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

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.

Multiple endocrine neoplasia type 2: A reveiw

Multiple endocrine neoplasias are rare hereditary syndromes some of them with malignant potential. Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant hereditary cancer syndrome due to germline variants in the REarranged during Transfection (RET) proto-oncogene. There are two distinct clinical entities: MEN 2A and MEN 2B. MEN 2A is associated with medullary thyroid carcinoma (MTC), phaeochromocytoma, primary hyperparathyroidism, cutaneous lichen amyloidosis and Hirschprung's disease and MEN 2B with MTC, phaeochromocytoma, ganglioneuromatosis of the aerodigestive tract, musculoskeletal and ophthalmologic abnormalities. Germline RET variants causing MEN 2 result in gain-of-function; since the discovery of the genetic variants a thorough search for genotype-phenotype associations began in order to understand the high variability both between families and within family members. These studies have successfully led to improved risk classification of prognosis in relation to the genotype, thus improving the management of the patients by thorough genetic counseling. The present review summarizes the recent developments in the knowledge of these hereditary syndromes as well as the impact on clinical management, including genetic counseling, of both individual patients and families. It furthermore points to future directions of research for better clarification of timing of treatments of the various manifestations of the syndromes in order to improve survival and morbidity in these patients.

Modulatory Role of Single Nucleotide Polymorphisms of Distinct Genetic Pathways on Clinical Behavior of Medullary Thyroid Carcinoma

BACKGROUND

Role of RET proto-oncogene as predisposing gene for Medullary Thyroid Carcinoma is well established which provides the basis for clinical management of patients. However clinical behavior of MTC varies considerably among patients. Several studies have investigated whether SNPs in low penetrance genes could modulate the clinical behavior of MTC but with conflicting or inconclusive results. The present study aimed to investigate the modifier effect of 13 SNPs of three distinct genetic pathways -Detoxification, Cell cycle regulation and RET on the clinico-pathological features of hereditary and sporadic MTC.

METHODS

SNPs were genotyped using RFLP or TaqMan method. The genotypes were correlated with various clinico-pathological parameters (age and calcitonin levels at MTC diagnosis, tumor volume, nodal and distant metastasis).

RESULTS

Nodal metastasis was the only clinico-pathological parameter showing significant association with any SNP. In the hereditary MTC group (n=77), incidence of nodal metastases was significantly higher in wild type allele for Cyp1A1m1, CDKN2A and CDKN2C (p=0.01 for all three). In sporadic MTC group (n=361) CDKN2C wild type allele had higher nodal metastasis (p=0.03).

CONCLUSION

In this largest MTC cohort with comprehensive analysis of modulatory role of 13 most frequently studied SNPs with MTC clinical outcome, we observed a statistically significant association of few SNPs with nodal metastasis. However as these SNPs did not show association with any other clinico-pathological parameters like tumor volume or Calcitonin, they may not be true modifier of MTC. Additional large cohort studies with clinico-pathological details and long-term follow-up are needed to identify genetic modifiers of MTC behavior.

Variability in Medullary Thyroid Carcinoma in RET L790F Carriers: A Case Comparison Study of Index Patients

Background: Previous studies have suggested that the variability in age of onset and aggressiveness of medullary thyroid carcinoma (MTC) in patients with multiple endocrine neoplasia type 2A (MEN 2A) carrying the same REarranged during Transfection (RET) mutation may be caused by additional RET germline variants or somatic variants. Methods: This study was a retrospective case comparison study of all MEN 2A index patients (n = 2) with the RET L790F germline mutation in Denmark. Whole blood and MTC tissue were analyzed for RET germline variants and other somatic variants (>500), respectively. Results: Patient 1 presented with MTC (T1aN1bM0) at age 14 years, while patient 2 presented with MTC (T1bN0M0) at age 70 years. No germline RET germline variants nor other variants were found to explain this MTC variability. Conclusions: We could not confirm the previously reported finding of a somatic RET variant as likely responsible for the early onset and aggressiveness of MTC in a RET germline mutation carrier. Also, we found no RET germline variants that could explain the MTC variability among our index patients. We did, however, identify a somatic FLT3 R387Q variant with an unknown potential as genetic modifier. Further large-scale studies are needed to investigate genetic modifiers in RET L790F carriers.

