Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

West Highland White Terrier West Highland White Terrier

Craniomandibular Osteopathy 

 

Related terms: temporomandibular joint fusion; Westie jaw, lion jaw

VeNom term: Craniomandibular osteopathy (VeNom code: 607)

Related conditions:

Outline: Crandiomandibular osteopathy is a disease in which there is excessive growth of the bones of the skull, particularly of the lower jaw. It causes increased bone mass, resulting in a wider and thicker lower jaw bone. This excess bone may prevent the jaw from opening and closing normally, and the temporomandibular jaw joint may fuse, causing total stiffness and immobility of the jaw. The abnormal bone growth associated occurs cyclically throughout the affected dog’s first year of life and commonly causes pain, a loss or lack of appetite and fever. By one year of age, the abnormal bone growth usually slows, regresses and sometimes recedes completely. However, often there is long-term impaired mouth function resulting in difficulty in opening and closing the mouth. Where the jaw joint is permanently fused, dogs may not be able to eat properly and may suffer malnutrition.

There is no known treatment to stop or prevent this condition and therapy is targeted at reducing any pain and swelling to relieve the dog’s discomfort. In cases of complete jaw fusion, surgery or euthanasia may be discussed with a veterinarian, in light of the poor quality of life for such affected dogs. 

Craniomandibular osteopathy is an autosomal recessive disease in West Highland white terriers, but there is no test to identify affected dogs or carriers of the gene. Affected dogs and their relatives should not be bred from since they may produce affected offspring if mated with another affected dog or a carrier.


Summary of Information

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1. Brief description

Craniomandibular osteopathy is a disease of the bones of the skull, and primarily affects the lower jaw, the bone surrounding the middle ear and the joint (the temporomandibular joint) between the upper jaw bone (maxilla) and the lower jaw (mandible) that primarily affects young dogs under a year of age. In dogs with craniomandibular osteopathy, there is excessive and abnormal bone growth, which causes increased bone mass, often on the lower jaw, and this makes the lower jaw wider and thicker. The excess bone may prevent the jaw from opening and closing normally, and occasionally the bone may fuse the temporomandibular joint, causing total stiffness and immobility of the jaw. Commonly, by around one year of age, the abnormal bone growth usually slows, regresses and sometimes recedes completely.

2. Intensity of welfare impact

Craniomandibular osteopathy is a disease of the bones of the skull, and primarily affects the lower jaw, the bone surrounding the middle ear and the joint (the temporomandibular joint) between the upper jaw bone (maxilla) and the lower jaw (mandible) that primarily affects young dogs under a year of age. In dogs with craniomandibular osteopathy, there is excessive and abnormal bone growth, which causes increased bone mass, often on the lower jaw, and this makes the lower jaw wider and thicker. The excess bone may prevent the jaw from opening and closing normally, and occasionally the bone may fuse the temporomandibular joint, causing total stiffness and immobility of the jaw. Commonly, by around one year of age, the abnormal bone growth usually slows, regresses and sometimes recedes completely..

3. Duration of welfare impact

Craniomandibular osteopathy is a disease of the bones of the skull, and primarily affects the lower jaw, the bone surrounding the middle ear and the joint (the temporomandibular joint) between the upper jaw bone (maxilla) and the lower jaw (mandible) that primarily affects young dogs under a year of age. In dogs with craniomandibular osteopathy, there is excessive and abnormal bone growth, which causes increased bone mass, often on the lower jaw, and this makes the lower jaw wider and thicker. The excess bone may prevent the jaw from opening and closing normally, and occasionally the bone may fuse the temporomandibular joint, causing total stiffness and immobility of the jaw. Commonly, by around one year of age, the abnormal bone growth usually slows, regresses and sometimes recedes completely.

4. Number of animals affected

West Highland white terriers are significantly more at risk of the disease than mixed breed dogs. Both males and females can be affected by the disease.

