Familial cystic parathyroid adenomatosis

A large extended family with hyperparathyroidism-jaw tumor syndrome due to deletion of the third exon of CDC73: clinical and molecular features

PURPOSE

We described the phenotype of a large 4-generation family with Hyperparathyrodism-Jaw Tumor syndrome (HPT-JT) associated with a rare deletion of exon 3 of the CDC73 gene.

METHODS

We collected medical, genetic data on 24 family members descended from a common ancestor carrying a heterozygous deletion of exon 3.

RESULTS

Thirteen carried the deletion, the penetrance was estimated at 50% at 40 years. Seven patients (39 ± 14.5 years) presented with HPT which could start at 13. Median plasmatic calcium and PTH levels were 3.13 ± 0.7 mmol/L and 115 ± 406 pg/ml, respectively. Kidney disease related to hypercalcemia were present in 57.1% of patients. All seven patients underwent surgery to remove a single parathyroid adenoma. One recurrence occurred 7 years post-surgery. No parathyroid carcinoma has been found to date. We found two atypical parathyroid adenomas. We described an additional somatic variant in exon 1 of gene CDC73 in two tumors. Jaw tumors were not necessarily associated with hyperparathyroidism, as shown in one case. Two kidney cysts were also reported. Variable phenotype expressivity was emphasized by clinical presentations in 2 monozygotic twins: acute hypercalcemia, kidney failure and ossifying fibroma in one twin, versus normocalcemic parathyroid adenoma in the other one.

CONCLUSION

We report a family carrier of a deletion of exon 3 of the CDC73 gene. This is characterized by a high level of hypercalcemia, deleterious kidney effects and atypical parathyroid adenomas without carcinomas. Onset and intensity of HPT remain unpredictable. The additional somatic mutation found in the parathyroid tumor could lead to these phenotypical variations.

Hereditary Endocrine Tumors and Associated Syndromes: A Narrative Review for Endocrinologists and Endocrine Surgeons

OBJECTIVE

Hereditary endocrine tumors (HET) were among the first group of tumors where predisposition syndromes were recognized. The utility of genetic awareness is having the capacity to treat at an earlier stage, screen for other manifestations and initiate family cascade testing. The aim of this narrative review is to describe the most common hereditary syndromes associated with frequently encountered endocrine tumors, with an emphasis on screening and surveillance.

METHODS

A MEDLINE search of articles for relevance to endocrine tumors and hereditary syndromes was performed.

RESULTS

The most common hereditary syndromes associated with frequently encountered endocrine tumors are described in terms of prevalence, genotype, phenotype, penetrance of malignancy, surgical management, screening and surveillance.

CONCLUSION

Medical practitioners involved in the care of patients with endocrine tumors, should have an index of suspicion for an underlying hereditary syndrome. Interdisciplinary care is integral to successful, long-term management of these patients and affected family members.

OVARIAN GRANULOSA CELL TUMOR IN A PATIENT WITH A PATHOGENIC VARIANT IN THE CDC73 GENE (HYPERPARATHYROIDISM-JAW TUMOR SYNDROME)

Objective

To report a patient with the hyperparathyroidism-jaw tumor syndrome (HPT-JT) who was found to have a rare ovarian tumor (granulosa cell tumor [GCT]). HPT-JT is caused by pathogenic variants in the CDC73 gene and results in primary hyperparathyroidism (PHPT), benign fibro-osseous jaw tumors, benign or malignant renal tumors and cysts, and benign or malignant uterine tumors. We believe this is the first reported case of HPT-JT and GCT.

Methods

The patient was a 31-year-old woman with abdominal pain who was found to have adult GCT. Her history was significant for a single gland parathyroidectomy at age 23 for PHPT. Her mother also had PHPT with 1-gland removal, as well as a history of renal cysts. Because of the personal and familial history of PHPT, she underwent germline sequencing of genes associated with PHPT including CASR, CDC73, CDKN1B, MEN1 and RET.

Results

Genetic testing revealed a CDC73 gene pathogenic variant (c.687_688dupAG) which creates a premature translational stop signal causing loss-of-function.

Conclusion

We report a case of ovarian GCT in a young patient with primary hyperparathyroidism and a CDC73 gene mutation. Ovarian granulosa cell tumor may be another CDC73-related tumor.

Clinical Features, Treatment, and Surveillance of Hyperparathyroidism-Jaw Tumor Syndrome: An Up-to-Date and Review of the Literature

Hyperparathyroidism-jaw tumor (HPT-JT) syndrome is an autosomal dominant disorder characterized by parathyroid tumors in association with fibro-osseous jaw tumors and uterine and renal lesions. HPT-JT syndrome is caused by germline mutations of the cell division cycle 73 (CDC73) gene that encodes the parafibromin, a 531-amino acid protein with antiproliferative activity. Primary hyperparathyroidism is the main finding of HPT-JT syndrome, usually caused by a single-gland parathyroid involvement (80% of cases), at variance with other variants of hereditary hyperparathyroidism, in which a multiglandular involvement is more frequent. Moreover, parathyroid carcinoma may occur in approximately 20% of cases. Surgery is the treatment of choice for primary hyperparathyroidism, but the extent of surgery remains controversial, varying between bilateral neck and focused exploration, with subtotal or limited parathyroidectomy. Recently, more limited approaches and parathyroid excisions have been suggested in order to decrease the risk of permanent hypoparathyroidism, the main surgical morbidity following more extensive surgical approaches. Ossifying fibromas of the mandible or maxilla may present only in a minority of cases and, even if benign, they should be surgically treated to avoid tumor growth and subsequent functional limitations. Benign and malignant uterine involvement (including leiomyomas, endometrial hyperplasia, adenomyosis, multiple adenomyomatous polyps, and adenosarcomas) is the second most common clinical feature of the syndrome, affecting more than 50% of CDC73-carrier women. Genetic testing should be performed in all family members of affected individuals, in young patients undergoing surgery for primary hyperparathyroidism, or in presence of other associated tumors, allowing early diagnosis and prompt treatment with more tailored surgery. Moreover, CDC73 mutation carriers should be also periodically screened for primary hyperparathyroidism and the other associated tumors. The present review was aimed to summarize the main clinical features of HPT-JT syndrome, focusing on genetic screening and surgical treatment, and to revise the available literature.

