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Progressive Retinal Atrophy (Shetland Sheepdog Type)

Progressive Retinal Atrophy (Shetland Sheepdog Type) is an inherited eye disease in dogs that leads to the gradual degeneration of the retina and loss of vision.

Affected Genes: CNGA1

Inheritance: Autosomal Recessive

Variant(canFam6):
chr13:43784443-43784446: 4 bp deletion AGTT

Breed: Shetland Sheepdog

General Information: Progressive Retinal Atrophy (PRA) in Shetland Sheepdogs is a genetic eye disorder characterized by the degeneration of both rod and cone photoreceptor cells in the retina, which are crucial for vision in low and bright light conditions, respectively. Initially, the rod cells are affected, resulting in night blindness and loss of peripheral vision. As the disease progresses, the cone cells also deteriorate, leading to vision deficits in bright light and eventual complete blindness. The average age of clinical diagnosis for dogs with this type of PRA is around 5 years, but onset can vary widely, with some dogs showing symptoms as early as 2 years and others as late as 11 years. This progressive condition ultimately leads to significant impairment of vision, affecting the dog’s quality of life.

How to Read Your Dog's Test Results for this Genetic Variant:

Two Variants Detected: Dog Likely Affected

One Variant Detected: Dog Unlikely Affected

No Variants Detected: No Effect

Gene / Testing Information: Genetic testing for the CNGA1 gene is crucial for identifying carriers and dogs affected by Progressive Retinal Atrophy (Shetland Sheepdog Type). This condition is inherited in an autosomal recessive pattern, meaning that a dog must inherit two copies of the mutated gene, one from each parent, to develop the disease. Carrier dogs, which possess one normal and one mutated gene, generally do not show symptoms but can pass the mutation to their offspring. Breeding two carriers significantly increases the risk of producing affected puppies, with each pup having a 25% chance of inheriting the disease and a 50% chance of being a carrier. Since symptoms of PRA typically appear in adulthood, it is essential to conduct genetic testing for the CNGA1 mutation before breeding to prevent the transmission of this condition. By avoiding the breeding of two carriers, breeders can eliminate the risk of producing affected puppies and work towards eradicating this mutation from breeding lines. Although testing for the CNGA1 mutation reduces the risk of PRA, it is important to note that other genetic mutations can also cause PRA, so a clear result for CNGA1 does not rule out the presence of the disease in a dog's lineage. Ensuring comprehensive genetic testing helps maintain the health and vision of future generations of Shetland Sheepdogs and other affected breeds.

References:
Wiik AC, Ropstad EO, Ekesten B, Karlstam L, Wade CM, Lingaas F. Progressive retinal atrophy in Shetland sheepdog is associated with a mutation in the CNGA1 gene. Anim Genet. 2015 46(5):515-521.