Autosomal Dominant Hypoparathyroidism Research Articles

The management of autosomal dominant hypoparathyroidism with CaSR mutation in pregnancy and breastfeeding

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Continuous synthetic PTH1-34 replacement therapy in the treatment of autosomal dominant hypoparathyroidism type 1

Continuous synthetic PTH1-34 replacement therapy in the treatment of autosomal dominant hypoparathyroidism type 1

Autosomal dominant hypoparathyroidism caused by germline mutation in GNA11: phenotypic and molecular characterization.

Most cases of autosomal dominant hypoparathyroidism (ADH) are caused by gain-of-function mutations in CASR or dominant inhibitor mutations in GCM2 or PTH. Our objectives were to identify the genetic basis for ADH in a multigenerational family and define the underlying disease mechanism. Here we evaluated a multigenerational family with ADH in which affected subjects had normal sequences in these genes and were shorter than unaffected family members. We collected clinical and biochemical data from 6 of 11 affected subjects and performed whole-exome sequence analysis on DNA from two affected sisters and their affected father. Functional studies were performed after expression of wild-type and mutant Gα11 proteins in human embryonic kidney-293-CaR cells that stably express calcium-sensing receptors. Whole-exome-sequencing followed by Sanger sequencing revealed a heterozygous mutation, c.179G>T; p.R60L, in GNA11, which encodes the α-subunit of G11, the principal heterotrimeric G protein that couples calcium-sensing receptors to signal activation in parathyroid cells. Functional studies of Gα11 R60L showed increased accumulation of intracellular concentration of free calcium in response to extracellular concentration of free calcium with a significantly decreased EC50 compared with wild-type Gα11. By contrast, R60L was significantly less effective than the oncogenic Q209L form of Gα11 as an activator of the MAPK pathway. Compared to subjects with CASR mutations, patients with GNA11 mutations lacked hypercalciuria and had normal serum magnesium levels. Our findings indicate that the germline gain-of-function mutation of GNA11 is a cause of ADH and implicate a novel role for GNA11 in skeletal growth.

Loss-of-Function and Gain-of-Function Mutations of Calcium-Sensing Receptor: Functional Analysis and the Effect of Allosteric Modulators NPS R-568 and NPS 2143

Activating mutations in the calcium-sensing receptor (CASR) gene cause autosomal dominant hypoparathyroidism, and heterozygous inactivating CASR mutations cause familial hypocalciuric hypercalcemia. Recently, there has been a focus on the use of allosteric modulators to restore the functional activity of mutant CASRs. In this study, the effect of allosteric modulators NPS R-568 and NPS 2143 on CASR mutants was studied in vitro. DNA sequence analysis of the CASR gene was undertaken in autosomal dominant hypoparathyroidism and familial hypocalciuric hypercalcemia Japanese patients, and the functional consequences for the Gi-MAPK pathway and cell surface expression of CASR were determined. Furthermore, we studied the effect of NPS R-568 and NPS 2143 on the signal transduction activity and cell surface expression of each mutant CASR. We identified 3 activating mutations (S122C, P569H, and I839T) and 2 inactivating mutations (A110T and R172G) in patients. The activating and inactivating mutations caused leftward and rightward shifts, respectively, in the dose-response curves of the signaling pathway. NPS R-568 rescued the signal transduction capacity of 2 inactivating mutants without increasing cell surface expression levels. NPS 2143 suppressed the enhanced activity of the activating mutants without altering cell surface expression levels, although A843E, which is a constitutively active mutant, was suppressed to a lesser degree. We have identified 4 novel mutations of CASR. Moreover, our results indicate that allosteric modulators can restore the activity of the loss- and gain-of-function mutant CASRs, identified in this study.

Calcium-sensing receptors, biology, and clinical significance: a systemic review

This is a study of calcium-sensing receptors (CaSR), biology, and clinical significance. The CaSR plays an essential role in the regulation of extracellular calcium (Ca 2+ ) homeostasis. CaSR is expressed in all tissues related to this control (parathyroid glands, thyroid C cells, kidneys, intestine, and bones) and also in tissues with apparently no role in the maintenance of extracellular Ca 2+ levels, such as the brain, skin, and pancreas. CaSR cloning was immediately followed by the association of genetic human diseases with inactivating and activating CaSR mutations: Familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism are caused by CaSR-inactivating mutations, whereas autosomal dominant hypoparathyroidism is secondary to CaSR-activating mutations. Study of CaSR functions aided the development of drugs that modify their functions either by stimulation (calcimimetic drugs) or by inhibition (calcilytic drugs). CaSR plays a major role in the maintenance of a physiological serum Ca 2+ concentration. There are a number of inherited and acquired conditions in which the level of expression and/or function of the CaSR are altered. Also, there are drugs that modify the function of calcium-sensing receptors (CaSR-based therapeutics).

