Genetic Testing For Diseases
While nearly every puppy buyer I speak to has some knowledge of Hip dysplasia, few understand that it is not a completely preventable condition despite the emphasis placed upon it; rarely are they aware that it is the inherent traits of the medium to large breed dog PLUS the environment that leads to dysplasia. And even fewer buyers are aware that we can do more toward completely preventing other diseases through a simple cheek swab of breeding stock.
In reality, we are far more likely to eradicate certain genetic diseases within Breeds than we are to ever eliminate dysplasia entirely because much of dysplasia is caused AFTER the puppy goes to his or her new home by the environment in which it is living. (After 30 generations (six decades) of selective breeding, dysplasia is still an issue!)
Many of the inheritable diseases require that both parents pass on a copy of the gene responsible for disease to a puppy. To avoid breeding dogs that could pass on these genes and have affected puppies, one or both parents are genetically tested. Unfortunately, there are many Breeders who are not taking advantage of the availability of these tests and may be spreading Carriers throughout the breeding stock they sell to other Breeders. Those untested dogs may be unwittingly bred to another Carrier and a percentage of the puppies born to them WILL be affected by these diseases to some degree or another. Breeders truly concerned about "improving/bettering the breed" will be testing at the very least the males used in their breeding programs for the following diseases (if your Breeder is NOT testing at least one of a breeding pair for the genes related to these diseases, ask them why). Aisling Labradors will have tested one or both parents for at least the diseases listed below (in some cases, additional testing will have been done).
Hereditary nasal parakeratosis (HNPK) - There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait. PAW PRINT GENETICS. This is a (disfiguring) disease that affects Labrador Retrievers and related breeds and leads to dry, rough, discolored crusts on the edges of the dog’s nose. The disease results from a mutation that causes the nose to dry out and can lead to chronic irritation and inflammation of the skin on and surrounding the dog’s nose. Symptoms of the disorder appear in young dogs typically between the ages of around 6 months to 1 year of age. In more severe cases of the disease, cracked skin around and on the tip of the nose can become infected and require medical attention. In later stages, the disease can also affect nose pigmentation with nose skin color changing from dark to lighter shades of color. Once diagnosed, continuous care is required to reduce the occurrence of crusting on and around the dog’s nose using topical treatments. GenSol Diagnostics
Exercise Induced Collapse - There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait. PAW PRINT GENETICS. EIC was first identified in the 1990s, but since then, it’s been seen increasingly in Labrador Retrievers. Because litter mates and other related dogs were found to be similarly affected, veterinarians came to understand the hereditary nature of the condition. It’s since become clear that the exact source of the genetic problem involves a mutation in a gene involved in the communication between nerves of the central nervous system. In EIC, dogs will collapse after 5 to 10 minutes of high-drive, trigger activities, such as chasing a ball or hunting. Though a large majority of these cases recover completely within a short timeframe (less than 30 minutes), some dogs have been known to die of the condition. VetStreet.com
Canine Degenerative Myelopathy (DM) - This mutation is found in many breeds of dog, though it is not clear for Labrador retrievers whether all dogs carrying two copies of the mutation will develop the disease. The variable presentation between breeds suggests that there are environmental or other genetic factors responsible for modifying disease expression. The average age of onset for dogs with degenerative myelopathy is approximately nine years of age. The disease affects the White Matter tissue of the spinal cord and is considered the canine equivalent to amyotrophic lateral sclerosis (Lou Gehrig’s disease) found in humans. Affected dogs usually present in adulthood with gradual muscle Atrophy and loss of coordination typically beginning in the hind limbs due to degeneration of the nerves. The condition is not typically painful for the dog, but will progress until the dog is no longer able to walk. The gait of dogs affected with degenerative myelopathy can be difficult to distinguish from the gait of dogs with hip dysplasia, arthritis of other joints of the hind limbs, or intervertebral disc disease. Late in the progression of disease, dogs may lose fecal and urinary continence and the forelimbs may be affected. Affected dogs may fully lose the ability to walk 6 months to 2 years after the onset of symptoms. Affected medium to large breed dogs, such as the Labrador retriever, can be difficult to manage and owners often elect euthanasia when their dog can no longer support weight in the hind limbs." Paw Print Genetics
