Neonatal Severe Hyperparathyroidism Research Articles

Molecular regulation of calcium‐sensing receptor (CaSR)‐mediated signaling

AbstractCalcium‐sensing receptor (CaSR), a family C G‐protein‐coupled receptor, plays a crucial role in regulating calcium homeostasis by sensing small concentration changes of extracellular Ca2+, Mg2+, amino acids (e.g., L‐Trp and L‐Phe), small peptides, anions (e.g., HCO3− and PO43−), and pH. CaSR‐mediated intracellular Ca2+ signaling regulates a diverse set of cellular processes including gene transcription, cell proliferation, differentiation, apoptosis, muscle contraction, and neuronal transmission. Dysfunction of CaSR with mutations results in diseases such as autosomal dominant hypocalcemia, familial hypocalciuric hypercalcemia, and neonatal severe hyperparathyroidism. CaSR also influences calciotropic disorders, such as osteoporosis, and noncalciotropic disorders, such as cancer, Alzheimer's disease, and pulmonary arterial hypertension. This study first reviews recent advances in biochemical and structural determination of the framework of CaSR and its interaction sites with natural ligands, as well as exogenous positive allosteric modulators and negative allosteric modulators. The establishment of the first CaSR protein–protein interactome network revealed 94 novel players involved in protein processing in endoplasmic reticulum, trafficking, cell surface expression, endocytosis, degradation, and signaling pathways. The roles of these proteins in Ca2+‐dependent cellular physiological processes and in CaSR‐dependent cellular signaling provide new insights into the molecular basis of diseases caused by CaSR mutations and dysregulated CaSR activity caused by its protein interactors and facilitate the design of therapeutic agents that target CaSR and other family C G‐protein‐coupled receptors.

Familial states of primary hyperparathyroidism: an update.

Familial primary hyperparathyroidism (PHPT) includes syndromic and non-syndromic disorders. The former are characterized by the occurrence of PHPT in association with extra-parathyroid manifestations and includes multiple endocrine neoplasia (MEN) types 1, 2, and 4 syndromes, and hyperparathyroidism-jaw tumor (HPT-JT). The latter consists of familial hypocalciuric hypercalcemia (FHH) types 1, 2 and 3, neonatal severe primary hyperparathyroidism (NSHPT), and familial isolated primary hyperparathyroidism (FIHP). The familial forms of PHPT show different levels of PHPT penetrance, developing earlier and with multiglandular involvement compared to sporadic counterpart. All these diseases exhibit Mendelian inheritance patterns, and for most of them, the genes responsible have been identified. DNA testing for predisposing mutations is helpful in index cases or in individuals with a high suspicion of the disease. Early recognition of hereditary disorders of PHPT is of great importance for the best clinical and surgical approach. Genetic testing is useful in routine clinical practice because it will also involve appropriate screening for extra-parathyroidal manifestations related to the syndrome as well as the identification of asymptomatic carriers of the mutation. The aim of the review is to discuss the current knowledge on the clinical and genetic profile of these disorders along with the importance of genetic testing in clinical practice.

Neonatal Severe Primary Hyperparathyroidism—Presentation, Management, and Follow-up of Seven Cases

Neonatal Severe Primary Hyperparathyroidism—Presentation, Management, and Follow-up of Seven Cases

Neonatal Severe Hyperparathyroidism: A Case Report

Background: Neonatal severe hyperparathyroidism is an extremely rare condition that presents in the first few months of life. Recognition at the early stage followed by prompt surgical intervention are of vital importance for survival. Hypotonia, respiratory distress, lethargy and delay in growth and development occur in association with the elevated serum parathormone levels and hypercalcemia. Definitive therapy involves total parathyroidectomy. Case Description: We are presenting a case with Neonatal severe hyperparathyroidism, who underwent total parathyroidectomy. The patient had been followed up with medical therapy until. Parathormone levels rapidly declined following total parathyroidectomy and the patient was discharged with full recovery. Literature Review: Sestamibi scintigraphy might fail to show an ectopic parathyroid gland. In such conditions, on table confirmation of parathyroid glands by frozen section and Intraoperative parathormone monitoring is vital at this point. Persistently elevated parathormone levels might suggest a remnant parathyroid tissue at the surgical site or an ectopic parathyroid gland that should be excised. Clinical Relavance: Neonatal severe hyperparathyroidism is a life-threatening disease. In the present case surgery performed at the early is life-saving due to the failure of medical therapy to control the disease.

