Khadija Iftikhar, Chaudhry Altaf Hussain, Hamid Saeed Malik, Rafia Mahmood.
Patterns of BCR/ABL gene rearrangements by fluorescence in situ hybridization (FISH) in chronic myeloid leukaemia.
Pak J Med Res Jan ;57(4):171-5.

Background: Chronic myeloid leukaemia (CML) is myeloproliferative disorder. The t (9;22), encoding the formation of the BCR/ABL1 fusion gene, is the hallmark chromosomal abnormality detected in CML. This translocation is detectable by RT-PCR or Conventional Karyotyping in 95% patients of CML. However, in 5-10% of cases, the patients fail to demonstrate the presence of Philadelphia chromosome at diagnosis, despite the presence of the BCR/ABL gene rearrangement. Objective: To study the atypical BCR/ABL gene rearrangement patterns by Fluorescence in situ hybridization (FISH) in patients of CML and to determine their clinico-haematological characteristics and response to treatment. Study design, settings and duration: A prospective study, conducted at the department of Haematology, Armed Forces Institute of Pathology, Rawalpindi, from 1st June 2017 to 30th May 2018. Subjects and Methods: The study group included all patients diagnosed as CML based on WHO criteria. RT-PCR and conventional cytogenetics were done on all samples. All patients negative on PCR and cytogenetics were then analyzed by FISH. Interphase FISH analysis on at least 500 nuclei, using a commercially available BCR/ABL1 dual colour dual fusion probe, was performed on initial presentation on bone marrow cells prepared according to standard cytogenetic techniques. Results: Two hundred three diagnostic samples of CML were analyzed of the total, 128 (63%) patients were male and 75 (36.9%) were female. Median age of diagnosis was 38 years. On FISH analysis, atypical signals patterns were observed in 16 (7.9%) patients. These atypical patterns included atypical BCR/ABL gene rearrangements with co-existence of der (9q) and der (22q) deletion in 13 (6.4%) patients and mBCR/ABL gene rearrangement associated to 9q deletion of non-rearranged chromosome 9 in 3 (1.5%) patients. Conclusion: Atypical patterns in CML though rare, however, should be kept in mind when morphological diagnosis supports CML. FISH, in conclusion, is a sensitive, specific and efficient tool to infer these BCR/ABL gene rearrangement patterns.

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