Loss of heterozygosity at 19p13.2 and 2q21 in tumours from familial clusters of non-medullary thyroid carcinoma.

Linkage studies have identified susceptibility loci for familial nonmedullary thyroid cancer (FNMTC), with and without cell oxyphilia, at chromosomal regions 19p13.2 and 2q21. There are few genetic analyses of FNMTC tumours reported at the present time and the eventual gene involved was not identified yet. The aim of this study was to assess the occurrence of loss of heterozygosity (LOH) at these loci in the tumours from familial clusters of NMTC. We have analysed LOH in 14 tumours from 9 two-case familial clusters of NMTC. Using paired blood (normal) and tumour DNA samples, we have genotyped ten microsatellite and one SNP markers throughout 19p13.2 and fourteen microsatellite markers at 2q21. Overall, eight (57%) and two (14%) out of the fourteen tumours analysed exhibited LOH at 19p13.2 and 2q21, respectively. In two families (22%), LOH for the same markers was demonstrable in the tumours of the two members of the same family. In one family (11%) LOH was demonstrable at both loci analysed. In four two-case familial clusters (44%), LOH at the 19p13.2 locus was found in only one of the tumour cases analysed. Detailed haplotype analysis showed that, in two families (22%), the pattern of LOH in tumours was consistent with selective retention of the haplotype shared by affected members. In the remaining cases, it was consistent with random allelic losses. In conclusion, we report the finding of LOH at the 19p13.2 and 2q21 loci in tumours from familial clusters of NMTC, providing evidence that inactivation of putative genes in these regions, acting as tumour-suppressors, may be involved in the development of tumours in the context of FNMTC.

Occurrence of the Cys611Tyr mutation and a novel Arg886Trp substitution in the RET proto-oncogene in multiple endocrine neoplasia type 2 families and sporadic medullary thyroid carcinoma cases originating from the central region of Portugal.

OBJECTIVE: Medullary thyroid carcinoma (MTC) occurs both sporadically and in the context of autosomal dominantly inherited multiple endocrine neoplasia type 2 (MEN2) syndromes: MEN2A, MEN2B, and familial medullary thyroid carcinoma (FMTC), which are caused by activating germline mutations in the RET proto-oncogene. The aim of this study was to characterize the RET mutational spectrum in MEN2 families and apparently sporadic MTC (AS-MTC) cases originating from the central region of Portugal. SUBJECTS AND METHODS: We studied a total of 82 individuals (64 affected and 18 family members), comprising five MEN2 families (four MEN2A and one MEN2B), as well as 53 AS-MTC cases. RET germline mutations were screened using PCR-DNA sequencing, SSCP and RFLP. The haplotypes associated with recurrent mutations were determined by fragment analysis of microsatellite markers, and by RFLP, in the case of intragenic polymorphisms. RESULTS: Frequency of the Cys611Tyr (TGC-TAC) mutation was significantly increased in this region of Portugal, due to the fact that three apparently unrelated MEN2A/FMTC families, out of the five in which mutations were identified, harboured this specific mutation. Haplotype analysis revealed that a common haplotype was shared between two of these three families. We have also characterized a novel RET mutation, Arg886Trp, located in the tyrosine kinase domain, which was found in an AS-MTC case. CONCLUSIONS: There are regional specificities in the relative frequency of RET mutations, which are consistent with a cluster-like distribution of specific disease-causing mutations, as a result of the inheritance of a shared haplotype. These data, along with the finding of a novel RET mutation (Arg886Trp), have important implications towards facilitating and improving the molecular diagnosis of hereditary MTC on a regional basis.