Glycogen Metabolism

Glycogen is a branched polymer and the storage form of carbohydrates Carbohydrates Carbohydrates are one of the 3 macronutrients, along with fats and proteins, serving as a source of energy to the body. These biomolecules store energy in the form of glycogen and starch, and play a role in defining the cellular structure (e.g., cellulose). Basics of Carbohydrates in the human body. Major sites of storage are the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver and skeletal muscles. Glycogen is the main source of energy during fasting or in between meals. Glycogen provides energy for up to 18 hours, after which energy requirements are met by fatty acid oxidation. The 2 metabolic pathways of glycogen are glycogenesis (glycogen synthesis) and glycogenolysis (glycogen breakdown). The key regulatory enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes in these processes are glycogen synthase (in glycogenesis) and glycogen phosphorylase (in glycogenolysis). These pathways proceed depending on the energy needs of the cells, generally modulated by hormonal and allosteric regulators. Abnormal accumulation of glycogen occurs with enzyme deficiencies causing different types of glycogen storage disorders.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Overview

Structure

  • Glycogen is an extensively branched polymer of alpha-d-glucose.
    • The animal analog to starch 
    • The straight chains are alpha-1,4 links, and the branched chains are alpha-1,6 links. 
  • Branching occurs every 8–10 units, making it more globular and less space consuming and allowing for increased solubility and quicker metabolization. 
Glycogen structure

Structure of glycogen:
Glycogen consists of a core protein and is surrounded by 30,000–50,000 glucose units.

Image: “Glycogen structure” by Mikael Häggström. License: CC0 1.0

Functions

  • The storage form of glucose, utilized when blood glucose (BG) level drops
  • Muscle glycogen:
    • Available for glycolysis Glycolysis Glycolysis is a central metabolic pathway responsible for the breakdown of glucose and plays a vital role in generating free energy for the cell and metabolites for further oxidative degradation. Glucose primarily becomes available in the blood as a result of glycogen breakdown or from its synthesis from noncarbohydrate precursors (gluconeogenesis) and is imported into cells by specific transport proteins. Glycolysis in the muscle; acts as a reserve fuel for the contraction of muscles
    • Skeletal muscle itself is unable to release glycogen into the bloodstream due to a lack of glucose-6-phosphatase (G6Pase). 
  • Liver glycogen is responsible for maintaining BG levels, especially during fasting or exercise.

Storage

  • The major sites of storage of glycogen are skeletal muscle and the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver:
    • Hepatic glycogen content: 10 g/100 g tissue 
    • Skeletal muscle glycogen content: 1–2 g/100 g
  • The total quantity of muscle glycogen is more than liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver glycogen due to larger muscle mass.

Metabolic pathways

There are 2 main metabolic pathways of glycogen:

  1. Glycogenesis: synthesis of glycogen 
  2. Glycogenolysis: breakdown of glycogen

Glycogenesis

Definition

  • The synthesis of glycogen, storing excess glucose for future use
  • Process is not de novo and involves the addition of glycosyl residues to already-existing glycogen molecules. 

Step 1

Isomerization of glucose-6-phosphate to glucose-1-phosphate

  • Glucose addition to glycogen is initiated by the phosphorylation of glucose to glucose-6-phosphate. 
    • Enzyme converting glucose to glucose-6-phosphate:
      • Hexokinase in the muscle 
      • Glucokinase in the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver 
    • Source of phosphate group: adenosine triphosphate (ATP)
  • Glucose-6-phosphate is then converted to glucose-1-phosphate by the enzyme phosphoglucomutase. 
  • Glucose + ATP → glucose-6-phosphate → glucose-1-phosphate

Step 2

Reaction of glucose-1-phosphate with uridine triphosphate (UTP) to form an activated form of glucose:

  • Glucose-1-phosphate reacts with UTP to form an active form of glucose known as uridine diphosphate glucose (UDP-glucose).
    • Enzyme: UDP-glucose pyrophosphorylase 
    • Inorganic pyrophosphate is released in the reaction.
  • Glucose-1-phosphate + UTP → UDP-glucose + pyrophosphate (PP)
Glycogen synthesis

Glycogen synthesis — Making the substrate:
Formation of UDP-glucose which is an active form in glycogenesis

Image by Lecturio.

