• Disease Overview
  • Synonyms
  • Signs & Symptoms
  • Causes
  • Affected Populations
  • Disorders with Similar Symptoms
  • Diagnosis
  • Standard Therapies
  • Clinical Trials and Studies
  • References
  • Programs & Resources
  • Complete Report

Glycogen Storage Disease Type III


Last updated: October 12, 2017
Years published: 1987, 1990, 1991, 2003, 2007, 2017


NORD gratefully acknowledges Terry G. J. Derks, MD, PhD, and Irene Hoogeveen, MD/PhD-student, Section of Metabolic Diseases, Beatrix Childrens’ Hospital, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands, and Matthew Kruchten, NORD Editorial Intern from the University of Notre Dame, for assistance in the preparation of this report.

Disease Overview


The human diet contains 3 macronutrients that can be stored by the body as energy: carbohydrates (as the natural carbohydrate polymer glycogen, in mainly the liver and muscle), protein (as muscle, the natural protein source of the body) and fat (in organs and fat tissue). There are at least 13 glycogen storage disease (GSD) subtypes, in which the energy stored as glycogen cannot be adequately produced or broken down. The liver GSD subtypes cause fasting intolerance (types 0, Ia, Ib, III, VI, IX and XI) or liver failure (type IV), with or without muscle symptoms. The fasting induced low blood glucose concentrations decrease the energy supply by the liver to organs like the brain.

The ketotic GSD subtypes 0, III, VI, IX, and XI are associated with fasting ketotic hypoglycemia. In these patients, the breakdown of glycogen (glycogenolysis) is defective. Their fasting intolerance is considered relatively mild compared to GSD type I patients, in whom both glycogenolysis and the generation of glucose from non-carbohydrate substances (gluconeogenesis) are impaired.


The first patient with GSD type III (GSD-III) was described in 1928 by the Dutch pediatrician Simon van Creveld. He described a 7-year-old boy with marked enlarged liver, obesity and small genitals. The fasting blood glucose concentration appeared to be very low, and concentrations of ketone bodies in urine were high. Based on additional investigations in the patient, Dr Van Creveld concluded that the body increasingly burned fat, resulted from “insufficient mobilization of glycogen”.

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  • amylo-1,6-glucosidase deficiency
  • Cori disease
  • AGL deficiency
  • glycogenosis type III
  • Forbes disease
  • limited dextrinosis
  • GDE deficiency
  • glycogen debrancher deficiency
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Signs & Symptoms

The median age at the first clinical presentations is in the first year of life. Most common presenting symptoms are enlarged liver (hepatomegaly) (98%), low blood sugar (hypoglycemia) (53%), failure to thrive (49%) and recurrent illness and/or infections (17%). Symptoms and signs of GSD-III, at least during the first 4 to 6 years of life, may be indistinguishable from GSD type I. The amount of glycogen in the liver and muscles is abnormally high, the liver is enlarged, and the abdomen protrudes. The muscles tend to be flaccid or weak.

A typical child with GSD-III has short stature, low blood sugar after fasting that does not respond to the hormone glucagon, and an elevated level of fatty substances in the blood, known as hyperlipidemia. Hypoglycemia is usually associated with increased ketone bodies, and ketonemia can precede hypoglycemia, reflecting activation of burning fat stores. Patients with GSD-III may also have difficulty fighting infections, and may experience unusually frequent nosebleeds. Enlarged heart muscle (cardiac hypertrophy) is common in individuals with GSD-IIIa and can already appear in early childhood. However, in most children, heart function remains within normal limits. Children with GSD-III often grow slowly during childhood and puberty may be delayed, but their adult height is usually normal. Most signs and symptoms improve significantly with adequate dietary management.

In adulthood, the liver manifestations of the disease usually subside, but progression to liver scarring (cirrhosis) and malignancy (carcinoma) may occur. Despite dietary management, muscle disease can get worse. As the cohort of adult GSD-III patients is still relatively young and small, the course of the disease over time is incompletely described.

Some affected individuals may have virtually no symptoms (asymptomatic) other than a protruding abdomen and an enlarged liver in childhood. These patients tend to lose these few symptoms during adolescence when their liver decreases progressively in size.


