Germline sequence variant S836S in the RET proto-oncogene is associated with low level predisposition to sporadic medullary thyroid carcinoma in the Spanish population

Molecular Basis and Natural History of Medullary Thyroid Cancer: It is (Almost) All in the RET

Medullary thyroid cancer (MTC) is a rare disease, which can be either sporadic (roughly 75% of cases) or genetically determined (multiple endocrine neoplasia type 2, due to REarranged during Transfection RET germline mutations, 25% of cases). Interestingly, RET pathogenic variants (mainly M918T) have also been reported in aggressive forms of sporadic MTC, suggesting the importance of RET signalling pathways in the pathogenesis of MTC. The initial theory of RET codon-related MTC aggressiveness has been recently questioned by studies suggesting that this would only define the age at disease onset rather than the aggressiveness of MTC. Other factors might however impact the natural history of the disease, such as RET polymorphisms, epigenetic factors, environmental factors, MET (mesenchymal-epithelial transition) alterations, or even other genetic alterations such as RAS family (HRAS, KRAS, NRAS) genetic alterations. This review will detail the molecular bases of MTC, focusing on RET pathways, and the potential mechanisms that explain the phenotypic intra- and interfamilial heterogeneity.

Modifier Role of Common RET Variants in Sporadic Medullary Thyroid Carcinoma

Background: Although the disease-causing effect of pathogenic variants in the gene RET has been unambiguously identified, there is a lack of consensus regarding the possible impact of common variants in this gene. Our study aimed to test whether variants in exons 10, 11, and 13–16 that are commonly detected during routine diagnostic testing might have any modifying effect on MTC. Methods: In sporadic MTC patients with no pathogenic variants but with or without common variants in RET, the following variants were evaluated: rs1799939 (p.G691S), rs1800861 (p.L769=), rs1800862 (p.S836=), rs2472737 in intron 14, and rs1800863 (p.S904=). Results: After Bonferroni correction, none of the variants were statistically significantly associated with disease outcome when analysed independently. The MTC group was divided into three genetically different clusters by unsupervised k-means clustering. Those clusters differed significantly in the age at diagnosis. A trend towards the association of given clusters with metabolic disorders and with remission state was identified. Conclusions: Although common variants in RET are not responsible for the risk of MTC, their analysis might turn out useful in the prediction of a patient’s clinical outcome. Importantly, this analysis would come with no additional cost in laboratories with a diagnostic procedure based on exon sequencing.

Current status of the prognostic molecular markers in medullary thyroid carcinoma

Medullary thyroid cancer (MTC) is a rare thyroid malignancy, which arises from parafollicular C-cells. It occurs in the hereditary or sporadic form. Hereditary type is a consequence of activation of the RET proto-oncogene by germline mutations, whereas about 80% of sporadic MTC tumors harbor somatic, mainly RET or rarely RAS mutations. According to the current ATA guidelines, a postoperative MTC risk stratification and long-term follow-up are mainly based on histopathological data, including tumor stage, the presence of lymph node and/or distant metastases (TNM classification), and serum concentration of two biomarkers: calcitonin (Ctn) and carcinoembryonic antigen (CEA). The type of RET germline mutation also correlates with MTC clinical characteristics. The most common and the best known RET mutation in sporadic MTC, localized at codon 918, is related to a more aggressive MTC course and poorer survival. However, even if histopathological or clinical features allow to predict a long-term prognosis, they are not sufficient to select the patients showing aggressive MTC courses requiring immediate treatment or those, who are refractory to different therapeutic methods. Besides the RET gene mutations, there are currently no other reliable molecular prognostic markers. This review summarizes the present data of genomic investigation on molecular prognostic factors in medullary thyroid cancer.

Influencers on Thyroid Cancer Onset: Molecular Genetic Basis

Thyroid cancer, a cancerous tumor or growth located within the thyroid gland, is the most common endocrine cancer. It is one of the few cancers whereby incidence rates have increased in recent years. It occurs in all age groups, from children through to seniors. Most studies are focused on dissecting its genetic basis, since our current knowledge of the genetic background of the different forms of thyroid cancer is far from complete, which poses a challenge for diagnosis and prognosis of the disease. In this review, we describe prevailing advances and update our understanding of the molecular genetics of thyroid cancer, focusing on the main genes related with the pathology, including the different noncoding RNAs associated with the disease.

Genetic risk association of CDKN1A and RET gene SNPs with medullary thyroid carcinoma: Results from the largest MTC cohort and meta-analysis

Background

Medullary thyroid carcinoma (MTC) is a rare subtype of thyroid cancer. Other than gain‐of‐function RET mutations, no other genetic, lifestyle or environmental risk associations have been established for MTC. Several case‐control studies and meta‐analysis have examined the risk association of different SNPs with MTC in different populations but with contradictory or inconclusive results.

Methods

In a large cohort of 438 Indian MTC cases and 489 gender and ethnicity matched healthy controls from 1000 genome project, a comprehensive risk association of 13 SNPs of three pathways—detoxification, cell cycle regulation and RET was performed along with meta‐analysis of RET SNPs.

Results

Multivariate logistic regression analysis identified a protective risk association of CDKN1ASer31Arg SNP with both hereditary (OR 0.26; 95% confidence interval [CI] 0.13‐0.55; P < .001) and sporadic MTC (OR 0.53; 95% CI 0.36‐0.78; P = .001). An increased risk association was identified for NAT2Y94Y SNP (OR 1.62, 95% CI 1.17‐2.25, P = .004) and CDKN2A3′UTR SNP (OR 1.89, 95% CI 1.19‐2.98, P = .006) with sporadic MTC and RET S904S with hereditary MTC (OR 2.82, 95% CI 1.64‐4.86, P < .001). Meta‐analysis of RET SNPs including our cohort identified increased risk association of all four RET SNPs with MTC.

Conclusion

In this largest SNP risk association study for MTC and the only risk association study of the 13 most commonly studied MTC associated SNPs in a single cohort of this rare cancer, a significant protective risk association of CDKN1ASer31Arg SNP with MTC was shown for the first time. Meta‐analysis identified significant risk association of all four RET SNPs, not observed in previous meta‐analysis.

Modifying impact of RET gene haplotypes on medullary thyroid carcinoma clinical course

The clinical course of medullary thyroid carcinoma (MTC) associated with the MEN2A syndrome as well as of sporadic MTC shows considerable heterogeneity. The disease picture varies not only between the same RET proto-oncogene mutation carriers but also among sporadic MTC patients with no RET germinal mutations, which suggests the involvement of additional modulators of the disease. However, genetic factors responsible for this heterogeneity of the MTC clinical course still remain unknown. The aim of this study was to determine if polymorphic variants or specific haplotypes of the RET gene may modify the MTC clinical course. We genotyped the following loci: c.73+9277T>C, c.135G>A, c.1296A>G, c.2071G>A, c.2307T>C, c.2508C>T and c.2712C>G in 142 MTC patients and controls. We demonstrated considerable differences in the genotypes distribution within c.73+9277T>C, c.135G>A and c.2307T>C loci Our results show that the c.73+9277T variant associated with a decreased activity of the MCS+9.7 RET enhancer is rare in hereditary MTC patients with primary hyperparathyroidism, and thus, may influence the MTC clinical picture. The decreased activity of the RET promoter enhancer reduces RET expression level and may counterbalance the activating mutation in this gene. Frequent co-occurrence of the c.73+9277T allele with p.E768D, p.Y791F, p.V804M or p.R844Q RET mutations may be associated with their attenuation and milder clinical picture of the disease. Haplotypes analysis showed that C-G-A-G-T-(C)-C (c.73+9277T>C - c.135G>A - c.1296A>G - c.2071G>A - c.2307T>G - (c.2508C>T) - c.2712C>G) alleles combination predisposes to pheochromocytomas and primary hyperparathyroidism. We consider that RET haplotypes defining may become an auxiliary diagnostic tool in MTC patients.

