Rare diseases · Sign or symptom
Exostoses
Formation of new noncancerous bone on top of existing bone
HP:0100777
What it means
An exostosis is a benign growth the projects outward from the bone surface. It is capped by cartilage, and arises from a bone that develops from cartilage.
Rare diseases that can present with this20
Very common80–99%
7Sometimes5–29%
8- 8p23.1duplication syndrome
- Autosomal dominant otospondylomegaepiphyseal dysplasia
- Bazex-Dupré-Christol syndrome
- Craniofacial dysostosis-diaphyseal hyperplasia syndrome
- Oculocerebrocutaneous syndrome
- Progressive non-infectious anterior vertebral fusion
- Proteus syndrome
- Seizures-scoliosis-macrocephaly 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
Tracking symptoms like this for someone? Eleplan keeps symptoms, diagnoses, medications and every specialist in one plan.
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.