Lactate Dehydrogenase Isoenzyme 1 in Testicular Germ Cell Tumors

In his thesis, Zondag (1964) described the lactate dehydrogenase (L-lactate: NAD+-oxidoreductase EC 1.1.1.27, LDH) isoenzyme patterns of human malignant diseases. Among other findings, he drew attention to the characteristic LDH isoenzyme pattern in germ cell tumors, which showed a predominance of LDH isoenzyme 1 (LDH-1), being deviant from those of other cancers. This LDH-1 pattern in tumor tissue has been confirmed in later investigations (Murakami and Said 1984; Takeuchi et al. 1979). Similarly, the serum activity is frequently raised in patients with tumors (von Eyben 1983). The increased LDH-1 level in testicular tumors could be due to polyploidization involving the gene locus encoding LDH-B, as LDH-1 is a homotetrameric combination of this subunit. The LDH-B gene is localized on the short arm of chromosome 12 (12p12.1–12p12.2), and multiple copies of isochromosome i(12p) are often present in human testicular germ cell tumors (Atkins and Baker 1982). The raised tissue LDH-1 could also be related to an increase in the rate of transcription of the LDH-B gene, an increased stability of the LDH-B mRNA, an increase in the translation of the LDH-B mRNA, or a combination of all these factors (Fig. 1).