Mutations In Calcium-sensing Receptor Gene Research Articles

ODP118 PTH (1-34) Replacement Therapy for Hypoparathyroidism due to Sporadic Calcium Sensing Receptor Gain-of-Function Point Mutation

Abstract Background The calcium sensing receptor (CASR) regulates parathyroid hormone secretion in response to extracellular calcium concentration. A gain-of-function mutation of the CASR lowers the set point for extracellular calcium sensing, resulting in both reduced parathyroid hormone secretion and increased urinary calcium excretion compared to other causes of hypoparathyroidism. Clinical Case After presenting with hypocalcemia-associated seizures at the age of two years, our patient had an undetectable serum parathyroid hormone level. He was started on calcitriol and calcium supplementation, however continued to have recurrent seizures throughout childhood. On ultrasound at age four, he exhibited nephrocalcinosis. DNA sequence analysis revealed a heterozygous T383G mutation nucleotide substitution on exon 3, resulting in the replacement of phenylalanine with cysteine at amino acid position 128. Our patient's base substitution likely represents a de novo mutation as we have confirmed that he has no family history of hypocalcemia. Notably, a different missense mutation at the same codon (F128L) co-segregated with autosomal dominant hypocalcemia in a large family, and functional studies confirm that mutation of this phenylalanine provides gain-of-function to the CASR. After enrolling in a clinical trial for continuous recombinant parathyroid hormone infusion at age seven, his symptoms of hypocalcemia abated. His seizures stopped, and anti-epileptic drugs were discontinued at age eight. After the clinical trial concluded, he was switched to teriparatide 10 micrograms three times daily, and serum calcium was maintained between 7.5 and 8.5 mg/dL. With the goal to minimize hypercalciuria and reduce the frequency of injections, teriparatide was discontinued, and recombinant parathyroid hormone (Natpara) 50 micrograms daily was started. This led to symptomatic hypocalcemia with muscle cramping and cognitive changes, and he was thus restarted on teriparatide with calcium carbonate supplementation. Despite maintenance of 24-hour urine calcium excretion ranging 325-388 mg, he developed bilateral flank pain. Computed tomography images revealed worsening nephrocalcinosis and bilateral nephrolithiasis. To reduce hypercalciuria and risk of stone formation, he was started on chlorthalidone, switched to calcium citrate, and encouraged to reduce dietary sodium intake. Conclusion This patient has a novel T383G activating mutation in CASR gene resulting in hypoparathyroidism and type 5 Bartter syndrome that has not been previously published in the literature. His hypocalcemia has remained stable on teriparatide for over 18 years, which to our knowledge, is the longest treatment duration using recombinant human parathyroid hormone for this purpose. We demonstrate a unique clinical challenge to balance treatment of hypoparathyroidism and hypocalcemia with teriparatide and supplemental calcium, while minimizing hypercalciuria and associated nephrocalcinosis. Presentation: No date and time listed

PREVALENCE OF SPINK 1 AND CASR GENE MUTATIONS IN ACUTE AND RECURRENT ACUTE PANCREATITIS : A STUDY FROM CENTRAL INDIA

Background: Genetic factors may play an important role in the pathogenesis of acute pancreatitis. It has been observed in various studies that the presence of risk factors alone like alcohol abuse or gall bladder stones does not lead to attacks of pancreatitis in all the patients. This leads to assumption that genetic factors may decrease the threshold for the development of pancreatitis in presence of one or more risk factors. We observed that there is a paucity of data regarding the role of genetics in acute pancreatitis (AP) and recurrent acute pancreatitis (RAP) in our part of the world and we aimed at studying the prevalence of genetic mutations in such patients. Methods: Our study intended to nd the prevalence of SPINK1 N34S (Serine protease inhibitor kazal type 1) and CaSR (Calcium sensing receptor) gene mutations in patients of AP and RAP. A total of 50 patients and 25 age and gender matched controls entered our study. Blood samples were obtained from all the cases and controls for routine investigations and genetic analysis. SPINK 1 N34S and CaSR gene mutation studies were done in all the patients and controls. Results: Alcohol (64%) followed by gallbladder stone disease (20%) was the most common aetiology of pancreatitis. SPINK 1 N34S mutation was present in 21 patients and 2 controls whereas CaSR gene mutation was present in 13 patients and 2 controls. Patients with SPINK 1 N34S and CaSR gene mutations were younger than the patients without these mutations. Prevalence of both SPINK1 N34S and CaSR gene mutations was higher in patients of RAP than AP. These mutations were not associated with aetiology or severity of pancreatitis. Conclusion: The prevalence SPINK 1 N34S and CaSR gene mutations was higher in patients of AP and RAP. Identication of these mutations in patients of AP can help in the identication of patients who are at increased risk of recurrent attacks of AP

