Genetic determinants of urolithiasis

Discovery of l-Lysine Dioxalate (LH1513) as a Novel Inhibitor of Calcium Oxalate Crystallization for Hyperoxaluria

Hyperoxaluria is caused by increased urinary excretion of oxalate leading to the formation of calcium oxalate (CaOx) stones. The lack of effective management strategies for hyperoxaluria prompted us to investigate molecular mimics as stone inhibitors, a strategy that we previously used successfully to discover small molecule inhibitors of l-cystine crystallization for the prevention of l-cystine stone formation in cystinuria. Herein, we report the discovery of l-lysine dioxalate (LH1513), a novel dioxamate derivative, as a more potent inhibitor of CaOx crystallization than citrate and pyruvate. Such inhibition was corroborated by in situ atomic force microscopy (AFM) measurements of crystal growth rates at the microscopic length scale. A triester prodrug of LH1513 was found to have sufficient oral bioavailability for a preliminary in vivo study demonstrating efficacy in preventing urinary CaOx crystal formation in an Agxt-knockout mouse model for hyperoxaluria.

The complex relationship between vitamin D and kidney stones: balance, risks, and prevention strategies

The association between vitamin D and kidney stones is characterized by a remarkable multi-dimensional complexity involving numerous physiological and metabolic pathways. Vitamin D is pivotal in maintaining calcium-phosphorus metabolic homeostasis and bone health. However, fluctuations in its intake, whether excessive or insufficient, May potentially increase the risk of kidney stones. Vitamin D exerts its influence on kidney stone formation indirectly by increasing the efficiency of intestinal calcium absorption and regulating renal calcium excretion. Moreover, there is a robust correlation between various states of vitamin D, particularly its active form, 1,25-dihydroxyvitamin D, and the development of numerous kidney stones. This finding underscores the necessity of individualized medical treatment in vitamin D supplementation and kidney stone prevention. When developing treatment strategies, it is essential to consider the patient's genetic background, lifestyle, environmental factors, and overall health. To prevent the formation of kidney stones, it is recommended that patients adopt a comprehensive approach, which May include measures such as moderate sun exposure, dietary modification, moderate exercise, and weight management. These preventive measures are designed to maintain healthy calcium and phosphorus metabolism and reduce kidney stone formation risk. Future studies should aim to elucidate the detailed mechanisms of vitamin D metabolism, individual differences, and the role of genes in this process. Furthermore, the role of lifestyle interventions in preventing kidney stones requires greater attention. Moreover, the implementation of large-scale, long-term prospective studies and randomized controlled trials will facilitate the assessment of the actual effects of diverse vitamin D supplementation strategies, thereby providing a robust scientific foundation for advancing more precise prevention strategies and clinical guidelines.

Blood Calcium, Genetic Risk, and Risk of Incident Kidney Stone: A Population-Based Cohort Study

OBJECTIVE

To investigate the association between blood calcium concentration and incident kidney stone as well as to assess the role played by genetic susceptibility.

METHODS

We performed a population-based cohort study based on participants from the UK Biobank. A multivariable Cox proportional hazards regression model was used to estimate hazard ratios (HRs) and 95% CIs of incident kidney stone for blood calcium level and polygenic risk score (PRS). In addition, the potential interaction was explored. The study was conducted from January 28, 2023, through June 4, 2023.

RESULTS

During the follow-up of 423,301 participants with a total of 5,490,332 person-years (median follow-up of 13.4 years), 4502 cases of kidney stone were recorded. Compared with the low blood calcium concentration group (first tertile), individuals in the high (third tertile) and moderate (second tertile) concentration groups had higher risks of kidney stone with HRs of 1.24 (95% CI, 1.15 to 1.33) and 1.11 (1.04 to 1.20), respectively. The PRS for kidney stone contained 40 independent single-nucleotide polymorphisms and was used to assign individuals to 3 groups according to the quintile. Participants with high (Q5) and moderate (Q2 to Q4) genetic risks had increased risks of kidney stone compared with low (Q1) genetic risk with HRs of 1.70 (1.53 to 1.89) and 1.31 (1.20 to 1.44), respectively. There was a joint cumulative risk of incident kidney stone between blood calcium concentration and genetic susceptibility.

CONCLUSIONS

Blood calcium concentration and PRS are significantly associated with incident kidney stone risk. Excessive blood calcium concentration might bring additional stone risk in populations at high genetic risk. A nonlinear correlation between blood calcium concentration and kidney stone risk was indicated.

Predictors of Recurrent Urolithiasis in Iran: Findings from a Nationwide Study

BACKGROUND

Prevention of urinary stone recurrence is the ultimate goal in urolithiasis patients. In this study, we aimed to investigate the national prevalence rate and possible determinants of increased urolithiasis recurrence risk in a nationwide study in Iran.

METHODS

All data regarding stone occurrence and recurrence episodes were extracted from the cross-sectional Iran National Stone Survey (INSS) study, and the possible determinants of recurrence were evaluated in the subset of 2913 patients who had a positive history of at least one episode of urolithiasis.

RESULTS

The national prevalence rate of recurrent urolithiasis was 2.6% (95% CI: 2.5, 2.8) in Iran. Moreover, the relative ratio of recurrent stone formers to all stone formers was 39.8% (95% CI: 38.0, 41.6). Our univariable truncated negative binomial regressions suggested that a positive history of urolithiasis in the patient's father (prevalence ratio [PR] [95% CI]=1.83 [1.39, 2.41], P<0.001), mother (PR [95% CI]=1.92 [1.39, 2.66], P<0.001) or brother (PR [95% CI]=1.32 [1.03, 1.69], P=0.026); and residence in urban areas (PR [95% CI]=1.27 [1.04, 1.55], P=0.016) were significant predictors of repetitive recurrence episodes. However, when incorporated into a multivariable truncated negative binomial regression model, the only significant predictors of more frequent recurrence episodes were a positive history in father (PR [95% CI]=1.66 [1.24, 2.22], P<0.001) and mother (PR [95% CI]=1.68 [1.20, 2.36], P=0.002); and urban residence (PR [95% CI]=1.24 [1.01, 1.51], P=0.031).

CONCLUSION

Our results indicate that a positive family history of urolithiasis in mother and father and residence in urban areas are the significant predictors of recurrence risk in urolithiasis patients in Iran.

Evaluation of genetic associations with clinical phenotypes of kidney stone disease

Introduction and Objective

We sought to replicate and discover genetic associations of kidney stone disease within a large-scale electronic health record (EHR) system.

Methods

We performed genome-wide association studies (GWASs) for nephrolithiasis from genotyped samples of 5,571 cases and 83,692 controls. Among the significant risk variants, we performed association analyses of stone composition and first-time 24-hour urine parameters. To assess disease severity, we investigated the associations of risk variants with age at first stone diagnosis, age at first procedure, and time from first to second procedure.

Results

The main GWAS analysis identified 10 significant loci, each located on chromosome 16 within coding regions of the UMOD gene, which codes for uromodulin, a urine protein with inhibitory activity for calcium crystallization. The strongest signal was from SNP 16:20359633-C-T (odds ratio [OR] 1.17, 95% CI 1.11-1.23), with the remaining significant SNPs having similar effect sizes. In subgroup GWASs by stone composition, 19 significant loci were identified, of which two loci were located in coding regions (brushite; NXPH1 , rs79970906 and rs4725104). The UMOD SNP 16:20359633-C-T was associated with differences in 24-hour excretion of urinary calcium, uric acid, phosphorus, sulfate; and the minor allele was positively associated with calcium oxalate dihydrate stone composition (p<0.05). No associations were found between UMOD variants and disease severity.

