and adaptive behavior that are approximately two or more standard deviations below the mean (approximately less than the 2nd/3rd percentile, corresponding roughly to an IQ threshold of 70). A diagnosis of intellectual disability should not be based solely on the results of tests of intellectual and adaptive functioning; rather, it is based on a combination of clinical assessment and judgment in conjunction with the results of standardized tests of intellectual and adaptive functioning.
Rare diseases that can present with this859
Always100%
8Very common80–99%
72- 10q22.3q23.3microdeletion syndrome
- 15q11q13microduplication syndrome
- 17q21.31microduplication syndrome
- 19q13.11microdeletion syndrome
- 1p21.3microdeletion syndrome
- 1p36deletion syndrome
- 1q21.1microduplication syndrome
- 1q41q42microdeletion syndrome
- 20q13.33microdeletion syndrome
- 2q31.1microdeletion syndrome
- 2q37microdeletion syndrome
- 3C syndrome
- 3-methylglutaconic aciduria type 4
- 3q29microdeletion syndrome
- 48,XXYY syndrome
- 48,XYYY syndrome
- 49,XXXXY syndrome
- 49,XXXYY syndrome
- 49,XYYYY syndrome
- 5q35microduplication syndrome
- 8p11.2deletion syndrome
- 8p inverted duplication/deletion syndrome
- 8q21.11microdeletion syndrome
- ABetaL34V amyloidosis
- Achalasia-microcephaly syndrome
- Acrocardiofacial syndrome
- Acrodysostosis
- Acromelic frontonasal dysplasia
- Adenylosuccinate lyase deficiency
- Adult polyglucosan body disease
- AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome
- Ahmad syndrome
- ALDH18A1-related De Barsy syndrome
- Alexander disease
- ALG11-CDG
- ALG1-CDG
- ALG9-CDG
- Allan-Herndon-Dudley syndrome
- Alopecia-contractures-dwarfism-intellectual disability syndrome
- Alopecia-contractures-dwarfism-intellectual disability syndrome
- Alopecia-intellectual disability syndrome
- Alpha-mannosidosis
- Alpha-mannosidosis, infantile form
- Alpha-N-acetylgalactosaminidase deficiency
- Alpha-N-acetylgalactosaminidase deficiency type 3
- Alpha-thalassemia-intellectual disability syndrome linked to chromosome 16
- Aniridia-cerebellar ataxia-intellectual disability syndrome
- Aniridia-ptosis-intellectual disability-familial obesity syndrome
- Aortic arch anomaly-facial dysmorphism-intellectual disability syndrome
- Arginine vasopressin resistance-intracranial calcification-short stature-facial dysmorphism syndrome
- Aspartylglucosaminuria
- Ataxia-deafness-intellectual disability syndrome
- Atkin-Flaitz syndrome
- Attenuated Chédiak-Higashi syndrome
- Atypical Rett syndrome
- Autism spectrum disorder due to AUTS2 deficiency
- Autosomal recessive cerebellar ataxia-epilepsy-intellectual disability syndrome due to TUD deficiency
- Autosomal recessive cerebellar ataxia-psychomotor delay syndrome
- Autosomal recessive cerebelloparenchymal disorder type 3
- Autosomal recessive congenital cerebellar ataxia due to MGLUR1 deficiency
- Autosomal recessive cutis laxa type 2A
- Autosomal recessive spastic paraplegia type 45
- Autosomal recessive spastic paraplegia type 54
- Autosomal recessive spastic paraplegia type 75
- Autosomal spastic paraplegia type 18
- Aymé-Gripp syndrome
- Bainbridge-Ropers syndrome
- Bamforth-Lazarus syndrome
- Bangstad syndrome
- Baraitser-Winter cerebrofrontofacial syndrome
- Beta-mannosidosis
- Beta-mercaptolactate cysteine disulfiduria
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, and Orphanet separately records 22 diseases where this sign is specifically absent. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Dull intelligence · Low intelligence · Mental retardation · Mental retardation, nonspecific · Mental-retardation · Nonprogressive intellectual disability · Nonprogressive mental retardation · Poor school performance
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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.