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.

Measuring Calcium-Sensing Receptor Agonist-Driven Insertional Signaling (ADIS) and Trafficking by TIRF Microscopy.

The calcium-sensing receptor (CaSR), which regulates parathyroid hormone secretion by sensing serum calcium concentrations, has developed unique trafficking mechanisms to respond to constant exposure to its orthosteric ligand calcium. CaSR rapidly responds to fluctuations in serum calcium by driving forward trafficking of the receptor to cell surfaces in a mechanism known as agonist-driven insertional signaling (ADIS). This increase in CaSR at cell surfaces is counterbalanced by both constitutive and agonist-driven internalization of the receptor. Deciphering these mechanisms is important to understand how mutations in the CaSR and components of its signaling and trafficking pathways cause human disorders of calcium homeostasis.This chapter describes a protocol to measure CaSR ADIS and endocytosis in parallel using total internal reflection fluorescence (TIRF) microscopy. This utilizes a mammalian expression construct comprising the full-length human CaSR with an N-terminal bungarotoxin minimal-binding site that can be labeled with commercially available fluorescent ligands to measure endocytosis, and a super-ecliptic pHluorin (SEP) to measure total cell surface expression and exocytic events. This protocol could easily be adapted to simultaneously assess forward trafficking and endocytosis of other membrane proteins by TIRF microscopy.

A Curious Case of Severe Recurrent Hypocalcemia.

Hypocalcemia, characterized by low blood calcium levels, can range from asymptomatic to life-threatening. Common causes include hypoparathyroidism and vitamin D deficiency (VDD). Pseudohypoparathyroidism is a rare metabolic disorder marked by resistance to parathyroid hormone (PTH). This report details a young female presenting with severe hypocalcemia, hyperphosphatemia, and elevated PTH levels. She also had an associated VDD, which complicated the clinical picture. Despite receiving intravenous calcium and oral supplementation, she required extended treatment and readmission. Genetic testing revealed a variant in the CACNA1S gene. Her condition eventually stabilized with a strict, adjusted treatment regimen. This case underscores the importance of a systematic diagnostic approach, prolonged intravenous calcium therapy, and close monitoring. Pseudohypoparathyroidism represents a rare cause of severe hypocalcemia, emphasizing the need for close monitoring and regular follow-up to achieve improved outcomes.

Receptor activity-modifying protein modulation of parathyroid hormone-1 receptor function and signaling.

Introduction: Receptor activity-modifying proteins (RAMPs) are known to modulate the pharmacology and function of several G-protein-coupled receptors (GPCRs), including the parathyroid hormone 1 receptor (PTH1R). However, the precise effects of different RAMPs on PTH1R signalling and trafficking remain poorly understood. This study investigated the impact of RAMP2 and RAMP3 on PTH1R function using a range of PTH and PTH-related protein (PTHrP)-derived ligands. Methods: We employed FRET imaging to assess PTH1R interactions with RAMPs. Cell surface expression of PTH1R was evaluated in the presence of RAMPs. PTH1R-mediated cAMP accumulation, ß-arrestin recruitment, and calcium signalling were measured in response to various ligands. Antibody-capture scintillation proximity assays were used to examine G-protein activation patterns. Results: PTH1R preferentially interacted with RAMP2 and, to a lesser extent, RAMP3, but not with RAMP1. RAMP3 co-expression reduced cell surface expression of PTH1R. RAMP2 significantly enhanced PTH1R-mediated signalling responses to PTH (1-34), PTHrP (1-34), PTH (1-84), and PTH (1-17) analogue ZP2307, while RAMP3 co-expression attenuated or abolished these responses. Full-length PTHrP analogues exhibited lower potency and efficacy than PTHrP (1-34) in activating PTH1R. RAMP2 increased the potency and/or efficacy of these analogues, whereas RAMP3 reduced these responses. RAMP2 differentially modulated G-protein activation by PTH1R in a ligand-dependent manner, with PTH (1-34) and PTHrP (1-34) inducing distinct patterns of G-protein subtype activation. Discussion: These findings highlight the complex role of RAMPs in regulating PTH1R signalling and trafficking, revealing differential effects of RAMP2 and RAMP3 on receptor function. The data suggest that targeting the PTH1R/RAMP2 complex may be a promising strategy for developing novel bone anabolic therapies by leveraging biased agonism and functional selectivity. Further research using physiologically relevant models is needed to elucidate the therapeutic potential of this approach.

