An association between the R990G polymorphism of the CaSR gene, coding for calcium-sensing receptor, and primary hypercalciuria was found in kidney stone formers. To confirm this relationship, we investigated hypercalciuric women without stones and studied the effect of CaSR gene in human embryonic kidney cells (HEK-293). We genotyped for CaSR A986S, R990G, and Q1011E polymorphisms, 119 normocalciuric and 124 hypercalciuric women with negative history of kidney stones. Homozygous (n=2) or heterozygous (n=21) women for the 990G allele considered as one group had an increased risk to be hypercalciuric (odds ratio=5.2; P=0.001) and higher calcium excretion (P=0.005) in comparison with homozygous women for the 990R allele (n=220). HEK-293 cells were transfected with the variant allele at the three CaSR gene polymorphisms and with the most common allele with no variants. The transient increment of intracellular calcium caused by the stepwise increase of extracellular calcium was evaluated in stable transfected cells loaded with fura-2 AM. The extracellular calcium concentration producing the half-maximal intracellular calcium response was lower in HEK-293 cells transfected with the 990G allele than in those transfected with the wild-type allele (P=0.0001). Our findings indicate that R990G polymorphism results in a gain-of-function of the calcium-sensing receptor and increased susceptibility to primary hypercalciuria.

Context: Primary hyperparathyroidism (PHPT) shows a great variability in clinical course and severity. Data concerning the association between polymorphic variants of the gene encoding the calciumsensing receptor (CaSR) and clinical characteristics of PHPT are not conclusive. Objective: To evaluate the frequency of three polymorphisms; A986S, R990G, and Q1011E of CaSR in patients with PHPT and to correlate the genotypes with clinical and biochemical parameters. Patients and methods: The study included 94 consecutive unrelated patients referred to our Departments for PHPT diagnosis and management between 2000 and 2005 and 137 age and sexmatched healthy subjects. Patients and controls were genotyped according to standard procedures. Due to the rarity of 990G allele, homozygous and heterozygous subjects were grouped in R/GCG/G set. All PHPT patients were studied for calcium metabolism parameters and renal and bone complications. Results: The proportion of CaSRvariants was similar in PHPT patients and controls. In PHPT patients, only R990G polymorphism was associated with disease parameters; in comparison with R/R, R/GCG/G patients showed lower mean serum parathyroid hormone (PTH) and phosphate levels (139.9G62.2 vs 199.9G136.3 pg/ml, P!0.05 and 0.69G0.12 vs 0.81G0.18 mmol/l, PZ0.031 respectively), higher mean 24-h urine calcium concentration and calcium excretion (9.05G2.05 vs 6.77G4.31 mmol/24 h, PZ0.012 and 67G20 vs 51G26 mmol/l GF, PZ0.039), and increased prevalence of nephrolithiasis (90.0 vs 44.2%, PZ0.007). Conclusions: The study showed that patients with PHPT, bearing the 990G allele, had lower serum PTH levels and higher urinary calcium excretion in comparison with the other genotype, suggesting an increased sensitivity of the variant receptor to extracellular calcium. Since this variant was associated with increased occurrence of nephrolithiasis, analysis of this polymorphism might help to predict renal complication of the disease.European Journal of Endocrinology 155 687-692

Three haplotype blocks were identified in the CaSR gene. The first block was characterized by six SNPs and included gene promoters. The rs7652589 and rs1501899 SNPs and the CATTCA haplotype of the first block were significantly more frequent in normocitraturic calcium kidney stone formers than controls. The risk of stones was increased in normocitraturic homozygous patients and heterozygotes for the CATTCA haplotype. The rate of stones was higher in stone formers with the CATTCA haplotype. In a three-generation family, calcium stones were associated with the CATTCA haplotype. The bioinformatic analysis identified a new site for the octamer-binding transcription factor 1 in the presence of the variant alleles at the rs7652589 and rs1501899 SNPs. This transcription factor may downregulate the transcription of vitamin D-dependent genes and the CaSR expression. Conclusion. SNPs and CATTCA haplotype of the CaSR gene first block is associated with kidney stones in normocitraturic patients.

Calcium nephrolithiasis is one of the most prevalent uronephrologic disorders in the western countries. Studies in families and twins evidenced a genetic predisposition to calcium nephrolithiasis. Family-based or case-control studies of single-candidate genes evidenced the possible involvement of calcium-sensing receptor (CASR), vitamin D receptor (VDR), and osteopontin (OPN) gene polymorphisms in stone formation. The only high-throughput genome-wide association study identified claudin 14 (CLDN14) gene as a possible major gene of nephrolithiasis. Specific phenotypes were related with these genes: CASR gene in normocitraturic patients, VDR gene in hypocitraturic patients with severe clinical course, and CLDN14 gene in hypercalciuric patients. The pathogenetic weight of these genes remains unclear, but an alteration of their expression may occur in stone formers. Technological skills, accurate clinical examination, and a detailed phenotype description are the basis to get new insight about the genetic basis of nephrolithiasis.

Minor allele at rs6776158 may predispose to calcium stones by decreasing transcriptional activity of the CaSR gene promoter 1 and CaSR expression in kidney tubules.

High calcium excretion is associated with a decreased trabecular BMD in elderly men and may predispose men to trabecular bone loss.

Background and objective: Single nucleotide polymorphisms (SNPs) of the calcium-sensing receptor (CASR) gene at the regulatory region were associated with idiopathic calcium nephrolithiasis. To confirm their association with nephrolithiasis, we tested patients with primary hyperparathyroidism (PHPT). Design: A genotype-phenotype association study. Methods: In all, 332 PHPT patients and 453 healthy controls were genotyped for the rs7652589 (GOA) and rs1501899 (GOA) SNPs sited in the noncoding regulatory region of the CASR gene. Allele, haplotype, and diplotype distribution were compared between PHPT patients and controls, and in stone forming and stone-free PHPT patients. Results: The allele frequency at rs7652589 and rs1501899 SNPs was similar in PHPT patients and controls. The A minor alleles at these two SNPs were more frequent in stone forming (nZ157) than in stone-free (nZ175) PHPT patients (rs7652589: 36.9 vs 27.1%, PZ0.007; rs1501899: 37.1 vs 26.4%, PZ0.003). Accordingly, homozygous or heterozygous PHPT patients for the AA haplotype (nZ174, AA/AA or AA/GG diplotype) had an increased stone risk (odds ratio 1.83, 95% confidence interval 1.2-2.9, PZ0.008). Furthermore, these PHPT patients had higher serum concentrations of ionized calcium and parathyroid hormone (1.50G0.015 mmol/l and 183G12.2 pg/ml) than patients with the GG/GG diplotype (nZ145, 1.47G0.011 mmol/l (PZ0.04) and 150G11.4 pg/ml (PZ0.049)). Using a logistic regression model, the increase in stone risk in PHPT patients was predicted by AA/AA or AA/GG diplotype, the highest tertile of serum ionized calcium values and the lowest tertile of age. Conclusions: Polymorphisms located in the regulatory region of the CASR gene may increase susceptibility of the PHPT patients to kidney stone production.

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