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Progressive Retinal Atrophy BBS2 (PRA-BBS2)

Progressive Retinal Atrophy BBS2 (PRA-BBS2)

Bardet-Biedl Syndrome 2 PRA

Progressive Retinal Atrophy (PRA) is a category of disorders where the retinal cells in a dog’s eye degenerate and die eventually leading to complete blindness. One type of PRA specific to Shetland Sheepdogs is due to a mutation in the BBS2 gene that leads to adult-onset eye disease. Symptoms will typically appear on average around 8-10 years of age but can present anywhere from 2 to 11 years of age. Initial symptoms include vision difficulties in dim light often referred to as night blindness. As the disease progresses, the affected dog will continue to suffer loss of night vision which then progresses to visual deficits in brighter light and can eventually lead to total blindness. In addition to PRA, affected dogs can exhibit additional features comparable to a human condition called Bardet-Biedl syndrome which includes an upturned nose, unusual wavy coat texture, and dental defects. It is important to note that not all cases of PRA in Shetland Sheepdogs are caused by this mutation.

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These dogs have two copies of the normal gene and will neither develop Progressive Retinal Atrophy BBS2 nor pass this mutation to their offspring.


These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They will not develop Progressive Retinal Atrophy BBS2 but will, if bred, pass the mutation to 50% of its offspring, on average.


These dogs have two copies of the mutation associated with this disease and are likely to develop Progressive Retinal Atrophy BBS2.

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Additional Details


Autosomal Recessive

Affected gene



Ch. 2




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. 2021; 12(11):1771. [PubMed: 34828377]