Surgical management of neonatal severe hyperparathyroidism.

Neonatal severe hyperparathyroidism (NSHPT) is a rare disease that can be lethal. Most patients require parathyroidectomy. Report experience in managing this severe disease. Retrospective chart review of case series. Tertiary health care center. We reviewed data on patients managed for NSHPT from June 2001 to January 2023. Demographic, clinical, and follow-up data were collected, and descriptive data were generated. Pre- and postoperative levels of parathyroid hormone (PTH) and serum calcium, and effect of autotransplantation. 19 RESULTS: The 13 males and 6 females had a a mean age of 46 days at referral. The mean preoperative parathyroid hormone (PTH) and serum calcium levels were 996 ng/L and 4.54 mmol/L, respectively. Twelve patients underwent ultrasonography preoperatively. Of these, six had prominent glands, while no glands were seen in the other six. A Sestamibi scan was done for 15 patients, of which nine showed negative results and six showed positive results, with three glands observed in the neck and three in the sublingual area. Nineteen patients underwent renal ultrasonography, with nine showing nephrocalcinosis. The mean age at surgery was 5.2 months. Total parathyroidectomy (four glands) was performed in 17 patients, and 15 underwent concurrent auto-transplantation. One patient had three glands removed, in addition to auto-transplantation. Another underwent single gland excision as a redo-surgery after previous surgery elsewhere. The mean postoperative follow-up duration was 6 years. The mean postoperative PTH and calcium levels were 25 ng/L and 1.64 mmol/L, respectively. Ultimately, all the patients were required to initiate calcium and vitamin D supplements, except for two patients who had undergone auto-transplantation. Molecular genetic screening of the calcium-sensing receptor gene reported likely pathogenic/pathogenic mutations in 16 of 19 patients (13 were homozygous, two were heterozygous, one was negative, and data was unavailable for the remaining three patients). Surgical treatment of NSHPT is effective. Preoperative radiological localization studies did not impact the treatment plan. Auto-transplantation proved ineffective in maintaining independence from medical supplements. The retrospective nature of the study may imply inaccuracybut since the data are gathered from electronic medical records, we believe it is highly accurate. The small sample size limits generalizability.

Targeting trafficking as a therapeutic avenue for misfolded GPCRs leading to endocrine diseases.

G protein-coupled receptors (GPCRs) are plasma membrane proteins associated with an array of functions. Mutations in these receptors lead to a number of genetic diseases, including diseases involving the endocrine system. A particular subset of loss-of-function mutant GPCRs are misfolded receptors unable to traffic to their site of function (i.e. the cell surface plasma membrane). Endocrine disorders in humans caused by GPCR misfolding include, among others, hypo- and hyper-gonadotropic hypogonadism, morbid obesity, familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism, X-linked nephrogenic diabetes insipidus, congenital hypothyroidism, and familial glucocorticoid resistance. Several in vitro and in vivo experimental approaches have been employed to restore function of some misfolded GPCRs linked to endocrine disfunction. The most promising approach is by employing pharmacological chaperones or pharmacoperones, which assist abnormally and incompletely folded proteins to refold correctly and adopt a more stable configuration to pass the scrutiny of the cell’s quality control system, thereby correcting misrouting. This review covers the most important aspects that regulate folding and traffic of newly synthesized proteins, as well as the experimental approaches targeted to overcome protein misfolding, with special focus on GPCRs involved in endocrine diseases.

Reduced affinity of calcium sensing-receptor heterodimers and reduced mutant homodimer trafficking combine to impair function in a model of familial hypocalciuric hypercalcemia type 1.

