Haploinsufficient embryos also present with anaemia, thrombocytopenia and reduced numbers of B-lymphocytes and CFU, indicating that MLL gene dosage is critical to blood development and may also be relevant in MLL1-rearranged leukaemia, as only one wild-type allele remains when the other one is involved in a chromosomal translocation [[76], [77], [78]]. Here, KMT2A is linked to leukemia.