The Molecular Basis of Calcium and Phosphorus Inherited Metabolic Disorders.

Calcium (Ca) and Phosphorus (P) hold a leading part in many skeletal and extra-skeletal biological processes. Their tight normal range in serum mirrors their critical role in human well-being. The signalling "voyage" starts at Calcium Sensing Receptor (CaSR) localized on the surface of the parathyroid glands, which captures the "oscillations" of extracellular ionized Ca and transfers the signal downstream. Parathyroid hormone (PTH), Vitamin D, Fibroblast Growth Factor (FGF23) and other receptors or ion-transporters, work synergistically and establish a highly regulated signalling circuit between the bone, kidneys, and intestine to ensure the maintenance of Ca and P homeostasis. Any deviation from this well-orchestrated scheme may result in mild or severe pathologies expressed by biochemical and/or clinical features. Inherited disorders of Ca and P metabolism are rare. However, delayed diagnosis or misdiagnosis may cost patient's quality of life or even life expectancy. Unravelling the thread of the molecular pathways involving Ca and P signaling, we can better understand the link between genetic alterations and biochemical and/or clinical phenotypes and help in diagnosis and early therapeutic intervention.

Alzheimer's Disease Presenilin-1 Mutation Sensitizes Neurons to Impaired Autophagy Flux and Propofol Neurotoxicity: Role of Calcium Dysregulation.

BACKGROUND: Disruption of intracellular Ca2+ homeostasis and associated autophagy dysfunction contribute to neuropathology in Alzheimer's disease (AD). OBJECTIVE: To study the effects of propofol on cell viability via its effects on intracellular Ca2+ homeostasis, and the impact of autophagy, in a neuronal model of presenilin-mutated familial AD (FAD). METHODS: We treated PC12 cells, stably transfected with either mutated presenilin-1 (L286V) or wild type (WT) controls, with propofol at different doses and durations, in the presence or absence of extracellular Ca2+, antagonists of inositol trisphosphate receptors (InsP3R, xestospongin C) and/or ryanodine receptors (RYR, dantrolene), or an inhibitor of autophagy flux (Bafilomycin). We determined cell viability, cytosolic Ca2+ concentrations ([Ca2+]c), vATPase protein expression, and lysosomal acidification. RESULTS: The propofol dose- and time-dependently decreased cell viability significantly more in L286V than WT cells, especially at the pharmacological dose (>50µM), and together with bafilomycin (40 nM). Clinically used concentrations of propofol (<20µM) tended to increase cell viability. Propofol significantly increased [Ca2+]c more in L286V than in WT cells, which was associated with decrease of vATPase expression and localization to the lysosome. Both toxicity and increased Ca2+ levels were ameliorated by inhibiting InsP3R/RYR. However, the combined inhibition of both receptors paradoxically increased [Ca2+]c, by inducing Ca2+ influx from the extracellular space, causing greater cytotoxicity. CONCLUSION: Impairment in autophagy function acts to deteriorate cell death induced by propofol in FAD neuronal cells. Cell death is ameliorated by either RYR or InsP3R antagonists on their own, but not when both are co-administered.

Association of klotho gene polymorphism and the regulation of calcium-phosphate metabolism disorders in patients with end-stage renal disease.

BACKGROUND: Klotho G-395-A gene polymorphism is associated with several diseases; however, its association with calcium-phosphate metabolism disorders in end-stage renal disease (ESRD) is unknown. METHODS: A total of 137 patients with ESRD and 80 healthy adults (control) were enrolled in the study. Patients with ESRD were divided into three subgroups: haemodialysis (A1, n = 52), peritoneal dialysis (A2, n = 30), and non-dialysis (A3, n = 55). The klotho G-395-A genotype was detected by TaqMan PCR assay, and ELISA was used to detect the soluble klotho protein (sKL) and fibroblast growth factor (FGF23). Intact parathyroid hormone (iPTH) and other related clinical biochemical parameters were also analyzed for all subjects. RESULTS: (i) Three genotypes (GG, GA and AA) of KL G-395A were detected, and a significant difference between the ESRD and control groups was observed, (ii) sKL was inversely associated with FGF23 in each subgroup and phosphate and positively associated with calcium in A1 and A3. FGF23 was positively associated with phosphate and inversely associated with calcium in each subgroup, (iii) a statistical difference in levels of sKL and FGF23 was observed between GG and AA, as well as between GA and AA. The expression of sKL was lowest and the level of FGF23 was highest in AA and (iv). GA + AA genotypes and FGF23 were risk factors and sKL might be protective factor of calcium-phosphate metabolism disorders. CONCLUSION: Soluble klotho protein and FGF23 were associated with the regulation of calcium and phosphate metabolism, and the A allele of the G-395A klotho gene polymorphism could be a risk factor on calcium-phosphate metabolism disorders in patients with ESRD.

