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.

We test all our miniature dachshunds for PRA cord 1, prior to breeding. This condition is inherited from both Mother and Father being a recessive gene. It is important that at least ONE parent be tested with a CLEAR result.Heather Coles, Registered Breeder AASHUDNA

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.

source: http://www.animalgenetics.us/Canine/cord1.htm