We are often contacted by customers looking to test for PRA. It sometimes comes as a surprise when we respond that we don’t have a test for PRA. This answer may sound strange at first until you realize that PRA is a category of diseases and not an actual genetic test. PRA stands for Progressive Retinal Atrophy and different versions of this eye disease can be found in different breeds. In fact, PRAs are among the most common causes of inherited blindness in domesticated dogs with well over a dozen different mutations in many different genes that have been identified and had genetic tests developed to help prevent inheritable diseases. Some examples of specific PRA mutations include PRA-PRCD found in many breeds, PRA-CORD1-CRD4 found in a limited number of breeds, and Dominant PRA found only in Mastiffs. The naming scheme used for the multitude of PRA tests also lacks standardization, further adding to the confusion surrounding PRA genetic testing.
The common symptom for all PRA diseases is the gradual degeneration or abnormal development of the rod and cone cells of the retina that are required for healthy eyes. Different types of PRA are nearly indistinguishable during clinical eye examinations as they have similar clinical signs that are easily recognized by a veterinary ophthalmologist. The age of onset (early versus late) and the speed at which the disease develops can be different for different types of PRA. There is no universally accepted naming scheme currently available for PRA but you can tell something about the disease based on whether it starts with “rod-cone” or “cone-rod” as part of the name. Rod cells play an important role in low light vision and their degeneration can lead to night blindness when these cells are affected. Alternatively, cone cells are important for color vision in bright light which means dogs with cone cell degeneration will have issues seeing well in brightly lit environments. The cell type named first is typically the one that is affected early in the disease but both cell types are eventually affected as the disease progresses and leads to eventual blindness.
PRA mutations can be inherited in one of three ways. The first and most common form of inheritance is recessive which requires two copies of the mutation (one from each parent) for the disease to manifest. Less common are dominant mutations that only require one copy of the mutation from either parent to initiate the disease. The final form of inheritance is X-linked which can affect males and females differently since males only inherit one copy of the X chromosome while females inherit two copies. This means that a male only needs to inherit one copy of the mutation to be susceptible while females must inherit two copies to be affected assuming a recessive inheritance pattern.
There are no available treatments for PRA so the only way to prevent disease is to know the genetic status of each parent and plan breeding pairs accordingly. You can read our blog here about our experience with our dog Dexter who had a form of PRA and was our inspiration for starting the company. At GenSol, our mission is to provide only the information you need for better breeding and healthcare decisions. We offer breed-specific panels to help you select only the PRA you need for your breed to avoid the confusion of testing for all PRAs and figuring out which results apply to your breed. The world of PRA testing can be confusing so if you are still unsure which PRA test to order, just reach out and we are always available to assist you.