Frequency of BCR-ABL fusion transcripts in Iranian patients with chronic myeloid leukemia

A specific chromosomal abnormality, the Philadelphia chromosome, is present in 90 - 95% of patients with chronic myeloid leukemia. The aberration results from a reciprocal translocation of chromosomes 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 transcript b2a2 or b3a2 codes for a p210 protein. Other fusion gene leads to the expression of an e1a2 transcript, which codes for a p190 protein. Other less common fusion genes are b3a3 or b2a3 (p203) and e19a2 (p230). The incidence of one or other rearrangement in chronic myeloid leukemia patients varies in different reports. In general, fusion transcripts are determined individually, a process which is labor- intensive in order to detect all major fusion transcripts. The objective of this study was to set up a multiplex RT-PCR assay for detection and to determine the frequency of different fusion genes in 75 Iranian patients with chronic myeloid leukemia.

Peripheral blood samples were analyzed by multiplex RT-PCR from 75 adult Iranian chronic myeloid leukemia patients to detect different types of BCR-ABL transcripts of the t(9;22).

All patients examined were positive for some type of BCR/ABL rearrangement. The majority of the patients (83%) expressed one of the p210BCR-ABL transcripts (b3a2, 62% and b2a2, 20%), while the remaining showed one of the transcripts of b3a3, b2a3, e1a2 or co-expression of b3a2 and b2a2. The rate of co-expression of the b3a2 and b2a2 was 5%.

In contrast to other reports, we did not see any co-expression of p210/p190. Co-expression may be due to alternative splicing or to phenotypic variation, with clinical course different from classic chronic myeloid leukemia.