Exercise-induced collapse

From Dog

Exercise-induced collapse is an autosomal-recessive (incomplete penetrance) genetic disorder of dogs characterized by muscle weakness, incoordination and life-threatening collapse and syncope after intense exercise[1].

The disease is caused by a missense mutation in the DNM1 (dynamin) gene which is essential for neurotransmission and synaptic vesicle endocytosis.

A breed predisposition has been reported in the Boykin Spaniel, Labrador Retriever[2], Chesapeake Bay Retriever, German Wirehaired Pointer, Old English Sheepdog, Curly-Coated Retriever, Pembroke Welsh Corgi[3] and mixed breed dogs.

In the Labrador Retriever, about 30 - 40% of the population are heterozygous carriers and 3 - 13% are affected and susceptible to collapse.

Most affected dogs are young at the time of veterinary presentation, usually under 12 months of age. Excitement and high environmental temperatures appear to increase the likelihood of collapse[4]. The dog frequently collapses after 5 - 20 minutes of high intensity exercise, such as in field trials or upland game hunting, and in some cases simple fetch and retrieves.

Blood tests are usually unrewarding, but serum troponin I levels should be tested to exclude underlying heart diseases[5].

Diagnosis of this condition usually requires a standardized strenuous exercise protocol. Affected dogs usually develop an abnormal gait during evaluation, as well as significant tachycardia and respiratory alkalosis[6].

Muscle biopsy characteristics and sequential lactate and pyruvate concentrations are usually normal.

Definitive diagnosis requires DNA testing.

An unrelated disease has been reported in the Border Collie and related herding breeds (Australian Shepherd, Shetland Sheepdog, Bearded Collie and Collie) which presents with exercise-induced collapse but are negative with DNA testing.

A differential diagnosis would include pyruvate dehydrogenase phosphatase 1 deficiency, myasthenia gravis, polyneuropathy, myokymia, exertional heatstroke and malignant hyperthermia.

There is no known treatment for this condition, but it is rarely fatal and most dogs have a good quality of life.

References

  1. Patterson EE et al (2008) A canine DNM1 mutation is highly associated with the syndrome of exercise-induced collapse. Nat Genet 40(10):1235-1239
  2. Takanosu M et al (2012) Genotyping of exercise-induced collapse in Labrador retrievers using an allele-specific PCR. Vet J 193(1):293-295
  3. Minor KM et al (2011) Presence and impact of the exercise-induced collapse associated DNM1 mutation in Labrador retrievers and other breeds. Vet J 189(2):214-219
  4. Taylor SM et al (2008) Exercise-induced collapse of Labrador retrievers: survey results and preliminary investigation of heritability. J Am Anim Hosp Assoc 44(6):295-301
  5. Mellor PJ et al (2006) High serum troponin I concentration as a marker of severe myocardial damage in a case of suspected exertional heatstroke in a dog. J Vet Cardiol 8(1):55-62
  6. Taylor SM et al (2009) Evaluations of labrador retrievers with exercise-induced collapse, including response to a standardized strenuous exercise protocol. J Am Anim Hosp Assoc 45(1):3-13