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.

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.

Role of RET genetic variants in MEN2-associated pheochromocytoma

BACKGROUND

RET polymorphisms have been involved in the clinical presentation and prognosis of multiple endocrine neoplasia type 2 (MEN2)-associated medullary thyroid carcinoma.

OBJECTIVE

To investigate the effect of RET variants on the penetrance of pheochromocytoma (PHEO) in MEN2 patients.

METHODS

The RET variants L769L, S836S, and G691S/S904S were evaluated in a cohort of 153 MEN2 patients attending a tertiary teaching hospital. A comparison of RET variant frequencies between patients with and without PHEO was performed. Kaplan-Meier curves and Cox regression analysis were used to estimate the effect of RET variants on the age-dependent penetrance.

RESULTS

A total of 48 (31.4%) patients presented with MEN2-associated PHEOs. The mean age at diagnosis was 35.5±13.4 years, 60.4% of patients were women, and 92.8% had RET mutations at codon 634. The frequencies of RET polymorphisms were as follows: 20.1% L769L, 4.75% S836S, and 17.3% S904S/G691S. We did not observe any association between the frequencies of L769L, S836S, or S904S/G691S variants and PHEO development (all P>0.05). However, individuals carrying two RET polymorphic alleles had an increased estimated risk of PHEO (2.63; 95% CI, 1.4-5.0; P=0.004) and were younger at diagnosis when compared with those with one or no polymorphism (29.6±6.3 and 39.3±14.4 years respectively; P=0.006). Accordingly, additional analysis using Cox proportional hazard models demonstrated that the presence of two RET variants was associated with an increased risk for early PHEO development (hazard ratio, 5.99 (95% CI, 2.24-16.03); P<0.001).

CONCLUSIONS

RET polymorphic alleles have an additive effect on the estimated risk of age-related PHEO penetrance in MEN2 patients.

Genome-wide copy number analysis in a family with p.G533C RET mutation and medullary thyroid carcinoma identified regions potentially associated with a higher predisposition to lymph node metastasis

CONTEXT

Our group described a p.G533C RET gene mutation in a large family with multiple endocrine neoplasia type 2 syndrome. Clinical heterogeneity, primarily associated with the presence of lymph node metastases, was observed among the p.G533C carriers.

OBJECTIVE

The aim of this study was to use single-nucleotide polymorphism-array technology to identify copy number variations (CNVs), which are present in the constitutional DNA and associated with the established clinical and pathological features of aggressive medullary thyroid carcinoma (MTC), primarily the presence of lymph node metastasis.

DESIGN

Fifteen p.G533C carriers with MTC were chosen for the initial screening. The subjects were divided into two groups according the presence (n = 8) or absence (n = 7) of lymph node metastasis. Peripheral blood DNA was independently hybridized using a genome-wide single-nucleotide polymorphism Array 6.0 platform. The results were analyzed using both Genotyping Console and PennCNV software. To identify the possible candidate regions associated with the presence of lymph node metastasis, cases (metastatic MTC) were compared with controls (nonmetastatic MTC). The identified CNVs were validated by quantitative PCR in an extended cohort (n = 32).

RESULTS

Using two different algorithms, we identified nine CNV regions that may contribute to susceptibility to lymph node metastasis. The validation step confirmed that a CNV loss impacting the FMN2 gene was potentially associated with a greater predisposition to lymph node metastasis in this family (P = .0179). Finally, we sought to investigate whether the development of lymph node metastasis might not depend on a single CNV but rather a combination of various CNVs. These analyses defined a CNV pattern related to a more aggressive phenotype in this family, with CNV deletions being enriched in the metastatic group (P = .0057).

CONCLUSION

Although hereditable specific RET mutations are important to determine cancer risk, germline CNVs in disease-affected individuals may predispose them to MTC aggressiveness.

A ten-year clinical update of a large RET p.Gly533Cys kindred with medullary thyroid carcinoma emphasizes the need for an individualized assessment of affected relatives

OBJECTIVE

Reviewing the clinical outcomes of a large kindred with a RET p.Gly533Cys mutation, 10 years after the first description of this kindred, has provided an important set of clinical data for healthcare decision-making.

