Management of Cystinuria

Renal Cystinuria and Immune Cells (T Lymphocytes) Dysfunction: What We Know about?

INTRODUCTION

Cystinuria (CYS) is the most common monogenic kidney stone disease.

METHODS

Starting from an unusual case of CYS associated to primary sclerosing cholangitis, inflammatory bowel disease (IBD), and autoimmune hepatitis in a young male, we carefully review the literature and propose here a working hypothesis regarding the potential risk of cystinuric patients to develop conditions due to immune system dysregulation. To corroborate this hypothesis, we retrospectively evaluate the frequency of dysimmunity in a monocentric cohort including 36 cystinuric patients compared to healthy and disease controls.

RESULTS

CYS patients have an increased prevalence of atopic disease compared to disease controls (p = 0.03) and 16.7% of CYS subjects were diagnosed with allergic disease to a variety of antigens.

CONCLUSION

Further studies are needed to define the relationship between proximal tubular transport defect of CYS and dysregulated immunity.

The Saudi urological association guidelines on urolithiasis

Aims

The Saudi Urolithiasis Guidelines are a set of recommendations for diagnosing, evaluating, and treating urolithiasis in the Saudi population. These guidelines are based on the latest evidence and expert consensus to improve patient outcomes and optimize care delivery. They cover the various aspects of urolithiasis, including risk factors, diagnosis, medical and surgical treatments, and prevention strategies. By following these guidelines, health-care professionals can improve care quality for individuals with urolithiasis in Saudi Arabia.

Panel

The Saudi Urolithiasis Guidelines Panel consists of urologists specialized in endourology with expertise in urolithiasis and consultation with a guideline methodologist. All panelists involved in this document have submitted statements disclosing any potential conflicts of interest.

Methods

The Saudi Guidelines on Urolithiasis were developed by relying primarily on established international guidelines to adopt or adapt the most appropriate guidance for the Saudi context. When necessary, the panel modified the phrasing of recommendations from different sources to ensure consistency within the document. To address areas less well covered in existing guidelines, the panel conducted a directed literature search for high quality evidence published in English, including meta analyses, randomized controlled trials, and prospective nonrandomized comparative studies. The panel also searched for locally relevant studies containing information unique to the Saudi Arabian population. The recommendations are formulated with a direction and strength of recommendation based on GRADE terminology and interpretation while relying on existing summaries of evidence from the existing guidelines.

A retrospective study on epidemiology and management of canine cystine uroliths in one part of Norway from 2015 to 2020

BACKGROUND

Urinary tract problems are a common complaint in small animal medicine and urolithiasis is considered to be an important cause of urinary tract disease in dogs. In this study the main aim was to investigate whether the occurrence of cystine urolithiasis increased during a five-year period. A second aim was to evaluate possible risk-factors as breed, age and gender. This study also evaluated how urine specific gravity, pH and level of cystine in urine responded to preventive strategies. Medical records of dogs with urolithiasis presented at nine Norwegian animal clinics and one animal hospital between 2015 and 2020 were retrospectively reviewed.

RESULTS

The incidence of cystine uroliths increased significantly during the five study years (R2 = 0.72, P = 0.0199). Dogs with cystine uroliths were significantly younger (5.0 years (n = 84, 95% CI [4.4-5.6])) when they were diagnosed with cystine uroliths compared to dogs with other types of uroliths (8.1 years (n = 255, 95% CI[7.8-8.5]) P < < 0.0001). Cystine levels in urine were increased in 93% of the dogs with cystine urolithiasis. Cystinuria decreased significantly after neutering (P < 0.0001). Breeds most commonly affected with cystine urolithiasis in this study were Staffordshire bull terrier, Danish Swedish farmdog and Chihuahua.

CONCLUSIONS

The results from this study supports a suggested genetic basis for cystine urolithiasis as described in previous studies. Neutering is considered an important part of preventing reoccurrence since cystine values decreased significantly after neutering.

2022 Recommendations of the AFU Lithiasis Committee: Medical management - from diagnosis to treatment

The morphological-compositional analysis of urinary stones allows distinguishing schematically several situations: dietary, digestive, metabolic/hormonal, infectious and genetic problems. Blood and urine testing are recommended in the first instance to identify risk factors of urinary stone disease in order to avoid recurrence or progression. The other objective is to detect a potential underlying pathology associated with high risk of urinary stone disease (e.g. primary hyperparathyroidism, primary or enteric hyperoxaluria, cystinuria, distal renal tubular acidosis) that may require specific management. Lifestyle-diet measures are the basis of the management of all stone types, but pharmacological treatments may be required. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendation (CPR) method and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis) [EAU 2022] and their adaptability to the French context.

