Calcium-sensing receptor gene polymorphism is not associated with bone mineral density in Italian postmenopausal women

Clinical phenotypes of Chinese primary hyperparathyroidism patients are associated with the calcium-sensing receptor gene R990G polymorphism

OBJECTIVE

The purpose of this study was to investigate the distribution of the A986S and R990G polymorphisms of the calcium-sensing receptor (CASR) gene in the Chinese population and whether there is an association between genetic variants and the risk of developing primary hyperparathyroidism (PHPT) and its associated clinical phenotypes.

METHODS

A total of 164 Chinese Han PHPT patients (M/F: 51/113) and 230 healthy controls (M/F: 50/180) were enrolled. The common clinical parameters of PHPT patients including biochemical markers, bone mineral density (BMD), kidney stone occurrence, and pathology results were analyzed. Genotyping was conducted for both the patients and controls, and it was carried out using standard procedures.

RESULTS

The R990G variant was more frequently present than the A986S variant in this group of Chinese PHPT patients. The R allele increased the risk of PHPT (odds ratio=1.134, 95% CI: 1.008, 1.277, and P=0.036). Patients with either the RR or RG genotype had lower blood calcium levels and higher alkaline phosphate levels than patients with the GG genotype. The lumbar BMD T-score was -2.20 (-2.63, -0.32) in patients with the GG genotype, and it was significantly lower in patients with the RR+RG genotype (-2.53 (-3.70, -1.72) P=0.036). Patients with the R allele had a significantly higher incidence of hyperplasia (25.0%) and carcinomas (7.1%) than those with the GG genotype (5.3 and 0% respectively; P=0.025). The prevalence of osteoporosis and parathyroid carcinomas was higher in Chinese PHPT patients with the R allele.

CONCLUSION

The R990G polymorphism is most frequently present in the Chinese population and among patients with PHPT. Additional studies in the Chinese population are needed to elaborate the relationship between genetics and PHPT.

THE CALCIUM-SENSING RECEPTOR IN NORMAL PHYSIOLOGY AND PATHOPHYSIOLOGY: A Review

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

Alanine to serine polymorphism at position 986 of the calcium-sensing receptor associated with coronary heart disease, myocardial infarction, all-cause, and cardiovascular mortality

BACKGROUND

Disorders of calcium homeostasis have been implicated in atherosclerosis. The calcium-sensing receptor (CASR) is crucial to the regulation of calcium metabolism. An alanine (A) to serine (S) polymorphism at codon 986 (A986S) of the CASR gene has been associated with higher calcium and osteoporosis; the association with coronary artery disease (CAD) has not been studied.

METHODS AND RESULTS

We investigated this polymorphism in individuals with CAD (n = 2561), including survivors of myocardial infarction (MI) (n = 1358) compared to 698 controls without angiographic CAD. Compared to AA homozygotes, the prevalence of CAD [multivariate odds ratio 1.25; 95% confidence interval (CI) 1.02-1.54] and previous MI (multivariate odds ratio 1.33; 95% CI 1.06-1.68) was increased in carriers of at least one S-allele. With each S-allele, the prevalence of CAD and MI increased 1.22-fold (95% CI 1.02-1.47) and 1.30-fold (95% CI 1.06-1.60), respectively. Fully adjusted hazard ratios for total and cardiovascular mortality per one S-allele were 1.24 (95% CI 1.05-1.46) and 1.38 (95% CI 1.13-1.67), respectively. In carriers of at least one S-allele, the adjusted hazard ratios for all-cause and cardiovascular death were 1.25 (95% CI 1.04-1.51) and 1.48 (95% CI 1.18-1.86), respectively. These associations were independent of cardiovascular risk factors, calcium and phosphate. The S-allele was associated with higher calcium (P < 0.001) and PTH (P < 0.02), and lower phosphate (P < 0.003) in CAD patients and controls.

CONCLUSION

Serine at position 986 of CASR may be an independent genetic predictor of angiographic CAD, previous MI, and cardiovascular mortality.

