Part of the official UK Kennel Club testing scheme in Irish Setter
Progressive retinal atrophy (PRA) is the most common form of inherited disease affecting the retina in dogs. Genetically different forms of PRA, caused by mutations in different genes, affect many breeds of dog with each form usually affecting one or a small number of breeds. PRA is characterised by progressive degeneration of the retina at the back of the eye and leads to vision loss and blindness.
This specific form of PRA is caused by a mutation in a gene called PDE6B and is indistinguishable from other forms of PRA in other breeds. The average age of onset of clinical signs is very early, around one month, and by 5 months of ages dogs are completely blind. In humans, mutations in PDE6B are associated with a condition known as Retinitis Pigmentosa and congenital stationary night blindness, symptoms of which include loss of peripheral vision and the ability to see at night. There is no cure for this form of PRA, but using the DNA test to identify dogs that carry the mutation in PDE6B will prevent further spread of this blinding condition in this lovely breed.
The single nucleotide insertion in the gene called PDE6B that causes Progressive Retinal Atrophy (RCD1 type) in Irish Setter is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Progressive Retinal Atrophy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Progressive Retinal Atrophy as a result of the PDE6B mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Progressive Retinal Atrophy 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 PDE6B 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 Progressive Retinal Atrophy, 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.