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About Muscle GSD
There are over a dozen forms of glycogen storage disease (GSD), and a number of sub-forms, that can affect skeletal muscle, the liver, or the heart. We are concerned with ones that affect skeletal muscle.
Slow and steady walking on the level.

Slow and steady all the way.

Taking a rest on a walking course.

Taking a rest, even on the flat.

Looking back at a level route.

A level route on an old railway.


Please note that there are differences between various sources in regard to the numbering and naming of GSDs, especially the ultra rare diseases.

Scheme of glycogen metabolism and glycolysis.

Scheme of glycogen metabolism and glycolysis.
Roman numerals denote muscle glycogenoses due to defects in the following enzymes:
II, acid α-glucosidase (AAG);
III, debrancher;
IV, brancher;

V, myophosphorylase;
VI, liver phosphorylase;
VII, muscle phosphofructokinase (PFK);
VIII, phosphorylase b kinase (PHK);
IX, phosphoglycerate kinase (PGK);
X, phosphoglycerate mutase (PGAM);
XI, lactate dehydrogenase (LDH);
XII, aldolase;
XIII, β-enolase;
XIV, triosephosphate isomerase (TPI).

  • Symbols in regular typeface denote glycogenoses characterized by physical activity intolerance, cramps, and myoglobinuria.

  • Symbols in italics denote glycogenoses characterized by fixed weakness.

Acta Myol. 2011 Oct;30(2):96-102.
Progress and problems in muscle glycogenoses.
DiMauro S, Spiegel R.


Our bodies require energy to perform day-to-day activities. To create this energy, our bodies use carbohydrates, fats, and protein. When we eat carbohydrates, our body breaks them down into glucose for energy. Any extra glucose is then converted to GLYCOGEN and stored in our skeletal muscles (80% of the body‘s carbohydrate reserve) and liver (20%). This stored fuel (glycogen) is then used for energy in in the skeletal muscles throughout our bodies.


GSDs are caused by a genetic defect that is inherited from one or both parents. Individuals with a GSD either have an absence or deficiency of one of the enzymes that are responsible for making, storing or using glycogen. 


Since glycogen is mainly stored in the muscles, liver or both, GSDs usually affect functioning in these areas, with some GSDs also affecting the heart. In general, symptoms of muscle GSD may include: muscle cramps, physical activity/exercise intolerance, and progressive weakness. Liver GSDs may result in an enlarged liver and low blood sugar. Onset, symptoms and severity vary depending on the type of GSD.  


At present there are around 20 distinct forms of GSD, split approximately half and half between liver and muscle GSDs. Some GSDs have several sub-forms.


Early diagnosis of muscle GSD is important to ensure proper clinical management. Unfortunately, some GSDs are considered ultra-rare with only a handful of diagnosed cases worldwide. We encourage patients with a GSD to get involved with national and international patient groups for support and information.


As more information about the natural history of muscle GSDs is gathered, future generations of people with these conditions will hopefully benefit from early diagnosis (especially with the help of genetic testing using Next Generation Sequencing), access to well-informed clinical management, and eventually an effective treatment or even a cure. As techniques of gene therapy become established, it may be that this approach will become available for even ultra-rare conditions such as muscle GSDs.

The GSDs we cover


IamGSD is focused on “McArdle Disease and related disorders of muscle glycogen where physical activity intolerance is the major symptom.” 
Our commitment is to help the worst affected.

From those severely affected to those who are high achieving –
IamGSD is here for everyone.


With IamGSD's Objectives, we will one day see everyone with a muscle GSD:

  • Obtain an early  diagnosis

  • Receive good advice

  • Access expert support, and

  • Achieve an excellent quality of life.

We support people to the highest functionality.

With more people diagnosed with McArdle disease than all the other muscle GSDs put together, that GSD is our primary focus. We are learning more about the other muscle GSDs and improving our coverage.

If you would like to contribute to our knowledge, or improve our offerings for a specific GSD, please send us a note via our contact form.

GSD2, Pompe Disease, is also a lysosomal disorder. It is rather different to other muscle GSDs.  We defer to the long established International Pompe Association.

This table is available only in English.
Interested in another muscle GSD?
We will be happy to include further muscle GSDs within our remit as and when they are reported to us.
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