The mitochondrial DNA control region might have useful diagnostic and prognostic biomarkers for thyroid tumors

Background: It is currently present in the literature that mitochondrial DNA (mtDNA) defects are associated with a great number of diseases including cancers. The role of mitochondrial DNA (mtDNA) variations in the development of thyroid cancer is a highly controversial topic. In this study, we investigated the role of mt-DNA control region (CR) variations in thyroid tumor progression and the influence of mtDNA haplogroups on susceptibility to thyroid tumors. Material & method: For this purpose, totally 108 hot thyroid nodules (HTNs), 95 cold thyroid nodules (CTNs), 48 papillary thyroid carcinoma (PTC) samples with their surrounding tissues and 104 healthy control subject9s blood samples were screened for entire mtDNA CR variations by using Sanger sequencing. The obtained DNA sequences were anaysed with the mistomaster, a web-based bioinformatics tool. Results: MtDNA haplogroup U was significantly associated with susceptibility to benign and malign thyroid entities on the other hand J haplogroup was associated with a protective role for benign thyroid nodules. Besides, 8 SNPs (T146C, G185A, C194T, C295T, G16129A, T16304C, A16343G and T16362C) in mtDNA CR region were associated with the occurrence of benign and malign thyroid nodules in Turkish population. By contrast with the healthy Turkish population and HTNs, frequency of C7 repeats in D310 polycytosine sequence was found higher in cold thyroid nodules and PTC samples. Beside this, the frequency of somatic mutations in mtMSI regions including T16189C and D514 CA dinucleotide repeats were found higher in PTC samples than the benign thyroid nodules. Conversely, the frequency of somatic mutations in D310 was detected higher in HTNs than CTNs and PTCs. Conclusion: mtDNA D310 instability do not play a role in tumorogenesis of the PTC but the results indicates that it might be used as a diagnostic clonal expansion biomarker for premalignant thyroid tumor cells. Beside this, D514 CA instability might be used as prognostic biomarker in PTCs. Also, we showed that somatic mutation rate is less frequent in more aggressive tumors when we examined micro- and macro carcinomas as well as BRAFV600E mutation.