Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme, catalyzing S-methylation of thiopurine drugs. TPMT exhibits autosomal codominant polymorphism. Patients carrying a variant genotype have low TPMT activity, and produce elevated levels of 6-thioguanine nucleotides (6-TGN) in their red blood cells (RBC). 6-TGN accumulation may result in azathioprine (AZA)-induced bone marrow myelosuppre...
