The rs56103835 variant in pre-MIR323B was previously associated with changes in plasma MTX levels and the occurrence of vomiting in patients with ALL; mature MIR453 may undergo alterations in its levels and biogenesis and, consequently, in its role in the regulation of target genes ABCC1, ABCB1, ABCC2, and ABCC4, included in the transport of the drug MTX. The gene discussed is ABCC2; the disease is acute lymphoblastic leukemia.