title: Evaluation of cardiac phenotype in horses with type 1 polysaccharide storage myopathy.
abstract: BACKGROUND
  Type 1 polysaccharide storage myopathy (PSSM1), an equine glycogen storage disorder caused by a gain of function mutation (R309H) in the gene encoding glycogen synthase (GYS1), is associated with the accumulation of amylase-resistant alpha-crystalline polysaccharide inclusions within skeletal muscle. Several glycogenoses in humans have a cardiac phenotype, and reports exist of horses with PSSM and polysaccharide inclusions in cardiac muscle.
  
  
  OBJECTIVE
  To investigate the hypothesis that horses with PSSM1 display a cardiac phenotype. Our objectives were to compare plasma cardiac troponin I (cTnI) concentration and the incidence of cardiac arrhythmias in PSSM1 homozygotes, heterozygotes, and control horses.
  
  
  METHODS
  One hundred and twenty-five Belgian and Percheron horses under the same management were genotyped for the R309H GYS1 mutation. From these, 8 age-, breed-, and sex-matched cohorts of each genotype were identified. Plasma cTnI concentration and incidence of cardiac arrhythmias (determined by 24-hour Holter ECG) were compared between the groups.
  
  
  RESULTS
  Although some PSSM1-affected horses had mildly increased plasma cTnI concentrations, there was no significant difference in cTnI concentrations between groups. There were no significant differences in the incidence of ectopic beats, cardiac conduction intervals or mean heart rate between groups.
  
  
  CONCLUSIONS
  We found no evidence of clinically relevant cardiac myocyte injury or arrhythmias in horses with PSSM1. Additional study is required to determine whether myocardial function may be compromised in this disorder.
authors.affiliation: Comparative Neuromuscular Diseases Laboratory, Veterinary Clinical Sciences, The Royal Veterinary College, London, UK. rnaylor@rvc.ac.uk
authors.forename: R J
authors.initials: RJ
authors.lastname: Naylor
authors.forename: V
authors.initials: V
authors.lastname: Luis-Fuentes
authors.forename: L
authors.initials: L
authors.lastname: Livesey
authors.forename: C B
authors.initials: CB
authors.lastname: Mobley
authors.forename: N
authors.initials: N
authors.lastname: Henke
authors.forename: K
authors.initials: K
authors.lastname: Brock
authors.forename: M
authors.initials: M
authors.lastname: Fernandez-Fuente
authors.forename: R J
authors.initials: RJ
authors.lastname: Piercy
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000662:veterinary; D015331:Cohort Studies; D005260:Female; D005838:Genotype; D006331:Heart Diseases / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D006720:Homozygote; D006734:Horse Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006736:Horses; D019656:Loss of Heterozygosity; D008297:Male; D009135:Muscular Diseases / Q000150:complications / Q000235:genetics / Q000662:veterinary*; D011134:Polysaccharides / Q000378:metabolism
chemical_list: D011134:Polysaccharides