Germline RET 634 mutation positive MEN 2A-related C-cell hyperplasias have genetic features consistent with intraepithelial neoplasia

Multifocal C-cell Hyperplasia and Marked Hypercalcitoninemia in a Diabetic Patient Treated With Glucagon-Like Peptide-1 Agonist With Concurrent Multinodular Goiter and Hyperparathyroidism

Thyroid C-cell hyperplasia (CCH) is divided into physiologic or reactive CCH and neoplastic CCH. Glucagon-like peptide-1 receptor agonists (GLP-1 Ra) is a group of medications used to treat type 2 diabetes that has documented C-cell stimulation effect in rodents, leading to subsequent CCH and medullary thyroid carcinoma (MTC) in rats and/or mice. Currently, there is no sufficient evidence supporting the association between GLP-1 Ra and human thyroid CCH and/or MTC. Here, we present a case of significant hypercalcitoninemia in a 53-year-old diabetic male patient receiving GLP-1 Ra treatment with concurrent multinodular goiter and hyperparathyroidism. Total thyroidectomy and central neck dissection revealed multifocal CCH involving bilateral thyroid lobes and several negative lymph nodes. Subsequent genetic testing did not detect germline mutation of RET gene. However, due to marked hypercalcitoninemia and massive thyromegaly, unsampled medullary thyroid microcarcinoma cannot be completely ruled out. The patient's postsurgical calcitonin level was back to normal. Our case indicates the significant clinical value of monitoring serum calcitonin levels in patients receiving GLP-1 Ra, especially in presence of other thyroid and/or parathyroid pathology that may be associated with increased calcitonin and/or CCH. Literature regarding the association between GLP-1 Ra and CCH is also reviewed.

Age-Related Changes in Calcitonin-Producing Thyroid C-Cells of Male Wistar Rats

Thyroid C-cells secrete the hormone calcitonin (CT) which acts as an inhibitor of bone resorption. Our aim was to examine the age-related changes in the structure and function of CT-producing C-cells, using histomorphometric, ultrastructural, and biochemical analyses. We used young adult (3-months-old), middle-aged (16-months-old), and old (24-months-old) male rats. The peroxidase-antiperoxidase method was applied for localization of CT. Stereological analysis was performed using the newCAST stereological software package. Serum samples were analyzed for the determination of CT, testosterone (T), calcium (Ca2+), and phosphorus (P). We found a significant increase in the volume density (Vv) of C-cells in both older groups (p < 0.05). The percentage of smaller volume range C-cells increased (p < 0.0001), while the proportion of greater volume range C-cells decreased (p < 0.05) with ageing. Ultrastructural analysis revealed a larger number of secretory granules in older rats. Serum CT increased (p < 0.001), while serum T and P were reduced (p < 0.01) in older rats. Serum Ca2+ was lower (p < 0.0001) in middle-aged rats compared to young adults. We revealed a 20% incidence of C-cell hyperplasia in older rats and one case of medullary thyroid carcinoma in an old rat. Our findings indicate that the ageing process causes significant histomorphometric changes at the thyroid C-cell level.

C Cell and Follicular Epithelial Cell Precursor Lesions of the Thyroid

CONTEXT

- The identification of precursor or dysplastic lesions in the thyroid is difficult. Pathology of the C cell has been extensively studied, and the preneoplastic nature of C-cell hyperplasia in the setting of familial medullary thyroid carcinomas is well established. However, the distinction between neoplastic and physiologic/reactive C-cell hyperplasia remains a challenge. Unlike C cells, the existence of a precursor lesion of follicular cell-derived tumors is less well established, and a dysplastic or preneoplastic follicular lesion has not been well defined.

OBJECTIVE

- To discuss putative precursor lesions in the thyroid arising from C cells and follicular epithelial cells.

DATA SOURCES

- Data were obtained from a review of the pertinent peer-reviewed literature.

