Hypocalciuric Hypercalcemia Research Articles

CASRdb: A Publicly Accessible Comprehensive Database for Disease-associated Calcium-sensing Receptor Variants.

Genetic testing of the calcium-sensing receptor (CASR) gene is crucial for confirming diagnoses of familial hypocalciuric hypercalcemia type I (FHH1) and autosomal dominant hypocalcemia type I (ADH1). Therefore, we created a publicly accessible comprehensive database of the disease-causing variants of the CASR gene. We used two sources for variant reports: (1) we conducted a systematic review in the Embase and Pubmed databases from inception to March 2023, using search strategies associated with CASR. We identified all articles reporting CASR variants associated with disorders of calcium metabolism. (2) Additionally, data associated with pathogenic (P) or likely pathogenic (LP) variants in the ClinVar and LOVD databases were retrieved. Benign or likely benign variants were excluded. Variants of uncertain significance (VUS) were included only if they were reported in the literature. We generated a library of CASR variants associated with phenotypes, which has been made available on a website. We identified a total of 498 variants, of which 121 (24.3%) were associated with ADH1 and 377 (75.7%) with FHH1. Most included variants were identified from the literature (117 activating and 352 inactivating variants), and the majority of these were not documented in ClinVar/LOVD (73/117, 62.4% activating variants; 207/352, 58.8% inactivating variants). We developed CASRdb, a database that compiles information on all CASR variants associated with disorders of calcium metabolism from existing literature and genomic databases. Our database stands out due to the substantially higher number of disease-associated variants it contains, highlighting its comprehensive nature. The website is available at http://casrdb.mgh.harvard.edu.

Heterogenous Origins of Calcium Homeostasis Disorders Arising from Five Heterozygous Calcium-Sensing Receptor Variants.

The human calcium-sensing receptor (CaSR) plays a key role in calcium homeostasis, and most identified CASR variants are associated with hypercalcemic and hypocalcemic disorders. Here we characterized the pharmacological implications of five heterozygous CASR variants from individuals with familial hypocalciuric hypercalcemia 1 [FHH1: Y63C, I81T, Q459R, W818stop] or autosomal dominant hypocalcemia 1 [ADH1: R955stop]. Total and cell surface expression levels of wild-type (WT) and variant CaSRs expressed in human embryonic kidney 293T (HEK293T) cells were determined using ELISA, and the pharmacological properties of the receptors were delineated in two functional assays. The Y63C and I81T variations in the extracellular domain (ECD) of CaSR yielded markedly reduced cell surface expression and Ca2+ responsiveness, while Q459R displayed WT-like expression and functional properties. Truncation of the 7-transmembrane domain (7TMD) in W818stop eliminated cell surface expression, whereas R955stop in the intracellular carboxy-terminal yielded modestly increased surface expression and Ca2+ potency compared with WT CaSR. Interestingly, the effectiveness of positive allosteric modulators (PAMs) at the variants varied. Ca2+-mediated signaling through Y63C and I81T was significantly augmented by 7TMD-binding PAMs (NPS R-568 and Evocalcet) but not by ECD-binding PAMs (Etelcalcetide and Nb4), whereas signaling through Q459R and R955stop were robustly potentiated by all four PAMs. While the molecular phenotypes exhibited by the five CaSR variants concord with the clinical phenotypes in individuals harboring them, CASR variant-induced calcium homeostasis disorders clearly arise from diverse molecular origins, and the effectiveness of calcimimetics in these disorders could differ depending on the specific variants.

Monitoring Calcium-Sensing Receptor (CaSR)-Induced Intracellular Calcium Flux Using an Indo-1 Flow Cytometry Assay.

