Glycogen Storage Disease Type VI
Glycogen Storage Disease Type I
Glycogen Storage Disease Type III
Glycogen Storage Disease
Glycogen Storage Disease Type IV
Glycogen Storage Disease Type II
Glycogen Storage Disease Type VII
Glucose-6-Phosphatase
Glycogen
alpha-Glucosidases
Glycogen Debranching Enzyme System
Glycogen Storage Disease Type V
Glycogen Storage Disease Type VIII
Glucan 1,4-alpha-Glucosidase
Antiporters
Glucose-6-Phosphate
Thermodynamic-based computational profiling of cellular regulatory control in hepatocyte metabolism. (1/5)
Thermodynamic-based constraints on biochemical fluxes and concentrations are applied in concert with mass balance of fluxes in glycogenesis and glycogenolysis in a model of hepatic cell metabolism. Constraint-based modeling methods that facilitate predictions of reactant concentrations, reaction potentials, and enzyme activities are introduced to identify putative regulatory and control sites in biological networks by computing the minimal control scheme necessary to switch between metabolic modes. Computational predictions of control sites in glycogenic and glycogenolytic operational modes in the hepatocyte network compare favorably with known regulatory mechanisms. The developed hepatic metabolic model is used to computationally analyze the impairment of glucose production in von Gierke's and Hers' diseases, two metabolic diseases impacting glycogen metabolism. The computational methodology introduced here can be generalized to identify downstream targets of agonists, to systematically probe possible drug targets, and to predict the effects of specific inhibitors (or activators) on integrated network function. (+info)Glycogen phosphorylase and its converter enzymes in haemolysates of normal human subjects and of patients with type VI glycogen-storage disease. A study of phosphorylase kinase deficiency. (2/5)
1. The properties of phosphorylase a, phosphorylase b, phosphorylase kinase and phosphorylase phosphatase present in a human haemolysate were investigated. The two forms of phosphorylase have the same affinity for glucose 1-phosphate but greatly differ in Vmax. Phosphorylase b is only partially stimulated by AMP, since, in the presence of the nucleotide, it is about tenfold less active than phosphorylase a. In a fresh human haemolysate phosphorylase is mostly in the b form; it is converted into phosphorylase a by incubation at 20degreesC, and this reaction is stimulated by glycogen and cyclic AMP. Once activated, the enzyme can be inactivated after filtration of the haemolysate on Sephadex G-25. This inactivation is stimulated by caffeine and glucose and inhibited by AMP and fluoride. The phosphorylase kinase present in the haemolysate can also be measured by the rate of activation of added muscle phosphorylase b, on addition of ATP and Mg2+. 2. The activity of phosphorylase kinase was measured in haemolysates obtained from a series of patients who had been classified as suffering from type VI glycogenosis. In nine patients, all boys, an almost complete deficiency of phosphorylase kinase was observed in the haemolysate and, when it could be assayed, in the liver. A residual activity, about 20% of normal, was found in the leucocyte fraction, whereas the enzyme activity was normal in the muscle. These patients suffer from the sex-linked phosphorylase kinase deficiency previously described by others. Two pairs of siblings, each time brother and sister, displayed a partial deficiency of phosphorylase kinase in the haemolysate and leucocytes and an almost complete deficiency in the liver. This is considered as being the autosomal form of phosphorylase kinase deficiency. Other patients were characterized by a low activity of total (a+b) phosphorylase and a normal or high activity of phosphorylase kinase in their haemolysate. (+info)The polymorphic locus for glycogen storage disease VI (liver glycogen phosphorylase) maps to chromosome 14. (3/5)
