Progressive Retinal Atrophy (Papillon Type)

Description

Progressive retinal degeneration (PRA) a common cause of adult-onset blindness in both humans and dogs.  In Papillons and the closely related breed Phalenes a set of variances, including a 1-bp deletion, followed by a 6-bp insertion causes a frameshift mutation in CNGB1 gene. The result of this variant causes a recessive form of PRA1.  The study further showed that this is a breed specific mutation and was not found in 334 healthy dogs from 10 other breeds as well as 121 PRA affected dogs from 44 additional breeds.

In affected animals photoreceptor cells in the retina begin to degenerate prematurely, typically progressing from a loss of night vision to complete blindness.  In Papillons, PRA1 is a late developing disease with an average onset between 5-6 years of age. Affected PRA1 dogs may not show any daylight vision loss for many years, sometimes for the remainder of their life.

PRA1 is inherited as an autosomal recessive disorder. A dog must have two copies of the mutated gene to be affected by PRA. A dog can have one copy of the mutation and not experience any symptoms of the disease. Dogs with one copy of the mutation are known as carriers, meaning that they can pass on the mutation to their offspring. If they breed with another carrier, there is a 25% chance that the offspring can inherit one copy of the mutated gene from each parent, and be affected by the disease.