KMT2A and neoplasm: MLL1, a H3K4me3‐specific methyltransferase, is deemed as a transcriptional coactivator.18 It plays an important role in regulating gene expression during early embryonic development and hematopoiesis.8, 19 In humans, translocation and aberrant expression of MLL1 is observed in many tumours, thereby indicating its proto‐oncogenic character.20, 21, 22 A study in MLL1‐deficient mouse revealed that MLL1 is crucial for the function of hematopoietic progenitor cells.7 MLL1 is also required for the development of the central nervous system.