Glycogen storage disease type IV is a rare hereditarymetabolic disorder. It is the result of a mutation in GBE1 gene, which causes a defect in the glycogen branching enzyme. Therefore, glycogen is not made properly and abnormal glycogen cells accumulate in cells; most severely in cardiac and muscle cells. The severity of this disease varies on the amount of enzyme produced. Glycogen Storage Disease Type IV is autosomal recessive, which means each parent has a mutant copy of the gene but show no symptoms of the disease.
It is a result of the absence of the glycogen branching enzyme amylo-1,4-1,6 transglucosidase, which is critical in the production of glycogen. This leads to very long unbranched glucose chains being stored in glycogen. The long unbranched molecules have a low solubility which leads to glycogen precipitation in the liver. These deposits subsequently build up in the body tissue, especially the heart and liver. The probable end result is cirrhosis and death within 5 years. In adults, the activity of the enzyme is higher and symptoms do not appear until later in life.