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available at http://www.ncbi.nlm.nih.gov/pubmed/31436119 Editorial Comment: In this study only 29% of patients with staghorn stones undergoing percutaneous nephrolithotomy had a metabolic stone. This rate is lower than that reported previously by the group from Vanderbilt University. This discrepancy could be due to the exclusion of patients with uric acid or cystine stones. The majority of staghorn metabolic stones in this study were calcium oxalate, which differs from the Vanderbilt series, where apatite stones were predominant. In this cohort oxalate excretion was higher in patients with staghorn stones, which could have been a driving factor for calcium oxalate stone formation. Dean G. Assimos, MD Reference 1. Viprakasit DP, Sawyer MD, Herrell SD et al: Changing composition of staghorn calculi. J Urol 2011; 186: 2285. Suggested Reading Mandel N, Mandel I, Fryjoff K et al: Conversion of calcium oxalate to calcium phosphate with recurrent stone episodes. J Urol 2003; 169: 2026. Re: Targeted Renal Knockdown of Na/H Exchanger Regulatory Factor Sip1 Produces Uric Acid Nephrolithiasis in Drosophila S. Ghimire, S. Terhzaz, P. Cabrero, M. F. Romero, S. A. Davies and J. A. T. Dow Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom, and Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine and Science, Rochester, Minnesota Am J Physiol Renal Physiol 2019; 317: F930eF940. doi: 10.1152/ajprenal.00551.2018 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/31364377 Editorial Comment: Uric acid kidney stone formation is a disease of low urine pH. The underlying mechanisms that cause low urine pH in these patients are still being defined. Investigators have shown in animal and cell models that reduced activity of the renal proximal tubule sodium-hydrogen antiporter NHE3 may have role. This activity is coupled with decreased production of ammonium. Whether a deficit in NHERF1 resulting in attenuated sodium and hydrogen exchange (NHE2) has a role in lowering urine pH and promoting uric acid stone formation in humans warrants further investigation. Dean G. Assimos, MD Suggested Reading Miller J, Chi T, Kapahi P et al: Drosophila melanogaster as an emerging translational model of human nephrolithiasis. J Urol 2013; 190: 1648. Patel ND, Ward RD, Calle J et al: Computerized tomography based diagnosis of visceral obesity and hepatic steatosis is associated with low urine pH. J Urol 2017; 198: 1085. Doizi S, Rodgers K, Poindexter J et al: Assessment of urinary inhibitor or promoter activity in uric acid nephrolithiasis. J Urol 2016; 195: 1799. UROLITHIASIS/ENDOUROLOGY 179 Copyright © 2020 American Urological Association Education and Research, Inc. Unauthorized reproduction of this article is prohibited.