An Uncommon Cause of Hypomagnesemia With Hypercalciuria and Nephrocalcinosis in a Young Woman

Background: Mutations of the calcium-sensing receptor (CaSR) gene resolve in a change of calcium homeostasis with autosomal dominant and/or sporadic hypocalcemia with hypercalciuria (ADH) (gain-of-function) and familial hypocalciuric hypercalcemia (loss-of-function-mutation). Additionally, genetic mutations in renal tubular transporters are also associated with hypomagnesemia, hypercalciuria and nephrocalcinosis. Such,,magnesium-losing-diseases“ are disorders like familiar hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) which shows a mutation in the Claudin 16 gene (CLD16) and the primary hypomagnesemia with secondary hypocalcaemia caused by a genetic defect in the Transient Receptor Potential Cation Channel Subfamily M Member 6 (TRPM6) gene. Clinical Case: A 35- year old woman with a first episode of pyelonephritis presented herself in our emergency unit in January 2020. Kidney ultrasound showed an advanced stage of nephrocalcinosis and normocalcemia, hypomagnesemia, suppressed PTH and hypercalciuria were observed in laboratory analyses. Several family members from her father`s side and her brother have all been diagnosed with nephrocalcinosis developed in young age. A gene sequencing of CASR and CLD16 gene provided no sequence or copy changes. Thiazide diuretic was initiated for correction of hypercalciuria, but the patient developed hypotonic blood pressure and stopped the drug. In November 2020 she unexpectedly died. Conclusions: In our patient ADH due an activating mutation of the CaSR gene was supposed, but no abnormality in gene sequence was detected. Since CaSR are not only expressed in PTH-secreting cells in the parathyroid but also along the nephron, particularly in the thick ascending limp of loop of Henle, activating mutations of CaSR gene will lead to a decreased reabsorption of divalent cations (like calcium and magnesium). Thus, this phenotype results in low or normal PTH, low or normal serum calcium levels, hypomagnesemia, high- normal urinary calcium and magnesium excretion (due to increased activation of the CaSR gene in kidneys) and nephrocalcinosis with recurrent nephrolithiasis. Thiazide diuretics are effective in these patients and vitamin D supplementation should be considered with caution. Therapeutic attempts using CASR antagonists (calcilytics) to treat ADH are currently investigated. However, familiar hypomagnesemia with hypercalciuria and nephrocalcinosis as well as primary hypomagnesemia with secondary hypocalcaemia should also be discussed as differential diagnoses in this case. The teaching point of our case is the need of magnesium testing and additional cardiological observation regarding possibly fatal arrhythmias in these subjects. Also genetic and metabolic phenotyping of all family members in such cases is important.

Autosomal Dominant Hypocalcemia With Atypical Urine Findings Accompanied by Novel CaSR Gene Mutation and VitD Deficiency.

IntroductionAutosomal dominant hypocalcemia (ADH) is caused by gain-of-function mutations of the calcium sensing receptor (CaSR). It is characterized by hypercalciuria in spite of hypocalcemia. Vitamin D deficiency increases calcium reabsorption in the distal tubules of the kidneys, resulting in hypocalciuria.Materials and methodsA 38-year-old female proband had hypocalcemia, hypocalciuria, and vitamin D deficiency. Her father and brother also had hypocalcemia, but her mother was normocalcemic. We analyzed the CaSR gene abnormality in this family. Polymerase chain reaction (PCR) and sequence analysis were performed to explore the CaSR gene mutation. Mutagenesis, transfection, and functional analysis were performed on the discovered genetic abnormalities.ResultPCR and sequence analysis revealed that the proband, her father, and brother had a novel heterozygous mutation of the CaSR genes that causes threonine to asparagine substitution at codon 186 (T186N). Using HEK293 cells transfected with wild-type or T186N CaSR complementary DNA, we assessed the intracellular Ca2+ concentration in response to changes in the extracellular Ca2+ concentration. The cells transfected mutant CaSR gene had higher activity than that of wild-type. Therefore, we determined our patient had ADH with a novel mutation of the CaSR gene and hypocalciuria resulting from a vitamin D deficiency. We administered vitamin D to the proband, which caused elevation of her urinary calcium level, a typical finding of ADH.ConclusionVitamin D deficiency was suggested to potentially mask hypercalciuria in ADH. Hypocalcemia with vitamin D deficiency should be diagnosed with care.

