Form of progressive retinal atrophy (PRA) of the Shetland Sheepdog associated with a mutation in the CNGA1 gene, which encodes a subunit of the cyclic nucleotide channel involved in phototransduction. It produces photoreceptor degeneration with progression to blindness. The disease is inherited recessively and the genetic test allows carrier screening.

Specific to the Shetland Sheepdog. Carrier frequencies are not consolidated in the literature; limited data.

- Initial night blindness
- Progressive attenuation of retinal vessels
- Reduced vision in low light conditions
- Hyperreflective tapetum
- Progressive blindness
- No ocular pain

CNGA1-linked PRA of the Shetland Sheepdog was characterized in canine genetics studies that searched for breed-specific variants within the heterogeneous group of canine PRAs. The identification of the CNGA1 mutation made it possible to incorporate a genetic test into breeding programs. The specific literature on this form is relatively limited.

- Test breeding animals before mating
- Do not mate two carriers: 25 % of the litter would be affected
- A carrier can be mated with a clear animal; test the offspring intended for breeding
- Periodic ophthalmological examination to rule out other forms of PRA in the breed

Differential diagnosis with other forms of PRA described in the Shetland Sheepdog and with acquired retinal degenerations. The electroretinogram is useful to confirm the retinal origin. A negative test for CNGA1 does not exclude other PRAs in the breed.

1. Wiik AC et al. 2015. Progressive retinal atrophy in Shetland sheepdog is associated with a mutation in the CNGA1 gene. Animal Genetics. PMID: 26202106
2. OMIA:001977-9615. Retinal atrophy, progressive, CNGA1-related. Online Mendelian Inheritance in Animals.