DESIGN AND PATIENTS

We identified 728 RET533 Brazilian relatives, spread out over 7 generations. We performed clinical examination, biochemical and imaging analyses in the proband and in 103 carriers.

MEASUREMENT AND RESULTS

The proband has been followed without evidence of structural disease in the last 10 years but with elevated calcitonin. The clinical and surgical features of 60 thyroidectomized RET533 relatives were also described. Forty-six patients had MTC (21-72 years), and 11 patients had C-cell hyperplasia (CCH) (5-42 years). Twelve MTC patients with lymph node metastases had a tumour size of 0·7-2·8 cm. Calcitonin level and CEA were correlated with disease stage, and none of the patients presented with an altered PTH or metanephrine. A 63-year-old woman developed pheochromocytoma and breast cancer. Two other RET533 relatives developed lung squamous cell carcinoma and melanoma.

CONCLUSIONS

A vast clinical variability in RET533 presentation was observed, ranging from only an elevated calcitonin level (3%) to local metastatic disease (25%). Many individuals were cured (42%) and the majority had controlled chronic disease (56%), reinforcing the need for individualized ongoing risk stratification assessment. The importance of this update relies on the fact that it allows us to delineate the natural history of RET 533 MEN2A 10 years after its first description.

Multiple endocrine neoplasia type 2A due to an exon 8 (G533C) mutation in a large North American kindred

BACKGROUND

Medullary thyroid cancer, although most commonly sporadic, may be part of the multiple endocrine neoplasia type 2 (MEN2) syndromes, generally due to mutations in the RET proto-oncogene. The majority of these mutations are located in exons 10, 11, and 13-16. More rarely, mutations in other exons have been described. We report for the first time a family from the United States with a rare mutation involving exon 8 of the RET proto-oncogene, corresponding to a p.Gly533Cys substitution (G533C) leading to the development of MEN2A syndrome in several affected family members. This mutation had only been previously described in a large family in Brazil and in 7.75% of patients with apparently sporadic medullary thyroid cancer (MTC) in Greece.

METHODS

Given a strong index of suspicion, a genetic analysis to evaluate for uncommon mutations in the RET proto-oncogene identified the presence of the G533C missense mutation, despite initial negative screening for common mutations. We describe a family with a total of 47 individuals from five generations with multiple members affected with this mutation.

RESULTS

Our data suggest that in patients with this mutation, pheochromocytoma is more common than previously reported, and that in some cases this mutation may be associated with a more aggressive phenotype than initially described.

CONCLUSIONS

MEN2A due to the G533C mutation in exon 8 may be more common and more aggressive than previously recognized. In patients with medullary thyroid cancer with negative screening for common mutations in the RET oncogene but a strong index of suspicion, DNA sequence analysis of less commonly involved exons should be considered.

Comprehensive analysis of RET gene should be performed in patients with multiple endocrine neoplasia type 2 (MEN 2) syndrome and no apparent genotype-phenotype correlation: an appraisal of p.Y791F and p.C634Y RET mutations in five unrelated Brazilian families

BACKGROUND

We previously identified a four-generation family with medullary thyroid cancer (MTC) and a germline p.Y791F RET mutation whose cancer lacked a strong genotype-phenotype correlation. The entire gene coding region of the RET gene should be sequenced when genotype-phenotype discrepancies are observed in patients with multiple endocrine neoplasia type 2 (MEN 2), even if a RET hotspot mutation has been identified.

METHODS

A new genetic test was performed in the index case of this family with the p.Y791F RET germline mutation. The entire coding region of the RET gene was investigated by direct sequencing of PCR products. Once a mutation was identified, the target exon was sequenced in all at-risk relatives.

RESULTS

An additional p.C634Y germline mutation in the RET gene was identified in the reported family. The double mutation occurred in cis and segregated with the phenotype. Through the Brazilian Genetic Screening Program developed at our institution, we additionally report the combination of these two mutations (p.C634Y/p.Y791F) in the RET gene in four other unrelated families. The overall penetrance of MTC and pheochromocytoma in patients with the p.C634Y/p.Y791F mutations was 79% and 13%, respectively.