Heterozygous loss-of-function mutation of the calcium sensing-receptor (CaSR), causes familial hypocalciuric hypercalcemia type 1 (FHH1), a typically benign condition characterized by mild hypercalcemia. In contrast, homozygous mutation of this dimer-forming G-protein coupled receptor manifests as the lethal neonatal severe hyperparathyroidism (NSHPT). To investigate the mechanisms by which CaSR mutations lead to these distinct disease states, we engineered wild-type (WT) and an exon 5-deficient disease-causing mutation, and transfected expression constructs into human embryonic kidney (HEK) cells. WT protein was mainly membrane-expressed whereas the mutant CaSR protein (mCaSR) was confined to the cytoplasm. Co-expression of WT CaSR directed mCaSR to the cell membrane. In assays of CaSR function, increases in extracellular [Ca2+] ([Ca2+]o) increased intracellular [Ca2+] ([Ca2+]i) in cells expressing WT CaSR while the response was reduced in cells co-expressing mutant and WT receptor. Untransfected cells or those expressing mCaSR alone, showed minimal, equivalent responses to increased [Ca2+]o. Immunoprecipitation experiments confirmed an association between mutant and wild-type CaSR. The affinity of the WT CaSR for calcium was three times greater than that of the heterodimer. The maximal functional response to [Ca]o was dependent on localization of CaSR to the membrane level and independent of homo- or heterodimerizations. In summary, these results suggest that heterodimerization of WT and mCaSR receptors, rescues the trafficking defect of the mutant receptors and also reduces the affinity of the WT-mutant heterodimer for [Ca]o. In contrast, the homozygous mutants do not produce functional receptors on cell membrane. These data indicate how substantial differences between signaling of hetero- and homodimeric mutants may lead to profound differences in the severity of disease in heterozygous and homozygous carriers of these mutations.

Disorders of the Calcium Sensing Signaling Pathway: From Familial Hypocalciuric Hypercalcemia (FHH) to Life Threatening Conditions in Infancy.

Familial hypocalciuric hypercalcemia (FHH) is a mostly benign condition of elevated calcium and PTH levels based on a hyposensitive calcium sensing receptor (CaSR) in FHH 1 or its downstream regulatory pathway in FHH2 and FHH3. In children, adolescents and young adults with FHH the main challenge is to distinguish the condition from primary hyperparathyroidism and thereby to avoid unnecessary treatments including parathyroidectomy. However, inheritance of FHH may result in neonatal hyperparathyroidism (NHPT) or neonatal severe hyperparathyroidism (NSHPT), conditions with high morbidity, and in the latter even high mortality. This review focuses on the genetic and pathophysiological framework that leads to the severe neonatal form, gives recommendations for counselling and summarizes treatment options.

Personalised medicines for familial hypercalcemia and hyperparathyroidism.

Loss-of-function calcium-sensing receptor (CASR) mutations cause mineral metabolism disorders, familial hypocalciuric hypercalcemia, or neonatal severe hyperparathyroidism and increase the risk of femoral fracture, chronic kidney disease, coronary heart disease, and other diseases. In severe cases, CaSR mutations are lethal. Off-label use of the CaSR-positive allosteric modulator (PAM), cinacalcet, corrects hypercalcemia in some patients with CaSR mutations. However, other patients remain unresponsive to cinacalcet, attesting to the need for novel treatments. Here, we compared the effects of cinacalcet to two other clinically approved synthetic CaSR activators, evocalcet and etelcalcetide, as well as a novel PAM, 1-(2,4-dimethylphenyl)-1-(4,5-dimethylthiazol-2-yl)ethan-1-ol (MIPS-VD-836-108) on clinically relevant CaSR mutations. We assessed the compounds in CaSR-expressing HEK293 cells for correction of mutation-induced impairments in intracellular calcium (Ca2+i) mobilization and cell surface expression. While cinacalcet, MIPS-VD-836-108 and evocalcet rescued the signaling of cell surface-expressed mutants, albeit to varying degrees, etelcalcetide was ineffective. Cinacalcet and evocalcet, but not MIPS-VD-836-108 or etelcalcetide, restored the expression of a R680H mutant. However, no compound rescued expression of I81K and C582R mutants or a receptor missing 77 amino acids in the extracellular domain mimicking deletion of CASRexon 5, which impairs CaSR function. These data suggest specific compounds may be clinically effective in some patients with CaSR mutations, but other patients will remain refractory to treatment with currently available CaSR-targeting activators, highlighting the need for new generation drugs to rescue both the signaling and expression of mutant CaSRs.

