Cerebellar cortical degeneration, also known as cerebellar abiotrophy, is a disease characterised by clinical signs of cerebellar dysfunction, such as ataxia-dysmetria, broad based stance, loss of balance and intentional tremors. Affected puppies start showing clinical signs around 3 weeks of age. They are slower and less coordinated than unaffected puppies, falling more often and unable to walk in a correct manner. Signs include tremor, ataxia (inability to coordinate the movement of muscles) and spastic paralysis.
The 8bp deletion in the gene called SPTBN2 that causes Neonatal Cerebellar Cortical Degeneration (NCCD) in Beagle is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop NCCD during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop NCCD as a result of the SPTBN2 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop NCCD 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 SPTBN2 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 NCCD, 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.