Germline RET Mutations Research Articles

A Case of Medullary Thyroid Carcinoma with de novo V804M RET Germline Mutation

Many cases of RET proto-oncogene mutations of hereditary medullary thyroid carcinoma (MTC) have been reported in Korea. However, MTC with V804M RET proto-oncogene germline mutations have not been reported in Korea. A 33-yr-old man was diagnosed with a 0.7-cm sized thyroid nodule. Laboratory testing revealed serum calcitonin was elevated. The patient underwent total thyroidectomy with central compartment neck dissection for the thyroid tumor. RET gene analysis was performed in both the index patient and his family. There were no V804M RET mutation and abnormal laboratory findings within his family except the index patient. Therefore, this patient was a de novo V804M RET germline mutation.

Differential Gene Expression of Medullary Thyroid Carcinoma Reveals Specific Markers Associated with Genetic Conditions

Medullary thyroid carcinoma accounts for 2% to 5% of thyroid malignancies, of which 75% are sporadic and the remaining 25% are hereditary and related to multiple endocrine neoplasia type 2 syndrome. Despite a genotype-phenotype correlation with specific germline RET mutations, knowledge of pathways specifically associated with each mutation and with non-RET-mutated sporadic MTC remains lacking. Gene expression patterns have provided a tool for identifying molecular events related to specific tumor types and to different clinical features that could help identify novel therapeutic targets. Using transcriptional profiling of 49 frozen MTC specimens classified as RET mutation, we identified PROM1, LOXL2, GFRA1, and DKK4 as related to RET(M918T) and GAL as related to RET(634) mutation. An independent series of 19 frozen and 23 formalin-fixed, paraffin-embedded (FFPE) MTCs was used for validation by RT-qPCR. Two tissue microarrays containing 69 MTCs were available for IHC assays. According to pathway enrichment analysis and gene ontology biological processes, genes associated with the MTC(M918T) group were involved mainly in proliferative, cell adhesion, and general malignant metastatic effects and with Wnt, Notch, NFκB, JAK/Stat, and MAPK signaling pathways. Assays based on silencing of PROM1 by siRNAs performed in the MZ-CRC-1 cell line, harboring RET(M918T), caused an increase in apoptotic nuclei, suggesting that PROM1 is necessary for survival of these cells. This is the first report of PROM1 overexpression among primary tumors.

A Rare Case of De novo C634G Germline Mutation of the RET Proto-Oncogene in a Patient With MEN 2A Syndrome With Aggressive Pheochromocytoma

Multiple endocrine neoplasia type 2A (MEN 2A) is an autosomal inherited disorder induced by mutations in the RET proto-oncogene. It is characterized by medullary thyroid carcinoma (MTC), accompanied in half of cases by pheochromocytoma and less frequently, by primary hyperparathyroidism. The aim of the study was to investigate a clinical case of a MEN 2A syndrome consisting of bilateral aggressive pheochromocytomas and MTC with loco-regional lymph node invasion caused by a rare de novo germline mutation in the RET proto-oncogene (Cys634Gly). We reported herein a 42-year-old man presented with hypertension refractory to various antihypertensive drug regimens administered over the preceding 3 years. Abdominal computed tomography scan showed a large right adrenal mass, and a smaller left adrenal nodule. Comprehensive biochemical analyses ( 24-hour urinary catecholamines and metabolites ) confirmed the diagnosis of pheochromocytoma. 123 I-metaiodobenzylguanidine scintigraphy revealed uptake in the left inferior thyroid nodule. Left t hyroid ultrasound-guided f ine needle aspiration established the diagnosis of MTC. The patient first underwent open right adrenalectomy, and 2 months later, total thyroidectomy with central neck compartment lymph node dissection. Screening for hyperparathyroidism was negative. On follow-up, the patient demonstrated no biochemical abnormalities, or clinical complaints. Genetic testing identified a point mutation in the RET proto-oncogene , confirming the diagnosis of MEN 2A. This missense mutation, located in exon 11, resulted in the replacement of a cysteine 634 residue with glycine. To the best of our knowledge, this is the first MEN 2A case reported with de novo Cys634Gly RET germline mutation in North America, and also worldwide with regard to the aggressiveness of this genotypic variant. doi: http://dx.doi.org/10.4021/jem120w

