Genetic testing in familial isolated hyperparathyroidism: unexpected results and their implications

Clinical and molecular genetics of parathyroid neoplasms

Primary hyperparathyroidism (HPT) results from the excessive secretion of parathyroid hormone from parathyroid tumours. While most HPT is sporadic, it is associated with a familial syndrome in a minority of cases. The study of these syndromes has helped define the pathophysiology of both familial and sporadic parathyroid neoplasms. Investigation of kindred with multiple endocrine neoplasia type 1 (MEN1) and the hyperparathyroidism-jaw tumour syndrome (HPT-JT) led to the discovery of the tumour suppressor genes MEN1 and HRPT2. We now recognise that somatic mutations in MEN1 and HRPT2 tumour suppressor genes are frequent events in sporadic parathyroid adenomas and carcinomas, respectively. Parathyroid tumours in the MEN2A syndrome result from mutational activation of the RET oncogene. The CCND1/PRAD1 oncogene was discovered by analysis of sporadic parathyroid tumours. Studies of familial isolated HPT and analysis of chromosomal loss and gain in parathyroid tumours suggest that other genes relevant to parathyroid neoplasia await identification.

Parathyroid carcinoma

Parathyroid carcinoma is a rare endocrine malignancy. The reported incidence is from 0.5 to 5% of primary hyperparathyroidism cases in various series. The cause is unknown, but clinical correlations with different genetic syndromes exist. Mutations in the HPRT2 gene seem to play a significant role in the pathogenesis of this disease. Men and women are equally affected, usually in the fourth or fifth decade of life. Most patients will present with signs and symptoms of hypercalcaemia. Cases of non-functioning carcinoma are exceedingly rare. Surgical resection is the most effective method of treatment and palliation. A significant proportion of patients will experience recurrence, and will need further surgical and, eventually, medical management of hypercalcaemia. The disease is progressive but slow growing. Most patients will require multiple operations to resect recurrent disease. The main cause of morbidity and mortality is the sequela of uncontrolled chronic hypercalcaemia rather than tumour burden. The current paper will review the epidemiology, pathogenesis, clinical presentation and diagnostic work-up of this disease. Surgical management in different scenarios is reviewed in detail, followed by other types of treatment and management of incurable disease.

Calcium-sensing receptor (CASR) mutations in hypercalcemic states: studies from a single endocrine clinic over three years

CONTEXT

Inactivating mutations of the calcium-sensing receptor (CASR) are implicated in different hypercalcemic syndromes, including familial hypocalciuric hypercalcemia (FHH), primary hyperparathyroidism (PHPT), and familial isolated hyperparathyroidism (FIHP). However, molecular diagnostics applied to large nonselected hypercalcemic cohorts from a single center have not been reported.

OBJECTIVE

Our objective was to describe the prevalence, type, and potential pathogenicity of CASR mutations in a series of cases with FHH (n = 17), PHPT (n = 165), and FIHP (n = 3) and controls (n = 198) presenting at a single endocrine clinic.

SUBJECTS

All were prospectively evaluated at the "Casa Sollievo della Sofferenza" Hospital in southern Italy over a 3-yr period.

METHODS

CASR screening was conducted by denaturing HPLC. The variant CASRs were functionally characterized by transient transfection studies in kidney cells in vitro.

RESULTS

A single novel missense variant was identified in one PHPT case. However, in FHH probands, mutations were found in eight of 17 (47%). With a hypercalcemic family member, mutation detection rate in FHH rose to seven of eight (87%), whereas only one of nine sporadic cases was positive, and none of the three FIHP cases had detectable CASR mutations. Five missense variant CASRs, identified in control subjects, performed as wild type in functional assays, whereas the missense mutant CASRs identified in the FHH patients, and in the one PHPT case, exhibited significant impairment. A novel intronic mutation (IVS4-19a-->c) found in one FHH family, created an abnormally spliced product in an in vitro minigene assay.

CONCLUSION

CASR testing, with functional analysis, provides critical confirmatory evidence in the differential diagnosis of hypercalcemic states.

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.

Mutation analysis of MEN1, HRPT2, CASR, CDKN1B, and AIP genes in primary hyperparathyroidism patients with features of genetic predisposition

OBJECTIVE

Primary hyperparathyroidism (PHPT), a common endocrine condition, is usually caused by sporadically occurring parathyroid adenoma. A subset of patients carry germline mutations in genes such as MEN1 (multiple endocrine neoplasia type 1), HRPT2 (hyperparathyroidism 2), and CASR (calcium-sensing receptor) predisposing to syndromic forms of PHPT or familial isolated hyperparathyroidism (FIHP). Recently, germline mutations in two novel genes AIP (aryl hydrocarbon receptor-interacting protein) and CDKN1B (cyclin-dependent kinase inhibitor 1B) have been found to be associated with endocrine tumors. The purpose of this study was to evaluate the role of MEN1, HRPT2, CASR, AIP, and CDKN1B genes in PHPT patients with clinical features suggestive of genetic predisposition.