Step 3

Formation of glycosidic bond 

  • In this step, attachment of the UDP-glucose to the hydroxyl group to the free end of a glycogen chain occurs.
    • Enzyme: glycogen synthase (rate-limiting enzyme of glycogenesis)
    • Glycogenin:
      • Classified as a glycosyltransferase
      • Core protein of the preexisting glycogen molecule to which glucose (from UDP-glucose) attaches
      • Acts as a primer to the synthesis of glycogen
  • UDP is released in the process.
  • The chain is formed via alpha-1,4-glycosidic bonds.
Growing the glycogen chain

Growing the glycogen chain—step 3 of glycogenesis:
Uridine diphosphate glucose (UDP-glucose) is attached to the hydroxyl group of an already-existing glycogen chain, releasing UDP in the process. The reaction is catalyzed by glycogen synthase, the key regulatory enzyme of glycogenesis.

Image by Lecturio.

Step 4

Branching of glycogen:

  • When a chain contains approximately 8–10 glucose units, branching follows (removing the growing chain from the nonreducing end of the chain).
  • A different enzyme then “reattaches” to a neighboring chain via bonds between carbons 1 and 6 (alpha-1,6-glycosidic bond).
    • Enzyme: amylo-(1,4→1,6)-transglycosylase 
      • Also called branching enzyme
      • Similar to glucosyltransferase activity and permits chain elongation by branching
    • Glycogen chains grow as glycogen synthase adds glucose residues and additional branches are produced.
Branching of glycogen chain mediated by the branching enzyme

Branching of glycogen chain mediated by the branching enzyme

Image by Lecturio.

Glycogenolysis

Definition

Breakdown of glycogen to release energy in between meals or after the depletion of glucose

Step 1

Breakdown of glycogen into glucose-1-phosphate

  • Glycogen is broken down into glucose-1-phosphate by phosphorolysis.
    • Enzyme: glycogen phosphorylase (key regulatory enzyme in glycogenolysis)
    • The reaction catalyzed is similar to hydrolysis, but a phosphate group is used to cleave bonds instead of water.
  • Alpha-1,4-glycosidic bonds are broken from the terminal end to release glucose-1-phosphate.
Glycogen breakdown

Glycogen breakdown:
Conversion of glycogen to glucose-1-phosphate by the enzyme glycogen phosphorylase

Image by Lecturio.

Step 2

Removal of alpha-1,6-glycosidic bonds (branches):

  • As glycogen is an extensively branched polymer, further processes follow to break the branches to release more glucose-1-phosphate.
  • Phosphorylase hydrolyzes alpha-1,4-glycosidic bonds until only 4 glucose residues are left before the alpha-1,6 branch. 
  • Further breakdown proceeds with the debranching enzyme (with a transferase and glucosidase activity).
    • 3 of the 4 glucose residues are removed, leaving 1 molecule.
    • The 3-glucose molecule chain (from the branch) is reattached to the nonreducing end of the linear chain, catalyzed by glucan transferase.
    • The single remaining molecule (in the branch) is removed by the alpha-1,6 glucosidase by hydrolysis.
  • The phosphorylase/debranching process repeats to generate glucose-1-phosphate for energy use.
Glycogenolysis (breakdown of bonds and debranching). Png

Glycogenolysis (breakdown of bonds and debranching):
Alpha-1,4-glycosidic bonds are broken from the terminal end, catalyzed by phosphorylase. The bonds between glucose residues (blue) are hydrolyzed, releasing glucose-1-phosphate. Phosphorylase hydrolyzes alpha-1,4-glycosidic bonds until only 4 glucose residues (orange) are left before the alpha-1,6 branch. The debranching enzyme (with a transferase and glucosidase activity) then acts on the remaining linked residues. Three of the 4 glucose residues (orange) are removed, leaving 1 molecule. The 3-glucose molecule chain (from the branch) is reattached to the nonreducing end of the linear chain, catalyzed by glucan transferase. The single remaining molecule (in the branch) is removed by the alpha-1,6 glucosidase by hydrolysis, releasing the glucose-1-phosphate. Phosphorylase/debranching process repeats to generate glucose-1-phosphate for energy use.

Image by Lecturio.

Step 3

Conversion of the released glucose-1-phosphate to glucose-6-phosphate:

  • Glucose-1-phosphate is converted to glucose-6-phosphate. 
  • Enzyme: phosphoglucomutase
  • Fate of glucose-6 phosphate:
    • In the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver:
      • Glycogen degradation occurs to maintain BG.
      • Via a reaction catalyzed by glucose-6-phosphatase, glucose is freed up from glucose-6-phosphate, releasing inorganic phosphate.
    • In the muscle:
      • Glycogenolysis proceeds to provide energy for muscle contraction.
      • Glucose-1-phosphate is converted to glucose-6-phosphate, which go to glycolysis Glycolysis Glycolysis is a central metabolic pathway responsible for the breakdown of glucose and plays a vital role in generating free energy for the cell and metabolites for further oxidative degradation. Glucose primarily becomes available in the blood as a result of glycogen breakdown or from its synthesis from noncarbohydrate precursors (gluconeogenesis) and is imported into cells by specific transport proteins. Glycolysis.
      • There is no glucose-6-phosphatase in muscle, so glycogen from the muscle does not help maintain BG.
  • Glycogen is also degraded in lysosomes (via alpha-glucosidase) but does not contribute to the maintenance of BG.
Glycogen breakdown — glycogen phosphorylase

Glycogen breakdown—glycogen phosphorylase:
Conversion of glucose-1-phosphate to glucose-6-phosphate by the enzyme phosphoglucomutase

Image by Lecturio.

