CASR Mutations Research Articles

A Case Presentation of Calcium in an Active Adolescent Male with CaSR Mutation Disorder

A Case Presentation of Calcium in an Active Adolescent Male with CaSR Mutation Disorder

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.

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 mM vs. 1.1 ± 0.23 mM, 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.

ODP280 A Unique Case of Coexisting Paraganglioma, Primary Hypoaldosteronism and Primary Hyperparathyroidism in a Single Patient

Abstract Introduction To date, case reports have shown an association between paraganglioma and primary hyperaldosteronism, and primary hyperparathyroidism with primary aldosteronism, but not for all three of the aforementioned endocrinopathies combined. Clinical Case A 54-year-old woman with history of uncontrolled HTN, hypokalemia, DM2, CKD stage III, Takotsubo cardiomyopathy and primary hyperparathyroidism presented to the hospital with back pain. CT scan showed a 4.3 cm necrotic retroperitoneal mass. Due to her labile blood pressure, ranging from 194/102 mmHg to 106/60 mmHg, endocrinology was consulted for evaluation of secondary hypertension. Plasma normetanephrines were 3447 pg/mL (n ≤ 57 pg/mL), 24-hour urine normetanephrines 5954 mcg/24 hours (n 122-676 mcg/24 hours) and 24-hour urine norepinephrines 476 mcg/24 hours (n 15-100 mcg/24 hours). 24-hour urine cortisol and 24-hour urine metanephrines were within normal limits. Plasma aldosterone level and plasma renin activity (PRA) were 19 ng/dL and 0.78 ng/mL/h (n 0.25-5.82 ng/mL/h),. However, the patient was also taking spironolactone and telmisartan which interfered with results, and withdrawal of interfering medications was considered unsafe. 68Ga-DOTATATE PET/CT showed mild uptake in a left para-aortic mass. Genetic testing did not show pathogenic mutations of AP2S1, CASR, MEN1, NF1, RET, SDHA, SDHAF2, SDHB, SDHC, TMEM127 or VHL genes. The patient was started on doxazosin and underwent successful removal of the left retroperitoneal mass consistent with paraganglioma. Six months later, surveillance testing showed normalization of fractionated plasma metanephrines and of 24-hour urine metanephrines. However, due to blood pressure of 152/100 mmHg and K of 2.8 mmol/L (n 3.5-4.7 mmol/L), concern was raised for primary hyperaldosteronism. After potassium repletion, labs showed plasma aldosterone of 37 ng/dL, PRA of 0.2 ng/mL/h (n 0.25-5.82 ng/mL/h) and ARR of 185 with potassium of 4.1 mmol/L (n 3.5-4.7 mmol/L) consistent with primary hyperaldosteronism. MRI of adrenal glands showed a left adrenal gland that was thickened and nodular but without discrete nodules &amp;gt; 1 cm. The patient was referred for adrenal vein sampling. Five years previously, the patient had been diagnosed with primary hyperparathyroidism, with PTH of 188.5 pg/mL (n 14-64 pg/dL), Calcium of 10.6 mg/dL (n 8.5-10.1 mg/dL) and GFR of 39. Pre-operative imaging with MRI neck had shown enlargement of two parathyroid glands. She had undergone two-gland parathyroidectomy with intraoperative PTH decrease of &amp;gt; 50% and normalization of calcium. However two weeks later, her PTH returned to pre-operative levels (with normal 25(OH)D) and continues to remains elevated. This has been attributed to underlying secondary hyperparathyroidism from her chronic kidney disease. Conclusion To our knowledge, this is a unique case of combined paraganglioma, primary hyperaldosteronism and primary hyperparathyroidism, as thorough literature review has not shown such a coexistence in the past. Presentation: No date and time listed

PSAT210 A Case of Asymptomatic Severe Hypocalcemia: Consideration of Genetic Causes

