Molecular Genetics of Parathyroid Disease

Lithium-associated hypercalcemia and hyperparathyroidism: A systematic review and meta-analysis

OBJECTIVES

We aimed to review and summarise the existing human literature on the association between lithium and hyperparathyroidism.

METHODS

A systematic literature search was carried out according to PRISMA guidelines (last search 27 February 2024), using MEDLINE, Web of Science, Embase and the Cochrane Library. A meta-analysis was performed to determine the prevalence of lithium-associated hypercalcemia (LAHca) in lithium-treated patients.

RESULTS

The pooled prevalence of LAHca based on total calcium and ionised calcium was comparable, at 3.17% and 4.23%, respectively. Calcium, and PTH if the patient is hypercalcaemic, is insufficiently measured in lithium-treated patients in clinical practice. Lithium use is associated with higher calcium and PTH levels, as well as a higher incidence of hyperparathyroidism. There is a high prevalence of multiglandular disease in lithium-associated hyperparathyroidism (LAH), with a pooled prevalence of 51.28%. Parathyroid surgery and cinacalcet are effective treatments for LAH. Regarding lithium discontinuation, there is anecdotal but conflicting evidence suggesting that it can result in the resolution of LAH in selected cases.

CONCLUSIONS

Lithium treatment increases the risk of hyperparathyroidism, a treatable complication with a pooled prevalence of around 4%, compared to 0.5% in the healthy population.

Imaging Recommendations for Diagnosis and Management of Primary Parathyroid Pathologies: A Comprehensive Review

Parathyroid pathologies are suspected based on the biochemical alterations and clinical manifestations, and the predominant roles of imaging in primary hyperparathyroidism are localisation of tumour within parathyroid glands, surgical planning, and to look for any ectopic parathyroid tissue in the setting of recurrent disease. This article provides a comprehensive review of embryology and anatomical variations of parathyroid glands and their clinical relevance, surgical anatomy of parathyroid glands, differentiation between multiglandular parathyroid disease, solitary adenoma, atypical parathyroid tumour, and parathyroid carcinoma. The roles, advantages and limitations of ultrasound, four-dimensional computed tomography (4DCT), radiolabelled technetium-99 (99mTc) sestamibi or dual tracer 99mTc pertechnetate and 99mTc-sestamibi with or without single photon emission computed tomography (SPECT) or SPECT/CT, dynamic enhanced magnetic resonance imaging (4DMRI), and fluoro-choline positron emission tomography (18F-FCH PET) or [11C] Methionine (11C -MET) PET in the management of parathyroid lesions have been extensively discussed in this article. The role of fluorodeoxyglucose PET (FDG-PET) has also been elucidated in this article. Management guidelines for parathyroid carcinoma proposed by the American Society of Clinical Oncology (ASCO) have also been described. An algorithm for management of parathyroid lesions has been provided at the end to serve as a quick reference guide for radiologists, clinicians and surgeons.

Massive 4-Gland Parathyroid Hyperplasia Initially Detected as a Parathyroid Adenoma

Parathyroid adenoma (PA) and parathyroid hyperplasia (PH) are common causes of primary hyperparathyroidism (PHPT), for which the only definitive treatment is surgery. Abnormalities in the parathyroid glands can be identified with various imaging modalities including ultrasound (US), sestamibi scan (MIBI), 4-dimensional computed tomography (4D-CT), and positron emission tomography/computed tomography (PET/CT). While it is not uncommon for parathyroid pathology to be undetected on imaging, this is more typical of low-volume hyperplasia and smaller-sized adenomas. We present the case of a 65-year-old man with PHPT who initially had a solitary parathyroid mass detected by US, but who was ultimately discovered to have massive PH with hyperplastic glands not visualized on US or MIBI. This atypical presentation may help guide providers in decisions on ordering and interpreting various imaging modalities for patients with PHPT. In this case, 4D-CT was the only modality in which large hyperplastic glands were identified, suggesting superior sensitivity. This case also highlights the importance of intraoperative parathyroid hormone testing to aid in diagnostic prediction.

Ectopic PTH-producing parathyroid cyst inside the thymus: a case report

BACKGROUND

The hallmark of hyperparathyroidism is hypersecretion of parathyroid hormone (PTH) which results in hypercalcemia and hypophosphatemia. While hypercalcemia due to malignancy is often brought about by PTH-related protein in adults, PTH-producing tumors are quite rare in clinical practice. Additionally, from the point of embryology, it is very difficult to examine ectopic PTH-producing tissue such as ectopic parathyroid glands. Furthermore, clear histopathological criteria are not present.

CASE PRESENTATION

A 57-year-old woman was referred to our hospital for hypercalcemia. Her parathyroid hormone (PTH) level was elevated, but there were no enlarged parathyroid glands. Although 99mTc-MIBI confirmed a localized and slightly hyperfunctioning parathyroid tissue in the anterior mediastinum, it was not typical as hyperfunctioning parathyroid. We finally diagnosed her as ectopic PTH-producing cyst-like tumor with venous sampling of PTH. She underwent anterosuperior mediastinal ectopic PTH-producing cyst-like tumor resection. It is noted that intact-PTH concentration of the fluid in the cyst was very high (19,960,000 pg/mL). Based on histopathological findings, we finally diagnosed her as ectopic PTH-producing parathyroid cyst inside the thymus. After resection of anterosuperior mediastinal thymus including ectopic PTH-producing parathyroid cyst, calcium and intact-PTH levels were decreased, and this patient was discharged without any sequelae.

CONCLUSIONS

We should know the possibility of superior mediastinal ectopic PTH-producing parathyroid cyst inside the thymus among subjects with ectopic PTH-producing parathyroid glands. Particularly when the cyst is present in the superior mediastinum, it is necessary to do careful diagnosis based on not only positive but also negative findings in 99mTc-MIBI. It is noted that the patient's bloody fluid in the cyst contained 19,960,000 pg/mL of intact-PTH, and its overflow into blood stream resulted in hyperparathyroidism and hypercalcemia. Moreover, in such cases, the diagnosis is usually confirmed after through histological examination of ectopic PTH-producing parathyroid glands. We think that it is very meaningful to let clinicians know this case.

Multiglandular Parathyroid Disease

Introduction: Multiglandular parathyroid disease (MGD) is an uncommon cause of primary hyperparathyroidism (pHPT) and has been reported in the literature in 8–33% of patients with pHPT. The aim of our study was to review the clinical characteristics and management of MGD and evaluation of surgical treatment failures. Methods: We performed a retrospective study of 163 patients with pHPT undergoing parathyroidectomy (PTX) at the Department of General and Endocrine Surgery between 1983 and 2018. All these patients were diagnosed with MGD. This group of patients was compared with a group of 856 patients with solitary disease operated for pHPT in the same period. Results: Among 163 patients—127 (79%) of them had two lesions, 28 (16%) had three, and 8 (5%) four. They were prevalently women over the age of 50. The diagnosis was based on PTH and ionized calcium studies and used sestamibi technetium-99m scintigraphy (MIBI) as well for us. Treatment was surgical. Conclusions: Parathyroidectomy (PTX) for multiglandular parathyroid disease (MGD) is associated with a higher operative risk of failure compared to solitary disease. Preoperative diagnosis and localization of the parathyroid glands is an extremely important element of treatment. Diagnosis is based on PTH and calcium levels. Ultrasonography (USG), MRI, and scintigraphy are very helpful in diagnosis. Mediastinal multiglandular parathyroid disease (MGD) is associated with increased surgical treatment failures. The treatment is surgical and consists of the removal of the masses or complete parathyroidectomy. Based on this study, we support the existence of multiple adenomas and advocate the removal of only macroscopically enlarged parathyroid glands in patients with primary hyperparathyroidism.