There are four subtypes of GSD-III:

GSD-IIIa is the most common type, affecting 85%, and affects both the liver and (cardiac and/or skeletal) muscles.

GSD-IIIb affects about 15% of individuals and only affects the liver. AGL molecular testing can display mutations specific to GSD-IIIb.

GSD-IIIc is extremely rare and believed to be caused by loss of activity of the glucosidase active site of the glycogen debranching enzyme.

GSD-IIId is extremely rare and believed to be caused by loss of activity of the transferase active site of the glycogen debranching enzyme.

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GSD-III is an inborn error of metabolism caused by mutations in the AGL gene that is located on chromosome 1p21. The AGL gene is responsible for the production of the debranching enzyme.

Glycogen is stored in the liver and muscles for future energy needs. Glycogen can then be converted into sugar (glucose). Glucose is used as a readily available source of energy during fasting or exercise. The debranching enzyme has two active (catalytic) sites called amylo-1,6-glucosidase and 4-alpha-glucanotransferase. Both sites on the enzyme are together with the phosphorylase and phosphorylase kinase enzymes (impaired in GSD types VI and IX, respectively) responsible for breaking down glycogen to raise the blood sugar concentration. Without normal debranching enzyme function, two changes take place. If glycogen can only be broken down partially, an insufficient amount of energy/glucose can be produced. The structure that is left, resembling a molecule called a “limit dextrin”, is excessively stored in liver, and (skeletal and cardiac) muscle tissues.


GSD-III is a genetic disorder characterized by variable liver, cardiac muscle and skeletal muscle abnormalities. Symptoms are associated with abnormalities in the AGL gene, causing deficiency of the glycogen debranching enzyme. GSD-III is inherited as an autosomal recessive trait.

Recessive genetic disorders occur when an individual inherits two copies of an altered gene for the same trait, one from each parent. If an individual inherits one normal gene and one gene for the disease, the person will be a carrier for the disease but usually will not show symptoms. The risk for two carrier parents to both pass the altered gene and have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents is 25%. The risk is the same for males and females.

All individuals carry mutations/variants in ± 4-5 genes. Parents who are close relatives (consanguineous) or who originate from closed communities have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

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Affected populations

All glycogen storage diseases together affect fewer than 1 in 40,000 persons in the United States. GSD-III has an incidence of about 1 in 100,000. The incidence of GSD-III is higher in North African Jews (± 1 in 5,400), Faroese (± 1 in 3,100) and the Inuit population in Nunavik, Canada (± 1 in 2,500).

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An enlarged liver and low blood sugar with high levels of ketones, transaminases, lipids and creatine kinase is indicative of GSD-III. Uric acid and fasting lactic acid levels are usually normal. In GSD-IIIb creatine kinase can be normal. Molecular genetic testing for mutations in the AGL gene can be used to confirm the diagnosis. Nowadays, liver and muscle biopsies are uncommon. In many countries besides the United States, studies in blood cells and skin fibroblasts are clinically available to confirm GDE deficiency.

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Standard Therapies


Dietary management is the cornerstone.

  • Infants and children with GSD-III are treated with a high-protein diet every 3-4 hours. The recommended daily amount of protein is ± 3-4 grams per kg bodyweight per day and should be well divided during the day. Cornstarch may already be introduced in the first year of life. This is a dietary complex starch like glycogen and the dose/frequency of supplementation is titrated to maintain normoglycemia. Although fructose and galactose can be metabolized, the (extend of) restrictions of so-called simple/fast carbohydrates is a matter of debate. These simple sugars include glucose, galactose (dairy sugar), lactose (galactose + glucose), fructose (fruit sugar), sucrose (fructose + glucose) and maltodextrin. The latter is frequently used as a food additive and typically a mixture of 3-17 glucose units. Special formulas are not required. Fasting should be avoided and for the overnight fast, (a combination of) a bedtime snack, frequent feeds, cornstarch, and/or continuous nocturnal gastric drip feeding may be needed.
  • Adolescents and adults have lower basic carbohydrate requirements. The recommended daily amount of protein is ± 25 % of the total caloric intake. A bedtime snack or an overnight high protein formula may be prescribed for patients with myopathy.
  • Good dietary control includes at home monitoring of blood glucose and ketones. Based on clinical observations, it is believed that the diet can prevent or resolve heart and/or muscle disease.
  • The role of and indications for ketogenic diets (and variations, including Atkins diet) and medium chain triglycerides (MCT) oil are debatable and deserve further, systematic research.

