A form of progressive retinal atrophy in the Shetland Sheepdog caused by a mutation in the BBS2 gene, linked to Bardet-Biedl syndrome. It produces progressive photoreceptor degeneration and gradual vision loss. It may be accompanied by other features of the syndrome in some individuals. It progresses to blindness.

Specific to the Shetland Sheepdog. Limited data on carrier frequencies; the disease is considered rare.

- Initial loss of night vision\n- Tapetal changes in the ocular fundus\n- Pupillary dilation\n- Progressive decrease in daytime vision\n- Blindness in advanced stages\n- Possible additional features associated with BBS syndrome

PRA in the Shetland Sheepdog was investigated as a distinct entity and was associated with a mutation in the BBS2 gene, the orthologue of the one implicated in human Bardet-Biedl syndrome. The finding broadened knowledge of canine PRAs linked to primary cilium genes. Genetic testing allows carrier control in the breed.

- Test breeding animals before mating\n- Do not cross two carriers\n- A carrier can be crossed with a clear dog; test the offspring intended for breeding\n- Do not breed affected animals\n- Bear in mind that other PRAs are described in the Shetland Sheepdog (for example the one linked to CNGA1); check with the laboratory which tests are characterised in the breed before including them in a panel

Hitti-Malin et al. (2021) describe a syndromic PRA: in addition to retinal degeneration, homozygotes present additional clinical features that are not fully characterised (the study does not detail polydactyly or specific renal anomalies). OMIA classifies the inheritance as probably autosomal recessive and the number of homozygotes described is small (limited data). Differential diagnosis with the other PRAs of the Shetland Sheepdog. There is no curative treatment; management is supportive with ophthalmological follow-up.

1. Hitti-Malin RJ et al. 2021. A Missense Variant in the Bardet-Biedl Syndrome 2 Gene (BBS2) Leads to a Novel Syndromic Retinal Degeneration in the Shetland Sheepdog. Genes (Basel). PMID: 34828377
2. Wiik AC et al. 2015. Progressive retinal atrophy in Shetland sheepdog is associated with a mutation in the CNGA1 gene. Animal Genetics. PMID: 26202106
3. OMIA:002484-9615. Bardet-Biedl syndrome 2. Online Mendelian Inheritance in Animals.