T(X;6)(p11;q23) is a rear but recurrent chromosomal translocation in infant acute myeloid leukemia (AML). It leads to the formation ofMYB-GATA1fusion gene that interferes with granulocyte lineage commitment thus causing AML preliminary with basophilic phenotype. Only males were seen previously in this entity [Dastugue et al. 1997, Belloni et al. 2011, Quelen et al. 2011]. Here we report extensive molecular characterization of 2 infant AML cases with t(X;6)(p11;q23)/MYB-GATA1enrolled in the Russian AML registration study with one of them being a girl.
A boy aged 5,5 mo. with WBC 27,7*109/L and 45% blasts in bone marrow was diagnosed AML, M5a by morphological, cytochemical and immunological observations. He was treated according to AML-BFM-2004 protocol and received allogenic HSCT from matched unrelated donor in the first remission. Patient stays in complete remission for 4 years now.
A girl aged 8 mo. was headed to a hospital with febrile fever and petechiae. She had initial WBC 33,8*109/L and 35% bone marrow blasts of basophilic phenotype. Spinal tap confirmed CNS involvement (cytosis 2,6/mm3, 3% blasts). Patient received induction therapy (cytarabine, etoposide, daunorubicin) and achieved a complete remission. However, she developed severe myelodepression and died of infection 3 mo. after the diagnosis.
MYB-GATA1.GTG-banded karyotyping showed a rearrangement between chromosomes 6 and X as a sole abnormality in both patients - insertion of chromosome 6 material into Xp11 band in a boy and reciprocal translocation t(X;6)(p11;q23) in a girl. FISH for relevant age-specific translocations, includingKMT2Arearrangements and t(7;12)(q36;p12)/ETV6-HLXB, was negative. RNA-seq (TruSeqRNA, Illumina, San-Diego, CA, USA) revealedMYB-GATA1fusion expression with exon 8 - exon 5 junction identical in both patients which was validated by RT-PCR and Sanger sequencing. Direct genomic PCR confirmed breakpoints withinMYBintron 8 andGATA1intron 4 and uncovered patient-specific junctions (see Figure).
Reciprocal fusions.The formation of reciprocal fusions was also shown in two studied patients. A boy demonstratedGATA1-TUBE(6q21) intron 4 - intron 7 junction. It is non-functional due to tail-to-tail transcriptional orientation. Such structures are likely to form sinceMYBandGATA1are located in an opposite genomic orientation, so our finding goes in line with previous unsuccessful attempts to look for reciprocalGATA1fusion transcripts expression [Quelen et al. 2011]. However, a girl patient had reciprocalGATA1-CD164fusion (exon 4 - exon 6) actively transcribed together with third fusionMYB-CD164. On the one hand, this confirms that additional event such as inversion of either chromosomal fragment is required for t(X;6)(p11;q23) to manifest. On the other hand, this is, to our knowledge, the first demonstration of reciprocalGATA1fusion transcript expression inMYB-GATA1-associated AML.
Wild-type MYB and GATA1 expression.AlongsideMYB-GATA1expression both patients demonstrated the overexpression of wild-typeMYBby qPCR. This is in agreement with MYB overexpression being a feature of undifferentiated cells and diminishing during differentiation [Bartunek et al. 2003].
Wild-typeGATA1expression (its lossper se) is of key importance inMYB-GATA1-associated AL. It was previously proposed that the loss of wild-typeGATA1is essential for leukemogenesis in male patients as the only copy of this gene is disturbed by chromosomal translocation [Quelen et al. 2011]. We observed no wild-typeGATA1expression in our male patient. However, in the female patient wild-type GATA1 expression was present.
Additional events.The samples were also screened for additional genetic events associated with myeloid neoplasia by targeted DNA NGS (QIAact Myeloid DNA UMI Panel, Qiagen, Hilden, Germany), fragment analysis (NPM1,FLT3-ITD) and Sanger sequencing (cKIT,FLT3-TKD). NoFLT3,NPM1and cKIT pathogenic variants were found. NoGATA1truncating mutations were found. Deleterious variants were found inNRASgene (p.G12C in a boy, p.G13D in a girl). Female patient also demonstrated pathogenic variants inKRAS(p.A59E) andJAK2(p.N683G).
Thus, here we report a first case of female patient with t(X;6)(p11;q23)/MYB-GATA1. This raises a question whetherGATA1insufficiency is the primary mechanisms of leukemogenesis in this genetic subgroup.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.