Autosomal Dominant Hypocalcemia Research Articles

CALIBRATE: A phase 3, randomized, open-label study evaluating the efficacy and safety of encaleret (CLTX-305) compared to standard of care in participants with autosomal dominant hypocalcemia type 1 [NCT05680818

CALIBRATE: A phase 3, randomized, open-label study evaluating the efficacy and safety of encaleret (CLTX-305) compared to standard of care in participants with autosomal dominant hypocalcemia type 1 [NCT05680818

An interesting case of co-existence of autosomal dominant hypocalcemia 1 with chronic myelogenous leukemia

An interesting case of co-existence of autosomal dominant hypocalcemia 1 with chronic myelogenous leukemia

Encaleret (CLTX-305) sustained normalization of mineral homeostasis in patients with autosomal dominant hypocalcemia type 1 over 18 months in a phase 2 study [NCT04581629

Encaleret (CLTX-305) sustained normalization of mineral homeostasis in patients with autosomal dominant hypocalcemia type 1 over 18 months in a phase 2 study [NCT04581629

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.

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

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

Treatment of Hypoparathyroidism by Re-Establishing the Effects of Parathyroid Hormone.

The conventional treatment of hypoparathyroidism (HypoPT) includes active vitamin D and calcium. Despite normalization of calcium levels, the conventional treatment is associated with fluctuations in calcium levels, hypercalciuria, renal impairment, and decreased quality of life (QoL). Replacement therapy with parathyroid hormone (PTH)(1-84) is an option in some countries. However, convincing beneficial effects have not been demonstrated, which may be due to the short duration of action of this treatment. Recently, palopegteriparatide (also known as TransCon PTH) has been marketed in Europe and is expected also to be approved in other countries. Palopegteriparatide is a prodrug with sustained release of PTH(1-34) designed to provide stable physiological PTH levels for 24 hours/day. A phase 3 study demonstrated maintenance of normocalcemia in patients with chronic HypoPT, with no need for conventional therapy. Furthermore, this treatment lowers urinary calcium and improves QoL. Another long-acting PTH analog with effects on the parathyroid hormone receptor (eneboparatide) is currently being tested in a phase 3 trial. Furthermore, the treatment of autosomal dominant hypocalcemia type 1 with a calcilytic (encaleret) is also being tested. All in all, improved treatment options are on the way that will likely take the treatment of HypoPT to the next level.

In vivo treatment with calcilytic of CaSR knock-in mice ameliorates renal phenotype reversing downregulation of the vasopressin-AQP2 pathway.

High concentrations of urinary calcium counteract vasopressin action via the activation of the Calcium-Sensing Receptor (CaSR) expressed in the luminal membrane of the collecting duct cells, which impairs the trafficking of aquaporin-2 (AQP2). In line with these findings, we provide evidence that, with respect to wild-type mice, CaSR knock-in (KI) mice mimicking autosomal dominant hypocalcaemia, displaya significant decrease in the total content of AQP2 associated with significantly higher levels of AQP2 phosphorylation at Ser261, a phosphorylation site involved in AQP2 degradation. Interestingly, KI mice also had significantly higher levels of phosphorylated p38MAPK, a downstream effector of CaSR and known to phosphorylate AQP2 at Ser261. Moreover, ATF1 phosphorylated at Ser63, a transcription factor downstream of p38MAPK, was significantly higher in KI. In addition, KI mice had significantly higher levels of AQP2-targeting miRNA137 consistent with a post-transcriptional downregulation of AQP2. In vivo treatment of KI mice with the calcilytic JTT-305, a CaSR antagonist, increased AQP2 expression and reduced AQP2-targeting miRNA137 levels in KI mice.Together, these results provide direct evidence for a critical role of CaSR in impairing both short-term vasopressin response by increasing AQP2-pS261, as well as AQP2 abundance, via the p38MAPK-ATF1-miR137 pathway. KEY POINTS: Calcium-Sensing Receptor (CaSR) activating mutations are the main cause of autosomal dominant hypocalcaemia (ADH) characterized by inappropriate renal calcium excretion leading to hypocalcaemia and hypercalciuria. Current treatments of ADH patients with parathyroid hormone, although improving hypocalcaemia, do not improve hypercalciuria or nephrocalcinosis. In vivo treatment with calcilytic JTT-305/MK-5442 ameliorates most of the ADH phenotypes of the CaSR knock-in mice including hypercalciuria or nephrocalcinosis and reverses the downregulation of the vasopressin-sensitive aquaporin-2 (AQP2) expression, providing direct evidence for a critical role of CaSR in impairing vasopressin response. The beneficial effect of calcilytic in reducing the risk of renal calcification may occur in a parathyroid hormone-independent action through vasopressin-dependent inhibition of cAMP synthesis in the thick ascending limb and in the collecting duct. The amelioration of most of the abnormalities in calcium metabolism including hypercalciuria, renal calcification, and AQP2-mediated osmotic water reabsorption makes calcilytic a good candidate as a novel therapeutic agent for ADH.

