Byline: Tahar. Gargah, Afif. Essid, Aymen. Labassi, Mourad. Hamzaoui, Mohamed. Lakhoua
Hereditary xanthinuria type I, a defect of purine matabolism, results from a genetic deficiency of xanthine oxidase. It is an uncommon cause of stone formation in children. We report here two children with xanthine urolithiasis. The first patient was an 8-year-old boy who presented with repeated episodes of hematuria evaluated with excretory urography, which demonstrated radio-lucent pelvic stone in the right kidney, causing hydronephrosis. He had pyelolithotomy, and the extracted stone consisted of pure xanthine. Family study revealed an asymptomatic xanthinuria in younger brother. The second patient was a 5-year-old boy who had a 2-week history of abdominal pain and gross hematuria. Conventional excretory intravenous urography showed a non-functioning right kidney. Nephrectomy was performed, and histology revealed end-stage pyelonephritis. The calculi consisted of pure xanthine. In both patients, plasma and urinary concentrations of uric acid were low but xanthine and hypoxanthine concentrations were markedly elevated. Xanthine uroli-thiasis is usually a benign condition, easy to prevent or cure by appropriate alkalinization, forced hydration and restriction of dietary purines. However asymptomatic, and therefore undiagnosed, stones may invade the kidney and urinary tract, resulting in destruction of parenchyma, nephrec-tomy and renal failure.
Xanthinuria type I, a rare hereditary disorder, is characterized by a marked and isolated defi-ciency of xanthine oxidase activity in the ti-ssues, resulting in hypouricemia and hypourico-suria.[sup]  Total urinary purine excretion is not in-creased, whereas excretion of xanthine and hy-poxanthine is considerably increased as a res-ponse to the elevated serum levels of these oxy-purines.[sup]  Clinical symptoms may include crystal-luric urolithiasis and acute renal failure. When unrecognized, xanthinuria can lead to nephrec-tomy or end-stage renal failure.[sup] , The following cases illustrate the interest of earlier recognition to prevent stone formation and to avoid neph-rectomy.
Case 1 An 8-year-old boy was referred to our center for evaluation of urolithiasis. He was born at term from apparently healthy consanguineous parents (first cousins), and he had no familial history of renal stone disease. His psychomotor develop-ment and physical growth were normal. The pa-tient presented with a 2-year history of intermi-ttent left flank associated with macroscopic hematuria explored by ultrasonography at 7 years of age, which was reported as normal. He su-ffered from repeated episodes of hematuria 12 months later, evaluated with excretory urogra-phy, which demonstrated radiolucent pelvic stone in the right kidney, causing distension of the intra-renal collecting system. The patient under-went pyelolithotomy and was referred to our department for further investigation of his renal stone disease.
Stone analysis demonstrated 100% xanthine composition. Serum...
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