Glycogen Storage Diseases Focus concept Disturbances in glycogen utilization res

Question

Glycogen Storage Diseases Focus concept Disturbances in glycogen utilization result if an enzyme involved in glycogen synthesis or degradation is missing Prerequisites . Glycogen synthesis and degradation pathways The link between glycogen metabolism and fat metabolism. Background Glycogen storage diseases are so named because a hallmark of the diseases is impaired glycogen storage due to a deficiency of one of the enzymes involved in either glycogen synthesis or glycogen degradation. Eight kinds of glycogen storage diseases have been identified so far. Each type is characterized by the lack of a specific enzyme. An understanding of glycogen metabolism is essential in the proper treatment of this disease, and identification of the deficient enzyme is required before a treatment protocol can be designed. Your patient is a fifteen-year-old Caucasian male named Alex K. Alex's mother has brought him to see you because she is concerned about his inability to perform any kind of strenuous exercise. During his physical education classes, Alex could not keep up with his classmates and often suffered painful muscle cramps if he did attempt to exercise. He appeared to be normal if at rest or performing light to moderate exercise. A physical examination reveals that his liver appears to be normal in size, but his muscles are flabby and poorly developed. A fasting glucose test showed that Alex was not hypo- or hyperglycemic. A number of biochemical tests were carried out to identify the type of glycogen storage disease in this patient. Questions 1. You decide to try Alex's response to glucagon. This test consists of injecting a high dose of glucagon intravenously and then drawing samples of blood periodically and measuring the glucose content of the samples. After the glucagon injection, Alex's blood sugar rises dramatically. Is this the response you would expect in a normal person? Explain. Liver and muscle biopsies are taken from Alex and analyzed. The biopsies reveal that glycogen content in the liver is normal, but muscle glycogen content is elevated. The biochemical structure of glycogen in both tissues appears to be normal. Suggest some possible explanations for these 2. observations.

Explanation / Answer

1. Glycogen storage disease is a metabolic disorder characterised by inefficient glycogen synthesis and breakdown or difficulties in glycolysis.

Glucagon helps to maintain normal blood sugar levels. When glucagon raises blood sugar levels, it means that not enough insulin is present in the body. The person is suffering from hypoglycemia.

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