Abstract
Telomeres are specialized structures at the ends of chromosomes, consisting of hundreds of repeated hexanucleotides (TTAGGG)n. Genetic integrity is partly maintained by the architecture of telomeres and it is gradually lost as telomeres progressively shorten with each cell replication, due to incomplete lagging DNA strand synthesis and oxidative damage. Telomerase is a reverse transcriptase enzyme that counteracts telomere shortening by adding telomeric repeats to the G-rich strand. It is composed of a telomerase RNA component and a protein component, telomerase reverse transcriptase. In the absence of telomerase or when the activity of the enzyme is low compared to the replicative erosion, apoptosis is triggered. Patients who have inherited genetic defects in telomere maintenance seem to have an increased risk of developing familial benign diseases or malignant diseases. At the somatic level, telomerase is reactivated in the majority of human carcinomas, suggesting that telomerase reactivation is a critical step for cancerogenesis.In sporadic thyroid carcinoma telomerase activity is detectable in nearly 50% of thyroid cancer tissues and some authors proposed that the detection of telomerase activity may be used for differentiating between benign and malignant thyroid tumours. Recently a germline alteration of telomere-telomerase complex has been identified in patients with familial papillary thyroid cancer, characterized by short telomeres and increased expression and activity of telomerase compared to patients with sporadic papillary thyroid cancer.In this report, we will review the role of telomere-telomerase complex in sporadic and familial thyroid cancer.
Highlights
Thyroid cancer (TC) is the most common endocrine malignancy and its incidence has increased significantly in many countries over the past three decades [1, 2]
TC comprises a group of tumors with different features and are subdivided into two major categories, depending on the cell type involved: 1) carcinomas originating from the follicular epithelium including the papillary (PTC), follicular (FTC) and hurthle (HTC) cell histotypes (Differentiated thyroid cancers, DTC) and the undifferentiated or anaplastic (ATC) histotype; 2) carcinomas originating from the parafollicular thyroid C cells, referred to as medullary thyroid cancer (MTC)
DTC are characterized by somatic mutations in the MAPKinase pathways represented by RET-papillary thyroid carcinomas (PTC) and TRK rearrangements, BRAF and RAS point mutations and PAX8PPAR rearrangements While BRAF, RET-PTC and TRK are limited to the papillary histotype, PAX8-PPAR rearrangements are limited to the follicular histotype and RAS mutations are shared in both histotypes
Summary
Thyroid cancer (TC) is the most common endocrine malignancy and its incidence has increased significantly in many countries over the past three decades [1, 2]. DTC is prevalently sporadic, but evidence of a familial clustering is accumulating over the last years with prevalence up to 10% in different series [5, 6] It is indicated as familial non-medullary thyroid carcinoma (FNMTC) and it is defined as the presence of thyroid cancer of follicular cell origin in two or more first-degree relatives [6]. FNMTC appears as the only manifestation in absence of any syndrome and no candidate genes In this case, one study, where the author applied an exact probability measure to a series of first-degree family members suggested that the presence of only two affected members in kindred may represent a fortuitous association of the disease [15].
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