ORPHA:96055
Tetrasomy 21 syndrome
Also known as: Isochromosome 21
Publications
63
40.3th percentile
Trials
0
Interventional, condition-specific
Researchers
1,006
Distinct authors in sample
Gene link
—
Readiness
2/6
Stages with a signal
Clinical definition (Orphanet)
Tetrasomy 21 is an extremely rare anomaly resulting from the presence of 4 copies of chromosome 21, characterized by features of trisomy 21 including /, muscular , 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.
How rare: <1 / 1 000 000 — fewer than one in a million. In a city the size of Kolkata, that might mean on the order of fifteen people.
Cross-references
Joined from Mondo / Orphanet. MeSH labels may enter searches; UMLS / OMIM / NCIT are stored for reference.
- MONDO:0019864
- UMLS:C4707057
Additional Mondo synonyms (1)
tetrasomy type 21
Research stages
Trial readiness signals
Where this condition sits on an open-data research pipeline — not how close a treatment is, and not medical advice. Empty stages often mean “not in these databases under this Mondo ID,” not “impossible.”
2/6 stages with a signal
Research-stage checklist from open sources (GenCC, literature, Monarch when enriched, ClinicalTrials.gov). Not a prognosis or care recommendation.
- Gene identifiedNot found
No GenCC disease–gene assertion in this build
- LiteraturePresent
63 matched papers (29 in last 10 years) Source
- Phenotype characterisedPresent
17 HPO annotations (e.g. Brachycephaly; Thickened nuchal skin fold; Upslanted palpebral fissure) Source
- Animal modelNot found
No Alliance genotype “model of” associations via Monarch for these Mondo IDs
- Orphan designationNot found
No FDA or EMA orphan-drug designation matched this disease via UMLS or preferred name Source
- Interventional trialNot found
No matched interventional trial under our ClinicalTrials.gov rules
Biology
Genes and phenotypes
Gene–disease validity from GenCC, plus phenotypes and animal models joined from Monarch Initiative via Mondo ID — not a clinical diagnosis aid.
Do we know what causes it?
Not yet — the cause hasn't been pinned down in GenCC.
No strong gene–disease assertion joined for this Orphanet entity.
Phenotypes (Monarch / HPO)
17
Associated phenotypes · MONDO:0019864
- Brachycephaly
- Thickened nuchal skin fold
- Upslanted palpebral fissure
- Hypotonia
- Complete atrioventricular canal defect
Showing 5 of 17 — open Monarch for the full list.
Animal models (Monarch / Alliance)
None returned for this Mondo ID. Empty here is not proof that no model organism work exists under another name or gene.
Monarch fetch 2026-07-29
Therapies
Designations, candidates, and chemicals
FDA OOPD and EMA orphan designations, Open Targets clinical candidates, and CTD chemical associations via MyDisease.info. These never change the interventional-trial headline.
Orphan designation (FDA · EMA)
No designation matched this disease via UMLS or preferred name on the FDA OOPD mirror or EMA orphan register. Absence here is not proof that none exists under another wording.
Open Targets candidates
No drugs or clinical candidates returned for this Mondo ID on Open Targets.
CTD chemicals (MyDisease.info)
No CTD chemical associations returned for this Mondo ID.
Literature
Is anyone studying this?
63
63 papers have ever been published on this condition (under this name). For scale, breast cancer has over 700,000. Median papers in the last 10 years for a rare disease in this dataset (publications denominator n=3967) is 59.
63 papers since the earliest indexed year in this search — median last-10-year count for a rare disease in this dataset is 59 (publications denominator n=3967).
29 in the last 10 years · high confidence · 40.3th percentile (publications denominator)
Phrase hits: 63 · MeSH hits: 0
Who's working on it?
1,006
Distinct author names in 63 sampled papers — named people below.
Who's working on it?
No interventional trial matched this name; these authors publish on it in the sampled literature — a practical starting point for contact.