SAT-370 Novel CASR Gene Mutation as a Cause of Familial Isolated Primary Hyperparathyroidism

BACKGROUND: Primary hyperparathyroidism (pHT) is one of the most common causes of hypercalcemia. About 10% of these patients have a familial cause of which MEN and the hyperparathyroid-jaw tumor syndrome (HJTs) are most common. Familial hypocalciuric hypercalcemia (FHH) due to loss of function mutations of the calcium sensing receptor (CASR) gene is an important familial mimic of this that needs to be distinguished. Beyond this are still a group of patients with familial isolated primary hyperparathyroidism (FIpHT). Recognition of this entity is important because of the different prognostic and surgical treatment strategy for their management compared to regular sporadic pHT. Clinical Case: A 58 yr old postmenopausal lady on topical HRT was referred for thyroid nodular disease. Her initial lab tests showed primary hyperparathyroidism with mild hypercalcemia. Her initial neck sonogram showed multiple benign appearing nodules that did not warrant biopsy. There was a history of hypothyroidism in her mother and thyroid cancer in a maternal cousin. In addition, her father and two sons have history of hypercalcemia that required repeated hospital admissions for treatment. Her two daughters to date have had no hypercalcemia, nephrolithiasis nor thyroid problems. There was no family history of jaw, renal nor brain or pituitary tumors and no history of severe dyspeptic disease nor familial cancers. She had hypercalciuria, normal bone density and non-obstructive nephrolithiasis. MEN-1 gene testing was normal. Parathyroid scan suggested a possible right sided parathyroid lesion and she had elective parathyroidectomy of an ectopic right parathyroid that was hypercellular on histology. The intra-operative PTH dropped following the lesion extraction by ~ 51%. Post operatively the patient’s mild pHT and hypercalcemia persists but imaging studies have been unrevealing. Further genetic testing for other possible etiologies of familial pHT were -ve for HJTs but revealed a novel somatic mutation of the CASR gene; c.1868G>A (p.Gly623Asp) whose present significance is unclear. This variant has been described in one family with FHH but In silico predictive analyses of the mutation suggests a possible deleterious effect. Given her known family history of symptomatic hypercalcemia this novel mutation appears to be a hitherto unrecognized cause for FIpHT. The patient is presently being conservatively managed and monitored. Conclusion: While familial pHT is relatively uncommon its recognition is important as it can inform planned surgical intervention and expected prognosis for anticipated cure. While MEN and HJTs are the most common etiologies for familial pHT other possibilities need to considered when the history suggests possible FIpHT and our case highlights a novel CASR mutation as diagnostic consideration.

SAT-077 Two Cases of Hypoparathyroidism Due to Activating Calcium Sensing Receptor Mutation

