The enzyme TPMT (full name: thiopurine S-methyltransferase) plays a role in breaking down drugs from the thiopurine group.
The enzyme TPMT is involved in the metabolisation of, amongst other things, the anti-tumour drugs mercaptopurine and thioguanine, as well as immunosuppressants like azathioprine. These drugs are used in the treatment of cancer and Crohn’s disease, in the event of organ transplants and to treat inflammatory diseases such as rheumatoid arthritis and inflammation of the bowel, liver or skin, for example.
Genetic predisposition
The activity of the enzyme TPMT varies from one individual to another.
This variation can be partly explained by genetic variations. In people with TPMT deficiency (reduced activity) drugs from the thiopurine group can build up in the body and cause side effects. Reduced activity of the enzyme TPMT is found in roughly 10% of the European population; the enzyme is completely inactive in 0.3% of Europeans.
When a genotype is determined variations in the TPMT gene are indicated by two so-called alleles. Each allele has a name consisting of an asterisk (*) and a number. An example of a possible TPMT genotype is TPMT*2/*3A.
At iGene we determine the following variants (alleles) of the TPMT gene:
TPMT*2, TPMT*3A, TPMT*3B, TPMT*3C, TPMT*4, TPMT*11, TPMT*14, TPMT*15, TPMT*23, TPMT*29 and other (classified as TPMT*1).