A type of inherited disorder in which there are problems with how a form of glucose (sugar) called glycogen is stored and used in the body. Certain enzymes that help make or break down glycogen are missing or do not work the way they should. This causes abnormal amounts or types of glycogen in the tissues, especially in the liver and in muscle tissue. There are many types of glycogen storage disease, which can cause problems in different parts of the body, including the liver, muscles, kidneys, and heart. Also called GSD.