Hereditary deficiency of lactate dehydrogenase M-subunit

A family with a complete deficiency of lactate dehydrogenase M-subunit was investigated. The propositus was an 18-year-old male who complained of exertional pigmenturia and easy fatigue. Marked discrepancy was observed in the ratio between creatine kinase and lactate dehydrogenase (CK/LDH). Electrophoretic analysis of serum LDH isoenzymes of the propositus demonstrated only one activity band of LDH H4. A complete lack of the LDH M-subunit was similarly demonstrated in erythrocytes, leukocytes and in the intermediate vastus muscle. LDH levels in the muscle specimen were markedly decreased in the patient, whereas CK and aspartate aminotransferase were almost the same as in a control subject. LDH isoenzymes of erythrocytes were analyzed in 5 siblings and in the parents. This demonstrated a complete lack of LDH M-subunit in 3 siblings. The ratio between H-subunit and M-subunit (H/M) in erythrocyte LDH suggested a partial absence of the M-subunit in two siblings and in the parents. An abortive increase of blood lactate and a marked increase in blood pyruvate were observed immediately after ischemic work of the forearm, accompanied by an increase in serum creatine kinase and myoglobinuria. The present case represents a newly described form of genetically determined myopathy.