Primary hyperparathyroidism and the presence of kidney stones are associated with different haplotypes of the calcium-sensing receptor

INTRODUCTION

Three single-nucleotide polymorphisms in the calcium-sensing receptor gene (CASR) encoding the missense substitutions A986S, R990G, and Q1011E have been associated with normal variation in extracellular calcium homeostasis, both individually and in haplotype combination. The aim of this study was to examine haplotype associations in primary hyperparathyroidism (PHPT).

PATIENTS AND METHODS

Patients with sporadic PHPT (n = 237) were recruited from endocrine clinics and healthy controls (n = 433) from a blood donor clinic, and levels of serum calcium, albumin, and PTH were measured. In PHPT patients, urinary calcium/creatinine clearances and bone mineral density at spine and femoral neck were measured and the presence of kidney stones and vertebral fractures identified. The CASR single-nucleotide polymorphisms were haplotyped by allele-specific sequencing.

RESULTS

Four haplotypes (ARQ, SRQ, AGQ, and ARE) of eight were observed, in keeping with significant linkage disequilibrium, but haplotype frequencies did not show significant Hardy-Weinberg disequilibrium. The SRQ haplotype was more common in PHPT (125 of 474 alleles) than in controls (170 of 866 alleles, P = 0.006) and showed a significant (P = 0.006) gene-dosage effect. There was no significant association between haplotype and bone mineral density or fractures, but association with kidney stones was significant (P = 0.0007). In the stone-forming subgroup, the SRQ haplotype was underrepresented and AGQ overrepresented. Patients bearing the AGQ haplotype had an odds ratio of 3.8 (95% confidence interval, 1.30-11.3) for presentation with renal stones compared with the rest.

CONCLUSION

Our data indicate that the CASR SRQ haplotype is significantly associated with PHPT in our population. Within the PHPT patient population, the AGQ haplotype is significantly associated with kidney stones.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Calcium-sensing receptor gene A986S polymorphism and bone mass in hypertensive women

BACKGROUND

The function of the calcium-sensing receptor (CaSR) is to maintain serum calcium concentration within a narrow physiological range. Two types of mutations have been described: activating that causes hypocalcemia and inactivating, which leads to hypercalcemia. The objective was to assess the effect of CaSR gene A986S polymorphism on the lumbar spine bone mass, calcium metabolism parameters and markers of bone remodeling in hypertensive women.

METHODS

The study included 48 patients (mean age 59 +/- 10 years) with mild-to-moderate hypertension, according to JNC VI and who did not present any associated diseases. We determined the following in all patients: Ca, P, Mg, PTHi, 25-vitamin D, 1,25-vitamin D, osteocalcin, deoxypyridinoline in urine, 24-h urine calcium. A bone densitometry of the lumbar spine was also performed. CaSR gene A986S polymorphism was also studied in all patients by PCR.

RESULTS

Genotype frequency was 69% for AA, 27% for AS and 4% for SS, with a prevalence of 82% for allele A and 18% for allele S. Patients with a lack of allele S had lower levels of p (3.5 +/- 0.5 vs. 4 +/- 0.4, p = .034). No differences in calcium plasma levels, urinary calcium excretion and bone mass were observed.

CONCLUSIONS

We found no clinical significance in the parameters studied of the CaSR gene A986S polymorphism in hypertensive women.

Le récepteur sensible au calcium : physiologie et pathologie

Calcium is a major ion in human metabolism and its level is highly controlled. This regulation is performed via the Calcium Sensing Receptor, a discovery which ten years ago led to the explanation of a number of clinical disorders. The syndromes caused by CaSR abnormalities are characterized by hypercalcemia or hypocalcemia, associated with inappropriate calciuria. An underlying genetic or auto-immune cause may be demonstrated. High blood calcium levels linked to mutations of the CaSR gene lead to familial hypocalciuric hypercalcemia and the neonatal and non neonatal forms with severe hypercalcemic. Hypocalcemia determined by mutations in the CaSR gene include autosomal dominant hypocalcemia and its sporadic form. Another clinical presentation similar to Bartter syndrome has been reported. Auto-antibodies directed against CaSRs, seen in auto-immune diseases, can lead to similar clinical presentations. Finally, CaSR polymorphisms modulate the range of blood calcium levels. With diagnosis of these diseases deleterious therapeutics can be avoided. The discovery of this receptor has led to new therapeutic prospects such as calcimimetics for hyperthyroidism.

