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Craniomandibular Osteopathy (Discovered in the Basset Hound)

Craniomandibular Osteopathy (CMO), also known as "lion's jaw," is a disorder of bone growth, with bones of the skull most consistently affected. During the growth period, the jaw bones become swollen and thickened, causing pain, drooling, and difficulty eating. The associated genetic variant has been identified in the Basset Hound.

Key Signs

Swelling and thickening of the jaw, Difficulties in chewing and opening mouth, Pain, Recurrent fever, Weight Loss, Behavior changes

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

Moderate likelihood

At risk dogs may show signs of this disease in their lifetime, although some 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

Craniomandibular Osteopathy is an inherited skeletal condition that appears in young, growing dogs with clinical signs typically first appearing between 3 and 8 months of age. CMO is characterized by pain, swelling, and thickening of the skull bones, especially the ramus of the mandible, calvarial bone near the jaw joint, and the tympanic bulla. The pain and inflammation can result in recurrent fever, weight loss, decreased appetite, drooling, unwillingness to open the mouth, and related changes in behavior. Bony spurs can occur and proliferate, and may or may not disappear with resolution of clinical signs once growth is finished. As CMO and Hypertrophic Osteodystrophy (HOD) are now thought to be part of the same condition, this condition may also affect the long bones, especially in the area of the growth plates, where rapid growth occurs. Recurrence has been reported in adults. The mode of inheritance for CMO is thought to be autosomal dominant with incomplete penetrance, meaning not all individuals who inherit the associated genetic variant will develop the condition.

There is no cure for CMO. Treatment consists of pain management with supportive and symptomatic care determined by the severity of the dog's clinical signs. Signs tend to resolve once the affected dog's growth period is finished, but multiple episodes of fever and pain may occur before resolution.

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 genetic variant is considered a risk factor for Craniomandibular Osteopathy (Discovered in the Basset Hound), and dogs with one or two copies of the variant are at increased risk for being diagnosed with this condition. However not all dogs with one or two copies of this variant will go on to develop associated signs. Breeding of dogs with one or two copies of the CMO variant 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 variant is bred with a clear dog with no copies of the CMO variant, about half of the puppies will have one copy and half will have no copies of the variant. Please note: It is possible that signs similar to the ones associated with this CMO variant could develop due to a different genetic or clinical cause.

Technical Details

Gene SLC37A2
Variant C>T
Chromosome 5
Coordinate 9,387,071

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Letko, A., Leuthard, F., Jagannathan, V., Corlazzoli, D., Matiasek, K., Schweizer, D., … Drögemüller C. (2020). Whole Genome Sequencing Indicates Heterogeneity of Hyperostotic Disorders in Dogs. Genes (Basel), 11(2), 163. View the article