PRA in Basenji (Bas-PRA)

Progressive retinal atrophy (PRA) includes a group of genetic diseases in certain breeds.  Similar to retinal dysplasia in humans, PRA is characterized by degeneration of photoreceptors leading to progressive loss of vision.

It is a very heterogeneous group of diseases with more than 12 different causal mutations, which have been already identified in canine populations.  They are divided according to the early or late onset of the disease and according to the mode of inheritance (autosomal dominant, recessive, X-linked).

Progressive retinal atrophy (Bas-PRA) with late onset has been described in Basenji breeds. The signs occur at the age from 5 to 7 years. The first sign is loss of vision in dim light that worsens progressively and culminates in blindness. The signs of Bas-PRA are very similar to those of PRA-prcd, whose causal mutation has been found in many breeds. However, the PRA-prcd mutation has not been proven in the affected dogs of Basenji breed.

In 2013, a non-stop mutation in S-antigen gene (c.1216T>C) leading to translation of 25 excessive amino acids (p.*405Rext*25) has been found. This mutation is responsible for Bas-PRA  in Basenji dogs (Goldstein et al., 2013).

The mutation causing Bas-PRA is inherited as an autosomal recessive genetic disorder. The disease occurs in dogs that inherit the mutant gene from each of the parents. These dogs are designated P/P (positive homozygotes). The molecular-genetic test can be used to confirm the diagnosis. The carriers of the mutant gene designated N/P (heterozygotes) have only one changed gene from one parent and exhibit no clinical signs. However, they pass the mutation to their offsprings. A cross of two heterozygotes (N/P) will theoretically yield 25% of healthy offspring, 50% of the offspring will be carriers of the mutation and 25% of the offspring will inherit the mutant gene from their parents and will be affected by Bas-PRA.

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Reference:

Goldstein, O., Jordan, J.A., Aguirre, G.D., Acland, G.M. : A non-stop S-antigen gene mutation is associated with late onset hereditary retinal degeneration in dogs. Mol Vis 19:1871-84, 2013. Pubmed reference: 24019744.