Calcium-sensing Receptor Gene Research Articles

New insights into renal calcium-sensing receptor activation.

Activation of the calcium-sensing receptor (CASR) in the parathyroid gland suppresses the release of parathyroid hormone (PTH). Furthermore, activation of the renal CASR directly increases the urinary excretion of calcium, by inhibiting transepithelial calcium transport in the nephron. Gain-of-function mutations in the CASR gene lead to autosomal dominant hypocalcemia 1 (ADH1), with inappropriately low PTH levels and hypocalcemia, indicative of excessive activation of the parathyroid CASR. However, hypercalciuria is not always observed. The reason why the manifestation of hypercalciuria is not uniform among ADH1 patients is not well understood. Direct activation of the CASR in the kidney has been cumbersome to study, and an indirect measure to effectively estimate the degree of CASR activation following chronic hypercalcemia or genetic gain-of-function CASR activation has been lacking. Studies have shown that expression of the pore-blocking claudin-14 is strongly stimulated by the CASR in a dose-dependent manner. This stimulatory effect is abolished after renal Casr ablation in hypercalcemic mice, suggesting that claudin-14 abundance may gauge renal CASR activation. Using this marker has led to unexpected discoveries regarding renal CASR activation. These new studies have informed on renal CASR activation thresholds and the downstream CASR-regulated calcium transport mechanisms.

Functional evaluation of a novel nonsense variant of the calcium-sensing receptor gene leading to hypocalcemia.

The calcium-sensing receptor (CASR) gene encodes a G protein-coupled receptor crucial for calcium homeostasis. Gain-of-function CASR variants result in hypocalcemia, while loss-of-function variants lead to hypercalcemia. This study aims to assess the functional consequences of the novel nonsense CASR variant [c.2897_2898insCTGA, p.(Gln967*) (Q967*)] identified in adolescent patient with chronic hypocalcemia, a phenotype expected for a gain-of-function variants. To functionally characterize the Q967* mutant receptor, both wild-type (WT) and mutant CASR were transiently transfected into HEK293T cells and calcium-sensing receptor (CaSR) protein expression and functions were comparatively evaluated using multiple read-outs. Western blot analysis revealed that the CaSR mutant protein displayed a lower molecular weight compared with the WT, consistent with the loss of the last 122 amino acids in the intracellular domain. Mitogen-activated protein kinase activation and serum responsive element luciferase assays demonstrated that the mutant receptor had higher baseline activity than the WT. Extracellular-signal-regulated kinase/c-Jun N-terminal kinase phosphorylation, however, remained consistently high in the mutant, without significant modulations following exposure to increasing extracellular calcium (Ca2+o) levels, suggesting that the mutant receptor is more sensitive to Ca2+o compared with the WT. This study provides functional validation of the pathogenicity of a novel nonsense CASR variant, resulting in an abnormally hyperfunctioning protein consistent with the patient's phenotype. Functional analyses indicate that mutant receptor is constitutively active and poorly sensitive to increasing concentrations of extracellular calcium, suggesting that the cytoplasmic tail may contain elements regulating signal transduction.

Epigenetic profiling reveals key genes and cis-regulatory networks specific to human parathyroids

In all terrestrial vertebrates, the parathyroid glands are critical regulators of calcium homeostasis and the sole source of parathyroid hormone (PTH). Hyperparathyroidism and hypoparathyroidism are clinically important disorders affecting multiple organs. However, our knowledge regarding regulatory mechanisms governing the parathyroids has remained limited. Here, we present the comprehensive maps of the chromatin landscape of the human parathyroid glands, identifying active regulatory elements and chromatin interactions. These data allow us to define regulatory circuits and previously unidentified genes that play crucial roles in parathyroid biology. We experimentally validate candidate parathyroid-specific enhancers and demonstrate their integration with GWAS SNPs for parathyroid-related diseases and traits. For instance, we observe reduced activity of a parathyroid-specific enhancer of the Calcium Sensing Receptor gene, which contains a risk allele associated with higher PTH levels compared to the wildtype allele. Our datasets provide a valuable resource for unraveling the mechanisms governing parathyroid gland regulation in health and disease.

