monosomy 21
MONDO:0018930Mondo
Findings
No curated finding names monosomy 21 yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
Monosomy 21 is a chromosomal anomaly characterized by the loss of variable portions of a segment of the long arm of chromosome 21 that leads to an increased risk of birth defects, developmental delay and intellectual deficit.
Definition from the Mondo Disease Ontology (MONDO:0018930), read 2026-09-29. CC BY 4.0.
Features
26 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.
- Failure to thrive in infancyHPOHP:0001531
- Very frequent (80% to 99% of cases)
- AnemiaHPOHP:0001903
- Frequent (30% to 79% of cases)
- Atrial septal defectHPOHP:0001631
- Frequent (30% to 79% of cases)
- Downslanted palpebral fissuresHPOHP:0000494
- Frequent (30% to 79% of cases)
- EpicanthusHPOHP:0000286
- Frequent (30% to 79% of cases)
- Global developmental delayHPOHP:0001263
- Frequent (30% to 79% of cases)
- High palateHPOHP:0000218
- Frequent (30% to 79% of cases)
- Intellectual disabilityHPOHP:0001249
- Frequent (30% to 79% of cases)
- Intrauterine growth retardationHPOHP:0001511
- Frequent (30% to 79% of cases)
- Low anterior hairlineHPOHP:0000294
- Frequent (30% to 79% of cases)
- Low-set earsHPOHP:0000369
- Frequent (30% to 79% of cases)
- MicroretrognathiaHPOHP:0000308
- Frequent (30% to 79% of cases)
Show the remaining 14
- Narrow foreheadHPOHP:0000341
- Frequent (30% to 79% of cases)
- Postnatal growth retardationHPOHP:0008897
- Frequent (30% to 79% of cases)
- Recurrent infectionsHPOHP:0002719
- Frequent (30% to 79% of cases)
- Secondary microcephalyHPOHP:0005484
- Frequent (30% to 79% of cases)
- ThrombocytopeniaHPOHP:0001873
- Frequent (30% to 79% of cases)
- Abnormal corpus callosum morphologyHPOHP:0001273
- Occasional (5% to 29% of cases)
Where it sits
- A kind of
Other names
4 names
Resolves to: monosomy 21
- Also called
- 21q deletion syndrome21q- syndromemonosomy type 21partial 21q monosomy