Evolution of Our Understanding of the Hyperparathyroid Syndromes: A Historical Perspective

We review advancing and overlapping stages for our understanding of the expressions of six hyperparathyroid (HPT) syndromes: multiple endocrine neoplasia type 1 (MEN1) or type 4, multiple endocrine neoplasia type 2A (MEN2A), hyperparathyroidism-jaw tumor syndrome, familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism, and familial isolated hyperparathyroidism. During stage 1 (1903 to 1967), the introduction of robust measurement of serum calcium was a milestone that uncovered hypercalcemia as the first sign of dysfunction in many HPT subjects, and inheritability was reported in each syndrome. The earliest reports of HPT syndromes were biased toward severe or striking manifestations. During stage 2 (1959 to 1985), the early formulations of a syndrome were improved. Radioimmunoassays (parathyroid hormone [PTH], gastrin, insulin, prolactin, calcitonin) were breakthroughs. They could identify a syndrome carrier, indicate an emerging tumor, characterize a tumor, or monitor a tumor. During stage 3 (1981 to 2006), the assembly of many cases enabled recognition of further details. For example, hormone non-secreting skin lesions were discovered in MEN1 and MEN2A. During stage 4 (1985 to the present), new genomic tools were a revolution for gene identification. Four principal genes ("principal" implies mutated or deleted in 50% or more probands for its syndrome) (MEN1, RET, CASR, CDC73) were identified for five syndromes. During stage 5 (1993 to the present), seven syndromal genes other than a principal gene were identified (CDKN1B, CDKN2B, CDKN2C, CDKN1A, GNA11, AP2S1, GCM2). Identification of AP2S1 and GCM2 became possible because of whole-exome sequencing. During stages 4 and 5, the newly identified genes enabled many studies, including robust assignment of the carriers and non-carriers of a mutation. Furthermore, molecular pathways of RET and the calcium-sensing receptor were elaborated, thereby facilitating developments in pharmacotherapy. Current findings hold the promise that more genes for HPT syndromes will be identified and studied in the near future. © 2018 American Society for Bone and Mineral Research.

Management of familial hyperparathyroidism syndromes: MEN1, MEN2, MEN4, HPT-Jaw tumour, Familial isolated hyperparathyroidism, FHH, and neonatal severe hyperparathyroidism

While primary hyperparathyroidism (PHPT) generally represents a common endocrine disorder, being the more frequent cause of hypercalcemia in outpatients, familial forms of PHPT (FPHPT) account for no more than 2-5% of the overall PHPT. In the last decades, many technical progresses in both molecular and biochemical-radiological evaluation have been made, and substantial advancements in understanding these disorders have been reached. Differences both in the pathogenesis and clinical presentation exist among the various hyperparathyroid syndromic forms, and, since FPHPT is frequently associated to other endocrine, proliferative and/or functional disorders, as also non-endocrine tumours, with varying clinical spectrum of occurrence in each syndrome, its early clinically detection for appropriately preventing complications (i.e. kidney and bone disorders) is strictly advised. In this review, the clinical-biochemical features and diagnostic procedures of each FPHPT form will be summarized and a general overview on surgical and pharmacological approaches to FPHPT has been also considered.

Parathyroid cysts: the Latin-American experience

BACKGROUND

Parathyroid cyst is an infrequent and unsuspected disease. There are more than 300 hundred cases reported in the world literature, a few of them are from Latin America. The experience of our centers and a review of the cases are presented.

METHODS

Case report of a series of patients with parathyroid cyst from our institutions according to the CARE guidelines (Case Reports). A search of Medline, Embase, BIREME (Biblioteca Regional de Medicina) LILACS (Literatura Latinoamericana y del Caribe en Ciencias de la Salud), Google Scholar and Scielo (Scientific Electronic Library on Line) databases and telephonic or email communications with other experts from Latin-America was performed .

RESULTS

Six patients with parathyroid cyst were found in our centers in Colombia. Most of them were managed with aspiration of the cyst. Two of them required surgery. Only one case was functional. Twelve reports from Latin America were found for a total of 18 cases in our region adding ours.

CONCLUSIONS

Parathyroid cysts are uncommonly reported in Latin America. Most of them are diagnosed postoperatively. Suspicion for parathyroid cyst should be raised when a crystal clear fluid is aspirated from a cyst. The confirmation of the diagnosis may be easily done if parathyroid hormone (PTH) level is measured in the cyst fluid.

Management of Ossifying Fibroma in a Suspicious Case of Hyperparathyroid-Jaw Tumor Syndrome

The purpose of this article is to report a case of ossifying fibroma in the mandible associated with hyperparathyroid-jaw tumor syndrome, in a 46-year-old Caucasian female, surgically resected and reconstructed with iliac crest bone, followed by implant placement. This is a rare syndrome with an autosomal dominant pattern, with the development of primary hyperparathyroidism mainly due to parathyroid adenomas. Fibro-osseous lesions in the jaws can be present and can also precede the development of the endocrine disorder. As renal abnormalities and uterine tumors can develop, an interdisciplinary approach is imperative for its diagnosis and management, due to the possibility of recurrence and potential for malignancy.

Parathyroid: The Pathology of Hyperparathyroidism

This review focuses on the pathologic entities associated with hyperparathyroidism in humans. A discussion of the lesions, their embryology, and pathologic features is included. Immunohistology, cytopathology, and a brief overview of molecular aspects of the lesion are included.

