Recent updates on Genetic Heart Diseases in Golden Retrievers:

The major inherited heart disease of Golden Retrievers is believed to be subvalvular aortic stenosis (SAS) although arrythmias, which may or may not be inherited, are seen in a similar percentage of Goldens. The most recent Golden Retriever breed health survey was conducted in 1998-1999 (Glickman et al , online), involved 1444 Golden retrievers owned by 746 people and indicated that of the 152 Goldens with heart conditions reported in the survey, 11.6% of these were diagnosed with SAS and 12.2% were diagnosed with arrythmias. The prevalence of another developmental heart disorder, cardiomyopathy, was half the prevalence of SAS. These statistics probably greatly under-report the actual disease prevalence as some of the heart conditions of Goldens, such as SAS, are difficult to diagnose. OFA maintains a registry and database of heart diseases in dogs and this database indicates that cardiac examinations have been equivocal in 0.8% of Goldens with 0.5% of Golden Retrievers affected (OFA, online). The actual prevalence of congenital heart disease is probably much higher as many owners do not submit reports from affected Goldens to OFA. Since OFA accumulates data such as the table above on elbow dysplasia, even from dogs in the closed registry, and future studies may be linked with DNA, owners are strongly encouraged to submit both positive and negative reports. (As mentioned previously, there is no charge to submit affected dogs.) While it is the owner's decision whether to include the data in the open or closed database, both databases can provide useful information. The open database reveals your dog's identity to all breeders but even the closed database can provide useful population data to future breeders. A study from the University of California, Davis, School of Veterinary Medicine indicates that Golden Retrievers have a 5.5 fold increased risk of SAS relative to dogs in general (Kienle et al , 1994).

In regards to the OFA database, it supplies information on dogs that are phenotypically normal but includes data from specialists (designated with an “S) and practitioners (designated with a “P”). While some of these veterinarians have the expertise needed to diagnose SAS, a veterinary cardiologist (designated with a “C”) is a veterinarian with post-graduate training in internal medicine with specialized training in heart disease who has passed an examination certifying both their general knowledge of internal medicine and their specialized expertise in heart disease (current training requirements are at http://www.acvim.org/uploadedFiles/gig/GIG06-07.pdf ) . The official title of such an individual is Diplomate, American College of Veterinary Internal Medicine, Specialty of Cardiology. Obviously, veterinary cardiologists are veterinarians who have demonstrated their knowledge of heart disease and it is for this reason that veterinarian cardiologist reports are recommended by GRCA in evaluating the cardiac status of Golden Retrievers.

SAS is particularly difficult to distinguish from murmurs that can occur in very fit and athletic dogs and the expertise of the examiner can be critical in making the diagnosis. OFA's maintains the database both for research and to provide a database for dogs that appear to be phenotypically normal when making breeding decisions but makes the following statement regarding SAS and cardiomyopathy:

“At this time inherited, developmental cardiac diseases like subaortic stenosis and cardiomyopathies are difficult to monitor since there is no clear cut distinction between normal and abnormal. The OFA will modify the congenital cardiac database when a proven diagnostic modality and normal parameters by breed are established. However at this time, the OFA cardiac database should not be considered as a screening tool for these diseases.”

Breeding studies on Newfoundlands indicate that SAS in Newfoundlands is inherited either as a defect involving multiple genes (polygenetic condition) or as a dominant gene that is modified by other genes (Pyle et al, 1972). The Canine Health Foundation sponsored a study of SAS in Golden Retrievers and Newfoundlands. In that study, SAS in Goldens and Newfoundlands, appeared to be inherited as a dominant gene with incomplete penetrance and variable expression (Lehmkuhl and Meurs, online abstract).

Thus, the current status of our knowledge is that Golden Retrievers are at increased risk for developing SAS, which is fatal in some dogs, and SAS is inherited. The diagnosis is difficult in mildly affected dogs.

The difficulty in diagnosing SAS is due to similarities between the heart murmur heard with SAS and the heart murmur which can be heard in athletic and excited dogs (these are called physiologic murmurs). For example, the incidence of grade I to II heart murmurs is 15.8% in unconditioned sled dogs, 27.8% in lightly conditioned sled dogs and 39.6% in highly conditioned sled dogs. As exercise increases, the heart rate decreases so that for unconditioned sled dogs the mean heart rate is 131 beats/minute, the mean resting heart rate in lightly conditioned sled dogs is 126 beats/minute and the mean heart rate in highly conditioned sled dogs is 102 beats/minute. In sled dogs, the presence of an athletic heart murmur appears to be associated with improved athletic performance (Constable et al , 1994). Thus, dogs that can develop athletic murmurs may be the best performers and not the dogs we want to exclude from breeding.

In differentiating SAS from physiologic murmurs, echocardiography with Doppler flow studies are frequently used but require great expertise from the examiner. The presence of a ring of tissue beneath the aortic valve which leads from the heart to the rest of the body is a definite indication of SAS but there are other, but less specific, indicators as well. These include increased flow rates through the aortic valve. However, recent studies in boxers suggest that while heart murmurs are associated with increased left ventricular outflow tract velocities in boxers, neither murmurs nor increased left ventricular outflow tract velocity are specific for SAS in boxers ( Koplitz et al, 2003). Such studies, have not yet been reported in Goldens, which makes distinguishing physiologic murmurs from SAS murmurs particularly difficult.

