TPMT*3C — thiopurine drug sensitivity
One copy of the TPMT*3C reduced-function variant detected.
You have one working copy and one less-active copy of the TPMT gene.
Intermediate metabolizer for thiopurines (azathioprine, mercaptopurine). Standard doses may cause toxicity (bone marrow suppression); dose reduction is recommended if these drugs are prescribed.
A class of drugs called thiopurines (azathioprine, mercaptopurine) — used for inflammatory bowel disease, autoimmune conditions, and certain leukaemias — can build up to harmful levels at standard doses for you. A lower dose is recommended if you're prescribed any of these.
What this means
Thiopurines (azathioprine, 6-mercaptopurine, thioguanine) are used in inflammatory bowel disease, autoimmune conditions, transplantation, and acute lymphoblastic leukaemia. TPMT inactivates them. Carriers of two reduced-function alleles accumulate the active drug to dangerous levels at standard doses. CPIC guidelines for thiopurine dosing are among the best-established pharmacogenetic interventions in clinical practice.
Thiopurines — azathioprine, 6-mercaptopurine, and thioguanine — are a family of drugs used for inflammatory bowel disease, several autoimmune conditions, after organ transplants, and to treat a kind of childhood leukaemia. The TPMT enzyme breaks these drugs down. If TPMT doesn't work well, the drug builds up to dangerous levels, damaging the bone marrow and dropping blood cell counts severely. Checking TPMT (and a related gene, NUDT15) before starting these medicines is one of the most well-established uses of genetic testing in everyday medicine, and many clinicians do it routinely.
Caveats
- Highly actionable if you are ever prescribed a thiopurine.
- Many clinicians now check TPMT (and the related NUDT15) routinely before starting these drugs.
- For most people not taking thiopurines, this remains background information.