Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy

Abstract

Type 1 polysaccharide storage myopathy (PSSM1) is a glycogen storage disorder of known cause whereas the basis for type 2 PSSM (PSSM2) is unknown. The same diet and exercise regime prescribed for PSSM1 is recommended for PSSM2; however, the benefit of these recommendations for PSSM2 is undocumented. The objectives of this study were to determine traits of PSSM2 Warmblood horses (WB), determine the changes in exercise responses that occur with a recommended low-starch/fat-supplemented diet and exercise regime, and determine if glycogen concentrations correspond to the severity of signs. Owners of PSSM2 WB (2008–2016), completed a retrospective questionnaire regarding their horse. Glycogen concentrations were analyzed in skeletal muscle of PSSM2 WB (n = 36) obtained prior to recommendations and in control WB with no evident myopathy (n = 23). Chi-square, Fisher’s exact, McNemar’s tests with Bonferroni correction and Mann Whitney testing were utilized. Abnormal exercise responses reported by owners, began at approximately 6 years of age and included a decline in performance, a reluctance to collect and reluctance to go forward in over 50% of horses. With the recommended diet and exercise regime, 80% of PSSM2 WB owners reported an overall improvement with significant decreases in the proportion of horses showing a decline in performance and rhabdomyolysis. However, 53% of PSSM2 WB were still not advancing as expected with reluctance to go forward and collect persisting in approximately one third of horses. Median muscle glycogen concentrations did not differ between PSSM2 WB and WB with no evident myopathy. PSSM2 WB with the highest glycogen concentrations were significantly more likely to show a decline in performance than those with lower glycogen concentrations. In conclusion, diet and exercise recommendations ideal for PSSM1 improve but do not eliminate the decline in performance and reluctance to go forward under saddle characteristic of PSSM2.

Integrated proteomic and transcriptomic profiling identifies aberrant gene and protein expression in the sarcomere, mitochondrial complex I, and the extracellular matrix in Warmblood horses with myofibrillar myopathy

“…MFM has recently been described in adult horses of Arabian and Warmblood (WB) breeds [ 8 , 9 ]. Adult WB horses are diagnosed with MFM at on average 11 years-of-age and show clinical signs of exercise intolerance, a reluctance to move forward under saddle, a mild lameness and mild to moderate muscle atrophy [ 9 , 10 ]. Thus, MFM can severely impact a horse’s athletic career and even breeding potential.…”

Candidate gene expression and coding sequence variants in Warmblood horses with myofibrillar myopathy

“…A diagnosis of myofibrillar myopathy (MFM) in Arabian and Warmblood horses (WB) is based on histological features that overlap with human MFM, including desmin aggregates and myofibrillar disarray in skeletal muscle fibres 1,2 . Clinical signs associated with MFM WB are usually apparent by 11 years of age and include exercise intolerance, a reluctance to move forward under saddle and a mild lameness not attributable to an underlying orthopaedic cause 1–3 . In humans, clinical signs of MFM are often apparent after the 4th decade of life 4–8 and include progressive muscle atrophy and the potential for respiratory compromise, cardiomyopathy and death 4,5,9,10 .…”

Type 2 polysaccharide storage myopathy in Quarter Horses is a novel glycogen storage disease causing exertional rhabdomyolysis

“…Additional reported clinical signs in PSSM2-QH included a low-grade lameness (n = 11), stiffness (8), fasciculations (7) and atrophy (2).…”

“…In Arabian and Warmblood horses diagnosed with PSSM2, glycogen is predominantly As-PS and concentrations are not abnormally increased compared with breed matched controls. [6][7][8] A subset of Arabian and Warmblood horses diagnosed with PSSM2 had aggregates of desmin in scattered myofibres and myofibrillar disarray in ultrastructural studies, leading to adoption of the term 'myofibrillar myopathy' for this subset of Warmblood and Arabian PSSM2 horses. 7,9 PSSM2 in these two breeds likely represents a potential early phase of myofibrillar myopathy.…”