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Craniomandibular Osteopathy           CMO Test     Code 252

Test Pricing

For breeds: Australian Shepherd, Cairn Terrier, Lancashire Heeler, Parson Russell Terrier, Scottish Terrier, and West Highland White Terrier  

Clinical signs/Disease description:  

Craniomandibular Osteopathy (CMO) is a non-neoplastic (non-cancerous), proliferating disease in dogs causing extensive developmental changes in the bones of the skull and jaw. Symptoms include firm swelling of the jaw, drooling, pain, and difficulty eating. This usually occurs when the dogs are from 4 to 7 months old. The jaw is bilaterally thickened and several bones become so large and tender that the mouth cannot be fully opened. The tenderness of the affected jaw is associated with intermittent fever of 3 or 4 days duration. This tenderness and fever may recur every 2 to 4 weeks during the bone proliferation phase. Radiography is the best method for diagnosing CMO. Treatment is symptomatic. Most animals can be made comfortable using corticosteroids. However, treatment does not result in cure. Although the primary disease process does not seem to cause death, in some cases euthanasia has been performed because of severe pain and malnutrition resulting from the inability to eat.    

CMO mutation:  

Recently, a single causal DNA mutation for CMO has been identified by researchers at the Institute of Genetics, Vetsuisse faculty, University of Bern, Switzerland, and the Department of Veterinary Biosciences and Research Programs Unit, Molecular Medicine, University of Helsinki and Folkhälsan Research Center, Finland.  The mutation is highly associated with CMO in Cairn Terriers, Scottish Terriers, and West Highland White Terriers. In this study, about 85% of the CMO affected dogs had two copies of the mutation, 10% had a single copy of the mutation, and 5% of CMO diagnosed dogs did not carry the mutation. The development of the CMO disease is obviously dependent on the genetic status of a dog for the CMO mutation, but is also influenced by other unknown genetic and/or environmental factors.  The mode of inheritance of the CMO mutation is best described as autosomal dominant with incomplete penetrance, meaning that dogs of both sexes that are homozygous mutant (with two copies of the mutation) have a comparably higher risk to develop CMO. Dogs heterozygous for the mutation (one copy of the mutation) might also develop the disease, but some of the dogs carrying the CMO mutation will live without showing clinical signs.  

CMO test:  

The CMO test is based on the CMO causing mutation and it will accurately provide the genotype of a tested dog as follows:  

Homozygous Normal:
These dogs have two copies of normal gene and are highly likely to be clear of CMO.  

Carriers (low risk): These dogs have one copy of the CMO mutation and one copy of the normal gene. These dogs are at low risk to develop CMO themselves as a result of the CMO mutation and they will pass the mutation on to approximately 50% of their offspring. The other 50% of their offspring will receive a normal copy of the gene.  

Homozygous Affected (high risk):
These dogs have two copies of the CMO mutation and have a high chance of developing CMO (more than 57 % of dogs studied in the research program with two copies of the CMO mutation were clinically affected with CMO and 84% of the dogs exhibiting symptoms of CMO were Homozygous Affected). Veterinarians and breeders should be aware that some of the homozygous affected dogs may look normal, without showing obvious signs of CMO disease, but they will transmit the mutation to all their offspring.  

There may be other causes of CMO in the breeds so there is a possibility that dogs can develop a genetically different form of CMO due to other mutations that are not detected by this test.  

Testing/Breeding recommendations:

Because of incomplete penetrance and varying expressivity, many of the dogs carrying the CMO mutation do not show clinical signs of the disease. These presumed healthy dogs carrying one or two copies of the mutation are used for breeding, whereby the disorder may be perpetuated. Within a cohort of 303 West Highland White terriers the frequency of the mutant allele was quite high, at about 36%.   The CMO test will help to effectively reduce the number of CMO cases in the three terrier breeds if testing is done prior to mating. We strongly discourage breeding homozygous affected dogs. Carriers may be still used in breeding, if they are mated with homozygous normal (clear) dogs. About 50% of the progeny from such breeding schemes will be free of CMO mutation and can be used for selecting the best breeding dogs with desirable traits. A strict exclusion of all carriers would greatly narrow the gene pool within the breed which may lead to an increase of other hereditary diseases.

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