Spinocerebellar Ataxia in Russell Terriers and Smooth-Haired Fox Terriers

SCA disease (Spinocelebellar Ataxia) has been found in Parson Russell Terriers, Jack Russell Terriers and Smooth-Haired Fox Terriers.

The first signs of this disease occur in the affected dogs at the age of 2 to 6 months. The disease is caused by degeneration of spinal nerves that carry information to the cerebellum. The symptoms are very similar to signs shown by dogs affected with Late Onset Ataxia (LOA) that begin with coordination difficulties when walking, running, turning and jumping. The problems with movement coordination can often progress.

Unlike (LOA), SCA can be associated with other problems. The majority of cases also develop myokymia, an involuntary twitching of the muscles. The mykomia also becomes progressively worse with the age and can result in generalized muscle spasms and over-heating. Some dogs may even have true epileptic seizures. The prognosis is not very good and most dogs at early age suffering from SCA are recommended for euthanasia.

The Spinocerebellar ataxia is caused by mutation in KCNJ10 gene (Gilliam et al. 2013). Mutation that causes SCA in Russell Terriers and Smooth-Haired Fox Terriers is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers).

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References:

D. Gilliam, J. R. Coates, G. S. Johnson, L. Hansen, T. Mhlanga-Mutangadura1, J. F. Taylor, G. C. Johnson, R. D. Schnabel, D. P. O'Brien: The Whole Genome Sequence of a Jack Russell Terrier with Progressive Spinocerebellar Ataxia and Myokymia Contains a Homozygous Disease-Associated KCNJ10 Missense Mutation (2013 The 7th International Conference on Advances in Canine and Feline Genomics and Inherited Diseases, Cambridges, Massachusetts, USA).