CONCLUSIONS

- Although the preneoplastic nature of C-cell hyperplasia in the setting of familial medullary thyroid carcinoma is well recognized, the preneoplastic nature/malignant potential of reactive/physiologic C-cell hyperplasia and its role in the development of sporadic, medullary thyroid carcinoma is still unclear. Current data suggest that benign follicular lesions may have malignant potential, and there may be a multifocal progression from benign to malignant. Atypical follicular lesions in the background of chronic lymphocytic thyroiditis may represent dysplastic or premalignant lesions.

The RET E616Q Variant is a Gain of Function Mutation Present in a Family with Features of Multiple Endocrine Neoplasia 2A

The REarranged during Transfection (RET) proto-oncogene is a receptor tyrosine kinase involved in growth and differentiation during embryogenesis and maintenance of the urogenital and nervous systems in mammals. Distinct mutations across hotspot RET exons can cause Multiple Endocrine Neoplasia Type 2A (MEN2A) characterised by development of medullary thyroid cancer (MTC), phaeochromocytoma (PCC) and primary hyperparathyroidism (PHPT), with a strong correlation between genotype and phenotype. Here, we report a 42-year-old man presented in the clinic with a unilateral PCC, with subsequent investigations revealing a nodular and cystic thyroid gland. He proceeded to thyroidectomy, which showed bilateral C-cell hyperplasia (CCH) without evidence of MTC. His brother had neonatal Hirschsprung disease (HSCR). Genetic testing revealed the presence of a heterozygous variant of unknown significance (VUS) in the cysteine-rich region of exon 10 in the RET gene (c.1846G>C, p.E616Q), in both affected siblings and their unaffected mother. Exon 10 RET mutations are known to be associated with HSCR and MEN2. Variants in the cysteine-rich region of the RET gene, outside of the key cysteine residues, may contribute to the development of MEN2 in a less aggressive manner, with a lower penetrance of MTC. Currently, a VUS in RET cannot be used to inform clinical management and direct future care. Analysis of RET^E616Q reveals a gain of function mutant phenotype for this variant, which has not previously been reported, indicating that this VUS should be considered at risk for future clinical management.

Hyperplasia in glands with hormone excess

Five syndromes share predominantly hyperplastic glands with a primary excess of hormones: neonatal severe primary hyperparathyroidism, from homozygous mutated CASR, begins severely in utero; congenital non-autoimmune thyrotoxicosis, from mutated TSHR, varies from severe with fetal onset to mild with adult onset; familial male-limited precocious puberty, from mutated LHR, expresses testosterone oversecretion in young boys; hereditary ovarian hyperstimulation syndrome, from mutated FSHR, expresses symptomatic systemic vascular permeabilities during pregnancy; and familial hyperaldosteronism type IIIA, from mutated KCNJ5, presents in young children with hypertension and hypokalemia. The grouping of these five syndromes highlights predominant hyperplasia as a stable tissue endpoint and as their tissue stage for all of the hormone excess. Comparisons were made among this and two other groups of syndromes, forming a continuum of gland staging: predominant oversecretions express little or no hyperplasia; predominant hyperplasias express little or no neoplasia; and predominant neoplasias express nodules, adenomas, or cancers. Hyperplasias may progress (5 of 5) to neoplastic stages while predominant oversecretions rarely do (1 of 6; frequencies differ P<0.02). Hyperplasias do not show tumor multiplicity (0 of 5) unlike neoplasias that do (13 of 19; P<0.02). Hyperplasias express mutation of a plasma membrane-bound sensor (5 of 5), while neoplasias rarely do (3 of 14; P<0.002). In conclusion, the multiple distinguishing themes within the hyperplasias establish a robust pathophysiology. It has the shared and novel feature of mutant sensors in the plasma membrane, suggesting that these are major contributors to hyperplasia.

