Glycogen Storage Disease Due To Muscle Phosphofructokinase Deficiency

Muscle phosphofructokinase (PFK) deficiency (Tarui's disease), or glycogen storage disease type 7 (GSD7), is a rare form of glycogen storage disease characterized by exertional fatigue and muscular exercise intolerance. It occurs in childhood.

Epidemiology

About 100 cases have been reported worldwide.

Clinical description

Clinical signs are muscular exercise intolerance (more severe than in type 5; see this term). Compensated hemolysis (increased bilirubin and reticulocytes) and hyperuricemia are associated. A rapidly fatal infant form has also been observed in 6 families.

Etiology

The condition is caused by mutations in the PFKM gene (12q13) encoding the muscular isoenzyme of PFK, a key enzyme in the regulation of anaerobic glycolysis which has 3 isoenzymes (for the muscle, liver, and platelets).

Diagnostic methods

The diagnosis is based on biological findings, revealing increased amounts of abnormal glycogen and enzyme deficiency (1 to 33% residual activity) in a muscle biopsy, whereas activity in erythrocytes is over 50%.

Differential diagnosis

Differential diagnoses include the other forms of glycogen storage disease (see these terms).

Genetic counseling

The condition is autosomal recessive, although a few cases with pseudodominance or symptomatic heterozygous individuals have been found.

Management and treatment

The only treatment is to avoid intensive exercise. It should be noted that carbohydrates induce lower muscular performance (due to the decreased amounts of free fatty acids and ketone bodies).

Prognosis

Myoglobinuria may lead to renal failure.