Genetic variability in ABCC4 rs9302061 and rs7317112 did not influence MTX metabolism, a result consistent with that of a previous study.20 However, den Hoed et al. 16 carried out a study on ABCC4 rs7317112 in Dutch children with ALL and indicated that the AA genotype was related to mucositis and high MTX plasma levels at 48 h. This evidence concerns the gene ABCC4 and acute lymphoblastic leukemia.