Abstract Calcium sensing receptor (CaSR) activating mutations are a rare etiology of calcium dyscrasias in the general population. Of these, hypocalciuric hypocalcemia and autosomal dominant hypocalcemia (ADH) type 1 are the most common subtypes, with a prevalence of 74.1 and 3.9 per 100,000, respectively. Although rare, these mutations should be considered in patients with a family history of hypocalcemia, particularly if asymptomatic, as the treatment goals and replacement strategies differ from typical primary hypoparathyroidism, with which they are often mistaken. We present a case of a 41-year-old male with a history of treated vitamin D deficiency and anxiety who presented to endocrinology clinic for severe asymptomatic hypocalcemia (serum calcium 6.0-7.0). Family history pertinent for a mother, sister, and brother also with hypocalcemia, and brother with single childhood hypocalcemic seizure at age 4. Patient reported being on and off calcium, calcitriol, and ergocalciferol for years and has never had any symptoms regardless of his regimen or serum calcium. Specifically, he had no personal history of paresthesia, muscle cramping, or kidney stones. No family history of osteoporosis, fracture, kidney stone, or renal disease. Laboratory evaluation over the last 30 years most pertinent for serum calcium 6.0-9.5 on varying supplement/medication regimens, low-normal PTH, initially elevated and now normal serum phosphorous, low-normal serum magnesium, and 24h urinary calcium quite variable but as high as &amp;gt;300mg/d (when serum calcium within normal limits). Genetic testing revealed a heterozygous DNA sequence change detected on exon 7 of the CaSR gene, which has been previously found to be a pathogenic cause of ADH. Activating mutations of the CaSR (typically ADH type 1) clinically present as hypocalcemia, low or low-normal PTH, hyperphosphatemia, hypomagnesemia, and increased urinary calcium. When starting the evaluation for these mutations, it is important to note that there are two types of ADH. Type 1 mutations occur as an activating mutation at the CaSR causing hypersensitivity to calcium, while type 2 activating mutations occur at a different locale (G alpha 11 subunit). Despite mutations at different sites, each type leads to a similar gain-of-function mutation and a very similar clinical presentation. The clinical significance of differentiating these diagnoses from primary hypoparathyroidism (PHP) lies in the goals of treatment and in the adverse effects of over-supplementation of calcium in ADH. In PHP, patients generally have symptomatic hypocalcemia, and calcium can and should be supplemented to prevent adverse events of chronic hypocalcemia. Contrastingly, in CaSR mutation conditions, mild and even significant hypocalcemia is well tolerated. If patients’ serum calcium is normalized, they often experience significant hypercalciuria and renal manifestations therein, such has nephrocalcinosis and nephrolithiasis. Therefore, treatment of patients with CaSR activating mutations should be aimed at relieving hypocalcemia symptoms, if any are present. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

The management of autosomal dominant hypoparathyroidism with CaSR mutation in pregnancy and breastfeeding

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Off-label use of cinacalcet in pediatric primary hyperparathyroidism: A French multicenter experience.

BackgroundCinacalcet is a calcimimetic approved in adults with primary hyperparathyroidism (PHPT). Few cases reports described its use in pediatric HPT, with challenges related to the risk of hypocalcemia, increased QT interval and drug interactions. In this study, we report the French experience in this setting.MethodsWe retrospectively analyzed data from 18 pediatric patients from 7 tertiary centers who received cinacalcet for PHPT. The results are presented as median (interquartile range).ResultsAt a median age of 10.8 (2.0–14.4) years, 18 patients received cinacalcet for primary HPT (N = 13 inactive CASR mutation, N = 1 CDC73 mutation, N = 1 multiple endocrine neoplasia type 1, N=3 unknown etiology). Cinacalcet was introduced at an estimated glomerular filtration rate (eGFR) of 120 (111–130) mL/min/1.73 m2, plasma calcium of 3.04 (2.96–3.14) mmol/L, plasma phosphate of 1.1 (1.0–1.3) mmol/L, age-standardized (z score) phosphate of −3.0 (−3.5;−1.9), total ALP of 212 (164–245) UI/L, 25-OHD of 37 (20–46) ng/L, age-standardized (z score) ALP of −2.4 (−3.7;−1.4), PTH of 75 (59–123) ng/L corresponding to 1.2 (1.0–2.3)-time the upper limit for normal (ULN). The starting daily dose of cinacalcet was 0.7 (0.6–1.0) mg/kg, with a maximum dose of 1.0 (0.9–1.4) mg/kg per day. With a follow-up of 2.2 (1.3–4.3) years on cinacalcet therapy, PTH and calcium significantly decreased to 37 (34–54) ng/L, corresponding to 0.8 (0.5–0.8) ULN (p = 0.01), and 2.66 (2.55–2.90) mmol/L (p = 0.002), respectively. In contrast, eGFR, 25-OHD, ALP and phosphate and urinary calcium levels remained stable. Nephrocalcinosis was not reported but one patient displayed nephrolithiasis. Cinacalcet was progressively withdrawn in three patients; no side effects were reported.ConclusionsCinacalcet in pediatric HPT can control hypercalcemia and PTH without significant side effects.