Labrador Centronuclear Myopathy (CNM) - "There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait. Unlike the late-onset of DM, the onset of the muscular disease known as centronuclear myopathy (CNM) typically occurs in young Labradors between 6 weeks and 7 months of age. Similar to DM, CNM is a disease that will greatly affect a dog’s ability to work or perform physical tasks. Affected dogs typically display an intolerance to exercise, a hopping gait, decreased reflexes, generalized skeletal muscle weakness and atrophy, and an increased likelihood of collapse when in cold temperatures. Many affected dogs also develop a loss of muscle contraction in the esophagus (megaesophagus) resulting in difficulties swallowing. Problems with swallowing can allow food particles and other material to enter the lungs, thus, leading to severe pulmonary infections known as aspiration pneumonia. CNM tends to progress in severity until stabilizing at around 1 year of age. However, affected dogs do not improve and will continue to have problems often requiring medical intervention throughout their life, especially in relation to respiratory disease. Dogs obtaining medical interventions when necessary can have a normal lifespan despite their abnormal physical status. However, there is currently no cure or effective treatment for CNM." Paw Print Genetics
Progressive Rod-Cone Degeneration (PRA-PRCD) - "There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait. Progressive retinal atrophy (PRA) is a category of different progressive conditions related to retinal atrophy that can eventually lead to blindness. Progressive rod-cone degeneration (PRA-PRCD) is one specific type of PRA that affects many dog breeds. It is an inherited eye disease with late onset of symptoms that are due to degeneration of both rod and cone cells of the retina. These cells are important for vision in dim and bright light. Most dogs begin to show symptoms of the disease at approximately 3-5 years of age that manifests as difficulty seeing at night (night blindness) and loss of peripheral vision. Although rate of onset and disease progression can vary by breed, PRA-PRCD typically results in eventual loss of sight and complete blindness in affected dogs. Paw Print Genetics
Note that in each of the above diseases for which a Breeder may test their breeding stock, there may be other causes. Breeders are not God and can only increase the odds that a puppy will not develop disease.
Breeders should also be considering inbreeding co-efficiency in their breeding choices.
Also note that the availability of testing for diseases is increasing. Responsible breeders are never done with their genetic testing process. As each new test relevant to their breed is discovered, one of each breeding pair should be tested for that disease at the very least.
After Genetic Testing
A dog carrying one copy of a defective gene is not taken out of the breeding stock if he/she is clear of all other defective genes and conforms to the Breed Standard. While "clear by parentage" is the ultimate goal of genetic testing breeding stock, there are always other considerations (for example, limiting the gene pool by too selective breeding which can lead to new diseases that are inheritable). Breeders who are improving/bettering the Breed will test any "keeper puppy" to ensure that a dog they have produced for breeding stock is "Clear" of the mutated gene entirely - this practice "improves" the breed in the next generation.
A carrier of any of the above named diseases can be bred to a non-carrier; none of the puppies will be affected by the INHERITED form of the disease as it takes two copies - one from each parent - of the defective gene for the disease to manifest. Some of the puppies will be carriers but not be affected by the disease; others will be clear of the defective gene entirely (these are the puppies that should be used in the next generation). (NOTE: Non-inherited forms of the disease can still potentially develop among puppies from selectively bred parents. See the disclaimers above which are included from/by all genetic testing companies.)
Puppies born to a dam and sire who are both clear of any defective gene for any of the diseases named will be deemed "clear by parentage".
What about the things for which there is no genetic test available?
While all responsible breeders test for the genetic diseases relevant to their breed and/or required by their Breed Club or the AKC; not every disease or disorder has an available test. Just like with human beings, sometimes something can go wrong and while there is a potential of that "something" being genetic or inherited, there just simply isn't a test for it yet or even enough evidence to suspect that it is "genetic".
