Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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

Familial hypocalciuric hypercalcemia (FHH) is caused by heterozygous loss-of-function mutations in the calcium-sensing receptor (CASR), in which the lifelong hypercalcemia is generally asymptomatic. Homozygous loss-of-function CASR mutations manifest as neonatal severe hyperparathyroidism (NSHPT), a rare disorder characterized by extreme hypercalcemia and the bony changes of hyperparathyroidism, which occur in infancy. Activating mutations in the CASR gene have been identified in several families with autosomal dominant hypocalcemia (ADH), autosomal dominant hypoparathyroidism, or hypocalcemic hypercalciuria. Individuals with ADH may have mild hypocalcemia and relatively few symptoms. However, in some cases seizures can occur, especially in younger patients, and these often happen during febrile episodes due to intercurrent infection. Thus far, 112 naturally-occurring mutations in the human CASR gene have been reported, of which 80 are unique and 32 are recurrent. To better understand the mutations causing defects in the CASR gene and to define specific regions relevant for ligand-receptor interaction and other receptor functions, the data on mutations were collected and the information was centralized in the CASRdb (www.casrdb.mcgill.ca), which is easily and quickly accessible by search engines for retrieval of specific information. The information can be searched by mutation, genotype-phenotype, clinical data, in vitro analyses, and authors of publications describing the mutations. CASRdb is regularly updated for new mutations and it also provides a mutation submission form to ensure up-to-date information. The home page of this database provides links to different web pages that are relevant to the CASR, as well as disease clinical pages, sequence of the CASR gene exons, and position of mutations in the CASR. The CASRdb will help researchers to better understand and analyze the mutations, and aid in structure-function analyses.
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PMID:CASRdb: calcium-sensing receptor locus-specific database for mutations causing familial (benign) hypocalciuric hypercalcemia, neonatal severe hyperparathyroidism, and autosomal dominant hypocalcemia. 1524 91

Secondary hyperparathyroidism (SHPT) is associated with parathyroid gland hyperplasia, increased parathyroid hormone (PTH) production and secretion, disturbed bone and mineral metabolism, soft tissue calcification and an increased risk of death. The condition is an almost universal complication of end-stage renal disease (ESRD) and currently is managed by treatment with phosphate binders and vitamin D compounds, both of which are associated with significant side effects, including hypercalcaemia and hyperphosphataemia. Therapy with calcimimetics is a new approach to the treatment of SHPT. These agents act at the calcium-sensing receptor (CaR), where they increase the sensitivity of the receptor to ionized serum calcium. Activation of the CaR results in a rapid reduction in PTH secretion. The calcimimetic drug cinacalcet HCl currently is undergoing clinical trials in dialysis patients who have uncontrolled SHPT, despite treatment with vitamin D compounds and/or phosphate binders. Clinical trials have confirmed that the drug rapidly reduces plasma PTH, phosphorus and calcium-phosphorus product (Ca x P) levels, and that levels of PTH, phosphorus and Ca x P remain suppressed for up to 3 years. In clinical trials, cinacalcet HCl was a well-tolerated drug; only nausea and vomiting occurred more frequently in patients who took cinacalcet HCl than in those who took placebo, and the occurrence of transient hypocalcaemia was limited to the initial phase of the treatment. Cinacalcet HCl is therefore a potentially highly effective and well-tolerated treatment for SHPT in patients with ESRD.
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PMID:Clinical experience with cinacalcet HCl. 1528 57

Heterozygous inactivating mutations of the calcium-sensing receptor (CaR) cause familial hypocalciuric hypercalcemia, whereas homozygous or compound heterozygous inactivating mutations normally cause neonatal severe hyperparathyroidism. In a case of neonatal severe hyperparathyroidism characterized by moderately severe hypercalcemia and very high PTH levels, coupled with evidence of hyperparathyroidism and effects on brain development not previously demonstrated, we detected point mutations on separate alleles of the CaR, resulting in premature stop codon substitutions at G94 and R648. This led to severely truncated receptors and an effective so-called knockout of functional CaR. FLAG-tagged, truncated receptors were expressed in HEK293 cells for functional analysis. Confocal microscopy demonstrated cytoplasmic localization of the G94stop receptor, whereas the R648stop receptor was present both in the cytoplasm and associated with the cell membrane. Only the R648stop receptor could be detected by Western analysis. Functional assays in which R648stop and wild-type receptor were cotransfected into HEK293 cells demonstrated a reduction in wild-type Ca(2+)-responsiveness by the R648stop receptor, even at physiological Ca(2+) levels, thus simulating familial hypocalciuric hypercalcemia in relatives of the infant who were heterozygous for the R648stop mutation. The R648stop receptor alone was nonresponsive to Ca(2+). This case contributes to our understanding of the clinical manifestation of a CaR knockout.
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PMID:Functional deletion of the calcium-sensing receptor in a case of neonatal severe hyperparathyroidism. 1529 96

