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Genetic Analyses of the HRPT2 Gene in Primary Hyperparathyroidism: Germline and Somatic Mutations in Familial and Sporadic Parathyroid Tumors

Departments of Endocrinology and Metabolism (F.C., E.P., S.B., G.D., L.C., E.A., A.P., C.M.), Oncology, Section of Pathology (P.V.), and Surgery (P.B., P.M.), University of Pisa, 56124 Pisa, Italy; Endocrine and Metabolic Sciences, University of Genoa (E.G.), 16132 Genoa, Italy; and Nephrology Unit, Circolo Hospital and Macchi Foundation (G.C.), 21100 Varese, Italy

Address all correspondence and requests for reprints to: Dr. Filomena Cetani, Dipartimento di Endocrinologia e Metabolismo, Università di Pisa, Via Paradisa 2, 56124 Pisa, Italy. E-mail: cetani{at}endoc.med.unipi.it.

	Abstract

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
We investigated the involvement of the HRPT2 gene by loss of heterozygosity analysis and direct sequencing in a kindred with hyperparathyroidism-jaw tumor syndrome (HPT-JT) and three kindreds with familial isolated primary hyperparathyroidism (FIHP). Seven patients with sporadic parathyroid cancers and 35 with parathyroid adenomas with no family history of primary hyperparathyroidism or HPT-JT were also studied. A germline heterozygous substitution G to A was found in the donor splice site of intron 1 in one of the three FIHP families. No mutations were identified in the HPT-JT kindred. A somatic HRPT2 mutation was found in four of seven patients with parathyroid cancers, two of which were unreported frameshift mutations (195insT and 195insA) in exon 2. Consistent with recent findings, two of seven patients with sporadic parathyroid cancer had germline mutations. Four adenomas showed loss of heterozygosity at HRPT2, whereas a somatic HRPT2 mutation was found in one. In conclusion, we provide additional evidence for a strong association between HRPT2 gene mutations and sporadic parathyroid cancer. The finding that two of the seven patients with sporadic parathyroid cancer carried an HRPT2 germline mutation suggests that they might have occult HPT-JT. Our results also confirm the need for testing HRPT2 gene in FIHP families.

	Introduction

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
PRIMARY HYPERPARATHYROIDISM (PHPT) is one of the most common endocrine syndromes, especially in postmenopausal women, in whom it reaches a prevalence of 2–3% (1). PHPT is usually a sporadic disorder, but in a minority of cases (<10%), it is part of hereditary syndromes, namely multiple endocrine neoplasia types 1 and 2A (MEN1 and MEN2A), hyperparathyroidism-jaw tumor syndrome (HPT-JT), familial hypocalciuric hypercalcemia (FHH), or familial isolated hyperparathyroidism (FIHP). Sporadic PHPT results from a single parathyroid adenoma in 80–85% of cases, multiglandular hyperplasia in 15–20% of cases, and carcinoma in less than 1% of cases (2).

The molecular pathogenesis of MEN1 and MEN2A has been clarified over the past 10 yr, and, with a few exceptions, germline mutations of the MEN1 and the RET genes have been found to be responsible (3, 4, 5, 6). Recently, germline mutations of the HRPT2 gene have been identified in more than half of HPT-JT kindreds (7, 8, 9) and unexpectedly in about one fifth of patients with apparently sporadic parathyroid cancer (10). FIHP may be due to an incomplete expression of these syndromic forms or to other entities. Indeed, abnormalities of MEN1 (11, 12, 13, 14, 15, 16, 17), HRPT2 (7, 8, 18, 19, 20), and calcium-sensing receptor (CASR) (19, 20, 21) genes have all been reported in a minority of FIHP kindreds. However, the majority of FIHP cases have currently unrecognized causes.

