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 are categorized by number and name and include:
- Type I (Von Gierke disease, defect in glucose-6-phosphatase)—most common type of GSD; accounts for 90% of all GSD 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 glycogen phosphorylase deficiency)
- Type VI (Hers’ disease, liver phosphorylase deficiency)
- Type VII (Tarui’s disease, muscle phosphofructokinase deficiency)
- Type IX (liver glycogen 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.
- Liver—The GSDs that mainly affect the liver are types I, III, IV, VI, and IX.
- Muscles—The GSDs that mainly affect muscles are types V and VII.
- Type II affects nearly all organs including the heart.