ORIGINAL PAPER Association between polymorphisms in osteopontin gene (SPP1) and first episode calcium oxalate urolithiasis Mohammad Reza Safarinejad • Nayyer Shafiei • Shiva Safarinejad Received: 29 March 2013 / Accepted: 3 June 2013 / Published online: 20 June 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract We examined whether single nucleotide poly- morphisms (SNPs) in SPP1 gene are associated with risk of calcium oxalate urolithiasis (COU). We genotyped nine known SNPs in SPP1 gene (rs11739060, rs28357094, rs2728127, rs11730582, rs1126772, rs9138, rs2853744, rs4754=p.Asp80Asp, and rs1126616=p.Ala236Ala). Geno- mic DNA from 1,026 individuals (n = 342 patients with first episode COU, and n = 684 healthy unrelated controls) was analyzed for nine SPP1 SNPs using polymerase chain reaction and melting curve analysis by means of a pair of fluorescence resonance energy transfer probes. Serum and urine osteopontin (OPN) levels were also measured using enzyme-linked immunosorbent assay kits. rs9138 AA genotype was protective (OR 0.62, 95 % CI 0.47–0.81; P = 0.004). rs28357094 TT genotype (OR 2.52, 95 % CI 1.74–3.79; P = 0.021), rs2728127 GG genotype (OR 2.64, 95 % CI 1.42–4.81; P = 0.002), and rs2853744 GG geno- type (OR 1.68, 95 % CI 1.22–3.87; P = 0.003) were pre- disposing. None of the other examined SPP1 SNPs was associated with COU susceptibility. Subjects with protec- tive and predisposing polymorphisms had increased and decreased serum levels of OPN, respectively. Urinary cal- cium/OPN ratios were higher and lower in subjects with predisposing and protective SNPs of SPP1 gene, respec- tively. Of 28 constructed haplotypes, 6 demonstrated sig- nificant association with COU risk. There was no sex difference in the obtained results. The SPP1 gene poly- morphisms are associated with the COU susceptibility. Keywords Polymorphism Á Susceptibility gene Á Urolithiasis Á Osteopontin Á SPP1 Introduction Urolithiasis is a worldwide problem and affects almost all races, ethnicities and populations. The reported prevalence rate in developed countries is between 4 and 20 % [1]. In Iran, the reported prevalence rate is 5.7 % (6.1 % in males and 5.3 % in females) [2]. Urolithiasis is a multi-factorial disease affected by environmental, hormonal, and genetic factors. A positive family history is a well-known risk factor for urinary stone disease [1]. Indeed urolithiasis is a polygenic disorder with partial penetrance [3]. The most common type of kidney stone is calcium oxalate mono- hydrate (COM). Osteopontin (OPN) plays an important role in oxalate stone formation [4]. OPN is a potent inhibitor of COM growth [5], stimulates the formation of calcium oxalate dihydrate (COD), and inhibits the aggre- gation of COM crystals [6]. In addition, OPN is among the principal component of the organic matrix of oxalate- containing urinary stones [7]. COM stones include about 800 lg osteopontin per 100 mg stone [8]. Osteopontin (MIM *166490) also named as Eta-I or SPP1 is an extracellular matrix protein and expressed in a variety of different cell types in the human body, including the kidney [9]. The human SPP1 gene is located on chro- mosome 4q21–25 and consists of seven exons [10]. SPP1 has a specific calcium crystal surface-adsorbing structure, and includes the Arg-Gly-Asp (RGD) sequence [4]. The expression of SPP1 in different cell types was significantly influenced by transcription factors, and the genetic poly- morphisms of the promoter [11]. The expression of SPP1 mRNA is increased in stone-forming rats [12]. In addition, M. R. Safarinejad (&) Á N. Shafiei Á S. Safarinejad Clinical Center for Urological Disease Diagnosis and Private Clinic Specialized in Urological and Andrological Genetics, P.O. Box 19395-1849, Tehran, Iran e-mail: info@safarinejad.com 123 Urolithiasis (2013) 41:303–313 DOI 10.1007/s00240-013-0582-7