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Query: UMLS:C0020437 (hypercalcemia)
 10,293 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In mammals a complicated homeostatic mechanism has evolved to maintain near consistency of extracellular calcium ion levels. The homeostatic mechanism involves several hormones, which comprise among others, parathyroid hormone and vitamin D. The recent resurge in vitamin D deficiency, as a global health issue, has increased interest in the hormone. In addition to vitamin D deficiency, other causes of rickets are calcium deficiency and inherited disorders of vitamin D and phosphorus metabolism. Vitamin D-resistant syndromes are caused by hereditary defects in metabolic activation of the hormone or by mutations in the vitamin D receptor, which binds the hormone with high affinity and regulates the expression of genes through zinc finger mediated DNA binding and protein-protein interaction. Current interest is to correlate the type/position of mutations that result in disorders of vitamin D metabolism or in vitamin D receptor function with the variable phenotypic features and clinical presentation. The calcium sensing receptor plays a key role in calcium homeostasis. Loss of function mutations in the calcium sensing receptor can cause familial benign hypocalciuric hypercalcemia in heterozygotes and neonatal severe hyperparathyroidism when homozygous mutations occur in the calcium sensing receptor. Gain of function mutation can cause the opposite effect causing autosomal dominant hypocalcemia. Mouse models using targeted gene disruption strategies have been valuable tools to study the effect of mutations on the calcium sensing receptor or in the vitamin D activation pathway. Dysfunctional calcium sensing receptors with function altering mutations may be responsive to treatment with allosteric modulators of the calcium sensing receptor. Vitamin D analogs which induce unusual structural conformations on the vitamin D receptor may have a variety of therapeutic indications. This review summarises recent advances in knowledge of the molecular pathology of inherited disorders of calcium homeostasis.
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PMID:Inherited disorders of calcium homeostasis. 1847 31

The cloning of the calcium sensing receptor (CaR) confirmed that parathyroid cells monitor extracellular calcium concentration ([Ca2+]ext) via a receptor-type mechanism. This lead to the hypothesis that abnormalities in the expression and/or function of the CaR could explain the biochemical abnormalities in primary hyperparathyroidism (PHPT). Cultured cells from parathyroid adenomas of patients operated for PHPT were used to monitor real-time changes in intracellular calcium concentration ([Ca2+]i) as measured by fluorescent microscopy using the Fura-2/AM dye. We found that CaR agonists trigger release of intracellular calcium pools and such responses are amplified by increasing the affinity of IP3 receptors. Using confocal microscopy to monitor membrane trafficking in living parathyroid cells labelled with the fluorescent dye FM1-43, we found that a decrease in [Ca2+]i rather than an absolute change in [Ca2+]ext is the main stimulus for exocytosis from human parathyroid cells. These data suggest that, in PHPT, a defective signalling mechanism from the CaR allows cells from parathyroid adenomas to maintain low [Ca2+]i with uninhibited PTH secretion in the face of hypercalcaemia. Over longer periods of time, CaR controls parathyroid proliferation via changes in tyrosine phosphorylation. We found that multiple proteins of molecular weight 20-65 kDa are phosphorylated within 10-60 min in response to CaR agonists. Further work demonstrated that high [Ca2+]i stimulates the expression of bcl-2 oncoprotein in cultured human parathyroid cells and that, in parathyroid adenomas, predominant expression of bcl-2 rather than bax oncoprotein might prevent apoptosis and explain the slow growth rate of these tumours. More recently, it became apparent that CaR stimulates cell proliferation in several cell types not involved in calcium homeostasis. Using archived histological material from 65 patients who died with metastatic breast cancer, we identified CaR expression predominantly in tumours from patients who developed bone rather than visceral metastases (35 of 49 versus 7 of 16; P < 0.01, chi-squared test). These data suggest that CaR expression has the potential to become a new biological marker predicting the risk of bone metastases in patients with breast cancer. A prospective study should investigate if patients with CaR-positive tumours are more likely to develop bone metastases and whether they could benefit more from prophylactic treatment with bisphosphonates or the newly developed CaR antagonists.
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PMID:The calcium sensing receptor: from understanding parathyroid calcium homeostasis to bone metastases. 1849 87

