By Alan Green

As we enter a new year, we at CVRC are grateful for all the support we have had from the local veterinary and pet owning community. Our commitment to excellence in medical care, service, and education is unwavering.

 It gives me great pleasure to introduce this month’s guest contributor. Dr. Jason King is a board certified veterinary neurologist and neurosurgeon. A South Carolina native, Dr. King has been with CVRC since we opened. He has helped pets from throughout the Southeast, as well as volunteering his time to assist our local South Carolina Aquarium.

The topic of Exercise Induced Collapse is pertinent to our canine companions, and especially our sporting breeds.

The Human Genome Project generated a lot of interest in studying the genetic basis for disease in people. There are now commercially available kits that you can buy over-the-counter to get your genome analyzed. In theory, this will allow you and your doctor to assess your risk for certain conditions and be on the lookout. Since the dog and cat genomes have been sequenced, is veterinary medicine heading in the same direction?

Exercise Induced Collapse (EIC) is a syndrome seen most often in Labrador retrievers. It has also been described in several other retrieving and non-retrieving breeds. The “poster child” for the disease is an excitable male black Labrador retriever from a field trial line. Most dogs are 12-17 months of age when the signs are first noted.

The syndrome is characterized by varying degrees of muscle weakness, incoordination and collapse. Strenuous exercise of 5-20 minutes duration has been noted to bring it on. Signs can range from mild rear limb weakness to complete collapse and even death!

Some claim that environmental factors play a role in EIC. Primarily high ambient temperatures, high humidity and prolonged strenuous exercise are triggers. These are situations we encounter, not uncommonly, here in the Lowcountry. And with our common passion for the great outdoors and sporting, it’s likely that there are several undiagnosed cases of this condition out there.

Recently, a genetic test for EIC has been made available. But tread carefully! It is not as straightforward as one might think. A strong genetic association was found with a mutation in the Dynamin1 (DMN1) gene. Dynamin 1 was assumed to be the causal mutation because it is very important in nerve signal transmission. Still, the cause-effect relationship between EIC and DNM1 is presumptive until the pathophysiology can be worked out.

Since every animal will have two copies of the gene, one from the sire and one from the dam; there are three possible combinations. A dog can have two normal copies (Clear), one normal and one mutated gene (Carrier), or two copies of the mutated gene (Affected). Pedigree analysis showed that an affected animal would have to have two mutated copies of the gene.

Further research turned up some more interesting facts related to the genetics of this condition. Another study looked at how common the mutation in the Dynamin 1 gene is in Labradors. It looked at animals from field-trial/hunt, service, pet, and confirmation show lines and found the mutation present 18-38 percent of the time. It turns out that 2-14 percent of the dogs tested had two mutated copies of the gene, “Affected” status. However, only 84 percent of the dogs with the mutated genes showed signs of collapse by four years of age. This means that the mutation is not necessarily sufficient in-and-of-itself to cause the condition!

In this study, the same mutation was also confirmed in Chesapeake Bay retrievers and curly coated retrievers that had shown signs of collapse. Surprisingly, the mutation was even found in Boykin spaniels (our state dog!), Pembroke Welsh corgis, and mixed breed dogs (believed to be Labrador retriever crosses) that also had a history of collapse.

There were almost 70 other dogs with a history of collapse that were evaluated in the same study. They represented two-dozen other breeds. And not a single one of them had the mutation.

Now that commercially available genetic testing is available for this and other conditions, the tendency will be to perform these tests for screening and breeding purposes. But beware! The interpretation of the genetics is not so simple. The American Kennel Club’s Canine Health Foundation says of EIC and breeding genetics: The EIC mutation is … seen in some of the most successful field trial lines, thus it unreasonable to suggest breeding only dogs that are “clear” of this mutation. However, “affected” dogs should not be bred, and “carrier” dogs should only be bread to “clear” dogs.

There are two valuable take home messages here. First, genetic testing is in its infancy and is just beginning to be commercially available. User beware, the interpretation of the test results can be very, very tricky! That’s where the expertise and knowledge of your family veterinarian comes in to play.

Second, a veterinarian should evaluate any dog that collapses after exercise. Though genetic tests might be discussed or submitted, there are many other diseases that have to be ruled out. If a dog is diagnosed with EIC, that animal can’t be worked for fear of sudden death. These dogs can still make great and happy pets, though, and there are even medical treatment options for severely affected animals.

Signs of Exercise Induced Collapse:

• Weakness
• Incoordination in the rear limbs
• Dazed or confused appearance after exercise
• Collapse
• Staggering
• Falling or leaning to one side
• Difficulty maintaining balance