Medullary thyroid carcinoma (MTC) and RET proto-oncogene: Mutation spectrum in the familial cases and a meta-analysis of studies on the sporadic form

Medullary thyroid carcinoma (MTC) is an uncommon malignant tumor arising from the calcitonin-producing parafollicular cells (C cells) of thyroid. It accounts for 5-10% of all thyroid cancers, and it mostly occurs as a sporadic entity (sMTC), but a familial pattern (fMTC) is also possible. RET proto-oncogene germline mutations are crucial for the onset and the progression of fMTC, and the occurrence of single nucleotide polymorphisms could predispose to the sporadic form. In order to clarify the role of this gene in MTC, we carefully reviewed the PubMed database using appropriate terms. First, we summarized current knowledge of the germline RET mutations, mutation spectrum, and prevalence. We then performed a meta-analysis on the available case-control association studies for sMTC. Finally, we carried out in silico predictions of the best associated variants in the attempt to better define their role in the disease. To date, a total of 39 different RET germline mutations have been identified in fMTC families. The most affected codons are 609, 611, 618, 620 (exon 10) and 634 (exon 11), encoding for the extracellular cysteine-rich domain, and codons 768 (exon 13) and 804 (exon 14) of the intracellular tyrosine kinase domain. Six polymorphisms with at least three studies were included in the meta-analysis (A45A [rs1800858], G691S [rs1799939], L769L [rs1800861], S836S [rs1800862], S904S [rs1800863], and IVS1-126G>T [rs2565206]). The meta-analysis demonstrated a modest association of sMTC susceptibility with S836S and a strong association with the IVS1-126G>T polymorphism. Besides RET polymorphisms, we also investigated the role of a few other low-penetrance alleles of genes involved in the RET pathway or in xenobiotic metabolism, but none of these were confirmed. Thus, despite the well-known molecular basis of fMTC, the genetic variants of the sporadic form are still poorly understood, and functional analyses are needed to better understand the consequence of such RET variants and to improve our knowledge on the disease.

A Rare Case of De novo C634G Germline Mutation of the RET Proto-Oncogene in a Patient With MEN 2A Syndrome With Aggressive Pheochromocytoma

Multiple endocrine neoplasia type 2A (MEN 2A) is an autosomal inherited disorder induced by mutations in the RET proto-oncogene. It is characterized by medullary thyroid carcinoma (MTC), accompanied in half of cases by pheochromocytoma and less frequently, by primary hyperparathyroidism. The aim of the study was to investigate a clinical case of a MEN 2A syndrome consisting of bilateral aggressive pheochromocytomas and MTC with loco-regional lymph node invasion caused by a rare de novo germline mutation in the RET proto-oncogene (Cys634Gly). We reported herein a 42-year-old man presented with hypertension refractory to various antihypertensive drug regimens administered over the preceding 3 years. Abdominal computed tomography scan showed a large right adrenal mass, and a smaller left adrenal nodule. Comprehensive biochemical analyses ( 24-hour urinary catecholamines and metabolites ) confirmed the diagnosis of pheochromocytoma. 123 I-metaiodobenzylguanidine scintigraphy revealed uptake in the left inferior thyroid nodule. Left t hyroid ultrasound-guided f ine needle aspiration established the diagnosis of MTC. The patient first underwent open right adrenalectomy, and 2 months later, total thyroidectomy with central neck compartment lymph node dissection. Screening for hyperparathyroidism was negative. On follow-up, the patient demonstrated no biochemical abnormalities, or clinical complaints. Genetic testing identified a point mutation in the RET proto-oncogene , confirming the diagnosis of MEN 2A. This missense mutation, located in exon 11, resulted in the replacement of a cysteine 634 residue with glycine. To the best of our knowledge, this is the first MEN 2A case reported with de novo Cys634Gly RET germline mutation in North America, and also worldwide with regard to the aggressiveness of this genotypic variant. J Endocrinol Metab. 2012;2(4-5):198-204 doi: https://doi.org/10.4021/jem120w

Novel p.C620L RET Mutation Detected in a Patient with Medullary Thyroid Carcinoma