IntroductionThe extracellular calcium-sensing receptor (CaSR) expressed mainly in the parathyroid gland and kidneys regulates calcium (Ca+2) homeostasis through parathyroid hormone (PTH) secretion. Activating mutations of CaSR can lead to autosomal dominant hypocalcemia and severe congenital hypoparathyroidism. Constitutively activated CaSR receptors blocks PTH release leading to hypocalcemia, hyperphosphatemia and decreased Ca+2 reabsorption from the kidney.Case 1:14 year old male presented for an evaluation of hypocalcemia and hyperphosphatemia found on routine blood work. He denied symptoms of hypocalcemia. He had normal vital signs, positive Chovstek sign but rest of exam was unremarkable. His lab results showed low Ca+2 8.1 mg/dl (8.6–10 mg/dl), high phosphorus 6 mg/dl (2.7–4.5 mg/dl) and inappropriately normal PTH 26.8 pg/ml (10–65 pg/ml). FISH was negative for DiGeorge. Genetic testing showed heterozygous CaSR gene mutation I822T, variant of uncertain significance. His father with primary hypoparathyroidism has the same CaSR gene mutation; mother is healthy and tested negative for this variant. Given the inheritance pattern of the mutation, it is likely a pathologic mutation. He is maintained on Calcium (1500 mg BID) and Calcitriol (0.5 mcg PO BID) and is doing well.Case 2:One day old premature 32-week old infant girl was found to have early onset neonatal hypocalcemia 6.1 mg/dl (6.2–11 mg/dl) during NICU admission for respiratory distress, inappropriately normal PTH 18.5 pg/ml and high phosphorus 8.8 mg/dl (4.6–7.9 mg/dl). She had no symptoms of hypocalcemia in the NICU or at home. She did not have any dysmorphic features. FISH was negative for DiGeorge. Genetic testing to sequence genes including AIRE, AP2S1, CASR, GNAS, HADHA, HADHB, PTH1R, SOX3, STX16, TBCE was done and revealed a novel heterozygous mutation in the CaSR gene for a missense variant c.2495T>C(p.lle832Thr) and STX16 c.644A>T, possibly benign variant. Unfortunately, the parents have not consented to testing yet. Further familial and functional characterization of this new variant is necessary to confirm its possible pathogenetic role in this hypocalcemic patient. Currently she is maintained on ergocalciferol 800 IU, calcitriol 0.25 mcg and sevelamer 3 packets daily and is doing well.Conclusion:In the workup for primary hypoparathyroidism without dysmorphic features and tests negative for DiGeorge, CaSR mutations should be investigated as part of the differential as we have identified variants in the CaSR gene in 2 children with asymptomatic hypocalcemia, one of which is a novel mutation which has never been reported before.

One pedigree analysis of a familial hypocalciuric hypercalcemia caused by a new heterozygous mutation in calcium-sensing receptor gene

Medical history and physical examinations were performed to assess the clinical manifestations and growth of one patient with familial hypocalciuric hypercalcemia(FHH). Clinical data, including histories of his parents and 3 maternal relatives were collected. Serum parathyroid hormone(PTH), calcium, phosphorus, 24-hour urinary calcium, and 24-hour urinary calcium to creatinine ratio(UCCR)were measured or calculated. Meanwhile, after peripheral blood samples were collected and genomic DNA was extracted, the whole exome sequencing to detect gene mutations of the proband was performed. Further family screenings were also performed by Sanger sequencing to assess the relationship between genotype and phenotype. The results showed that the proband with motor developmental delays had severe hypercalcemia(4.20 mmol/L), while his mother without clinical symptoms had a higher blood calcium within the normal range(2.57 mmol/L). However, their urinary calcium levels were both low(UCCR< 0.01). The C→T heterozygous missense mutation was found by exome sequencing at nucleotide 1243 within exon 4 of calcium sensing receptor(CaSR)gene in the proband, which caused a substitution of Arginine to Tryptophan(R415W). Sanger sequencing confirmed the same mutation in his mother. There was no mutation in other family members. (Chin J Endocrinol Metab, 2018, 34: 583-586) Key words: Hypercalcemia; Calcium-sensing receptor; Familial hypocalciuric hypercalcemia

A Novel Mutation of the Calcium Sensing Receptor Gene in a Franconian Kindred: Heterozygous Mutation c.1697_1698delTG Exon 6.

Familial hypocalciuric hypercalcemia (FHH) belongs to the disorders of a disturbed calcium homeostasis. Genetically, the disorder is inherited in an autosomal-dominant trait and represents an inactivating mutation of the calcium sensing receptor (CaSR) gene. We identified a Franconian kindred in which 6 individuals could be tested by molecular genetic means. In 5 individuals of 3 generations, the mutation could be classified as c.1697_1698delTG. This novel germline mutation creates a premature stop codon leading to a loss of 510 amino acids of the protein. The detection of CaSR gene mutations is suitable to differentiate states of hypercalcemia and may help to avoid invasive procedures such as parathyroidectomies.

