DNA testing & simple inherited disorders

 

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What do DNA tests check for?

DNA tests allow owners and breeders to check a dog’s genetic status for known simple inherited disorders. These conditions are caused by a mutation at just one gene. As a result, the inheritance of these diseases is predictable, and producing puppies affected by the disease can be avoided provided that the test results for both parents are known. Often a specific mutation known to cause a simple, single gene disorder may be known to occur in individual breeds, or related breeds, although the percentage of dogs affected by the disease is usually, but not always, very low. These diseases are most commonly tested for in purebred dogs by responsible breeders, but can also occur in cross breeds and mixed breeds.

Why test your dog?

Breeders are able to test their breeding stock for known inherited diseases before the dogs are bred from. Testing all potential breeding stock, where relevant, allows breeders to determine the chance a dog may pass a disease causing gene on to its offspring, giving them the information required to avoid producing clinically affected puppies. Making informed decisions from health test results enable breeders to adapt their breeding programmes and reduce the risk of the diseases appearing in future generations.

Which DNA tests are recommended for my breed?

Before breeding, check whether any simple inherited disorders are known to affect your breed. Information on the tests that are recommended can be found on the Kennel Club’s Breed Information Centre, or you may wish to contact your veterinary surgeon, Breed Club or your dog's breeder. An extensive list of breed specific health tests, and which laboratories perform the analysis, can be found here.

How to DNA test your dog

A small number of tests require a blood sample, which needs to be drawn by a qualified person, but DNA tests are becoming increasingly based on a simple mouth swab that is totally non-invasive and can be performed by the dog's owner. A small brush is used to gently rub the inside of the dog's cheek. Loose cheek cells stick to the bristles of the brush, which is then dried and returned to the laboratory. The cheek cells are broken open to liberate their DNA, which is produced in sufficient amounts to allow the genetic status of any dog to be determined.

How do I know if a dog has been DNA tested?

The Kennel Club's online health resource, Mate Select, allows you to search for health test results for any dog registered on the Kennel Club's Breed Register. Searching the database is easy and only requires the dog's registered name, registration number or stud book number. It will display any health screening test results received and recorded by the Kennel Club from any Official Kennel Club DNA testing schemes (see below for more information), or from the British Veterinary Association/Kennel Club (BVA/KC) health schemes.  Not all DNA test results are published on Mate Select, but you can find a list of DNA tests recorded by the Kennel Club.

What is an Official Kennel Club DNA Testing Scheme?

These testing schemes involve collaboration between the Kennel Club, the Breed Clubs and the DNA testing facility. Under any one of these schemes, the breeder/owner agrees for the result of their tested dog to be sent independently to the Kennel Club by the testing laboratory. The Kennel Club then notes the result on the dog's record in the registration database, and is published:

  • In the next available Breed Records Supplement
  • On any new registration certificate issued for the dog
  • On the registration certificates of any future progeny of the dog
  • On the Health Test Results Finder in the Kennel Club's online health resource, Mate Select

A list of breed specific official Kennel Club DNA testing schemes and dogs tested under these schemes can be found here.

How can DNA tests become official Kennel Club schemes?

The Kennel Club is happy to consider a club's request to add a new DNA test to its lists and would normally need a formal request from the breed's Breed Health Co-ordinator, or a majority request from the Breed Clubs. In most cases, the test would need to be run by a laboratory already recognised by the Kennel Club. All DNA tests must be able to record a definitive result for an individual dog, and must be based on robust science. The Kennel Club continues to work alongside Breed Clubs, Breed Health Co-ordinators, and canine health professionals in a collaborative effort to improve the health of pedigree dogs.

What statistics are known about DNA testing?

Statistics on the number of dogs DNA tested and recorded by the Kennel Club can be accessed in the Kennel Club’s Dog Health Group Annual Report.

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.

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.

Autosomal-dominant conditions

An autosomal-dominant condition means that a dog need only inherit one copy 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 potential puppies produced can be predicted. Dogs that have been tested for an autosomal-dominant condition can be described as either: clear, heterozygous affected or homozygous affected, but what do these terms mean?

Clear

The dog does not have any copies of the abnormal genes associated with the condition you have tested for. The dog will not be clinically affected by the disorder.

Heterozygous affected

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 be clinically affected by the disorder and may pass one copy of the abnormal gene associated with the condition on to its offspring.

Homozygous 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 and the associated condition on to its offspring.

Potentially producing affected puppies

Potentially producing affected puppies that may develop the condition you have tested will have a serious impact on canine health and welfare. Matings which could 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.

DNA linkage test

Most DNA tests look for a particular gene that is known to cause a particular condition.  Sometimes scientists are unable to find the exact gene, but are able to know approximately where in a dog’s genome it is located.  Genes and other genetic markers are often inherited together because they are near one another on the same chromosome.  While it may be difficult to identify the exact gene causing a condition, scientists are sometimes able to find sections of DNA that are usually linked to, and inherited alongside, the unknown gene. By identifying these linked genetic markers, breeders are able to know, with considerable confidence, the genetic status of their dogs.  These DNA tests may not be quite as accurate as tests where the gene is known – they rely on the link between the marker and the disease causing gene being maintained - but can still be highly accurate and laboratories will often estimate how accurate their test is. Health conditions which have a linkage test will still be either autosomal dominant or autosomal recessive and the breeding advice will remain the same as per conditions with these modes of inheritance, but breeders should be aware that these test are not always 100% accurate.

Making balanced breeding decisions

As well as considering the implications of a dog’s DNA test results, there are other equally important factors to consider when deciding whether two dogs should be mated together, such as temperament, genetic diversity, conformation, other available health test results, the general health of the dogs, etc. Your breeding decisions should always be well balanced and take into consideration the qualities and compatibility of both the sire and dam that you are considering.

Are DNA test results published?

The names and results of Kennel Club registered dogs that are tested for conditions which are part of the Kennel Club’s official testing schemes will be recorded on the Kennel Club database for recording on their database and will be made available:

  • In the next available Breed Records Supplement
  • On any new registration certificate issued for the dog and
  • On the registration certificates of any future progeny of the dog
  • On the Health Test Results Finder in the Kennel Club's online health resource, Mate Select

What statistics are known about inherited DNA tests results?

Statistics on the number of dogs scored by the scheme and their results can be accessed in the Kennel Club’s Dog Health Group Annual Report.

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