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The calcium-sensing receptor (CaSR) provides the major mechanism for the detection of extracellular calcium concentration in several cell types, via the induction of G-protein-coupled signalling. Accordingly, CaSR plays a pivotal role in calcium homeostasis, and the CaSR gene defects are related to diseases characterized by serum calcium level changes. Activating mutations of the CaSR gene cause enhanced sensitivity to extracellular calcium concentration resulting in autosomal dominant hypocalcemia or Bartter-syndrome type V. Inactivating CaSR gene mutations lead to resistance to extracellular calcium. In these cases, familial hypocalciuric hypercalcaemia (FHH1) or neonatal severe hyperparathyroidism (NSHPT) can develop. FHH2 and FHH3 are associated with mutations of genes of partner proteins of calcium signal transduction. The common polymorphisms of the CaSR gene have been reported not to affect the calcium homeostasis itself; however, they may be associated with the increased risk of malignancies.

The history of parathyroid hormone (PTH) replacement therapy for hypoparathyroidism begins in 1929. In 2015, the Food and Drug Administration approved recombinant human PTH(1-84) [rhPTH(1-84)] as a treatment for hypoparathyroidism. Long-term studies of rhPTH(1-84), up to 6 years, have demonstrated continued efficacy of this replacement agent. Approaches to optimize PTH treatment in hypoparathyroidism include subcutaneous pump delivery systems, long-lived carrier molecules, and long-acting PTH analogues that show promise to prolong efficacy. Calcilytic compounds have been explored as a treatment for autosomal dominant hypocalcemia. Calcilytics are negative modulators of the calcium-sensing receptor and may present a therapeutic opportunity to increase endogenous PTH synthesis and secretion.

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by gain-of-function pathogenic variants in the gene encoding the calcium-sensing receptor (CaSR). It is characterized by variable degrees of hypocalcemia, hyperphosphatemia, and hypomagnesemia, with inappropriately low levels of parathyroid hormone (PTH) and hypercalciuria. Conventional therapy includes oral calcium and activated Vitamin D supplementation, which can lead to or exacerbate hypercalciuria. As a result, patients may develop nephrolithiasis and/or nephrocalcinosis, which can progress to renal insufficiency. Calcilytics (antagonists of the CaSR) have demonstrated in in vitro and in vivo models of ADH1, as well as in a small clinical trial (Roberts et al, JBMR 2019), the ability to shift the dose-response relationship between extracellular calcium and the cellular response of cells bearing the mutant CaSR towards normal. This shift has the potential to increase endogenous PTH secretion which in turn may promote skeletal release of calcium into the bloodstream, production of endogenous calcitriol, renal excretion of phosphate, and renal reabsorption of calcium. Additionally, direct effects of calcilytics on renal CaSRs may further reduce renal calcium and magnesium excretion in ADH1. Taken together, this class of drugs has the capacity to restore normal mineral homeostasis, without calcium and activated vitamin D supplements and without attendant risks of iatrogenic hypercalciuria. This Phase 2b, open-label, dose-ranging study will evaluate the safety, tolerability, pharmacodynamics, and pharmacokinetics of the calcilytic encaleret (CLTX-305) in up to 16 participants with ADH1 (NCT04581629). The study will consist of 3 periods. In periods 1 and 2, participants will undergo a 1-week inpatient evaluation to study the safety and tolerability of daily and twice-daily doses of encaleret. Period 3 will follow participants for up to 24 weeks of continuous outpatient dosing, with periodic inpatient and outpatient assessments. The primary endpoint of period 3 is the change from baseline in albumin-corrected blood calcium concentration. Secondary endpoints of the study include the change in urine calcium (fractional and 24-hour excretion), 1,25-dihydroxy-Vitamin D, phosphate, magnesium, and other blood/urine biomarkers. Enrollment for this study at the National Institutes of Health (NIH) began in September 2020 with topline results expected in 2021. This study is supported by Calcilytix Therapeutics, Inc. and the NIH Intramural Research Program.

