Analysis of MLL-derived transcripts in infant acute monocytic leukemia with a complex translocation (1;11;4)(q21;q23;p16).

It has been proposed, on the basis of cytogenetic studies and molecular analysis of MLL-derived transcripts in acute leukemia with 11q23 rearrangement, that only one fusion gene transcript present on the der(11) chromosome is critical for leukemogenesis. This view is challenged by a recent observation in a case of leukemia with a complex translocation that results in MLL being fused in-frame to two different partner genes. We investigated a case of infant monocytic leukemia with a complex translocation, (1;11;4)(q21;q23;p16). Molecular studies revealed MLL rearrangement by both fluorescence in situ hybridization and Southern blot analysis, and MLL/AF1q, but not the reciprocal message (i.e., AF1q/MLL), was amplified by polymerase chain reaction. Sequence analysis of MLL/AF1q revealed an in-frame fusion between MLL exon 6 and the breakpoint located six bases upstream of the ATG start site for AF1q. Our data suggest that only one form of MLL fusion gene is implicated in leukemogenesis in our case to t(1;11;4).