Stargart disease is an inherited eye disease that affects dogs, primarily Labrador Retrievers. Onset of significant clinical signs is late in life, with affected dogs presenting with observable visual problems around 10 years of age. As with other retinal degenerations, such as progressive retinal atrophy, Stargardt disease is characterised by the degeneration of the rod and cone photoreceptor cells of the retina. Dog therefore experience visual deficits in bright and low light conditions. It is a progressive disease and symptoms will get worse as the dog ages.
The frameshift insertion in the gene called ABCA4 that causes Stargardt Disease in Labrador retriever is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Stargardt Disease during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Stargardt Disease as a result of the ABCA4 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Stargardt Disease 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 ABCA4 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 Stargardt Disease, 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.