Dilated Cardiomyopathy is an inherited disorder of the heart affecting several breeds of dog. This disease shows Incomplete Penetrance, meaning that not all dogs at risk (those with one or two copies of the Mutation) will develop the disease. In affected dogs, the heart muscle is weak and the chambers become dilated with thin walls. These enlarged hearts have poor contractility and are prone to arrhythmias. Affected dogs present with clinical signs of poor heart function between 1 to 8 years of age. Affected dogs develop clinical signs as they age ranging from mild exercise intolerance to sudden death or congestive heart failure. Signs of heart disease include exercise intolerance, fatigue, coughing, difficulty breathing, rapid breathing, fainting and sudden death. Affected dogs that don’t die suddenly from arrhythmias usually die from congestive heart failure around 7 years of age. Different disease genes and environmental factors play a role in the development of dilated cardiomyopathy in dogs. Therefore not all dogs with this disease will have the same genetic mutation.
Breed-Specific Information for the Australian Shepherd
The Mutation of the PDK4 gene associated with dilated cardiomyopathy in other breeds has been identified in the Australian Shepherd. Although dilated cardiomyopathy has been found in Australian Shepherds, and this mutation has been identified in Australian Shepherds, a clear association between this mutation and this disease in Australian Shepherds has not been reported. It is unknown for this breed if dogs carrying one or two copies of this mutation develop the clinical signs of dilated cardiomyopathy. In a European report, 7 out of 24 healthy Australian Shepherds tested in the United Kingdom and Germany were found to have one copy of the mutation and were therefore carriers of the mutation.
Genetic testing of the PDK4 gene will reliably determine whether a dog is a genetic Carrier of the PDK4 Mutation associated with dilated cardiomyopathy. However, this mutation has only been identified as a cause of dilated cardiomyopathy in the Doberman pinscher. Dilated Cardiomyopathy due to this mutation is inherited in an Autosomal Dominant manner in Dobermans meaning that they only need to inherit one copy of the mutated gene to be at an increased risk of developing the disease. Each pup that is born to an affected dog has a 50% chance of inheriting one copy of the PDK4 gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood and because the mutation shows Incomplete Penetrance, genetic testing should be performed before breeding. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of Doberman pinschers known to have the mutation is not recommended (please see information below for breeds other than the Doberman pinscher). Dogs that are not carriers of the mutation have no increased risk of having affected pups due to this mutation.
*NOTE: The PDK4 gene mutation was originally identified in the Doberman pinscher and has only been associated with dilated cardiomyopathy in this breed. Though this mutation has been identified in several other breeds, including those known to develop dilated cardiomyopathy, a correlation between this mutation and dilated cardiomyopathy has not been established for these breeds. For this reason, dogs from breeds other than the Doberman pincher that have been found to have inherited this mutation should not be removed from breeding programs based upon the results of this genetic test alone. The most cautious approach for these dogs would be to make breeding decisions based upon cardiac exam results and recommendations from a board certified veterinary cardiologist.
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.
Meurs KM, Lahmers S, Keene BW, White SN, Oyama MA, Mauceli E, Lindblad-Toh K. A splice site mutation in a gene encoding for PDK4, a mitochondrial protein, is associated with the development of dilated cardiomyopathy in the Doberman pinscher. Hum Genet. 2012 Aug; 131(8):1319-25.
Owczarek-Lipska M, Mausberg TB, Stephenson H, Dukes-McEwan J, Wess G, Leeb T. A 16-bp deletion in the canine PDK4 gene is not associated with dilated cardiomyopathy in a European cohort of Doberman Pinschers. Anim Genet. 2013 Apr;44(2):239.