Increased serum myosin light chain 3 level in neuromuscular diseases

A radioimmunoassay for human skeletal muscle myosin light chain 3 (MLC-3) was developed. The serum level of MLC-3 was evaluated in 143 patients suffering from neuromuscular diseases. Increased MLC-3 level was observed in muscular dystrophies. There were significant positive correlations between serum levels of MLC-3 and creatine kinase (CK) in Duchenne and limb-girdle type muscular dystrophy, but the regression lines were different. Patients with neurogenic amyotrophy, especially amyotrophic lateral sclerosis, also showed elevated MLC-3 levels with or without high CK, and the frequency of increase in MLC-3 was greater than that of CK. The results of the present study suggest that circulating MLC might be a useful marker for muscle breakdown not merely in myopathies but in neurogenic disorders.