Over-representation of a germline RET sequence variant in patients with sporadic medullary thyroid carcinoma and somatic RET codon 918 mutation

Abstract

The aetiology of sporadic medullary thyroid carcinoma is unknown. About 50% harbour a somatic mutation at codon 918 of RET (M918T). To investigate whether other RET sequence variants may be associated with or predispose to the development of sporadic medullary thyroid carcinoma, we analysed genomic DNA from the germline and corresponding tumour from 50 patients to identify RET sequence variants. In one patient, tumour DNA showed a novel somatic 12 bp in-frame deletion in exon 15. More interestingly, we found that the rare polymorphism at codon 836 (c.2439C4T; S836S) occurred at a signi®cantly higher frequency than that in control individuals without sporadic medullary thyroid carcinoma (Fisher's exact test, P=0.03). Further, among the nine evaluable cases with germline c.2439C/T, eight also had the somatic M918T mutation in MTC DNA which was more frequent than in patients with the more common c.2439C/C (89% vs 40%, respectively; Fisher's exact test, P=0.01). These ®ndings suggest that the rare sequence variant at codon 836 may somehow play a role in the genesis of sporadic medullary thyroid carcinoma.Keywords: tyrosine kinase; polymorphism; germline mutation; somatic mutation; medullary thyroid cancer Medullary thyroid carcinoma (MTC) comprises approximately 5 ± 10% of all thyroid malignancies (Bergholm et al., 1990). About 75% of all MTCs are believed to be sporadic (Bergholm et al., 1990;Raue et al., 1993), and the remaining 25% comprise the autosomal dominant multiple endocrine neoplasia type 2 (MEN 2) syndromes, MEN 2A, MEN 2B and familial MTC (Farndon et al., 1986;Schimke, 1984). Germline mutations of the RET protooncogene a ecting exons 10, 11, 13, 14, 15 and 16 have been found to be associated with MEN 2 (Bolino et al., 1995;Carlson et al., 1994;Donis-Keller et al., 1993;Eng et al., 1994Eng et al., , 1995Farndon et al., 1986;Gimm et al., 1997;Hofstra et al., 1994;Mulligan et al., 1993;Schimke, 1984; Smith et al., 1997). Speci®cally, germline mutation at codon 918 (M918T) in exon 16 is associated with 495% of MEN 2B , which is characterized by a more severe form of MTC and phaeochromocytoma occurring at a young age and classic stigmata such as ganglioneuromatosis and a marfanoid habitus. Functional, biochemical and limited animal modelling studies have demonstrated that the RET mutations which characterize MEN 2 are capable of activation, sometimes in a constitutive manner, of the RET signalling pathway (Borrello et al., 1995;Ceccherini et al., 1997;Michiels et al., 1997;Pasini et al., 1997;Santoro et al., 1995). The MEN 2B-type mutation, M918T, has been shown to alter substrate speci®city (Borrello et al., 1995;Santoro et al., 1995;Songyang et al., 1995). Interestingly, a median of 50% of sporadic MTC harbour somatic M918T mutations (Eng and Mulligan, 1997). Despite our rapidly accumulating knowledge of the genetics and biochemistry of RET, it is not really known how M918T occurs. Further, while a number of the MEN 2-and MTC-associated RET mutations have been shown to be functionally signi®cant, it is no...

Association of RET codon 691 polymorphism in radiation-induced human thyroid tumours with C-cell hyperplasia in peritumoural tissue

“…It may be suggested that the GGT?AGT polymorphism causes the creation of a cryptic splice donor, splice acceptor or splice enhancer, therefore leading to an altered protein that may contribute to the development of C-cell hyperplasia. Similar mechanisms have been previously hypothesised in the cases of polymorphisms associated with sporadic MTC and Hirschsprung disease (Borrego et al, 1999;Fitze et al, 1999;Gimm et al, 1999). Unfortunately, RNA from our radio-induced thyroid tumours was not available to test this hypothesis.…”

Mutation analysis of NTRK2 and NTRK3, encoding 2 tyrosine kinase receptors, in sporadic human medullary thyroid carcinoma reveals novel sequence variants

“…In a previous study, we showed that somatic mutations in NTRK1 are not common in sporadic MTCs. 10 In the present study, we did not find any somatic mutations of NTRK2 and NTRK3 in tumor DNA from 31 independent patients with sporadic MTC. Hence, we conclude that sequence variants in these genes are not likely to be responsible for differences in expression at the protein level, as previously reported.…”

“…Mutation analysis, however, did not reveal any non-polymorphic sequence variants. 10 In agreement with this finding, immunohistochemical analysis instead suggested a role for NTRK2 (also known as TRKB 16 ) and NTRK3 (also known as TRKC 17 ), which are also neurotrophin receptors, in the pathogenesis of MTC. 17 In advanced stages of MTC, NTRK2 expression was substantially reduced compared to NTRK3 expression, which was increased.…”

“…Patients were classified as having sporadic MTC when no germline mutations could be identified in the RET protooncogene. 10 In addition, there was no family history of MTC, pheochromocytoma or parathyroid disease. At operation, tumor tissue and corresponding peripheral blood samples were obtained from all patients and flash frozen in liquid nitrogen.…”

“…A rare germline polymorphism in exon 14 (S836S) has been found to be over-represented in patients with sporadic MTC when compared to control groups. 9,10 In general, while somatic missense mutations in RET are found in sporadic MTC, translocations or inversions involving RET are found in another type of thyroid carcinoma, papillary thyroid carcinoma (PTC). [11][12][13] Similar to RET, another tyrosine kinase receptor, NTRK1, also known as TRKA, is involved in the pathogenesis of PTC.…”