Regulation of Glycogen Metabolism

Regulation overview

  • Glycogen metabolism is controlled by allosteric (metabolites indicate the cellular energy state and help in modulation) and hormonal regulation
  • Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and different effectors coordinate to produce the appropriate effect necessary to meet the energy needs.
  • The main regulatory mechanism involved is phosphorylation, affecting the 2 main enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes:
    • Glycogen phosphorylase (activated by phosphorylation)
    • Glycogen synthase (activated by dephosphorylation)
  • The regulating hormones include:
    • Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin (promotes glycogenesis)
    • Glucagon and epinephrine (promote glycogenolysis)

Regulation of glucagon degradation

Glucagon and epinephrine activate adenylate cyclase in the cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane via G proteins.

  • 3’,5’-cyclic adenosine monophosphate (cAMP):
    • Formed when adenylate cyclase converts ATP to cAMP
    • Activates protein kinase A (PKA)
  • PKA:
    • Phosphorylates glycogen synthase (making it less active), thus decreasing glycogen synthesis
    • Phosphorylates phosphorylase kinase → activating glycogen phosphorylase b to phosphorylase a → increasing glycogenolysis
  • In the muscle:
    • Calcium (Ca²⁺): activates phosphorylase kinase (which activates phosphorylase b to a)
    • Adenosine monophosphate (AMP):
      • During muscle contraction: ATP → ADP → AMP
      • ↑ AMP stimulates glycogenolysis by converting phosphorylase b to phosphorylase a

Regulation of glycogen synthesis

  • After a meal → ↑ insulin, ↓ glucagon
    • A fed state does not activate cAMP cascade (in effect, protein kinase is inactive).
    •  ↑ Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin activates phosphatases:
      • Dephosphorylates phosphorylase kinase and phosphorylase a, making them inactive
      • Dephosphorylates glycogen synthase, which activates the enzyme and, in effect, increases glycogen synthesis
  • In the muscle:
    • After a meal: ↓ cAMP, AMP, and Ca²⁺
    • Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin also facilitates transport of glucose into muscle cells, increasing glycogen synthesis.

Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and glycogen metabolism

Table: Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and glycogen metabolism
Hormone Glycogenesis Glycogenolysis Serum Glucose
Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin Activation Inhibition Decreases
Glucagon Inhibition Activation Increases
Epinephrine Inhibition Activation Increases

Glycogen metabolism and regulating mechanisms

Table: Effectors of glycogen metabolism and regulating mechanisms
Effectors Glycogenolysis Glycogenesis
cAMP
PK
AMP (muscle)
Calcium/muscle contraction
cAMP: cyclic adenosine monophosphate
PK: protein kinase
AMP: adenosine monophosphate
Table: Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview of glycogen metabolism and regulating mechanisms
Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview Glycogenolysis Glycogenesis
Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin
Glucagon
Epinephrine
Table: Regulatory enzyme of glycogen metabolism and regulating mechanisms
Regulatory Enzyme Glycogenolysis Glycogenesis
Glycogen synthase Activated (enzyme is phosphorylated) Inactivated
Glycogen synthase Inactivated Activated (enzyme is dephosphorylated)
Glycogen metabolism diagram

Glycogen metabolism and regulatory factors:
Epinephrine, glucagon, and AMP activate glycogen phosphorylase, thus glycogenolysis is promoted, producing glucose for energy consumption. Insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin activates glycogen synthase, facilitating glycogen buildup.

Image by Lecturio.

Clinical Relevance

Glycogen storage disease: a group of inherited disorders characterized by abnormalities in glycogen metabolism, resulting in an abnormal accumulation of glycogen in the tissues.

