PRA-prcd – Progressive Retinal Atrophy

My Research Notes on PRA-PRCD

PRA has multiple variants which effect different breeds. Research to date shows that Cocker Spaniels are effected by the prcd variant, it is commonly abbreviated as PRCD or PRA-prcd. This is the most widespread variant, and occurs in many other breeds.

Progressive rod-cone degeneration (PRA-prcd) is an inherited disease that causes blindness in dogs affecting the photoreceptor cells in the eye involved in both night and day vision.

The age of onset varies between individual Cocker Spaniels with PRCD. Evidence of retinal disease can first be seen on an Electroretinogram in dogs older than 2.5 years of age, but most affected dogs will not show signs of vision loss until 8 to 12 years of age or later.

Although there can be individual variation in the age of onset and the rate of disease progression, the disease eventually progresses to complete blindness in most dogs.

Evidence of retinal disease can first be seen on an Electroretinogram in dogs older than 2.5 years of age, but most affected dogs will not show signs of vision loss until 8 to 12 years of age or later.

PRA-prcd symptoms often start with vision problems in dim light (night blindness) and loss of peripheral vision. You may notice your dog becomes reluctant to go into dark rooms or outside at night, or becomes uncertain and fearful in the dark. This is due to the atrophy of retinal rod cells, which are important for night vision.

Over time affected dogs continue to lose night vision and begin to show visual deficits in bright light. Bumping into things becomes especially noticeable in new surroundings. The dog becomes completely blind as the retinal cone cells atrophy. The pupil is wide and the increased reflection of the fundus can be seen when the light is focused on the enlarged pupil.

Mode of Inheritance
 Autosomal Recessive
This is a heredity condition passed on from the parents. If you're getting a puppy make sure that at least one parent has been DNA tested Clear, to ensure you're puppy wont be affected by this condition.
Onset
 Late Onset (7+)
The medium is 7+yrs. But clinical symptoms can develop as early as 3yrs, And some never display symptoms.
Testing Available
 DNA
DNA testing is available from international laboratories. (It can not be done at your local vets).  
Clinical Diagnosis
Clinical symptoms often begin with signs of night blindness followed by day blindness. Specialist Veterinary Ophthalmologists can test your cocker spaniel for clinical signs of eye disease including PRCD, but only once the symptoms develop. Your local vet may be able to offer initial advice and make a referral if required.
Breeding Strategy
 1 clear parent
To ensure progeny are not affected by this condition at least 1 parent must be "clear"

My thoughts on developing minimum breed standard testing. As PRA can be scientifically determined using DNA, it should be required in any programme. There is no reason to undertake clinical evaluations for PRA . * See other Eye Conditions.

Reliable genetic testing for determining breeding strategies is important so the gene diversity is retained and a depressed gene pool does not create other problems within the breed

Cocker Spaniels that don't carry the mutation have no risk of having PRCD affected pups. And successful breeding strategies have breed clear to carrier/affected slowly reducing the incident of the disease.

Because symptoms do not appear until adulthood, genetic testing should be performed before breeding. At least one parent should be confirmed clear of the mutation in order to eliminate this from breeding lines and to avoid the potential of producing affected progeny, breeding of known carriers to each other is not recommended.

Because there are multiple types of PRA caused by mutations in other genes, a normal result in PRCD does not exclude the possibility of other types of PRA being identified in the future. Its important to continue monitoring your dogs, gathering information and keep learning.

Eye exams can detect the early clinical signs of different forms PRA, and cataracts which often develop concurrently.

American College of Veterinary Ophthalmologists

Blue Book.

Progressive Retinal Atrophy (PRA  - Specifically PRA-prcd)
PRA is a degenerative disease of the retinal visual cells which progresses to blindness. Studies have shown that the principal form of PRA in the English Cocker Spaniel is prcd which is a late onset variant form of PRA.

The mutation is allelic to that present in Miniature Poodles, Labradors, and American Cockers. The locus is termed the progressive rod-cone degeneration (prcd) gene and 30+ breeds are affected.
Historical Note:
Central progressive retinal atrophy/retinal pigment epithelial dystrophy (CPRA/RPED) was previously a condition listed for this breed. However as the condition is no longer identified in the breed, the condition has been removed. CPRA occurred in England, but was uncommon elsewhere.

ACVO "quotes" Ref: ©2022 Orthopedic Foundation for Animals and American College of Veterinary Ophthalmologists. ENGLISH COCKER SPANIEL PAGE 404-406 (under fair use for education & research)

The average annual number of dogs being clinically tested in America declined approx. 50% from 475 to 254 testing, presumably due to the availability of DNA testing for breed specific variants.

PRA-Prcd Articles

PRA-prcd Around The World

The Global Frequency Analyses of Canine Progressive Rod-Cone Study shows that genetic testing informed breeding decisions to produce fewer affected dogs.

However, the presence of dogs affected (homozygous) for the disease variant, pra-prcd, was still observed fourteen years after DNA test availability, potentially due to crosses of unknown carriers. In view - that isn't good enough...Its vital that breeders are testing to reduce all incidences.

The genetic testing has proven to be a invaluable tool and an intrinsic part of breeding healthy cockers and reducing the likelihood of disease.

Check Out The Progress Made In Reducing PRA-Prcd

PRA-graph

Huge progress made in reducing PRA-prcd by Cocker Spaniel Breeders This graph is part of a 15yr time-trend study, to evaluate how test results changed over time.
Genotype and allele frequencies in the top five tested breeds for prcd-PRA (2004–2019)
(A) prcd-PRA homozygous variant genotype
(B) prcd-PRA heterozygous genotype
(C) prcd-PRA disease-associated variant allele

This progress in reducing PRA-prcd in Cocker Spaniels over 15years has been achieved by breeders understanding and implementing breeding strategies based on DNA Testing.
Just imagine what those results would be now!

Informal data collected from RKC & CSDB
Other databases had insufficient validation of data to be included, and some of these dogs may be duplicated in the CSDB.
Data lasted updated February 2024

% are more important when considering these statistics rather than the numbers recorded above, as some dogs results may have been duplicated in different databases