A patient with an apparent sporadic medullary thyroid carcinoma was tested for RET germline mutations by Sanger sequencing of RET exons 10, 11, and 13-16. The patient was heterozygous for two known mutations causative of Multiple Endocrine Neoplasia type 2 disorder, and both mutations were within codon 620 of RET exon 10, c.1859G > T (p.C620F) and c.1860C > G (p.C620W). In order to determine if these adjacent mutations were in cis or in trans, an unlabeled probe method and high-resolution melting analysis were utilized. The mutations were confirmed to occur in cis, representing a novel mutation, c.1859_1860delinsTG (p.C620L). Sanger sequencing of parental samples did not identify any changes at codon 620, so the p.C620L mutation is also de novo. The early age of onset for medullary thyroid carcinoma and the presence of lymph node metastasis in this patient suggests individuals with the p.C620L mutation should be treated and screened (for pheochromocytomas and parathyroid hyperplasia) as Multiple Endocrine Neoplasia type 2 patients with other RET codon 620 mutations (American Thyroid Association risk level B).

The Timing of Total Thyroidectomy inRETGene Mutation Carriers Could Be Personalized and Safely Planned on the Basis of Serum Calcitonin: 18 Years Experience at One Single Center

Medullary thyroid carcinoma (MTC) is a calcitonin (CT)-producing C-cell tumor. In hereditary cases, a germline RET mutation is found in 98% of families. Because MTC is cured only if intrathyroidal, prophylactic thyroidectomy is recommended in the gene carrier (GC). The aim was to determine whether thyroidectomy performed when stimulated CT becomes detectable is as safe as prophylactic thyroidectomy and to identify the serum CT cutoff able to distinguish intrathyroidal from extrathyroidal MTC. Eighty-four GC were prospectively enrolled; 53 of the 84 underwent total thyroidectomy, one refused surgery, and 30 with normal basal and stimulated CT were under surveillance. The follow-up ranged from 2 to 18 yr. GC operated on for elevated stimulated CT included 27 GC with a positive peak CT at the screening and four cases who became positive after 4 yr. All of them had intrathyroidal MTC and no node metastases; all were cured after a mean follow-up of 7.5 yr. Among those operated on for detectable basal CT, intrathyroidal tumors were found when CT was below 60 pg/ml, whereas either node metastases or larger tumors were observed when CT was above 60 pg/ml. No correlation among serum CT, age, and type of RET mutation was observed. Thirty GC were still biochemically negative at the annual control. The time of thyroidectomy in GC with negative CT could be personalized and safely planned when stimulated CT becomes positive, independent of the type of RET mutation and patient's age. In this series, a basal CT below 60 pg/ml was always associated to an intrathyroidal localization of MTC.

Germline Mutations of the TMEM127 Gene in Patients with Paraganglioma of Head and Neck and Extraadrenal Abdominal Sites

Hereditary pheochromocytoma is associated with germline mutations of a set of susceptibility genes to which the TMEM127 gene has recently been added. Patients with TMEM127 mutations have been thus far exclusively identified with adrenal tumors. A population-based series of 48 consecutive individuals from the European-American Pheochromocytoma Paraganglioma Registry with multiple paraganglial tumors and, of these, one extraadrenal paraganglial tumor were selected for this study. They all had normal results when screened for germline mutations of the genes RET, VHL, SDHB, SDHC, and SDHD. Germline mutation analysis of the TMEM127 gene included a search for intragenic mutations and large rearrangements. Of the 48 eligible patients with extraadrenal paraganglial tumors, two (4.2%) were found to have TMEM127 mutations. One patient had multiple head and neck paraganglioma and one retroperitoneal extraadrenal and adrenal tumor. TMEM127 germline mutations confer risks of extraadrenal paraganglial tumors in addition to the documented adrenal pheochromocytoma. Thus, surveillance for extraadrenal and adrenal paraganglial tumors is likely warranted in TMEM127 mutation carriers, although the true prevalence should be evaluated in patients with extraadrenal paraganglial tumors.

