Spinocerebellar ataxia (also known as Cerebellar ataxia, CA) in the Italian Spinone is a progressive neurodegenerative disease characterised by incoordination, a “prancing” gait, and loss of balance often resulting in falling. Clinical signs start to appear at four months of age and progress to a degree of dysfunction which leads to euthanasia of affected dogs at one year of age on average.
The mutation associated with this disease is technically very challenging to assay directly. This test therefore targets DNA markers that are linked to the mutation i.e. although they don’t cause the disease they have been shown to be inherited with the disease and are therefore a reliable indicator of the disease genotype.
The triplet repeat expansion in the gene called IPTR1 that causes spinocerebellar ataxia (SCA) in the Italian Spinone 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 IPTR1 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 IPTR1 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.