The genetics of cystinuria - an update and critical reevaluation.

PURPOSE OF REVIEW: We aimed to critically evaluate how the establishment of genotype-based treatment for cystinuria has been hampered due to the large number of variants of unknown significance (VUS) within the disease causing genes as well as challenges in accessing a large enough sample size for systematic analysis of endpoint parameters that truly reflect disease severity. This review further discusses how to overcome these hurdles with the establishment of a cystinuria-specific refinement of the current American College of Medical Genetics and Genomics (ACMG)-criteria of variant interpretation. RECENT FINDINGS: Novel tools such as AlphaMissense combined with the establishment of a refined ACMG criterion will play a significant role in classifying VUS within the responsible disease genes SLC3A1 (rBAT) and SLC7A9 (BAT1). This will also be essential in elucidating the role of promising candidate genes, such as SLC7A13 (AGT1), which have been derived from murine model systems and still need further research to determine if they are involved in human cystinuria. SUMMARY: Cystinuria was one of the first disorders to receive a gene-based classification, nonetheless, the clinically actionable implications of genetic diagnostics is still minor. This is due to poorly characterized genotype-phenotype correlations which results in a lack of individualized (genotype-) based management and metaphylaxis.

Entering into 2.0 cystinuric management with a medical digital tool to monitor urine pH: a prospective, randomized study.

BACKGROUND AND OBJECTIVES: Individuals with cystinuria can experiment recurrent lithiasis events due to the relative insolubility of cystine at physiological urine pH, resulting in renal function decline. The Lit-Control® pH Meter is a medical device that accurately allows urine pH self-monitoring. The main objective of this study was to compare the usability of the Lit-Control® pH Meter with the reactive strips for self-monitoring of urinary pH at home by patients with cystinuria, and their overall satisfaction with each tool. PATIENTS AND METHODS: We included 28 patients (9 females and 19 males, age 19-76 years), who were randomly assigned to monitor their urine pH with reactive strips (n = 17) or the Lit-Control® pH-meter (n = 11). RESULTS: After six months of use, the satisfaction with the two methods was similarly high, but the patients rated (0-10 scale) the pH meter better in terms of ease of learning (mean ±â€¯SD, 8.11 ±â€¯0.60 vs. 7.06 ±â€¯1.18; P = 0.038), ease to prepare (8.22 ±â€¯0.67 vs. 7.25 ±â€¯1.18; P = 0.034), and ease of use (8.22 ±â€¯0.67 vs. 7.25 ±â€¯1.39; P = 0.062). Overall, patients did not reach the alkalinization goals (pH between 7.0 and 8.0). CONCLUSIONS: The Lit-Control® pH Meter demonstrated to be an easy-to-use device that can facilitate urinary pH control by cystinuric patients. A prospective study is warranted to assess the correlation between urine pH monitoring, a treat to target approach, and the recurrence of cystine stones.

Case-based review of dietary management of cystinuria.

PURPOSE: The currently recommended treatment strategy for cystine stone formers is based on a progressive approach that starts with the most conservative measures. In patients with cystinuria, increased patient compliance with dietary management and medical treatment is associated with fewer stone interventions. In this case-based review, the dietary management of cystine stone former was reviewed under the guidance of evidence-based medicine. METHODS: The dietary management of the 13-year-old cystinuria patient, who underwent 18 endourological stone interventions, was reviewed in the light of evidence-based medicine. A literature search was performed in Pubmed, MEDLINE, Embase, and Cochrane Library databases according to PRISMA guidelines published from 1993 to September 2022. A total of 304 articles were included in this paper. RESULTS: In managing patients with cystinuria, hyperhydration, and alkalinization of the urine with medical treatment, the rational use of cystine-binding drugs by taking into account individual situations has come to the fore. A limited study has argued that a vegetarian diet is effective as the alkaline load from fruits and vegetables can reduce the amount of alkalizing substances required to achieve urinary alkalinization above pH 7.5, making it particularly suitable for the dietary treatment of cystine stone disease. CONCLUSION: Life-long follow-up with dietary modification, hyperhydration, and personalized medical therapy (alkalinization and cystine-binding drugs) are critical in preventing chronic kidney disease and kidney failure in cystinuria.

Phenotypic characterization of a pediatric cohort with cystinuria and usefulness of newborn screening.