The calcium-sensing receptor (CaSR) has a critical role in maintaining serum calcium concentrations within the normal physiological range, and mutations in the receptor, or components of its signaling and trafficking pathway, cause disorders of calcium homeostasis. Inactivating mutations cause neonatal severe hyperparathyroidism or familial hypocalciuric hypercalcemia (FHH), while gain-of-function mutations cause autosomal dominant hypocalcemia (ADH). Characterizing the functional impact of mutations of the CaSR, and components of the CaSR-signaling pathway, is clinically important to enable correct diagnoses of FHH and ADH, optimize management, and prevent inappropriate parathyroidectomy or vitamin D supplementation. CaSR signals predominantly by activating the G-alpha subunit-11 to mobilize calcium release from intracellular stores. Thus, measurement of CaSR-induced intracellular calcium (Ca2+i) signaling is the gold standard method to investigate the pathogenicity of CaSR genetic variants. This protocol describes a method to assess CaSR-induced Ca2+I signaling using the Indo-1 calcium indicator dye and flow cytometry. This method has been used to assess multiple genetic variants in CaSR and components of its signaling and trafficking pathway in HEK293 cells.

7297 Clinical Characterization Of FHH Patients With Functional Assessment Of Novel CaSR Variants

Abstract Disclosure: R. Tora: None. L. Canaff: None. J. Welch: None. L. Bliss: None. L.S. Weinstein: None. W.F. Simonds: None. S.K. Agarwal: None. J. Blau: None. D. Goltzman: None. S. Jha: None. Familial Hypocalciuric Hypercalcemia (FHH) is characterized by hypercalcemia and low urinary calcium excretion from birth and its diagnosis is confirmed by the presence of a pathogenic germline heterozygous variant in CaSR, AP2S1, or GNA11. Establishing the diagnosis is important as it prevents unnecessary parathyroidectomies as surgery is not curative. We identified patients with germline variants in CaSR, AP2S1, or GNA11 seen at our institute and performed a retrospective review of available clinical parameters. 43 patients (31 kindreds) with 28 unique CaSR variants (15 pathogenic, 13 variants of uncertain significance [VUS]) and one pathogenic AP2S1 variant were identified. Median age at diagnosis was 35 [IQR: 25 - 39] years, with the youngest patient diagnosed at 4.5 months. Median serum calcium was 10.70 [10.25 - 11.00] mg/dL (ref: 8.4 - 10.2) with a median PTH of 51.7 [35.8 - 74.0] pg/mL (ref: 15 - 65). The median fractional excretion of calcium (FECa) was 1.00 [0.54 - 1.40] while median serum magnesium was 2.30 [2.19 - 2.43] mg/dL (ref: 1.6 - 2.6). 5/43 (12%) patients developed kidney stones and 6/43 (14%) men ≤ 50 years and premenopausal women developed osteoporosis with median age at diagnosis of 38 [28.50 - 45.75] years and no alternate underlying secondary cause. Longitudinal follow-up available on 9/43 patients with median duration of 14.4 ± 4.5 years showed no significant changes in serum and urine biochemistries. 23/43 (53%) patients had undergone failed parathyroidectomy prior to diagnosis, of which 20/23 (87%) had multiple glands removed including one who became hypoparathyroid. Functional characterization was performed for 8/13 CaSR VUS (p.D217G, p.C546Y, p.F563S, p.C694Y, p.A880P, p.E109Q, p.D382N, and p.A880S) in HEK293 cells by examining intracellular Ca2+ and ERK/MAPK responses to extracellular Ca2+ using NFAT-Luc and SRE-Luc constructs, respectively. Compared to the wild type (WT) receptor, p.D217G, p.C546Y, p.F563S, and p.C694Y showed less of the cell-membrane-localized mature glycosylated species in Western blots and a significant rightward shift in their concentration-response curve in both SRE- and NFAT-Luc assays. p.A880P showed a significant rightward shift in its concentration-response curve, while p.E109Q, p.D382N, and p.A880S showed no differences on Western blot or concentration-response curves as compared to WT. Further work to characterize the remaining variants (p.T14A, p.T609M, p.V268_P278del, p.G36R, and p.F589V) is ongoing. We conclude that the diagnosis of FHH is frequently missed and that patients with the disease may rarely develop target organ damage. Presentation: 6/2/2024

