<p>High resolution analysis of DNA copy number abnormalities and loss-of-heterozygosity on acute myeloblastic leukemia samples utilizing SNP arrays has demonstrated that in contrast to pediatric ALL, de novo AML is characterized by a very low burden of genomic alterations (Radtke, et al., PNAS, 2009). Samples for this study represented a cross-section of the different subtypes of pediatric AML. The only AML subtype that was an outlier from the above observations was acute megakaryocytic leukemia (AML FAB-M7), with the majority of these cases being characterized by complex chromosomal rearrangements and a high number of copy number alterations. To more fully define the genomic landscape of this subtype, we performed transcriptome sequence analysis on 14 pediatric FAB-M7 cases and mutation recurrence screening in a panel of 62 adult and pediatric AML FAB-M7 samples using the Illumina platform. Our results identified chromosomal rearrangements resulting in the expression of novel fusion transcripts in 11/14 cases. Remarkably, in 7/14 cases we detected an inversion on chromosome 16 that results in the juxtaposition of the CBFA2T3 gene next to the GLIS2 gene resulting in a CBFA2T3-GLIS2 chimeric gene that encoded an in frame fusion protein. This fusion led to the acquisition or preservation of self-renewal in colony forming assays, providing functional evidence for a role in leukemogenesis. In addition to novel chimeric transcripts, we found mutations in genes previously identified to play a role in megakaryoblastic leukemia that carry a proliferative advantage to the cell, such as JAK2 and MPL. These data demonstrate that AML FAB-M7 is characterized by cooperating Class I and Class II mutations leading to leukemogenesis.</p>

Transcriptome Sequencing of Pediatric AML FAB-M7

An Inv(16)(p13.3q24.3)-encoded CBFA2T3-GLIS2 fusion protein defines an aggressive subtype of pediatric acute megakaryoblastic leukemia.