Exon 7 deletion in the bcr-abl gene is frequent in chronic myeloid leukemia patients and is not correlated with resistance against imatinib.
Chronic myeloid leukemia (CML) patients treated with imatinib develop frequent resistance generally due to a point mutation. Recently, large rearrangements of abl sequence have also been described. In this study, we focused on the complete deletion of exon 7. We screened for bcr-abl(delexon7) in 63 resistant patients by high-resolution melting (HRM) analysis and direct sequencing. Moreover, we analyzed expression of abl(delexon7) and bcr-abl(delexon7) in 17 CML patients at diagnosis, 32 patients at resistance, and 20 negative controls by quantitative PCR or fragment length analysis. bcr-abl(delexon7) was detected on 34 (54%) among 63 resistant patients by HRM, showing an increase in the sensitivity of screening, because only 3.2% could be detected by direct sequencing. This deletion was not associated with a point mutation (P = 0.3362). In addition, abl(delexon7) was found in all tested samples with the same pattern of expression, suggesting an alternative splicing mechanism. In the bcr-abl component, there was no statistical difference between CML patients at diagnosis and resistant patients (P = 0.2815) as regarding bcr-abl(delexon7) proportion, thus arguing against involvement of deletion in resistance. Moreover, among two patients harboring bcr-abl(delexon7) at diagnosis, one experienced a complete disappearance of this transcript, and the other decreased >75% at resistance. In conclusion, bcr-abl(delexon7) is frequently observed in CML patients when using sensitive techniques. It seems to be the result of an alternative splicing mechanism and to be independent from the occurrence of resistance.
Department of Clinical Cytology and Cytogenetics, Nîmes University Hospital, Nîmes, France.
Jean-Baptiste
JB
Gaillard
Cécile
C
Arnould
Sophie
S
Bravo
Daniel
D
Donadio
Carole
C
Exbrayat
Eric
E
Jourdan
Dorothée
D
Reboul
Jean
J
Chiesa
Thierry
T
Lavabre-Bertrand
D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005091:Exons; D016044:Fusion Proteins, bcr-abl / Q000235:genetics*; D017353:Gene Deletion; D005787:Gene Frequency; D056726:Genetic Association Studies; D005820:Genetic Testing / Q000379:methods; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000235:genetics*; D009691:Nucleic Acid Denaturation / Q000235:genetics; D010879:Piperazines / Q000627:therapeutic use*; D020033:Protein Isoforms / Q000235:genetics; D011743:Pyrimidines / Q000627:therapeutic use*; D013696:Temperature
D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D020033:Protein Isoforms; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl