First case of B ALL with KMT2A-MAML2 rearrangement: a case report

Abstract

Background: A large number of chromosomal translocations of the human KMT2A gene, better known as the MLL gene, have so far been characterized. Genetic rearrangements involving KMT2A gene are frequently involved in lymphoid, myeloid and mixed lineage leukemia. One of its rare fusion partners, the mastermind like 2 (MAML2) gene has been reported in four cases of myeloid neoplasms after chemotherapy so far: two acute myeloid leukemias (AML) and two myelodysplasic syndrome (MDS), and two cases of secondary T-cell acute lymphoblastic leukemia (T-ALL).

Case presentation: Here we report the case of a KMT2A - MAML2 fusion discovered by Next-Generation Sequencing (NGS) analysis in front of an inv11 (q21q23) present in a 47-year-old female previously treated for a sarcoma in 2014, who had a B acute lymphoid leukemia (B ALL).

Conclusion: It is, to our knowledge, the first case of B acute lymphoblastic leukemia with this fusion gene. At the molecular level, two rearrangements were detected using RNA sequencing juxtaposing exon 7 to exon 2 and exon 9 to intron 1-2 of the KMT2A and MAML2 genes respectively, and one rearrangement using Sanger sequencing juxtaposing exon 8 and exon 2.

Keywords: KMT2A rearrangement; MAML2 gene; Next-Generation Sequencing; Secondary ALL.

Fig. 1

Cytogenetic analysis at initial diagnosis. Ish inv. (11) (q21, 5’MLL+)(q23, 3’MLL+) ×2 [4].nucish (Mllx3, 5’MLLsep3’MLLx2) [58/100]. FISH study using a LSI KMT2A break apart probe (Vysis, Abbott Molecular Inc.): (a) an interphase cell showing one non-rearranged orange/green signal fusion and two centomeric (red) and two telomeric (green) separate signals, (b) a metaphase cell showing a normal chromosome 11 and two inverted chromosome 11, (c) karyotype from bone marrow aspirate showing complex chromosome abnormalities

Fig. 2

RT-PCR analysis of KMT2A-MAML2 fusion gene. RT-PCR for the KMT2A-MAML2 fusion was performed from patient’s RNA. 1 μg total RNA were reverse-transcribed into cDNA in a 20 μl total volume using random hexamer primers according to EAC protocol (Gabert et al.,2003). PCR reactions contained 1× PCR buffer (Applied Biosystems), 20 nmol dNTPs (Applied Biosystems), 300 nM primer of each primer, 1.25 units of AmpliTaq Gold polymerase (Applied Biosystems), and 5 μl of cDNA in a 50-μl reaction volume. Specific primers were used and were localized on exon 8 of KMT2A (5′-GTCCAGAGCAGAGCAAACAG-3′) and intron 1–2 of MAML2 (5′-TCCCATCTCCAAGTCTCAGC-3′) (Lane 1), on exon 8 of KMT2A and exon 2 of MAML2 (5′-GAGTCTCTCCTGGCTCCTTC-3′) (Lane 2) and on exon 7 of KMT2A (5′-ATCCTGCCCCAAAGAAAAGC-3′) and exon 2 of MAML2 (Lane 3). PCR products were analyzed with Agilent DNA 1000 kit using the 2100 bioanalyzer

Fig. 3

KMT2A and MAML2 fusion transcripts. The KMT2A exon 7 and exon 8 were fused in-frame with MAML2 exon 2 corresponding to variant 1 (VAR1) and variant 3 (VAR3) respectively. The variant 2 (VAR2) was the resulting of a breakpoint within KMT2A exon 9 and within MAML2 intron 1–2