Craniomandibular Osteopathy (CMO)
Craniomandibular osteopathy (CMO) is a non-neoplastic (non-tumorous) disease affecting young dogs. It is most common in Scottish terriers, West Highland white terriers, and cairn terries, but has been diagnosed also in Labrador retrievers, Great Danes, Irish Setters, English Bulldogs, Boxers and Doberman pinschers. Craniomandibular osteopathy has been for the first time diagnosed and described in five West Highland white terriers in 1958. Disorder’s equivalents have been recognized in human patients. Caffey disease, also known as infantile cortical hyperostosis, is a common bone disorder in babies. It characterized by excessive new bone formation, condition known as hyperostosis. Another human disorder that shares radiographic and histologic findings in disorderly bone with CMO is Padget’s diseases, relatively common non-neoplastic proliferative bone disorder in elderly people.
Characteristics and Symptoms
As ability to eat and drink is crucial for living, disorders of eating or drinking system can be extremely severe. The process of eating and drinking are coordinated by activities of the brain and its hunger and thirst centre, as well as physical functions of nose, mouth, esophagus and gastrointestinal tract. Holding and chewing of the food is allowed by dog’s bones of the skull, muscles of chewing, attached ligaments, and tendons. Two primary bones of the dog’s mouth are the mandible (the lower jawbone) and the maxilla (the upper jawbone). These two bones meet at the temporomandibular joint (TMJ), which is crucial for opening and closing of the jaw, coordinated by the muscles of the cheek.
Craniomandibular osteopathy (CMO) causes excessive bone formation along the mandible (the lower jaw) and the temporomandibular joint, resulting in difficulties and pain when opening the mouth during eating or drinking.
Symptoms of the disorder appear between 4 to 8 months of puppy’s age, can vary from mild to severe and they appear equally in both genders, male and female. Craniomandibular osteopathy symptoms include progressively worsening pain upon opening the mouth, loss of appetite, difficulty opening the mouth, difficulty picking up food with the mouth and chewing, excessive drooling, bulging eyes due to swelling inside the skull and jaw swelling. The jaw is thickened from both sides (bilaterally), causing several bones to become so large and tender that full opening of the mouth becomes impossible. The tenderness pf the jaw is accompanied with fever of 3 to 4 days of duration. Fever is reoccurring with every new bone proliferation phase, which is happening every 2 to 4 weeks. Lymphadenopathy or temporal muscle atrophy may be present, as well as hypertrophic bones in the soft tissues adjacent to long bones. CMO can be diagnosed with radiography, which will show abnormal bone growth. Blood tests show normal erythrocytes, leukocytes, haemoglobin, calcium, phosphorus and alkaline phosphatase levels.
Craniomandibular osteopathy (CMO) is not a death-causing disorder, but due to severe pain and problems caused by inability to eat and drink, euthanasia is performed on affected dogs. Symptoms can be eased with usage of corticosteroids and non-steroidal drugs, such as aspirin. These drugs can make process of eating and drinking for dogs more comfortable, but treatment of disorder with them does not result in cure.
Researches of frequency of affected dogs have shown that of 81 affected dogs, 44 were West Highland white terriers, 22 were Scottish Terriers and 2 were Cairn Terriers, meaning that Scottish tearrier breeds make 84% of affected dogs. Moreover, all together incidence of CMO among different dog breeds is low, but it is a significant problem for Westies owners. Further researchers showed that most of affected dogs develop symptoms at age between 2-6 months (47.1%), but certain dogs also developed symptoms at age older than 2 years (4.5%).
Craniomandibular osteopathy (CMO) is caused by a mutation in SLC37A2 gene and has been recognized as disorder with autosomal dominant with incomplete penetrance mode of inheritance.
SCLA37A2 is a transporter protein in osteoclasts, and it plays a central role in glucose homeostasis within these cells that participate in osteogenesis. Mutations within this gene cause improper glucose supply in the osteoclasts, resulting in abnormal development of the bone and hyperostosis.
Considering the mutated gene, dog can be clear homozygous, carrier heterozygous and affected homozygous. Heterozygous carrier has one copy of mutated gene, is at low risk of developing symptoms of CMO and has 50% chance of passing the mutation on their offspring. Affected homozygous dog has two copies of mutated gene and is at high risk of developing disorder’s symptoms. Studies have shown that 84% of the dogs showing symptoms of CMO were homozygous affected. However, it is possible that some of the homozygous affected dogs look normal, and without showing any symptoms, but they will 100% transmit the mutation to all their offspring. Research has shown that within population of 303 West Highland white terriers, frequency of the mutated gene was high, about 36%.
Marjo K. Hytönen,Affiliations Meharji Arumilli, Anu K. Lappalainen, AffiliationMarta Owczarek-Lipska, Vidhya Jagannathan, AffiliationSruthi Hundi, AffiliationsElina Salmela, AffiliationsPatrick Venta, Eva Sarkiala, Tarja Jokinen, Daniela Gorgas, Juha Kere, Pekka Nieminen, Cord Drögemüller , Hannes Lohi et al. (2016.): Molecular Characterization of Three Canine Models of Human Rare Bone Diseases: Caffey, van den Ende-Gupta, and Raine Syndromes. PLoS Genet 12(5): e1006037. doi:10.1371/journal.pgen.1006037