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About the conditions

McArdle Disease is an inherited muscle condition. It is also known as Glycogen Storage Disease Type V or myophosphorylase deficiency. 


sobre la enfermedad   McArdle Disease is an inherited muscle condition. It is also known as Glycogen Storage Disease Type V or myophosphorylase deficiency. People with this condition are missing an enzyme called myophosphorylase that is necessary to convert carbohydrate stored as glycogen in the muscle cells back into glucose to use for energy. This results in a significant shortage of energy at the start of activity and throughout all intense activity. This leads to fatigue, pain and cramping. 


If activity is continued in the presence of pain, it develops into muscle breakdown that can lead to serious complications, such as acute kidney failure and compartment syndrome in the affected muscle/s. 


It is thought that approx. 3,000 cases may have been diagnosed worldwide, and it is estimated that there may be twice as many again who have never managed to obtain a diagnosis. Altogether the prevalence may be 1 in 100,000 people. It is thought that a similar number of people may be affected by all the other related conditions combined.



Children and their parents are typically aware of symptoms from age about 5, but the average delay before diagnosis is achieved is about 20 to 25 years. Children get labeled as lazy, unfit, malingerers, etc, and they frequently have a hard time at school. It often takes a severe episode resulting in hospitalisation with rhabdomyolysis (muscle breakdown) before the problems are fully investigated and a diagnosis achieved.



If there is pain on activity, which resolves quickly if the activity is paused on the onset of symptoms, and if a blood test reveals a raised level of Creatine Kinase, then this is highly suggestive of McArdle Disease. Many cases can now be diagnosed by DNA analysis. About 150 different mutations of the PYGM gene on chromosome 11 have been identified so far. A small number of these are very common. If necessary, a muscle biopsy is conducted, as it can reveal the lack of the enzyme and usually an excess of glycogen.
Early diagnosis is a great help in that people can then learn to manage their condition and make suitable choices about lifestyle, employment and activity levels.


Degrees affected

Some people are severely restricted in their daily lives whilst others find their condition to be just a minor inconvenience. If people avoid activity and exercise due to the cramping and pain, they will risk muscle wasting, which results in even more severe problems. Conversely, if people push themselves too hard, they may accumulate muscle damage in the long term, which will also result in severe problems. Other medical issues, such as diabetes or heart disease, can complicate the situation and make symptoms worse and management more difficult.



There is no cure for McArdle Disease and to date no drug treatment. Improving aerobic fitness through regular gentle exercise is generally accepted as the most appropriate treatment. Diet is still controversial, with some people doing better on a higher than normal amount of carbohydrate in their diet whilst others report being better on a higher amount of protein. A sugary drink before planned activity may be helpful, but this must be limited in use due to the risks of weight gain and diabetes. It is hoped that research will lead to improved treatments becoming available in the future. There are a number of interesting lines of investigation.



At present the, best approach is to:

  • Learn how to adapt activity to reduce risks;

  • Get to know the signals from the muscles telling you when to slow down or pause what you are doing;
Increase aerobic fitness;

  • Avoid becoming overweight.

People with McArdle Disease can be assisted by medical professionals such as neuromuscular consultants, physiotherapists, dieticians and psychologists. They can also gain from contact with other people with the condition and with support groups.




We are researchers in the field of neuromuscular disorders who investigate, at the clinical and research level, on glycogen storage disease type V (GSD V) (OMIM® number 232600), also known as McArdle Disease and other related ultra-rare muscle glycogenoses. We represent twenty institutes from across Europe, plus Turkey and the US, which make up the founding consortium of EUROMAC.


The aim of the project is to identify as many patients as possible across all European countries and to collect important clinical and epidemiological data. We hope to create the largest international cohort of people with such rare conditions


You will receive news of EUROMAC’s work and reports of any studies and trials undertaken by partner institutes based on information from the registry.


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