Parathyroid cancer and the CDC73 tumor suppressor gene

Parathyroid carcinoma (PC) is a rare endocrine neoplasm, usually causing severe primary hyperparathyroidism, that frequently causes death from unmanageable hypercalcemia. PC is frequently associated with somatic inactivating mutations of the CDC73 gene (previously called HRPT2), a gene discovered in association with the familial hyperparathyroidism-jaw tumor syndrome. DNA analysis for CDC73 mutation should be performed on all patients with seemingly sporadic PC since some 25% will carry a germline mutation. It is often difficult to make a firm diagnosis of PC by histopathology alone. That diagnosis often depends on the presence of local tissue invasion or distant metastases. If PC is suspected, en bloc resection at initial surgery is recommended. Medical therapy with cinacalcet, bisphosphonates or denosumab may temporarily ameliorate the hypercalcemia of inoperable PC.

Two cases of multiple ossifying fibromas in the jaws

BACKGROUND

The clinicopathologic characteristics of multiple ossifying fibroma (OF) are unclear due to the condition's rarity, making diagnosis challenging. Sporadic multiple OFs must be distinguished from hyperparathyroidism-jaw tumour syndrome (HPT-JT) related OF and other fibro-osseous lesions.

METHODS

Multiple OF cases were identified from ossifying fibroma cases. Clinical data including age, sex, anatomic site, radiographic features, clinical impression, treatment and available follow-up data as well as serum calcium, phosphorus, and parathyroid hormone (PTH) were recorded. GNAS and HRPT2 genetic mutations were examined in the two present cases. Case reports of sporadic multiple ossifying fibroma and HPT-JT-related OF were also reviewed.

RESULTS

The two present cases were confirmed as sporadic multiple OF, with no genetic GNAS and HRPT2 mutations found. The incidence of sporadic multiple ossifying fibroma was 2.0% (2/102). The total 18 sporadic multiform OF cases were characterized as followed: 13 (72.2%) female; 5 (27.8%) male; mean age 28.6 years; 2/16 (11.1%) cases only in the mandible; 4/18 (22.2%) cases only in the maxilla; and 12/18 (66.7%) cases in both the maxilla and mandible. Radiographically, the lesions were radiolucent in 5/18 (27.8%) cases and mixed density in 13/18 (72.2%) cases. Along with 24 cases of HPT-JT related OF were reviewed, sixteen (66.7%) patients were diagnosed with a single lesion, and 8 patients (33.3%) were diagnosed with multiple jaw lesions.

CONCLUSIONS

Sporadic multiple OFs are very rare, but must be distinguished from HPT-JT related OF. We strongly recommend that patients diagnosed with multiple ossifying fibromas receive serum PTH testing and mutation screening of HRPT2.

VIRTUAL SLIDES

http://www.diagnosticpathology.diagnomx.eu/vs/1194507146115753.

A large functioning parathyroid cyst in a patient with multiple endocrine neoplasia type 1

A 62-year-old woman presented with a mass on the left side of the neck. Biochemical testing revealed primary hyperparathyroidism. Further, a prolactinoma was detected, and the patient's son and daughter also had primary hyperparathyroidism, indicating that the patient had multiple endocrine neoplasia type 1 (MEN1). Neck ultrasonography revealed several cystic nodules (≤ 30 mm) that appeared to be adenomatous. After parathyroidectomy with autotransplantation, the largest cystic mass, in the left lower thyroid lobe, was pathologically diagnosed as a functioning parathyroid cyst, and all laboratory data returned to normal. On genetic analysis of blood, we found a novel single base insertion (duplication) in exon 10 codon 552 of the MEN1 gene (c1659dupT) that creates an early stop codon. This is the first case report of a parathyroid cyst resulting from parathyroid hyperplasia in a MEN1 patient.

The EIF4EBP3 translational repressor is a marker of CDC73 tumor suppressor haploinsufficiency in a parathyroid cancer syndrome

Germline mutation of the tumor suppressor gene CDC73 confers susceptibility to the hyperparathyroidism-jaw tumor syndrome associated with a high risk of parathyroid malignancy. Inactivating CDC73 mutations have also been implicated in sporadic parathyroid cancer, but are rare in sporadic benign parathyroid tumors. The molecular pathways that distinguish malignant from benign parathyroid transformation remain elusive. We previously showed that a hypomorphic allele of hyrax (hyx), the Drosophila homolog of CDC73, rescues the loss-of-ventral-eye phenotype of lobe, encoding the fly homolog of Akt1s1/ PRAS40. We report now an interaction between hyx and Tor, a central regulator of cell growth and autophagy, and show that eukaryotic translation initiation factor 4E-binding protein (EIF4EBP), a translational repressor and effector of mammalian target of rapamycin (mTOR), is a conserved target of hyx/CDC73. Flies heterozygous for Tor and hyx, but not Mnn1, the homolog of the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor associated with benign parathyroid tumors, are starvation resistant with reduced basal levels of Thor/4E-BP. Human peripheral blood cell levels of EIF4EBP3 were reduced in patients with CDC73, but not MEN1, heterozygosity. Chromatin immunoprecipitation demonstrated occupancy of EIF4EBP3 by endogenous parafibromin. These results show that EIF4EBP3 is a peripheral marker of CDC73 function distinct from MEN1-regulated pathways, and suggest a model whereby starvation resistance and/or translational de-repression contributes to parathyroid malignant transformation.

Molecular diagnosis of parathyroid carcinoma: a reality in the near future

INTRODUCTION

Parathyroid carcinoma (PC) is a rare endocrine malignancy that still suffers from a problem of delayed clinical diagnosis. Consequently, it usually is not recognized preoperatively and often is not conclusively identified during the operation either.

AREAS COVERED

The role played by parafibromin in the development of PC, representing an important advance in understanding the pathogenesis of this malignancy, is discussed. Through a careful search of the international literature, using "parathyroid carcinoma", "molecular genetics of parathyroid carcinoma" and "parathyroid tumorigenesis" as key words, other less mentioned molecular mechanisms are reappraised as potential molecular markers of PC; we also discuss their potential role in 20 parathyroid outgrowths. Finally, both the major efforts and the limitations of reported molecular diagnostic techniques and diagnostic markers are considered.

