t(11;14)(q23;q24) Generates an MLL-Human Gephyrin Fusion Gene along with a de facto Truncated MLL in Acute Monoblastic Leukemia

More than 20 different partner genes with MLL have been cloned from leukemia cells with translocations involving chromosome 11 band q23 (11q23). All reported partner genes fused in-frame to MLL and the fusion cDNA encode chimeric MLL proteins with a significant portion derived from the partner genes. We analyzed one patient with de novo acute monoblastic leukemia with t(11;14)(q23;q24) and identified that a human homologue of gephyrin (human gephyrin ) fused with MLL . Gephyrin is a rat glycine receptor-associated protein, which forms submembranous complexes and anchor glycine or γ-aminobutyric acid A receptors to microtubules. Alternative splicing of human gephyrin gene created two different forms of fusion cDNA. In one form, human gephyrin gene fused in-frame to MLL exon 9, and the chimeric product had COOH terminus of human gephyrin protein, including the tubulin binding site. In the other, the reading frame terminated shortly after the fusion point. As a result, only seven amino acids with no known function were attached to the NH 2 terminus of MLL protein. The functional significance of this de facto truncated MLL gene product is not clear.