GSD7 – TARUI DISEASE
Also known as muscle phosphofructokinase deficiency. People with Tarui’s have nearly identical symptoms as McArdle’s people but do not experience the same “second wind”.
Estimated cases diagnosed worldwide: <200.
Tarui disease results from a deficiency in the PFKM gene, impairing synthesis of muscle phosphofructokinase.
The clinical features of GSD7 are similar to those of GSD5 (McArdle disease) with onset of more severe fatigue and muscle pain early in exercise. Because people with Tarui disease cannot utilise glucose, there is said to be no “second wind”. Sometimes there is nausea and vomiting after intense exercise. Symptoms are evident in childhood. Patients may display a hemolytic anemia.
GSD7 is caused by a deficiency of the phosphofructokinase enzyme which is needed to facilitate the breakdown of glucose into energy in muscle during exercise. The body breaks down muscle (rhabdomyolysis) when trying to attain energy, which causes symptoms such as muscle pain, cramping, fatigue and tenderness. The red protein myoglobin is released and red-brown urine may be seen.
The enzyme deficiency is due to abnormalities in the muscle phosphofructokinase gene and is inherited as an autosomal recessive genetic disorder.
Diagnosis is by genetic testing or muscle biopsy, which will show a deficiency of muscle phosphofructokinase and a modest accumulation of glycogen. Treatment primarily consists of avoiding strenuous exercise. Some patients have been helped by a high protein diet, others by a low carbohydrate high fat diet. It has been reported that only 100 to 200 cases have been identified worldwide.