PATIENTS AND DESIGN

Medical records of patients treated for PHPT from 1974 to 2001 at Oulu University Hospital were reviewed. Patients with multiglandular or recurrent/persistent disease, other MEN1- related manifestations, aged 40 yr or younger at onset or with a family history of PHPT/MEN1-related tumor were invited to the study. Twenty patients with previously diagnosed MEN1 were excluded. Participants were interviewed and blood samples obtained for biochemical screening and mutation analysis of MEN1, HRPT2, CASR, AIP, and CDKN1B.

RESULTS

Of the 56 invited patients, 29 took part in the study. One patient was found to carry the c. 1356_1367del12 MEN1 founder mutation. Mutations in other genes were not detected.

CONCLUSIONS

Apart from MEN1, mutations in other genes predisposing to PHPT seem to be rare or non-existing in Northern Finnish PHPT patients. No evidence was found for a role of AIP or CDKN1B in PHPT predisposition.

The MEN1 gene and pituitary tumours

Sporadic multiple endocrine neoplasia type 1 (MEN1) is defined as the occurrence of tumours in two of three main endocrine tissue types: parathyroid, pituitary and pancreaticoduodenal. A prolactinoma variant or Burin variant of MEN1 was found to occur in three large kindreds, with more prolactinomas and fewer gastrinomas than typical MEN1. MEN1 tumours differ from common tumours by showing features from the MEN1 gene (e.g. larger pituitary tumours). They also show various expressions of tumour multiplicity; however, pituitary tumour in MEN1 is usually solitary. Diagnosis in MEN1 carriers during childhood is not directed at cancers but at benign morbid tumours. Morbid prolactinoma occurred at the age of 5 years in one MEN1 individual; hence, this is the earliest age at which to recommend tumour surveillance in carriers. The MEN1 gene shows biallelic inactivation in 30% of some types of common variety endocrine tumours (e.g. parathyroid adenoma, gastrinoma, insulinoma and bronchial carcinoid), but in only 1-5% of common pituitary tumours. Heterozygous knockout of MEN1 in mice provides a robust model of MEN1 and has been found to support further research on anti-angiogenesis therapy for pituitary tumours. The rarity of MEN1 mutations in some MEN1-like states aids the identification of other mutated genes, such as AIP, HRPT2 and p27(Kip1). We present recent clinical and basic findings about the MEN1 gene, particularly concerning hereditary vs. common variety pituitary tumours.

Genetic causes of hypercalciuric nephrolithiasis

Renal stone disease (nephrolithiasis) affects 3-5% of the population and is often associated with hypercalciuria. Hypercalciuric nephrolithiasis is a familial disorder in over 35% of patients and may occur as a monogenic disorder that is more likely to manifest itself in childhood. Studies of these monogenic forms of hypercalciuric nephrolithiasis in humans, e.g. Bartter syndrome, Dent's disease, autosomal dominant hypocalcemic hypercalciuria (ADHH), hypercalciuric nephrolithiasis with hypophosphatemia, and familial hypomagnesemia with hypercalciuria have helped to identify a number of transporters, channels and receptors that are involved in regulating the renal tubular reabsorption of calcium. Thus, Bartter syndrome, an autosomal disease, is caused by mutations of the bumetanide-sensitive Na-K-Cl (NKCC2) co-transporter, the renal outer-medullary potassium (ROMK) channel, the voltage-gated chloride channel, CLC-Kb, the CLC-Kb beta subunit, barttin, or the calcium-sensing receptor (CaSR). Dent's disease, an X-linked disorder characterized by low molecular weight proteinuria, hypercalciuria and nephrolithiasis, is due to mutations of the chloride/proton antiporter 5, CLC-5; ADHH is associated with activating mutations of the CaSR, which is a G-protein-coupled receptor; hypophosphatemic hypercalciuric nephrolithiasis associated with rickets is due to mutations in the type 2c sodium-phosphate co-transporter (NPT2c); and familial hypomagnesemia with hypercalciuria is due to mutations of paracellin-1, which is a member of the claudin family of membrane proteins that form the intercellular tight junction barrier in a variety of epithelia. These studies have provided valuable insights into the renal tubular pathways that regulate calcium reabsorption and predispose to hypercalciuria and nephrolithiasis.

Discriminative power of three indices of renal calcium excretion for the distinction between familial hypocalciuric hypercalcaemia and primary hyperparathyroidism: a follow-up study on methods

BACKGROUND

Familial hypocalciuric hypercalcaemia (FHH) must be differentiated from primary hyperparathyroidism (PHPT) because prognosis and treatment differ. In daily practice this discrimination is often based on the renal calcium excretion or the calcium/creatinine clearance ratio (CCCR). However, the diagnostic performance of these variables is poorly documented.

AIM

To appraise the power of various simple biochemical variables to differentiate between FHH and PHPT using calcium sensing receptor (CASR) gene analysis and histopathological findings as gold standards.