Familial hypocalcaemia – think about calcium sensor receptor (CASR)

<h3>Aim</h3> Activating mutations of CaSR gene have been shown to cause hypercalciuric hypocalcaemia1. The CaSR plays a key role in maintaining calcium homeostasis by regulating parathyroid hormone (PTH) and renal calcium reabsorption. Activating mutation of CaSR causes increased sensitivity to Ca++ and hence down regulation of PTH secretion. <h3>Method</h3> This is a case series where we report a pedigree with clinical picture consistent with familial autosomal dominant hypoparathyroidism. The proband, an 18-month-old girl was found to have incidental hypocalcaemia. We identified 4 other affected individuals in the family, including the father of the proband and his twin brother. All affected individuals had mild hypocalcaemia, low normal serum parathyroid levels and borderline high phosphate levels. Treatment with vitamin D and oral calcium did not improve their serum calcium levels. The father of proband has shown evidence of hypercalciuria and has recently been treated for urolithiasis. Mutation analysis identified a novel activating mutation of the CaSR gene [c.407C&gt;T (p.Pro136Leu)] in all 3 family members who were tested. <h3>Conclusion</h3> Activating mutation of the CaSR inhibits PTH secretion and renal calcium reabsorption despite hypocalcaemia. Treatment with vitamin D and calcium can increase hypercalciuria leading to nephrocalcinosis and renal impairment1,2. Asymptomatic individuals should not be overtreated in an attempt to normalise serum calcium.

Identification and characterization of C106R, a novel mutation in the DNA‐binding domain of GCMB, in a family with autosomal‐dominant hypoparathyroidism

Glial cells missing B (GCMB) is a transcription factor that is expressed in the parathyroid hormone (PTH)-secreting cells of the parathyroid glands. Several mutations in GCMB have been reported to cause hypoparathyroidism (HP). We identified a family with two individuals in two generations (mother and son), who are affected by autosomal-dominant hypoparathyroidism (AD-HP). A novel heterozygous mutation in exon 2 of GCMB was identified in both affected individuals that changes cysteine at position 106 of the putative DNA-binding domain of GCMB to arginine (C106R). We performed mutational analysis of the genes encoding GCMB, pre-pro PTH, GATA3 and CaSR using polymerase chain reaction (PCR)-amplified genomic DNA. The identified GCMB mutant was characterized by functional studies including nuclear localization, electrophoretic mobility shift assays (EMSA) and luciferase reporter assays, and homology modelling was performed to generate a three-dimensional structural model for the DNA-binding domain of GCMB to predict the structural consequences of the identified mutation. The C106R mutant of GCMB failed to interact with the DNA consensus recognition motif, as determined by EMSA. Furthermore, in comparison with wild-type GCMB, the C106R mutant demonstrated reduced transactivation in luciferase reporter assays; however, the mutant GCMB failed to reduce the activity of the wild-type protein. Consistent with the EMSA findings, homology modelling analysis suggested that replacement of cysteine 106 with arginine would interfere with DNA binding. We have identified a novel GCMB mutation that may explain AD-HP in our family. However, the exact mechanism by which this heterozygous mutation leads to the disease in the described family remains to be elucidated.