Hypocalcemia Diagnosis in the Surgical Environment.

Hypocalcemia, characterized by a total serum calcium level below 8.5 mg/dL (corrected for albumin) or an ionized serum calcium level below 4.65 mg/dL, presents a spectrum of clinical manifestations ranging from asymptomatic to life-threatening. Common after neck procedures, early detection and appropriate management are essential. Diagnostic tools include assessing calcium levels, correcting for albumin, and determining the underlying cause through tests like intact parathyroid hormone, serum phosphorus, magnesium, and creatinine. Treatment involves calcium replacement and addressing the root cause, with potential complications such as neuromuscular excitability and cardiac arrhythmias. Prognosis varies based on severity and underlying factors, emphasizing the importance of avoiding diagnostic pitfalls and overtreatment in chronic cases. ECG and genetic testing contribute to accurate diagnosis, aiding in differentiating causes like autosomal dominant hypocalcemia. Recognizing factitious hypocalcemia related to hypoalbuminemia or binding protein alterations is crucial. Understanding the pH-calcium relationship guides clinical evaluation. Holistic management requires a collaborative approach, emphasizing patient engagement and follow-up care.

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

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

SAT218 Refractory Hypocalcemia From Combined Autosomal Dominant Hypocalcemia Type 2 And Postsurgical Hypoparathyroidism

Abstract Disclosure: M. Sonmez Ince: None. F. Hannan: None. N. Esfandiari: None. M. Hussain: None. M.R. Haymart: None. R.V. Thakker: None. G.A. Clines: None. Background: Autosomal dominant hypocalcemia type 2 (ADH2), due to activating mutations in GNA11, is a rare disorder that causes hypocalcemia with low or inappropriately normal PTH. Postsurgical hypoparathyroidism (PSHP) is the most common etiology for hypoparathyroidism. The patient described was afflicted by both conditions and had persistent hypocalcemia despite aggressive management. Clinical Case: A 50-year-old female was found to have an enlarged thyroid on exam and subsequently diagnosed with papillary thyroid cancer (PTC). She underwent a total thyroidectomy without parathyroid autotransplantation since parathyroid glands were not identified during intraoperative pathologic survey. Surgical pathologic examination confirmed PTC with the identification of a single and small intrathyroidal parathyroid gland. Due to the patient’s low risk (T1N0M0), radioactive iodine ablation was not performed. Before thyroidectomy, serum corrected calcium was 6.4-8.5 mg/dL (8.6-10.3 mg/dL) and PTH was 9-21 pg/mL (10-65 pg/mL) during the previous 20 years. Following thyroidectomy, the patient had multiple emergency department visits due to hypocalcemia, hand cramping, and paresthesias. The patient was diagnosed with postsurgical hypoparathyroidism: corrected calcium 5.6-6.7 mg/dL, 24-hour urine calcium 112 mg (100-300 mg/24hour), magnesium 1.4-1.9 mg/dL (1.6-2.6 mg/dL), phosphorus 3-8.2 mg/dL (2.7-4.6 mg/dL). PTH remained <6 pg/mL. The patient was then referred to an academic endocrinology. TSH, AM cortisol, 25-vitamin D, iron, ceruloplasmin, copper, and 21-hydroxylase antibody concentrations were normal. Genetic testing revealed a pathogenic GNA11 variant (c.178C>T, p.(Arg60Cys)); no mutations were identified with CASR or AP2S1. Despite aggressive management with total daily oral calcitriol up to 12 mcg daily, calcium 8 grams, and chlorthalidone, the patient required calcium infusions thrice weekly. Despite the addition of teriparatide 20 mcg BID, the patient remained dependent on calcium infusions, with improvement after the addition of IV calcitriol. Recently, continuous teriparatide delivery was started using an Omnipod insulin pump that has significantly reduced the patient’s dependence on calcium infusions with serum calcium that are now 8-9 mg/dL. Conclusion: ADH2, due to gain-of-function mutations of GNA11, that encodes the Gα11 protein, causes life-long hypocalcemia that is often asymptomatic and undiagnosed. We report here the first documented case of combined ADH2 and PSHP. This case highlights that patients with ADH2 likely have hypoplastic parathyroid glands and that caution is required with procedures that may disrupt parathyroid gland function. Furthermore, the refractory nature of this patient’s hypocalcemia may suggest that GNA11 mutations in the kidney and skeleton reduce the effectiveness of standard hypocalcemia treatments. 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

