Genetics of hypercalciuria and calcium nephrolithiasis: from the rare monogenic to the common polygenic forms

The Use of Genetic Testing in Nephrolithiasis Evaluation: A Retrospective Review From a Multidisciplinary Kidney Stone Clinic

OBJECTIVE

To describe genetic and clinical characteristics for patients undergoing genetic testing at our multidisciplinary kidney stone clinic.

METHODS

A retrospective review was performed on patients evaluated in our stone clinic and referred to genetics between 2018 and 2022. Patient demographic, clinical, stone, and genetic data were included. We assessed the specific variants identified in our cohort, both those with a pathogenic association and variants of unknown significance.

RESULTS

Of 825 patients seen in our stone clinic from 2018-2022, 50 patients were referred to genetics. Among these patients, 33/50 (66%) underwent genetic testing and were included in the analysis. Of those who underwent genetic testing, a variant was identified in 19/33 (58%) patients, and 9/33 (27%) of these were a known pathogenic variant. Among patients with a pathogenic variant identified, the majority had a family history of stones (55.6%), calcium-based stones (77.8%), had their first stone prior to age 18 (66.7%), were recurrent stone formers (100%), and had been managed medically (88.9%) or surgically (88.9%) prior to testing. When comparing patients with a pathogenic variant, variants of unknown significance, and no variant, there were no significant differences in demographic or clinical parameters.

CONCLUSION

In our stone practice, more than half of patients who underwent genetic testing were found to have a variant. However, the majority of these variants were of unknown significance. Further evaluation regarding how genetic testing can impact nephrolithiasis management is needed.

Radiomics and Clinical Features for Distinguishing Kidney Stone-Associated Urinary Tract Infection: A Comprehensive Analysis of Machine Learning Classification

Background

This study investigated the abilities of radiomics and clinical feature models to distinguish kidney stone-associated urinary tract infections (KS-UTIs) using computed tomography.

Methods

A retrospective analysis was conducted on a single-center dataset comprising computed tomography (CT) scans and corresponding clinical information from 461 patients with kidney stones. Radiomics features were extracted from CT images and underwent dimensionality reduction and selection. Multiple machine learning (Three types of shallow learning and four types of deep learning) algorithms were employed to construct radiomics and clinical models in this study. Performance evaluation and optimal model selection were done using receiver operating characteristic (ROC) curve analysis and Delong test. Univariate and multivariate logistic regression analyzed clinical and radiomics features to identify significant variables and develop a clinical model. A combined model integrating radiomics and clinical features was established. Model performance was assessed by ROC curve analysis, clinical utility was evaluated through decision curve analysis, and the accuracy of the model was analyzed via calibration curve.

Results

Multilayer perceptron (MLP) showed higher classification accuracy than other classifiers (area under the curve (AUC) for radiomics model: train 0.96, test 0.94; AUC for clinical model: train 0.95, test 0.91. The combined radiomics-clinical model performed best (AUC for combined model: train 0.98, test 0.95). Decision curve and calibration curve analyses confirmed the model's clinical efficacy and calibration.

Conclusions

This study showed the effectiveness of combining radiomics and clinical features from CT scans to identify KS-UTIs. A combined model using MLP exhibited strong classification abilities.

Prevalence and related factors of nephrolithiasis among medical staff in Qingdao, China: a retrospective cross-sectional study

BACKGROUND

Certain occupations may predispose individuals to urolithiasis, a multi-factorial disease. The study aimed to evaluate the prevalence and related factors of nephrolithiasis in medical staff in Qingdao, China.

METHODS

Physical examination results of 5115 in-service medical staff aged 22-60 years old were retrospectively analyzed. Multivariable logistic regression analysis and stratified analyses by age and gender were applied to explore the related factors of nephrolithiasis in these medical staff.

RESULTS

The overall nephrolithiasis prevalence in medical staff in Qingdao, China was 4.65%. Doctors were more prone to nephrolithiasis than nurses (5.63% vs. 3.96%, P = 0.013) and the peak prevalence (6.69%) was observed in medical staff working in the emergency department (ED). Male gender (OR = 1.615, 95% CI = 1.123-2.323, P = 0.010), overweight or obesity (OR = 1.674, 95% CI = 1.266-2.214, P < 0.001), work seniority ≥ 10 years (OR = 2.489, 95%CI = 1.675-3.699, P < 0.001) and working in the ED (OR = 1.815, 95% CI = 1.202-2.742, P = 0.005) were independent predictors for nephrolithiasis in medical staff based on the results of multivariate logistic regression analysis. The associations between overweight or obesity and nephrolithiasis risk as well as between work seniority ≥ 10 years and nephrolithiasis risk in medical staff were independent of age or gender in stratified analysis.

CONCLUSIONS

Nephrolithiasis prevalence in medical staff in Qingdao, China seemed not to be higher than that in the general population. Medical staff with work seniority ≥ 10 years and working in the ED should pay abundant attention to take measures to modify their nephrolithiasis risk.

Renal calcification in children with renal tubular acidosis: What a paediatrician ‎should ‎know‎

Renal tubular acidosis (RTA) can lead to renal calcification in children, which can cause various complications and impair renal function. This review provides pediatricians with a comprehensive understanding of the relationship between RTA and renal calcification, highlighting essential aspects for clinical management. The article analyzed relevant studies to explore the prevalence, risk factors, underlying mechanisms, and clinical implications of renal calcification in children with RTA. Results show that distal RTA (type 1) is particularly associated with nephrocalcinosis, which presents a higher risk of renal calcification. However, there are limitations to the existing literature, including a small number of studies, heterogeneity in methodologies, and potential publication bias. Longitudinal data and control groups are also lacking, which limits our understanding of long-term outcomes and optimal management strategies for children with RTA and renal calcification. Pediatricians play a crucial role in the early diagnosis and management of RTA to mitigate the risk of renal calcification and associated complications. In addition, alkaline therapy remains a cornerstone in the treatment of RTA, aimed at correcting the acid-base imbalance and reducing the formation of kidney stones. Therefore, early diagnosis and appropriate therapeutic interventions are paramount in preventing and managing renal calcification to preserve renal function and improve long-term outcomes for affected children. Further research with larger sample sizes and rigorous methodologies is needed to optimize the clinical approach to renal calcification in the context of RTA in the pediatric population.

Bone density, microarchitecture and estimated strength in stone formers: a cross-sectional HR-pQCT study

BACKGROUND

Low areal bone mineral density (BMD), increased fracture risk and altered bone remodeling have been described among stone formers (SFs), but the magnitude of these findings differs by age, sex, menopausal status and urinary calcium (uCa). This study aimed to investigate volumetric BMD (vBMD), bone microarchitecture and biomechanical properties by high-resolution peripheral quantitative computed tomography (HR-pQCT) and finite element analysis (FEA) in young SFs, irrespective of calciuria, further distinguishing trabecular from cortical compartments.

METHODS

HR-pQCT/FEA was performed at the distal tibia (DT) and distal radius (DR) in 106 SFs (57 males and 49 premenopausal females; median age 37 years) and compared with 106 non-SFs (NSFs) retrieved from an existing database, matched for age, sex and body mass index (BMI). Biochemical/hormonal serum and urinary parameters were obtained from SFs.