Clinical, Molecular Characterization and Long-Term Follow-Up of a Patient with Neonatal Severe Hyperparathyroidism

Clinical, Molecular Characterization and Long-Term Follow-Up of a Patient with Neonatal Severe Hyperparathyroidism

Suspecting neonatal severe primary hyperparathyroidism in late onset neonatal sepsis

Suspecting neonatal severe primary hyperparathyroidism in late onset neonatal sepsis

Generation of an induced pluripotent stem cell line HPCASRi002-A from a patient with neonatal severe primary hyperparathyroidism caused by a compound heterozygous mutation in the CASR gene

Neonatal severe primary hyperparathyroidism (NSHPT) is a rare autosomal recessive disorder of calcium homeostasis that manifests shortly after birth with hypercalcemia and bone disease. NSHPT, in most cases, is attributed to mutations in the calcium-sensing receptor (CASR) gene. We reprogrammed dermal fibroblasts derived from a patient with NSHPT carrying a compound heterozygous mutation in the CASR gene into induced pluripotent stem cells (iPSCs). The established iPSCs expressed pluripotency markers, maintained normal karyotype and differentiated into all three germ layers. This line is a valuable resource for modeling of hyperparathyroidism related to CASR mutations.

Genetic causes of neonatal and infantile hypercalcaemia

The causes of hypercalcaemia in the neonate and infant are varied, and often distinct from those in older children and adults. Hypercalcaemia presents clinically with a range of symptoms including failure to thrive, poor feeding, constipation, polyuria, irritability, lethargy, seizures and hypotonia. When hypercalcaemia is suspected, an accurate diagnosis will require an evaluation of potential causes (e.g. family history) and assessment for physical features (such as dysmorphology, or subcutaneous fat deposits), as well as biochemical measurements, including total and ionised serum calcium, serum phosphate, creatinine and albumin, intact parathyroid hormone (PTH), vitamin D metabolites and urinary calcium, phosphate and creatinine. The causes of neonatal hypercalcaemia can be classified into high or low PTH disorders. Disorders associated with high serum PTH include neonatal severe hyperparathyroidism, familial hypocalciuric hypercalcaemia and Jansen’s metaphyseal chondrodysplasia. Conditions associated with low serum PTH include idiopathic infantile hypercalcaemia, Williams-Beuren syndrome and inborn errors of metabolism, including hypophosphatasia. Maternal hypocalcaemia and dietary factors and several rare endocrine disorders can also influence neonatal serum calcium levels. This review will focus on the common causes of hypercalcaemia in neonates and young infants, considering maternal, dietary, and genetic causes of calcium dysregulation. The clinical presentation and treatment of patients with these disorders will be discussed.

Successful Early Treatment of Severe Neonatal Hyperparathyroidism With Cinacalcet

Introduction: Neonatal severe hyperaparathyroidism (NSHPT) can cause significant bone disease early in life and prompt treatment is therefore necessary. Cinacalcet is a calcimimetic primarily used in adult patients with hypercalcemia to treat secondary hyperparathyroidism, but has only been trialed in neonates with NSHPT. Successful treatment appears to be dependent on the mutation leading to hypercalcemia. We describe a neonate born with severe hypercalcemia and a suspected mutation of the calcium sensing receptor (CaSR) who received successful early treatment with cinacalcet and decrease in calcium levels.Case Report: A full-term baby girl was found to have rapid breathing at 2.5 hours of life requiring CPAP. A chest x-ray demonstrated bone demineralization with rib fractures. Lab evaluation demonstrated hypercalcemia (total calcium = 12 mg/dl) with an inappropriately elevated PTH level of 386 pg/mL, hypophosphatemia (3.3 mg/dL), normal magnesium (2.0 mg/dL), a normal urine calcium to creatinine ratio of 0.26 and calcium to creatinine clearance ratio of 0.05 and a slightly low vitamin D-25 of 28.8 ng/mL.The father had a history of asymptomatic hypercalcemia without a diagnosis. Paternal genetic testing identified a heterozygous pathogenic CASR defect: c. 554G>A (p.Arg185Gln). This has been described in patients with NSHPT.The patient was initially treated with IV fluids and Lasix, but calcium levels did not decrease. Cinacalcet therapy was given on day of life 10. Patient had a decreased PTH to 231 pg/ mL after one day. After 26 days of treatment, patient’s PTH level decreased to 63 pg/mL. Patient was weaned off of CPAP and was discharged home.Discussion: Cinacalcet, a calcimimetic that works at the level of the CASR, was able to successfully and significantly decrease PTH levels in a neonate patient with NSHPT. Treatment options are limited in patients with this condition and we believe prompt treatment with this therapy facilitated patient’s discharge. The patient’s osteopenia secondary to the NSHPT and subsequent rib fractures resulted in a prolonged requirement of CPAP. Early recognition and treatment, even prior to results of genetic testing, prevented further fractures. We demonstrate the potential benefit of calcimimetics in a case of NSHPT where conventional treatment was ineffective. More importantly, we anticipate improvement in osteopenia and any future comorbidities secondary to this condition. Continued success with this treatment is yet to be evaluated.

