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Cystinuria is the most common monogenic nephrolithiasis disorder. Because of its poor solubility at a typical urine pH of less than 7, cystine excretion results in recurrent urinary cystine stone formation. A high prevalence of high blood pressure and of chronic kidney disease has been reported in these patients. Alkaline hyperdiuresis remains the cornerstone of the preventive medical treatment. To reach a urine pH between 7.5 and 8 and a urine specific gravity less than or equal to 1.005 should be the goal of medical treatment. D-penicillamine and tiopronin, two cysteine-binding thiol agents, should be considered as second line treatments with frequent adverse events that should be closely monitored., (Copyright © 2020 Société francophone de néphrologie, dialyse et transplantation. Published by Elsevier Masson SAS. All rights reserved.)

Cystinuria (OMIM 220100) is an autosomal recessive hereditary disorder in which high urinary cystine excretion leads to the formation of cystine stones because of the low solubility of cystine at normal urinary pH. We developed clinical practice recommendation for diagnosis, surgical and medical treatment, and follow-up of patients with cystinuria. Elaboration of these clinical practice recommendations spanned from June 2018 to December 2019 with a consensus conference in January 2019. Selected topic areas were chosen by the co-chairs of the conference. Working groups focusing on specific topics were formed. Group members performed systematic literature review using MEDLINE, drafted the statements, and discussed them. They included geneticists, medical biochemists, pediatric and adult nephrologists, pediatric and adult urologists experts in cystinuria, and the Metabolic Nephropathy Joint Working Group of the European Reference Network for Rare Kidney Diseases (ERKNet) and eUROGEN members. Overall 20 statements were produced to provide guidance on diagnosis, genetic analysis, imaging techniques, surgical treatment (indication and modalities), conservative treatment (hydration, dietetic, alkalinization, and cystine-binding drugs), follow-up, self-monitoring, complications (renal failure and hypertension), and impact on quality of life. Because of the rarity of the disease and the poor level of evidence in the literature, these statements could not be graded. This clinical practice recommendation provides guidance on all aspects of the management of both adults and children with cystinuria, including diagnosis, surgery, and medical treatment., (Copyright © 2020 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Objective: To evaluate medical treatments, in terms of adverse events (AEs) and therapeutic goals, in a large series of patients with cystinuria., Patients and Methods: Data from 442 patients with cystinuria were recorded retrospectively. Crystalluria was studied in 89 patients. A mixed-effects logistic regression model was used to estimate how urine pH, specific gravity and cysteine-binding thiols (CBT) correlate with risk of cystine crystalluria., Results: Alkalizing agents and CBT agents were given to 88.8% (n = 381) and 55.3% (n = 238) of patients, respectively. Gastrointestinal AEs were reported in 12.3%, 10.4% and 2.6% of patients treated with potassium bicarbonate, potassium citrate and sodium bicarbonate, respectively (P = 0.008). The percentages of patients who experienced at least one AE with tiopronin (24.6%) and with D-penicillamine (29.5%) were similar (P = 0.45). Increasing urine pH and decreasing urine specific gravity significantly reduced the risk of cystine crystalluria, whereas D-penicillamine and tiopronin treatments did not reduce this risk (odds ratio [OR] 1 for pH ≤6.5; OR 0.52 [95% confidence interval {95% CI} 0.28-0.95] for 7.0 8.0, P <0.001)., Conclusion: Adverse events were frequent with D-penicillamine and tiopronin. Alkaline hyperdiuresis was well tolerated and reduced cystine crystalluria. Urine specific gravity ≤1.005 and urine pH >7.5, while warning about calcium-phosphate crystallization, should be the goals of medical therapy., (© 2019 The Authors BJU International © 2019 BJU International Published by John Wiley & Sons Ltd.)

