TPMT gene polymorphism detection by conventional PCR in pediatric acute lymphoblastic leukemia and its toxic effect

Introduction The purine analog mercaptopurine is a key medication for the successful treatment of childhood acute lymphoblastic leukemia, particularly for the consolidation and continuation therapies. Thiopurine S-methyltransferase (TPMT) catalyzes the inactivation of mercaptopurine. TPMT single-nucleotide polymorphisms can prospectively identify patients at higher risk for mercaptopurine toxicity. Patients and methods The TPMT genotype was determined by in-house conventional PCR followed by digestion of the product with restriction enzymes, MwoI FastDigest and AccI FastDigest. The study was carried out on a total of 80 participants: 40 pediatric patients with standard risk B-cell acute lymphoblastic leukemia and 40 age-matched and sex-matched healthy controls. Mercaptopurine was given to the patients in consolidation phase with oral dose of 75 mg/m 2 daily for 4 weeks. Toxicity of the drug was assessed at the end of this phase by complete blood profile and liver function tests. Results In the patients group, 97.5% were of the wild-type homozygous TPMT*1/*1 genotype and 2.5% were of the heterozygous TPMT*1/*3A genotype. In the control group, we identified 90% with the TPMT*1/*1 genotype, 7.5% with the TPMT*1/*3A genotype, and 2.5% with the TPMT*1/*3C genotype. Among the wild-type *1/*1 genotype patients in the patient group, 32.5% of patients suffered from either hepatoxicity and/or myelosuppression. Conclusion The homozygous wild-type TPMT*1/*1 genotype was the most frequent genotype in both cases and controls. TPMT*1/*3A was the most prevalent mutant genotype in this study. Although some patients had wild-type allele genotyping, they developed signs of toxicity.