Pediatric hyperparathyroidism: review and imaging update

Hyperparathyroidism, due to increased secretion of parathyroid hormones, may be primary, secondary or tertiary. Most pediatric patients with sporadic primary hyperparathyroidism will be symptomatic, presenting with either end-organ damage or nonspecific symptoms. In younger patients with primary hyperparathyroidism, there is a higher prevalence of familial hyperparathyroidism including germline inactivating mutations of the calcium-sensing receptor genes that result in either neonatal severe hyperparathyroidism or familial hypocalciuric hypercalcemia. Parathyroid scintigraphy and ultrasound are complementary, first-line imaging modalities for localizing hyperfunctioning parathyroid glands. Second-line imaging modalities are multiphase computed tomography (CT) and magnetic resonance imaging. In pediatrics, multiphase CT protocols should be adjusted to optimize radiation dose. Although, the role of these imaging modalities is better established in preoperative localization of hyperfunctioning parathyroid glands in primary hyperparathyroidism, the same principles apply in secondary and tertiary hyperparathyroidism. In this manuscript, we will review the embryology, anatomy, pathophysiology and preoperative localization of parathyroid glands as well as several subtypes of primary familial hyperparathyroidism. While most of the recent imaging literature centers on adults, we will focus on the issues that are pertinent and applicable to pediatrics.

EP124 - Neonatal severe hyperparathyroidism caused by homozygous mutation in CASR gene: A rare cause of life-threatening hypercalcemia

eP124 - Neonatal severe hyperparathyroidism caused by homozygous mutation in CASR gene: A rare cause of life-threatening hypercalcemia

Cell Surface Calcium-Sensing Receptor Heterodimers: Mutant Gene Dosage Affects Ca2+ Sensing but Not G Protein Interaction.

ABSTRACTThe calcium‐sensing receptor is a homodimeric class C G protein‐coupled receptor (GPCR) that senses extracellular Ca2+ (Ca2+ o) via a dimeric extracellular Venus flytrap (VFT) unit that activates G protein‐dependent signaling via twin Cysteine‐rich domains linked to transmembrane heptahelical (HH) bundles. It plays a key role in the regulation of human calcium and thus mineral metabolism. However, the nature of interactions between VFT units and HH bundles, and the impacts of heterozygous or homozygous inactivating mutations, which have implications for disorders of calcium metabolism are not yet clearly defined. Herein we generated CaSR‐GABAB1 and CaSR‐GABAB2 chimeras subject to GABAB‐dependent endoplasmic reticulum sorting to traffic mutant heterodimers to the cell surface. Transfected HEK‐293 cells were assessed for Ca2+ o‐stimulated Ca2+ i mobilization using mutations in either the VFT domains and/or HH bundle intraloop‐2 or intraloop‐3. When the same mutation was present in both VFT domains of receptor dimers, analogous to homozygous neonatal severe hyperparathyroidism (NSHPT), receptor function was markedly impaired. Mutant heterodimers containing one wild‐type (WT) and one mutant VFT domain, however, corresponding to heterozygous familial hypocalciuric hypercalcemia type‐1 (FHH‐1), supported maximal signaling with reduced Ca2+ o potency. Thus two WT VFT domains were required for normal Ca2+ o potency and there was a pronounced gene‐dosage effect. In contrast, a single WT HH bundle was insufficient for maximal signaling and there was no functional difference between heterodimers in which the mutation was present in one or both intraloops; ie, no gene‐dosage effect. Finally, we observed that the Ca2+ o‐stimulated CaSR operated exclusively via signaling in‐trans and not via combined in‐trans and in‐cis signaling. We consider how receptor asymmetry may support the underlying mechanisms. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Severe primary hyperparathyroidism in a 3-day-old neonate

