A rare chronic myeloid leukemia case with Philadelphia chromosome, BCR-ABL e13a3 transcript and complex translocation involving four different chromosomes

Abstract

The so-called Philadelphia (Ph) chromosome is present in more than 90% of chronic myeloid leukemia (CML) patients. Around 5-10% of these patients show complex translocations involving other chromosomes in addition to and/or besides chromosomes 9 and 22. CML cases with fusion transcripts, such as e13a3, in which ABL exon 3 rather than exon 2 has fused to BCR, are extremely rare. Such reported cases with the e13a3 transcript showed the Ph chromosome on karyotype analysis. This study reported a rare Ph chromosome-positive CML case with new complex chromosomal aberrations and an e13a3 BCR-ABL transcript that has yet to be established. A four-chromosome translocation involving chromosomal regions 12p11.2, 19q13.3, 9q34.1 and 22q11.2, besides a trisomy 8 and a derivative chromosome 12, were identified using high resolution multicolor banding. Reverse transcription polymerase chain reaction products showed the presence of BCR-ABL fusion transcript e13a3, and this signifies the major BCR breakpoint. The significance of the observed rearrangements and their possible role in the progression of CML was investigated.

Figure 1

GTG-banding revealed a complex karyotype involving two further chromosomes besides chromosomes 9 and 22. Derivative chromosomes are indicated by the arrowheads.

Figure 2

Karyotype and chromosomal aberrations were confirmed using molecular cytogenetic approaches. (A) M-FISH confirmed the complexity of the karyotype: 48,XX,+8,+der(12),t(9;12),t(12;19),t(19;22). (B-E) The application of aMCB analysis using probe sets for chromosomes 9, 12, 19 and 22 is shown. The normal chromosomes are shown to the left of the image, and the derivative of the four chromosomes to the middle and right. Using aMCB probes, the light gray areas show unstained regions on the derivative chromosomes. (F) Fluorescence in situ hybridization (FISH) using probes for BCR (green) and ABL (red) confirmed the involvement of chromosome 19 in the rearrangement present in this case. #, chromosome; der, derivative chromosome; Ph, Philadelphia chromosome.

Figure 3

Gel electrophoresis of the nested RT-PCR products. Lane M, 501-110 bp marker; lane 1, negative control; lane 2, positive control (b3a2, 353 bp); lane 3, β2-microglobuline (535 bp); lane 4, BCR-ABL (b2a3, 104 bp) from the patient and lane 5, M½100 bp molecular weight marker.