The cytogenetic and molecular analysis of chronic myeloid leukemia in a tertiary care hospital of Sindh, Pakistan

We performed a Cross sectional study to determine the frequency of Philadelphia chromosome and frequency of standard and variant translocation in chronic myeloid leukemia cases by the collaboration of Pathology department of Liaquat University of Medical and Health Sciences, Jamshoro and Isra University Hospital, Hyderabad from May to September 2014. A sample of 145 diagnosed cases of CML was selected according to inclusion. Bone marrow and peripheral Blood samples were collected in sodium heparinized bottles. Cytogenetic analysis was performed by karyotyping according to ISCN guidelines for human cytogenetic nomenclature using cytovision system for image analysis, reverse transcription polymerase chain reaction (RT-PCR) was performed to identify the various BCR-ABL transcripts. Ph+ and Ph-chromosomes were noted in 133 (91.7) and 12 (8.2%) of cases respectively. Of 133 Ph+ chromosome, standard chromosome was noted in 121 (90.9%), simple variant in 9 (6.7) and complex variants were noted in 3 (2.2%) of cases. Ph + 133 (91.7%) showed bcr-abl positivity in all subjects. Of 12 (8.2%) Ph-subjects, 7 (%) were bcr-abl positive and 5 (%) were bcr-able negative. Sensitivity and specificity of bcr-abl transcripts was calculated at 95% and 100% respectively. The present study reports Philadelphia chromosome in 90.9% and variant cytogenetic abnormalities are low similar to reported from other countries. Proper assessment of the variant translocations requires better categorization of these translocations. Introduction Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the presence of the Philadelphia chromosome (Ph) which is the derivative chromosome 22 of the translocation t (9; 22) (q34.1; q11.2). Due to this rearrangement, the break-point cluster region (BCR) gene at position 22q11 [1,2] is juxtaposed to the c-Abelson (ABL1) gene at 9q34, resulting in the BCR-ABL1 fusion gene, encoding a constitutively active tyrosine kinase protein. The identification of this abnormality is important for the diagnosis of the disease as determined by the WHO Tumor Classification1and for treatment purposes. The first therapeutic choice, tyrosine kinase inhibitors, has shown great therapeutic efficacy [2]. The Ph is detected by G-band karyotyping in around 90% of CML patients among whom 5–10% may have variant types [3-5]. Variant Ph chromosomes are characterized by the involvement of another chromosome in addition to chromosome 9 or 22. It can be a simple type of variant when only one additional chromosome is involved, or complex, in which two or more chromosomes, besideschromosomes 9 and 22, take part in the translocation [6,7]. Variant Ph breakpoints occur in hotspots across the genome, usually in the G-light bands, within the cytosine and guanine (CG) richest parts of the genome [8]. However, the mechanism of variant Ph generation and the molecular bases of biological differences between classic Ph and variant Ph chromosomes are not fully understood [9]. Recently, Albano et al. [10] reported a study they performed on gene expression profiling (GEP) using microarrays to identify some of these differences [10]. The prognostic significance of variant Ph chromosomes has already been discussed [11] and it has been shown that the variant aberration does not impact on cytogenetic or molecular responses or even on clinical outcome. Variant Ph chromosomes are distinguished from additional chromosomal abnormalities or clonal evolution that drives disease progression. The clonal evolution is a reflection of a genetic instability that characterizes the transition to advanced phase [12]. In this situation, i (17q), a second Ph and +8 are frequently found [1]. A search of local literature showed only a few studies had been conducted and reported, hence there is an urgent need to conduct more studies to explore cytogenetic and molecular abnormalities in chronic myeloid leukemia cases in our local population of Sind. Subjects and methods This cross sectional study was conducted at pathology department of Liaquat University of Medical and Health Sciences, Jamshoro and Isra University Hospital, Hyderabad from May to September 2014. A sample of 145 newly diagnosed cases of CML was included. Patients with acute leukemia, polycythemia, essential thrombocythemia and myelofibrosis, multiple myeloma were excluded from the study. Diagnosed cases of CML were included, while patients with acute leukemia, lymphoma, and multiple myeloma. Written informed consent was taken from the patients. The study was approved by the ethical committee of Isra University Hyderabad. Bone marrow and Blood samples were collected in sodium heparinized vacutainer by applying appropriate techniques. CBC was performed on automatic hematoanalyzer, Sysmex XN 1000i. Cytogenetic analysis was performed by karyotyping according to Correspondence to: IkramdinUjjan, Department of Pathology, Liaquat University of Medical and Health Sciences, Jamshoro, Sindh, Pakistan, Tel: 092 22 9213135; Fax: 092 22 9210100, E-mail: Ikramujjan1973@yahoo.com