Potential genetic biomarker of Saudi Arabian patients with colorectal cancer.

Colorectal cancer (CRC) is one of the leading causes of cancer deaths globally. We implemented a comprehensive literature review regarding CRC genetics studies to offer a perception into the genes associated with CRC recognized in Saudi patients. Definite genetic variants in ABCB1, ADIPOQ, CTNNB1, SFRP3, LRP6, CYP19A1, PARP-1, TDG genes exhibited significant protection against CRC development in Saudi population. Whereas, other gene mutations in ABCB1, ABCC1, CASR, IL-17F, NOTCH1, NOTCH4, PRNCR1, TDG, TLR2, TLR4, TLR-9, TSLP, TSLPR and TNF-α genes showed irrelevant correlation with CRC risk in Saudi Arabia. On the other hand, specific mutations in ABCC1, ADIPOQ, CYP1A1, KIR, IL-17A, MMP2, NOTCH3, PRNCR1, RETN, TDG, TLR2, BRAF, PARP-1, TLR4, TLR-9, TNF-α, TSLP and XRCC1 genes demonstrated a substantial augmented CRC risk development in Saudi patients. Furthermore, ATR, ATM, BMI1, CCAT1, Chk1, Chk2, COX-2, FoxM1, FSCN1, Ki67, MALAT1, miR-29, miR-34a, miR-92, miR-182-5, PANDAR, PIK3CA, TIGAR over-expression revealed a robust association with CRC in Saudi Arabia (KSA). Moreover, gene alterations in APC, EGFR, FBXW7, TP53, PTEN, K-ras genes were concomitant in CRC. As well as, lower expression of MLH1, MSH2, MSH6, PMS2, EPCAM and MUTYH genes were recognized in LS patients and future CRC Saudi patients. These gene mutations may be used as diagnostic and/or prognostic genetic markers in CRC Saudi patients and could offer a potential therapeutic target for CRC management.

Differential parathyroid and kidney Ca2+-sensing receptor activation in autosomal dominant hypocalcemia 1.

SummaryBackgroundParathyroid Ca2+-sensing receptor (CaSR) activation inhibits parathyroid hormone (PTH) release, while activation of renal CaSRs attenuates Ca2+ transport and increases expression of the pore-blocking claudin-14. Patients with autosomal dominant hypocalcemia 1 (ADH1), due to activating CASR mutations, exhibit hypocalcemia but not always hypercalciuria (elevated Ca2+ in urine). The latter promotes nephrocalcinosis and renal insufficiency. Although CaSRs throughout the body including the kidney harbor activating CASR mutations, it is not understood why only some ADH1 patients display hypercalciuria.MethodsActivation of the CaSR was studied in mouse models and a ADH1 patient. In vitro CaSR activation was studied in HEK293 cells.FindingsCldn14 showed blood Ca2+ concentration-dependent regulation, which was absent in mice with kidney-specific Casr deletion, indicating Cldn14 is a suitable marker for chronic CaSR activation in the kidney. Mice with a gain-of-function mutation in the Casr (Nuf) were hypocalcemic with low plasma PTH levels. However, renal CaSRs were not activated at baseline but only after normalizing blood Ca2+ levels. Similarly, significant hypercalciuria was not observed in a ADH1 patient until blood Ca2+ was normalized. In vitro experiments indicate that increased CaSR expression in the parathyroid relative to the kidney could contribute to tissue-specific CaSR activation thresholds.InterpretationOur findings suggest that parathyroid CaSR overactivity can reduce plasma Ca2+ to levels insufficient to activate renal CaSRs, even when an activating mutation is present. These findings identify a conceptually new mechanism of CaSR-dependent Ca2+ balance regulation that aid in explaining the spectrum of hypercalciuria in ADH1 patients.FundingErasmus+ 2018/E+/4458087, the Canadian Institutes for Health research, the Novo Nordisk Foundation, the Beckett Foundation, the Carlsberg Foundation and Independent Research Fund Denmark.

