EZH2 and EED, two core components of PRC2, had been shown to be required for MLL leukaemia, although the underlying mechanisms remain largely unknown.44, 45 While these studies highlight the importance of HMTs in MLL leukaemia, emerging evidence also reveals an equally important role of histone demethylases (HDMs) that counteract the functions of HTMs in modulating the epigenetic regulation of gene expression in both normal and cancer settings. This evidence concerns the gene KMT2A and leukemia.