Glycogen Storage Diseases Types I-VII

Updated: Jul 28, 2017
  • Author: Catherine Anastasopoulou, MD, PhD, FACE; Chief Editor: George T Griffing, MD  more...
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Overview

Background

Glycogen storage disease type I

Glycogen storage disease (GSD) type I, also known as von Gierke disease, is a group of inherited autosomal recessive metabolic disorders of the glucose-6- phosphatase system which helps maintain glucose homeostasis. Von Gierke described the first patient with GSD type I in 1929 under the name hepatonephromegalia glycogenica. [1] In 1952, Cori and Cori demonstrated that glucose-6-phosphatase (G6Pase) deficiency was a cause of GSD type I. [2] In 1978, Narisawa et al proposed that a transport defect of glucose-6-phosphate (G6P) into the microsomal compartment may be present in some patients with GSD type I. [3] Thus, GSD type I is divided into GSD type Ia caused by G6Pase deficiency and GSD type Ib resulting from deficiency of a specific translocase T1. These subtypes are clinically indistinguishable from one another, except for the fact that patients with GSD type Ib have altered neutrophil functions predisposing them to gram-positive bacterial infections.

Later, other translocases were discovered, adding 2 more subtypes of GSD to the disease spectrum. GSD type Ic is deficiency of translocase T2 that carries inorganic phosphates from microsomes into the cytosol and pyrophosphates from the cytosol into microsomes. GSD type Id is deficiency in a transporter that translocates free glucose molecules from microsomes into the cytosol.

For practical purposes, depending on the enzyme activity and the presence of mutations in the G6Pase and T genes, respectively, GSD type I may be subdivided into 2 major forms. GSD type Ia demonstrates deficient G6Pase activity in the fresh and frozen liver tissue. GSD type Ib demonstrates normal G6Pase activity in the frozen tissue samples and lowered activity in the fresh specimens. [4]

Glycogen storage disease type II

GSD type II, also known as alpha glucosidase deficiency (GAA, acid maltase deficiency) or Pompe disease, is a prototypic lysosomal disease. Pompe initially described the disease in 1932. Its clinical presentation clearly differs from other forms of GSD, because it is caused by the deficiency of the lysosomal enzyme, alpha-1,4-glucosidase, leading to the pathologic accumulation of normally structured glycogen within the lysosomes of most tissues, differs Three forms of the disease exist: infantile-onset, late-onset juvenile and adult onset. In the classic infantile for, the main clinical signs are cardiomyopathy and muscular hypotonia (smooth and skeletal muscle). In the juvenile and adult form, the involvement of the skeletal muscle dominates the clinical presentation. [5] The images below illustrate histologic findings of GSD type II.

Glycogen storage disease type II. Photomicrograph Glycogen storage disease type II. Photomicrograph of the liver. Note the intensively stained vacuoles in the hepatocytes (periodic acid-Schiff, original magnification X 27).
Glycogen storage disease type II. Photomicrograph Glycogen storage disease type II. Photomicrograph of the liver. Note the regular reticular net and hepatocytes vacuolization (Gordon-Sweet stain, original magnification X 25).

Glycogen storage disease type III

GSD type III is also known as Forbes-Cori disease or limit dextrinosis. It is an autosomal recessive disorder in which there is an AGL gene mutations which causes deficiency in glycogen debranchinging enzyme and limited storage of dextrin. The disease presents with variable cardiac muscle, skeletal muscle and liver involvement and has different subtypes. GSD IIIa is the most common subtype, affecting about 85% of patients with this disease. GSD IIIb is less severe and less common, affecting 15% of patients with the disease. [6, 7]  In contrast to GSD type I, liver and skeletal muscles are involved in GSD type III. Glycogen deposited in these organs has an abnormal structure. Differentiating patients with GSD type III from those with GSD type I solely on the basis of physical findings is not easy. [8]

Glycogen storage disease type IV

GSD type IV, also known as amylopectinosis, Glycogen Branching enzyme deficiency (GBE) or Andersen disease, is a rare disease that leads to early death. In 1956, Andersen reported the first patient with progressive hepatosplenomegaly and accumulation of abnormal polysaccharides. The main clinical features are liver insufficiency and abnormalities of the heart and nervous system. [9]  

Glycogen storage disease type V

GSD type V, also known as McArdle disease, affects the skeletal muscles. It is an autosomal recessive disorder in which there is a deficiency of glycogen phosphorylase.McArdle reported the first patient in 1951. Initial signs of the disease usually develop in adolescents or adults. Muscle phosphorylase deficiency adversely affecting the glycolytic pathway in skeletal musculature causes GSD type V. Like other forms of GSD, McArdle disease is heterogeneous. [10, 11]

Glycogen storage disease type VI

GSD type VI, also known as Hers disease, belongs to the group of hepatic glycogenoses and represents a heterogenous disease. Hepatic phosphorylase deficiency or deficiency of other enzymes that form a cascade necessary for liver phosphorylase activation cause the disease. [12] In 1959, Hers described the first patients with proven phosphorylase deficiency.

