Common Symptoms
Spinocerebellar Ataxia (SCA) is an early onset, inherited neurologic disease affecting dogs. Dogs with this disease present with incoordination and loss of balance between 2 to 6 months of age. The disease is progressive with affected dogs developing a “prancing” gait and often falling. With this form of ataxia dogs may also have episodes of muscle twitching and rigidity that can appear like seizures but dogs are aware of their surroundings during these attacks. The episodes of muscle twitching get worse with age and dogs are at risk of overheating. Affected dogs can also experience true epileptic seizures. Dogs with spinocerebellar ataxia are usually euthanized at a young age due to a poor quality of life.
Breed-Specific Information for the Chihuahua
The Mutation of the KCNJ10 gene associated with spinocerebellar Ataxia has been identified in a Chihuahua. Although the mutation in KCNJ10 has been identified in this breed, it is unclear if this specific mutation is the genetic cause of SCA in Chihuahuas. Although the exact frequency and significance of this mutation in the Chihuahua population is unknown, a Chihuahua was tested and found to have two copies of the mutation.
Testing Tips
Genetic testing of the KCNJ10 gene in Chihuahuas will reliably determine whether a dog is a genetic Carrier of spinocerebellar Ataxia. Spinocerebellar Ataxia 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 the same 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 KCNJ10 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation 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 this mutation 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
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Gilliam D, O'Brien DP, Coates JR, Johnson GS, Johnson GC, Mhlanga-Mutangadura T, Hansen L, Taylor JF, Schnabel RD. A Homozygous KCNJ10 Mutation in Jack Russell Terriers and Related Breeds with Spinocerebellar Ataxia with Myokymia, Seizures, or Both. J Vet Intern Med. 2014
[PubMed: 24708069]
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Rohdin C, Gilliam D, O'Leary CA, O'Brien DP, Coates JR, Johnson GS, Jaderlund KH. A KCNJ10 mutation previously identified in the Russell group of terriers also occurs in smooth-haired fox terriers with hereditary ataxia and in related breeds. Acta Vet Scand. 2015 May 23;57:26.
[PubMed: 25998802]
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SCA testing in Parson Russell Terriers http://www.offa.org/stats_dna.html?dnatest=SCA