Table: Glycogen storage diseases
Type Diseases Enzyme Deficiency Clinical Features
0 Lewis disease Glycogen synthase
  • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Hyperketonemia
  • Early mortality
Von Gierke disease Glucose-6-phosphatase
  • Glycogen accumulation in the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver and renal tubule cells
  • Hepatomegaly
  • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Lactic acidosis
  • Ketosis
  • Hyperlipidemia (HLD)
Pompe disease Lysosomal ?-1,4 and ?-1,6 glucosidase (acid maltase)
  • Lysosomal accumulation of glycogen
  • Heart failure (HF)
  • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Overview of Cardiomyopathies (CM)
  • Muscle hypotonia and dystrophy
  • Early mortality
Forbes-Cori disease Debranching enzyme (amylo-1,6-glucosidase)
  • Fasting hypoglycemia
  • Hepatomegaly
  • Myopathy
  • Stunted growth
Andersen disease 1,4-?-glucan branching enzyme
  • Accumulation of abnormal glycogen
  • Hepatosplenomegaly
  • Neuromuscular presentation
  • Death from HF or liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver failure
McArdle disease Muscle phosphorylase
  • Poor exercise tolerance
  • Abnormally high muscle glycogen
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
  • Myoglobinuria
Hers disease Liver phosphorylase
  • Hepatomegaly
  • Glycogen accumulation in the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
  • Mild hypoglycemia
Tarui disease Muscle phosphofructokinase (PFK)
  • Poor exercise tolerance
  • Low blood lactate post-exercise
  • Hemolytic anemia Hemolytic Anemia Hemolytic anemia (HA) is the term given to a large group of anemias that are caused by the premature destruction/hemolysis of circulating red blood cells (RBCs). Hemolysis can occur within (intravascular hemolysis) or outside the blood vessels (extravascular hemolysis). Hemolytic Anemia (HA)
Hepatic phosphorylase kinase deficiency Liver phosphorylase kinase
  • Hepatomegaly
  • Glycogen accumulation in the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
  • Mild hypoglycemia
Phosphorylase kinase deficiency Liver and muscle phosphorylase kinase
  • Hepatomegaly
  • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Exercise intolerance
PGAM deficiency Phosphoglycerate mutase
  • Exercise intolerance
  • Muscle cramps
  • Myoglobinuria
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
ⅩⅠ Lactate dehydrogenase A deficiency Lactate dehydrogenase A
  • Fatigability
  • Myoglobinuria
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
XII Aldolase A deficiency Aldolase A
  • Myoglobinuria
  • Hemolysis
  • Jaundice Jaundice Jaundice is the abnormal yellowing of the skin and/or sclera caused by the accumulation of bilirubin. Hyperbilirubinemia is caused by either an increase in bilirubin production or a decrease in the hepatic uptake, conjugation, or excretion of bilirubin. Jaundice
  • Fatigability
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
XIII Beta-enolase deficiency (muscle) Beta-enolase
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
  • Exercise intolerance
XIV Phosphoglucomutase I deficiency (muscle) Phosphoglucomutase I
  • Exercise intolerance
  • Rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is characterized by muscle necrosis and the release of toxic intracellular contents, especially myoglobin, into the circulation. Rhabdomyolysis
  • Myoglobinuria
XV Glycogenin I deficiency (muscle) Glycogenin I
  • Arrhythmias
  • Muscle weakness
Fanconi-Bickel syndrome GLUT2
  • Fanconi syndrome
  • Growth retardation
  • Galactosemia Galactosemia Galactosemia is a disorder caused by defects in galactose metabolism. Galactosemia is an inherited, autosomal-recessive condition, which results in inadequate galactose processing and high blood levels of monosaccharide. The rare disorder often presents in infants with symptoms of lethargy, nausea, vomiting, diarrhea, and jaundice. Galactosemia
PGAM: Phosphoglycerate mutase
GLUT2: Glucose transporter 2

References

  1. Berg, JM, Tymoczko, JL, & Stryer, L. (Eds.). (2002). Glycogen Metabolism. In Berg, JM, et al. (Eds.), Biochemistry (5th ed.). WH Freeman. https://www.ncbi.nlm.nih.gov/books/NBK21190/
  2. Craigen, W, Darras, B. (2019). Overview of inherited disorders of glucose and glycogen metabolism. UpToDate. Retrieved Oct 30, 2021 from https://www.uptodate.com/contents/overview-of-inherited-disorders-of-glucose-and-glycogen-metabolism
  3. Le, T, Bhushan, V, & Sochat, M. (Eds.). (2021). “ Biochemistry—metabolism. In Le, T, at al. (Ed.), First Aid for USMLE Step 1 (pp. 86–87).
  4. Murray, R, Granner, D, Rodwell, V. (2006). Metabolism of glycogen. In Murray, R., et al. (Eds.), Harper’s Illustrated Biochemistry (27th ed., pp. 159–166).
  5. Swanson, T, Kim, S, & Glucksman, M. (2010). Glycogen metabolism. In Swanson, T, et al. (Eds.), Biochemistry, Molecular Biology and Genetics (5th ed., pp. 97–104). Lippincott, Williams & Wilkins.

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