What are glycogen storage diseases?

Glycogen storage diseases are due to deficiencies of one of the enzymes that break down glycogen (the starch in which sugars are stored in the liver). As a result of the enzyme deficiency, toxic glycogen accumulates in the liver and skeletal muscles. Frequent findings include an enlarged liver and spleen and poor weight gain and further down the road cirrhosis of the liver and portal hypertension. Children with this disease may experience low blood sugar without any other symptoms.