A MissenseGlial Cells Missing Homolog B(GCMB) Mutation, Asn502His, Causes Autosomal Dominant Hypoparathyroidism

Glial cells missing B (GCMB), the mammalian homolog of the Drosophila GCM gene, encodes a 506-amino-acid parathyroid-specific transcription factor. To date, only two different heterozygous GCMB mutations have been reported in three kindreds with autosomal dominant hypoparathyroidism. Our objective was to investigate a family with autosomal dominant hypoparathyroidism for PTH, CaSR, and GCMB mutations. Leukocyte DNA was used with exon-specific primers for PCR amplification and the DNA sequences of the PCR products determined. Functional analyses using fluorescence microscopy, EMSAs, and luciferase reporter assays were undertaken. Informed consent was obtained using protocols approved by a national ethical committee. DNA sequence analysis revealed an A to C transversion at codon 502 of GCMB, which altered the wild-type asparagine (Asn) to histidine (His). Functional studies, using transient transfections of COS7 cells with GCMB wild-type and mutant (Asn502His) tagged constructs, demonstrated that the wild-type and mutant proteins localized to the nucleus and retained the ability to bind the GCM-consensus DNA recognition motif. However, a luciferase reporter assay demonstrated that the Asn502His mutation resulted in a reduction in gene transactivation. Moreover, cotransfection of the wild-type with mutant did not lead to an increase in luciferase activity, thereby demonstrating a dominant-negative effect of the Asn502His mutant that would be consistent with an autosomal dominant inheritance. Our results, which have identified the first dominant missense GCMB mutation, help to increase our understanding of the mechanism underlying gene transactivation that is a prerequisite for the function of this parathyroid gland-specific transcription factor.

Glial Cells Missing-2 (GCM2) transactivates the calcium-sensing receptor gene: effect of a dominant-negative GCM2 mutant associated with autosomal dominant hypoparathyroidism

Glial cells missing-2 (GCM2) is a transcription factor expressed in the parathyroid hormone (PTH)-secreting cells of the parathyroid gland and is essential for their development. Thus far, downstream targets of GCM2 have not been identified. Here, we show that both promoters (P1 and P2) of the calcium-sensing receptor (CASR) gene, a differentiation marker for the parathyroid gland, are transactivated by wild-type GCM2. GCM response elements within CASR P1 (-451 to -441; relative to the transcription start site at +1) and CASR P2 (-166 to -156) were identified by mutated promoter-reporter studies as well as oligonucleotide precipitation assays. Primary hypoparathyroidism is a heterogeneous group of conditions characterized by hypocalcemia and hyperphosphatemia due to deficient PTH secretion. A few cases of familial isolated hypoparathyroidism with autosomal recessive inheritance have been identified that are caused by homozygous inactivating mutations in the GCM2 gene. We describe the GCM2 mutations in two families with hypoparathyroidism, one inherited in an autosomal recessive fashion and the other in an autosomal dominant manner. In transfection studies using a promoter-reporter construct having synthetic multimerized GCM elements in the promoter, the dominantly inherited mutant GCM2 exerted a dominant-negative effect on wild-type GCM2 activity, whereas recessively inherited mutants did not. In addition, we show that the transactivation of the CASR promoter-reporter constructs by wild-type GCM2 is completely abolished in the presence of the dominant-negative mutant GCM2.

Dominant-NegativeGCMBMutations Cause an Autosomal Dominant Form of Hypoparathyroidism

Hypoparathyroidism (HP) is characterized by low PTH levels, hypocalcemia, and hyperphosphatemia. Heterozygous mutations in pre-pro-PTH or the calcium-sensing receptor (CaSR) cause some forms of autosomal dominant HP (AD-HP). Furthermore, homozygous mutations in glial cells missing B (GCMB) have been implicated in autosomal recessive HP (AR-HP). In most other HP patients, however, the molecular defect remains undefined. Our objectives were to determine the genetic defect in the affected members of two unrelated families with AD-HP and define the underlying disease mechanism. Several family members affected by AD-HP were investigated. The proband in family A had low calcium detected on routine blood testing, whereas the proband in family B had symptomatic hypocalcemia. Mutational analysis of the genes encoding pre-pro-PTH, CaSR, and GCMB was performed using PCR-amplified genomic DNA of the probands and other available members of each family. The identified GCMB mutants were characterized by Western blot analysis and luciferase reporter assay using DF-1 fibroblasts. Two novel heterozygous mutations located in the last GCMB exon (c.1389delT and c.1399delC in families A and B, respectively) were identified that both lead to frame-shifts and replacement of the putative second transactivation domain within carboxyl-terminal region by unrelated amino acid sequence. The mutant GCMB proteins were well expressed, and both showed dose-dependent inhibition of the transactivation capacity of wild-type protein in luciferase reporter assays. The dominant-negative effect observed in vitro for both GCMB mutations provides a plausible explanation for the impaired PTH secretion observed in the two unrelated families with AD-HP.

