PGX TPMT and NUDT15 Genotyping For detection of TPMT and NUDT15 variants affecting drug metabolism Clinical Background • NUDT15 is a negative regulator of thiopurine activation and toxicity. • TPMT and NUDT15 affect thiopurine drugs such as azathioprine, 6-mercaptopurine or 6- thioguanine. • Defects in the TPMT gene lead to decreased methylation and decreased inactivation of 6MP, which enhances bone marrow toxicity and may cause myelosuppression, anemia, bleeding tendency, leukopenia and infection. • NUDT15 catalyzes the conversion of cytotoxic thioguanine triphosphate (TGTP) metabolites to the less toxic thioguanine monophosphate. • Metabolizer phenotypes can be predicted by the TPMT and NUDT15 genotypes. • The clinical impact of the TPMT and NUDT15 genotype is influenced by involvement of other metabolic pathways and other non-genetic factors. Epidemiology • TPMT variant frequency is ethnicity dependent. TPMT*3A is present in approximately 3% of Caucasians, Mediterranean descent, South Americans; 5% Mexican descent and 1% Middle Eastern descent. TMPT*3C is present in approximately 5% of individuals of African descent. • NUDT15 variant frequency is ethnicity dependent. NUDT15*3 is present in approximately 7% of individuals of south/central Asian descent. NUDT15*5 is present in approximately 1% of individuals of East Asian descent. • The poor metabolizer phenotype is caused by two non-functional alleles. Genetics • The TPMT gene has nine exons and is located on chromosome 6p22.3. • The NUDT15 gene has three exons and is located on chromosome 13q14.2. • Inheritance is autosomal recessive. • Penetrance is drug-dependent. Indications for Ordering Indiana University School of Medicine Genetics Testing Laboratories 975 W. Walnut St., IB350 Indianapolis, IN. 46202 Tel. 317-274-7597 • Pre-therapeutic testing to identify individuals who should avoid, or may require unconventional doses of medications metabolized by TPMT and NUDT15. Interpretation • If no variants are detected either for TPMT or NUDT15, this suggests a *1 allele and normal enzymatic activity. • If one decreased functional or non-functional variant is detected, intermediate-to-normal enzymatic activity is predicted. • If two non-functional variants are present on opposite alleles, this predicts low enzymatic activity and a poor metabolizer phenotype. • Genotype results should be interpreted in the context of the individual clinical situation. Consultation with a clinical pharmacy professional is recommended. Methodology • Real-time polymerase chain reaction (PCR) and hydrolysis probe analysis. Variants in TPMT and NUDT15 Assay Predicted enzyme Allele variant dbSNP activity TPMT*1 Assumed when no variant detected Normal TPMT*2 c.238G>C rs1800462 No function Indiana University School of Medicine Genetics Testing Laboratories 975 W. Walnut St., IB350 Indianapolis, IN. 46202 Tel. 317-274-7597 TPMT*3A c.460G>A and c.719A>G rs1800460 and rs1142345 No function TPMT*3B c.460G>A rs1800460 No function TPMT*3C c.719A>G rs1142345 No function NUDT15*1 Assumed when no variant detected Normal NUDT15*3 c.415C>T (also in *2 haplotype) rs116855232 No function NUDT15*5 c.52G>A rs186364861 Uncertain function Indiana University School of Medicine Genetics Testing Laboratories 975 W. Walnut St., IB350 Indianapolis, IN. 46202 Tel. 317-274-7597 .