Common Symptoms
Progressive retinal Atrophy, cone-Rod dystrophy 3 (PRA-crd3) is an adult-onset inherited eye disease affecting Glen of Imaal Terriers. PRA-crd3 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. Affected dogs initially have changes in reflectivity and appearance of a structure behind the retina called the Tapetum that is typically observed on a veterinary eye exam at 3 years of age. Between 3 and 5 years of age affected dogs show signs of vision loss in dim light (night blindness) and loss of peripheral vision. Gradually visual deficits progress to complete vision loss over several years.
Testing Tips
Genetic testing of the ADAM9 gene in Glen of Imaal Terriers will reliably determine whether a dog is a genetic Carrier of PRA-crd3. PRA-crd3 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 inheriting one copy and being a carrier of the ADAM9 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. 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. Glen of Imaal Terriers that are not found to have this specific mutation have no increased risk of having affected pups. However, because there are multiple types of progressive retinal Atrophy caused by mutations in other genes, a normal result in ADAM9 does not exclude progressive retinal atrophy 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.
References
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Goldstein O, Mezey JG, Boyko AR, Gao C, Wang W, Bustamante CD, Anguish LJ, Jordan JA, Pearce-Kelling SE, Aguirre GD, Acland GM. An ADAM9 mutation in canine cone-rod dystrophy 3 establishes homology with human cone-rod dystrophy 9. Mol Vis. 2010 Aug 11;16:1549-69.
[PubMed: 20806078]
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Kropatsch R, Petrasch-Parwez E, Seelow D, Schlichting A, Gerding WM, Akkad DA, Epplen JT, Dekomien G. Generalized progressive retinal atrophy in the Irish Glen of Imaal Terrier is associated with a deletion in the ADAM9 gene. Mol Cell Probes. 2010 Dec;24(6):357-63.
[PubMed: 20691256]