CASR gene activating mutations in two families with autosomal dominant hypocalcemia

BackgroundAutosomal dominant hypocalcemia (ADH) is an endocrine disorder caused by activating mutations of the calcium-sensing receptor (CASR) gene which plays a major role in maintaining calcium homeostasis. Biochemical features of ADH are hypocalcemia and hypercalciuria with inappropriately low levels of parathyroid hormone (PTH). We report on two four-generation families affected by ADH. AimTo identify mutations of CASR gene in subjects affected by familial idiopathic hypoparathyroidism. To perform functional assays of identified CASR variants by transient transfection on HEK293 cells. ResultsWe identified two CASR variants (Q681R and P221L): the Q681R variant was novel while the P221L had been previously published. Functional assays on the Q681R variant showed that it did not alter the whole expression nor the correct plasmamembrane localization, but enhanced the signaling function, increasing the sensitivity of the receptor as compared to the WT. ConclusionsWe report two activating CASR mutations in two families affected by ADH and the functional assays performed on the novel variant Q681R. Our work enlarged the spectrum of mutations of the CASR and contributed to a better elucidation of the protein function.

A novel CaSR mutation presenting as a severe case of neonatal familial hypocalciuric hypercalcemia

BackgroundFamilial Hypocalciuric Hypercalcemia (FHH) is a generally benign disorder caused by heterozygous inactivating mutations in the Calcium-Sensing Receptor (CaSR) gene resulting in altered calcium metabolism.ObjectiveWe report a case of unusually severe neonatal FHH due to a novel CaSR gene mutation that presented with perinatal fractures and moderate hypercalcemia.Case overviewA female infant was admitted at 2 weeks of age for suspected non-accidental trauma (NAT). Laboratory testing revealed hypercalcemia (3.08 mmol/L), elevated iPTH (20.4 pmol/L) and low urinary calcium clearance (0.0004). Radiographs demonstrated multiple healing metaphyseal and rib fractures and bilateral femoral bowing. The femoral deformity and stage of healing were consistent with prenatal injuries rather than non-accidental trauma (NAT). Treatment was initiated with cholecalciferol, 400 IU/day, and by 6 weeks of age, iPTH levels had decreased into the high-normal range. Follow up radiographs demonstrated marked improvement of bone lesions by 3 months. A CaSR gene mutation study showed heterozygosity for a T>C nucleotide substitution at c.1664 in exon 6, resulting in amino acid change I555T in the extracellular domain consistent with a missense mutation. Her mother does not carry the mutation and the father is unknown. At 18 months of age, the child continues to have relative hyperparathyroidism and moderate hypercalcemia but is otherwise normal.ConclusionThis neonate with intrauterine fractures and demineralization, moderate hypercalcemia and hyperparathyroidism was found to have a novel inactivating missense mutation of the CaSR not detected in her mother. Resolution of bone lesions and reduction of hyperparathyroidism was likely attributable to the natural evolution of the disorder in infancy as well as the mitigating effect of cholecalciferol treatment.

A novel germline inactivating mutation in the CASR gene in an Italian kindred affected by familial hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) syndrome is a rare benign condition, inherited as an autosomal dominant trait, in which inactivating mutations of the calcium-sensing receptor (CASR) gene affects the body's ability to regulate calcium homeostasis. Its outcome is featured by increased levels of serum calcium, moderate hypophosphatemia, and inadequately normal or elevated circulating parathyroid hormone levels. Affected patients are mostly asymptomatic and do not benefit from surgical resection of their mildly enlarged parathyroids. We evaluated for hypercalcemia an Italian family that was identified via a young adult male proband referred to our center for parathyroidectomy. The patients and the family members were evaluated both biochemically and genetically as suspected FHH subjects. An in vitro functional study was performed by site-directed mutagenesis, and CASR activity was monitored by measuring intracellular calcium ([Ca(2)(+)](i)). The patient had a novel germline heterozygous CASR mutation (c.361_364GATT; p.D121del/fsX122). The mutation caused a premature stop codon at codon 122, exiting a truncated protein. The biochemical phenotype of all family members carrying the heterozygous deletion was concordant with classic FHH syndrome. Our findings confirm the role of CASR gene mutational analysis to offer a valuable addition for the recognition of FHH in hypercalcemic patients not yet characterized for a positive familial history of hypercalcemia, the only condition that identifies CASR gene mutations in hypercalcemia.