Personalised medicines for familial hypercalcemia and hyperparathyroidism.

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

Novel Glial Cells Missing-2 (GCM2) variants in parathyroid disorders.

ObjectiveThe aim of this study was to analyze variants of the gene glial cells missing-2 (GCM2), encoding a parathyroid cell-specific transcription factor, in familial hypoparathyroidism and in familial isolated hyperparathyroidism (FIHP) without and with parathyroid carcinoma.DesignWe characterized 2 families with hypoparathyroidism and 19 with FIHP in which we examined the mechanism of action of GCM2 variants.MethodsLeukocyte DNA of hypoparathyroid individuals was Sanger sequenced for CASR, PTH, GNA11 and GCM2 mutations. DNA of hyperparathyroid individuals underwent MEN1, CDKN1B, CDC73, CASR, RET and GCM2 sequencing. The actions of identified GCM2 variants were evaluated by in vitro functional analyses.ResultsA novel homozygous p.R67C GCM2 mutation which failed to stimulate transcriptional activity in a luciferase assay was identified in affected members of two hypoparathyroid families. Oligonucleotide pull-down assay and in silico structural modeling indicated that this mutant had lost the ability to bind the consensus GCM recognition sequence of DNA. Two novel (p.I383M and p.T386S) and one previously reported (p.Y394S) heterozygous GCM2 variants that lie within a C-terminal conserved inhibitory domain were identified in three affected individuals of the hyperparathyroid families. One family member, heterozygous for p.I138M, had parathyroid carcinoma (PC), and a heterozygous p.V382M variant was found in another patient affected by sporadic PC. These variants exerted significantly enhanced in vitrotranscriptional activity, including increased stimulation of the PTH promoter.ConclusionsWe provide evidence that two novel GCM2 R67C inactivating mutations with an inability to bind DNA are causative of hypoparathyroidism. Additionally, we provide evidence that two novel GCM2 variants increased transactivation of the PTH promoter in vitro and are associated with FIHP. Furthermore, our studies suggest that activating GCM2 variants may contribute to facilitating more aggressive parathyroid disease.

One in a billion: a patient with Marfan syndrome and familial hypocalciuric hypercalcaemia.

SummaryMarfan syndrome is an autosomal dominant multisystem disorder that has an estimated incidence of 1 in 5000. It is caused by mutations in the FBN1 gene, which encodes the extracellular matrix protein type 1 fibrillin. Familial hypocalciuric hypercalcaemia (FHH), also inherited in an autosomal dominant pattern, is a rare benign disorder characterised by hypercalcaemia, hypocalciuria and relative hyperparathyroidism with normal or high plasma PTH levels, with an estimated incidence of between 1 in 10 000 to 1 in 100 000. We report a unique case of a 26-year-old man referred for investigation of hypercalcaemia, who also had clinical features of Marfan syndrome but no previous genetic investigations. Calculated fractional urinary excretion of calcium was low (0.0005) following correction of vitamin D deficiency, raising the possibility of FHH. Genetic testing for Marfan syndrome and FHH, via a hyperparathyroidism multiplex gene panel test, revealed a novel truncating variant in the FBN1 gene (c.8481T>G; p.(Tyr2827Ter)), consistent with Marfan syndrome; and a pathogenic truncating variant in the CaSR gene (c.741dupT; p.[Asp248Ter]), which confirmed the diagnosis of FHH. The patient’s mother was subsequently found to have mild hypercalcaemia (adjusted calcium 2.76 mmol/L) and is also heterozygous for the same CaSR mutation. Genetic testing of his father confirmed the presence of the same FBN1 gene mutation. This case illustrates the importance of making robust diagnoses in the era of modern genomic medicine, confirming FHH as the cause of hypercalcaemia means that no treatment is warranted and the patient can be reassured.Learning pointsFamilial hypocalciuric hypercalcaemia (FHH) should always be excluded during the investigation of hypercalcaemia by measuring urinary calcium: creatinine clearance ratio.Diagnosing FHH is important as the condition is benign and misdiagnosing patients with primary hyperparathyroidism could potentially lead to unnecessary morbidity from parathyroid surgery.Genetic testing is increasingly available for a variety of inherited conditions including Marfan syndrome and FHH. Patients who present with clinical features suggestive of a particular genetic condition should undergo prompt, appropriate confirmatory testing wherever possible.Taking a thorough family history is vital when assessing patients presenting with endocrine conditions, as this could prompt cascade testing and appropriate genetic counselling where necessary.