Relationship of calcium-sensing receptor gene polymorphism CASR rs 1042636, CASR rs 1802757, and cinacalcet response among Egyptian hemodialysis patients with secondary hyperparathyroidism

Introduction: Secondary hyperparathyroidism (SHPT) is a common complication associated with morbidity and mortality among hemodialysis (HD) patients. Objectives: The current study aims to evaluate the frequency of CASR gene polymorphism variants related to parathyroid hormone (PTH) regulation (CASR rs1042636 and CASR rs1802757) and to test the hypothesis that single nucleotide polymorphisms (SNPs) in the CASR gene alter the response to cinacalcet among Egyptian HD patients with SHPT. Patients and Methods: A case-control study that included 50 HD patients with intact parathyroid hormone (iPTH) ≥300 pg/mL treated with cinacalcet for a 6-month duration and 40 healthy volunteers as a control group. Eligible patients were recruited from Ain Shams university hospitals. Blood samples were collected from patients and controls to assess allele frequencies of CASR gene polymorphism variants using real-time polymerase chain reaction (PCR), corrected calcium (Ca), phosphorus (P), Ca×P product, iPTH level, and alkaline phosphatase before and after treatment. HD patients were categorized into two groups based on the reduction percentage; responders’ patients (iPTH ≥20%) and non-responders to cinacalcet treatment. Results: Of 50 HD patients, 48 (96%) carried the rs1042636 AA wild gene, while only two (4%) carried the rs1042636 AG mutant gene, 42 (87.5%) carried the rs1802757 CC wild genotype, and 6 (12.5%) carried the CT mutant genotype. The minor alleles T and G were (6.3% and 2%) respectively, with no statistically significant difference between the patient and control groups regarding the CASR genotypes or alleles distribution. There was no significant difference between responders and non-responder’s patient groups regarding CASR genotypes or allele frequencies. Moreover, no significant correlation between CASR genotypes or alleles to delta change of Ca, P, Ca×P product, or PTH was seen. However, CASR rs1802757 CT mutant genotype was associated with a significant reduction in alkaline phosphatase levels after treatment. Conclusion: There is no significant association between the gene polymorphism CASR rs1042636 or CASR rs1802757 and the reduction in PTH levels as a response to cinacalcet treatment among Egyptian HD patients with SHPT.

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.

Functional analysis reveals calcium-sensing receptor gene regulating cell-cell junction in renal tubular epithelial cells.

Calcium-sensing receptor (CASR) influences the expression pattern of multiple genes in renal tubular epithelial cells. The objective of this inquiry was to explore the molecular mechanisms of CASR in renal tubular epithelial cells and nephrolithiasis. HK-2 cells were transfected with lentiviruses carrying either CASR (named CASR) or an empty vector negative control (named NC), as well as shRNA intended to target CASR (named shCASR) or its corresponding negative control (named shNC). CCK-8 assay was used to detect the effect of CASR on the proliferation of HK-2 cells. RNA-Sequencing was applied to explore potential pathways regulated by CASR in HK-2 cells. PCR and western blot results showed that CASR expression was significantly increased in CASR cells and was decreased in shCASR cells when compared to their corresponding negative control, respectively. CCK-8 assay revealed that CASR inhibited the proliferation of HK-2 cells. RNA-Sequencing results suggested that the shCASR HK-2 cells exhibited a significant up-regulation of 345 genes and a down-regulation of 366 genes. These differentially expressed genes (DEGs) were related to cell apoptosis and cell development. In CASR HK-2 cells, 1103 DEGs primarily functioned in mitochondrial energy metabolism, and amino acid metabolism. With the Venn diagram, 4 DEGs (Clorf116, ENPP3, IL20RB, and CLDN2) were selected as the hub genes regulated by CASR. Enrichment analysis revealed that these hub genes were involved in cell-cell junction, and epithelial cell development. In summary, our investigation has the potential to offer novel perspectives on CASR regulating cell-cell junction in HK-2 cells.

Exploring Adaptive Phenotypes for the Human Calcium-Sensing Receptor Polymorphism R990G.

Rainforest hunter-gatherers from Southeast Asia are characterized by specific morphological features including a particularly dark skin color (D), short stature (S), woolly hair (W), and the presence of steatopygia (S)-fat accumulation localized in the hips (DSWS phenotype). Based on previous evidence in the Andamanese population, we first characterized signatures of adaptive natural selection around the calcium-sensing receptor gene in Southeast Asian rainforest groups presenting the DSWS phenotype and identified the R990G substitution (rs1042636) as a putative adaptive variant for experimental follow-up. Although the calcium-sensing receptor has a critical role in calcium homeostasis by directly regulating the parathyroid hormone secretion, it is expressed in different tissues and has been described to be involved in many biological functions. Previous works have also characterized the R990G substitution as an activating polymorphism of the calcium-sensing receptor associated with hypocalcemia. Therefore, we generated a knock-in mouse for this substitution and investigated organismal phenotypes that could have become adaptive in rainforest hunter-gatherers from Southeast Asia. Interestingly, we found that mouse homozygous for the derived allele show not only lower serum calcium concentration but also greater body weight and fat accumulation, probably because of enhanced preadipocyte differentiation and lipolysis impairment resulting from the calcium-sensing receptor activation mediated by R990G. We speculate that such differential features in humans could have facilitated the survival of hunter-gatherer groups during periods of nutritional stress in the challenging conditions of the Southeast Asian tropical rainforests.

