Department of Cytogenetics, Molecular Genetics and Reproductive Biology, Farhat Hached University Teaching Hospital, Sousse, Tunisia.
J Cancer Res Clin Oncol. 2011 Sep;137(9):1329-36. doi: 10.1007/s00432-011-1002-4. Epub 2011 Jul 8.
The BCR/ABL gene rearrangement is generated by a reciprocal translocation t(9;22)(q34;q11) in chronic myeloid leukemia (CML) patients. In most cases, it is cytogenetically visualized by the Philadelphia (Ph) chromosome. About 5-10% of CML patients lack cytogenetic evidence of the Ph translocation but show BCR/ABL fusion by fluorescence in situ hybridization (FISH) or reverse transcriptase-polymerase chain reaction (RT-PCR). Deletions around the breakpoints on derivative chromosome 9 including 5'ABL and 3'BCR sequences occur in 10-15% of Ph-positive CML patients and are thought to have prognostic significance.
We explored cryptic rearrangements involving chromosomes 9 and 22 in 3 CML patients with an apparently normal bone marrow karyotypes using multiplex RT-PCR and FISH with commercial and home-brew probes.
The BCR/ABL fusion transcripts were detected by RT-PCR. Using commercial FISH probes, the BCR/ABL fusion gene was found on chromosome 22 in two patients and on chromosome 9 in one patient. Consecutive FISH assays clarified the mechanism of the masked Ph chromosome: in the 3 patients, Ph rearrangement resulted from double mechanism consisting in standard translocation t(9;22)(q34;q11) followed by a second reversed translocation t(9;22)(q34;q11). One patient achieved major cytogenetic response after 6 months of imatinib therapy, and one patient had successful bone marrow transplant.
In this study, we have characterized three Ph-negative CML patients with cryptic BCR/ABL rearrangement generated after an uncommon mechanism involving two sequential translocations and confirm that the BCR/ABL hybrid gene may be located on other sites than 22q11. Ph-negative CML patients with BCR/ABL fusion gene have the same prognosis as patients with classical t(9;22).
BCR/ABL 基因重排是由慢性髓性白血病（CML）患者的相互易位 t（9；22）（q34；q11）产生的。在大多数情况下，它通过费城（Ph）染色体在细胞遗传学上可视化。大约 5-10%的 CML 患者缺乏 Ph 易位的细胞遗传学证据，但通过荧光原位杂交（FISH）或逆转录聚合酶链反应（RT-PCR）显示 BCR/ABL 融合。在 Ph 阳性 CML 患者中，约 10-15%的衍生染色体 9 周围的断点发生缺失，包括 5'ABL 和 3'BCR 序列，被认为具有预后意义。
我们使用多重 RT-PCR 和商业及自制探针的 FISH 探索了 3 例骨髓核型正常的 CML 患者中涉及染色体 9 和 22 的隐匿性重排。
通过 RT-PCR 检测到 BCR/ABL 融合转录本。使用商业 FISH 探针，在 2 例患者中发现 BCR/ABL 融合基因位于染色体 22 上，在 1 例患者中发现位于染色体 9 上。连续的 FISH 检测阐明了隐匿性 Ph 染色体的机制：在 3 例患者中，Ph 重排在标准易位 t（9；22）（q34；q11）后，通过第二种反向易位 t（9；22）（q34；q11）形成。1 例患者在伊马替尼治疗 6 个月后获得主要细胞遗传学反应，1 例患者成功进行了骨髓移植。
在这项研究中，我们描述了 3 例隐匿性 BCR/ABL 重排的 Ph 阴性 CML 患者，这些重排是由涉及两个连续易位的不常见机制产生的，并证实 BCR/ABL 杂交基因可能位于 22q11 以外的其他部位。具有 BCR/ABL 融合基因的 Ph 阴性 CML 患者与具有经典 t（9；22）的患者具有相同的预后。
