Mutational analysis of the RET proto-oncogene in 71 Japanese patients with medullary thyroid carcinoma

Updates in the advances of sporadic medullary thyroid carcinoma: from the molecules to the clinic

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine malignancy that originates in parafollicular cells. It is well-known that a quarter of MTC are involved in hereditary multiple endocrine neoplasia type 2 syndromes, whereas most MTC are sporadic. Unlike the commonly encountered gastrointestinal or pulmonary neuroendocrine tumors, most sporadic MTCs have distinct genetic alterations featured by somatic changes of either Rearranged during Transfection (RET) or RAS point mutation. The increasing application of next-generation sequencing, whole-exome sequencing, and other molecular detection techniques enables us to understand MTC comprehensively concerning its detailed molecular changes and their clinical correlations. This article reviews the advances in genetic alterations and their prognostic impact in sporadic MTC among different populations and discusses the associated tumor immune microenvironments and the potential role of immunotherapy targeting PD-L1/PD-1 in treating MTC. Furthermore, the current multikinase inhibitor targeting therapy for sporadic MTC has been summarized here and its efficacy and drug toxicity are discussed. Updates in advance of the role of calcitonin/procalcitonin/calcitonin-related polypeptide alpha (CALCA) gene transcripts in diagnosing and handling MTC are also mentioned. The treatment of advanced MTC is still challenging and might require a combination of several modalities.

Genetic screening for monogenic hypertension in hypertensive individuals in a clinical setting

BACKGROUND

Monogenic hypertension describe a series of hypertensive syndromes that are inherited by Mendelian laws. Sometimes genetic testing is required to provide evidence for their diagnoses, precise classification and targeted treatment. This study is the first to investigate the clinical utility of a causative gene screening and the combined yield of gene product expression analyses in cases with suspected monogenic hypertension.

METHODS

We performed a large-scale multi-centre clinical genetic research of 1179 expertly selected hypertensive individuals from the Chinese Han population. Targeted sequencing were performed to evaluate 37 causative genes of potential cases of monogenic hypertension. Pathogenic and likely pathogenic variants were classified using the American College of Medical Genetics guidelines. Additionally, 49 variants of unknown significance (VUS) that had relatively high pathogenicity were selected and analysed using immunoblot protein expression assays.

RESULTS

21 pathogenic or likely pathogenic variants were identified in 33 of 1179 cases (2.80%). Gene product expression analyses showed 27 VUSs harboured by 49 individuals (4.16%) could lead to abnormally expressed protein levels. Consequently, combining genetic screening with gene product expression analyses increased the diagnostic yield from 2.80% to 6.79%. The main aetiologies established were primary aldosteronism (PA; 27, 2.29%) and pheochromocytoma and paraganglioma (PPGL; 10, 0.85%).

CONCLUSION

Molecular diagnoses obtained using causative gene screening combined with gene product expression analyses initially achieved a modest diagnostic yield. Our data highlight the predominant roles of PA and PPGL. Furthermore, we provide evidence indicating the enhanced diagnostic ability of combined genetic and functional evaluation.

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.

Primary hyperparathyroidism: an overview

Primary hyperparathyroidism is a common condition that affects 0.3% of the general population. Primary and tertiary care specialists can encounter patients with primary hyperparathyroidism, and prompt recognition and treatment can greatly reduce morbidity and mortality from this disease. In this paper we will review the basic physiology of calcium homeostasis and then consider genetic associations as well as common etiologies and presentations of primary hyperparathyroidism. We will consider emerging trends in detection and measurement of parathyroid hormone as well as available imaging modalities for the parathyroid glands. Surgical indications and approach will be reviewed as well as medical management of primary hyperparathyroidism with bisphosphonates and calcimimetics.

Small supernumerary marker chromosome originating from chromosome 10 associated with an apparently normal phenotype