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.

SAT224 Nonsurgical Hypoparathyroidism: 40 Years After Diagnosis

Abstract Disclosure: L.I. Kaplan: None. A. Yuen: None. P.D. Greenberg: None. Background: The majority of cases of hypoparathyroidism occur after neck surgery. The most common nonsurgical cause is autoimmune, either in isolation or part of Autoimmune Polyglandular Syndrome Type 1. Hypomagnesemia is a functional cause. Hypoparathyroidism can occur as part of genetic syndromes that include congenital anomalies, short stature and developmental delay. Non-syndromic genetic etiologies including Autosomal Dominant Hypocalcemia type 1 (ADH1), a gain of function mutation in the calcium sensing receptor (CaSR) that can present in infancy, childhood or adulthood with hypocalcemia (50% symptomatic), hypercalcuria (10%) and basal ganglia calcification (35%). For ADH1, targeted therapies are being developed. Clinical Case: A 90-year-old male was diagnosed with hypoparathyroidism at age 50 when he presented with hand cramping and was found to have hypocalcemia with low PTH. He was started on calcitriol and calcium supplementation. Many years later he started following at our endocrine clinic. Past medical history includes prostate cancer treated with radiation and androgen deprivation therapy, HTN, and pre-diabetes. He has no history of neck surgery, other endocrinopathies, candidiasis, vitiligo or congenital anomalies. He has no family history of hypocalcemia and has two children without calcium abnormalities. His DEXA shows stable +T scores in LS spine and bilateral hips. He has not had brain imaging. Nephrocalcinosis was not reported on renal ultrasound. More than 10 years ago, he presented with severe hypercalcemia, acute renal failure (Ca 13.5 mg/dl, Cr 6.0mg/dl, Phos 5.5mg/dl) and ureteral stones after taking over the counter calcium supplements in excess. He underwent stone removal with return to baseline renal function. Subsequently, he underwent knee replacement surgeries and required IV calcium until he was able to swallow pills. Since this time, he has been managed on calcitriol, calcium carbonate, vitamin D3, and chlorthalidone with close follow up for adjustment of regimen to target Ca 8.0-8.5 mg/dl. He has not had a recurrence of severe hypercalcemia, hyperphosphatemia or nephrolithiasis. He feels well and lives at home with his wife. Lab values over the past 10 years are as follows: Ca 8.1-10.6 mg/dl (8.5-10.5), Alb 4.0-4.6 g/dl (3.5-5.4), Phos 4.3-5.5 mg/dl (2.8-4.5), Mg 1.7-1.9 mg/dl (1.3-2.1), K 3.7-4.4 mEq/L (3.6-5.2), Cr 1.0-1.5 mg/dl (0.5-1.3), PTH 0.00-1.4 pg/ml (10-55), 25 OH Vit D 18-58 ng/ml (32-100), 1,25 OH Vit D3 25.5-37.2 pg/ml (19.9-79.3), 24hr Urine Ca 162- 384 mg/24 hrs (50-400). Clinical lessons: Chronic hypoparathyroidism can be well managed with close follow up and frequent lab monitoring. This patient should be referred for genetic testing, particularly to look for ADH1 mutation in the CaSR gene as targeted treatments are being developed. His children should be tested for any mutations found in him. Presentation: Saturday, June 17, 2023

OR23-02 Genotype-Phenotype Correlation In Calcium Sensing Receptor (Casr) Gene Gain-Of-Function Mutations: A Case Series And Report Of 2 Novel Mutations

