Thiopurinemethyl Transferase Deficiency: TPMT Genotyping

Diagnostic Use

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme which catalyses the S-methylation of thiopurine drugs. TMPT converts 6-MP to metabolites other than the thioguanine nucleotides thought to be responsible for their main cytotoxic action. Haematological side effects of thiopurines are influenced by TPMT deficiency (myelosuppression). A standard dose of thiopurine drugs in homozygous mutant individuals is likely to cause pancytopaenia and sometimes death and there is a growing body of evidence suggesting heterozygotes are also at higher risk of haematological complications (note that normal individuals still have a background risk of developing haematological complications).

Department

Genetics - Molecular Pathology

Delphic Registration Code

TPMT

Laboratory Handling

Registration

Send samples for either TPMT or TPMT genotyping to Specialist Biochemistry

Separating

Specialist Biochemistry - fridge

Laboratory

Do not freeze or separate samples

Constituent Tests

• Genomic DNA Extraction

Synonyms

TPMT
Thiopurine methyltransferase genotyping

Turnaround Time

4 weeks

Test Code

7302

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

1.0

Minimum Sample Volume (ml)

0.5

Additional Specimen Information

This test requires nucleated cells. Please do not centrifuge or freeze blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Aliquot Instructions

Sample Type

• Whole Blood

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Please do not centrifuge or freeze blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Test Method

Common polymorphisms in the TPMT gene give rise to individuals with low or zero TPMT activity. Allele-specific PCR is used to test for the presence of the point mutations G238C (*2 allele) and A719G (*3 allele). These account for 85-90% of the inactive TPMT alleles in the general population.

Non-Funded Test Cost

$140.77 (Exclusive of GST)

Billing Code

7328

Genomic DNA must be extracted from the specimen prior to testing. This incurs an additional charge (see GDNA). Laboratories may prefer to submit DNA for testing. Please provide a minimum of 5 micrograms of DNA at 20 nanograms/microlitre.

NUDT15, along with TPMT, is an enzyme involved in the metabolism of thiopurines. NUDT15 genotyping is also available at CHL.

Contact Information

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