Glycogen storage disease type 0
(GSD0), a form of glycogen storage disease (GSD), is a rare abnormality of glycogen metabolism (how the body uses and stores glycogen, the storage form of glucose). Unlike other types of GSD, GSD0 does not involve excessive or abnormal glycogen storage, and causes moderately decreased glycogen stores in the liver. Symptoms typically begin in infancy or in early childhood and may include drowsiness, sweating, lack of attention, fasting hypoglycemia associated with hyperketonemia, seizures, and other findings. It is caused by a deficiency of the enzyme glycogen synthetase in the liver, due to mutations in the GYS2 gene. It is inherited in an autosomal recessive manner. Treatment involves a specific diet that includes frequent meals with high protein intake during the day, and uncooked starch in the evening. The prognosis is usually favorable when the disease is correctly managed. This condition differs from another form of GSD0 which chiefly affects the muscles and heart (Glycogen storage disease type 0, muscle) and is thought to be caused by mutations in the GYS1 gene. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.