Small supernumerary marker chromosomes (sSMC) originating from chromosome 10 are rare. Only seven cases have been documented, and among those three cases were diagnosed prenatally. We reported on another prenatal diagnosis of a de novo mosaic sSMC in an apparently normal female fetus whose mother had conceived with assisted reproductive technology (ART) procedures. G-banding analysis of amniotic cells was performed. Spectral karyotyping (SKY) and fluorescence in situ hybridization (FISH) studies with chromosome 10-specific alphoid satellite DNA probe were used to identify the chromosome 10 origin of the sSMC. Further FISH study with telomeric sequence probes showed that the sSMC lacked a hybridization signal, suggesting that the marker could be a ring chromosome. FISH studies using BAC clone probes specific for the regions within 10p11.2, 10q11.1, and 10q11.2 showed that the short arm breakpoint was located between 29.8 and 30.7 Mb from the 10p telomere, and that the long arm breakpoint was located less than 43.6 Mb from the 10p telomere. The karyotype of the fetus was 47,XX,+mar. ish der(10)(SKY+ CEP 10+, CTD-2130I7+, RP11-89J23-)/46,XX. Oligonucleotide microarray-based copy number variations (CNV) analysis was also performed and showed a 6.7 Mb duplication from 10p11.2 to 10q11.2 (36.2-42.9 Mb) with Affymetrix SNP-array 6.0 genotype: arr cgh. 10p11.2q11.2(CN_519687 --> CN_541524) X 3. At the 1-year follow-up, the baby did not have any findings of the trisomy 10p syndrome. This observation provided further credence to the concept that additional chromosome material of proximal 10p11.2 may not contribute to the trisomy 10p syndrome phenotype.

A novel mutation (D631del) of the RET gene was associated with MEN2A in a Chinese pedigree

Germline mutations in the RET proto-oncogene (RET gene) are well documented as the genetic causes of multiple endocrine neoplasia type 2A (MEN2A). We performed genetic analysis by direct RET gene mutation analysis in a Chinese MEN2A family and compared these results with biochemical screening tests and pathological examinations. Twenty-one exons and flanking introns of the RET gene were amplified using polymerase chain reaction (PCR). The PCR products were subjected to sequencing directly, or cloned into pGEM-T plasmids and sequenced. Restriction fragment length polymorphism (RFLP) was employed to confirm the mutation on the RET sequence. A novel heterozygous mutation of a 3-bp (GAC) deletion at codon 631 (D631del) of exon 11, resulting in the deletion of an aspartic acid at the locus, was identified in four MEN2A patients and one phenotypically normal family member. The average clinical onset-age of four MEN2A patients was 33.7 years, no cervical lymph node metastasis was found in MEN2A patients with medullary thyroid carcinoma in the family. The study indicated that the novel heterozygous deletion mutation at D631 of RET gene was co-segregated with MEN2A phenotype and promoted the development of MEN2A. This report is the first description of the D631del mutation in the family with MEN2A.

Management of medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is responsible for 13.4% of the total deaths attributable to thyroid cancer in human beings and research on MTC over the last 40 years has identified the RET proto-oncogene as a very relevant component of development of both sporadic and hereditary MTC. An activating germline RET proto-oncogene mutation responsible for a multiple endocrine neoplasia syndrome type 2 (MEN2) or a familial hereditary MTC syndrome is carried by 25% to 35% of patients with MTC. The recognition of RET proto-oncogene mutations by genetic sequencing has allowed us to differentiate hereditary from sporadic MTC, so that it is now possible to identify and treat children at risk for this disease before development of metastasis. Thanks to this discovery, we can now establish the association of MTC with other tumors in the context of MEN2 syndrome; determine adequate follow-up, prognosis, and treatment for patients with hereditary disease; and use this information to develop new therapies against both sporadic and hereditary MTCs.

First description of parathyroid disease in multiple endocrine neoplasia 2A syndrome

Hyperparathyroidism and/or parathyroid hyperplasia, medullary thyroid carcinoma (MTC), and pheochromocytomas compose the hallmarks of the multiple endocrine neoplasia type 2A (MEN 2A) syndrome. Revisiting a report in 1939 of a patient with hyperparathyroidism and parathyroid hyperplasia led to a search for evidence of MEN 2A. From medical records and discussion with family members, longitudinal follow-up of the patient and her descendants was obtained. Molecular diagnostics were integrated in the care of subsequent generations. The literature on hyperparathyroidism and MEN 2A was reviewed. Children of the proband exhibited all components of MEN 2A and the RET mutation of 634 TGC>CGC. The pedigree was typical for this mutation. Papers on anthropologic studies demonstrate skeletal evidence of hyperparathyroidism in humans centuries ago. The initial report of the proband preceded the publications defining both MTC and MEN 2A. The values of in-depth family histories and genetic analyses are exemplified.