Disorders of Mechanisms of Calcium Metabolism Control as Potential Risk Factors of Prostate Cancer.

Prostate cancer significantly affects the overall morbidity and mortality of malignant tumours in highly developed countries. Important risk factors include family predisposition and regional, racial and dietary determinants. The scientific literature contains a great deal of data on the role of calcium and dairy products in general in the process of neoplastic transformation of the prostate. This is most likely linked to the fact that changes in the concentration of calcium ions control such varied life processes as secretion of hormones and neurotransmitters, the level of cyclic nucleotides, and cell growth, division and differentiation. Research is conducted to demonstrate that disorders of cell cycle control due to differences in calcium ion concentrations may be crucial for the development and prevention of cancer. Disturbances of calcium homeostasis in the body can be caused by various mechanisms, such as excessive calcium intake in the diet, vitamin D deficiency, structural and functional changes in vitamin D receptor (VDR), Calcium-Sensing Receptor (CaSR), and parathyroid hormone receptor (PTH-1-R), changes in calcium ion channels, phosphate metabolism disorders (phosphatonin and the Klotho protein), changes in the level of parathyroid hormone-related protein (PTHrP), and others. The article presents data on the mechanisms maintaining calcium homeostasis at the molecular level and genetic aspects playing a role in the pathogenesis of prostate cancer. The data cited on the occurrence of abnormal mechanisms of calcium metabolism in prostate cancer suggest the need for individualized intake of this element in the diet, especially in the case of patients with a family history of PCa.

[Disorders Caused by Mutations in Calcium-Sensing Receptor and Related Diseases.]

Sensing of extracellular calcium(Ca2+)levels involves the Ca-sensing receptor(CaSR), its downstream signaling molecule Gα11, and the adaptor-related protein complex 2(AP2)that plays a role in clathrin-dependent endocytosis of CaSR. Inactivating mutations in CaSR cause familial hypocalciuric hypercalcemia type 1(FHH1)and neonatal severe hyperparathyroidism(NSHPT), while activating mutations lead to autosomal dominant hypocalcemia type 1(ADH1)and Bartter syndrome type Ⅴ. Recent studies have identified that inactivating mutations in Gα11 and σ-subunit of AP2(AP2σ)also cause FHH, and these conditions have been classified as FHH2 and FHH3, respectively. In addition, it has been revealed that activating mutations in Gα11 are responsible for ADH(ADH2). Calcimimetics and calcilytics may be beneficial in the treatment of these disorders.

Effects of HA released calcium ion on osteoblast differentiation.

Hydroxyapatite (HA) is a widely used calcium phosphate implant substitute and has dissolution property. Although HA has been shown a beneficial effect on osteoblast differentiation, the exact mechanism is still unclear. In the present study, we proposed that Ca(2+) released from HA activated the expression bone associated proteins, OPN and BSP, mediated by L-type calcium channel and calcium/calmodulin-dependent protein kinase (CaMK) 2 which resulted into improved osteoblast differentiation. Results showed that HA elevated ALP expression as well as OPN and BSP expression in MC3T3-E1 cells. The result from western blot of CaMK2alpha indicated that HA released Ca(2+) activated CaMK2 through L-type calcium channel. Furthermore, upregulation of OPN and BSP mRNA expression was significantly inhibited when blocking both the L-type calcium channel and CaMK2. These findings suggested that HA accelerated the osteoblast differentiation by releasing Ca(2+).