SAT231 Next-generation Sequencing For Detection Of Underlying Genetic Causes Of Nonsurgical Hypoparathyroidism: Preliminary Results From A Sponsored Testing Program

Abstract Disclosure: M. Mannstadt: Advisory Board Member; Self; Takeda, Calcilytix, Amolyt. Research Investigator; Self; Takeda, Calcilytix, Amolyt. A. Mathew: Employee; Self; BridgeBio Pharma. A. Sridhar: Employee; Self; BridgeBio Pharma. L.S. Smith: Employee; Self; BridgeBio Pharma. M. Roberts: Employee; Self; BridgeBio Pharma. S. Adler: Employee; Self; BridgeBio Pharma. Hypoparathyroidism is a rare endocrine disorder characterized by inadequate production of parathyroid hormone to maintain normal blood calcium levels. Hypoparathyroidism is most frequently caused by damage to or removal of the parathyroid glands but can also be associated with genetic etiologies. Genetic forms of hypoparathyroidism can present as isolated or as part of a syndrome and include disorders of parathyroid gland formation, parathyroid hormone secretion, and damage to the parathyroid gland through autoimmunity. Genetic testing may uncover the underlying etiology of nonsurgical hypoparathyroidism and can help confirm clinical diagnosis, guide medical treatment, and identify affected family members. A sponsored genetic testing program was made available for patients with suspected genetic hypoparathyroidism who met program eligibility criteria. The next-generation sequencing panel has evolved to include 26 genes known to be associated with hypoparathyroidism: ACADM, AIRE, ATP1A1, CASR, CHD7, CLDN16, CLDN19, CNNM2, DHCR7, EGF, FAM111A, FXYD2, GATA3, GCM2, GNA11, HADHA, HADHB, KCNA1, NEBL, PTH, SEMA3E, SLC12A3, SOX3, TBCE, TBX1 and TRPM6. A total of 169 samples between December 2020 and December 2022 were tested from participants with a mean±SD age of 23.4±20.4 (range 0-81) who were diagnosed with nonsurgical/idiopathic hypoparathyroidism (73.9%), hypocalcemia suspected to be of genetic cause (23.7%) or had a relative with a confirmed diagnosis of genetic hypoparathyroidism (2.4%). Pathogenic or likely pathogenic variants, and variants of uncertain significance were identified in 64 individuals (37.9%). Amongst these 64 participants, 77 variants were detected with 46.9% of variant harboring individuals documented as having unknown or no family history. In order of frequency, the relative number of individuals with detected variants are as follows: CASR 56.3% (36/64), AIRE 12.5% (8/64), TBX1 9.38% (6/64), GATA3 7.8% (5/64), GNA11 6.25% (4/64), CHD7 3.13% (2/64), FAM111A 3.13% (2/64), PTH 3.13% (2/64), ACADM 1.6% (1/64), GCM2 1.6% (1/64), HADHB 1.6% (1/64) and TBCE 1.6% (1/64). Of note, 5 individuals had variants identified in more than 1 gene. Notably, these data demonstrate that genetic testing may identify clinically-relevant variants in approximately 2 of 5 individuals with nonsurgical hypoparathyroidism. The most common genetic form of hypoparathyroidism was found to be autosomal dominant hypocalcemia type 1 (21.3% of individuals tested; 36/169), caused by gain-of-function variants in the CASR gene. Overall, this ongoing sponsored testing program provides an efficient path to aid in the diagnosis of genetic causes and may ultimately improve the understanding and management of nonsurgical hypoparathyroidism. Presentation: Saturday, June 17, 2023

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.

Temperature sensing by the calcium-sensing receptor.