EXPERT OPINION

Currently, several critical issues still need to be addressed, such as the lack of: i) common criteria for the histopathological diagnosis of parathyroid malignancy and ii) timely appropriated preoperative diagnosis of PC. The latter issue would be of fundamental importance to assist the surgeon in performing a complete resection of all carcinomatous tissue at the time of the initial surgery, allowing for the greatest likelihood of a cure.

Parathyroid cancer

Parathyroid cancer is an uncommon malignancy and rare cause of primary hyperparathyroidism (HPT) with a high morbidity and patient death in advanced cases usually resulting from intractable hypercalcemia. Inactivation of the HRPT2/CDC73 gene, encoding the putative tumor-suppressor protein parafibromin and discovered in the context of the hyperparathyroidism-jaw tumor (HPT-JT) syndrome, is a common, somatic event in most parathyroid cancers. Approximately 25% of patients with apparently sporadic parathyroid cancer carry germline HRPT2/CDC73 mutation. Germline DNA analysis for HRPT2/CDC73 mutation is recommended in all patients with parathyroid cancer because of the potential benefit for first-degree relatives, who should nevertheless undergo serum calcium screening. The histopathologic diagnosis of parathyroid cancer is nonspecific unless vascular, lymphatic, capsular, or soft tissue invasion is seen, or metastases are clinically evident. Immunohistochemical analysis of parathyroid tumors for loss of parafibromin expression offers promise as a diagnostic tool. En bloc tumor resection offers the highest chance of cure in patients with suspected parathyroid carcinoma. No adjuvant chemotherapy regimen has yet proven effective, and the role of local adjuvant radiotherapy is being evaluated. Metastatic disease can be palliated with surgical debulking. Medical therapy with the calcimimetic cinacalcet and bisphosphonates can ameliorate hypercalcemia in patients with inoperable disease.

Cytoplasmic polyadenylation element binding protein is a conserved target of tumor suppressor HRPT2/CDC73

Parafibromin, a tumor suppressor protein encoded by HRPT2/CDC73 and implicated in parathyroid cancer and the hyperparathyroidism-jaw tumor (HPT-JT) familial cancer syndrome, is part of the PAF1 transcriptional regulatory complex. Parafibromin has been implicated in apoptosis and growth arrest, but the mechanism by which its loss of function promotes neoplasia is poorly understood. In this study we report that a hypomorphic allele of hyrax (hyx), the Drosophila homolog of HRPT2/CDC73, rescues the loss-of-ventral-eye phenotype of lobe (Akt1s1). Such rescue is consistent with previous reports that hyx/parafibromin is required for the nuclear transduction of Wingless (Wg)/Wnt signals and that Wg signaling antagonizes lobe function. A screen using double hyx/lobe heterozygotes identified an additional interaction with orb and orb2, the homologs of mammalian cytoplasmic polyadenylation element binding protein (CPEB), a translational regulatory protein. Hyx and orb2 heterozygotes lived longer and were more resistant to starvation than controls. In mammalian cells, knockdown of parafibromin expression reduced levels of CPEB1. Chromatin immunoprecipitation (ChIP) showed occupancy of CPEB1 by endogenous parafibromin. Bioinformatic analysis revealed a significant overlap between human transcripts potentially regulated by parafibromin and CPEB. These results show that parafibromin may exert both transcriptional and, through CPEB, translational control over a subset of target genes and that loss of parafibromin (and CPEB) function may promote tumorigenesis in part by conferring resistance to nutritional stress.

Defective nucleolar localization and dominant interfering properties of a parafibromin L95P missense mutant causing the hyperparathyroidism-jaw tumor syndrome

The hyperparathyroidism-jaw tumor syndrome (HPT-JT) is a familial cancer syndrome that can result from germline inactivation of HRPT2/CDC73, a putative tumor suppressor gene that encodes parafibromin, a component of the transcriptional regulatory PAF1 complex with homology to the yeast protein Cdc73p. The vast majority of HRPT2/CDC73 germline mutations identified have been truncation or frameshift mutations, and loss of function due to missense mutation is rare. We report here a kindred with HPT-JT due to a germline L95P missense mutation in parafibromin. The mutant parafibromin was studied in vitro to understand the basis of its presumed loss-of-function. When transfected in cultured cells, the L95P mutant was expressed to a lower level than wild-type (wt) parafibromin, a difference that was not overcome by inhibition of the proteasomal degradation pathway. The L95P mutant parafibromin retained the ability to assemble with endogenous PAF1 complex components as evidenced by co-immunoprecipitation. Analysis of subcellular localization showed that the L95P mutant was markedly deficient in nucleolar localization compared to the wt, an impairment likely resulting from disruption of a putative nucleolar localization signal immediately upstream of the L95P mutation. Transfection of the L95P parafibromin mutant, but not the wt, enhanced cell cycle progression and increased cell survival in NIH-3T3 and HEK 293 cells, resulting apparently from dominant interference with endogenous parafibromin action. The simultaneous loss of nucleolar localization and acquisition of a growth stimulatory phenotype with the L95P mutation raise the possibility that parafibromin must interact with targets in the nucleolus to fully execute its tumor suppressor functions.

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

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

Primary hyperparathyroidism: a current perspective

CONTEXT

Primary hyperparathyroidism (P-HPT) is one of the most common of all endocrine disorders. Eighty percent to 85% of cases are due to parathyroid adenomas while hyperplasia and carcinoma account for 10% to 15% and less than 1%, of cases, respectively. The past decade has witnessed remarkable advances in the understanding of the molecular basis of parathyroid hyperplasia and neoplasia. Additionally, imaging studies and the development of the intraoperative assay for parathyroid hormone have transformed the diagnosis and management of patients with these disorders.

OBJECTIVE

To review the pathology of parathyroid lesions associated with P-HPT, their molecular and genetic bases, including heritable hyperparathyroidism syndromes, and their clinical diagnosis and management.

DATA SOURCES

Review of pertinent epidemiology, pathology, radiology, and surgery literature on the diagnosis, classification, and treatment of P-HPT.