DESIGN

Follow-up approach (direct design).

MATERIALS

We included 54 FHH patients (17 males and 37 females, aged 18-75 years) with clinically significant mutations in the CASR gene and 97 hypercalcaemic patients with histologically verified PHPT (17 males and 80 females, aged 19-86 years). All PHPT patients became normocalcaemic following successful neck exploration.

RESULTS

Based on receiver operating characteristic (ROC) curve analysis, the CCCR was only marginally better, as judged by the area under curve (AUC = 0.923 +/- 0.021 (SE)), than the 24-h calcium/creatinine excretion ratio (AUC = 0.903 +/- 0.027) and the 24-h calcium excretion (AUC = 0.876 +/- 0.029). However, overlap performance analysis disclosed that the CCCR included fewer patients with PHPT together with the FHH patients than the other two variables at different cut-off points. Based on the ROC curve, the optimal cut-off point for diagnosing FHH using CCCR was < 0.0115, which yielded a diagnostic specificity of 0.88 and a sensitivity of 0.80. Overlap analysis revealed that a cut-off point for CCCR at < 0.020 would sample 98% (53/54) of all patients with FHH and include 35% (34/97) of the PHPT patients.

CONCLUSION

Our results support the use of the CCCR as an initial screening test for FHH. We suggest a two-step diagnostic procedure, where the first step is based on the CCCR with a cut-off at < 0.020, and the second step is CASR gene analysis in patients with FHH or PHPT.

THE CALCIUM-SENSING RECEPTOR IN NORMAL PHYSIOLOGY AND PATHOPHYSIOLOGY: A Review

The discovery of a G protein-coupled, calcium-sensing receptor (CaR) a decade ago and of diseases caused by CaR mutations provided unquestionable evidence of the CaR's critical role in the maintenance of systemic calcium homeostasis. On the cell membrane of the chief cells of the parathyroid glands, the CaR "senses" the extracellular calcium concentration and, subsequently, alters the release of parathyroid hormone (PTH). The CaR is likewise functionally expressed in bone, kidney, and gut--the three major calcium-translocating organs involved in calcium homeostasis. Intracellular signal pathways to which the CaR couples via its associated G proteins include phospholipase C (PLC), protein kinase B (AKT); and mitogen-activated protein kinases (MAPKs). The receptor is widely expressed in various tissues and regulates important cellular functions in addition to its role in maintaining systemic calcium homeostasis, i.e., protection against apoptosis, cellular proliferation, and membrane voltage. Functionally significant mutations in the receptor have been shown to induce diseases of calcium homeostasis owing to changes in the set point for calcium-regulated PTH release as well as alterations in the renal handling of calcium. Gain-of-function mutations cause hypocalcemia, whereas loss-of-function mutations produce hypercalcemia. Recent studies have shown that the latter clinical presentation can also be caused by inactivating autoantibodies directed against the CaR Newly discovered type II allosteric activators of the CaR have been found to be effective as a medical treatment for renal secondary hyperparathyroidism.

Multiple endocrine neoplasia syndromes

The multiple endocrine neoplasia (MEN) syndromes are rare autosomal-dominant conditions that predispose affected individuals to benign and malignant tumors of the pituitary, thyroid, parathyroids, adrenals, endocrine pancreas, paraganglia, or nonendocrine organs. The classic MEN syndromes include MEN type 1 and MEN type 2. However, several other hereditary conditions should also be considered in the category of MEN: von Hippel-Lindau syndrome, the familial paraganglioma syndromes, Cowden syndrome, Carney complex, and hyperparathyroidism jaw-tumor syndrome. In addition, researchers are becoming aware of other familial endocrine neoplasia syndromes with an unknown genetic basis that might also fall into the category of MEN. This article reviews the clinical features, diagnosis, and surgical management of the various MEN syndromes and genetic risk assessment for patients presenting with one or more endocrine neoplasms.

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.

Hypercalcaemic and hypocalcaemic conditions due to calcium-sensing receptor mutations

The extracellular calcium (Ca2+o)-sensing receptor (CaSR) enables the parathyroid glands and other CaSR-expressing cells involved in calcium homeostasis, such as the kidney and bone, to sense alterations in the level of Ca2+o and to respond with changes in function that are directed at normalizing the blood calcium concentration. Several disorders of Ca2+o sensing arise from inherited or acquired abnormalities that 'reset' the serum calcium concentration upwards or downwards. Heterozygous inactivating mutations of the CaSR produce a benign form of hypercalcaemia, termed 'familial hypocalciuric hypercalcaemia', while homozygous mutations produce a much more severe hypercalcaemic disorder resulting from marked hyperparathyroidism, called 'neonatal severe hyperparathyroidism'. Activating mutations cause a hypocalcaemic syndrome of varying severity, termed 'autosomal-dominant hypocalcaemia or hypoparathyroidism' as well as Bartter's syndrome type V. Calcimimetic CaSR activators and calcilytic CaSR antagonists have also been developed with potential for use in the treatment of these disorders.

