MLLT1 and leukemia: Some of the most prevalent KMT2A fusions including KMT2A-MLLT3 (aka MLL-AF9) or KMT2A-MLLT1 (aka MLL-ENL) were shown to have leukaemia-inducing activity at multiple levels of the haematopoietic hierarchy resulting in either lymphoid, myeloid or mixed-lineage leukemia3.