Breeds Affected: Tibetan Spaniel, Tibetan Terrier
Samples Accepted: Blood, Buccal Swabs
Disease Information: Progressive Retinal Atrophy III (PRA3) in the Tibetan Spaniel and Tibetan Terrier is late-onset, usually detected upon ophthalmology exam when affected dogs are between 4-7 years old. Cells in the retina degenerate, leading to first to difficulty seeing in dim light, and usually progressing to full blindness.
Inheritance Information: PRA3 is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/pra3 The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/pra3 carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
pra3/pra3 The dog is affected. If bred to a normal animal, 100% of the offspring will be carriers. If bred to a N/pra3 carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/pra3 x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/pra3 x N/pra3) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (pra3/pra3) should not be used for breeding.
Test Information: This mutation test identifies a SINE insertion in the FAM161A gene.
Downs, L.M., Mellersh, C.S.: An Intronic SINE Insertion in FAM161A that Causes Exon-Skipping Is Associated with Progressive Retinal Atrophy in Tibetan Spaniels and Tibetan Terriers. PLoS One 9:e93990, 2014. Pubmed reference: 24705771. Doi: 10.1371/journal.pone.0093990.
Further information is available at the Online Mendelian Inheritance in Animals website.