The calcium sensing receptor (CaSR) is a Family C/3 G protein-coupled receptor that translates changes in extracellular Ca(2+) into diverse intracellular signals. Loss-of-function mutations in human CaSR cause familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism. CaSR must navigate a number of endoplasmic reticulum quality control checkpoints during biosynthesis, including a conformational/functional checkpoint. Here we examine the biosynthesis of 25 CaSR mutations causing familial hypocalciuric hypercalcemia /neonatal severe hyperparathyroidism using immunoprecipitation, biotinylation, and functional assays. We define classes of CaSR mutants based on their biosynthetic profile. Class I CaSR mutants are not rescued to the plasma membrane. To dissect the organellar compartments that class I mutants can access, we engineered a cleavage site for the proprotein convertase furin into the extracellular domain of wild-type CaSR and class I mutants. Based on absence or presence of cleavage fragments, we find most mutants are degraded from the endoplasmic reticulum (no furin-mediated cleavage), whereas others access the Golgi (furin-mediated cleavage) before degradation. Class II CaSR mutants show increased expression and/or enhanced plasma membrane localization upon treatment with MG132 or the pharmacochaperone NPS R-568, permitting assay of functional activity. Of the 10 CaSR mutants that exhibit plasma membrane localization, only two did not show enhanced functional activity after rescue with NPS R-568. The established approaches can be used with current and newly identified CaSR mutations to identify the location of biosynthetic block and to determine the likelihood of rescue by allosteric agonists.
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PMID:Pharmacochaperone-mediated rescue of calcium-sensing receptor loss-of-function mutants. 1938 9

We report a patient with familial hypocalciuric hypercalcemia (FHH) associated with primary hyperparathyroidism (PHPT) and incidental papillary thyroid carcinoma. The patient showed hypercalcemia, high parathyroid hormone (PTH) levels and low urinary calcium excretion. A computed tomography (CT) scan revealed an enlarged parathyroid gland. Ultrasonography (US) and aspiration cytology revealed microcarcinoma of the left lobe of the thyroid gland. Screening studies of his family revealed that four of five family members had hypocalciuric hypercalcemia and normal PTH level. Sequencing analysis of the calcium sensing receptor gene revealed a novel heterozygous mutation (3193delA) in the patient and his family members with hypercalcemia, but one with normocalcemia. The patient underwent total thyroidectomy, central node dissection and extirpation of the enlarged parathyroid gland. Surgery is not indicated for FHH; however, FHH may be accompanied with parathyroid adenoma causing PHPT, as reported here, for which surgical treatment is indicated.
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PMID:A patient with primary hyperparathyroidism associated with familial hypocalciuric hypercalcemia induced by a novel germline CaSR gene mutation. 1942 60

The calcium sensing receptor (CaSR) and fibroblast growth factor 23 (FGF-23) play central roles in the regulation of calcium and phosphorus metabolism, respectively. CaSR controls parathyroid hormone secretion and renal calcium reabsorption. Inactivating mutations of the CaSR result in conditions characterized by hypercalcemia and hypocalciuria, whereas activating lesions cause hypoparathyroidism and hypercalciuria. Calcimimetics are a group of agonists for the CaSR that have been shown to be powerful agents in the treatment of secondary hyperparathyroidism. FGF-23 acts on the kidney to inhibit the reabsorption of phosphate and the synthesis of 1,25(OH)(2)D. Disorders of increased FGF-23 function are associated with hypophosphatemia, inappropriately low 1,25(OH)(2)D levels, and either rickets or osteomalacia. Conversely, decreased FGF-23 activity results in hyperphosphatemia, increased 1,25(OH)(2)D levels, and abnormal soft-tissue calcification. In chronic kidney disease, increases in FGF-23 are being investigated as markers of disease progression.
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PMID:Emerging topics in pediatric bone and mineral disorders 2008. 1961 58

Familial hypocalciuric hypercalcemia (FHH) is known to be caused by heterozygous inactivating mutations of the calcium sensing receptor (CaSR) gene. We report an infant with transient neonatal hypercalcemia who was found to be homozygous for a polymorphism at A986S of the CaSR.
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PMID:Neonatal hypercalcemia due to polymorphisms of the calcium sensing receptor. 1969 4

Hypercalcemia and hypophosphatemia are symptoms of two relatively rare hereditary diseases and are extraordinarily important from the standpoint of the differential diagnosis. Mutation in calcium sensing receptor gene (CaSR) clinically manifests as familial hypocalciuric hypercalcemia (FHH) or as the much more serious neonatal hyperparathyreosis. Hypercalciuric hypocalcemia is extremely rare. Prognosis for the most frequent mutations in the CaSR gene FHH is considered benign; nevertheless, if overlooked it can lead to an incorrect diagnosis of primary hyperparathyreosis, which has a fundamentally different prognosis and treatment. Familial hypophosphatemia sometimes occurs as hereditary rickets, which is a consequence of insufficient production of vitamin D-hormone or abnormal function of vitamin D receptors (VDR). The disease manifests as X-linked dominant hypophosphatemic rickets or autosomal dominant hypophosphatemic rickets. Autosomal recessive form is very rare. Oncogenic hypophosphatemia should be excluded in differential diagnosis. In this review the issues of pathogenesis, differential diagnosis and treatment of FHH and hypophosphatemic rickets are discussed.
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PMID:[Familial hypercalcemia and hypophosphatemia: importance in differential diagnosis of disorders in calcium-phosphate metabolism]. 2057 89

