Frequency of Bcr-Abl Fusion Oncogene Splice Variants Associated with Chronic Myeloid Leukemia (CML)

BCR-ABL fusion oncogene originates from the reciprocal translocation of chromosome 9 and 22 t(9;22) (q34;q11). It translates a chimeric protein, p210, characterized by constitutive activation of its tyrosine kinase, which triggers leukemogenic pathways resulting in onset of chronic myeloid leukemia (CML). In CML, the classic fusion is b2a2 or b3a2 fusing exon 13 (b2) or exon 14 (b3) of BCR to exon 2 (a2) of ABL. The type of bcr/abl transcripts may be associated with different prognosis and hence useful in therapeutic plan. This study was conducted to calculate the frequency of these splice variants as the frequencies of different fusion oncogenes associated with leukaemia can vary in different geographical regions due to interplay of genetic variation in different ethnic populations, diverse environmental factors and living style. A very sensitive nested RT-PCR was established to detect BCR-ABL splice variants in CML. Sensitivity of RT-PCR assay was of the order of 10. Thirty CML patients were subjected to BCR-ABL analysis. Out of 30 Pakistani patients, 19 (64%) expressed b3a2 while 11 (36%) expressed b2a2 transcript. This shows that BCR-ABL splice variants differ in their frequencies which may have an effect on biology and implications for prognosis and management of BCR-ABL positive Leukemias.