C-cell hyperplasia as an incidental finding in a patient with papillary thyroid microcarcinoma

C-cell hyperplasia (CCH) is considered as a preneoplastic lesion associated with various endocrinopathies. Traditionally it is subdivided into reactive (benign) CCH and neoplastic. We report here a case of a young male, where CCH was an incidental finding after total thyroidectomy for papillary thyroid cancer.

Incidental thyroid C cell hyperplasia: clinical significance and implications in practice

Incidental C cell hyperplasia (CCH) following thyroidectomy for other indications may rarely be encountered, which may raise concerns about its clinical significance and proper management. CCH can be classified as physiological (reactive) or neoplastic. Reactive CCH has no malignant potential and can be observed in association with many other thyroid diseases (including differentiated thyroid cancer); in contrast, neoplastic CCH should be considered as a preneoplastic stage in the spectrum of C cell disease, ultimately leading to the development of medullary thyroid cancer (MTC). Neoplastic CCH is commonly observed in patients with germ-line mutations in the RET oncogene (commonly in families with a history of hereditary MTC, i.e. familial MTC or multiple endocrine neoplasia type 2 (MEN2)). CCH should be considered in patients with hypercalcitoninemia without nodular thyroidopathy. Total thyroidectomy, which is commonly performed for the majority of thyroid diseases, is an adequate treatment and achieves cure, even in patients with neoplastic CCH. There is no role for cervical lymph node dissection in patients with pure CCH. In conclusion, reactive CCH has no malignant potential, in contrast to neoplastic CCH. Total thyroidectomy achieves cure of patients with CCH.

Tumor heterogeneity: mechanisms and bases for a reliable application of molecular marker design

Tumor heterogeneity is a confusing finding in the assessment of neoplasms, potentially resulting in inaccurate diagnostic, prognostic and predictive tests. This tumor heterogeneity is not always a random and unpredictable phenomenon, whose knowledge helps designing better tests. The biologic reasons for this intratumoral heterogeneity would then be important to understand both the natural history of neoplasms and the selection of test samples for reliable analysis. The main factors contributing to intratumoral heterogeneity inducing gene abnormalities or modifying its expression include: the gradient ischemic level within neoplasms, the action of tumor microenvironment (bidirectional interaction between tumor cells and stroma), mechanisms of intercellular transference of genetic information (exosomes), and differential mechanisms of sequence-independent modifications of genetic material and proteins. The intratumoral heterogeneity is at the origin of tumor progression and it is also the byproduct of the selection process during progression. Any analysis of heterogeneity mechanisms must be integrated within the process of segregation of genetic changes in tumor cells during the clonal expansion and progression of neoplasms. The evaluation of these mechanisms must also consider the redundancy and pleiotropism of molecular pathways, for which appropriate surrogate markers would support the presence or not of heterogeneous genetics and the main mechanisms responsible. This knowledge would constitute a solid scientific background for future therapeutic planning.

Heterogeneous topographic profiles of kinetic and cell cycle regulator microsatellites in atypical (dysplastic) melanocytic nevi

Atypical (dysplastic) melanocytic nevi are clinically heterogeneous malignant melanoma precursors, for which no topographic analysis of cell kinetic, cell cycle regulators and microsatellite profile is available. We selected low-grade atypical melanocytic nevi (92), high-grade atypical melanocytic nevi (41), melanocytic nevi (18 junctional, 25 compound) and malignant melanomas (16 radial growth phase and 27 vertical growth phase). TP53, CDKN2A, CDKN1A, and CDKN1B microsatellite patterns were topographically studied after microdissection; Ki-67, TP53, CDKN2A, CDKN1A, and CDKN1B expressions and DNA fragmentation by in situ end labeling for apoptosis were topographically scored. Results were statistically analyzed. A decreasing junctional-dermal marker expression gradient was observed, directly correlating with atypical melanocytic nevus grading. High-grade atypical melanocytic nevi revealed coexistent TP53-CDKN2A-CDKN1B microsatellite abnormalities, and significantly higher junctional Ki67-TP53 expression (inversely correlated with CDKN1A-CDKN1B expression and in situ end labeling). Malignant melanomas showed coexistent microsatellite abnormalities (CDKN2A-CDKN1B), no topographic gradient, and significantly decreased expression. Melanocytic nevi and low-grade atypical melanocytic nevi revealed sporadic junctional CDKN2A microsatellite abnormalities and no significant topographic kinetic differences. High-grade atypical melanocytic nevi accumulate junctional TP53-CDKN1A-CDKN1B microsatellite abnormalities, being progression TP53-independent and better assessed in the dermis. Melanocytic nevi and low-grade atypical melanocytic nevi show low incidence of microsatellite abnormalities, and kinetic features that make progression unlikely.