Abstract Disclosure: D.S. Ali: None. F. Marini: None. F. Alsarraf: None. H.H. Alalwani: None. A. Alamri: None. A.A. Khan: Advisory Board Member; Self; Amgen Inc, Takeda. Grant Recipient; Self; Amgen Inc, Alexion Pharmaceuticals, Inc., Takeda, Ultragenyx, Radius Health, Inc. M. Brandi: Consulting Fee; Self; Alexion Pharmaceuticals, Inc. Speaker; Self; Amgen Inc, Alexion Pharmaceuticals, Inc., Eli Lilly & Company. Background: Autosomal dominant hypocalcemia (ADH1) is a genetic disorder characterized by low serum calcium and low or inappropriately normal parathyroid hormone levels. It is caused by a heterozygous activating mutation of the calcium-sensing receptor (CaSR) gene. ADH1 has been linked to 113 unique germline mutations, of which 96% are missense mutations. There is a lack of clear genotype-phenotype correlation in the reported literature. Methods: We described a case series of six unrelated ADH1 probands, each with a gain-of-function CaSR mutation, and two children of one of these cases, comparing clinical, biochemical, and complication profiles and matching our identified mutations to those previously reported in the literature. Results: Of our cases 75% are familial and 25% are secondary to de novo mutation. Our 6 unrelated ADH1 probands showed distinct clinical presentations, while 3 cases within the same pedigree shared similar presentation and clinical characteristics including presentation in infancy, hypocalcemic seizures (2/3; 66.7%), hypomagnesemia, hyperphosphatemia, and hypercalciuria. The biochemical profile differed among the 6 cases in the degree of hypocalcemia, associated hypercalciuria, hypomagnesemia, and/or hypokalemia. Response to therapy also differed. When comparing our cases to previously published cases, we noted that mutations in the 5th transmembrane domain of the CaSR (TM5) carry a more severe form of the disease and may be associated with a higher rate of hypocalcemic seizures, basal ganglia calcifications as well as nephrocalcinosis, nephrolithiasis and renal insufficiency compared to mutations in the extracellular regions. Hypomagnesemia was present in 100% of the cases harboring mutations in TM5. We also describe two novel activating mutations of the CaSR gene; c.2468T>A, p.lle823Asn and c.1756G>A, p.Glu586Lys. Both of these were not reported either on the most common databases of human mutations or in the literature. In silico analysis of p.lle823Asn by PolyPhen-2 predicted the Ile to Asn substitution at position 823 as “probably damaging”, while the p.Glu586Lys substitution was suggested to have a “benign” nature. Our patient with the former mutation had a history of seizure and nephrolithiasis, while our patient with the latter mutation is mildly symptomatic, presented in her 40s, and is on low doses of active vitamin D and calcium supplements. Conclusion: As a result of these genetic and clinical comparisons, we propose that a genotype-phenotype correlation may exist because our cases showed similar presentation, characteristics, and severity, with respect to published cases with the same or similar mutations. We also contended that the severity of the presentation is highly influenced by the specific CaSR variant. These findings, however, require further evaluation and assessment with a systematic review. Presentation: Saturday, June 17, 2023

OR23-03 Sustained Normalization Of Mineral Homeostasis In Autosomal Dominant Hypocalcemia Type 1: Results From A Phase 2 Study Over 18 Months Of Encaleret (CLTX-305) Treatment (NCT04581629)

Abstract Disclosure: R.I. Gafni: Advisory Board Member; Self; Ascendis Pharma, Hypoparathyroidism Association. Grant Recipient; Self; Calcilytix Therapeutics. I.R. Hartley: Grant Recipient; Self; Calcilytix Therapeutics. K.L. Roszko: Grant Recipient; Self; Calcilytix Therapeutics. E.F. Nemeth: Consulting Fee; Self; Calcilytix Therapeutics. K.A. Pozo: Grant Recipient; Self; Calcilytix Therapeutics. A. Mathew: Employee; Self; Calcilytix Therapeutics. M. Roberts: Employee; Self; Calcilytix Therapeutics. S.H. Adler: Employee; Self; Calcilytix Therapeutics. M.T. Collins: Grant Recipient; Self; Calcilytix Therapeutics. Autosomal dominant hypocalcemia type 1 (ADH1), caused by gain-of-function calcium-sensing receptor gene (CASR) variants, is characterized by low parathyroid hormone (PTH) levels, hypocalcemia, hypercalciuria, hyperphosphatemia and hypomagnesemia. Conventional therapy (calcium and active vitamin D) worsens hypercalciuria, which may result in renal complications. Calcilytics that act as negative allosteric modulators of the calcium-sensing receptor (CaSR), like encaleret, decrease the sensitivity of hyperactive receptors to extracellular calcium and normalize biochemical abnormalities in ADH1 rodent models. This Phase 2b open-label study of the oral investigational calcilytic encaleret was comprised of 3 periods followed by a long-term extension (LTE). Conventional therapy was discontinued prior to encaleret initiation. Periods 1&2 included dose-finding and safety/tolerability evaluation. Period 3 (P3) optimized dosing and assessed safety and efficacy over 24 outpatient weeks; participants were then allowed to continue in the LTE. Thirteen adults with ADH1 were enrolled and encaleret was individually titrated to normalize albumin-corrected calcium (cCa) and minimize hypercalciuria. Encaleret was well-tolerated with no serious adverse events reported. There were no treatment discontinuations or withdrawals prior to the LTE; one participant withdrew during the LTE for family planning. The mean±SD encaleret sulfate dose at the end of P3, Week 24 (P3W24) was 86±70mg BID, remaining stable at LTE Month 12 (LTEM12) (n=11) (71±62mg BID). Mean±SD values taken 4-hours post-dose for P3W24 and LTEM12 compared to baseline (BL) are presented. PTH levels were low at BL (6.3±7.8 pg/mL [nl 10-65]), normal at P3W24 (35.3±10.2), and remained consistent through LTEM12 (36.9±15.2 [p<0.01]). Similarly, hypocalcemia at BL (cCa=7.1±0.4 mg/dL [nl 8.4-10.2]) was normal at P3W24 (9.2±0.5); eucalcemia was maintained through LTEM12 (9.2±0.4 [p<0.01]). BL hypercalciuria (395±216 mg/d [nl <250-300]) decreased to 202±83 at P3W24 and normalization was sustained through LTEM12 (177±94 [p<0.05]). BL blood phosphate (4.5±1.1 mg/dL [nl 2.3-4.7]) decreased by P3W24 (3.4±0.4) and was maintained at LTEM12 (3.4±0.5 [p<0.01]). Blood magnesium increased (BL 1.7±0.2 mg/dL [nl 1.6-2.6]); P3W24 2.0±0.2; LTEM12 2.1±0.2 [p<0.01]). Bone turnover markers increased from BL (n=7) (CTX=253±111 pg/mL; P1NP=34±10 mcg/L) by P3W24 (n=13) (CTX=744±565; P1NP=104±87) and remained elevated at LTEM12 (CTX=988±652; P1NP=83±49 [p<0.01]. This study represents a molecularly targeted, precision medicine approach to the treatment of ADH1. The consistent and sustained results from over 18 months of outpatient encaleret treatment are clinically meaningful and support Phase 3 evaluation of the efficacy and safety of encaleret as the first potential treatment indicated for ADH1. Presentation: Saturday, June 17, 2023

