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  Discussion on Research Summary: GSY1 defects in Warm Bloods
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DrO

Posted on Tuesday, May 24, 2011 - 1:55 pm:

Edited from this studies conclusion: PSSM associated with the GYS1 mutation is one identifiable cause of Exertional Rhabdomyolysis in Warmblood horses. Signs of ER are not always manifest in glycogen synthase (GYS1) defect 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.

For more on the GSY1 defect see the article on Rhabdomyolysis under the Genetic Testing topic.
DrO

Equine Vet J. 2011 Mar;43(2):240-5.
Epidemiological and genetic study of exertional rhabdomyolysis in a Warmblood horse family in Switzerland.
Johlig L, Valberg SJ, Mickelson JR, Klukowska J, Reusser HR, Straub R, Gerber V.
Source

Equine Clinic, Vetsuisse Faculty of the University of Berne, Switzerland; Tierklinik Hübschenacher, Switzerland; Department of Veterinary Population Medicine, University of Minnesota, USA; Department of Veterinary Biomedical Sciences, University of Minnesota, USA; and Institute of Genetics, Vetsuisse Faculty of the University of Berne, Switzerland.
Abstract

Reasons for performing study: Exertional rhabdomyolysis (ER) and its familial basis in Warmblood horses is incompletely understood. Objectives: 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. Conclusion and potential relevance: 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.
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