A complex chromosome rearrangement forms the BCR‐ABL fusion gene in leukemic cells with a normal karyotype

Abstract

Chromosome in situ hybridization studies showed that the normal karyotype of leukemic cells from a patient with Ph1-negative, BCR-positive chronic myeloid leukemia (CML) concealed a complex t(9;22;20)(q34;q11;p13). The close association of 5'-BCR and 3'-ABL was demonstrated by field inversion gel electrophoresis, and in situ hybridization showed that BCR-ABL was located on the short arm of chromosome 20. Our findings further indicate that chromosome rearrangement is the cause of BCR-ABL gene fusion in leukemic cells that show a normal karyotype. Results from in situ hybridization studies were consistent with formation of the t(9;22;20) by a two step chromosomal rearrangement, but field inversion gel electrophoresis results indicated a more complex rearrangement.

Simple competitive two-step RT-PCR assay to monitor minimal residual disease in CML patients after bone marrow transplantation

“…It may but may not be true. Precisely, the results of quantification should be expressed by the number of the BCR/ABL transcript units per 10 6 leukocytes. This unit represents the number of BCR/ABL transcripts in an idealized leukemic cell, ie number of transcripts in a leukemic cell of a 100% Ph-positive patient at the stage of CML diagnosis.…”

“…If a basic assumption for absolute quantification, E T = E C , is fulfilled the gradient equals zero and equation 4 is simplified: log(T n /C n ) = log(T 0 /C 0 ) (6) In this case the ratio of initial target and competitor amounts is maintained throughout all PCR cycles tested. If a constant amount of target (T 0 ) is mixed with different amounts of competitor (C 0 ) and co-amplified for a fixed number of cycles, plotting log(T n /C n ) as a function of log(C 0 ), a straight line with gradient −1 should be obtained even in the case of E T E C (but the ratio of E T to E C is constant) (equation 5).…”

“…In all cases, samples of peripheral blood were analyzed. The disease intensity was expressed as the number of leukemic cells in 10 6 leukocytes. This value may not reflect the absolute number of leukemic cells in all instances but it permits an indication of BCR/ABL expression level to which clinicians can easily relate.…”

“…[1][2][3] The BCR/ABL gene results from the reciprocal chromosome translocation t(9;22)(q34,q11) karyotypically detected as Ph chromosome 4,5 or from various complex translocations including chromosomes 9 and 22 with karyotypically undetected Ph chromosome. 6,7 Two highly predominant types of fusion gene exist, depending on whether exon 2 or exon 3 of the major BCR region is fused to exon 2 of the ABL gene. 3,8,9 The BCR/ABL encodes a chimeric protein p210 considered to play a crucial role in leukemogenesis.…”

“…A sensitive method for detecting even very small numbers of leukemic cells is of crucial importance for the early detection of disease recovery and for commencement of the therapy at a time when the malignant clone is still small and the probability of therapeutic success is high. The most sensitive among all current methods is the two-step nested reverse transcription-polymerase chain reaction (RT-PCR), amplifying a cDNA segment of BCR/ABL fusion gene, which permits the detection of a single leukemic cell in 10 5 -10 6 normal cells. This sensitivity exceeds that of other methods by several orders of magnitude.…”