Human liver glycogen phosphorylase deficiency, also known as glycogen storage disease type VI (GSD VI) or Hers disease, is characterized by hepatomegaly and reduced or absent glycogenolytic response to the injection of glucagon. The recently isolated cDNA encoding the liver isozyme of glycogen phosphorylase was used to map the gene and identify restriction-fragment polymorphisms in normal Caucasians as a prerequisite for detecting linked GSD VI abnormalities. Results of restriction-enzyme analysis using a downstream fragment of the liver glycogen phosphorylase cDNA indicated the existence of a single gene copy per haploid genome. Hybridization of this downstream liver phosphorylase probe to dual laser-excited, sorted human chromosomes localized the gene to human chromosome 14. When the downstream probe was tested on genomic DNA cut with seven different restriction enzymes, a single MspI restriction-fragment-length polymorphism (RFLP) was observed in a single individual. In contrast, similar Southern blots performed with an upstream portion of the cDNA encoding liver phosphorylase revealed common RFLPs for four of eight enzymes tested, with minor polymorphic allele frequencies ranging from 33% to 44%. One of the four enzymes (TaqI) revealed two independent polymorphisms. If random distribution of these haplotypes among normal and disease loci, is assumed, approximately 92% of fetuses at risk for Hers disease will be informative when tested with the upstream liver phosphorylase probe. (+info)Mutations in the liver glycogen phosphorylase gene (PYGL) underlying glycogenosis type VI. (4/5)
Deficiency of glycogen phosphorylase in the liver gives rise to glycogen-storage disease type VI (Hers disease; MIM 232700). We report the identification of the first mutations in PYGL, the gene encoding the liver isoform of glycogen phosphorylase, in three patients with Hers disease. These are two splice-site mutations and two missense mutations. A mutation of the 5' splice-site consensus of intron 14 causes the retention of intron 14 and the utilization of two illegitimate 5' splice sites, whereas a mutation of the 3' splice-site consensus of intron 4 causes the skipping of exon 5. Two missense mutations, N338S and N376K, both cause nonconservative replacements of amino acids that are absolutely conserved even in yeast and bacterial phosphorylases. We also report corrections of the PYGL coding sequence, sequence polymorphisms, and a partial PYGL gene structure with introns in the same positions as in PYGM, the gene of the muscle isoform of phosphorylase. Our findings demonstrate that PYGL mutations cause Hers disease, and they may improve laboratory diagnosis of deficiencies of the liver phosphorylase system. (+info)Identification of a mutation in liver glycogen phosphorylase in glycogen storage disease type VI. (5/5)
Glycogen storage disease type VI (GSD6) defines a group of disorders that cause hepatomegaly and hypoglycemia with reduced liver phosphorylase activity. The course of these disorders is generally mild, but definitive diagnosis requires invasive procedures. We analyzed a Mennonite kindred with an autosomal recessive form of GSD6 to determine the molecular defect and develop a non-invasive diagnostic test. Linkage analysis was performed using genetic markers flanking the liver glycogen phosphorylase gene ( PYGL ), which was suspected to be the cause of the disorder on biochemical grounds. Mennonite GSD6 was linked to the PYGL locus with a multipoint LOD score of 4.7. The PYGL gene was analyzed for mutations by sequencing genomic DNA. Sequencing of genomic DNA revealed a splice site abnormality of the intron 13 splice donor. Confirmation of the genomic mutation was performed by sequencing RT-PCR products, which showed heterogeneous PYGL mRNA lacking all or part of exon 13 in affected persons. This study is the first to demonstrate that a mutation in the PYGL gene can cause GSD6. This mutation is estimated to be present on 3% of Mennonite chromosomes and the disease affects 0.1% of that population. Determination of this mutation provides a basis for the development of a simple and non-invasive diagnostic test for the disease and the carrier state in this population and confirms biochemical data showing the importance of this gene in glucose homeostasis. (+info)Glycogen Storage Disease Type VI, also known as Hers disease, is a rare inherited metabolic disorder caused by deficiency of the liver enzyme called glycogen phosphorylase. This enzyme is responsible for breaking down glycogen, which is a stored form of glucose, into glucose-1-phosphate during the process of glycogenolysis.
In GSD Type VI, the lack of this enzyme leads to an abnormal accumulation of glycogen in the liver, causing hepatomegaly (enlarged liver) and elevated liver enzymes. The symptoms of this condition are usually milder compared to other types of GSD, and may include fatigue, weakness, and hypoglycemia (low blood sugar), especially after prolonged fasting or physical exertion.