RESULTS

SFs exhibited significantly lower trabecular number (TbN) and higher trabecular separation (TbSp) than NSFs at both anatomical sites and lower cortical porosity in the DR. In a subgroup analysis separated by sex, female SFs presented significantly lower TbvBMD, relative bone volume fraction (BV/TV) and TbN and higher TbSp than NSFs at both sites, while male SFs showed significantly lower stiffness and failure load. Multivariate analysis showed TbN to be independently associated with sex and BMI at both sites and with uCa at the DR.

CONCLUSIONS

The present findings suggest that bone disease represents an early event among SFs, associated at least in part with calcium excretion and mainly characterized by trabecular bone microarchitecture impairment, especially among women, but with reduced bone strength parameters in men.

Dietary Management of Chronic Kidney Disease and Secondary Hyperoxaluria in Patients with Short Bowel Syndrome and Type 3 Intestinal Failure

Short gut syndrome can lead to type 3 intestinal failure, and nutrition and hydration can only be achieved with parenteral nutrition (PN). While this is a lifesaving intervention, it carries short- and long-term complications leading to complex comorbidities, including chronic kidney disease. Through a patient with devastating inflammatory bowel disease’s journey, this review article illustrates the effect of short gut and PN on kidney function, focusing on secondary hyperoxaluria and acute precipitants of glomerular filtration. In extensive small bowel resections colon in continuity promotes fluid reabsorption and hydration but predisposes to hyperoxaluria and stone disease through the impaired gut permeability and fat absorption. It is fundamental, therefore, for dietary intervention to maintain nutrition and prevent clinical deterioration (i.e., sarcopenia) but also to limit the progression of renal stone disease. Adaptation of both enteral and parenteral nutrition needs to be individualised, keeping in consideration not only patient comorbidities (short gut and jejunostomy, cirrhosis secondary to PN) but also patients’ wishes and lifestyle. A balanced multidisciplinary team (renal physician, gastroenterologist, dietician, clinical biochemist, pharmacist, etc.) plays a core role in managing complex patients, such as the one described in this review, to improve care and overall outcomes.

Protective Effects of Quercetin on Oxidative Stress-Induced Tubular Epithelial Damage in the Experimental Rat Hyperoxaluria Model

Background and Objectives: The most common kidney stones are calcium stones and calcium oxalate (CaOx) stones are the most common type of calcium stones. Hyperoxaluria is an essential risk factor for the formation of these stones. Quercetin is a polyphenol with antioxidant, anti-inflammatory, and many other physiological effects. The aim of this study was to investigate the protective effect of quercetin in hyperoxaluria-induced nephrolithiasis. Materials and Methods: Male Wistar-Albino rats weighing 250–300 g (n = 24) were randomized into three groups: Control (n = 8), ethylene glycol (EG) (n = 8), and EG + quercetin (n = 8). One percent EG-water solution was given to all rats except for the control group as drinking water for five weeks. Quercetin-water solution was given to the EG + quercetin group by oral gavage at a dose of 10 mg/kg/day. Malondialdehyde (MDA), catalase (CAT), urea, calcium, and oxalate levels were analyzed in blood and urine samples. Histopathological assessments and immunohistochemical analyses for oxidative stress and inflammation indicators p38 mitogen-activated protein kinase (p38-MAPK) and nuclear factor kappa B (NF-kB) were performed on renal tissues. Results: The MDA levels were significantly lower in the quercetin-treated group than in the EG-treated group (p = 0.001). Although CAT levels were higher in the quercetin-treated group than the EG-administered group, they were not significantly different between these groups. The expression of p38 MAPK was significantly less in the quercetin-treated group than the EG group (p < 0.004). There was no statistically significant difference between the quercetin and EG groups in terms of NF-kB expression. Conclusions: We conclude that hyperoxaluria activated the signaling pathways, which facilitate the oxidative processes leading to oxalate stone formation in the kidneys. Our findings indicated that quercetin reduced damage due to hyperoxaluria. These results imply that quercetin can be considered a therapeutic agent for decreasing oxalate stone formation, especially in patients with recurrent stones due to hyperoxaluria.

Association between intelectin-1 variation and human kidney stone disease in northeastern Thai population

An interplay of multiple genetic and environmental factors implicates an incidence of human kidney stone disease (KSD). However, the genetic factors associated with KSD are not completely known or understood. To identify KSD-associated genetic variations among the northeastern Thai patients, a genome-wide association study (GWAS) was conducted. We initially employed genotyping of single nucleotide polymorphism (SNP) using Genome-Wide Human SNP Array 6.0 in 105 patients and in 105 normal control subjects. To overcome the limitation of small sample size, we set forth to analyze SNPs as clusters based on the concept of linkage disequilibrium (LD) and haplotype. Using this analysis, 29 genes were identified. Three candidate SNPs, including rs2039415, rs2274907, and rs3747515, were selected on the basis of haplotype analysis, potentially functional SNPs, and the functions of associated genes. Further genotyping of these SNPs in a larger sample size (altogether 216 patients and 216 control subjects) showed that the candidate SNP rs2274907 remained significantly different between case and control subjects in both genotype frequencies (OR 2.44, 95% CI 1.38-4.30; p = 0.0015) and allele frequencies (OR 1.54, 95% CI 1.17-2.03; p = 0.0021). The non-synonymous SNP rs2274907 (c.326T > A) located in exon 4 of the ITLN1 gene results in a substitution of valine (V) by aspartate (D) at position 109 (p.V109D). This substitution could affect the predicted hydrogen (H)-bonds between lysine (K) 107 and glutamine (Q) 104, which supports its association with KSD in this population.

[Nephrocalcinosis in children]

Nephrocalcinosis is defined by calcium phosphate or calcium oxalate deposits in the kidney parenchyma, particularly in tubular epithelial cells and interstitial tissue. It should be differentiated from urolithiasis where calcium salts deposits are located in the kidney and urinary tract. The epidemiology of nephrocalcinosis in children is unknown but the condition is not so rare, with an increased incidence in preterm infants. Often detected as an incidental finding, nephrocalcinosis may be classified according to the radiological type: medullary, cortical or diffuse. Nephrocalcinosis in children can be caused by a variety of etiology. The most common causes concern medullary nephrocalcinosis and include hereditary tubular disorders, in particular distal renal tubular acidosis and Dent disease, metabolic disorders such as idiopathic hypercalciuria and hyperoxaluria, and iatrogenic causes such as vitamin D intoxication. In the newborn, the main cause is hypercalciuria of the premature baby, whose multifactorial origin is largely iatrogenic. Primary hyperoxaluria which can lead to early onset nephrocalcinosis and usually to chronic kidney disease should always be considered and further investigated. In order to provide a specific diagnosis, it is essential to take into account the family history, the clinical context and complete laboratory data. Early initiation of an appropriate etiological treatment is recommended and may prevent or delay the progression to chronic kidney disease in some cases.

