Glycogenosis type X. Phosphoglycerate mutase (PGAM) deficiency.
Incidence
Probable AR. All American patients identified to date have been African-American and all carry a nonsense mutation at codon 78, with one patient also carrying a mutation at codon 89.
Clinical Characteristics
Phosphoglycerate mutase deficiency (GSD X) may be clinically indistinguishable from phosphofructokinase deficiency. It is characterized clinically by cramps, muscle necrosis and myoglobinuria after strenuous exercise. The diagnosis is done by measuring the enzyme (PGAM) in muscle. EMG unrevealing.
Precipitants
Exercise may triger cramps and myoglobinuria.
Provocation Tests
Ischaemic exercise test: Lactate should increase higher than 2 mmol/L with exercise normally. In this condition, there is no increase of lactate, and cramps may appear during the test, like in McArdle disease.
Diagnostic Procedures
The diagnosis is done by measuring the enzyme in muscle. Mutations have been identified in this condition. These can now be detected in DNA isolated from the blood. This analysis provides a practical alternative to muscle biopsy for initial screening.