HRPT2 gene analysis and the diagnosis of parathyroid carcinoma

Parathyroid carcinoma is an uncommon cause of primary hyperparathyroidism (PHPT) and is usually associated with more severe clinical manifestations than its much more common benign counterpart, the parathyroid adenomas. The histopathological distinction between benign and malignant parathyroid tumors is difficult. Currently, pathological diagnosis of parathyroid carcinoma is restricted to lesions showing unequivocal growth, as evidenced by perineural invasion, full-thickness capsular invasion with growth into adjacent tissues, or metastasis. Major advances in the molecular pathogenesis of parathyroid carcinoma have been made by the cloning of the HRPT2 gene, which encodes parafibromin, a 531-amino acid putative tumor-suppressor protein. Germline mutations of HRPT2 confer susceptibility to the hyperparathyroidism-jaw tumor syndrome (HPT-JT), an autosomal dominant syndrome with high but incomplete penetrance. Somatic inactivating mutations of the HRPT2 gene have been reported in the majority of apparently sporadic parathyroid carcinomas but, unexpectedly, germline HRPT2 mutation have been found in up to 30% of these patients. Several studies have been performed to evaluate whether parafibromin immunostaining might have some diagnostic utility. Loss of parafibromin immunoreactivity has been found in the majority of parathyroid carcinomas, in 50% of equivocal carcinomas and, very rarely, in benign adenomas. On the other hand, with the exception of HPT-JT-related tumors, loss of parafibromin associated with HRPT2 mutations strongly predicts parathyroid malignancy. In clinical practice, parafibromin immunostaining and HRPT2 gene analysis could be particularly useful in the subset of parathyroid tumors with equivocal histology.

Inherited disorders of calcium homeostasis

In mammals a complicated homeostatic mechanism has evolved to maintain near consistency of extracellular calcium ion levels. The homeostatic mechanism involves several hormones, which comprise among others, parathyroid hormone and vitamin D. The recent resurge in vitamin D deficiency, as a global health issue, has increased interest in the hormone. In addition to vitamin D deficiency, other causes of rickets are calcium deficiency and inherited disorders of vitamin D and phosphorus metabolism. Vitamin D-resistant syndromes are caused by hereditary defects in metabolic activation of the hormone or by mutations in the vitamin D receptor, which binds the hormone with high affinity and regulates the expression of genes through zinc finger mediated DNA binding and protein-protein interaction. Current interest is to correlate the type/position of mutations that result in disorders of vitamin D metabolism or in vitamin D receptor function with the variable phenotypic features and clinical presentation. The calcium sensing receptor plays a key role in calcium homeostasis. Loss of function mutations in the calcium sensing receptor can cause familial benign hypocalciuric hypercalcemia in heterozygotes and neonatal severe hyperparathyroidism when homozygous mutations occur in the calcium sensing receptor. Gain of function mutation can cause the opposite effect causing autosomal dominant hypocalcemia. Mouse models using targeted gene disruption strategies have been valuable tools to study the effect of mutations on the calcium sensing receptor or in the vitamin D activation pathway. Dysfunctional calcium sensing receptors with function altering mutations may be responsive to treatment with allosteric modulators of the calcium sensing receptor. Vitamin D analogs which induce unusual structural conformations on the vitamin D receptor may have a variety of therapeutic indications. This review summarises recent advances in knowledge of the molecular pathology of inherited disorders of calcium homeostasis.

Familial isolated primary hyperparathyroidism caused by mutations of the MEN1 gene

BACKGROUND

Familial isolated primary hyperparathyroidism (FIHP) is an autosomal dominant disorder that can represent an early stage of either the multiple endocrine neoplasia type 1 (MEN1) or hyperparathyroidism-jaw tumor (HPT-JT) syndromes; alternatively, the condition can be caused by an allelic variant of MEN1 or HRPT2 (hyperparathyroidism 2 gene), or caused by a distinct entity involving another locus. We have explored these possibilities in a patient with primary hyperparathyroidism, whose mother had a history of renal calculi and primary hyperparathyroidism.

INVESTIGATIONS

Serum biochemistry and radiological investigations for primary hyperparathyroidism, MEN1 and HPT-JT, and genetic testing for MEN1 and HRPT2 mutations were undertaken.

DIAGNOSIS

FIHP with primary hyperparathyroidism as the sole endocrinopathy due to a previously unreported heterozygous missense germline MEN1 mutation, Tyr351Asn. In addition, another unreported heterozygous missense germline MEN1 mutation, Trp220Leu, was identified in an unrelated male patient with FIHP, whose mother and sister also had primary hyperparathyroidism. DNA from a parathyroid tumor from the sister revealed a loss of heterozygosity in which the mutant allele was retained. This is consistent with Knudson's 'two-hit' model of hereditary cancer and a tumor suppressor role for MEN1 in FIHP.

