Proliferative bone disease of the mandible and the temporomandibular region that affects terrier breeds (Cairn, Scottish and West Highland white terrier). It presents with painful inflammation and difficulty eating, typically intermittently and self-limiting. It is caused by a splicing variant in SLC37A2 and shows autosomal dominant inheritance with incomplete penetrance.

Documented in Cairn terrier, Scottish terrier and West Highland white terrier (OMIA:002244-9615). In the Basset hound a different causal variant has been described. No reliable carrier frequencies per breed are available: limited data.

- Painful inflammation of the mandible and the temporal region
- Difficulty and pain when chewing or opening the mouth
- Reduced appetite and weight loss during episodes
- Intermittent and often self-limiting course
- On radiography: craniomandibular bone proliferation

Padgett and Mostosky (1965) described CMO in the West Highland white terrier and proposed autosomal recessive inheritance. Hytönen et al. (2016) identified a splicing variant in SLC37A2 (c.1332C>T) in Cairn, Scottish and West Highland white terriers and showed that the pattern is better explained by dominant inheritance with incomplete penetrance, with overlap of unaffected homozygotes and affected heterozygotes. Letko et al. (2020) described a different variant (c.1446+1G>A) in a Basset hound.

- Test breeding animals of the affected breeds if a test is available.
- Avoid crossing two carriers.
- Because of the incomplete penetrance and the mild or self-limiting phenotype, do not automatically exclude on the basis of genotype; assess each case.
- Combine the genetic data with clinical and radiological examination.

The genotype does not equal the phenotype: there are homozygotes without signs and affected heterozygotes, consistent with a dominant model of incomplete penetrance. CMO is often self-limiting and improves when the growth plates close. A different causal variant exists in the Basset hound, so the test should be chosen according to the breed.

1. Hytönen MK, Arumilli M, Lappalainen AK, et al. Molecular Characterization of Three Canine Models of Human Rare Bone Diseases: Caffey, van den Ende-Gupta, and Raine Syndromes. PLoS Genet. 2016;12(5):e1006037. PMID: 27187611.
2. Letko A, Leuthard F, Jagannathan V, et al. Whole Genome Sequencing Indicates Heterogeneity of Hyperostotic Disorders in Dogs. Genes (Basel). 2020;11(2):163. PMID: 32033218.
3. OMIA:002244-9615. Craniomandibular osteopathy, SLC37A2-related in Canis lupus familiaris. https://omia.org/OMIA002244/9615/