Autosomal Dominant Hypoparathyroidism with Severe Hypomagnesemia and Hypocalcemia, Successfully Treated with Recombinant PTH and Continuous Subcutaneous Magnesium Infusion

Activating calcium sensor receptor (CaSR) mutations often present with hypocalcemia and hypomagnesemia. Severe hypocalcemia with this mutation has been reported but severe hypomagnesemia has not been well described. To identify the cause of severe hypocalcemia and hypomagnesemia in a young child, and explore the efficacy of continuous subcutaneous magnesium therapy as a safer alternative to intravenous magnesium. A 2-8/12 year-old female with severe hypocalcemia and hypomagnesemia of unknown etiology. Genetic analysis was performed on the proband and both parents. The proband was treated with human parathyroid hormone (teriparatide) and a continuous infusion of subcutaneous magnesium sulfate initially using a Deltec insulin pump and subsequently a Curlin infusion pump. The patient has a known de novo mutation in the CASR gene (A843E). She could not be adequately managed with enteral and intravenous electrolyte replacement even after adding teriparatide. She responded well to adjunctive therapy with continuous subcutaneous magnesium. Severe hypomagnesemia can be part of the phenotype of activating CaSR mutations. Subcutaneous magnesium should be considered in patients with difficult to control hypomagnesemia.

Gene expression analysis of Gata3 −/− mice by using cDNA microarray technology

Transcription factor Gata3 is implicated in the formation of autosomal dominant hypoparathyroidism, sensorineural deafness, and renal anomaly (HDR) syndrome. We pursued to identify the potential Gata3 target genes by profiling the gene expression pattern in E9.5 Gata3 −/− mouse embryos. Altogether four independent microarray hybridizations were carried out on NIA Mouse15K cDNA arrays. We discovered two hundred and sixty one genes that are downregulated in Gata3 mutant embryos at E9.5 (with a minimal 2.0-fold change). The majority of the differentially expressed genes belong to two functional groups — genes involved in transcription regulation and cellular signaling. One of the genes discovered to be downregulated in Gata3 mutant embryos was tumor suppressor gene Disabled 2. The validity of this finding was checked by using the whole mount in situ hybridization technology. This study revealed that the sites, where Dab2 is downregulated in the mutant embryos partly overlap with the Gata3 expression domains, including the mid-embryo region, branchial arches and facio-acoustic (VII–VIII) neural crest complex. This is the first time when tumor supressor gene Dab2 is shown to be implicated in the defective phenotype of Gata3 mutant mice.

CASRdb: calcium-sensing receptor locus-specific database for mutations causing familial (benign) hypocalciuric hypercalcemia, neonatal severe hyperparathyroidism, and autosomal dominant hypocalcemia.

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.

Extracellular calcium-sensing receptor: structural and functional features and association with diseases.

The recently cloned extracellular calcium-sensing receptor (CaR) is a G protein-coupled receptor that plays an essential role in the regulation of extracellular calcium homeostasis. This receptor is expressed in all tissues related to this control (parathyroid glands, thyroid C-cells, kidneys, intestine and bones) and also in tissues with apparently no role in the maintenance of extracellular calcium levels, such as brain, skin and pancreas. The CaR amino acid sequence is compatible with three major domains: a long and hydrophilic aminoterminal extracellular domain, where most of the activating and inactivating mutations described to date are located and where the dimerization process occurs, and the agonist-binding site is located, a hydrophobic transmembrane domain involved in the signal transduction mechanism from the extracellular domain to its respective G protein, and a carboxyterminal intracellular tail, with a well-established role for cell surface CaR expression and for signal transduction. CaR cloning was immediately followed by the association of genetic human diseases with inactivating and activating CaR mutations: familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism are caused by CaR-inactivating mutations, whereas autosomal dominant hypoparathyroidism is secondary to CaR-activating mutations. Finally, we will comment on the development of drugs that modulate CaR function by either activating (calcimimetic drugs) or antagonizing it (calcilytic drugs), and on their potential therapeutic implications, such as medical control of specific cases of primary and uremic hyperparathyroidism with calcimimetic drugs and a potential treatment for osteoporosis with a calcilytic drug.

