Somatic mutations of the mitochondrial genome in Chinese patients with Ewing sarcoma.

Somatic mutations in mitochondrial DNA (mtDNA) have been long proposed to drive initiation and progression of human malignancies. Our previous study revealed a high prevalence of somatic mutations in the D-loop region of mtDNA in Ewing sarcoma (EWS). However, it is unclear whether somatic mutations also occur in the coding regions of mtDNA in EWS. To test this possibility, in the present study, we sequenced the whole mitochondrial genome from 20 cases of EWS specimens and their corresponding peripheral blood samples. We identified a total of 6 somatic mutations in the mtDNA coding regions in our EWS series, and 5 of them were missense or frame-shift mutations that have the potential to directly influence proper mitochondrial function. In combination with our earlier observations on the D-loop fragment, 70% (14/20) of EWS tissues appeared to harbor somatic mtDNA mutations. Among the identified 25 somatic mutations, 19 (76%) were located in the D-loop control region, 1 (4%) was in the sequence of the tRNA(Val) gene, 1 (4%) was in the mitochondrial ATP synthase subunit 6 gene, and 4 (16%) occurred in genes encoding components of the mitochondrial respiratory complexes. In addition, patients carrying somatic mtDNA mutations did not show significant association with their clinicopathologic characteristics. Together, these findings suggest that somatic mtDNA mutations occur in both protein coding and noncoding regions of mtDNA, which may play critical roles in the pathogenesis of EWS and should be further explored for its possible use as a novel marker for monitoring EWS occurrence and advancement.