A novel AF9 breakpoint in MLL-AF9-positive acute monoblastic leukemia.

MLL-AF9 is the most frequent MLL rearrangement in childhood acute myeloid leukemia (AML) and it may be also found in acute lymphoblastic leukemia (ALL) of patients younger than 1-year-old (infants). We report a novel AF9 breakpoint site, located between previously reported sites A and B, detected in an infant who was diagnosed with AML-FAB M5. The occurrence of this new breakpoint should be considered when designing RT-PCR assays for the screening of MLL abnormalities. The precise characterization of the MLL-AF9 transcript is important to carry out the minimal residual disease analysis during the follow-up of the patients.