The identification of genes responsible for the syndromic form of familial PHPT has increased our knowledge about parathyroid tumorigenesis. Overexpression of the cyclin D1/PRAD1 oncogene can be associated with sporadic parathyroid adenomas (22), whereas mutations of the MEN1 gene can be found in both familial (3) and sporadic (23, 24, 25) parathyroid tumors, but not in parathyroid cancers (26). A relatively high frequency (up to 15%) of parathyroid cancer has been reported in patients with HPT-JT (7, 27, 28, 29), which raised the possibility that HRPT2 gene abnormalities might be involved in the pathogenesis of sporadic parathyroid cancer. Indeed, studies of the HRPT2 gene have shown that both somatic and germline mutations are associated with the majority of these tumors, and that HRPT2 functions as a tumor suppressor gene (8, 10).

In the present study we investigated further the involvement of the HRPT2 gene in the pathogenesis of both familial and sporadic parathyroid tumors, including carcinomas. We found that HRPT2 mutations are present in the majority of parathyroid cancers, occasionally in FIHP families, and rarely in sporadic parathyroid adenomas.

	Patients and Methods

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
All patients gave their informed consent for genetic studies. The study was approved by our internal review board.

PHPT patients

The diagnosis of PHPT was based on increased total or ionized serum calcium [>10.2 mg/dl (>2.55 mmol/liter) and >5.28 mg/dl (>1.32 mmol/liter), respectively] and inappropriately elevated serum PTH levels (Table 1).

One HPT-JT and three unrelated FIHP kindreds were studied (Fig. 1 and Table 1). The proband of HPT-JT family (A) had the typical jaw tumor, and her sister had cystic kidney lesions. One FIHP kindred (D) has been previously linked to the HRPT2 locus (14). Subjects III-5 and III-6 of family D underwent parathyroidectomy elsewhere for PHPT and did not agree to participate in the study.

View larger version (20K): [in this window] [in a new window]   FIG. 1. Pedigrees and phenotypes of the HPT-JT (A) and FIHP (B–D) families. Women are indicated by circles, and men by squares. Filled symbols indicate members affected by hyperparathyroidism; open symbols indicate unaffected members; dotted symbols indicate individuals with unknown phenotype and genotype; dashed symbols indicate deceased family members. Family members are indicated by generation (Roman numbers) and individual (Arabic numbers). The proband is indicated by an arrow. Subjects III-5 and III-6 underwent parathyroidectomy elsewhere and did not agree to participate in the study.

	Sporadic parathyroid adenomas

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
The samples used in the present study were part of a series of 60 obtained from patients with sporadic PHPT with single gland disease previously evaluated for loss of heterozygosity (LOH) at 11q13 (25). Twenty showed LOH. Thirty-five of the remaining 40, characterized for being negative for LOH at 11q13, were studied. We could not study the remaining five tissue samples because they had been used for other experiments. No patient had a family history for PHPT. Follow-up after surgery ranged from 6 months to 9 yr (mean, 4.2 yr). All patients had normocalcemia during follow-up, with no evidence of recurrent disease.

	Sporadic parathyroid carcinomas

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
The clinical data of six of seven patients (no. 1–6) have been previously reported (30). Briefly, all patients underwent parathyroidetomy and afterward had evidence of either local recurrence (n = 5) or distant metastases (n = 4; three lung and one bone). The interval between the initial parathyroidectomy and the first recurrence of tumor ranged from 6 months to 3 yr (mean, 1.5 yr). The remaining patient (no. 7), recently referred to our clinic, had a diagnosis of parathyroid cancer at the age of 45 yr, and local recurrence and lung metastases developed later. The interval between the initial parathyroidectomy and the first recurrence was 12 yr. The patient always remained hypercalcemic [mean serum calcium, 15 mg/ml (3.75 mmol/liter)] during the follow-up, but no chemotherapy or external neck irradiation was administered. He died of cardiac failure at 62 yr. Intravenous pamidronate was used in most of these patients in an attempt to reduce the degree of hypercalcemia.

	Tissue samples

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
Thirty-five parathyroid adenomas from patients with sporadic PHPT, 10 specimens (six primary tumors and four lung metastases) from seven patients with parathyroid cancer, and five parathyroid adenomas from two FIHP kindreds were studied. Parathyroid samples from two additional familial cases were not available (see below). The sporadic and familial adenoma samples came from patients who underwent parathyroidectomy at the Department of Surgery of the University of Pisa. The cancer specimens were collected from patients undergoing parathyroid surgery in Pisa (n = 4), Genoa (n = 2), and Ferrara (n = 1).

