Advances in Brief ALL-1 Tandem Duplication in Acute Myeloid Leukemia with a Normal Karyotype Involves Homologous Recombination between Alii Elements1

Rearrangements of the ALL-1 gene by reciprocal translocations involv ing chromosome band Hq23 are frequently associated with human acute leukemia. We have previously reported the detection of ALL-1 gene rearrangements in adult patients with acute myeloid leukemia lacking cytogenetic evidence of Hq23 translocations. These included 2 of 19 patients with normal karyotypes as well as 3 of 4 patients with trisomy 11 as a sole cytogenetic abnormality. Rearrangement of the ALL-1 genes in two of the patients with trisomy 11 was shown to result from a direct tandem duplication of a portion of the gene spanning exons 2—6. Here we report the characterization of the ALL-1 gene rearrangement in one of the previously reported acute myeloid leukemia patients with a normal karyotype. ALL-1 rearrangement in this patient results from a direct tandem duplication of a portion of the gene spanning exons 2—8. RNA polymerase chain reaction and DNA sequence analysis show that the partially dupli cated ALL-1 gene is transcribed into niKNA capable of encoding a par tially duplicated protein. Sequence analysis of the genomic fusion region provides evidence for -4/u-mediated homologous recombination as a mechanism for partial duplication of the ALL-I gene.