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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”.
SYMPTOMS

Muscle pain and fatigue on everyday activity and exercise. Fixed contracture with rhabdomyolysis. Raised baseline CK.

SECONDARY

Myoglobinuria, nausea and vomiting following strenuous exercise.

ONSET

Infantile, childhood, late-onset.



 

INVOLVED

Skeletal muscle.

TREATMENT

Avoid anaerobic exercise. Maintain a healthy diet, low in carbohydrates.


 

OUTLOOK

Good with avoidance of anaerobic and iosmetric  activity.
 

Tarui disease results from a deficiency in the PFKM gene, impairing synthesis of muscle phosphofructokinase. 
CLINICAL FEATURES

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.

ENERGY SHORTAGE

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.

GENETIC CONDITION

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

DIAGNOSIS

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.