Progressive retinal Atrophy (PRA) (giant schnauzer type) is an inherited eye disease affecting Giant Schnauzers. PRA (giant schnauzer type) causes degeneration of both Rod and cone type Photoreceptor Cells of the Retina. These are important for vision in dim and bright light, respectively. Affected dogs present with changes in reflectivity and appearance of a structure behind the retina called the Tapetum. A veterinarian may observe this during an eye exam. Additionally, thinning of the retinal blood vessels may also be observed. Affected dogs will have gradual vision loss, eventually progressing to complete blindness in most cases.
Breed-Specific Information for the Giant Schnauzer
The Mutation of the NECAP1 gene associated with progressive retinal Atrophy (giant schnauzer type) has been identified in giant schnauzers. Though the exact frequency in the overall giant schnauzer population is unknown, approximately 6% out of 322 giant schnauzers tested were carriers of the mutation and less than 1% were at-risk.
Genetic testing of the NECAP1 gene will reliably determine whether a dog is a genetic Carrier of PRA (giant schnauzer type). PRA (giant schnauzer type) is inherited in an Autosomal Recessive manner in dogs. This means that dogs must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the NECAP1 gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood, genetic testing should be performed before breeding. To eliminate this mutation from breeding lines and avoid the potential of producing affected pups, breeding known carriers to each other is not recommended. Dogs that do not carry the mutation have no increased risk of having affected pups. However, because there are multiple types of PRA caused by mutations in other genes, a normal result in NECAP1 does not exclude PRA in a pedigree.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Hitti RJ, Oliver JAC, Schofield EC, Bauer A, Kaukonen M, Forman OP, Leeb T, Lohi H, Burmeister LM, Sargan D, Melleresh CS. Whole Genome Sequencing of Giant Schnauzer Dogs with Progressive Retinal Atrophy Establishes NECAP1 as a Novel Candidate Gene for Retinal Degeneration. Genes (Basel). 2019 May 21;10(5). pii: E385. doi: 10.3390/genes10050385.