Declaration: Novel SLC3A1 mutation in a cystinuria patient with xanthine stones: a case report

BACKGROUND

Cystinuria and xanthinuria are both rare genetic diseases involving urinary calculi. However, cases combining these two disorders have not yet been reported.

CASE PRESENTATION

In this study, we report a case of cystinuria with xanthine stones and hyperuricemia. The 23-year-old male patient was diagnosed with kidney and ureteral stones, solitary functioning kidney and hyperuricemia after admission to the hospital. The stones were removed by surgery and found to be composed of xanthine.

CONCLUSION

Genetic testing by next-generation sequencing technology showed that the patient carried the homozygous nonsense mutation c.1113 C> A (p.Tyr371*) in the SLC3A1 gene, which was judged to be a functionally pathogenic variant. Sanger sequencing revealed that the patient's parents carried this heterozygous mutation, which is a pathogenic variant that can cause cystinuria. The 24-h urine metabolism analysis showed that the cystine content was 644 mg (<320 mg/24 h), indicating that the patient had cystinuria, consistent with the genetic test results. This case shows that cystinuria and xanthine stones can occur simultaneously, and provides evidence of a possible connection between the two conditions. Furthermore, our findings demonstrate the potential value of genetic testing using next-generation sequencing to effectively assist in the clinical diagnosis and treatment of patients with urinary calculi.

Cystine Stones: Developments in Minimally Invasive Surgery and Their Impact on Morbidity and Stone Clearance

Cystinuria is a rare genetic condition that is responsible for cystine stones. Besides stone recurrence, patients with cystine stones have reduced health-related quality of life, increased rates of chronic kidney disease and hypertension. Although lifestyle measures, medical therapy and close follow up are essential to reduce and monitor cystine stone recurrences, surgical intervention is frequently needed for most cystinuria patients. Shock wave lithotripsy, ureteroscopy, percutaneous nephrolithotomy and active surveillance all have a role, and technological advances in endourology are vital in achieving a stone-free status and to prevent recurrences. The complexity of managing cystine stones necessitates a multidisciplinary team discussion, patient involvement and an individualised approach in a specialist centre for optimum management. Thulium fibre laser and virtual reality may have an increasing role in the future of cystine stone management.

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.

[Interpretation of the metabolic study in renal lithiasis and its treatment]

Urolithiasis is a common disease, and is an important health problem that is associated with a great economic burden. The nature of stone disease varies according by dietary and lifestyle factors, including, among others, climate variations. The majority of patients will suffer a new lithiasic episode at some point in their life, unless preventive measures, such as changing lifestyles and dietary habits, are put in place to avoid it. The risk factors involved in lithogenesis should be evaluated in order to reduce recurrences. In the majority of these patients, metabolic changes are observed in the urine that predispose lithogenesis. The kind of evaluation depends on stone composition and on the clinical presentation. A diagnosis of systemic and renal diseases of lithogenic nature can be diagnosed with these studies, and they also enable the adoption of precise prophylactic measures that achieve control of recurrence in a great number of patients.

Cystinuria: urine sediment as a diagnostic test

Objectives

To demonstrate the importance of carrying out the urinary sediment study with the correct interpretation and crystals typification as a clinical laboratory diagnostic tool, as well as the elaboration of protocols that determine the need to realize this type of microscopic urinary sediment examination routinely.

Case presentation

Elderly male patient with no personal or family history of interest that presented with left iliac fossa fixed and non-irradiated pain lasting three days. This is the first time that he suffered pain episodes of this type. The urine analysis reveals proteinuria, hematuria and the sediment shows abundant flat and hexagonal crystals, typical of cystine. Amino acid analysis confirms the finding, showing high dibasic amino acids and cystine concentrations.

Conclusions

The study of the urinary sediment by the clinical laboratory reveals the presence of a case of cystinuria due to the appearance of their pathognomonic crystals at an advanced age and without a previous history. The case reported in this paper is of interest for clinical laboratory practice, as it demonstrates the utility of urine sediment examination in the diagnosis of a genetic disease that manifests as a simple renal colic.

