KMT2A and leukemia: Despite the fact that reciprocal gene fusions represent the majority of stable MLL rearrangements, a plethora of additional MLL aberrations namely gene-internal duplications, inversions, deletions, insertions, and complex rearrangements were identified in leukemia patients (Meyer et al., 2013), underscoring the fact that the MLLbcr bears intrinsic features causing exceptionally high fragility.