Genetic variants dedected:
TPMT alleles *1, *2, *3A, *3B and *3C.
Thiopurines are widely used in the treatment of leukemias and autoimmune disorders, and as immunosuppressants after organ transplantation. Thiopurine compounds are converted to therapeutically inactive metabolites by the enzyme thiopurine S-methyltransferase (TPMT) which exists in different isoforms. Some TPMT isoforms have substantially reduced enzyme activity which leads to accumulation of higher thiopurine concentrations when receiving standard dosage. Myelosuppression, a toxic effect on the bone marrow, may thus occur. Identification of a patient’s individual TPMT isoform is crucial for avoiding toxic effects of thiopurines.