Multiplex ligation-dependent probe amplification (MLPA) screening for exon copy number variation in the calcium sensing receptor gene: no large rearrangements identified in patients with calcium metabolic disorders.

BACKGROUND: Mutation screening of the CASR by DNA sequencing is commonly used in the diagnosis of disorders of calcium metabolism, such as familial hypocalciuric hypercalcaemia (FHH). Exon copy number variation is not detected by currently used molecular genetic screening methods, and might be a genetic cause of inherited forms of hyper- or hypocalcaemia caused by the CASR. OBJECTIVE: We wanted to further evaluate possible genetic causes for disorders of calcium metabolism, by investigating the prevalence of exon copy number variations, such as large deletions or duplications of the CASR. PATIENTS AND METHODS: The study included 257 patient samples referred to our laboratory for molecular genetic analysis of the CASR gene. A total of 245 were patients suspected to have FHH, while the remaining 12 samples represent patients with a phenotype of idiopathic hypocalcaemia/hypoparathyroidism. All samples were previously found negative for CASR mutations. Multiplex ligation-dependent probe amplification was used to screen the patients for exon copy number variations. RESULTS: All exons were amplified with mean normalised ratios between 0.98 and 1.06. We did not identify any exon copy number variation in the CASR. Bioinformatic analyses revealed that the CASR gene contains 52% repeated elements, of which approximately 6% consist of Alu elements. CONCLUSIONS: The present study indicates that including CASR MLPA analysis as a routine part of the diagnostic setup is not necessary, but could still be of interest in cases with a clear family history and no evidence of missense mutations in the CASR gene.

Case histories.

The conditions related to abnormalities of calcium and bone metabolism are large in number and cover problems of hypocalcaemia, hypercalcaemia, primary and secondary osteoporosis, rickets resulting from both vitamin D and phosphate metabolic disorders, and a series of miscellaneous conditions. Included in this chapter is a series of 36 cases drawn from our clinics and from colleagues who have presented these clinical problems at recent Advanced Courses in Paediatric Bone and Calcium Metabolism run by the British Paediatric and Adolescent Bone group. The series of cases is not fully comprehensive but is designed to cover the major aspects of bone and calcium related disorders and can be added to online in due course.

[Basic and clinical aspects of calcimimetics. Structure and function of calcium-sensing receptor].

Calcium-sensing receptor (CaSR) is a G-protein coupled receptor identified as a essential molecule for the regulation of parathyroid hormone (PTH) secretion by extracellular calcium (Ca). Binding of extracellular Ca to CaSR activates several intracellular signaling pathways including increase of intracellular Ca, and inhibits PTH secretion. CaSR is expressed in several tissues other than parathyroid glands including kidney and C-cells in thyroid, and contributes to enhanced renal excretion of Ca and secretion of calcitonin in response to the increase of extracellular Ca. The importance of CaSR in the maintenance of extracellular Ca is also shown by hypercalcemic and hypocalcemic diseases caused by inactivating and activating mutations in CaSR gene, respectively.

Clinical lessons from the calcium-sensing receptor.

The extracellular calcium ion (Ca(2+)(e))-sensing receptor (CaR) enables key tissues that maintain Ca(2+)(e) homeostasis to sense changes in the Ca(2+)(e) concentration. These tissues respond to changes in Ca(2+)(e) with functional alterations that will help restore Ca(2+)(e) to normal. For instance, decreases in Ca(2+)(e) act via the CaR to stimulate secretion of parathyroid hormone-a Ca(2+)(e)-elevating hormone-and to increase renal tubular calcium reabsorption; each response helps promote normalization of Ca(2+)(e) levels. Further work is needed to determine whether the CaR regulates other parameters of renal function (e.g. 1,25-dihydroxyvitamin D(3) synthesis, intestinal absorption of mineral ions, and/or bone turnover). Identification of the CaR has also elucidated the pathogenesis and pathophysiology of inherited disorders of mineral and electrolyte metabolism; moreover, acquired abnormalities of Ca(2+)(e)-sensing can result from autoimmunity to the CaR, and reduced CaR expression in the parathyroid may contribute to the abnormal parathyroid secretory control that is observed in primary and secondary hyperparathyroidism. Finally, calcimimetics-allosteric activators of the CaR-treat secondary hyperparathyroidism effectively in end-stage renal failure.

