C/CTwo copies of TPMT*3C — very low or absent enzyme activity. Standard thiopurine doses can cause severe, life-threatening myelosuppression, and CPIC recommends drastically reduced dosing or an alternative drug. This is one of the clearest gene-drug pairs in medicine.
T/COne copy of TPMT*3C, a no-function allele. TPMT breaks thiopurines down; with one working copy the drug builds up more than expected, and CPIC recommends starting azathioprine, mercaptopurine or thioguanine at a reduced dose with closer blood-count monitoring.
T/TNo copy of *3C at this position. Normal TPMT activity is the usual result, though other TPMT alleles exist.
This is a pharmacogenomic result with a published dosing guideline behind it. Tell a prescriber or pharmacist rather than acting on it — and never stop or change a prescribed medicine on the strength of a genotype.
Source: CPIC Guideline for Thiopurine Dosing Based on TPMT and NUDT15 Genotypes: 2018 Update, Clinical Pharmacology & Therapeutics (PMID 30447069).
Questions about rs1142345
What is rs1142345?
rs1142345 is a single position in the genome, in or near the TPMT gene. Published research associates it with tpmt *3c — thiopurine tolerance. A single variant does not decide an outcome — it shifts a probability, and for most common variants the shift is small.
Does rs1142345 affect how medicines work?
TPMT carries pharmacogenomic findings for Thiopurines. That is educational information, not a prescription or a dosing guide. Any decision to start, stop or change a medicine belongs with the clinician or pharmacist managing your treatment.
Does having rs1142345 mean I will get this?
No. Common variants like this one move a probability slightly and, on their own, rarely decide anything about one person. Nothing on this page is a diagnosis, and health decisions should be made with a clinician who can see your whole picture.
Where does the information about rs1142345 come from?
CPIC Guideline for Thiopurine Dosing Based on TPMT and NUDT15 Genotypes: 2018 Update, Clinical Pharmacology & Therapeutics (PMID 30447069). Every variant on MyGeneLog comes from public primary sources and is published with its citation and the date it was checked.