Nationwide French Study of RET Variants Detected from 2003 to 2013 Suggests a Possible Influence of Polymorphisms as Modifiers

BACKGROUND

The presence of single nucleotide polymorphisms (SNPs) in the REarranged during Transfection (RET) gene has been investigated with regard to their potential role in the development or progression of medullary thyroid cancer or pheochromocytomas (PHEO) in patients with the multiple endocrine neoplasia type 2 (MEN2) syndrome. The aim of this study was to evaluate the spectrum of RET variants in France between 2003 and 2013, and to evaluate the impact of SNPs on the MEN2 A phenotype.

METHODS

In this retrospective cohort study, RET variants were screened in 5109 index cases, and RET pathogenic variants were screened in 2214 relatives. Exons 5, 8, 10, 11, 13, 14, 15, and 16 were characterized by Sanger sequencing. RET pathogenic variants, RET variants with unknown functional significance (VUS), and four RET SNP variants-G691S (rs1799939), L769L (rs1800861), S836S (rs1800862), and S904S (rs1800863)-were characterized and are reported in index cases. In silico analysis and classification following the recommendation of the American College of Medical Genetics and Genomics was performed for RET VUS. Each patient's age at the time of diagnosis, sex, and the endocrine neoplasias present at molecular diagnosis were recorded.

RESULTS

Twenty-six single VUS in RET without any well-defined risk profiles were found in 33 patients. Nine of these were considered probably pathogenic, 11 of uncertain significance, and six as probably benign. Three double pathogenic variants found in three patients were classified as pathogenic. A study of the entire cohort showed that patients carrying pathogenic variants or VUS in RET together with PHEO were diagnosed earlier than the others. The presence of the G691S SNP, or a combination of SNPs, increased the risk of developing PHEO but did not modify the date of the diagnosis. No association was found between SNPs and medullary thyroid cancer or hyperparathyroidism.

CONCLUSIONS

The findings propose a classification of 15 of the 26 VUS in RET without any well-defined risk profiles and suggest that the G691S SNP, or a combination of SNPs, may be associated with the development of PHEO.

Effect of 3'UTR RET Variants on RET mRNA Secondary Structure and Disease Presentation in Medullary Thyroid Carcinoma

Background

The RET S836S variant has been associated with early onset and increased risk for metastatic disease in medullary thyroid carcinoma (MTC). However, the mechanism by which this variant modulates MTC pathogenesis is still open to discuss. Of interest, strong linkage disequilibrium (LD) between RET S836S and 3'UTR variants has been reported in Hirschsprung's disease patients.

Objective

To evaluate the frequency of the RET 3’UTR variants (rs76759170 and rs3026785) in MTC patients and to determine whether these variants are in LD with S836S polymorphism.

Methods

Our sample comprised 152 patients with sporadic MTC. The RET S836S and 3’UTR (rs76759170 and rs3026785) variants were genotyped using Custom TaqMan Genotyping Assays. Haplotypes were inferred using the phase 2.1 program. RET mRNA structure was assessed by Vienna Package.

Results

The mean age of MTC diagnosis was 48.5±15.5 years and 57.9% were women. The minor allele frequencies of RET polymorphisms were as follows: S836S, 5.6%; rs76759170, 5.6%; rs3026785, 6.2%. We observed a strong LD among S836S and 3’UTR variants (|D’| = -1, r² = 1 and |D’| = -1, r² = 0,967). Patients harboring the S836S/3’UTR variants presented a higher percentage of lymph node and distant metastasis (P = 0.013 and P<0.001, respectively). Accordingly, RNA folding analyses demonstrated different RNA secondary structure predictions for WT(TCCGT), S836S(TTCGT) or 3’UTR(GTCAC) haplotypes. The S836S/3’UTR haplotype presented a greater number of double helices sections and lower levels of minimal free energy when compared to the wild-type haplotype, suggesting that these variants provides the most thermodynamically stable mRNA structure, which may have functional consequences on the rate of mRNA degradation.

Conclusion

The RET S836S polymorphism is in LD with 3’UTR variants. In silico analysis indicate that the 3’UTR variants may affect the secondary structure of RET mRNA, suggesting that these variants might play a role in posttranscriptional control of the RET transcripts.

A complex endocrine conundrum

We describe a case of recurrent primary hyperparathyroidism, manifested as 3 metachronous parathyroid adenomata, in a 50 year-old woman who also had Hashimoto hypothyroidism, gastric gastrointestinal stromal tumour (GIST), cysts in liver and kidneys, 5 intestinal polyps (one of these a villous adenoma), diverticulitis and telangiectasia of lips. She did not have medullary thyroid carcinoma (MTC). Genetic analysis of the CDC73 gene [for Hyperparathyroidism-jaw tumor (HPT-JT)], MEN1 for Multiple Endocrine Neoplasia Type1, CDKN1B for MEN4, SDHB and SDHD for Paraganglioma/Pheochromocytoma susceptibility, VHL for von Hippel-Lindau Syndrome, BMPR1A and SMAD4 for Juvenile Polyposis Syndrome (JPS) (sequencing and MLPA), karyotype and array CGH (44 K) were all normal. She was found to be homozygous for a synonomous germline variant in exon 14 (p. Ser836Ser) of the RET oncogene. This RET variant is of unclear clinical significance, and has been previously reported both in normal individuals and in individuals with MTC. It is unlikely that homozygosity for the RET variant has been casual in the multiple pathologies that our patient has developed.

Quantitative assessment of the association between L769L and S836S polymorphisms at RET gene and medullary thyroid carcinoma risk

RET single nucleotide polymorphisms (SNPs) have been implicated in the pathogenesis and progression of medullary thyroid carcinoma (MTC). Epidemiologic studies have evaluated the association between RET L769L and S836S polymorphisms and predisposition to MTC. However, the results were inconclusive. A literature search was performed using the PubMed database for relevant studies published through October 31, 2013. A total of 13 eligible studies were selected for this meta-analysis, including 1,117 cases and 1,916 controls for L769L and 1,230 cases and 2,246 controls for S836S. The carrier frequency of the variant alleles was 26.3 % in patients with MTC and 24.6 % in controls for L769L polymorphism, and 6.6 % in patients with MTC and 5.0 % in controls for S836S polymorphism. In our pooled analysis of all these studies, the results of our meta-analysis suggested that the RET L769L variant was not significantly associated with an elevated MTC risk (odds ratio (OR) 1.06, 95 % confidence interval (CI) 0.94-1.19). And there was no evidence for the association between the S836S variant and MTC risk (OR 1.20, 95 % CI 0.97-1.49). Moreover, no significant differences were found when considering patients or controls heterozygous or homozygous for RET L769L and S836S polymorphisms. In conclusion, this meta-analysis suggests that RET L769L and S836S polymorphisms may not be associated with MTC development.

