Thiopurine Methyltransferase (TPMT)

PG4KDS - Priority Genes



Thiopurine methyltransferase (TPMT) is an enzyme that breaks down (metabolizes) thiopurines. Thiopurines include three medications: 6- mercaptopurine (6-MP), 6-thioguanine (6-TG), and azathioprine (see this link http://www.pharmgkb.org/search/annotatedGene/tpmt/index.jsp. 6-MP and 6-TG are often used to treat leukemia or lymphoma. Like many drugs, their effectiveness and side effects can vary from person to person. One of the reasons why this difference occurs is because each person’s ability to metabolize thiopurines is different based on variations in the TPMT gene. Every person can be classified into one of 3 possible genotype groups. We use a different starting dose of 6-MP and 6-TG for the different genotype groups. By changing the dose based on a patient’s genotype, there are fewer side effects (due to low blood counts).

Priority genotypes