CONCLUSIONS

Although heritable causes of P-HPT including multiple endocrine neoplasia 1 and 2A and hyperparathyroidism-jaw tumor syndrome account for a minority of cases of P-HPT, advances in the characterization of the affected genes have provided insights into the genetic basis of sporadic parathyroid neoplasms. Alterations in cyclin D1 and loss of heterozygosity of chromosome 11q in adenomas and hyperplasias have provided support for clonality of these lesions. Parafibromin, the protein product of the HRPT2 gene responsible for hyperparathyroidism-jaw tumor syndrome, has been implicated in the development of sporadic parathyroid carcinomas and loss of immunohistochemical expression of this protein has been suggested to be of value in making the diagnosis of parathyroid carcinoma. Sestamibi scanning and ultrasound have revolutionized the planning of surgical approaches and the intraoperative parathyroid hormone assay has become the standard in guiding completion or extension of surgery.

Aberrant methylation of the HRPT2 gene in parathyroid carcinoma

OBJECTIVES

The incidence of parathyroid carcinoma in hyperparathyroidism-jaw tumor syndrome (HPT-JT) is reported to be as high as 15%. We used a methylation-specific polymerase chain reaction (MS-PCR) technique to investigate whether hypermethylation is one mechanism of HRPT2 gene inactivation in parathyroid tumors.

METHODS

DNA was extracted from samples of parathyroid tumors embedded in paraffin. MS-PCR was performed on 11 parathyroid carcinomas, 37 sporadic parathyroid adenomas from control subjects, and 6 parathyroid adenomas from 3 patients with HPT-JT. Methylated and unmethylated PCR products from 2 tumors (Nos. 2 and 6) were cloned. Clones containing inserts were sequenced.

RESULTS

Two of 11 (18%) parathyroid carcinomas showed amplification patterns consistent with methylation, compared to 0 of 37 sporadic parathyroid adenomas, and 1 of 6 (17%) parathyroid tumor samples from 3 HPT-JT patients. These results were confirmed by sequencing multiple clones from each of these samples.

CONCLUSIONS

There is increasing evidence that loss of HRPT2 gene expression is strongly associated with parathyroid carcinomas. Our data indicate that methylation of the HRPT2 promoter may be another mechanism by which HRPT2 gene inactivation gives rise to parathyroid carcinomas.

Nuclear localization of the parafibromin tumor suppressor protein implicated in the hyperparathyroidism-jaw tumor syndrome enhances its proapoptotic function

Parafibromin is a tumor suppressor protein encoded by HRPT2, a gene recently implicated in the hereditary hyperparathyroidism-jaw tumor syndrome, parathyroid cancer, and a subset of kindreds with familial isolated hyperparathyroidism. Human parafibromin binds to RNA polymerase II as part of a PAF1 transcriptional regulatory complex. The mechanism by which loss of parafibromin function can lead to neoplastic transformation is poorly understood. Because the subcellular localization of parafibromin is likely to be critical for its function with the nuclear PAF1 complex, we sought to experimentally define the nuclear localization signal (NLS) of parafibromin and examine its potential role in parafibromin function. Using site-directed mutagenesis, we define a dominant bipartite NLS and a secondary NLS, both in the NH(2)-terminal region of parafibromin whose combined mutation nearly abolishes nuclear targeting. The NLS-mutant parafibromin is significantly impaired in its association with endogenous Paf1 and Leo1. We further report that overexpression of wild-type but not NLS-mutant parafibromin induces apoptosis in transfected cells. Inhibition of endogenous parafibromin expression by RNA interference inhibits the basal rate of apoptosis and apoptosis resulting from DNA damage induced by camptothecin, a topoisomerase I inhibitor. These experiments identify for the first time a proapoptotic activity of endogenous parafibromin likely to be important in its role as a tumor suppressor and show a functional role for the NLS of parafibromin in this activity.

Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumour syndrome

BACKGROUND

A subset of familial isolated primary hyperparathyroidism (FIHP) is a variant of hyperparathyroidism-jaw tumour syndrome (HPT-JT). AIM/PATIENTS AND METHODS: We investigated the involvement of the HRPT2, MEN1 and CASR genes in 11 provisional FIHP families and two HPT-JT families.

RESULTS

Germline mutations of HRPT2 were found in two of the 11 FIHP families and one of the two HPT-JT families. One FIHP family with parathyroid carcinoma and atypical adenomas and another FIHP family with cystic parathyroid adenoma had novel frameshift mutations of 518-521del and 62-66del, respectively. In a patient with HPT-JT, a de novo germline mutation of 39delC was detected. Novel somatic HRPT2 mutations of 70-73del and 95-102del were found in two of five parathyroid tumours in a family with a 518-521del mutation. Biallelic inactivation of HRPT2 by a combination of germline and somatic mutation was confirmed in the parathyroid tumours. The finding that two families diagnosed with FIHP carried HRPT2 mutations suggests that they have occult HPT-JT. In the remaining 10 families, one family had a missense MEN1 mutation. No mutations of CASR were detected.

CONCLUSION

Our results confirm the need to test for HRPT2 in FIHP families, especially those with parathyroid carcinomas, atypical adenomas or adenomas with cystic change.

Dental findings in a family with hyperparathyroidism–jaw tumor syndrome and a novel HRPT2 gene mutation

Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is an important diagnosis because of the possible involvement of other family members and risk of malignant disease. We report clinical and genetic studies in a previously undocumented Australian family with HPT-JT. The proband and his sister presented with bilateral or recurrent mandibular radiolucencies diagnosed histopathologically as cemento-ossifying fibromas. Mutation screening of the recently identified disease gene HRPT2 was performed by direct sequencing in 3 affected members. This revealed a novel mutation in exon 1 of HRPT2 (nt 20AGGACG --> GGGAG), which is predicted to inactivate the parafibromin protein through protein truncation and premature termination of translation. The terminology used for the jaw lesions in this syndrome warrants review to become more consistent. Cemento-ossifying fibroma is the preferred term to better reflect the pathologies found in most individuals and families,and to emphasize the significance of the jaw lesions in the diagnosis of the syndrome.

