Type 0 Glycogen Storage Disease

Synonyms:
Glycogen Synthase Deficiency

Type 0 Glycogen Storage Disease (GSD 0) is caused by a deficiency in the enzyme named glycogen synthase. This enzyme is needed for the body to make glycogen. When a person has glycogen synthase deficiency the amount of glycogen that the body can store in the liver is very low. Low amounts of glycogen in the liver mean that when a person is not eating (fasting) their blood sugar levels can get very low (hypoglycemia).

In patients with Type 0 Glycogen Storage Disease, the symptom of fasting hypoglycemia typically develops when a baby no longer gets fed during the night (late infancy). Early in infancy, children usually have no symptoms, but weaning from overnight feeds is often difficult. Children may have early-morning (before eating breakfast) drowsiness, appearance of looking pale, vomiting and fatigue, and sometimes convulsions associated with low blood glucose. During gastrointestinal illnesses ("stomach bugs") or periods of poor eating, children may appear to be very tired and lazy. Usually low blood sugar (hypoglycemia) is found as part of the labwork that the doctor or hospital does in order to figure out as to why a child is not acting energetic.

Children with GSD 0 may grow a bit slower than expected (have a mild growth delay). In general, people with Type 0 Glycogen Storage Disease do not have learning problems (they are developmentally normal). When exercising, people with GSD 0 may become tired more quickly than other individuals. Furthermore a person with GSD 0 may have muscle cramps because the body is trying to make energy from accumulated lactic acid. A person with Type 0 Glycogen Storage Disease will typically look no different from a person who does not have GSD 0. The liver will not be larger than normal. A doctor examining the first morning urine of someone with GSD 0 may see some signs (increased glucose and ketones in urine) that might make the diagnosis of diabetes as the first thing mentioned to a family.

Any child with a history of needing frequent meals or snacks and with hypoglycemia (where a doctor sees ketones in the urine) may have Type 0 Glycogen Storage Disease. Detailed blood and urine tests performed by a doctor may show patterns that are unique to GSD 0. If a doctor looks at a piece of liver from a person with GSD 0, they will see very little glycogen. Genetic DNA testing that is performed on a blood sample is now available.

The goal of treatment for Type 0 Glycogen Storage Disease is to prevent low blood sugar (hypoglycemia) by avoiding fasting. Frequent meals and snacks can be given every 3-4 hours during the day. Uncooked cornstarch can act as a "slow release" form of glucose for the body. Given in the proper amounts, it will prevent hypoglycemia overnight. A diet high in protein may help with the cramping, tiredness, and fatigue that many people with GSD 0 experience.

At this time, GSD 0 is considered very rare. However, because testing for Type 0 glycogen storage disease just recently became available, doctors think that GSD 0 is more common than previously thought. GSD Type 0 affects both males and females. People with GSD 0 have been described from Eastern Europe, Western Europe, North America, and South America.

Genes are instructions for the body. Glycogen synthase deficiency is caused by a change in the glycogen synthase-2 (GYS2) gene. GSD 0 is inherited within families in an autosomal recessive fashion.

Links:

GSD Type 0 info on Online Mendelian Inheritance in Man searchable database [OMIM]

Liver Glycogen Synthase Deficiency on OMIM

Muscle Glycogen Synthase Deficiency on OMIM

Type 0 GSD from eMedicine/Medscape

“Hepatic Glycogen Synthase Deficiency” article from Molecular Genetics and Metabolism