MONDO_0012503 (thiopurine S-methyltransferase deficiency) can be described as follows. An inherited metabolic disease that is has its basis in the disruption of thiopurine S-methyltransferase activity. Also known as: TPMT deficiency, inborn error of thiopurine S-methyltransferase activity, inborn thiopurine S-methyltransferase activity disorder, poor metabolism of thiopurines-1, rare inborn error of thiopurine S-methyltransferase activity.