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.

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.