Environmental pollution impact on the severity of some rheumatic diseases: a comparative analytical study on inflammatory and non-inflammatory samples.

OBJECTIVE: Environmental pollution of heavy metals is increasingly a problem and has become of great concern due to the adverse effects it causes worldwide. Heavy metal exposure has been implicated in health problems, including fibromyalgia and rheumatoid arthritis. We aim to evaluate the rule of chronic heavy metals toxicity on the induction of vitamin D3 (VD) deficiency and parathyroid hormone (PTH) disturbances in an inflammatory disease like rheumatoid arthritis (RA) and non-inflammatory disease like fibromyalgia syndrome (FMS). METHODS: This comparative analytical study was conducted on sixty adults (age ≥ 18 years). Participants were divided into three groups. Group I: twenty patients diagnosed with RA according to the specific ACR/EULAR criteria for RA. Group II: twenty patients diagnosed with FMS according to the specific 2010 (ACR) criteria for FMS. Group III: twenty healthy adults. All patients and controls were subjected to routine laboratory tests as well as the measurement of PTH, VD and estimation of serum levels of lead, cadmium, and chromium. RESULTS: VD was significantly inversely correlated to PTH, lead, cadmium, chromium, and activity scores in the RA and FMS groups. Lead, Cadmium and Chromium had a significant independent risk on the VD level in RA patients, while lead had a significant independent risk on the VD level in FMS patients. CONCLUSION: Heavy metals may affect VD synthesis, leading to hypovitaminosis D and secondary hyperparathyroidism in RA and FMS patients. Heavy metals play a key role in the pathogenesis of RA, FMS, and their disease activity.

Primary Hyperparathyroidism With Undetectable Intact Parathyroid Hormone.

Hypercalcemia can result from either hyperparathyroidism or non-parathyroid conditions. When hypercalcemia is accompanied by undetectable parathyroid hormone (PTH) levels, hyperparathyroidism is rarely considered the diagnosis. Herein, we report the case of a 65-year-old Caucasian woman referred to our hospital for further evaluation of hypercalcemia. Her symptoms included fatigue and brain fog, with undetectable PTH levels. A comprehensive workup, including a series of laboratory and imaging tests, excluded common non-parathyroid causes such as malignancy and familial hypocalciuric hypercalcemia. Ultrasound identified a likely enlarged parathyroid gland, which was further confirmed by a sestamibi scan. After 2 weeks of cinacalcet treatment, the patient's calcium levels decreased, indicating the parathyroid gland as the likely source of hypercalcemia. Parathyroidectomy was subsequently performed, revealing a 1927 mg adenoma. Postoperatively, the patient's calcium levels normalized, PTH levels became detectable within the normal range, and her symptoms resolved, with a marked improvement in energy. This case demonstrates that primary hyperparathyroidism can present with hypercalcemia and undetectable PTH. A genetic mutation in the PTH gene within the adenoma may explain the undetectable PTH levels preoperatively.