Carcinoma de paratiróide

Carcinoma de paratiróide é uma condição rara, correspondendo na maior parte das casuísticas a menos de 1% dos casos de hiperparatiroidismo primário (HPP). No entanto, pela sua gravidade, e com o prognóstico dependente do diagnóstico precoce e de uma conduta agressiva, é fundamental que a suspeita clínica seja feita pré-operatoriamente. As características clínicas são compatíveis com um caso de HPP grave, sintomático, com tumor cervical >1,5cm, podendo ser palpável. A definição anátomo-patológica pode ser difícil em muitos casos. Nossa casuística (1983-2004) compreende 7 casos, todos sintomáticos, com síndrome hipercalcêmica e doença óssea presente na maioria. Em 6/7 o tumor era palpável, e todos apresentavam quadro bioquímico compatível. Três pacientes faleceram em quadro de hipercalcemia refratária. Dados recentes apontam para uma mutação no gene HRPT2 como base molecular para o desenvolvimento destes tumores. A conduta é cirúrgica e deve incluir hemitiroidectomia e exploração cervical ampliada, procurando focos metastáticos. O pós-operatório é compatível com a gravidade da alteração metabólica pré-existente, sendo comum a tendência a hipocalcemia. O prognóstico de longo prazo depende do diagnóstico precoce, do sucesso cirúrgico e do controle da hipercalcemia. Novas possibilidades terapêuticas, na forma de bisfosfonatos e drogas calcimiméticas, bem como a possibilidade de diagnóstico genético, tendem a melhorar o prognóstico desta grave condição.

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.

Parathyroid carcinoma: an overview

Parathyroid carcinoma is a rare tumor that is responsible for <1% of cases of hyperparathyroidism in most parts of the world. An increased incidence of this tumor has been reported in patients with the hyperparathyroidism-jaw tumor (HPT-JT) syndrome, but the etiology of most other cases is unknown. Parathyroid carcinomas tend to occur a decade earlier than adenomas, and the sex ratio approaches unity in contrast to the female preponderance of adenomas. Most patients with carcinomas present with marked hypercalcemia and are more likely to have associated bone and renal disease than those with adenomas. Although fibrosis and mitotic activity are common in carcinomas, these features are not specific for malignancy. The diagnosis of carcinoma should be restricted to those tumors that show invasion of blood vessels, perineural spaces, soft tissues, thyroid gland, or other adjacent structures or to tumors with documented metastases. Mutations of the HRPT2 gene (1q21-q32), which are responsible for the HPT-JT syndrome, have been implicated in the development of a high proportion of parathyroid carcinomas. A subset of patients with mutation-positive carcinomas have germline mutations of the HRPT2 gene. This finding suggests that some patients with apparent sporadic parathyroid carcinomas may have the HPT-JT syndrome or a variant of this syndrome. Because of the high frequency of local recurrence following incomplete excision, an en bloc resection is the preferred surgical approach for treatment of parathyroid carcinomas.

Uterine tumours are a phenotypic manifestation of the hyperparathyroidism-jaw tumour syndrome

The hyperparathyroidism-jaw tumour (HPT-JT) syndrome is an autosomal dominant disorder characterized by parathyroid tumours, which are frequently carcinomas, and ossifying jaw fibromas. In addition, some patients may develop renal tumours and cysts. The gene causing HPT-JT, which is referred to as HRPT2 and is located on chromosome 1q31.2, encodes a 531 amino acid protein called PARAFIBROMIN. To date 42 mutations, of which 22 are germline, have been reported and 97% of these are inactivating and consistent with a tumour suppressor role for HRPT2. We have investigated another four HPT-JT families for germline mutations, searched for additional clinical phenotypes, and examined for a genotype-phenotype correlation. Mutations were found in two families. One family had a novel deletional-insertion at codon 669, and the other had a 2 bp insertion at codon 679, which has been reported in four other unrelated patients. These five unrelated patients and their families with the same mutation were not found to develop the same tumours, thereby indicating an absence of a genotype-phenotype correlation. An analysis of 33 HPT-JT kindreds revealed that affected women in 13 HPT-JT families suffered from menorrhagia in their second to fourth decades. This often required hysterectomy, which revealed the presence of uterine tumours. This resulted in a significantly reduced maternal transmission of the disease. Thus, the results of our analysis expand the spectrum of HPT-JT-associated tumours to include uterine tumours, and these may account for the decreased reproductive fitness in females from HPT-JT families.

Parafibromin, product of the hyperparathyroidism-jaw tumor syndrome gene HRPT2, regulates cyclin D1/PRAD1 expression

Parafibromin is the 531-amino-acid protein product encoded by HRPT2, a putative tumor suppressor gene recently implicated in the autosomal dominant hyperparathyroidism-jaw tumor familial cancer syndrome, sporadic parathyroid cancer, and a minority of families with isolated hyperparathyroidism. Parafibromin contains no identified functional domains but bears sequence homology to Cdc73p, a budding yeast protein component of the RNA polymerase II-associated Paf1 complex. This study addressed the expression and functional properties of human parafibromin. A survey of human and mouse tissues analysed with polyclonal antibodies to parafibromin showed specific immunoreactivity in adrenal and parathyroid glands, kidney, heart, and skeletal muscle. Subcellular fractionation and laser confocal microscopy of normal human parathyroid gland demonstrated expression of parafibromin in both the cytoplasmic and nuclear compartments. Parafibromin was expressed in four parathyroid adenomas but was absent from two parathyroid carcinomas. Transient overexpression of wild-type parafibromin, but not its Leu64Pro missense mutant implicated in parathyroid cancer and familial isolated hyperparathyroidism, inhibited cell proliferation, and blocked expression of cyclin D1, a key cell cycle regulator previously implicated in parathyroid neoplasia. These results demonstrate that human parafibromin is a nucleocytoplasmic protein with functions consistent with its postulated role as a tumor suppressor protein.