7633 Novel CASR Gene Mutation in a patient with Familial Hypocalciuric Hypercalcemia and Papillary Thyroid Cancer

Abstract Disclosure: A. Parihar: None. E.S. Nylen: None. S.M. Gandhi: None. Familial Hypocalciuric Hypercalcemia (FHH) is predominantly caused by loss-of-function mutations in the calcium-sensing receptor (CaSR) characterized by a benign elevation in calcium and PTH which can be mistaken for primary hyperparathyroidism (PHPT). Missense mutations in the CaSR gene causing FHH have been documented but not much is known regarding their clinical significance. We describe a patient with FHH found to have a novel variant mutation. A 37-year-old male with hypogonadism and fatty liver was incidentally found to have hypercalcemia suggestive of PHPT with elevated PTH (102-114 pg/ml), normal vitamin D, and Fractional Excretion of Calcium (FECa) of 0.014. His father also had hypercalcemia and had undergone parathyroid surgery. The patient denied kidney stones and had a normal bone density. Subsequent Sestamibi and 4D CT scan suggested parathyroid adenoma on the left mid-lower pole of the thyroid. Neck ultrasound also showed a left 1.2 x 1 x 1 cm thyroid nodule as well as a left neck mass with calcifications. Fine needle aspiration was positive for metastatic Papillary thyroid cancer(PTC) in the left neck mass and patient underwent total thyroidectomy along with subtotal parathyroidectomy and lateral neck dissection. Thyroid pathology confirmed multifocal PTC with lymph node involvement that were BRAF V600 positive. Parathyroid pathology was benign hyperplasia. The PTH level decreased appropriately intraoperatively (69%), but postoperatively a rise was noted with levels remaining 70-90 pg/ml with normal calcium levels. Repeat FECa was 0.007, supporting the diagnosis of FHH. Given patient’s father also had hypercalcemia, genetic testing was pursued. This revealed CaSR gene missense mutation (c.1382T>C p.Leu461Pro, heterozygous). This variation is not present in population databases and has been classified as a variant of uncertain significance. It can be difficult to distinguish PHPT from FHH based on FECa as in this case. The patient also had PTC which is not known to be associated with FHH. Due to uncertain significance of this novel CaSR missense mutation, long term follow-up and further familial genetic testing will help better understand clinical implications. Presentation: 6/2/2024

7752 Navigating Hypercalcemia in Pregnancy: A Case Report

Abstract Disclosure: J. Gabbay: None. S. Steinmetz-Wood: None. Introduction: Primary hyperparathyroidism (PHPT) in pregnancy is rare but presents many diagnostic and therapeutic challenges. Prompt diagnosis and treatment are important due to associated maternal and fetal risks, however evaluation of urine calcium to differentiate from Familial Hypocalciuric Hypercalcemia (FHH) becomes less reliable due to physiologic changes in pregnancy, sestamibi scans. CT scans require radiation, parathyroidectomy introduces surgical risk, and medical alternatives like bisphosphonates can interfere with fetal skeletal development. Clinical Case: A 24-year-old woman who presented to the emergency room for progressive nausea and abdominal pain was found to be pregnant with elevated serum calculated calcium to 11.4 mg/dL (2.84 mmol/L). She had a history of renal stones, longstanding hypercalcemia of unknown etiology and a remote family history of parathyroid “issues”. Follow up laboratory work showed a PTH of 75.8 pg/ml (8.04 pmol/L) with an elevated 24-hour urine calcium and a low 25OH vitamin D. Given her history of kidney stones and overt symptoms it was our clinical judgement that this was not a case of FHH. She was started on IV fluids twice weekly. After an unrevealing neck ultrasound, an MRI neck showed a 7 mm lesion along the posterior aspect of the left thyroid suggestive of a parathyroid adenoma. Sestamibi scan was avoided due to the risks of radiation to the developing fetus. Given the presumptive diagnosis of parathyroid adenoma, the lack of response to aggressive hydration, and the maternal and fetal risks of hypercalcemia during pregnancy, parathyroidectomy was pursued in her second trimester. Intra-operative inspection and biopsy showed the lesion to be only a lymph node. She underwent 4-gland exploration and the left inferior parathyroid gland, which appeared abnormal and enlarged, was removed. The intra-operative PTH dropped only from 98 to 80 (10.4 to 8.5 pmol/L). She otherwise had an unremarkable hospital course and at discharge her calcium was normal with an undetectable PTH, which can be an expected finding in pregnancy. On follow up she was feeling well with sustained normocalcemia and low PTH levels. Given the age at which her hyperparathyroidism started, she was referred to genetics for further evaluation. Clinical Lessons/Conclusion: There were significant biochemical and radiological limitations in the management of this case. Normally an inappropriately normal PTH with elevated serum calcium and normal urine calcium/creatinine clearance ratio confirms the diagnosis of PHPT, however in pregnancy it should be noted that FHH could also present with normal or elevated urine calcium due to absorptive hypercalciuria in pregnancy. Additional clinical history and reasoning was needed for management as well as a skilled surgeon, where preoperative localization was limited and was not ultimately helpful. Presentation: 6/2/2024