Background and Objectives: Cystinuria is an autosomal recessive disorder affecting renal cystine reabsorption; it causes 1% and 8% of stones in adults and children, respectively. This study aimed to determine epidemiologic and clinical characteristics as well as comorbidities among cystinuric patients, focusing on CKD and high BP., Design, Setting, Participants, & Measurements: This retrospective study was conducted in France, and involved 47 adult and pediatric nephrology and urology centers from April 2010 to January 2012. Data were collected from 442 cystinuric patients., Results: Median age at onset of symptoms was 16.7 (minimum to maximum, 0.3-72.1) years and median diagnosis delay was 1.3 (0-45.7) years. Urinary alkalinization and cystine-binding thiol were prescribed for 88.8% and 52.2% of patients, respectively, and 81.8% had at least one urological procedure. Five patients (1.1%, n=4 men) had to be treated by dialysis at a median age of 35.0 years (11.8-70.7). Among the 314 patients aged ≥16 years, using the last available plasma creatinine, 22.5% had an eGFR≥90 ml/min per 1.73 m(2) (calculated by the Modification of Diet in Renal Disease equation), whereas 50.6%, 15.6%, 7.6%, 2.9%, and 0.6% had an eGFR of 60-89, 45-59, 30-44, 15-29, and <15, respectively. Among these 314 patients, 28.6% had high BP. In multivariate analysis, CKD was associated with age (odds ratio, 1.05 [95% confidence interval, 1.03 to 1.07]; P<0.001), hypertension (3.30 [1.54 to 7.10]; P=0.002), and severe damage of renal parenchyma defined as a past history of partial or total nephrectomy, a solitary congenital kidney, or at least one kidney with a size <10 cm in patients aged ≥16 years (4.39 [2.00 to 9.62]; P<0.001), whereas hypertension was associated with age (1.06 [1.04 to 1.08]; P<0.001), male sex (2.3 [1.3 to 4.1]; P=0.003), and an eGFR<60 ml/min per 1.73 m(2) (2.7 [1.5 to 5.1]; P=0.001)., Conclusions: CKD and high BP occur frequently in patients with cystinuria and should be routinely screened., (Copyright © 2015 by the American Society of Nephrology.)

Cystinuria is a purely renal, rare genetic disease caused by mutations in cystine transporter genes and characterized by defective cystine reabsorption leading to kidney stones. In 14% of cases, patients undergo nephrectomy, but given the difficulty to predict the evolution of the disease, the identification of markers of kidney damage would improve the follow-up of patients with a higher risk. The aim of the present study is to develop a robust, reproducible, and noninvasive methodology for proteomic analysis of urinary exosomes using high resolution mass spectrometry. A clinical pilot study conducted on eight cystinuria patients versus 10 controls highlighted 165 proteins, of which 38 were up-regulated, that separate cystinuria patients from controls and further discriminate between severe and moderate forms of the disease. These proteins include markers of kidney injury, circulating proteins, and a neutrophil signature. Analysis of selected proteins by immunobloting, performed on six additional cystinuria patients, validated the mass spectrometry data. To our knowledge, this is the first successful proteomic study in cystinuria unmasking the potential role of inflammation in this disease. The workflow we have developed is applicable to investigate urinary exosomes in different renal diseases and to search for diagnostic/prognostic markers. Data are available via ProteomeXchange with identifier PXD001430.

We prospectively determined cystine crystal volume (Vcys) in urine specimens from all consecutive patients with cystine urolithiasis followed at our institution over the past decade, in order to assess its predictive value as to the risk of recurrent cystine stone formation. A total of 57 patients (29 males, 28 females) with homozygous cystinuria entered in the study between January 1990 and December 2000, including 15 children aged less than 15 years and 42 patients aged 15 years or more. The clinical and radiological course was followed until December 2001, for a total of 243 patient-years of follow-up. From study entry until the end of follow-up, we serially examined first voided morning urine specimens in all patients, with determination of the number of cystine crystals per mm3, and the average size of crystals, thus allowing us to calculate Vcys using a simple formula based on crystal geometry. Recurrence was diagnosed on the basis of serial radiographic examinations using X-rays and echography. Overall, cystine crystals were present in 179 (39%) of the 460 examined urine specimens. Cystine crystalluria was significantly more frequent among the 27 patients who developed new cystine stones (SF) than in the other 30 who remained stone-free (63.3 vs 25.5% of samples, P<0.001). The presence of crystals in > or =50% of serially examined urine samples was more frequently found in patients with recurrent stone formation than in non-recurrent patients (24/27 vs 2/30, P<0.001). The average Vcys value was significantly higher in recurrent SF than in stone-free patients (8,173 +/- 1,544 vs 233 +/- 150 micro3/mm3, P<0.001) and there was no overlap in the individual values of recurrent vs stone-free patients. A Vcys value > or =3,000 micro3/mm3 was observed at least once prior to each of the 63 stone recurrences observed in 27 patients (2.3 per patient on the average). In addition, Vcys reflected the efficacy of treatment, with Vcys mean values of 12,097 +/- 3,214 micro3/mm3 at baseline, falling to 2,648 +/- 658 micro3/mm3 on basic therapy (hyperdiuresis plus alkalinization) alone, 1,141 +/- 522 micro3/mm3 on tiopronin therapy (median dose 1,000 mg/day) and 791 +/- 390 micro3/mm3 on D-penicillamine therapy (median dose 900 mg/day) whereas captopril had no effect (5,114 +/- 2,128 micro3/mm3). Based on the results of the present study, cystine crystalluria appears to accurately reflect active stone formation in cystinuric patients. Determination of total Vcys provides a simple, cheap and accurate means of predicting the risk of cystine stone recurrence with a Vcys value > or =3000 micro3/mm3 as the threshold risk value. We propose that serial Vcys determination be performed simultaneously with the measurement of urine pH and specific gravity to optimally monitor the medical treatment of cystine patients.