Identification of Novel Type of ETV6-TTL Fusion Gene in Pediatric Myeloid/NK Cell Precursor Acute Leukemia Having t(12;13)(p13;q14).

The t(12;13)(p11-13:q11-14) is a recurring chromosomal abnormality found in different types of hematological malignancies. Three genes on 13q12-14, CDX2, FLT3, and TTL have been identified as fusion partners of ETV6(TEL) on 12p13. These genes create different forms of fusion transcripts with ETV6. In the present study, we identified novel types of ETV6-TTL fusion transcripts in a case of a 9 year-old female who developed myeloid/NK cell precursor acute leukemia with t(12;13)(p13;q14). Cytogenetic analyses of the leukemic cells of the patient using a regular G-banding revealed 47, XX, del(2)(q?), -9, der(12)t(12;13)(p13;q14), add(13)(q1?2), +mar1, +mar2 [13/20]. Fluorescence in situ hybridization using YAC clone revealed that ETV6 gene was split in metaphase chromosomes of patient’s leukemic cells. We performed reverse-transcriptase-polymerase chain reaction (RT-PCR) analysis to detect the fusion transcripts of ETV6-CDX2, ETV6-FLT3 or TTL-ETV6, however, no fusion transcripts of previously described types were detected. We next performed RT-PCR analysis using various sets of primers to detect unknown types of fusion transcripts involving these genes, and detected novel types of fusion transcripts of ETV6-TTL. These fusion transcripts consisted of exons 1 to 5 of ETV6 and exons 5 to 8 of TTL, and exons 1 to 6 of ETV6 and exon 9 or exons 8 to 9 of TTL. No reciprocal fusion transcripts were detected. Predicted fusion proteins consisted of N-terminal ETV6 lacking whole or part of ETS-binding domain and C-terminal TTL. Previous report showed major type of TTL-ETV6 fusion transcript consisted of exons 1 to 5 of TTL and exons 2 to 8 of ETV6 which contained both helix-loop-helix and ETS-binding domains. These results suggested that novel types of ETV6-TTL act as different fusion proteins from previously reported TTL-ETV6 in leukemogenesis. At the cytogenetic level, it may be difficult to distinguish ETV6-CDX2, ETV6-FLT3, and ETV6-TTL. Further accumulation of the patients with t(12;13) and further analysis of these novel types of fusion transcripts may clarify the pathogenesis of t(12;13)-leukemia.