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. In livestock, environmental GSD is caused by intoxication with the alkaloid castanospermine.