Glycogen Storage Disease Type VII

Also known as Tarui disease or muscle phosphofructokinase deficiency.

The clinical features of Type VII are similar to those of Type V. Patients experience onset of fatigue and muscle pain early in exercise. Exercise intolerance is evident in childhood, as with Type V, but symptoms are more severe. Type VII is caused by a deficiency of the phosphofructokinase enzyme which is needed to facilitate the breakdown of glycogen into energy in muscle. This results in reduced amount of energy available to muscles during exercise.

The body breaks down muscle when trying to attain energy, which causes symptoms such as muscle pain, cramping, fatigue and tenderness. With the breakdown of muscle (rhabdomyolysis) and the release of the red protein myoglobin, red-brown urine may be seen.

Diagnosis is by muscle biopsy, which will show a deficiency of muscle phosphofructokinase and a modest accumulation of glycogen. Patients may also display a hemolytic anemia. Treatment primarily consists of avoiding strenuous exercise. Some patients have been helped by a high protein diet.

The enzyme deficiency is due to abnormalities in the muscle phosphofructokinase gene. GSD VII is inherited as an autosomal recessive genetic disorder.

• Comprehensive article on Type VII - from Sweden