Glycogen storage disease type VII

GSD type VII, also known as Tarui disease, arises as a result of phosphofructokinase (PFK) deficiency. The enzyme is located in skeletal muscles and erythrocytes. Tarui reported the first patients in 1965. The clinical and laboratory features are similar to those of GSD type V. [13]

Medscape Reference Endocrinology articles on GSD

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Pathophysiology

Glycogen storage disease type I

G6Pase is mainly found in the liver, kidneys and intestines to maintain glycogenolysis and gluconeogenesis. Because of insufficient G6Pase activity, G6P cannot be converted into free glucose, and instead is metabolized to lactic acid or incorporated into glycogen. The excess glycogen that is formed is stored as molecules with normal structure in the cytoplasm of hepatocytes, renal and intestinal mucosa cells. The excess storage of glycogen causes enlarged liver and kidneys, which dominate the clinical presentation of this disease. The chief biochemical alteration is non ketotic hypoglycemia, while secondary biochemical abnormalities are hyperlactatemia, metabolic acidosis, hyperlipidemia, and hyperuricemia which cause metabolic decompensation. [14]

In hypoglycemia, the deficiency of G6Pase blocks the process of glycogen degradation and gluconeogenesis in the liver, preventing the production of free glucose molecules. As a consequence, patients with GSD type I have fasting hypoglycemia. Despite the metabolic block, the endogenous glucose formation is not fully inhibited. In young patients, production of free glucose reaches half that of healthy individuals, whereas adult patients may produce as much as two thirds of the healthy amount of free glucose. Hypoglycemia inhibits insulin secretion and stimulates glucagon and cortisol release.

In hyperlactatemia and acidosis, undegraded G6P, galactose, fructose, and glycerol are metabolized via the G6P pathway to lactate, which is used in the brain as an alternative source of energy. The elevated blood lactate levels cause metabolic acidosis.

In hyperuricemia, blood uric acid levels are raised because of the increased endogenous production and reduced urinary elimination caused by competition with the elevated concentrations of lactate, which should be excreted.

In hyperlipidemia, elevated endogenous triglyceride synthesis from nicotinamide adenine dinucleotide (NADH), NAD phosphate (NADPH), acetyl-coenzyme A (CoA), glycerol, and diminished lipolysis causes hyperlipidemia. Triglycerides increase the risk of fatty liver infiltration, which contributes to the enormous amount of liver enlargement. Despite significantly elevated serum triglyceride levels in patients, vascular lesions and atherosclerosis are rare complications. The increased serum apolipoprotein E concentrations that promote the clearance of triglycerides may explain the rarity of such complications.

Glycogen storage disease type II

Alpha-1,4-glucosidase acts hydrolyzing the alpha 1,4 and 1,6 glucosidic linkages of the glycogen molecule within the lysosome, hence, causes its degradation. In the GSD II, this enzyme is deficient, leading to the progressive accumulation of glycogen in the lysosomes and cytoplasm of different tissues causing its destruction.

GSD type 2 is an autosomal recessive disorder with significant heterogeneity. Multiple mutations in the gene encoding for the enzyme (17q25.2-q25.3) have been identified. These factors contribute to the different phenotypic presentation of the disease. Some patients have a deficiency in precursor protein synthesis, while in others, because of inadequate processing, the amount of mature molecule is insufficient or the enzyme has no catalytic activity. [15] Depending on the degree of residual enzyme activity, GSD type II manifests in infantile, juvenile, or adult forms. Mutations where the enzyme activity is minimal or absent (activity <1% of normal control) leads to severe infantile onset form, develops. In cases where the enzyme activity is reduced(activity of 2-40%) then it presents as an early non classic onset or late onset. GSD II is progressive in all ages. [16]

Glycogen storage disease type III

Deficiency of the cytosolic debrancher enzyme, a monomeric high-molecular-weight protein that consists of 2 catalytic units (amylo-1,6-glucosidase and oligo-1,4-1,4-glucanotransferase), causes GSD type III. This enzyme is located on the AGL gene on chromosome 1p21.It is inherited in an autosomal recessive fashion. Abnormal glycogen with short external branches is stored in the liver, heart, and skeletal muscle cells. [17]  The accumulated glycogen resembles the limit dextrin, which is a product of glycogen degradation by phosphorylase. Two forms of the disease exist. In GSD type IIIa, the liver, skeletal muscles, and cardiac muscle are involved. In GSD type IIIb, only the liver is involved.