A novel loss-of-function mutation of PBK associated with human kidney stone disease

Kidney stone disease (KSD) is a prevalent disorder that causes human morbidity worldwide. The etiology of KSD is heterogeneous, ranging from monogenic defect to complex interaction between genetic and environmental factors. Since mutations of genes responsible for KSD in a majority of families are still unknown, our group is identifying mutations of these genes by means of genomic and genetic analyses. In this study, we identified a novel loss-of-function mutation of PBK, encoding the PDZ binding kinase, that was found to be associated with KSD in an affected Thai family. Glycine (Gly) substituted by arginine (Arg) at position 43 (p.Gly43Arg) in PBK cosegregated with the disease in affected members of this family, but was absent in 180 normal control subjects from the same local population. Gly43 is highly evolutionarily conserved in vertebrates, and its substitution affects protein structure by alterations in H-bond forming patterns. This p.Gly43Arg substitution results in instability of the variant PBK protein as examined in HEK293T cells. The variant PBK protein (p.Gly43Arg) demonstrated decreased kinase activity to phosphorylate p38 MAPK as analyzed by immunoblotting and antibody microarray techniques. Taken together, these findings suggest a possible new mechanism of KSD associated with pathogenic PBK variation.

Inherited conditions resulting in nephrolithiasis

PURPOSE OF REVIEW

Prevalence of pediatric urolithiasis is increasing, which is definitively visible in increasing numbers of presentations in emergency or outpatient clinics. In pediatric patients, a genetic or metabolic disease has to be excluded, so that adequate treatment can be installed as early as possible. Only then either recurrent stone events and chronic or even end-stage kidney disease can be prevented.

RECENT FINDINGS

The genetic background of mostly monogenic kidney stone diseases was unravelled recently. In hypercalcuria, for example, the commonly used definition of idiopathic hypercalciuria was adopted to the genetic background, here three autosomal recessive hereditary forms of CYP24A1, SLC34A1 and SLC34A3 associated nephrocalcinosis/urolithiasis with elevated 1.25-dihydroxy-vitamin D3 (1.25-dihydroxy-vitamin D3) (calcitriol) levels. In addition either activating or inactivating mutations of the calcium-sensing receptor gene lead either to hypocalcemic hypercalciuria or hypercalcemic hypocalciuria. In primary hyperoxaluria, a third gene defect was unravelled explaining most of the so far unclassified patients. In addition, these findings lead to new treatment options, which are currently evaluated in phase III studies.

SUMMARY

Kidney stones are not the disease itself, but only its first symptom. The underlying disease has to be diagnosed in every pediatric patient with the first stone event.

Phosphate disorders and clinical management of hypophosphatemia and hyperphosphatemia

Serum phosphorus levels range from 2.5 and 4.5mg/dL (0.81-1.45 mmol/L) in adults, with higher levels in childhood, adolescence, and pregnancy. Intracellular phosphate is involved in intermediary metabolism and other essential cell functions, while extracellular phosphate is essential for bone matrix mineralization. Plasma phosphorus levels are maintained within a narrow range by regulation of intestinal absorption, redistribution, and renal tubular absorption of the mineral. Hypophosphatemia and hyperphosphatemia are common clinical situations, although changes are most often mild and oligosymptomatic. However, acute and severe conditions that require specific treatment may occur. In this document, members of the Mineral and Bone Metabolism Working Group of the Spanish Society of Endocrinology and Nutrition review phosphate disorders and provide algorithms for adequate clinical management of hypophosphatemia and hyperphosphatemia.

LIFESTYLE RISK FACTORS AND BONE MASS IN RECURRENT STONE-FORMING PATIENTS: A CROSS-SECTIONAL STUDY IN 144 SUBJECTS

Patients with urolithiasis, particularly hypercalciuria, may have reduced bone mineral density (BMD). There are numerous risk factors contributing to reduction of BMD such as advanced age, sedentary lifestyle, smoking, low calcium intake, etc. The aim of our study was to investigate the association of lifestyle risk factors and daily intake of milk and dairy products with determinants of BMD in a group of recurrent calcium stone formers (RSF) compared with healthy subjects (HS). The study was carried out at the Department of Mineral Research, Faculty of Medicine in Osijek, Croatia. The study included 144 subjects, i.e. 56 RSF and 78 HS. BMD was assessed by dual-energy x-ray absorptiometry. A standard self-reported questionnaire was used to collect data on lifestyle risk factors. Current dietary intake was assessed by personal interview that included questions about milk and dairy product intake. Low BMD was observed in 44.64% of RSF and 35.90% of HS. RSF consumed significantly less milk and dairy products than HS. Calcium restriction in dietary recommendations might be unnecessary due to the impact on bone mineral loss in RSF and dual-energy x-ray absorptiometry should be included in the routine evaluation of RSF.

The idiopathic hypercalciuria reviewed. Metabolic abnormality or disease?

Idiopathic hypercalciuria (IH) is defined as that clinical situation in which an increase in urinary calcium excretion is observed, in the absence of hypercalcemia and other known causes of hypercalciuria. In recent years, its diagnosis in pediatric age has been more frequent because it has been known that it can debut with very different symptoms, in the absence of kidney stone formation. The discovery of genetic hypercalciuric stone-forming rats has allowed us to glimpse the pathophysiological mechanism of IH since they show many data in common with humans with IH as normal levels of blood calcium, intestinal calcium hyperabsorption, increased bone resorption and a defect in the renal tubular calcium reabsorption. In 1993, it was shown that in these animals there is an increase in the number of vitamin D receptors (VDR) in the intestine, which favors an increase in the functional capacity of calcitriol-VDR complexes that explains the increase in intestinal transport of calcium. The same happens at the bone level producing a greater resorption. In our opinion, IH is a 'metabolic anomaly' or, better, an inheritable constitutive metabolic characteristic. In this sense, what patients with IH would inherit is the availability of having a greater number of VDRs in their cells than those with normal urinary calcium excretion. IH cannot be considered a sensu stricto disease, so pharmacological treatment must be individualized.

Prevalence of low molecular weight proteinuria and Dent disease 1 CLCN5 mutations in proteinuric cohorts

BACKGROUND

Dent disease type 1 (DD1) is a rare X-linked disorder caused mainly by CLCN5 mutations. Patients may present with nephrotic-range proteinuria leading to erroneous diagnosis of focal segmental glomerulosclerosis (FSGS) and unnecessary immunosuppressive treatments.

METHODS

The following cohorts were screened for CLCN5 mutations: Chronic Kidney Disease in Children (CKiD; n = 112); Multicenter FSGS-Clinical Trial (FSGS-CT) (n = 96), and Novel Therapies for Resistant FSGS Trial (FONT) (n = 30). Urinary α₁-microglobulin (α₁M), albumin (A), total protein (TP), and creatinine (Cr) were assessed from CKiD subjects (n = 104); DD1 patients (n = 14); and DD1 carriers (DC; n = 8). TP/Cr, α₁M/Cr, α₁M/TP, and A/TP from the CKiD cohort were compared with DD1 and DC.

RESULTS

No CLCN5 mutations were detected. TP/Cr was lower in DC and CKiD with tubulointerstitial disease than in DD1 and CKiD with glomerular disease (p < 0.002). α₁M/Cr was higher in DD1 than in CKiD and DC (p < 0.001). A/TP was lower in DD1, DC, and CKiD with tubulointerstitial disease and higher in CKiD with glomerular disease (p < 0.001). Thresholds for A/TP of ≤ 0.21 and α₁M/Cr of ≥ 120 mg/g (> 13.6 mg/mmol) creatinine were good screens for Dent disease.

CONCLUSIONS

CLCN5 mutations were not seen in screened CKiD/FSGS cohorts. In our study, a cutoff of TP/Cr > 600 mg/g (> 68 mg/mmol) and A/TP of < 0.3 had a high sensitivity and specificity to distinguish DD1 from both CKiD glomerular and tubulointerstitial cohorts. α₁M/Cr ≥ 120 mg/g (> 13.6 mg/mmol) had the highest sensitivity and specificity when differentiating DD1 and studied CKiD populations.