This case report discusses a 65-year-old woman who was found to have high calcium levels in her blood, a condition known as hypercalcemia. Typically, hypercalcemia can result from either a condition where the parathyroid glands produce too much parathyroid hormone (PTH) or from other non-parathyroid-related issues like cancer. However, when hypercalcemia occurs with undetectable levels of PTH, it is unusual for hyperparathyroidism to be the cause. In this patient's case, she experienced symptoms like fatigue and brain fog, but her initial tests showed undetectable PTH levels. Further tests ruled out other common causes of high calcium, such as cancer or a genetic condition called familial hypocalciuric hypercalcemia. An ultrasound and a special scan called a sestamibi scan revealed an enlarged parathyroid gland, suggesting the presence of a parathyroid adenoma, a non-cancerous tumor. To confirm this, the doctors gave the patient a medication called cinacalcet, which is known to lower calcium levels if the parathyroid glands are involved. After two weeks of treatment, her calcium levels dropped, indicating that the parathyroid gland was indeed the source of the problem. The patient underwent surgery to remove the adenoma, which weighed nearly two grams. Following the surgery, her calcium levels returned to normal, and her PTH levels became detectable again within the normal range. Her symptoms, including fatigue, improved significantly, and she reported feeling more energetic. This case is unusual because it demonstrates that primary hyperparathyroidism can still be the cause of hypercalcemia even when PTH levels are initially undetectable. The doctors suspect that a genetic mutation in the adenoma might explain why PTH levels were undetectable before surgery. This case emphasizes the importance of thorough clinical evaluation, even when initial test results are not typical.

Promotion of mandibular distraction osteogenesis by parathyroid hormone via macrophage polarization induced through iNOS downregulation.

Objective: To investigate whether Parathyroid hormone (PTH) can promote mandibular distraction osteogenesis by regulating macrophage polarization and the underlying mechanisms of this phenomenon. Methods: Forty-eight Rabbits were used to establish the mandibular distraction osteogenesis experimental model, randomly divided into 2 groups. Intermittent post-operative injections of 20 µg/kg PTH and normal saline were administered to the experimental and control groups, respectively. Regenerated new bone was examined using HE staining, osteoclast numbers were determined through tartrate-resistant acid phosphatase (TRAP) staining, and macrophage polarization markers arginase 1 (Arg1) and inducible nitric oxide synthase (iNOS) expressions were elucidated using immunohistochemistry (IHC), the mRNA expression of CD206, CD11C, Arg1 and iNOS were detected using qPCR. Results: The bone trabeculae in the experimental group were thicker, with a more homogeneous structure and more new osteoid than in the control group. In the area of distraction osteogenesis, the osteoclast count in the experimental group was higher than in the control group (P < 0.05). IHC results indicated differential expressions of Arg1 and iNOS in the experimental group compared to the control group (P < 0.05). Relative mRNA expressions of CD11c and iNOS were lower in the experimental group than in the control group (P < 0.05), whereas the expressions of CD206 and Arg1 mRNA were higher in the experimental group compared to the control group (P < 0.05). Conclusion: Intermittent PTH injections increased macrophage quantity in the mandible generated by distraction osteogenesis, downregulated iNOS, upregulated Arg1, and promoted macrophage polarization from M1 to M2 phenotype, thereby promoting mandibular distraction osteogenesis.

Enhancing parathyroid preservation in papillary thyroid carcinoma surgery using nano-carbon suspension.

This study evaluates the clinical significance of nano-carbon suspension in total thyroidectomy with cervical lymph node dissection for papillary thyroid carcinoma (PTC). The objective of this study was to assess the efficacy of nano-carbon suspension in enhancing parathyroid gland preservation, reducing postoperative complications, and improving surgical precision. A retrospective analysis on 219 PTC patients who underwent total thyroidectomy with cervical lymph node dissection between March 2014 and March 2018 was conducted. Patients were divided into two groups: an experimental group (n = 107) that received nano-carbon suspension and a control group (n = 112) that did not. Comparative analyses included demographics, surgical parameters, postoperative calcium and parathyroid hormone (PTH) levels, the number of dissected lymph nodes, and the incidence of complications. Baseline characteristics, including age, sex, and BMI, showed no statistically significant differences between the experimental and control groups. Postoperative calcium levels were significantly more stable in the experimental group, with median levels of 2.22 mmol/L on day 1 versus 2.06 mmol/L in the control group (P < 0.001), and 2.29 mmol/L at week 1 versus 2.22 mmol/L (P < 0.001). PTH levels were higher in the experimental group (35 pg/mL on day 1 versus 28 pg/mL, P < 0.001; 37 pg/mL at week 1 versus 30 pg/mL, P < 0.001). The experimental group had a greater median number of dissected lymph nodes (median 11.00 versus 7.00, P < 0.001) and a lower pathological parathyroid gland count (6.5% versus 23.2%, P < 0.001). Postoperative numbness and twitching were significantly reduced (4.7% versus 16.1%, P = 0.006), and the recurrence rate at 12 months was lower (4.7% versus 12.5%, P = 0.040). The use of Nano-carbon suspension in thyroidectomy and cervical lymph node dissection for PTC enhances parathyroid gland preservation, improves surgical precision, and reduces specific postoperative complications, supporting its standard adoption in thyroid cancer surgeries to optimize patient outcomes.

