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
Glycogen phosphorylase residues from the outer branch to the other end, and then a α1-6 glucosidase enzyme is required to break the remaining (single glucose) α1-6 residue that remains in the new linear chain. After all this is done, glycogen phosphorylase can continue. The enzyme is specific to α1-4 chains, as the molecule contains a 30-angstrom-long crevice with the same radius as the helix formed by the glycogen chain; this accommodates 4-5 glucosyl residues, but is too narrow for branches. This crevice connects the glycogen storage site to the active, catalytic site. Glycogen phosphorylase has a pyridoxal phosphate (PLP, derived from Vitamin