The diagnosis of GSD Type VI is typically made through biochemical tests that measure the activity of the glycogen phosphorylase enzyme in liver tissue, as well as genetic testing to identify mutations in the gene responsible for the enzyme's production. Treatment may involve dietary management, such as frequent feeding and avoidance of prolonged fasting, to prevent hypoglycemia. In some cases, medication may be necessary to manage symptoms and prevent complications.
Glycogen Storage Disease Type I (GSD I) is a rare inherited metabolic disorder caused by deficiency of the enzyme glucose-6-phosphatase, which is necessary for the liver to release glucose into the bloodstream. This leads to an accumulation of glycogen in the liver and abnormally low levels of glucose in the blood (hypoglycemia).
There are two main subtypes of GSD I: Type Ia and Type Ib. In Type Ia, there is a deficiency of both glucose-6-phosphatase enzyme activity in the liver, kidney, and intestine, leading to hepatomegaly (enlarged liver), hypoglycemia, lactic acidosis, hyperlipidemia, and growth retardation. Type Ib is characterized by a deficiency of glucose-6-phosphatase enzyme activity only in the neutrophils, leading to recurrent bacterial infections.
GSD I requires lifelong management with frequent feedings, high-carbohydrate diet, and avoidance of fasting to prevent hypoglycemia. In some cases, treatment with continuous cornstarch infusions or liver transplantation may be necessary.
Glycogen Storage Disease Type III, also known as Cori or Forbes disease, is a rare inherited metabolic disorder caused by deficiency of the debranching enzyme amylo-1,6-glucosidase, which is responsible for breaking down glycogen in the liver and muscles. This results in an abnormal accumulation of glycogen in these organs leading to its associated symptoms.
There are two main types: Type IIIa affects both the liver and muscles, while Type IIIb affects only the liver. Symptoms can include hepatomegaly (enlarged liver), hypoglycemia (low blood sugar), hyperlipidemia (high levels of fats in the blood), and growth retardation. In Type IIIa, muscle weakness and cardiac problems may also occur.
The diagnosis is usually made through biochemical tests and genetic analysis. Treatment often involves dietary management with frequent meals to prevent hypoglycemia, and in some cases, enzyme replacement therapy. However, there is no cure for this condition and life expectancy can be reduced depending on the severity of the symptoms.
Glycogen storage disease (GSD) is a group of rare inherited metabolic disorders that affect the body's ability to break down and store glycogen, a complex carbohydrate that serves as the primary form of energy storage in the body. These diseases are caused by deficiencies or dysfunction in enzymes involved in the synthesis, degradation, or transport of glycogen within cells.
There are several types of GSDs, each with distinct clinical presentations and affected organs. The most common type is von Gierke disease (GSD I), which primarily affects the liver and kidneys. Other types include Pompe disease (GSD II), McArdle disease (GSD V), Cori disease (GSD III), Andersen disease (GSD IV), and others.
Symptoms of GSDs can vary widely depending on the specific type, but may include:
* Hypoglycemia (low blood sugar)
* Growth retardation
* Hepatomegaly (enlarged liver)
* Muscle weakness and cramping
* Cardiomyopathy (heart muscle disease)
* Respiratory distress
* Developmental delays
Treatment for GSDs typically involves dietary management, such as frequent feedings or a high-protein, low-carbohydrate diet. In some cases, enzyme replacement therapy may be used to manage symptoms. The prognosis for individuals with GSDs depends on the specific type and severity of the disorder.
Glycogen Storage Disease Type IV (GSD IV), also known as Andersen's disease, is a rare inherited metabolic disorder that affects the body's ability to break down glycogen, a complex carbohydrate that serves as a source of energy for the body.
In GSD IV, there is a deficiency in the enzyme called glycogen branching enzyme (GBE), which is responsible for adding branches to the glycogen molecule during its synthesis. This results in an abnormal form of glycogen that accumulates in various organs and tissues, particularly in the liver, heart, and muscles.
