Juvenile Dilated Cardiomyopathy (JDCM) is a fatal, genetically inherited form of heart disease that causes sudden death in young dogs. DNA testing to screen for this genetic condition is available and breeders should test for JDCM to inform mating decisions. All prospective ETT puppy owners should ask the breeder if the sire and dam of a puppy have been tested for JDCM.
- Symptoms of Juvenile Dilated Cardiomyopathy
- Diagnosis and Treatment
- Genetic Inheritance of Juvenile Dilated Cardiomyopathy
- DNA Testing for Juvenile Dilated Cardiomyopathy
1. Symptoms of Juvenile Dilated Cardiomyopathy
Affected dogs usually appear healthy with no signs of heart disease present before rapid deterioration or sudden cardiac arrest, typically before reaching six months of age although affected dogs are reported to have passed as early as 10 weeks of age and as late as 1 year of age. The only external abnormality identified to date is that affected male puppies may have unilateral or bilateral cryptorchidism (undescended testicle on one or both sides).
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2. Diagnosis and Treatment
There is no cure for JDCM, and it is a fatal condition for affected dogs.
JDCM is an inherited condition but it cannot be passed on where both parents have tested clear. If parents have not been tested, or only one has tested clear, the presence of the mutation can be identified by gene testing.
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3. Genetic Inheritance of Juvenile Dilated Cardiomyopathy
JDCM is more prevalent in the population of Toy Manchester Terriers in the USA than in English Toy Terriers in the UK, and the disease was introduced into the UK population of ETTs through imports of Toy Manchester Terriers that were then introduced into UK breeding programmes.
JDCM is inherited as an autosomal recessive trait, meaning that puppies must inherit the mutation from both parents to be at risk. Dogs carrying only one copy of the gene are typically unaffected but can pass the mutation to offspring, which makes genetic testing vital for responsible breeders.
Research performed at the University of Minnesota, in collaboration with University of Pennsylvania and the University of Prince Edward Island, has discovered that JDCM in the ETT/ Toy Manchester Terriers is caused by an autosomal recessive mutation in a cardiac potassium channel. To date, they have tested a number of dogs with JDCM, and all had two copies of the mutation. The disease is fully penetrant, meaning that all dogs with two copies of the mutation develop JDCM.
A carrier will have a single copy of the mutation, and it is estimated that around 20% of the global Toy Manchester Terrier and English toy Terrier population are carriers of the mutation. Carriers do not develop the disease but can produce affected puppies if bred to another carrier. However, this does not mean that carriers need to be taken out of the breeding pool, as that could rapidly reduce breed diversity.
If carriers are only bred to clear dogs, there is no risk of producing affected puppies.
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4. DNA Testing for Juvenile Dilated Cardiomyopathy
DNA testing is available to identify whether a dog is a carrier of JDCM. The JDCM test screens for a specific DNA mutation that has been discovered in a cardiac potassium channel gene. The mutation is inherited in an autosomal recessive manner. Typically, the test requires a straightforward swab taken from inside the cheek.
Test kits can be ordered through:
Both of these testing providers can also test for Xanthinuria and Von Willebrand’s Disease (vWD). We recommend that all breeders carry out DNA tests for JCDM and Xanthinuria on potential sires and dams, as well as having Patella Luxation Tests as a minimum.
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Interpreting Test Results
- ‘D’ indicates the deleterious (JDCM) form of the gene
- ‘N’ indicates the normal form of the gene
A dog’s particular combination of N or D forms of the gene is known as its genotype.
Clear (N/N):
Clear dogs have no copies of the mutation, and cannot pass the mutation on to offspring.
Carrier (D/N):
A carrier dog has only one copy of the mutation. Since the mutation is recessive, one copy will not cause JDCM. Carriers will, on average, pass the mutation on to half of their offspring. This does not mean that they need to be taken out of the breeding pool, but they should only be bred to clear dogs to avoid producing affected puppies.
Affected (D/D):
An affected dog has two copies of the mutation that causes JDCM (this is also referred to as being homozygous affected). We do not know if these dogs are fertile, as few have survived to sexual maturity. However, we do not recommend breeding an affected dog. Based on the data available so far, we believe that this is a fully penetrant mutation. This means that all affected dogs will develop JDCM, and pass away at a young age (most likely in their first year of life). Males often have cryptorchidism (undescended testicles). However, affected dogs otherwise can appear healthy with no signs of heart disease until they suddenly pass.
Carriers of JDCM should not be bred to other carriers and mated only to partners who have tested clear of JDCM. It is essential that breeders test for JDCM to inform their breeding decisions to avoid producing JDCM affected dogs.
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Breeding Outcomes
- Clear (N/N) x Clear (N/N) = 100% Clear (N/N)
- Clear (N/N) x Carrier (D/N) = 50% Clear (N/N), 50% Carrier (D/N)
(This is an average, individual litters may see anywhere from 100% Clear to 100% Carrier) - Carrier (D/N) x Carrier (D/N) = 25% Clear (N/N), 50% Carrier (D/N), 25% Affected (D/D)
(This is an average, individual litters may see more or less of any result)
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Submission of JDCM Test Results
All DNA tests carried out through Laboklin will automatically be submitted to the Royal Kennel Club on your behalf.
Scanned copies or photographs of the DNA results certificate from the University of Minnesota should be emailed to health.results@thekennelclub.org.uk
In order to strengthen and build the DNA database for the English Toy Terrier (B&T) please send all historical results to: health.results@thekennelclub.org.uk photographs or scanned copies of the certificates accepted.
All results submitted, whether automatically through Laboklin or sent by the breeder/owner directly to the RKC, will be logged and added to the RKC’s Health Test Results Finder.
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