MLL-SEPT5 Fusion Transcript in Two de novo Acute Myeloid Leukemia Patients With t(11;22)(q23;q11)

Dear Editor, Rearrangements involving mixed lineage leukemia (MLL) are common chromosome aberrations in infant, pediatric and adult acute leukemia, which are generally associated with poor prognosis. To date, more than 79 partner genes have been identified [1]. MLL fusion partners can be classified into four groups: nuclear proteins (MLLT3, MLLT10, and MLLT1), cytoplasmatic proteins (GAS7, SH3GL1, EPS15, and MLLT4), histone acetyltransferases (EP300, CREBBP), and the septin family (SEPT2, SEPT5, and SEPT6) [2]. In pediatric and adult AML, the most frequent fusion partners are represented by MLLT3-AF9 (9p22), MLLT10-AF10 (10p12), ELL (19p13.1), MLLT4-AF6 (6q27), and MLLT1-ENL (19p13.3) [1, 3]. However, as a partner gene, the SEPT5 gene has been reported in only five AML cases (Table 1). Here we present two cases of de novo AML with MLL-SEPT5 transcript. Chromosomal analysis revealed a karyotype of 46, XX/XY, t(11;22)(q23;q11.2). Reverse transcription polymerase chain reaction (RT-PCR) analysis indicated an MLL-SEPT5 fusion transcript. Sanger sequencing of the PCR product confirmed the fusion between MLL and SEPT5. Notably, a new fusion transcript between MLL exon 8 and SEPT5 intron 2 was detected in one of the patients. Patient 1 was a 21-yr-old man who presented with fever, oral ulcer, and tonsillitis. His hemoglobin level was 8.5 g/dL, white blood cell count was 35.45 ×10/L, and platelet count was 29×10/L. Bone marrow aspiration was hypercellular, containing 81% blasts. Immunophenotypic analysis showed that the blasts were positive for CD45, CD33, CD117, CD15, and HLADR, but negative for other markers. Cytogenetic studies revealed the karyotype of 46, XY, t(11;22)(q23;q11.2) [8]/46,XY [2]. Fluorescence in situ hybridization analysis using a MLL-specific probe showed a split in the MLL gene (Fig. 1). He received three courses of induction chemotherapy in our hospital followed by a mother-to-son haploidentical bone marrow transplantation. To date, he is in complete remission. To validate MLL-SEPT5 existence, we performed RT-PCR and direct DNA sequencing. Total RNA was extracted from the bone marrow cells using TRIzol reagent (Invitrogen, Paisley, UK) and chloroform. cDNA was obtained by RT-PCR using the M-MLV reverse transcriptase (Promega, Madison, WI, USA). The resulting cDNA was amplified by PCR using 2×Hieff PCR Master Mix (Yaeson, Shanghai, China) and the following primers: 5 ́-GCTCCACCCATCAAACCAAT-3 ́ from exon 5 of MLL and 5 ́-TTCTTCTCAATGTCCACCGT-3 ́ from exon 4 of SEPT5 (Fig. 2). PCR products were sequenced on both strands by using an Applied Biosystems ABI 3730 XL DNA analyzer (Thermo Fisher Scientific,