- 01Abdullah J16 papers · 2000
Neurosurgical Division, School of Medical Sciences, University Science Malaysia, Kelantan, Malaysia
Papers in Europe PMC - 02
- 03Isa M10 papers · 2000
Neurosurgical Division, School of Medical Sciences, University Science Malaysia, Kelantan, Malaysia
Papers in Europe PMC - 04
- 05Khalid B7 papers · 2000
Medicine, Faculty of Medicine. Hospital Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
Papers in Europe PMC - 06
- 07
- 08
- 09Ismarulyusda I5 papers · 2000
Medicine, Faculty of Medicine. Hospital Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
Papers in Europe PMC - 10Khairul O5 papers · 2000
Dept of Biomedical Sciences, Faculty of Allied Health Sciences, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
Papers in Europe PMC
Clinical research
Is a treatment being tested?
0
interventional trials for this specific condition
No interventional trial testing a treatment matched this specific condition name on ClinicalTrials.gov (observational studies and pan-disease registries are listed separately when present).
Data as of 11 September 2026 · last trial check 11 September 2026
No matched interventional trials. This is true for 77.2% of diseases in the trials denominator (5501 of 7126). Here are the researchers publishing on it.
high confidence · 38.6th percentile (trials denominator)
Recruiting interventional trials
From the matched ClinicalTrials.gov set
No interventional trial testing a treatment was found for this specific condition name on ClinicalTrials.gov.
Broader category tetrasomy also has no matched interventional trial. See who's working on it — people publishing on this disease are often the practical next contact when no trial is listed.
Broader category: tetrasomy
0
Interventional trials for the parent category, exclusive of NCT IDs already counted above. Eligibility for this subtype is not guaranteed.
Parent-category matching found a broader label but no interventional trials under it. How we count trials.
Other registries (secondary)
Broader net from EU CTIS, ISRCTN, and ICTRP when available — deduped against ClinicalTrials.gov IDs already counted above. Dual-model LLM relevance gates what we keep. These rows are not added to the interventional headline.
raw 0 · after dedupe 0 · already on CT.gov 0 · kept 0 · parent 0 · uncertain 0 · dropped 0 · fetched 2026-07-30
Source notes: ictrp: Error: ICTRP public search unavailable (WHO portal is SPA-only; SOAP needs partnership). Tried: https://apps.who.int/tri
No secondary-registry studies passed dual-model relevance for this condition name (after dedupe).
Where to find support
Condition-specific patient organisations, when Orphanet lists them, are on the disease’s Orphanet page. We also link umbrella groups that support undiagnosed and ultra-rare families.
Orphanet entry for Tetrasomy 21 syndrome — check Associations / patient organisations on that page.
India — NPRD
Last verified 2026-07-26This ORPHAcode is not on our curated NPRD list (direct or Mondo-parent match). That does not decide clinical eligibility; families in India should ask a notified Centre of Excellence about current coverage.
Hand-curated for this project. ORPHAcode mappings are best-effort and may be incomplete or imprecise for umbrella categories. Parent (Mondo) matches mean the policy lists a broader category — confirm eligibility with a Centre of Excellence. Financial entitlements summarised from public policy statements and may change. This is not official government guidance.
How we counted this
Europe PMC query (preferred label + any corrected label + Orphanet and Mondo exact synonyms, stoplisted; unioned with resolved MeSH labels when available). UMLS / OMIM / NCIT cross-references are stored on the overview but are not added to the query string.
"Tetrasomy 21 syndrome" OR "Isochromosome 21" OR "tetrasomy type 21"
ClinicalTrials.gov query (quoted phrases + MeSH via query.cond, plus recall-expansion terms when used):
"Tetrasomy 21 syndrome" OR "Isochromosome 21" OR "tetrasomy type 21"
Study-type breakdown: 0 interventional · 0 observational · 0 expanded access. Only interventional studies enter the trial headline.
Parent-category trials query:
"tetrasomy"
Query health: ok — strategies attempted: phrase; with hits: phrase
Run this search on ClinicalTrials.gov
Confidence reasoning
- Preferred label is multi-word and distinctive
- No synonyms dropped by stoplist
- No label/synonym collisions with other diseases in this corpus
Ingested 2026-07-27T04:50:09.756Z