Medullary thyroid carcinoma (MTC) occurs as a sporadic form (75%) or as an autosomal dominant inherited familial disorder (25%) called familial MTC (FMTC) or as multiple endocrine neoplasia type 2 (MEN2) syndromes. Germ-line mutations in the rearranged during transfection (RET) proto-oncogene in exons 10, 11, 13, 14, 15 and 16 are known to be a cause of most of the familial forms. In this paper we report molecular genetic testing of 106 families with MTC (358 tested persons) from the Czech Republic in which we directly sequenced these six exons of the RET proto-oncogene. We detected germ-line mutations in 100% of MEN2B families (4/4 families), 90% of MEN2A families (9/10), 40% of FMTC families (4/10) and 7% of apparently sporadic MTC (6/82). Eleven different germ-line mutations were revealed. MEN2B was associated with mutation Met918 Thr in exon 16. In one MEN2B family beside this mutation the Tyr791 Phe was also found, which has not yet been reported. MEN2A was restricted to different mutations in exon 11 (codon 634). In FMTC and 'sporadic' MTC families the mutations in exons 10, 11, 13 and 14 were detected. The genotype/phenotype correlations are given. Genetic testing revealed germ-line mutations in 23 index patients, 24 family members and excluded them in 53 relatives.

Department of Molecular Endocrinology Institute of Endocrinology Národní 8 Prague 1 11694 Czech Republic

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