Mammalian Target of Rapamycin Pathway Activation Is Associated to RET Mutation Status in Medullary Thyroid Carcinoma

The genetic pathways involved in medullary thyroid carcinomas (MTC), except for RET mutations, are largely unknown, as is the detailed mapping of proteins activated as a consequence of RET tyrosine kinase phosphorylation. The present study was designed to screen for the presence of mutations in other genes downstream to RET activation and to detect the activation patterns of a panel of intracellular regulators of cell growth. Forty-nine cases of MTC were analyzed for mutations in RET, BRAF, N-, H-, and K-RAS, and phosphatidylinositol-3 (PI3) kinase genes. Immunohistochemical analysis was performed using antibodies against several intracellular transducers. The effect of mammalian target of rapamycin (mTOR) inhibition was assessed in vitro onto TT cells by means of methyl thiazolyl tetrazolium and Western blot assays. BRAF, K-, H-, and N-RAS, and PI3 kinase mutations were absent in all cases examined. Germline RET mutations were detected in 20% of cases overall, whereas somatic RET mutations represented 53% of sporadic tumors. RET mutational status was associated to age, presence of multifocal tumors, and nodal status, but not disease outcome. Protein expression of markers investigated was highly heterogeneous, with a strong association between phospho-mTOR, phospho-AKT, and phospho-p70S6K, positively correlated to the presence of germline RET mutations. Moreover, selective mTOR inhibition affected cell proliferation of RET-mutant TT cells. Taken together, our findings indicate that mTOR intracellular signaling pathway is functionally activated in MTC with a preferential expression in cases with germline RET mutations; genes downstream to RET tyrosine kinase such as BRAF, RAS isoforms, and PI3 kinase are not mutated in MTC.

Molecular Analysis of the RET Proto-Oncogene Key Exons in Patients with Medullary Thyroid Carcinoma: A Comprehensive Study of the Iranian Population

Germ-line mutations of RET proto-oncogene are the known cause of hereditary medullary thyroid carcinoma (MTC), which account for approximately 25% of all MTC cases and occur as multiple endocrine neoplasia type 2 syndromes. Here, we present the first comprehensive genetic screening and analysis of MTC among Iranian families. A total of 55 patients with MTC (male to female ratio=1:1.6; average age of disease onset = 33 ± 13 years) from 53 independent families participated in this study. All of the patients had undergone total thyroidectomy between 1999 and 2006, and 51 of them were clinically characterized as apparently sporadic cases. Genomic DNA samples were obtained and following highly-specific polymerase chain reaction amplification of the 6 RET key exons (10, 11, 13, 14, 15, and 16) were subjected to direct DNA sequencing without a requirement for a purification step. Sequence analysis revealed that 9 (17.6%) of the apparently sporadic cases (from 8 kindreds) carried an RET germ-line mutation. Of the seven different mutations identified among all of the families studied, five were in the cysteine codons, with Cys634Arg having the highest prevalence (45.5%) among the afflicted families. Mutation carriers have an earlier age of onset (21 ± 6) versus the sporadic cases (37 ± 12). This is the first comprehensive genetic screening and analysis of MTC among Iranian families. The results further confirm the need and advantages of DNA sequencing for identification of hereditary MTC cases. There does not seem to be a meaningful correlation between single nucleotide polymorphism patterns and the average age of disease onset. Geographical distribution of the sporadic cases, however, shows a significant concentration toward the Northern regions of the country, noticeably the provinces situated directly to the south of the Caspian Sea.

RET proto-oncogene mutations are restricted to codon 618 in Cypriot families with multiple endocrine neoplasia 2.

RET germline mutations predispose to the development of inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2). Several variants of the RET proto-oncogene including G691S and S904S have been suggested to act as genetic modifiers at the age of onset ofMEN2. The aim of this study is to characterize clinically and molecularly 7 Cypriot patients with familial medullary thyroid carcinoma (FMTC) and 1 with MEN2A and also to determine the allelic frequencies of the RET variants G691S and S904S. Seven probands from FMTC families and 1 from MEN2A were screened for the presence of RET mutations and the G691S and S904S variants. Additionally, 226 healthy Cypriots, who served as controls were analysed in an attempt to compare the frequencies of G691S and S904S RET variants to those observed in the 8 patients. The clinical diagnosis of the probands was based on clinical presentation and supported with biochemical findings. The germline C618R mutation of exon 10 was identified in all 8 probands and in 15 relatives from 7 different families. No significant difference in the G691S/S904S variants allele frequencies between patients (4/16 or 25%) and controls (124/452 or 27.4%) was found. Mutational screening of the RET gene identified a common mutation (C618R) in all 8 (7 FMTC and 1 MEN2A) unrelated Cypriot patients which may be explained by a founder effect. Additionally, no association of the G691S/S904S variants was linked with the disease.