Pathogenicity of DNA variants and double mutations in multiple endocrine neoplasia type 2 and von Hippel-Lindau syndrome

CONTEXT

Cancer genetics is fundamental for preventive medicine, in particular in pheochromocytoma-associated syndromes. Variants in two susceptibility genes, SDHC and RET, were found in a kindred with head and neck paraganglioma. This observation of coincident DNA variants, both reported as pathogenic, in two known susceptibility genes prompted the question of their pathogenic relevance.

OBJECTIVE

Our objective was to elucidate the pathogenic role of the detected variants and study the prevalence of such variants.

PATIENTS

Patients were registrants from the European-American Pheochromocytoma-Paraganglioma and German von Hippel-Lindau Disease Registries.

DESIGN

Analysis of germline mutation screening results for all pheochromocytoma-paraganglioma susceptibility genes, including RET [multiple endocrine neoplasia type 2 (MEN 2)] and VHL [von Hippel-Lindau disease (VHL)]. Cases in which more than one DNA variant was found were clinically reevaluated, and cosegregation of the disease with the variant was analyzed within the registrants' families. A total of 1000 controls were screened for the presence of detected variants, and in silico analyses were performed.

RESULTS

Three variants were identified, RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser. The frequencies of RET p.Ser649Leu (0.07%) and p.Tyr791Phe (0.9%) compared with controls excluded the two variants' role in the etiology of MEN 2 and VHL. None of the carriers of the RET variants who underwent prophylactic thyroidectomy showed medullary thyroid carcinoma. Clinical reinvestigation of 18 variant carriers excluded MEN 2. VHL variant p.Pro81Ser, also previously described as a mutation, did not segregate with the VHL in one family. In silico analyses for these variants predicted unmodified protein function.

CONCLUSIONS

RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser are definitely not pathogenic mutations for VHL and MEN 2. Misinterpretation results in irreversible clinical consequences.

Constitutive RET tyrosine kinase activation in hereditary medullary thyroid cancer: clinical opportunities

The ground-breaking discovery of genotype-phenotype relationships in hereditary medullary thyroid cancer has greatly facilitated early prophylactic thyroidectomy. Its timing depends not solely on a positive gene test but, more importantly, on the type of the REarranged during Transfection (RET) mutation and its underlying mode of RET receptor tyrosine kinase activation. In the past decade, the therapeutic corridor opened by molecular information has been defined down to a remarkable level of detail. Based on mutational risk profiles, preemptive thyroidectomy is recommended at 6 months of age for carriers of highest-risk mutations, before the age of 5 years for carriers of high-risk mutations, and before the age of 5 or 10 years for carriers of least-high-risk mutations. Additional lymph node dissection may not be needed in the absence of increased preoperative basal calcitonin levels. Better comprehension of RET function should enable the design of targeted therapies for RET carriers beyond surgical cure in whom the DNA-based 'window of opportunity' has been missed.