The accumulation of this abnormal glycogen can lead to progressive damage and failure of these organs, resulting in a variety of symptoms such as muscle weakness, hypotonia, hepatomegaly (enlarged liver), cardiomyopathy (heart muscle disease), and developmental delay. The severity of the disease can vary widely, with some individuals experiencing milder symptoms while others may have a more severe and rapidly progressing form of the disorder.
Currently, there is no cure for GSD IV, and treatment is focused on managing the symptoms and slowing down the progression of the disease. This may include providing nutritional support, addressing specific organ dysfunction, and preventing complications.
Glycogen Storage Disease Type II, also known as Pompe Disease, is a genetic disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA). This enzyme is responsible for breaking down glycogen, a complex sugar that serves as energy storage, within lysosomes. When GAA is deficient, glycogen accumulates in various tissues, particularly in muscle cells, leading to their dysfunction and damage.
The severity of Pompe Disease can vary significantly, depending on the amount of functional enzyme activity remaining. The classic infantile-onset form presents within the first few months of life with severe muscle weakness, hypotonia, feeding difficulties, and respiratory insufficiency. This form is often fatal by 1-2 years of age if left untreated.
A later-onset form, which can present in childhood, adolescence, or adulthood, has a more variable clinical course. Affected individuals may experience progressive muscle weakness, respiratory insufficiency, and cardiomyopathy, although the severity and rate of progression are generally less pronounced than in the infantile-onset form.
Enzyme replacement therapy with recombinant human GAA is available for the treatment of Pompe Disease and has been shown to improve survival and motor function in affected individuals.
Glycogen Storage Disease Type VII, also known as Tarui's disease, is a rare inherited metabolic disorder caused by a deficiency of the enzyme phosphofructokinase (PFK), which is required for glycogenolysis – the breakdown of glycogen to glucose-1-phosphate and ultimately into glucose. This enzyme deficiency results in the accumulation of glycogen, particularly in muscle and red blood cells, leading to symptoms such as exercise-induced muscle cramps, myoglobinuria (the presence of myoglobin in the urine), and hemolytic anemia. The disease can also cause muscle weakness, fatigue, and dark-colored urine after strenuous exercise. It is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to develop the condition.
Glucose-6-phosphatase is an enzyme that plays a crucial role in the regulation of glucose metabolism. It is primarily located in the endoplasmic reticulum of cells in liver, kidney, and intestinal mucosa. The main function of this enzyme is to remove the phosphate group from glucose-6-phosphate (G6P), converting it into free glucose, which can then be released into the bloodstream and used as a source of energy by cells throughout the body.
The reaction catalyzed by glucose-6-phosphatase is as follows:
Glucose-6-phosphate + H2O → Glucose + Pi (inorganic phosphate)
This enzyme is essential for maintaining normal blood glucose levels, particularly during periods of fasting or starvation. In these situations, the body needs to break down stored glycogen in the liver and convert it into glucose to supply energy to the brain and other vital organs. Glucose-6-phosphatase is a key enzyme in this process, allowing for the release of free glucose into the bloodstream.
Deficiencies or mutations in the gene encoding glucose-6-phosphatase can lead to several metabolic disorders, such as glycogen storage disease type I (von Gierke's disease) and other related conditions. These disorders are characterized by an accumulation of glycogen and/or fat in various organs, leading to impaired glucose metabolism, growth retardation, and increased risk of infection and liver dysfunction.
Glycogen is a complex carbohydrate that serves as the primary form of energy storage in animals, fungi, and bacteria. It is a polysaccharide consisting of long, branched chains of glucose molecules linked together by glycosidic bonds. Glycogen is stored primarily in the liver and muscles, where it can be quickly broken down to release glucose into the bloodstream during periods of fasting or increased metabolic demand.
In the liver, glycogen plays a crucial role in maintaining blood glucose levels by releasing glucose when needed, such as between meals or during exercise. In muscles, glycogen serves as an immediate energy source for muscle contractions during intense physical activity. The ability to store and mobilize glycogen is essential for the proper functioning of various physiological processes, including athletic performance, glucose homeostasis, and overall metabolic health.
