MCARDLE DISEASE FAQs
We are developing a list of answers to your questions. We aim for each answer to be succinct, or we will direct you to other pages or resources.
Please bear in mind that our answers have to be in general terms for the typical person with McArdle’s.
The FAQs are only available in English at this time.
Select a subject, then click on a question.
What is the baseline level of Creatine Kinase (CK) in people with McArdle’s?
Several papers have reported that the average basal level (i.e. baseline, with no particular injury) is approx. 2,400 iu/L. That compares to the usually quoted normal range of up to 190 iu/L. (Be aware that some countries report in different units.)
Are liver enzymes raised in McArdle disease?
The enzymes ALT and AST are routinely moderately raised in people with McArdle’s. Although called liver enzymes, they are also released when muscle is damaged. If other liver enzymes are raised these should be investigated.
What causes the dark red/brown urine?
This may show up when you either do a lot of damage in a large muscle group, or less damage but in many muscles at the same time. It is called myoglobinuria (myo = muscle, globin = a red coloured protein, uria = urine). (Myoglobin should not be confused with haemoglobin, which is also red-colored, in blood.) Myoglobin is released from muscle into the blood when the muscle is damaged. Large amounts of myoglobin reaching the kidneys can cause damage and block them. If that happens it causes acute renal failure (a.k.a. acute kidney injury – AKI) and is a medical emergency. It is a very good idea to learn to manage activity well, so as to avoid such episodes of severe injury.
Who discovered McArdle disease?
It was Dr Brian McArdle, who published a paper in 1951 describing a man with what we now know of as McArdle disease or Glycogen Storage Disease type 5.
Is there a treatment for McArdle disease?
The best treatment at present is to improve aerobic fitness of our muscles by regular exercise within our limits. Many people can also benefit from strengt training to build muscle mass. Both these approaches should ideally be guided by an experienced physiotherapist. There is as yet no medical treatment.
What research is going on into McArdle disease?
This web site has a top menu item for “Research” where you will find details of past and present research projects. Go to our “Current research” page for details of current trials, and a link to the web site “ClinicalTrials.gov” where you can search a list of relevant clinical trials.
How is McArdle disease diagnosed?
Once McArdle’s is suspected the usual way is genetic testing (a DNA test). Before this you may have a CK blood test, a forearm exercise test to look for a failure of lactate to rise, or an exercise test for “second wind”. Only rarely these days is a muscle biopsy performed.
How many people have McArdle disease?
As of 2020 we believe that approx. 4,000 to 5,000 people are diagnosed around the world. However, the number still undiagnosed may be very much greater. If the current best estimate of 1 in every 100,000 people being affected is correct, there may be about 75,000 cases worldwide. However, very many of those may never get diagnosed.
Why is McArdle’s referred to as an “ultra rare” disease?
In the US a rare disease is defined as one affecting only 1 person in 1,500. In the European Union it is 1 in 2,000. A study in the Dallas Fort Worth area estimated that 1 person in 100,000 has McArdle’s. We don't know of any country which has diagnosed to that level, most are near 1 in 200,000. One paper proposed that the true incidence might be nearer 1 in 40,000. So it seems that McArdle's is about 20 to 100 times as rare as a “rare disease”.
What are the types of DNA/genetic testing used in McArdle’s?
What are the different names for McArdle disease?
• Myophosphoryalse deficiency.
• Muscle phosphorylase deficiency. (Myo = muscle.)
How is McArdle disease inherited?
The inheritance pattern is autosomal recessive. This means that the person inherits two copies of the PYGM gene with a causative mutation in it, one from their father and one from their mother. The parents will normally be carriers, having no symptoms themselves, in which case there is a 25% risk of each child inheriting the condition. If one parent actually has the condition and the other parent is a carrier, then the risk is 50%.
Is McArdle disease progressive?
The condition itself is not progressive.
Is there some information I can give to my family doctor/GP?
There is a booklet specially created for this purpose, the 20 page “Medical Overview”. We suggest you give a copy to your doctor, and have a copy with you whenever you see any specialist about other medical conditions. I gives them a quick overview of McArdle’s and is structured to direct them to the key points that they need. You and your doctor can read the booklet on-line or download a PDF. Go to Medical Overview.
Is it possible to build muscle mass and strength?
Contrary to earlier beliefs, it has now been shown that resistance training (weight lifting) in people with McArdle disease is possible, with care and preferably under the supervision of a physiotherapist or personal trainer experienced with McArdle disease.
The principle is to utilise the immediate ATP energy and the phosphocreatine system in the muscle cell to undertake a brief session, lasting around 6 to 10 seconds. You must then rest to recover these systems in about 3 minutes, but during that time you can move on to exercise other muscle groups, then return to the first group.
Please refer to these papers in our Research section:
• Feasibility of resistance training in adult McArdle patients: clinical outcomes and muscle strength and mass benefits
• Case Report: Resistance Exercise Training in McArdle Disease: Myth or Reality?
When do I need to seek medical attention?
Please go to our page on Medical Emergencies. You will see the blue section which provides guidance on when to seek medical attention.
What is rhabdomyolysis?
• Rhabdomyolysis is a medical term for muscle breakdown. When muscle is damaged it releases breakdown products into the bloodstream. This can be caused by a range of medical conditions including McArdle disease, but can also be caused by excessive exercise, crush inuries, severe dehydration, drug use, etc.
• McArdle patients who have learnt to manage well are likely to never be aware of rhabdomyolysis or myoglobinuria, unless they get caught out by circumstances forcing them to do something that they would normally avoid (e.g. running from danger).
What is a fixed contracture?
What is compartment syndrome?
In a very small number of people something called “compartment syndrome” has developed. This is caused by muscle swelling which leads to increased pressure within the fascia (strong membrane) around the affected muscle group. If left untreated it can permanently damage the muscle and affect the circulation. Surgical intervention is usually required to relieve the pressure with the fascia.
What is the path of recovery from rhabdomyolysis?
Depending on the level of muscle damage caused, after being discharged from medical care you need to have at least a few days rest and not use the damaged muscle very much until it feels fully recovered. For a while you are likely to be at increased risk of a repeat episode.
As long as you seek prompt attention for an episode, especially if you have acute renal failure, there is every reason to expect a full recovery. Kidney function usually returns to normal once the by-products of muscle breakdown have been flushed through.