PTH mutation with primary hyperparathyroidism and undetectable intact PTH

Genetic aspects underlying the normocalcemic and hypercalcemic phenotypes of primary hyperparathyroidism

PURPOSE

Hypercalcemic primary hyperparathyroidism (PHPT) is a common endocrine disorder that has been very well characterized. In contrast, many aspects of normocalcemic primary hyperparathyroidism (NPHPT) such as natural history, organ damage, and management are still matter of debate. In addition, both the pathophysiology and molecular basis of NPHPT are unclear. We investigated whether PHPT and NPHPT patient cohorts share the same pattern of genetic variation in genes known to be involved in calcium and/or bone metabolism.

RESEARCH DESIGN AND METHODS

Genotyping for 9 single nucleotide polymorphisms (SNPs) was performed by Real-Time PCR (TaqMan assays) on 27 NPHPT and 31 PHPT patients evaluated in a tertiary referral Center. The data of both groups were compared with 54 in house-controls and 503 subjects from the 1000 Genomes Project. All groups were compared for allele/haplotype frequencies, on a single locus, two loci and multi-locus basis.

RESULTS

The NPHPT group differed significantly at SNPs in OPG and ESR1. Also, the NPHPT cohort was peculiar for pairwise associations of genotypes and for the overrepresentation of unusual multilocus genotypes.

CONCLUSIONS

Our NPHPT patient set harbored a definitely larger quota of genetic diversity than the other samples. Specific genotypes may help in defining subgroups of NPHPT patients which deserve ad hoc clinical and follow-up studies.

The parathyroid glands and parathyroid hormone: Insights from PTH gene mutations

Nine mutations have been discovered in the parathyroid hormone (PTH) gene since it was initially sequenced in 1983. An autosomal dominant C18R mutation in the signal peptide was first reported in 1990, followed by an exon skipping mutation, leading to loss of exon 2 in 1992; the latter mutation prevents PTH biosynthesis, as exon 2 contains the initiation codon. The S23P and S23X mutations affecting the same residue were reported in 1999 and 2012, respectively, while in 2008, the somatic mutation, R83X, was detected in a parathyroid adenoma tissue sample from a patient with overt hyperparathyroidism. In 2013, the heterozygous p.Met1_Asp6del mutation was discovered incidentally in a case-control study, while another heterozygous mutation, M14K, was detected in the signal peptide 4 years later. In 2015, a homozygous R56C mutation was reported, and was the first hypoparathyroidism-causing mutation identified that affects the mature bioactive portion of PTH; this mutation has significantly contributed to the understanding of the molecular mechanisms involved in signal transduction through the PTH receptor. Recently, a novel homozygous S32P mutation was identified, which is also situated in the bioactive portion of PTH. The discovery of these nine mutations in the PTH gene and determination of the molecular mechanisms underlying their effects has provided deep insights into the synthesis, processing, and secretion of PTH. Future attempts to discover other such mutations will help elucidate as yet unknown functions of PTH, with potential clinical implications.

Structural pharmacology of PTH and PTHrP

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) regulate extracellular phosphate and calcium homeostasis as well as bone remodeling. PTH is a classic endocrine peptide hormone whose synthesis and negative feedback by multiple factors control release from the parathyroid glands. PTHrP is ubiquitously expressed (pre- and postnatally) and acts in an autocrine/paracrine manner. This review considers the structural pharmacology and actions of PTH and PTHrP, biological consequences of inherited mutations, engineered analogs that illuminate similarities and differences in physiologic actions, and targeted therapeutic opportunities.