Conclusions

We replicated germline variants associated with kidney stone disease risk at UMOD and reported novel variants associated with stone composition. Genetic variants of UMOD are associated with differences in 24-hour urine parameters and stone composition, but not disease severity.

Genes polymorphism as risk factor of recurrent urolithiasis: a systematic review and meta-analysis

INTRODUCTION

Urolithiasis is one of the most prevalent diseases worldwide. Its prevalence is rising, both in developing and developed countries. It is known that genetic factors play big roles in the development of urolithiasis. One of the suspected factors is gene polymorphism. This study aims to find an accurate estimate of the association between genetic polymorphism and the risk of recurrent urolithiasis.

METHODS

A systematic review and meta-analysis were performed on 12 studies from 3 databases that investigated gene polymorphism as an risk factor of urolithiasis. The review was done using Review Manager® version 5.3.

RESULTS

Insignificant heterogenicity was found in this study. Populations from Asia and the Middle East are more likely to experience recurrent urolithiasis. Additionally, variation in the VDR and urokinase genes, particularly in the Asian population, increases the risk of developing recurrent urolithiasis.

CONCLUSIONS

Gene polymorphisms have significant roles in the development of urolithiasis, especially in the Middle Eastern region.

Mendelian randomization analysis reveals fresh fruit intake as a protective factor for urolithiasis

OBJECTIVE

Previous studies have proposed that food intakes are associated with the risk of urolithiasis. Here, we conducted a two-sample Mendelian randomization (MR) study to evaluate the causal effects of different food intakes on urolithiasis.

METHODS

Independent genetic variants associated with different food intakes at a genome-wide significant level were selected from summary-level statistics of genome-wide association studies from the UK Biobank. The association of these instrumental variables with urolithiasis was studied in a cohort from FinnGen Consortium.

RESULTS

Among the 15 studied food intake exposures, tea intake (odds ratio [OR] = 0.433, 95% confidence interval [CI] = 0.281-0.667, p value = 1.470 × 10-4) and fresh fruit intake (OR = 0.358, 95% CI = 0.185-0.694, p value = 0.002) were found to significantly reduce the risk of the calculus of kidney and ureter. The association remained consistent in the sensitivity analyses. After adjusting for the effects of vitamin D and vitamin C, fresh fruit intake remained the reverse causal association with the calculus of kidney and ureter.

CONCLUSIONS

Genetically proxied fresh fruit intake is causally associated with a reduced risk of the calculus of kidney and ureter.

Dietary supplements and medicinal plants in urolithiasis: diet, prevention, and cure

BACKGROUND

Urolithiasis has been a major health concern for centuries, primarily owing to the limited treatment options in the physician's armamentarium. However, various studies have underscored a lesser incidence of urolithiasis in cohorts predominantly consuming fruits and vegetables. This article aims to review various dietary plants, medicinal herbs and phytochemicals in the prevention and management of urolithiasis.

METHODS

To provide context and evidence, relevant publications were identified on Google Scholar, PubMed and Science-Direct using keywords such as urolithiasis, nephrolithiasis, urolithiasis, renal stones, phytochemicals and dietary plants.

RESULTS

Growing bodies of evidence suggest the incorporation of plant-based foods, medicinal and herbal supplements, and crude drugs containing phytochemicals into the staple diet of people. The anti-urolithiatic activity of these plant bioactives can be attributed to their antioxidant, antispasmodic, diuretic, and inhibitory effect on the crystallization, nucleation and crystal aggregation effects. These mechanisms would help alleviate the events and symptoms that aid in the development and progression of renal calculi. In addition, it will also avoid the exacerbation of secondary disorders like inflammation and injury, which can initiate a vicious circle in turn worsening the disease progression.

CONCLUSION

In conclusion, the results presented in the review demonstrate the promising role of various dietary plants, medicinal and herbal supplements, and phytochemicals in preventing and managing the precipitation of uroliths. However, more conclusive and cogent evidence from preclinical and clinical studies is required to substantiate their safety, efficacy and toxicity profiles in humans.

Past, present and future of genomics for kidney stone disease

PURPOSE OF REVIEW

To summarize the latest findings and developments in genomics for kidney stone disease (KSD) that help to understand hereditary pathomechanisms, identify high risk stone formers, provide early treatment and prevent recurrent kidney stone formation.

RECENT FINDINGS

Several gene loci associated to KSD have presently been discovered in large Genome-wide association studies. Monogenic causes are rare, but are thought to have higher penetrance, while polygenic causes are more frequent with less penetrance. Although there is a great effort identifying genetic causes of KSD, targeted therapies are scarce.

SUMMARY

There have been great advancements in genetic research in identifying genetic variants associated with KSD. Identifying these variants and understanding the underlying pathophysiology will not only provide individual risk assessment but open the way for new treatment targets and preventive care strategies.

Comparison of paravertebral block vs. general anesthesia for percutaneous nephrolithotomy: A retrospective study

Background

General anesthesia is used in the majority of patients undergoing percutaneous nephrolithotomy. To reduce the general anesthesia-related risks and complications, this study evaluated the efficacy and safety of the paravertebral block as a novel and alternative anesthetic method for percutaneous nephrolithotomy.

Methods

This was a retrospective study. A total of 198 patients under percutaneous nephrolithotomy were included. Among them, 76 patients received paravertebral block and 122 received general anesthesia. Patients' characteristics, surgical outcomes, anesthetic outcomes, and perioperative complications and the visual analog scale (VAS) were recorded to evaluate the efficacy and safety of paravertebral block compared with general anesthesia. Intergroup differences of the parameters were analyzed using an independent t-test and χ²-tests appropriate.

Results

Seventy-six patients who underwent paravertebral block completed the surgery successfully, three patients were supplemented with propofol for discomfort during ureteroscopy, and two patients were supplemented with remifentanil for incomplete nerve blockade. Patients who underwent paravertebral block had a higher American Society of Anesthesiologists grade and heart function grade, including patients with contraindications to general anesthesia. Intraoperative and postoperative adverse events and the anesthesia costs were less in patients who underwent paravertebral block. VAS pain scores during the postoperative period in patients who underwent paravertebral block were lower than those in patients who underwent general anesthesia without the use of patient-controlled intravenous analgesia.

Conclusion

In this retrospective study, paravertebral block was found to be effective and safe in providing intraoperative anesthesia for percutaneous nephrolithotomy, and had less adverse events and anesthesia costs. Paravertebral block is an attractive alternative anesthesia for patients at increased risk of comorbidities following general or neuraxial anesthesia.

Use of whole-exome sequencing to identify novel monogenic gene mutations and genotype-phenotype correlations in Chinese Han children with urolithiasis

The incidence of urolithiasis (UL) in children has been increasing. Although the pathogenesis of pediatric UL is controversial and remains unclear, multiple monogenic causes of UL have been identified. We aim to investigate the prevalence of inherited UL causes and explore the genotype-phenotype correlation in a Chinese pediatric group. In this study, we analyzed the DNA of 82 pediatric UL patients using exome sequencing (ES). The data of metabolic evaluation and genomic sequencing were subsequently analyzed together. We detected 54 genetic mutations in 12 of 30 UL-related genes. A total of 15 detected variants were described as pathogenic mutations, and 12 mutations were considered likely pathogenic. Molecular diagnoses were made in 21 patients with pathogenic or likely pathogenic variants. Six novel mutations that were not previously reported were identified in this cohort. Calcium oxalate stones were detected in 88.9% cases (8/9) with hyperoxaluria-related mutations, while 80% of individuals (4/5) with cystinuria-causing defects were diagnosed with cystine stones. Our study highlights the significant genetic abnormalities in pediatric UL and demonstrates the diagnostic power of ES for screening patients with UL.

