Any of numerous types of hereditary enzyme deficiency resulting in altered metabolism of glycogen. The problems are classified in two groups, those affecting the liver and those involving striated muscle, both primary glycogen storage sites. Symptoms in the liver group range from symptomatic hypoglycemia with ketosis to asymptomatic liver enlargement (hepatomegaly). In the muscle group, they range from weakness and cramps to fatal heart enlargement.

Learn more about glycogen storage disease with a free trial on Britannica.com.