POAG/PLL in the Shar Pei

Shar Pei are known to suffer from primary open angle glaucoma (POAG) but have also been reported to be affected by primary lens luxation (PLL).


Primary glaucoma is a painful and blinding disease associated with high pressure inside the eye. It is an inherited condition and is subdivided into two types: primary open angle glaucoma (POAG) and primary closed angle glaucoma (PCAG).

In the Shar Pei both POAG and PLL appear to be caused by the same mutation.

In POAG/PLL, glaucoma results from reduced drainage of fluid from the eye. This causes a build-up of pressure which, in turn, leads to pain and blindness. The eyes become enlarged and the lens of the eye becomes wobbly or even falls completely out of its normal position. Most dogs become affected at approximately 4 – 6 years of age.

How common is the disease?
We do not yet know exactly how common POAG/PLL is in the Shar Pei but the condition is frequently encountered by veterinary ophthalmologists both in the UK and in the USA.

How is the disease inherited?

The disorder shows an autosomal recessive mode of inheritance, which means that two copies of the defective gene (one inherited from each parent) have to be present for a dog to be affected by the disease.

Individuals with one copy of the defective gene and one copy of the normal gene, called carriers, show no signs of disease but can pass the defective gene onto their offspring.

When two carriers are crossed, 25% (on average) of the offspring will be affected by the disease, 25% will be clear and the remaining 50% will themselves be carriers.

Breeders & owners using the POAG/PLL DNA test obtained from any of the 3 labs below will be sent results identifying their dog as belonging to one of three categories. If your dog is registered with the UK Kennel Club, the results will also be published on the Kennel Club website.

In all cases the terms ‘normal’ and ‘mutation’ refer to the position in the DNA where this POAG/PLL mutation is located in the Shar Pei; it is not possible to learn anything about any other region of DNA from this test.

Categories;

CLEAR: These dogs have two copies of the normal gene and will not develop POAG/PLL as a result of the mutation we are testing for, although we cannot exclude the possibility they might develop a similar condition due to other causes or the effect of other, unidentified mutations.

CARRIER: these dogs have one copy of the mutation and one normal copy of DNA. These dogs will not develop POAG/PLL themselves as a result of the POAG/PLL mutation but they will pass the mutation on to approximately 50% of their offspring.

AFFECTED: these dogs have two copies of the POAG/PLL mutation and will almost certainly develop POAG/PLL during their lifetime.

 

Note: It cannot be excluded the possibility that carriers might develop a similar condition due to other mutations they might carry that are not detected by this test.

What shall I do if my dog is genetically affected?
If the DNA test reveals that your dog is affected with POAG/PLL then your dog will either already have signs of the POAG/PLL or will develop the disease in later life.

Discuss the DNA test result with your veterinary surgeon. In most situations, a referral to a veterinary ophthalmologist will be required for a detailed eye examination and discussion of what treatment, if any, is appropriate. Ongoing monitoring of the eyes will be required.

Breeding Advice;
Carriers can still be bred to clear dogs. On average, 50% of such a litter will be clear and 50% carriers; there can be no affected dogs produced from such a mating.

Pups which will be used for breeding can themselves be DNA tested to determine whether they are clear or carriers of POAG.

You can purchase the POAG/PLL DNA Test Kit from Animal DNA Diagnostics, Laboklin or Pet Genetics Lab.

Note that Pet Genetics Lab offer the POAG/PLL test as part of their Foresight Health Test package. Foresight Health takes advantage of the latest testing methods to test for multiple inherited diseases in one test. 

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The following information has been obtained online from the UK Kennel Club (KC) website;

New DNA Testing Scheme for the Shar Pei;

The Kennel Club has approved a new official DNA testing scheme for primary open angle glaucoma/primary lens luxation (POAG/PLL) in the Shar Pei, following consultation with the breed’s health co-ordinator on behalf of the breed clubs.

