Determination of mitochondrial DNA copy number in functional and non-functional thyroid nodules and papillary thyroid carcinomas in Turkish community

Thyroid nodules are generally benign and 4%-6.5% of total thyroid nodules are at risk of malignancy. Although about 85% of thyroid nodules are cold, 10% are normal and 5% are hot, according to their functional properties, its prevalence may vary depending on the iodine source in the environment and geographical location. The malignant potential of hot thyroid nodules is 1% or less, and this risk varies between 5% and 15% in cold thyroid nodules. However, papillary thyroid cancer (PTC) is the most common type of cancer among thyroid cancers and covers more than 80% of thyroid cancer cases. However, there are 103-104 copies of mtDNA in each cell. Also, the exact copy number of mitochondrial DNA (mtDNA) in a cell is not known, and the mtDNA copy number varies between each cell type, depending on the metabolic needs of the cells. There are few publications in the literature on the detection of mtDNA copy changes in benign thyroid nodules and papillary thyroid cancer. The aim of this study; detection of mitochondrial DNA (mtDNA) copy number changes in functional and nonfunctional thyroid nodules and PTKs in Turkish population and to determine the relationship between tumorogenesis of PTKs and mtDNA copy number changes. DNA samples obtained from 74 hot nodules, 64 cold nodules, and 48 PTC tumor tissues belonging to patients diagnosed with toxic MNG, MNG or PTC, and healthy surrounding tissue samples close to these nodules were included in the study. However, due to technical and financial insufficiency, mtDNA copy number could be determined in 5 nodules of only 5 of 48 PTC patients. Determination of mtDNA copy number was performed by relative quantification method using SYBR green I fluorescent dye on a LightCycler 480 II real-time PCR device. While an increase was observed in mtDNA copy number in 49 (66.2%) of 74 hot nodules scanned, a decrease was observed in 16 (21.6%) nodules and no change was detected in 9 (12.2%). On the other hand, while an increase in mtDNA copy number was observed in 22 (34.4%) of 64 cold nodules scanned, a decrease was observed in 21 (32.8%) nodules and no change was detected in 21 (32.8%) (χ²: 15.098; p: 0.001). It was determined that mtDNA copy number increased in 2 of 5 PTK tissues, decreased in 2, and mtDNA copy number did not change in 1 of them. However, the effect of mtDNA T16189C variant on mtDNA copy number could not be investigated due to insufficient number of cases (3 individuals in total) with mtDNA T16189C variant for statistical analysis in the current patient population. As a result, it has been determined that cold nodules with a high cancer potential have a greater decrease in mtDNA copy number than hot nodules. These findings support the information in the literature that the decrease in mtDNA copy number is associated with the tumorigenesis process in human cancers.