All tissues were obtained at the time of surgery, immediately snap-frozen in liquid nitrogen, and stored at –80 C until use. Fresh tissue of three primary cancers (patients 2, 6, and 7) and one lung metastasis (patient 7) were not available, and paraffin-embedded tissues were used.

Histological examination of the adenoma samples showed a typical appearance, characterized by an encapsulated lesion consisting of small uniform cells arranged with a delicate capillary network. A rim of normal or atrophic parathyroid tissue was often evident outside the capsule. Parathyroid cancers showed a trabecular arrangement of tumor cells divided by thick fibrous bands, numerous mitotic figures, and blood vessel, capsular, and surrounding soft tissue invasion.

All parathyroid specimens were carefully reviewed by our pathologist (P.V.) to confirm the histological diagnosis by the use of homogeneous criteria, to eventually describe the presence of cystic features, and to check that all samples had a sufficient proportion of tumor cells for DNA analyses (>70%).

	Genetic studies

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
LOH analysis.

Genomic DNA was isolated from peripheral blood leukocytes and parathyroid tissue by standard proteinase K-sodium dodecyl sulfate digestion and the phenol/chloroform method. Allelic deletions of chromosome 1 were assessed in all sporadic parathyroid adenoma and cancer specimens and in five FIHP parathyroid tumors (families B and D; Table 1). Microsatellite markers flanking the HRPT2 gene (D1S215, D1S222, D1S428, D1S412, and D1S413) were initially used (14). In addition, two recently described intragenic HRPT2 polymorphisms in introns 10 and 14 were studied (10). Allelic deletions of chromosome 11 at 11q13 were assessed as described previously (25). Forward primers were conjugated with 5' fluorescent dye (Sigma Genosys Ltd., Pampisford, UK). PCR products were analyzed using an ABI PRISM 310 (Applied Biosystems, Foster City, CA) or Beckman Ceq 8000 sequencer (Beckman Coulter, Fullerton, CA). Data collection and analysis were performed with GENESCAN software (Applied Biosystems) and Fragment Analysis Module (Beckman Coulter).

Gene nucleotide sequence analysis.

All coding region as well as the exon-intron junctions of the HRPT2 gene (7) were PCR-amplified from the proband of kindreds and from tumor DNA samples, as described previously (7), with minimal modifications. Primer sequences are available on request. In addition, the coding region and exon-intron junctions of the MEN1 (all kindreds) (3) and CASR (families B and C) (31) genes were PCR-amplified from the proband. The region of interest (see Results) was also amplified in family members. PCR products were purified with the Concert Ready Purification kit (Invitrogen Life Technologies, Milan, Italy). Nucleotide sequences were determined on double strands at least twice by direct sequencing of the PCR products using a DNA sequencing kit (Dye Terminator Cycle Sequencing Ready Reaction, Applied Biosystems) and an automated DNA sequencer (ABI PRISM 310, Applied Biosystems). The region of interest was also amplified and sequenced in 50 unrelated normal individuals of Italian origin (100 chromosomes).

Where matched blood samples were available, we investigated whether the mutations identified were somatic or germline by sequencing the germline DNA.

	Results

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
LOH analysis

The results of LOH studies are summarized in Tables 1 and 2. Unless otherwise stated, the reported data were concordant for both intragenic and flanking HRPT2 microsatellite markers.

LOH analysis at HRPT2 and 11q13 was carried out in parathyroid tumors from two of the three FIHP kindreds (families B and D). All tumors were constitutionally heterozygous at both loci for at least one marker. LOH at HRPT2 locus, but not at 11q13, was found in two of the three members of family D and in the tumor of family B (Table 1). In the latter, LOH was identified only using intragenic markers.

Sporadic parathyroid adenomas and carcinomas

All tissues were informative at 1q24–32. LOH at HRPT2 was detected in four adenomas (11.4%; Fig. 2). Retention of heterozygosity was demonstrated in the remaining 31 adenomas. LOH at HRPT2 locus was found in eight cancer specimens of six patients (five primary tumors and three lung metastases; Table 2 and Fig. 3). The tumor sample of patient 1 was LOH positive only for intragenic markers. Retention of heterozygosity was present in the primary tumor and lung metastases of one patient (Table 2).

