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Glycogen Storage Disease Type II: An autosomal recessively inherited glycogen storage disease caused by GLUCAN 1,4-ALPHA-GLUCOSIDASE deficiency. Large amounts of GLYCOGEN accumulate in the LYSOSOMES of skeletal muscle (MUSCLE, SKELETAL); HEART; LIVER; SPINAL CORD; and BRAIN. Three forms have been described: infantile, childhood, and adult. The infantile form is fatal in infancy and presents with hypotonia and a hypertrophic cardiomyopathy (CARDIOMYOPATHY, HYPERTROPHIC). The childhood form usually presents in the second year of life with proximal weakness and respiratory symptoms. The adult form consists of a slowly progressive proximal myopathy. (From Muscle Nerve 1995;3:S61-9; Menkes, Textbook of Child Neurology, 5th ed, pp73-4)Glycogen Storage Disease Type I: An autosomal recessive disease in which gene expression of glucose-6-phosphatase is absent, resulting in hypoglycemia due to lack of glucose production. Accumulation of glycogen in liver and kidney leads to organomegaly, particularly massive hepatomegaly. Increased concentrations of lactic acid and hyperlipidemia appear in the plasma. Clinical gout often appears in early childhood.alpha-Glucosidases: Enzymes that catalyze the exohydrolysis of 1,4-alpha-glucosidic linkages with release of alpha-glucose. Deficiency of alpha-1,4-glucosidase may cause GLYCOGEN STORAGE DISEASE TYPE II.Glycogen Storage Disease: A group of inherited metabolic disorders involving the enzymes responsible for the synthesis and degradation of glycogen. In some patients, prominent liver involvement is presented. In others, more generalized storage of glycogen occurs, sometimes with prominent cardiac involvement.Glucan 1,4-alpha-Glucosidase: An enzyme that catalyzes the hydrolysis of terminal 1,4-linked alpha-D-glucose residues successively from non-reducing ends of polysaccharide chains with the release of beta-glucose. It is also able to hydrolyze 1,6-alpha-glucosidic bonds when the next bond in sequence is 1,4.Glycogen Storage Disease Type III: An autosomal recessive metabolic disorder due to deficient expression of amylo-1,6-glucosidase (one part of the glycogen debranching enzyme system). The clinical course of the disease is similar to that of glycogen storage disease type I, but milder. Massive hepatomegaly, which is present in young children, diminishes and occasionally disappears with age. Levels of glycogen with short outer branches are elevated in muscle, liver, and erythrocytes. Six subgroups have been identified, with subgroups Type IIIa and Type IIIb being the most prevalent.Glycogen Storage Disease Type IV: An autosomal recessive metabolic disorder due to a deficiency in expression of glycogen branching enzyme 1 (alpha-1,4-glucan-6-alpha-glucosyltransferase), resulting in an accumulation of abnormal GLYCOGEN with long outer branches. Clinical features are MUSCLE HYPOTONIA and CIRRHOSIS. Death from liver disease usually occurs before age 2.Enzyme Replacement Therapy: Therapeutic replacement or supplementation of defective or missing enzymes to alleviate the effects of enzyme deficiency (e.g., GLUCOSYLCERAMIDASE replacement for GAUCHER DISEASE).GlycogenGlycogen Storage Disease Type VII: An autosomal recessive glycogen storage disease in which there is deficient expression of 6-phosphofructose 1-kinase in muscle (PHOSPHOFRUCTOKINASE-1, MUSCLE TYPE) resulting in abnormal deposition of glycogen in muscle tissue. These patients have severe congenital muscular dystrophy and are exercise intolerant.Glucose-6-Phosphatase: An enzyme that catalyzes the conversion of D-glucose 6-phosphate and water to D-glucose and orthophosphate. EC 3.1.3.9.Glycogen Storage Disease Type VI: A hepatic GLYCOGEN STORAGE DISEASE in which there is an apparent deficiency of hepatic phosphorylase (GLYCOGEN PHOSPHORYLASE, LIVER FORM) activity.Glycogen Debranching Enzyme System: 1,4-alpha-D-Glucan-1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase/dextrin 6 alpha-D-glucanohydrolase. An enzyme system having both 4-alpha-glucanotransferase (EC 2.4.1.25) and amylo-1,6-glucosidase (EC 3.2.1.33) activities. As a transferase it transfers a segment of a 1,4-alpha-D-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-D-glucan. As a glucosidase it catalyzes the endohydrolysis of 1,6-alpha-D-glucoside linkages at points of branching in chains of 1,4-linked alpha-D-glucose residues. Amylo-1,6-glucosidase activity is deficient in glycogen storage disease type III.Glycogen Storage Disease Type V: Glycogenosis due to muscle phosphorylase deficiency. Characterized by painful cramps following sustained exercise.Glycogen Storage Disease Type VIII: An x-linked recessive hepatic glycogen storage disease resulting from lack of expression of phosphorylase-b-kinase activity. Symptoms are relatively mild; hepatomegaly, increased liver glycogen, and decreased leukocyte phosphorylase are present. Liver shrinkage occurs in response to glucagon.Antiporters: Membrane transporters that co-transport two or more dissimilar molecules in the opposite direction across a membrane. Usually the transport of one ion or molecule is against its electrochemical gradient and is "powered" by the movement of another ion or molecule with its electrochemical gradient.Glucose-6-Phosphate: An ester of glucose with phosphoric acid, made in the course of glucose metabolism by mammalian and other cells. It is a normal constituent of resting muscle and probably is in constant equilibrium with fructose-6-phosphate. (Stedman, 26th ed)Adenoma, Liver Cell: A benign epithelial tumor of the LIVER.1,4-alpha-Glucan Branching Enzyme: In glycogen or amylopectin synthesis, the enzyme that catalyzes the transfer of a segment of a 1,4-alpha-glucan chain to a primary hydroxy group in a similar glucan chain. EC 2.4.1.18.Glycogen Storage Disease Type IIb: An X-linked dominant multisystem disorder resulting in cardiomyopathy, myopathy and INTELLECTUAL DISABILITY. It is caused by mutation in the gene encoding LYSOSOMAL-ASSOCIATED MEMBRANE PROTEIN 2.Fructose-1,6-Diphosphatase Deficiency: An autosomal recessive fructose metabolism disorder due to absent or deficient fructose-1,6-diphosphatase activity. Gluconeogenesis is impaired, resulting in accumulation of gluconeogenic precursors (e.g., amino acids, lactate, ketones) and manifested as hypoglycemia, ketosis, and lactic acidosis. Episodes in the newborn infant are often lethal. Later episodes are often brought on by fasting and febrile infections. As patients age through early childhood, tolerance to fasting improves and development becomes normal.Monosaccharide Transport Proteins: A large group of membrane transport proteins that shuttle MONOSACCHARIDES across CELL MEMBRANES.Lysosomal Storage Diseases: Inborn errors of metabolism characterized by defects in specific lysosomal hydrolases and resulting in intracellular accumulation of unmetabolized substrates.Liver Glycogen: Glycogen stored in the liver. (Dorland, 28th ed)Glycogen Synthase: An enzyme that catalyzes the transfer of D-glucose from UDPglucose into 1,4-alpha-D-glucosyl chains. EC 2.4.1.11.Hypoglycemia: A syndrome of abnormally low BLOOD GLUCOSE level. Clinical hypoglycemia has diverse etiologies. Severe hypoglycemia eventually lead to glucose deprivation of the CENTRAL NERVOUS SYSTEM resulting in HUNGER; SWEATING; PARESTHESIA; impaired mental function; SEIZURES; COMA; and even DEATH.Starch: Any of a group of polysaccharides of the general formula (C6-H10-O5)n, composed of a long-chain polymer of glucose in the form of amylose and amylopectin. It is the chief storage form of energy reserve (carbohydrates) in plants.Liver: A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.Dependovirus: A genus of the family PARVOVIRIDAE, subfamily PARVOVIRINAE, which are dependent on a coinfection with helper adenoviruses or herpesviruses for their efficient replication. The type species is Adeno-associated virus 2.Genetic Therapy: Techniques and strategies which include the use of coding sequences and other conventional or radical means to transform or modify cells for the purpose of treating or reversing disease conditions.Amylopectin: A highly branched glucan in starch.