Molecular biology of primary hyperparathyroidism

As molecular biology and genetic mapping receive wider application to human disease, genetic alterations have been identified with increased frequency in some patients with primary hyperparathyroidism(HPT). These alterations have been found in molecules related to cellular signaling and growth (RET proto-oncogene)and in tumor suppressors that control cell cycle progression and gene transcription (cyclin D1 and the MEN1 gene product. Although primary HPT can usually be treated surgically without knowledge of which specific genetic alteration has occurred, this information may assist clinicians in identifying which patients will go on to develop multiglandular or recurrent disease. In addition,such an approach would facilitate more appropriate postoperative surveillance, as well as counseling and screening of family members who may be at high risk for HPT.

Intraparathyroid cyst: a tumour of branchial origin and a possible pitfall for targeted parathyroid surgery

BACKGROUND

Parathyroid cysts account for 0.5% of parathyroid pathologies. They usually contain sky-high levels of parathyroid hormone (PTH) but are not necessarily associated with primary hyperparathyroidism (PHPT). Their origin is subject to debate. We provide evidence for a branchial origin and illustrate some potential problems they pose for targeted parathyroid surgery.

METHODS

The present study is a single institution retrospective study of 1702 parathyroid and 10 021 thyroid operations performed over a period of 12 years (1990-2001). Twenty-three cases of parathyroid cyst were found: three palpable neck masses, four cases associated with PHPT and 16 incidental findings at the time of thyroid surgery. Intracystic PTH measurements and immunostaining of the lining wall of the cyst were obtained in 16 out of 23 and 18 out of 23 cases, respectively.

RESULTS

Intracystic PTH levels were elevated in 15 out of 16 cases (average 3877, range 36 000-23 pg\mL). The wall of the cyst stained positively for epithelial cuboidal cell markers (CK +ve) and negatively for PTH (PTH -ve) in 18 out of 18 cases. In only one quarter of the cases associated with PHPT was the cyst the hypersecreting gland, nevertheless it contained less than the average PTH level (1440 vs 3877) and did not take up sestamibi. Results were conflicting in the other three cases. Histological studies on the present series suggest a branchial pouch origin.

CONCLUSION

Despite containing high levels of PTH, parathyroid cysts are of branchial origin and when associated with PHPT are rarely responsible for the disease. Targeted parathyroid surgery should not rely only on ultrasound and intraparathyroid PTH measurements.

HRPT2 mutations are associated with malignancy in sporadic parathyroid tumours

BACKGROUND

Hyperparathyroidism is a common endocrinopathy characterised by the formation of parathyroid tumours. In this study, we determine the role of the recently identified gene, HRPT2, in parathyroid tumorigenesis.

METHODS

Mutation analysis of HRPT2 was undertaken in 60 parathyroid tumours: five HPT-JT, three FIHP, three MEN 1, one MEN 2A, 25 sporadic adenomas, 17 hyperplastic glands, two lithium associated tumours, and four sporadic carcinomas. Loss of heterozygosity at 1q24-32 was performed on a subset of these tumours.

RESULTS

HRPT2 somatic mutations were detected in four of four sporadic parathyroid carcinoma samples, and germline mutations were found in five of five HPT-JT parathyroid tumours (two families) and two parathyroid tumours from one FIHP family. One HPT-JT tumour with germline mutation also harboured a somatic mutation. In total, seven novel and one previously reported mutation were identified. "Two-hits" (double mutations or one mutation and loss of heterozygosity at 1q24-32) affecting HRPT2 were found in two sporadic carcinomas, two HPT-JT-related and two FIHP related tumours.

CONCLUSIONS

The results in this study support the role of HRPT2 as a tumour suppressor gene in sporadic parathyroid carcinoma, and provide further evidence for HRPT2 as the causative gene in HPT-JT, and a subset of FIHP. In light of the strong association between mutations of HRPT2 and sporadic parathyroid carcinoma demonstrated in this study, it is hypothesised that HRPT2 mutation is an early event that may lead to parathyroid malignancy and suggest intragenic mutation of HRPT2 as a marker of malignant potential in both familial and sporadic parathyroid tumours.

Hyperparathyroidism-jaw tumour syndrome

Amongst hyperparathyroidism-related syndromes, hyperparathyroidism-jaw tumour syndrome is one of the least common and relatively unknown but its clinical and genetic aspects are not less interesting or important. With the recent identification of its genes, we can now better characterize the disease, both clinically and genetically, which will certainly impact the field of endocrinology and oncology. In this article, we review the clinico-pathological features and genetic basis of this syndrome with the hope that it will create awareness and interest in this disease amongst clinicians and basic scientists.

Limited versus radical parathyroidectomy in familial isolated primary hyperparathyroidism

BACKGROUND

Familial isolated primary hyperparathyroidism (FIHPT) is characterized by earlier onset, higher incidence of multiglandular disease, and higher recurrence rate when compared with sporadic primary hyperparathyroidism. Excision of 3.5 or 4 glands with autotransplantation has been recommended; however, these approaches lead to permanent hypoparathyroidism in 13% to 41% of patients. It is reported that many patients with FIHPT return to normocalcemia after single-gland excision. The use of preoperative localization and intraoperative parathyroid hormone assay permits limited resection of only hypersecreting glands. We report the outcome of this operative approach.

METHODS

Fifteen consecutive patients with FIHPT underwent limited parathyroidectomy with resection guided by intact parathyroid hormone secretion in 2 university centers. Patients were followed up postoperatively for serum calcium and intact parathyroid hormone levels.

RESULTS

With an operative success of 93%, 14 patients had only single-gland excision and 80% had unilateral neck exploration. All initial patients had their hypercalcemia corrected. In 4 reoperations, permanent hypoparathyroidism occurred in 2 patients. One recurrence was observed in 40 (8-122) months of follow-up.

