Progressive Retinal Atrophy, PRA3 (Tibetan Terrier and Spaniel Type)

Other Names: Progressive Retinal Atrophy Type III, PRA3
Affected Genes: FAM161A
Inheritance: Autosomal Recessive
Mutation: chr10:61822359-61822373 (canFam3): 14 bp duplication (dup TAAAATCAAATAAA)

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Common Symptoms

Progressive retinal Atrophy, PRA3 is a late-onset inherited eye disease affecting Tibetan terriers. Progressive retinal atrophy (PRA) occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. In general, the rod type cells are affected first and affected dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision. Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. The reported average age of clinical diagnosis in dogs affected with this type of PRA is about 5 years of age.

Breed-Specific Information for the Tibetan Terrier

The Mutation of the FAM161A gene associated with progressive retinal Atrophy, PRA3 has been identified in the Tibetan terrier, although its overall frequency in this breed is unknown.

Testing Tips

Genetic testing of the FAM161A gene in Tibetan terriers will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy, PRA3. Progressive retinal atrophy, PRA3 is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the FAM161A gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Tibetan terriers that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of PRA caused by mutations in other genes, a normal result in FAM161A does not exclude PRA in a pedigree.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Downs LM, Mellersh CS. An Intronic SINE Insertion in FAM161A that Causes Exon-Skipping Is Associated with Progressive Retinal Atrophy in Tibetan Spaniels and Tibetan Terriers. PLoS One. 2014 Apr 4;9(4):e93990. [PubMed: 24705771]