Muscle and serum enzymes and isoenzymes in muscular dystrophies.

Total activity of creatine kinase (CK), lactate dehydrogenase (LD), aldolase (Ald), glutamico-oxaloacetic transaminase (GOT), and LD-isoenzyme distribution was studied in serum and muscle biopsies from normal persons and 117 patients with different types of muscular dystrophy: 82 Duchenne type (DMD), 12 BEcker type, 7 facioscapulohumeral (FSHMD), and 16 limb girdle (LGMD). Total enzyme activity in sera and muscle homogenates was determined by spectrophotometric assays. LD isoenzymes were separated by electrophoresis on agarose gel plates in barbital buffer (pH 8.6), scanned and quantitated. The amounts of the 2 types (M and H) of LD isoenzymes were calculated and the ratio of M/H in serum and muscle was used as an index to differentiate among the types of muscular dystrophy. Serum enzyme activity was elevated to variable degrees reflecting a corresponding decrease in muscle enzymes in the different muscular dystrophies. Patterns of LD isoenzymes in serum and muscle were specific to each type of muscle disease. Increase in serum LD5 (the muscle LD fraction) was a common feature in muscle damage. Changes in the amounts of M and H types in the subunits of LD correlated to the existence and severity of muscle damage. The mean muscle M/H ratio was 6.4 in controls, 1.8 in early DMD, 0.1 in late DMD, 3.0 in Becker type, 3.8 in FSHMD and 3.9 in LGMD. The muscle LD isoenzyme distribution in DMD showed a shift toward a more aerobic fetal muscle pattern. This is a result of the gradual disappearance of the mature anaerobic LD-type (M) and the increase in synthesis of the aerobic fetal LD-type (H) during the progression of the disease. This report provides a comparative study of the LD isoenzyme patterns in muscular dystrophies which may help in differential diagnosis.