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Craniomandibular Osteopathy (Discovered in Scottish Terrier breeds)

Craniomandibular Osteopathy (CMO), also known as "lion's jaw", is a disorder of the skull where the jaw bones show swelling and thickening, causing pain, drooling, and difficulties in eating.

Found in

1 in 420 dogs

in our testing

Key Signs

Swelling and thickening of the jaw, Difficulties in chewing, Pain, Recurrent fever

Age of Onset

0 to 2 yrs

Juvenile onset


Autosomal Dominant

For autosomal dominant disorders, dogs with one or two copies of the disease variant are at risk of developing the condition. Inheriting two copies of the risk variant may make the risk higher or the condition more severe. They may produce puppies affected with the disorder if bred.

Likelihood of the Condition

Low-moderate likelihood

At risk dogs may show signs of this disease in their lifetime, although many will not develop the condition due to absence of additional risk factors.

What to Do

Here’s how to care for a dog with CMO

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 CMO

The first clinical signs of CMO typically appear at the age of 4 to 7 months. The skull bones and especially the mandible seem enlarged due to swelling and thickening of the jaw. The condition causes pain, which manifests in drooling, difficulties in eating, and unwillingness to open mouth. In addition, recurrent fever may be associated with CMO. Bone changes may disappear once the dog's growth period is finished, but before that multiple episodes of fever and pain may occur.

Treatment is pain management, supportive care, and symptomatic depending on 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 mutation is considered a risk factor for Craniomandibular Osteopathy, and dogs with one or two copies of the mutation are at increased risk. However not all dogs with one or two copies of this mutation will show signs of disease. Use of dogs with one or two copies of the disease mutation is not recommended, as there is a risk that the resulting litter will contain affected puppies. For example if a dog with one copy of the CMO mutation is bred with a clear dog with no copies of the CMO mutation, about half of the puppies will have one copy (carriers) and half will have no copies of the CMO mutation. Please note: It is possible that disease signs similar to the ones caused by the CMO mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene SLC37A2
Variant C>T
Chromosome 5
Coordinate 9,387,327

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Hytönen, M. K., Arumilli, M., Lappalainen, A. K., Owczarek-Lipska, M., Jagannathan, V., Hundi, S., … Lohi, H. (2016). Molecular Characterization of Three Canine Models of Human Rare Bone Diseases: Caffey, van den Ende-Gupta, and Raine Syndromes. PLoS Genetics, 12(5), 1–20. View the article