2012 European thyroid association guidelines for genetic testing and its clinical consequences in medullary thyroid cancer

Twenty-five percent of medullary thyroid cancers (MTC) are familial and inherited as an autosomal dominant trait. Three different phenotypes can be distinguished: multiple endocrine neoplasia (MEN) types 2A and 2B, in which the MTC is associated with other endocrine neoplasias, and familial MTC (FMTC), which occurs in isolation. The discovery that germline RET oncogene activating mutations are associated with 95-98% of MEN 2/FMTC syndromes and the availability of genotyping to identify mutations in affected patients and their relatives has revolutionized the diagnostic and therapeutic strategies available for the management of these patients. All patients with MTC, both those with a positive familial history and those apparently sporadic, should be submitted to RET genetic screening. Once an RET mutation has been confirmed in an index patient, first-degree relatives should be screened rapidly to identify the 50% who inherited the mutation and are therefore at risk for development of MTC. Relatives in whom no RET mutation is identified can be reassured and discharged from further follow-up, whereas RET-positive subjects (i.e. gene carriers) must be investigated and a therapeutic strategy initiated. These guideline recommendations are derived from the most recent studies identifying phenotype-genotype correlations following the discovery of causative RET gene mutations in MEN 2 eighteen years ago. Three major points will be discussed: (a) identification of patients and relatives who should have genetic screening for RET mutations, (b) management of asymptomatic gene carriers, and (c) ethics.

Additive effect of RET polymorphisms on sporadic medullary thyroid carcinoma susceptibility and tumor aggressiveness

OBJECTIVE

RET single nucleotide polymorphisms (SNPs) have been implicated in the pathogenesis and progression of medullary thyroid carcinoma (MTC). Here, we investigated the influence of multiple RET variants (G691S, L769L, S836S, and S904S) on the risk of MTC and tumor behavior.

DESIGN AND METHODS

One hundred and seven MTC patients and 308 cancer-unaffected control individuals were included. SNPs were analyzed using Custom TaqMan Genotyping Assays. Haplotypes based on the combination of allelic variants were inferred using a Bayesian statistical method.

RESULTS

The minor allele frequencies in MTC patients were as follows: L769L: 28.0%, S836S: 8.9%, and G691S/S904S: 22.2%. The RET L769L and S836S SNPs were associated with increased risk of MTC (odds ratio (OR)=1.95, 95% CI: 1.2-3.1, P=0.005 and OR=2.29, 95% CI: 1.2-4.5, P=0.017 respectively). The adjusted OR for individuals harboring haplotypes with three or more polymorphic alleles was 3.79 (95% CI: 1.5-9.5; P=0.004), indicating an additive effect of these variants on the risk for MTC. Among MTC patients, no significant associations were observed between RET variants and age of diagnosis or tumor size but serum calcitonin levels increased according to the number of risk alleles (P=0.003). Remarkably, patients carrying haplotypes with three or four risk alleles had increased risk for lymph node and distant metastases at diagnosis (OR=5.84, 95% CI: 1.1-31.2, P=0.039). Further analysis using Kaplan-Meier model demonstrated that metastatic disease occurred earlier in individuals harboring multiple risk alleles.

CONCLUSION

Our results demonstrated an additive effect of RET polymorphic alleles on the estimated risk of developing aggressive MTC.

Clinical relevance of RET variants G691S, L769L, S836S and S904S to sporadic medullary thyroid cancer

BACKGROUND

Based on reports of higher frequencies among patients with sporadic medullary thyroid cancer (MTC) relative to external controls, the RET (REarranged during Transfection) variants G691S, L767L, S836S and S904S have been considered disease modifiers, suggesting greater lifetime risks of MTC. Other studies, employing different external controls, failed to confirm this association. Using a complementary approach, this study aimed at exploring differences in clinico-pathological characteristics among patients with sporadic MTC carrying no (wildtype), one (heterozygotes) or both (homozygotes) homologue RET variants in the germline, with wildtype cases acting as internal controls.

METHODS

Included in this investigation were 150 patients with complete genetic information on G691S, L769L, S836S and S904S RET alleles operated on for sporadic MTC at a tertiary referral centre.

RESULTS

Not one statistically significant dose-response relationship was identified between any RET variant (wildtype vs RET heterozygotes vs homologue RET homozygotes) and patient age at MTC diagnosis, gender, primary tumour size, extrathyroidal extension, numbers of involved and removed lymph nodes, or distant metastasis. L769L and S836S homozygotes, unlike G691S and S904S homozygotes, were either rare or absent, limiting the analyses to comparisons of heterozygosity versus wildtype. On time-to-event analysis, G691S, L769L, S836S or S904S carriers and noncarriers developed MTC at similar rates.

CONCLUSIONS

In carriers and noncarriers of the RET variants G691S, L767L, S836S and S904S, sporadic MTC appeared clinically and pathologically indistinguishable. This observation, along with the inconclusive evidence of previous association studies, calls for larger longitudinal association studies with age- and sex-matched external controls and additional functional studies of RET biology.

Molecular basis of medullary thyroid carcinoma: the role of RET polymorphisms

Medullary thyroid carcinoma is a rare malignant tumor originating in parafollicular C cells. It accounts for 5 to 8% of all thyroid cancers. MTC develops in either sporadic (75%) or hereditary form (25%). Genetic and molecular studies have demonstrated the involvement of the RET proto-oncogene in hereditary MTC and, less often, in its sporadic form. Although a strong genotype-phenotype correlation has been described, wide clinical heterogeneity is observed among families with the same RET mutation or even in carriers of the same kindred. In recent years, several single nucleotide polymorphisms of the RET gene have been described in the general population as well as in patients with MTC. Some studies have reported associations between the presence of polymorphisms and development or progression of MTC. Nonetheless, other studies failed to demonstrate any effect of the RET variants. Differences in the genetic background of distinct populations or methodological approaches have been suggested as potential reasons for the conflicting results. Here, we review current knowledge concerning the molecular pathogenesis of sporadic and hereditary MTC. In particular, we analyze the role of RET polymorphisms in the clinical presentation and prognosis of MTC based on the current literature.

Association studies in thyroid cancer susceptibility: are we on the right track?

It is widely accepted that thyroid cancer is strongly determined by the individual genetic background. In this regard, it is expected that sporadic thyroid cancer is the result of multiple low- to moderate-penetrance genes interacting with each other and with the environment, thus modulating individual susceptibility. In the last years, an important number of association studies on thyroid cancer have been published, trying to determine this genetic contribution. The aim of this review is to provide a comprehensive and critical evaluation of the associations reported so far in thyroid cancer susceptibility in case-control studies performed in both non-medullary (papillary and follicular) and medullary thyroid cancers, including their potential strengths and pitfalls. We summarize the genetic variants reported to date, and stress the importance of validating the results in independent series and assessing the functional role of the associated loci.