Association of TRPV5, CASR, and CALCR genetic variants with kidney stone disease susceptibility in Egyptians through main effects and gene–gene interactions

Kidney stone disease (KSD) represents an urgent medical problem because of increasing its prevalence. Several functional polymorphisms in genes involved in the renal handling of calcium were associated with KSD pathogenesis. Among those, the rs4236480 of transient receptor potential vanilloid member 5 (TRPV5) gene, the rs1801725 of calcium-sensing receptor (CASR) gene, and the rs1801197 of calcitonin receptor (CALCR) gene appear to be of great importance. Due to the scarce data on the Egyptians, this study aimed to evaluate the association of these candidate genetic variants with the risk of developing KSD in an Egyptian population. To do so, the biochemical parameters were measured along with the genotyping of the three polymorphisms using allelic discrimination assay in 134 KSD patients and 86 age and sex-matched healthy subjects. The results showed that the genotypic distributions and allelic frequencies of the studied variants were significantly different between cases and controls. The three polymorphisms increased the risk of KSD significantly under all the tested genetic models (OR ranges from 2.152 to 5.994), except for the recessive model of the CALCR rs1801197 polymorphism after Bonferroni correction. The gene–gene interaction analyzed by multifactor dimensionality reduction selected the three-locus combination as the best model associated with the susceptibility to KSD with OR 9.706. Further, synergistic interactions were identified between TRPV5 rs4236480 and CALCR rs1801197 variants and CASR rs1801725 and CALCR rs1801197 variants. In conclusion, the TRPV5 rs4236480, CASR rs1801725, and CALCR rs1801197 polymorphisms showed a significant association with the risk of KSD in the Egyptian population. Furthermore, their complex interactions might have an impact on the genetic susceptibility to develop KSD.

Stone disease in low-middle income countries. Could augmented reality have a role in its management?

Urolithiasis is a global phenomenon. Cystolithiasis is common in parts of Africa due to low protein intake and dehydration from endemic diarrhoeal illnesses. Nephrolithiasis is less prevalent than in high income countries, probably due to a variety of lifestyle issues, such as a more elemental diet, higher physical activity and less obesity. Although renal stones are less common in low-middle income countries (LMICs), the social and economic impacts of nephrolithiasis are still considerable; many stones present late or with complications such as upper urinary tract obstruction or urosepsis. These may lead to the development of chronic kidney disease, or end-stage renal failure in a small proportion of cases, conditions for which there is very poor provision in most LMICs. Early treatment of nephrolithiasis by the least invasive method possible can, however, reduce the functional consequences of urinary stone disease. Although ESWL is uncommon, and endoscopic interventions for stone are not widespread in most of Africa, percutaneous nephrolithomy and ureteroscopic renal surgery are viable techniques in those regional centres with infrastructure to support them. Longitudinal mentoring has been shown to be a key step in the adoption of these minimally invasive procedures by local surgeons, something that has been difficult during the COVID-19 pandemic due to travel restriction. Augmented reality (AR) technology is an alternative means of providing remote mentoring, something that has been trialled by Urolink, the MediTech Trust and other global non-governmental organisations during this period. Our preliminary experience suggests that this is a viable technique for promulgating skills in LMICs where appropriate connectivity exists to support remote communication. AR may also have long term promise for decreasing the reliance upon short-term surgical visits to consolidate competence, thereby reducing the carbon footprint of global surgical education.

Genetic Polymorphisms and Kidney Stones Around the Globe: A Systematic Review and Meta-Analysis

Objective: This study explores associations between recurrent kidney stones and genetic polymorphisms.

Methods: Meta-analysis of polymorphisms in renal stone cases versus control groups. Four electronic databases (PubMed, SCOPUS, EMBASE, and Web of Science) were searched up to 30 May 2021, using the keywords: “kidney stone” or “kidney calculi,” or “urolithiasis” or “nephrolithiasis” or “urinary calculi” and “genome” or “genetic” or “mutation” or “single nucleotide polymorphism.” Forrest plots, ORs, 95% CI, Chi-square (χ2)-test, and index of heterogeneity (I2) were calculated. Only studies with Newcastle–Ottawa scale (NOS) ≥ 6 were included for quality control, and Funnel, Begg’s, and Eager’s plots assessed publication bias. PROSPERO: CRD42022250427.

Results: Among 7,671 searched articles, 72 were included. Polymorphisms in VDR (OR: 1.20; 95% CI: 1.06–1.36), CASR (OR = 1.24; 95% CI: 1.01–1.52), Osteopontin (OR = 1.38; 95% CI: 1.09–1.74), and Urokinase genes (OR = 1.52; 95% CI: 1.02–2.28) showed a significant association with risk of urinary stone formation, while Klotho gene showed a protective effect (OR = 0.75; 95% CI: 0.57–0.99). The VDR gene polymorphism was frequent in Asians, whereas CASR polymorphism was frequent in European and North American populations.

Conclusion: Multifactorial nature of the stone formation, emphasizing the role of environmental factors, might explain contradictory results in the literature. While polymorphisms in VDR, CASR, Osteopontin, and Urokinase genes were associated with urinary stone formation, the Klotho gene showed a protective effect.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

Extended genetic analysis of exome sequencing for primary hyperoxaluria in pediatric urolithiasis patients with hyperoxaluria

PURPOSE

Next generation sequencing-based exome sequencing can be used to identify genetic abnormalities in patients believed to be suffering from primary hyperoxaluria. We outline our efforts to improve the diagnostic capacity of exome sequencing for these patients.

METHODS

We conducted a retrospective analysis of exome sequencing data from 77 pediatric urolithiasis patients with hyperoxaluria of unknown origin. Canonical exome sequencing analysis was performed to identify pathogenic variants in three known primary hyperoxaluria-related genes (AGXT, GRHPR, HOGA1) as per the guidelines of the American College of Medical Genetics. Then, extended exome sequencing analyses of 5'-untranslated region, non-canonical splicing site and copy number variant were performed on patients with negative diagnostic results in these three genes.

RESULTS

Canonical exome sequencing analyses led to the diagnosis of primary hyperoxaluria in 20/77 (26%) patients, including eight, four, and eight patients diagnosed with type 1, 2 and 3 primary hyperoxaluria, respectively. Non-canonical splicing site analyses discovered a pathogenic variant in the HOGA1 gene, which led to the diagnosis of six additional patients with type 3 primary hyperoxaluria, while copy number variant analyses from exome sequencing data identified a 1.8 kb copy number loss that impacted the AGXT gene, resulting in the diagnosis of an additional type 1 primary hyperoxaluria case.

CONCLUSIONS

Extended non-canonical splicing site and copy number variant analyses improve the diagnostic yield of canonical exome sequencing analysis for primary hyperoxaluria from 26% (20/77) to 35% (27/77) in 77 pediatric urolithiasis patients with hyperoxaluria.