Alpha-glucosidases are a group of enzymes that break down complex carbohydrates into simpler sugars, such as glucose, by hydrolyzing the alpha-1,4 and alpha-1,6 glycosidic bonds in oligosaccharides, disaccharides, and polysaccharides. These enzymes are located on the brush border of the small intestine and play a crucial role in carbohydrate digestion and absorption.
Inhibitors of alpha-glucosidases, such as acarbose and miglitol, are used in the treatment of type 2 diabetes to slow down the digestion and absorption of carbohydrates, which helps to reduce postprandial glucose levels and improve glycemic control.
The Glycogen Debranching Enzyme System, also known as glycogen debranching enzyme or Amy-1, is a crucial enzyme complex in human biochemistry. It plays an essential role in the metabolism of glycogen, which is a large, branched polymer of glucose that serves as the primary form of energy storage in animals and fungi.
The Glycogen Debranching Enzyme System consists of two enzymatic activities: a transferase and an exo-glucosidase. The transferase activity transfers a segment of a branched glucose chain to another part of the same or another glycogen molecule, while the exo-glucosidase activity cleaves the remaining single glucose units from the outer branches of the glycogen molecule.
This enzyme system is responsible for removing the branched structures of glycogen, allowing the linear chains to be further degraded by other enzymes into glucose molecules that can be used for energy production or stored for later use. Defects in this enzyme complex can lead to several genetic disorders, such as Glycogen Storage Disease Type III (Cori's disease) and Type IV (Andersen's disease), which are characterized by the accumulation of abnormal glycogen molecules in various tissues.
Glycogen Storage Disease Type V, also known as McArdle's disease, is a genetic disorder that affects the body's ability to break down glycogen, a complex carbohydrate stored in muscles, into glucose, which provides energy for muscle contraction.
This condition results from a deficiency of the enzyme myophosphorylase, which is responsible for breaking down glycogen into glucose-1-phosphate within the muscle fibers. Without sufficient myophosphorylase activity, muscles become easily fatigued and may cramp or become rigid during exercise due to a lack of available energy.
Symptoms typically appear in childhood or adolescence and can include muscle weakness, stiffness, cramps, and myoglobinuria (the presence of myoglobin, a protein found in muscle cells, in the urine) following exercise. Diagnosis is usually confirmed through genetic testing and enzyme assays. Treatment typically involves avoiding strenuous exercise and ensuring adequate hydration and rest before and after physical activity. In some cases, dietary modifications such as high-protein or high-carbohydrate intake may be recommended to help manage symptoms.
Glycogen Storage Disease Type VIII, also known as Phosphorylase Kinase Deficiency, is a rare genetic metabolic disorder that affects the production and breakdown of glycogen in the body. Glycogen is a complex carbohydrate that serves as the primary form of energy storage in the body.
In this condition, there is a deficiency or dysfunction of the enzyme phosphorylase kinase (PhK), which plays a crucial role in activating glycogen phosphorylase, an enzyme responsible for breaking down glycogen into glucose-1-phosphate during periods of increased energy demand.
The deficiency or dysfunction of PhK leads to the abnormal accumulation of glycogen in various tissues, particularly in the liver and muscles. This accumulation can result in hepatomegaly (enlarged liver), hypoglycemia (low blood sugar levels), growth retardation, and muscle weakness.
Glycogen Storage Disease Type VIII is inherited in an autosomal recessive manner, meaning that an individual must inherit two defective copies of the gene, one from each parent, to develop the condition. There are four subtypes of GSD Type VIII, classified based on the specific genetic mutation and the severity of symptoms.
Treatment for Glycogen Storage Disease Type VIII typically involves managing the symptoms and complications associated with the disorder, such as providing a high-carbohydrate diet to prevent hypoglycemia and addressing any liver or muscle dysfunction. Regular monitoring by a healthcare team experienced in metabolic disorders is essential for optimizing treatment and ensuring appropriate management of this complex condition.
