A form of progressive retinal atrophy (PRA) described in the Shih Tzu and associated with a nonsense mutation in the JPH2 gene, which encodes junctophilin 2. It causes progressive photoreceptor degeneration with visual loss leading to blindness. It is inherited in an autosomal recessive manner and is one of the breed-specific genetic variants of PRA.

Shih Tzu. No reliable figures are available for carrier frequency in the general population.

- Initial nyctalopia (night blindness)\n- Progressive reduction of daytime vision\n- Tapetal changes on fundus examination\n- Secondary cataracts in advanced stages

PRA in the Shih Tzu was associated with JPH2 through whole-genome sequencing in affected dogs. Urkasemsin et al. (2021) identified the homozygous nonsense variant c.452A>C (p.L151X), present in all affected dogs and absent in unaffected ones, and proposed it as the cause of PRA in the breed. It is one of the breed-specific genetic variants of PRA, within the heterogeneous group of canine PRAs.

- Genotype breeding animals before mating\n- Do not mate two carriers: 25% risk of affected homozygotes\n- Prioritize lines free of the mutant JPH2 variant\n- A carrier may be mated to a clear animal; offspring intended for breeding must be tested

Differential diagnosis from other late-onset PRAs (prcd, IMPG2, PCARE) and from primary cataracts of the Shih Tzu. Serial ophthalmological evaluation complements genotyping.

1. Urkasemsin G et al. (2021) Whole genome sequencing identifies a homozygous nonsense mutation in the JPH2 gene in Shih Tzu dogs with progressive retinal atrophy. Anim Genet 52(5):714-719. PMID: 34231238
2. OMIA:002943-9615. Retinal atrophy, progressive, JPH2-related in Canis lupus familiaris. https://omia.org/OMIA002943/9615/