Glycogen storage disease type 0 glycogen primer. Its action is highly regulated by a mechanism of phosphorylation and dephosphorylation and modulated by counter-regulatory hormones including insulin, epinephrine, and glucagon. Mutations in the gene for liver glycogen synthetase (GYS2, 138571) result in decreased or absent activity of liver glycogen synthetase and moderately decreased amounts of structurally normal glycogen in the liver. Mutational studies of patients with glycogen-storage disease type 0 do not demonstrate correlations between genotype and phenotype. [3] A different gene (GYS1, 138570) encodes muscle glycogen synthetase, which has normal activity in patients with glycogen-storage disease type 0A. In the early stages of fasting, the
Glucose 6-phosphate an allosteric activator of glycogen synthase, which makes sense because when the level of glucose is high the body should store the excess glucose as glycogen. On the other hand, glycogen synthase is inhibited when it is phosphorylated by protein kinase during times of high stress or low levels of blood glucose, via hormone induction by glucagon or adrenaline. When the body needs glucose for energy, glycogen phosphorylase, with the help of an orthophosphate, can cleave away a molecule from the glycogen chain. The cleaved molecule is in the form of glucose-1-phosphate, which can be converted into G6P by phosphoglucomutase.