Progressive Retinal Atrophy (BBS2)

Description

Progressive Retinal Atrophy (PRA) is a generalized disorder in which the cells in the retina of a dog degenerate and die, in most cases eventually leading to complete blindness. PRA is the dog equivalent of Retinitis Pigmentosa in humans. Different forms of PRA have been reported in over 100 dog breeds and can be genetically heterogeneous both between and within breeds.

The retina is a membrane located in the back of the eye that contains two types of cells known as photoreceptors. These cells take light coming into the eyes and relay it back to the brain as electrical impulses. These impulses are interpreted by the brain as vision. In dogs suffering from PRA, the photoreceptors begin to degenerate, causing an inability to interpret changes in light resulting in a loss of vision. Rod cells, which normally function in low-light environments, begin to degenerate first. This leads to night-blindness. The cone cells, which normally function in bright-light or daytime conditions, will deteriorate next. This often leads to complete blindness over time.

Shetland Sheepdogs affected by BBS2 PRA typically begin to show symptoms of night blindness early in life, which gradually progresses to total blindness as the condition advances. The mutation is inherited in an autosomal recessive manner, meaning that a dog must inherit two copies of the mutated gene, one from each parent, to develop the disease. Dogs with only one copy are carriers and do not exhibit symptoms but can pass the gene to their offspring. Genetic testing is crucial for identifying carriers and affected individuals, which helps breeders make informed decisions to avoid producing affected puppies. While there is no cure for BBS2 PRA, early diagnosis allows for better management of the condition, enabling affected dogs to adapt to their vision loss and maintain a good quality of life.

Because Shetland Sheepdog PRA is a recessive disorder, a dog must have two copies of the mutation in order for the disease to manifest. This means that a dog can have one copy of the mutation and not experience any signs or symptoms of BBS2-PRA. This dog would be known as a carrier. The carrier can then pass on either the normal gene or the mutated gene to any offspring. If two carriers are bred, there is a 25% per puppy that they will develop symptoms of BBS2-PRA.