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.