Generalised PRA 1 (Golden Retriever Type) Overview
Generalised PRA 1 (Golden Retriever Type)
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Category: Ophthalmologic - Associated with the eyes and associated structures
Gene: Solute carrier family 4 member 3 (SLC4A3) on chromosome 37
Variant Detected: C.2601-2602 Insertion C p.Glu868Arg-frameshiftX104
Severity: Scale 3 has a moderate degree of severity, as it is not a fatal disease, though it can decrease the quality of life.
Mode of Inheritance: Autosomal Recessive
Test Overview: Progressive retinal atrophy (PRA) is a collection of inherited diseases affecting the retina that cause blindness. Each breed exhibits a specific age of onset and pattern of inheritance, and the actual mechanism by which the retina loses function can vary. The result of almost all types of PRA is similar - generally an initial night blindness, with a slow deterioration of vision (often starting with peripheral vision) until the dog is completely blind. The age at which the dog becomes fully blind also varies, depending on the genetic disruption present and the breed. Affected eyes are not painful, unless complicated by a secondary problem, such as cataract or uveitis (inflammation due to a leaking cataract). Progressive retinal atrophy (PRA) has been classified in several different ways. The simplest of these is by age of onset. Early onset PRA occurs when the affected dog is night blind from birth, and generally is completely blind between 1 - 5 years of age. Late onset PRA is where the dog is night blind at some time over 1 year of age, and full blindness will occur at a somewhat later stage in life. Another is by the type of genetic abnormality causing the PRA. PRA may be inherited by recessive, dominant or sex-linked mechanisms in dogs. For many types of PRA in many breeds a DNA test is now available to allow for easy screening for the disease. Despite the complexity of the disease and its many forms, ultimately all forms have one thing in common – degeneration of the retina causing progressive loss of vision. DNA tests are not yet available for all affected breeds. And because breeds may also be prone to several forms of PRA (and not all may have a genetic test available) examination of the retina by a veterinary ophthalmologist remains a mainstay of the diagnostic testing regimen. In some breeds with a late onset PRA, serial eye examinations may be required before the signs of retinal degeneration become apparent. The electroretinogram (ERG) is a diagnostic test that the veterinary ophthalmologist may choose to use in some cases and is a very sensitive method of detecting loss of photoreceptor function. An ERG can be a very good screening test for puppies that may have an early onset form of PRA. Golden retrievers may suffer from several types of PRA, one of which has been termed golden retriever PRA 1 (GR_PRA1). This is a late onset form of PRA, with clinical signs often not seen until around 6 years of age, although the age of onset varies somewhat between individuals. This is an autosomal recessive condition affecting the SLC4A3 gene, and a genetic test is available. As with all dogs suffering from PRA, there is no cure. Dogs generally adapt quite well to blindness - especially when it develops gradually - as long as their surroundings remain familiar (e.g. furniture does not get rearranged, they do not move house etc). They should always be kept on a lead outside the yard, and care should be taken not to startle them. Balls containing bells (as an example) can be used as toys for mental stimulation.
Recommended Screening: 1. DNA test all breeding animals prior to entering into breeding program (e.g. at 1 year of age). 2. Examination by a specialist veterinary ophthalmologist beginning with the puppy eye exam and then annually from 1 year of age.
Research Citation(s): Downs LM, Wallin-Hakansson B, Boursnell M, Marklund S, Hedhammar A, Truve K, Hubinette L, Lindblad-Toh K, Bergstrom T, Mellersh CS. A frameshift mutation in golden retriever dogs with progressive retinal atrophy endorses SLC4A3 as a candidate gene for human retinal degenerations. PLoS One. 2011;6(6):e21452
Associated Breed(s): Golden Retriever, Goldendoodle, Mixed Breed, Groodle,