Glycogen storage diseases are a family of inherited metabolic disorders in which defects in the enzymes of glycogen synthesis or breakdown cause glycogen to accumulate abnormally — or to be unavailable when needed — in the liver, muscles, or both. The best-known, von Gierke disease (Type I), leaves infants with dangerously low blood sugar, an enlarged liver, and stunted growth because the liver cannot release glucose from its stores; McArdle disease (Type V) cripples muscle energy, causing cramps on exertion. Management is largely dietary and precisely tailored: frequent cornstarch feeds to drip-feed glucose overnight, high-protein diets for muscle forms, and avoidance of fasting. Though individually rare, together they illuminate the machinery of energy metabolism.