Frequent Intronic Insertion of ABL Gene Detected in Thai Chronic Myeloid Leukemia [CML] Patients Carrying Both e13a2 and e14a2 Variants
Kriangpol Wiriyaukaradecha MSc1, Chakrit Bunyoo MSc1, Wandee Udomchaiprasertkul MSc1, Kamonwan Soonklang MSc2, Narongrit Sritana MSc1, Chirayu Auewarakul MD, PhD3,4
Affiliation : 1 Molecular and Genomic Research Laboratory, Division of Research and International Relations, HRH Princess Chulabhorn College of Medical Science, Bangkok, Thailand 2 Data Management Unit, Division of Research and International Relations, HRH Princess Chulabhorn College of Medical Science, Bangkok, Thailand 3 Faculty of Medicine and Public Health, HRH Princess Chulabhorn College of Medical Science, Bangkok, Thailand 4 Division of Hematology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Bangkok, Thailand
Background : Reverse-transcription polymerase chain reaction [RT-PCR] and quantitative RT-PCR [RQ-PCR] are valuable
tools for investigating CML patients with BCR-ABL fusion gene. Several insertion and deletion mutations can also be
identified.
Objective : To determine frequencies of e14a2 and e13a2 variants and explore existence of intronic ABL mutations in Thai
CML patients.
Materials and Methods : The frequency of e14a2 and e13a2 variants was analyzed in 1,035 CML cases by RT-PCR and/or
RQ-PCR. Cloning of pCRTM4-TOPO plasmid and sequencing were performed to confirm the insertion sequences of
mutations.
Results : Collected samples of blood or bone marrow of CML patients were analyzed by RT-PCR (682 cases) and RQ-PCR
(353 cases). The prevalence of e14a2, e13a2, and both variants in BCR-ABL positive cases were 61.9% (109/176), 32.4%
(57/176), and 5.7% (10/176), respectively. Interestingly, an unexpected band larger than both e13a2 and e14a2 bands was
detected in majority of the cases, which co-expressed both e13a2 and e14a2 sequences by RT-PCR. Sequencing analysis
revealed that the 49-bp insertion was a part of ABL intron 1b. The insertion consisted of a stop codon, leading to only the
BCR part of the fusion gene translated. This particular sequence of insertion had previously been reported only in one
Japanese ALL patient.
Conclusion : The frequencies of e14a2 and e13a2 BCR-ABL variants were similar to those previously reported in Western
and Asian studies. The intron 1b insertion was frequently observed in Thai CML patients carrying both variants in this
study. However, its clinical importance should be further characterized.
Keywords : BCR/ABL, Chronic Myeloid Leukemia [CML], Intronic insertion
