Thiopurine S-methyltransferase (TPMT) is an enzyme involved in the metabolism of purine analogs such as azathioprine, 6-mercaptopurine and thioguanine, drugs that are used as chemotherapeutic and immunosuppressant agents in diseases such as lymphoid malignancies, leukemias, inflammatory bowel disease, and other immune conditions (Relling et al., 2011; Appell et al., 2013). Here, TPMT is linked to inflammatory bowel disease.