Primary hyperparathyroidism: Disease of diverse genetic, symptomatic, and biochemical phenotypes

Genetic, symptomatic, and biochemical heterogeneity of patients with primary hyperparathyroidism (PHPT) has become apparent in recent years. An in-depth, evidence-based review of the phenotypes of PHPT was conducted. This review was intended to provide the resulting information to surgeons who operate on patients with hyperparathyroidism. This review revealed that the once relatively clear distinction between familial and sporadic PHPT has become more challenging by the finding of various germline mutations in patients with seemingly sporadic PHPT. On the one hand, the genetic and clinical characteristics of some syndromes in which PHPT is an important component are now better understood. On the other hand, knowledge is emerging about novel syndromes, such as the rare multiple endocrine neoplasia type IV (MEN4), in which PHPT occurs frequently. It also revealed that, currently, the classical array of symptoms of PHPT is seen rarely upon initial presentation for evaluation. More common are nonspecific, nonclassical symptoms and signs of PHPT. In areas of the world where serum calcium levels are checked routinely, most patients today are "asymptomatic" and they are diagnosed after an incidental finding of hypercalcemia; however, some of them have subclinical involvement of bones and kidneys, which is demonstrated on radiographs, ultrasound, and modern imaging techniques. Last, the review points out that there are three distinct biochemical phenotypes of PHPT. The classical phenotype in which calcium and parathyroid hormone levels are both elevated, and other disease presentations in which the serum levels of calcium or intact parathyroid hormone are normal. Today several, distinct phenotypes of the disease can be identified, and they have implications in the diagnostic evaluation and treatment of patients, as well as possible screening of relatives.

Hyperplastic thyroid nodule masquerading as parathyroid adenoma in a patient with tubercular lymphadenitis induced hypercalcaemia

Serum intact parathyroid hormone (iPTH) levels are high or high normal in patients with parathyroid adenoma. Rarely these patients can have normal or low serum iPTH values. With sandwich immunometric assays, an exceptionally high serum iPTH level can lead to falsely low measurement due to the 'hook effect'. Here, we describe the case of a 66-year-old female patient with PTH-independent hypercalcaemia which mimicked parathyroid adenoma. A multidisciplinary team approach helped in the diagnosis and management leading to complete recovery.

Novel Use of Calcimimetic Activity to Diagnose Primary Hyperparathyroidism in a Patient With Persistently Low-Normal Parathyroid Hormone Level

Primary hyperparathyroidism (PHPT) is the most common etiology of hypercalcemia in the ambulatory setting and usually presents with an intact parathyroid hormone (PTH) level that is elevated or inappropriately near the upper limit of the laboratory reference range. However, PHPT with low-normal PTH level is reported in the peer-reviewed literature, and this atypical presentation may delay diagnosis of PHPT. We present a case of PHPT with persistently low-normal PTH level in which the PTH dependence of hypercalcemia was demonstrated by the response to treatment with the calcimimetic agent cinacalcet.

Rare PTH Gene Mutations Causing Parathyroid Disorders: A Review

Since parathyroid hormone (PTH) was first isolated and its gene (PTH) was sequenced, only eight PTH mutations have been discovered. The C18R mutation in PTH, discovered in 1990, was the first to be reported. This autosomal dominant mutation induces endoplasmic reticulum stress and subsequent apoptosis in parathyroid cells. The next mutation, which was reported in 1992, is associated with exon skipping. The substitution of G with C in the first nucleotide of the second intron results in the exclusion of the second exon; since this exon includes the initiation codon, translation initiation is prevented. An S23P mutation and an S23X mutation at the same residue were reported in 1999 and 2012, respectively. Both mutations resulted in hypoparathyroidism. In 2008, a somatic R83X mutation was detected in a parathyroid adenoma tissue sample collected from a patient with hyperparathyroidism. In 2013, a heterozygous p.Met1_Asp6del mutation was incidentally discovered in a case-control study. Two years later, the R56C mutation was reported; this is the only reported hypoparathyroidism-causing mutation in the mature bioactive part of PTH. In 2017, another heterozygous mutation, M14K, was detected. The discovery of these eight mutations in the PTH gene has provided insights into its function and broadened our understanding of the molecular mechanisms underlying mutation progression. Further attempts to detect other such mutations will help elucidate the functions of PTH in a more sophisticated manner.