View larger version (40K): [in this window] [in a new window]   FIG. 2. Microsatellite polymorphism analysis using polymorphic DNA markers and automated sequence analysis of the HRPT2 gene. A, Parathyroid adenoma. Tumor DNA shows a biallelic inactivation of the gene due to LOH (left panels, arrows), associated with a somatic mutation at the splice site of intron 1 (IVS+1GA; right panels; reverse sequence). B, FIHP family D proband. There is a germline DNA mutation at the splice site of intron 1 (IVS+1GA; reverse sequence).

View larger version (29K): [in this window] [in a new window]   FIG. 3. LOH and mutations of the HRPT2 gene in patients with sporadic parathyroid cancer. A, Tumor DNA shows a biallelic inactivation of the gene due to LOH (left panels, arrows), associated with a somatic mutation (195insT) in exon 2 (right panels). B, Retained heterozygosity (left panels) and heterozygous mutation (right panels) in exon 7 of the HRPT2 gene (R234X) in tumor and germline DNAs from patient 2.

Familial cases. An unreported HRPT2 germline heterozygous substitution G to A was found in the donor splice site of intron 1 (IVS1+1GA) in the proband (IV-2) and affected members (III-3 and IV-4) of the FIHP family D (Table 1 and Fig. 2). The mutation was not detected in unaffected family members or 50 unrelated normal individuals of Italian origin. No mutations were identified in the HPT-JT kindred or in the other two FIHP families (B and C; Table 1). A known polymorphism (IVS12–86CT) was found in the HPT-JT kindred (8). Mutational analyses of MEN1 and CASR genes showed negative results (Table 1).

Sporadic parathyroid adenomas and carcinomas. The four adenomas showing LOH at HRPT2 gene were screened for mutations in tumor DNA, and only one had a mutation, a substitution G to A in the donor splice site of intron 1 (IVS1+1GA). This mutation was not detected in the patient’s germline DNA (Fig. 2).

All specimens from the seven patients with sporadic parathyroid cancer were screened for HRPT2 mutations. Four cases, all but one LOH-positive, showed a somatic HRPT2 mutation (Table 2). Primary tumors and lung metastases, if present, showed the same HRPT2 mutation (Fig. 3). Two were unreported frameshift mutations, a 1-bp insertion in exon 2 of HRPT2 (195insT and 195insA) that predict an alteration of the reading frame with truncation at codon 104 in exon 4. The other two mutations (700CT in exon 7 and 25CT in exon 1) resulted in a premature stop codon (R234X and R9X, respectively). These mutations have been previously reported in a parathyroid cancer (R234X) (10) and in an HPT-JT family (R9X) (7). Peripheral DNA was analyzed in all patients. Unexpectedly, this analysis showed that the R234X mutation was a germline mutation in patients 2 and 7 (Table 2 and Fig. 3). We cannot exclude a common ancestor among these two kindreds even though no connection was established between the genealogical trees of these patients. The remaining HRPT2 mutations were confined to the tumor DNA. The HRPT2 mutations described here were not found in 50 unrelated normal individuals of Italian origin.

	Discussion

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 
PHPT is commonly encountered as a sporadic disorder caused by parathyroid adenoma and, less frequently, by hyperplasia and carcinoma (2). Approximately 10% of patients have familial forms of PHPT. Syndromes with familial PHPT include MEN, FHH, and HPT-JT. It is still debated whether FIHP is a variant of MEN1 or HPT-JT, an atypical form of FHH, or a distinct genetic entity. The recent finding of inactivating mutations of the MEN1, CASR, and HRPT2 genes in FIHP families suggests that at least some kindreds may represent a variant of these syndromes (7, 8, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21). In this study we report the results of a mutational analysis of HRPT2 gene and LOH analysis at 1q24–32 in one HPT-JT family, three unrelated FIHP families, and a series of sporadic parathyroid adenomas and cancers.

