GSD Type 7

Also known as Tarui disease

Defect phosphofruktokinase (PFK) deficiency

Cause Genetic defect results in the absence of enzymatic activity in the muscles.

Incidence Least common type of GSD and considered very rare. 100 cases worldwide reported.

Signs & Symptoms

• Increased uric acid which may lead to gout.
• High blood bilirubin which can cause gallbladder stones.
• Classic and late-onset forms present with muscle weakness (most pronounced following exercise), fixed limb weakness,muscle contractures, jaundice and joint pain.
• Fatal infantile variant presents muscle weakness, cataracts, joint contractures

Diagnosis

• Laboratory studies (CK values are usually increased, lactic acid does not increase following exercise)
• Imaging studies ( Brain imaging scans in infantile-onset, MRI of calf muscle)
• Electromyography (EMG)
• Echocardiography and ECG
• Ischemic forearm test
• Biochemical assay – definitive
• Muscle biopsy – definitive

Treatment

• Medical Care – specific medical is not required for Taui disease however, patients are advised to avoid high carbohydrate meals because they may exacerbate the exercise intolerance.
• Patients should avoid vigorous exercises because it may lead to myoglobinuria which can result to renal failure.

Prognosis

• Infantile variant – poor
• Classic and late onset are relatively mild disorders with minor lifestyle restrictions.