Three Siblings With Familial Isolated Hypoparathyroidism: A Diagnostic Journey From CASR to Novel GCM2 Variant.

We report a patient who initially presented at 4 days old with hypocalcemia, hypoparathyroidism, and elevated phosphorous level. Treatment was initiated with calcitriol, calcium carbonate (CaCO3), vitamin D, and low phosphorous formula. Family history was positive for an activating calcium sensing receptor (CASR) variant (R990G) identified previously in 2 older siblings who were treated with CaCO3 and calcitriol. However, genetic studies were negative for the CASR variant in our patient. She maintained a large calcium requirement and was admitted for multiple episodes of hypocalcemia. Further investigation revealed that the CASR variant identified in the older siblings was now considered a benign, nondisease-causing variant. Whole exome sequencing on our proband revealed a homozygous pathogenic variant in the GCM2 gene (Gln392*) consistent with a molecular diagnosis of familial isolated hypoparathyroidism. Genetic studies revealed the 2 older siblings harbor the same genetic changes and parents are heterozygous carriers for this allele. Due to persistent hypocalcemia, we initiated teriparatide. She weaned off calcitriol and achieved normocalcemia on teriparatide, CaCO3, and vitamin D. Siblings transitioned to the same treatment without complications. These findings demonstrate the importance of adequate diagnostic genetic testing and the role of variant reanalysis over time in promoting accurate diagnoses.

Carotid intima-media thickness, fibroblast growth factor 23, and mineral bone disorder in children with chronic kidney disease.

BACKGROUND: Carotid intima-media thickness (cIMT) is a measure of atherosclerotic vascular disease and a surrogate biomarker for cardiovascular risk in patients with chronic kidney disease (CKD). Mineral and bone disorders (MBD) are complications of CKD, contributing to vascular calcification and accelerated atherosclerosis. Increased fibroblast growth factor 23 (FGF23)-the earliest detectable serum abnormality associated with CKD-MBD-has been linked with cardiovascular disease in patients with CKD. This study aimed to identify factors and analyze the relationship associated with high cIMT, high FGF23, and poor MBD control in children with CKD. METHODS: A cross-sectional study was conducted in Yogyakarta, Indonesia recruiting children with CKD. The correlations and factors between cIMT, FGF23, and MBD were explored. RESULTS: We recruited 42 children aged 2-18 years old with CKD stages 2 to 5D. There were no significant correlations between cIMT and factors including advanced CKD, use of dialysis, body mass index, hypertension, anemia, MBD, FGF23 levels, and left ventricular mass index (LVMI). Patients with advanced CKD had poorly controlled anemia, hypertension, and higher LVMI. In multivariate analysis, CKD stages, hypertension stages, the presence of MBD, and LVMI were associated with FGF23 levels (p < 0.05). CONCLUSIONS: FGF23 levels increased with CKD progression, and MBD was more prevalent in advanced kidney disease. Elevated FGF23 is potentially associated with increased MBD prevalence in late-stage CKD. A larger study is needed to confirm the factors affecting cIMT in children with CKD.

Lower Parathyroid Hormone Levels are Associated With Reduced Fracture Risk in Japanese Patients on Hemodialysis.