Congenital Defects: Just like in humans, sometimes something can go wrong during gestation that affects one or more puppies. Exposure to some form of a toxin can cause birth defects; positioning in the uterine horn in a large litter can affect the development of a limb or the tail, an excess or deficiency in, for example, Vitamin A during gestation can cause developmental issues (i.e. an undeveloped leg or a crooked tail) in one puppy but not in the entire litter.
Puppies can be born showing a recessive trait like a shorter tail or a longer tail than we are used to seeing and some puppies are born with mis-markings - a white spot or line on their chest, a white foot, and so on because Labradors, like all pure bred dog breeds, originated from the mating of different breeds to produce a new breed.
Single Disease testing vs broad based testing:
It is NOT necessary that a Breeder use a company like Embark which offers testing for every known gene that may or may not lead to a disease. Companies like Embark use a test similar to what FTDNA or Ancestry use for humans and much of what is tested is "junk DNA".
Many Breeders use companies like Gensol or Pawprints where specific genes relevant to the Breed can be tested either in a limited panel or one at a time as they become available (each of the genes for the above mentioned diseases can be ordered as Single Tests). Testing in this way is often far more expensive than the broad based test offered by Embark and others and is likely far more accurate.
The reality is that companies like Embark have jumped on the DNA testing bandwagon but are mostly used by pet owners to determine the breed of their rescued dog. The database there, just like any human junk DNA testing company, is only as good as the dogs that are in the database and results are commonly adjusted after more dogs have been entered.
If a Breeder attempts to tell you that their program is better because they use Embark or another broad generic testing company; they are not telling you the truth.
When should a dog be removed from a Breeding Program?:
When there is no genetic test available, a dog or a bitch will be removed from a breeding program if a life altering/threatening pattern emerges among the off-spring of that dog or bitch. A pattern meaning that multiple offspring suffer from one particular issue indicating a possible genetic component and not random accidents of nature/environmental factors. Responsible breeders welcome information from their puppy owners about illnesses puppies from their breeding program may present. The information allows them to keep notes on each litter and each Dam and Sire used in those breedings to determine if there may be an issue. For example, if a breeder uses two unrelated bitches in their program and the same Sire for repeat litters in which there emerges a pattern, it is a simple matter to determine that it is the Sire and not the Bitches who may be passing on an undesirable trait or predisposition. On the other hand, if one Bitch bred to different Sires has a pattern in her offspring, then the issue is with the Bitch. This how Breeders operated before the availability of genetic testing and is still used for those issues for which we still await that availability.
Responsible breeders do not breed a dog with either a history of any major illness itself or who was born with a congenital (present from birth) issue. For example, a Bitch or Dog diagnosed with severe allergies or immune issues (i.e. Chronic Demodectic Mange) should never be bred nor should a puppy born with a crooked tail be bred. While these issues may be inherited, that has yet to be proven, but good breeders take no chances. Some of these congenital issues may create an issue of greater significance in the next generation.
Many times, a young puppy is diagnosed with some sort of immune issue and their owner will be told by their Vet or by others on the internet that they should tell the Breeder to remove one or both parents from the breeding program. Demodectic Mange is one example (there are two forms of Demodectic Mange - localized and chronic), While a gene may eventually be discovered that can be used to test breeding stock for localized(juvenile) mange, there is, at this time, ample evidence that this is an issue stemming from an immature and overstressed immune system in individual puppies. (Stress may be from immunizations and the transition from the litter and Dam to their new home etc.)
Localized Demodectic Mange (also called Juvenile Demodectic Mange) manifests typically AFTER the second or final round of vaccinations indicating that it is caused by an overstressed and immature immune system. All dogs have mites but typically, the maturing immune system deals with the issue keeping the mite population at a managable level. Every now and then something goes awry. Eighty-five percent of localized Demodectic Mange is diagnosed in young puppies! The last born in a litter and the less aggressive nursers during the first 12 - 24 hours after birth and the runts of any litter appear more likely to be diagnosed with it because these puppies have less of their Dam's immunity passed to them in the all important first 12 - 24 hours after birth. We recommend supplementing Vitamin C/probiotics to puppies at least throughout the immunization period (8 - 20 weeks).