Abstract
BackgroundIndividuals with glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) experience muscle weakness and exercise limitation that worsen through adulthood. However, normative data for markers of physical capacity, such as strength and cardiovascular fitness, are limited. Furthermore, the impact of the disease on muscle size and quality is unstudied in weight bearing skeletal muscle, a key predictor of physical function. We aim to produce normative reference values of aerobic capacity and strength in individuals with GSD IIIa, and to investigate the role of muscle size and quality on exercise impairment.ResultsPeak oxygen uptake (V̇O2peak) was lower in the individuals with GSD IIIa than predicted based on demographic data (17.0 (9.0) ml/kg/min, 53 (24)% of predicted, p = 0.001). Knee extension maximum voluntary contraction (MVC) was also substantially lower than age matched predicted values (MVC: 146 (116) Nm, 57% predicted, p = 0.045), though no difference was found in MVC relative to body mass (1.88 (2.74) Nm/kg, 61% of predicted, p = 0.263). There was a strong association between aerobic capacity and maximal leg strength (r = 0.920; p = 0.003). Substantial inter-individual variation was present, with a high physical capacity group that had normal leg strength (MVC), and relatively high V̇O2peak, and a low physical capacity that display impaired strength and substantially lower V̇O2peak. The higher physical capacity sub-group were younger, had larger Vastus Lateralis (VL) muscles, greater muscle quality, undertook more physical activity (PA), and reported higher health-related quality of life.ConclusionsV̇O2peak and knee extension strength are lower in individuals with GSD IIIa than predicted based on their demographic data. Patients with higher physical capacity have superior muscle size and structure characteristics and higher health-related quality of life, than those with lower physical capacity. This study provides normative values of these important markers of physical capacity.
Highlights
Individuals with glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) experience muscle weakness and exercise limitation that worsen through adulthood
Glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) is a rare inherited metabolic disorder caused by pathogenic variants in the AGL gene which spans 85 kb of DNA on chromosome 1p21.2 and is composed of 35 exons [1]
Associations between cardio‐respiratory fitness, muscle strength, and muscle characteristics There was a strong association between aerobic capacity and maximal leg strength
Summary
Individuals with glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) experience muscle weakness and exercise limitation that worsen through adulthood. Glycogen storage disease IIIa (GSD IIIa) (OMIM #232400) is a rare inherited metabolic disorder caused by pathogenic variants in the AGL gene which spans 85 kb of DNA on chromosome 1p21.2 and is composed of 35 exons [1]. GSD IIIa primarily affects the liver, skeletal muscle and the heart, causing hypoglycaemia, hepatomegaly and (cardio)myopathy [3, 4] Because of these pathologies, patients suffer from muscle weakness and exercise limitation that worsen through adulthood [3, 5] and can result in patients becoming wheelchair bound [6]
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