Key Comment: The mutation associated with EIC has been identified in a number of breeds - particularly hunting/working breeds. As the EIC phenotype requires an environmental stimulus in most cases, it should be noted that dogs could be genetically affected for EIC without displaying the condition. It may be valuable to breeders of those breeds where the mutation has been detected to use a genetic test, where breed-specific research is ongoing.

Clinical Comment: EIC appears to be autosomal recessive in inheritance but is unique in that the clinical signs are environmentally induced in dogs homozygous for the mutation. Affected dogs appear normal, and are capable of moderate exercise without incident. However, shortly after any strenuous exercise or excitement, they develop a wobbly gait with hindlimb weakness and incoordination, wide based stance, and walking with crouched hind legs. Signs can progress to full body weakness, extensor rigidity, and confusion. In extreme cases, it has been reported as fatal. Research indicates that the d-EIC mutation for this test may be particularly important to Labrador retrievers concerned about EIC, based on the N. American and European dog populations in the study. A number of hunting/retrieving breeds have been investigated, with phenotype confirmed in some, and suspected in additional breeds. In addition, there are likely other, unrelated causes of excercise intollerance and collapse. Breeds where phenotype and mutation has been established: Labrador Retrievers (and their crosses), Chesapeake Bay Retrievers, Curly-coated Retrievers, Boykin Spaniels, Pembroke Welsh Corgi. Breeds where the mutation has been detected: American Cocker Spaniel, Bouvier des Flanders, Clumber Spaniel, English Cocker Spaniel, German Wirehaired Pointer, Old English Sheepdog, Hungarian Shorthaired Vizsla, Hungarian Wirehaired Vizsla.

Veterinary Comment: Affected dogs have normal muscle mass, normal patellar reflexes before an episode of EIC, normal findings on muscle biopsy and are capable of moderate exertion without showing signs (Taylor et al., 2008, Patterson et al., 2008). Signs begin within 2 minutes after cessation of 5 to 15 minutes of strenuous exercise. Affected dogs develop a wobbly gait with hindlimb weakness and incoordination, wide based stance, and walking with crouched hind legs. Signs can progress to full body weakness, extensor rigidity, confusion, loss of consciousness, and rarely death. Episodes frequently last 5-10 minutes, often with complete recovery after 30 minutes. Loss of patellar reflexes persists after initial recovery.