Tenascin C in medullary thyroid microcarcinoma and C-cell hyperplasia

Tenascin C (Tn-C) is an extracellular matrix glycoprotein that is expressed early in carcinogenesis including intraepithelial neoplastic lesions of different organs. In this study, we analyze whether stroma reaction seen by Tn-C expression is detected early in tumorigenesis of medullary thyroid carcinoma (MTC) including medullary microcarcinoma and C-cell hyperplasia (CCH), which is accepted to be a precursor lesion of MTC in the setting of RET oncogene germ-line mutation. Tn-C was expressed in the stroma of all medullary microcarcinoma and in the stroma next to CCH. Stromal Tn-C expression was significantly more often seen in CCH with concomitant MTC than in isolated CCH of hereditary as well as nonhereditary cases (p = 0.001 and p = 0.016, respectively). We conclude that Tn-C expression and thus early stroma remodeling is seen in medullary microcarcinoma and CCH. Stromal Tn-C expression seems to be an indicator of a further step in carcinogenesis of MTC irrespective of a RET oncogene germ-line mutation.

Microsatellite abnormalities and somatic down-regulation of mismatch repair characterize nodular-trabecular muscle-invasive urothelial carcinoma of the bladder

AIMS

To correlate histological infiltration patterns with genetic and mismatch repair (MMR) profiles in muscle-invasive bladder urothelial carcinomas (UroC).

METHODS AND RESULTS

Infiltration patterns were assessed in the deep compartment of muscle-invasive UroC (nodular-trabecular, 45 cases; infiltrative, 27 cases). Tumour compartment (superficial and deep to muscularis mucosa) analysis included: microsatellite pattern of TP53, RB1, WT1 and NF1 by polymerase chain reaction/denaturing gradient gel electrophoresis; mitotic, Ki67, in situ end labelling (ISEL) indices and DNA ploidy. MMR was assessed by MLH1 and MSH2 sequencing and immunohistochemistry in UroC with two or more abnormal microsatellite loci. Statistical differences were tested using anova and Fisher's exact tests. Infiltrative UroC showed lower Ki67 index 14.94 +/- 4.28, ISEL index 14.1 +/- 10.0 and shorter median survival (20 months) than nodular-trabecular UroC (Ki67 index 20.65 +/- 4.94, ISEL 20.2 +/- 22.7, 37-month survival, respectively). The genetic profile was significantly different for RB1 (P = 0.0003) and NF1 (P = 0.0023) only, being more frequently abnormal in nodular-trabecular UroC. A significant decrease in MLH1 or MSH2 protein expression with no gene mutations was identified in UroC with microsatellite abnormalities and a nodular-trabecular growth pattern.

CONCLUSIONS

Somatic down-regulation of MMR proteins in nodular-trabecular muscle-invasive UroC results in RB1/NF1 microsatellite abnormalities, correlating with higher cellular turnover and longer survival.

Absence of RET gene point mutations in sporadic thyroid C-cell hyperplasia

Progression from C-cell hyperplasia (CCH) to medullary thyroid carcinoma (MTC) has been demonstrated to date only in familial forms, whereas in nonfamilial MTC, such hypothesis is suggested by the rare concurrence of both lesions, although no epidemiological and molecular data are available to prove or disprove this event. Therefore, the clinical management of patients with sporadic CCH is controversial. To evaluate the malignant potential of sporadic CCHs, pure laser-microdissected C-cell populations of 24 CCH cases, either reactive or associated with nonfamilial MTC, were analyzed for MTC-associated protein neural cell adhesion molecule expression and RET point mutations in exons 10, 11, 15, and 16, by using immunohistochemistry and polymerase chain reaction-single-strand conformation polymorphism/heteroduplex electrophoresis/direct sequencing, respectively. No RET mutations were found in any of the 24 CCH cases, whereas M918T mutation was detected in three concomitant MTCs. Neural cell adhesion molecule was immunoreactive in the majority of CCH associated with MTC even in the absence of morphological atypia, but not in reactive forms. The absence of RET alterations in all cases of CCH examined supports the hypothesis that the development of MTC is independent of pre-existing CCH in the nonfamilial setting; thus, sporadic CCH should not be considered a risk factor for nonfamilial MTC.

