EHA Library - The official digital education library of European Hematology Association (EHA)

The aim of this study was to evaluate TPMT gene polymorphisms (TPMT*2, TPMT*3B, TPMT*3C, TPMT*3A) and detection its cytoplasmic enzyme levels and myelosuppression and hepatotoxicity effects in children with acute lymphoblastic leukemia (ALL) treated with 6-MP.

98 patients with standard risk paediatric ALL in maintenance phase were selected.  PCR-RFLP method was performed to detect mutations in exon7 (460G>A; TPMT*3B), and in exon 10 (719A>G; TPMT*3C). TPMT*2 (238G>C) allele, in exon 5 was analyzed by allele-specific PCR method. Exons 7 and 10 in 19 patients and exone 5 of 2 patients were also sequenced to confirm the results obtained by PCR-RFLP and AS-PCR methods. The enzyme level of 70/98 patients was assessed by ELISA. Then Correlation between genotype, phenotype and side effects such as myelosuppression and hepatotoxicity was analyzed by statistical methods.

Frequency of TPMT*1\*3B genotype was 1.1% and the frequency of TPMT*3B allele variant was 0.71%. No allele variant was detected  in TPMT*2 and TPMT*3C,*3A, *4, *7, *8, *10 (4 allele variants (TPMT *4, *7, *8, *10) were analyzed by sequencing) . The concentration of enzyme was low in 8 (11.4%) individuals. There was no meaningful association between phenotype and genotype of TPMT enzyme.  A significant correlation was found between low concentration of TPMT enzyme and myelossuppresion (P=0.04, leucopenia, P=0.02 neutropenia ).  There was no statistical difference between low and normal concentration of TPMT enzyme and hepatotoxicity (P=0.12).

The results of this study showed that there is a relationship between low enzyme concentration and myelosuppression in some patients who were treated with 6-MP. Therefore, to avoid some side effects of 6-MP such as myelosuppression, studying common and rare TPMT gene variant as well as measurement of TPMT enzyme level is recommended.