Progressive Retinal Atrophy (PRA)
What is Progressive Retinal Atrophy (PRA)?
Progressive Retinal Atrophy is a collective term used to describe a group of eye diseases in which the retina (which lies at the back of the eye) degenerates and is eventually destroyed. The cells of the retina receive light stimuli from the external environment and transmit the information to the brain, where it is interpreted to become vision. In Progressive Retinal Atrophy (PRA), degeneration of the retinal cells causes impaired vision, eventually resulting in total blindness. The retina has 9 inner layers, the outermost of which consists of the photoreceptor (light sensitive) cells - the rods and cones. Rods are responsible for vision in dim light (night vision) and cones are responsible for vision in bright light (daytime and colour vision). The outer layer of the retina is the retinal pigmented epithelium (RPE). In dogs, the retina is not mature until 6 or 7 weeks of age.
The term 'progressive retinal atrophy' covers several types of inherited degeneration (deterioration) of the retina. Sub-classifications of PRA (see below) are based on the age at which dogs show signs of the disease and the type of retinal cells which are affected.
Progressive Retinal Atrophy (PRA) is known to be inherited in the English Springer Spaniel. Although not widespread, it is important to be aware of it and to use common sense and caution, whether breeding English Springers or looking for one to own.
All ESS breeders are advised to follow the ‘Ethical Guidelines' for DNA and clinical eye testing, which have been agreed by all eight UK ESS Breed Clubs.
Sub classifications of PRA:
(a) Generalised Progressive Rod-Cone Degeneration (GPRA):
Primarily affects the photoreceptor (light sensitive) cells. Both eyes are similarly affected (bi-lateral) and dogs eventually become totally blind. It is regarded, in the English Springer Spaniel, as mostly being a late onset (5+ years old) condition, but it can appear as early as 2 years of age.
In 2007, researchers announced that a mutation in the RPGRIP1 gene (known as the Cord1 mutation) had been identified as a major risk factor for the development of one specific form of PRA in English Springer Spaniels. A DNA test for this mutation was developed and is now available in the UK and worldwide. A Kennel Club Breed Scheme for the PRA Cord 1 mutation was introduced in 2008 and ESS breeders are advised to use the available DNA test, to eliminate the possibility of producing genetically affected offspring.
(b) Retinal Pigment Epithelial Dystrophy - RPED (also known as Centralised PRA - CPRA):
The abnormality is in the retinal pigmented epithelium (RPE). The photoreceptor cells will also degenerate eventually. The rate of vision loss is much slower than with generalised PRA, and not all dogs become totally blind. CPRA is detectable between the ages of 12 - 18 months by clinical eye examination.
Ongoing research into PRA in English Springer Spaniels:
Since the Cord1 PRA mutation was discovered, it has been difficult to explain why some genetically affected dogs lose their eyesight rapidly, at a very young age, yet others do not go blind until much later on, or even not at all throughout their lifetimes. There have also been some dogs clinically diagnosed with PRA that are not genetically affected for the Cord1 mutation, indicating that the English Springer Spaniel is one of a number of breeds carrying more than one genetic mutation for PRA.
In 2016 a study into PRA in the ESS was launched by the Canine Genetics Research Team at the Animal Health Trust (AHT). The objective was to establish whether there is a secondary ‘modifier’ mutation that determines whether ESSs that are genetically affected for the Cord1 mutation will develop an early onset, progressive form of PRA, or whether their clinical signs will not develop until much later on in life.
The study used a very large collection of 925 ESS DNA samples that were donated through a special recruitment campaign during the first half of 2016. The researchers were also trying to determine if there are other genetic mutations that cause different forms of PRA in English Springer Spaniels, so these samples were also useful for further validation of any new variants found, which could help in the development of modified, more effective DNA tests for PRA in the future. Sadly, the Animal Health Trust went into liquidation and was closed in July 2020. Thankfully, all the biological samples and their scientific data have been secured and moved to Cambridge University. It is hoped that the AHT's valuable work can be continued by researchers elsewhere in the future.
DNA Test for CORD1 PRA:
The PRA DNA test currently available for ESS is exclusively for the Cord1 mutation - it will not detect any other mutation that may be responsible for any other form of PRA. Other forms of PRA that may also exist in the breed have not yet been genetically identified and can therefore only be detected by clinical eye testing.
Breeders are advised to use the DNA test for the PRA Cord 1 mutation. This test is a requirement for the sire and dam of all ESS litters registered under the Kennel Club Assured Breeder Scheme (or they must be 'hereditarily' clear).
Kennel Club Recording of PRA CORD1 DNA Test Results:
An official ESS/Kennel Club Breed Scheme is in place, whereby PRA Cord1 DNA test results notified to the KC will be added to the details of KC registered dogs. The results will be published in the Breed Records Supplement and appear on the Health Test Results Finder on the Kennel Club website.
To find PRA Cord1 DNA test results for individual dogs click on Health Test Results Finder.
To find lists of PRA Cord1 tested dogs and their genetic status, click HERE. Scroll down to 'Health' and click on 'More about health', then 'Priority health schemes and tests'. **These lists do not include ‘hereditarily clear’ dogs (i.e. dogs that have themselves not been tested as they are the product of two CLEAR parents).
Clinical Eye Testing:
The ESS Breed Clubs advise all ESS owners and breeders to make use of the official BVA/KC/ISDS Eye Testing Scheme for annual clinical eye examination of all ESS breeding stock until at least the age of 8 years, or until they are no longer used for breeding (whichever is the later).
GPRA and RPED (CPRA) are listed for English Springer Spaniels under the Known Inherited Ocular Disease (KIOD) List of the official KC/BVA/ISDS Eye Scheme (previously known as Schedule A). Results of clinical eye tests carried out under the Scheme for these conditions are recorded on each dog's KC registration record and published by the KC in the Breed Records Supplement and on the KC website Health Test Results Finder.
If any ESS owner needs help or further information on PRA, we would be happy to hear from you. We would also be grateful if you can report any diagnosis of PRA online HERE. All information provided will be treated in the strictest confidence.
For further information or advice, please contact the