The frequency of selected polymorphic variants of the RET gene in patients with medullary thyroid carcinoma and in the general population of central Poland

The object of this work was to compare the frequency of three polymorphic changes in the RET proto-oncogene: L769L, S836S, and S904S in patients with medullary thyroid carcinoma (MTC; n = 246) and in the general population (n = 420 for single-nucleotide polymorphism [SNP] L769L and S904S; n = 411 for SNP 836). We tried to investigate how the harbored SNPs affect the age at onset of sporadic medullary thyroid carcinoma (sMTC) and MTC in carriers of known pathogenic mutations at codons 634 and 791 of the RET gene. A statistically significant difference was found in the frequency of the heterozygous change L769L in patients with sMTC (48.3%) and in unaffected individuals (39.5%). The presence of the polymorphic change L769L in the RET gene predisposes to the development of sMTC and also lowers the age of onset of MTC in carriers of the homozygous polymorphic variant L769L. The presence of this polymorphic change in MTC patients carrying, at the same time, the RET codon 634 mutation lowers the age of onset of MTC in this group.

DNA-based test: when and why to apply it to primary hyperparathyroidism clinical phenotypes

Several cancer-related genes have been discovered and molecular test for the cancer genetic risk assessment has been widely increasing. Disorders such as Multiple Endocrine Neoplasia syndromes have received benefits from the identification of the responsible genes whose mutations account for the genetic susceptibility to develop endocrine tumours. Primary hyperparathyroidism (PHPT)is a clinical phenotype frequently associated to Multiple Endocrine Neoplasia syndromes, but it can also represent the unique endocrinopathy recurring as a familial cluster. In recent years, care options have been made available to patients and families with hereditary PHPT, and the process of systematically assessing the genetic risk has been becoming increasingly important. This review aims to help health providers not frequently dealing with genetic testing use and it will introduce some general concepts concerning genetic diagnosis issues. As an example the role and the practical usefulness of DNA-based diagnosis in patients affected by different forms of congenital PHPT is described, with a close look on why, when and how genetic testing should be performed in these subjects and their relatives. Some practical recommendations and suggestions concerning on how to deal when a suspect or known case of familial PHPT has to be faced conclude this manuscript.

Evaluation of RET polymorphisms in a six-generation family with G533C RET mutation: specific RET variants may modulate age at onset and clinical presentation

CONTEXT

We previously described a six-generation family with G533C RET mutation and medullary thyroid carcinoma, in the largest family reported do date. Of particular interest, phenotype variability regarding the age of onset and clinical presentation of the disease, was observed.

OBJECTIVE

We evaluate whether single SNPs within RET oncogene or haplotype comprising the RET variants (defined by Haploview) could predispose to early development of MTC in this family and influence the clinical manifestation.

DESIGN

Eight SNPs were selected based on their previous association with the clinical course of hereditary or sporadic MTC, in particular promoting an early onset of disease. The variants were initially tested in 77 G533C-carriers and 100 controls using either PCR-direct sequencing or PCR-RFLP. Association between a SNP or haplotype and age at diagnosis or presence of lymph node metastasis was tested in 34 G533C-carries with MTC. Different bioinformatic tools were used to evaluate the potential effects on RNA splicing.

RESULTS

An association was found between IVS1-126G > T and age at diagnosis. The variant [IVS8 +82A > G; 85-86 insC] was associated with the presence of lymph node metastases at diagnosis. In silico analysis suggested that this variant may induce abnormal splicing. This in silico analysis predicted that the [IVS8 +82A > G; 85-86 insC] could alter the splicing by disrupting and/or creating exonic splicing enhancer motifs.

CONCLUSIONS

We here identified two RET variants that were associated with phenotype variability in G533C-carriers, which highlights the fact that the modifier effect of a variant might depend on the type of mutation.

The influence of gender, age, and RET polymorphisms on C-cell hyperplasia and medullary thyroid carcinoma

BACKGROUND

RET germline mutations predispose to the development of hereditary medullary thyroid carcinoma (hMTC). Several single nucleotide polymorphisms (SNPs) are described associated with sporadic MTC (sMTC). However, the findings regarding their influence on the clinical course and biological behavior of this disorder are discordant. To clarify the contradictory findings, we studied the association of certain SNPs considering age, gender, and histopathology in a large Austrian cohort with C-cell hyperplasia (CCH) and MTC.

METHODS

Genotyping of SNPs located in RET codons 691, 769, 836, and 904 from 199 patients with MTC and CCH (basal calcitonin > 10 pg/mL, pentagastrin stimulated > 100 pg/mL) was performed, and the results were analyzed considering gender, age at diagnosis, and histopathology.

RESULTS

No significant difference of SNP frequencies was found in the study patients versus normal controls. In sMTC and sporadic CCH (sCCH) no significant association of SNP frequency with the age at diagnosis was found. In patients with sporadic C-cell disease (sCCH and sMTC), 3.7 times more males than females suffered synchronously from papillary or follicular thyroid cancer (20/97 [20.6%] males; 3/54 [5.6%] females; p = 0.02). sCCH was revealed more frequently in males (89/97, 91.7%) than in females (27/54, 50%; p = 10(-8)). In contrast to males, the ratio of CCH to total C-cell disease was significantly higher in females with hereditary (26/32, 81%) compared to those with sporadic disease (27/54, 50%; p = 0.006).

CONCLUSIONS

In this study RET SNPs had no clinical impact on the development of sporadic C-cell disease when the age of diagnosis or gender is considered. C-cell disease seems to predispose males to the development of papillary and follicular thyroid cancer. In addition, at least in females with CCH RET germline mutation, screening is recommended even if the family history is negative for MTC.

RET genotypes in sporadic medullary thyroid cancer: studies in a large Italian series

BACKGROUND

Highly discrepant data about the different distribution of RET germline single nucleotide polymorphisms (SNPs) among patients with sporadic medullary thyroid cancer (sMTC) and controls are available.

DESIGN AND PATIENTS

In the present case-control study, a wide panel of seven RET SNPs has been tested in the largest sMTC series and in a matched control group.

RESULTS

None of the investigated polymorphisms show a significantly different distribution in patients with sMTC when compared to controls. Twenty haplotypes and 57 genotypes were generated, and their association with the disease and with the clinical features were statistically evaluated. Interestingly, 14 genotypes were found to be unique to sMTC patients and 25 to controls. Two haplotypes and three genotypes, all including the intronic variants IVS1-126 and IVS14-24, were significantly associated with sMTC patients and with a higher tumour aggression. The functional activity of the only nonsynonymous RET variant (c.2071C > A, G691S) was tested for the first time. Interestingly, Western blot analyses showed that the fraction of Ret9-G691S protein located at the plasma membrane level was overrepresented when compared to Ret9-WT, suggesting facilitated targeting at the cell membrane for this variant. However, no transforming activity was shown in a focus formation assay on cells carrying the Ret9-G691S, against a possible oncogenic role of G691S variant.

CONCLUSIONS

RET genotypes including two intronic RET variants were associated with the risk of developing sMTC and to more aggressive behaviour. Further studies are warranted to elucidate whether these RET genotypes are in linkage disequilibrium with another susceptibility gene or whether these variants could play a role in the genesis of sMTC per se.

Somatic mutations in the RET proto-oncogene in sporadic medullary thyroid carcinomas

The frequency and prognostic relevance of RET proto-oncogene somatic mutations in sporadic medullary thyroid carcinoma (MTC) remain controversial. In order to study somatic mutations in the RET proto-oncogene in sporadic MTCs found in the Czech population and to correlate these mutations with clinical and pathological characteristics, we investigated 48 truly sporadic MTCs by sequencing classical risk exons 10, 11, 13, 14, 15 and 16. From the 48 tumors studied, 23 (48%) had somatic mutation in the RET proto-oncogene in exons 10, 11, 15 or 16. The classical somatic mutation Met918Thr in exon 16 was only found in 13 tumors (27%). In five cases, multiple somatic mutations and deletions were detected. A statistically significant correlation between the presence of somatic mutation with more advanced pathological TNM stages was observed. Other clinical and pathological characteristics did not show any statistical significant association with the presence or absence of somatic mutation.

