الفهرس 
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Abstract
Introduction and review of literature: Uric acid (UA) nephrolithiasis are the second most common stone type. It occurs up to 10% of stone formers worldwide. They have a high risk of recurrence. Aim of the work: Uric acid (UA) stones tend to affect one kidney and recur in the same side. This work looks after the predictors of laterality of UA renal stones. Furthermore, factors affecting recurrence and genetic alterations in patients with UA stones will be assessed. Patients and Methods: The study included 34 patients having unilateral lucent nephrolithiasis subjected to percutaneous nephrolithotomy with main stone composition of UA as proved by stone analysis. Differential urine samples were collected using ureteral catheters from the renal pelvis of stone-harboring kidney (SHK) and stone-free kidney (SFK) before the procedure and compared regarding the same metabolic urinary components. A group of matched 34 stone-free subjects were invited to participate as a control. The study and control groups were compared regarding presentation of four genes (related to UA formation) and metabolic features of 24-hour urine samples (urine volume, pH, uric acid, citric acid, urea nitrogen). Subgroup analysis for de novo and recurrent stone formers was also performed. Results: There were no significant differences among UA stone former and healthy control groups. Comparing SHK and SFK, only urine urea nitrogen concentration was significantly lower in samples of SHK (p=0.017). These findings were consistent in the subgroup analysis among de novo cases (p=0.037) and less evident in the recurrent stone formers. A negative correlation was found between percentage of UA component in the stone and 24h urea nitrogen concentration (r=-0.37, P=0.028). There was a significant difference in expression of SLC 22A12-rs3825016 gene between study and control group (p=0.0001). Conclusion: A protective role of urine urea nitrogen against UA nephrolithiasis was depicted however, further prospective studies are awaited. Recommendations: Further prospective studies are needed to draw a solid conclusion about role of protective role of the urea nitrogen against UA nephrolithiasis.