Glycogenosis type 0 (Glycogen storage disease type 0) - Genes GYS1 or GYS2.

The type 0 Glycogen (also known as GSD 0) is a disorder caused by the body's inability to form glycogen. This disease has two types: GSD 0 muscle, where the formation of glycogen in the muscles deteriorate, and GSD 0 liver, where glycogen formation in the liver deteriorates.

Signs and symptoms of muscle GSD 0 usually begin in early childhood. Often, those affected manifest pain and muscle weakness , or syncope after moderate physical activity, such as climbing stairs. Loss of consciousness that occurs with fainting usually lasts up to several hours. Some individuals have muscular GSD 0 arrhythmia, known as long QT syndrome. In all individuals affected by such capacity deteriorates heart to pump blood effectively and increases the risk of cardiac arrest and sudden death, especially after physical activity. Sudden cardiac death may occur in childhood or adolescence in people with muscular GSD 0.

Meanwhile, people with GSD 0 liver, often show signs and symptoms of the disease in childhood. People with this type have hypoglycemia after fasting. Signs of hypoglycemia are evident when affected infants start to sleep through the night and stop feeding during it. These children show lethargy, pallor and nausea. During episodes of fasting, concentrations of ketones in the blood can increase, leading to ketosis. Often these signs and symptoms of hepatic GSD 0 improve the short term when foods and sugar levels in the body stabilize ingested. 0 GSD characteristics vary liver. They can be mild and go unnoticed for years, or may include developmental delay and lack of growth.

This process is due to mutations in the GYS1 and GYS2 genes. These genes encode different versions of glycogen synthase. Both versions of glycogen synthase having the same function but perform this function in different regions of the body.

The GYS1 gene, located on the long arm of chromosome 19 (19q13.3), encodes an enzyme called muscle glycogen synthase. Muscle glycogen synthase is encoded in most cells, but is most abundant in heart muscle and skeletal muscles. Muscle glycogen synthase helps bind molecules to form glycogen simple glucose. Most glucose that is ingested with food is stored as glycogen in muscle cells. During contractions of the heart muscle or rapid or sustained skeletal muscle movements, glycogen stored in muscle cells is broken down to supply energy to cells. They have identified at least four mutations in the GYS1 gene in people with type 0 glycogenosis affecting cardiac and skeletal muscle. Most mutations lead to a deficiency of functional muscle glycogen synthase, resulting in a complete absence of glycogen in muscle cells. Normally, glycogen is formed from excess glucose is not used immediately by glucose after meals ingested during cell. In people with GSD 0, which can not form glycogen, additional glucose is released by the body. As a result, people with muscular GSD 0 have no stored energy, leading to muscle pain, weakness or fainting episodes after moderate physical activity. Since no glycogen in the heart muscle, affected individuals also have a higher risk of cardiac arrest and sudden death, particularly after physical activity.

The GYS2 gene, located on the short arm of chromosome 12 (12p12.2), encoding an enzyme called hepatic glycogen synthase. Hepatic glycogen synthase is encoded only in the liver cells, which helps form glycogen linking molecules simple glucose. Glucose ingested with food is stored in the body as glycogen. Glycogen is stored in the liver can break down quickly when glucose is needed to maintain normal blood glucose levels between meals. They have identified approximately 20 mutations in the gene GYS2 in people with glycogenosis type 0 which affects the liver. Most mutations result in a deficiency of functional glycogen synthase, which causes a complete absence of glycogen in liver cells. Normally, glycogen is formed from excess glucose is not used immediately by after ingested during meals cells. In people with GSD 0, which can not form glycogen, excess glucose is released by the body. As a result, those affected have no stored energy during fasting periods. During these periods, affected individuals may exhibit hypoglycemia and nausea, as well as other signs and symptoms of the disease.

This disease is inherited in an autosomal recessive pattern, that is, both copies of the gene in every cell must have mutations for alteration is expressed. The parents of an individual with an autosomal recessive disease have a copy of the mutated gene, but usually show no signs and symptoms of the disease.

Tests in IVAMI: in IVAMI perform detection of mutations associated with glycogen storage disease type 0, by complete PCR amplification of the exons of GYS1 and GYS2 genes, respectively, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).