Polimorfismos genéticos: implicações na patogênese do carcinoma medular de tireóide

O carcinoma medular de tireóide (CMT) é uma neoplasia maligna rara, ocorrendo na forma esporádica ou hereditária. Mutações germinativas no proto-oncogene RET são responsáveis pelo CMT hereditário. No entanto, a maioria dos casos de CMT ocorre em indivíduos sem história familiar, na qual a patogênese da doença ainda é pouco compreendida. Os polimorfismos do gene RET são descritos na população geral assim como em pacientes com CMT. Embora estas variações alélicas aparentemente não confiram qualquer atividade transformadora no receptor RET, estudos sugerem que essas alterações genéticas podem modificar a suscetibilidade à doença e o fenótipo clínico em pacientes com CMT esporádico ou hereditário. Uma maior freqüência dos polimorfismos localizados nos exons 11 (G691S), 13 (L769L), 14 (S836S) e 15 (S904) é descrita em pacientes com CMT provenientes de países americanos e europeus. Na presente revisão, analisamos criticamente os resultados obtidos nos diferentes estudos e descrevemos a freqüência dos polimorfismos do RET em pacientes brasileiros com CMT esporádico.

RET proto-oncogene genotyping using unlabeled probes, the masking technique, and amplicon high-resolution melting analysis

Single bp mutations in the RET proto-oncogene can cause multiple endocrine neoplasia type 2 syndromes. The conventional approach for genotyping RET mutations is sequencing the exons. A closed-tube RET genotyping assay using a saturating DNA dye, unlabeled probes, and amplicon high-resolution melting analysis was developed. The method required two sequential polymerase chain reaction stages, a primary and secondary assay. The primary assay analyzed RET exons 10, 11, 13, 14, and 16 with a total of seven reactions using eight unlabeled probes. The primary assay genotyped wild-type exons, a common exon 13 polymorphism, and an exon 16 mutation, whereas other RET sequence variation was detected. The primary unlabeled probe data limited the possible genotypes for the detected RET sequence variation, which permitted genotyping in a secondary assay with only two to five reactions. Six probes were designed with the masking technique and masked selected sequence variations to allow unambiguous analysis of other mutations elsewhere under the probe. After this two-stage RET genotyping assay, less than 0.2% of exons tested would require sequencing for genotype. A blinded study generated from five wild type and 29 available RET sequence variation samples was 100% concordant with sequencing. Amplicon high-resolution melting analysis with unlabeled probes and the masking technique is a fast, accurate method for genotyping the >50 RET sequence variations.

A common variant located in the 3'UTR of the RET gene is associated with protection from Hirschsprung disease

Complex diseases are common genetic disorders showing familial aggregation but no typical Mendelian inheritance. Hirschsprung disease (HSCR), a developmental disorder characterized by the absence of enteric neurons in distal segments of the gut, shows a complex pattern of inheritance, with the RET protooncogene acting as a major gene and additional susceptibility loci playing minor roles. In the last years, we have identified a "protective" RET haplotype, which is underrepresented in HSCR patients with respect to controls. Here, we demonstrate that the protective effect of this haplotype is due to a variant located in the 3' untranslated region (UTR) of the RET gene, which slows down the physiological mRNA decay of the gene transcripts. Such a functional effect of this common RET variant explains the under-representation of the whole haplotype and its role as a modifying factor in HSCR pathogenesis.

Familial medullary carcinoma prevention, risk evaluation, and RET in children of families with MEN2

The ability to predict the risk of MEN2 and medullary thyroid carcinoma (MTC) by genetic RET proto-oncogene analysis has provided an essential tool in identifying patients in whom thyroid cancer can be prevented by prophylactic thyroidectomy but emphasizes the need for clear policy guidelines. Children of families with RET cysteine mutations (exons 10, 11, 13, and 16) may develop early metastatic tumours and require prophylactic thyroidectomy. The 918 mutation associated with MEN2B is associated with early aggressive behaviour and distant metastatic spread. This has led to active screening of affected families underlining the need for specific intervention strategies.

AIM

To evaluate the risk to children of families with MEN2 and to assess the risk and determine the treatment.

METHODS

Twenty-five patients from 10 families with MEN2 phenotypes were screened for RET mutations. Polymerase chain reaction amplification was performed on all 21 exons of the RET proto-oncogene, followed by heteroduplex single-strand conformation polymorphism (HEX-SSCP) analysis. Polymerase chain reaction products demonstrating variation in the HEX-SSCP gels were subjected to automated DNA sequencing analysis.

RESULTS

Eleven significant RET mutations were detected in affected families. Eight index cases received initial thyroidectomy for established MTC (plus 2 advised). In the family members screened, 3 prophylactic thyroidectomies (2 with early MTC) were performed and a further 2 recommended. An exon 10 C620W missense mutation (the "Janus" gene) was detected in a patient with Hirschsprung's disease plus 1 family member.

CONCLUSION

RET analysis of MEN has revolutionized the management of children of families with MEN2 and allowed surgical prediction and prophylaxis to take place. The presence of an exon 10 C620W mutation in association with Hirschsprung's disease was difficult to assess. We suggest possible guidelines for management of families with MTC and the role of genetic testing in their evaluation.

Significance of the RET proto-oncogene polymorphisms in Turkish sporadic medullary thyroid carcinoma patients

Several single nucleotide polymorphisms (SNP) of the RET gene have been identified in medullary thyroid carcinoma (MTC) patients as well as in the general population. However, the relevance of SNP for MTC patients is still controversial, whether these allelic variants play other interacting, predisposing or modifying roles in clinical behavior of MTC. The aim of this work is to elaborate allelic frequencies of the RET proto-oncogene polymorphisms in Turkish sporadic MTC patients and to demonstrate if there is an association between SNP and the clinical disease features, specifically the age at onset of MTC and lymph node involvement at diagnosis. We analyzed the allelic frequencies of SNP of the exon 11, 13, 14 and 15 of the RET proto-oncogene in blood samples from 50 sporadic MTC patients, using the polymerase chain reaction methodology followed by DNA sequencing. The observed allelic frequencies were 24% for G691S polymorphism in exon 11, 29% for L769L polymorphism in exon 13, 5% for S836S polymorphism in exon 14, and 26% for S904S polymorphism in exon 15. These frequencies are similar to those reported in other countries. We did not observe any significant association of all four SNP with the age at onset of MTC. Our results indicate a possible association between the presence of lymph node involvement at the time of diagnosis (extent of disease) and L769L or S836S polymorphism. However, it is not possible to draw definitive conclusions that these two polymorphisms play a significant role in clinical behavior of MTC. Further studies are needed to evaluate the role of this polymorphism in the clinical behavior of MTC.