A Shar Pei health day was held collaboratively by the Kennel Club, the Shar Pei Club of Great Britain, the Midland Shar Pei Club and the Animal Health Trust (AHT) on 26th February. 2017 There were 43 dogs swabbed for DNA tests on the day by the AHT.

Cathryn Mellersh, Head of Canine Genetics at the AHT said “We were thrilled with the uptake for the new DNA test at the health day; we tested 43 dogs and unfortunately the frequency of the mutation was very high among those dogs.  This means that it is vitally important that carriers continue to be used for breeding, at least for the next few generations as not using carriers could lead to an unacceptable reduction in the genetic diversity of the breed.  

POAG is recessive in the Shar Pei, so carriers can be safely bred to clear dogs without the risk of producing clinically affected offspring, although any puppies that might be used for breeding should themselves be tested prior to breeding.

I would like to congratulate the breed for the enthusiasm with which they are embracing the DNA test and the effectiveness and honesty with which they are distributing information about primary open angle glaucoma and the new DNA test”.

The Kennel Club constantly reviews DNA testing schemes in conjunction with breed clubs to ensure that breeders are supported with resources which help them to make responsible breeding decisions.

Breeding Advice;

Most DNA tested dogs can be used responsibly in a breeding programme, but the decisions you make when choosing which dogs to mate must be informed and carefully planned. 

Before looking at the breeding advice below, it is important to know which type of DNA test you have used, or are considering using. There are currently three different types of DNA tests available:

  • Those that test for autosomal-recessive conditions (most DNA tests)

  • Those that test for autosomal-dominant conditions

  • Linkage tests

 

Autosomal-recessive conditions;

An autosomal-recessive condition means that a dog must inherit two copies of an abnormal gene before its health is affected. Each dog inherits one copy of a gene from its mother and one from its father. If the health status of both sire and dam are known, the likely health status of any puppies produced can be predicted. This means that any dog can be used responsibly in a breeding programme without the risk of producing clinically affected puppies, provided that the right mate is selected. Dogs that have been tested for an autosomal-recessive condition can be described as either: clear, carrier or affected, but what do these terms mean?

 

Clear;

The dog does not have any copies of the abnormal gene associated with the condition you have tested for. The dog will not be clinically affected by the disorder and will only pass on a normal copy of the gene to any offspring. Clear dogs can be mated to any dogs without producing affected puppies.

 

Carrier;

The dog has one copy of the normal gene and one copy of the abnormal gene associated with the condition you have tested for. The dog will not usually be clinically affected by the disorder, but may pass one copy of the normal gene, or one copy of the abnormal gene on to its offspring. Carrier dogs can only be mated to clear dogs without the risk of producing affected puppies. Mating a carrier to a carrier, or a carrier to an affected dog is putting the health of future puppies at risk.

 

Affected;

The dog has two copies of the abnormal gene associated with the condition you have tested for. The dog will be clinically affected by the disorder and will pass one copy of the abnormal gene on to any potential offspring. Affected dogs can only be mated to clear dogs without risking producing affected puppies, however all resulting puppies will be carriers. Mating an affected dog to a carrier, or another affected dog is putting the health of future puppies at risk.

The table below shows the outcome of mating combinations;

 
POAG/PLL DNA Table

Potentially producing affected puppies;

Producing affected puppies that will develop the condition you tested for will have a serious impact on canine health and welfare. A mating which may produce affected puppies should never knowingly be carried out. If this mating accidentally occurs, it is important to test all of the puppies before they are bred from or are passed on to new homes. Veterinary advice should be sought as to the clinical management of any affected puppies.

A note on breeding from carriers and affected dogs;

Breeding only from clear dogs can have a significant impact on genetic diversity within a breed, increasing inbreeding and therefore the likelihood of new inherited diseases emerging.