Intraoperative parathyroid hormone (PTH) testing in patients with primary hyperparathyroidism and PTH levels in the normal range

Background

Primary hyperparathyroidism is a common endocrine disorder. Hypercalcemia with normal PTH levels is very unusual and can lead to diagnostic difficulties. There are very few very few studies in the literature and all with limited numerical samples. The goal of the present study was to determine the real incidence and characteristics of primary hyperparathyroidism with normal PTH and to evaluate if intraoperative PTH testing is useful in these patients.

Methods

We performed a retrospective review of 314 patients who had undergone parathyroidectomy to treat primary hyperparathyroidism between January 2002 and December 2016. Patients were divided in two groups according to biochemical preoperative findings: in Group A were included patients with normal serum PTH, in Group B those with increased serum PTH.

Results

Nine patients (3.7%) were included in group A and 235 in group B. Patients in group A were younger (51.5 ± 12.9 years vs 59.6 ± 12.5); preoperative serum calcium and the incidence of coexisting thyroid disease were similar between the two groups. Symptomatic patients were more frequent in Group A (77.8% vs 39.1%; p = 0.048). There were no significant differences regarding preoperative localization studies and surgical procedure. Intraoperative PTH determination demonstrated sensitivity of 86% in group A and 97% in group B, specificity and positive predictive value of 100% in both the groups, negative predictive value of 67% in group A and 79% in group B. Histopathological examination demonstrated a single gland disease in 8 (88.9%) patients in group A and a multi gland disease in 1 (11.1%), in group B single gland disease was found in 218 (92.8%) patients and multi gland disease in 17 (7.2%). Unsuccessful surgery with persistent or recurrent hyperparathyroidism occurred in 1 (11.1%) patient in group A and 4 (1.7%) in group B.

Conclusions

Primary hyperparathyroidism with normal PTH is rare but physicians should be aware of this possibility in patients with hypercalcaemia. Patients with normal PTH levels are younger and more frequently symptomatic. Intraoperative PTH testing plays an important role in the operative management even in such patients.

Diagnosis, management, histology and genetics of sporadic primary hyperparathyroidism: old knowledge with new tricks

Primary hyperparathyroidism (pHPT) is a common endocrinopathy resulting from inappropriately high PTH secretion. It usually results from the presence of a single gland adenoma, multiple gland hyperplasia or rarely parathyroid carcinoma. All these conditions require different management, and it is important to be able to differentiate the underlined pathology, in order for the clinicians to provide the best therapeutic approach. Elucidation of the genetic background of each of these clinical entities would be of great interest. However, the molecular factors that control parathyroid tumorigenesis are poorly understood. There are data implicating the existence of specific genetic pathways involved in the emergence of parathyroid tumorigenesis. The main focus of the present study is to present the current optimal diagnostic and management protocols for pHPT as well as to review the literature regarding all molecular and genetic pathways that are to be involved in the pathophysiology of sporadic pHPT.

Autosomal Dominant PTH Gene Signal Sequence Mutation in a Family With Familial Isolated Hypoparathyroidism

CONTEXT

Familial isolated hypoparathyroidism (FIH) is a genetically heterogeneous disorder due to mutations of the calcium-sensing receptor (CASR), glial cells missing-2 (GCM2), guanine nucleotide binding protein α11 (GNA11), or parathyroid hormone (PTH) genes. Thus far, only four cases with homozygous and two cases with heterozygous mutations in the PTH gene have been reported.

OBJECTIVE

To clinically describe an FIH family and identify and characterize the causal gene mutation.

DESIGN

Genomic DNA of the family members was subjected to CASR, GCM2, GNA11, and PTH gene mutational analysis. Functional assays were performed on the variant identified.

PARTICIPANTS

Six subjects of a three-generation FIH family with three affected individuals having severe hypocalcemia and inappropriately low serum PTH.