5. Diagnosis

A veterinarian will diagnose this disease on physical examination and radiography (X-ray) of the jaw area.

6. Genetics

Craniomandibular osteopathy is an autosomal recessive disease in West Highland white terriers. This means that the disease affects both sexes, and that an affected dog will have inherited two copies of the gene mutation, one from each of their parents. Dogs that inherit one copy of the gene mutation from one parent and a normal copy from the other parent will not be clinically affected but are carriers of the disease, and may pass the disease onto their offspring. The actual gene/s involved in the development of craniomandibular osteopathy are unknown.

7. How do you know if an animal is a carrier or likely to become affected?

There is no genetic test currently available that can identify whether individual dogs are affected or carriers of the disease. We do know that West Highland white terriers are more commonly affected by the disease than other breeds, and that it affects young dogs.

8. Methods and prospects for elimination of the problem

Dogs affected with craniomandibular osteopathy should not be bred from, even if they appear to recover completely when they reach breeding age, since they may produce affected offspring if mated with another affected dog or with a carrier. Breeding of parents and siblings of affected animals should also be avoided since they are likely to be carriers of the condition, and therefore may produce affected offspring.


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1. Clinical and pathological effects

1. Clinical and pathological effects

Craniomandibular osteopathy is a disease of the bones of the skull, and primarily affects the mandible (lower jaw), tympanic bullae (bone surrounding the middle ear) and the temporomandibular joint (the joint between the upper bone, maxilla, and the lower jaw). In dogs with craniomandibular osteopathy, there is excessive and abnormal bone growth, which causes increased bone mass.  

As part of the normal bone and skull development of young puppies, in unaffected young animals, during periods of growth, bone is broken down by osteoclast cells and replaced by new, immature bone along the inner and outer surface of the bones., In dogs with craniomandibular osteopathy, there is excessive replacement of the immature bone, such that the bones become enlarged (Riser et al. 1967). The bone growth is non-cancerous and causes irregular and bilateral enlargements on both sides of the skull (Riser & Newton 1985). It most often occurs on the outer surfaces of the lower jaw, and this makes the lower jaw wider and thicker (see Figure 1). This results in the outward appearance of an abnormally large jaw and is why the condition is sometimes known as “Lion Jaw”. The excess bone may prevent the jaw from opening and closing normally, and occasionally the bone may fuse the temporomandibular joint, causing complete stiffening and immobility of the jaw.  

Figure 1. Radiographic images of top) the skull of a healthy dog, showing normal jaw width and bottom) a dog with craniomandibular osteopathy, showing increased bone in the lower jaw. Images are reproduced with the kind permission of Fairfield Vets (http://www.fairfieldvets.co.uk/ic/dog/lucy-lion.htm).

Commonly, by one year of age, the abnormal bone growth slows, regresses and sometimes recedes completely (Riser et al 1967). This period of self-limitation coincides with the completion of regular bone development in healthy young animals.

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2. Intensity of welfare impact

During periods of bone growth, affected dogs often have a swollen and painful lower jaw. They may feel pain and discomfort when chewing and eating food, and therefore affected dogs can lose their appetite, lose weight and become lethargic. Affected dogs can show fevers of up to 104oF that last 3 to 4 days and are repeated every 10 to 14 days (ie likely during periods of bone growth; Riser et al 1967). As a result of the excessive bone growth, dogs may have difficulty opening and closing their mouths, and may drool excessively.   

In most cases, the clinical signs stop when there is regression of bone growth, and dogs can go on to live a normal life, clinically unaffected by the disease. Where there has been more severe bone growth, and where the jaw joint is not functioning properly, and they have difficulties opening and closing their mouth, dogs will not be able to eat properly and may suffer malnutrition.

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3. Duration of welfare impact

The excessive bone growth of Craniomandibular osteopathy affects young dogs, usually between 3 to 8 months of age. The excess bone growth usually stops at or before one year of age, but it may or may not regress. In one study, the size of bone growth had decreased to half the size for 9 dogs by 13 months of age (Riser et al 1967).

