tetrasomy 21
Findings
No curated finding names tetrasomy 21 yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
Tetrasomy 21 is an extremely rare autosomal anomaly resulting from the presence of 4 copies of chromosome 21, characterized by features of trisomy 21 including developmental delay/intellectual disability, muscular hypotonia, short neck with redundant skin, brachycephaly, microcephaly, flat face, epicanthus, upslanted palpebral fissures, small ears, protruding tongue, single transverse palmar crease, brachydactyly, hypoplastic iliac wings, together with additional features such as prematurity, intrauterine growth retardation, high and broad forehead, hypertelorism. Haematological malignancies are also associated and may occur earlier than in trisomy 21.
Definition from the Mondo Disease Ontology (MONDO:0019864), read 2026-09-29. CC BY 4.0.
Features
17 features
What the disease is reported to present with, and how often among people who have it — never how often a feature means the disease. HPO, annotations 2026-09-02.
- BrachycephalyHPOHP:0000248
- Frequent (30% to 79% of cases)
- BrachydactylyHPOHP:0001156
- Frequent (30% to 79% of cases)
- Global developmental delayHPOHP:0001263
- Frequent (30% to 79% of cases)
- HypotoniaHPOHP:0001252
- Frequent (30% to 79% of cases)
- Intellectual disabilityHPOHP:0001249
- Frequent (30% to 79% of cases)
- MicrocephalyHPOHP:0000252
- Frequent (30% to 79% of cases)
- Protruding tongueHPO
Show the remaining 5
- Depressed nasal bridgeHPOHP:0005280
- Occasional (5% to 29% of cases)
- HypertelorismHPOHP:0000316
- Occasional (5% to 29% of cases)
- MacroglossiaHPOHP:0000158
- Occasional (5% to 29% of cases)
- Sandal gapHPOHP:0001852
- Occasional (5% to 29% of cases)
- Transient myeloproliferative syndromeHPOHP:0005534
- Occasional (5% to 29% of cases)
Where it sits
- A kind of
Other names
2 names
Resolves to: tetrasomy 21
- Also called
- Isochromosome 21tetrasomy type 21