Immunohistochemical Profile of Parathyroid Tumours: A Comprehensive Review

Immunohistochemistry remains an indispensable tool in diagnostic surgical pathology. In parathyroid tumours, it has four main applications: to detect (1) loss of parafibromin; (2) other manifestations of an aberrant immunophenotype hinting towards carcinoma; (3) histogenesis of a neck mass and (4) pathogenetic events, including features of tumour microenvironment and immune landscape. Parafibromin stain is mandatory to identify the new entity of parafibromin-deficient parathyroid neoplasm, defined in the WHO classification (2022). Loss of parafibromin indicates a greater probability of malignant course and should trigger the search for inherited or somatic CDC73 mutations. Aberrant immunophenotype is characterised by a set of markers that are lost (parafibromin), down-regulated (e.g., APC protein, p27 protein, calcium-sensing receptor) or up-regulated (e.g., proliferation activity by Ki-67 exceeding 5%) in parathyroid carcinoma compared to benign parathyroid disease. Aberrant immunophenotype is not the final proof of malignancy but should prompt the search for the definitive criteria for carcinoma. Histogenetic studies can be necessary for differential diagnosis between thyroid vs. parathyroid origin of cervical or intrathyroidal mass; detection of parathyroid hormone (PTH), chromogranin A, TTF-1, calcitonin or CD56 can be helpful. Finally, immunohistochemistry is useful in pathogenetic studies due to its ability to highlight both the presence and the tissue location of certain proteins. The main markers and challenges (technological variations, heterogeneity) are discussed here in the light of the current WHO classification (2022) of parathyroid tumours.

Analyzing Genetic Differences Between Sporadic Primary and Secondary/Tertiary Hyperparathyroidism by Targeted Next-Generation Panel Sequencing

Secondary hyperparathyroidism (SHPT) is characterized by excessive serum parathyroid hormone levels in response to decreasing kidney function, and tertiary hyperparathyroidism (THPT) is often the result of a long-standing SHPT. To date, several genes have been associated with the pathogenesis of primary hyperparathyroidism (PHPT). However, the molecular genetic mechanisms of uremic hyperparathyroidism (HPT) remain uncharacterized. To elucidate the differences in genetic alterations between PHPT and SHPT/THPT, the targeted next-generation sequencing of genes associated with HPT was performed using DNA extracted from parathyroid tissues. As a result, 26 variants in 19 PHPT or SHPT/THPT appeared as candidate pathogenic mutations, which corresponded to 9 (35%) nonsense, 8 (31%) frameshift, 6 (23%) missense, and 3 (11%) splice site mutations. The MEN1 (23%, 6/26), ASXL3 (15%, 4/26), EZH2 (12%, 3/26), and MTOR (8%, 2/26) genes were frequently mutated. Sixteen of 25 patients with PHPT (64%) had one or more mutations, whereas 3 (21%) of 21 patients with SHPT/THPT had only 1 mutation (p = 0.001). Sixteen of 28 patients (57%) with parathyroid adenoma (PA) had one or more mutations, whereas 3 of 18 patients (17%) with parathyroid hyperplasia (PH) had just one mutation (p = 0.003). Known driver mutations associated with parathyroid tumorigenesis such as CCND1/PRAD1, CDC73/HRPT2, and MEN1 were identified only in PA (44%, 7/16 with mutations). Our results suggest that molecular genetic abnormalities in SHPT/THPT are distinct from those in PHPT. These findings may help in analyzing the molecular pathogenesis underlying uremic HPT development.

Genetic Alteration Profiles and Clinicopathological Associations in Atypical Parathyroid Adenoma

Genomic aberrations associated with atypical parathyroid adenoma (AA) are poorly understood. Thus, herein, we sought to expand our current understanding of the molecular basis of atypical parathyroid adenomas. We analyzed 134 samples that had been surgically obtained from parathyroid tumors, including parathyroid carcinomas, atypical parathyroid adenomas, and parathyroid adenomas. The tumors were harvested from formalin-fixed, paraffin-embedded tissues. Fifteen tumor-related genes from recently published genome sequencing data were subjected to targeted sequencing analysis, and an average sequencing depth of 500x was achieved. Sixteen (16/50, 32%) AA tumors harbored at least one of the following genomic alterations: CDC73 (12, 24%), EZH2 (4, 8%), HIC1 (1, 2%), and CDKN2A (1, 2%). Our study identified, for the first time, a relatively high frequency of genomic alterations in patients with AA in a Chinese population. This suggests that AA arises de novo, rather than developing from a parathyroid adenoma. Altogether, these findings will improve our understanding of the malignant potential of parathyroid tumors at the molecular level.

Parathyroidectomy for tertiary hyperparathyroidism after second kidney transplantation: a case report

Successful kidney transplantation usually resolves secondary hyperparathyroidism (SHPT). However, some patients fail to normalize, and their condition is often referred to as tertiary hyperparathyroidism (THPT). Surgical consensus on the timing of post-transplant parathyroidectomy (PTX) for THPT has not been reached. Herein, we report a case of a 58-year-old post-transplant woman, considering the concrete timing of PTX for both SHPT and THPT. She initiated hemodialysis with end-stage renal disease at the age of 24, and underwent first kidney transplantation at the age of 28. When peritoneal dialysis (PD) was induced due to the worsening kidney function at the age of 50, the serum intact parathyroid hormone (iPTH) level remarkably increased (2332 pg/mL). Although cinacalcet was administered, the patient's iPTH levels were not sufficiently suppressed for seven years. Diagnostic images including ultrasound, computed tomography, and ^99mTc-methoxyisobutylisonitrile scintigraphy indicated THPT as the reason for prolonged post-transplant hypercalcemia. Therefore, PTX was performed 14 months after the second transplantation. Histology showed nodular hyperplasia of all parathyroid glands, indicating autonomous secretion of parathyroid hormone. In general, patients with more severe THPT are recognized with more severe SHPT prior to transplantation during the dialysis period. We should consider a referral for surgery based on the individual risk factors. We recommend to perform parathyroidectomy earlier, before the kidney transplantation in the clinical suspicion of severe SHPT.

Minimally invasive parathyroidectomy guided by intraoperative parathyroid hormone monitoring (IOPTH) and preoperative imaging versus bilateral neck exploration for primary hyperparathyroidism in adults

BACKGROUND

Bilateral neck exploration (BNE) is the traditional approach to sporadic primary hyperparathyroidism. With the availability of the preoperative imaging techniques and intraoperative parathyroid hormone assays, minimally invasive parathyroidectomy (MIP) is fast becoming the favoured surgical approach.

OBJECTIVES

To assess the effects of minimally invasive parathyroidectomy (MIP) guided by preoperative imaging and intraoperative parathyroid hormone monitoring versus bilateral neck exploration (BNE) for the surgical management of primary hyperparathyroidism.

SEARCH METHODS

We searched CENTRAL, MEDLINE, WHO ICTRP and ClinicalTrials.gov. The date of the last search of all databases was 21 October 2019. There were no language restrictions applied.

SELECTION CRITERIA

We included randomised controlled trials comparing MIP to BNE for the treatment of sporadic primary hyperparathyroidism in persons undergoing surgery for the first time.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened titles and abstracts for relevance. Two review authors independently screened for inclusion, extracted data and carried out risk of bias assessment. The content expert senior author resolved conflicts. We assessed studies for overall certainty of the evidence using the GRADE instrument. We conducted meta-analyses using a random-effects model and performed statistical analyses according to the guidelines in the latest version of the Cochrane Handbook for Systematic Reviews of Interventions.