Primary Hyperoxaluria Type 3 Can Also Result in Kidney Failure: A Case Report

Primary hyperoxaluria (PH) is a group of genetic disorders that result in an increased hepatic production of oxalate. PH type 3 (PH3) is the most recently identified subtype and results from mutations in the mitochondrial 4-hydroxy-2-oxoglutarate aldolase gene (HOGA1). To date, there have been 2 cases of kidney failure reported in PH3 patients. We present a case of a young man with a history of recurrent urinary tract infections and voiding dysfunction who developed kidney failure at 33 years of age. He developed a bladder stone and bilateral staghorn calculi at 12 years of age. Initial metabolic evaluation revealed hyperoxaluria with very low urinary citrate excretion on multiple measurements for which he was placed on oral citrate supplements. Further investigation of the hyperoxaluria was not completed as the patient was lost to follow-up observation until he presented at 29 years of age with chronic kidney disease stage 4 (estimated glomerular filtration rate 24mL/min/1.73m²). Hemodialysis 3 times a week was started at 33 years of age, and subsequent genetic testing revealed a homozygous HOGA1 mutation (C.973G>A p.Gly325Ser) diagnostic of PH3. The patient is currently being evaluated for all treatment options including possible liver/kidney transplantation. All cases of a childhood history of recurrent urinary stone disease with marked hyperoxaluria should prompt genetic testing for the 3 known PH types. Hyperhydration and crystallization inhibitors (citrate) are standard of care, but the role of RNA interference agents for all 3 forms of PH is also under active study.

Calcium and Vitamin D Supplementation and Their Association with Kidney Stone Disease: A Narrative Review

Kidney stone disease is a multifactorial condition influenced by both genetic predisposition and environmental factors such as lifestyle and dietary habits. Although different monogenic polymorphisms have been proposed as playing a causal role for calcium nephrolithiasis, the prevalence of these mutations in the general population and their complete pathogenetic pathway is yet to be determined. General dietary advice for kidney stone formers includes elevated fluid intake, dietary restriction of sodium and animal proteins, avoidance of a low calcium diet, maintenance of a normal body mass index, and elevated intake of vegetables and fibers. Thus, balanced calcium consumption protects against the risk for kidney stones by reducing intestinal oxalate availability and its urinary excretion. However, calcium supplementation given between meals might increase urinary calcium excretion without the beneficial effect on oxalate. In kidney stone formers, circulating active vitamin D has been found to be increased, whereas higher plasma 25-hydroxycholecalciferol seems to be present only in hypercalciuric patients. The association between nutritional vitamin D supplements and the risk for stone formation is currently not completely understood. However, taken together, available evidence might suggest that vitamin D administration worsens the risk for stone formation in patients predisposed to hypercalciuria. In this review, we analyzed and discussed available literature on the effect of calcium and vitamin D supplementation on the risk for kidney stone formation.

Klotho gene polymorphism in renal stone formers from Northwestern India

Klotho gene is an important gene involved in calcium homeostasis, and polymorphisms of this gene may render the individual prone to renal stone formation. We evaluated G395A single nucleotide polymorphisms (SNPs) of Klotho gene at rs1207568 in renal stone patients of North India. This was a prospective study involving 150 patients of renal stone disease (aged 15-60 years) and 100 age- and sex-matched controls. The DNA was isolated and subjected to polymerase chain reaction (PCR) for identifying the G395A Klotho SNPs at rs1207568. Confronting two pair primers were used, and gel electrophoresis showing two bands at 175,252 bp was considered as GG genotype, three bands at 121,175 and 252 bp as GA and two bands at 121 and 252 bp as AA genotype. The association between genotype and cases was evaluated by using Chi-square test and logistic regression analysis. Cases and controls were well matched for age (40.65 vs 42.06, p = 0.063) and sex (p = 0.420). Significantly high proportion of patients with renal stones had GG genotype as compared to controls (odds ratio (OR) 2.37(1.39,4.03), p = 0.001). None of the participants (cases and controls) had homozygous recessive AA genotype. The risk of stone formation was significantly higher in the population carrying G allele {OR 1.94 (1.225-3.073), p 0.004}. Mean serum calcium was higher in stone formers with GG genotype as compared to those with GA genotype (9.16 mg/dl vs 8.91 mg/dl; p = 0.06). GG genotype of G396A Klotho gene SNPs is associated with renal stone formation. The G allele carrier is twice at risk of renal stone formation. The absence of AA genotype in north-western Indian population remains a curiosity.

Derivation and validation of genome-wide polygenic score for urinary tract stone diagnosis

Urinary tract stones have high heritability indicating a strong genetic component. However, genome-wide association studies (GWAS) have uncovered only a few genome wide significant single nucleotide polymorphisms (SNPs). Polygenic risk scores (PRS) sum cumulative effect of many SNPs and shed light on underlying genetic architecture. Using GWAS summary statistics from 361,141 participants in the United Kingdom Biobank, we generated a PRS and determined association with stone diagnosis in 28,877 participants in the Mount Sinai BioMe Biobank. In BioMe (1,071 cases and 27,806 controls), for every standard deviation increase, we observed a significant increment in adjusted odds ratio of a factor of 1.2 (95% confidence interval 1.13-1.26). In comparison, a risk score comprised of GWAS significant SNPs was not significantly associated with diagnosis. After stratifying individuals into low and high-risk categories on clinical risk factors, there was a significant increment in adjusted odds ratio of 1.3 (1.12-1.6) in the low- and 1.2 (1.1-1.2) in the high-risk group for every standard deviation increment in PRS. In a 14,348-participant validation cohort (Penn Medicine Biobank), every standard deviation increment was associated with a significant adjusted odds ratio of 1.1 (1.03 - 1.2). Thus, a genome-wide PRS is associated with urinary tract stones overall and in the absence of known clinical risk factors and illustrates their complex polygenic architecture.

Genetic polymorphisms in CLDN14 (rs219780) and ALP (rs1256328) genes are associated with risk of nephrolithiasis in Egyptian children

OBJECTIVE

Nephrolithiasis results from metabolic and anatomic abnormalities together with genetic factors. Claudin 14 (CLDN14) is a protein that regulates the passage of small solutes through the kidneys. Alkaline phosphatase (ALPL) hydrolyzes the pyrophosphate to free phosphate, proposing its enabling role in nephrolithiasis development. Solute carrier family 13 member 2 (SLC13A2) encodes Na+-Pi cotransporter 2a, which is responsible for the renal absorption of phosphate. We aimed to detect the association between CLDN14, ALPL, and SLC13A2 genetic variants and susceptibility to nephrolithiasis in the Egyptian pediatric population.

MATERIAL AND METHODS

We enrolled 204 consecutive pediatric patients with nephrolithiasis, and 126 normal individuals served as controls. Real-time polymerase chain reaction analysis of CLDN14 rs219780, ALPL rs1256328, and SLC34A1 rs11746443 single-nucleotide polymorphisms (SNPs) was performed.

RESULTS

We found that individuals carrying the T allele of CLDN14 rs219780 and ALPL rs1256328 SNPs had a significantly higher risk of nephrolithiasis than the controls (p=0.001 and 0.001, respectively). Genetic association analyses identified that CLDN14 rs219780 and ALPL rs1256328SNPs were significantly associated with the nephrolithiasis status (odds ratio [OR] =4.51; 95% confidence interval [CI]=2.758-7.374; p=0.001 and OR=6.088; 95% CI=3.651-10.152; p=0.001, respectively). The sequence variant ALPL rs1256328 T allele had a significant correlation with the increased serum alkaline phosphatase levels in children with nephrolithiasis (p=0.02). No significant association was found between SLC34A1 rs11746443 SNP and the risk of nephrolithiasis (p=0.5).

CONCLUSION

CLDN14 rs219780 and ALPL rs1256328 SNPs might raise the risk of nephrolithiasis in Egyptian children, and might be used as genetic markers in these patients.

