Investigation of the association between Osteopontin gene polymorphism at 9250. position and urolithiasis

Osteopontin (OPN) (bone sialoprotein 1 (BSP1), early T lymphocyte activation 1 (Eta-1), secreted phosphoprotein 1 (SPP1) ) is found to be expressed various tissues including bone, kidney and in also T lymphocytes, macrophages, endothelial cells, smooth muscle cells and epithelial cells. OPN has an important role in various disorders as such; autoimmune disorders such as multiple sclerosis (MS), sistemic lupus erythematosus (SLE), rheumatoid arthrit (RA); characterized chronic inflammation related diseases e.g; Crohn disease, obesity, cardiovascular disease and renal injury and in various cancer types. Recent studies shows that OPN rs1126616 polymorphism is associated with urolithiasis, primary biliary sclerosis (PBC) and SLE. In the literature, other defined SNP?s in OPN gene have also been investigated in order to define their role in urolithiasis.The aim of our study was to investigate OPN rs1126616 polymorphism in 64 urolithiasis patients together with 50 healthy controls having no history of kidney stone in their families. Stones were analyzed for chemical composition by the use of X-Ray diffraction method. The analysis revealed that 62 of our patients were having calcium oxalate (CaOx) stone and only 2 struvite stone. The study groups were genotyped by using PCR-RFLP method.In urolithiasis patients the genotype frequencies for OPN rs1126616 revealed the following results; CC, 37.5%; CT, 43.7%; TT, 18.7% and in control group the results were as follows; CC, 80%; CT, 4%; TT, 16%. In patient group the frequency of carrying at least one mutant T allele was found to be 62.5% and in control group 20%. The patient and control groups were also analyzed according to their body mass index (BMI). The groups were classified regarding to their BMI being bigger than or smaller than 25 kg/m2. The results showed that 66.7% of patients with BMI>25 kg/m2 were carrying at least one mutant T allele wheras the healthy controls with BMI>25 kg/m2 were all having CC (wildtype).Our results showed that OPN rs1126616 polymorphism is found to be significantly higher in Turkish urolithiasis patients. These results might be indicating the important role of OPN in urolithiasis. Our urolithiasis patients having BMI>25 kg/m2 clearly showed that they are carrying at least one polymorphic allele. Interestingly, the link between urolithiasis and obesity need to be further studied in our population