Glucan 1,4-alpha-glucosidase, also known as amyloglucosidase or glucoamylase, is an enzyme that catalyzes the hydrolysis of 1,4-glycosidic bonds in starch and other oligo- and polysaccharides, breaking them down into individual glucose molecules. This enzyme specifically acts on the alpha (1->4) linkages found in amylose and amylopectin, two major components of starch. It is widely used in various industrial applications, including the production of high fructose corn syrup, alcoholic beverages, and as a digestive aid in some medical supplements.
Antiporters, also known as exchange transporters, are a type of membrane transport protein that facilitate the exchange of two or more ions or molecules across a biological membrane in opposite directions. They allow for the movement of one type of ion or molecule into a cell while simultaneously moving another type out of the cell. This process is driven by the concentration gradient of one or both of the substances being transported. Antiporters play important roles in various physiological processes, including maintaining electrochemical balance and regulating pH levels within cells.
Glucose-6-phosphate (G6P) is a vital intermediate compound in the metabolism of glucose, which is a simple sugar that serves as a primary source of energy for living organisms. G6P plays a critical role in both glycolysis and gluconeogenesis pathways, contributing to the regulation of blood glucose levels and energy production within cells.
In biochemistry, glucose-6-phosphate is defined as:
A hexose sugar phosphate ester formed by the phosphorylation of glucose at the 6th carbon atom by ATP in a reaction catalyzed by the enzyme hexokinase or glucokinase. This reaction is the first step in both glycolysis and glucose storage (glycogen synthesis) processes, ensuring that glucose can be effectively utilized for energy production or stored for later use.
G6P serves as a crucial metabolic branch point, leading to various pathways such as:
1. Glycolysis: In the presence of sufficient ATP and NAD+ levels, G6P is further metabolized through glycolysis to generate pyruvate, which enters the citric acid cycle for additional energy production in the form of ATP, NADH, and FADH2.
2. Gluconeogenesis: During periods of low blood glucose levels, G6P can be synthesized back into glucose through the gluconeogenesis pathway, primarily occurring in the liver and kidneys. This process helps maintain stable blood glucose concentrations and provides energy to cells when dietary intake is insufficient.
3. Pentose phosphate pathway (PPP): A portion of G6P can be shunted into the PPP, an alternative metabolic route that generates NADPH, ribose-5-phosphate for nucleotide synthesis, and erythrose-4-phosphate for aromatic amino acid production. The PPP is essential in maintaining redox balance within cells and supporting biosynthetic processes.
Overall, glucose-6-phosphate plays a critical role as a central metabolic intermediate, connecting various pathways to regulate energy homeostasis, redox balance, and biosynthesis in response to cellular demands and environmental cues.
A liver cell adenoma is a benign tumor that develops in the liver and is composed of cells similar to those normally found in the liver (hepatocytes). These tumors are usually solitary, but multiple adenomas can occur, especially in women who have taken oral contraceptives for many years. Liver cell adenomas are typically asymptomatic and are often discovered incidentally during imaging studies performed for other reasons. In rare cases, they may cause symptoms such as abdominal pain or discomfort, or complications such as bleeding or rupture. Treatment options include monitoring with periodic imaging studies or surgical removal of the tumor.
1,4-Alpha-Glucan Branching Enzyme (GBE) is an enzyme that plays a crucial role in the synthesis of glycogen, a complex carbohydrate that serves as the primary form of energy storage in animals and fungi. GBE catalyzes the transfer of a segment of a linear glucose chain (alpha-1,4 linkage) to an alpha-1,6 position on another chain, creating branches in the glucan molecule. This branching process enhances the solubility and compactness of glycogen, allowing it to be stored more efficiently within cells.
Defects in GBE are associated with a group of genetic disorders known as glycogen storage diseases type IV (GSD IV), also called Andersen's disease. This autosomal recessive disorder is characterized by the accumulation of abnormally structured glycogen in various tissues, particularly in the liver and muscles, leading to progressive liver failure, muscle weakness, cardiac complications, and sometimes neurological symptoms.