8082 Primary Hyperparathyroidism or Familial Hypocalciuric Hypercalcemia? Why Not Both?

Abstract Disclosure: C.A. Zmijewski: None. P.D. Greenberg: None. S.R. Saul: None. Background: Although considered two separate entities, primary hyperparathyroidism (PHPT) and familial hypocalciuric hypercalcemia (FHH) can present concurrently. Case: A 68-year-old male with hypertension was referred to Endocrinology for hypercalcemia and osteoporosis. The patient reported a long-standing history of intermittent hypercalcemia, first diagnosed at age 30 with a strong family history, both his father and son. He denied symptoms of hypercalcemia, history of nephrolithiasis and fractures, and was not taking calcium supplementations. Labs were notable for intermittent elevations in calcium, the highest being 10.9 mg/dL (8.5-10.5 mg/dL), in addition to phosphorus levels as low as 1.7 mg/dL (2.5-4.5 mg/dL). Vitamin D was replete at 50 ng/mL (32-100 ng/mL) and the highest parathyroid hormone (PTH) was 124 pg/mL (10-66 pg/mL). The 24-hour urine for calcium was 117 mg (100-300 mg) with a Ca/Cr 0.01. DEXA scan showed T scores -2.2 at the right femoral neck and -3.4 at the distal radius (Z score -2.3). Due to the significant osteoporosis, a work-up for secondary causes was completed and was unremarkable. The differential diagnosis for the osteoporosis, elevated parathyroid hormone, and intermittent hypercalcemia included PHPT vs FHH or possibly, a combination. Additional imaging included a renal ultrasound which was negative for nephrolithiasis, Sestamibi and 4D-CT which were both negative for a parathyroid adenoma. Genetic testing confirmed a mutation in the CASR gene. Due to the inability to localize a possible lesion, the decision was made to treat the osteoporosis with zoledronic acid. Conclusion: PHPT is a common endocrine disorder; approximately 100,000 people in the United States develop PHPT annually. Conversely, FHH is a rare endocrine disorder with an incidence rate of 1 in 78,000. PHPT occurs due to the over-secretion of PTH by one or more parathyroid glands. FHH is an inherited autosomal dominant disorder, most commonly due to an inactivating mutation in the calcium-sensing receptor (CASR) gene. Distinguishing PHPT from FHH is important because PHPT is cured with surgery while FHH does not require treatment. Hypercalcemia from FHH, as opposed to PHPT, is suggested by the absence of symptoms, a positive family history, normal or high PTH, and hypocalciuria. However, it can be challenging to separate the two especially in atypical presentations (PTH can be normal in PHPT and elevated in FHH, and Ca/Cr can be < 0.01 in PHPT). But what if these two conditions were to co-exist? Case reports have described patients with concurrent PHPT and FHH (parathyroid adenoma confirmed with pathology and CASR gene mutation confirmed with genetic testing). In these cases, parathyroidectomy can still be considered in co-existing PHPT and FHH to alleviate symptoms and prevent complications of hypercalcemia. Though a rare occurrence, PHPT and FHH have been shown to co-exist in prior case reports. Presentation: 6/1/2024

Familial hypocalciuric hypercalcemia in an infant: diagnosis and management quandaries.

