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Lactate dehydrogenase (LD; EC 1.1.1.27) isoenzymes are formed by random combinations of two different subunits encoded by structurally distinct genes, LDHA and LDHB (1). Expression of mammalian LDHA and LDHB is regulated during development and is tissue specific; therefore, alterations in the serum LD isoenzyme pattern serve as indicators of pathologic conditions and cancer development (2). Different phenotypes of LD isoenzyme patterns in cancer patients may originate from changes in expression of LDHA or LDHB caused by other regulatory genes or promoter methylation or from mutations involving deletions, duplications, or increased copy numbers. We previously observed in a retinoblastoma cell line a high proportion of LD1 with an extra band that migrated between LD2 and LD3. The unique LD isoenzyme pattern was attributable in part to transcriptional silencing by hypermethylation of the LDHA promoter (3). We also found that the increased concentrations of electrophoretically slow-moving LD isoenzymes in many gastric cancer cell lines are attributable to transcriptional silencing of LDHB expression by aberrant promoter methylation (4).We recently encountered a male patient with mediastinal germ cell tumor who showed high serum LD activity and high LD1 isoenzyme activity. In germ cell tumors, increased LD1 concentrations often correlate with total copy number for the short arm of chromosome 12, which is where LDHB is located (5), but not all germ cell tumors show this increased copy number for chromosome 12. We therefore hypothesized that the high LD1 isoenzyme activity could be caused by aberrant methylation of the LDHA promoter.The patient, a 21-year-old man, was admitted to our hospital because of fever and abnormal chest x-ray results. Laboratory tests revealed increased serum LD activity (299 U/L; reference interval, 101–193 U/L). Serum α-fetoprotein was increased to 2535 …

High Lactate Dehydrogenase Isoenzyme 1 in a Patient with Malignant Germ Cell Tumor Is Attributable to Aberrant Methylation of the LDHA Gene