BACKGROUND: Cystinuria is an inherited metabolic disease involving the defective transport of cystine and the dibasic amino acids in the renal proximal tubules that causes the formation of stones in the urinary system. In our regional child health program, cystinuria is included in newborn metabolic screening. Our objectives are the phenotypic characterization of our cystinuric pediatric cohort and to present our experience in neonatal cystinuria screening. METHODS: The study of clinical cases of pediatric patients diagnosed with cystinuria over a period of 32 years. All patients were studied at demographic, clinical, laboratory, radiological, and therapeutic levels. RESULTS: We diagnosed 86 pediatric patients with cystinuria; 36% of them had the homozygous biochemical phenotype. 95.3% of the patients were detected by neonatal metabolic screening. We performed urine biochemical analyses of parents with additional diagnoses of 63 adult patients. The mean follow-up time was 16.8 ± 8.5 years. 11.6% of patients developed one or more episodes of urinary tract infection during that period. Chronic kidney disease, proteinuria, and hypertension were uncommon (1.2%). 10.5% developed kidney stones at the mean age of presentation of 7.78 ± 7.6 years; 33% were recurrent. The risk of developing lithiasis was higher for homozygous biochemical-phenotype patients. Hypercalciuria was a significant risk factor in the development of lithiasis. CONCLUSIONS: Our clinical data suggest that diagnosing cystinuria through neonatal screening could be a useful strategy for the detection of presymptomatic cases, in order to establish preventive measures, as well as for the detection of relatives at risk. A higher resolution version of the Graphical abstract is available as Supplementary information.

Gene therapy for kidney disease: targeting cystinuria.

PURPOSE OF REVIEW: The aim of this study was to summarize recent findings in kidney gene therapy while proposing cystinuria as a model kidney disease target for genome engineering therapeutics. RECENT FINDINGS: Despite the advances of gene therapy for treating diseases of other organs, the kidney lags behind. Kidney-targeted gene delivery remains an obstacle to gene therapy of kidney disease. Nanoparticle and adeno-associated viral vector technologies offer emerging hope for kidney gene therapy. Cystinuria represents a model potential target for kidney gene therapy due to its known genetic and molecular basis, targetability, and capacity for phenotypic rescue. SUMMARY: Although gene therapy for kidney disease remains a major challenge, new and evolving technologies may actualize treatment for cystinuria and other kidney diseases.

Cystinuria: an update on pathophysiology, genetics, and clinical management.

Cystinuria is the most common genetic cause of nephrolithiasis in children. It is considered a heritable aminoaciduria as the genetic defect affects the reabsorption of cystine and three other amino acids (ornithine, lysine, and arginine) in the renal proximal tubule. Patients affected by this condition have elevated excretion of cystine in the urine, and because of this amino acid's low solubility at normal urine pH, patients tend to form cystine calculi. To date, two genes have been identified as disease-causative: SLC3A1 and SLC7A9, encoding for the two subunits of the heterodimeric transporter. The clinical features of this condition are solely related to nephrolithiasis. The diagnosis is usually made during infancy or adolescence, but cases of late diagnosis are common. The goal of therapy is to reduce excretion and increase the solubility of cystine, through both modifications of dietary habits and pharmacological treatment. However, therapeutic interventions are not always sufficient, and patients often have to undergo several surgical procedures during their lives to treat recurrent nephrolithiasis. The goal of this literature review is to synthesize the available evidence on diagnosis and management of patients affected by cystinuria in order to provide physicians with a practical tool that can be used in daily clinical practice. This review also aims to shed some light on new therapy directions with the aim of ameliorating kidney outcomes while improving adherence to treatment and quality of life of cystinuric patients.

Cystinuria: Review of a Life-long and Frustrating Disease.

Cystinuria, accounting for about 1-2% of kidney stones in adults, carries significant morbidity beginning at a young age [1]. Cystine stone formers have more stone events compared to other stone formers, as well as more surgical interventions, potentially contributing to faster progression to chronic kidney disease (CKD), and end-stage kidney disease (ESKD) [2]. Successful medical therapy for cystine stone formers may be limited by adherence to the extensive lifestyle changes and the adverse side effect profiles of some interventions, leading to decreased quality of life for these patients relative to other stone formers.

Milestones in treatments for inborn errors of metabolism: Reflections on Where chemistry and medicine meet.

From Sir Archibald Garrod's initial description of the tetrad of albinism, alkaptonuria, cystinuria, and pentosuria to today, the field of medicine dedicated to inborn errors of metabolism has evolved from disease identification and mechanistic discovery to the development of therapies designed to subvert biochemical defects. In this review, we highlight major milestones in the treatment and diagnosis of inborn errors of metabolism, starting with dietary therapy for phenylketonuria in the 1950s and 1960s, and ending with current approaches in genetic manipulation.

[Cystinuria]. / Cystinurie.

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.

Cystinuria poorly responding to treatment - the risk of chronic kidney disease.

