The newly detected mutations in the RET proto-oncogene in exon 16 as a cause of sporadic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) occurs as a sporadic form or, less frequently, as an autosomal dominant inherited familial disorder. Germline mutations in the RET proto-oncogene in exons 10, 11, 13, 14, 15, and 16 are found in most of the familial cases (nearly 95%). Somatic mutations in sporadic MTC are detected in 23-69% of patients. The most frequent somatic mutation is located in exon 16 at codon 918, and only a small percentage of mutations are found in exons 10, 11, 13, and 15. We have searched for somatic mutations in Czech MTC patients using direct sequencing. We report here two new somatic missense mutations in exon 16 of the RET proto-oncogene associated with the sporadic MTC detected in two Czech men. A homozygous mutation at codon 922 TCC(Ser)-->CCC(Pro) as a result of loss of heterozygosity was revealed in the first patient. In the second one a heterozygous mutation at codon 930 ACG(Thr)-->ATG(Met) was found.