Background: Previous reports suggest that although a diagnostic muscle biopsy can confirm the presence of Pompe disease, the absence of a definitive biopsy result does not rule out the diagnosis. Methods: In this study, we reviewed patients with a limb-girdle syndrome who demonstrated nonspecific abnormalities of muscle, without evidence of the classical changes of acid maltase deficiency. These patients were rescreened for Pompe disease using dried blood spot (DBS) testing. Results: Twenty-seven patients provided blood samples for the DBS test. Four patients underwent subsequent genetic testing. Genetic analysis demonstrated that one patient tested positive for Pompe disease and one patient had one copy of a pathogenic variant. Conclusions: In conclusion, the ability of a diagnostic muscle biopsy to definitively rule out the presence of Pompe disease is limited. There is a role for a screening DBS in all patients presenting with a limb-girdle syndrome without a clear diagnosis.

In a previous study of young Norwegian–Swedish coldblooded trotters (NSCT), aged 17–24 months, a high proportion (>30%) of type I fibres in the gluteus medius was found in 33 of 141 horses. These findings were surprising and the purpose of the present study was to find an explanation for the high type I fibre proportion in these horses. Possible explanations might be an inaccuracy in the procedure of analysing the biopsy sample, inaccuracy in the method of sampling or a muscular disorder in these individuals. Further, the high type I fibre proportion might be age related. The accuracy of the procedure for determination of the fibre composition from a biopsy sample was tested by analysing the same biopsy sample at two different occasions in nine horses. Four of the nine horses had high type I fibre proportions on both occasions and the five others had proportions within the expected range on both occasions. The repeatability of the procedure was tested by an agreement analysis, where the agreement index (AI) is calculated. This analysis revealed an AI of 0.70, where an AI >0.5 shows a good repeatability. Eight of the nine horses were re-sampled at the age of 3 years. At this age, all horses had type I fibre proportions < 30%. The biopsy technique with an absolute depth of 4 cm might give a relatively more superficial sample of the muscle in larger horses, which may explain the age-related differences. However, in young horses, high proportions of type I fibre seemed to be found in the larger individuals. The light sedation given to the horses before sampling may also have influenced the relative sampling depth. Muscular disorders were ruled out as performances in the 3-year season did not differ between 33 horses with high type I fibre percentage and 106 horses with normal type I fibre percentage. In conclusion, the high proportion of type I fibres in some young NSCT was not caused by the analysing procedure or by muscular disorders, but is probably related to the sampling point within the muscle.

An optimally functional musculoskeletal system is crucial for athletic performance and even minor perturbations can limit athletic ability. The introduction of the muscle biopsy technique in the 1970s created a window of opportunity to examine the form and function of equine skeletal muscle. Muscle histochemical and biochemical analyses have allowed characterization of the properties of equine muscle fibres and their influence on, and adaptation to, physical exertion. Analyses of exercise responses during standardized treadmill exercise and field studies have illustrated the role of cellular energetics in determining athletic suitability for specific disciplines, mechanisms of fatigue, adaptations to training and the affect of diet on metabolic responses. This article provides a review of the tools available to study muscle energetics in the horse, discusses the muscular metabolic pathways and summarizes the energetics of exercise.