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Craniomandibular Osteopathy (CMO) is an inherited bone disease affecting West Highland White Terriers. 

CMO is also know as Lion Jaw.

The disease is characterised by excess bony growth in young dogs.

CMO affects the mandibles (jaws), sometimes the temporomandibular joints, occasionally skull bones and more rarely long bones of the legs.

Clinical symptoms typically begin between 4 and 8 months of age and include periodic intense jaw pain, swelling of the jaws, difficulty eating, pain when opening the mouth and drooling. A lump of extra bone on the mandible and very often noticeable.

The condition generally disappears spontaneously about a year after symptoms are first seen.

There is a DNA test for CMO possible results are Affected, Carrier or Clear.

Affected dogs should never be bred from.

Carrier dogs can be bred to clear dogs

Clear dogs do not carry the gene and  therefore can not pass it on.​

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