Hypoparathyroidism is a rare endocrine disorder most commonly caused by anterior neck surgery. The next most common cause is thought to be autoimmune disorders. After this, less common causes include iron or copper overload, tumor infiltration of the parathyroid glands, or radiation treatment. Rare patients have inherited or genetic forms of hypoparathyroidism, either presenting as isolated hypoparathyroidism or with syndromic features.

Hypoparathyroidism, a disorder characterized by hypocalcemia ensuing from inadequate parathyroid hormone secretion, is a rather rare disorder caused by multiple etiologies. When not caused by inadvertent damage or removal of the parathyroids during neck surgery, it is usually genetically determined. Epidemiological figures of this disease are still scarce and mainly limited to countries where non-anonymous databases are available and to surgical case series. Both the surgical and non-surgical forms pose diagnostic challenges. For surgical hypoparathyroidism, transient forms have to be ruled out even in the long term, in order to avoid unnecessary chronic replacement therapy with calcium and calcitriol. Regarding non-surgical hypoparathyroidism, once referred to as idiopathic, a systematic clinically and genetically-driven approach to define the precise diagnosis have to be pursued. In the case of syndromic hypoparathyroidism, patients have to be screened for associated abnormalities. Autoimmune, non-genetic hypoparathyroidism is still a diagnosis of exclusion, since no specific autoantibodies are specific for this condition.

Background: Autosomal dominant hypocalcemia (ADH) is characterized by hypocalcemia and hyperphosphatemia due to hypoparathyroidism. ADH type 1 is caused by gain-of-function variants in CASR gene coding the calcium-sensing receptor. Recently, ADH type 2 caused by gain-of-function variants in GNA11 gene coding G-protein subunit α11 has been recognized. Case: A 32-year-old female patient visited our hospital because she suffered from hyperhidrosis, exertional dyspnea, and palpitations. She had a past medical history of paroxysmal kinesigenic dyskinesia confirmed by genetic analysis of PRRT2. Although her sister has unspecified epilepsy, no members of her kindred have episodes of tetany. Her height was 155.7 cm and weight was 64.1 kg. She had goiter with tremor and tachycardia and was diagnosed as Graves’ disease (fT3 >32.55 pg/mL, fT4 >7.77 ng/dL, TSH A resulted in p.Phe341Leu. There were no relevant pathogenic variants in other candidate genes such as CASR, PTH, and GCM2. Treatment with 2 µg/day of alfacalcidol and 1200 mg/day of calcium aspartate could not normalize serum calcium level (7.0 mg/dL) and serum phosphate level (5.3 mg/dL) even after 1 year. Conclusions: The pathogenicity of the variant, p.Phe341Leu, in GNA11 gene was previously confirmed [1]. ADH type 2 is extremely rare as our literature review found only four previous reports; 17 patients in 5 families [1–4]. Phenotypes of the present case are mild and skeletal growth is normal. Meanwhile, we are having difficulty in management of her hypocalcemia, even though Graves’ disease might affect her bone metabolism. Optimal therapy for ADH type 2 needs further investigation. References: [1] Nesbit et al. Mutations Affecting G-protein Subunit α11 in Hypercalcemia and Hypocalcemia. N Engl J Med. 2013; 368: 2476–2486. [2] Li et al. Autosomal Dominant Hypoparathyroidism Caused by Germline Mutation in GNA11: Phenotypic and Molecular Characterization. J Clin Endocrinol Metab. 2014; 99: 1774–83. [3] Piret et al. Identification of a G-Protein Subunit-α11 Gain-of-Function Mutation, Val340Met, in a Family With Autosomal Dominant Hypocalcemia Type 2 (ADH2). J Bone Miner Res. 2016; 31: 1207–14. [4] Tenhola et al. Impaired Growth and Intracranial Calcifications in Autosomal Dominant Hypocalcemia Caused by a GNA11 Mutation. Eur J Endocrinol. 2016; 175: 211–8.

Germline loss- and gain-of-function mutations of G-protein α-11 (Gα11), which couples the calcium-sensing receptor (CaSR) to intracellular calcium (Ca(2+) i) signaling, lead to familial hypocalciuric hypercalcemia type 2 (FHH2) and autosomal dominant hypocalcemia type 2 (ADH2), respectively, whereas somatic Gα11 mutations mediate uveal melanoma development by constitutively up-regulating MAPK signaling. Cinacalcet and NPS-2143 are allosteric CaSR activators and inactivators, respectively, that ameliorate signaling disturbances associated with CaSR mutations, but their potential to modulate abnormalities of the downstream Gα11 protein is unknown. This study investigated whether cinacalcet and NPS-2143 may rectify Ca(2+) i alterations associated with FHH2- and ADH2-causing Gα11 mutations, and evaluated the influence of germline gain-of-function Gα11 mutations on MAPK signaling by measuring ERK phosphorylation, and assessed the effect of NPS-2143 on a uveal melanoma Gα11 mutant. WT and mutant Gα11 proteins causing FHH2, ADH2 or uveal melanoma were transfected in CaSR-expressing HEK293 cells, and Ca(2+) i and ERK phosphorylation responses measured by flow-cytometry and Alphascreen immunoassay following exposure to extracellular Ca(2+) (Ca(2+) o) and allosteric modulators. Cinacalcet and NPS-2143 rectified the Ca(2+) i responses of FHH2- and ADH2-associated Gα11 loss- and gain-of-function mutations, respectively. ADH2-causing Gα11 mutations were demonstrated not to be constitutively activating and induced ERK phosphorylation following Ca(2+) o stimulation only. The increased ERK phosphorylation associated with ADH2 and uveal melanoma mutants was rectified by NPS-2143. These findings demonstrate that CaSR-targeted compounds can rectify signaling disturbances caused by germline and somatic Gα11 mutations, which respectively lead to calcium disorders and tumorigenesis; and that ADH2-causing Gα11 mutations induce non-constitutive alterations in MAPK signaling.

Objective: To discuss the case of a woman and her father with autosomal dominant hypocalcemia (ADH), a rare disorder caused by an activating mutation of the calcium-sensing receptor (CaSR).Methods: Previous ADH case reports were obtained by Medline search and from an updated CaSR database.Results: A 37-year-old female presented with intermittent leg cramps and hypocalcemia. Her father had been previously diagnosed with asymptomatic hypocalcemia at age 54. Genetic analysis in both individuals revealed identical missense mutations in nucleotide c.2489G>A that resulted in a glycine to aspartic acid change at codon 830 (G830D) in the CaSR.Conclusion: The same mutation of the CaSR gene was identified in a woman and her father. This warrants the need for genetic testing in adults with mild hypocalcemia and a family history of hypocalcemia.Abbreviations: ADH = autosomal dominant hypocalcemia CaSR = calcium-sensing receptor iPTH = intact parathyroid hormone OMIM = Online Mendelian Inheritance in Man TMD = transmembrane domain

The calcium sensing receptor (CaSR) plays an important role in calcium homeostasis. Activating mutations of CaSR cause autosomal dominant hypocalcemia by affecting parathyroid hormone secretion in parathyroid gland and calcium resorption in kidney. They can also cause a type 5 Bartter syndrome by inhibiting the apical potassium channel in the thick ascending limb of the loop of Henle in the kidney. This study presents a patient who had autosomal dominant hypocalcemia with Bartter syndrome due to an activating mutation Y829C in the transmembrane domain of the CaSR. Symptoms of hypocalcemia occurred 12 days after birth and medication was started immediately. Medullary nephrocalcinosis and basal ganglia calcification were found at 7 years old and at 17 years old. Three hypercalcemic episodes occurred, one at 14 years old and two at 17 years old. The Bartter syndrome was not severe while the serum calcium concentration was controlled, but during hypercalcemic periods, the symptoms of Bartter syndrome were aggravated.

Subcutaneous Parathyroid Hormone in ADH1 In this letter, the investigators report that continuous subcutaneous infusion of parathyroid hormone (1-34) in six patients who were between the ages of 5 ...