BCRABL Quantitation

The BCR-ABL fusion gene is detected in 95% of CML cases, in 25-30% of adult ALL and 2-5% of childhood ALL .The BCRABL fusion transcript is the result of the reciprocal translocation between the long arms of chromosome 9 and chromosome 22 - [t(9;22)]. The resulting BCRABL fusion product can be detected by real-time PCR (qPCR).

The breakpoint in the ABL-gene is generally 5’ of the exon a2. The major breakpoint region (M-bcr) identified in the BCR gene, lies within a 5.8kb large fragment, spanning exons b1 to b5. The most common M-bcr fusion transcripts are b3a2 and b2a2 or a mixture of both, although some other less common transcripts are also identified, ie b2a3, b3a3 .

Protocols for the treatment of leukaemia are based on prognostic factors which include pre-treatment characteristics such as age, WBC count, immunophenotypic profiles, specific chromosomal abnormalities, aberrant fusion genes and mutations. However, patient outcome cannot be reliably predicted on the basis of these prognostic factors alone, underlining the importance of minimal residual disease (MRD) testing.