Glycogen storage disease type 0 Glycogen storage disease type 0 Glycogen storage disease type 0 is a disease characterized by a deficiency in the glycogen synthase enzyme (GSY). Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is often classified as a glycogen storage disease because it is another defect of glycogen storage and can cause similar problems. There are two isoforms (types) of glycogen synthase enzyme; GSY1 in muscle and GSY2 in liver, each with a corresponding form of the disease. Mutations in the liver isoform (GSY2), causes fasting hypoglycemia, high blood ketones, increased free fatty acids
Glycogen-branching enzyme deficiency caused by an autosomal recessive mutation to the GBE1 gene, which leads glycogen branching enzyme activity that is reduced to absent. Subsequently, glycogen molecules are produced with few branches, which greatly decreasing the number of nonreducing ends, drastically slowing the rate at which the molecule can be synthesized or broken down. This causes low levels of muscle glycogen that is very resistant to amylase. Lacking proper glycogen storage, the horse's brain, heart muscle, and skeletal muscles cannot function, leading to rapid death. Most foals with glycogen-branching enzyme deficiency (GBED) are aborted (usually in the second trimester), or are stillborn, and