Comparison of gluteus medius muscle activity in Haflinger and Noriker horses with polysaccharide storage myopathy.

Ulrike Schroeder,Caroline Hahn,Rebeka Roza Zsoldos,Theresia Franziska Licka,Johann Soelkner,Negar Khayatzadeh

doi:10.1111/jpn.13504

Abstract

Type 1 polysaccharide storage myopathy caused by genetic mutation in the glycogen synthase 1 gene is present in many breeds including the Noriker and Haflinger horses. In humans, EMG has already been used to document changes in the muscle activity patterns of patients affected by human glycogen storage disorders. Therefore, the aim of the present study was to describe gluteus muscle activity with surface electromyography (sEMG) in Haflinger and Noriker horses with known GYS1 mutation status during walk and trot. Thirty‐two horses (11 Haflinger and 21 Noriker horses) with homozygous non‐affected (GG), heterozygous affected (GA) and homozygous affected (AA) status of GYS1 mutation without overt clinical signs of any myopathy were selected for the current study. Using surface electromyography gluteus medius muscle activity at walk and at trot was measured, and muscle activity was described in relation to the maximum observed value at the same sensor and the same gait. In order to further describe the signals in detail comprising both frequencies and amplitudes, the crossings through the baseline and the 25, 50 and 75 percentile lines were determined. The result of the relative muscle activity did not show a consistent difference between affected and non‐affected horses. Genetically affected (GA and AA) horses showed significantly less density of muscle activity for both gaits and horse breeds except for the crossings per second at the baseline and 75 percentile at walk in the Haflinger horses and 75 percentile at trot in the Noriker horses. The medians of all calculated density values were significantly lower in the GA Haflingers compared to the GG Haflingers (p = 0.012) and also in the AA Norikers compared to the GG Norikers (p = 0.011). Results indicate that the GYS1 mutation reduces the number of functional muscle fibres detected by sEMG measurements even in the absence of overt clinical signs.

Highlights

In the equine gluteus medius muscle (GM), regional fibre variations have been reported (Bruce & Turek, 1985; Grotmol et al, 2002)
These human glycogen storage diseases are in some regards similar to equine PSSM, a muscular defect in horses, which is defined by the irregular build-up of the normal form of sugar stored in muscle as well as an irregular form of sugar in muscle tissue (Valberg et al, 2011)
Two types of PSSM are differentiated: type 1 PSSM is the form of PSSM caused by the genetic mutation in the glycogen synthase 1 gene (GYS1), while type 2 PSSM is characterized by abnormal polysaccharide in muscle biopsies without this GYS1 mutation (McCue et al, 2009)

Summary

Introduction

In the equine gluteus medius muscle (GM), regional fibre variations have been reported (Bruce & Turek, 1985; Grotmol et al, 2002). Fast bursts of work such as joint movements during locomotion type II fibres are used, these are located in the superficial layer of the muscle Such muscle functions can be affected by several equine disorders, such as myopathies creating dysfunctional muscle fibres (McCue et al, 2008). Glycogen storage diseases of muscles exist, and these are caused by mutations in genes controlling enzymes that metabolize glycogen and glucose These human glycogen storage diseases are in some regards similar to equine PSSM, a muscular defect in horses, which is defined by the irregular build-up of the normal form of sugar stored in muscle (glycogen) as well as an irregular form of sugar (amylase-resistant polysaccharide) in muscle tissue (Valberg et al, 2011). Type 1 PSSM is inherited as an autosomal dominant trait, and only one parent needs to pass it on, with a risk that offspring will develop the clinical disease

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