CONCLUSION

Our data emphasises that a comprehensive analysis of the RET gene may reveal multiple germline mutations in MEN 2 patients who exhibit an atypical clinical course of the disease.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Genes of detoxification are important modulators of hereditary medullary thyroid carcinoma risk

CONTEXT

Different inherited profiles of genes involved in cellular mechanisms of activation and detoxification of carcinogenic products can provide specific protection or determine the risk for cancer. Low-penetrance polymorphic genes related to the biotransformation of environmental toxins have been associated with susceptibility to and the phenotype of, human tumours.

OBJECTIVE

To investigate the role of germline inheritance of polymorphisms in CYP1A2*F, CYP1A1 m1, GSTP1, NAT2 and TP53 genes in hereditary medullary thyroid carcinoma (HMTC) patients.

DESIGN

This study was developed in University of Campinas (Unicamp).

PATIENTS

We studied 132 patients with HMTC, 88 first-degree relatives of HMTC patients and 575 control individuals.

MEASUREMENTS

All patients with MTC and their relatives were sequenced for the RET gene and five genes were genotyped using TaqMan(®) system.

RESULTS

We observed that the inheritance of CYP1A2*F (OR = 2·10; 95% CI = 1·11-3·97; P = 0·022), GSTP1 (OR = 4·41; 95% CI = 2·47-7·88; P < 0·001) and NAT2 (OR = 2·54; 95% CI = 1·16-5·58; P = 0·020) variants increased the risk for HMTC. In addition, multiple regression analysis showed that the inheritance of GSTP1 polymorphisms was associated with the diagnosis in older patients (B = 8·0229; 95% IC = ± 5·5735; P = 0·0054). Concerning the group of HTMC relatives, CYP1A2*F (OR = 2:40; 95% CI = 1·19-4·86; P = 0·015), CYP1A1 m1 (OR = 2·79; 95% CI = 1:04-7·51; P = 0·042), GSTP1 (OR = 2·86; 95% IC = 1·53-5·32; P < 0·001) and NAT2 (OR = 2·25; 95% IC = 1·20-4·22; P = 0·012) were associated with HMTC risk.

CONCLUSIONS

We have demonstrated that the inheritance of specific genes determining the individual response to environmental toxins may contribute to the risk and phenotypic variability that exists in patients with HMTC. Moreover, we identified a group at risk in relatives of HMTC patients.

The optimal range of RET mutations to be tested: European comments to the guidelines of the American Thyroid Association

In the 9^th ETA-CRN Meeting (September 2009, Lisbon) some recommendations from the American Thyroid Association (ATA) guidelines for the management of medullary thyroid cancer (MTC) were discussed by an European Panel of Experts (EPE). Among the 12 ATA recommendations related to hereditary MTC and to the optimal range of RET mutations to be tested (recommendations 1-5 and 9-15), 7 were shared and 5 were not shared by the EPE. In the present paper, the related comments and suggestions will be reported and discussed.

The involvement of the RET variant G691S in medullary thyroid carcinoma enlightened by a meta-analysis study

Medullary thyroid carcinoma (MTC) is a rare tumor, partially explained by mutations in the rearranged during transfection (RET) proto-oncogene. The nonsynonymous RET polymorphism G691S has been reported as associated with MTC, but findings are discordant. We sought to clarify the role of G691S in MTCs through in silico analysis, genetic association in our patients and a meta-analysis with extensive literature revision. Ninety-three Italian patients were compared to 85 healthy individuals. Results were included in a meta-analysis together with 11 case-control association studies identified through PubMed, EMBASE and Web of Science, with a combined sample of 968 cases and 2,115 controls. No association of G691S with MTC was found in our sample; however, we observed an excess of homozygotes for the variant, significantly higher among females. The overall allelic association in the meta-analysis was significant under the fixed-effect model (odds ratio [OR] = 1.22 [95% confidence intervals: 1.06-1.39], p = 0.0049), but borderline under the random effect model (OR = 1.21 [0.99-1.46], p = 0.0575), with a moderate/high heterogeneity (I(2) = 44.6%, p = 0.047). Under the recessive model of transmission, applied to the eight studies with available genotype frequencies, results were significant under both effect models (OR = 2.016 and OR = 2.022, p = 0.0004). No heterogeneity was anymore detectable. In silico analyses on G691S confirmed a change of the phosphorylation pattern that might account for the enhanced signaling transduction previously reported for G691S in several cancers, thus also explaining its overrepresentation in MTCs. The G691S variant allele does increase the risk for MTC, with a recessive mechanism of action, apparently more evident among females.