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.

C-cell hyperplasia

Routine calcitonin assay programs and recent studies on the natural history of familial medullary thyroid carcinoma (MTC) have greatly added to our understanding of C-cell hyperplasia (CCH) and refined its classification. This article is an update on CCH physiopathology related to clinical presentation. With this combined approach, two types of CCH that differ by their physiological characteristics can be identified: neoplastic CCH and reactive (also called physiological) CCH. Neoplastic CCH is caused by a germline mutation of the RET protooncogene in a multiple endocrine neoplasia type 2 (MEN 2) syndrome. It progresses to MTC following a time line that depends on the RET mutation involved. CCH may actually be a misnomer for a neoplastic condition that some authors have proposed to call "in situ-MTC". Reactive CCH is considered to be caused by a stimulus that is external to the C-cell, and its premalignant potential is not documented. Many situations such as hypercalcemia, hyperparathyroidy, chronic lymphocytic thyroiditis or follicular tumors have been associated with reactive CCH, the pathogenesis of which remains unclear. But C-cell density in normal patients is subject to important variability, and several studies have demonstrated the dramatic male predominance in physiological CCH when hypercalcitoninemia was a random discovery. These data suggest that a number of conditions which were previously associated with reactive CCH might be purely fortuitous. Our clinical/pathological confrontation contributes to appropriately distinguishing between various CCH types, and in turn to identify the best way of managing patients.

Somatic VHL gene alterations in MEN2-associated medullary thyroid carcinoma

Background

Germline mutations in RET are responsible for multiple endocrine neoplasia type 2 (MEN2), an autosomal dominantly inherited cancer syndrome that is characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, and parathyroid hyperplasia/adenoma. Recent studies suggest a "second hit" mechanism resulting in amplification of mutant RET. Somatic VHL gene alterations are implicated in the pathogenesis of MEN2 pheochromocytomas. We hypothesized that somatic VHL gene alterations are also important in the pathogenesis of MEN2-associated MTC.

Methods

We analyzed 6 MTCs and 1 C-cell hyperplasia (CCH) specimen from 7 patients with MEN2A and RET germline mutations in codons 609, 618, 620, or 634, using microdissection, microsatellite analysis, phosphorimage densitometry, and VHL mutation analysis.

Results

First, we searched for allelic imbalance between mutant and wild-type RET by using the polymorphic markers D10S677, D10S1239, and RET on thyroid tissue from these patients. Evidence for RET amplification by this technique could be demonstrated in 3 of 6 MTCs. We then performed LOH analysis using D3S1038 and D3S1110 which map to the VHL gene locus at 3p25/26. VHL gene deletion was present in 3 MTCs. These 3 MTCs also had an allelic imbalance between mutant and wild-type RET. Mutation analysis of the VHL gene showed a somatic frameshift mutation in 1 MTC that also demonstrated LOH at 3p25/26. In the 2 other MTCs with allelic imbalance of RET and somatic VHL gene deletion, no somatic VHL mutation could be detected. The CCH specimen did neither reveal RET imbalance nor somatic VHL gene alterations.

Conclusion

These data suggest that a RET germline mutation is necessary for development of CCH, that allelic imbalance between mutant and wild-type RET may set off tumorigenesis, and that somatic VHL gene alterations may not play a major role in tumorigenesis of MEN2A-associated MTC.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Molecular genetics of multiple endocrine neoplasia types 1 and 2

Six multiple endocrine neoplasia (MEN) syndromes have received a level of attention that might seem disproportionate to their low prevalence. The attention has been given because their hormonal excesses cause striking metabolic expressions and because they might clarify pathways disrupted in more common tumours. The recent discovery of the main gene in each MEN syndrome has furthered our understanding of not only hereditary but also sporadic tumours and has fostered new avenues of research.

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

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