MANAGEMENT

The patient underwent parathyroidectomy and has remained normocalcemic over a follow-up period of 6 years. The other four patients have remained normocalcemic for a follow-up period of 4-15 years following parathyroidectomy. None has developed abnormalities of the MEN1 syndrome, providing further support that FIHP is a distinct genetic variant of the MEN1 syndrome.

Hiperparatireoidismo primário familiar isolado: análise e descrição de uma família com seis casos índices

Objetivamos descrever e analisar uma família com seis casos de hiperparatireoidismo familiar isolado (HFI), uma rara doença hereditária de padrão autossômico dominante, caracterizada por hiperparatireoidismo primário sem associação com outras doenças ou tumores endocrinológicos. O diagnóstico foi realizado através da demonstração de hipercalcemia, aumento dos níveis de paratormônio e tumores de paratireóide à histopatologia, excluindo-se neoplasias endócrinas múltiplas do tipo 1 (NEM 1) e do tipo 2a (NEM 2a), além da síndrome hiperparatireoidismo/tumor de mandíbula (HPT/TM). Analisamos a descrição dos exames diagnósticos iniciais, a abordagem cirúrgica, os laudos histopatológicos pós-operatórios e suas evoluções. A primeira paciente operada neste instituto há 20 anos, recidivou onze anos após, e possuía uma irmã com diagnóstico prévio, o que motivou a investigação de outros familiares. A observação do caráter familial nesses pacientes contribuiu para a facilitação diagnóstica e encaminhamento terapêutico dos mesmos, assim como a orientação clínica e genética à família.

Mutations in genes causing human familial isolated hyperparathyroidism do not account for hyperparathyroidism in Keeshond dogs

The roles of the calcium sensing receptor gene (CaSR) and the multiple endocrine neoplasia gene (MEN1) were investigated in Keeshond dogs with familial hyperparathyroidism. Mutations in these genes have been shown to cause familial isolated hyperparathyroidism (FIH) in humans. Affected dogs were identified through measurement of blood calcium and parathyroid hormone levels. Parathyroid tissue and whole blood was used to clone the cDNAs and individual exonic sequences of both candidate genes. No sequence abnormalities were identified when comparing normal and affected dogs, suggesting that a mapping strategy may be the most appropriate approach for identifying the genetic basis of this valuable comparative canine disease model.

Contribution of genetic analysis in screening for MEN1 among patients with sporadic disease and one or more typical manifestation

Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal dominant hereditary syndrome (OMIM 131100) due to MEN1 gene mutations, predisposing to the development of hyperplasic and tumoral lesions of neuroendocrine tissues. Since the identification of the gene in 1997, more than 400 different mutations of MEN1 have been registered. Genotypic analysis of MEN1 remains fastidious and must be reserved to targeted situations. If the lesions appear in a familial assessed context, there is a strong argument to search for MEN1 mutation. This is not the case in a sporadic context. With experience acquired in our laboratory, we evaluated the frequency of MEN1 mutations in patients with sporadic presentations. Our aim was to better define criteria for MEN1 genotypic analysis. One hundred and twenty four blood samples from unrelated patients, who gave their written informed consent, were analyzed. These patients exhibited 1 to 4 manifestations of MEN1 without any familial context. After DNA extraction, the analysis was undertaken by PCR-sequencing of all the MEN1 coding exons and exon/intron boundaries or by PCR of the pre-screened fragments alone, a technique made possible by indirect screening mutation methods. Mutations were identified by comparing the sequences to the reference MEN1 sequence available from GENBANK (U93237.1). Mutations were identified in 19 patients, with variable prevalence according to clinical manifestations: 100% for patients with 4 manifestations, 45.5% for patients with 3 manifestations, 19% for patients with 2 manifestations and 2% for patients with only one manifestation. Mutations were: 11 point variations (58%), including 2 splicing sites and 8 frameshift mutations (42%) including 5 deletions, 2 insertions and 1 insertion/deletion; one mutation was identified twice. We showed a relationship between clinical presentation and MEN1 mutation identification, especially with the number of clinical manifestations but also with the type of manifestation. Pancreatic manifestations were significantly linked with probability of mutation. In a sporadic context with at least two established manifestations of MEN1, the overall probability of identifying a mutation was 26%, warranting MEN1 genotypic analysis.

Clinical lessons from the calcium-sensing receptor

The extracellular calcium ion (Ca(2+)(e))-sensing receptor (CaR) enables key tissues that maintain Ca(2+)(e) homeostasis to sense changes in the Ca(2+)(e) concentration. These tissues respond to changes in Ca(2+)(e) with functional alterations that will help restore Ca(2+)(e) to normal. For instance, decreases in Ca(2+)(e) act via the CaR to stimulate secretion of parathyroid hormone-a Ca(2+)(e)-elevating hormone-and to increase renal tubular calcium reabsorption; each response helps promote normalization of Ca(2+)(e) levels. Further work is needed to determine whether the CaR regulates other parameters of renal function (e.g. 1,25-dihydroxyvitamin D(3) synthesis, intestinal absorption of mineral ions, and/or bone turnover). Identification of the CaR has also elucidated the pathogenesis and pathophysiology of inherited disorders of mineral and electrolyte metabolism; moreover, acquired abnormalities of Ca(2+)(e)-sensing can result from autoimmunity to the CaR, and reduced CaR expression in the parathyroid may contribute to the abnormal parathyroid secretory control that is observed in primary and secondary hyperparathyroidism. Finally, calcimimetics-allosteric activators of the CaR-treat secondary hyperparathyroidism effectively in end-stage renal failure.

