Comparison of gluteus medius muscle activity in Haflinger and Noriker horses with polysaccharide storage myopathy.
Authors: Zsoldos Rebeka Roza, Khayatzadeh Negar, Soelkner Johann, Schroeder Ulrike, Hahn Caroline, Licka Theresia Franziska
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary: Gluteus Medius Activity in GYS1-Affected Haflingers and Norikers Polysaccharide storage myopathy type 1 (PSSM1), caused by mutations in the glycogen synthase 1 gene, affects many horse breeds including Haflingers and Norikers, yet subclinical changes in muscle function remain poorly characterised. Researchers used surface electromyography to measure gluteus medius muscle activity during walk and trot in 32 horses (11 Haflingers and 21 Norikers) stratified by GYS1 genotype—homozygous normal (GG), heterozygous affected (GA), and homozygous affected (AA)—all without obvious clinical myopathy signs. Whilst relative muscle activity showed no consistent pattern, genetically affected horses demonstrated significantly reduced muscle activity density in both gaits; heterozygous Haflingers showed lower median activity density than homozygous normal controls (p = 0.012), as did homozygous affected Norikers versus their normal counterparts (p = 0.011). These findings suggest that the GYS1 mutation functionally reduces the number of recruited muscle fibres detectable by electromyography, even before horses develop overt clinical signs—a critical observation for practitioners monitoring at-risk individuals. Understanding subclinical neuromuscular changes may inform early intervention strategies and management decisions in genetically affected horses that currently appear clinically sound.
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Practical Takeaways
- •Horses carrying GYS1 mutations show reduced gluteal muscle activity during movement even when asymptomatic, suggesting subclinical neuromuscular changes occur before clinical disease manifests
- •sEMG can be used as a diagnostic tool to detect early muscle dysfunction in genetically affected horses before overt clinical signs develop
- •Both Haflinger and Noriker breeds require genetic screening for GYS1 mutations as both carriers and affected horses show measurable muscle activity changes
Key Findings
- •Genetically affected horses (GA and AA genotypes) showed significantly lower density of muscle activity in gluteus medius at both walk and trot compared to non-affected (GG) horses
- •GA Haflinger horses had significantly lower median density values compared to GG Haflingers (p = 0.012)
- •AA Noriker horses had significantly lower median density values compared to GG Norikers (p = 0.011)
- •GYS1 mutation reduces functional muscle fibers detectable by sEMG even without overt clinical myopathy signs