Design of drug-like hepsin inhibitors against prostate cancer and kidney stones

Hepsin, a transmembrane serine protease abundant in renal endothelial cells, is a promising therapeutic target against several cancers, particularly prostate cancer. It is involved in the release and polymerization of uromodulin in the urine, which plays a role in kidney stone formation. In this work, we design new potential hepsin inhibitors for high activity, improved specificity towards hepsin, and promising ADMET properties. The ligands were developed in silico through a novel hierarchical pipeline. This pipeline explicitly accounts for off-target binding to the related serine proteases matriptase and HGFA (human hepatocyte growth factor activator). We completed the pipeline incorporating ADMET properties of the candidate inhibitors into custom multi-objective optimization functions. The ligands designed show excellent prospects for targeting hepsin via the blood stream and the urine and thus enable key experimental studies. The computational pipeline proposed is remarkably cost-efficient and can be easily adapted for designing inhibitors against new drug targets.

Phosphate Transport in Epithelial and Nonepithelial Tissue

Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.

High-phytate/low-calcium diet is a risk factor for crystal nephropathies, renal phosphate wasting, and bone loss

Phosphate overload contributes to mineral bone disorders that are associated with crystal nephropathies. Phytate, the major form of phosphorus in plant seeds, is known as an indigestible and of negligible nutritional value in humans. However, the mechanism and adverse effects of high-phytate intake on Ca²⁺ and phosphate absorption and homeostasis are unknown. Here, we show that excessive intake of phytate along with a low-Ca²⁺ diet fed to rats contributed to the development of crystal nephropathies, renal phosphate wasting, and bone loss through tubular dysfunction secondary to dysregulation of intestinal calcium and phosphate absorption. Moreover, Ca²⁺ supplementation alleviated the detrimental effects of excess dietary phytate on bone and kidney through excretion of undigested Ca²⁺-phytate, which prevented a vicious cycle of intestinal phosphate overload and renal phosphate wasting while improving intestinal Ca²⁺ bioavailability. Thus, we demonstrate that phytate is digestible without a high-Ca²⁺ diet and is a risk factor for phosphate overloading and for the development of crystal nephropathies and bone disease.

Risk of Kidney Stones: Influence of Dietary Factors, Dietary Patterns, and Vegetarian-Vegan Diets

Nephrolithiasis is a common medical condition influenced by multiple environmental factors, including diet. Since nutritional habits play a relevant role in the genesis and recurrence of kidney stones disease, dietary manipulation has become a fundamental tool for the medical management of nephrolithiasis. Dietary advice aims to reduce the majority of lithogenic risk factors, reducing the supersaturation of urine, mainly for calcium oxalate, calcium phosphate, and uric acid. For this purpose, current guidelines recommend increasing fluid intake, maintaining a balanced calcium intake, reducing dietary intake of sodium and animal proteins, and increasing intake of fruits and fibers. In this review, we analyzed the effects of each dietary factor on nephrolithiasis incidence and recurrence rate. Available scientific evidence agrees on the harmful effects of high meat/animal protein intake and low calcium diets, whereas high content of fruits and vegetables associated with a balanced intake of low-fat dairy products carries the lowest risk for incident kidney stones. Furthermore, a balanced vegetarian diet with dairy products seems to be the most protective diet for kidney stone patients. Since no study prospectively examined the effects of vegan diets on nephrolithiasis risk factors, more scientific work should be made to define the best diet for different kidney stone phenotypes.

The rs1256328 (ALPL) and rs12654812 (RGS14) Polymorphisms are Associated with Susceptibility to Calcium Nephrolithiasis in a Taiwanese population

Nephrolithiasis is a common disease affecting almost all populations, with an increasing prevalence over the past decades. Previous studies revealed several functional polymorphisms associated with the pathogenesis of nephrolithiasis. However, data on Asian populations are limited. In this study, three candidate polymorphisms were selected from previous studies to investigate the correlations with nephrolithiasis in a Taiwanese population. In total, 454 nephrolithiasis patients were recruited from Kaohsiung Medical University Hospital, with SNP frequency for 1513 subjects of general population from the Taiwan Biobank (TWB) as a genotypic reference. Results revealed that subjects with minor TT genotype at rs1256328 (alkaline phosphatase, liver/bone/kidney (ALPL)) have higher susceptibility to nephrolithiasis (odds ratio (OR) = 2.03, p = 0.0013). In addition, subjects carrying the minor AA genotype at rs12654812 (regulator of G protein signaling 14 (RGS14)) have higher susceptibility to nephrolithiasis (OR = 1.91, p = 0.0017). Among nephrolithiasis patients, subjects with GG at rs7627468 (calcium-sensing receptor (CASR)) have lower pH level in urine (p = 0.0088). Importantly, rs7627468 is associated with the expressions of IQCB1 and EAF2. rs12654812 could influence the expression of RGS14 itself, MXD3, and FGFR4. In summary, this study successfully validated the genetic roles of rs1256328 and rs12654812 in human nephrolithiasis.

Diagnostic Accuracy of Doppler Twinkling Artifact for Identifying Urinary Tract Calculi

Introduction

Flank pain is a frequent cause of emergency department visits and is often due to renal or ureteric colic. Ultrasound is often the initial imaging study used for the detection of urinary tract calculi. Twinkling artifact is a Doppler artifact usually seen on echogenic rough surfaces such as calculi. Its presence can improve the sensitivity and specificity of ultrasound in stone detection. The objective of the current study was to determine the diagnostic accuracy of the Doppler twinkling artifact for detecting urinary calculi using non-contrast computed tomography as the gold standard.

Materials and methods

In this cross-sectional study, both male and female patients of any age having flank pain, burning micturition with or without hematuria were included. Ultrasound was performed and the presence or absence of Doppler twinkling artifact on calculus was noted. Following ultrasound, patients underwent plain CT scan and findings of stones were documented. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of Doppler twinkling artifact was calculated considering CT findings as the gold standard.

Results

Out of the total 221 patients, 146 (66.1%) were males and 75 (33.9%) were females. The mean age of the patients was 45.98 ± 16.30 years. Urinary tract calculi on ultrasound were observed in 74 (33.50%) patients, while on CT urinary tract calculi were observed in 127 (57.50%) patients. Diagnostic accuracy of Doppler twinkling artifact was found to be 71.49% with sensitivity, specificity, positive predictive value, and negative predictive value of 54.33%, 94.68%, 93.24%, and 60.54%, respectively.

Conclusion

Doppler twinkling artifact has low sensitivity, high specificity, and suboptimal diagnostic accuracy for the diagnosis of urinary tract calculi. Integration of this artifact has a lower sensitivity as compared to non-contrast CT scan. Multicentric studies with larger sample size and focusing on interobserver and intraobserver variability are recommended to have a consensus regarding Doppler twinkling artifact in the evaluation of renal and ureteric calculi.

Chlorthalidone Is Superior to Potassium Citrate in Reducing Calcium Phosphate Stones and Increasing Bone Quality in Hypercalciuric Stone-Forming Rats

BACKGROUND

The pathophysiology of genetic hypercalciuric stone-forming rats parallels that of human idiopathic hypercalciuria. In this model, all animals form calcium phosphate stones. We previously found that chlorthalidone, but not potassium citrate, decreased stone formation in these rats.

METHODS

To test whether chlorthalidone and potassium citrate combined would reduce calcium phosphate stone formation more than either medication alone, four groups of rats were fed a fixed amount of a normal calcium and phosphorus diet, supplemented with potassium chloride (as control), potassium citrate, chlorthalidone (with potassium chloride to equalize potassium intake), or potassium citrate plus chlorthalidone. We measured urine every 6 weeks and assessed stone formation and bone quality at 18 weeks.