With simple autosomal recessive disorders, a carrier will not be affected by the condition you have tested for, but they could pass on a copy of the faulty gene if they themselves are bred from. Only when a dog inherits two copies of a faulty gene (one from its mother and one from its father) will it be affected. When used responsibly, carriers are an important part of any breeding plan and should not be overlooked. By breeding from carriers, you can keep good, healthy dogs in the breeding population, helping to maintain genetic diversity. Ultimately, however, over the course of a few generations it would be beneficial to aim to produce only clear puppies, thereby reducing the frequency of the disease causing variant of the gene in the breed.

Similarly an affected dog could still be used in a breeding programme, but this will very much be dependent on the condition and whether the dog's welfare would be affected by the mating/whelping process. They should only be mated to clear dogs, to ensure no affected puppies are produced.

Clear dogs are only known to be clear for the condition that they have been tested for, and may carry other unknown mutations which can be passed on to their offspring - it is almost certain that all individuals carry some versions of genes that if inherited in duplicate would result in disease. If a particular dog has many offspring that go on to breed themselves, these unknown mutations may then increase in frequency in the breed and a new inherited disease could emerge. In other words, no dog is completely risk-free, but there are ways a breeder can reduce the risk of known and unknown inherited disease. 

If you are considering a mating that may produce carrier puppies, then there are several precautions that it is strongly recommended you take.

  • It is important that carriers and affected dogs should never be used to produce affected dogs and so should never knowingly be mated to another dog that has one or more copies of the faulty gene. This means that carriers should never be bred to other carriers of the same condition or to affected dogs. 

  • Affected dogs should only ever be mated to a dog that is either tested clear or is hereditarily clear for the condition (i.e. both its parents are DNA tested clear). 

 

Sticking to these rules will mean that you can still use these dogs for breeding, while maintaining genetic diversity within the breed.

  • Never over use a carrier or affected dog for mating.  If a dog has one or two copies of a known faulty gene it should never be over used for breeding. Over using these dog’s risks increasing the frequency of the faulty gene within the population, making it more difficult for future generations to breed without increasing the risk of producing affected dogs.

  • Do your research. If all breeders decided to use carriers or affected dogs for mating, then there is a possibility that as the frequency of mutant genes increases, then the proportion of 'clear' dogs would decline. You can use carriers & affected, but you always want to make sure you have a big enough supply of clear dogs. You may wish to talk to health representatives at your local Breed Club who will have access to summary information on the results of dogs that have been DNA tested and can advise you appropriately on the current situation in your breed.

  • Any possible carrier puppies that go on to be bred from should be DNA tested prior to mating. If you do decide to produce puppies that are potentially carriers, but are concerned that they may be used by their new owners for breeding, then you may wish to consider placing an endorsement on the puppy, or include a statement in your puppy contract that any puppies used for breeding must be tested prior to mating and if the puppy is a carrier, it must only be mated to a clear dog.

 

Many people are concerned about breeding from a carrier or an affected dog because they are worried about making carriers more prevalent in the breed. Remember that every organism is already a carrier for many autosomal recessive conditions. Often, there is no way to know that these faulty genes are present until they are expressed in a dog with two copies of the gene or unless a DNA test is available. DNA tests are available for only some of the known mutations in dogs, but there are likely to be many more recessive mutations that we know nothing about. Every time you breed any dog you are already most likely breeding a dog that is a carrier for an autosomal recessive condition (this will be the same for all organisms including humans). The only difference with breeding a dog that has tested positive for a carrier is that you know what disease the autosomal recessive gene can cause.

POAG/PLL List of Clear Dogs

POAG/PLL List of Carrier Dogs

POAG/PLL List of Affected Dogs

You can purchase the POAG/PLL DNA Test Kit from Animal DNA Diagnostics, Laboklin or Pet Genetics Lab.

Note that Pet Genetics Lab offer the POAG/PLL test as part of their Foresight Health Test package. Foresight Health takes advantage of the latest testing methods to test for multiple inherited diseases in one test. 

End Note; All our breeding stock are tested for POAG/PLL.

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Location: England UK
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