Cystinuria is the genetic condition for the increased excretion of cystine in the urine. Patients mainly suffer from afflictions related to the presence and passage of kidney stones. The currently available treatment methods include conservative treatment based on increased fluid intake, appropriate diet, medications and urological procedures. The causal treatment has not yet been invented. A CASE REPORT: A patient case was described whose first symptomatic kidney stones appeared after the second year of life. Urinary cystine excretion was significantly increased - 25,431 µmol/1g creatinine (norm: 167-333 µmol/1g creatinine), which was also shown, but lower, in both parents of the patient. Despite the early initiation of therapy including low sodium diet, abundant hydration, alkalization, captopril and compliance with stringent restrictions, the level of urinary cystine excretion was still not within the normal range. There have been many modifications to the therapy and dose increases of drugs, but without visible results. The patient underwent several urological procedures, including: ESWL (Extracorporeal shock wave lithotripsy), URSL (Ureteroscopic lithotripsy), PCNL (Percutaneous nephrolithotomy) and open surgery to remove cystine deposits that were still produced in the kidneys. In addition, for many years the disease was complicated by recurrent urinary tract infections, underweight and lesions like epithelial metaplasia in the bladder. Renal parameters were repeatedly examined. Elevated results such as: serum creatinine 0.9 mg/dl, cystatin C concentration 1.10 mg/l, albumin-creatinine index 0.197, creatinine clearance 50.7 ml/min /1.73 m2 and eGFR 73 ml/min/1.73 m2 allowed for the diagnosis of chronic kidney disease before the age of 18. After many years of conservative treatment, only the introduction of thiopronine, still little known in Poland, reduced the level of cystine excreted in the urine. The inclusion of the drug reduced the tendency to produce kidney stones, which allowed to inhibit the progression of renal failure. CONCLUSIONS: Despite many years of research and modern drugs, cystinuria is still a disease with which patients are associated for the rest of their lives. The ongoing research, along with attempts to understand the genetic and epigenetic mechanisms responsible for the emergence of mutations in the main genes causing the disease and the course of the disease, gives hope for finding a method of causal treatment for cystinuria.

An Update on Evaluation and Management in Cystinuria.

Cystinuria is the most common cause of inherited stone disease and is caused by the failure of absorption of filtered dibasic amino acids including cystine in the proximal tubules. It is associated with a very high recurrence rate in affected patients, with the potential for significant morbidity in such patients due to the need for repeated surgical interventions. A multimodal and multispecialty approach in a dedicated centre is the key to improving treatment outcomes and patient adherence to the treatment. This article reviews the latest knowledge on the clinical and diagnostic features and summarises key developments to aid clinicians in diagnosis and management options, together with future directions for the care of these patients.

[A Case of Long-Term Treatment with Extracorporeal Shock Wave Lithotripsy and Follow-Up for Cystine Calculi by Cystinuria].

For the management of patients with cystinuria, forced hydration and medication have been used to prevent stone recurrence and growth, but not a few cystine stones require surgical intervention. However, the long-term follow-up data about surgical intervention for cystine stones is lacking. Here, we report a case of cystine calculi of cystinuria with many sessions of extracorporeal shock wave lithotripsy (ESWL) during the long-term follow-up period. A 13-year-old woman went to a local clinic with right flank pain in January 1993, and abdominal ultrasonography revealed right kidney stones. She was admitted to our hospital for treatment using ESWL. Analysis of the stone components revealed the stone to be composed of cystine. During the next 25 years, she received 157 sessions of ESWL and 2 sessions of transurethral ureterolithotripsy (TUL). Current examination revealed that although the lower pole of her right kidney is slightly atrophic, her renal function is stable and kidney stones remain small. Our case suggests that early intervention by ESWL could prevent stone growth and the deterioration in renal function.

Reporte de un caso de Cistinuria: Uso de herramientas de diagnóstico a nivel nacional / Report of a case of cystinuria: Use of diagnostic tools at national level

La cistinuria es una enfermedad genética que se engloba dentro de alteraciones congénitas del transporte de aminoácidos con formación de cálculos en las vías urinarias, si bien es poco frecuente se caracteriza por su elevada recurrencia. En este trabajo presentamos el caso de una paciente de 34 años, con antecedentes de haber perdido un riñón por episodios anteriores de litiasis y con múltiples recidivas que es diagnosticada mediante la detección de cistina por espectroscopía infrarroja como componente único de 96 fragmentos de cálculos removidos mediante nefrolitotomía percutánea. La paciente fue evaluada laboratorialmente mediante el perfil metabólico y la cristaluria. Las indicaciones de tratamiento específicas incluyeron la administración de agentes alcalinizantes, régimen nutricional, y entrenamiento para control de pH urinario. Es importante señalar la agresividad de la litiasis de cistina con las consecuencias que puede tener la calidad de vida del paciente, y por tanto la importancia de contar con capacidades instaladas a nivel país para el diagnóstico y seguimiento de litiasis genéticas como la causada por la cistinuria(AU)

Cystinuria is a genetic disease that is included among congenital defects of renal amino acids transport that causes urinary stone formation. Although it is rare, it is characterized by its high recurrence. We present the case of a 34-year-old patient that lost one of her kidney because of recurrent episodes of lithiasis, and that was diagnosed by the detection of cystine with infrared spectroscopy as the sole component of 96 stone fragments removed by percutaneous nephrolithotomy. The patient was evaluated by metabolic profile and crystalluria. The specific treatment indications included the administration of alkalinizing agents, nutritional regimen, and training for personal measurement of urinary pH. This case highlights the aggressiveness of cystine stones with the consequences that may have on the quality of the patient life, and therefore the importance of having installed proper diagnostic capacities at national level to detect and monitor treatment efficacy in genetic lithiasis such as cystinuria(AU)

Conversion from Cystine to Noncystine Stones: Incidence and Associated Factors.