Masking selected sequence variation by incorporating mismatches into melting analysis probes

Hybridization probe melting analysis can be complicated by the presence of sequence variation (benign polymorphisms or other mutations) near the targeted mutation. We investigated the use of "masking" probes to differentiate alleles with similar probe melting temperatures. Selected sequence variation was masked by incorporating mismatches (deletion, unmatched nucleotide, or universal base) into hybridization probes at the polymorphic location. Such masking probes create a probe/target mismatch with all possible alleles at the selected polymorphic location. Any allele with additional variation at another site is identified by a lower probe melting temperature than alleles that vary only at the masked position. This "masking technique" was applied to RET protooncogene and HPA6 mutation detection using unlabeled hybridization probes, a saturating dsDNA dye, and high-resolution melting analysis. Masking probes clearly distinguished all targeted mutations from polymorphisms when at least 1 base pair (bp) separated the mutation from the masked variation. We were able to mask polymorphisms immediately adjacent to mutations, except in certain cases, such as those involving single-base deletion probes when both adjacent positions had the same polymorphic nucleotides. The masking probes can also localize mutations to specific codons or nucleotide positions. Masking probes can simplify melting analysis of complex regions and eliminate the need for sequencing.

RET as a diagnostic and therapeutic target in sporadic and hereditary endocrine tumors

The RET gene encodes a receptor tyrosine kinase that is expressed in neural crest-derived cell lineages. The RET receptor plays a crucial role in regulating cell proliferation, migration, differentiation, and survival through embryogenesis. Activating mutations in RET lead to the development of several inherited and noninherited diseases. Germline point mutations are found in the cancer syndromes multiple endocrine neoplasia (MEN) type 2, including MEN 2A and 2B, and familial medullary thyroid carcinoma. These syndromes are autosomal dominantly inherited. The identification of mutations associated with these syndromes has led to genetic testing to identify patients at risk for MEN 2 and familial medullary thyroid carcinoma and subsequent implementation of prophylactic thyroidectomy in mutation carriers. In addition, more than 10 somatic rearrangements of RET have been identified from papillary thyroid carcinomas. These mutations, as those found in MEN 2, induce oncogenic activation of the RET tyrosine kinase domain via different mechanisms, making RET an excellent candidate for the design of molecular targeted therapy. Recently, various kinds of therapeutic approaches, such as tyrosine kinase inhibition, gene therapy with dominant negative RET mutants, monoclonal antibodies against oncogene products, and nuclease-resistant aptamers that recognize and inhibit RET have been developed. The use of these strategies in preclinical models has provided evidence that RET is indeed a potential target for selective cancer therapy. However, a clinically useful therapeutic option for treating patients with RET-associated cancer is still not available.

Analysis of RET polymorphisms and haplotypes in the context of sporadic medullary thyroid carcinoma

CONTEXT

Little is known about the etiology of sporadic medullary thyroid carcinoma (sMTC). While germline gain-of-function mutations in the RET proto-oncogene cause hereditary MTC, the molecular mechanisms leading to the sporadic forms remain obscure. Our group had evidence about the existence of a low-penetrance susceptibility locus for sMTC in linkage disequilibrium with RET variants S836S/IVS1-126G>T, and probably in 5' with respect to both variants. In this study we sought to identify such locus. On the other hand, because an overrepresentation of G691S/S904S variants in patients with sMTC had been previously reported, we sought to determine if such association was present in our series.

DESIGN

We performed a case-control study analysing a wide spectrum of RET variants in the 5' region of the gene, as well as the variants G691S/S904S. Haplotype distribution were also analyzed. A total of 58 patients with sMTC were included in the study. In addition, 100 unselected, unrelated race-, age-, and gender-matched normal controls were also evaluated.

MAIN OUTCOME

Although the overrepresentation of IVS1-126G>T remains present in our current sMTC series, thus supporting our previous hypothesis, no differences were obtained among cases and controls in the distribution of the variants tested upstream this position. On the other hand, the frequency and distribution of G691S/S904S variants were similar in both groups of study, leading to exclude their role in sMTC in our series.

CONCLUSIONS

These findings would suggest that the major genetic events contributing to the appearance of sMTC may reside in several different RET loci. In this way, we could hypothesize about the existence of at least two sMTC loci, linked to S836S-IVS1-126G>T, or to G691S-S904S, respectively.

Mutation scanning of the RET protooncogene using high-resolution melting analysis

BACKGROUND

Single-base pair missense mutations in exons 10, 11, 13, 14, 15, and 16 of the RET protooncogene are associated with the autosomal dominant multiple endocrine neoplasia type 2 (MEN2) syndromes: MEN2A, MEN2B, and familial medullary thyroid carcinoma. The current widely used approach for RET mutation detection is sequencing of the exons.

METHODS

Because RET mutations are rare and the majority are heterozygous mutations, we investigated RET mutation detection by high-resolution amplicon melting analysis. This mutation scanning technique uses a saturating double-stranded nucleic acid binding dye, LCGreen, and the high-resolution melter, HR-1, to detect heterozygous and homozygous sequence variations. Mutant genotypes are distinguished from the wild-type genotype by an altered amplicon melting curve shape or position.

RESULTS

Samples of 26 unique RET mutations, 4 nonpathogenic polymorphisms, or the wild-type genotype were available for this study. The developed RET mutation-scanning assay differentiated RET sequence variations from the wild-type genotype by altered derivative melting curve shape or position. A blinded study of 80 samples (derived from the 35 mutant, polymorphism, or wild-type samples) demonstrated that 100% of RET sequence variations were differentiated from wild-type samples. For exons 11 and 13, the nonpathogenic polymorphisms could be distinguished from the pathogenic RET mutations. Some RET mutations could be directly genotyped by the mutation scanning assay because of unique derivative melting curve shapes.

CONCLUSION

RET high-resolution amplicon melting analysis is a sensitive, closed-tube assay that can detect RET protooncogene sequence variations.

Analysis of inherited genetic variants in ret proto-oncogene of Brazilian patients with apparently sporadic medullary thyroid carcinoma

Mutations in different exons of ret proto-oncogene are responsible for the development of medullary thyroid carcinoma (MTC). The mutations can occur as sporadic or as part of multiple endocrine neoplasia (MEN) type 2 hereditary syndromes. Here we report the first focused study of sporadic MTC in Brazilian patients regarding clinical and molecular analysis of ret proto-oncogene. Our study seeks to estimate the risk of hereditary MTC cases among apparently sporadic cases in a Brazilian population and describe ret genetic variants in their germinative lineage. Germinative sequence variants were screened by DNA sequencing and denaturing gradient gel electrophoresis (DGGE) analysis of exons 10, 11, 13, 14, 15, and 16 of 24 Brazilian patients with apparently sporadic MTC. We identified 1 inherited case of 24 (4%) patients with apparently sporadic MTC. Polymorphisms for the ret proto-oncogene coding region were identified in codon 769 of exon 13 (LeuCTT--> LeuCTG) at a frequency of 13% (3/24) and in codon 904 of exon 15 (SerTCC--> SerTCG) at a frequency of 16.6% (4/24). The observed frequency (4%) of inherited disease among apparent sporadic MTC strengthens routine application of ret proto-oncogene germinative DNA screening in all cases of apparently sporadic MTC ascertained at Brazilian cancer hospitals.