Predominant RET Germline Mutations in Exons 10, 11, and 16 in Iranian Patients with Hereditary Medullary Thyroid Carcinoma

Medullary thyroid carcinoma occurs in both sporadic (75%) and hereditary (25%) forms. The missense mutations of RET proto-oncogene in MTC development have been well demonstrated. To investigate the spectrum of predominant RET germline mutations in exons 10, 11, and 16 in hereditary MTC in Iranian population, 217 participants were included. Genomic DNAs were extracted from the leukocytes using the standard Salting Out/Proteinase K method. Mutation detection was performed through PCR-RFLP and DNA sequencing. In 217 participants, 43 missense mutations were identified in exons 10 (6%), 11 (13%), and 16 (0.9%). Moreover, a novel germline mutation was detected in exon 11 (S686N). Also four different polymorphisms were found in intron 16 in eight patients. The obtained data showed the frequency profile of RET mutations in Iranian individuals with MTC (19.8%). The most frequent mutation in our population was C634G whereas in most population it was C634R. Altogether, these results underline the importance of the genetic background of family members of any patient with MTC.

Targeting RET Receptor Tyrosine Kinase Activation in Cancer

After ligand binding induces dimerization, the RET receptor tyrosine kinase activates multiple signal transduction pathways. Constitutively activating mutations and chromosomal rearrangements are the primary oncogenic event in a significant number of medullary thyroid cancers (MTC) and papillary thyroid cancers (PTC), respectively. When specific germline mutations in RET are identified early, prophylactic thyroidectomy can be timed to remove at-risk tissue in patients with multiple endocrine neoplasia 2 (MEN2) syndromes who would otherwise develop MTC. Conventional therapy for progressive metastatic MTC is limited. Small-molecule tyrosine kinase inhibitors can target multiple kinases at nanomolar concentrations, including RET, and have shown efficacy against a variety of malignancies. Initial clinical evidence suggests that several of these inhibitors, including sorafenib, vandetanib, motesanib, sunitinib, and XL-184, may have some benefit in treating progressive MTC. Although initial success seen in these trials seems to be modest, it represents a major breakthrough in the treatment of patients with widespread metastatic MTC.

Risk profiles and penetrance estimations in multiple endocrine neoplasia type 2A caused by germline RET mutations located in exon 10

Multiple endocrine neoplasia type 2 is characterized by germline mutations in RET. For exon 10, comprehensive molecular and corresponding phenotypic data are scarce. The International RET Exon 10 Consortium, comprising 27 centers from 15 countries, analyzed patients with RET exon 10 mutations for clinical-risk profiles. Presentation, age-dependent penetrance, and stage at presentation of medullary thyroid carcinoma (MTC), pheochromocytoma, and hyperparathyroidism were studied. A total of 340 subjects from 103 families, age 4-86, were registered. There were 21 distinct single nucleotide germline mutations located in codons 609 (45 subjects), 611 (50), 618 (94), and 620 (151). MTC was present in 263 registrants, pheochromocytoma in 54, and hyperparathyroidism in 8 subjects. Of the patients with MTC, 53% were detected when asymptomatic, and among those with pheochromocytoma, 54%. Penetrance for MTC was 4% by age 10, 25% by 25, and 80% by 50. Codon-associated penetrance by age 50 ranged from 60% (codon 611) to 86% (620). More advanced stage and increasing risk of metastases correlated with mutation in codon position (609→620) near the juxtamembrane domain. Our data provide rigorous bases for timing of premorbid diagnosis and personalized treatment/prophylactic procedure decisions depending on specific RET exon 10 codons affected.

