Glucose (a type of sugar) is a key source of energy (fuel) for the body. The body stores glucose as glycogen. Glycogen Storage Disease (GSD) is a condition where, due to an inherited abnormality, the body cannot release glucose from the glycogen stores. When this happens, the level of glucose in the blood (the blood sugar level) can drop too low. The key to the management of this disorder is to maintain normal blood glucose/sugar levels.