The calcium-sensing receptor and related diseases.

The calcium-sensing receptor (CASR) adjusts the extracellular calcium set point regulating PTH secretion and renal calcium excretion. The receptor is expressed in several tissues and is also involved in other cellular functions such as proliferation, differentiation and other hormonal secretion. High extracellular calcium levels activate the receptor resulting in modulation of several signaling pathways depending on the target tissues. Mutations in the CASR gene can result in gain or loss of receptor function. Gain of function mutations are associated to Autossomal dominant hypocalcemia and Bartter syndrome type V, while loss of function mutations are associated to Familial hypocalciuric hypercalcemia and Neonatal severe hyperparathyroidism. More than one hundred mutations were described in this gene. In addition to calcium, the receptor also interacts with several ions and polyamines. The CASR is a potential therapeutic target to treatment of diseases including hyperparathyroidism and osteoporosis, since its interaction with pharmacological compounds results in modulation of PTH secretion.

The calcium-sensing receptor and related diseases / O receptor sensor de cálcio e doenças associadas

The calcium-sensing receptor (CASR) adjusts the extracellular calcium set point regulating PTH secretion and renal calcium excretion. The receptor is expressed in several tissues and is also involved in other cellular functions such as proliferation, differentiation and other hormonal secretion. High extracellular calcium levels activate the receptor resulting in modulation of several signaling pathways depending on the target tissues. Mutations in the CASR gene can result in gain or loss of receptor function. Gain of function mutations are associated to Autossomal dominant hypocalcemia and Bartter syndrome type V, while loss of function mutations are associated to Familial hypocalciuric hypercalcemia and Neonatal severe hyperparathyroidism. More than one hundred mutations were described in this gene. In addition to calcium, the receptor also interacts with several ions and polyamines. The CASR is a potential therapeutic target to treatment of diseases including hyperparathyroidism and osteoporosis, since its interaction with pharmacological compounds results in modulation of PTH secretion.

O receptor sensor de cálcio (CASR) ajusta o set point do cálcio extracelular através da regulação da secreção de PTH e da excreção renal de cálcio. O receptor é expresso em diversos tecidos e também está envolvido em outras funções celulares como proliferação, diferenciação e secreção de outros hormônios. Concentrações altas de cálcio extracelular ativam o receptor resultando em modulação de inúmeras vias de sinais intracelulares dependendo do tecido-alvo. Mutações no gene do CASR podem resultar em ganho ou perda de função do receptor. Mutações com ganho de função são associadas à Hipocalcemia autossômica dominante e à Síndrome de Bartter tipo V, enquanto que mutações com perda de função são associadas à Hipercalcemia hipocalciúrica familiar e ao Hiperparatireoidismo neonatal grave. Mais de cem mutações foram descritas neste gene. Além do cálcio, o receptor também interage com inúmeros íons e poliaminas. CASR é um alvo terapêutico potencial para tratamento de doenças incluindo hiperparatireoidismo e osteoporose, pois a sua interação com compostos farmacológicos resulta em modulação da secreção de PTH.

Vitamin D and calcium receptors: links to hypercalciuria.