Clinical Value of CASR Gene Polymorphism on Cinacalcet Response in Hemodialysis Patients with Secondary Hyperparathyroidism

Abstract Background Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD) patients on dialysis, associated with increased cardiovascular mortality and morbidity. Aim to evaluate frequency of variants of CaSR genes related to PTH regulation and to assess the effect of these single nucleotide polymorphisms on cinacalcet response among prevalent hemodialysis patients (HD) with SHPT. Patients and Methods This study included 50 prevalent HD patients with SHPT were recruited from Ain Shams University Hospitals' dialysis units. Clinical stable end-stage renal disease (ESDR) (35 males (70%) and 15 females (30%)), ≥ 18 years old on adequate HD for ≥ 6 months, with intact PTH (iPTH) ≥300 pg/ml and had been treated by cinacalcet. The patient was followed retrospectively for 6 months by measuring serum calcium, phosphorous, alkaline phosphatase, PTH to evaluate the response of cinacalcet. CASR gene and single nucleotide polymorphism (SNP) (rs1042636 and rs1802757) were measured by real-time PCR. Results CASR Gene/SNP rs1042636 (A/G), AA homozygous gene (wild gene) was present in n = 48 (96%) while AG heterozygous gene was present in n = 2 (4%). CASR Gene/SNP rs1802757(C/T), CC homozygous gene (wild gene) was present in n = 42 patients (84%) while CT heterozygous gene was present in n = 6 patients (12%). 21 patients (42%) responded to treatment of SHPT with reduction percent and 29 patients (58%) were non-responding to cinacalcet treatment for 6 months duration. The results showed no significant correlation between CASR gene polymorphism and response to treatment (p-value >0.05). Conclusion There is no statistically significant correlation between single nucleotide polymorphisms (SNPs) of the calcium sensing receptor gene (CASR) and response to cinacalcet as treatment of SHPT among HD patients, for further investigation studies.

CaSR modulates proliferation of the superficial zone cells in temporomandibular joint cartilage via the PTHrP nuclear localization sequence.