Introduction: Secondary hyperparathyroidism (SHPT) affects bone metabolism and may lead to bone fragility. However, there is conflicting evidence as to whether parathyroid hormone (PTH) levels are associated with fracture risk and whether the relationship is linear or U-shaped. Methods: We examined the association between PTH levels and the risk of any fracture and site-specific fractures in a nationwide cohort of 180,333 patients on hemodialysis. We also examined the association between the percent change in PTH levels during the preceding 1 year and subsequent fracture. Results: At baseline, the median intact PTH level was 141 pg/ml (interquartile range, 78-226 pg/ml). During 1 year of follow-up, there were a total of 3762 fractures requiring hospitalization (1361 hip, 551 vertebral, and 1850 other). In an adjusted analysis, higher baseline PTH levels were associated with an incrementally increased risk of any fracture (odds ratio [OR] per doubling of intact PTH, 1.06; 95% confidence interval, 1.03-1.09). The association between PTH levels and fracture risk was more pronounced for hip fractures but not found for vertebral fractures. The absolute risk difference associated with higher PTH levels appeared to be more pronounced in older individuals, females, and those with lower body mass index (BMI). Change in PTH levels was also associated with fracture risk: the adjusted OR for fracture decreased linearly with decreasing PTH levels over 1 year, regardless of the preceding PTH levels. Conclusion: Lower PTH levels are associated with a graded reduction in fracture risk. Further studies are needed to determine whether intensive PTH control reduces fracture risk.

Multiple Reaction Monitoring-Mass Spectrometric Immunoassay Analysis of Parathyroid Hormone Fragments with Vitamin D Deficiency in Patients with Diabetes Mellitus.

Current immunoassay techniques for analyzing clinically relevant parathyroid hormone (PTH) circulating fragments cannot distinguish microheterogeneity among structurally similar molecular species. This hinders the identification of molecular species and the capture of target analyte information. Since structural modifications are important in disease pathways, mass spectrometry can detect, identify, and quantify heterogeneous ligands captured by antibodies. We aimed to create a sensitive and selective multiple reaction monitoring-mass spectrometric immunoassay analysis (MRM-MSIA)-based method for detecting and quantifying PTH fragments or proteoforms for clinical research. Our study established MRM transitions using triple-quadrupole tandem mass spectrometry for the signature peptides of five PTH fragments. This method was validated according to FDA guidelines, employing the mass spectrometric immunoassay (MSIA) protocol to bolster detection selectivity and sensitivity. This validated approach was applied by analyzing samples from type 2 diabetes mellitus (T2DM) patients with and without vitamin D deficiency. We found serum PTH fragments associated with vitamin D deficiency in patients with and without T2DM. We developed and validated the MRM-MSIA technique specifically designed for the detection and quantification (amino acid (aa38-44), (aa45-51), and (aa65-75)) of these fragments associated with vitamin D deficiency and T2DM. This study is the first to accurately quantify plasma PTH fragments using MRM-MSIA, demonstrating its potential for clinical diagnostics.

Short and long-term effects of kidney donation on mineral and bone metabolism.

BACKGROUND: Living kidney donors (LKD) experience an abrupt decline in glomerular filtration rate (GFR) resulting in abnormalities of mineral and bone metabolism (MBD), and this may have implications for skeletal health. We prospectively studied acute and long term MBD adaptation of LKD from two kidney transplant centers (São Paulo, Brazil and Miami, USA). METHODS: Renal function and MBD parameters longitudinally after kidney donation (baseline - D0, day 1, 14, 180 and 360 post-operatively) were measured in 74 patients (40 y, 73% female, 54% Brazilian). A subset of 20 donors from Brazil were reassessed after 10 years of nephrectomy. RESULTS: At baseline, Brazilian donors presented lower intact FGF23 (20.8 vs. 80.1 pg/mL, P < 0.01) and higher PTH (47.4 vs. 40.1, P = 0.04) than their US counterparts. GFR decreased to 63% of its baseline levels just after donation but improved 10% during the first year. PTH levels increased on D1, returning to baseline levels on D14, while FGF23 remained higher than baseline over the first year. LKD had a significant reduction of serum phosphate on D1, which returned to baseline levels on D180. A higher fractional excretion of phosphate (FEP) was noted since D14. After 10 years of donation, 20 LKD presented a sustained reduction in GFR (74.8 ± 14mL/min). There was a return to baseline in serum FGF23 [21.8 (18-30) pg/mL] and FEP, accompanied by an increase in serum calcium. PTH remained elevated (57.9 ± 18 pg/mL), whereas serum calcitriol and Klotho were lower than before the donation. CONCLUSIONS: The abrupt decline in kidney mass is associated with an increase in PTH and FGF23 that is not explained by phosphate retention. In a long-term evaluation, LKD showed a sustained drop in GFR, with lower serum calcitriol and Klotho, and higher PTH. The effects of these changes should be investigated in further studies.