RESULTS

No mutations were detected in the CASR, GCM2, and GNA11 genes. A heterozygous variant that segregated with the disease was identified in PTH gene exon 2 (c.41T>A; p.M14K). This missense variant, in the hydrophobic core of the signal sequence, was predicted in silico to impair cleavage of preproPTH to proPTH. Functional assays in HEK293 cells demonstrated much greater retention intracellularly but impaired secretion into the medium of the M14K mutant relative to wild type. The addition of the pharmacological chaperone, 4-phenylbutyric acid, led to a reduction of cellular retention and increased accumulation in the cell medium of the M14K mutant.

CONCLUSIONS

We report a heterozygous PTH mutation in an FIH family and demonstrate accumulation of the mutant intracellularly and its impaired secretion. An accurate genetic diagnosis in such hypoparathyroid patients is critical for appropriate treatment and genetic counseling.

Hypercalcemic Disorders in Children

Hypercalcemia is defined as a serum calcium concentration that is greater than two standard deviations above the normal mean, which in children may vary with age and sex, reflecting changes in the normal physiology at each developmental stage. Hypercalcemic disorders in children may present with hypotonia, poor feeding, vomiting, constipation, abdominal pain, lethargy, polyuria, dehydration, failure to thrive, and seizures. In severe cases renal failure, pancreatitis and reduced consciousness may also occur and older children and adolescents may present with psychiatric symptoms. The causes of hypercalcemia in children can be classified as parathyroid hormone (PTH)-dependent or PTH-independent, and may be congenital or acquired. PTH-independent hypercalcemia, ie, hypercalcemia associated with a suppressed PTH, is commoner in children than PTH-dependent hypercalcemia. Acquired causes of PTH-independent hypercalcemia in children include hypervitaminosis; granulomatous disorders, and endocrinopathies. Congenital syndromes associated with PTH-independent hypercalcemia include idiopathic infantile hypercalcemia (IIH), William's syndrome, and inborn errors of metabolism. PTH-dependent hypercalcemia is usually caused by parathyroid tumors, which may give rise to primary hyperparathyroidism (PHPT) or tertiary hyperparathyroidism, which usually arises in association with chronic renal failure and in the treatment of hypophosphatemic rickets. Acquired causes of PTH-dependent hypercalcemia in neonates include maternal hypocalcemia and extracorporeal membrane oxygenation. PHPT usually occurs as an isolated nonsyndromic and nonhereditary endocrinopathy, but may also occur as a hereditary hypercalcemic disorder such as familial hypocalciuric hypercalcemia, neonatal severe primary hyperparathyroidism, and familial isolated primary hyperparathyroidism, and less commonly, as part of inherited complex syndromic disorders such as multiple endocrine neoplasia (MEN). Advances in identifying the genetic causes have resulted in increased understanding of the underlying biological pathways and improvements in diagnosis. The management of symptomatic hypercalcemia includes interventions such as fluids, antiresorptive medications, and parathyroid surgery. This article presents a clinical, biochemical, and genetic approach to investigating the causes of pediatric hypercalcemia. © 2017 American Society for Bone and Mineral Research.

Genome-wide association study evaluating single-nucleotide polymorphisms and outcomes in patients with advanced stage serous ovarian or primary peritoneal cancer: An NRG Oncology/Gynecologic Oncology Group study

OBJECTIVE

This study evaluated single nucleotide polymorphisms (SNPs) associated with progression free (PFS) and overall survival (OS) in patients with advanced stage serous EOC.

METHODS

Patients enrolled in GOG-172 and 182 who provided specimens for translational research and consent were included. Germline DNA was evaluated with the Illumina's HumanOMNI1-Quad beadchips and scanned using Illumina's iScan optical imaging system. SNPs with allele frequency>0.05 and genotyping rate>0.98 were included. Analysis of SNPs for PFS and OS was done using Cox regression. Statistical significance was determined using Bonferroni corrected p-values with genomic control adjustment.

