Journal of veterinary internal medicine2008; 22(5); 1228-1233; doi: 10.1111/j.1939-1676.2008.0167.x

Glycogen synthase 1 (GYS1) mutation in diverse breeds with polysaccharide storage myopathy.

Abstract: A missense mutation in the GYS1 gene was recently described in horses with polysaccharide storage myopathy (PSSM). Objective: The first objective was to determine the prevalence of the GYS1 mutation in horses with PSSM from diverse breeds. The second objective was to determine if the prevalence of the GYS1 mutation differed between horses diagnosed with PSSM based on grade 1 (typically amylase-sensitive) or grade 2 (typically amylase-resistant) polysaccharide. Methods: Eight hundred and thirty-one PSSM horses from 36 breeds. Methods: Horses with PSSM diagnosed by histopathology of skeletal muscle biopsy samples were identified from the Neuromuscular Disease Laboratory database. Eight hundred and thirty-one cases had blood or tissue that was available for DNA isolation; these 831 cases were genotyped for the GYS1 mutation by restriction fragment length polymorphism. Results: The PSSM mutation was identified in horses from 17 different breeds. The prevalence of the GYS1 mutation in PSSM horses was high in Draft- (87%) and Quarter Horse-related breeds (72%) and lower in Warmbloods (18%) and other light horse breeds (24%), when diagnosis was based on grade 2 diagnostic criteria. Overall, the PSSM mutation was present in 16% of grade 1 and 70% of grade 2 PSSM horses. Conclusions: GYS1 mutation causes PSSM in diverse breeds and is the predominant form of PSSM in Draft- and Quarter Horse-related breeds. False-positive diagnosis, as well as the possibility of a second glycogenosis in horses with neuromuscular disease (type 2 PSSM), might explain the absence of the GYS1 mutation in horses diagnosed with excessive glycogen accumulation in muscle.
Publication Date: 2008-08-06 PubMed ID: 18691366DOI: 10.1111/j.1939-1676.2008.0167.xGoogle Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't


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The research investigates the prevalence and influence of a glycogen synthase 1 gene mutation in various horse breeds, particularly those diagnosed with a condition known as polysaccharide storage myopathy. The study informs that the gene mutation is found to be a significant cause in horse breeds such as Draft and Quarter Horse.

Study Objectives

The study aims to examine:

  • The prevalence of GYS1 gene mutation in horses from multiple breeds suffering from polysaccharide storage myopathy (PSSM), a disease affecting the horse’s muscles.
  • Whether prevalence rates of the mutation differ between horses diagnosed with different grades of polysaccharides: grade 1 (typically amylase-sensitive) and grade 2 (typically amylase-resistant).


  • The study analyzed 831 horses of 36 breeds diagnosed with PSSM with observable muscle biopsy samples.
  • This large sample of cases had blood or tissue accessible for DNA isolation to genotype them for the GYS1 gene mutation; this was achieved by using the method of restriction fragment length polymorphism.


  • Researchers found the PSSM mutation in horses from 17 different breeds.
  • The prevalence of the mutation was higher in Draft (87%) and Quarter Horse-related breeds (72%) compared to Warmbloods (18%) and other light horse breeds (24%) when the diagnosis was made according to grade 2 diagnostic criteria.
  • A view of the entire data showed the mutation was present in 16% of grade 1 and 70% of grade 2 PSSM horses.


  • The study concludes that the GYS1 gene mutation is a significant cause of PSSM across varied horse breeds, predominantly in Draft and Quarter Horse-related breeds.
  • Researchers also theorize the possibility of false-positive diagnoses or the existence of another type of glycogen storage disorder (type 2 PSSM) in these horses that could explain the absence of the GYS1 mutation in those diagnosed with excessive glycogen accumulation in their muscles.

Cite This Article

McCue ME, Valberg SJ, Lucio M, Mickelson JR. (2008). Glycogen synthase 1 (GYS1) mutation in diverse breeds with polysaccharide storage myopathy. J Vet Intern Med, 22(5), 1228-1233.


ISSN: 0891-6640
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 22
Issue: 5
Pages: 1228-1233

Researcher Affiliations

McCue, M E
  • Department of Veterinary Population Medicine, University of Minnesota College of Veterinary Medicine, St Paul, MN, USA.
Valberg, S J
    Lucio, M
      Mickelson, J R

        MeSH Terms

        • Animals
        • Breeding
        • Genetic Predisposition to Disease
        • Glycogen Storage Disease / epidemiology
        • Glycogen Storage Disease / genetics
        • Glycogen Storage Disease / veterinary
        • Glycogen Synthase / genetics
        • Glycogen Synthase / metabolism
        • Horse Diseases / genetics
        • Horses
        • Muscle, Skeletal / pathology
        • Mutation
        • Polysaccharides / metabolism


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