Efficacy and Safety of TransCon PTH in Adults with Hypoparathyroidism: 52-Week Results From the Phase 3 PaTHway Trial.

CONTEXT: Conventional therapy for hypoparathyroidism aims to alleviate symptoms of hypocalcemia but does not address insufficient parathyroid hormone (PTH) levels. OBJECTIVE: Assess the long-term efficacy and safety of TransCon PTH (palopegteriparatide) for hypoparathyroidism. DESIGN: Phase 3 trial with a 26-week double-blind, placebo-controlled period followed by a 156-week open-label extension (OLE). SETTING: 21 sites across North America and Europe. PARTICIPANTS: 82 adults with hypoparathyroidism were randomized and received study drug and 78 completed week 52. INTERVENTION(S): All OLE participants received TransCon PTH administered once daily. MAIN OUTCOME MEASURE(S): Multi-component efficacy endpoint: proportion of participants at week 52 who achieved normal serum calcium (8.3-10.6 mg/dL) and independence from conventional therapy (≤600 mg/day of elemental calcium and no active vitamin D). Other efficacy endpoints included patient-reported outcomes (PROs) and bone mineral density (BMD). Safety was assessed by 24-hour urine calcium and treatment-emergent adverse events (TEAEs). RESULTS: At week 52, 81% (63/78) met the multi-component efficacy endpoint, 95% (74/78) achieved independence from conventional therapy, and none required active vitamin D. PROs showed sustained improvements in quality of life, physical functioning, and well-being. Mean BMD Z-scores decreased toward age- and sex-matched norms from baseline to week 52. Mean (SD) 24-hour urine calcium excretion decreased from 376 (168) mg/day at baseline to 195 (114) mg/day at week 52. Most TEAEs were mild or moderate and none led to trial discontinuation during the OLE. CONCLUSIONS: At week 52 of the PaTHway trial, TransCon PTH showed sustained efficacy, safety, and tolerability in adults with hypoparathyroidism.

Dietary phosphorus and renal disease in cats: where are we?

PRACTICAL RELEVANCE: Phosphorus is an essential nutrient required for the normal function of every cell in the body and a deficiency in dietary phosphorus may lead to adverse effects. Conversely, high dietary phosphorus may cause kidney damage in otherwise healthy adult cats, particularly when provided in highly bioavailable forms and when the calcium-to-phosphorus ratio is low. For cats that have chronic kidney disease (CKD), phosphorus is the most important mineral in its pathogenesis and morbidity. As the disease progresses, elevated phosphorus may increase the risk of complications such as soft tissue mineralization, which can lead to a further decrease in renal function. Additionally, the hormones secreted in response to increased circulating phosphorus have harmful effects, such as bone resorption, and can cause cardiovascular pathology. Very low phosphorus diets can also be problematic in cats with early CKD, potentially leading to hypercalcemia. CLINICAL CHALLENGES: There is currently a lack of maximum safety limits for dietary phosphorus in accepted nutritional guidelines in North American and Europe, which makes it difficult to assess the safety of some higher phosphorus cat foods. Additionally, information regarding phosphorus bioavailability is unknown for many diets and there are no commercially available tests. Similarly, there is no consensus regarding phosphorus requirement and recommended intake in cats with International Renal Interest Society stage 1-4 CKD despite there being targets for serum phosphorus. AIMS: This review evaluates dietary phosphorus in healthy cats and cats with renal disease, and describes how newer research is informing evolving clinical approaches in feline nutrition. AUDIENCE: The article is aimed at general practitioners, internal medicine specialists and veterinary nutritionists. EVIDENCE BASE: Information provided in this article is drawn from the published literature.