Glycogen storage disease type IV

GSD IV is an autosomal recessive disorder caused by the mutation of the GBE1 gene (3p14) in which there is deficiency or reduced activity of the glycogen branching enzyme. The glycogen branching enzyme (GBE) is an enzyme that catalyze the formation of α-1,6-glycosidic bonds to the linear α-1,4-glycosidic bonds that forms the skeleton of the glycogen molecule. In case of deficiency, abnormal glycogen is formed, with long linear α-1,4 polymers and less branches. The abnormal glycogen has long branches that resemble amylopectin. The importance of the presence of polymer branches, relies in the fact that it provides multiple free ends that are easily available to the amylase to break down glucose molecules during glycogenolysis. Accumulation of abnormally structured glycogen in the liver, heart, and neuromuscular system characterizes this disease. Different phenotypes have been identified, based on genetical heterogeneity: fatal perinatal neuromuscular subtype, congenital neuromuscular subtype, classic (progressive) hepatic subtype, non-progressive hepatic subtype and the childhood neuromuscular subtype. [18]  

Glycogen storage disease type V

GSD type V is an autosomal recessive disorder in which there is a deficiency of the enzyme glycogen phosphorylase. This enzyme is required in the first step of glycogen catabolism, where glycogen is released in G1P molecules. This leads to varying degrees of exercise intolerance secondary to affected muscle metabolism. [19]  During the early phase of moderate physical exertion, the principal sources of energy are glycogen and anaerobic glycolysis. [20] This phase is distinct from the resting phase when energy for the skeletal muscles is obtained through fatty acid oxidation. With further physical activity, glucose and fatty acids become irreplaceable energy sources for the skeletal muscles. However, during intense physical exertion, the skeletal muscles use energy released from endogenous glycogen (glycogenolysis by way of muscle phosphorylase), and signs of muscle fatigue occur after glycogen depletion. This effect is the reason patients with McArdle disease tolerate moderate physical activity relatively well, while intense and isometric physical exertion leads to disturbances and symptoms of the disease. The muscle glycogen concentration is increased, but its molecules are normal in structure.

Glycogen storage disease type VI

GSD type VI is an autosomal recessive disorder, caused by the deficiency of the hepatic glycogen phosphorylase, which is a rate-limiting enzyme that is necessary during glycogenolysis. It catalyzes the α1,4 glucosidic cleavage, releasing glucose 1-phosphate. Hepatic phosphorylase is activated in a series of reactions that requires adenylate cyclase, protein kinase A, and phosphorylase kinase (the cause of the GSD IX). Glucagon stimulates the chain of reactions involved in the activation of phosphorylase.

Glycogen storage disease type VII

PFK catalyzes the irreversible conversion of fructose-6-phosphate to fructose-1,6-biphosphate. PFK consists of 3 subunits: muscle (M), liver (L), and platelet (P). Each subunit is coded by a gene located on different chromosomes: The PFKM gene is located on chromosome 1; the PFKL gene, on chromosome 21; and the PFKP gene, on chromosome 10. The PFKL subunit is expressed in the liver and kidneys, whereas muscles contain only the M subunit. Therefore, muscles harbor only homotetramers of M subunits, and erythrocytes contain L and M subunits, which randomly tetramerize to form M4, L4, and 3 additional hybrid forms of the holoenzyme (ie, M3L, M2L2, ML3). [21]

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Epidemiology

Frequency

United States

Without systematic neonatal screening, no reliable data on the frequency of specific types of GSD exist. Based on the results of combined US and European studies, the cumulative incidence is estimated at 1 in 20,000-43,000 live births. [17]

GSD type 1 is the most common type of GSD which accounts for 24.6% of all patients with GSD. 80% of cases of GSD type 1 are classified as type 1a. 

The precise frequency of GSD type II is not known because no systematic neonatal screening programs exist; however, GSD type II may be found in 15.3% of all patients with GSD. In the United States, the incidence of all 3 forms of GSD type II, calculated on the basis of mutated gene frequencies in healthy individuals of different ethnic backgrounds, has been estimated at 1 in 40,000 live births.

Combined data from the United States and other countries suggest that GSD type III accounts for 24.2% of all patients with GSD.

Because of its rarity, the precise incidence is not known, but GSD type IV is believed to represent 3.3% of all GSD cases with an overall incidence of approximately 1:600,000-1:800,000.

GSD type V is rare. McArdle disease accounts for 2.4% of all patients with GSD.

GSD type VI is a rare condition, probably due to underdiagnosis. GSD IV and GSD IX (enzymes that regulate liver phosphorylase) accounts for 25%- 30% of all patients with GSD. Prevalence is estimated of 1:100,000. Most of these are GSD IX. The X-linked form of hepatic phosphorylase kinase deficiency is the most common among patients with GSD type VI.