PURPOSE OF REVIEW: In idiopathic hypercalciuria, patients have increased intestinal Ca absorption and decreased renal Ca reabsorption, with either elevated or normal serum levels of 1,25-dihydroxyvitamin D. As 1,25-dihydroxyvitamin D exerts its biologic effects through interactions with the vitamin D receptor, we examine the actions of this receptor and 1,25-dihydroxyvitamin D in animals with genetic hypercalciuria. RECENT FINDINGS: In genetic hypercalciuric stone-forming rats intestinal calcium transport is increased and renal calcium reabsorption is reduced, yet serum 1,25-dihydroxyvitamin D levels are normal. Elevated intestinal and kidney vitamin D receptors suggest that increased tissue 1,25-dihydroxyvitamin D-vitamin D receptor complexes enhance 1,25-dihydroxyvitamin D actions on intestine and kidney, and vitamin D-dependent over-expression of renal calcium-sensing receptor alone can decrease tubule calcium reabsorption. In TRPV5-knockout mice, ablation of the renal calcium-influx channel decreases tubular calcium reabsorption, and secondary elevations in 1,25-dihydroxyvitamin D increase intestinal calcium transport. SUMMARY: 1,25-Dihydroxyvitamin D or vitamin D receptor may change intestinal and renal epithelial calcium transport simultaneously or calcium-transport changes across renal epithelia may be primary with a vitamin D-mediated secondary increase in intestinal transport. The extent of homology between the animal models and human idiopathic hypercalciuria remains to be determined.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis: blocking endocytosis restores surface expression of a novel Claudin-16 mutant that lacks the entire C-terminal cytosolic tail.

Mutations in the gene for Claudin-16 (CLDN16) are linked to familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), a renal Mg2+ and Ca2+ wasting disorder that leads to progressive kidney failure. More than 20 mutations have been identified in CLDN16, which, with a single exception, affect one of two extracellular loops or one of four transmembrane domains of the encoded protein. Here, we describe a novel missense mutation, Cldn16 L203X, which deletes the entire C-terminal cytosolic domain of the protein. Surface expression of Cldn16 L203X is strongly reduced and the protein is instead found in the endoplasmic reticulum (ER) and lysosomes. ER-retained Cldn16 L203X is subject to proteasomal degradation. Cldn16 L203X present in lysosomes reaches this compartment following transport to the plasma membrane and endocytosis. Blocking clathrin-mediated endocytosis increases surface expression of Cldn16 L203X. Thus, endocytosis inhibitors may provide a novel therapeutic approach for FHHNC patients carrying particular Cldn16 mutations.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis associated with CLDN16 mutations.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), an autosomal recessive renal tubular disorder, is characterized by the impaired tubular reabsorption of magnesium and calcium in the thick ascending limb of the loop of Henle and an eventual progression to end-stage renal disease. Recent studies have reported that this disease is caused by mutations in the CLDN16 gene, which encodes the tight junction protein, paracellin-1. Paracellin-1 belongs to the claudin family and regulates the paracellular transport of magnesium and calcium. Here, we report on two Korean siblings with typical clinical features of FHHNC in association with compound heterozygous mutations, G233C and 800delG, in CLDN16. Their parents were asymptomatic heterozygous carriers of the single mutations. This is the first report of FHHNC in Korea, and the mutations reported are novel.

Genetic hypercalciuria.

Hypercalciuria is an important, identifiable, and reversible risk factor in stone formation. The foremost and most fundamental step in dissecting the genetics of hypercalciuria is understanding its pathophysiology. Hypercalciuria is a complex trait. This article outlines the various factors that compromise the attempt to dissect the genetics of hypercalciuria, summarizes the clinical and experimental monogenic causes of hypercalciuria, and outlines the initial results from attempts in studying polygenic hypercalciuria. Finally, the problem is set in perspective of the current database, technologic advances and limitations are highlighted, and prospects of further advances in the field are speculated upon.

Clinical and laboratory features of calcium-sensing receptor disorders: a systematic review.

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.

Genetics of hypercalciuria and calcium nephrolithiasis: from the rare monogenic to the common polygenic forms.

Idiopathic calcium nephrolithiasis is a multifactorial disease with a pathogenesis that involves a complex interaction of environmental and individual factors. This review discusses what is known about monogenic renal calcium stone-related disorders, provides an update on genetic research in calcium nephrolithiasis and such intermediate phenotypes as idiopathic hypercalciuria, discusses the problems that these conditions pose to clinicians and geneticists interested in their pathogenesis, and proposes some method tools potentially useful in this research frame of reference.