Rapid mutation screening for HRPT2 and MEN1 mutations associated with familial and sporadic primary hyperparathyroidism

Familial hyperparathyroidism, a disease of the parathyroid glands, may occur in conjunction with pituitary and pancreatic tumors (multiple endocrine neoplasia type I), kidney and bone tumors (hyperparathyroidism jaw tumor syndrome), or alone (familial isolated hyperparathyroidism). This study describes the development and validation of rapid scanning for mutations in two tumor suppressor genes linked to familial hyperparathyroidism-MEN1 and HRPT2. Denaturing high-performance liquid chromatography mutation scanning for MEN1 was performed using a set of 10 amplicons covering the nine coding exons and flanking intronic regions and for HRPT2 using a set of three amplicons for exons 1, 2, and 7 and flanking intronic regions, in which 80% of the mutations identified to date are located. All 52 MEN1 mutations or polymorphisms, 46 known and six unknown, were successfully detected. Mutation detection in exon 9 was not confounded by the presence of the common polymorphism D418D. In addition, all 10 HRPT2 mutations were successfully detected, and a two-step approach was able to distinguish IVS2 common polymorphisms from exon 2 mutations. The development of rapid denaturing high performance liquid chromatography mutation scanning of MEN1 and HRPT2 facilitates a molecular diagnosis of the associated familial syndromes for both clinically affected and at-risk family members.

The calcium-sensing receptor: physiology, pathophysiology and CaR-based therapeutics

The extracellular calcium (Ca(o)2+)-sensing receptor (CaR) enables the parathyroid glands and other CaR-expressing cells to sense alterations in the level of Ca(o)2+ and to respond with changes in function that are directed at normalizing the blood calcium concentration. In addition to the parathyroid gland, the kidney is a key site for Ca(o)2(+)-sensing that enables it to make physiologically relevant alterations in divalent cation and water metabolism. Several disorders of Ca(o)2(+)-sensing arise from inherited or acquired abnormalities that "reset" the serum calcium concentration upward or downward. Inactivating mutations produce a benign form of hypercalcemia when present in the heterozygous state, termed Familial Hypocalciuric Hypercalcemia (FHH), while homozygous mutations produce a much more severe hypercalcemic disorder resulting from marked hyperparathyroidism, called Neonatal Severe Hyperparathyroidism (NSHPT). Activating mutations cause a hypocalcemic syndrome of varying severity, termed autosomal dominant hypocalcemia or hypoparathyroidism. Inactivating or activating antibodies directed at the CaR produce the expected hyper- or hypocalcemic syndromes, respectively. "Calcimimetic" CaR activators and "calcilytic" CaR antagonists have been developed. The calcimimetics are currently in use for controlling severe hyperparathyroidism in patients receiving dialysis treatment for end stage renal disease or with parathyroid cancer. Calcilytics are being evaluated as a means of inducing a "pulse" in the circulating parathyroid hormone (PTH) concentration, which would mimic that resulting from injection of PTH, an established anabolic form of treatment for osteoporosis.

Primary hyperparathyroidism and the presence of kidney stones are associated with different haplotypes of the calcium-sensing receptor

INTRODUCTION

Three single-nucleotide polymorphisms in the calcium-sensing receptor gene (CASR) encoding the missense substitutions A986S, R990G, and Q1011E have been associated with normal variation in extracellular calcium homeostasis, both individually and in haplotype combination. The aim of this study was to examine haplotype associations in primary hyperparathyroidism (PHPT).

PATIENTS AND METHODS

Patients with sporadic PHPT (n = 237) were recruited from endocrine clinics and healthy controls (n = 433) from a blood donor clinic, and levels of serum calcium, albumin, and PTH were measured. In PHPT patients, urinary calcium/creatinine clearances and bone mineral density at spine and femoral neck were measured and the presence of kidney stones and vertebral fractures identified. The CASR single-nucleotide polymorphisms were haplotyped by allele-specific sequencing.

RESULTS

Four haplotypes (ARQ, SRQ, AGQ, and ARE) of eight were observed, in keeping with significant linkage disequilibrium, but haplotype frequencies did not show significant Hardy-Weinberg disequilibrium. The SRQ haplotype was more common in PHPT (125 of 474 alleles) than in controls (170 of 866 alleles, P = 0.006) and showed a significant (P = 0.006) gene-dosage effect. There was no significant association between haplotype and bone mineral density or fractures, but association with kidney stones was significant (P = 0.0007). In the stone-forming subgroup, the SRQ haplotype was underrepresented and AGQ overrepresented. Patients bearing the AGQ haplotype had an odds ratio of 3.8 (95% confidence interval, 1.30-11.3) for presentation with renal stones compared with the rest.

