Glycogen Storage Disease IV (GSD IV), also known as Andersen Disease, is a type of glycogen storage disease. Unlike other GSDs, GSD IV is not characterized by excessive amount of normal glycogen in the body tissues. Instead, this condition is typified by accumulation of abnormal glycogen with very long outer branches, which resemble amylopectin. GSD IV is characterized by progressive hepatic scarring or cirrhosis, and hepatic failure. The disorder is severe and starts off usually in infancy. Initial features of the condition may be a failure to thrive, as well as hepatosplenomegaly. There is also a rarer neuromuscular form of the disease, which shows varying degrees of severity.

GSD IV is caused by mutations in the gene encoding the glycogen branching enzyme, GBE1. Mutations in this gene result in the production of abnormal glycogen with fewer branch points and longer alpha 1-4 linked polymers. This abnormal glycogen is recognized as foreign by the body's immune system, which attacks the hepatic and muscle tissues in which it is stored. This autoimmune reaction is what leads to the characteristic scarring seen in these tissues, and the features of the disease are a result of this scarring process.