Rare diseases · Sign or symptom
Preaxial hand polydactyly
Extra thumb
HP:0001177
What it means
Supernumerary digits located at the radial side of the hand. Polydactyly (supernumerary digits) involving the thumb occurs in many distinct forms of high variability and severity. Ranging from fleshy nubbins over varying degrees of partial duplication/splitting to completely duplicated or even triplicated thumbs or preaxial (on the radial side of the hand) supernumerary digits.
Rare diseases that can present with this35
Very common80–99%
6Common30–79%
6Sometimes5–29%
22- Branchio-oculo-facial syndrome
- Curry-Jones syndrome
- Duane retraction syndrome
- Greig cephalopolysyndactyly syndrome
- Intellectual disability-cardiac anomalies-short stature-joint laxity syndrome
- IVIC syndrome
- Johnson neuroectodermal syndrome
- Lung agenesis-heart defect-thumb anomalies syndrome
and 14 more in this range
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. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Polydactyly affecting the thumb · Preaxial polydactyly of hands · Supernumerary thumb · thumb polydactyly
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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.