Late-onset form of progressive retinal atrophy (PRA) of the Golden Retriever, the canine equivalent of human retinitis pigmentosa. It causes photoreceptor degeneration with loss of night vision first and complete blindness afterwards. It is inherited in an autosomal recessive manner and is associated with a frameshift mutation in the SLC4A3 gene, which encodes an anion exchanger expressed in the retina.

Golden Retriever. In the original study (Downs et al. 2011) the variant explained about half of the PRA cases analysed (present in ~56 % of cases and in ~87 % of obligate carriers), with approximate frequencies of 4 % in the United Kingdom, 6 % in Sweden and 2 % in France, and not detected in the United States. Other population frequencies: limited data.

- Initial loss of night vision (nyctalopia)
- More hyperreflective tapetum and progressive vascular attenuation
- Photoreceptor degeneration in the fundus
- Progression to complete blindness
- Age of onset around 7 years, variable
- No associated systemic or cardiac signs

PRA in the Golden Retriever is genetically heterogeneous, and the prcd variant explains only a minority of cases. Downs and colleagues (2011) carried out a genome-wide association study with 27 cases and 19 controls and mapped a new locus on chromosome 37. Within the region, they sequenced the candidate gene SLC4A3 and identified a cytosine insertion in exon 16 (c.2601_2602insC) that introduces a frameshift and a premature stop codon. The variant, named GR_PRA1, recessive and with complete penetrance in the lines where it segregates, explains about half of European cases and enabled a targeted genetic test.

- Test Golden Retriever breeding animals with the SLC4A3 (GR_PRA1) test before breeding
- Do not mate two carriers: 25 % risk of affected homozygotes
- A carrier may be mated to a clear animal; offspring intended for breeding must be tested
- Combine screening with the prcd and GR_PRA2 tests, since PRA is heterogeneous in the breed
- Exclude affected animals from breeding

Differential diagnosis with other forms of Golden Retriever PRA (prcd due to PRCD, GR_PRA2 due to TTC8) and with acquired retinopathies. Electroretinography and ophthalmoscopic examination guide the diagnosis, but confirmation is molecular. A negative result for GR_PRA1 does not rule out PRA caused by other variants, so a complete PRA panel in the breed is advisable.

1. Downs LM et al. 2011, una mutación con cambio de marco en Golden retriever con atrofia progresiva de retina avala SLC4A3 como gen candidato (PMID 21738669)
2. OMIA:001572 PRA GR-PRA1 (SLC4A3)