MAIN RESULTS

We identified five eligible studies, all conducted in European university hospitals. They included 266 adults, 136 participants were randomised to MIP and 130 participants to BNE. Data were available for all participants post-surgery up to one year, with the exception of missing data for two participants in the MIP group and for one participant in the BNE group at one year. Nine participants in the MIP group and 11 participants in the BNE group had missing data at five years. No study had a low risk of bias in all risk of bias domains. The risk ratio (RR) for success rate (eucalcaemia) at six months in the MIP group compared to the BNE group was 0.98 (95% confidence interval (CI) 0.94 to 1.03; P = 0.43; 5 studies, 266 participants; very low-certainty evidence). A total of 132/136 (97.1%) participants in the MIP group compared with 129/130 (99.2%) participants in the BNE group were judged as operative success. At five years, the RR was 0.94 (95% CI 0.83 to 1.08; P = 0.38; 1 study, 77 participants; very low-certainty evidence). A total of 34/38 (89.5%) participants in the MIP group compared with 37/39 (94.9%) participants in the BNE group were judged as operative success. The RR for the total incidence of perioperative adverse events was 0.50, in favour of MIP (95% CI 0.33 to 0.76; P = 0.001; 5 studies, 236 participants; low-certainty evidence). Perioperative adverse events occurred in 23/136 (16.9%) participants in the MIP group compared with 44/130 (33.9%) participants in the BNE group. The 95% prediction interval ranged between 0.25 and 0.99. These adverse events included symptomatic hypocalcaemia, vocal cord palsy, bleeding, fever and infection. Fifteen of 104 (14.4%) participants experienced symptomatic hypocalcaemia in the MIP group compared with 26/98 (26.5%) participants in the BNE group. The RR for this event comparing MIP with BNE at two days was 0.54 (95% CI 0.32 to 0.92; P = 0.02; 4 studies, 202 participants). Statistical significance was lost in sensitivity analyses, with a 95% prediction interval ranging between 0.17 and 1.74. Five out of 133 (3.8%) participants in the MIP group experienced vocal cord paralysis compared with 2/128 (1.6%) participants in the BNE group. The RR for this event was 1.87 (95% CI 0.47 to 7.51; P = 0.38; 5 studies, 261 participants). The 95% prediction interval ranged between 0.20 and 17.87. The effect on all-cause mortality was not explicitly reported and could not be adequately assessed (very low-certainty evidence). There was no clear difference for health-related quality of life between the treatment groups in two studies, but studies did not report numerical data (very low-certainty evidence). There was a possible treatment benefit for MIP compared to BNE in terms of cosmetic satisfaction (very low-certainty evidence). The mean difference (MD) for duration of surgery comparing BNE with MIP was in favour of the MIP group (-18 minutes, 95% CI -31 to -6; P = 0.004; 3 studies, 171 participants; very low-certainty evidence). The 95% prediction interval ranged between -162 minutes and 126 minutes. The studies did not report length of hospital stay. Four studies reported intraoperative conversion rate from MIP to open procedure information. Out of 115 included participants, there were 24 incidences of conversion, amounting to a conversion rate of 20.8%.

AUTHORS' CONCLUSIONS

The success rates of MIP and BNE at six months were comparable. There were similar results at five years, but these were only based on one study. The incidence of perioperative symptomatic hypocalcaemia was lower in the MIP compared to the BNE group, whereas the incidence of vocal cord paralysis tended to be higher. Our systematic review did not provide clear evidence for the superiority of MIP over BNE. However, it was limited by low-certainty to very low-certainty evidence.

Lithium-Associated Hypercalcemia: Pathophysiology, Prevalence, Management

BACKGROUND

Lithium-associated hypercalcemia (LAH) is an ill-defined endocrinopathy. The aim of the present study was to determine the prevalence of hypercalcemia in a cohort of bipolar patients (BP) with and without concomitant lithium treatment and to study surgical outcomes for lithium-associated hyperparathyroidism.

METHODS

Retrospective data, including laboratory results, surgical outcomes and medications, were collected from 313 BP treated with lithium from two psychiatric outpatient units in central Sweden. In addition, data were collected from 148 BP without lithium and a randomly selected control population of 102 individuals. Logistic regression was used to compare odds of hypercalcemia in these respective populations.

RESULTS

The prevalence of lithium-associated hypercalcemia was 26%. Mild hypercalcemia was detected in 87 out of 563 study participants. The odds of hypercalcemia were significantly higher in BP with lithium treatment compared with BP unexposed to lithium (adjusted OR 13.45; 95% CI 3.09, 58.55; p = 0.001). No significant difference was detected between BP without lithium and control population (adjusted OR 2.40; 95% CI 0.38, 15.41; p = 0.355). Seven BP with lithium underwent surgery where an average of two parathyroid glands was removed. Parathyroid hyperplasia was present in four patients (57%) at the initial operation. One patient had persistent disease after the initial operation, and six patients had recurrent disease at follow-up time which was on average 10 years.

CONCLUSION

The high prevalence of LAH justifies the regular monitoring of calcium homeostasis, particularly in high-risk groups. If surgery is necessary, bilateral neck exploration should be considered in patients on chronic lithium treatment. Prospective studies are needed.

Differential expression of miRNA199b-5p as a novel biomarker for sporadic and hereditary parathyroid tumors

MicroRNAs (miRNAs) are dysregulated in many tumors; however, miRNA regulation in parathyroid tumors remains poorly understood. To identify differentially expressed miRNAs between sporadic and hereditary parathyroid tumors and to analyze their correlation with clinicopathological features, a microarray containing 887 miRNAs was performed; then, the differentially expressed miRNAs were validated by qRT-PCR using 25 sporadic and 12 hereditary parathyroid tumors and 24 normal parathyroid tissue samples. A receiver operating characteristic curve (ROC) analysis was applied to evaluate the utility of the miRNAs for distinguishing parathyroid tumor types. Compared to the miRNAs in the normal parathyroid tissues, 10 miRNAs were differentially expressed between the sporadic and hereditary parathyroid tumors. Seven of these miRNAs (let-7i, miR-365, miR-125a-3p, miR-125a-5p, miR-142-3p, miR-193b, and miR-199b-5p) were validated in the parathyroid tumor samples. Among these miRNAs, only miR-199b-5p was differentially expressed (P < 0.001); miR-199b-5p was significantly downregulated and negatively associated with PTH levels (γ = −0.579, P = 0.002) in the sporadic tumors but was upregulated in the hereditary tumors. This miRNA showed 67% sensitivity and 100% specificity for distinguishing sporadic and hereditary parathyroid tumors. These results reveal altered expression of a miRNA between sporadic and hereditary parathyroid tumors and the potential role of miR-199b-5p as a novel biomarker for distinguishing these two types of parathyroid tumors.

Whole-Exome Sequencing Identifies Novel Recurrent Somatic Mutations in Sporadic Parathyroid Adenomas

Primary hyperparathyroidism is commonly caused by excess production of parathyroid hormone from sporadic parathyroid adenomas. However, the genetic architecture of sporadic primary hyperparathyroidism remains largely uncharacterized, especially in the Chinese population. To identify genetic abnormalities that may be involved in the etiology of sporadic parathyroid adenomas and to determine the mutation frequency of previously identified genes in the Chinese population, we performed whole-exome sequencing of 22 blood-tumor pairs from sporadic parathyroid adenomas. The most important finding is the recurrently mutated gene, ASXL3, which has never been reported in parathyroid tumors before. Moreover, we identified two different somatic mutations in the CDC73 gene and one somatic mutation in the EZH2 gene. The Y54X mutation in the CDC73 gene was previously identified in parathyroid carcinomas, which proved that parathyroid adenomas and carcinomas might possess similar molecular signatures. No mutations in the MEN1 or CCND1 genes were observed in our study. Thus, our data provide insights into the genetic pathogenesis of sporadic parathyroid adenomas and are valuable for the development of diagnostic and therapeutic approaches for sporadic primary hyperparathyroidism.

65 YEARS OF THE DOUBLE HELIX: Endocrine tumour syndromes in children and adolescents

As medicine is poised to be transformed by incorporating genetic data in its daily practice, it is essential that clinicians familiarise themselves with the information that is now available from more than 50 years of genetic discoveries that continue unabated and increase by the day. Endocrinology has always stood at the forefront of what is called today 'precision medicine': genetic disorders of the pituitary and the adrenal glands were among the first to be molecularly elucidated in the 1980s. The discovery of two endocrine-related genes, GNAS and RET, both identified in the late 1980s, contributed greatly in the understanding of cancer and its progression. The use of RET mutation testing for the management of medullary thyroid cancer was among the first and one of most successful applications of genetics in informing clinical decisions in an individualised manner, in this case by preventing cancer or guiding the choice of tyrosine kinase inhibitors in cancer treatment. New information emerges every day in the genetics or system biology of endocrine disorders. This review goes over most of these discoveries and the known endocrine tumour syndromes. We cover key genetic developments for each disease and provide information that can be used by the clinician in daily practice.