Until such studies are conducted, a couple of suggestions may help breeders in taking their dogs to heart exams. Owner may want to avoid situations that can produce physiologic murmurs and increase false positive diagnoses. Athletic murmurs occur in dogs that are subjected to regular exercise programs. In general, SAS murmurs appear before one year of age and examinations any time after a year of age are considered permanent. To eliminate the confusion, if a Golden is over a year of age and is about to start a conditioning program, it is best to have the cardiologist examine the heart before the heavy conditioning begins. If your dogs is already in a heavy conditioning program, record how often, how intensely and for how long your dog exercises and bring this with you to the exam (for example, if you tell the cardiologist that the dog has been exercising at 5 mph, 20 minutes/day, 6 days a week on a treadmill, there is a good reason for your dog to have a murmur though your dog could have had mild SAS before developing an athletic murmur which can be very difficult for anyone to sort out). The baseline exam is also usually an exam in a relaxed dog. Do not let a couple of young Goldens play in the exam room before their exam - this can result in changes associated with exercise during their baseline exam and can produce murmurs on auscultation and raise flow rates on Doppler exams. If your dog can't stay relaxed in a vet's office, use common sense, leave them in a crate in a cool quiet location or teach them to “stay”. Many cardiologists will exercise your dog as part of the exam – just don't present them with an exercised dog for the baseline exam. Finally, consider working with a single veterinary cardiologist to understand and control congenital heart disease. A cardiologist who has examined multiple dogs within a pedigree and their close relatives has a great deal more information with which to distinguish physiologic murmurs from SAS murmurs.

Research which benefits our Goldens is continuing. Please expect that this research will improve diagnostic techniques and help prevent the inherited diseases that affect our Golden Retrievers. We believe that this increased knowledge will prevent Golden suffering and bring the power to control these diseases to the breeder. Recent research updates have increased our understanding of breed differences in hip dysplasia, our understanding of genetic influences on elbow dysplasia, have identified pigmentary uveitis as an inherited eye defect of Goldens which causes pain and blindness, and have suggested the need for additional studies on Doppler examinations in athletic or excited young dogs. The future of our breed should be healthier and is very exciting.

References

Constable, P.D., K.W. Hinchcliff, J. Olson, and R.L. Hamlin. Athletic heart syndrome in dogs competing in a long-distance sled race. J. Appl. Physiol. 76: 433-438, 1994.

Glickman, L., N. Glickman, & R. Thorpe. The Golden Retriever Club of America National Health Survey 1998-1999. Available online at The Golden Retriever Club of America National Health Survey .

Kealy, R.D., D.F. Lawler, J.M. Ballam, G. Lust, D.N. Biery, G.K. Smith, and S.L. Mantz. Evaluation of the effect of limited food consumption on radiographic evidence of osteoarthritis in dogs. J Am Vet Med Assoc 217: 1678-1680, 2000.

Kealy, R.D., D.F. Lawler, J.M. Ballum, S.L. Mantz, D.N. Biery, E.H. Greeley, G. Lust, M. Segre, G.K. Smith, and H.D. Stowe. Effects of diet restriction on life span and age-related changes in dogs. J Am Vet Med Assoc 220: 1315-20, 2002.

Keller, G. The use of health databases and selective breeding, a guide for dog and cat breeders and owners, 4 th edition, 2003. available online at http://www.offa.org/monographweb.pdf

Kienle, R.D., W.P. Thomas, and P.D. Pion. The natural clinical history of canine congenital subaortic stenosis. J Vet Intern Med. 8: 423-431, 1994.

Koplitz S.L., K.M. Meurs, J.B. Bonagura, and V. Luis Fuentes . Left ventricular outflow tract size in boxer dogs. 2003 American College of Veterinary Internal Medicine Forum.

Lehmkuhl, L..B., and K.M. Meurs. Completed Grant No. 1419: Inheritance and Molecular Genetic Evaluation in Newfoundlands and Golden Retrievers with Subvalvular Aortic Stenosis .

OFA. Congenital Cardiac Disease Statistics. Available online at http://www.offa.org/cardiacstatbreed.html

Pyle, R.L., D.F. Patterson, and S. Chacko The Genetics and Pathology of Discrete Subaortic Stenosis in the Newfoundland Dog. , American Heart Journal, Vol. 92, No. 3, pp. 324-334, September 1976

Sapienza JS, FJ Simo, and A Prades-Sapienza. Golden Retriever uveitis: 75 cases (1994-1999). Vet Ophthalmol. 3:241-246, 2000.

Smith , G.K., PD Mayhew, AS Kapatkin, PJ McKelvie, FS Shofer, and TP Gregor. Evaluation of risk factors for degenerative joint disease associated with hip dysplasia in German Shepherd Dogs, Golden Retrievers, Labrador Retrievers, and Rottweilers. J Am Vet Med Assoc. 219: 1719-24, 2001.