There are few case reports describing small cell lung carcinoma (SCLC), which secrete parathyroid hormone (PTH)-related protein (PTHrP) and result in hypercalcemia. We have established a novel cell line, derived from a 37-year-old woman with SCLC, which produced PTH, PTH-rP, and a part of proopiomelanocortin (POMC), and led to hypercalcemia. The cell line, named SS-1, was grown as floating cell clusters in DMEM/F12 medium supplemented with 10% fetal bovine serum and had a population doubling time of 72 h. The modal chromosome number was 47 (88%); marker chromosomes were not observed. The SS-1 cell line secreted not only PTHrP but also PTH, and both were decreased by CaCl(2) administration. Decreasing the concentration of Ca(++) in the growth medium stimulated the secretion of both PTHrP and PTH. The cell line had calcium sensing receptor (Cas-R). Since PTHrP and PTH secretion from the SS-1 cells was related to Ca(++) concentration in the growth medium, the cell line might be useful for the study of PTH-rP and PTH regulation as well as for SCLC analysis. In addition, the cells secreted N terminal POMC, the precursor of adrenocorticotropic hormone, in response to stimulation with corticotropin releasing hormone. In summary, we established a novel cell line, SS-1 from SCLC, which produced PTHrP, PTH and N terminal POMC.
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PMID:Establishment and characterization of a novel cell line derived from a human small cell lung carcinoma that secretes parathyroid hormone, parathyroid hormone-related protein, and pro-opiomelanocortin. 2071 9

Calcium sensing receptor (CaSR) mutations implicated in familial hypocalciuric hypercalcemia, pancreatitis and idiopathic epilepsy syndrome map to an extended arginine-rich region in the proximal carboxyl terminus. Arginine-rich motifs mediate endoplasmic reticulum retention and/or retrieval of multisubunit proteins so we asked whether these mutations, R886P, R896H or R898Q, altered CaSR targeting to the plasma membrane. Targeting was enhanced by all three mutations, and Ca(2+)-stimulated ERK1/2 phosphorylation was increased for R896H and R898Q. To define the role of the extended arginine-rich region in CaSR trafficking, we independently determined the contributions of R890/R891 and/or R896/K897/R898 motifs by mutation to alanine. Disruption of the motif(s) significantly increased surface expression and function relative to wt CaSR. The arginine-rich region is flanked by phosphorylation sites at S892 (protein kinase C) and S899 (protein kinase A). The phosphorylation state of S899 regulated recognition of the arginine-rich region; S899D showed increased surface localization. CaSR assembles in the endoplasmic reticulum as a covalent disulfide-linked dimer and we determined whether retention requires the presence of arginine-rich regions in both subunits. A single arginine-rich region within the dimer was sufficient to confer intracellular retention comparable to wt CaSR. We have identified an extended arginine-rich region in the proximal carboxyl terminus of CaSR (residues R890 - R898) which fosters intracellular retention of CaSR and is regulated by phosphorylation. Mutation(s) identified in chronic pancreatitis and idiopathic epilepsy syndrome therefore increase plasma membrane targeting of CaSR, likely contributing to the altered Ca(2+) signaling characteristic of these diseases.
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PMID:Calcium sensing receptor mutations implicated in pancreatitis and idiopathic epilepsy syndrome disrupt an arginine-rich retention motif. 2079 21

Primary hyperparathyroidism (PHPT) is a common endocrinopathy, mostly caused by a monoclonal parathyroid adenoma. The hereditary syndromes include multiple endocrine neoplasia types 1 (MEN 1) and 2A (MEN 2A), hereditary hyperparathyroidism-jaw tumor (HPTJT), familial isolated hyperparathyroidism (FIHP), familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT). Mutations of MEN1 and CDKN1B genes are responsible for MEN 1 in 70-80% and about 2% of cases, respectively. MEN1 and CDKN1B genes have also a role in the pathogenesis of sporadic parathyroid adenomas. HRPT2/CDC73 gene mutations are responsible for HPT-JT and sporadic parathyroid carcinoma. MEN1 and HRPT2/CDC73 genes mutations have also been found in a subset of FIHP families. FHH and NSHPT represent the mildest and severest variants of PHPT, caused by heterozygous and homozygous mutations in the calcium sensing receptor (CASR) gene, respectively.
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PMID:Molecular pathogenesis of primary hyperparathyroidism. 2198 78


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