The surgical management of primary hyperparathyroidism: an updated review

Patients with primary hyperparathyroidism often present clinically asymptomatic with various biochemical compositions of serum calcium, parathyroid hormone, vitamin D and urinary calcium. Understanding the subtle differences in clinical and biochemical presentations is key for timely diagnosis and referral to an experienced parathyroid surgeon. Surgery remains the only option for cure of primary hyperparathyroidism, which now favors a directed parathyroidectomy with intra-operative adjuncts. However it is important to understand and revise the surgical approach for patients with hereditary conditions or nonlocalizing studies. Revised guidelines from the Fourth International Workshop on the Management of Asymptomatic Primary Hyperparathyroidism in 2013 and the American Association of Endocrine Surgeons in 2016 are reviewed in this paper for an updated review of this condition.

Recurrent Hyperparathyroidism Due to a Novel CDC73 Splice Mutation

The recognition of hereditary causes of primary hyperparathyroidism (pHPT) is important because clinical care and surveillance differ significantly between sporadic and hereditary pHPT. In addition, the increasing number of genetic tests poses a challenge to classify mutations as benign or pathogenic. Functional work-up of variants remains a mainstay to provide evidence for pathogenicity. We describe a 52-year-old male patient with recurrent pHPT since age 35 years. Despite several neck surgeries with complete parathyroidectomy, he experienced persistent pHPT, necessitating repeated surgery for a forearm autotransplant, which finally resulted in unmeasurable parathyroid hormone (PTH) levels. Genetic testing revealed a new CDC73 variant (c.238-8G>A [IVS2-8G>A]), initially classified as a variant of uncertain significance. Parathyroid tissue from the initial surgeries showed loss of heterozygosity. Using an RT-PCR approach, we show that the mutation leads to the use of a cryptic splice site in peripheral mononuclear cells. In addition, a minigene approach confirms the use of the cryptic splice site in a heterologous cell system. The novel c.238-8G>A CDC73 variant activates a cryptic splice site, and the functional data provided justify the classification as a likely pathogenic variant. Our results underscore the importance of functional work-up for variant classification in the absence of other available data, such as presence in disease-specific databases, other syndromic clinical findings, or family history. In addition, the presented case exemplifies the importance to consider a hereditary condition in young patients with pHPT, particularly those with multi-gland involvement. © 2017 American Society for Bone and Mineral Research.

Machine learning to identify multigland disease in primary hyperparathyroidism

BACKGROUND

20%-25% of patients with primary hyperparathyroidism will have multigland disease (MGD). Preoperatative imaging can be inaccurate or unnecessary in MGD. Identification of MGD could direct the need for imaging and inform operative approach. The purpose of this study is to use machine learning (ML) methods to predict MGD.

METHODS

Retrospective review of a prospective database. The ML platform, Waikato Environment for Knowledge Analysis, was used, and we selected models for (1) overall accuracy and (2) preferential identification of MGD. A review of imaging studies was performed on a cohort predicted to have MGD.

RESULTS

2010 patients met inclusion criteria: 1532 patients had single adenoma (SA) (76%) and 478 had MGD (24%). After testing many algorithms, we selected two different models for potential integration as clinical decision-support tools. The best overall accuracy was achieved using a boosted tree classifier, RandomTree: 94.1% accuracy; 94.1% sensitivity, 83.8% specificity, 94.1% positive predictive value, and 0.984 area under the receiver operating characteristics curve. To maximize positive predictive value of MGD prediction, a rule-based classifier, JRip, with cost-sensitive learning was used and achieved 100% positive predictive value for MGD. Imaging reviewed from the cohort of 34 patients predicted to have MGD by the cost-sensitive model revealed 39 total studies performed: 28 sestamibi scans and 11 ultrasounds. Only 8 (29%) sestamibi scans and 4 (36%) ultrasounds were correct.

CONCLUSIONS

ML methods can help distinguish MGD early in the clinical evaluation of primary hyperparathyroidism, guiding further workup and surgical planning.

MEN1 mutations and potentially MEN1-targeting miRNAs are responsible for menin deficiency in sporadic and MEN1 syndrome-associated primary hyperparathyroidism

Inherited, germline mutations of menin-coding MEN1 gene cause multiple endocrine neoplasia type 1 (MEN1), while somatic MEN1 mutations are the sole main driver mutations in sporadic primary hyperparathyroidism (PHPT), suggesting that menin deficiency has a central role in the pathogenesis of PHPT. MiRNAs are small, noncoding RNAs posttranscriptionally regulating gene expression. Our aim was to investigate both the role of MEN1 mutations and potentially MEN1-targeting miRNAs as the underlying cause of menin deficiency in MEN1-associated and sporadic PHPT tissues. Fifty six PHPT tissues, including 16 MEN1-associated tissues, were evaluated. Diagnosis of MEN1 syndrome was based on identification of germline MEN1 mutations. In silico target prediction was used to identify miRNAs potentially targeting MEN1. Menin expression was determined by immunohistochemistry while expression of miRNAs was analyzed by quantitative real-time PCR. Sporadic PHPT tissues were subjected to somatic MEN1 mutation analysis as well. Lack of nuclear menin was identified in all MEN1-associated and in 28% of sporadic PHPT tissues. Somatic MEN1 mutations were found in 25% of sporadic PHPTs. The sensitivity and specificity of menin immunohistochemistry to detect a MEN1 mutation were 86 and 87%, respectively. Expression levels of hsa-miR-24 and hsa-miR-28 were higher in sporadic compared to MEN1-associated PHPT tissues; however, no difference in miRNA levels occurred between menin-positive and menin-negative PHPT tissues. Menin deficiency is the consequence of a MEN1 mutation in most menin-negative PHPT tissues. Elevated expression of hsa-miR-24 and hsa-miR-28 mark the first epigenetic changes observed between sporadic and MEN1-associated PHPT.

Surgical management of a giant parathyroid adenoma through minimal invasive parathyroidectomy. A case report

•

While parathyroid adenomas account for approximately 80% of PHPT cases, they rarely present as giant parathyroid adenomas.

•

Preoperative workup diagnosed the patient with PHPT and helped in accurate localization of the hyperactive parathyroid gland.

•

Despite the size of the adenoma, it was successfully removed through minimal invasive parathyroidectomy, through a 2 cm incision.

•

Post-surgical recovery was uneventful with normalization of parathormone levels and the patient relieved of her symptoms.

Introduction

Primary hyperparathyroidism is a common endocrine disorder mostly associated to parathyroid adenomas. Although those tend to be small in size, rare cases of giant parathyroid adenomas may be present.

Case presentation

A 42 year old female was admitted in our department due to weakness and vague abdominal pain for the past 8 months. Preoperative laboratory exams indicated primary hyperparathyroidism as a cause to her symptomatology, with elevated values of parathormone and normal values of serum calcium. Ultrasound scan and 99 m Tc-MIBI of her cervical region uncovered a giant 3 × 2 cm parathyroid adenoma, located in the lower left thyroid lobe. Despite its size, the gland was successfully removed through implementation of minimal invasive parathyroidectomy. She was uneventfully discharged on the 1st postoperative day.

Discussion

Although a common reason for developing hyperparathyroidism, parathyroid adenomas may rarely present with exaggerated dimensions and weight. Physical examination is usually unremarkable, while patients may present with symptomatology associated with elevated calcium levels. Treatment of this medical condition consists of surgical removal of the pathologic parathyroid gland either by bilateral neck exploration or through minimal invasive parathyroidectomy. Preoperative localization plays an important role in the second case, since the method focuses on resection of a pre-op marked hyperactive parathyroid gland, through a small incision.

