Type VII Glycogen Storage Disease
Muscle Phosphofructokinase Deficiency, Tarui Disease
The phosphofructokinase enzyme is needed to facilitate the breakdown of glycogen into energy in muscle. Patients with this type of GSD have a deficient amount of this enzyme in their muscle tissue. With this deficiency, effective glycogen breakdown (glycolysis) during muscle stress cannot be accomplished, resulting in pain, weakness, and cramping in the exercising muscle.
The clinical features of Type VII Glycogen Storage Disease are similar to those of Type V GSD. Patients experience early onset of fatigue and muscle pain with exercise. The body breaks down muscle when trying to attain energy, which causes many symptoms such as muscle pain, muscle cramping, muscle fatigue, and muscle tenderness. With the breakdown of muscle (rhabdomyolysis) and the release of the red protein myoglobin, myoglobinuria may develop, as evidenced by dark-red or red-brown urine. However, exercise intolerance is evident in childhood and symptoms are more severe than in Type V GSD.
Diagnosis of Type VII Glycogen Storage Disease is done by muscle biopsy, with a deficiency of the muscle phosphofructokinase enzyme and a modest accumulation of glycogen found. Patients may also display a hemolytic anemia.
Tarui Disease from National Organization for Rare Disorders [NORD]
GSD Type VII from Online Mendelian Inheritance in Man searchable database [OMIM]
Glycogen Storage Disease Type VII from the AGSD-UK
Type VII GSD info from eMedicine/Medscape
Tarui disease from the Swedish Information Centre for Rare Diseases