Glycogen Storage Disease Type 5: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Glycogen Storage Disease Type 5?
A primary care doctor is often the first doctor a person sees about these symptoms. That doctor may refer the patient to a neurologist, who treats nerve and muscle problems, or a geneticist, who specializes in inherited conditions. Care works best when these doctors coordinate the plan.
What it is
Glycogen storage disease type 5 is a rare inherited condition that affects how muscles use sugar for energy. It is also called McArdle disease. People with this condition lack enough of an enzyme called muscle phosphorylase, which normally breaks down glycogen, the stored sugar in muscle cells. Without it, muscles cannot release that stored energy during exercise.
Symptoms
The main symptom is muscle fatigue and weakness that starts within the first few minutes of exercise. Some people feel their energy return if they keep going at a gentle pace, a pattern called second wind. Dark urine after hard exercise can mean muscle tissue is breaking down. Symptoms often appear in childhood or the teen years, but some people are not diagnosed until adulthood.
Causes and who gets it
This disease is passed down through families. A child must receive one changed copy of the PYGM gene from each parent to have the condition. Parents who carry only one changed gene usually have no symptoms. It affects both males and females and occurs in roughly one in 100,000 people.
How doctors diagnose it
Doctors often start by asking about exercise problems and family history. A blood test can measure creatine kinase, a substance that rises when muscle is damaged. Genetic testing can confirm the diagnosis with a blood sample. A muscle biopsy is used less often now that genetic testing is available.
Treatment
There is no cure, but many people manage the condition well with lifestyle changes. Regular, moderate exercise such as walking often helps muscles work better over time, and warming up slowly can prevent cramps. Doctors usually advise against intense exercise that causes pain, because it can damage muscle cells. Some people are told to avoid statins, cholesterol drugs that can stress muscles.
When to see a doctor
Anyone who feels weak, cramped, or exhausted within minutes of starting exercise should talk to a doctor, especially if a family member has similar problems. Dark colored urine after exercise needs prompt medical attention. Sudden severe weakness or very dark urine calls for urgent care.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance for visits, while a concierge doctor usually charges more and often works alongside insurance. These doctors can order blood tests, review genetic testing results, coordinate exercise and diet plans, and watch for muscle problems over time. When a neurologist or geneticist is needed, they can refer the patient and stay involved in follow up care.
Common questions
Can people with McArdle disease exercise?
Yes, most people can and should stay active. Gentle, steady exercise with a slow warm up is usually better than intense bursts of activity.
Is McArdle disease life threatening?
Most people live normal lifespans with the condition. The main danger is severe muscle breakdown after extreme exercise, which can harm the kidneys.
Can it be passed to my children?
A child must inherit a changed gene from both parents to have the disease. Parents who each carry one changed gene have a 25 percent chance of passing it to a child.
Sources
- MedlinePlus - Glycogen storage disease type V
- NIH Genetic and Rare Diseases Information Center - Glycogen storage disease, type V
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