A family of multiple endocrine neoplasia type 2A (MEN 2A) with Cys630Tyr RET germline mutation: report of a case

Since the majority of multiple endocrine neoplasia type 2A (MEN 2A) patients have missense mutations at codon 634 and those with the Cys630 RET genotype mutations are extremely rare, limited clinical information is available about this rare type. We report here three members of one Japanese MEN 2A family with the Cys630Tyr genotype. A 67-year-old woman presented a firm thyroid nodule, and preoperative examination revealed medullary thyroid carcinoma with primary hyperparthyoidism and no pheochromocytoma. At surgery, bilateral medullary thyroid carcinomas and parathyroid adenoma were found. No lymph node metastasis was identified. Computed tomography scans and laboratory examination of blood have shown no evidence of tumor recurrence and no abnormality of parathyroid function during the 4 years after surgery. A 40-year-old man, the proband's son, was shown to have the same RET mutation, underwent total thyroidectomy prophylactically, and only microscopic foci of medullary thyroid carcinoma were found. A 10-year-old boy, the proband's grandson also having the same RET mutation, showed normal basal serum calcitonin level and has been followed up conservatively. To our knowledge, 18 patients of 6 families with the Cys630 mutations have been reported so far. This is only the second reported case with primary hyperparathyroidism. RET 630 mutations might be associated with lower penetrance of primary hyperparthyoidism and pheochromocytoma.

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.

A rare extracellular D631Y germline mutation of the RET proto-oncogene in two Korean families with multiple endocrine neoplasia 2A

A mutation in codon 631 of exon 11 of the RET proto-oncogene is extremely rare in the patients with multiple endocrine neoplasia type 2A (MEN 2A). We report here on a rare extracellular mutation of the RET gene that led to the substitution of a tyrosine for an aspartate in codon 631 (D631Y, GAC to TAC) in two Korean families with MEN 2A. Eleven individuals from two unrelated families were found to have the D631Y germline mutation. Among them, medullary thyroid carcinoma (MTC) was identified in five patients: four of them had MEN 2A and one had familial MTC. They had tumors 2 cm or less in the greatest dimension that were limited to the thyroid, and they had a relatively old age above 30 at the time of diagnosis. Pheochromocytoma was detected in six patients including the four patients who had MEN 2A. All had adrenal tumors greater than 3 cm in the greatest dimension, and four of them had bilateral tumors. Two of six patients suffering with pheochromocytoma had no clinical evidence of MTC at the time of diagnosis. None had any evidence of hyperparathyroidism. This genetic profile might be related to the less vigorous clinical disease behavior and the late onset of MTC. In addition, pheochromocytoma might be the first manifestation prior to the development of MTC in some patients with the D631Y mutation. This report is the first description of the clinical characteristics of the D631Y germline mutation in the families with MEN 2A.

RET and neuroendocrine tumors

The RET proto-oncogene encodes a receptor tyrosine kinase that is a main component of the signaling pathway activated by the glial cell line-derived neurotrophic factor family ligands. Gene targeting studies revealed that signaling through RET plays a crucial role in neuronal and renal organogenesis. It is well-known that germline mutations in RET lead to the human inherited diseases, multiple endocrine neoplasia type 2 (MEN 2) and Hirschsprung's disease, and that somatic rearrangements of RET cause papillary thyroid carcinoma. Due to marked advances in understanding of the molecular mechanisms of the development of MEN 2, a consensus on MEN 2 management associated with RET status is being reached and currently put into general use as a guideline. In this review, we summarize progress in the study of RET from bench to bedside, focusing on pathophysiology of neuroendocrine tumors.

RET tyrosine kinase signaling in development and cancer

The variety of diseases caused by mutations in RET receptor tyrosine kinase provides a classic example of phenotypic heterogeneity. Gain-of-function mutations of RET are associated with human cancer. Gene rearrangements juxtaposing the tyrosine kinase domain to heterologous gene partners have been found in sporadic papillary carcinomas of the thyroid (PTC). These rearrangements generate chimeric RET/PTC oncogenes. In the germline, point mutations of RET are responsible for multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Both MEN 2 mutations and PTC gene rearrangements potentiate the intrinsic tyrosine kinase activity of RET and, ultimately, activate the RET downstream targets. Loss-of-function mutations of RET cause Hirschsprung's disease (HSCR) or colonic aganglionosis. A deeper understanding of the molecular signaling of normal versus abnormal RET activity in cancer will enable the development of potential new treatments for patients with sporadic and inherited thyroid cancer or MEN 2 syndrome. We now review the role and mechanisms of RET signaling in development and carcinogenesis.

