Different biochemical markers have been used to characterize ALL.
Terminal deoxynucleotidyl transferase (Tdt)
- Unusual DNA polymerizing enzyme.
- Catalyzes the polymerization of deoxynucleoside monophosphates into a single strand DNA primer without the need for template instruction.
- Found in nucleus
- Role in immunoglobulin and T-cell antigen receptor rearrangement.
- Significant Tdt activity is not present in normal lymphocytes but is present in cortical thymocytes and in leukemic lymphoblasts arising from T-cell and B-cell precursor lineage.
- Tdt activity helps to make the diagnosis of ALL and to differentiate from AML
