title: Epidemiological and genetic study of exertional rhabdomyolysis in a Warmblood horse family in Switzerland.
abstract: BACKGROUND
  Exertional rhabdomyolysis (ER) and its familial basis in Warmblood horses is incompletely understood.
  
  
  OBJECTIVE
  To describe the case details, clinical signs and management of ER-affected Warmblood horses from a family with a high prevalence of ER, to determine if histopathological signs of polysaccharide storage myopathy (PSSM) and the glycogen synthase (GYS1) mutation are associated with ER in this family, and to investigate potential risk factors for development of ER.
  
  
  METHODS
  A family consisting of a sire with ER and 71 of his descendants was investigated. History of episodes of ER, husbandry, feeding and use was assessed by interviewing horse owners using a standardised questionnaire. All horses were genotyped for GYS1. In 10 ER-affected horses, muscle histopathology was evaluated.
  
  
  RESULTS
  Signs of ER were reported in 39% of horses and 51% of the entire family possessed the GYS1 mutation. Horses possessing the GYS1 mutation had a 7.1-times increased risk for developing ER compared to those with the normal genotype (95% confidence interval [CI] 2.37-21.23, P = 0.0005). All muscle samples from horses in the family with ER showed polysaccharide accumulation typical for PSSM, amylase-resistant in 9/10 cases. There was evidence (odds ratio 5.6, CI 1.00-31.32, P = 0.05) that fat or oil feeding improved clinical signs of ER. No other effects of environmental factors associated with clinical signs of ER were identified.
  
  
  CONCLUSIONS
  PSSM associated with the GYS1 mutation is one identifiable cause of ER in Warmblood horses. Signs of ER are not always manifest in GYS1 positive horses and there are also other causes for ER in Warmblood horses. Breeding animals with the GYS1 mutation results in a high prevalence of ER due to its dominant mode of inheritance.
authors: Equine Clinic, University of Berne, Switzerland.
authors: L
authors: L
authors: Johlig
authors: S J
authors: SJ
authors: Valberg
authors: J R
authors: JR
authors: Mickelson
authors: J
authors: J
authors: Klukowska
authors: H R
authors: HR
authors: Reusser
authors: R
authors: R
authors: Straub
authors: V
authors: V
authors: Gerber