Novel Heterozygous Calcium Sensing Receptor (CASR) Genetic Variant in Child with Unique Phenotype: Hypocalcemia, Mandibular Hypoplasia, Renal Cysts and Type E Brachydactyly

Background: There are over 230 disease-causing variants in the calcium-sensing receptor gene (CaSR). Gain-of-function missense mutations in CaSR cause Autosomal Dominant Hypocalcemia (ADH) characterized by hypocalcemia (hCa), hypoparathyroidism (hPTH), and hypercalciuria. Patients with ADH are sensitive to fluctuations in serum calcium (Ca); and supplementation with Ca and vitamin D can cause inappropriate renal calcium retention leading to hypercalcemic events and long-term renal complications. Clinical Case: A 15-year-old adopted (at age 18 months) Korean female was initially diagnosed with hPTH and chronic hCa after presenting with hCa seizures. Laboratory values showed hCa (7.7 mg/dL), hyperphosphatemia (7.6 mg/dL) and hPTH (< 3 pg/mL.) Initially, she was treated with Ca supplementation (20 mg/kg/day elemental Ca), and calcitriol (0.01 mcg/kg/day). She presented at age 4 with hematuria and was found to have obstructive nephrolithiasis requiring operative intervention. Renal ultrasound (US) showed bilateral medullary nephrocalcinosis. She continued treatment with Ca and calcitriol. At age 6, a thiazide diuretic and potassium citrate supplement were added due to hypercalciuria. She had recurrent nephrolithiasis and persistent nephrocalcinosis. Follow-up renal US also showed bilateral renal cysts. Biweekly laboratory evaluation demonstrated an exuberant response to calcium supplementation. Serum Ca levels oscillated between 7.0 -10 mg/dL, but she showed minimal symptoms of hCa. At age 14, she was also recognized to have submandibular hypoplasia and brachydactyly of the 4th and 5th metacarpals and metatarsals bilaterally and genetic testing for CaSR gene mutation was requested. Sshe developed acute kidney injury and hypercalcemia, possibly precipitated by viral illness. However, 3 weeks before, calcitriol dose was increased to 1.25 mcg twice a day (0.07 mcg/kg/day). At admission, serum Ca was 12.7 mg/dL, iPTH 5.2 mg/dL, phosphorus 4.5 mg/dL, BUN 36 mg/dL, creatinine 1.85 mg/dL. Symptoms included headache, muscle spasm and throat spasm. She received intravenous fluids and recovered, but had an extended hospital stay. Targeted genetic analysis of the CaSR gene was completed, and identified a heterozygous variant (c.2506G>T, p.V836L) which is predicted to be likely pathogenic and cause ADH. After CaSR gene mutation identification, the calcitriol and also elemental Ca dosing were decreased to achieve a low Ca level (~7 mg/dL) with normal urine Ca/creatinine ratio. Patient remains asymptomatic. Conclusion: This is the first case of a novel mutation in the CaSR (c.2506G>T, p.V836L) associated with ADH, brachydactyly, renal cysts, and mandibular hypoplasia. Timely genetic testing for ADH in patients with newly diagnosed hPTH can lead to changes in therapy and improved prognosis.