Familial hypocalciuric hypercalcemia (FHH) is typically a benign condition characterized by elevated serum calcium, low urinary calcium excretion, and non-suppressed circulating levels of parathyroid hormone (PTH), usually requiring no intervention. FHH is inherited in an autosomal-dominant manner. Three subtypes are described, representing variants in genes with critical roles in extracellular calcium-sensing. FHH1, due to heterozygous inactivating variants in the calcium-sensing receptor gene (CASR), accounts for the majority of cases. FHH2, due to variants in GNA11, encoding the α-subunit of the downstream signaling protein, G11, is the rarest form of FHH. FHH3, resulting from variants in AP2S1, may present with a more pronounced phenotype than FHH1 or FHH2. We describe herein a newborn girl presenting with in utero femoral fractures, hypercalcemia, hypophosphatemia, and elevated circulating PTH. She was diagnosed with mild hyperparathyroidism and provided supplemental phosphate upon hospital discharge. However, serum calcium and PTH remained elevated at 5mo of age. The combination of low-calcium formula and cinacalcet improved the biochemical profile. No pathogenic variants in the coding region of CASR were identified; subsequent whole exome sequencing revealed a G- > T transition at c.44 (p.R15L) in AP2S1. Family studies identified this variant in the father and an affected brother. The mother was unexpectedly found to be hypocalcemic and was diagnosed with idiopathic hypoparathyroidism. This case demonstrates successful treatment of FHH3 using a low-calcium formula to limit dietary calcium availability and cinacalcet to modify PTH levels.

An Overview of Familial Hypocalciuric Hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) is one of the rare reasons for hypercalcemia. FHH is an autosomal dominant disease that is inheritable. The most common calcium sensitive receptors (CaSR) develop because of the inactivation of. In addition, they also develop due to the function loss of AP2S1 and GNA11. The FHH sickness is characterized by hypercalcemia, hypocalciuria, the regular or increased level of the parathyroid hormone, and normal renal function. The symptoms of hypercalcemia are usually not observed. It is often diagnosed by calculating the calcium/creatine clearance ratio of a 24-hour urine sample, and then genetically looking at it. FHH is usually a benign disorder, and when symptomatic and rarely complications develop, calcimimetics are used or parathyroidectomy can be performed. In conclusion, FHH is a benign and genetically transmitted, moderate cause of hypercalcemia. It is rare and usually asymptomatic.

Loss-of-Function Thr347Ala Variant in the G Protein Subunit-α11 Causes Familial Hypocalciuric Hypercalcemia 2 (FHH2).

To date, only four loss-of-function variants in the GNA11 gene encoding the G protein subunit α11 (Gα11) leading to familial hypocalciuric hypercalcemia 2 (FHH2) have been characterized. Gα11 is involved in calcium-sensing receptor (CaSR) signaling, and loss-of-function variants in GNA11 lead to reduced agonist potency at CaSR and an FHH phenotype. We have identified a family with a heterozygous GNA11 Thr347Ala variant and characterized its impact on calcium homeostasis in FHH2 patients and the signaling properties of CaSR through the Gα11-Thr347Ala variant in vitro. The index patient and her family had clinical, biochemical, and genetic analyses performed. The expression levels of Gα11 and the cell-surface expression levels of CaSR in human embryonic kidney 293A Gq/11 knock-out cells (ΔGq/11-HEK293A) co-transfected with CaSR and Gα11 (wild type (WT) or Thr347Ala) were determined, and the functional properties exhibited by calcium at CaSR were characterized in an inositol monophosphate (IP1) accumulation assay. Heterozygous carriers of the GNA11 Thr347Ala variant had mild asymptomatic hypercalcemia, hypocalciuria, and inappropriately high normal parathyroid hormone (PTH) levels considering their elevated serum calcium levels. Whereas the variant did not impact Gα11 expression or CaSR cell surface expression levels, calcium displayed a moderately but significantly lower agonist potency at CaSR/Gα11-Thr347Ala-transfected cells compared with CaSR/Gα11-WT-transfected cells in the IP1 accumulation assay (EC50 values of 5.67 mM and 4.38 mM, respectively). This identification of a novel GNA11 variant causing FHH2 substantiates the important role of Gα11 for CaSR signaling and Ca2+ homeostasis.

