Progressive retinal atrophy (PRA) is the most common form of inherited disease affecting the retina in dogs; the retina detects light and sends images to the brain. Progressive degeneration of the retina at the back of the eye is characteristic of PRA and leads to vision loss and blindness. PRA is not painful to dogs, and the first signs of the disease tend to be bumping in to objects, such as a piece of furniture that has been moved. Mutations in different genes cause genetically different forms of PRA. It affects many different breeds of dog, but each genetically distinct form usually affects one or a small number of breeds.
At least two genetically distinct forms of progressive retinal atrophy are found in Golden Retrievers. Research suggests that there may be at least one form that has not yet been identified. A mutation in a gene called TTC8 causes the specific form of PRA detected by this test. In humans TTC8 is also known as BBS8 and is associated with Bardet Biedl Syndrome and with non-syndromic Retinitis Pigmentosa. PRA is the primary feature in dogs homozygous with the mutation in TTC8, but they can also present with other characteristic such as obesity, renal anomalies, sperm defects and anosmia. The average age of onset of ophthalmic clinical signs is around 5 years, but can be variable. There is no cure for this form of PRA, but using the DNA test to identify dogs that carry the mutation in TTC8 will prevent further spread of this blinding condition in this lovely breed.