Evaluation and Medical Management of Patients with Cystine Nephrolithiasis: A Consensus Statement

Purpose: Cystinuria is a genetic disorder with both autosomal recessive and incompletely dominant inheritance. The disorder disrupts cystine and other dibasic amino acid transport in proximal tubules of the kidney, resulting in recurrent kidney stone formation. Currently, there are no consensus guidelines on evaluation and management of this disease. This article represents the consensus of the author panel and will provide clinicians with a stepwise framework for evaluation and clinical management of patients with cystinuria based on evidence in the existing literature. Materials and Methods: A search of MEDLINE^®/PubMed^® and Cochrane databases was performed using the following key words: "cystine nephrolithiasis," "cystinuria," "penicillamine, cystine," and "tiopronin, cystine." In total, as of May 2018, these searches yielded 2335 articles, which were then evaluated for their relevance to the topic of evaluation and management of cystinuria. Evidence was evaluated by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. Results: Twenty-five articles on the topic of cystinuria or cystine nephrolithiasis were deemed suitable for inclusion in this study. The literature supports a logical evaluation process and step-wise treatment approach beginning with conservative measures: fluid intake and dietary modification. If stone formation recurs, proceed to pharmacotherapeutic options by first alkalinizing the urine and then using cystine-binding thiol drugs. Conclusions: The proposed clinical pathways provide a framework for efficient evaluation and treatment of patients with cystinuria, which should improve overall outcomes of this rare, but highly recurrent, form of nephrolithiasis.

CRISPR/Cas9 engineering of albino cystinuria Type A mice

Cystinuria Type A is a relatively common genetic kidney disease occurring in 1 in 7,000 people worldwide that results from mutation of the cystine transporter rBAT encoded by Slc3a1. We used CRISPR/Cas9 technology to engineer cystinuria Type A mice via genome editing of the C57BL/6NHsd background. These mice are an improvement on currently available models as they are on a coisogenic genetic background and have a single defined mutation. In order to use albinism to track Cas9 activity, we co-injected gRNAs targeting Slc3a1 and tyrosinase (Tyr) with Cas9 expressing plasmid DNA into mouse embryos. Two different Slc3a1 mutational alleles were derived, with homozygous mice of both demonstrating elevated urinary cystine levels, cystine crystals, and bladder stones. We used whole genome sequencing to evaluate for potential off-target editing. No off-target indels were observed for the top 10 predicted off-targets for Slc3a1 or Tyr. Therefore, we used CRISPR/Cas9 to generate coisogenic albino cystinuria Type A mice that could be used for in vivo imaging, further study, or developing new treatments of cystinuria.

Urinary Stone Disease: Diagnosis, Medical Therapy, and Surgical Management

Clinical suspicion of urolithiasis should be evaluated with low-dose computed tomography as the first-line imaging modality for nonpregnant, adult patients. A period of observation may be appropriate for ureteral stones less than 10 mm, and medical expulsive therapy may be beneficial for facilitating passage of distal ureteral stones. Regardless of stone type, patients should adhere to a low-sodium diet and attempt to achieve a urine volume of more than 2.5 L daily. Individuals with calcium stones should maintain a normal calcium diet, and if stones persist, citrate therapy or thiazide diuretics in the setting of hypercalciuria may be indicated.

Retrograde intrarenal surgery in the management of pediatric cystine stones

OBJECTIVE

To investigate the efficacy and safety of retrograde intrarenal surgery (RIRS) in the treatment of pediatric cystine stones.

STUDY DESIGN

Data of the pediatric patients who underwent RIRS for kidney stones were retrospectively evaluated. A total of 14 children with cystine stones managed with RIRS were identified. In addition to the patient demographics and stone characteristics, all retrospectively obtained operative data were evaluated and discussed in detail, with an emphasis on the success and complication rates.

RESULTS

Mean age of the 14 cases was 10.9 ± 2.2 years (range: 7-15). Mean stone size was 13.6 ± 2.4 mm (range: 10-18) (Summary table). Of these stones, four were located in the renal pelvis, three were in the lower, three were in the middle and the remaining four were located in upper calyx. Ureteral access sheath was used in 12 (85.7%) patients. The double-J ureteral stent was placed pre-operatively in one case and was inserted postoperatively in 12 cases. Mean operation time was 38.2 ± 7.2 min (range: 30-50). Complications were observed in two cases: mild ureteral laceration in the first and fever on the second postoperative day in the second patient. All of the patients were stone free on sonographic evaluation at the 4-week follow-up evaluation. Although potassium citrate treatment was initiated in 11 patients, tiopronin treatment was initiated in four patients for recurrence prophylaxis during long-term follow-up. During a mean follow-up period of 25.7 ± 5.2 months, stone recurrence was noted in one patient.