Role of intron 5 C/T polymorphism of the calcium sensing receptor gene in the regulation of the serum FSH and LH in post-menopausal women

OBJECTIVE

High extracellular calcium concentration (Cao(2+)) acts to inhibit calcium sensing receptor (CaR) signalling on cellular surfaces in parathyroid glands. This receptor is, however, also expressed on the membranes of some non-calciotropic endocrine cells, including pituitary-derived cells. The aim of our study was to analyse relationships between the CaR gene and the circulating FSH and LH in normal post-menopausal women.

METHODS

A total of 95 untreated euparathyroid post-menopausal women were investigated in the study. The serum FSH and LH levels were evaluated in relationship to allele combinations of the CaR gene (C/T polymorphism in the intron 5 and A986S polymorphism in exon 7), using an analysis of co-variance (ANCOVA) model.

RESULTS

Distribution of TT, TC and CC allele combinations (intron 5 C/T polymorphism) was 51, 43 and 6 %, respectively. Higher serum FSH and LH levels were found in carriers of C allele than in women without this allele (p < 0.002 and p < 0.03, respectively). No correlations were found between A986S polymorphism and serum FSH and LH levels.

CONCLUSIONS

Serum FSH and LH levels are associated with intron 5 C/T (but not A986S) polymorphism of the CaR gene in untreated post-menopausal women. The physiological role of the CaR gene in the regulation of the gonadotropic function needs to be further investigated.

Blood ionized calcium is associated with clustered polymorphisms in the carboxyl-terminal tail of the calcium-sensing receptor

Blood ionized calcium (iCa) is a quantitative trait subject to genetic influence. iCa is maintained in a narrow range through the action of the calcium-sensing receptor (CASR) controlling PTH secretion and calcium excretion. A CASR single nucleotide polymorphism (SNP) prevalent in Caucasian populations (A986S) has shown significant association with iCa in a cohort of young women, but association with the neighboring SNPs, R990G and Q1011E, has not been examined. We studied 377 unrelated adults (184 men and 193 women) recruited as healthy adults from a blood donor clinic. The subjects were not taking any medications, nor did they have disorders of calcium metabolism. Relative frequencies for the CASR 986S, 990G, and 1011E minor alleles were 24%, 4%, and 3% respectively. At the A986S locus, subjects with the AA genotype had significantly lower iCa (P = 0.0001) than subjects with one or two S alleles (mean +/- se, 1.221 +/- 0.003 vs. 1.239 +/- 0.003 mmol/liter). For the R990G site, subjects with the RR genotype had higher iCa than those with one copy of the 990G allele (1.230 +/- 0.002 vs. 1.213 +/- 0.007 mmol/liter; P = 0.032). With respect to the 1011 locus, iCa was lower in QQ genotype subjects than in the QE group (1.227 +/- 0.002 vs. 1.255 +/- 0.008 mmol/liter; P = 0.002). After resolution of phase for the doubly heterozygous subjects, analysis was conducted on haplotypes across all three loci. As expected, subjects with SRQ and ARE haplotypes are relatively hypercalcemic, and those with AGQ are hypocalcemic, relative to subjects with the common ARQ haplotype. Multiple regression analysis with clinical covariates (age, sex and menopausal status, creatinine, and PTH) showed that 16.5% of the total variance in iCa may be explained, and the seven CASR haplotypes contribute significantly (P < 0.0001) and substantially (49.1% of the explained variance) to the model, with the following corrected iCa means: ARQ/AGQ, 1.21 +/- 0.01; ARQ/ARQ, 1.22 +/- 0.01; ARQ/SRQ, 1.24 +/- 0.01; SRQ/AGQ, 1.24 +/- 0.03; SRQ/SRQ, 1.25 +/- 0.01; ARQ/ARE, 1.25 +/- 0.01; and SRQ/ARE, 1.27 +/- 0.01. Our data confirm the association between iCa and the A986S locus and suggest that R990G and Q1011E are also predictive. Given the significant between-population variations in frequency of variant alleles in this CASR SNP cluster, tri-locus haplotyping may prove to be more informative in studies of association between variation in CASR and disease.