Meeting report of the "Symposium on kidney stones and mineral metabolism: calcium kidney stones in 2017"

A symposium on kidney stones and mineral metabolism held on December 2017 in Brussels, Belgium was the first international multidisciplinary conference of the International Collaborative Network on Kidney Stones and Mineral Metabolism. This meeting addressed epidemiology, underlying pathophysiological mechanisms, genetics, pathological, as well as clinical and research topics. The participants included clinicians and recognized experts in the field from Europe and the United States interacted closely during the symposium which promoted a chance to explore new frontiers in the field of kidney stone disease. This manuscript summarizes some of the major highlights of the meeting.

Phosphaturia in kidney stone formers: Still an enigma

Calcium kidney stones are common worldwide. Most are idiopathic and composed of calcium oxalate. Calcium phosphate is present in around 80% and may initiate stone formation. Stone production is multifactorial with a polygenic genetic contribution. Phosphaturia is found frequently among stone formers but until recently received scant attention. This review examines possible mechanisms for the phosphaturia and its relevance to stone formation from a wide angle. There is a striking lack of clinical data. Phosphaturia is associated, but not correlated, with hypercalciuria, increased 1,25 dihydroxy-vitamin D [1,25 (OH)₂D], and sometimes evidence of disturbances in proximal renal tubular function. Phosphate reabsorption in the proximal renal tubules requires tightly regulated interaction of many proteins. Paracellular flow through intercellular tight junctions is the major route of phosphate absorption from the intestine and can be reduced therapeutically in hyperphosphatemic patients. In monogenic defects stones develop when phosphaturia is associated with hypercalciuria, generally explained by increased 1,25 (OH)₂D production in response to hypophosphatemia. Calcification does not occur in disorders with increased FGF23 when phosphaturia occurs in isolation and 1,25 (OH)₂D is suppressed. Candidate gene studies have identified mutations in the phosphate transporters, but in few individuals. One genome-wide study identified a polymorphism of the phosphate transporter gene SLC34A4 associated with stones. Others did not find mutations obviously linked to phosphate reabsorption. Future genetic studies should have a wide trawl and should focus initially on groups of patients with clearly defined phenotypes. The global data should be pooled.

Genetische Nierensteinerkrankungen

Die Inzidenz und Prävalenz von Steinerkrankungen haben in den letzten Jahren deutlich zugenommen. Es ist von entscheidender Bedeutung, möglichst frühzeitig eine richtige Diagnose der zugrunde liegenden Erkrankung zu stellen, um die richtige Therapie einzuleiten und damit möglicherweise schwerwiegende Folgen, wie terminales Nierenversagen, zu verhindern. Bei Kindern lassen sich in ca. 75 % der Fälle genetische oder anatomische Ursachen identifizieren. Die verschiedenen zugrunde liegenden Erkrankungen für die jeweiligen lithogenen Risikofaktoren werden hier präsentiert und die entsprechenden Therapieoptionen, sofern vorhanden, erläutert.

Understanding the gut-kidney axis in nephrolithiasis: an analysis of the gut microbiota composition and functionality of stone formers

OBJECTIVES

The involvement of the gut microbiota in the pathogenesis of calcium nephrolithiasis has been hypothesised since the discovery of the oxalate-degrading activity of Oxalobacter formigenes, but never comprehensively studied with metagenomics. The aim of this case-control study was to compare the faecal microbiota composition and functionality between recurrent idiopathic calcium stone formers (SFs) and controls.

DESIGN

Faecal samples were collected from 52 SFs and 48 controls (mean age 48±11). The microbiota composition was analysed through 16S rRNA microbial profiling approach. Ten samples (five SFs, five controls) were also analysed with deep shotgun metagenomics sequencing, with focus on oxalate-degrading microbial metabolic pathways. Dietary habits, assessed through a food-frequency questionnaire, and 24-hour urinary excretion of prolithogenic and antilithogenic factors, including calcium and oxalate, were compared between SFs and controls, and considered as covariates in the comparison of microbiota profiles.

RESULTS

SFs exhibited lower faecal microbial diversity than controls (Chao1 index 1460±363vs 1658±297, fully adjusted p=0.02 with stepwise backward regression analysis). At multivariate analyses, three taxa (Faecalibacterium, Enterobacter, Dorea) were significantly less represented in faecal samples of SFs. The Oxalobacter abundance was not different between groups. Faecal samples from SFs exhibited a significantly lower bacterial representation of genes involved in oxalate degradation, with inverse correlation with 24-hour oxalate excretion (r=-0.87, p=0.002). The oxalate-degrading genes were represented in several bacterial species, whose cumulative abundance was inversely correlated with oxaluria (r=-0.85, p=0.02).

CONCLUSIONS

Idiopathic calcium SFs exhibited altered gut microbiota composition and functionality that could contribute to nephrolithiasis physiopathology.

Heritable traits that contribute to nephrolithiasis

Urinary stones tend to cluster in families. Of the known risk factors, evidence is strongest for heritability of urinary calcium excretion. Recent studies suggest that other stone risk factors may have heritable components including urinary pH, citrate and magnesium excretion, and circulating vitamin D concentration. Several risk factors assumed purely environmental may also have heritable components, including dietary intake and thirst. Thus, future studies may reveal that genetics plays an even stronger role in urinary stone pathogenesis than previously known.

Loss-of-function mutations of SCN10A encoding NaV1.8 α subunit of voltage-gated sodium channel in patients with human kidney stone disease

Human kidney stone disease (KSD) causes significant morbidity and public health burden worldwide. The etiology of KSD is heterogeneous, ranging from monogenic defects to complex interaction between genetic and environmental factors. However, the genetic defects causing KSD in the majority of affected families are still unknown. Here, we report the discovery of mutations of SCN10A, encoding Na_V1.8 α subunit of voltage-gated sodium channel, in families with KSD. The region on chromosome 3 where SCN10A locates was initially identified in a large family with KSD by genome-wide linkage analysis and exome sequencing. Two mutations (p.N909K and p.K1809R) in the same allele of SCN10A co-segregated with KSD in the affected family. Additional mutation (p.V1149M) of SCN10A was identified in another affected family, strongly supporting the causal role of SCN10A for KSD. The amino acids at these three positions, N909, K1809, and V1149, are highly conserved in vertebrate evolution, indicating their structural and functional significances. Na_V1.8 α subunit mRNA and protein were found to express in human kidney tissues. The mutant proteins expressed in cultured cells were unstable and causing reduced current density as analyzed by whole-cell patch-clamp technique. Thus, loss-of-function mutations of SCN10A were associated with KSD in the families studied.

