Glycogen Storage Diseases

(Glycogenoses; GSD)

Definition

Glucose is a simple sugar. It is a form of carbohydrate. It is the main source of energy for our bodies. Glycogen is the storage form of glucose in our bodies.Glycogen storage diseases (GSDs) are a group of inherited genetic disorders. They cause glycogen to be improperly formed or released in the body. This results in a build up of abnormal amounts or types of glycogen in tissues.The main types of GSDs include:
  • Type 0, Liver glycogen synthase deficiency
  • Type I, Von Gierke disease, defect in glucose-6-phosphatase enzyme, the most common type of GSD accounting for 25% of all cases
  • Type II , Pompe’s disease, acid maltase deficiency
  • Type III, Cori’s disease, debrancher enzyme deficiency
  • Type IV, Andersen’s disease, brancher enzyme deficiency
  • Type V, McArdle’s disease, muscle phosphorylase deficiency
  • Type VI, Hers’ disease, liver phosphorylase deficiency
  • Type VII, Tarui’s disease, muscle phosphofructokinase deficiency
  • Type IX, phosphorylase kinase deficiency
Glycogen is mainly stored in the liver or muscle tissue. As a result, GSDs usually affect functioning of the liver, the muscles, or both.

Causes

GSDs are caused by a genetic enzyme defect. It is inherited from one or both parents.Normally, enzymes help convert glucose into glycogen for storage. Other enzymes convert the glycogen back to glucose when energy is needed. This happens during activity like exercise. With GSD, some of these enzymes are defective, deficient, or absent.The abnormal glycogen builds up in the liver and/or muscle tissues.

Risk Factors

The main risk factor for GSDs is having a family member with this disease. The risk varies with the type of GSD.

Symptoms

Each type of GSD has specific symptoms.

Type 0:

Type 0 symptoms commonly appear in late infancy when night feedings stop. In the early morning the child may low blood sugar which could cause:
  • Paleness
  • Vomiting
  • Extreme fatigue
  • Convulsions
The children may also have a mild growth delay. They also may have poor exercise tolerance.

Type I:

Type I may appear as early as 3 months old. Common symptoms include:
  • Protruding abdomen from an enlarged liver and seizures from low blood sugar are common in infants
  • Signs of low blood sugar including
    • Paleness
    • Irritability
    • Fatigue
    • Seizures
  • Growth delay
Enlarged Liver
enlarged liver
Copyright © Nucleus Medical Media, Inc.

Type II:

Type II is broken into the time of symptom onset. Infants generally show symptoms at 4-8 months of age. Type II can also form in childhood, adolescence, or adulthood.Infant-onset Type II GSD symptoms include:
  • Muscle weakness and floppiness
  • Delayed motor skills
  • Weak breathing
  • Progressive heart muscle enlargement and reduced pumping may lead to fatal heart failure within first year of life
Late-onset Type II GSD symptoms include:
  • Progressive muscle weakness that spreads from the legs into the arms
  • Difficulty breathing

Type III:

Type III may appear in childhood. Common symptoms include:
  • Muscle weakness
  • Growth delay during childhood
  • Swollen abdomen due to an enlarged liver
  • Signs of low blood sugar including
    • Paleness
    • Irritability
    • Fatigue

Type IV:

Type IV appears during infancy. Common symptoms include:
  • Physical and mental development stops at a certain point and does not continue as normal
  • Progressive muscle weakness
  • Poor muscle development
  • Progressive cirrhosis of the liver, which may lead to liver failure

Type V:

Common symptoms of Type V include:
  • Muscle cramps during exercise
  • Extreme muscle fatigue during exercise
  • Potential fainting or seizure after exercise
  • Red or brown-colored urine after exercise

Type VI, IX:

Symptoms may not appear in people with Types VI or XI. When they do occur, symptoms include:
  • Enlarged liver in infancy
  • Mild growth delay
  • Anxiety, sweating, confusion, or seizures associated with low blood sugar

Type VII:

Common symptoms of Type VII include:
  • Muscle cramps and tenderness with exercise
  • Muscle fatigue with exercise
  • Red or brown-colored urine after exercise

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