The cord1-PRA (Cone-rod dystrophy 1) is an inherited disease of the eye that occurs in English Springer Spaniel, Miniature Long-Haired Dachshunds and Smooth-Haired Dachshunds.
The retina is a thin layer of neural cells that lines the back of the eyeball. The vertebrate retina contains photoreceptor cells (rods and cones) that respond to light. The cones mediate high-resolution vision and colour vision. The rods mediate lower-resolution, black-and-white, night vision.
The degeneration of the retina results in loss of vision, often leading to blindness. There is currently no treatment for the disease.
In contrast to rod-cone dystrophies, where firstly, rod cells are affected and secondly, degeneration of the cone cells results in complete blindness of the dog, cone-rod dystrophies are characterised by the relatively early loss of cone photoreceptors.
The earliest ophtalmoscopic signs could appear about six month of age but some dogs with the mutation are not diagnosed until much later in life, so owner may never see behavioural changes and never recognise that the dog can pass the mutation onto its offspring.
Since diagnosis of retinal diseases in dogs may prove difficult, the genetic test on cord1-PRA helps to diagnose a specific form of a disease and is also a useful tool for breeders to eliminate the mutated gene from the dog population.