Association between Total Serum Calcium and the A986S Polymorphism of the Calcium-Sensing Receptor Gene

Serum calcium is under tight physiological control, but it is also a quantitative trait with substantial genetic regulation. Mutations of the CASR gene cause familial hypocalciuric hypercalcemia or autosomal dominant hypoparathyroidism, depending on whether they decrease or increase, respectively, ligand binding to the receptor protein. We described an association between ionized calcium and a common polymorphism (A986S) found in the cytoplasmic tail of this G protein-coupled receptor. We report here on an independent study of 387 healthy young women. Genotyping was performed by allele-specific amplification and serum chemistries were measured by automated clinical assay. Frequencies of SS, AS, and AA genotypes were 6, 107, and 274, respectively, yielding a 986S allele frequency of 15.4%. Mean total serum calcium (CaT) was significantly higher in the SS (9.88 ± 0.29 mg/dL, P = 0.015) and AS groups (9.45 ± 0.05 mg/dL, P = 0.002), than in the AA group (9.23 ± 0.04 mg/dL). In multiple regression modeling, the A986S genotype remained an independently significant predictor of CaT (P < 0.0001) when serum albumin, globulin, inorganic phosphate, and creatinine covariates were included. These data are the first to show significant association between a common polymorphism and concentrations of a serum electrolyte. The A986S polymorphism is also a potential predisposing factor in disorders of bone and mineral metabolism.

The A986S polymorphism of the calcium-sensing receptor (CASR) gene is a significant contributor to inter-individual variability of serum calcium

Serum calcium is under tight physiological control, but it is also a quantitative trait with a substantial genetic component. Mutations of the CASR gene cause familial hypocalciuric hypercalcemia and autosomal dominant hypoparathyroidism, depending on whether they decrease or increase, respectively, the activity of the protein. We described an association between ionized calcium and a common polymorphism (A986S) found in the cytoplasmic tail of this G protein-coupled receptor (Lancet 1999;353:112). We report here on an independent study of 387 healthy young women. Genotyping was performed by allele-specific amplification and serum chemistries were measured by automated clinical assay. Frequencies of SS, AS, and AA genotypes were 6, 107, and 274, respectively, yielding a 986S allele frequency of 15%. Mean total serum calcium (Car) was significantly higher in the SS (9.88 ± 0.29 mg/dL, p=.015) and AS groups (9.45 ± 0.05 mg/dL, p=.002), than in the AA group (9.23 ± 0.04 mg/dL). In multiple regression modelling, the A986S genotype remained an independently significant predictor of Car (p<.0001) when serum total protein, albumin, phosphate, magnesium, and creatinine covariates were included. These data are among the first to show significant association between a common polymorphism and a serum electrolyte assay. The A986S polymorphism is also a potential predisposing factor in disorders of bone and mineral metabolism.

A Ca(2+)-sensing receptor mutation causes hypoparathyroidism by increasing receptor sensitivity to Ca2+ and maximal signal transduction.

Activating mutations of the Ca(2+)-sensing receptor (CaR) gene cause autosomal dominant hypoparathyroidism. Functional expression studies have been reported for several mutations, but have produced conflicting results. Thus, the mechanism by which these mutations activate the receptor is unclear. We describe here a new family with autosomal dominant hypoparathyroidism. The mother and three daughters experienced muscle spasms and/or seizures from early childhood. They were treated with oral calcium and vitamin D analogs, and all four patients developed hypercalciuria, nephrocalcinosis, and renal insufficiency. In this family, we identified a heterozygous missense mutation (F612S) involving the extracellular region of the CaR. The mutation cosegregated with disease. It was not present in 50 normal control individuals. We used site-directed mutagenesis to introduce this mutation into the CaR cDNA, and then expressed the mutant receptor in human embryonic kidney (HEK)-293 cells. In these cells, the accumulation of inositol phosphates was measured as a function of extracellular Ca2+ concentration. Compared with the wild-type receptor, the mutant receptor showed a left-shift in the concentration-response curve and an increase in the maximal response to high Ca2+ concentration. These effects did not appear to be mediated by changes in levels of receptor expression, as judged by ELISA, or by changes in receptor glycosylation, as judged by Western analysis. We conclude that this CaR mutation causes hypoparathyroidism by a dual increase in receptor sensitivity to extracellular Ca2+ and maximal signal transduction capacity.

A familial syndrome of hypocalcemia with hypercalciuria due to mutations in the calcium-sensing receptor.

