A rare genetic condition that causes you to get easily tired during physical activity is called McArdle disease. It also causes muscle-related symptoms and cannot be cured. However, doctors may help manage it with specific types of physical activity and dietary changes.
In other words, McArdle disease is an inherited disorder that negatively affects the skeletal muscles. Sometimes, it is called glycogen storage disease type 5 (GSD5). It occurs when a person has a deficiency of an enzyme known as muscle glycogen phosphorylase (myophosphorylase). As a result, the affected person begins to experience symptoms such as painful muscle cramps and weakness (especially during physical activity).
Usually, McArdle disease affects teens, 20s, or 30s. It may also develop later in life. The name of this condition is the name of the health care professional (Dr. Brian McArdle) who first reported it in 1951.
In general, this is a rare condition that affects about 1 in 50,000 to 200,000 people in the U.S.
Symptoms
The symptoms in people with this disease vary significantly because they depend on some factors. These include the severity of the disease, existing health problems, gender, and age. While the most common symptom is tiredness during physical activity (exercise intolerance), it may also cause other symptoms. Examples include:
- Muscle pain or stiffness
- Weakness
- Muscle cramps
- Fatigue (extreme tiredness)
Most of the time, the previous symptoms occur soon after beginning physical activity and improve with rest. Moreover, McArdle disease often does not cause any symptoms if you do not engage in physical activity. However, people with this condition are often able to perform mild to moderate exercise (such as walking). You should avoid heavy exercises, including squatting or standing on your tiptoes, lifting heavy objects, and others. Do not hesitate to see a doctor if you notice you have the previous symptoms only during physical activity.
Causes
This is an inherited genetic disorder that occurs due to a mutation in the PYGM gene. It is responsible for producing enzymes called myophosphorylase (muscle glycogen phosphorylase). Furthermore, this enzyme is only in skeletal muscle cells, and they help break down glycogen (stored glucose in the muscles) into glucose-1-phosphate. The body also uses this enzyme to process and then convert it into glucose, which is a simple sugar. However, sugar is the primary source of energy in the body. The symptoms of McArdle disease occur because the muscles use lots of glucose during physical activity.
In people with this genetic disorder, mutations in the PYGM gene cause a deficiency or a complete lack of myophosphorylase. It means the body cannot process glycogen properly. Thus, the muscles do not get enough glucose and become tired easily. Nowadays, researchers have found about 170-180 variants that negatively affect the PYGM gene.
Inheritance Pattern
This condition is often inherited from the biological parents during pregnancy in an autosomal recessive pattern. It means both biological parents passed on the abnormal gene. However, if you get only one abnormal gene, the condition does not occur, but you become a carrier, and the abnormal gene may pass to your children in the future.
What Are The Potential Complications of McArdle Disease?
Approximately 50% of people who develop McArdle disease experience rhabdomyolysis (muscle breakdown). It is a serious condition that may cause sudden and severe kidney failure and hyperkalemia (high Potassium levels in the blood). However, it may also cause other complications. Check some of them below:
- Myoglobinuria (dark urine) – This complication often occurs due to the release of myoglobin from damaged muscles. As a result, it causes dark brown or red-colored urine, which often indicates kidney damage.
- Permanent muscle weakness – Sometimes, people may experience progressive and long-term (chronic) muscle weakness that often occurs in the shoulders and back with aging.
- Gout – There is an increased risk for people with McArdle disease to develop this complication. It causes joint pain and swelling.
- Acute kidney failure – This complication often occurs after rhabdomyolysis and a severe form of myoglobinuria. It is also considered a medical emergency that requires immediate treatment. Otherwise, it may lead to permanent damage to the kidneys and even death.
- Other complications – In some cases, older adults may develop a rare eye disorder known as pattern retinal dystrophy. It negatively affects the vision and, without treatment, may also cause permanent vision loss (also known as blindness).
While this article does not contain all possible complications of McArdle disease, you can consult with your healthcare professional about measures to reduce the risk or even prevent the previous ones. In addition, this disorder cannot be prevented because it occurs when specific abnormal genes are passed from the biological parents to their biological children. Sometimes, doctors may recommend performing a genetic test to make sure you do not have the abnormal gene that causes this muscle disorder. In general, it is very important to understand the risks of having children with McArdle disease.
Diagnosis
Most of the time, the diagnosis of this disease begins with a physical examination to check for abnormalities linked to the disease. They may also ask some questions about your symptoms and family history to gather more information about your condition. In any case, to confirm or exclude McArdle disease, doctors perform the following tests and procedures. These include:
- Creatine kinase blood test – This test is often performed to check the release of creatine kinase (CK) in the blood. Those who suffer from McArdle disease often have high levels of CK in the blood.
- Grade exercise stress test – During this test, you will perform physical exercise, and doctors will check how well you tolerate the activity.
- Muscle biopsy – This test involves a sample of the skeletal muscle for testing. Doctors usually check for signs of McArdle disease.
- Genetic test – Sometimes, doctors perform this test to check for the abnormal gene that causes this disease.
Treatment
Unfortunately, there is no way to cure this disease. That’s why the treatment goal is to relieve the symptoms, prevent life-threatening complications, and improve your quality of life. However, a total lack of physical activity is also harmful to health, but doctors often recommend mild to moderate intensity exercise.
According to some studies, moderate-intensity graded aerobic exercise therapy helps people with this disease reduce symptoms. Generally, you should see a physical therapist to make the best exercise plan for you.
The symptoms may also improve if you adopt a high-carbohydrate eating plan. It helps muscles obtain sufficient energy from blood glucose rather than from muscle glycogen. Doctors often recommend:
- 65% of calorie intake from complex carbohydrates (such as those found in vegetables, fruits, bread, pasta, and rice)
- 20% of the calories should be taken from fats
- 15% of the calories from protein
Frequently Asked Questions
When should I go to the ER?
Immediately call 911 or go to the nearest emergency room (ER) if any of the following symptoms occur. Examples include:
- Muscle swelling or weakness
- Sore muscles
- Dark urine
- Dehydration
- Reduced urination
- Nausea
- Loss of consciousness
What is the life expectancy of someone with McArdle disease?
Most people with this disease who get treatment have the same life expectancy as people without this condition. In rare cases, people may develop a fatal form of this disease called infantile McArdle disease. In such cases, the symptoms appear shortly after birth and quickly get worse.
Is there a cure for McArdle disease?
It is not possible to cure this condition, but with early diagnosis and proper treatment, people can have mild symptoms. Usually, dietary changes are also a part of the treatment. If you have additional questions, ask your healthcare provider.
