Myoadenylate deaminase deficiency.
Incidence
Probable AR. Rare. It may be asymptomatic.
Clinical Characteristics
Myoadenylate deaminase deficiency is often clinically indistinguishable from myophosphorylase deficiency (McArdle disease). However, the average age of onset is somewhat later and the attack of exercise-induced cramping tends to be less severe. Patients may have just myalgia post exercise. Between attacks the children are normal. CPK is elevated in half of the patients. EMG is often normal. The ischemic forearm exercise test produce a normal increase in plasma lactate but the increase of plasma ammonium does not occur. Diagnosis is confirmed by enzyme analysis measuring adenylate kinase in muscle by biochemical analysis or specific histochemical staining in the muscle. Half of the patients may have other enzyme deficiencies or collagen vascular disease. Muscle biopsy is normal.
Precipitants
Exercise may triger cramps and myalgias.
Provocation Tests
The ischemic forearm exercise test produce a normal increase in plasma lactate but the normal increase of plasma ammonium does not occur.
Diagnostic Procedures
Diagnosis is confirmed by enzyme analysis measuring adenylate kinase in muscle by biochemical analysis or specific histochemical staining in the muscle.