Disrupting the binding of HOXA9 at this enhancer via CRISPR editing resulted in significant downregulation of FLT3. Collectively, our results determined FLT3 as a downstream effector of HOXA9 and established the axis of MLL-r fusion, HOXA9, and FLT3 in MLL-r leukemia. The gene discussed is HOXA9; the disease is leukemia.