Inactivating calcium‐sensing receptor mutations in patients with primary hyperparathyroidism

Primary hyperparathyroidism (HPT) is characterised by autonomous secretion of PTH from enlarged parathyroid glands leading, in most patients, to asymptomatic hypercalcaemia. Familial hypocalciuric hypercalcaemia (FHH) is an autosomal dominant disorder caused by inactivating mutations in the calcium-sensing receptor (CaSR) gene; it is characterised by lifelong and usually asymptomatic hypercalcaemia. Establishing the correct diagnosis is important because surgery can be curative in HPT, but ineffective in FHH. There is overlap in the diagnostic criteria for the two disorders and some patients carrying inactivating mutations in the CaSR gene, which is suggestive of FHH, also have HPT with hyperplastic parathyroid glands or adenomas. DESIGN AND PATIENTS CaSR gene mutations were analysed and clinical and biochemical parameters evaluated in 139 consecutive outpatients presenting with hypercalcaemia and suspected of having HPT. Six different mutations of the CaSR gene were found in eight patients. In four patients, classical FHH was suspected based on clinical and biochemical results and was confirmed by the CaSR mutations. In the other four patients, HPT was diagnosed based on the biochemical profile or symptoms; in these four patients, the parathyroids were operated on and single adenomas were histologically confirmed. In all four patients, serum calcium decreased postoperatively; and in three patients, serum calcium normalised postoperatively. The CaSR mutations in these patients were R25X, E250K and Q926R. The coexistence of HPT and FHH in four of 139 patients suggests a pathogenetic role of CaSR mutations in HPT. Despite also having a CaSR mutation, these patients benefited from parathyroid surgery.

Mutations of calcium-sensing receptor gene: two novel mutations and overview of impact on calcium homeostasis

Genetic disorders of calcium metabolism arise in a familial or sporadic setting. The calcium-sensing receptor (CASR) plays a key role in maintaining calcium homeostasis and study of the CASR gene can be clinically useful in determining etiology and appropriate therapeutic approaches. We report two cases of novel CASR gene mutations that illustrate the varying clinical presentations and discuss these in terms of the current understanding of CASR function. A 16-year-old patient had mild hypercalcemia associated with low-normal urinary calcium excretion and normal-to-high parathyroid hormone (PTH) levels. Because of negative family history, familial hypocalciuric hypercalcemia was originally excluded. The second patient was a 54-year-old man with symptomatic hypocalcemia, hyperphosphatemia, low PTH, and mild hypercalciuria. Familial investigation revealed the same phenotype in the patient's sister. The coding region of the CASR gene was sequenced in both probands and their available first-degree relatives. The first patient had a novel heterozygous inactivating CASR mutation in exon 4, which predicted a p.A423K change; genetic analysis was negative in the parents. The second patient had a novel heterozygous activating CASR mutation in exon 6, which predicted a p.E556K change; the affected sister of the proband was also positive. We reported two novel heterozygous mutations of the CASR gene, an inactivating mutation in exon 4 and the first activating mutation reported to date in exon 6. These cases illustrate the importance of genetic testing of CASR gene to aid correct diagnosis and to assist in clinical management.

New mutation in the CASR gene in a family with familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT)

A loss of calcium-sensing receptor (CASR) function due to inactivating mutations can cause familial hypocalciuric hypercalcemia (FHH) or neonatal severe hyperparathyroidism (NSHPT). NSHPT represents the most severe expression of FHH and courses as a life-threatening condition. The aim of this study was to identify and characterize a CASR mutation in a female infant brought to the health service due to dehydration, apathy, lack of breast feeding and severe hypercalcemia. Molecular analysis was performed on genomic DNA of the index case and her parents. A novel homozygous mutation (p.E519X) in CASR was identified in the proband; both mother and father had the same mutation in heterozygous state, confirming their FHH condition. The mutation results in a truncated and inactive protein due to the lack of transmembrane and intracellular domains. The identification of this novel CASR gene mutation established the basis of hypercalcemia in this family and allowed a genetic counseling.

Identification and functional analysis of novel calcium-sensing receptor gene mutation in familial hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) is a benign disorder with heterozygous inactivating mutations in the calcium-sensing receptor (CASR) gene. The present study describes the identification and functional analysis of a novel CASR gene mutation leading to FHH. The proband is a 33-yr-old woman (Ca 11.0 mg/dL, intact-PTH 68 pg/mL, FECa 0.17 %). Leukocyte DNA was isolated in four family members and a novel heterozygous mutation (D190G, GAT>GGT) in exon 4 of CASR gene was identified by direct sequence analysis. The mutant CASR expression vector was constructed by mutagenesis procedure and its response to Ca(2+) was characterized by transient transfection into human embryonic kidney (HEK) 293 cells and treatment with increasing extracellular Ca(2+) concentrations. HEK cells didn't activate intracellular signaling (MAPK activation) in response to increases of extracellular Ca(2+) concentrations when the mutant receptor was expressed normally at the cell surface. The novel heterozygous mutation (D190G) identified in the present study showed that the reduction of activity of CASR to extracellular Ca(2+) caused FHH in patients and our study demonstrated the importance of Asp-190 participated in response to Ca(2+) in CASR.