Comparison of fractional excretion of calcium from different urine samples in the differentiation between primary hyperparathyroidism and familial hypocalciuric hypercalcemia

Comparison of fractional excretion of calcium from different urine samples in the differentiation between primary hyperparathyroidism and familial hypocalciuric hypercalcemia

Molecular regulation of calcium-sensing receptor (CaSR)-mediated signaling.

Calcium-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 PO4 3-), 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.

Gα11 deficiency increases fibroblast growth factor 23 levels in a mouse model of familial hypocalciuric hypercalcemia.

Fibroblast growth factor 23 (FGF23) production has recently been shown to increase downstream of Gαq/11-PKC signaling in osteocytes. Inactivating mutations in the gene encoding Gα11 (GNA11) cause familial hypocalciuric hypercalcemia (FHH) due to impaired calcium-sensing receptor signaling. We explored the effect of Gα11 deficiency on FGF23 production in mice with heterozygous (Gna11+/-) or homozygous (Gna11-/-) ablation of Gna11. Both Gna11+/- and Gna11-/- mice demonstrated hypercalcemia and mildly raised parathyroid hormone levels, consistent with FHH. Strikingly, these mice also displayed increased serum levels of total and intact FGF23 and hypophosphatemia. Gna11-/- mice showed augmented Fgf23 mRNA levels in the liver and heart, but not in bone or bone marrow, and also showed evidence of systemic inflammation with elevated serum IL-1β levels. Furin gene expression was significantly increased in the Gna11-/- liver, suggesting enhanced FGF23 cleavage despite the observed rise in circulating intact FGF23 levels. Gna11-/- mice had normal renal function and reduced serum levels of glycerol-3-phosphate, excluding kidney injury as the primary cause of elevated intact FGF23 levels. Thus, Gα11 ablation caused systemic inflammation and excess serum FGF23 in mice, suggesting that patients with FHH - at least those with GNA11 mutations - may be at risk for these complications.

Genetic profile of a large Spanish cohort with hypercalcemia.

The disorders in the metabolism of calcium can present with manifestations that strongly suggest their diagnosis; however, most of the time, the symptoms with which they are expressed are nonspecific or present only as a laboratory finding, usually hypercalcemia. Because many of these disorders have a genetic etiology, in the present study, we sequenced a selection of 55 genes encoding the principal proteins involved in the regulation of calcium metabolism. A cohort of 79 patients with hypercalcemia were analyzed by next-generation sequencing. The 30% of our cohort presented one pathogenic or likely pathogenic variant in genes associated with hypercalcemia. We confirmed the clinical diagnosis of 17 patients with hypocalciuric hypercalcemia (pathogenic or likely pathogenic variants in the CASR and AP2S1 genes), one patient with neonatal hyperparathyroidism (homozygous pathogenic variant in the CASR gene), and another patient with infantile hypercalcemia (two pathogenic variants in compound heterozygous state in the CYP24A1 gene). However, we also found variants in genes associated with primary hyperparathyroidism (GCM2), renal hypophosphatemia with or without rickets (SLC34A1, SLC34A3, SLC9A3R1, VDR, and CYP27B1), DiGeorge syndrome (TBX1 and NEBL), and hypophosphatasia (ALPL). Our genetic study revealed 11 novel variants. Our study demonstrates the importance of genetic analysis through massive sequencing to obtain a clinical diagnosis of certainty. The identification of patients with a genetic cause is important for the appropriate treatment and identification of family members at risk of the disease.

