FLT3 tyrosine kinase activating mutations in CD117/KIT⁺ T-ALL samples. RT-PCR analysis of the juxtamembrane region suggested length mutations (ITDs) in cases 1 (A) and 2 (B). Sequence analysis of PCR products demonstrated the insertion of 21 (case 1) and 60 (case 2) base pairs in positions 1863 and 1894 of the juxtamembrane region of the FLT3 kinase gene, respectively. In case 3, the D835Y mutation (MUT) in the activation loop of FLT3 was detected when compared with the wild-type (WT) allele. (C) Mutation position annotation is based in the FLT3 reference sequence NM_004119.