Protective effect of pentoxifylline on oxidative renal cell injury associated with renal crystal formation in a hyperoxaluric rat model

The aim of the study is to investigate the effects of pentoxifylline (PTX) on the renal tubular cell injury and stone formation in a hyperoxaluric rat model induced by ethylene glycol and its possible underlying mechanisms. The study was performed with 30 male Wistar rats and randomized into three groups of teen. The sham-control (group 1) received only drinking water orally. The EG/untreated (group 2) received drinking water containing 0.75% EG for 4 weeks orally. The EG/PTX treated (group 3) received drinking water containing 0.75% EG for 4 weeks orally and PTX. Urine and blood were collected to determine some parameters. The kidneys were also removed for histological examination. Serum and urinary parameters were significantly improved in the EG/PTX treated. In the EG/PTX-treated group, the MDA, TOS and MPO activity reduced and the TAS, SOD, CAT and GSH-Px activities were increased markedly compared with the group 2. In urine of the group 2 rats, a large number of CaOx crystals were displayed and most tubules that contained crystals were dilated and showed degeneration, necrosis, and desquamation of the lining epithelium. Only few CaOx crystals were r in EG/PTX-treated animal's urine. Mild tissue damage was observed in PTX-treated rats. iNOS expression was significantly elevated in the group 2. In contrast, in the EG/PTX-treated group, eNOS expression in renal tubular epithelial cells was increased. Current study indicates that PTX may partially reduce renal tubular injury resulting from hyperoxaluria-induced oxidative and nitrosative stress.

Renal stones

Renal stone disease is a worldwide problem which carries significant morbidity. It frequently requires specialist urology intervention. Patients with recurrent disease and those at high risk require specialist investigations and review. Certain cases benefit from medical and surgical intervention. In this review, we discuss the pathophysiology, risk assessment, specialist investigations and various interventions, their rationale and evidence base. This review aims to provide an update of the previous publication in 2001 in this journal on this topic.

Nephrolithiasis and Nephrocalcinosis in Childhood-Risk Factor-Related Current and Future Treatment Options

Nephrolithiasis, urolithiasis, and nephrocalcinosis (NC) have become common causes of hospitalization and referral to pediatric outpatient clinics. It is of utmost importance to start with diagnostic evaluation directly after the first passage of a kidney stone, or if NC is diagnosed, in each pediatric patient. This is necessary, as in about 80% of children a metabolic reason for stone disease is detected. Current treatment options are scarce and mainly include general measures like an increased fluid intake or elevating the solubility of a lithogenic substance. According to the given lithogenic risk factor(s), specific treatment options are available and are being summarized in this review. Furthermore, an outlook on potential future treatment options, including innovative strategies such as mRNA-based or recombinant enzyme substitution therapy, is given.

PDE1A polymorphism contributes to the susceptibility of nephrolithiasis

Background

Previous studies have confirmed a family risk of nephrolithiasis (NL), but only 15% of all cases are associated with an identified monogenic factor. In clinical practice, our group encountered a patient with NL combined with cystic kidney disease that had 3 affected family members. No known mutations association with NL was detected in this family, and thus further investigation of the molecular cause of NL was deemed to be necessary.

Results

Quality analysis from the sequencing stage showed a more than 80-fold average depth and 95% coverage for each sample, and six mutations within six genes were chosen as candidate variants for further validation. Genotyping of rs182089527in the phosphodiesterase 1A (PDE1A) gene in the validation cohort indicated that the alternative allele was present in 15 patients with heterozygosity and in 1 patient with homozygosity, and exhibited significant enrichment in NL patients (Fisher’s exact test, adjusted p = 0.0042) and kidney cystic patients (Fisher’s exact test, adjusted p = 0.067) compared to controls. In addition, function analysis displayed a significant decrease in the protein and mRNA expression levels resulting from the rs182089527 mutant sequence compared with the wild-type sequence. Moreover, patients with this mutation displayed a high level of creatinine and urea in urinalysis.

Conclusions

Our study provides genetic evidence that the rs182089527 mutation in PDE1A is involved in the development of NL and kidney cysts, which should help to improve personalized medicine for diagnosis and treatment.

Electronic supplementary material

The online version of this article (dio: 10.1186/s12864-017-4247-8) contains supplementary material, which is available to authorized users.

Protective impact of resveratrol in experimental rat model of hyperoxaluria

PURPOSE

Resveratrol (RES) is a polyphenol with antioxidant, anti-inflammatory, and many other physiological effects on tissues. In the present study, the effect of resveratrol in hyperoxaluria driven nephrolithiasis/nephrocalcinosis is investigated.

METHODS

Wistar-Albino rats of 250-300 g (male, n = 24) were included in the present study. The rats were randomized into three groups: Group 1 consisted of the controls (n = 8), Group 2 of hyperoxaluria (1% ethylene glycol (EG), n = 8), and Group 3 of the treatment (1% EG + 10 mg/kg of RES, n = 8) group. At the beginning and fifth week of the study, two rats from each group were placed in metabolic cages for 24 h and their urine was collected. At the end of the study, the rats were killed and their blood was collected from the vena cava inferior. The right kidneys of the rats were used for biochemical and the left ones for immunohistochemical analyzes. Malondialdehyde (MDA), catalase, urea, calcium, oxalate, and creatinine clearance were studied in the blood, urine, and kidney tissues. Moreover, routine histological evaluation, and p38-MAPK and NFkB immunohistochemical analyses were conducted.

RESULTS

In the hyperoxaluria group, urinary oxalate levels were higher than the control group; yet, lower in the treatment group compared to hyperoxaluria group (p < 0.05). Serum MDA levels in the hyperoxaluria group were higher than the control group; but in the treatment group it is lower than the hyperoxaluria group (p < 0.05). P38 MAPK activity was higher in the hyperoxaluria group compared to the control (p < 0.05). However, in terms of p38 MAPK activity, there were no statistically significant difference between hyperoxaluria and the treatment group (p < 0.069). Whereas NFkB activity in the hyperoxaluria group is higher than the control (p < 0.001), no statistically significant difference was observed with the treatment group.

CONCLUSIONS

In the present study, resveratrol was seen to prevent hyperoxaluria. With preventing oxidative stress factors and Randall plaque formation caused by free oxygen radicals, resveratrol can be an alternative treatment option that can increase the success rate in preventing stone recurrence in the future.

Calcium urolithiasis course in young stone formers is influenced by the strength of family history: results from a retrospective study

The role of the strength of family history of stones (FHS), i.e., degree of relatives with the disease, on the course of calcium urolithiasis (CU) is not fully understood, particularly in young patients where genetic background has the greatest influence on disease expression. Thus, with a retrospective cross-sectional design, we examined baseline clinical parameters and urinary chemistries of 369 subjects (196 M) with CU and 96 controls (41 M) aged between 15 and 25 at the time of the first visit at our stone clinic. Subjects with metabolic syndrome traits, known causes of CU or CU onset before the age of 15 were excluded. Clinical and metabolic parameters were compared among stone formers (SF) and controls, stratified by gender, the presence and type of FHS determined through the kinship coefficient of relatives with stones. No significant differences in clinical course were found between SF with and without FHS, except for the presence of bilateral stones (OR 2.01, 95% CI 1.20-3.39, p < 0.01). A significant age-, sex- and disease duration-adjusted trend for a higher number of colics (p for trend = 0.001), number of stones (p for trend = 0.002), stone rate (p for trend = 0.003) and the presence of retained stones (OR 1.60, 95% CI 1.14-2.21, p = 0.006) was detected with increasing FHS strength. Urinary chemistries were unaffected by FHS in both SF and controls, except for a higher calcium excretion in females with FHS (p < 0.05). The type of FHS, thus, significantly influences the clinical course of CU in young SF, mainly irrespective of urinary factors.

