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What is McArdle's Disease? :Glycogen Storage Disease Type 5 Symptoms-Causes- Second Wind Phenomenon

Subscribe for increasing your medical knowledge👍 What is McArdle's Disease? : Symptoms-Causes- Second Wind Phenomenon What is McArdle Disease? McArdle disease is a deficiency of muscle phosphorylase. This is an important substance needed to break down glycogen in your muscle cells. The condition causes fatigue and muscle pain during exercise. The disease can lead to dark urine. Severe, uncontrolled McArdle disease can cause life-threatening kidney problems. How is McArdle disease diagnosed? Diagnosis begins with a blood test to check whether a muscle enzyme, creatine kinase (CK), is at high levels. This indicates muscle damage. In the past, muscle biopsy – the removal of a small amount of muscle tissue for examination - was the primary way of diagnosing this condition. How common is McArdle's Disease? McArdle disease is one of the most common glycogen storage disorders. Although the exact prevalence is not known, it has been estimated to be 1 in 100,000 patients in the United States. More than 100 mutations in PYGM have been associated with this disorder. Why is there little lactic acid formed in McArdle's Disease? It is generally assumed that patients with McArdle disease do not produce lactate during exercise. Because glycogen breakdown is completely blocked whereas oxidation of extramuscular glucose supplies is preserved, these patients provide an opportunity to selectively study glucose metabolism. Who discovered McArdle's Disease? McArdle disease (glycogen storage disease Type V; MD) is a myopathy caused by genetic defects in myophosphorylase, the skeletal muscle isoform of the enzyme glycogen phosphorylase. The first case was described in 1951 by Brian McArdle What is second wind phenomenon in McArdle disease? Patients with McArdle's disease (McA) typically show the “second-wind” phenomenon, a sudden decrease in heart rate (HR) and an improved exercise tolerance occurring after a few minutes of exercise. Etiology The condition is caused by mutations in the PYGM gene (11q13), leading to muscle phosphorylase deficiency. Mutation p.R50X may account for 40% to 50% of the alleles in Caucasian populations. Diagnostic methods The diagnosis is based on biological findings revealing a lack of lactate elevation in blood during ischemic forearm test, excess glycogen, and deficient phosphorylase activity in the muscle biopsy. Differential diagnosis The differential diagnosis should include GSD type 7 (see this term). Genetic counseling The condition is autosomal recessive. Management and treatment Treatment is based on controlled physical training in order to develop mitochondrial oxidation capacities in muscles, and programmed glucose intake according to exercising periods. Diets with high protein intake have yielded variable results. Prognosis Prognosis is favorable when severe rhabdomyolysis is avoided. However, myoglobinuria may lead to potentially life-threatening renal failure. What are the symptoms of McArdle disease? Better able to do aerobic exercise after 8 to 10 minutes (second-wind phenomenon) Brownish red urine, especially after periods of activity. Easily tiring during activity, with stiffness or weakness soon after starting exercise. Muscle cramping. Muscle pain. What causes McArdle disease? McArdle disease (also known as glycogen storage disease type V) is a disorder affecting muscle metabolism. The condition is caused by the lack of an enzyme called muscle phosphorylase. This results in an inability to break down glycogen 'fuel' stores. McArdle disease leads to pain and fatigue with strenuous exercise. Why is there no lactic acidosis in McArdle disease? It is generally assumed that patients with McArdle disease do not produce lactate during exercise. Because glycogen breakdown is completely blocked whereas oxidation of extramuscular glucose supplies is preserved, these patients provide an opportunity to selectively study glucose metabolism. Other Names for This Condition glycogen storage disease type 5 glycogenosis 5 GSD type V GSD V McArdle disease McArdle syndrome McArdle type glycogen storage disease McArdle's disease muscle glycogen phosphorylase deficiency muscle phosphorylase deficiency myophosphorylase deficiency PYGM deficiency Complications Severe rhabdomyolysis may lead to acute kidney injury. Progression to chronic kidney disease has not been described. Seizures may occur but are extremely rare. Potential hyperuricaemia; overproduction of adenosine monophosphate (AMP), with accelerated liberation of hypoxanthine and xanthine into the blood, possibly leading to hyperuricaemia. Exams and Tests The following tests may be performed: Electromyography (EMG) Genetic testing Lactic acid in blood MRI