Genome-Wide Analysis of Microdeletions and Identification of NF1 Inactivation in Acute Myelogenous Leukemia.

Abstract 165

Genomic aberrations are of dominant importance to the biology and clinical outcome of patients with acute myelogenous leukemia (AML). To further our understanding of such aberrations in AML, we analyzed DNA from highly purified AML blasts and paired buccal cells from 95 patients for subchromosomal copy number changes and allele identities using ultra-high-density Affymetrix SNP 6.0 array-based genomic profiling. A total of 358 somatically acquired copy number changes were detected in 95 AML genomes. We detected 16 losses and 22 gains of entire chromosomes, 285 subchromosomal losses and 35 subchromosomal gains. No recurrent high-level amplifications or recurrent homozygous deletions were identified. Eight of the 34 AML cases (24%) with normal karyotype each had one lesion detected through 6.0 array profiling, all but one of which was less than 4Mb in length.

Focusing on microdeletions as potential indicators of the locations of novel tumor suppressor genes or genes with importance to AML biology, we identified 60 deletions that were less than 1 Mb in length and 158 deletions of less than 5 Mb, the vast majority of which were undetectable by conventional cytogenetics.

Through fine mapping of microdeletions on 17q, we identified Neurofibromin 1 (NF1) null states due to mutations or absent expression in ∼7% of AML. NF1 mutations were present in the hematopoetic stem cell compartment (CD34+/CD38- cell population) and siRNA-mediated NF1 suppression using recombinant lentiviruses significantly increased colony formation of primary AML blasts in methylcellulose. Further, AML blasts without functional NF1 displayed sensitivity to rapamycin-induced apoptosis, thus identifying a dependence on mTOR signaling for survival.

As an additional validation of using microdeletions to guide pathogenetic gene discovery, we identified deletions involving RUNX1, IRF8, Core Binding Factor Beta (CBFB) and Casitas B-cell lymphoma B (CBLB), genes known to be altered in AML. IRF8 expression was found to be absent in ∼30% of all AML but sequencing of all coding exons of IRF8 of 48 AML cases did not disclose somatically acquired mutations.

In summary, this comprehensive description of subchromosomal copy number changes and microdeletions in adult AML substantially adds to our knowledge of the pathological anatomy of the AML genome and should inform future searches for novel genes with importance to AML biology.