You too sometimes feel sore and weak when you exercise or do something that requires a little effort, right? That's normal. But for some people, this condition is a bit too much. Even doing something small makes you tired quickly, and your muscles become sore and tight. Today we are going to talk about a rare but very important condition to be aware of. This is called McArdle's disease, or `glycogen storage disease type 5 (GSD5)`.
What is McArdle Disease?
Simply put, McArdle's disease is a genetic condition that runs in our families . It mainly affects your skeletal muscles . That is, the muscles we use to move around, lift things, and walk.
This disease is caused by a deficiency or complete absence of a special enzyme in our muscles called `muscle glycogen phosphorylase` or `myophosphorylase`. When this enzyme is completely absent, our muscles are unable to produce the necessary energy. That is why symptoms such as muscle pain, stiffness, and fatigue appear during exercise or when we are tired.
Symptoms usually begin to appear after the age of 15-20, or in the 20s or 30s . However, it can sometimes appear at any age. The disease is named "McArdle" after Dr. Brian McArdle, who first reported it in 1951.
How common is this disease?
McArdle disease is actually a very rare condition . According to researchers, it affects between one in 50,000 and one in 200,000 people in the United States.
What are the symptoms?
The symptoms of this disease can vary greatly from person to person. Some people may experience very mild symptoms, while others may be more severely affected.
The main and most common symptom is exercise intolerance, which means feeling tired quickly when doing physical activity . Other symptoms are:
- Muscle cramps
- Weakness
- Fatigue
- Muscle pain
- Muscle stiffness
All of these symptoms can appear as soon as you start exercising. But they usually subside after a short rest . Surprisingly, some people find that after initially feeling tired, if they take a short rest and then do the same exercise again, they can do it better than before. This is called a "second wind." It's like having a second wind. When you don't exercise, you usually don't feel any symptoms.
You may be able to do light, gentle exercise, such as walking on level ground, without any problems. However, strenuous physical activity can quickly cause symptoms. In particular, exercises that involve holding the muscles in place without moving, such as isometric exercises , squatting, and standing on your toes, can damage the muscles. Think of the discomfort you feel when lifting a gas cylinder or carrying a heavy bag.
Can this cause serious problems? (Complications)
Yes, sometimes serious problems can occur. About half of people with McArdle disease develop a condition called `rhabdomyolysis` after intense exercise . This is when the muscles break down.
Rhabdomyolysis is a serious, life-threatening condition that can lead to sudden kidney failure (acute kidney failure) and dangerously high levels of potassium in the blood (hyperkalemia).
Therefore, you need to be very careful about how much and how hard you exercise. This will help prevent the condition `rhabdomyolysis`. If you experience any symptoms such as muscle swelling, dark urine (brown, red, tea-colored) , you should seek medical advice immediately .
Why is this happening? What are the reasons for this?
McArdle disease is a genetic condition . Specifically, it is caused by mutations in the gene `PYGM`. Normally, this `PYGM` gene instructs our body to make an enzyme called `myophosphorylase`.
This enzyme is only found in our skeletal muscle cells. It breaks down glycogen (stored sugar) in the muscles into glucose-1-phosphate. This glucose-1-phosphate is then further converted into glucose. Glucose is our body's main source of energy . When we exercise, our muscles use a lot of this glucose.
Now, when the `myophosphorylase` enzyme is produced less or not at all due to changes in the `PYGM` gene, our muscle cells are unable to properly break down `glycogen` and produce energy (`glucose`). That's why the muscles get tired quickly.
Researchers have so far identified 179 different variations (variants) affecting the `PYGM` gene.
How McArdle disease is inherited
You inherit the disease from your biological parents, in an ``autosomal recessive`` pattern . Simply put, both parents must be ``carriers`` of the altered gene, meaning they both have the gene . Carriers usually do not show symptoms. However, if both parents are carriers and pass the altered gene on to their children, the disease will develop.
How do doctors diagnose this? (Diagnosis)
Doctors mainly use a forearm exercise test to diagnose this disease. This involves taking blood samples before and after you do a small amount of exercise with your forearm. Specifically, they look at the levels of `lactic acid` and `ammonia` .
