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The scope of GSD VI now also includes glycogen storage disease type VIII, [2] IX [2] (caused by phosphorylase b kinase deficiency) and X [2] (deficiency protein kinase A). The incidence of GSD VI is approximately 1 case per 65,000–85,000 births, [2] representing approximately 30% all cases of glycogen storage disease.
A glycogen storage disease (GSD, also glycogenosis and dextrinosis) is a metabolic disorder caused by a deficiency of an enzyme or transport protein affecting glycogen synthesis, glycogen breakdown, or glucose breakdown, typically in muscles and/or liver cells.
Without this process, the body is unable to liberate glycogen from the liver and convert it into blood glucose, leading to an accumulation of stored glycogen in the liver. Hepatomegaly from the accumulation of stored glycogen in the liver is considered a form of non-alcoholic fatty liver disease.
Glycogen breakdown is highly regulated in the body, especially in the liver, by various hormones including insulin and glucagon, to maintain a homeostatic balance of blood-glucose levels. [8] When glycogen breakdown is compromised by mutations in the glycogen debranching enzyme, metabolic diseases such as Glycogen storage disease type III can ...
Clinical manifestations of glycogen storage disease type III are divided into four classes: [3] GSD IIIa, is the most common, (along with GSD IIIb) and which clinically includes muscle and liver involvement; GSD IIIb, which clinically has liver involvement but no muscle involvement; GSD IIIc which clinically affects liver and muscle.
The two organs most commonly affected are the liver and the skeletal muscle. Glycogen storage diseases that affect the liver typically cause hepatomegaly and hypoglycemia; those that affect skeletal muscle cause exercise intolerance, progressive weakness and cramping. [1] Glucose-6-phosphate isomerase deficiency affects step 2 of glycolysis.
[4] [5] In the liver, glycogen can make up 5–6% of the organ's fresh weight: the liver of an adult, weighing 1.5 kg, can store roughly 100–120 grams of glycogen. [ 4 ] [ 6 ] In skeletal muscle, glycogen is found in a low concentration (1–2% of the muscle mass): the skeletal muscle of an adult weighing 70 kg stores roughly 400 grams of ...
[3] [17] This drop in insulin allows the liver to increase glycogenolysis. [3] [17] Glycogenolysis is the process of glycogen breakdown that results in the production of glucose. [3] [17] Glycogen can be thought of as the inactive, storage form of glucose. [3] Decreased insulin also allows for increased gluconeogenesis in the liver and kidneys.