Familial PHPT

No HRPT2 mutations were found in the HPT-JT family, but the absence of HRPT2 gene mutations does not exclude this diagnosis, which was based on clinical grounds. Indeed, HRPT2 mutations could be detected by Carpten et al. (7) in only 14 of 24 HPT-JT families, most of whom had full expression of HPT-JT and proven linkage to 1q24-q32. We could not perform LOH analysis at the HRPT2 locus in the tumor of the proband because the tumor DNA was not available. The possible involvement of as yet unidentified mutations in the HRPT2 promoter or other regulatory regions may be responsible for HPT-JT in HRPT2 mutation-negative kindreds.

Concerning FIHP families, an unreported inactivating mutation of the HRPT2 (IVS1+1GA) gene was found in family D, in which LOH at 1q24–32 was previously reported (14), suggesting that biallelic inactivation of HRPT2 is associated with the disease. This mutation is located in the donor splice site of intron 1 and leads to a truncated protein. The mutation was not detected in unaffected members or 50 unrelated normal individuals, suggesting that it had a pathogenetic role. We previously described this family as a variant of HPT-JT because of the following findings: 1) the presence of LOH at HRPT2 locus; 2) the presence of cystic lesions in the parathyroid tumors, reminiscent of the picture typically found in HPT-JT kindreds; and 3) the absence of kidney lesions and jaw tumor. The identification of an HRPT2 gene mutation in this family confirms that it can be classified as a variant of HPT-JT. Simonds et al. (18) proposed the term occult to classify kindreds identified as HPT-JT only on the basis of genetic analysis. It is well known that HPT-JT is associated with an increased risk of parathyroid carcinoma. Interestingly, two of the three patients of this family who underwent parathyroidectomy had an atypical adenoma, a lesion that may represent a low grade parathyroid carcinoma (32).

No mutations of the HRPT2 gene were detected in the remaining two FIHP families (B and C). However, LOH analysis of the HRPT2 gene in family B showed allelic loss, suggesting that this gene is involved. Microsatellite studies in family C were not performed because no parathyroid tissue was available. Genotyping of 1q markers could have been useful to rule out the possibility that mutations in an intron producing abnormal splicing or in the promoter of the gene could be involved. However, this analysis was not performed because of the small number of affected and unaffected siblings. Alternatively, these gene alterations could have been excluded by cDNA studies, but no parathyroid tissue (family B) was available for such experiments.

Previous studies in 55 FIHP families have identified four different HRPT2 mutations (Fig. 4). Three are germline mutations (679insAG in exon 7 and IVS2+1GC in intron 2, predicting a truncated protein, and L64P in exon 2, a missense mutation) found in three different families (8, 18, 20). The L64P mutation has also been reported recently in another family (18). The fourth is a somatic mutation (W43X, in exon 1, predicting a truncated protein) (7). The 679insAG mutation has been found in a sporadic parathyroid cancer (10). Our family as well as those reported by others (7, 8, 18, 20) lack the typical clinical manifestations of the HPT-JT syndrome.

View larger version (7K): [in this window] [in a new window]   FIG. 4. Distribution of HRPT2 gene mutations in FIHP families (no. 7, 8, 16, and 18). The mutation in bold is from the present study. IVS+1GA, 191TC (L64P), IVS2+1GC, and 679insAG are germline mutations. W43X is a somatic mutation.

One of the puzzling aspects of FIHP is the absence of some of the manifestations of the syndromic forms despite the fact that the same gene is affected. Several possible mechanisms might account for this finding. 1) There may be incomplete penetrance of some of the manifestations, such as the gnathic and renal features in HPT-JT (21, 33). 2) A difference in the spectrum of mutations: missense/in-frame deletion mutations may lead to incomplete MEN1 phenotype, whereas truncating or nonsense mutations are more frequently observed in the full-blown syndrome (3). A similar pattern of gene alterations was also suggested for HRPT2 mutations (20), but recent results from our and other groups (7, 8, 18, 19) have ruled out this possibility. 3) Different mutations of the same gene may result in various degree of structure change, and accordingly, the capability of the mutated protein of interacting with other proteins may be variously affected. Indeed, either naturally occurring or engineered MEN1 gene mutations have been shown to differently affect the binding of menin with JunD (34). 4) Influences from environmental factors and the presence of modifier genes may contribute to phenotypic variations, as reported in familial adenomatous polyposis (35).

