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Veterinarian Technician May 2013 (Vol 34, No 5)

Genetic Testing for Exercise-Induced Collapse in Labrador Retrievers

by Jessica Erace, LVT

    Many genetic tests are available for dogs and cats in the United States. Most of the tests are for dogs and were primarily developed to facilitate inherited disease screening for breeders. Some tests are of interest to companion animal practitioners for diagnosing occult disease or to rule out (or in) certain diseases or conditions.

    The Condition

    Exercise-induced collapse (EIC) is best described as exertion-related paresis of the pelvic limbs, which often progresses to total collapse. A typical manifestation of EIC is a dog that eagerly plays fetch or catches a Frisbee for 5 to 15 minutes before suddenly appearing ataxic in the hind end, staggering, and collapsing partially or totally. Many owners identify a sudden change in gait as the first sign of trouble.a In the vast majority of cases, affected dogs do not lose consciousness and may even try to continue playing while dragging their hind end. They maintain normal mentation and experience a relatively quick recovery after exercise stops. EIC can occur in any weather and on any substrate, including in water. Dogs that experience EIC while swimming may drown, so dogs suspected of having had an EIC episode should be kept out of water and supervised while outdoors. Very rarely, dogs with a history of EIC have experienced sudden death during exercise.

    EIC has been identified as a phenomenon distinct from previously recognized causes of weakness or collapse (e.g., occult dilated cardiomyopathy, arrhythmia, laryngeal paralysis, myasthenia gravis, seizure) in large-breed dogs and is not associated with hyperthermia or electrolyte abnormalities. The distinct etiology and strong breed association made EIC a good candidate for dedicated genetic research.

    The Genetics

    The identification of an autosomal recessive mutation in a specific gene (DNM1) associated with EIC was published in 2008 after extensive research at the University of Minnesota (UMN).1 DNM1 is necessary to sustain neurotransmission during intense activity; therefore, dogs that are homozygous for the mutation are extremely likely to experience EIC, and those that have not yet collapsed may be expected to under certain circumstances.a As the mutated gene is recessive, heterozygous dogs are unlikely to experience EIC, and their identification is more important for breeding purposes. The Veterinary Diagnostic Laboratory (VDL) at UMN provides succinct and specific information on its discovery of the EIC gene.

    The DNM1 mutation was recently recognized in retriever crosses (mixed breeds) and pedigreed dogs with known or suspected Labrador crosses in their genetic background.2

    The Test

    The canine EIC test can be performed on whole blood (from an EDTA tube), tissue (dewclaws of neonates), semen, or buccal swabs. Testing at the VDL is performed 2 days per week, every week, at a cost of $65 per patient. There is no volume-discount pricing. VDL’s turnaround time can be up to 3 weeks, depending on the submission date and when the next batch of tests is performed. Although individual researchers associated with UMN hold the patent for the test, an online search shows that a few private veterinary DNA laboratories also advertise an EIC test for a similar fee and only accept buccal swab samples.

    Most laboratories include pedigree, microchip, or tattoo information with results if the veterinarian submitting the test verifies this information during sample collection. The test can be performed on Labrador crosses or other retrievers; as mentioned, defects in DNM1 may be found in mixed-breed dogs or dogs with shared heritage (i.e., pedigreed dogs with known or suspected Labrador crosses in their genetic background).

    Related Testing: Exercise Intolerance in Clumber and Sussex Spaniels

    Clumber and Sussex spaniels can carry an autosomal recessive gene for pyruvate dehydrogenase phosphatase 1 deficiency. Affected dogs experience profound exhaustion with any type of exertion. A test for pyruvate dehydrogenase phosphatase 1 is available from various canine genetic testing laboratories.

    A distinct collapse disorder has been recognized in border collies.3 Border collie collapse (BCC) is also exercise-associated and occurs during or shortly after strenuous exercise; however, BCC is characterized by abnormal mentation and gait. BCC is not the same as EIC, and the EIC test is not useful for border collies. Research on BCC is ongoing, and veterinarians who have treated affected border collies are encouraged to contact UMN. Researchers are also seeking sample submissions from border collies that are at least 3 years of age and have performed strenuous activity regularly without experiencing BCC (i.e., “normal” dogs). Information on BCC and instructions on research participation can be found on the VDL Web site.3

    More Information

    For more information on EIC and BCC, including treatment recommendations and instructions for sample submission, visit the VDL Web site.

    aTaylor SM. Exercise Induced Collapse in Labrador Retrievers [handout]. www.usask.ca/wcvm/wcvm_people/profiles/handouts/EIC.JULY.2010.pdf. July 2010.

    1. Patterson EE, Minor KM, Tchernatynskaia AV, et al. A canine DNM1 mutation is highly associated with the syndrome of exercise-induced collapse. Nat Genet 2008;40(10):1235-1239.

    2.Minor KM, Patterson EE, Keating MK, et al. Presence and impact of the exercise-induced collapse associated DNM1 mutation in Labrador retrievers and other breeds. Vet J 2011;189(2):214-219.

    3. University of Minnesota Veterinary and Biomedical Sciences. Border Collie Collapse. http://www.cvm.umn.edu/vbs/faculty/Mickelson/lab/EIC/bordercollieEIC/home.html. Accessed November 2012.

    References »

    NEXT: Guest Editorial: World Vets: Not Just an Ordinary Day at the Office

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