What is Prcd-PRA? PRA or Progressive Retinal Atrophy is a group of genetic diseases that causes progressive, irreversible damage to the retina. Prcd (progressive rod-cone degeneration) is one form of this disease. It can usually be diagnosed through physical signs by veterinary opthamologists when a dog is 4 to 6 years old. It first appears as night blindness as the rod cells lose their ability to function. Gradually, then the cone cells lose function, resulting in a degeneration of sight in daylight. Affected dogs will eventually go blind. There is no treatment or cure.
The prcd form of PRA is found in Golden Retriever, Labrador Retrievers, Chesapeake Bay Retrievers, English Cocker Spaniels, Portuguese Water Dogs, and other breeds. Fortunately, this form of the disease is the genetically the same across all the breeds it’s been seen in and can be tested for using a DNA test developed by OptiGen.
Prcd-PRA is a recessive inherited trait—like blue eyes in humans. The offspring can only become affected by the disease if they are passed two recessive genes—one from each parent. A DNA test can determine if a dog is affected, a carrier of the gene, or clear.
- Affected: (Homozygous Mutant) If the dog is affected, it carries two recessives and will eventually go blind. An affected dog will pass on one recessive gene to ALL its offspring.
- Carrier: (Heterozygous) If the dog is a carrier, it has only one recessive; it will likely not go blind from prcd. However, the carrier can pass on to its offspring either the recessive gene or a clear gene.
- Clear/Normal: (Homozygous Normal) If the dog is clear, then its DNA does not carry the prcd gene. It can only pass on its clear gene.
What Does It Mean for Breeders?
The information above shows how important it is to have ALL dogs who are to be bred tested for the prcd-PRA gene. Even though a dog may have no physical symptoms of the disease, it can still be a carrier of it. When it is bred with another carrier, each offspring has a 25% chance of being affected, 25% chance of being clear, and a 50% chance of being a carrier. If a carrier is bred to an affected dog, the odds get worse. Each offspring, then, has a 50% chance of being affected and a 50% chance of being a carrier. Only when bred to a clear dog, do the numbers get better. Each puppy will then have a 50% chance of being a carrier and a 50% chance of being clear.
Therefore, it is important to determine, not only whether or not your dog is carrying the prcd-PRA gene but also whether or not the dog you breed to has the gene. With this knowledge, both the dam’s owner and the sire’s owner can make responsible decisions regarding their breeding programs.
Does this mean I shouldn’t breed a dog that’s a carrier of the prcd-PRA gene? Only you can determine that. However, the genetic testing allows a breeder to choose breeding partners wisely. Choosing breeding partners that are clear allows for the possibility of preventing the recessive gene from being passed on to future generations.
The Other PRA
There is another form of PRA that can not currently be tested for using this DNA test. This form of the disease has been diagnosed in dogs through physical examination, although subsequent DNA tests came back clear/normal. This form of the disease is thought to be more prevalent in Europe.
For more information on prcd-PRA, please visit the following pages: