The genotyping of ITPA 94C > A (rs1127354) and IVS2+21A > C (rs7270101), TPMT*2 238G > C (rs1800462), TPMT*3B 460G > A (rs1800460) and *3C 719A > G (rs1142345), and NUDT15 415C > T (rs116855232) in Middle Eastern children with ALL treated with 6-MP showed that (i) TPMT and NUDT15 variants are uncommon in the Middle East; (ii) ITPA variants are more common in Lebanese than in Kurdish children; and (iii) the most significant ADRs were found in carriers of NUDT15, TPMT*3A, and ITPA risk variants [138]. This evidence concerns the gene NUDT15 and acute lymphoblastic leukemia.