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Testing recommended prior to initiation of thiopurine therapy. Thiopurine drug therapy is used for autoimmune diseases, inflammatory bowel disease, acute lymphoblastic leukemia, and to prevent rejection after solid organ transplant. Thiopurine methyltransferase (TPMT) is an enzyme that breaks down (metabolises) a class of drugs called thiopurines. Examples of thiopurines include azathioprine, mercaptopurine, and thioguanine. These drugs are used to suppress the immune system and are prescribed to treat various immune-related conditions or blood disorders (e.g., leukaemia). The activity level of the TPMT enzyme, or the genetics underlying the enzyme's activity, is tested before thiopurine drug therapy to make sure that individuals treated with the drugs can metabolise them. TPMT genetic test (genotype) is a genetic test that can identify genetic variations in the TPMT gene. Three milliliter EDTA blood sample can be collected and sent to laboratory for testing purpose. Genomic DNA from patient sample isolated and used for Polymerase chain reaction including gene responsible for Thiopurine methyltransferase. Single nucleotide polymorphism (SNP) analyzed by sequence data received by DNA sequencing technology.

About one person in every 300 is severely deficient in TPMT, and about 10 per cent of the population has lower than normal levels of TPMT. The side effects can be avoided if TPMT production is tested before starting thiopurine treatment. This genetic test provides information about a person's likely response to thiopurines, but it will not quantify how much TPMT enzyme is actually being made by the body. There can be significant person-to-person and ethnic variability in TPMT production, even in people with the same gene variations. Gene (Transcript) Allele TPMT (NM_000367) TPMT*2 : rs1800462, c.238G>C TPMT*3A : rs1800460, c.460G>A; rs1142345, c.719A>G TPMT*3B : rs1800460, c.460G>A TPMT*3C : rs1142345, c.719A>G. This test was developed and its performance characteristics determined by geneOmbio Technologies Pvt Ltd. There are ways to determine whether an individual is at risk of side effects from thiopurine therapy: This test identifies individual genetic differences associated with risk for thiopurine toxicity. Each person has two copies of the TPMT gene. Most people have two copies of "wild type" TPMT that produce sufficient TPMT enzyme. Approximately 10 per cent of people have one wild-type gene and one gene variation associated with decreased TPMT (heterozygous) and intermediate enzyme activity. While numerous variations (SNP) can occur in TPMT, above mentioned five variations in particular that have been proven to be associated with TPMT deficiencies.