抄録
A case of complete deficiency of lactate dehydrogenase subunit H has been presented. Deficiency of LDH H-subunit of this case is one of inborn errors of metabolism. The propositus (J. A.) is a 64 year-old male with mild diabetes, which has been under good control by restricted diet and torazamide. Low serum LDH activity was noticed upon recent laboratory check-up, and finally, complete absence of LDH H-subunit was discovered by serum isoenzyme study. In addition, the erythrocytes, leukocytes, platelets as well as saliva of the propositus were found to be deficient in LDH H-subunit. LDH of the propositus was composed only of M-subunit. Hence, the LDH isoenzyme patterns of the serum, blood cell and saliva in the propositus showed only one band, LDH-5 (MMMM tetramer). It is of special interest that erythrocytes fructose 1, 6-diphosphate, dihydroxyacetone phosphate, as well as glyceraldehyde 3-phosphate concentration in the propositus were found to be definitely increased. These data strongly suggest that disturbance in erythrocyte glycolysis exists at the glyceraldehyde 3-phosphate dehydrogenase step. However, the erythrocyte glyceraldehyde 3-phosphate dehydrogenase activity in this case was within the normal range, which suggests indirectly that the cause of this disturbance in glycolysis might be due to high NADH and relatively low NAD caused by block of LDH step. In the whole blood of the propositus, lactate concentration came out to be low, whereas that of pyruvate was within the normal range.
The studies on reduction of methemoglobin with glucose and lactate suggest that LDH activity plays only a minor role in the reduction of methemoglobin in human erythrocytes.