Neonatal severe primary hyperparathyroidism (NSHPT) is a rare and life-threatening autosomal recessive genetic disorder caused by a wide range of inactivating mutations in Calcium sensing receptors. We introduced a three-day-old neonate with poor feeding, failure to thrive, and lethargy. The laboratory results showed uncontrolled hypercalcemia with hyperparathyroidism; therefore, the patient was referred to a pediatric surgeon for parathyroidectomy. We showed that neonates with NSHPT could be treated with total parathyroidectomy with autotransplant without transplant-induced hypercalcemia.

Pediatric parathyroid disease

Parathyroid glands are critical for calcium and phosphate homeostasis. Parathyroid disease is relatively rare in the pediatric population, but there are some important pediatric-specific considerations and conditions. This article reviews parathyroid physiology, disorders of hyper- and hypo- function, operative management, and uniquely pediatric diagnoses such as neonatal severe hyperparathyroidism. Advances in preoperative imaging, intra-operative gland identification, and management of post-thyroidectomy hypocalcemia are also presented in detail. This article combines a review of fundamentals with recent advances in care, emphasizing pediatric-specific publications.

SUN-366 Neonatal Severe Hyperparathyroidism: Extreme Hypercalcemia as a Robust Marker for Homozygous Dosage of Pathogenic CASR Variants

Context: Neonatal severe hyperparathyroidism (NSHPT) is a rare and life-threatening emergency. It includes generalized hyperparathyroid bone disease and respiratory distress from combinations among a narrowed thorax, rib fractures, hypotonia, and biochemical disturbances. Successful therapy is compatible with long life and a healthy prognosis. However, neuromotor retardation may persist after otherwise successful therapy. The time and amplitude of hypercalcemia likely correlate with irreversible neuromotor retardation; thus, early intervention seems critical in many cases. NSHPT is usually caused by homozygous or heterozygous pathogenic variant(s) of the CASR; a heterozygous variant of this gene is also the usual cause of familial hypocalciuric hypercalcemia (FHH or FHH1). Homozygotes and heterozygotes with NSHPT are often not distinguished in the current literature. In theory, their management should differ. Optimum treatment in homozygotes is early total parathyroidectomy with induction of postoperative hypoparathyroidism. Optimal management of heterozygotes is more complex. It consists in temporizing measures and varies from careful observation without surgery, to bisphosphonates and/or calcimimetics, and to subtotal parathyroidectomy. The heterozygotes can then develop into healthy babies with asymptomatic FHH1.Evidence Acquisition: Each case met strict criteria for “severe” and neonatal disease. We analyzed the core biochemical parameters of the maximal serum calcium and maximal PTH. To compare different immunoassays, PTH was analyzed as a ratio (thus without units) of the raw data divided by the upper limit of its normal range. Each case also required information about the allelic dosage of the pathogenic or likely pathogenic CASR variant(s).Evidence Synthesis: There were 36 cases with homozygous pathogenic CASR variants and 21 cases with heterozygous pathogenic or likely pathogenic variants. Maximal serum calcium was far higher in homozygotes 5.8 +/- 1.5 versus 3.2 +/- 0.2 (P<.001) (normal 2.2–2.6 mM). Maximal serum PTH as a ratio was also far higher in homozygotes 17 +/- 12 versus 8 +/- 9 (P=.003) (normal ratio 0.3–1.0). We defined extreme hypercalcemia empirically as any calcium value above 4.5 mM. No heterozygote had a maximal calcium above 3.7 mM; however, 30 of 36 (81%) of the homozygotes had maximal calcium above 4.5 mM. Whenever tested early, this extreme hypercalcemia was usually recognized in the first week of life.Conclusions: Extreme hypercalcemia greater than 4.5 mM was newly identified as a conservative cutoff that was 100% predictive of homozygosity for pathogenic CASR variants. Extreme hypercalcemia in NSHPT is an early, facile, rapid, and inexpensive determinant of homozygosity for pathogenic variants of the CASR. It should be sought and used to promote early and definitive total parathyroidectomy, whenever it is identified in NSHPT.