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Osteochondromatosis (Discovered in the American Staffordshire Terrier)

Osteochondromatosis is a condition causing benign bone tumors, called osteochondromas, to form during puppyhood.

Key Signs

Lameness, Ataxia

Age of Onset

0 to 2 yrs

Juvenile onset


Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

High likelihood

At risk dogs are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with Osteochondromatosis

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about Osteochondromatosis

Affected dogs develop osteochondromas during bone development. Osteochondromas develop either in the metaphysis of the long bones or in the flat bones of the skeleton. Osteochondromas usually cease to grow when the dog has reached skeletal maturity. Clinical signs depend on the location of the lesions but include lameness and ataxia. Some osteochondromas can also be asymptomatic.

Therapy is limited to symptomatic treatments and general supportive care specific to the severity of the dog's clinical signs.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to develop. A carrier dog with one copy of the Osteochondromatosis mutation can be safely bred with a clear dog with no copies of the Osteochondromatosis mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Osteochondromatosis mutation. Puppies in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected puppies. Please note: It is possible that disease signs similar to the ones caused by the Osteochondromatosis mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene EXT2
Variant C>A
Chromosome 18
Coordinate 45,101,754

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Friedenberg, S. G., Vansteenkiste, D., Yost, O., Treeful, A. E., Meurs, K. M., Tokarz, D. A., & Olby, N. J. (2018). A de novo mutation in the EXT2 gene associated with osteochondromatosis in a litter of American Staffordshire Terriers. Journal of Veterinary Internal Medicine, 32(3), 986–992. View the article