Renal Uptake of Fatty Acids (FFA) in Patients With Idiopathic Uric Acid Nephrolithiasis (IUAN)

Inclusion Criteria: * In the IUAN group (N=10), we will include adult subjects with documented IUAN, age \> 21 years, either sex, any ethnicity * In the Control group (N=10), we will include volunteers with no history of stone disease matched for age (within 5 years), gender, ethnicity, BMI (within 10%) and diabetes status Exclusion Criteria: * Contraindications to SPECT/CT, pregnancy, breastfeeding, chronic renal disease (eGFR \< 60 ml/min/1.73m2), proteinuria, genetic diseases of the kidney, inborn defects of lipid metabolism, alcohol abuse, liver disease (patients with highly elevated total bilirubin, elevated liver enzymes AST, ALT and alkaline phosphatase and those with an established liver disease), anemia, and pharmacological treatment with insulin or insulin-sensitizing drugs such as thiazolidinediones (TZD). * Patients on antidyslipidemic drugs, alkali therapy or allopurinol will be instructed to discontinue these drugs 2 weeks prior to the study.