Neoplasia endócrina múltipla tipo 2

O termo neoplasia endócrina múltipla tipo 2 (NEM 2) foi sugerido em 1968, por Steiner e cols., para diferenciar a síndrome clínica caracterizada pela presença de carcinoma medular de tireóide (CMT), feocromocitoma e hiperparatireoidismo, então denominada síndrome de Sipple, da síndrome de Wermer ou NEM tipo 1, que acomete as glândulas paratireóides, pâncreas e hipófise. Sizemore e cols. (1974) complementaram a diferenciação através da classificação da NEM 2 em 2 subgupos: pacientes com CMT, feocromocitoma, hiperparatireoidismo e aparência normal (NEM 2A) e pacientes sem acometimento das paratireóides e fenótipo caracterizado por ganglioneuromatose intestinal e hábitos marfanóides (NEM 2B). CMT é usualmente o primeiro tumor a ser diagnosticado. O diagnóstico do CMT determina que seja avaliada a extensão da doença e rastreamento do feocromocitoma e hiperparatireoidismo. O diagnóstico de CMT esporádico ou hereditário é realizado através da análise molecular do proto-oncogene RET. Neste artigo são discutidos os aspectos fisiopatológicos, as anormalidades genéticas e os aspectos clínicos da NEM 2. A abordagem diagnóstica e terapêutica nos indivíduos afetados, carreadores assintomáticos e familiares em risco também são discutidos. Os avanços relacionados ao rastreamento genético e intervenção precoce permitiram uma melhoria no prognóstico a longo prazo. No entanto, ainda não dispomos de tratamento eficaz para doença metastática.

Investigation of loss of heterozygosity and SNP frequencies in the RET gene in papillary thyroid carcinoma

In both medullary carcinoma and papillary carcinoma of the thyroid, altered expression of the RET gene is implicated in tumorigenesis. Recent studies suggest that loss of heterozygosity (LOH) at the G691S SNP may be associated with tumors from patients with a history of radiation exposure. We investigated LOH for three RET SNPs (G691S, S904S, and L769L) in tumor and normal tissue from 46 patients from Ukraine and Belarus who were exposed to radioactive fallout following the Chernobyl nuclear accident and were operated for papillary thyroid carcinoma between 1995 and 2000. Normal tissue from 28 patients was heterozygous for at least one SNP; DNA from the corresponding tumor samples was also heterozygous, indicating that no LOH had taken place. To assess SNP frequencies in a radiation-associated thyroid cancer cohort, we investigated a further 68 unpaired post-Chernobyl samples. For G691S, there was considerable deviation from Hardy-Weinberg equilibrium; more detailed analysis showed that this was linked to age at onset of disease. Among younger patients, the distribution of genotypes conformed to Hardy-Weinberg equilibrium; among older patients, we observed marked deviation (p = 0.0072), with significant over-representation of the rare S allele relative to the younger groups (Fisher's exact, p = 0.0233). This suggests that SNPs in the RET oncogene may play a role in sporadic papillary thyroid carcinoma.

RET proto-oncogene mutations are restricted to codon 634 and 618 in Korean families with multiple endocrine neoplasia 2A

Identification of the germline mutation in the RET proto-oncogene is important for the diagnosis of hereditary medullary thyroid carcinoma (MTC). Hereditary forms account for approximately 25%-30% of all cases of MTC. The objective of this study was to evaluate the prevalence of the RET mutation and the genotype-phenotype relation in Korean patients with MTC. Genomic DNAs were obtained from 33 patients with MTC (M:F = 10:23, 39.8 +/- 12.0 years) who underwent total thyroidectomy between 1997 and 2003 at the Samsung Medical Center. Exons 10, 11, 13, 14, 15 and 16 of the RET proto-oncogene were amplified with specific primers using polymerase chain reaction (PCR). Sequence analysis was performed on the polymerase chain reaction (PCR) product using an automatic sequence analyzer. Nine of the 33 patients (M:F = 3:6, 33.3 +/- 10.0 years) were identified as having RET mutations. Six patients had multiple endocrine neoplasia (MEN) 2A and one had familial medullary thyroid carcinoma (FMTC). The remaining two patients were thought to have sporadic MTC. Five of the patients with MEN 2A had RET mutations in codon 634 of exon 11 (3 patients, C634Y; 2 patients, C634R) and the other patient with MEN 2A had a RET mutation in codon 618 of exon 10 (C618R). The patient with FMTC had a mutation in codon 634 (C634W). The two patients with sporadic MTC had RET mutations in codon 634 (1 patient, C634Y; 1 patient, C634S). We were not able to identify any genotype-phenotype relations because of the limited number of patients. Twenty-seven percent (9/33) of the patients with MTC in this study had RET mutations. Taking other studies into account, 77% (10/13) of Korean families with MEN 2A, including 7 other families in three reports from Korea, had RET mutations in codon 634 (5 families, C634Y; 4 families, C634R; 1 family, C634W), and 23% (3/13) had RET mutations in codon 618 (2 families, C618R; 1 family, C618S). RET proto-oncogene mutations were restricted to codon 634 and 618 in Korean families with MEN 2A.

Polymorphisms in the RET proto-oncogene and the phenotypic presentation of familial medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) occurs in a sporadic or as an autosomal dominant hereditary form. Inherited forms of MTC are related to mutations in the RET proto-oncogene. We screened genomic DNA from 11 patients with MTC for mutations in exons 10, 11, 13, 14, 15, and 16 of the RET proto-oncogene. Subsequently, we also evaluated a family of 1 patient with presumed diagnosis of sporadic MTC. Three patients with MEN2A from two unrelated families presented mutations in exon 11 (C634Y and C634R). A heterozygous mutation in exon 14 (V804M) was identified in the patient with the presumed sporadic MTC. We also observed two different polymorphisms: S904S in exon 15 (2 patients) and L769L in exon 13 (4 patients). The L769L polymorphism has been associated with earlier onset of sporadic MTC. On the other hand, mutations in exon 14 are associated with MTC of later onset and lower aggressiveness. Indeed, the carrier of the V804M mutation associated with L769L polymorphism presented MTC at 32 years of age, in contrast to her asymptomatic mother, who had only the V804M mutation and had MTC diagnosed by fine-needle aspiration biopsy at 60 years of age. In conclusion, the present study confirms the need for genetic screening to differentiate sporadic and hereditary forms of MTC. In addition, the genetic study allows the identification of asymptomatic carriers of hereditary forms of MTC. Finally, we speculated that the L769L polymorphism of the RET proto-oncogene may be related to earlier age of onset in the patient with the V804M mutation.

Evaluation of a DHPLC-based assay for rapid detection of RET germline mutations in Italian patients with medullary thyroid carcinoma

Causative gain-of-function mutations of the RET tyrosine-kinase receptor gene have been reported in more than 95% of inherited cases of medullary thyroid carcinoma (MTC; OMIM# 155240). Most RET activating mutations are clustered in mutational "hot spots" in exons 10, 11, 13, 14, 15 and 16 and are usually detected by single-strand conformation polymorphism (SSCP) followed by direct sequencing. To improve sensitivity, time and costs of mutational screening we have developed a denaturing high performance chromatography (DHPLC) protocol, based on the detection of heteroduplex molecules by ion-pair reverse-phase liquid chromatography under partially denaturing conditions. The mutational screening of RET exons 10, 11, 13-16 was performed in a total of 111 subjects, including 45 MTC patients and 49 relatives with known RET mutations and 17 individuals, being at risk of hereditary MTC and carrying unknown RET alleles. Heteroduplex peaks with a distinct and reproducible DHPLC elution profile allowed the detection of both rare and common RET mutations. Overall, the DHPLC-based methodology showed a high level of sensitivity and accuracy, nearing 100%. Furthermore, our protocol showed the ability to identify: 1) all the mutated codons of RET located in the "hot spots" domain; 2) the different point mutations occurring in the same codon of RET gene; 3) less frequent or rare mutations; 4) polymorphisms. As such, it can be proposed as a relatively simple and highly accurate method for a rapid genetic testing for members of MTC families.