RESULTS

Potassium citrate reduced urine calcium compared with controls, chlorthalidone reduced it further, and potassium citrate plus chlorthalidone reduced it even more. Chlorthalidone increased urine citrate and potassium citrate increased it even more; the combination did not increase it further. Potassium citrate, alone or with chlorthalidone, increased urine calcium phosphate supersaturation, but chlorthalidone did not. All control rats formed stones. Potassium citrate did not alter stone formation. No stones formed with chlorthalidone, and rats given potassium citrate plus chlorthalidone had some stones but fewer than controls. Rats given chlorthalidone with or without potassium citrate had higher bone mineral density and better mechanical properties than controls, whereas those given potassium citrate did not.

CONCLUSIONS

In genetic hypercalciuric stone-forming rats, chlorthalidone is superior to potassium citrate alone or combined with chlorthalidone in reducing calcium phosphate stone formation and improving bone quality.

Renal phosphate handling and inherited disorders of phosphate reabsorption: an update

Renal phosphate handling critically determines plasma phosphate and whole body phosphate levels. Filtered phosphate is mostly reabsorbed by Na⁺-dependent phosphate transporters located in the brush border membrane of the proximal tubule: NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Here we review new evidence for the role and relevance of these transporters in inherited disorders of renal phosphate handling. The importance of NaPi-IIa and NaPi-IIc for renal phosphate reabsorption and mineral homeostasis has been highlighted by the identification of mutations in these transporters in a subset of patients with infantile idiopathic hypercalcemia and patients with hereditary hypophosphatemic rickets with hypercalciuria. Both diseases are characterized by disturbed calcium homeostasis secondary to elevated 1,25-(OH)₂ vitamin D₃ as a consequence of hypophosphatemia. In vitro analysis of mutated NaPi-IIa or NaPi-IIc transporters suggests defective trafficking underlying disease in most cases. Monoallelic pathogenic mutations in both SLC34A1 and SLC34A3 appear to be very frequent in the general population and have been associated with kidney stones. Consistent with these findings, results from genome-wide association studies indicate that variants in SLC34A1 are associated with a higher risk to develop kidney stones and chronic kidney disease, but underlying mechanisms have not been addressed to date.

Low Sodium Diet Decreases Stone Formation in Genetic Hypercalciuric Stone-Forming Rats

BACKGROUND

Urine (u) calcium (Ca) excretion is directly dependent on dietary sodium (Na) intake leading to the recommendation for Na restriction in hypercalciuric kidney stone formers. However, there is no direct evidence that limiting Na intake will reduce recurrent stone formation.

MATERIALS AND METHODS

We used genetic hypercalciuric stone-forming (GHS) rats, which universally form Ca phosphate (P) kidney stones, fed either a low Na (LNa, 0.05%) or normal Na (NNa, 0.4%) Na diet (D) for 18 weeks. Urine was collected at 6-week intervals. Radiographic analysis for stone formation and bone analyses were done at the conclusion of the study.

RESULTS

Mean uCa was lower with LNaD than NNaD as was uP and LNaD decreased mean uNa and uChloride. There were no differences in urine supersaturation (SS) with respect to calcium phosphate (CaP) or Ca oxalate (CaOx). However, stone formation was markedly decreased with LNaD by radiographic analysis. The LNaD group had significantly lower femoral anterior-posterior diameter and volumetric bone mineral density (vBMD), but no change in vertebral trabecular vBMD. There were no differences in the bone formation rate or osteoclastic bone resorption between groups. The LNaD group had significantly lower femoral stiffness; however, the ultimate load and energy to fail was not different.

CONCLUSION

Thus, a low Na diet reduced uCa and stone formation in GHS rats, even though SS with respect to CaP and CaOx was unchanged and effects on bone were modest. These data, if confirmed in humans, support dietary Na restriction to prevent recurrent Ca nephrolithiasis.

Sonographic Evaluation of Urolithiasis Formation with Positive Family History in the Population of Lahore

Background:

The purpose of the research is to know the sonographic evaluation of urolithiasis formation with positive family history in population of Lahore because urolithiasis is a major problem in Pakistan. According to a survey in 1985–1987 the incidence rate reaches to 8.3/100,000 individuals in the Punjab. In Pakistan, urolithiasis is the sixth major cause of surgery. The study was conducted to rule out the role of positive family history in people suffering from urolithiasis.

Materials and Methods:

This was an observational cross-sectional study conducted at the Radiology department of the University of Lahore teaching hospital and Gilani Ultrasound center-Afro-Asian Institute, Lahore, Pakistan. A total of 125 patients were included in the study which were diagnosed with urolithiasis and individuals with any other abnormality were excluded from the study. The duration of the study was from January 2017 to April 2017. Data were tabulated and analyzed using SPSS version 24. The data were reported using descriptive and inferential statistics. The quantitative variable like age was assessed using mean standard deviation and standard errors. The qualitative variables like gender were reported using percentages and frequencies.

Results:

Urolithiasis is commonly seen in the males (77 individuals out of 125) as compared to females (48 individuals out of 125) and mid pole of right kidney is the most common site of the renal stones deposition (13.6%), and the relationship of father is mostly seen as familial history (39.2%).

Conclusion:

It is concluded that positive family history is the major predisposing factor in urolithiasis and one of the cause in the development of stones in the urinary tract or in other words people who have a history of urolithiasis in blood relations have more tendency of stone formation in any part of their lives. Its positive aspect is that we can do a screening in blood relations, especially whose parents or family members diagnosed with stones and can do preventive measures for that. Moreover, its negative aspect is that there are several causes of the stone formation in the urinary tract.

Genetics of common complex kidney stone disease: insights from genome-wide association studies

Kidney stone disease is a common disorder in Western countries that is associated with significant suffering, morbidity, and cost for the healthcare system. Numerous studies have demonstrated familial aggregation of nephrolithiasis and a twin study estimated the heritability to be 56%. Over the past decade, genome-wide association studies have uncovered several sequence variants that confer increased risk of common complex kidney stone disease. The first reported variants were observed at the CLDN14 locus in the Icelandic population. This finding has since been replicated in other populations. The CLDN14 gene is expressed in tight junctions of the thick ascending limb of the loop of Henle, where the protein is believed to play a role in regulation of calcium transport. More recent studies have uncovered variants at the ALPL, SLC34A1, CASR, and TRPV5 loci, the first two genes playing a role in renal handling of phosphate, while the latter two are involved in calcium homeostasis. Although genetic data have provided insights into the molecular basis of kidney stone disease, much remains to be learned about the contribution of genetic factors to stone formation. Nevertheless, the progress made in recent years indicates that exciting times lie ahead in genetic research on kidney stone disease.

Common Variants in ALPL Gene Contribute to the Risk of Kidney Stones in the Han Chinese Population

OBJECTIVE

Kidney stone formation is a complex disorder that likely results from both dietary and genetic factors. A recent study identified an association between the risk of kidney stones and polymorphisms in the ALPL gene, but the study needs replication. To confirm whether the ALPL gene is universally associated with kidney stones, the present study further investigated polymorphisms of the ALPL gene in a Han Chinese population.

METHODS

A total of 331 kidney stone patients and 553 unrelated healthy controls were included in the present case-control study. We conducted genetic analyses to detect the association of 19 tagging single nucleotide polymorphisms (SNPs) with kidney stones. In addition, we examined the relations between targeted SNP(s) and several clinical characteristics of kidney stones in the patients.