The calcium-sensing receptor regulates the secretion of parathyroid hormone in response to changes in extracellular calcium concentrations, and mutations that result in a loss of function of the receptor are associated with familial hypocalciuric hypercalcemia. Mutations involving a gain of function have been associated with hypocalcemia in two kindreds. We examined the possibility that the latter type of mutation may result in a phenotype of familial hypocalcemia with hypercalciuria. We studied six kindreds given a diagnosis of autosomal dominant hypoparathyroidism on the basis of their hypocalcemia and normal serum parathyroid hormone concentrations, a combination that suggested a defect of the calcium-sensing receptor. The hypocalcemia was associated with hypercalciuria, and treatment with vitamin D resulted in increased hypercalciuria, nephrocalcinosis, and renal impairment. Mutations in the calcium-sensing-receptor gene were identified by DNA-sequence analysis and expressed in human embryonic kidney cells (HEK-293). Five heterozygous missense mutations (Asn118Lys, Phe128Leu, Thr151Met, Glu191Lys, and Phe612Ser) were detected in the extracellular domain of the calcium-sensing-receptor gene and shown to cosegregate with the disease. Analysis of the functional expression of three of the mutant receptors in HEK-293 cells demonstrated shifts in the dose-response curves so that the extracellular calcium concentrations needed to produce half-maximal increases in total inositol phosphate in the cells were significantly (P=0.02 to P<0.001) lower than those required for the wild-type receptor. Gain-of-function mutations in the calcium-sensing receptor are associated with a familial syndrome of hypocalcemia with hypercalciuria that needs to be distinguished from hypoparathyroidism.

The Ca(2+)-sensing receptor gene (PCAR1) mutation T151M in isolated autosomal dominant hypoparathyroidism.

Isolated autosomal dominant hypoparathyroidism is a heterogeneous disorder characterized by parathyroid hormone (PTH) deficiency, hypocalcemia and hyperphosphatemia. The candidate gene approach was used to study a large Norwegian family. The loci for the PTH gene, PTH receptor gene and RET protooncogene were excluded using dinucleotide markers and restriction fragment length polymorphism analysis. Complete cosegregation of this trait was found with the chromosomal region 3q13, using the short tandem repeat markers D3S1267, D3S1269, D3S1303, D3S1518, and RHO. This region contains the candidate locus for the Ca(2+)-sensing receptor (PCAR1). By single-strand conformation polymorphism (SSCP) analysis of all PCAR1 exons followed by automated sequencing, we identified a C to T transition in exon 2 (cDNA position 452) on the mutant allele in the family. The mutation predicts a substitution of Thr to Met in amino acid position 151 (T151M). A StyI restriction site created by the nucleotide substitution was used to confirm the mutation on all alleles, as well as to exclude it among 100 normal alleles (blood donors). SSCP analysis also identified a novel polymorphism of PCAR1 intron 4 (1609-88t --> c) on normal alleles. The T151M mutation is located in the extracellular N-terminal domain of PCAR1, which belongs to the superfamily of G protein-coupled receptors. We suggest that this is a gain-of-function mutation that increases the sensitivity of the receptor to [Ca2+], thereby decreasing the calcium set point.

Mutations in the Ca(2+)-sensing receptor gene cause autosomal dominant and sporadic hypoparathyroidism.

Parathyroid hormone secretion is negatively regulated by a 7-transmembrane domain, G-protein coupled Ca(2+)-sensing receptor. We hypothesized that activating mutations in this receptor might cause autosomal dominant hypoparathyroidism (ADHP). Consistent with this hypothesis, we identified, in two families with ADHP, heterozygous missense mutations in the Ca(2+)-sensing receptor gene that cosegregated with the disorder. None of 50 normal controls had either mutation. We also identified a de novo, missense Ca(2+)-sensing receptor mutation in a child with severe sporadic hypoparathyroidism. The amino acid substitution in one ADHP family affected the N-terminal, extracellular domain of the receptor. The other mutations involved the transmembrane region. Unlike patients with acquired hypoparathyroidism, patients with these mutations had hypercalciuria even at low serum calcium concentrations. Their greater hypercalciuria presumably reflected activation of Ca(2+)-sensing receptors in kidney cells, where the receptor negatively regulates calcium reabsorption. This augmented hypercalciuria increases the risk of renal complications and thus has implications for the choice of therapy.