Progressive Retinal Atrophy, Syndromic Retinal Degeneration (Shetland Sheepdog Type)

Other Names: Bardet-Biedl Syndrome, Progressive Retinal Atrophy (Discovered in the Shetland Sheepdog - BBS2 variant)
Affected Genes: BBS2
Inheritance: Autosomal Recessive
Mutation: chr2:58970967 (canFam4): G/C
Breed(s): Shetland Sheepdog

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Common Symptoms

Progressive Retinal Atrophy, Syndromic Retinal Degeneration (Shetland Sheepdog Type) is an eye disease affecting dogs. Affected dogs begin showing clinical symptoms related to retinal degeneration at around 6 to 10 years of age, though age of onset can vary. Initial clinical signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the Retina called the Tapetum that can be observed on a veterinary eye exam. Progression of the disease leads to thinning of the retinal blood vessels, signifying decreased blood flow to the retina. Affected dogs initially have vision loss in dim light (night blindness) and loss of peripheral vision, which may progress to complete blindness. In addition to progressive retinal atrophy, affected dogs may show other clinical signs of variable severity including an upturned nose, dental abnormalities, an abnormal coat, kidney, disease, and obesity, However, each affected dog may develop a unique combination and severity of clinical signs.

Testing Tips

Genetic testing of the BBS2 gene will reliably determine whether a dog is a genetic Carrier of Progressive Retinal Atrophy, Syndromic Retinal Degeneration (Shetland Sheepdog Type). This disease is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the BBS2 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal atrophy caused by mutations in other genes, a normal result in BBS2 does not exclude progressive retinal atrophy in a pedigree.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Hitti-Malin RJ, Burmeister LM, Lingaas F, Kaukonen M, Pettinen I, Lohi H, Sargan D, Mellersh CS. A Missense Variant in the Bardet-Biedl Syndrome 2 Gene (BBS2) Leads to a Novel Syndromic Retinal Degeneration in the Shetland Sheepdog. Genes (Basel). 2021 Nov 8;12(11):1771. [PubMed: 34828377]