The extracellular calcium-sensing receptor (CaSR) plays a pivotal role in the regulation of extracellular calcium such that abnormalities, which result in a loss or gain of function, lead to hypercalcemia or hypocalcemia, respectively, in patients. Mice carrying CaSR knockout alleles develop hypercalcemia that mimics the disorders observed in humans. To date, there is no mouse model for an activating CaSR mutation. Here, we describe such a mouse model, named Nuf, originally identified for having opaque flecks in the nucleus of the lens in a screen for eye mutants. Nuf mice also display ectopic calcification, hypocalcemia, hyperphosphatemia, and inappropriately reduced levels of plasma parathyroid hormone. These features are similar to those observed in patients with autosomal dominant hypocalcemia. Inheritance studies of Nuf mice revealed that the trait was transmitted in an autosomal-dominant manner, and mapping studies located the locus to chromosome 16, in the vicinity of the CaSR gene (Mouse Genome Database symbol Gprc2a). DNA sequence analysis revealed the presence of a Gprc2a missense mutation, Leu723Gln. Transient expression of wild-type and mutant CaSRs in human embryonic kidney 293 cells demonstrated that the mutation resulted in a gain of function of the CaSR, which had a significantly lower EC(50). Thus, our results have identified a mouse model for an activating CaSR mutation, and the development of ectopic calcification and cataract formation, which tended to be milder in the heterozygote Nuf mice, indicates that an evaluation for such abnormalities in autosomal dominant hypocalcemia patients who have activating CaSR mutations is required.
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PMID:Activating calcium-sensing receptor mutation in the mouse is associated with cataracts and ectopic calcification. 1534 4

The kidney plays an important role in calcium homeostasis. In this review we discuss new concepts in tubular calcium transport, related proteins and the clinical implications of these new findings. Most calcium reabsorption occurs in the proximal tubules via the passive paracellular pathway, but calcium reabsorption also occurs in the thick ascending limb of Henle's loop (50% via the transcellular pathway). Finally, at the level of the distal convoluted tubule and connecting tubule calcium is reabsorbed via the active transcellular route. The Calcium-sensing receptor, localised along the thick ascending limb of Henle's loop, regulates the urinary calcium excretion in response to changes in extracellular calcium concentration. The Epithelial Calcium Channel 1 is a highly Ca2+-sensitive channel that is predominantly present in the connecting tubule. The Calbindin D(28k) is a cytoplasmatic protein expressed in the distal tubule, it is involved both in transcellular calcium diffusion and in the control of intracellular calcium concentration. Heterozygous mutations in the gene for the calcium sensing receptor, which result in a loss of function by the receptor, are associated with familial hypocalciuric hypercalcaemia. Mutations involving a gain of function have been associated with hypocalcaemia with normal serum parathyroid hormone concentration. Bartter's syndrome, caused by a dysfunction of thick ascending limb cells, is associated with calcium wasting. On the contrary, Gitelman's syndrome, caused by a dysfunction of the distal tubule, is characterised by hypocalciuria and hypomagnesemia.
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PMID:[New concepts of tubular calcium transport in the kidney: clinical implications]. 1535 41

Familial benign hypocalciuric hypercalcemia (FBHH), in which calcium homeostasis is disordered, can be distinguished from mild primary hyperparathyroidism by the finding of a heterozygous loss-of-function mutation in the calcium-sensing receptor (CaSR). Here, we report a Polish kindred with FBHH, the proband of which had undergone an unsuccessful parathyroidectomy. Direct sequence analysis of exon 4 of her CASR gene identified a heterozygous R227Q mutation in the extracellular domain of the receptor. This mutation segregated with other affected family members. A de novo heterozygous R227L mutation had previously been identified in a case of neonatal hyperparathyroidism. We performed a functional analysis by transiently transfecting wild-type and mutant (R227Q, R227L) CaSRs in human embryonic kidney (HEK293) cells. Both mutant receptors were expressed at a similar level to that of the wild-type, demonstrated a 160-kDa molecular species consistent with having undergone full maturation, and were visualized on the cell surface. Although both mutants were impaired in their MAPK responses to increasing extracellular calcium concentrations relative to wild type, this was more marked for R227L (EC(50) = 9.7 mM) than R227Q (EC(50) = 7.9 mM) relative to wild type (EC(50) = 3.7 mM). When cotransfected with wild-type CaSR to mimic the heterozygous state, the curves for both R227Q and R227L were right shifted intermediate to the curves for wild type and the respective mutant. This differential responsiveness may account, in part, for the markedly different clinical presentation of the R227Q mutation, classic FBHH, vs. the neonatal hyperparathyroidism of the R227L mutation.
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PMID:Functional characterization of calcium-sensing receptor codon 227 mutations presenting as either familial (benign) hypocalciuric hypercalcemia or neonatal hyperparathyroidism. 1557 18

Familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT) are consequent to inactivating mutations of the calcium-sensing receptor (CaR) gene. FHH is usually associated with heterozygous inactivating mutations of the CaR gene, whereas NSHPT is usually due to homozygous inactivation of the CaR gene. FHH is generally asymptomatic and is characterized by mild to moderate lifelong hypercalcemia, relative hypocalciuria, and normal intact PTH, whereas individuals with NSHPT frequently show life-threatening hypercalcemia. In this study, we report a novel inactivating mutation of the CaR gene, identified in a 9-yr-old Brazilian girl who was found to be severely hypercalcemic during investigation of a 6-month history of headaches and vomits. Direct sequencing of the CaR gene from this patient showed a novel homozygous mutation (L13P) in exon 2. Functional characterization by intracellular calcium measurement by fluorometry showed that the mutant receptor had a dose-response curve shifted to the right relative to that of wild type. The proband's consanguineous parents, who had mild asymptomatic hypercalcemia, showed the same mutation in the heterozygous form. The mutation described in this study is the inactivating missense mutation present at the most N-terminal end among the known CaR missense mutations. This study reinforces the fact that patients with homozygous inactivation of the CaR gene may present with severe hypercalcemia in different phases of life.
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PMID:Severe hypercalcemia in a 9-year-old Brazilian girl due to a novel inactivating mutation of the calcium-sensing receptor. 1557 40

Mutations in the calcium-sensing receptor gene (CaSR) may result in disorders of calcium homeostasis manifesting as familial benign hypocalciuric hypercalcaemia (FBHH), neonatal severe hyperparathyroidism (NSHPT) or autosomal dominant hypocalcaemia with hypercalciuria (ADHH). FBHH may have a population prevalence as high as one in 16 000, and ADHH one in 70 000. NSHPT is very rare. The FBHH condition is usually asymptomatic. Parathyroidectomy does not result in normal serum calcium, and no active treatment is indicated. To differentiate FBHH from primary hyperparathyroidism (PHPT), a guideline which includes measurement of serum calcium, intact parathyroid hormone (PTH), magnesium and fasting urinary calcium excretion is proposed. Screening of family members for hypercalcaemia, and occasionally a search for mutations in the CaSR gene, may be required. The NSHPT condition may manifest with hypercalcaemia, (usually) very elevated serum PTH concentration, subperiosteal erosions and fractures. Milder cases may be managed medically, but respiratory failure, extreme hypercalcaemia and failure to thrive are indications for early parathyroidectomy. The ADHH condition may result in asymptomatic hypocalcaemia, but some affected family members have minor symptoms, and a minority experience seizures in infancy which can recur into adulthood. A significant proportion of cases previously reported as idiopathic hypoparathyroidism (IHP) may in fact be due to mutations in the CaSR gene. In a moderately hypocalcaemic patient with no other clearly discernible cause, an elevated urine calcium:creatinine ratio is suggestive of ADHH, as is the presence of a first-degree relative with hypocalcaemia. If treatment with vitamin D analogues is undertaken, serum and urine calcium should be monitored, advice which applies equally to ADHH and IHP.
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PMID:Clinical and laboratory features of calcium-sensing receptor disorders: a systematic review. 1558 33

Calcium-sensing receptor gene (CASR) mutations that alter the function of the G protein coupled Ca (2+)-sensing receptor are reported in patients with familial hypocalciuric hypercalcemia (FHH), autosomal dominant hypocalcemia (ADH), and neonatal severe hyperparathyroidism (NSHPT). In search for novel disease causing mutations in the CASR gene, we screened exons 2 - 7 of the CASR gene of a family with FHH using single-strand conformation polymorphism analysis. We identified a novel CASR mutation (c.518 T > C; L173 P) in exon 4 encoding for the extracellular domain of the Ca (2+)-sensing receptor. This region seems to represent a hot spot within the CASR gene with at least 13 reported disease causing mutations thus far.
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PMID:Identification of a novel calcium-sensing receptor gene mutation causing familial hypocalciuric hypercalcemia by single-strand conformation polymorphism analysis. 1566 92

The discovery of a G protein-coupled, calcium-sensing receptor (CaR) a decade ago and of diseases caused by CaR mutations provided unquestionable evidence of the CaR's critical role in the maintenance of systemic calcium homeostasis. On the cell membrane of the chief cells of the parathyroid glands, the CaR "senses" the extracellular calcium concentration and, subsequently, alters the release of parathyroid hormone (PTH). The CaR is likewise functionally expressed in bone, kidney, and gut--the three major calcium-translocating organs involved in calcium homeostasis. Intracellular signal pathways to which the CaR couples via its associated G proteins include phospholipase C (PLC), protein kinase B (AKT); and mitogen-activated protein kinases (MAPKs). The receptor is widely expressed in various tissues and regulates important cellular functions in addition to its role in maintaining systemic calcium homeostasis, i.e., protection against apoptosis, cellular proliferation, and membrane voltage. Functionally significant mutations in the receptor have been shown to induce diseases of calcium homeostasis owing to changes in the set point for calcium-regulated PTH release as well as alterations in the renal handling of calcium. Gain-of-function mutations cause hypocalcemia, whereas loss-of-function mutations produce hypercalcemia. Recent studies have shown that the latter clinical presentation can also be caused by inactivating autoantibodies directed against the CaR Newly discovered type II allosteric activators of the CaR have been found to be effective as a medical treatment for renal secondary hyperparathyroidism.
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PMID:The calcium-sensing receptor in normal physiology and pathophysiology: a review. 1569 70


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