There are two types of ataxia in the Jack Russell Terrier, Cerebellar Ataxia and Spino-Cerebellar Ataxia, also referred to as SCA. These are two different genetic diseases, and at this time, we only have a genetic test for SCA.
Cerebellar Ataxia
This type of Ataxia is often referred to as Early Onset Ataxia and affects the balance as soon as puppies open their eyes. Puppies have no control over head movement and abnormal eye movements (tremoring) can be seen. Instead of crawling in a forward motion, the puppies roll. As they grow, attempts to come to a standing position will result in a very wide tripod stance. Their head will sway with no control and when they eat, they will move up and down quickly to regain steadiness.
If they survive to six weeks, most have mastered standing, eating and some very awkward movement techniques. They will have difficulty moving forward and will frequently fall. Puppies will also exhibit an uncoordinated gait, spastic motion in all limbs, and a goose-stepping stride which will progress to a stilted stride in all limbs.
Some breeders may think they see improvement but, as intelligent as Jacks are, they have just learned to compensate.
The disease is a fast progressing disease and most puppies are euthanized early as the prognosis is a short life.
The JRTRF continues to support mapping and research at the University of Missouri in an attempt to isolate the gene for Cerebellar Ataxia.
Spino-Cerebellar Ataxia
The University of Missouri, with support from the JRTRF, isolated the gene responsible for SCA in 2012. SCA is a recessive genetic disease. This means an affected terrier must have two copies of the gene; one copy inherited from each carrier parent. It is a fast progressing disease and the onset can be as early as 3-4 months, but the majority of symptoms start at eight months. This type of Ataxia, when accompanied with myokymia, results in a very poor quality of life.
The symptoms of Spino-Cerebellar Ataxia are: an uncoordinated gait, initially worse in the rear limbs, with goose stepping. The gait is spastic and eventually the front legs are affected. The falling becomes more frequent. Rippling of muscles (myokymia) may occur in some dogs, especially during excitement. Myokymia is worm-like movement or tremors within the muscles of the limbs and face. There may be episodes of collapse, respiratory distress and overheating that occur along with worm-like movement or tremor in the muscles. Seizures may manifest in some dogs. The life expectancy is unpredictable and is dependent upon the severity of the myokymia activity.
To test for SCA, you have two options. You can do test with blood submitted to the University of Missouri or you can order a genetic testing kit from OFA and the testing is done at UMO. Testing information and links to the OFA website can be found at www.jrt-research.com