Progressive Retinal Atrophy (PRA) in Shetland Sheepdogs (Shelties)
Progressive Retinal Atrophy, or PRA, is a generalized disorder in which the cells in the retina of a dog's eye degenerate and die. In most cases, this eventually leads to complete blindness. PRA is the dog equivalent of retinitis pigmentosa in humans. Different forms of PRA have been reported in over 100 dog breeds and can be genetically heterogeneous both between and within breeds.
The retina is a membrane located in the back of the eye that contains two types of cells known as photoreceptors. These cells take light coming into the eyes and relay it back to the brain as electrical impulses. These impulses are intrepreted by the brain as vision. In dogs suffering from PRA, the photoreceptor cells begin to degenerate, causing an inability to interprete changes in light. Rod cells, which are normally function in low-light, begin to degenerate first, leading to night-blindness. The cone cells, which normally function in bright-light or daytime conditions, will deterioate next. This often leads to complete blindness over time.
In Shetland sheepdogs, a 4-bp deletion in exon 9 in the CNGA1 gene is associated with a breed-specific form of PRA. Not all PRA in Shelties is caused by this mutation. Additional forms of PRA can be found in Shelties.
PRA is inherited as an autosomal recessive disorder. A dog must have two copies of the mutated gene in order to be affected by PRA. Dogs with one copy of the mutation are known as carriers, and do not experience any symptoms of the disease. If two carriers are bred with one another, there is a 25% chance per puppy born that they will exhibit symptoms of sheltie-specific PRA, and a 50% chance per puppy born that they will be carriers of sheltie-specific PRA.
Animal Genetics accepts buccal swab, blood, and dewclaw samples for testing. Sample collection kits are available and can be ordered at test now.
Test Is Relevant to the Following Breeds:
- Shetland Sheepdog (Sheltie)
Animal Genetics offers DNA testing for Progressive Retinal Atrophy or PRA. The genetic test verifies the presence of the PRA mutated gene and presents results as one of the following:
|PRA/PRA||Affected||The dog carries two copies of the mutant gene and is homozygous for the PRA. The dog is affected, and will always pass a copy of the mutated gene to its offspring.|
|PRA/n||Carrier||Both the normal and mutant copies of the gene detected. Dog is a carrier for the PRA mutation, and can pass on a copy of the defective gene to its offspring 50% of the time.|
|n/n||Clear||Dog tested negative for the PRA gene mutation, and will not pass on the defective gene to its offspring.|