Hypercalciuria in familial hyperkalemia and hypertension accompanies hyperkalemia and precedes hypertension: description of a large family with the Q565E WNK4 mutation.

Familial hyperkalemia and hypertension (FHH; pseudohypoaldosteronism type II) is an autosomal dominant disorder characterized by hyperkalemia, hypertension, and low renin. WNK1 kinase overexpression and WNK4 kinase inactivating missense mutations cause FHH. When expressed in frog oocyte, WNK4 inhibits Na-Cl cotransporter surface expression, and WNK1 relieves this inhibition. We have reported hypercalciuria in subjects with the WNK4 Q565E mutation. In contrast, in subjects with WNK1 overexpression, normocalciuria was found. Here we report a major extension of our previously described kindred that contains 34 subjects, 18 of them affected by the mutation. Hypertension was diagnosed in 13 affected subjects at the age of 31 +/- 12 yr. Five of the affected or obligatory affected subjects had stroke, in four at the age of 50-62 yr. Seven subjects with FHH were diagnosed 27 yr previously. All four subjects who were normotensive at diagnosis became hypertensive during follow-up. The mean time between detection of hyperkalemia and appearance of hypertension was 13 yr. In the extended kindred, compared with the unaffected subjects, affected subjects had hyperkalemia, low transtubular potassium gradient, hyperchloremia, low bicarbonate, higher aldosterone, and marked suppression of renin. Urinary calcium levels in affected and unaffected subjects were 0.85 +/- 0.27 and 0.28 +/- 0.12 mmol/mmol creatinine, respectively (P < 0.0001). Hypercalciuria was accompanied by lower serum calcium levels [9.44 +/- 0.15 vs. 9.81 +/- 0.31 mg/dl (2.36 +/- 0.04 vs. 2.45 +/- 0.08 mmol/liter); P = 0.01], supporting a mechanism of renal calcium leak. The six affected, currently normotensive subjects had the same degree of hyperkalemia, hypercalciuria, and low renin as the affected hypertensive subjects. We conclude that in FHH with WNK4 mutations, with time all affected subjects will apparently develop hypertension. Hypercalciuria accompanies hyperkalemia, and both precede hypertension. Based on the recent findings that WNK4 regulates the renal outer medullary potassium channel as well as epithelial Cl(-)/base exchanger and the Na(+)-K(+)-2Cl(-) cotransporter, we suggest that WNK4 interacts with a calcium channel or transporter.

Diseases associated with the extracellular calcium-sensing receptor.

The human calcium-sensing receptor (CaSR) is a 1078 amino acid cell surface protein, which is predominantly expressed in the parathyroids and kidney, and is a member of the family of G protein-coupled receptors. The CaSR allows regulation of parathyroid hormone (PTH) secretion and renal tubular calcium reabsorption in response to alterations in extracellular calcium concentrations. The human CaSR gene is located on chromosome 3q21.1 and loss-of-function CaSR mutations have been reported in the hypercalcaemic disorders of familial benign (hypocalciuric) hypercalcaemia (FHH, FBH or FBHH) and neonatal severe primary hyperparathyroidism (NSHPT). However, some individuals with loss-of-function CaSR mutations remain normocalcaemic. In addition, there is genetic heterogeneity amongst the forms of FHH. Thus, the majority of FHH patients have loss-of-function CaSR mutations, and this is referred to as FHH type 1. However, in one family, the causative gene for FHH is located on 19p13, referred to as FHH type 2, and in another family it is located on 19q13, referred to as FHH type 3. Gain-of-function CaSR mutations have been shown to result in autosomal dominant hypocalcaemia with hypercalciuria (ADHH) and Bartter's syndrome type V. CaSR auto-antibodies have been found in FHH patients who did not have loss-of-function CaSR mutations, and in patients with an acquired form (i.e. autoimmune) of hypoparathyroidism. Thus, abnormalities of the CaSR are associated with three hypercalcaemic and three hypocalcaemic disorders.