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Exercised Induced Collapse (EIC) is a genetic syndrome, predominately occurring in Labrador Retrievers. Affected dogs show signs of muscle weakness, lack of coordination, and life-threatening collapse when participating in strenuous exercise or activity. Dogs that have EIC are prone to mild-to-severe collapse that can range from dragging of the hind legs to complete collapse. Most affected dogs have been from field-trial breedings. Black, yellow and chocolate Labradors of both sexes are affected, with the distribution of colors and sexes closely reflecting the typical distribution in field trials (black males are most common.) Affected dogs can tolerate mild to moderate exercise, but just 5 to 20 minutes of strenuous activity or even extreme excitement can induce weakness or collapse. EIC is also seen in Chesapeake Bay Retrievers and Curly Coated Retrievers. Dogs Affected with EIC usually cannot tolerate intense retriever training, but can live normal lives as house pets.
For years veterinarians evaluated affected dogs for episodes of collapse, and speculated that their episodes were due to heat intolerance, low blood sugar, cardiac arrhythmias or possibly metabolic myopathies. Now, EIC has been established as an autosomal recessive syndrome caused by a mutation in the DNM1 gene, which causes a defect in nerve communication during intense exercise. To be effected a dog must receive a defective gene from both parents.
In dogs with EIC, certain factors can cause collapse:
Responsible breeding is the key to preventing EIC. The EIC mutation is fairly prevalent (25%) in Labrador Retrievers and 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. Whenever a dam or sire of a litter is a known carrier of EIC, puppies should be tested before 7 weeks of age.
Signs to look for include:
There is a specific DNA test for EIC. The University of Minnesota Veterinary Diagnostic Laboratory offers testing of blood, semen, dew claw or cheek swab and provides three levels of results: Clear, Carrier, or Affected. A Clear result means that the dog has two copies of the normal EIC gene. A Carrier result means that the dog has one copy of a normal EIC gene and one mutated copy of the gene. Carrier dogs do not show signs of EIC. Carrier dogs, pass on the mutated gene, on average, to half of their offspring. An affected result means that a dog that has two copies of the mutated EIC gene. These dogs are susceptible to collapse episodes under their trigger conditions. An affected dog will pass on the mutated EIC gene to all of its offspring. By mating an affected dog to a clear dog, a litter that is made up of 100 percent carrier offspring will be produced no clears, but also no affecteds.
Signs become apparent in young dogs as they enter heavy training - usually between 7 months and 2 years of age. Dogs with EIC are always normal at rest and are usually described as being extremely fit and athletic.
Treatment for EIC consists of avoiding intensive exercise in conjunction with extreme excitement, and ending exercise at the first sign of weakness. However, numerous anecdotal reports show that dogs may be able to resume trigger activities (i.e. competition, retrieving) when they are treated with the anti-seizure medication, Phenobarbital. Phenobarbital and other sedative drugs may simply decrease the dog's level of excitement or anxiety, thereby decreasing the likelihood of collapse. In some dogs; however, Phenobarbital administration will cause noticeably impaired judgment, interfering with training or trialing. Phenobarbital also has potential side effects, so it should only be administered under the direction and monitoring of a veterinarian.
Dogs symptomatic for EIC must be retired from the activities that cause them to collapse. When trigger activities are limited, dogs with EIC can live normal lives. Many affected field trial dogs have been adopted out as pets, and if intense exercise, excitement and training stressors are avoided, dogs with EIC typically never experience another episode of collapse.
CHF has funded the research that determined the genetic cause of EIC in the Labrador Retriever. Subsequent grants have been approved to investigate the genetic cause of EIC in other sporting breeds.
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