Molecular test for cone-rod dystrophy 1 (Cord1) progressive retinal atrophy, a hereditary retinal degeneration that initially affects the cones and later the rods and leads to progressive blindness. It affects the ocular system (photoreceptors) and forces the animal to adapt to gradual visual loss. The test reports the clear/carrier/affected status for the corresponding variant.

Applicable breeds: Curly coated retriever, Dachshund and English springer spaniel. The carrier frequency varies between breeds (published data for the Dachshund with moderate figures); the figures for the Curly coated retriever and English springer spaniel are more limited and should be verified in the specific literature.

- Early-onset daytime visual loss (cones)
- Progressive bilateral retinal atrophy
- Complete blindness in advanced stages
- Fundus changes: tapetal hyperreflectivity and vascular attenuation

Cord1 PRA is associated with a variant in the RPGRIP1 gene initially described in the Miniature Long-haired Dachshund and later extended to other breeds, including the Curly coated retriever and the English springer spaniel (Mellersh et al. 2006). The variant produces a cone-rod dystrophy with progressive visual loss. Penetrance is incomplete: some homozygotes do not develop the disease, suggesting the existence of genetic modifiers.

- Genotype breeding animals before mating
- Do not cross carrier×carrier (25 % risk of homozygotes for the variant); carrier×clear produces 0 % homozygotes and 50 % carriers
- Given the incomplete penetrance, a homozygote without clinical signs may still be bred with caution and only with a clear individual, assessing the ocular examination before mating
- After a confirmed clinical case, do not repeat the parental cross and communicate the status to the buyer

Annual ocular examination (ECVO) as a complement to confirm or rule out the disease in asymptomatic homozygotes, given the risk of incomplete penetrance. Differentiate Cord1 from other PRAs (prcd-PRA, rcd1/rcd2/rcd3) by age of onset and fundus pattern. Cone-rod dystrophy has a different pattern from rod PRA: daytime and colour vision loss before night vision. Verify the exact variant offered by each laboratory.

1. Mellersh CS et al. 2006, la mutación canina de RPGRIP1 establece la distrofia de conos y bastones del Dachshund de pelo largo miniatura como homóloga de la enfermedad humana (PMID 16806805)
2. Lhériteau E et al. 2009, el perro deficiente en RPGRIP1 como modelo canino para terapia génica (PMID 19223988)
3. Miyadera K et al. 2012, variaciones genéticas y fenotípicas en enfermedades retinianas hereditarias del perro (PMID 22065099)
4. OMIA:001258 PRA Cord1 (RPGRIP1)