Conclusion

Clinicians must be alerted of hyperparathyroidism in patients presenting with calcium associated symptomatology. Diagnosis is straightforward through laboratory exams, while surgery offers the only permanent treatment option.

Molecular genetics and epigenetics of nonfamilial (sporadic) parathyroid tumours

Primary hyperparathyroidism (pHPT) is a common endocrine disease characterized by excessive secretion of parathyroid hormone and an increased level of serum calcium. Overall, 80-85% of pHPT cases are due to a benign, single parathyroid adenoma (PA), and 15% to multiglandular disease (multiple adenomas/hyperplasia). Parathyroid carcinoma (PC) is rare, accounting for <0.5-1% of pHPT cases. Secondary hyperparathyroidism (sHPT) is a complication of renal failure, with the development of parathyroid tumours and hypercalcaemia. Recurrent mutations in the MEN1 gene have been confirmed by the whole-exome sequencing in 35% of PAs, suggesting that non-protein-coding genes, regulatory elements or epigenetic derangements may also have roles in the majority of PAs. DNA translocations with cyclin D1 overexpression occur in PAs (8%). In PCs, mutations in CDC73/HRPT2 are common. Activation of the WNT/β-catenin signalling pathway (accumulation of nonphosphorylated β-catenin) by an aberrantly truncated LRP5 receptor has been seen for the majority of investigated PAs and sHPT tumours, and possibly by APC inactivation through promoter methylation in PCs. Promoter methylation of several other genes and repressive histone H3 lysine 27 trimethylation by EZH2 of the HIC1 gene may also contribute to parathyroid tumorigenesis. It is possible that a common pathway exists for parathyroid tumour development. CCND1 (cyclin D1) and EZH2 overexpression, accumulation of nonphosphorylated β-catenin and repression of HIC1 have all been observed to occur in PAs, PCs and sHPT tumours. In addition, hypermethylation has been observed for the same genes in PAs and PCs (e.g. SFRP1, CDKN2A and WT1). Whether β-catenin represents a 'hub' in parathyroid tumour development will be discussed.

Molecular pathways associated with transcriptional alterations in hyperparathyroidism

Hyperparathyroidism is characterized by the oversecretion of parathyroid hormone biochemically and increased cell proliferation histologically. Primary and secondary hyperparathyroidism exhibit distinct pathophysiology but share certain common microscopic features. The present study performed the first genome-wide expression analysis directly comparing the expression profile of primary and secondary hyperparathyroidism. Microarray gene expression analyses were performed in parathyroid tissues from 2 primary hyperparathyroidism patients and 3 secondary hyperparathyroidism patients. Unsupervised hierarchical clustering analysis identified two natural subgroups containing different types of hyperparathyroidism. Combined with additional data extracted from a publicly available database, a meta-signature was constructed to represent an intersection of two sets of differential expression profile. Multiple pathways were identified that are aberrantly regulated in hyperparathyroidism. In primary hyperparathyroidism, dysregulated pathways included cell adhesion molecules, peroxisome proliferator-activated receptor signaling pathway, and neuroactive ligand-receptor interaction. Pathways implicated in secondary hyperparathyroidism included tryptophan metabolism, tight junctions, renin-angiotensin system, steroid hormone biosynthesis, and O-glycan biosynthesis. The present study demonstrates that different pathophysiology is associated with differential gene profiling in hyperparathyroidism. Several pathways are involved in parathyroid dysregulation and may be future targets for therapeutic intervention.

5-Hydroxymethylcytosine discriminates between parathyroid adenoma and carcinoma

Background

Primary hyperparathyroidism is characterized by enlarged parathyroid glands due to an adenoma (80–85 %) or multiglandular disease (~15 %) causing hypersecretion of parathyroid hormone (PTH) and generally hypercalcemia. Parathyroid cancer is rare (<1–5 %). The epigenetic mark 5-hydroxymethylcytosine (5hmC) is reduced in various cancers, and this may involve reduced expression of the ten-eleven translocation 1 (TET1) enzyme. Here, we have performed novel experiments to determine the 5hmC level and TET1 protein expression in 43 parathyroid adenomas (PAs) and 17 parathyroid carcinomas (PCs) from patients who had local invasion or metastases and to address a potential growth regulatory role of TET1.

Results

The global 5hmC level was determined by a semi-quantitative DNA immune-dot blot assay in a smaller number of tumors. The global 5hmC level was reduced in nine PCs and 15 PAs compared to four normal tissue samples (p < 0.05), and it was most severely reduced in the PCs. By immunohistochemistry, all 17 PCs stained negatively for 5hmC and TET1 showed negative or variably heterogeneous staining for the majority. All 43 PAs displayed positive 5hmC staining, and a similar aberrant staining pattern of 5hmC and TET1 was seen in about half of the PAs. Western blotting analysis of two PCs and nine PAs showed variable TET1 protein expression levels. A significantly higher tumor weight was associated to PAs displaying a more severe aberrant staining pattern of 5hmC and TET1. Overexpression of TET1 in a colony forming assay inhibited parathyroid tumor cell growth.

Conclusions

5hmC can discriminate between PAs and PCs. Whether 5hmC represents a novel marker for malignancy warrants further analysis in additional parathyroid tumor cohorts. The results support a growth regulatory role of TET1 in parathyroid tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0197-2) contains supplementary material, which is available to authorized users.

Primary hyperparathyroidism

Primary hyperparathyroidism is a common endocrine disorder caused by overactivation of parathyroid glands resulting in excessive release of parathyroid hormone. The resultant hypercalcemia leads to a myriad of symptoms. Primary hyperparathyroidism may increase a patient's morbidity and even mortality if left untreated. During the last few decades, disease presentation has shifted from the classic presentation of severe bone and kidney manifestations to most patients now being diagnosed on routine labs. Although surgery is the only curative therapy, many advances have been made over the past decades in the diagnosis and the surgical management of primary hyperparathyroidism. The aim of this review is to summarize the characteristics of the disease, the work up, and the treatment options.

Sporadic multiple parathyroid gland disease--a consensus report of the European Society of Endocrine Surgeons (ESES)

BACKGROUND

Sporadic multiglandular disease (MGD) has been reported in literature in 8-33 % of patients with primary hyperparathyroidism (pHPT). This paper aimed to review controversies in the pathogenesis and management of sporadic MGD.

METHODS

A literature search and review was made to evaluate the level of evidence concerning diagnosis and management of sporadic MGD according to criteria proposed by Sackett, with recommendation grading by Heinrich et al. and Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. Results were discussed at the 6th Workshop of the European Society of Endocrine Surgeons entitled 'Hyperparathyroidism due to multiple gland disease: An evidence-based perspective'.

RESULTS

Literature reports no prospective randomised studies; thus, a relatively low level of evidence was achieved. Appropriate surgical therapy of sporadic MGD should consist of a bilateral approach in most patients. Unilateral neck exploration guided by preoperative imaging should be reserved for selected patients, performed by an experienced endocrine surgeon and monitored by intraoperative parathormone assay (levels of evidence III-V, grade C recommendation). There is conflicting or equally weighted levels IV-V evidence supporting that cure rates can be similar or worse for sporadic MGD than for single adenomas (no recommendation). Best outcomes can be expected if surgery is performed by an experienced parathyroid surgeon working in a high-volume centre (grade C recommendation). Levels IV-V evidence supports that recurrent/persistence pHPT occurs more frequently in patients with double adenomas hence in situations where a double adenoma has been identified, the surgeon should have a high index of suspicion during surgery and postoperatively for the possibility of a four-gland disease (grade C recommendation).

CONCLUSIONS

Identifying preoperatively patients at risk for MGD remains challenging, intraoperative decisions are important for achieving acceptable cure rates and long-term follow-up is mandatory in such patients.

