两例Ph染色体阳性慢性粒细胞白血病患者具有少见型bcr/abl融合基因

Abstract

目的研究2例Ph染色体阳性慢性粒细胞白血病慢性期(CML-CP)患者异常的bcr/abl融合基因结构.方法分别采用常规的M-及μ-型bcr/abl融合转录子特异性引物进行逆转录-聚合酶链反应(RT-PCR),对RT-PCR扩增产物测序进行序列同源性分析,以确定扩增产物的成分及bcr/abl融合转录子类型,其中1例根据测序结果设计引物并通过PCR研究其DNA水平bcr与abl基因融合方式.结果2例患者临床表现均符合典型CML-CP特征,RT-PCR扩增后均未见典型的M-及μ-型扩增带,而分别出现一条异常的条带,产物大小分别介于M-及μ-bcr/abl之间及小于M-bcr/abl.经序列分析证明RT-PCR产物均含有bcr及abl基因序列,例1的bcr基因断裂发生在第18外显子(e18)内部,abl基因融合位点为常见的外显子2(a2)处,它们之间插入了40 bp的部分abl基因内含子1b序列,为一种新型的符合阅读框架结构的bcr/abl融合转录子e18-int-a2.经PCR证明该融合发生在DNA水平.例2的融合转录子中缺失典型M-bcr/abl(b2a2)融合基因中abl基因外显子2(a2),为e13a3(b2a3)型.结论少见型bcr/abl融合基因可见于典型Ph染色体阳性CML患者并产生异常的R-PCR扩增带.

To investigate the unusual bcr/abl fusion gene structures of two Ph chromosome positive chronic myelogenous leukemia (CML) patients in chronic phase (CP).By using general M- and micro -bcr/abl specific primers respectively, bcr/abl fusion transcripts were detected by reverse transcription-polymerase chain reaction (RT-PCR). The RT-PCR products sequencing was performed, the DNA sequences were analyzed in Genebank and the bcr and abl sequences at the fusion site were identified. DNA was amplified by PCR using a set of primers designed according to the sequencing result of RT-PCR products.Two patients showed typical manifestations of CML-CP. Their RT-PCR products were different from usual M- or micro -type; one was longer than M-bcr/abl but shorter than micro -bcr/abl, the other one was shorter than M-bcr/abl. The RT-PCR products sequencing showed that both products contained bcr and abl gene sequences. The first patient's bcr gene was broken within exon 18, and fused to abl gene exon 2(a2), and a 40 bp of partial abl intron 1b fragment was inserted between them, resulting in a novel in-frame bcr/abl fusion transcript-e18-int-a2 which has not been reported in the literature so far. In the second patient, deletion of abl exon2(a2) led to exon 13(b2) of bcr gene fusing with abl exon 3(a3).Uncommon bcr/abl fusion gene may occur in typical Ph(+) CML patient.