What is PRA?

Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. It is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait).[1] There is no treatment.

Progressive vision loss in any dog in the absence of glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA

Testing in the Chinese Crested includes:

The Canine Eye Registration Foundation (CERF)

After the painless examination of the dogs eyes, the A.C.V.O. Diplomate will complete the CERF form and indicate any specific disease(s) found. Breeding advice will be offered based on guidelines established for that particular breed by the genetics Committee of the A.C.V.O

OPTIGEN is a service company established to provide DNA based diagnoses and information about inherited diseases of dogs..

Optigen prcd-pra test determines the other form of pra...“prcd” stands for “progressive rod-cone degeneration” which is the type of PRA known in several breeds.

Identification of dogs that do not carry disease genes is the key to eliminating autosomal recessive diseases, like prcd-PRA. The OptiGen prcd test for CC provides almost 100% identification of these dogs. Called "genetically clear", "noncarriers" or, more formally, "homozygous normals," such dogs pass the normal gene on to all their pups with a very high probability - which means that their pups have a very low risk of being affected with prcd. These "clear" dogs can be bred to any mate - even to a prcd-affected dog that may be a desirable breeding prospect for other reasons.

Homozygous means both copies of the gene in your dog are the SAME - both normal or both prcd. A carrier has one normal and one prcd gene.

The OptiGen prcd test is a marker test rather than a mutation-based gene test. This means that it identifies dogs by a "fingerprint" on chromosome 9 near the prcd gene locus, rather than by detecting the prcd mutation itself. The result of the test is a genotype or pattern - a fingerprint - that allows the separation of dogs into three groups: pattern/genotypes A, B and C. Due to the properties of the DNA markers, there is a low risk of recombination - or dissociation - between these markers and the prcd gene.

Also keep in mind that not all retinal disease is PRA and not all PRA is the prcd form of PRA. Accurate diagnosis is essential. A dog can test as Pattern A or B, yet have a different type of PRA.

The gene is recessive and only if a dog gets a gene from EACH parent, it will develop PRA.
A single-carrier will NOT develop PRA, but will pass on a gene to ½ of it's offspring, and an PRA affected dog will give a gene to each and one of it's offspring.

Fig.1.The normal retina. Note the many prominent blood vessels.  Fig. 2. A mid-stage PRA retina. Notice how the vascularity has been markedly reduced.
Chinese Crested Genetic testing is the key to insuring breed improvement.
There are many issues facing the chinese crested but this is one of most importance!
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