Part of the official UK Kennel Club testing scheme in Jack Russell Terrier and Parson Russell Terrier
Spinocerebellar Ataxia (SCA) is an early onset, inherited neurologic disease affecting dogs. Affected dogs typically 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 by 2 years of age due to a poor quality of life.
The single nucleotide substitution in the gene called KCNJ10 that causes spinocerebellar ataxia (SCA) in many breeds is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop SCA during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop SCA as a result of the KCNJ10 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop SCA should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the KCNJ10 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with SCA, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.