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Muscle carnitine was measured in 3 severely handicapped children with acute myoglobinuria. Muscle total carnitine levels were 9.6 +/- 3.0 nmol/mg non collagen protein (m +/- SD, control 15.7 +/- 2.8, n = 19), and free 6.5 +/- 3.0 nmol/mg non collagen protein (m +/- SD, control 12.9 +/- 3.7, n = 19), muscle free carnitine was significantly low in them. Serum carnitine was measured in 22 severely handicapped children. Serum total carnitine was 48.9 +/- 12.3 nmol/ml (m +/- SD, control 60.3 +/- 11.7, n = 14), and free 37.7 +/- 10.0 nmol/ml (m +/- SD, control 46.0 +/- 12.5, n = 14), serum carnitine was also significantly decreased. Secondary muscle and serum carnitine depletion might be one of the potential cause of myoglobinuria in severely handicapped children.

A 14-year-old boy had myoglobinuria and renal failure after intense exercise; a year earlier he had experienced a milder episode. There was no consanguinity and no family history of neuromuscular diseases or hemolytic anemia. Strength was normal. Forearm ischemic exercise caused prolonged contracture with no rise of venous lactate. Muscle morphology showed only a mild increase of lipid droplets. Glycogen concentration was normal. Muscle phosphoglycerate kinase (PGK) activity was 5% of the normal mean, and all other glycolytic enzymes were normal. The residual PGK activity of muscle was heat stable but showed slower than normal electrophoretic mobility and decreased Michaelis constants for 3-phosphoglycerate and adenosine triphosphate. The enzyme defect was also expressed in erythrocytes and in fibroblast and muscle cultures. PGK activity was decreased in tissues from the patient's mother but normal in the father. PGK deficiency is an X-linked recessive trait usually associated with hemolytic anemia, mental retardation, and seizures; myopathy had not been recognized previously. Muscle PGK deficiency is now added to two other newly recognized glycolytic defects, phosphoglycerate mutase and lactate dehydrogenase deficiencies, as a cause of recurrent myoglobinuria.

Muscle phosphoglycerate mutase (PGAM) activity was markedly decreased (6% of the normal mean) in a 17-year-old girl with recurrent myoglobinuria after intense exercise. Muscle biopsy showed increased PAS stain; glycogen concentration was twice normal. Studies of anaerobic glycolysis in vitro showed decreased lactate production with glycogen, and with all hexose phosphate glycolytic intermediates, which was corrected by addition of purified PGAM to the reaction mixtures. A defect of the M subunit of PGAM was documented by electrophoretic, heat lability, and mercury inhibition studies. Intermediate PGAM activities (39 and 50% of normal) were found in muscle biopsies from the patient's asymptomatic parents. These data confirm the clinical, morphologic, and biochemical features described in the first patient with PGAM deficiency and suggest autosomal-recessive transmission of the trait.

Biochemical analysis using biopsied muscle specimens was performed on 72 cases who had symptoms suggesting metabolic myopathies. Sixteen out of 72 cases (22%) were diagnosed as having chemically confirmed metabolic defects. Of these 16 cases, 9 had defects in the glycolytic pathway (glycogen storage disease type II; 3 cases, type III; 1 case, type V; 3 cases, phosphoglycerate kinase deficiency; 1 case, phosphoglucomutase deficiency; 1 case) and 7 cases in mitochondrial metabolism (complex IV deficiency; 4 cases, carnitine deficiency; 3 cases). Among 14 cases who were strongly suspected as having a defect in the glycolytic pathway because of abnormal ischemic forearm test, 6 (43%) showed biochemically proved glycolytic defects. These data suggest that care should be taken when evaluating the results of ischemic forearm test. In addition, we should carefully interpret the muscle histochemistry, because histochemical stains including PAS might be fairly normal in the defects with second step glycolytic pathway.

A 52-year-old man complained since adolescence of cramps and pigmenturia after 15 to 30 minutes of intense exercise. There was no family history of neuromuscular diseases, and strength was normal. The rise of venous lactate after forearm ischemic exercise was abnormally low. Histochemical and ultrastructural studies of a muscle biopsy showed mild increase of glycogen, which was confirmed by biochemical analysis. Studies of anaerobic glycolysis in vitro showed decrease lactate formation with glycogen and with all hexosephosphate glycolytic intermediates, suggesting a defect below the phosphofructokinase reaction. Muscle phosphoglycerate mutase (PGAM) activity was 5.7% of the lowest control, while all other enzymes of glycolysis had normal activities. Electrophoretic, heat lability, and mercury inhibition studies showed that the small residual activity of PGAM in the patient's muscle was represented by the brain (BB) isoenzyme, suggesting a genetic defect of the M subunit that predominates in normal muscle. The prevalence of the BB isoenzyme in other tissues, including muscle culture, may explain why symptoms were confined to muscle.