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Glycogen storage disease type VII
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Glycogen storage disease type VII

Glycogen storage disease type VII is a rare inherited disorder that prevents muscle cells from breaking down glycogen, leading to muscle pain, cramping, and weakness.

Overview & Symptoms

Glycogen storage disease type VII (GSDVII), also known as Tarui disease, is an inherited disorder caused by an inability to break down a complex sugar called glycogen in muscle cells. A lack of glycogen breakdown interferes with the function of muscle cells.

There are four types of GSDVII, which are differentiated by their signs and symptoms and the age at which symptoms first appear:

  • Classical form: This is the most common form, with features usually appearing in childhood. It is characterized by muscle pain and cramps, often following moderate exercise; strenuous exercise can lead to nausea and vomiting. During exercise, muscle tissue can abnormally break down, releasing a protein called myoglobin into the urine (myoglobinuria). If untreated, myoglobinuria can damage the kidneys and lead to kidney failure. Some individuals develop high levels of uric acid in the blood (hyperuricemia), elevated levels of bilirubin that can cause yellowing of the skin and eyes (jaundice), and elevated levels of the enzyme creatine kinase in their blood.
  • Severe infantile form: Infants with this form have low muscle tone (hypotonia) at birth, which leads to progressive muscle weakness (myopathy). Affected infants have a weakened and enlarged heart and difficulty breathing normally. Individuals with this form usually do not survive past their first year of life.
  • Late-onset form: In this form, myopathy is typically the only feature. Muscle weakness appears in adulthood, although some individuals have difficulty with sustained exercise starting in childhood. The weakness generally affects the muscles closest to the center of the body (proximal muscles).
  • Hemolytic form: This form is characterized by hemolytic anemia, in which red blood cells are broken down prematurely, causing a shortage of red blood cells. Individuals with the hemolytic form do not experience muscle pain or weakness related to the disorder.

Frequency

GSDVII is thought to be a rare condition; more than 100 cases have been described in the scientific literature.

Causes & Genetics

Mutations in the PFKM gene cause GSDVII. This gene provides instructions for making the PFKM subunit of an enzyme called phosphofructokinase, which plays a key role in breaking down glycogen to provide energy to muscle cells. In skeletal muscles used for movement, the phosphofructokinase enzyme is composed solely of PFKM subunits.

In skeletal muscle, the cells' main source of energy is stored as glycogen, which is normally broken down rapidly into glucose when energy is needed. Mutations in the PFKM gene result in the production of subunits with little or no function. As a result, functional phosphofructokinase is not formed in skeletal muscles, and glycogen cannot be completely broken down, causing partially broken down glycogen to build up in muscle cells. Muscles lacking access to this energy source become weakened and cramped following moderate strain and may begin to break down. In other tissues, different subunits likely compensate for the lack of PFKM subunits, which may explain why other tissues are not affected.

Associated Gene

  • PFKM

Inheritance Pattern

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • Glycogenosis 7
  • GSD VII
  • GSD7
  • Muscle phosphofructokinase deficiency
  • PFKM deficiency
  • Phosphofructokinase deficiency
  • Tarui disease

Frequently Asked Questions

GSD VII typically causes muscle pain, cramps, and weakness that start soon after moderate‑intensity exercise and are disproportionate to the effort. You may also develop dark urine (myoglobinuria) within hours of activity, nausea, or vomiting—symptoms not seen with ordinary fatigue. If these signs recur, especially with a family history of muscle disease, ask your physician for a specific work‑up (creatine kinase, lactate after exercise, and genetic testing for PFKM mutations).
diet that limits rapid‑release carbohydrates can reduce the amount of glycogen stored in muscle, decreasing the substrate that cannot be broken down. Many patients benefit from a higher‑protein, moderate‑fat diet with complex carbs (whole grains, legumes) and avoid sugary drinks, candy, and large meals right before exercise. Some clinicians also recommend a trial of ribose or creatine supplementation, but these should be discussed with a metabolic specialist before starting.
Low‑intensity, steady‑state activities such as walking, gentle swimming, or cycling for short periods are usually tolerated better than high‑intensity or anaerobic bursts. Aim for sessions under 20 minutes, keep heart rate below the anaerobic threshold, and always hydrate well. If you notice myoglobinuria (dark urine) or worsening pain, stop the activity and rest; repeated episodes can damage the kidneys.
Dark, tea‑colored urine indicates myoglobin release from muscle. If it appears after exercise, drink plenty of fluids (2–3 L/day) to flush the kidneys and avoid further strenuous activity for 24–48 hours. Seek urgent medical care if the urine remains dark for more than 12 hours, you develop flank pain, decreased urine output, or swelling—these are signs of acute kidney injury that may require intravenous fluids or hospitalization.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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