RESULTS

Genetic association analyses using logistic regression models identified one ALPL SNP, rs1256328, which was significantly associated with the kidney stone disease status (OR = 1.52, p = 0.0009). No significant results were obtained through association tests between genotypes of this SNP and the various clinical characteristics of kidney stone patients.

CONCLUSION

The ALPL SNP, rs1256328, was identified as being significantly associated with kidney stone disease status in a large Chinese Han cohort. Our study replicated a previous genome-wide association study that was conducted in an Icelandic population.

Genetic Risk Factors for Idiopathic Urolithiasis: A Systematic Review of the Literature and Causal Network Analysis

CONTEXT

Urolithiasis has a high prevalence and recurrence rate. Prevention is key to patient management, but risk stratification is challenging. In particular, genetic predisposition for urinary stones is not fully understood.

OBJECTIVE

To review current evidence of potential causative genes for idiopathic urolithiasis and map their relationships to one another. This evidence is essential for future establishment of molecular targeted therapy.

EVIDENCE ACQUISITION

A systematic literature review from 2007 to 2017 was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-analyses guidelines. The search was restricted to human studies conducted as either case-control or genome-wide association studies, and published in English. We also performed a causal network analysis of candidate genes gained from the systematic review using Ingenuity Pathway Analysis (IPA).

EVIDENCE SYNTHESIS

During the systematic screening of literature, 30 papers were selected for the review. A total of 20 genes with 42 polymorphisms/variants were found to be associated with urolithiasis risk. Their functional roles were mainly categorized as stone matrix, calcium and phosphate regulation, urinary concentration and constitution, and inflammation/oxidative stress. IPA network analysis revealed that these genes connected via signaling pathways and a proinflammatory/oxidative environment.

CONCLUSIONS

This systematic review provides an updated gene list and novel causal networks for idiopathic urolithiasis risk. Although some genes such as SPP1, CASR, VDR, CLDN14, and SLC34A1 were identified by several studies and recognized by prior reviews, further investigation elucidating their roles in stone formation will be essential for future studies.

PATIENT SUMMARY

In this review, we summarized recent literature regarding genes responsible for kidney stone risk. Based on a detailed review of 30 articles and computational network analysis, we concluded that disorder of mineral regulation with local inflammation in the kidney may cause kidney stone disease.

Epidemiology of stone disease across the world

Nephrolithiasis is a highly prevalent disease worldwide with rates ranging from 7 to 13% in North America, 5-9% in Europe, and 1-5% in Asia. Due to high rates of new and recurrent stones, management of stones is expensive and the disease has a high level of acute and chronic morbidity. The goal of this study is to review the epidemiology of stone disease in order to improve patient care. A review of the literature was conducted through a search on Pubmed^®, Medline^®, and Google Scholar^®. This review was presented and peer-reviewed at the 3rd International Consultation on Stone Disease during the 2014 Société Internationale d'Urologie Congress in Glasgow. It represents an update of the 2008 consensus document based on expert opinion of the most relevant studies. There has been a rising incidence in stone disease throughout the world with a narrowing of the gender gap. Increased stone prevalence has been attributed to population growth and increases in obesity and diabetes. General dietary recommendations of increased fluid, decreased salt, and moderate intake of protein have not changed. However, specific recommended values have either changed or are more frequently reported. Geography and environment influenced the likelihood of stone disease and more information is needed regarding stone disease in a large portion of the world including Asia and Africa. Randomized controlled studies are lacking but are necessary to improve recommendations regarding diet and fluid intake. Understanding the impact of associated conditions that are rapidly increasing will improve the prevention of stone disease.

Might E-cadherin promoter polymorphisms of rs16260 and rs5030625 associate with the risk of nephrolithiasis?

Purpose

To study whether −160 C > A (rs16260) and −347 G > GA (rs5030625) single nucleotide polymorphisms of the regulatory region (rSNPs) of CDH1 gene modulate the risk of nephrolithiasis.

Methods

Genomic DNA of 101 patients with calcium oxalate nephrolithiasis and 114 healthy controls were screened for both polymorphisms, using polymerase chain reaction-restriction fragments length polymorphism method (PCR-RLFP). Haplotype frequencies were also analyzed. To determine the association of rSNPs of CDH1 gene with the clinicopathological features of nephrolithiasis, nearly all possible etiological factors were documented. These factors were family history, gender, age, body mass index, liquid consumption, eating habits, tea–coffee and meat (oxalate rich) consumption, adequate physical activity, and all serum and urine levels—the serum levels of Na, K, Cl, phosphate, Ca, Mg, uric acid, albumin, blood urea nitrogen (BUN), creatinine and serum parathyroid hormone (PTH) as well as 24 h urine excretions of creatinine, Na, K, Cl, phosphate, Ca, Mg, citrate, oxalate, uric acid, albumin and BUN.

Results

Significant differences were found between rs16260 and the risk of nephrolithiasis. Patients having CA genotype of rs16260 CDH1 polymorphism were associated with an almost trifold increased risk for developing kidney stone than those with the AA genotype (95 % CI 1.08–7.28, OR 2.8, P = 0.033). We also found that non-A allele carriers (CC) had significantly higher nephrolithiasis risk associated with the clinicopathological characteristics including serum calcium (P = 0.027) and 24 h urinary magnesium level (P = 0.042). Moreover, we did find a directly proportional relationship between the CA genotype and serum calcium levels (P = 0.041). There was no significant difference between patients and controls in terms of the distribution of rs5030625 genotypes and alleles (P > 0.05). Likewise, no associations between the rs16260 and rs5030625 haplotypes and susceptibility to kidney stone were observed (P > 0.05).

Conclusion

Regulatory variants of rs16260 of the CDH1 gene may confer susceptibility to nephrolithiasis. This may have important implications for understanding the pathophysiological mechanisms of the disease and suggesting novel targets for drug treatment.

Common and rare variants associated with kidney stones and biochemical traits

Kidney stone disease is a complex disorder with a strong genetic component. We conducted a genome-wide association study of 28.3 million sequence variants detected through whole-genome sequencing of 2,636 Icelanders that were imputed into 5,419 kidney stone cases, including 2,172 cases with a history of recurrent kidney stones, and 279,870 controls. We identify sequence variants associating with kidney stones at ALPL (rs1256328[T], odds ratio (OR)=1.21, P=5.8 × 10⁻¹⁰) and a suggestive association at CASR (rs7627468[A], OR=1.16, P=2.0 × 10⁻⁸). Focusing our analysis on coding sequence variants in 63 genes with preferential kidney expression we identify two rare missense variants SLC34A1 p.Tyr489Cys (OR=2.38, P=2.8 × 10⁻⁵) and TRPV5 p.Leu530Arg (OR=3.62, P=4.1 × 10⁻⁵) associating with recurrent kidney stones. We also observe associations of the identified kidney stone variants with biochemical traits in a large population set, indicating potential biological mechanism.

Kidney stone formation is influenced by genetic factors and recurrent stone formation places a significant burden on health care systems. Here Oddsson et al. perform a large-scale genome-wide association study and uncover new genetic variants associated with kidney stone susceptibility and associated biochemical traits.