RESULTS

The initial GWAS analysis included 1,124,677 markers in 396 patients. To obtain the final data set, quality control checks were performed and limited to serous tumors and self-identified Caucasian race. In total 636,555 SNPs and 289 patients passed all the filters. The pre-specified statistical level of significance was 7.855e^-08. No SNPs met this criteria for PFS or OS, however, two SNPs were close to significance (rs10899426 p-2.144e^-08) (rs6256 p-9.774e^-07) for PFS and 2 different SNPs were identified (rs295315 p-7.536e^-07; rs17693104 p-7.734e^-07) which were close to significance for OS.

CONCLUSIONS

Using the pre-specified level of significance of 1×10^-08, we did not identify any SNPs of statistical significance for OS or PFS, however several were close. The SNP's identified in this GWAS study will require validation and these preliminary findings may lead to identification of novel pathways and biomarkers.

Genetics of parathyroid tumours

Primary hyperparathyroidism (PHPT), due to parathyroid tumours, may occur as part of a complex syndrome or as an isolated (nonsyndromic) disorder, and both forms can occur as familial (i.e. hereditary) or nonfamilial (i.e. sporadic) disease. Syndromic PHPT includes multiple endocrine neoplasia (MEN) types 1 to 4 (MEN1 to MEN4) and the hyperparathyroidism-jaw tumour (HPT-JT) syndrome. Syndromic and hereditary PHPT are often associated with multiple parathyroid tumours, in contrast to sporadic PHPT, in which single parathyroid adenomas are more common. In addition, parathyroid carcinomas may occur in ~15% of patients with the HPT-JT syndrome. MEN1 is caused by abnormalities of the MEN1 gene which encodes a tumour suppressor; MEN2 and MEN3 are due to mutations of the rearranged during transfection (RET) proto-oncogene, which encodes a tyrosine kinase receptor; MEN4 is due to mutations of a cyclin-dependent kinase inhibitor (CDNK1B); and HPT-JT is due to mutations of cell division cycle 73 (CDC73), which encodes parafibromin. Nonsyndromic PHPT, which may be hereditary and referred to as familial isolated hyperparathyroidism, may also be due to MEN1, CDC73 or calcium-sensing receptor (CASR) mutations. In addition, ~10% of patients presenting below the age of 45 years with nonsyndromic, sporadic PHPT may have MEN1, CDC73 or CASR mutations, and overall more than 10% of patients with PHPT will have a mutation in one of 11 genes. Genetic testing is available and of value in the clinical setting, as it helps in making the correct diagnosis and planning the management of these complex disorders associated with parathyroid tumours.

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.

A Homozygous [Cys25]PTH(1-84) Mutation That Impairs PTH/PTHrP Receptor Activation Defines a Novel Form of Hypoparathyroidism

