An inherited metabolic disorder characterized either by defects in glycogen synthesis or defects in the breaking down of glycogen. It results either in the creation of abnormal forms of glycogen or accumulation of glycogen in the tissues. The disease is disorder of glycogen metabolism (Monarch Disease Ontology term MONDO_0002412). Also known as: GSD, glycogen metabolism disorder, glycogen storage disease, glycogen storage disorder, glycogenoses, glycogenosis, inborn error of glycogen metabolic process, inborn glycogen metabolic process disorder.