GSD type VII is rare and is present in only 0.2% of all cases of GSD. GSD type VII most frequently affects Japanese persons and Jewish persons with Russian ancestry.

International

Approximately 2.3 children per 100,000 births have some form of GSD in British Columbia, Canada.

In GSD type II, frequencies similar to those in the United States have been found in the Netherlands (1 in 40,000 births), as well as in Taiwan and southern China (1 in 50,000 births). In a study from Australia, birth prevalence of GSD type II, including early and late-onset phenotypes, was estimated as 1 in 146,000.

Race

No racial or ethnic differences exist for GSD types I, II, IV, V, and VI.

Although GSD type III is distributed universally throughout the world, the highest incidence (1 in 5420 births) has been recorded in non-Ashkenazi Jews in northern Africa.

The patients most commonly reported with GSD type VII are of Japanese or Ashkenazi Jewish descent.

Sex

GSD types I-V and VII affect both sexes with equal frequency.

GSD type VI affects both sexes with equal frequency; however, in the X-linked form, most patients are males.

Age

As with other genetically determined diseases, GSD type I develops during conception, yet the first signs of the disease may appear at birth or later. Median age of disease onset is between the 3rd and 4th month. 

In GSD type II, the age of onset depends on the clinical form of disease. The infantile form develops during the first months of life. In the juvenile form, initial clinical symptoms appear in persons aged 1-15 years. The adult form of disease appears in person aged 10-30 years and, less commonly, later.

In GSD type III, the first signs of the disease may appear shortly after birth or within several months afterwards.

In GSD type IV, patients appear healthy at birth, but they fail to thrive soon after birth, and hepatomegaly and/or splenomegaly may be observed in the next few months.

In GSD type V, the first signs of the disease usually develop in persons aged 10-20 years of age. There are case reports of the disease in babies shortly after birth, but this presentation is rare. 

In GSD type VI, the disease appears in the first months of life.

In GSD type VII, depending on the genetic variety, the disease usually develops in persons aged 10-20 years and, less frequently, earlier or later in life.

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Prognosis

GSD type I

The prognosis is better than in the past provided that all the available dietary and medical measures are implemented.

GSD type II

Without treatment, the prognosis in the infantile form is poor.

The prognosis varies in the juvenile form.

The prognosis is relatively good in the adult form

GSD type III

The prognosis of GSD III is better than that of GSD I with many patients surviving into adulthood. GSD IIIb is a milder form of the disease, while the prognosis of GSD IIIa depends largely on the extent of cardiac involvement. 

GSD type IV

The prognosis is poor. Most children with GSD type IV die by age 2-4 years because of hepatic insufficiency.

GSD types V and VII

The prognosis varies.

GSD type VI

The course is benign.

The size of the liver decreases with age and returns to baseline at or around puberty.

All the patients attain normal height.

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Mortality/Morbidity

In GSD type I, acute hypoglycemia may be fatal. Early death is now uncommon with improving care and treatment. Late complications, such as renal failure, hypertension, or malignant alteration of hepatic adenomas, may be responsible for mortality in adolescent and adult patients. See Complications.

In GSD type II, morbidity and mortality differ among the subtypes of the disease. The infantile form has a lethal outcome caused by progressive cardiorespiratory insufficiency that usually begins by the end of the first year of life. The juvenile form has a slower course. Some patients may survive the third decade of life. Death is usually due to respiratory insufficiency, although a few cases have been described that were caused by the rupture of an intracranial aneurysm formed from glycogen accumulation in the smooth muscle cells of the arterial wall. The adult form manifests in older patients. Death due to respiratory insufficiency (sleep apnea) may occur many years after the first signs of the disease have appeared.

In GSD type III, the cirrhosis found in some patients is of a mild degree without a significant impact on the course of the disease.

In GSD type IV, the classic form, progressive liver cirrhosis rapidly leads to hepatic insufficiency so that a fatal outcome may be expected before the end of the second year of life (see Complications). Rarely, children with GSD type IV may survive longer.

In GSD type V, myoglobinuria from repeated prolonged exercise may eventually lead to renal failure and death. [19]

In GSD type VI, serious complications are unknown.

In GSD type VII, skeletal muscles and erythrocytes are affected. Rhabdomyolysis may cause acute renal failure because of myoglobinuria.

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Patient Education

GSD type I

First, instruct parents, and later adult patients, concerning the measures required to control hypoglycemia and other metabolic abnormalities; such measures include proper care and nutrition.

Explain the important role played by continuous overnight feeding by means of a nasogastric tube. Teach parents to place the tube by themselves and control the entire feeding process.

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