Digenic mutations of human OCRL paralogs in Dent's disease type 2 associated with Chiari I malformation

OCRL1 and its paralog INPP5B encode phosphatidylinositol 5-phosphatases that localize to the primary cilium and have roles in ciliogenesis. Mutations in OCRL1 cause the X-linked Dent disease type 2 (DD2; OMIM# 300555), characterized by low-molecular weight proteinuria, hypercalciuria, and the variable presence of cataracts, glaucoma and intellectual disability without structural brain anomalies. Disease-causing mutations in INPP5B have not been described in humans. Here, we report the case of an 11-year-old boy with short stature and an above-average IQ; severe proteinuria, hypercalciuria and osteopenia resulting in a vertebral compression fracture; and Chiari I malformation with cervico-thoracic syringohydromyelia requiring suboccipital decompression. Sequencing revealed a novel, de novo DD2-causing 462 bp deletion disrupting exon 3 of OCRL1 and a maternally inherited, extremely rare (ExAC allele frequency 8.4×10⁻⁶) damaging missense mutation in INPP5B (p.A51V). This mutation substitutes an evolutionarily conserved amino acid in the protein’s critical PH domain. In silico analyses of mutation impact predicted by SIFT, PolyPhen2, MetaSVM and CADD algorithms were all highly deleterious. Together, our findings report a novel association of DD2 with Chiari I malformation and syringohydromyelia, and document the effects of digenic mutation of human OCRL paralogs. These findings lend genetic support to the hypothesis that impaired ciliogenesis may contribute to the development of Chiari I malformation, and implicates OCRL-dependent PIP₃ metabolism in this mechanism.

Progress in Understanding the Genetics of Calcium-Containing Nephrolithiasis

Renal stone disease is a frequent condition, causing a huge burden on health care systems globally. Calcium-based calculi account for around 75% of renal stone disease and the incidence of these calculi is increasing, suggesting environmental and dietary factors are acting upon a preexisting genetic background. The familial nature and significant heritability of stone disease is known, and recent genetic studies have successfully identified genes that may be involved in renal stone formation. The detection of monogenic causes of renal stone disease has been made more feasible by the use of high-throughput sequencing technologies and has also facilitated the discovery of novel monogenic causes of stone disease. However, the majority of calcium stone formers remain of undetermined genotype. Genome-wide association studies and candidate gene studies implicate a series of genes involved in renal tubular handling of lithogenic substrates, such as calcium, oxalate, and phosphate, and of inhibitors of crystallization, such as citrate and magnesium. Additionally, expression profiling of renal tissues from stone formers provides a novel way to explore disease pathways. New animal models to explore these recently-identified mechanisms and therapeutic interventions are being tested, which hopefully will provide translational insights to stop the growing incidence of nephrolithiasis.

Glomerular Pathology in Dent Disease and Its Association with Kidney Function

BACKGROUND AND OBJECTIVES

Dent disease is a rare X-linked disorder characterized by low molecular weight proteinuria and often considered a renal tubular disease. However, glomerulosclerosis was recently reported in several patients. Thus, Dent disease renal histopathologic features were characterized and assessed, and their association with kidney function was assessed.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Clinical renal pathology reports and slides (where available) were collected from 30 boys and men in eight countries who had undergone clinical renal biopsy between 1995 and 2014.

RESULTS

Median (25th, 75th percentiles) age at biopsy was 7.5 (5, 19) years with an eGFR of 69 (44, 94) ml/min per 1.73 m2 and a 24-hour urine protein of 2000 (1325, 2936) mg. A repeat biopsy for steroid-resistant proteinuria was performed in 13% (four of 30) of the patients. Prominent histologic findings included focal global glomerulosclerosis in 83% (25 of 30; affecting 16%±19% glomeruli), mild segmental foot process effacement in 57% (13 of 23), focal interstitial fibrosis in 60% (18 of 30), interstitial lymphocytic infiltration in 53% (16 of 30), and tubular damage in 70% (21 of 30). Higher percentages of globally sclerotic glomeruli, foot process effacement, and interstitial inflammation were associated with lower eGFR at biopsy, whereas foot process effacement was associated with steeper annual eGFR decline.

CONCLUSIONS

These associations suggest a potential role for glomerular pathology, specifically involving the podocyte, in disease progression, which deserves further study. Furthermore, Dent disease should be suspected in boys and men who have unexplained proteinuria with focal global glomerulosclerosis and segmental foot process effacement on renal biopsy.

The influence of maternal and paternal history on stone composition and clinical course of calcium nephrolithiasis in subjects aged between 15 and 25

Our aim was to compare the influence of maternal history of stones (MHS) and paternal history of stones (PHS) on composition of calculi and disease course in a group of patients with calcium nephrolithiasis (CN) aged between 15 and 25, the age range with the maximal influence of family history on disease expression. One-hundred thirty-five patients (68 F) with CN and one stone-forming parent were retrospectively selected from the database of our outpatient stone clinic, and categorized according to MHS or PHS. Data about stone disease course and composition of passed calculi, determined by chemical analysis or Fourier-transformed infrared spectrophotometry, were collected together with information on blood chemistry and 24-h urinary profile of lithogenic risk. The characteristics of disease course and stone composition were compared using logistic regression tests adjusted for age, sex, and BMI or analysis of covariance where appropriate. Patients with MHS (n = 46) had significantly higher urinary calcium/creatinine ratio and ammonium, a higher prevalence of urological treatments (57 vs 27 %, p < 0.001) and mixed calcium oxalate/calcium phosphate stone composition (69 vs 35 %, p = 0.002) than those with PHS. At multivariate logistic regression models, MHS was independently associated with urological treatments (OR 4.5, 95 %CI 1.9-10.7, p < 0.001) and the formation of calculi with mixed calcium oxalate/calcium phosphate composition (OR 5.8, 95 %CI 1.9-17.9, p = 0.002). The method of stone analysis did not affect this result. In conclusion, in subjects aged 15-25, MHS is associated with mixed calcium stones and with a higher risk for urological procedures, and should be, therefore, considered in the management of urolithiasis.

Kidney stones

Kidney stones are mineral deposits in the renal calyces and pelvis that are found free or attached to the renal papillae. They contain crystalline and organic components and are formed when the urine becomes supersaturated with respect to a mineral. Calcium oxalate is the main constituent of most stones, many of which form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface. Stone formation is highly prevalent, with rates of up to 14.8% and increasing, and a recurrence rate of up to 50% within the first 5 years of the initial stone episode. Obesity, diabetes, hypertension and metabolic syndrome are considered risk factors for stone formation, which, in turn, can lead to hypertension, chronic kidney disease and end-stage renal disease. Management of symptomatic kidney stones has evolved from open surgical lithotomy to minimally invasive endourological treatments leading to a reduction in patient morbidity, improved stone-free rates and better quality of life. Prevention of recurrence requires behavioural and nutritional interventions, as well as pharmacological treatments that are specific for the type of stone. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more-effective drugs.

