Form of progressive retinal atrophy described in the Tibetan Spaniel and the Tibetan Terrier. It produces progressive degeneration of the retinal photoreceptors, first the rods and later the cones. Affected dogs lose night vision and, over time, day vision, progressing towards blindness. It does not cause pain but is incurable.

Specific to the Tibetan Spaniel and the Tibetan Terrier. Limited data on carrier frequencies; the disease is uncommon after the introduction of genetic control.

- Initial loss of night vision (nyctalopia)\n- Brighter than normal tapetum\n- Pupillary dilation\n- Progressive decrease in day vision\n- Blindness in advanced stages\n- No ocular pain

PRA of the Tibetan Spaniel and Tibetan Terrier was investigated as an entity distinct from PRCD PRA, common to many breeds. Downs and Mellersh identified a SINE insertion in the FAM161A gene as the cause of this form, called PRA3. The molecular characterization enabled the development of a specific genetic test (PRA3) for breeders of both Tibetan breeds. (The SAG mutation corresponds to a different PRA, described in the Basenji and other breeds.)

- Test breeding dogs before mating\n- Do not mate two carriers\n- A carrier can be mated to a clear dog; test offspring intended for breeding\n- Also consider the PRCD test, since both PRAs can coexist in the breed

Onset is usually in the young adult. Differential diagnosis with other PRAs (PRCD, crd) and with acquired retinopathies; the fundus shows tapetal hyperreflectivity and disc atrophy, and the ERG first records decreased rod responses. There is no treatment. The FAM161A variant does not explain all PRA of the Tibetan breeds (genetic heterogeneity; Downs and Mellersh 2014), so a negative result does not rule out the disease.

1. Downs LM, Mellersh CS. 2014. An intronic SINE insertion in FAM161A that causes exon-skipping is associated with progressive retinal atrophy in Tibetan Spaniels and Tibetan Terriers (PLoS One) (PMID 24705771).
2. Downs LM, Aguirre GD. 2016. FAM161A and TTC8 are differentially expressed in non-allelic early onset retinal degeneration (Adv Exp Med Biol) (PMID 26427412).
3. OMIA:001918-9615 (Retinal atrophy, progressive, FAM161A-related; razas Tibetan Spaniel, Tibetan Terrier y English Shepherd).