Cerebellar cortical degeneration (CCD) has been reported in many breeds. Clinical signs typically include head tremors, delayed or absent reflexes, and uncoordinated movements (Ataxia). Clinical signs first become apparent at around 3 months old and become progressively more severe over weeks to months. There is no treatment or cure and affected dogs are often euthanised due to poor quality of life concerns.
The single nucleotide substitution in the gene called SNX14 that causes cerebellar cortical degeneration (CCD) in many breeds is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop CCD during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop CCD as a result of the SNX14 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop CCD 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 SNX14 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 CCD, 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.