What is GSD?
Type VII Glycogen Storage Disease
Overview:
- Synonyms: Muscle phosphofructokinase deficiency, Tarui disease
- Cause: Mutations in the PFKM gene lead to deficiency of phosphofructokinase
- Incidence: Approximately 1 in 1,000,000
- Effect: Impaired glycolysis results in lack of available energy for the muscles with exercise
Subtypes:
The severity and manifestations depend on the organs involved and the amount of enzyme activity present.
| Subtype | Age of Presentation | Manifestations |
| Severe Infantile | Infancy | Hypotonia at birth
Severe weakness Heart enlargement and cardiomyopathy |
| Classic | Childhood | Muscle pain and cramps |
| Late Onset | Adulthood | Muscle pain and cramps |
| Hemolytic | Variable | Hemolytic anemia without muscle symptoms |
Classic Symptoms:
- Muscle pain particularly after exercise
- Muscle cramps
- Muscle contractures
- Rhabdomyolysis
- Nausea and vomiting
- Elevated CK
- Elevated Uric acid
- Jaundice
- Hemolytic anemia
Diagnosis:
- Genetic testing: Identifies mutations in the PFKM gene
- Enzymatic testing: Phosphofructokinase enzyme activity can be measured on blood
- Muscle Biopsy: While rarely needed, a biopsy shows excessive glycogen in the muscles
Treatment:
- A low carbohydrate, high protein diet is recommended
- A ketogenic diet may be beneficial
- Avoidance of strenuous exercise is critical
Prognosis:
- The prognosis is good except for the severe, infantile form.
- Renal failure from rhabdomyolysis can occur if intense exercise is performed
- This is a life-long disease