CONCLUSION

Our data indicate that the CASR SRQ haplotype is significantly associated with PHPT in our population. Within the PHPT patient population, the AGQ haplotype is significantly associated with kidney stones.

Familial isolated hyperparathyroidism is linked to a 1.7 Mb region on chromosome 2p13.3-14

BACKGROUND

Familial isolated hyperparathyroidism (FIHP) is an autosomal dominantly inherited form of primary hyperparathyroidism. Although comprising only about 1% of cases of primary hyperparathyroidism, identification and functional analysis of a causative gene for FIHP is likely to advance our understanding of parathyroid physiology and pathophysiology.

METHODS

A genome-wide screen of DNA from seven pedigrees with FIHP was undertaken in order to identify a region of genetic linkage with the disorder.

RESULTS

Multipoint linkage analysis identified a region of suggestive linkage (LOD score 2.68) on chromosome 2. Fine mapping with the addition of three other families revealed significant linkage adjacent to D2S2368 (maximum multipoint LOD score 3.43). Recombination events defined a 1.7 Mb region of linkage between D2S2368 and D2S358 in nine pedigrees. Sequencing of the two most likely candidate genes in this region, however, did not identify a gene for FIHP.

CONCLUSIONS

We conclude that a causative gene for FIHP lies within this interval on chromosome 2. This is a major step towards eventual precise identification of a gene for FIHP, likely to be a key component in the genetic regulation of calcium homeostasis.

The calcium-sensing receptor and related diseases

The calcium-sensing receptor (CASR) adjusts the extracellular calcium set point regulating PTH secretion and renal calcium excretion. The receptor is expressed in several tissues and is also involved in other cellular functions such as proliferation, differentiation and other hormonal secretion. High extracellular calcium levels activate the receptor resulting in modulation of several signaling pathways depending on the target tissues. Mutations in the CASR gene can result in gain or loss of receptor function. Gain of function mutations are associated to Autossomal dominant hypocalcemia and Bartter syndrome type V, while loss of function mutations are associated to Familial hypocalciuric hypercalcemia and Neonatal severe hyperparathyroidism. More than one hundred mutations were described in this gene. In addition to calcium, the receptor also interacts with several ions and polyamines. The CASR is a potential therapeutic target to treatment of diseases including hyperparathyroidism and osteoporosis, since its interaction with pharmacological compounds results in modulation of PTH secretion.

Surgical approach to the patient with familial hyperparathyroidism

Familial hyperparathyroidism encompasses the diagnoses of multiple endocrine neoplasia (MEN) type 1, MEN type 2A, and familial isolated primary hyperparathyroidism. All patients should undergo bilateral neck exploration and identification of all four or more parathyroid glands to evaluate for gross abnormalities. MEN-1 patients should have subtotal parathyroidectomy and cervical thymectomy because this operation achieves an appropriate balance between optimizing the potential for cure yet minimizing the risk of permanent hypocalcemia. However, MEN-2A patients may best be treated by selective resection of abnormal parathyroid glands, although some experts recommend a total parathyroidectomy and autotransplantation in the forearm. Familial isolated hyperparathyroidism is a rare disorder, and authors have described success in treatment with subtotal parathyroidectomy or limited adenoma resections. Some patients with familial isolated hyperparathyroidism also have jaw tumors, and members of these families are more likely to have parathyroid carcinoma. Concurrent cryopreservation of parathyroid tissue for all of these disorders is recommended if there is any concern for possible permanent hypoparathyroidism.

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.

A report of a national mutation testing service for the MEN1 gene: clinical presentations and implications for mutation testing

INTRODUCTION

Mutation testing for the MEN1 gene is a useful method to diagnose and predict individuals who either have or will develop multiple endocrine neoplasia type 1 (MEN 1). Clinical selection criteria to identify patients who should be tested are needed, as mutation analysis is costly and time consuming. This study is a report of an Australian national mutation testing service for the MEN1 gene from referred patients with classical MEN 1 and various MEN 1-like conditions.

RESULTS

All 55 MEN1 mutation positive patients had a family history of hyperparathyroidism, had hyperparathyroidism with one other MEN1 related tumour, or had hyperparathyroidism with multiglandular hyperplasia at a young age. We found 42 separate mutations and six recurring mutations from unrelated families, and evidence for a founder effect in five families with the same mutation.

DISCUSSION

Our results indicate that mutations in genes other than MEN1 may cause familial isolated hyperparathyroidism and familial isolated pituitary tumours.

