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Acute Lymphoblastic Leukemia



Biochemical Characteristics


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


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