Molecular genetic diagnostic program of multiple endocrine neoplasia type 2A and familial medullary thyroid carcinoma syndromes in Hungary.

Medullary thyroid carcinoma (MTC) occurs usually in sporadic form, but about a quarter of the cases are hereditary and appear as part of one of the multiple endocrine neoplasia type 2 (MEN2) syndromes. Mutations in the RET protooncogene are known to be the cause of the MEN2A and familial medullary thyroid carcinoma (FMTC) syndromes in the majority of the families. Direct DNA testing allows prophylactic thyroidectomy to be offered to individuals carrying a mutation in the above codons, and in mutation-negative cases it reduces the yearly screening-related burden on family members at risk of the disease. By DNA sequencing and PCR-restriction fragment length polymorphisms, 65 MTC probands were examined for mutations in residues 609, 611, 618, 620 of exon 10, and in residues 634, 768, 804 of exons 11, 13, and 14 respectively of the RET protooncogene. In our study, mutations in the above codons were detected in all of the 14 clinically MEN2A and FMTC families. One of these mutations, TGC609 TCC has not been reported previously. Of the 14 probands with the mutation, 25 relatives also had the identified mutation and 18 relatives proved to be non-carriers. Among the 51 probands with clinically sporadic MTC, none was found to carry a mutation in the above positions even if indirect signs of MTC, pheochromocytoma or hyperparathyroidism could be detected in some families. The frequency of the TGC634AGC mutation is unexpectedly high in our samples, which can probably be attributed to a founder effect. We conclude that screening for mutations in these codons is effective in families fulfilling the strict clinical criteria of MEN2A or FMTC.

[Molecular genetic study of medullary thyroid cancer]. / A medullaris pajzsmirigyrák molekuláris genetikai vizsgálata.

Around 25% of medullary thyroid carcinoma (MTC) cases are familial and follow an autosomal dominant mode of inheritance. In these cases, MTC is part of an inherited cancer syndrome that has three distinct forms: MEN2A, MEN2B and familial MTC (FMTC). MEN2A is the most frequent syndrome, followed by FMTC and MEN2B. In 95% of MEN2A families and 85% of FMTC families, the germ-line missense mutations underlying the disease affect one of the five cysteine codons of the extracellular domain of the RET proto-oncogene. The mutated codons are 609, 611, 618 and 620 in exon 10, and 634 in exon 11. The most frequent mutations (80% in MEN2A, and 50% in FMTC) occur in codon 634. In our laboratory, the mutations of the codon 634 was detected by two independent methods: DNA sequencing and restriction fragment length polymorphism with polymerase chain reaction (PCR-RFLP). We have so far examined 105 persons at risk and found 19 positive cases. A positive genetic diagnosis allows preventive thyroidectomy, with a resultant cause-specific survival similar to that for the general population. In the event of a negative result, the family members of the affected proband are relieved of the physical and emotional consequences of the disease and the follow-up procedures. We plan to screen all 240 known Hungarian MTC patients and their relatives.

[Clinical application of analysis of microsatellite markers in the prenatal diagnosis of cystic fibrosis]. / Mikroszatellita elemzés klinikai alkalmazása a cisztikus fibrózis praenatalis diagnosztikájában.

Cystic Fibrosis (CF) is an autosomal recessive hereditary disease, caused by the defect of a membrane transport protein. The defect is due to the mutation of the gene coding this protein. To date, these mutations have been analysed by direct mutational analyses in prenatal diagnosis. During gene sequencing, intragenic polymorphic markers (microsatellites) were identified, enabling the indirect analysis of the mutant allele. The markers characterize the given allele, so that the inheritance according to the Mendelian rules could be followed. We introduced a DNA-diagnostic method based on the amplification of three intragenic microsatellites. This new and efficient prenatal diagnostic tool would provide more reliable test results for previously screened CF families, in which direct mutation analysis was not informative.