The superficial zone cells in mandibular condylar cartilage are proliferative. The present purpose was to delineate the relation of calcium-sensing receptor (CaSR) and parathyroid hormone-related peptide nuclear localization sequence (PTHrP87-139 ), and their role in the proliferation behaviors of the superficial zone cells. A gain- and loss-of-function strategy were used in an in vitro fluid flow shear stress (FFSS) model and an in vivo bilateral elevation bite model which showed mandibular condylar cartilage thickening. CaSR and PTHrP87-139 were modulated through treating the isolated superficial zone cells with activator/SiRNA and via deleting CaSR or parathyroid hormone-related peptide (PTHrP) gene in mice with the promoter gene of proteoglycan 4 (Prg4-CreERT2 ) in the tamoxifen-inducible pattern with or without additional injection of Cinacalcet, the CaSR agonist, or PTHrP87-139 peptide. FFSS stimulated CaSR and PTHrP expression, and accelerated proliferation of the Prg4-expressing superficial zone cells, in which process CaSR acted as an up-streamer of PTHrP. Proteoglycan 4 specific knockout of CaSR or PTHrP reduced the cartilage thickness, suppressed the proliferation and early differentiation of the superficial zone cells, and inhibited cartilage thickening and matrix production promoted by bilateral elevation bite. Injections of CaSR agonist Cinacalcet could not improve the phenotype caused by PTHrP mutation. Injections of PTHrP87-139 peptide rescued the cartilage from knockout of CaSR gene. CaSR modulates proliferation of the superficial zone cells in mandibular condylar cartilage through activation of PTHrP nuclear localization sequence. Our data support the therapeutic target of CaSR in promoting PTHrP production in superficial zone cartilage.

Novel Calcium-Sensing Receptor (CASR) Mutation in a Family with Autosomal Dominant Hypocalcemia Type 1 (ADH1): Genetic Study over Three Generations and Clinical Characteristics

Introduction: Activating mutation of the calcium-sensing receptor gene (CASR) reduces parathyroid hormone secretion and renal tubular reabsorption of calcium, defined as autosomal dominant hypocalcemia type 1 (ADH1). Patients with ADH1 may present with hypocalcemia-induced seizures. Calcitriol and calcium supplementation in symptomatic patients may exacerbate hypercalciuria, leading to nephrocalcinosis, nephrolithiasis, and compromised renal function. Methods: We report on a family with seven members over three generations with ADH1 due to a novel heterozygous mutation in exon 4 of CASR: c.416T>C. Results: This mutation leads to substitution of isoleucine with threonine in the ligand-binding domain of CASR. HEK293T cells transfected with wild type or mutant cDNAs demonstrated that p.Ile139Thr substitution led to increased sensitivity of the CASR to activation by extracellular calcium relative to the wild-type CASR (EC₅₀ of 0.88 ± 0.02 m<sc>M</sc> vs. 1.1 ± 0.23 m<sc>M</sc>, respectively, p < 0.005). Clinical characteristics included seizures (2 patients), nephrocalcinosis and nephrolithiasis (3 patients), and early lens opacity (2 patients). In 3 of the patients, serum calcium and urinary calcium-to-creatinine ratio levels obtained simultaneously over 49 patient-years were highly correlated. Using the age-specific maximal-normal levels of calcium-to-creatinine ratio in the correlation equation, we obtained age-adjusted serum calcium levels that are high enough to reduce hypocalcemia-induced seizures and low enough to reduce hypercalciuria. Conclusion: We report on a novel CASR mutation in a three-generation kindred. Comprehensive clinical data enabled us to suggest age-specific upper limit of serum calcium levels, considering the association between serum calcium and renal calcium excretion.

Primary and secondary hyperparathyroidism present different expressions of calcium-sensing receptor

BackgroundDecreased calcium-sensing receptor (CaSR) has been observed in hyperparathyroidism (HPT) without a known mechanism. The purpose of this study was to evaluate the expression of CaSR in primary (PHPT) and secondary (SHPT) subtypes.MethodsImmunohistochemical (IHC) staining and quantitative real-time PCR (qRT-PCR) assay were used to measure the differences in expression of CaSR protein and gene in PHPT and SHPT human samples, compared to matched controls.ResultsCaSR protein was differentially downregulated in SHPT and PHPT compared to normal parathyroid tissues (2.42 ± 0.5 vs. 3.2 ± 0.62, P < 0.05; 1.8 ± 0.83 vs. 3.2 ± 0.62, P < 0.05, respectively). Furthermore, SHPT tissues exhibited significantly higher levels of CaSR mRNA (0.29 ± 0.23 vs. 0.01 ± 0.12, P < 0.05) and protein (2.42 ± 0.5 vs. 1.8 ± 0.83, P < 0.05) than those in PHPT tissue samples.ConclusionDepressed CaSR expression was a critical pathological hallmark of HPT. We found a differential decline of CaSR, in terms of both mRNA and protein levels, in PHPT and SHPT human samples. We think that CaSR dysregulation occurred at the very beginning of disease onset in PHPT, while a similar pathological scenario appeared at the later stage of SHPT. Future studies should be directed to dissect the mechanistic involvement of CaSR in PHPT and SHPT in order to bring treatment precisions in HPT management.

