Progressive Retinal Atrophy, more commonly known as PRA, is a general term for a group of diseases causing degeneration of the retina, leading to a loss of vision. One form of this disorder is known as cord1-PRA, which stands for cone-rod dystrophy-PRA. Cord1-PRA is a genetic disorder associated with a recessive mutation in the RPGRIP1 gene, which codes for an important photoreceptor protein in the eye. Like many forms of PRA, cord1-PRA is breed specific, and is known to occur in Miniature Dachshunds, Poodles and English Springer Spaniels.
Cone-rod dystrophy first affects the cones in the retina, which are the photoreceptors responsible for detecting bright light or daylight. Rods, or low-light photoreceptors, begin degenerating secondarily. This is different than other forms of PRA, such as prcd-PRA, in which the rods are affected first, followed by the cones. Unfortunately, most dogs affected by cord1-PRA will eventually become blind, and there is no cure at this time.
The age of onset can vary with this disorder, some dogs will first begin experiencing problems around 6 months in age, though the average age of onset is around 5 years of age.
A small percentage of dogs do not experience any symptoms until as late as 10 years of age. It is not yet known why some dogs will experience late-onset PRA, however, it is likely due to the presence of other genetic modifiers that have not been determined at this time.
Because this disorder is recessive, a dog must have two copies of the mutated gene to exhibit symptoms associated with PRA. A dog can be a carrier of cord1-PRA, meaning it only has one copy of the mutation, and not show any outward signs of retinal degeneration. A carrier can still pass on the mutated gene to any offspring; mating two carrier dogs can produce offspring affected by cord1-PRA.