Normally, lactic acid levels should increase by about three times after exercise. However, if your lactic acid levels are not elevated in this test, it is a sign that you may have McArdle's disease.
There are other tests that can help confirm this disease:
- Creatine kinase (CK) blood test: When muscles are damaged, an enzyme called creatine kinase (CK) builds up in the blood. People with McArdle's disease may have consistently high levels of CK.
- Graded exercise stress test: This can test for the phenomenon known as "second wind." The doctor will have you do a few rounds of exercise, rest in between, and see if you can do the exercise well after the rest.
- Muscle biopsy: In this test, a doctor takes a small sample of your skeletal muscle and sends it to a lab to be looked at under a microscope. A pathologist looks at the tissue to see if there are any signs of McArdle disease.
- Genetic testing: This may be able to identify the specific genetic mutation that causes McArdle disease.
What can we do about this? (Treatment)
Unfortunately, there is no cure for McArdle's disease. The main treatment is to avoid activities that aggravate your symptoms. However, not doing any physical activity at all is not good for your health either.
Research has shown that moderate-intensity, graded aerobic exercise therapy can be beneficial for people with McArdle disease. People who do this type of exercise have significantly reduced exercise intolerance, and they can also experience that "second wind" more quickly during exercise. You can work with your doctor and a physical therapist to find the best exercise therapy plan for you.
Studies also show that eating a diet high in carbohydrates can help reduce the severity of symptoms during exercise. This helps your muscles use glucose (sugar) in your blood for energy instead of glycogen. Your doctor or a registered dietitian can recommend a meal plan like this:
- 65% of your daily calories should come from complex carbohydrates (from things like vegetables, fruits, bread, pasta, and rice).
- 20% of calories from fat .
- 15% of calories from protein .
It can also be helpful to consume a simple sugar, such as a sugary sports drink, shortly before exercising.
How is it to live with this?
Most people with McArdle disease live normal lives . Some people may experience persistent weakness and muscle wasting (`atrophy`) later in life, usually in their 60s or 70s.
The most important thing is to be aware of the symptoms of the aforementioned `rhabdomyolysis` condition and to prevent it from occurring as much as possible, as it is the main complication of this disease.
What is the life expectancy of someone with this disease?
McArdle disease usually does not affect lifespan .
However, very rarely, there is a condition called `infantile McArdle syndrome` , which appears almost immediately after birth. This is fatal – the symptoms are severe and get worse quickly.
Can McArdle's disease be prevented?
Since this is a genetic condition, there is nothing we can do to prevent it .
If you are concerned about your risk of inheriting McArdle disease or other genetic disorders before you have a child, it is a good idea to talk to your doctor about genetic counseling .
When should I see a doctor?
If your symptoms get worse, or if your ability to do your usual physical activities changes, see your doctor.
You may also need to see a physical therapist and/or nutritionist regularly for guidance on your treatment plan.
When should you go to an Emergency Treatment Unit (ETU) ?
If you have symptoms of `rhabdomyolysis`, you should go to an emergency room (ETU) as soon as possible . The symptoms are:
- Muscle swelling
- Muscle weakness
- Soreness and pain when touching the muscles
- Dark urine (brown, red, tea-colored)
- Dehydration
- Decreased urination
- Nausea
- Loss of consciousness
McArdle disease can make it difficult to do some physical activities. But the good news is that it can be managed and doesn't have a major impact on your overall health. Your doctor will work with you to find the best treatment plan for you.
Take-Home Message
Okay, so let's remind you of a few things we've talked about that we think are important to you:
McArdle disease is a genetic condition caused by a deficiency of an enzyme that helps muscles produce energy.
The main symptoms are getting tired quickly, muscle pain, and rolling over when exercising.
Be aware of the serious complication called `rhabdomyolysis`. If you experience these symptoms, see a doctor immediately.
Although there is no specific cure for this, it can be managed well with appropriate exercise and diet and you can live a normal life.
If you have any further questions about this, don't hesitate to talk to your doctor.
Remember, you are not alone. With the right knowledge and support, you can cope with this situation.
` McArdle Disease, GSD5, McArdle Disease, Muscle Pain, Exercise, Genetic Disease, Glycogen, Myophosphorylase, Rhabdomyolysis, Exercise Intolerance
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