Clinical Presentation and Management Approach in a Case of Familial Hypocalciuric Hypercalcemia Type 3 Due to APS21 Gene Mutation

Familial hypocalciuric hypercalcemia (FHH) is a genetic disorder caused by dysfunctional calcium homeostasis. Thus far, three types of FHH are known to be caused by mutations inCASR (FHH1), GNA11 (FHH2), and AP2S1 (FHH3). The patient in this case report is a 36-year old male that initially presented for a second opinion after being diagnosed with Primary Hyperparathyroidism(PHPT) with subsequent parathyroidectomy done at another institute, and developed recurrent symptomatic hypercalcemia. Prior to considering this patient for further surgical options, he underwent genetic testing, which revealed he had c.43C>T (p.Arg15Cys) mutation in the AP2S1 gene diagnostic of Familial Hypocalciuric Hypercalcemia Type 3 (FHH3). The patient’s father and sister also have hypercalcemia, and have been offered genetic testing. There have been cases reported of patients with FHH3 that have symptomatic hypercalcemia and that have associated cognitive issues. Many patients with FHH can be misdiagnosed and may undergo unnecessary parathyroidectomy. This case report further elucidates the need to raise awareness of FHH.

Differential activation of parathyroid and renal Ca 2+ ‐sensing receptors underlies the renal phenotype in autosomal dominant hypocalcemia 1

Parathyroid Ca2+-sensing receptor (CaSR) activation inhibits parathyroid hormone (PTH) release, while activation of CaSRs in kidneys and intestine attenuates local transepithelial Ca2+ transport. In patients with autosomal dominant hypocalcemia 1 (ADH1) due to activating CASR mutations, treatment of symptomatic hypocalcemia can be complicated by treatment-induced hypercalciuria, resulting in nephrocalcinosis and renal insufficiency. Although CaSRs throughout the body are activated by increased extracellular Ca2+ concentrations, it is not understood why some ADH1 patients have reduced PTH, but not hypercalciuria at presentation, despite CaSR expression in both kidney and parathyroid. Activation of the CaSR was studied in mouse models and a ADH1 patient. In vitro CaSR activation was studied in HEK293 cells. Mice with a gain-of-function mutation in Casr are hypocalcemic with reduced plasma PTH levels. However, renal CaSRs are not activated as indicated by normal urinary calcium handling and unaltered renal Cldn14 expression. Activation of renal CaSRs only occurred after increasing plasma Ca2+ levels. Similarly, calcimimetic administration to wildtype mice induced hypocalcemia without activating renal CaSRs. Moreover, significant hypercalciuria was not observed in an ADH1 patient until blood Ca2+ was normalized. In vitro experiments suggest that increased CaSR levels in the parathyroid relative to the kidney contribute tissue-specific CaSR activation thresholds. Here we delineate tissue-specific CaSR activation thresholds, where parathyroid CaSR overactivity can reduce plasma Ca2+ to levels insufficient to activate renal CaSRs, even with overactivating mutations. These findings may aid in the management of ADH1 patients.

Severe courses of neonatal FHH in paternally inherited CaSR mutations: Implications for perinatal monitoring and treatment

Severe courses of neonatal FHH in paternally inherited CaSR mutations: Implications for perinatal monitoring and treatment

A series of clinical cases of familial hypocalciuric hypercalcemia syndrome

Familial hypocalciuric hypercalcemia (FHH) - rare disease with predominantly autosomal dominant inheritance. FHH typically develops due to a heterozygous inactivating mutation in the calcium-sensitive receptor gene (CASR), less commonly due to heterozygous mutations in GNA11 and AP2S1. CASR mutations lead to an increase in the threshold for calcium sensitivity, which requires a higher concentration in serum to reduce the release of PTH. These changes are accompanied by an increase of calcium and magnesium reabsorption in the proximal tubules, which leads to hypercalcemia and hypocalciuria. Basically, FHH may be asymptomatic or accompanied by mild hypercalcemia. FHH doesn't require surgical treatment, unlike primary hyperparathyroidism (PHPT), therefore, differential diagnosis of these two conditions is extremely important. In addition, immediate relatives of a proband with FHH also require the exclusion of disease inheritance. We analyzed a series of clinical cases with a genetically confirmed diagnosis of FHH. Our clinical cases indicate a variety of clinical manifestations and the difficulties of differential diagnosis with PHPT.