Clinicopathological correlates of hyperparathyroidism

Hyperparathyroidism is a common endocrine disorder with potential complications on the skeletal, renal, neurocognitive and cardiovascular systems. While most cases (95%) occur sporadically, about 5% are associated with a hereditary syndrome: multiple endocrine neoplasia syndromes (MEN-1, MEN-2A, MEN-4), hyperparathyroidism-jaw tumour syndrome (HPT-JT), familial hypocalciuric hypercalcaemia (FHH-1, FHH-2, FHH-3), familial hypercalciuric hypercalcaemia, neonatal severe hyperparathyroidism and isolated familial hyperparathyroidism. Recently, molecular mechanisms underlying possible tumour suppressor genes (MEN1, CDC73/HRPT2, CDKIs, APC, SFRPs, GSK3β, RASSF1A, HIC1, RIZ1, WT1, CaSR, GNA11, AP2S1) and proto-oncogenes (CCND1/PRAD1, RET, ZFX, CTNNB1, EZH2) have been uncovered in the pathogenesis of hyperparathyroidism. While bi-allelic inactivation of CDC73/HRPT2 seems unique to parathyroid malignancy, aberrant activation of cyclin D1 and Wnt/β-catenin signalling has been reported in benign and malignant parathyroid tumours. Clinicopathological correlates of primary hyperparathyroidism include parathyroid adenoma (80-85%), hyperplasia (10-15%) and carcinoma (<1-5%). Secondary hyperparathyroidism generally presents with diffuse parathyroid hyperplasia, whereas tertiary hyperparathyroidism reflects the emergence of autonomous parathyroid hormone (PTH)-producing neoplasm(s) from secondary parathyroid hyperplasia. Surgical resection of abnormal parathyroid tissue remains the only curative treatment in primary hyperparathyroidism, and parathyroidectomy specimens are frequently encountered in this setting. Clinical and biochemical features, including intraoperative PTH levels, number, weight and size of the affected parathyroid gland(s), are crucial parameters to consider when rendering an accurate diagnosis of parathyroid proliferations. This review provides an update on the expanding knowledge of hyperparathyroidism and highlights the clinicopathological correlations of this prevalent disease.

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.

PTH-C1: a rat continuous cell line expressing the parathyroid phenotype

The lack of a continuous cell line of epithelial parathyroid cells able to produce parathyroid hormone (PTH) has hampered the studies on in vitro evaluation of the mechanisms involved in the control of parathyroid cell function and proliferation. The PT-r cell line was first established from rat parathyroid tissue in 1987, but these cells were known to express the parathyroid hormone-related peptide (Pthrp) gene, but not the Pth gene. In an attempt to subclone the PT-r cell line, a rat parathyroid cell strain was isolated and named PTH-C1. During 3 years, in culture, PTH-C1 cells maintained an epithelioid morphology, displaying a diploid chromosome number, a doubling time around 15 h during the exponential phase of growth, and parathyroid functional features. PTH-C1 cell line produces PTH and expresses the calcium sensing receptor (Casr) gene and other genes known to be involved in parathyroid function. Most importantly, the PTH-C1 cells also exhibit an in vitro secretory response to calcium. Altogether these findings indicate the uniqueness of the PTH-C1 cell line as an in vitro model for cellular and molecular studies on parathyroid physiopathology.

Recurrent ZFX mutations in human sporadic parathyroid adenomas

The molecular abnormalities leading to sporadic parathyroid adenomas, a common type of human endocrine neoplasm, are heterogeneous and incompletely understood. Using whole exome and direct sequencing of parathyroid adenoma DNA samples, we identified recurrent somatic mutations in the ZFX gene. ZFX is a member of Krueppel C2H2 type zinc finger protein family, was initially described as a homolog of ZFY, and has been implicated as a transcription factor regulating embryonic stem cell renewal. The ZFX mutations we identified were strikingly specific, focused in each tumor on one encoded residue in a hotspot of two consecutive highly conserved arginine residues (R786/787; arginine to glutamine, threonine or leucine) in a zinc finger domain near the C-terminus of the protein. The intragenic specificity of these recurrently selected mutations, their confirmed expression within the tumors, the absence of loss of heterozygosity, and the absence of these mutations among over 4000 ZFX alleles in the dbSNP137 database, strongly suggest a novel role for ZFX as a human proto-oncogene. Further, these observations highlight the mutated zinc-finger domain as a new focal point for understanding ZFX's normal and tumorigenic functions, and for development of molecularly-targeted therapeutics.

Genetic and epigenetic changes in sporadic endocrine tumors: parathyroid tumors

Parathyroid neoplasia is most commonly due to benign parathyroid adenoma but rarely can be caused by malignant parathyroid carcinoma. Evidence suggests that parathyroid carcinomas rarely, if ever, evolve through an identifiable benign intermediate, with the notable exception of carcinomas associated with the familial hyperparathyroidism-jaw tumor syndrome. Several genes have been directly implicated in the pathogenesis of typical sporadic parathyroid adenoma; somatic mutations in the MEN1 tumor suppressor gene are the most frequent finding, and alterations in the cyclin D1/PRAD1 oncogene are also firmly established molecular drivers of sporadic adenomas. In addition, good evidence supports mutation in the CDKN1B/p27 cyclin-dependent kinase inhibitor (CDKI) gene, and in other CDKI genes as contributing to disease pathogenesis in this context. Somatic defects in additional genes, including β-catenin, POT1 and EZH2 may contribute to parathyroid adenoma formation but, for most, their ability to drive parathyroid tumorigenesis remains to be demonstrated experimentally. Further, genetic predisposition to sporadic presentations of parathyroid adenoma appears be conferred by rare, and probably low-penetrance, germline variants in CDKI genes and, perhaps, in other genes such as CASR and AIP. The HRPT2 tumor suppressor gene is commonly mutated in parathyroid carcinoma.

The histone methyltransferase EZH2, an oncogene common to benign and malignant parathyroid tumors

Primary hyperparathyroidism (pHPT) resulting from parathyroid tumors is a common endocrine disorder with incompletely understood etiology. In renal failure, secondary hyperparathyroidism (sHPT) occurs with multiple tumor development as a result of calcium and vitamin D regulatory disturbance. The aim of this study was to investigate a potential role of the histone 3 lysine 27 methyltransferase EZH2 in parathyroid tumorigenesis. Parathyroid tumors from patients with pHPT included adenomas and carcinomas. Hyperplastic parathyroid glands from patients with HPT secondary to uremia and normal parathyroid tissue specimens were included in this study. Quantitative RT-PCR, western blotting, bisulfite pyrosequencing, colony formation assay, and RNA interference were used. EZH2 was overexpressed in a subset of the benign and in all malignant parathyroid tumors as determined by quantitative RT-PCR and western blotting analyses. Overexpression was explained by EZH2 gene amplification in a large fraction of tumors. EZH2 depletion by RNA interference inhibited sHPT-1 parathyroid cell line proliferation as determined by tritium-thymidine incorporation and colony formation assays. EZH2 depletion also interfered with the Wnt/β-catenin signaling pathway by increased expression of growth-suppressive AXIN2, a negative regulator of β-catenin stability. Indeed, EZH2 contributed to the total level of aberrantly accumulated transcriptionally active (nonphosphoylated) β-catenin in the parathyroid tumor cells. To our knowledge EZH2 gene amplification presents the first genetic aberration common to parathyroid adenomas, secondary hyperplastic parathyroid glands, and parathyroid carcinomas. This supports the possibility of a common pathway in parathyroid tumor development.