High prevalence of exon 8 G533C mutation in apparently sporadic medullary thyroid carcinoma in Greece

OBJECTIVE

Genetic screening for ret mutation has become routine practice in the evaluation of medullary thyroid carcinoma (MTC). Approximately 25% of these tumours are familial, and they occur as components of the multiple endocrine neoplasia type 2 syndromes (MEN 2A and 2B) or familial MTC. In familial cases, the majority of mutations are found in exons 10, 11, 13, 14 or 15 of the ret gene. A rare mutation involving exon 8 (G533C) has recently been reported in familial cases of MTC in Brazil and Greece; some of these cases were originally thought to be sporadic. The aim of this study was to re-evaluate a series of sporadic cases of MTC, with negative family history, and screen them for germline mutations in exon 8.

DESIGN AND PATIENTS

Genomic DNA was extracted from peripheral lymphocytes in 129 unrelated individuals who had previously been characterized as 'sporadic' based on the negative family history and negative screening for ret gene mutations. Samples were analysed in Applied Biosystems 7500 real-time PCR and confirmed by sequencing.

MEASUREMENTS AND RESULTS

The G533C exon 8 mutation was identified in 10 of 129 patients with sporadic MTC. Asymptomatic gene carriers were subsequently identified in other family members.

CONCLUSION

In our study, we found that 7·75% patients with apparently sporadic MTC do carry G533C mutation involving exon 8 of ret. We feel that there is now a need to include exon 8 mutation screening in all patients diagnosed as sporadic MTC, in Greece.

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.

Evidence that polymorphisms in detoxification genes modulate the susceptibility for sporadic medullary thyroid carcinoma

AIM

Polymorphic low-penetrance genes have been consistently associated with the susceptibility to a series of human tumors, including differentiated thyroid cancer.

METHODS

To determine their role in medullary thyroid cancer (MTC), we used TaqMan SNP method to genotype 47 sporadic MTC (s-MTC) and a control group of 578 healthy individuals for CYP1A2*F, CYP1A1m1, GSTP1, NAT2 and 72TP53. A logistic regression analysis showed that NAT2C/C (OR=3.87; 95% CI=2.11-7.10; P=2.2×10(-5)) and TP53C/C genotypes (OR=3.87; 95% CI=1.78-6.10; P=2.8×10(-4)) inheritance increased the risk of s-MTC. A stepwise regression analysis indicated that TP53C/C genotype contributes with 8.07% of the s-MTC risk.

RESULTS

We were unable to identify any relationship between NAT2 and TP53 polymorphisms suggesting they are independent factors of risk to s-MTC. In addition, there was no association between the investigated genes and clinical or pathological features of aggressiveness of the tumors or the outcome of MTC patients.

CONCLUSION

In conclusion, we demonstrated that detoxification genes and apoptotic and cell cycle control genes are involved in the susceptibility of s-MTC and may modulate the susceptibility to the disease.

Over-representation of the G12S polymorphism of the SDHD gene in patients with MEN2A syndrome

OBJECTIVE

To evaluate whether germline variants of the succinate dehydrogenase genes might be phenotypic modifiers in patients with multiple endocrine neoplasia type 2. Mutations of genes encoding subunits of the succinate dehydrogenase are associated with hereditary paraganglioma/pheochromocytoma syndrome. Pheochromocytoma is one of the main manifestations of multiple endocrine neoplasia type 2 caused by germline mutation of the rearranged during transfection proto-oncogene.

