Germline mutation of RET proto-oncogene's exons 17 and 18 in Iranian medullary thyroid carcinoma patients

Thyroid carcinoma is the most common endocrine malignancy. Medullary thyroid carcinoma (MTC) approximately accounts for 5-10% of all thyroid carcinoma. Nowadays, it is obviously, the mutations in REarranged during transfection (RET) proto-oncogene, especially, mutations in exons 10, 11 and 16 are associated with MTC pathogenesis and occurrence. Thus, early diagnosis of MTC by mutation detection in RET proto-oncogene allows to identify patients who do not have any developed symptoms. The aim of this study was to screening of germline mutations in RET proto-oncogene exons 17 and 18 in MTC patients and their first degree relatives in Iranian population.
In this cross-sectional study, three hundred eleven participates (190 patients, 121 their relatives) were referred to endocrine research center, Shahid Beheshti University of Medical Science during September 2013 until September 2015. The inclusion criteria were pathological and clinical diagnosis. After whole blood sampling, genomic DNA was extracted from peripheral blood leucocytes using the standard Salting Out/Proteinase K method. Nucleotide change detection in exons 17 and 18 was performed using PCR and direct DNA sequencing methods.
In this study, twenty missense mutations [CGC>TGC, c.2944C>T, p.Arg982Cys (rs17158558)] which included 16 heterozygote and 4 homozygote mutations were found in codon 982 (exon 18). In the present study, 154 G>A (rs2742236) and 4 C>T (rs370072408) nucleotide changes were detected in exons 18 and intron 17 respectively. There was no mutation in exon 17.
It seems that because of arginine to cysteine substitutions in RET tyrosine kinase protein structure and its polyphen score (0.955) and SIFT score (0.01) the mutation in codon 982 (exon 18) could be have pathogenic effects. On the other hands, the mentioned mutation frequency was 6.4% among MTC patients, so this mutation of exon 18 could be checked in genetic screening tests of RET proto-oncogene. Although this needs more study.