Scintigraphy Negative Ultrasound positive parathyroid adenoma in familial hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) is a rare, lifelong, benign condition with an autosomal dominant pattern of inheritance. FHH is clinically distinguished by mild to moderate PTH-dependent hypercalcemia and normal to significantly reduced urinary calcium excretion despite elevated serum calcium. FHH is usually caused by a heterozygous loss-of-function mutation in the calcium-sensing receptor gene (CASR). It should be differentiated from primary hyperparathyroidism (PHPT). The reported case of a 10-year-old girl presented with symptomatic hypercalcemia, elevated intact parathyroid hormone, and a vitamin D deficiency. 99mTc-Sestamibi scan failed to detect any abnormalities, but high-resolution ultrasound (HRUS) of the neck revealed a right inferior parathyroid adenoma, which was excised with a focused parathyroidectomy. Although the patient’s calcium and iPTH levels normalized initially, they started rising within a few days. Bangladesh J. Nuclear Med. 26(1): 62-65, 2023

Generation of an induced pluripotent stem cell line CSSi015-A (9553), carrying a point mutation c.2915C > T in the human calcium sensing receptor (CasR) gene

Familial Hypocalciuric Hypercalcemia (FHH1) is a rare autosomal dominant disease with low penetrance, caused by inactivating mutations of the calcium-sensing receptor (CaSR) gene, characterized by significant hypercalcemia, inappropriately normal serum PTH levels and a low urinary calcium level. Human induced pluripotent stem cells (hiPSCs) from a patient carrying a previously identified heterozygous mutation, a p.T972M amino acid substitution in cytoplasmic tail of CasR, were produced using a virus, xeno-free and non-integrative protocol.

Amlodipine downregulates gene expression that involved in the signaling pathways of coagulation process in COVID-19 patients: An observational clinical study.

The SARS-CoV-2 virus has the property of activating the coagulation process, which is responsible for producing thrombotic events which is considered as one of the most serious COVID-19 complications. Hypertension is a hazard factor for COVID-19 complications, and people who are treated with calcium entry blockers may halt the occurrence of thrombotic events. to evaluate the effect of amlodipine on some genes involved in the activation of the coagulation procedure in COVID-19 patients with hypertensive. observational, cross-sectional study. This study was carried out in the Department of Pharmacy at Al-Kut University College in Wasit, Iraq, in conjunction with Al Zahraa Hospital from June 2021 to March 2022. A total of 45 COVID-19 patients participated in this study who were grouped into as follows: Group I (n = 23) who had no previous history of hypertension and Group II (n = 22) who had previous hypertension and were treated with amlodipine. Expression of the calcium-sensing receptor (CaSR), coagulation factor V (F5), and methylenetetrahydrofolate dehydrogenase (NADP+ dependent) 1 Like (MTHFD1L) genes was determined. P values were calculated by Chi-square test for categorized facts and the Mann-Whitney test for incessant data. P ≤ 0.05 was considered statistically significant. Group II patients had significantly lower levels of CaSR, F5, and MTHFD1L gene expression compared with the corresponding levels in Group I patients. The expression level of MTHFD1L was elevated significantly in patients who had currently high blood pressure compared with normotensive patients in both the groups. Amlodipine is preferred in hypertensive patients who have COVID-19 because it attenuates the levels of gene expression that have an impact on the coagulation process.

