Cytogenetics, FISH and RT-PCR Analysis of Acute Promyelocytic Leukemia: Structure of the Fusion Point in a Case Lacking Classic t(15;17) Translocation

Abstract

The chimeric gene product PML-RAR α, the result of a reciprocal t(15;17) translocation, plays an important role in the pathogenesis of acute promyelocytic leukemia (APL). In the present study on clinical effects of cytogenetics and molecular events in APL, we performed chromosome analysis, fluorescence in situ hybridization (FISH) using gene-specific probe, and reverse transcription-polymerase chain reaction (RT-PCR) analysis in 10 patients with APL. Patients were treated with all- trans retinoic acid (ATRA) and/or chemotherapy, and all achieved complete remission. Cytogenetic analysis revealed the classic translocation t(15;17) in nine of 10 patients, and a remaining patient had an apparently normal karyotype. Interphase FISH was performed in nine patients, and revealed the presence of PML-RAR α fusion gene in all patients. RT-PCR analysis in 10 patients showed that eight expressed long (L)-form type, one expressed a short (S)-form type, and the other expressed a variable (V)-form type. Metaphase FISH of the patient with normal karyotype revealed a juxtaposed PML-RAR α fusion signal on one chromosome 17 homologue, an RAR α signal on the other chromosome 17 homologue, and one PML signal on each chromosome 15 homologue. Moreover, V-form of the PML-RAR α transcript was detected, and a portion of RAR α intron 2 was found inserted in the breakpoint region. ATRA differentiation induction therapy was effective in treating this patient, a result infrequently reported in cytogenetic and molecular investigations of APL.