Tetrasomy 21 syndrome
Synonyms: Isochromosome 21
- Type
- Malformation syndrome
- Group
- Disorder
- Age of onset
- Antenatal, Infancy, Neonatal
- Status
- active
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.
Names in Orphadata languages
12 of 12 languages| Lang | Name | Synonyms |
|---|---|---|
| en | Tetrasomy 21 syndrome | Isochromosome 21 |
| fr | Syndrome de tétrasomie 21 | = en |
| de | Tetrasomie 21 | Isochromosom 21 |
| es | Síndrome de tetrasomía 21 | Isocromosoma 21 |
| it | Sindrome tetrasomia 21 | Isocromosoma 21 |
| nl | Tetrasomie 21-syndroom | Isochromosoom 21 |
| pt | Tetrassomia 21 | |
| pl | Zespół tetrasomii chromosomu 21 | Izochromosom 21 |
| cs | Tetrazomie 21 | Izochromozom 21 |
| uk | Тетрасомія 21 | Ізохромосома 21 |
| zh | 21四体 | 21号等臂染色体 |
| tr | Tetrazomi 21 | İzokromozom 21 |
Definition in:
Cross-references
qualifier = Orphanet mapping relation| Source | Code | Qualifier | ICD relation | Validation |
|---|---|---|---|---|
| ICD-10 | Q99.8 | NTBT | attributed | validated |
| ICD-11 | LD7Y | NTBT | index | validated |
| MONDO | 0019864 | E | validated | |
| UMLS | C4707057 | E | validated | |
| GARD | 12480 | E | validated |
E exact · NTBT this ORPHAcode is narrower than the target · BTNT broader than the target · ND not decided.
Classification
Preferential parent (Orphanet linearisation):
Parents in the classifications (1):
- ORPHA:98132Partial autosomal duplication/triplication syndrome
rare developmental anomalies during embryogenesis; rare genetic diseases
No children.
Genes
0 directOrphanet records no gene directly on this code.
Prevalence and incidence
2 records| Type | Class | Value | Area | Qualification | Validation | Source |
|---|---|---|---|---|---|---|
| Cases/families | 13 cases | Worldwide | Case(s) | Validated | 18372039[PMID] | |
| Point prevalence | <1 / 1 000 000 | — | Worldwide | Class only | Validated | ORPHANET_18372039[PMID] |
Value is Orphadata's ValMoy: the mean estimate per 100 000 for prevalence and incidence, the number of cases or families for case reports.
HPO phenotypes
17 annotations · validated 2025-09-02| HPO | Term (as annotated by Orphanet) | Diagnostic |
|---|---|---|
| Frequent (79-30%) | ||
| HP:0000248 | Brachycephaly | |
| HP:0001156 | Brachydactyly | |
| HP:0001263 | Global developmental delay | |
| HP:0001252 | Hypotonia | |
| HP:0001249 | Intellectual disability | |
| HP:0000252 | Microcephaly | |
| HP:0010808 | Protruding tongue | |
| HP:0000311 | Round face | |
| HP:0000954 | Single transverse palmar crease | |
| HP:0000474 | Thickened nuchal skin fold | |
| HP:0000582 | Upslanted palpebral fissure | |
| Occasional (29-5%) | ||
| HP:0001674 | Complete atrioventricular canal defect | |
| HP:0005280 | Depressed nasal bridge | |
| HP:0000316 | Hypertelorism | |
| HP:0000158 | Macroglossia | |
| HP:0001852 | Sandal gap | |
| HP:0005534 | Transient myeloproliferative syndrome | |
Annotation source: 31493343[PMID]_34472202[PMID]_3161017[PMID]
Sources for this card
- Orphanet page: orpha.net/en/disease/detail/96055
- This record as JSON: /data/d/96055.json