PRA-CORD2 – Progressive Retinal Atrophy
PRA-CORD2 is an inherited disorder that belongs in group of eye disorders known as progressive retinal atrophy. Progressive retinal atrophy (PRA) includes autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. It is a canine equivalent to retinitis pigmentosa (RP), an inherited eye disorder affecting human beings. The first case of PRA was observed in England more than hundred years ago.
Characteristics and Symptoms
In general, PRA is characterized by disturbance of vision in dark, visual field defects, and abnormalities in the electroretinogram. It appears in both eyes simultaneously. The age of onset and rate of retinal degeneration varies between the different forms of the conditions. Some forms of PRA are common to multiple dog breeds, while others are recognized in just a single breed. Until now, it has been identified in more than 100 dog breeds. Almost all forms of PRA are inherited in a recessively manner, with exceptions in some breeds such as Old English Mastiffs, Bullmastiffs, Siberian Husky and Samoyed where forms of PRA are inherited as dominant or X-linked disorders.
There are two types of photoreceptors in the eye, rods and cones. Rods have an important role for vision in dim light and also night vision. PRA causes rode degeneration and in this way leads to night blindness. Researchers estimated that PRA causes death of around 95% of the dog’s photoreceptors. Dog owners or breeders recognize PRA by ”glow” or ”increased shine” in the eyes. The disease is progessive. Initial stage is characterized by night blindness, while advanced stage of PRA can cause full blindness in the dog. After the appearance of first symptoms, it usually takes one year for the disorder to progress from initial to the advanced stange, causing severe and irreverisble damage to the dog’s eye.
PRA-CORD2 is a specific form of PRA that belongs in a group known as cone-rode dystrophies (CORD). The cone-rode dystrophies affect humans and dogs. Characteristic of CORD is that cones are affected firstly and the rods secondly, which is the opposite in other forms of PRA. But nevertheless, dog with PRA-CORD2 will lose its ability of vision with time and there is no cure currently available. The first symptoms usually occur between 10 months to 3 years of age.
PRA-CORD2 is an inherited autosomal recessive disease. It is caused by a mutation in NPHP4 (nephronophthisis 4) gene. Based on reasearches, it is estimated tgat around 9.5% of Wire-haired dachshund population posseses the defected gene responsible for this disorder. Carriers of the gene are heterozygous and do not develope the disease’s symptoms. When mating two carrier dogs, each future cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.