Hypocalcemia and hyperphosphatemia are encountered in idiopathic hypoparathyroidism (IHP) and pseudohypoparathyroidism type Ib (PHP1B). In contrast to PHP1B, which is caused by resistance toward parathyroid hormone (PTH), the genetic defects leading to IHP impair production of this important regulator of mineral ion homeostasis. So far, only five PTH mutations were shown to cause IHP, each of which is located in the hormone's pre-pro leader segment and thus impair hormone secretion. In three siblings affected by IHP, we now identified a homozygous arginine-to-cysteine mutation at position 25 (R25C) of the mature PTH(1-84) polypeptide; heterozygous family members are healthy. Depending on the assay used for evaluating these patients, plasma PTH levels were either low or profoundly elevated, thus leading to ambiguities regarding the underlying diagnosis, namely IHP or PHP1B. Consistent with increased PTH levels, recombinant [Cys25]PTH(1-84) and wild-type PTH(1-84) were secreted equally well by transfected COS-7 cells. However, synthetic [Cys25]PTH(1-34) was found to have a lower binding affinity for the PTH receptor type-1 (PTH1R) than PTH(1-34) and consequently a lower efficiency for stimulating cAMP formation in cells expressing this receptor. Consistent with these in vitro findings, long-term infusion of [Cys25]PTH(1-34) resulted only in minimal calcemic and phosphaturic responses, despite readily detectable levels of [Cys25]PTH(1-34) in plasma. The mineral ion abnormalities observed in the three IHP patients are thus most likely caused by the inherited homozygous missense PTH mutation, which reduces bioactivity of the secreted hormone. Based on these findings, screening for PTH(1-84) mutations should be considered when clinical and laboratory findings are consistent with PHP1B, but GNAS methylation changes have been excluded. Differentiating between IHP and PHP1B has considerable implications for genetic counseling, therapy, and long-term outcome because treatment of IHP patients with inappropriately high doses of active vitamin D and calcium can contribute to development of nephrocalcinosis and chronic kidney disease.

An Essential Role for Parathyroid Hormone in Gill Formation and Differentiation of Ion-Transporting Cells in Developing Zebrafish

In vertebrates, parathyroid hormone (PTH) is important for skeletogenesis and Ca(2+) homeostasis. However, little is known about the molecular mechanisms by which PTH regulates skeleton formation and Ca(2+) balance during early development. Using larval zebrafish as an in vivo model system, we determined that PTH1 regulates the differentiation of epithelial cells and the development of craniofacial cartilage. We demonstrated that translational gene knockdown of PTH1 decreased Ca(2+) uptake at 4 days after fertilization. We also observed that PTH1-deficient fish exhibited reduced numbers of epithelial Ca(2+) channel (ecac)-expressing cells, Na(+)/K(+)-ATPase-rich cells, and H(+)-ATPase-rich cells. Additionally, the density of epidermal stem cells was decreased substantially in the fish experiencing PTH1 knockdown. Knockdown of PTH1 caused a shortening of the jaw and impeded the development of branchial arches. Results from in situ hybridization suggested that the expression of collagen 2a1a (marker for proliferating chondrocytes) was substantially reduced in the cartilage that forms the jaw and branchial aches. Disorganization of chondrocytes in craniofacial cartilage also was observed in PTH1-deficient fish. The results of real-time PCR demonstrated that PTH1 morphants failed to express the transcription factor glial cell missing 2 (gcm2). Coinjection of PTH1 morpholino with gcm2 capped RNA rescued the phenotypes observed in the PTH1 morphants, suggesting that the defects in PTH1-deficient fish were caused, at least in part, by the suppression of gcm2. Taken together, the results of the present study reveal critical roles for PTH1 in promoting the differentiation of epidermal stem cells into mature ionocytes and cartilage formation during development.

Functional activities of mutant calcium-sensing receptors determine clinical presentations in patients with autosomal dominant hypocalcemia

OBJECTIVE

Autosomal dominant hypocalcemia (ADH) is a congenital isolated hypoparathyroidism caused by activating mutations in the calcium-sensing receptor (CASR) gene. The clinical features of ADH are heterogeneous; some patients are asymptomatic, and others show severe hypocalcemia with Bartter's syndrome. We therefore recruited 12 patients with ADH to clarify the determinants of their clinical presentation.

DESIGN AND METHODS

We studied two sporadic and 10 familial cases of ADH. Serum concentrations of calcium, intact PTH, and magnesium (Mg(2+)) were measured in each patient. Fractional excretion of Mg (FE(Mg)) was calculated in spot urine samples. A nuclear factor of activated T cells luciferase assay was used to analyze the responsiveness of each mutant CaSR to extracellular Ca(2+).

