Part of the official UK Kennel Club testing scheme in Swedish Vallhund
Retinopathy in the Swedish Vallhund is a unique type of retinal degeneration in dogs, and differs from other progressive retinal atrophies described in dogs. The age of onset and rate of progression vary considerably. In the early stages of disease vision remains normal, but it progresses first to signs of night-blindness and eventually impaired day vision as well.
The line insertion in the gene called MERKT that causes Retinopathy in Swedish Vallhunds is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Retinopathy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Retinopathy as a result of the MERKT mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Retinopathy 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 MERKT 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 MERKT , 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.