CONCLUSION

Limited parathyroidectomy allows successful single-gland excision in many patients with FIHPT, thus decreasing the risk of hypoparathyroidism. In these patients, a low incidence of hypoparathyroidism may be preferable to the possibility of late recurrence.

Familial parathyroid carcinoma in a child

Familial hyperparathyroidism and parathyroid carcinoma are rare diseases. A case of parathyroid carcinoma in an 8-year-old girl whose mother had previously undergone parathyroidectomy for primary hyperparathyroidism is reported. Parathyroid carcinoma in a preadolescent child has not been described previously, and may have a familial basis.

Genetic and clinical characterization of sporadic cystic parathyroid tumours

OBJECTIVE

The hyperparathyroidism--jaw tumour (HPT--JT) syndrome is one of the familial disorders characterized by primary hyperparathyroidism and has been linked to the chromosomal region of 1q32--q21. The parathyroid tumours related to this syndrome have shown loss of wild-type alleles at this locus suggesting that inactivation of a tumour suppressor gene might be responsible for the disease. In the majority of these tumours cysts are a prominent feature. By loss of heterozygosity (LOH) studies, we investigated the region of interest in an attempt to clarify its possible role in a series of cystic sporadic parathyroid adenomas.

DESIGN AND SUBJECTS

A total of 30 patients diagnosed with sporadic hyperparathyroidism were included in the study, genotyped with 17 polymorphic microsatellite markers at chromosome 1q, and additional markers from 1p and 11q13 which are commonly involved in sporadic parathyroid tumours. The cystic parathyroid tumours were characterized clinically, and immunohistochemistry against PTH was carried out to confirm the parathyroid origin of the cysts.

RESULTS

LOH was found in six of 30 tumours (20%) on 1q, six of 30 tumours (20%) on 1p and five of 30 tumours (17%) on 11q13. We found a significant correlation between allelic alterations and the clinical parameters, tumour weight and PTH. Furthermore, we found a significant difference between tumour weight and PTH in cases of cystic parathyroid tumours compared with unselected sporadic cases.

CONCLUSIONS

These results suggest that cystic parathyroid tumours might represent a new subgroup among parathyroid tumours based on the genetic and clinical findings. Loss of heterozygosity at 1q further supports the presence of a tumour suppressor gene at this locus.

Hyperparathyroidism-jaw tumor syndrome: the HRPT2 locus is within a 0.7-cM region on chromosome 1q

Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is an autosomal dominant disease characterized by the development of multiple parathyroid adenomas and multiple fibro-osseous tumors of the maxilla and mandible. Some families have had affected members with involvement of the kidneys, variously reported as Wilms tumors, nephroblastomas, and hamartomas. The HPT-JT gene (HRPT2) maps to chromosome 1q25-q31. We describe further investigation of two HPT-JT families (K3304 and K3349) identified through the literature. These two expanded families and two previously reported families were investigated jointly for linkage with 21 new, closely linked markers. Multipoint linkage analysis resulted in a maximum LOD score of 7.83 (at recombination fraction 0) for markers D1S2848-D1S191. Recombination events in these families reduced the HRPT2 region to approximately 14.7 cM. In addition, two of these four study families (i.e., K3304 and K11687) share a 2.2-cM length of their (expanded) affected haplotype, indicating a possible common origin. Combining the linkage data and shared-haplotype data, we propose a 0.7-cM candidate region for HRPT2.

Familial hyperparathyroidism associated with jaw fibroma: case report and literature review

A 53-year-old female suffering from renal stones and hypercalcaemia was diagnosed as having primary hyperparathyroidism caused by hyperplasia of the parathyroid glands. She underwent total parathyroidectomy and implantation of parathyroid tissue. After one year, she underwent surgery for a jaw tumour. The pathological findings indicated it to be a cementifying fibroma. Jackson et al. (1990) reported the familial association of hyperparathyroidism with jaw tumours, and they suggested that this condition represents a new clinical syndrome. We believe that our case belongs to this syndrome.

Dominant familial syndromes with endocrine hyperfunction: An additional syndrome?

At least 8 separate dominant syndromes have been described which have hyperfunctioning endocrine tumors as an important component. Scattered reports in the literature suggest that there may be an additional syndrome, in which extra-adrenal paragangliomas (often multiple), pituitary adenomas, and parathyroid hyperplasia coexist. Of 3 such cases described to date, 2 have included information about the family history, which in each case suggested dominant inheritance. This would presumably be a less common syndrome than the others recognized previously, so that full evaluation of endocrine findings and family history in future cases will be important for developing our understanding of the syndrome.

Etiologies of parathyroid gland dysfunction in primary hyperparathyroidism

Primary hyperparathyroidism is caused by defects in the parathyroid gland. Investigations have implicated three interesting genes whose mutation can cause primary hyperparathyroidism. Familial hypocalciuric hypercalcemia is believed to be an atypical form of primary hyperparathyroidism with an inherited defect in calcium recognition expressed not only in all parathyroid chief cells (thus a polyclonal defect) but in some renal tubular cells as well. In typical primary hyperparathyroidism a monoclonal parathyroid tumor is usually the central cause. Either of two apparently different genes on the long arm of chromosome 11 has been implicated in development of a parathyroid tumor clone. One gene (D11S287) was shown to have undergone a rearrangement with the parathyroid hormone gene on the short arm of the same chromosome (pericentromeric inversion) in a small fraction of tumors; the D11S287 locus may encode a growth stimulator. Another gene, the locus for familial multiple endocrine neoplasia type 1 (FEMEN1), is likely to encode a growth inhibitor. Inactivation of this gene or another nearby gene by somatic mutation has been indirectly implicated in one-quarter of sporadic parathyroid adenomas and in more than half of parathyroid tumors in FMEN1. In conclusion, studies have suggested three different mechanisms for parathyroid gland dysfunction in primary hyperparathyroidism: (1) a defect in calcium recognition, (2) a monoclonal tumor from overexpression of a growth stimulator, or (3) a monoclonal tumor from inactivation of a growth inhibitor.