[Lactate Dehydrogenase M subunit deficiency].

Lactate Dehydrogenase(LDH) M subunit deficiency was first discovered by urinary discoloration and discrepancy in laboratory data. The response to ischemic forearm work is characteristic(absence of an increased venous lactate concentration after ischemic work and a marked increase in venous pyruvate are found). The increase of pyruvate concentration is specific to LDH-M subunit deficiency. Glycolysis was markedly retarded in the patient's muscle in the glyceraldehyde 3-phosphate dehydrogenase(GAPDH) step, possibly due to the impaired reoxidation of NADH produced by GAPDH activity. Then the excessive NADH is reoxidized by alpha-glycerophosphate and glycerol. Therefore, ATP production is significantly impaired and muscle tissue is damaged. Molecular analysis revealed a detection of 20 base-pairs in exon 6 in LDH-M subunit deficiency. This mutation results in a frame-shift translation and premature termination.