CONCLUSIONS

We therefore suggest that routine germline MEN1 mutation testing of all cases of "classical" MEN1, familial hyperparathyroidism, and sporadic hyperparathyroidism with one other MEN1 related condition is justified by national testing services. We do not recommend routine sequencing of the promoter region between nucleotides 1234 and 1758 (Genbank accession no. U93237) as we could not detect any sequence variations within this region in any familial or sporadic cases of MEN1 related conditions lacking a MEN1 mutation. We also suggest that testing be considered for patients <30 years old with sporadic hyperparathyroidism and multigland hyperplasia.

Genetic analyses in familial isolated hyperparathyroidism: implication for clinical assessment and surgical management

OBJECTIVE

Familial isolated primary hyperparathyroidism (FIPH) can result from either incomplete expression of a syndromic form of familial primary hyperparathyroidism [multiple endocrine neoplasia type 1 (MEN 1), hyperparathyroidism-jaw tumour syndrome (HPT-JT) or familial hypocalciuric hypercalcaemia (FHH)] or still unrecognized causes. Design Genetic analyses of MEN1, HRPT2 and CASR genes in FIHP.

PATIENTS

Seven well-characterized Italian kindreds with FIHP, with negative clinical features for MEN 1, HPT-JT and FHH. The mean age (+/- SD) at diagnosis was 45 +/- 17 years (range 18-70 years) in the probands and 42 +/- 18 years (range 15-69 years) in the other affected subjects.

MEASUREMENTS

Direct sequencing of germline DNA of the MEN1, HRPT2 and CASR genes from probands. The region of interest was amplified in some family members.

RESULTS

Germline MEN1 mutations were detected in three kindreds. Multiglandular involvement was found in all but one affected subject belonging to the three kindreds with MEN1 mutations. In these patients persistence/relapse of the disease was observed unless an extensive parathyroidectomy (excision of 3(1)/(2) glands) had been performed, with the exception of one patient, who is currently normocalcaemic 168 months after excision of two glands. No mutations of MEN1, HRPT2 and CASR genes were identified in the remaining four families.

CONCLUSIONS

MEN1 genotyping appears worthwhile in FIHP families, as the finding of mutation(s) may predict multiglandular involvement and therefore have practical surgical implications, and prompt further investigation in the family, with the possibility of identifying new cases and beginning a programme of periodic surveillance for emergence of tumours in all carriers.

Das familiäre Nebenschilddrüsenkarzinom

In contrast to primary hyperparathyroidism, parathyroid carcinoma is a rare disease. In patients with hyperparathyroidism jaw tumor (HPT-JT) syndrome, caused by germline mutations in HRPT2, the development of parathyroid carcinoma is estimated to be 10-15%. This review summarizes the clinical and molecular genetic data of about 100 patients in the literature and three of our own cases. Unfortunately, osteofibromas, which might enable timely diagnosis of HPT-JT syndrome, occur in only about 30% of patients; about 80% have uniglandular disease. Based on the current data, a general recommendation to perform prophylactic parathyroidectomy cannot be given. However, thorough screening of patients at risk is mandatory. Of note in patients thought to have sporadic parathyroid carcinoma, germline HRPT2 mutations are found in up to 20%. Hence, any patient with parathyroid carcinoma should undergo HRPT2 mutation analysis.

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.

Clinical testing for multiple endocrine neoplasia type 1 in a DNA diagnostic laboratory

PURPOSE

Based on results of diagnostic MEN1 testing, we have attempted to further define the mutational spectrum of the MEN1 gene and the clinical features most frequently associated with MEN1 mutations.

METHODS

Mutation testing was performed on blood samples by PCR amplification and sequencing of exons 2 to 10 of the MEN1 gene and the corresponding intron-exon junctions. Pedigree phenotypic information was obtained by written questionnaire.

RESULTS

Among 288 presumably unrelated pedigrees, 73 independent mutations were found in 89 families. Five mutations were found in 2 pedigrees, and 4 mutations were seen in more than 2 pedigrees. There were 17 nonsense mutations (23.3%), 2 in-frame deletions (2.7%), 18 frameshift-deletion mutations (24.7%), 10 frameshift-insertion or -duplication mutations (13.7%), 13 splice-site mutations (17.8%), and 13 presumptive missense mutations (17.8%). Thirty-nine of 56 pedigrees with parathyroid and pancreatic islet neoplasia tested positive, compared with 4/24 and 8/32 pedigrees affected with hyperparathyroidism or hyperparathyroidism and pituitary tumors. MEN1 mutations were found in 6/20 sporadic patients, all of whom had both parathyroid and pancreatic neoplasms. Of 14 mutation-negative sporadic patients, 10 exhibited hyperparathyroidism and pituitary tumors without islet cell neoplasia. Somatic mosaicism was detected in 1 sporadic patient.

CONCLUSION

Patients from pedigrees with hyperparathyroidism and pancreatic islet tumors are most likely to test positive for MEN1 mutations. Mutations are less often detected in patients from pedigrees with hyperparathyroidism alone or in combination with pituitary tumors without pancreatic islet neoplasia. Sporadic cases are less likely to test positive than familial cases, in part due to somatic mosaicism.

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.