Whether GPCRs support the sensing of temperature as well as other chemical and physical modalities is not well understood. Introduction: Extracellular Ca2+ concentration (Ca2+ o) modulates core body temperature and the firing rates of temperature-sensitive CNS neurons, and hypocalcemia provokes childhood seizures. However, it is not known whether these phenomena are mediated by Ca2+ o-sensing GPCRs, including the calcium-sensing receptor (CaSR). In favor of the hypothesis, CaSRs are expressed in hypothalamic regions that support core temperature regulation, and autosomal dominant hypocalcemia, due to CaSR activating mutations, is associated with childhood seizures. Methods: Herein, we tested whether CaSR-dependent signaling is temperature sensitive using an established model system, CaSR-expressing HEK-293 cells. Results: We found that the frequency of Ca2+ o-induced Ca2+ i oscillations but not the integrated response was linearly dependent on temperature in a pathophysiologically relevant range. Chimeric receptor analysis showed that the receptor's C-terminus is required for temperature-dependent modulation and experiments with the PKC inhibitor GF109203X and CaSR mutants T888A and T888M, which eliminate a key phosphorylation site, demonstrated the importance of repetitive phosphorylation and dephosphorylation. Discussion and Conclusion: CaSRs mediate temperature-sensing and the mechanism, dependent upon repetitive phosphorylation and dephosphorylation, suggests that GPCRs more generally contribute to temperature-sensing.

A hypercalcemic episode in an adolescent with autosomal dominant hypocalcemia.

A hypercalcemic episode in an adolescent with autosomal dominant hypocalcemia.

Monogenic causation of pediatric nephrolithiasis

Nephrolithiasis is a condition in which crystals precipitate out of the urine forming kidney stones in the renal calyces and pelvis. Approximately 80% of stones are composed of calcium oxalate and calcium phosphate. In recent years, there has been a significant increase in the prevalence of nephrolithiasis across populations, specifically in that of the pediatric population. The etiology of stone disease is multifactorial, and includes environmental, dietary, hormonal, and genetic factors. Evidence for monogenic causation (also known as Mendelian or single-gene disorders) in nephrolithiasis includes the finding that 30% of children with stone disease report a positive family history, with monogenic nephrolithiasis accounting for approximately 30% of cases. Monogenic nephrolithiasis can occur in isolation or may be the result of an underlying genetic disorder including autosomal dominant hypocalcemia (ADH), primary hyperoxalurias, and hereditary hypophosphatemic rickets with hypercalciuria (HHRH), to name a few. Currently, there are 41 known genes that represent monogenic causes of human nephrolithiasis. Since early detection of these mutations can in some cases prevent the progression to end stage kidney disease in pediatric patients, establishing the genetic basis for nephrolithiasis is increasingly important. Here we provide an overview of kidney stone disease in children with a focus on monogenic causation in the pediatric population.

АУТОСОМНО-ДОМИНАНТНАЯ ГИПОКАЛЬЦИЕМИЯ: ОПИСАНИЕ СЕМЕЙНОГО НАБЛЮДЕНИЯ

Autosomal dominant hypocalcemia (ADH), or familial hypocalciuric hypercalcemia (FHH) is a rare hereditary disease manifested by hypocalcemia and hypercalciuria due to a malfunction of the calcium-sensitive receptor (mutations in the CASR or GNA11 genes). A familial clinical case of ADH is presented: the disease was diagnosed in a 36 y/o female and her two male children of 11 and 1.5 y/o. The disease was detected in an older child aged 7 years on the basis of convulsive syndrome, decreased blood calcium and parathyroid hormone, increased calciuria and detection of a mutation in the CASR gene (c.344-358del TTGCTCAAAACAAAA/ p.116 120delAQNKI). The initial manifestations of the disease in the form of a convulsive syndrome were observed in a child starting his 2nd day of life and were regarded as a manifestation of epilepsy, which was then followed by a long non-convulsive period. The patient needs constant therapy with alfacalcidol and has nephrocalcinosis. Based on the diagnosis made, the disease was also confirmed in his mother as the asymptomatic hypocalcemia and a mutation in the CASR gene were found. The woman does not need drug therapy, does not have nephrocalcinosis. In the youngest child, the diagnosis was suspected at birth on the basis of convulsions, hypocalcemia and was subsequently confirmed then by the detection of a mutation in the CASR gene. The course of the disease in the youngest child is severe, aggravated by the presence of perinatal CNS lesions and epilepsy. The patient has been receiving therapy with alfacalcidol since birth, has manifestations of severe nephrocalcinosis with a decrease in the filtration function of the kidneys. To stop the convulsive syndrome the patient needs to maintain a higher level of blood calcium, which is complicated due to hypercalciuria and causes chronic kidney disease. Conclusion: the observed familial case demonstrates the polymorphism of the course of the disease, and, given the rarity of the disease and the nonspecificity of manifestations, the description of this case will improve the awareness of medical practitioners of various specialties about the disease for its timely diagnosis.

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.

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