Calcium-sensing receptor in cancer: good cop or bad cop?

The extracellular calcium-sensing receptor (CaR) is a versatile 'sensor' for di- and polycationic molecules in the body. CaR plays a key role in the defense against hypercalcemia by "sensing" extracellular calcium levels in the parathyroid and kidney, the key organs maintaining systemic calcium homeostasis. Although mutation of CaR gene has so far not been associated with any malignancy, aberrant functions of CaR have implications in malignant progression. One situation is loss of CaR expression, resulting in loss of growth suppressing effects of elevated extracellular Ca(2+) by CaR, reported in parathyroid adenoma and in colon carcinoma. Another situation is activation of CaR, resulting in increased production of parathyroid hormone-related peptide (PTHrP), a primary causal factor in hypercalcemia of malignancy and a contributor to metastatic processes involving bone. CaR signaling and effects have been studied in several cancers including ovarian cancers, gastrinomas, and gliomas in addition to comparatively detailed studies in breast, prostate, and colon cancers. Studies on H-500 rat Leydig cells, a xenotransplantable model of humoral hypercalcemia of malignancy has shed much light on the mechanisms of CaR-induced cancer cell growth and survival. Pharmacological agonists and antagonists of CaR hold therapeutic promise depending on whether activation of CaR is required such as in case of colon cancer or inactivating the receptor is required as in the case of breast- and prostate tumors.

Novel mutations in the calcium sensing receptor gene in tropical chronic pancreatitis in India

Objective. Tropical chronic pancreatitis (TCP) is a form of chronic pancreatitis seen in many tropical countries in young non-alcoholic subjects who are often malnourished. Nutritional deficiencies, either at the macro or micro level, and food toxins have been implicated in its causation, although there is no final proof to confirm this suggestion. Mutations of SPINK1 and CFTR genes have been proposed as disease modifiers, or as determinants of phenotypes. Mutations involving the calcium sensing receptor (CASR) have been suggested to increase the risk of chronic pancreatitis (CP), since high intracellular levels of calcium activate trypsinogen within the acinar cells. A combination of CASR and SPINK1 gene mutations has been proposed to predispose to idiopathic CP. The purpose of this study was to report on novel mutations in CASR, identified in TCP patients. Material and methods. We screened our TCP patients for mutations in CASR and SPINK1 genes. In a cohort of 35 patients and an equivalent number of controls, genomic DNA was screened for mutations in CASR and SPINK1 by direct DNA sequencing. Results. Four new mutations were found in the CASR gene. A combination of both SPINK1 (N34S) and CASR mutations was seen in 6% of the patients, while 22% harbored a single mutation. Conclusions. Our study suggests, for the first time, that CASR mutation may be a risk for TCP, and that this risk may be further increased if there is an associated SPINK1 mutation.

Molecular Genetic Analysis of the Calcium Sensing Receptor Gene in Patients Clinically Suspected to Have Familial Hypocalciuric Hypercalcemia: Phenotypic Variation and Mutation Spectrum in a Danish Population

The autosomal dominantly inherited condition familial hypocalciuric hypercalcemia (FHH) is characterized by elevated plasma calcium levels, relative or absolute hypocalciuria, and normal to moderately elevated plasma PTH. The condition is difficult to distinguish clinically from primary hyperparathyroidism and is caused by inactivating mutations in the calcium sensing receptor (CASR) gene. We sought to define the mutation spectrum of the CASR gene in a Danish FHH population and to establish genotype-phenotype relationships regarding the different mutations. A total of 213 subjects clinically suspected to have FHH, and 121 subjects enrolled as part of a family-screening program were studied. Genotype-phenotype relationships were established in 66 mutation-positive index patients and family members. We determined CASR gene mutations, and correlating levels of plasma calcium (albumin corrected), ionized calcium (pH 7.4), and PTH were measured. We identified 22 different mutations in 39 FHH families. We evaluated data on circulating calcium and PTH for 11 different mutations, representing a spectrum of clinical phenotypes, ranging from calcium concentrations moderately above the upper reference limit, to calcium levels more than 20% above the upper reference limit. Furthermore, the mean plasma PTH concentration was within the normal range in eight of 11 studied mutations, but mild to moderately elevated in families with the mutations p.C582Y, p.C582F, and p.G553R. The present data add 19 novel mutations to the catalog of inactivating CASR mutations and illustrate a variety of biochemical phenotypes in patients with the molecular genetic diagnosis FHH.