Case report: Familial hypoparathyroidism with elevated parathyroid hormone due to an inactivating PTH mutation.

Introduction: So far, only 11 PTH mutations have been described as causes of familial isolated hypoparathyroidism (FIH). In this report, we describe a family with FIH but with significant elevation of functionally inactive PTH due to a PTH mutation. We also show a positive therapeutic outcome of recombinant human PTH (teriparatide) therapy in one of the siblings who was not well controlled on large doses of calcitriol and calcium replacement therapy. Case description: The proband is a 34-year-old woman who has a history of chronic severe hypocalcemia (HypoCa) since birth. She and her three brothers (33-year-old male twins, and a 21-year-old male) were diagnosed with pseudohypoparathyroidism type 1b (PHPT 1b) based on the presence of chronic HypoCa (serum Ca 1.6-1.85 mmol/l) since birth associated with significantly elevated plasma PTH levels in the range of 310-564 pg/dl (normal range 10-65) and absence of signs of Albright hereditary osteodystrophy. Molecular studies: WES showed no pathogenic, likely pathogenic or variants of unknown significance in any known calcium-associated genetic disorder but a bi-allelic variant in the PTH itself ((NM_000315.4:c.128G>A, p.Gly43Glu). This was confirmed by Sanger sequencing in the patient and her affected brothers. Management: Because the patient's HypoCa was not controlled on large doses of calcitriol and calcium carbonate, a trial of teriparatide 20 mcg SC daily was started and resulted in normalization of calcium, decline in PTH levels and significant improvement in her general wellbeing. Conclusion: High PTH in the presence of congenital hypocalcemia is not always due to receptor or post-receptor defect and can be due to a biologically inactive mutated PTH. In such cases, treatment with teriparatide may result in stabilization of biochemical profile and improvement in quality of life.

Recurrent acute pancreatitis as an initial presentation of primary hyperparathyroidism: A case report.

BACKGROUND: With 4.9 to 35 instances per 100000 cases, hyperparathyroidism is one of the rarest causes of acute pancreatitis. The major cause of primary hyperparathyroidism is a parathyroid adenoma, which can manifest clinically in various ways. CASE SUMMARY: We discuss the unusual case of a 13-year-old boy with recurrent pancreatitis as the initial presentation of primary hyperparathyroidism. The cause of his recurrent pancreatitis remained unknown, and the patient had multiple admissions with acute pancreatitis over 3 years. His diagnosis was delayed due to the initial normal levels of parathyroid hormone, which were later reported elevated in a subsequent episode where ultrasound neck and thyroid scintigraphy revealed a parathyroid adenoma as the underlying cause. After the diagnosis was made, he underwent surgical resection of the adenoma. CONCLUSION: This case study stresses the importance of considering uncommon causes for recurrent pancreatitis.

COVID-19-Induced Refractory Symptomatic Hypocalcemia in a Patient With Parathyroid Gland Reimplantation.

