Glycogen storage disease type 0 fructose results in a marked rise in blood lactate levels. Liver biopsy for microscopic analysis and enzyme assay is required for definitive diagnosis. Diagnosis may include linkage analysis in families with affected members and sequencing of the entire coding region of the GSY2 gene for mutations. Histologic analysis of liver tissue demonstrates moderately decreased amounts of periodic acid-Schiff (PAS)–positive, diastase-sensitive glycogen stores. Evidence of increased fat accumulation in the liver may be observed, as in other glycogen-storage diseases. Electron microscopic analysis of liver sections shows normal glycogen structure. Muscle glycogen stores are normal. There are two types of this\\e condition
Glycogen phosphorylase Glycogen phosphorylase is regulated by both allosteric control and by phosphorylation. Hormones such as epinephrine, insulin and glucagon regulate glycogen phosphorylase using second messenger amplification systems that are linked to G proteins. Glucagon activates adenylate cyclase through a seven transmembrane receptor coupled to G which, in turn, activates adenylate cyclase to increase intracellular concentrations of cAMP. cAMP binds to and releases an active form of protein kinase A (PKA). Next, PKA phosphorylates phosphorylase kinase, which, in turn, phosphorylates glycogen phosphorylase b, transforming it into the active glycogen phosphorylase a. This phosphorylation is added onto the glycogen phosphorylase b serine 14.