RESULTS

Genomic analysis revealed five known activating mutations and a novel mutation, E481K, in the CASR. Patients with the A843E, C131W, or F788C mutation showed hypomagnesemia with elevated FE(Mg). Intact PTH in these patients was consistently near the detection limit. In contrast, patients with the P221L, K47N, or E481K mutation exhibited normal Mg(2+) levels. In these patients, intact PTH increased in response to low calcium, and their maximum intact PTH exceeded the lower limit of the reference range. Functional analysis showed an association between the disease severity and the in vitro activity of the mutant CaSR.

CONCLUSIONS

The functional activity of mutant CaSR determines the serum Mg(2+) level, renal Mg(2+) handling, and intact PTH in patients with ADH. The presence of hypomagnesemia with elevated FE(Mg) may indicate the diagnosis of ADH among patients with PTH-deficient hypoparathyroidism.

Primary hyperparathyroidism with low intact PTH levels in a 14-year-old girl

CONTEXT

Primary hyperparathyroidism (PHPT) is usually associated with hypercalcemia and inappropriately elevated serum PTH.

OBJECTIVE

Our objective was to identify the reason(s) for a low serum intact PTH in a child with PHPT.

SUBJECT AND METHODS

A 14-yr-old Caucasian girl presented with pancreatitis, nephrolithiasis, hypercalcemia ranging from 13.2 to 17.5 mg/dl, and a low serum intact PTH. She had an ultrasound and technetium-99m-sestamibi scintigraphy confirming the presence of a parathyroid adenoma.

RESULTS

The preoperative serum intact PTH assays performed at Quest Diagnostics, Nichols Institute, were low even after serial dilutions, whereas the intraoperative turbo PTH assay was elevated at 3618 pg/ml. C-terminal and cyclase-activating PTH assays for PTH were also elevated. PTH gene sequence analysis performed from DNA extracted both from the parathyroid adenoma and the patient's peripheral blood leukocytes was negative for a mutation in the PTH gene sequence.

CONCLUSIONS

The contrasting values on the intact PTH assay and the turbo PTH assay suggest that the adenoma was producing an aberrant PTH molecule that was not detected by the routine intact PTH assay. Because there was no change in PTH gene sequence, this could be indicative of a posttranslational change in the PTH molecule that would not be recognized solely by DNA sequencing. Therefore, a low or normal PTH measurement against the backdrop of clinical and biochemical hyperparathyroidism needs measurement with a variety of assays.

Mutational analysis of GCMB, a parathyroid-specific transcription factor, in parathyroid adenoma of primary hyperparathyroidism

Sporadic primary hyperparathyroidism (PHPT), one of the most common endocrine disorders, is characterized by hypercalcemia and elevated PTH levels. The majority of cases are caused by a benign parathyroid adenoma, but somatic or de novo germ-line mutations that lead to adenoma formation have only been identified in few glands. GCMB is a parathyroid-specific transcription factor, which causes hypoparathyroidism when inactivated on both parental alleles or when a dominant-negative, heterozygous mutation is present. It is overexpressed in some parathyroid adenomas, and we therefore tested the hypothesis that GCMB mutations can be a cause of parathyroid adenomas. Nucleotide sequence analysis was performed on all coding exons and exon-intron borders of GCMB in 30 sporadic parathyroid adenomas and we identified several known polymorphisms that were either heterozygous or homozygous. In addition, one of the 30 investigated glands revealed a novel heterozygous missense mutation, c.1144G>A, which introduced methionine at position 382 for valine (V382M), a conserved amino acid residue. Western blot analysis using mutant GCMB (GCMB-V382M) from lysates of transiently transfected DF-1 fibroblasts, luciferase assays using extracts from these cells, and electrophoretic mobility assays failed to reveal differences between wild-type and mutant GCMB in expression level, transactivational capacity, and DNA-binding ability. Furthermore, pulse-chase experiments demonstrated no difference in half-life of wild-type and mutant protein. We conclude that mutations in the transcription factor GCMB do not seem to play a major role in the pathogenesis of PHPT.