Effect of Potassium Citrate on Calcium Phosphate Stones in a Model of Hypercalciuria

Potassium citrate is prescribed to decrease stone recurrence in patients with calcium nephrolithiasis. Citrate binds intestinal and urine calcium and increases urine pH. Citrate, metabolized to bicarbonate, should decrease calcium excretion by reducing bone resorption and increasing renal calcium reabsorption. However, citrate binding to intestinal calcium may increase absorption and renal excretion of both phosphate and oxalate. Thus, the effect of potassium citrate on urine calcium oxalate and calcium phosphate supersaturation and stone formation is complex and difficult to predict. To study the effects of potassium citrate on urine supersaturation and stone formation, we utilized 95th-generation inbred genetic hypercalciuric stone-forming rats. Rats were fed a fixed amount of a normal calcium (1.2%) diet supplemented with potassium citrate or potassium chloride (each 4 mmol/d) for 18 weeks. Urine was collected at 6, 12, and 18 weeks. At 18 weeks, stone formation was visualized by radiography. Urine citrate, phosphate, oxalate, and pH levels were higher and urine calcium level was lower in rats fed potassium citrate. Furthermore, calcium oxalate and calcium phosphate supersaturation were higher with potassium citrate; however, uric acid supersaturation was lower. Both groups had similar numbers of exclusively calcium phosphate stones. Thus, potassium citrate effectively raises urine citrate levels and lowers urine calcium levels; however, the increases in urine pH, oxalate, and phosphate levels lead to increased calcium oxalate and calcium phosphate supersaturation. Potassium citrate induces complex changes in urine chemistries and resultant supersaturation, which may not be beneficial in preventing calcium phosphate stone formation.

1,25(OH)₂D₃ induces a mineralization defect and loss of bone mineral density in genetic hypercalciuric stone-forming rats

Genetic hypercalciuric stone-forming (GHS) rats, bred to maximize urine (u) calcium (Ca) excretion, demonstrate increased intestinal Ca absorption, increased bone Ca resorption, and reduced renal Ca reabsorption, all leading to elevated uCa compared to the parental Sprague-Dawley (SD) rats. GHS rats have increased numbers of vitamin D receptors (VDRs) at each site, with normal levels of 1,25(OH)₂D₃ (1,25D), suggesting their VDR is undersaturated with 1,25D. We have shown that 1,25D induces a greater increase in uCa in GHS than SD rats. To examine the effect of the increased VDR on the osseous response to 1,25D, we fed GHS and SD rats an ample Ca diet and injected either 1,25D [low dose (LD) 12.5 or high dose (HD) 25 ng/100 g body weight/day] or vehicle (veh) daily for 16 days. Femoral areal bone mineral density (aBMD, by DEXA) was decreased in GHS+LD and GHS+HD relative to GHS+veh, while there was no effect on SD. Vertebral aBMD was lower in GHS compared to SD and further decreased in GHS+HD. Both femoral and L6 vertebral volumetric BMD (by μCT) were lower in GHS and further reduced by HD. Histomorphometry indicated a decreased osteoclast number in GHS+HD compared to GHS+veh or SD+HD. In tibiae, GHS+HD trabecular thickness and number increased, with a 12-fold increase in osteoid volume but only a threefold increase in bone volume. Bone formation rate was decreased in GHS+HD relative to GHS+veh, confirming the mineralization defect. The loss of BMD and the mineralization defect in GHS rats contribute to increased hypercalciuria; if these effects persist, they would result in decreased bone strength, making these bones more fracture-prone. The enhanced effect of 1,25D in GHS rats indicates that the increased VDRs are biologically active.

Persistence of 1,25D-induced hypercalciuria in alendronate-treated genetic hypercalciuric stone-forming rats fed a low-calcium diet

Genetic hypercalciuric stone-forming (GHS) rats demonstrate increased intestinal Ca absorption, increased bone resorption, and reduced renal tubular Ca reabsorption leading to hypercalciuria and all form kidney stones. GHS have increased vitamin D receptors (VDR) at these sites of Ca transport. Injection of 1,25(OH)2D3 (1,25D) leads to a greater increase in urine (u)Ca in GHS than in control Sprague-Dawley (SD), possibly due to the additional VDR. In GHS the increased uCa persists on a low-Ca diet (LCD) suggesting enhanced bone resorption. We tested the hypothesis that LCD, coupled to inhibition of bone resorption by alendronate (alen), would eliminate the enhanced 1,25D-induced hypercalciuria in GHS. SD and GHS were fed LCD and half were injected daily with 1,25D. After 8 days all were also given alen until euthanasia at day 16. At 8 days, 1,25D increased uCa in SD and to a greater extent in GHS. At 16 days, alen eliminated the 1,25D-induced increase in uCa in SD. However, in GHS alen decreased, but did not eliminate, the 1,25D-induced hypercalciuria, suggesting maximal alen cannot completely prevent the 1,25D-induced bone resorption in GHS, perhaps due to increased VDR. There was no consistent effect on mRNA expression of renal transcellular or paracellular Ca transporters. Urine CaP and CaOx supersaturation (SS) increased with 1,25D alone in both SD and GHS. Alen eliminated the increase in CaP SS in SD but not in GHS. If these results are confirmed in humans with IH, the use of bisphosphonates, such as alen, may not prevent the decreased bone density observed in these patients.

Kidney stones: a fetal origins hypothesis

Kidney stones are common, with a multifactorial etiology involving dietary, environmental, and genetic factors. In addition, patients with nephrolithiasis are at greater risk of hypertension, diabetes mellitus, metabolic syndrome, and osteoporosis, although the basis for this is not fully understood. All of these renal stone-associated conditions have also been linked with adverse early-life events, including low-birth weight, and it has been suggested that this developmental effect is due to excess exposure to maternal glucocorticoids in utero. This is proposed to result in long-term increased hypothalamic-pituitary-axis activation; there are mechanisms through which this effect could also promote urinary lithogenic potential. We therefore hypothesize that the association between renal stone disease and hypertension, diabetes mellitus, metabolic syndrome, and osteoporosis may be related by a common pathway of programming in early life, which, if validated, would implicate the developmental origins hypothesis in the etiology of nephrolithiasis.

1,25(OH)₂D₃-enhanced hypercalciuria in genetic hypercalciuric stone-forming rats fed a low-calcium diet

The inbred genetic hypercalciuric stone-forming (GHS) rats exhibit many features of human idiopathic hypercalciuria and have elevated levels of vitamin D receptors (VDR) in calcium (Ca)-transporting organs. On a normal-Ca diet, 1,25(OH)2D3 (1,25D) increases urine (U) Ca to a greater extent in GHS than in controls [Sprague-Dawley (SD)]. The additional UCa may result from an increase in intestinal Ca absorption and/or bone resorption. To determine the source, we asked whether 1,25D would increase UCa in GHS fed a low-Ca (0.02%) diet (LCD). With 1,25D, UCa in SD increased from 1.2 ± 0.1 to 9.3 ± 0.9 mg/day and increased more in GHS from 4.7 ± 0.3 to 21.5 ± 0.9 mg/day (P < 0.001). In GHS rats on LCD with or without 1,25D, UCa far exceeded daily Ca intake (2.6 mg/day). While the greater excess in UCa in GHS rats must be derived from bone mineral, there may also be a 1,25D-mediated decrease in renal tubular Ca reabsorption. RNA expression of the components of renal Ca transport indicated that 1,25D administration results in a suppression of klotho, an activator of the renal Ca reabsorption channel TRPV5, in both SD and GHS rats. This fall in klotho would decrease tubular reabsorption of the 1,25D-induced bone Ca release. Thus, the greater increase in UCa with 1,25D in GHS fed LCD strongly suggests that the additional UCa results from an increase in bone resorption, likely due to the increased number of VDR in the GHS rat bone cells, with a possible component of decreased renal tubular calcium reabsorption.