Breeds Affected: Russell group Terriers (Jack Russell Terrier, Parson Russell Terrier, Russell Terrier)
Samples Accepted: Blood, Buccal Swabs
Disease Information: Spinocerebellar Ataxia (SCA) appears to have different variations of symptoms and ages of onset in the Russell group of Terriers. One subtype is associated with symptoms that usually appear between 2-12 months of age, and includes progressive difficulty coordinating fine muscle movements and loss of balance. Myokymia, with sudden muscle contractions or tremors, affects more than half of the dogs in this group; seizures may also be present. For this reason, the disease may also be known as Spinocerebellar Ataxia with Myokymia, Seizures or both (SAMS). Most dogs are humanely euthanized because of poor quality of life.
Inheritance Information: Spinocerebellar Ataxia (SCA) is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/sca The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/sca carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
sca/sca The dog is affected – if bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/sca carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/sca x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/sca x N/sca) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (sca/sca) should not be used for breeding.
Test Information: This test identifies a single nucleotide change in the KCNJ10 gene.
Gilliam, D., O’Brien, D.P., Coates, J.R., Johnson, G.S., Johnson, G.C., Mhlanga-Mutangadura, T., Hansen, L., Taylor, J.F., Schnabel, R.D.: A homozygous KCNJ10 mutation in Jack Russell Terriers and related breeds with spinocerebellar ataxia with myokymia, seizures, or both. J Vet Intern Med 28:871-7, 2014. Pubmed reference: 24708069. DOI: 10.1111/jvim.12355
Further information is available at the Online Mendelian Inheritance in Animals website.