Progressive Retinal Atrophy (PRA2 type)

Find out if your Golden Retriever could develop Progressive Retinal Atrophy (PRA) caused by TTC8 at CAGT.

UK only
CODE PRA2-TTC8
Categories ,
Breed(s) ,
Aliases , ,

Results from this test will be reported as detailed in the Registry Reporting list.

Overview

Progressive retinal atrophy (PRA) is the most common form of inherited disease affecting the retina in dogs; the retina detects light and sends images to the brain. Progressive degeneration of the retina at the back of the eye is characteristic of PRA and leads to vision loss and blindness. PRA is not painful to dogs, and the first signs of the disease tend to be bumping in to objects, such as a piece of furniture that has been moved. Mutations in different genes cause genetically different forms of PRA. It affects many different breeds of dog, but each genetically distinct form usually affects one or a small number of breeds.

At least two genetically distinct forms of progressive retinal atrophy are found in Golden Retrievers. Research suggests that there may be at least one form that has not yet been identified. A mutation in a gene called TTC8 causes the specific form of PRA detected by this test. In humans TTC8 is also known as BBS8 and is associated with Bardet Biedl Syndrome and with non-syndromic Retinitis Pigmentosa. PRA is the primary feature in dogs homozygous with the mutation in TTC8, but they can also present with other characteristic such as obesity, renal anomalies, sperm defects and anosmia. The average age of onset of ophthalmic clinical signs is around 5 years, but can be variable. There is no cure for this form of PRA, but using the DNA test to identify dogs that carry the mutation in TTC8 will prevent further spread of this blinding condition in this lovely breed.

Autosomal Recessive

The single nucleotide insertion in the gene called TTC8 that causes progressive retinal atrophy (PRA) in golden retrievers is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop PRA during their lives, and may also have or develop obesity, renal anomalies, sperm defects and anosmia. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop PRA as a result of the TTC8 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop PRA should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.

Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the TTC8 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with PRA, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.

Gene TTC8
Variant Single nucleotide Deletion (c.669delA)
Assay Type Variant Specific
Inheritance Autosomal Recessive
Severity Low-Moderate: Affected animals experience discomfort or dysfunction of some kind, but life expectancy is not affected.
Publication

1. Downs LM, Wallin-Hakansson B, Bergstrom T, et al. (2014) A novel mutation in TTC8 is associated with progressive retinal atrophy in the golden retriever. Canine Genet Epidemiol. 1(4): 4. DOI: 10.1186/2052-6687-1-4.

2. Mäkeläinen S, Hellsand M, Van Der Heiden AD, et al. (2020) Deletion in the Bardet–Biedl Syndrome Gene TTC8 Results in a Syndromic Retinal Degeneration in Dogs. Genes. 11(9): 1090. DOI: 10.3390/genes11091090.

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