Glycogen storage disease type 0

Glycogen storage disease type 0 is a disease characterized by a deficiency in the glycogen synthase enzyme (GSY). Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is often classified as a glycogen storage disease because it is another defect of glycogen storage and can cause similar problems. There are two isoforms (types) of glycogen synthase enzyme; GSY1 in muscle and GSY2 in liver, each with a corresponding form of the disease. Mutations in the liver isoform (GSY2), causes fasting hypoglycemia, high blood ketones, increased free fatty acids and low levels of alanine and lactate. Conversely, feeding in these patients results in hyperglycemia and hyperlactatemia.

The goal for treatment of Glycogen storage disease type 0 is to avoid hypoglycemia. This is accomplished by avoiding fasting by eating every 1–2 hours during the day. At night, uncooked corn starch can be given because it is a complex glucose polymer. This will be acted on slowly by pancreatic amylase and glucose will be absorbed over a 6 hour period.

The overall frequency of glycogen storage disease is approximately 1 case per 20,000–25,000 people. Glycogen storage disease type 0 is a rare form, representing less than 1% of all cases. The identification of asymptomatic and oligosymptomatic siblings in several glycogen storage disease type 0 families has suggested that glycogen storage disease type 0 is underdiagnosed.

The major morbidity is a risk of fasting hypoglycemia, which can vary in severity and frequency. Major long term concerns include growth delay, osteopenia, and neurologic damage resulting in developmental delay, intellectual deficits, and personality changes.

No sexual predilection is observed because the deficiency of glycogen synthetase activity is inherited as an autosomal recessive trait.

Glycogen storage disease type 0 is most commonly diagnosed during infancy and early childhood.