Importantly, mice on a doxycycline-supplemented diet, in which the activated CRISPR/Cas9 reagents excised the LMO1 enhancer mutation and thus suppressed LMO1 overexpression, exhibited lower leukaemic engraftment at week 4 and improved survival compared to mice on a regular diet, providing clear evidence that this enhancer variant is important for the pathogenesis of this leukaemia. This evidence concerns the gene LMO1 and leukemia.