DISCUSSION

Treatment of patients with cystine stones is challenging, due to high risk of rapid recurrence in the presence of residual fragments. Besides allowing complete stone clearance in all cases in the current series, RIRS is a highly reproducible method that can be safely performed, even in recurrences. The major limitations of the current study were low number of patients and short follow-up period.

CONCLUSION

The results clearly indicated that RIRS is a safe treatment modality in the management of pediatric cystine stones.

Do Urinary Cystine Parameters Predict Clinical Stone Activity?

PURPOSE

An accurate urinary predictor of stone recurrence would be clinically advantageous for patients with cystinuria. A proprietary assay (Litholink, Chicago, Illinois) measures cystine capacity as a potentially more reliable estimate of stone forming propensity. The recommended capacity level to prevent stone formation, which is greater than 150 mg/l, has not been directly correlated with clinical stone activity. We investigated the relationship between urinary cystine parameters and clinical stone activity.

MATERIALS AND METHODS

We prospectively followed 48 patients with cystinuria using 24-hour urine collections and serial imaging, and recorded stone activity. We compared cystine urinary parameters at times of stone activity with those obtained during periods of stone quiescence. We then performed correlation and ROC analysis to evaluate the performance of cystine parameters to predict stone activity.

RESULTS

During a median followup of 70.6 months (range 2.2 to 274.6) 85 stone events occurred which could be linked to a recent urine collection. Cystine capacity was significantly greater for quiescent urine than for stone event urine (mean ± SD 48 ± 107 vs -38 ± 163 mg/l, p <0.001). Cystine capacity significantly correlated inversely with stone activity (r = -0.29, p <0.001). Capacity also correlated highly negatively with supersaturation (r = -0.88, p <0.001) and concentration (r = -0.87, p <0.001). Using the suggested cutoff of greater than 150 mg/l had only 8.0% sensitivity to predict stone quiescence. Decreasing the cutoff to 90 mg/l or greater improved sensitivity to 25.2% while maintaining specificity at 90.9%.

CONCLUSIONS

Our results suggest that the target for capacity should be lower than previously advised.

How should patients with cystine stone disease be evaluated and treated in the twenty-first century?

Cystinuria continues to be one of the most challenging stone diseases. During the latest decades our knowledge of the molecular basis of cystinuria has expanded. Today 160 different mutations in the SLC3A1 gene and 116 in the SLC7A9 gene are listed. The full implications of type A, B or AB status are not yet fully understood but may have implications for prognosis, management and treatment. Despite better understanding of the molecular basis of cystinuria the principles of recurrence prevention have remained essentially the same through decades. No curative treatment of cystinuria exists, and patients will have a life long risk of stone formation, repeated surgery, impaired renal function and quality of life. Therapy to reduce stone formation is directed towards lowering urine cystine concentration and increasing cystine solubility. Different molecules that could play a role in promoting nucleation and have a modulating effect on cystine solubility may represent new targets for cystinuria research. Investigation of newer thiol-containing drugs with fewer adverse effects is also warranted. Determining cystine capacity may be an effective tool to monitor the individual patient's response. Compliance in cystinuric patients concerning both dietary and pharmacological intervention is poor. Frequent clinical follow-up visits in dedicated centres seem to improve compliance. Cystinuric patients should be managed in dedicated centres offering the complete range of minimal invasive treatment modalities, enabling a personalized treatment approach in order to reduce risk and morbidity of multiple procedures.

Multimodal treatments of cystine stones: an observational, retrospective single-center analysis of 14 cases

Purpose

To document the experiences of a single institution in evaluating the clinical courses and treatment outcomes of patients with cystine stones.

Materials and Methods

The clinical data of 14 patients with cystine stones who were treated at our institution from March 1994 to July 2012 were reviewed. These data included age at first visit, gender, family history, body mass index, presence of a single kidney, stone locations, stone burden, routine urinalysis, and culture. In addition, we also analyzed data on surgery, shock wave lithotripsy, medical treatment, stone recurrence or regrowth, and overall treatment success rates.

