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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Glycogen storage disease type III

Reviewed December 2014

What is glycogen storage disease type III?

Glycogen storage disease type III (also known as GSDIII or Cori disease) is an inherited disorder caused by the buildup of a complex sugar called glycogen in the body's cells. The accumulated glycogen is structurally abnormal and impairs the function of certain organs and tissues, especially the liver and muscles.

GSDIII is divided into types IIIa, IIIb, IIIc, and IIId, which are distinguished by their pattern of signs and symptoms. GSD types IIIa and IIIc mainly affect the liver and muscles, and GSD types IIIb and IIId typically affect only the liver. It is very difficult to distinguish between the types of GSDIII that affect the same tissues. GSD types IIIa and IIIb are the most common forms of this condition.

Beginning in infancy, individuals with any type of GSDIII may have low blood sugar (hypoglycemia), excess amounts of fats in the blood (hyperlipidemia), and elevated blood levels of liver enzymes. As they get older, children with this condition typically develop an enlarged liver (hepatomegaly). Liver size usually returns to normal during adolescence, but some affected individuals develop chronic liver disease (cirrhosis) and liver failure later in life. People with GSDIII often have slow growth because of their liver problems, which can lead to short stature. In a small percentage of people with GSDIII, noncancerous (benign) tumors called adenomas may form in the liver.

Individuals with GSDIIIa may develop muscle weakness (myopathy) later in life. These muscle problems can affect both heart (cardiac) muscle and the muscles that are used for movement (skeletal muscles). Muscle involvement varies greatly among affected individuals. The first signs and symptoms are typically poor muscle tone (hypotonia) and mild myopathy in early childhood. The myopathy may become severe by early to mid-adulthood. Some people with GSDIIIa have a weakened heart muscle (cardiomyopathy), but affected individuals usually do not experience heart failure. Other people affected with GSDIIIa have no cardiac muscle problems.

How common is glycogen storage disease type III?

The incidence of GSDIII in the United States is 1 in 100,000 individuals. This condition is seen more frequently in people of North African Jewish ancestry; in this population, 1 in 5,400 individuals are estimated to be affected.

GSDIIIa is the most common form of GSDIII, accounting for about 85 percent of all cases. GSDIIIb accounts for about 15 percent of cases. GSD types IIIc and IIId are very rare, and their signs and symptoms are poorly defined. Only a small number of affected individuals have been suspected to have GSD types IIIc and IIId.

What genes are related to glycogen storage disease type III?

Mutations in the AGL gene cause GSDIII. The AGL gene provides instructions for making the glycogen debranching enzyme. This enzyme is involved in the breakdown of glycogen, which is a major source of stored energy in the body. Between meals the body breaks down stores of energy, such as glycogen, to use for fuel.

Most AGL gene mutations lead to the production of a nonfunctional glycogen debranching enzyme. These mutations typically cause GSD types IIIa and IIIb. The mutations that cause GSD types IIIc and IIId are thought to lead to the production of an enzyme with reduced function. All AGL gene mutations lead to storage of abnormal, partially broken down glycogen molecules within cells. A buildup of abnormal glycogen damages organs and tissues throughout the body, particularly the liver and muscles, leading to the signs and symptoms of GSDIII.

Related Gene(s)

Changes in this gene are associated with glycogen storage disease type III.

  • AGL

How do people inherit glycogen storage disease type III?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of glycogen storage disease type III?

These resources address the diagnosis or management of glycogen storage disease type III and may include treatment providers.

  • Gene Review: Glycogen Storage Disease Type III (
  • Genetic Testing Registry: Glycogen storage disease type III (

You might also find information on the diagnosis or management of glycogen storage disease type III in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about glycogen storage disease type III?

You may find the following resources about glycogen storage disease type III helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for glycogen storage disease type III?

  • AGL deficiency
  • Cori disease
  • Cori's disease
  • debrancher deficiency
  • Forbes disease
  • glycogen debrancher deficiency
  • GSD3
  • limit dextrinosis

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about glycogen storage disease type III?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding glycogen storage disease type III?

autosomal ; autosomal recessive ; benign ; breakdown ; cardiac ; cardiomyopathy ; cell ; chronic ; cirrhosis ; deficiency ; enzyme ; gene ; glycogen ; heart failure ; hypoglycemia ; hypotonia ; incidence ; inherited ; liver failure ; muscle tone ; population ; recessive ; short stature ; stature

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Cheng A, Zhang M, Okubo M, Omichi K, Saltiel AR. Distinct mutations in the glycogen debranching enzyme found in glycogen storage disease type III lead to impairment in diverse cellular functions. Hum Mol Genet. 2009 Jun 1;18(11):2045-52. doi: 10.1093/hmg/ddp128. Epub 2009 Mar 19. (
  • Frisbie JH, O'Connell DJ, Tow DE, Sasahara AA, Belko JS. Autologous radioiodinated fibrinogen, simplified. J Nucl Med. 1975 May;16(5):393-401. (
  • Gene Review: Glycogen Storage Disease Type III (
  • Kishnani PS, Austin SL, Arn P, Bali DS, Boney A, Case LE, Chung WK, Desai DM, El-Gharbawy A, Haller R, Smit GP, Smith AD, Hobson-Webb LD, Wechsler SB, Weinstein DA, Watson MS; ACMG. Glycogen storage disease type III diagnosis and management guidelines. Genet Med. 2010 Jul;12(7):446-63. doi: 10.1097/GIM.0b013e3181e655b6. Erratum in: Genet Med. 2010 Sep;12(9):566. (
  • Lucchiari S, Pagliarani S, Salani S, Filocamo M, Di Rocco M, Melis D, Rodolico C, Musumeci O, Toscano A, Bresolin N, Comi GP. Hepatic and neuromuscular forms of glycogenosis type III: nine mutations in AGL. Hum Mutat. 2006 Jun;27(6):600-1. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: December 2014
Published: February 8, 2016