No evidence of RET germline mutations in familial pituitary adenoma

Pituitary adenomas are common in the general population. Although most of them are sporadic, some occur in a familial setting. In familial pituitary adenoma patients it is common that no germline defects are found after screening of aryl hydrocarbon receptor interacting protein (AIP) and other genes known to underlie the condition, suggesting the existence of yet unknown predisposition genes. Recently, the RET proto-oncogene was found to be a novel in vivo interaction partner of AIP in the pituitary gland. Here, we have screened patients from 16 AIP mutation negative (AIPmut-) pituitary adenoma families for RET germline mutations to assess whether RET could play a role in pituitary adenoma predisposition, similar to AIP. We found five novel germline RET changes: one in RET Exon 4 and the rest in noncoding regions of RET. Two changes, c.1560*G > A and -1285 G > A, were segregated in affected family members. We also analyzed the RET region with enhancer element locator (EEL) to identify RET regulatory elements, and to see whether the changes resided in these. None of the variants mapped to the regions predicted by EEL. Expression of RET was examined in ten AIPmut- and seven AIP mutation positive (AIPmut+) somatotropinomas by immunohistochemistry, with a trend showing reduced expression in the latter (P = 0.05). We conclude that the RET variants are presumably not related to pituitary adenoma predisposition, although reduced RET expression may play a role in AIP-related genesis of somatotropinomas.

A novel germline CDKN1B mutation causing multiple endocrine tumors: clinical, genetic and functional characterization

Multiple endocrine neoplasia (MEN) syndromes are characterized by tumors involving two or more endocrine glands. Two MEN syndromes have long been known: MEN1 and MEN2, caused by germline mutations in MEN1 or RET, respectively. Recently, mutations in CDKN1B, encoding the cyclin-dependent kinase (Cdk) inhibitor p27, were identified in patients having a MEN1-like phenotype but no MEN1 gene mutations. Currently, the molecular mechanisms mediating the role of p27 in tumor predisposition are ill defined. We here report a novel germline missense variant in CDKN1B (c.678C>T, p.P69L) found in a patient with multiple endocrine tumors. We previously reported a nonsense p27 mutation (c.692G>A, p.W76X) in two patients with MEN1-like phenotype. Functional assays were used to characterize p27P69L and p27W76X in vitro. We show that p27P69L is expressed at reduced level and is impaired in both binding to Cdk2 and inhibiting cell growth. p27W76X, which is mislocalized to the cytoplasm, can no longer efficiently bind Cyclins-Cdks, nor inhibit cell growth or induce apoptosis. In the patient's tumor tissues, p27P69L associates with reduced/absent p27 expression and in one tumor with loss-of-heterozygosity. Our results extend previous findings of CDKN1B mutations in patients with MEN1-related states and support the hypothesis of a tumor suppressor role for p27 in neuroendocrine cells. © 2010 Wiley-Liss, Inc.

Hirschsprung-associated enterocolitis develops independently of NOD2 variants

Backgroud/Purpose Hirschsprung-associated enterocolitis (HAEC) represents a cause for significant pre- and postoperative morbidity and mortality in Hirschsprung disease (HD). Although multiple studies on HAEC have been performed and several mechanisms have been presumed, the pathogenesis of this condition remains unclear. As changes in colonic mucosal defense are key factors suggested in both Crohn's disease (CD) and HAEC pathogenesis, the aim of the current study was to investigate genetic alterations in the most important susceptibility gene for Crohn's enterocolitis ( NOD2) to see whether carriers of polymorphisms within the NOD2 gene are predisposed to the development of HAEC. Methods Genotyping for the NOD2 variants in exon 4 (p.Arg702Trp [rs2066844]), exon 8 (p.Gly908Arg [rs2066845]), and exon 11 (p.1007fs [rs2066847]) was performed in 52 white children with HD (41 boys, 11 girls), 152 healthy controls, and 152 children with CD (onset of disease <17 years; mean, 11.8 years). Seventeen patients with HD (32.7%) were carriers of a RET germline mutation, 35 children (67.3%) had short segment disease, and 17 (32.7%) had long segment disease. Results Ten children (19.2%) with HD were heterozygous carriers of at least one NOD2 variant vs 17 (11.2%) in the healthy control group and 69 (45.4%) in the CD cohort. Hirschsprung-associated enterocolitis was observed in 7 children (13.5%), with 4 having short segment HD and 3 with long segment HD; but none of them were carriers of NOD2 variants. Conclusion Our study shows that NOD2 variants described to be causatively associated with CD do not predispose to the development of HAEC. As data on the molecular basis of HAEC are limited, the distinct mechanisms involved in the pathogenesis of this complication remain unclear.

