Progressive retinal Atrophy, cone-Rod dystrophy (PRA-crd) is an early onset, inherited eye disease affecting dogs. PRA-crd occurs as a result of degeneration of both rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Abnormalities can be seen on an Electroretinogram by 5 weeks of age. However, diagnosis during a standard veterinary ophthalmic exam is not typically possible until 10 months to 3 years of age. In affected dogs, Cone Cells degenerate first resulting in blindness in bright light (“day blindness”). Over time, affected dogs also develop rod cell dysfunction in the retina resulting in complete blindness. Complete retinal atrophy and blindness is usually seen by 6 years of age, although disease progression is variable in affected dogs.
Breed-Specific Information for the Standard Smooth Dachshund
Standard Smooth Dachshund is included as a breed susceptible to progressive retinal Atrophy, cone-Rod dystrophy because of its close relatedness to the Standard Wirehaired Dachshund breed, which is known to develop this disease due to Mutation of the NPHP4 gene. The frequency of the causal mutation in the general Standard Smooth Dachshund population is unknown.
Genetic testing of the NPHP4 gene in Standard Smooth Dachshunds will reliably determine whether a dog is a genetic Carrier of PRA-crd. PRA-crd is inherited in an Autosomal Recessive manner in dogs meaning that they 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 that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of being a carrier of the NPHP4 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Standard Smooth Dachshunds that are not carriers of 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 NPHP4 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.
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Ropstad EO, Bjerkas E, Narfstrom K. Clinical findings in early onset cone-rod dystrophy in the standard wire-haired dachshund. Vet Ophthalmol. 2007 Mar-Apr;10(2):69-75.
Wiik AC, Thoresen SI, Wade C, Lindblad-Toh K, Lingaas F. A population study of a mutation allele associated with cone-rod dystrophy in the standard wire-haired dachshund. Anim Genet. 2009 Aug; 40(4):572-4.
Wiik AC, Wade C, Biagi T, Ropstad EO, Bjerkås E, Lindblad-Toh K, Lingaas F. A deletion in nephronophthisis 4 (NPHP4) is associated with recessive cone-rod dystrophy in standard wire-haired dachshund. Genome Res. 2008 Sep; 18(9):1415-21.