Liver transplantation is indicated only for patients with severe hepatic cirrhosis, liver dysfunction and /or liver cancer (hepatocellular carcinoma).

Clinical Testing and Follow-Up

Emergency letters should be provided and shared care with local physicians should be organized. Liver ultrasound and baseline heart tests (electrocardiogram and echocardiograms) are usually recommended to determine the medical needs for individual patients based on the severity of the condition.

Genetic counseling is recommended for families of children with glycogen storage diseases.

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Clinical Trials and Studies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov.  All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

Some current clinical trials also are posted on the following page on the NORD website:


For information about clinical trials sponsored by private sources, contact:

For information about clinical trials conducted in Europe, contact:

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Weinstein DA, Koeberl DD, Wolfsdorf JI. Type III Glycogen Storage Disease. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:453.

Chen YT, Burchell A. Glycogen Storage Diseases. In: Scriver CR, Beaudet AL, Sly WS, et al. Eds. The Metabolic Molecular Basis of Inherited Disease. 7th ed. McGraw-Hill Companies. New York, NY; 1995:935-65.

Greene HL. Glycogen Storage Diseases. In: Bennett JC, Plum F. Eds. Cecil Textbook of Medicine. 20th ed. W.B. Saunders Co., Philadelphia, PA; 1996:1082-83.

Sentner CP, Hoogeveen IJ, Weinstein DA, et al. Glycogen storage disease type III: diagnosis, genotype, management, clinical course and outcome. Journal of Inherited Metabolic Disease. 2016;39:697-704. doi:10.1007/s10545-016-9932-2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987401/

Hoogeveen IJ, van der Ende RM, van Spronsen FJ, et al. Normoglycemic Ketonemia as Biochemical Presentation in Ketotic Glycogen Storage Disease. JIMD Rep. 2016;28:41-47. https://www.ncbi.nlm.nih.gov/pubmed/26526422

Kishnani PS, Austin SL Arn P, et al. Glycogen storage disease type III diagnosis and management guidelines. Genet Med. 2010 Jul;12(7):446-63. doi: 10.1097/GIM.0b013e3181e655b6. https://www.ncbi.nlm.nih.gov/pubmed/20631546

Lucchiari, S., et al. Clinical, biochemical and genetic features of glycogen debranching enzyme deficiency. Acta Myologica 2007;26.1:72.

Endo Y, Horinishi A, Vorgerd M, et al. Molecular analysis of the AGL gene: heterogeneity of mutations in patients with glycogen storage disease type III from Germany, Canada, Afghanistan, Iran, and Turkey. J Hum Genet. 2006;51(11):958-63. Epub 2006 Sep 19.

Lucchiari S, Donati MA, Parini R, et al. Molecular characterization and identification of six novel mutations in AGL. Hum Mutat. 2002;20:480.

Dagli A, Sentner CP, Weinstein DA. Glycogen Storage Disease Type III. 2010 Mar 9 [Updated 2016 Dec 29]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26372/ Accessed October 11, 2017.

Tegay DH. Genetics of Glycogen-Storage Disease Type III. Medscape. Updated: Oct 24, 2014. Available at: http://emedicine.medscape.com/article/942618-overview. Accessed October 11, 2017.

McKusick VA, Ed. Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University.Glycogen Storage Disease III. Entry Number; 232400Available at: http://omim.org/entry/232400 Last Edit Date: 08/04/2016. Accessed October 11, 2017.

Parent/Patient Organizations

Belgium – Association Belge BOKS

France – Association Francophone des Glycogénoses

Germany – Selbsthilfegruppe Glykogenose Deutchland e.V.

Italy – Associazione Italiana Glicogenosi

Latin-America – Comunidad Latinoamericana de Glucogenosis Hepáticas

Spain – Asociacion Española de Enfermos de Glucogenosis (A.E.E.G)

Scandinavia – Scandinavian Association for Glycogen Storage Diseases (SAGSD)

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Patient Organizations

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