Progressive retinal atrophy (PRA) refers to a group of genetic disease that occur in a number of dog breeds. The disease is characterised by vision impairment caused by degeneration of the retina in both eyes leading to blindness. The mutation responsible for this disease has already been identified in a number of breeds and DNA tests have been developed to enable breeders to avoid breeding affected dogs. PRA in shelties is clinically similar to PRA in other breeds but the mutation leading to the disease in shelties was not identified. In a recent study scientists found that in shelties there is more than one PRA variant.Scientists have been able to identify one of the mutations that causes PRA in this breed and a DNA test is now available from Laboklin.
In Shelties, the disease shows a varying age on onset. In a study on affected shelties, PRA was diagnosed between the age of 2 and 11.
PRA in shelties is recessive which means that a dog will only develop the disease when it inherits two copies of the mutation, one from each parent. If a dog inherits one copy of the mutant gene from one parent and one copy of the healthy gene from the other parent, it will not develop the disease associated with this mutation but it can pass the mutation to its offspring.
A dog that carries one copy of the mutation (carrier) will not be affected by this mutation but it should only be bred to a clear dog.
The DNA test enable breeders to identify if the dog is clear, carrier or affected and plan their breeding program to avoid having affected puppies.
It is important to point out that this test detects the mutation that causes one variant of PRA. There is at least one more, yet unidentified, mutation responsible for other PRA variant(s) in shelties, which is not detected by this test. The breed also suffers from an additional form of retinal degeneration called Slow Progressing Retinopathy ( SPR ) that progresses more slowly and does not cause such obvious visual impairment as does PRA (Karlstam et al. 2011). This test does not detect SPR. The test is useful to eliminate one form of PRA.