Glycogen storage disease due to muscle and heart glycogen synthase deficiency

Glycogen storage disease due to muscle and heart glycogen synthase deficiency (also known as GSD type 0b or glycogen storage disease 0, muscle type) is an extremely rare inherited metabolic disorder caused by mutations in the GYS1 gene, which encodes the muscle isoform of glycogen synthase. This enzyme is essential for the synthesis of glycogen in skeletal muscle and cardiac tissue. When this enzyme is deficient or absent, the body cannot properly store glycogen in these tissues, leading to impaired energy availability during physical exertion and potentially affecting cardiac function. Clinical features of this condition primarily involve the skeletal muscles and heart. Affected individuals may experience exercise intolerance, muscle weakness, and fatigue due to the inability to adequately store and mobilize glycogen in muscle tissue. Cardiac involvement can manifest as hypertrophic cardiomyopathy or other forms of cardiac dysfunction, which may present in childhood and can be life-threatening. Some patients may also experience episodes of syncope (fainting) or cardiac arrhythmias. The severity of symptoms can vary among affected individuals. There is currently no specific curative treatment for this condition. Management is primarily supportive and symptomatic, focusing on monitoring and treating cardiac complications, managing exercise intolerance, and providing appropriate dietary guidance. Cardiac surveillance with regular echocardiography and electrocardiography is important. Patients are generally advised to avoid strenuous physical activity. Given the extreme rarity of this disorder, clinical experience is limited, and management strategies are largely based on individual case reports.

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