A Drosophila model of multiple endocrine neoplasia type 2

Dominant mutations in the Ret receptor tyrosine kinase lead to the familial cancer syndrome multiple endocrine neoplasia type 2 (MEN2). Mammalian tissue culture studies suggest that RetMEN2 mutations significantly alter Ret-signaling properties, but the precise mechanisms by which RetMEN2 promotes tumorigenesis remain poorly understood. To determine the signal transduction pathways required for RetMEN2 activity, we analyzed analogous mutations in the Drosophila Ret ortholog dRet. Overexpressed dRetMEN2 isoforms targeted to the developing retina led to aberrant cell proliferation, inappropriate cell fate specification, and excessive Ras pathway activation. Genetic analysis indicated that dRetMEN2 acts through the Ras-ERK, Src, and Jun kinase pathways. A genetic screen for mutations that dominantly suppress or enhance dRetMEN2 phenotypes identified new genes that are required for the phenotypic outcomes of dRetMEN2 activity. Finally, we identified human orthologs for many of these genes and examined their status in human tumors. Two of these loci showed loss of heterozygosity (LOH) within both sporadic and MEN2-associated pheochromocytomas, suggesting that they may contribute to Ret-dependent oncogenesis.

The finding of a somaticdeletion in RET exon 15 clarified the sporadic nature of amedullary thyroid carcinoma suspected to be familial

Medullary thyroid carcinoma (MTC) occurs both sporadically and in the autosomal dominantly inherited multiple endocrine neoplasia (MEN) type 2 syndromes. The distinction between both is important for future clinical management. We report a family initially described as a familial MTC by pentagastrin stimulation test and clinical outcome, in which we found a 12 bp deletion within the catalytic domain of the protooncogene RET in the index case tumor alone. Linkage study suggests that it is a sporadic MTC. Therefore, in view of these results, in kindred with just one MTC case, borderline pentagastrin test values must be carefully assessed. In addition, this and other mutations can help us to understand some features about domains that play an important role in the normal function of this tyrosine kinase receptor and involved in MTC.

New target region of allelic loss in hepatocellular carcinomas within a 1-cM interval on chromosome 6q23

BACKGROUND/AIMS

Frequent allelic losses on the long arm of chromosome 16 in several types of human cancers have suggested that 16q harbors one or more genes that are important for suppressing tumorigenesis in the tissues in question.

METHODS

To identify the locations of putative tumor suppressor genes involved in hepatocellular carcinoma, we examined 96 primary hepatocellular carcinomas for their patterns of allelic loss at 18 microsatellite marker loci distributed along this chromosome arm.

RESULTS

Allelic loss at one or more loci was observed in 48 (50%) of these tumors. The highest frequency of loss of heterozygosity (42%) was observed with marker D6S311 on chromosome 6q23. Through detailed deletion mapping of tumors having partial or interstitial deletions, we identified two commonly deleted regions at 6q23 and at 6q26-27.

CONCLUSIONS

The common region at 6q23 lay within a 1-cM interval, flanked by D6S977 and D6S311. The previously documented deletion region that includes the M6P/IGF2R locus was confined to a 20-cM region at band 6q26-27 in our panel of tumors. The location we defined at 6q23 for a putative suppressor of hepatocellular carcinoma has not been reported before.

Sporadic endocrine tumours and their relationship to the hereditary endocrine neoplasia syndromes

In the last years of the previous century the genes involved in the aetiology of five endocrine tumour syndromes have been identified. The tumour-suppressor gene that is responsible for Von Hippel-Lindau Disease was cloned in 1993; multiple endocrine neoplasia (MEN) types 2A and 2B and familial medullary thyroid carcinoma were found to be caused by activating mutations in the ret proto-oncogene in 1993 and 1994, and most recently the menin-gene, another tumour-suppressor gene, was shown to be associated with MEN-1. As usual, the answer to one question leads to innumerable new questions. And so, now we want to know the extent to which germ-line mutations (de novo, or otherwise previously undetected) in these genes play a role in the occurrence of the various endocrine tumours that are associated with these syndromes in apparently sporadic cases. We also want to know if the nature of the (germ-line) mutation conveys any information about the characteristics (phenotype) of the disease. We want to know the role of somatic mutations in these genes in truly sporadic tumours. And finally we want to know the exact function of the proteins that are encoded by these genes. The paper by Roijers et al. [1] elsewhere in this issue is an example of a small but well-directed step on the way to address some of these questions with respect to the menin-gene. It addresses the problem of patient selection when looking for germ-line mutations in apparently sporadic MEN-1 patients. In this review we want to give a brief summary of the present status with regard to some of the questions mentioned above, in relation to the endocrine tumour syndromes caused by the vhl, ret and menin genes.

