P.73Correlation of gluteus medius muscle activities at walk and trot with myopathy changes on biopsies of the exact same locations in horses without clinical signs of type 1 polysaccharide storage myopathy

Abstract

In the native Austrian breed of Haflinger horses, abnormal polysaccharide accumulations and signs of myopathy in skeletal muscle are commonly caused by type 1 polysaccharide storage myopathy (T1PSSM), based on the genetic mutation of the glycogen synthase 1 (GYS1) gene. In the absence of clinical signs, mild histological myopathy changes in muscle fibres on biopsy as well as changes in the gluteus muscle activity pattern could be documented in Haflinger horses. Surface electromyography (sEMG) of the gluteus medius muscle during walk and trot as well as superficial muscle biopsies in the exact same location taken immediately after sEMG measurements are available of 13 Haflinger horses with homozygous non-affected status (GG, n=5) and heterozygous affected status (GA, n=6) of the GYS1 gene. Thus the aim of the present study is to investigate the correlation between sEMG activity parameters and histology scores for myopathy, to elucidate which histology changes are potentially useful to quantify the functional effect. Parameters used for sEMG signal analysis comprising frequency and amplitude information were the crossings per second (C/s) of the signal through the baseline and the 25, 50, and 75 percentile lines of the sEMG signal at the same location during the same gait. Of the biopsies of the same horses at the same location taken after the sEMG measurement myopathy changes were scored for anguloid atrophy, necrosis or macrophages, central nuclei, and fiber size variation, and numbers of fibers with characteristic cPAS inclusions were expressed as percentage of total fibers counted. There was a significant negative correlation between C/s parameters and myopathy scores over all horses; however, this was not significant within the GA horses alone for any of the myopathy characteristics documented. This may indicate that the functional relevance of the histology parameters in these clinically not affected horses is more of a qualitative than of a quantitative nature.