Found in most cases of infant acute lymphoblastic leukaemia (ALL) and acute myeloblastic leukaemia (AML), the fusion of MLL and its partner gene leads to a gain of function of the MLL gene, which affects the differentiation of the hematopoietic pluripotent stem cells or lymphoid and myeloid committed stem cells [122]. The gene discussed is KMT2A; the disease is acute myeloid leukemia.