1. ¹Nephrology and Dialysis Unit, Postgraduate School of Nephrology, Vita Salute University, IRCCS San Raffaele Hospital, Milan, Italy
2. ²Postgraduate School of Nephrology, University of Milan, Milan, Italy
3. ³Laboratory of Medical Genetics, IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena Hospital, Milan, Italy
4. ⁴Institute of Pediatrics and Neonatology, University of Milan, Milan, Italy
5. ⁵Department of Medical and Surgical Science, Policlinico of Padua, Padua, Italy
6. ⁶Bone Metabolic Unit, IRCCS San Raffaele Hospital, Milan, Italy
7. ⁷Department of Medical Chemistry, Biochemistry and Biotechnology, University of Milan, Milan, Italy
8. ⁸Hypertension and Preventive Nephrology Unit, IRCCS Multimedica, Milan, Italy

Correspondence: G Vezzoli, Unità di Nefrologia e Dialisi, IRCCS Ospedale San Raffaele, via Olgettina 60, Milano 20132, Italy. E-mail: vexxoli.giuseppe@hsr.it

Received 3 July 2006; Revised 20 December 2006; Accepted 27 December 2006; Published online 28 February 2007.

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.