Natalia Sutiman1, Sylvia Chen2, Khoon Lin Ling3, Sai Wei Chuah3, Wai Fook Leong1, Vinayak Nadiger1, Madeline Tjai1, Chris San Choon Kong3, Brian John Schwender3, Webber Chan3, Hang Hock Shim3, Wee Chian Lim4, Chiea Chuen Khor5,6,7, Yin Bun Cheung8,9, Balram Chowbay1,2,10. 1. Clinical Pharmacology, SingHealth, Singapore. 2. Clinical Pharmacology Laboratory, National Cancer Centre Singapore, Singapore. 3. Department of Gastroenterology & Hepatology, Singapore General Hospital, Singapore. 4. Department of Gastroenterology, Tan Tock Seng Hospital, Singapore. 5. Singapore Eye Research Institute, Singapore National Eye Centre, Singapore. 6. Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore. 7. Division of Human Genetics, Genome Institute of Singapore, Singapore. 8. Center for Quantitative Medicine, Duke-NUS Medical School, Singapore. 9. Tampere Centre for Child Health Research, University of Tampere & Tampere University Hospital, Tampere, Finland. 10. Office of Clinical Sciences, Duke-NUS Graduate Medical School, Singapore.
Abstract
BACKGROUND: Genetic variants of TPMT and NUDT15 have been reported to predict the inter-patient variability in response and toxicity profiles of patients receiving thiopurine therapy. However, the clinical utility of TPMT genotyping in guiding thiopurine doses has been questionable, in part due to underlying differences in the prevalence of TPMT variants in both Caucasian and Asian populations. Several NUDT15 variants have been associated with thiopurine-induced leukopenia, particularly in Asian cohorts. So far, none have been reported in a multiethnic Asian population. AIM: To investigate the associations between TPMT and NUDT15 variants with thiopurine-induced myelotoxicity in 129 Asian inflammatory bowel disease patients. MATERIALS & METHODS: Pyrosequencing was performed to screen for TPMT and NUDT15 variants. Intracellular steady-state metabolite concentrations were quantified using liquid chromatography-tandem mass spectrometry. RESULTS: Significant declines in nadir white blood cell, absolute neutrophil count and platelet counts were observed with increasing copy numbers of the risk T allele at NUDT15 c.415C>T locus (overall p < 0.05) within 4, 8 and 12 weeks and 6 months after thiopurine initiation. Patients with low and intermediate NUDT15 activity, as inferred from haplotype pairs, had significantly higher risks of leukopenia (p = 0.000253) and neutropenia (p = 0.002) compared with patients with normal NUDT15 activity. CONCLUSION: These findings highlight the critical relevance of NUDT15 pharmacogenetics in predicting for thiopurine-induced myelotoxicity and confirm the lack of significance of TPMT variants in Asian inflammatory bowel disease patients.
BACKGROUND: Genetic variants of TPMT and NUDT15 have been reported to predict the inter-patient variability in response and toxicity profiles of patients receiving thiopurine therapy. However, the clinical utility of TPMT genotyping in guiding thiopurine doses has been questionable, in part due to underlying differences in the prevalence of TPMT variants in both Caucasian and Asian populations. Several NUDT15 variants have been associated with thiopurine-induced leukopenia, particularly in Asian cohorts. So far, none have been reported in a multiethnic Asian population. AIM: To investigate the associations between TPMT and NUDT15 variants with thiopurine-induced myelotoxicity in 129 Asian inflammatory bowel diseasepatients. MATERIALS & METHODS: Pyrosequencing was performed to screen for TPMT and NUDT15 variants. Intracellular steady-state metabolite concentrations were quantified using liquid chromatography-tandem mass spectrometry. RESULTS: Significant declines in nadir white blood cell, absolute neutrophil count and platelet counts were observed with increasing copy numbers of the risk T allele at NUDT15 c.415C>T locus (overall p < 0.05) within 4, 8 and 12 weeks and 6 months after thiopurine initiation. Patients with low and intermediate NUDT15 activity, as inferred from haplotype pairs, had significantly higher risks of leukopenia (p = 0.000253) and neutropenia (p = 0.002) compared with patients with normal NUDT15 activity. CONCLUSION: These findings highlight the critical relevance of NUDT15 pharmacogenetics in predicting for thiopurine-induced myelotoxicity and confirm the lack of significance of TPMT variants in Asian inflammatory bowel diseasepatients.
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