RET proto-oncogene mutations in thyroid carcinomas: clinical relevance

Different forms of RET mutations are found in papillary and medullary thyroid carcinomas. Rearrangements with other genes (RET/PTC oncogene) play a causative role in a significant proportion of papillary thyroid carcinomas. In this case, several factors influence the frequency and the type of RET/PTC, such as exposure to radiation, age and histological variant of the papillary tumor. On the other hand, the presence of the mutation does not seem to influence the biological behavior of the tumor or its response to conventional treatment modalities. In the setting of medullary thyroid cancer, germline RET point-mutations are implicated in the pathogenesis of virtually all hereditary forms and somatic point-mutations in nearly half of the sporadic forms. The clinical impact of this finding is that family members at-risk of hereditary MTC may be screened by genetic analysis, to distinguish those carrying or not-carrying the mutation. The last can be reassured on their status and relieved from further follow-up. Those with the mutation may be treated at a pre-clinical stage of the disease or even before the disease is started. The present review is focused on the clinical implication of RET gene mutations in thyroid cancer patients.

Identification of a 1-Mb common region at 16q24.1-24.2 deleted in hepatocellular carcinoma

To identify the location of one or more putative tumor suppressor genes that may be involved in hepatocellular carcinoma (HCC), we examined 96 such tumors for their patterns of allelic loss at 21 microsatellite marker loci distributed along chromosome arm 16q. Allelic loss at one or more loci was observed in 58 (60%) of these tumors. Detailed deletion mapping identified a distinct commonly deleted region located within an interval flanked by D16S534 and D16S3091 at 16q24.1-24.2. By constructing a physical map consisting of a YAC contig across the region, the extent of the deleted region was determined to be less than 1 Mb. Among the tumors for which clinical data were available, allelic loss at 16q24.1-24.2 was more frequent in tumors arising from liver cirrhosis compared to HCCs arising from chronic hepatitis (30/42, 71%, vs. 13/33, 39%; P = 0. 0054). Additionally, allelic loss at 16q24.1-24.2 was frequently observed in small tumors and early-stage tumors as well as in tumors of more advanced phenotype.

Localization of a target region of allelic loss to a 1-cM interval on chromosome 16p.13.13 in hepatocellular carcinoma

To identify the location of the putative tumor suppressor gene on chromosome 16p that may be involved in hepatocellular carcinoma (HCC), we examined 96 primary HCCs and evaluated their patterns of allelic loss at 10 microsatellite marker loci distributed along this chromosome arm. Allelic loss at one or more loci was observed in 46 (48%) of these tumors. Through detailed deletion mapping of tumors having partial or interstitial deletions, we identified a commonly deleted region at a 1-cM interval, flanked by D16S519 and D16S3078 at 16p13.13, defining the location of a putative tumor suppressor gene for HCC. This region contains the gene for JAB (JAK-binding protein), which is responsible for negative-feedback regulation of the JAK-STAT pathway induced by cytokine stimulation, raising the possibility that inactivation of this gene may participate in hepatocarcinogenesis via genetic and/or epigenetic changes.

Mechanism of Ret activation by a mutation at aspartic acid 631 identified in sporadic pheochromocytoma

Mutations at aspartic acid 631 in Ret were reported in sporadic pheochromocytoma and medullary thyroid carcinoma. We replaced this aspartic acid with four other amino acids including tyrosine, glycine, asparagine, and alanine and investigated the transforming activity of these mutant cDNAs. Among them, RET cDNA with a mutation of aspartic acid to tyrosine (D631Y) that was reported in sporadic pheochromocytoma showed high transforming activity. The D631Y mutation activated Ret by inducing its disulfide-linked dimerization in the transfectant as observed for multiple endocrine neoplasia (MEN) 2A mutations at cysteine 609, 611, 618, 620, 630, or 634. Further mutation analysis suggested that cysteine 630 or 634 could be involved in the disulfide-linked Ret dimerization induced by the D631Y mutation.