FLT3-activating mutations in infant MLL. (A) ITD of the JM domain of FLT3 in the MV4-11 cell line (C indicates positive control) and 4 examples of infant MLL patients negative for FLT3/ITDs as determined by PCR. (B) Amplified PCR product covering the EcoRV site within the activation loop of FLT3, undigested (U) and digested in both a patient positive (+) and negative (-) for this type of mutation. (C) Sequence analysis of the activation loop mutation found in 1 of 36 patients tested.