There is no treatment to stop or prevent this condition and therapy is targeted at reducing any pain and swelling to relieve the dog’s discomfort. Most affected animals experience bouts of clinical signs (i.e. pain) over the first year of their life, but thereafter are capable of a normal life. Affected dogs may have impaired mouth function long-term and difficulties opening and closing their mouth but this does not usually negatively affect the dog. Where there is complete fusion of the jaw, surgery may be considered but this has limited success (Roush 2006). For this reason, and especially where there is extreme pain, euthanasia may discussed with a veterinarian, in light of the poor quality of life for dogs.

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4. Number of animals affected

Both males and females can be affected by the disease.

West Highland white terriers are significantly more at risk of the disease than mixed breed dogs. In one study of cases from the Veterinary Medical Database at Purdue University, there were 35 cases of craniomandibular osteopathy between 1986 and 1995, and 19 of these were of West Highland white terriers (LaFond et al 2002).

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5. Diagnosis

TA veterinarian will diagnose this disease on physical examination and radiography (X-ray) of the jaw area. In advanced cases, the veterinarian may be unable to open the mouth of affected dogs more than 1 or 2 cm (Roush 2006)

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6. Genetics

Pedigree analysis has revealed that craniomandibular osteopathy is an autosomal recessive disease in West Highland white terriers (Padgett & Mostosky 1986). This means that the disease affects both sexes, and that an affected dog will have inherited two copies of the gene mutation, one from each of their parents. Dogs that inherit one copy of the gene mutation from one parent and a normal copy from the other parent will not be clinically affected but are carriers of the disease, and may pass the disease onto their offspring.

The gene/s involved in the development of craniomandibular osteopathy are as yet unknown.

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7. How do you know if an animal is a carrier or likely to become affected?

There is no current routine genetic test that can identify whether dogs are affected or are carriers of the disease. We do know however that West Highland white terriers are more commonly affected by the disease than other breeds, and that it affects young dogs.

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8. Methods and prospects for elimination of the problem

Affected dogs should not be bred from, even if they appear to recover completely when they reach breeding age, since they may produce affected offspring if mated with another affected dog or a carrier. Breeding of parents and siblings should also be avoided since they are likely to be carriers of the condition, and therefore may produce affected offspring (Farrell et al 2015).

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9. Acknowledgements

UFAW thanks Dr Emma Buckland (BSc PhD), Dr David Brodbelt (MA VetMB PhD DVA DipECVAA MRCVS) and Dr Dan O’Neill (MVB BSc MSc PhD MRCVS) for their work in compiling this section.

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10. References

Farrell LL, Schoenebeck JJ, Wiener P, Clements DN and Summers KM (2015) The challenges of pedigree dog health: approaches to combating inherited disease. Canine Genetics and Epidemiology 2: 3

LaFond E, Breur GJ and Austin CC (2002) Breed Susceptibility for Developmental Orthopedic Diseases in Dogs. Journal of the American Animal Hospital Association 38: 467–477

Padgett GA and Mostosky UV (1986) The mode of inheritance of craniomandibular osteopathy in West Highland White terrier dogs. American Journal of Medical Genetics 25: 9–13

Riser WH and Newton CD (1984) Chapter 54 Craniomandibular osteopathy. In: Textbook of Small Animal Orthopaedics. Eds: Newton CD and Nunamaker DM. JB Lippincott Company

Riser WH, Parkes LJ and Shirer JF (1967) Canine Craniomandibular Osteopathy1. Veterinary Radiology 8: 23–31

Roush JK (2006) Chapter 117 - Miscellaneous diseases of bone. In: Birchard SJ, Sherding RG, and Roush JK (eds.) Saunders Manual of Small Animal Practice pp. 1186–1193Thi

© UFAW 2016


Credit for main photo above:

By Mider [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC-BY-SA-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons