Progressive retinal atrophy (PRA3)

Canine progressive retinal atrophies (PRA) are genetically heterogeneous diseases characterized by retinal degeneration and subsequent blindness. While there are PRA mutations that are shared by multiple breeds, many seem to be private to a single breed or are found in breeds sharing similar ancestral backgrounds. Typical signs found by ophthalmoscopic examination are widespread tapetal hyper-reflectivity and retinal vascular attenuation. Genetic testing complements clinical eye examinations with the advantage of detecting known PRA mutations before breeding age or before clinical signs present.
In the breeds Tibetan Spaniel and Tibetan Terrier, a genetic variant of the FAM161A gene has been found to cause a PRA form which is called PRA3. The FAM161A gene encodes for a ciliary protein expressed at the photoreceptors of the retina. Affected dogs show the typical symptoms of PRA at a relatively late age of onset, approximately at 5 years of age. However, not all ophthalmological PRA affected Tibetan Spaniels and Tibetan Terriers could be explained by PRA3. Therefore, additional unknown PRA causing variants are suspected besides to the PRA3 variant in both breeds and also besides to the rcd4-PRA variant in Tibetan Terriers.