Ehlers-Danlos Syndrome (Poodle Type, Variants 1 and 2)

Common Symptoms

Ehlers-Danlos syndrome is an inherited Connective Tissue disease affecting Chihuahuas. Affected dogs typically present prior to 2 years of age with loose (hypermobile) joints, fragile blood vessels, and excessively elastic skin that is easily torn or bruised and can be stretched beyond limits seen in normal dogs. Dogs may display open wounds or scars from previous injuries and are at increased risk for joint dislocation.

Breed-Specific Information for the Chihuahua

The TNXB G/A, chr12:1490385 (Variant 2) Mutation associated with Ehlers-Danlos syndrome has been identified in Chihuahuas. The TNXB G/A, chr12:1499124 (Variant 1) mutation associated with this condition has been found in a Chihuahua-poodle mixed breed dog. The overall frequency of these mutations in the general Chihuahua population is unknown.

Testing Tips

Genetic testing of the TNXB gene in Chihuahuas will reliably determine whether a dog is a genetic Carrier of Ehlers-Danlos syndrome. This test examines the genome for two genetic mutations in the TNXB gene associated with this disease. Dogs inheriting a single copy of either Mutation are considered carriers of the disease and will not develop clinical signs. Dogs which have either inherited two copies of the same mutation (one from each parent) or have inherited one copy of both mutations (one from each parent) are expected to be affected with Ehlers-Danlos syndrome.

Ehlers-Danlos syndrome is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of either mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the TNXB gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate these mutations from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Chihuahuas that are not carriers of these mutations have no increased risk of having affected pups.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

References

• Bauer A, de Lucia M, Leuthard F, Jagannathan V, Leeb T. Compound heterozygosity for TNXB genetic variants in a mixed-breed dog with Ehlers-Danlos syndrome. Anim Genet. 2019 Oct;50(5):546-549. doi: 10.1111/age.12830. [PubMed: 31365140]