A Decade Mutational Screening: Exon 16 of RET Proto- Oncogene Mutations in Medullary Thyroid Carcinoma

Research Article

Annals Thyroid Res. 2016; 2(1): 40-44.

A Decade Mutational Screening: Exon 16 of RET Proto- Oncogene Mutations in Medullary Thyroid Carcinoma

Sheikholeslami S¹, Zarif Yeganeh M¹, Razavi SA1,2, Nasiri S³ and Hedayati M¹*

¹Cellular and Molecular Research Center, Shahid Beheshti University of Medical Sciences, Iran

²Department of Biology, Islamic Azad University, Iran

³Department of Surgery, Tehran University of Medical Sciences, Iran

*Corresponding author: Mehdi Hedayati, Cellular and Molecular Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Received: April 06, 2016; Accepted: May 25, 2016; Published: May 30, 2016


Objective: Medullary Thyroid Cancer (MTC) is a rare neuroendocrine tumor and accounts for around 5% of all cases of thyroid cancer. Approximately 75% of cases are sporadic, and 25% are hereditary (Multiple Endocrine Neoplasia [MEN] 2A, MEN2B, and Familial [F] MTC). The REarranged during Transfection (RET) proto-oncogene is known to be a genetic cause of MTC, and it seems MTC is the most prevention among endocrine cancer. Therefore, the objective of this study was to identify, and quantify the frequency of, germline mutations in exon 16 of the RET proto-oncogene.

Methods: A total of 422 participants were assessed. Genomic DNA was extracted from leukocytes using the standard salting out/proteinase K method, and mutation detection was performed using PCR and direct DNA sequencing.

Results: In total, three single nucleotide polymorphisms and one mutation were identified in the study population. As expected, the M918T mutation was found only in MEN2B cases. Cysteine to adenine substitution at position 10:43617610 were found in one FMTC family, with C611Y mutation at exon 10. This had not been previously reported and established in the NCBI BioSystems Database.

Conclusion: The data obtained showed the frequency profile of RET mutations in exon 16 among Iranian individuals with MTC and their relatives. Determination of the specific genetic mutation can guide patient management and screening.

Keywords: Medullary Thyroid Carcinoma; Multiple Endocrine Neoplasia type 2B; RET proto-oncogene; Exon 16


RET: REarranged during Transfection; MTC: Medullary Thyroid Carcinoma; sMTC: sporadic MTC; FMTC: Familial MTC; MEN2A: Multiple Endocrine Neoplasia 2A; MEN2B: Multiple Endocrine Neoplasia 2B; PCR: Polymerase Chain Reaction


Thyroid cancer is the most common endocrine malignancy, and its incidence has risen in recent decades. In 2015, SEER has reported which Thyroid cancer represents 3.8% of all new cancer cases in the United State (SEER1). It is classified into four main histological groups: Papillary Thyroid Cancer (PTC), Follicular Thyroid Cancer (FTC), Medullary Thyroid Cancer (MTC), and anaplastic, thyroid carcinoma [1-3].

MTC is a rare neuroendocrine malignancy that accounts for up to 5% of all thyroid cancers, but it`s morbidity and mortality remain high if untreated. It occurs in sporadic and familial forms. The familial forms have been subdivided into two distinct syndromes: multiple endocrine neoplasia (MEN 2A; 55% of all cases), (MEN 2B; 5%-10%) syndromes and familial MTC (FMTC; 35%-40%) [4-8].

MTC is generally the first manifestation of MEN2A because of its higher penetrance. Unilateral or bilateral pheochromocytoma (>50% of cases) and hyperparathyroidism (15–30% of cases) are the other manifestations [8].

MEN2B is characterized by the earlier (usually 10 years earlier than that for MEN2A) occurrence of more aggressive MTC, pheochromocytoma (40–50% of patients), marfanoidfacies, ganglioneuromatosis, and gastrointestinal disorders [8-10].

FMTC refers to an occurrence in which MTC is the only manifestation. In order to diagnose FMTC, it is essential to demonstrate the absence of primary hyperparathyroidism and pheochromocytoma in one or two generations within a family, or provide evidence of an identified RET mutation in families with FMTC [11,12].

Germlinemissense, and point mutations on chromosome 10q 11.2 are associated with all variants of the MTC phenotype. RET is exactly located on mentioned location with 21 exons, and encodes a plasma membrane-bound tyrosine kinas. The gene is an abbreviation of REarranged during Transfection and was so named after it was found to be rearranged during transfection with DNA from lymphoma cells in 3T3 cell lines [6,13].

The RET protein is composed of three domains: extracellular, transmembrane, and intercellular. RET point mutations mostly affect exons 10, 11, and 16, and less common mutations are found in exon 5, 8, 13, 14, and 15 [7]. RET point mutations in the extracellular domain involving codons 609, 611, 618, and 620 of exon10, and 634 of exon 11 lead to the MEN2A and FMTC phenotypes [7,14]. Approximately 95% of MEN2B cases occur via the replacement of methionine with threonine in codon 918 [10,4]. Two somatic missense mutations, S922P and T930M, in exon 16 of the RET proto-oncogene were detected in two sporadic MTC cases [15]. Table 1 shows the all nucleotide changes in exon 16. The polyphen score of nucleotide changes in codon 922, 923, 932 are as high as M918T. Some of them strictly correlate with the aggressiveness of MTC and is associated with a peculiar clinical phenotype [16].