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Also known as debrancher enzyme deficiency, GSD3a is a rare disease of variable severity affecting primarily the liver, heart and skeletal muscle.
Estimated cases diagnosed worldwide: <1,000.



Enlarged liver, low blood sugars with fasting, growth delayed during childhood. Muscle weakness, heart involvement.


Hyperlipidemia, osteoporosis, polycystic ovary syndrome.


Infancy, early childhood and adulthood.


Liver, heart, and skeletal muscle.


Regular feeding, including overnight, and management of associated conditions.


Variable depending on disease severity.

IAMGSD would welcome hearing from patients or doctors who could help us to improve and expand our information on this rare muscle GSD.


Helpful hints for living well with Cori disease, this book covers many practical topics including travel, financial help, diet and nutrition, exercise, the health service and aids for living. It is hoped people will use the tips to cope with the day-to-day challenges of living with GSD3.

This 124 page, pocket-sized paperback is published by AGSD-UK, but anyone may download a free PDF from their website.

ABOUT GSD3 and 3a

GSD3 is an inherited disorder that causes a buildup of glycogen in certain organs and tissues - especially in the liver and muscles. It is caused by mutations in the AGL gene and is inherited in an autosomal recessive manner. Symptoms typically present in infancy, but may occur in adulthood.  

Individuals with GSD3 vary remarkably depending on which sub-type they have - 3a, 3b, 3c and 3d.  GSD 3a is the most common type (85%) and affects both the liver and (cardiac and/or skeletal) muscles. GSD 3b affects about 15% of individuals, and only affects the liver.  GSD3c and 3d are extremely rare.


The primary features of GSD3a may include the following:

  • A swollen abdomen due to an enlarged liver.  This will shrink in size in adulthood, but liver cirrhosis or adenomas may then present as problems.

  • Muscle weakness is usually absent or minimal in childhood, but slowly progresses to become a more prominent feature in the third or fourth decade of life.

  • Exercise intolerance.

  • Problems maintaining blood sugar level.

  • Delay in growth.

  • Problems with the heart, such as cardiomyopathy, may occur, yet most individuals are unaffected.

  • High levels of fat in the blood (hyperlipidemia)

  • Osteoporosis

  • Polycystic ovary syndrome


GSD3 can be diagnosed though DNA analysis or liver and/or muscle biopsy. Through muscle biopsy, the pattern of glycogen debranching enzyme (GDE) deficiency in different tissues determines the specific subtype. Individuals with GSD3a have deficient enzyme activity in both liver and muscle. Nowadays, genetic testing is more commonly used to confirm diagnosis of GSD3.  


At present, the goal of treatment is to maintain normal blood sugar levels. This is achieved through a diet high in protein and cornstarch taken at frequent intervals.  Please refer to the American College of Medical Genetics (2010) guidelines for a more detailed overview.

ACMG management guidelines.

Another set of guidelines were prepared by a group led by Dr Terry Derks of the University of Groningen Medical Centre, The Netherlands, and published in the Journal of Inherited Metabolic Disease, April 2016; Volume 39 – pp697-704. The full text is available free of charge under open access.

Download PDF of guidelines 


The prognosis for individuals with GSD3a can be very varied according to the severity of symptoms presented.  


IamGSD shared an online global survey for GSD3 on our website. The survey has been finalized and much of the results are captured in this infographic. The flags represent the locations of the participants, with input from around the globe! The study was sponsored by Ultragenyx and operated by Endpoint Outcomes. 

Click on the infographic thumbnail at left to download a 20mb PDF of the survey report.


There is a Facebook “Private” group for people with all types of GSD3. There are members around the world, although largely from English speaking areas such as UK, North America and Australia. This is a peer-to-peer group of affected individuals and family members sharing their personal experiences related to GSD3.  The information shared in this group must not be used as a substitute for proper medical management. 

GSD3 Facebook group.

A German-language private Facebook group for
ketotic GSDs: types 0, 3, 6 and 9.


Dagli A, Sentner CP, Weinstein DA. Glycogen Storage Disease Type III. 2010 Mar 9 [Updated 2016 Dec 29]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2018.

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