The effects of NUDT15 and TPMT variants on mercaptopurine treatment in Vietnamese pediatric acute lymphoblastic leukemia patients

6-mercaptopurine (6-MP) plays a critical role in the treatment of pediatric acute lymphoblastic leukemia (ALL). NUDT15 and TPMT gene variants have been strongly associated with myelotoxicity caused by using 6-MP. Therefore, the purpose of this study is to investigate the frequency of NUDT15 and TPMT polymorphisms, as well as the impact of NUDT15 variants on the use of 6-MP to treat pediatric ALL in Vietnam. Sanger sequencing was applied to detect NUDT15 and TPMT gene variants in 70 pediatric ALL patients. Duration of drug interruption, level of neutropenia, and 6-MP tolerance dose were recorded. NUDT15 variants were detected from 23 out of 70 (32.9%) patients. Three well-known haplotype variants were identified as NUDT15 *2 (p.V18_V19insGV and p.R139C), *3 (p.R139C), and *6 (p.V18_V19insGV); besides, a novel NUDT15 p.R11Q was not previously reported. The NUDT15 wild-type, heterozygous variant, and homozygous variant genotypes were 67.1%, 30.1%, and 2.8%, respectively. Two TPMT heterozygous polymorphisms were TPMT*3C and *6, accounted for 2.8%. Patients with intermediate and low activity NUDT15 were given the median 6-MP tolerance dose of 55.2 and 37.2 versus 69.5 mg/m2/day of patients with NUDT15 normal activity (p = 0.0001). Patients with homozygous variant diplotype were drastically sensitive to 6-MP, with an average dose intensity of 49.6%, compared to 73.6% and 92.7% of those with heterozygous and wild-type diplotype, respectively (p = 0.0001). Our results suggest that 6-MP dose adjustment should be based on NUDT15 variants in pediatric Vietnamese ALL patients.