METHODS

Polymorphisms of the succinate dehydrogenase genes were analyzed in 77 rearranged during transfection mutation carriers, 47 patients with sporadic medullary thyroid cancer, 48 patients with sporadic Pheo, and 100 healthy individuals. Exons 10-16 of the rearranged during transfection proto-oncogene were analyzed by direct DNA sequencing, and all exons of the von Hippel-Lindau, succinate dehydrogenase B, and succinate dehydrogenase subunit D genes were tested by direct DNA sequencing and multiple ligation probe analysis. The G12S polymorphism of the succinate dehydrogenase subunit D gene was determined by restriction fragment length polymorphism.

RESULTS

Of the 77 rearranged during transfection mutation carriers, 55 from 16 families had multiple endocrine neoplasia type 2A, three from three families had multiple endocrine neoplasia type 2B, and 19 from two families had familial medullary thyroid carcinoma. Eight of 55 (14.5%) patients with multiple endocrine neoplasia type 2A had this variant whereas it was absent in multiple endocrine neoplasia type 2B, familial medullary thyroid carcinoma, sporadic medullary thyroid carcinoma, and sporadic pheochromocytoma groups, and its prevalence in controls was 1% (p<0.002 multiple endocrine neoplasia type 2A versus controls). No associations between G12S and age of manifestation, incidence of pheochromocytoma or hyperparathyroidism, or level of serum calcitonin were observed.

CONCLUSION

The high prevalence of the G12S variant in patients with multiple endocrine neoplasia type 2A raises questions about its role as a genetic modifier, but this proposal remains to be established.

Personalized medicine: caught between hope, hype and the real world

Genomic and personalized medicine have become buzz phrases that pervade all fields of medicine. Rapid advances in "-omics" fields of research (chief of which are genomics, proteinomics, and epigenomics) over the last few years have allowed us to dissect the molecular signatures and functional pathways that underlie disease initiation and progression and to identify molecular profiles that help the classification of tumor subtypes and determine their natural course, prognosis, and responsiveness to therapies. Genomic medicine implements the use of traditional genetic information, as well as modern pangenomic information, with the aim of individualizing risk assessment, prevention, diagnosis, and treatment of cancers and other diseases. It is of note that personalizing medical treatment based on genetic information is not the revolution of the 21st century. Indeed, the use of genetic information, such as human leukocyte antigen-matching for solid organ transplantation or blood transfusion based on ABO blood group antigens, has been standard of care for several decades. However, in recent years rapid technical advances have allowed us to perform high-throughput, high-density molecular analyses to depict the genomic, proteinomic, and epigenomic make-up of an individual at a reasonable cost. Hence, the so-called genomic revolution is more or less the logical evolution from years of bench-based research and bench-to-bedside translational medicine.

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.

The RET p.G533C mutation confers predisposition to multiple endocrine neoplasia type 2A in a Brazilian kindred and is able to induce a malignant phenotype in vitro and in vivo

BACKGROUND

We have previously described a p.G533C substitution in the rearranged during transfection (RET) oncogene in a large family with medullary thyroid carcinoma. Here, we explore the functional transforming potential of RET p.G533C mutation.

METHODS

Plasmids expressing RET mutants (p.G533C and p.C634Y) and RET wild type were stable transfected into a rat thyroid cell line (PCCL3). Biological and biochemical effects of RET p.G533C were investigated both in vitro and in vivo. Moreover, we report the first case of pheochromocytoma among the RET p.G533C-carriers in this Brazilian family and explore the RET mutational status in DNA isolated from pheochromocytoma.

RESULTS

Ectopic expression of RET p.G533C and p.C634Y activates RET/MAPK/ERK pathway at similar levels and significantly increased cell proliferation, compared with RET wild type. We additionally show that p.G533C increased cell viability, anchorage-independent growth, and micronuclei formation while reducing apoptosis, hallmarks of the malignant phenotype. RET p.G533C down-regulates the expression of thyroid specific genes in PCCL3. Moreover, RET p.G533C-expressing cells were able to induce liver metastasis in nude mice. Finally, we described two novel RET variants (G548V and S556T) in the DNA isolated from pheochromocytoma while they were absent in the DNA isolated from blood.

CONCLUSIONS

Our in vitro and in vivo analysis indicates that this mutation confers a malignant phenotype to PCCL3 cells. These findings, in association with the report of first case of pheochromocytoma in the Brazilian kindred, suggest that this noncysteine mutation may be more aggressive than was initially considered.

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.