Sporadic parathyroid adenomas and carcinomas

HRPT2 gene mutations were found in six of seven patients with parathyroid cancer, confirming the results of previous studies (8, 10). No specimen showed a cystic pattern, which is a feature of parathyroid lesion associated with HPT-JT. The mutations were located in exons 1, 2, and 7 and are predicted to prematurely truncate the protein. Five of the six mutated cancers also showed LOH, confirming that HRPT2 is a tumor suppressor gene (7). The remaining two cancers [no. 1 (no HRPT2 mutation, but LOH-positive) and no. 2 (HRPT2 mutated, but LOH-negative] could have had a second mutation in the intronic and/or regulatory region of HRPT2 gene. Two of our cancer patients had germline HRPT2 mutations despite the apparent sporadic occurrence of their disease. A similar finding of unsuspected germline mutations has been reported by Shattuck in three additional cases (10). These cancers may represent an occult form of HPT-JT, and clinical monitoring for jaw tumor and kidney lesions is advised. Alternatively, patients harboring HRPT2 germline mutations may represent familial cases of isolated parathyroid cancers. Genetic testing will be mandatory in these kindreds; analysis of their parents may establish whether these are new germline mutations and whether additional genetic studies are needed in all relatives or only in the offspring. Monitoring of serum calcium will be recommended in gene carriers to recognize early and treat appropriately a potential parathyroid cancer.

Four of 35 (11.4%) adenomas showed LOH at the HRPT2 locus, and a somatic HRPT2 mutation was identified in one. The histological reexamination confirmed that all LOH-positive adenomas were benign parathyroid tumors without cystic lesions. A similar percentage of LOH using markers flanking the HRPT2 locus was reported by Carpten et al. (7) and Howell et al. (8) in parathyroid adenomas, but mutations were detected in only two of the 48 cases studied by the former and in none of the 25 studied by the latter. Taken together, these data suggest that the HRPT2 gene has a minor role in benign parathyroid tumorigenesis and that another gene on chromosome 1 may be involved in LOH-positive tumors. As underlined above, mutations in noncoding or regulatory regions of the HRPT2 gene could not be excluded.

The strong association between HRPT2 mutations and parathyroid malignancy suggests the need for long-term monitoring of patients with benign parathyroid adenomas harboring HRPT2 mutations.

In conclusion, the results of the present study provide additional evidence for the linkage between HRPT2 gene mutations and sporadic parathyroid cancer. The finding that one third of our cancer patients carried an HRPT2 germline mutation suggests that these patients may have an occult HPT-JT syndrome. Our results also confirm the need for testing for the HRPT2 gene in FIHP families.

	Acknowledgments

 
We thank Prof. Silvano Presciuttini (Dipartimento di Patologia Sperimentale, Biotecnologie Mediche, Infettivologia e Epidemiologia of the University of Pisa) for referring the HPT-JT family and for the useful discussion, and Dr. Michele Marinò (Dipartimento di Endocrinologia e Metabolismo of the University of Pisa) for reading the manuscript. We also thank the families who graciously agreed to participate in the study.

	Footnotes

 
This work was supported by grants from the University of Pisa (Fondi di Ateneo per la Ricerca) and the Ministero dell’Istruzione, dell’Università e della Ricerca (Project: Studies of New Oncogenes Involved in Parathyroid Tumorigenesis).

Abbreviations: CASR, Calcium-sensing receptor; FHH, familial hypocalciuric hypercalcemia; FIHP, familial isolated hyperparathyroidism; HPT-JT, hyperparathyroidism-jaw tumor syndrome; LOH, loss of heterozygosity; MEN, multiple endocrine neoplasia; PHPT, primary hyperparathyroidism.

Received February 16, 2004.

Accepted July 29, 2004.

	References

Top Abstract Introduction Patients and Methods Sporadic parathyroid adenomas Sporadic parathyroid carcinomas Tissue samples Genetic studies Results Discussion References

 

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