A novel mouse model for familial hypocalciuric hypercalcemia (FHH1) reveals PTH-dependent and independent CaSR defects

The Calcium-sensing receptor (CaSR) senses extracellular calcium, regulates parathyroid hormone (PTH) secretion, and has additional functions in various organs related to systemic and local calcium and mineral homeostasis. Familial hypocalciuric hypercalcemia type I (FHH1) is caused by heterozygous loss-of-function mutations in the CaSR gene, and is characterized by the combination of hypercalcemia, hypocalciuria, normal to elevated PTH, and facultatively hypermagnesemia and mild bone mineralization defects. To date, only heterozygous Casr null mice have been available as model for FHH1. Here we present a novel mouse FHH1 model identified in a large ENU-screen that carries an c.2579 T > A (p.Ile859Asn) variant in the Casr gene (CasrBCH002 mice). In order to dissect direct effects of the genetic variant from PTH-dependent effects, we crossed CasrBCH002 mice with PTH deficient mice. Heterozygous CasrBCH002 mice were fertile, had normal growth and body weight, were hypercalcemic and hypermagnesemic with inappropriately normal PTH levels and urinary calcium excretion replicating some features of FHH1. Hypercalcemia and hypermagnesemia were independent from PTH and correlated with higher expression of claudin 16 and 19 in kidneys. Likewise, reduced expression of the renal TRPM6 channel in CasrBCH002 mice was not dependent on PTH. In bone, mutations in Casr rescued the bone phenotype observed in Pth null mice by increasing osteoclast numbers and improving the columnar pattern of chondrocytes in the growth zone. In summary, CasrBCH002 mice represent a new model to study FHH1 and our results indicate that only a part of the phenotype is driven by PTH.

Renal Transplantation in Rare Monogenic Urinary Stone Disease – A Single-center Experience

Introduction: Monogenic urinary stone disease (MUSD) tends to be more severe with early onset of symptoms and a higher risk of chronic kidney disease than sporadic USD. The literature on the outcome after renal transplant in patients with certain MUSD is scarce. Materials and Methods: This is a retrospective single-center observational study conducted in a tertiary care renal transplant unit in North India between 2018 and 2021. The renal transplant recipients who developed an end-stage renal disease (ESRD) due to renal calculus disease/nephrocalcinosis were included in the study. All the patients presented to us in an anuric state, and hence, a 24-h urine metabolic profile could not be performed. Ear, nose, and throat and ophthalmological evaluations were done to rule out extrarenal manifestations. These patients were subjected to genetic analysis, i.e., clinical exome sequencing using next-generation sequencing. Results: Out of 283 live renal transplants, 11 patients developed ESRD due to nephrocalcinosis/renal calculus disease. Out of 11, only 4 had genetic mutations and the rest did not have any identifiable genetic mutations. The gene mutations were identified in ADCY10, CLDN16, CaSR, and SLC3A4. The patient with ADCY10 mutation had a strong family history. The clinical phenotype and in silico parameters analysis predicted the variant to be damaging except the one with CaSR mutation which causes Hypocalciuric hypercalcemia syndrome, type 1. Three of four underwent surgical intervention at younger age. All underwent successful live-related renal transplantation, with good graft function on follow-up, without any recurrence of calculus in the allograft. Conclusion: Renal transplantation can be safely proceeded in patients with the above monogenic mutations. Genetic analysis should be a part of pretransplant evaluation in young onset nephrolithiasis and end-stage kidney disease patients to look for a monogenic cause, to assess the risk of recurrence postrenal transplant.

GCM2 p.Tyr394Ser variant in Ashkenazi Israeli patients with suspected familial isolated hyperparathyroidism.

