Rare diseases · Sign or symptom
Triphalangeal thumb
Finger-like thumb
HP:0001199
What it means
A thumb with three phalanges in a single, proximo-distal axis. Thus, this term applies if the thumb has an accessory phalanx, leading to a digit like appearance of the thumb.
The requirement for a single PD axis relates to the issue that partial forms of Preaxial polydactyly may comprise a partially duplicated thumb with two distal phalanges and a single proximal phalanx. That finding is instead coded as a mild form of thumb polydactyly. Note that this finding can be readily assessed by examination and/or physical manipulation of the thumb.
Rare diseases that can present with this31
Very common80–99%
7Common30–79%
11- Acrocallosal syndrome
- Acro-renal-ocular syndrome
- Autosomal dominant deafness-onychodystrophy syndrome
- Fetal hydantoin syndrome
- Holt-Oram syndrome
- IVIC syndrome
- MMEP syndrome
- Multinodular goiter-cystic kidney-polydactyly syndrome
- PHAVER syndrome
- Thalidomide embryopathy
- Thumb deformity-alopecia-pigmentation anomaly syndrome
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: Accessory phalanx of the thumb · Digitalized thumb · Triphalangeal thumbs · Triphalangy of thumb
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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.