Complex three-way translocation involving MLL, ELL, RREB1, and CMAHP genes in an infant with acute myeloid leukemia...

Rearrangements affecting the MLL gene in hematological malignancies are associated with poor prognosis. Most often they are reciprocal translocations and more rarely complex forms involving at least 3 chromosomes. We describe an unusual case with cutaneous leukemic infiltrates that waxed and waned until progression to acute myeloid leukemia, AML-M5. The leukemic cells harbored a novel apparent 3-way translocation t(6;19;11)(p22.2;p13.1;q23.3). We utilized advanced molecular cytogenetic methods including 24-color karyotyping, high-resolution array comparative genomic hybridization (aCGH) and DNA sequencing to characterize the genomic complement in the leukemic cells from aspirated bone marrow cells at AML diagnosis. Karyotyping showed 47,XY,t(6;19;11)(p22;p13;q23),+der(6)t(6;11)(p22;q23)[17]/48,sl,+8[3]/48,sl,+8,der(12)t(1;12)(q11;p13)[3]/ 48,sdl,der(Y)t(Y;1)(q12;q11),+8[7] conferring MLL-ELL fusion. Oligo-aCGH analysis confirmed gains of 6p22qter and 11q23.3qter involving the CMAHP and MLL genes, respectively. DNA sequencing disclosed an additional breakpoint at 6p24.3 (at RREB1 gene). Retrospective fluorescence in situ hybridization revealed presence of the MLL-involving rearrangement in the initial stages of disease before clear morphological signs of bone marrow involvement. The patient responded well to therapy and remains in remission>6 years from diagnosis. This apparent 3-way translocation is remarkable because of its rarity and presentation with myeloid sarcoma, and may, as more cases are characterized, further our understanding onto how such complex translocations contribute to promote leukemogenesis and respond to therapy.