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.
A form of PRA in Shetland Sheepdogs is caused by a mutation in a gene called BBS2. In humans, mutations in BBS2 are associated with a condition known as Bardet Biedl syndrome. This novel form of PRA, is unusual as it presents with other characteristics including a wavy, atypical textured coat, upturned nose and dental defects. There is evidence that this syndrome may also cause kidney abnormalities and obesity due to an enhanced motivation for food, but further studies are required to confirm this. The age of onset of this form of PRA is variable. Dogs that are homozygous for the BBS2 mutation will almost certainly develop PRA during their lifetime and may also display some or all of the other characteristics associated with the syndrome. Research undertaken by the Kennel Club Genetics Centre indicates approximately 1 in 38 Shetland Sheepdogs are carriers of the BBS2 mutation. There is no cure for PRA but using the DNA test to identify dogs that carry this mutation will prevent further spread of this blinding condition in this lovely breed.