Progressive Retinal Atrophy (PRA) in the Giant Schnauzer
We are pleased to announce that research at the Kennel Club Genetics Centre at the Animal Health Trust has identified a new mutation causing Progressive Retinal Atrophy (PRA) in Giant Schnauzer dogs.
We are calling this form PRA5 to distinguish it from other genetic forms of PRA that occur in other breeds.
The DNA test for this mutation will be available from the 19th of June 2019.
PRA is an inherited retinal disease in dogs which worsens over time, sadly leading to blindness. There are multiple forms of PRA which are variable across and within breeds. The genetic mutation causing PRA is often unique to a dog breed, and some breeds have been found to have more than one mutation in the breed causing the disease.
As there is no cure for PRA, the availability of DNA tests aims to identifying any affected or carriers of this mutation to help prevent more puppies being born with this blinding condition, and to stop it becoming more widespread in the future.
How common is the disease?
Our study found that this form of PRA is rare in the Giant Schnauzers tested showing an allele frequency in our sample set, excluding third generation relatives to affected dogs (as a frequency more representative of the general population) of 0.015 and a carrier frequency of 2.87%. This means that approximately 1 in 35 dogs will be carriers of this genetic mutation.
Our sample set included a mixture of pepper and salt, and black giant schnauzers and we identified carriers in both colour types. We also found this in carrier states in additional breeds of German origin, including Spitz and Dachshund varieties although the significance of this finding is unknown at present.
The disorder shows an autosomal recessive mode of inheritance, which means that two copies of the defective gene (one inherited from each parent) have to be present for a dog to be affected by the disease.
How is the disease inherited?
Individuals with one copy of the PRA-causal mutation and one copy of the normal gene, called carriers, show no signs of disease but can pass the defective gene onto their offspring.
When two carriers are crossed, 25% (on average) of the offspring will be affected by the disease, 25% will be clear and the remaining 50% will themselves be carriers. Please note that these percentages refer to a statically significantly number of dogs, distribution will vary in individual litters.
Breeders using our DNA test will be sent results identifying their dog as belonging to one of three categories. In all cases the terms “normal” and “mutation” refer to the position in the DNA where this PRA mutation is located in the Giant Schnauzer. It is not possible to learn anything about any other region of DNA from this test.
CLEAR: These dogs have two copies of the normal gene and will not develop PRA as a result of the PRA4 mutation we are testing for. Although we cannot exclude the possibility they might develop a similar condition due to other causes or the effect of other, unidentified mutations.
CARRIER: These dogs have one copy of the mutation and one normal copy of DNA. These dogs will not develop PRA themselves as a result of the PRA4 mutation, but they will pass the mutation on to approximately 50% of their offspring.
AFFECTED: These dogs have two copies of the PRA4 mutation and will almost certainly develop PRA during their lifetime.
We cannot exclude the possibility that carriers might develop a similar condition due to other mutations they might carry that are not detected by this test.
Our advice is to breed with carrier animals for the first few generations after the development of a DNA test. This ensures that desirable traits in the breed are also captured.
Carriers can still be bred to clear dogs. On average, 50% of such a litter will be clear and 50% carriers; there can be no affected dogs produced from such a mating.
Published 2019 – 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 2019, 10, 385.