Germline and somatic mutations in cyclin-dependent kinase inhibitor genes CDKN1A, CDKN2B, and CDKN2C in sporadic parathyroid adenomas

The molecular pathogenesis of sporadic parathyroid adenomas is incompletely understood. The possible role of cyclin-dependent kinase inhibitor (CDKI) genes was raised by recognition of cyclin D1 as a parathyroid oncogene, identification of rare germline mutations in CDKI genes in patients with multiple endocrine neoplasia type 1; that in rodents, mutation in Cdkn1b caused parathyroid tumors; and subsequently through identification of rare predisposing germline sequence variants and somatic mutation of CDKN1B, encoding p27(kip1), in sporadic human parathyroid adenoma. We therefore sought to determine whether mutations/variants in the other six CDKI genes CDKN1A, CDKN1C, CDKN2A, CDKN2B, CDKN2C, and CDKN2D, encoding p21, p57, p14(ARF)/p16, p15, p18, and p19, respectively, contribute to the development of typical parathyroid adenomas. In a series of 85 sporadic parathyroid adenomas, direct DNA sequencing identified alterations in five adenomas (6 %): Two contained distinct heterozygous changes in CDKN1A, one germline and one of undetermined germline status; one had a CDKN2B germline alteration, accompanied by loss of the normal allele in the tumor (LOH); two had variants of CDKN2C, one somatic and one germline with LOH. Abnormalities of three of the mutant proteins were readily demonstrable in vitro. Thus, germline mutations/rare variants in CDKN1A, CDKN2B, and CDKN2C likely contribute to the development of a significant subgroup of common sporadic parathyroid adenomas, and somatic mutation in CDKN2C further suggests a direct role for CDKI alteration in conferring a selective growth advantage to parathyroid cells, providing novel support for the concept that multiple CDKIs can play primary roles in human neoplasia.

MEN1 intragenic deletions may represent the most prevalent somatic event in sporadic primary hyperparathyroidism

OBJECTIVE

Primary hyperparathyroidism (pHPT) is characterised by an inappropriate over production of parathyroid hormone and it is the most frequent pathological condition of the parathyroid glands. A minority of the cases belong to familial forms, but most of them are sporadic. The genetic alterations underlying the sporadic forms of pHPT remain poorly understood. The main goal of our study is to perform the molecular characterisation of a series of sporadic pHPT cases.

DESIGN AND METHODS

We have studied matched blood and tumour from 24 patients with pHPT, who went to a medical appointment in Hospital Pedro Hispano. Informed consent was obtained from all individuals. The MEN1, RET and CDKN1B molecular study was carried out in the germline DNA by PCR/SSCP and direct sequencing. Parathyroid tumours were further analysed by the same methods for MEN1, CDKN1B and CTNNB1 genetic alterations. The multiplex ligation-dependent probe amplification technique enabled the evaluation of MEN1 gene deletions. Protein expression for menin, cyclin D1, parafibromin, p27(Kip1), β-catenin and Ki-67 was conducted by immunohistochemistry.

RESULTS

The study of parathyroid tumours detected two somatic MEN1 mutations (c.249_252delGTCT and c.115_163del49bp) and revealed the presence of MEN1 intragenic deletions in 54% (13/24) of the tumours. In RET and CDKN1B genes only previously described, non-pathogenic variants were found. Cyclin D1 protein was overexpressed in 13% (3/24) of tumours.

CONCLUSIONS

These results suggest that MEN1 alterations, remarkably intragenic deletions, may represent the most prevalent genetic alteration in sporadic parathyroid tumours.

Evidence of a stabilizing mutation of β-catenin encoded by CTNNB1 exon 3 in a large series of sporadic parathyroid adenomas

Aberrant accumulation of β-catenin plays an important role in a variety of human neoplasms. This can be caused by stabilizing mutation of β-catenin (CTNNB1, exon 3) or by mutation or deregulated expression of other components of the WNT/β-catenin signaling pathway. Accumulation of non-phosphorylated active β-catenin has been reported to commonly occur in parathyroid adenomas from patients with primary hyperparathyroidism (pHPT), either due to the aberrantly spliced internally truncated WNT receptor LRP5 (LRP5Δ) or to a stabilizing mutation of β-catenin. The S37A mutation was reported to occur in 7.3 % in a single study of parathyroid adenomas, while in other studies no stabilizing mutations of β-catenin exon 3 were identified. The aim of this study was to determine the mutational frequency of the CTNNB1 gene, specifically exon 3 in a large series of parathyroid adenomas. One hundred and eighty sporadic parathyroid adenomas were examined for mutations in exon 3 of CTNNB1 by direct DNA sequencing, utilizing previously published primer sequences. The mutation S33C (TCT>TGT) was detected by direct-DNA sequencing of PCR fragments in 1 out of 180 sporadic parathyroid adenomas (0.68 %). Like serine 37, mutations of serine 33 have been reported in many neoplasms with resulting β-catenin stabilization, enhanced transcription, and oncogenic activities. Immunohistochemical analysis revealed an overexpression of the β-catenin protein in the lone mutant tumor. Taking also previous studies into account we conclude that activating mutations of the regulatory GSK-3β phosphorylation sites serine 33 and 37, encoded by CTNNB1 exon 3, rarely occur in parathyroid adenomas from patients with pHPT.

Diagnosis and management of parathyroid cancer

Parathyroid cancer is rare, but often fatal, as preoperative identification of malignancy against the backdrop of benign parathyroid disease is challenging. Advanced genetic, laboratory and imaging techniques can help to identify parathyroid cancer. In patients with clinically suspected parathyroid cancer, malignancy of any individual lesion is established by three criteria: demonstration of metastasis, specific ultrasonographic features, and a ratio >1 for the results of third-generation:second-generation parathyroid hormone assays. Positive findings for all three criteria dictate an oncological surgical approach, as appropriate radical surgery can achieve a cure. Mutation screening pinpoints associated conditions and asymptomatic carriers. Molecular profiling of tumour cells can identify high-risk features, such as differential expression of specific micro-RNAs and proteins, and germ line mutations in CDC73, but is unsuitable for preoperative assessment owing to the potential risks associated with biopsy. A validated, histopathology-based prognostic classification can identify patients in need of close follow-up and adjuvant therapy, and should prove valuable to stratify clinical trial cohorts: low-risk patients rarely die from parathyroid cancer, even on long-term follow-up, whereas 5-year mortality in high-risk patients is around 50%. This insight has improved the approach to parathyroid cancer by enabling risk-adapted surgery and follow-up.

Whole-exome sequencing studies of nonhereditary (sporadic) parathyroid adenomas

CONTEXT

Genetic abnormalities, such as those of multiple endocrine neoplasia type 1 (MEN1) and Cyclin D1 (CCND1) genes, occur in <50% of nonhereditary (sporadic) parathyroid adenomas.

OBJECTIVE

To identify genetic abnormalities in nonhereditary parathyroid adenomas by whole-exome sequence analysis.

DESIGN

Whole-exome sequence analysis was performed on parathyroid adenomas and leukocyte DNA samples from 16 postmenopausal women without a family history of parathyroid tumors or MEN1 and in whom primary hyperparathyroidism due to single-gland disease was cured by surgery. Somatic variants confirmed in this discovery set were assessed in 24 other parathyroid adenomas.

RESULTS

Over 90% of targeted exons were captured and represented by more than 10 base reads. Analysis identified 212 somatic variants (median eight per tumor; range, 2-110), with the majority being heterozygous nonsynonymous single-nucleotide variants that predicted missense amino acid substitutions. Somatic MEN1 mutations occurred in six of 16 (∼35%) parathyroid adenomas, in association with loss of heterozygosity on chromosome 11. However, no other gene was mutated in more than one tumor. Mutations in several genes that may represent low-frequency driver mutations were identified, including a protection of telomeres 1 (POT1) mutation that resulted in exon skipping and disruption to the single-stranded DNA-binding domain, which may contribute to increased genomic instability and the observed high mutation rate in one tumor.

CONCLUSIONS

Parathyroid adenomas typically harbor few somatic variants, consistent with their low proliferation rates. MEN1 mutation represents the major driver in sporadic parathyroid tumorigenesis although multiple low-frequency driver mutations likely account for tumors not harboring somatic MEN1 mutations.

