R990G polymorphism of calcium-sensing receptor does produce a gain-of-function and predispose to primary hypercalciuria

Abstract

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.

Antilipolytic effect of calcimimetics depends on the allelic variant of calcium-sensing receptor gene polymorphism rs1042636 (Arg990Gly)

“…For this particular SNP, the causal effect has been demonstrated at the protein level, as evidenced by the influence on the response to the calcimimetic cinacalcet in patients 12 and in cells transfected with CASR expressing each of the two genotypes. 13 In summary, our data suggest that the antilipolytic effect of cinacalcet depends on the CASR gene polymorphism rs1042636 (Arg990Gly). As a suppressor of FFA release from adipocytes, cinacalcet treatment of CKD patients may be additionally beneficial preventing excess circulating FFA levels, and clinical studies evaluating this novel potential benefit are warranted.…”

“…12 Transfected cells expressing CASR with glycine in position 990 respond more strongly to a calcimimetic added to the culture medium than those with arginine. 13 During our studies on the antilipolytic effect of cinacalcet in human adipocytes, we observed in a considerable number of samples a null response to the calcimimetic (unpublished data). On the basis of the above-mentioned evidence, we investigated whether the phenotype of an antilipolytic response to cinacalcet could be explained by the genotype of rs1042636.…”

New Insights Into the Pathogenesis of Idiopathic Hypercalciuria

“…In a study from Italy, the relative risk of hypercalciuria was increased in individuals carrying this haplotype, both among stone formers [52] and non-stone formers [51], but it explained only 4.1% of the total variance in urinary calcium excretion, and was not felt to be a major gene determining IH.…”

“…Calcium sensing receptor-A polymorphism has been identified in the gene encoding the calcium sensing receptor which produces a gain-of-function of the receptor when transfected into HEK-293 cells [51]. In a study from Italy, the relative risk of hypercalciuria was increased in individuals carrying this haplotype, both among stone formers [52] and non-stone formers [51], but it explained only 4.1% of the total variance in urinary calcium excretion, and was not felt to be a major gene determining IH.…”

Cinacalcet HCl therapy in East Asian patients and rs1042636 carriers

“…It is important to note that allele frequencies of this SNP are reversed between East Asians and Blacks/Whites, i.e., 5-10% of Blacks and Whites carry the glycine allele, while 5-10% of East Asians carry the arginine allele [2]. Cell culture data back this up: in transfected HEK cells, Vezzoli et al [3] showed that rs1042636 causes indeed a gain-of-function in the CaSR molecule, the allele dose of one glycine allele equalling about 30 mg once daily of cinacalcet. East Asian patients need lower cinacalcet HCl doses than Whites or Blacks.…”