Carcinoma medular de tireóide: aspectos moleculares, clínico-oncológicos e terapêuticos

O carcinoma medular de tireóide (CMT) pode ocorrer na forma esporádica ou familiar. O CMT hereditário é parte das síndromes de neoplasia endócrina múltipla (NEM) 2A e 2B, carcinoma medular de tireóide familiar (CMTF) ou outras formas. Mutações de linhagem germinativa do proto-oncogene RET causam a forma hereditária da neoplasia e os testes genéticos atualmente disponíveis formam a base para o manejo adequado da hereditariedade do tumor, visto que o diagnóstico precoce melhora significativamente o prognóstico no indivíduo afetado e nos carreadores. Nos últimos anos, vários estudos têm demonstrado uma correlação entre mutações codon-específica do RET e os diferentes fenótipos da NEM 2A, que pode, em parte, ser explicada por diferenças na intensidade da indução da dimerização do receptor. No presente artigo, revisamos os avanços nos mecanismos moleculares, diagnóstico e tratamento, bem como relatamos a nossa experiência no manejo dessa forma rara de neoplasia tireoidiana.

A novel germ-line point mutation in RET exon 8 (Gly(533)Cys) in a large kindred with familial medullary thyroid carcinoma

Familial medullary thyroid carcinoma is related to germ-line mutations in the RET oncogene, mainly in cysteine codon 10 or 11, whereas noncysteine mutations in codons 13-15 are rare. We now report a new missense point mutation in exon 8 of the RET gene (1597G-->T) corresponding to a Gly(533)Cys substitution in the cysteine-rich domain of RET protein in 76 patients from a 6-generation Brazilian family with 229 subjects, with ascendants from Spain. It is likely that the mutation causes familial medullary thyroid carcinoma (FMTC), because no other mutation was found in RET, the mutation cosegregates with medullary thyroid carcinoma (MTC) or C cell hyperplasia (CCH) in patients subjected to surgery, and family members without the mutation are clinically unaffected. The histological analysis of 35 cases submitted to thyroidectomy revealed that 21 patients had MTC after the age of 40 yr and 8 before the age of 40 yr, 4 presented MTC or CCH before the age of 18 yr, 2 died due to MTC at the age of 53 and 60 yr, and CCH was found in a 5-yr-old child, suggesting a clinical heterogeneity. To improve the diagnosis of FMTC, analysis of exon 8 of RET should be considered in families with no identified classical RET mutations.

Segregation of the V804L mutation and S836S polymorphism of exon 14 of the RET gene in an extended kindred with familial medullary thyroid cancer

In multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid cancer (FMTC), the majority of germline mutations are restricted to specific positions in exons 10 and 11 of the RET gene. However, germline mutations may very occasionally occur in other exons, including exon 14 of the RET gene. Interestingly, an increased frequency of a rare germline sequence variant of the RET exon 14, S836S, has been detected in patients with sporadic medullary thyroid cancer (MTC), and this variant has been proposed to play a role in the genesis of MTC and, perhaps, FMTC. In this study we report the segregation of a germline V804L mutation and a germline sequence variant S836S in exon 14 of the RET gene in an extended Hungarian FMTC kindred comprising 80 individuals of four generations. Molecular analysis of the RET gene was performed by direct DNA sequencing in 23 family members, of whom 12 had the V804L mutation, three had the V804L mutation and S836S polymorphism in separate alleles, and six had the S836S polymorphism, all in heterozygous forms. Two of the family members had neither mutation nor polymorphism of the RET gene. Three of the family members who had the V804L mutation and one member who could not be tested for mutation were operated for non-metastatic MTC, while one member with MTC who had the V804L mutation refused surgery. In all patients affected with MTC, the disease developed relatively late in life and never caused death. None of the other family members carrying the V804L mutation and/or the S836S polymorphism had clinical or biochemical evidence of MTC. These observations suggest that the co-existence of the V804L mutation and S836S polymorphism in separate alleles does not seem to aggravate the relatively low-risk disease phenotype characteristic in most patients with codon 804 mutations of the RET exon 14.

A founding locus within the RET proto-oncogene may account for a large proportion of apparently sporadic Hirschsprung disease and a subset of cases of sporadic medullary thyroid carcinoma

Hirschsprung disease (HSCR) is a common congenital disorder characterized by aganglionosis of the gut. The seemingly unrelated multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant disorder characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, and hyperparathyroidism. Yet, germline mutations in the RET proto-oncogene are associated with both MEN 2 and HSCR. In the former, gain-of-function mutations in a limited set of codons is found, whereas, in the latter, loss-of-function mutations are found. However, germline RET mutation is associated with only 3% of a population-based series of isolated HSCR, and little is known about susceptibility to sporadic MTC. We have found previously that specific haplotypes comprising RET coding single-nucleotide polymorphisms (SNPs) comprising exon 2 SNP A45A were strongly associated with HSCR, whereas haplotypes associated with exon 14 SNP S836S were associated with MTC. In this study, we describe three novel intron 1 SNPs, and, together with the coding SNP haplotypes, the data suggest the presence of distinct ancestral haplotypes for HSCR and sporadic MTC in linkage disequilibrium with a putative founding susceptibility locus/loci. The data are consistent with the presence of a very ancient, low-penetrance founder locus approximately 20-30 kb upstream of SNP A45A, but the failure of the SNPs to span the locus presents challenges in modeling mode of transmission or ancestry. We postulate that this founding locus is germane to both isolated HSCR and MTC but also that different mutations in this locus would predispose to one or the other.

Evaluation of germline sequence variants of GFRA1, GFRA2, and GFRA3 genes in a cohort of Spanish patients with sporadic medullary thyroid cancer

The etiology of sporadic medullary thyroid carcinoma (sMTC) remains elusive. While germline gain-of-function mutations in the RET proto-oncogene cause hereditary MTC, somatic RET mutations have been described in a variable number of sMTC. So far, S836S of RET, is the only variant whose association with sMTC has been found in several European cohorts. Because RET variants seem to be associated with MTC, it is plausible that variants in genes encoding for RET coreceptors may play a role in the pathogenesis of sMTC. Recently, we described two possible low penetrance susceptibility alleles in the gene encoding RET coreceptor GFRalpha1, -193C > G and 537T > C, in a German series of sMTC. In this study, we have genotyped nine polymorphisms within GFRA1-3 genes for 51 Spanish sMTC, and 100 normal controls. Our results show that no statistical signification was found when Spanish sMTC patients were compared to controls. Taken together with the observations in the German sMTC series, the present findings suggest that GFRA1-193C > G and 537T > C could be in linkage disequilibrium with other loci responsible for the disease with a founder effect in Germany. Alternatively, the combined observations might also suggest that, if indeed the polymorphisms are functional, the effect is small.