The enzyme glycogen synthase is needed for the body to make glycogen. There are liver and muscle types of GSD0, both are inherited in the autosomal recessoive pattern.
A fault in the GYS2 gene results in very low amounts of glycogen stored in the liver. A person between meals can develop very low blood sugar levels, known as hypoglycemia. Early in infancy children usually have no symptoms. The hypoglycemia typically develops once night feeding stops. Before breakfast children may have drowsiness, look pale, have vomiting, fatigue and sometimes convulsions. If a GP investigates a child lacking energy, hypoglycemia is often discovered through morning urine samples.
A fault in the GYS1 gene results in very low amounts of glycogen stored in the skeletal muscles. This muscle type is extremely rare and little is known about it.