PURPOSE: Patients with cystinuria are often treated with medical alkalization and shock wave lithotripsy, although each treatment is hypothesized to increase the risk of calcium phosphate stones. We performed a multicenter retrospective review to evaluate whether stones of another composition develop in patients with cystinuria and with what frequency. MATERIALS AND METHODS: We retrospectively reviewed the records of a multi-institutional cohort of patients with cystinuria. We assessed medications, stone analyses, 24-hour urinalyses and types of procedures. We compared patients who formed only cystine stones vs those with noncystine stones. RESULTS: We identified 125 patients from a total of 5 institutions who were followed a mean of 5.2 years (range 0 to 26). Stones with noncystine components were submitted by 37 patients (29.6%). Potassium citrate medication was not associated with a noncystine composition (p = 0.1877). Regarding surgical management 18 patients (13%) underwent at least 1 shock wave lithotripsy session (range 0 to 9) and 79 (63%) underwent percutaneous nephrolithotomy at least once (range 0 to 10). When stratified based on pure cystine vs converted stones, the average total number of shock wave lithotripsy and percutaneous nephrolithotomy procedures was higher in the group with cystine and subsequent noncystine stone compositions (0.94 vs 0.10, p <0.0001, and 1.7 vs 1.5, p = 0.0053, respectively). On logistic regression male gender (OR 3.1, p = 0.0280) and the number of shock wave lithotripsy sessions (OR 3.0, p = 0.0170) were associated with an increased likelihood of the development of stones with a noncystine composition. CONCLUSIONS: Stones with noncystine components develop in more than 25% of patients with cystinuria, underscoring the importance of continued stone analysis. In this study prior shock wave lithotripsy was associated with conversion to a noncystine stone composition while urinary alkalization therapy was not associated.

Early Recognition and Management of Rare Kidney Stone Disorders.

Kidney stones, especially those that present in childhood/adolescence, may be due to rare inherited disorders such as cystinuria. Early recognition and prompt treatment can help reduce or even prevent the serious long-term complications of these rare stone disorders.

Case Study - Case Studies in Cystinuria.

The diagnosis and treatment of patients with rare inherited metabolic disorders associated with recurrent and often obstructive kidney stones are important to the prevention of chronic kidney disease or end stage renal disease. Two case studies in this article describe the diagnosis and management of cystinuria, the most common rare kidney stone disorder.

Case Report: Cystinuria and Polycystic Kidney Disease.

Cystinuria and polycystic kidney disease are 2 genetic disorders that affect the genitourinary tract but rarely together. This case report presents 2 pediatric patients diagnosed with polycystic kidney disease and cystinuria requiring surgical treatment. Both subjects presented acutely with stone disease. Imaging studies and stone analysis established the diagnoses. Although coexistence of these 2 conditions is rare, cystinuria should be considered in the differential diagnosis when evaluating patients with cystic disease who develop renal calculi.

[Cystinic nephrolythiasis: clinical experience and new diagnostic and therapeutic perspectives]. / Nefrolitiasi cistinica: dall'esperienza clinica alle nuove prospettive diagnostiche e terapeutiche.

Cystinuria is an inherited autosomal recessive disease with a prevalence 1:7000 and typical age of onset in the second decade of life. This nephrolithiasis is not always well known and well studied and for this reason it is often underdiagnosed. Cystinuria is characterized by increased urinary excretion of cystine and dibasic amino acids (lysine, ornithine, arginine) caused by defective transport of these amino acids across the luminal membrane of proximal tubule and small intestine cells. Two mutated genes responsible of this tubular defect are SLC3A1 on chromosome 2 and SLC7A9 on chromosome 19. Clinical manifestations of cystinuria are essentially those related to stones formation and their movement across the urinary tract, like flank pain/abdomen pain and hematuria, as occurred in other nephrolithiasis types. Diagnosis is based on biochemical urine analysis, stone analysis and imaging. Genetic study of this disease may be a new and stimulating approach to better understand the defects and identify new therapeutic targets. A wider knowledge and a more detailed approach to cystinuria may help to ameliorate patients quality of life, to prevent recurrences and complications and to develop more specific and adequate treatments.