title: Polymorphism of vitamin D receptor gene start codon in patients with calcium kidney stones.
abstract: BACKGROUND
  A linkage has been detected between vitamin D receptor (VDR) locus and calcium kidney stone disease. In order to assess the eventual role of VDR gene start codon polymorphisms in stone production, we analyzed the genotype-phenotype association in a group of patients with calcium kidney stones.
  
  
  METHODS
  One hundred and fifty-five patients were studied. VDR genotypes were characterized at the translation start site by restriction fragment length polymorphism analysis, using endonuclease FokI. Phenotypes of calcium-phosphate metabolism were compared in patients with different genotypes: strontium enteral absorption (used as a surrogate marker for calcium absorption), bone mineral density (BMD), calcium and phosphate excretion were measured.
  
  
  RESULTS
  Genotype distribution was not different in hypercalciuric and normocalciuric stone formers. Enteral strontium absorption, calcium excretion and BMD did not vary with the patient's genotype. Serum concentrations of phosphate (p=0.022) and renal threshold for phosphate excretion (p=0.026) were lower in patients with genotype FF (homozygous for the absence of the FokI site) than in those with genotype ff (homozygous for the presence of the FokI site). The lower phosphatemia was confirmed in FF hypercalciuric patients, but not in normocalciuric ones. Serum concentrations of phosphate and calcitriol in the group of hypercalciuric patients were inversely correlated with the genotype FF.
  
  
  CONCLUSIONS
  The FokI genotype does not appear to be involved in the causes of idiopathic hypercalciuria and kidney stones. Hypercalciuric patients with FF genotype may be a subgroup with low plasma concentrations of phosphate, predisposed to tubular leakage of phosphate.
authors.affiliation: Division of Nephrology Dialysis and Hypertension, San Raffaele Scientific Institute, Milan, Italy. vezzoli.giuseppe@hsr.it
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Vezzoli
authors.forename: Laura
authors.initials: L
authors.lastname: Soldati
authors.forename: Maria Carla
authors.initials: MC
authors.lastname: Proverbio
authors.forename: Donatella
authors.initials: D
authors.lastname: Adamo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rubinacci
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bianchi
authors.forename: Stefano
authors.initials: S
authors.lastname: Mora
mesh_terms: D000328:Adult; D002118:Calcium / Q000652:urine; D018387:Codon, Initiator / Q000235:genetics*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics*; D005260:Female; D005838:Genotype; D006801:Humans; D007669:Kidney Calculi / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D018167:Receptors, Calcitriol / Q000235:genetics*
chemical_list: D018387:Codon, Initiator; D018167:Receptors, Calcitriol; C035042:endodeoxyribonuclease FokI; D015252:Deoxyribonucleases, Type II Site-Specific; D002118:Calcium