Results

The mean age of our patients at their first visit was 19.6±5.0 years, and eight patients were males. The median stone burden and mean urine pH before each surgery were 6.5 cm² and 6.5±0.9, respectively. Two patients had a family history of cystine stones. Patients underwent surgery an average of 2.7 times. The median interval between surgeries was 27.3 months, and 1 open surgery, 12 percutaneous nephrolithotomies, and 25 ureterorenoscopies were performed. Potassium citrate or sodium bicarbonate was used in nine cases. D-Penicillamine was continuously used in three patients. Patients had an average incidence of 3.2 recurrences or regrowth of stones during the median follow-up period of 60.5 months.

Conclusions

Patients with cystine stones have high recurrence or regrowth rates and relatively large stone burdens. Adequate treatment schedules must therefore be established in these cases to prevent possible deterioration of renal function.

Synergistic mutations in SLC3A1 and SLC7A9 leading to heterogeneous cystinuria phenotypes: pitfalls in the diagnostic workup

BACKGROUND

Cystinuria is an inherited disorder of a renal tubular amino acid transporter and leads to increased cystine excretion with the risk of urinary stone formation. Phenotypical classification is based on urinary amino acid concentration as type I (silent), type non-I (hyper-excretors), mixed or untyped. Genotypic classification is based on mutations in SLC3A1 (type A) or SLC7A9 (type B).

CASE-DIAGNOSIS/TREATMENT

We present six family members with a complex phenotypic profile based on mutations in both genes. The index patient presents a known homozygous mutation (p.T189M) in SLC3A1 and a homozygous mutation (c.225C > T) in SLC7A9. Based on a bioinformatics analysis and published findings, we considered p.T189M to be pathogenic and initially classified c.225C > T as a silent variant. However, segregation analysis detected homozygosity for p.T189M also in non-affected individuals, whereas homozygous c.225C > T segregated with the phenotype. RNA studies confirmed c.225C > T to cause aberrant splicing.

CONCLUSIONS

Based on our findings, we conclude that c.225C > T in SLC7A9 determines the clinical phenotype in this family, whereas additional SLC3A1 mutations aggravate the phenotype in heterozygotes for c.225C > T in SLC7A9 without resulting in cystinuria in the homozygous state. Our results underline the need for careful biochemical characterization of family members of an index case of cystinuria. Genetic analysis of both cystinuria genes may be necessary due to the synergistic effects of mutations in two genes.

The effect of prophylactic treatment with Shohl's solution in children with cystinuria

OBJECTIVE

To investigate the effect of prophylactic treatment with Shohl's solution on the rates of stone recurrence in paediatric patients with cystinuria.

PATIENTS AND METHODS

Between June 2007 and October 2011, 185 patients aged 16 years and younger whose stones had been completely removed by percutaneous nephrolithotomy (PCNL) were assessed for metabolic risk factors. Seventeen (9%) patients with positive cyanide-nitroprusside tests (CNT) and cystine stones enrolled in this study, and a Shohl's solution was used for alkalinisation. The patients were followed up for a mean period of two years for stone recurrence.

RESULTS

Of the patients, 10 (59%) were male, and 7 (41%) were female (p = 0.13). Twelve patients (70.5%) continued to receive medical prophylaxis regularly, whereas 5 (29.5%) patients did not. The mean pre-treatment and post-treatment urinary pH values were 5.8 ± 0.5 (5-7) and 7.5 ± 0.4 (6.5-8), respectively (p < 0.001). The pre-treatment and post-treatment specific gravities of the urine were 1021.5 ± 5.4 (1010-1030) and 1006 ± 2.3 (1004-1015), respectively (p < 0.001). The rates of recurrence were 16.6% among those who continued prophylaxis and 100% among those who did not receive prophylaxis (p = 0.001). The most common combination of metabolic anomalies was cystinuria and hypocitraturia (p < 0.001).

CONCLUSIONS

This study demonstrated that detailed clinical and laboratory evaluations should be performed for all children with cystine stone disease, and, appropriate prophylactic treatment should be recommended to prevent the reformation of stones.

Cystinuria: mechanisms and management

Cystinuria is a relatively uncommon cause of pediatric stone disease, but has significant morbidity if not properly controlled because of its significant stone recurrence rate. Cystinuria is caused by the inability of the renal tubules to reabsorb filtered cystine, which is poorly soluble at a typical urine pH <7. Although many advances have been made in the understanding of the genetic and physiological basis of cystinuria, the cornerstones of treatment still involve stone prevention with dietary measures and pharmacological therapy, coupled with surgical interventions for stone removal. Pharmacological treatments can carry significant side effects that must be monitored and can limit therapy as well as impede compliance. Most patients will require surgical intervention for stone removal, although compliance with prevention strategies reduces the need for intervention.

