Epidemiological and genetic study of exertional rhabdomyolysis in a Warmblood horse family in Switzerland.
Authors: Johlig L, Valberg S J, Mickelson J R, Klukowska J, Reusser H R, Straub R, Gerber V
Journal: Equine veterinary journal
Summary
# Editorial Summary: Exertional Rhabdomyolysis in Warmblood Horses A Swiss research team investigated familial exertional rhabdomyolysis (ER) in a Warmblood pedigree descended from an affected sire, examining whether polysaccharide storage myopathy (PSSM) and the glycogen synthase (GYS1) mutation explained the high disease prevalence in this family. Through questionnaire-based assessment of 72 horses and genetic testing combined with muscle histopathology, they found that 39% of the family exhibited clinical ER, whilst 51% carried the GYS1 mutation—horses with this mutation faced a 7.1-fold increased risk of developing ER compared to those with normal genotype. All muscle samples from affected horses demonstrated polysaccharide accumulation characteristic of PSSM (amylase-resistant in 9 of 10 cases), and dietary supplementation with fat or oil showed evidence of clinical improvement (odds ratio 5.6). The findings confirm that GYS1-associated PSSM is a significant but not exclusive cause of ER in Warmbloods, with the mutation's dominant inheritance pattern explaining why selective breeding of carriers can rapidly establish high disease prevalence within families. Practitioners should consider GYS1 mutation screening in bloodlines with recurrent ER, optimise dietary management towards higher fat/oil provision in susceptible horses, and recognise that GYS1-negative cases may reflect alternative metabolic or physiological aetiologies requiring different investigation strategies.
Read the full abstract on PubMed
Practical Takeaways
- •GYS1-positive Warmblood horses have substantially elevated ER risk; genetic testing should inform breeding decisions and management protocols for at-risk animals
- •Dietary modification with fat or oil supplementation may help manage clinical signs in ER-affected horses, warranting trial in practice settings
- •Not all GYS1-positive horses develop ER, and other genetic and environmental causes exist; clinical assessment and muscle biopsy remain valuable diagnostic tools
Key Findings
- •39% of horses in the family showed signs of exertional rhabdomyolysis, with 51% carrying the GYS1 mutation
- •GYS1 mutation carriers had a 7.1-fold increased risk of developing ER (95% CI 2.37-21.23, P=0.0005)
- •All 10 ER-affected horses examined showed polysaccharide accumulation typical of PSSM on muscle histopathology, with 9/10 cases being amylase-resistant
- •Fat or oil supplementation showed evidence of improving clinical ER signs (odds ratio 5.6, P=0.05)