RF30 | PSAT178 Severe Hyperparathyroidism in a Newborn: Response to Cinacalcet

Abstract Background Neonatal severe hyperparathyroidism (NSHPT) is a rare potentially lethal disorder caused by inactivating mutations in the calcium sensing receptor (CASR) gene. In newborns it presents with multiple bone fractures often confused with forms of osteogenesis imperfecta. Diagnostic and therapeutic experience with this condition is limited, hence here we describe a term baby we identified and treated with this disorder. Case Description A 39-week-old Hispanic female, born small for gestational age (BW 2.38 kg) via vaginal delivery to a 33-year-old G3P2 healthy mother was noted to have relative asymmetry of the thighs/hips. X-rays revealed bone demineralization and multiple fractures including distal femur and proximal tibia bilaterally and rib fractures in various stages of healing. Initially, osteogenesis imperfecta was thought likely and Endocrinology was consulted. Laboratories showed hypercalcemia (calcium 12.1 mg/dL (normal 8.5-11.2), elevated serum PTH 439 pg/mL (12-72). Serum phosphorus (4.2 mg/dL), 25-OH Vitamin D (44 ng/mL) and alkaline phosphatase (232 IU/L) were normal; urine calcium/creatinine ratio was low (0.006 mg/mg). EKG showed non-specific T wave abnormalities and echocardiogram mild pulmonary hypertension. Neck ultrasound and sestamibi scan showed no parathyroid mass. She was placed on oxygen due to desaturations and had poor tone and suck. Father had documented hypercalcemia (calcium 12.6 mg/dL, PTH 53 pg/mL). Paternal aunt and grandmother also had history of hypercalcemia. Serum levels of calcium and PTH remained elevated for 2 weeks despite treatment with IV fluids and furosemide and a low calcium/vitamin D formula. On day 12 we began a trial of cinacalcet, a type 2 calcimimetic, at starting doses of 0.4 mg/kg/day divided BID orally. Over 4 days the patient showed a dramatic reduction in serum levels of calcium and PTH to 8.6 mg/dL and 24 pg/mL, respectively. Over time her clinical course improved with better tone and suck and normal oxygenation. Cinacalcet was titrated up to 2.3 mg/kg/day (2mg PO tid) and baby discharged on day 20. Gene sequencing revealed a known heterozygous pathogenic variant in an exon 4 hotspot of the CASR gene, c.658C&amp;gt;T (p.Arg220Trp), consistent with familial hypocalciuric hypercalcemia. Father was confirmed to have the same pathogenic variant as the child. She has now been followed for 6 months, all fractures are healing with persistently normal PTH and calcium levels. She is thriving, her development appears to be normal, able to eat orally, sit, track and smile. Conclusion Neonatal severe hyperparathyroidism can occur in infants who are heterozygous for a CASR mutation and can manifest as multiple congenital fractures. A family history of asymptomatic parental hypercalcemia/hyperparathyroidism and targeted gene sequencing can be diagnostic of NSHPT. Activators of the CASR are a promising therapy for heterozygous CASR loss-of-function pathogenic variants and can lead to reversal of skeletal demineralization and markedly improved clinical status. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Monday, June 13, 2022 1:18 p.m. - 1:23 p.m.

ODP118 PTH (1-34) Replacement Therapy for Hypoparathyroidism due to Sporadic Calcium Sensing Receptor Gain-of-Function Point Mutation

Abstract Background The calcium sensing receptor (CASR) regulates parathyroid hormone secretion in response to extracellular calcium concentration. A gain-of-function mutation of the CASR lowers the set point for extracellular calcium sensing, resulting in both reduced parathyroid hormone secretion and increased urinary calcium excretion compared to other causes of hypoparathyroidism. Clinical Case After presenting with hypocalcemia-associated seizures at the age of two years, our patient had an undetectable serum parathyroid hormone level. He was started on calcitriol and calcium supplementation, however continued to have recurrent seizures throughout childhood. On ultrasound at age four, he exhibited nephrocalcinosis. DNA sequence analysis revealed a heterozygous T383G mutation nucleotide substitution on exon 3, resulting in the replacement of phenylalanine with cysteine at amino acid position 128. Our patient's base substitution likely represents a de novo mutation as we have confirmed that he has no family history of hypocalcemia. Notably, a different missense mutation at the same codon (F128L) co-segregated with autosomal dominant hypocalcemia in a large family, and functional studies confirm that mutation of this phenylalanine provides gain-of-function to the CASR. After enrolling in a clinical trial for continuous recombinant parathyroid hormone infusion at age seven, his symptoms of hypocalcemia abated. His seizures stopped, and anti-epileptic drugs were discontinued at age eight. After the clinical trial concluded, he was switched to teriparatide 10 micrograms three times daily, and serum calcium was maintained between 7.5 and 8.5 mg/dL. With the goal to minimize hypercalciuria and reduce the frequency of injections, teriparatide was discontinued, and recombinant parathyroid hormone (Natpara) 50 micrograms daily was started. This led to symptomatic hypocalcemia with muscle cramping and cognitive changes, and he was thus restarted on teriparatide with calcium carbonate supplementation. Despite maintenance of 24-hour urine calcium excretion ranging 325-388 mg, he developed bilateral flank pain. Computed tomography images revealed worsening nephrocalcinosis and bilateral nephrolithiasis. To reduce hypercalciuria and risk of stone formation, he was started on chlorthalidone, switched to calcium citrate, and encouraged to reduce dietary sodium intake. Conclusion This patient has a novel T383G activating mutation in CASR gene resulting in hypoparathyroidism and type 5 Bartter syndrome that has not been previously published in the literature. His hypocalcemia has remained stable on teriparatide for over 18 years, which to our knowledge, is the longest treatment duration using recombinant human parathyroid hormone for this purpose. We demonstrate a unique clinical challenge to balance treatment of hypoparathyroidism and hypocalcemia with teriparatide and supplemental calcium, while minimizing hypercalciuria and associated nephrocalcinosis. Presentation: No date and time listed