Characterization of patients with heterozygous cystinuria

OBJECTIVE

To characterize a contemporary cohort of patients with heterozygous (TZ) cystinuria and compare them with a concurrent cohort of patients with homozygous (MZ) cystinuria.

METHODS

A retrospective review of prospectively collected data was performed for 42 consecutive patients presenting with a positive cyanide-nitroprusside test from September 2009 to September 2011. Clinical data were collected, including the findings from a detailed metabolic stone workup that included two 24-hour urine collections with quantitative cystine. The patients were divided into 2 groups: those with TZ (30-400 mg/d) and those with MZ (>400 mg/d) cystinuria.

RESULTS

One patient was excluded because the cystine excretion was within the normal range (<30 mg/d), 35 (83.3%) and 6 (14.3%) had TZ and MZ cystinuria, respectively. Compared with those with TZ cystinuria, those with MZ cystinuria were significantly younger at the first stone episode (median 48 years, range 14-67, vs 17, range 6-44, P = .002), more were female (20% vs 66.7%; P = .03), and more patients had bilateral stones (8.6% vs 50%; P = .03). Finally, the patients with MZ cystinuria had more stone episodes than those with TZ cystinuria (3 vs 1; P = .04). From the detailed metabolic stone evaluation, the incidence of hyperuricemia was significantly greater in the MZ patients (17.1% vs 66.7%; P = .02). Although all the MZ patients developed pure cystine stones, 18 (51.4%), 7 (20.0%), and 3 (8.6%) of the TZ patients developed calcium oxalate, uric acid, and cystine stones, respectively (P < .001). In the TZ group, 11 patients (31.4%) had false-negative results on subsequent cyanide-nitroprusside testing.

CONCLUSION

Significant differences were found between the patients with TZ and MZ cystinuria in terms of age at the first stone episode, male/female ratio, incidence of hyperuricemia, and stone composition. The clinical significance remains to be elucidated.

New horizons in the management of patients with cystinuria

PURPOSE OF REVIEW

Although the formation of cystine stones is seen in only a small fraction of all patients with urolithiasis, this disease is associated with a pronounced morbidity. The difficult clinical management of these patients, with the aim of arresting or decreasing the rate of recurrent stone formation, is well recognized. This review summarizes some recent knowledge.

RECENT FINDINGS

An early and correct diagnosis of cystinuria is fundamental for a successful course of the disease in these patients. Formation starts early in life, and attention to this diagnosis is necessary for the paediatric stone formers. New radiological and biochemical improvements seem useful in this respect. A combination of medical tools is usually necessary to influence the very often, troublesome stone-forming activity. Urine dilution, alkalization and chelating therapy have remained the cornerstones of the therapeutic approach. The importance of a high urine pH has been further emphasized, and the possibility to use acetazolamide is a promising improvement of the medical treatment. In order to increase the compliance and reduce the need of active stone removal, special stone clinics seem to be of particular value. The understanding of the genetic background might open future treatment alternatives.

SUMMARY

Patients afflicted by cystine stone disease need an aggressive medical treatment, gentle stone-removing surgery and careful follow-up.

Cystinuria

Cystinuria is an inherited disorder characterized by the impaired reabsorption of cystine in the proximal tubule of the nephron and the gastrointestinal epithelium. The only clinically significant manifestation is recurrent nephrolithiasis secondary to the poor solubility of cystine in urine. Although cystinuria is a relatively common disorder, it accounts for no more than 1% of all urinary tract stones. Thus far, mutations in 2 genes, SLC3A1 and SLC7A9, have been identified as being responsible for most cases of cystinuria by encoding defective subunits of the cystine transporter. With the discovery of mutated genes, the classification of patients with cystinuria has been changed from one based on phenotypes (I, II, III) to one based on the affected genes (I and non-type I; or A and B). Most often this classification can be used without gene sequencing by determining whether the affected individual's parents have abnormal urinary cystine excretion. Clinically, insoluble cystine precipitates into hexagonal crystals that can coalesce into larger, recurrent calculi. Prevention of stone formation is the primary goal of management and includes hydration, dietary restriction of salt and animal protein, urinary alkalinization, and cystine-binding thiol drugs.