Glycogen storage disease type vii

Glycogen Storage Disease Type VII

Glycogen Storage Disease Type VII (GSD VII), also known as Tarui's disease, is a rare inherited metabolic disorder characterized by a deficiency of the enzyme phosphofructokinase (PFK) in muscle cells. This enzyme deficiency impairs the breakdown of glycogen into glucose, which is necessary for energy production during exercise. As a result, individuals with GSD VII experience exercise intolerance, muscle pain, and other related symptoms.

Pathophysiology

GSD VII is caused by mutations in the PFKM gene, which encodes the muscle isoform of phosphofructokinase. This enzyme plays a crucial role in glycolysis, the metabolic pathway that converts glucose into pyruvate, generating energy in the form of ATP. In individuals with GSD VII, the lack of functional PFK leads to an accumulation of glycogen in muscle tissues and an inability to efficiently produce energy during anaerobic exercise.

Clinical Presentation

Patients with GSD VII typically present with symptoms during childhood or adolescence, although adult-onset cases have been reported. Common symptoms include:

• Exercise intolerance
• Muscle cramps and pain during or after physical activity
• Myoglobinuria, which can cause dark-colored urine following exercise
• Fatigue

In some cases, patients may also experience hemolytic anemia due to the involvement of PFK in red blood cells.

Diagnosis

The diagnosis of GSD VII is based on clinical evaluation, laboratory tests, and genetic analysis. Key diagnostic steps include:

• Muscle biopsy: Histological examination may reveal glycogen accumulation.
• Enzyme assay: Measurement of PFK activity in muscle tissue can confirm the deficiency.
• Genetic testing: Identification of mutations in the PFKM gene.

Management

There is currently no cure for GSD VII, and management focuses on alleviating symptoms and preventing complications. Strategies include:

• Dietary modifications: A high-protein, low-carbohydrate diet may help reduce symptoms.
• Exercise management: Avoidance of strenuous exercise and gradual conditioning may improve tolerance.
• Supportive care: Monitoring for complications such as myoglobinuria and anemia.

Prognosis

The prognosis for individuals with GSD VII varies depending on the severity of the enzyme deficiency and the presence of complications. With appropriate management, many patients can lead relatively normal lives, although they may need to avoid certain physical activities.

Also see

• Glycogen storage disease
• Glycolysis
• Metabolic myopathy
• Phosphofructokinase