Background: Several cases of severe hypocalcemia in the setting of COVID-19 have been reported. The proposed mechanisms include direct viral interaction with ACE2 receptors in the parathyroid gland, viral chelation of calcium, worsening hypovitaminosis D, critical illness leading to unbound fatty acids binding calcium, and inflammatory cytokines leading to PTH resistance. Given the life-threatening nature of hypocalcemia, this underrecognized phenomenon should be on the forefront of the clinician's attention. This case highlights a rare manifestation of COVID-19 and further complicated by the patient's reimplanted parathyroid gland. Presentation: A 73-year-old female with primary hyperparathyroidism status post parathyroidectomy with reimplantation in the left forearm presented with 4 days of viral syndrome, found to have tetany and Chvostek's sign on physical exam. Pertinent laboratory abnormalities included calcium 5.3 mg/dL, ionized calcium 0.44 mmol/L, magnesium 1.4 mg/dL, phosphorous 5.5 mg/dL, PTH 242 pg/mL, and 25-OH vitamin D 56 ng/mL. Chest CT revealed multifocal pneumonia consistent with positive COVID-19 testing. She was subsequently admitted to the ICU for severe, symptomatic hypocalcemia and was initiated on a continuous calcium infusion, remdesivir, baricitinib, and steroids. Tetany resolved after 9 g calcium repletion, and she was transferred to the medical floor with an ionized calcium of 0.83 mmol/L. On hospital day 3, repeat ionized calcium was 0.78 mmol/L despite ongoing repletion. Given the persistence of hypocalcemia, a repeat PTH level was obtained which remained high at 487 pg/mL, suggesting ongoing PTH interference in the setting of COVID-19. PTH was obtained from the right (nonimplanted) arm which was normal at 74 pg/mL. This indicated an appropriate PTH response from the reimplanted gland, and that ongoing hypocalcemia may be due to insufficient PTH function to maintain systemic calcium levels or a peripheral interference with PTH level. With continued calcium supplementation and treatment of COVID-19, the patient's calcium stabilized at 8.6 mg/dL. She was discharged on oral calcium supplementation with endocrinology follow-up. Conclusion: Acute hypocalcemia strongly correlates with a profound inflammatory response in COVID-19 patients. This case corroborates the cytokine/PTH hypothesis. This patient had a high PTH sampled near the reimplanted gland but an inappropriately normal PTH from the nonimplanted arm, indicating that direct viral interaction interfering with PTH release is an unlikely mechanism. This case represents a scenario where PTH can be sampled directly from the source and this type of model could aid in the process of determining the etiology of hypocalcemia in COVID-19.

Causal effects of serum calcium, phosphate, and 25-hydroxyvitamin D on kidney function: a genetic correlation, pleiotropic analysis, and Mendelian randomization study.

Background: Existing studies investigating the impact of serum calcium (Ca), phosphate (P), 25 hydroxyvitamin D (25[OH]D), and parathyroid hormone (PTH) levels on kidney function have produced inconsistent results. Further research is needed to establish the direct causal relationship between these factors and kidney function. Methods: The study used genome-wide association study datasets for exposure and outcome, mainly derived from the UK Biobank and CKDGen Consortium, with sample sizes ranging from 3,310 to 480,699 individuals of European ancestry. Heritability and genetic correlations among these phenotypes were assessed using linkage disequilibrium score regression (LDSC) and phenotypes with a heritability z-score <4 were excluded from further analyses. Pleiotropic analyses were performed to identify potential horizontal pleiotropic variants at gene and LD-independent locus levels. Mendelian randomization (MR) analysis, using instrumental variables (IVs) based on two distinct selection criteria, was conducted to investigate the potential causal relationships between serum Ca, P, 25(OH)D, PTH, and kidney function. Results: PTH was excluded from further analysis due to a heritability z-score < 4. Genetic correlations were observed between serum Ca and urine albumin-to-creatinine ratio (UACR) (rg = 0.202, P-value = 5.0E-04), between serum 25(OH)D and estimated glomerular filtration rate using serum creatinine (eGFRcrea) (rg = -0.094; P-value = 1.4E-05), and between serum 25(OH)D and blood urea nitrogen (BUN) (rg = 0.127; P-value = 1.7E-06). In univariable MR analysis using IVs based on two different selection criteria, it consistently demonstrated that genetically predicted serum Ca consistently showed an increase in UACR (beta 0.11, P-value 2.0E-03; beta 0.13, P-value 2.0E-04). Similarly, serum P was associated with a decrease in eGFRcrea (beta -0.01, P-value 2.0E-04; beta -0.005, P-value 2.0E-03) and an increase in BUN (beta 0.02, P-value 3.0E-03; beta 0.02, P-value 7.5E-07). The influence of serum P on kidney function was further supported in multivariable MR analysis. However, genetically predicted 25(OH)D did not have a significant impact on kidney function. Conclusions: Elevated serum Ca or P levels could both impair kidney function, whereas 25(OH)D has no impact on renal function.