Primary hyperparathyroidism in children and adolescents

Primary hyperparathyroidism (PHPT) is a common endocrine disorder in adults in whom the typical presentation is incidentally discovered as asymptomatic hypercalcemia. PHPT is much less common in children and adolescents, but has greater morbidity in this age group, as most young patients with PHPT will have symptomatic hypercalcemia or complications such as kidney stones, abdominal pain, and skeletal fragility. An important feature of PHPT in younger patients is the relatively high prevalence of germline inactivating mutations of the CASR gene, which encodes the calcium-sensing receptor. Biallelic CASR mutations cause neonatal severe hyperparathyroidism, a life-threatening condition that presents within days of life with marked hypercalcemia, respiratory distress, failure to thrive, and skeletal demineralization. By contrast, more common heterozygous CASR mutations are generally associated with a benign variant of PHPT termed familial hypocalciuric hypercalcemia. Appropriate management of PHPT in children and adolescents requires distinction between familial hypocalciuric hypercalcemia, which generally requires no specific treatment, and other forms of PHPT that are best treated by parathyroidectomy.

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.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

Cinacalcet as alternative treatment for primary hyperparathyroidism: achievements and prospects

Primary hyperparathyroidism (pHPT), which most frequently occurs asymptomatically, is a common endocrine disease associated with increased morbidity and mortality. The newly introduced management guidelines as well as the recent availability of the first calcimimetic offer a highly promising therapeutic option for patients with pHPT. Cinacalcet, the first available calcimimetic, increases the sensitivity of the calcium-sensing receptor (CaR) to circulating serum calcium, thereby safely reducing serum calcium and PTH concentrations in patients with mild-to-moderate pHPT, intractable disease, and also parathyroid carcinoma. Cinacalcet has proved efficient in short- and long-term controls of hypercalcemia and, though bone mineral density was not improved, the available data point to cinacalcet as the treatment of choice in non-operable patients with pHPT. These results encompass a wide spectrum of disease severity. Results are pending as to whether cinacalcet decreases mortality and morbidity in pHPT, confirmation of which would conclusively recommend this drug as a valid alternative to surgery.

Parathyroid tumors and related disorders

Primary hyperparathyroidism (P-HPT) is a common endocrine disorder that occurs as a result of adenomas (80-85%), hyperplasias (10-15%) or carcinomas (<1%) of the parathyroid glands. Molecular genetic analyses of heritable P-HPT syndromes have provided considerable insight into the understanding of sporadic parathyroid tumors and hyperplasias. This review will focus on the criteria for classification of parathyroid proliferative disorders and will highlight our understanding of these lesions at the molecular level. Advances in radiological imaging techniques together with the rapid intraoperative parathyroid hormone assay will be reviewed with respect to current treatment approaches for P-HPT.

Aberrant WNT/β-catenin signaling in parathyroid carcinoma

Background

Parathyroid carcinoma (PC) is a very rare malignancy with a high tendency to recur locally, and recurrent disease is difficult to eradicate. In most western European countries and United States, these malignant neoplasms cause less than 1% of the cases with primary hyperparathyroidism, whereas incidence as high as 5% have been reported from Italy, Japan, and India. The molecular etiology of PC is poorly understood.

Results

The APC (adenomatous polyposis coli) tumor suppressor gene was inactivated by DNA methylation in five analyzed PCs, as determined by RT-PCR, Western blotting, and quantitative bisulfite pyrosequencing analyses. This was accompanied by accumulation of stabilized active nonphosphorylated β-catenin, strongly suggesting aberrant activation of the WNT/β-catenin signaling pathway in these tumors. Treatment of a primary PC cell culture with the DNA hypomethylating agent 5-aza-2'-deoxycytidine (decitabine, Dacogen(r)) induced APC expression, reduced active nonphosphorylated β-catenin, inhibited cell growth, and caused apoptosis.

Conclusion

Aberrant WNT/β-catenin signaling by lost expression and DNA methylation of APC, and accumulation of active nonphosphorylated β-catenin was observed in the analyzed PCs. We suggest that adjuvant epigenetic therapy should be considered as an additional option in the treatment of patients with recurrent or metastatic parathyroid carcinoma.

Parathyroid carcinoma

Parathyroid carcinoma is a rare tumor that is prone to recurrence and poor local-regional control. Despite advances in technologies that have shown promise for accurate diagnosis, the mainstay of initial diagnosis remains pathologic analysis and clinical assessment. A surgeon's intraoperative analysis is important in managing patients with parathyroid carcinoma. If parathyroid carcinoma is suspected intraoperatively, a more aggressive surgical strategy should be implemented. This article presents a case series and summary of the existing parathyroid carcinoma literature.

Leptin: the link between overweight and primary hyperparathyroidism?

Primary hyperparathyroidism is one of the most common causes of hypercalcemia. Most cases result from sporadic benign monoclonal adenomas or hyperplasia. Increased body weight is consistently present in cohorts of patients with primary hyperparathyroidism. It has been shown that fat mass is the major determinant of serum parathyroid hormone levels independent of vitamin D status. Leptin, an adipocyte-derived hormone with mitogenic activity, regulates energy homeostasis and mineral metabolism. Serum leptin levels increase in parallel to the amount of adipose stores. Interestingly, a positive association between leptin and parathyroid hormone levels is observed. Patients with primary hyperparathyroidism have higher serum leptin levels than healthy subjects. In addition, leptin administration in mice increases circulating levels of parathyroid hormone. We hypothesize that leptin involves pathogenesis of primary hyperparathyroidism and represents a link between hyperparathyroidism and increased body weight.

Parathyroid Klotho and FGF-receptor 1 expression decline with renal function in hyperparathyroid patients with chronic kidney disease and kidney transplant recipients

Current studies suggest that short-term exposure of parathyroid glands to fibroblast growth factor 23 (FGF23) reduces parathyroid hormone secretion. However, patients with chronic kidney disease (CKD) develop secondary hyperparathyroidism despite high levels of serum FGF23, indicating a parathyroid FGF23 'resistance'. Here we analyzed the expression of the FGF23 receptors Klotho and FGF receptor 1 (FGFR1) in 88 hyperplastic parathyroid glands from 31 patients with CKD (including 21 renal allograft recipients), and their regulation in isolated bovine and human hyperplastic parathyroid cells. Glandular expression was variable, yet the Klotho and FGFR1 mRNA levels declined in parallel with the decreasing glomerular filtration rate, significantly decreasing over CKD stages. We found no association between the expression of Klotho, FGFR1, and the proliferation marker Ki67. In vitro treatment of bovine cells with FGF23 or calcium reduced the Klotho level, whereas active vitamin D(3) compounds increased its expression. Phosphate and parathyroid hormone had no effect. Treatment had less impact on Klotho in cultured human cells than in the bovine healthy cell model, whereas FGFR1 expression was induced in the hyperplastic cells. Thus parathyroid Klotho and FGFR1 decrease with declining renal function, possibly because of alterations in mineral metabolism related to the failing kidney. This could explain the observed parathyroid resistance to FGF23 in late CKD.

Analysis of aberrantly spliced HRPT2 transcripts and the resulting proteins in HPT-JT syndrome

The risk for parathyroid carcinoma is high in those with the HPT-JT syndrome. Parafibromin is a protein derived from HRPT2 gene and its inactivation has been coupled to familial form of parathyroid malignancy. We previously identified altered transcripts resulting from splice site mutation of the HRPT2 gene in a family with this syndrome. In the present work, we investigated the stability of the altered HRPT2 transcripts and translation products produced in the HPT-JT syndrome. We quantified the differentially expressed HRPT2 mRNAs using real-time RT-PCR and developed a novel monoclonal parafibromin antibody to study the expression of parafibromin in the HPT-JT syndrome. The relative quantification ratios of the wild type HRPT2 mRNA, 23 bp deleted HRPT2 mRNA, and 70 bp deleted HRPT2 mRNA in the HPT-JT syndrome were 0.68, 0.17 and 0.15, respectively. But endogenous parafibromin expression was not detectable in the HPT-JT syndrome carcinoma. The altered HRPT2 mRNAs resulting from the splice site mutation in the HPT-JT syndrome were stable, but their parafibromin translation products from the HPT-JT syndrome carcinoma were probably degraded rapidly. Additional studies that aim to fully characterize the consequences of altered HRPT2 mRNAs in HPT-JT syndrome are required to explore these possibilities.