Frequency of BCR-ABL Fusion Transcript in Iranian Patients with Chronic Myeloid Leukemia

Abstract

Introduction: Reverse transcriptase-polymerase chain reaction (RT-PCR) assay is a useful tool for the detection of fusion transcript resulting from specific chromosomal translocation of the leukemia cells. A specific chromosomal abnormality, the Philadelphia chromosome (Ph), is present in 90% to 95% of CML patients.The aberration results from a reciprocal translocation between chromosome 9 and 22, creating a BCR-ABL fusion gene.There are two major forms of the BCR/ABL fusion gene,  involving ABL exon 2, but including different exons of BCR gene. The transcripts b2a2 or b3a2 code for a p210 protein. Another fusion gene leads to the expression of an e1a2 transcript, which codes for a p190 pro-tein. Another, less common fusion genes are b3a3 or b2a3 (p203) and e19a2 (p230). The incidence of one or other rearrangement in chronic myeloid leukemia (CML) patients varies in different reported se-ries. In general, fusion transcripts are determined individually, a process which is labor intensive in or-der to detect all major fusion transcripts. Methods: This study was designed to determine the frequency of different fusion genes in 75 iranian patients with CML. peripheral blood samples were analyzed by multiplex reverse transcriptase poly-merase chain reaction (RT-PCR) from adult patients to detect all types of BCR-ABL transcripts of the t (9:22) and found that all cases were positive for some type of BCR/ABL rearrangement. Results: Most of our patients showed b3a2 fusion gene (62%), while the remaining showed one of the transcripts of b2a2, b3a3, b2a3, e1a2 or coexpression of b3a2 and b2a2. The rate of coexpression of the b3a2 and b2a2 was 5%. Conclusion: In contrast to the other reports, we did not see any coexpression of p210/p190. This may reflect either the sensitivity of the detection techniques used or the possibility of genetic differences be-tween the populations studied. Coexpression may be due to alternative splicing or to phenotypic varia-tion, with clinical course different from classical CML.