A germline mutation can be identified in up to 10% of patients with primary hyperparathyroidism (PHPT). In 2017, a high frequency of the GCM2 [(NM_ 004752.4) c.1181A> C; p.Tyr394Ser; rs142287570] variant was reported in PHPT Ashkenazi Jews (AJ). To evaluate the presence of the GCM2 p.Tyr394Ser variant in Israeli patients addressed for genetic evaluation to characterize their phenotype and clinical management. Patients with PHPT who underwent addressed for genetic screening for suspected familial hypocalciuric hypercalcemia (FHH), a family history of isolated hyperparathyroidism (FIHP), or failed parathyroidectomy with persistent PHPT were recruited. Those with normal initial selected gene sequencing or hyperparathyroid genetic panel completed the GCM2 p.Tyr394Ser variant sequencing. The prevalence of this variant was evaluated using our local genomic database. A total of 42 single individuals from unrelated kindreds were evaluated. A disease-causing mutation was found in 11 (26.1%) patients: 10 were diagnosed with FHH (eight CASR and two AP2S1 mutations), and one patient had a CKN2B mutation. In 28 of the remaining patients, the GCM2 p.Tyr394Ser variant was positive in three (10.7%), and all were AJ. Within AJ (15/28, 53.5%), the rate of the p.Tyr394Ser variant was 3/15 (20%), and of those, two had a history of familial isolated hyperparathyroidism. Multi-glandular parathyroid adenoma/hyperplasia was also observed in two of these patients. No clinical or laboratory findings could discriminate patients with the GCM2 p.Tyr394Ser variant from those with FHH. Cinacalcet normalized the calcium levels in one patient. The prevalence of the GCM2 p.Tyr394Ser variant in 15,407 tests in our local genomic database was 0.98%. In contrast to previous observations, the GCM2 p.Tyr394Ser variant-associated phenotype may be mild in AJ with FIHP, sometimes mimicking FHH. Because surgery may be curative, surgeons should be aware of the possibility of multiple gland diseases in these patients. The clinical spectrum and clinical utility of screening for this variant warrant further investigation.

OBSTETRICAL AND NEONATAL OUTCOMES AMONG PREGNANCIES COMPLICATED BY HYPERPARATHYROIDISM: SYSTEMATIC REVIEW

Background: Primary hyperparathyroidism (PHPT) is a relatively common disorder of the parathyroid glands, causing skeletal, renal, and cardiac complications. As etiological features of PHPT, single adenoma, hyperplasia, carcinoma, and familiar causes (MEN multiple endocrine neoplasia, FHH familiar hypocalciuric hypercalcemia, hyperparathyroidismjaw tumor syndrome) are presented. Primary hyperparathyroidism in pregnancy has an incidence of 1, which is underestimated due to the plethora of undiagnosed cases. The aim: This study aims to show about obstetrical and neonatal outcomes among pregnancies complicated by hyperparathyroidism. Methods: By comparing itself to the standards set by the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020, this study was able to show that it met all of the requirements. So, the experts were able to make sure that the study was as up-to-date as it was possible to be. For this search approach, publications that came out between 2013 and 2023 were taken into account. Several different online reference sources, like Pubmed and SagePub, were used to do this. It was decided not to take into account review pieces, works that had already been published, or works that were only half done. Result: In the PubMed database, the results of our search brought up 10 articles, whereas the results of our search on SagePub brought up 60 articles. The results of the search conducted for the last year of 2013 yielded a total 2 articles for PubMed and 14 articles for SagePub. The result from title screening, a total 1 articles for PubMed and 10 articles for SagePub. In the end, we compiled a total of 7 papers. We included five research that met the criteria. Conclusion: Pregnancy complicated by PHPT may lead to serious maternal and infant complications. MDT consultation ensures timely diagnosis, comprehensive treatment for the patients and better pregnancy outcomes.

A large in-frame deletion of the calcium-sensing receptor extracellular domain causes familial hypocalciuric hypercalcaemia type 1 (FHH1) and is partially responsive to cinacalcet

A large in-frame deletion of the calcium-sensing receptor extracellular domain causes familial hypocalciuric hypercalcaemia type 1 (FHH1) and is partially responsive to cinacalcet