Concurrent chromothripsis events in a case of TP53 depleted acute myeloid leukemia with myelodysplasia-related changes.

Acute myeloid leukemia with myelodysplasia-related changes (AML-MRC) is a heterogeneous hematological disorder defined by morphological, genetic, and clinical features. Patients with AML-MRC often show cytogenetic changes, which are associated with poor prognosis. Straightforward criteria for AML-MRC diagnosis and a more rigorous characterization of the genetic abnormalities accompanying this disease are needed. Here we describe an informative AML-MRC case, showing two separate, but concurrent, chromothripsis events, occurred at the onset of the tumor, and originating an unbalanced t(5;7) translocation and a derivative chromosome 12 with a highly rearranged short arm. Conversely, despite chromothripsis has been often associated with genomic amplification in cancer, in this case a large marker chromosome harboring amplified sequences from chromosomes 19 and 22 arose from a stepwise mechanism. Notably, the patient also showed a TP53 mutated status, known to be associated with an increased susceptibility towards chromothripsis and a poor prognosis. Our results indicate that multiple chromothripsis events may occur early in neoplastic transformation and act in a synergistic way with progressive chromosomal alterations to determine a dramatic impact on disease outcome, as suggested by the gene expression profile analysis.

Genomic segmental duplications on the basis of the t(9;22) rearrangement in chronic myeloid leukemia.

A crucial role of segmental duplications (SDs) of the human genome has been shown in chromosomal rearrangements associated with several genomic disorders. Limited knowledge is yet available on the molecular processes resulting in chromosomal rearrangements in tumors. The t(9;22)(q34;q11) rearrangement causing the 5'BCR/3'ABL gene formation has been detected in more than 90% of cases with chronic myeloid leukemia (CML). In 10-18% of patients with CML, genomic deletions were detected on der(9) chromosome next to translocation breakpoints. The molecular mechanism triggering the t(9;22) and deletions on der(9) is still speculative. Here we report a molecular cytogenetic analysis of a large series of patients with CML with der(9) deletions, revealing an evident breakpoint clustering in two regions located proximally to ABL and distally to BCR, containing an interchromosomal duplication block (SD_9/22). The deletions breakpoints distribution appeared to be strictly related to the distance from the SD_9/22. Moreover, bioinformatic analyses of the regions surrounding the SD_9/22 revealed a high Alu frequency and a poor gene density, reflecting genomic instability and susceptibility to rearrangements. On the basis of our results, we propose a three-step model for t(9;22) formation consisting of alignment of chromosomes 9 and 22 mediated by SD_9/22, spontaneous chromosome breakages and misjoining of DNA broken ends.