Testing of dogs: PRA3

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PRA3 in Tibetan Terriers and Tibetan Spaniels

The Progressive Retinal Atrophy (PRA) is a term used for a group of inherited retinal diseases characterized by degeneration of photoreceptor cells. The disease starts with rod degeneration leading to night blindness and loss of spatial vision. The first symptoms that are noticed by the dog owner are worse coordination in darkness and bumping into objects. The subsequent progressive degeneration of cones leads to cataract and complete blindness.

Various forms of PRA with similar symptoms have been diagnosed in more than 100 dog breeds.  However, they differ among the individual breeds and individual dogs in aetiology, age of onset and progression of the disease.  So far 19 various breed-specific mutations have been discovered and still new mutations are being discovered.  Most dog breeds are still waiting for exact identification of the mutation responsible for PRA.

In Tibetan Terriers (TT) and Tibetan Spaniels (TS) a mutation in FAM161A-gene has been identified. This mutation is obviously the main cause of PRA in TS and TT.  It is a SINE sequence insertion (short interspersed nuclear element) in the exon 5. The insertion causes shifting of the reading frame that leads to premature insertion of a stop codon and shortening of the protein product.  The disease in Tibetan Spaniels and Tibetan Terriers is called PRA3 and seems that it is limited only to these two related breeds.  The onset of PRA3 is relatively late at approximately 5 years of age.

Mutation that causes PRA3 is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers).

This disease is incurable, but its spreading throughout the dog population can be avoided by genetic testing and selection of suitable parents. The genetic tests are carried out only once in dog´s life as the genotype does not change with the age of the dog.

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References:

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 9(4): e93990. doi:10.1371/journal.pone.0093990

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Usual turnaround time: 7 business days
1 test price: 52.00 $ without VAT