The Calcium-Sensing Receptor Is Essential for Calcium and Bicarbonate Sensitivity in Human Spermatozoa.

The calcium-sensing receptor (CaSR) is essential to maintain a stable calcium concentration in serum. Spermatozoa are exposed to immense changes in concentrations of CaSR ligands such as calcium, magnesium, and spermine during epididymal maturation, in the ejaculate, and in the female reproductive environment. However, the role of CaSR in human spermatozoa is unknown. This work aimed to investigate the role of CaSR in human spermatozoa. We identified CaSR in human spermatozoa and characterized the response to CaSR agonists on intracellular calcium, acrosome reaction, and 3',5'-cyclic adenosine 5'-monophosphate (cAMP) in spermatozoa from men with either loss-of-function or gain-of-function mutations in CASR and healthy donors. CaSR is expressed in human spermatozoa and is essential for sensing extracellular free ionized calcium (Ca2+) and Mg2+. Activators of CaSR augmented the effect of sperm-activating signals such as the response to HCO3- and the acrosome reaction, whereas spermatozoa from men with a loss-of-function mutation in CASR had a diminished response to HCO3-, lower progesterone-mediated calcium influx, and were less likely to undergo the acrosome reaction in response to progesterone or Ca2+. CaSR activation increased cAMP through soluble adenylyl cyclase (sAC) activity and increased calcium influx through CatSper. Moreover, external Ca2+ or Mg2+ was indispensable for HCO3- activation of sAC. Two male patients with a CASR loss-of-function mutation in exon 3 presented with normal sperm counts and motility, whereas a patient with a loss-of-function mutation in exon 7 had low sperm count, motility, and morphology. CaSR is important for the sensing of Ca2+, Mg2+, and HCO3- in spermatozoa, and loss-of-function may impair male sperm function.

Disordered Gut Microbiota in Children Who Have Chronic Pancreatitis and Different Functional Gene Mutations.

OBJECTIVES:Chronic pancreatitis (CP) is a serious condition whose pathogenic mechanism is unclear. Interactions of host genetic factors with gut microbiota have a role, but little is known, especially in children with CP (CCP), in which the external factors are less important. Our objective was to identify the main gut microbiota genera in CCP and to characterize the functional mutations of these patients.METHODS:We used 16S rRNA sequencing to compare the gut microbiota of healthy controls with patients who had CCP and different functional gene mutations.RESULTS:CCP is characterized by gut microbiota with remarkably reduced alpha diversity. Receiver operating characteristic curve analyses indicated that the abundances of 6 genera—Faecalibacterium, Subdoligranulum, Phascolarctobacterium, Bifidobacterium, Eubacerium, and Collinsella—were significantly decreased in CCP, with an area under curve (AUC) of 0.92 when considering all 6 genera together. Functional analysis of gut microbiota in CCP indicated reduced ribosomal activity, porphyrin and chlorophyll metabolism, starch and sucrose metabolism, and aminoacyl-tRNA biosynthesis, but an enrichment of phosphotransferase system pathways. The abundance of Butyricicoccus was significantly decreased in CCP in the presence of CFTR mutations when combined with mutations in CASR, CTSB, SPINK1, and/or PRSS1. The abundance of Ruminococcaceae was significantly increased in CCP when there were mutations in CASR, CTSB, SPINK1, and/or PRSS1. Patients with CCP but no gene mutations had greater abundances of Veillonella and reduced abundances of Phascolarctobacterium.DISCUSSION:CCP is associated with a depletion of probiotic gut microbiota, and CCP patients with different functional gene mutations have different gut microbiota.