ABCC4 and mucositis: 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.