Nephrolithiasis, kidney failure and bone disorders in Dent disease patients with and without CLCN5 mutations

Dent disease (DD) is a rare X-linked recessive renal tubulopathy characterised by low-molecular-weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis and/or nephrolithiasis. DD is caused by mutations in both the CLCN5 and OCRL genes. CLCN5 encodes the electrogenic chloride/proton exchanger ClC-5 which is involved in the tubular reabsorption of albumin and LMW proteins, OCRL encodes the inositol polyphosphate 5-phosphatase, and was initially associated with Lowe syndrome. In approximately 25 % of patients, no CLCN5 and OCRL mutations were detected. The aim of our study was to evaluate whether calcium phosphate metabolism disorders and their clinical complications are differently distributed among DD patients with and without CLCN5 mutations. Sixty-four male subjects were studied and classified into three groups: Group I (with CLCN5 mutations), Group II (without CLCN5 mutations) and Group III (family members with the same CLCN5 mutation). LMWP, hypercalciuria and phosphaturic tubulopathy and the consequent clinical complications nephrocalcinosis, nephrolithiasis, bone disorders, and chronic kidney disease (CKD) were considered present or absent in each patient. We found that the distribution of nephrolithiasis, bone disorders and CKD differs among patients with and without CLCN5 mutations. Only in patients harbouring CLCN5 mutations was age-independent nephrolithiasis associated with hypercalciuria, suggesting that nephrolithiasis is linked to altered proximal tubular function caused by a loss of ClC-5 function, in agreement with ClC-5 KO animal models. Similarly, only in patients harbouring CLCN5 mutations was age-independent kidney failure associated with nephrocalcinosis, suggesting that kidney failure is the consequence of a ClC-5 dysfunction, as in ClC-5 KO animal models. Bone disorders are a relevant feature of DD phenotype, as patients were mainly young males and this complication occurred independently of age. The triad of symptoms, LMWP, hypercalciuria, and nephrocalcinosis, was present in almost all patients with CLCN5 mutations but not in those without CLCN5 mutations. This lack of homogeneity of clinical manifestations suggests that the difference in phenotypes between the two groups might reflect different pathophysiological mechanisms, probably depending on the diverse genes involved. Overall, our results might suggest that in patients without CLCN5 mutations several genes instead of the prospected third DD underpin patients’ phenotypes.

The elementome of calcium-based urinary stones and its role in urolithiasis

Urolithiasis affects around 10% of the US population with an increasing rate of prevalence, recurrence and penetrance. The causes for the formation of most urinary calculi remain poorly understood, but obtaining the chemical composition of these stones might help identify key aspects of this process and new targets for treatment. The majority of urinary stones are composed of calcium that is complexed in a crystalline matrix with organic and inorganic components. Surprisingly, mitigation of urolithiasis risk by altering calcium homeostasis has not been very effective. Thus, studies to identify other therapeutic stone-specific targets, using proteomics, metabolomics and microscopy techniques, have been conducted, revealing a high level of complexity. The data suggest that numerous metals other than calcium and many nonmetals are present within calculi at measurable levels and several have distinct distribution patterns. Manipulation of the levels of some of these elemental components of calcium-based stones has resulted in clinically beneficial changes in stone chemistry and rate of stone formation. The elementome--the full spectrum of elemental content--of calcium-based urinary calculi is emerging as a new concept in stone research that continues to provide important insights for improved understanding and prevention of urinary stone disease.

Nephrotic-range Albuminuria as the presenting symptom of Dent-2 disease

Dent disease is a rare X-linked tubulopathy with low molecular weight proteinuria, hypercalciuria, nephrolithiasis, nephrocalcinosis and progressive renal failure. We describe the case of a 9-year-old boy who presented with nephrotic-range albuminuria at the age of 3 years. In the absence of a clear diagnosis, a renal biopsy was performed at 4 years, which revealed minimal change disease. Due to the presence of low molecular weight proteinuria, even in the absence of hypercalciuria, a diagnosis of Dent disease was considered. While there were no mutations in the CLCN5 gene, the diagnosis was confirmed by the presence of a missense mutation (p.Arg318Cys) in the OCRL gene.

CONCLUSION

Given the large phenotypic variability of the disease and based on our experience, we believe that children with low molecular weight proteinuria, even without hypercalciuria, should be investigated for Dent disease.

Heritability of urinary traits that contribute to nephrolithiasis

BACKGROUND AND OBJECTIVES

Kidney stones and their risk factors aggregate in families, yet few studies have systematically estimated heritabilities and genetic correlations of the numerous urinary traits associated with risk of kidney stones.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four-hour urine samples were collected from the Genetic Epidemiology Network of Arteriopathy cohort of families in Rochester, Minnesota, to measure urinary determinants of supersaturation. Diet was assessed using the Viocare food frequency questionnaire. Heritabilities and genetic correlations among the urinary traits were estimated using variance components methods.

RESULTS

Samples were available from 811 individuals (344 men, 467 women; mean age 66 ± 9 years). Age, sex, and weight were significantly correlated with the majority of urinary traits. Many urine excretions (calcium, magnesium, citrate excretion) had strong evidence for heritability (P<0.01) both before and after adjusting for the identified covariates. Among significantly heritable urinary traits, genetic factors explained 20%-36% of interindividual variation after adjustment for covariates. Urinary calcium excretion was significantly genetically correlated with urinary magnesium and with urinary citrate excretion (P<0.05). Although eGFR influenced many urinary traits, controlling for eGFR did not greatly affect estimated heritabilities.

CONCLUSIONS

Evidence from this cohort suggests a strong heritable component to many urinary nephrolithiasis risk factors. Further study of genetic influences on urinary traits relevant for kidney stone pathogenesis is warranted.

The relation between bone and stone formation

Hypercalciuria is the most common metabolic abnormality found in patients with calcium-containing kidney stones. Patients with hypercalciuria often excrete more calcium than they absorb, indicating a net loss of total-body calcium. The source of this additional urinary calcium is almost certainly the skeleton, the largest repository of calcium in the body. Hypercalciuric stone formers exhibit decreased bone mineral density (BMD), which is correlated with the increase in urine calcium excretion. The decreased BMD also correlates with an increase in markers of bone turnover as well as increased fractures. In humans, it is difficult to determine the cause of the decreased BMD in hypercalciuric stone formers. To study the effect of hypercalciuria on bone, we utilized our genetic hypercalciuric stone-forming (GHS) rats, which were developed through successive inbreeding of the most hypercalciuric Sprague-Dawley rats. GHS rats excrete significantly more urinary calcium than similarly fed controls, and all the GHS rats form kidney stones while control rats do not. The hypercalciuria is due to a systemic dysregulation of calcium homeostasis, with increased intestinal calcium absorption, enhanced bone mineral resorption, and decreased renal tubule calcium reabsorption associated with an increase in vitamin D receptors in all these target tissues. We recently found that GHS rats fed an ample calcium diet have reduced BMD and that their bones are more fracture-prone, indicating an intrinsic disorder of bone not secondary to diet. Using this model, we should better understand the pathogenesis of hypercalciuria and stone formation in humans to ultimately improve the bone health of patients with kidney stones.

When to suspect a genetic disorder in a patient with renal stones, and why

Nephrolithiasis is a common disorder, with a rising prevalence in the general population. Its pathogenesis is still unclear, but a role for genetics has long been recognized, especially in cases of the more common calcium nephrolithiasis. Although relatively rare, monogenic causes of hypercalciuria and nephrolithiasis do exist and their timely recognition is important from a prognostic and therapeutic viewpoint. This article reviews the clinical and laboratory findings characterizing inherited causes of nephrolithiasis with a view to helping clinicians to recognize and manage these rare conditions.

