Genetic basis of Exercise Induced Collapse - in Labrador Retrievers and related breeds is an autosomal recessive genetic disorder caused by mutations in the dynamin-1 (DNM1) gene. Affected dogs inherit two copies of the mutated gene (one from each parent), whereas carriers have one copy and do not show clinical signs but can pass the mutation on. Up to 35-40% of Labradors in the USA may be carriers, and about 6% may be affected. The mutation disrupts synaptic vesicle recycling in nerve cells, particularly during intense exercise, leading to collapse.
Pathophysiology - The defective dynamin-1 protein impairs normal nerve signal transmission during strenuous exercise or excitement. Episodes usually start in young adult dogs (6 months to 3 years) and are triggered by 5-20 minutes of vigorous exercise. The initial sign is hind limb weakness or wobble, progressing rapidly to collapse while mental awareness is preserved. Excitement, heat, and humidity may worsen symptoms. After episodes, dogs typically recover fully within about an hour. Despite abnormal episodes, dogs appear normal between collapses.
Complications - Sudden hind limb weakness and collapse during/after exercise, which may be confused with other neurological or cardiac disorders but without loss of consciousness. Occasional reported deaths from severe episodes, highlighting the importance of prompt cessation of exercise at first signs. Recurrences are common with repeated triggers. No progressive worsening or neurological impairment outside episodes.
Why This Matters to Breeders and Vets - Breeders should perform genetic testing to identify carriers and avoid breeding two carriers to prevent producing affected puppies, as the disease is inherited recessively and common carrier frequency means unintentional propagation is possible. Veterinarians need to recognize the clinical presentation and recommend testing for diagnosis. Management is mainly preventive: affected dogs should avoid strenuous exercise, excitement, and heat to prevent episodes. There is currently no reliable cure; some anecdotal reports of supplements or low-dose phenobarbitone help but lack consistent evidence. Affected dogs should be withdrawn from jobs involving intense physical activity to avoid collapse and injury.
Summary - Exercise Induced Collapse (EIC) in Labrador Retrievers is an autosomal recessive neuromuscular disorder caused by mutations in the dynamin-1 gene, leading to exercise-triggered episodes of hind limb weakness and collapse starting in young adulthood. Although episodes resolve without lasting effects and dogs remain alert, the risk of sudden collapse and occasional death makes early diagnosis and management critical. Genetic testing helps identify carriers to guide breeding decisions and reduce disease prevalence. Avoiding triggers and exercise cessation at the first sign of weakness are key to managing affected dogs, as no cure exists.