Multiple endocrine neoplasia type 2 syndromes (MEN 2): results from the ItaMEN network analysis on the prevalence of different genotypes and phenotypes

Multiple endocrine neoplasia type 2 (MEN 2) is a genetic disease characterized by medullary thyroid carcinoma (MTC) associated (MEN 2A and 2B) or not familial MTC (FMTC) with other endocrine neoplasia due to germline RET gene mutations. The prevalence of these rare genetic diseases and their corresponding RET mutations are unknown due to the small size of the study population. We collected data on germline RET mutations of 250 families with hereditary MTC followed in 20 different Italian centres. The most frequent RET amino acid substitution was Val804Met (19.6%) followed by Cys634Arg (13.6%). A total of 40 different germline RET mutations were present. Six families (2.4%) were negative for germline RET mutations. The comparison of the prevalence of RET germline mutations in the present study with those published by other European studies showed a higher prevalence of Val804Met and Ser891Ala mutations and a lower prevalence of Leu790Phe and Tyr791Phe (P<0.0001). A statistically significant higher prevalence of mutations affecting non-cysteine codons was also found (P<0.0001). Furthermore, the phenotype data collection showed an unexpected higher prevalence of FMTC (57.6%) with respect to other MEN 2 syndromes (34% MEN 2A and 6.8% of MEN 2B). In conclusion, we observed a statistically significant different pattern of RET mutations in Italian MEN 2 families with respect to other European studies and a higher prevalence of FMTC phenotype. The different ethnic origins of the patients and the particular attention given to analysing apparently sporadic MTC for RET germline mutations may explain these findings.

Synchronous Metastatic Medullary and Papillary Thyroid Carcinomas in a Patient with Germline RET Mutation: Case Report, Molecular Analysis, and Implications for Pathogenesis

The occurrence of medullary thyroid carcinoma (MTC) in patients with germline RET mutation is well established, but the occasional occurrence of papillary thyroid carcinoma (PTC) in this setting remains unexplained. We report a case of synchronous MTC and PTC in a patient with germline RET mutation, and investigate the molecular pathogenesis of these two tumors. A 48-year-old man presented with cervical lymphadenopathy and was found to have metastatic MTC involving cervical and mediastinal lymph nodes. He underwent thyroidectomy and debulking of metastatic disease. The resected thyroid showed bilateral MTC and a 1-cm PTC. His lymph node metastases were predominantly MTC along with a small focus of metastatic PTC. Molecular testing using peripheral blood revealed a germline RET point mutation (Val804Met). Both tumors were analyzed for the BRAF (Val600Glu) mutation and the RET/PTC1 translocation. The PTC was positive for the BRAF mutation but negative for RET/PTC1. The MTC was negative for both abnormalities. We conclude that the MTC was caused by the germline RET mutation, while the PTC was caused by a somatic BRAF mutation. The occurrence of PTC in patients with germline RET mutations appears to be purely coincidental.

High Penetrance of Pheochromocytoma Associated with the Novel C634Y/Y791F Double Germline Mutation in theRETProtooncogene

Previous studies have shown that double RET mutations may be associated with unusual multiple endocrine neoplasia type 2 (MEN 2) phenotypes. Our objective was to report the clinical features of patients harboring a previously unreported double mutation of the RET gene and to characterize this mutation in vitro. Sixteen patients from four unrelated families and harboring the C634Y/Y791F double RET germline mutation were included in the study. Large pheochromocytomas measuring 6.0-14 cm and weighing up to 640 g were identified in the four index cases. Three of the four tumors were bilateral. High penetrance of pheochromocytoma was also seen in the C634Y/Y791F-mutation-positive relatives (seven of nine, 77.7%). Of these, two cases had bilateral tumors, one presented with multifocal tumors, two cases had large tumors (>5 cm), and one case, which was diagnosed with a large (5.5 x 4.5 x 4.0 cm) pheochromocytoma, reported early onset of symptoms of the disease (14 yr old). The overall penetrance of pheochromocytoma was 84.6% (11 of 13). Development of medullary thyroid carcinoma in our patients seemed similar to that observed in patients with codon 634 mutations. Haplotype analysis demonstrated that the mutation did not arise from a common ancestor. In vitro studies showed the double C634Y/Y791F RET receptor was significantly more phosphorylated than either activated wild-type receptor or single C634Y and Y791F RET mutants. Our data suggest that the natural history of the novel C634Y/Y791F double mutation carries a codon 634-like pattern of medullary thyroid carcinoma development, is associated with increased susceptibility to unusually large bilateral pheochromocytomas, and is likely more biologically active than each individual mutation.