SLC34A3 intronic deletion in a new kindred with hereditary hypophosphatemic rickets with hypercalciuria

OBJECTIVE

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is an autosomal recessive form of hypophosphatemia with hyperphosphaturia, hypercalciuria, and hypercalcemia. In two reports on six affected kindreds with HHRH, the disease was mapped to chromosome 9q34, which contains the SLC34A3 gene that encodes the renal type 2c sodium-phosphate cotransporter. Our objective was to define the clinical course of these cases in a family with HHRH and to screen for SLC34A3 gene in order to determine whether these mutations are responsible for HHRH.

METHODS

After clinical and biochemical evaluations, the entire SLC34A3 gene was screened using PCR amplification followed by direct sequencing technique. In this paper, we describe a new kindred with HHRH and a case of progressive and complicated HHRH presenting at age 27 years.

RESULTS

We found 101-bp deletion in intron 9 of the SLC34A3 gene. The index patient was homozygous for this mutation which has been previously reported in a Caucasian population. This is the first report for presence of SLC34A3 intron 9 deletion in an Iranian population.

CONCLUSIONS

These data showed that HHRH can be easily missed or underdiagnosed. Genetic evaluation of patients with familial hypercalciuria, hypophosphatemia and nephrolithiasis is needed for further information on the prevalence and management of this rare disorder.

Nephrocalcinosis and urolithiasis in children

The incidence of adult urolithiasis has increased significantly in industrialized countries over the past decades. Sound incidence rates are not available for children, nor are they known for nephrocalcinosis, which can appear as a single entity or together with urolithiasis. In contrast to the adult kidney stone patient, where environmental factors are the main cause, genetic and/or metabolic disorders are the main reason for childhood nephrocalcinosis and urolithiasis. While hypercalciuria is considered to be the most frequent risk factor, several other metabolic disorders such as hypocitraturia or hyperoxaluria, as well as a variety of renal tubular diseases, e.g., Dent's disease or renal tubular acidosis, have to be ruled out by urine and/or blood analysis. Associated symptoms such as growth retardation, intestinal absorption, or bone demineralization should be evaluated for diagnostic and therapeutic purposes. Preterm infants are a special risk population with a high incidence of nephrocalcinosis arising from immature kidney, medication, and hypocitraturia. In children, concise evaluation will reveal an underlying pathomechanism in >75% of patients. Early treatment reducing urinary saturation of the soluble by increasing fluid intake and by providing crystallization inhibitors, as well as disease-specific medication, are mandatory to prevent recurrent kidney stones and/or progressive nephrocalcinosis, and consequently deterioration of renal function.

The genetic components of idiopathic nephrolithiasis

Nephrolithiasis is a cause of significant morbidity and medical care expenses worldwide. Its prevalence has increased steadily during the last three decades among both adults and children. This trend suggests that changing environmental factors play a significant role in the risk of developing kidney stones although, conversely, there are many indications that genes play an important role in this condition as well. A limited number of monogenic forms have been identified, but the majority of nephrolithiasis cases are the result of complex, multi-factorial interactions between genetic inheritance and environmental exposure. Scientific evidence indicates that inheritance accounts for about half of the risk of common forms, making these forms suitable for investigation by genetic analysis. Here, we review the numerous studies that have been conducted to establish the role of genes in determining the risk of nephrolithiasis, the differential contribution of genes to this risk, and the confounding influence that environmental variables have on genetic studies.

Effects of a low-salt diet on idiopathic hypercalciuria in calcium-oxalate stone formers: a 3-mo randomized controlled trial

BACKGROUND

A direct relation exists between sodium and calcium excretion, but randomized studies evaluating the sustained effect of a low-salt diet on idiopathic hypercalciuria, one of the main risk factors for calcium-oxalate stone formation, are still lacking.

OBJECTIVE

Our goal was to evaluate the effect of a low-salt diet on urinary calcium excretion in patients affected by idiopathic calcium nephrolithiasis.

DESIGN

Patients affected by idiopathic calcium stone disease and hypercalciuria (>300 mg Ca/d in men and >250 mg Ca/d in women) were randomly assigned to receive either water therapy alone (control diet) or water therapy and a low-salt diet (low-sodium diet) for 3 mo. Twenty-four-hour urine samples were obtained twice from all patients: one sample at baseline on a free diet and one sample after 3 mo of treatment.

RESULTS

A total of 210 patients were randomly assigned to receive a control diet (n = 102) or a low-sodium diet (n = 108); 13 patients (2 on the control diet, 11 on the low-sodium diet) withdrew from the trial. At the follow-up visit, patients on the low-sodium diet had lower urinary sodium (mean +/- SD: 68 +/- 43 mmol/d at 3 mo compared with 228 +/- 57 mmol/d at baseline; P < 0.001). Concomitant with this change, they showed lower urinary calcium (271 +/- 86 mg/d at 3 mo compared with 361 +/- 129 mg/d on the control diet, P < 0.001) and lower oxalate excretion (28 +/- 8 mg/d at 3 mo compared with 32 +/- 10 mg/d on the control diet, P = 0.001). Urinary calcium was within the normal range in 61.9% of the patients on the low-salt diet and in 34.0% of those on the control diet (difference: +27.9%; 95% CI: +14.4%, +41.3%; P < 0.001).

CONCLUSION

A low-salt diet can reduce calcium excretion in hypercalciuric stone formers. This trial was registered at clinicaltrials.gov as NCT01005082.

Artificial neural networks for assessing the risk factors for urinary calcium stones according to gender and family history of stone

OBJECTIVE

In a previous work, we evidenced that artificial neural networks (ANNs) were more informative than classical statistical analyses for assessing the risk of idiopathic calcium nephrolithiasis in male stone-formers.

MATERIAL AND METHODS

We compared risk factors for idiopathic calcium nephrolithiasis (age, body mass index, calcemia, calcium oxalate supersaturation, and 24-h calciuria, oxaluria, uricosuria, citraturia, urea, and sodium) in four populations: men and women with and without a family history of stone (FHS). A total of 119 males (58 with an FHS, 61 without) and 59 females (30 with an FHS, 29 without) were compared to healthy controls. For each variable, receiver operating characteristic (ROC) curve indices were calculated by means of ANNs.

RESULTS

In men without an FHS, the most discriminant variables were 24-h urea (ROC curve index 0.76), supersaturation (ROC curve index 0.72), 24-h calciuria (ROC curve index 0.68), 24-h uricosuria (ROC curve index 0.64), 24-h oxaluria (ROC curve index 0.63), 24-h sodium (ROC curve index 0.62), and calcemia (ROC curve index 0.60). In men with an FHS, only supersaturation (ROC curve index 0.67) was discriminant. In women without FHS, calcemia (ROC curve index 0.67), 24-h calciuria (ROC curve index 0.64), and 24-h uricosuria (ROC curve index 0.62) were discriminant. In women with an FHS, supersaturation (ROC curve index 0.70), 24-h uricosuria (ROC curve index 0.69), 24-h urea (ROC curve index 0.68), and 24-h calciuria (ROC curve index 0.67) were discriminant.

CONCLUSIONS

Risk factors for idiopathic calcium nephrolithiasis were roughly the same in men with or without an FHS, and in women with an FHS. In these patients, calcium oxalate supersaturation and 24-h urea were the most discriminant factors. Conversely, in women without an FHS, calcium abnormalities (calcemia, 24-h calciuria) were discriminant and should prompt a search for infraclinical primary hyperparathyroidism or sarcoidosis.