Any of a group of metabolic disorders characterized by excessive storage of glycogen.

A glycogen storage disease (GSD, also glycogenosis and dextrinosis) is a metabolic disorder caused by a deficiency of an enzyme or transport protein affecting glycogen synthesis, glycogen breakdown, or glucose breakdown, typically in muscles and/or liver cells. GSD has two classes of cause: genetic and environmental. Genetic GSD is caused by any inborn error of carbohydrate metabolism (genetically defective enzymes or transport proteins) involved in these processes...