Deutsch
Hrvatski
Русский
Português
Progressive Retinal Atrophy Golden Retriever Type 2 (GR-PRA2)
| Acronym: | GR2-PRA, PRA-GR2, GR-PRA2 |
| Gene: | TTC8 |
| Mutation: | c.669delA |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Progressive retinal atrophy Golden Retriever type 2 (GR2-PRA) is one form of progressive retinal atrophy (PRA) affecting Golden Retrievers. Until now, in Golden Retrievers there have been identified three different forms of PRA caused by 3 different mutations. Progressive retinal atrophy (PRA) comprises autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. There are more than 20 mutations responsible for specific forms of PRA, and some breeds, including Golden Retrievers, can be affected by more than only one form of PRA. In general, forms of PRA are characterized by disturbance of dark vision, visual field defects, and abnormalities in the electroretinogram. The age of onset and rate of retinal degeneration varies between the different forms of the conditions. Vision in dim light and also night vision is possible due to normal functioning rods. PRA causes rode degeneration, which leads to night blindness. The research estimated that PRA causes the death of around 95% of the dog’s photoreceptors. Dog owners or breeders can recognize PRA by ”glow” or ”increased shine” in the eyes. The disease is progressive. The initial stage of PRA is night blindness, while in severe cases advanced stage of PRA causes secondary cataracts or full blindness in the dog.
The mutation responsible for GR2-PRA is a newly discovered deletion in the TTC8 gene. Interestingly, a mutation in the human TTC8 gene has been associated with Retinitis Pigmentosa, the human equivalent of PRA. The disorder is inherited in an autosomal recessive manner and it affects females and males equally. Considering the mutated gene, a dog can be clear, carrier, or affected. Heterozygotes are carriers and they have no symptoms. When mating two carriers, future cubs have a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being clear (unaffected and not a carrier). There is no cure for GR2-PRA, and the only way to prevent it, is to breed dogs that are not carriers of the mutation. Defected genes for autosomal recessive disease can be passed for many generations without affected individuals occurring until two carriers are bred to one another. The only way to find out if there is a chance of getting an affected puppy is to do progressive retinal atrophy Golden retriever type 2 genetic testing.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Downs LM, Wallin-Håkansson B, Boursnell M, , Bergström T, Mellersh CS. (2014.): A novel mutation in TTC8 is associated with progressive retinal atrophy in the golden retriever. Canine Genetics and Epidemiology 1:4