[Detection of BCR/ABL Fusion Gene and ASS1 Gene Deletion by Using Tricolor Dual-fusion Probe]

Objective: To analyze the significance of various abnormal signal patterns appreared in CML and B-ALL patients by using BCR/ABL/ASS1 tricolor dual-fusion probe, and to explore its application value in detecting BCR/ABL fusion gene and ASS1 gene deletion.

Methods: 50 newly diagnosed CML patients and 50 newly diagnosed B-ALL patients were detected by fluorescence in situ hybridization (FISH) with BCR/ABL/ASS1 tricolor dual-fusion probe. Meanwhile, karyotype analysis was performed on all the patients using the 24 hours short-term culture and R-banding.

Results: Among the 50 CML patients, Ph⁺ was found in 49 cases, 5 normal interphase karyotype was observed in 1 case. FISH detection showed that BCR/ABL fusion gene existed in all patients (100%), while the positive signal pathway showed that 1R1G2B2F was observed in 39 cases (78%), 2R1G2B1F in 2 cases (4%) and 1R1G2B1F in 6 cases (12%), simultaneous existence of 1R1G1B1F and 1R1G2B3F in 1 case (2%), 2R1G1B1F in 1 case (2%) 1R1G3B3F in 1 case (2%). FISH detection also showed that the karyotype of 6 case at ASS1 gene deletion (1R1G1B1F) all were simple t (9; 22) translocation, and other abnormalities not were observed. Among 50 cases of B-ALL, Ph⁺ was found in 13 cases, the numerical aberration and structural aberration of non t (9; 22) in 16 cases, normal karyotype in 20 cases, absence of mitotic phase in 1 case. FISH detection showed that 16 cases (32%) had BCR/ABL fusion gene including 13 cases (26%) of 1R1G2B2F, 1 case (2%) of stimultaneous exitance of 1R1G2B2F and 1R1G3B3F 1 case (2%) of 2R1G1B1F, 1 case (2%) of 1R1G3B2F. FISH detection also showed that 3 cases had BCR/ABL fusion gene, including 1 case with ASS1 gene deletion (2R1G1B1F), 1 case with classical t (9; 22) translocation (1R1G2B2F) and 1 case with BCR/ABL fusion gene and increase of ASS1 gene copy (1R1G3B3F).

Conclusion: Tricolor dual-fusion FISH probe for detecting BCR/ABL fusion gene and ASS1 gene deletion is simple, rapid, sensitive and stable. It can detect various forms of molecular fusion and avoid the false positive results due to coincidental overlap of signals generated by D-FISH probe and ES-FISH probe. In addition, this detection method not only can directly observe the presence or absence of ASS1 gene deletion, but also improve the reliability of the positive results of newly diagnosed BCR/ABL fusion gene and accuracy of monitoring results of minimal residual disease for the subsequent visit.