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Canine Mendelian disease record

Osteochondromatosis (Discovered in the American Staffordshire Terrier)

Osteochondromatosis (Discovered in the American Staffordshire Terrier). Autosomal recessive. Observed in 0 of 266 breeds tested in the Sniff Atlas, with measured variant frequencies drawn from 242,663 dogs (Donner 2023). Whether a dog carrying this variant is at risk depends on the disease’s inheritance pattern; outcome also depends on penetrance, modifiers, and environment. The frequencies below describe variant prevalence, not confirmed disease incidence.

OMIA identifier
OMIA:001214-9615
Autosomal recessive
Linked gene
EXT2
Human counterpart
In humans, this gene is EXT2. OMIM 608210 In people, EXT2 appears tolerant of loss-of-function variation (gnomAD v4.1 constraint, LOEUF 0.78). Constraint measures intolerance to loss-of-function only and does not indicate importance; some tolerant genes cause disease through other mechanisms. In people, variants in the EXT2 gene have conflicting classifications in ClinVar, and none is expert-reviewed. The evidence is unsettled, not that variants here are benign.
Source dataset
Sniff Atlas v1.0.1 / DOI
The human connection

A model of human exostoses, multiple, type 2

Dogs with this condition carry a change in EXT2. In people, changes in the same gene cause exostoses, multiple, type 2. That makes affected dogs a naturally-occurring model of the human disease, and it is part of why studying dogs moves medicine forward for everyone. It does not mean your dog has the human disease. It means the two share an underlying biology.

In people, the disease is described as: This gene is involved in the heparin/heparin sulfate biosynthesis, cell organization/biogenesis and development of the cytoskeleton in chondrocytes.

In humans it is also called: exostoses (Multiple) 2 Gene, exostoses, multiple caused by mutation in EXT2, EXT2 exostoses, multiple, EXT2 Gene.

MONDO:0007586 OMIM 133701

Mapped from OMIA via the human disease's OMIM entry to the Mondo Disease Ontology (Monarch Initiative, CC-BY 4.0). Sniff renders this as a model-of link; the canine disease remains the subject of this page.

About this disease

From OMIA's curated record

Documented in OMIA (Online Mendelian Inheritance in Animals). This describes the disease as recorded in the published literature, not a prediction for any individual dog. As of 2026-06-03.

Clinical features

Osteochondromatosis is a skeletal developmental disorder that results in exostoses (cartilage capped bone outgrowths) that develop during the growth period (Pacifici, 2017). Depending on the location and size of the exostoses, osteochondromatosis can clinically present asymptotically, or can cause pain, lameness, paresis and paralysis (Czerwik et al. 2019). Clinical signs often occur due to compression of nearby tissues, including nerve root compression (causing pain) or spinal cord compression (causing paralysis) (Friedenberg et al., 2018). [IT thanks DVM student Lilli Wilhelm, who provided the basis of this contribution in April 2022]

Molecular genetics

Friedenberg et al. (2018) reported a likely de novo causal variant in American Staffordshire Terriers as "One heterozygous variant (c.969C > A) is predicted to result in a stop codon in exon 5 of the [EXT2] gene. Sanger sequencing identified the identical mutation in all affected offspring. The mutation was absent in the unaffected offspring, both parents, all available grandparents, and 26 healthy unrelated American Staffordshire Terriers." These same authors note that "Because this mutation arose de novo, the identical mutation is unlikely to be the cause of osteochondromatosis in other dogs. However, de novo mutations in EXT2 are common in humans with osteochondromatosis, and by extension, it is possible that dogs with osteochondromatosis could be identified by sequencing the entire EXT2 gene."

Pathology

Whilst the pathophysiology and progression of the condition remains unclear, the disease is associated with abnormal migration of chondrocytes from the epiphyseal growth plates towards the bony cortex (Czerwik et al., 2019). The heterotopic cartilage cells that become ossified causes irregular bone formation on bone surfaces (Doige, 1987). The exostoses mainly occur on tissues that undergo endochondral ossification, including long bones, ribs and spinous processes of vertebrae (Doige, 1987). Growth of osteochondromas ceases at the time of physeal closure, known as skeletal maturity (Mozos et al., 2002). [IT thanks DVM student Lilli Wilhelm, who provided the basis of this contribution in April 2022]

Human analog

OMIA links this condition to its human counterpart in OMIM (Mendelian Inheritance in Man), the place to read across to the deeper human literature for the same biology.

Disease · OMIM 133701 Gene · OMIM 608210

Source: OMIA (Nicholas, Tammen & the Sydney Informatics Hub), entry OMIA:001214-9615, doi:10.25910/2AMR-PV70 (CC-BY 4.0).

The evidence

Published references

The peer-reviewed papers behind this disease, curated by OMIA. Starred entries are OMIA-designated landmark papers. Showing 6 of 17.

  1. Lumbar myelopathy caused by multiple cartilaginous exostoses in a dog. · Top Companion Anim Med · 2021 · PMID 33631383
  4. Primary synovial osteochondromatosis of the stifle in an English Mastiff. · Vet Comp Orthop Traumatol · 2012 · PMID 22286965
  5. A newly recognized pattern of canine osteochondromatosis. · Vet Radiol Ultrasound · 2002 · PMID 11954808
  6. Malignant transformation of solitary spinal osteochondroma in two mature dogs. · Vet Radiol Ultrasound · 1999 · PMID 10608692

References curated by OMIA (Nicholas, Tammen & the Sydney Informatics Hub), doi:10.25910/2AMR-PV70 (CC-BY 4.0). Full list at the OMIA entry.

Your breed

See what Osteochondromatosis (Discovered in the American Staffordshire Terrier) looks like in your dog's breed.
Variant frequency by breed

Observed only in small-sample breeds

Maximum variant frequency per breed across variants in the Donner 2023 cohort, with . The list below is split into well-sampled breeds (n ≥ 50 tested) and small-sample breeds (n < 50, where the Wilson CI typically spans more than 20 percentage points and frequencies should not be compared directly to the well-sampled entries). Frequencies are population-level, not per-litter or per-line.

Scope of this record

Scope

This record carries the breed-level carrier frequencies from the Donner 2023 cohort. Penetrance data (the fraction of at-risk dogs that develop the phenotype) is not yet quantified for this disease in the Sniff Atlas v1.0.1. The OMIA entry is the authoritative reference for the clinical phenotype, inheritance pattern, and gene assignment.

Predicted disease relevance at the per-dog level is UNPROVEN. The variant frequency is measured; phenotype outcome depends on penetrance, environment, and modifier loci. Consult a veterinarian for clinical interpretation.

How to cite this record

Citations

If you use this record in published work, cite the Sniff Atlas (the published dataset that carries the breed-level carrier frequencies) and the upstream sources:

  • Sniff Atlas v1.0.1 for the per-breed carrier frequencies:

    Gehring, M. (2026). Sniff Atlas v1.0.1. Zenodo. https://doi.org/10.5281/zenodo.20566358. CC-BY 4.0.

  • OMIA for the disease definition, inheritance, and gene assignment:

    Nicholas, F. W., & Tammen, I. (2024). OMIA. Sydney Informatics Hub, The University of Sydney. https://doi.org/10.25910/2AMR-PV70. Entry: OMIA:001214-9615.

  • Donner et al. 2023 for the breed × variant carrier-frequency cohort:

    Donner, J., Freyer, J., Davison, S., Anderson, H., Blades, M., Honkanen, L., et al. (2023). Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLOS Genetics, 19(2), e1010651. https://doi.org/10.1371/journal.pgen.1010651.

Full citation formats (BibTeX, RIS, CITATION.cff) at sniff.world/cite.

Related

Related

Last updated
Sources: Sniff Atlas v1.0.1 · OMIA OMIA:001214-9615 · Donner et al. 2023 · gnomAD v4.1 (Karczewski 2020) · ClinVar (Landrum 2018)