Identification and Functional Characterization of a Novel Mutation in the Calcium-Sensing Receptor Gene in Familial Hypocalciuric Hypercalcemia: Modulation of Clinical Severity by Vitamin D Status

Familial hypocalciuric hypercalcemia (FHH) is a benign condition associated with heterogeneous inactivating mutations in the calcium-sensing receptor (CASR) gene. The objective of the study was to identify and characterize a CASR mutation in a moderately hypercalcemic, hyperparathyroid individual and his family and assess the influence of vitamin D status on the clinical expression of the defect. We studied a kindred with FHH, in which the proband (a 34-yr-old male) was initially diagnosed with primary hyperparathyroidism due to frankly elevated serum PTH levels. CASR gene mutation analysis was performed on genomic DNA of the proband and family members. The mutant CASR was functionally characterized by transient transfection studies in kidney cells in vitro. A novel heterozygous mutation (F180C, TTC>TGC) in exon 4 of the CASR gene was identified. Although the mutant receptor was expressed normally at the cell surface, it was unresponsive with respect to intracellular signaling (MAPK activation) to increases in extracellular calcium concentrations. The baby daughter of the proband presented with neonatal hyperparathyroidism with markedly elevated PTH. Vitamin D supplementation of both the proband and the baby resulted in reduction of serum PTH levels to the normal range. The serum calcium level remained at a constant and moderately elevated level. The identification of a novel CASR gene mutation established the basis of the hypercalcemia in the kindred. Concomitant vitamin D deficiency modulates the severity of the presentation of FHH.

Mutations in the calcium-sensing receptor: A new genetic risk factor for chronic pancreatitis?

Objective. In 2003 we identified a family with familial hypocalciuric hypercalcemia (FHH) (heterozygous CASR gene mutation L173P) and a mutation in the pancreatic secretory trypsin inhibitor gene (SPINK1) (N34S). While family members with an isolated calcium-sensing receptor gene (CASR) mutation remained healthy, a combination of the CASR and SPINK1 gene mutation caused chronic pancreatitis (CP). We thus speculate that the combination of two genetic defects affecting calcium homeostasis and pancreatic enzyme activation might represent a novel approach in chronic inherited pancreatic disease. We therefore sought to explore whether CASR gene mutations were prevalent in a cohort of patients with CP and confirmed SPINK1 mutations. Material and methods. A cohort of 19 families (n=170) with a history of idiopathic CP (ICP) was screened for mutations within the CASR gene; 104 members of that cohort had a mutation (N34S) within the SPINK1 gene and 66 of those were suffering from CP. The entire CASR gene was screened for single strand conformation polymorphism under varying polyacrylamide gel conditions and subjected to direct dideoxy nucleotide sequencing of amplified cDNA. Results. Single-strand conformation polymorphisms were observed in 59 samples, clustering of exons 3, 4 and 7. DNA sequence analysis revealed a yet unreported missense mutation in exon 7 (R896H) and two conservative mutations in exon 4 (F391F) and exon 7 (E790E). Furthermore, an intronic polymorphism in nucleotide position 493-19 G > A was detected in 19 out of 170 members of that cohort. Conclusions. We identified three novel calcium-sensing receptor gene mutations (1 missense mutation, 2 silent mutations and 1 intronic polymorphism) in a cohort of 19 families with ICP. In particular, the kindred with the R896H mutation presenting with a similar pedigree to the family described above may indicate a role for CASR gene mutations in SPINK1-related CP. Again, only the patient with the combination of both CASR and N34S SPINK1 gene mutation developed pancreatitis, whereas in the healthy parents and children only an isolated CASR or N34S SPINK1 gene mutation could be detected. We suggest that the CASR gene is a novel yet undetected co-factor in a multifactorial genetic setting of SPINK1-related pancreatitis that alters the susceptibility for pancreatitis in these patients.