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. 

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 available in the UK and worldwide.  A KC/ESS Breed Scheme for the PRA CORD1 mutation was introduced in 2008, meaning that all CORD1 DNA test results from accredited laboratories are now automatically recorded on the dog's KC registration record and made publicly accessible on Health Test Results Finder.  

(b)  Retinal Pigment Epithelial Dystrophy (RPED), now known as Retinopathy with Vitamin E Deficiency (RVED): 

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.  RPED/RVED is detectable between the ages of 12 - 18 months by clinical eye examination.  

As there is a known link between RPED and vitamin E loss, the condition has been re-named Retinopathy with Vitamin E Deficiency (RVED) to make it more relevant.

In 2025 the BVA/RKC/ISDS Eye Panel Group reviewed the low prevalence of RPED/RVED in ESS, having received no reports of the condition in the previous five years and very low prevalence before that.  As a result, it was removed as a listed condition for ESS under the official Eye Scheme Known Inherited Ocular Disease (KIOD) list, with effect from January 2026.  Generalised PRA remains on the list.

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 don't 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.

It has long been suspected that a second ‘modifier’ gene called MAP9 determines whether dogs with two copies of the CORD1 mutation will develop early or late onset PRA.  In 2016 a study into PRA in the ESS by the Canine Genetics Research Team at the Animal Health Trust (AHT) looked at a large collection of 925 ESS DNA samples but didn't find any with two copies of the MAP9 mutation.  Unfortunately, this mutation is extremely difficult to test for and the study wasn't technically able to identify dogs with just one copy (i.e. carriers).  Sadly, the Animal Health Trust went into liquidation and was closed in July 2020, but thankfully all the DNA samples and their scientific data have been secured and moved to Cambridge University, and it is hoped that the AHT's valuable work can be continued by other researchers in the future.

Further research is ongoing elsewhere in the world.  A genetic study published in April 2024 (Donner et al) investigated the frequency of both the CORD1 (RPGRIP1) and MAP9 mutations in 132 different breeds, using data mainly from US dogs.  The study indicated that the ESS breed population does carry the MAP9 modifier mutation, but the number of dogs expected to inherit two copies of both the CORD1 and MAP9 mutations is very small. 

A clinical study of 494 ESS in the USA (123 genetically affected for CORD1) published in October 2024 (Kwok et al) demonstrated that the CORD1 (RPGRIP1) mutation is associated with clinical visual defects that develop slowly, without obvious symptoms at first. 

What do we currently know?

From all the research that has been carried out so far, we can summarise what we know as follows:

• Both the CORD1 (RPGRIP1) and MAP9 mutations influence an individual dog’s risk of developing retinal degeneration;

• Dogs that have two abnormal copies of both genes (i.e. ‘homozygous’ for both) will likely develop early onset, rapidly progressing PRA;

• Dogs that have two copies of only the CORD1 (RPGRIP1) mutation will likely develop visual impairment later in life, or possibly not at all.

What is the advice for ESS breeders?

With our current understanding, all we can really say is that having two abnormal copies of the CORD1 (RPGRIP1) mutation is necessary but not sufficient to cause early onset PRA.  In the absence of a commercially available DNA test for the MAP9 modifier, the best breeders can do is avoid mating two dogs (e.g. two CORD1 carriers) that could produce offspring with two copies of the CORD1 (RPGRIP1) mutation, in order to minimise the risk of both early and late onset PRA.

For that reason, the CORD1 DNA test is still considered to be relevant and is therefore included in the RKC Health Standard as a Best Practice health test.  Hopefully, further research and the future development of a commercially available MAP9 DNA test will help to unravel the genetic mysteries of this disorder.

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.

PRA (CORD1) DNA testing is a 'Best Practice' health test under the Kennel Club Health Standard for ESS (or dogs must be "hereditarily clear").

All ESS breeders are advised to follow the ‘Ethical Guidelines' for DNA and clinical eye testing, which are supported by the UK ESS Breed Clubs.

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 a list of PRA Cord1 tested dogs and their genetic status, click HERE.   Note: This list doesn't 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). 

PRA is 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

 ESS Breed Clubs Health Co-ordinators