PRA in Giant Schnauzer

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).

In Giant Schnauzer, the clinical symptoms occur approximately at four years of age. In this breed the disease is caused by a missense mutation of a gene encoding NECAP endocytosis (NECAP1): c.544G> A (p.Gly182Arg). Although the NECAP1 is highly expressed in canine retinal tissue, the involvement of this gene in the degeneration of the retina has not been revealed so far and that in no animal species.  A small number of cases indicates that it is a new form of PRA in this breed and the DNA test can help to prevent the spread of the disease.

Currently, there is no effective cure for PRA; therefore, the use of genetic technologies to identify gene variants causing PRA is crucial to reduce the occurrence of this disease in the population of dogs.

PRA is inherited in an autosomal recessive pattern.  It means that the disorder will develop only in dogs that inherited the mutated allel from both parents (recessive homozygous for the mutation). Heterozygote is a dog that inherited the mutated allel only from one of its parents and shows no symptoms and is clinically healthy.  However, this dog is a carrier of the mutation and can pass it to its offsprings. When mating two heterozygous dogs, 25% of the pups will be healthy, 50% will be carriers of the mutation and 25% inherit the mutated allel from both parents and will develop PRA. Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

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Reference:

Hitti, R.J., Oliver, J.A.C., Schofield, E.C., Bauer, A., Kaukonen, M., Forman, O.P., Leeb, T., Lohi, H., Burmeister, L.M., Sargan, D., Mellersh, C.S.: Whole Genome Sequencing of Giant Schnauzer Dogs with Progressive Retinal Atrophy Establishes NECAP1 as a Novel Candidate Gene for Retinal Degeneration. Genes (Basel) 10:, 2019. Pubmed reference: 31117272