What is nephrocalcinosis?

Risk factors and implications associated with ultrasound-diagnosed nephrocalcinosis in cats with chronic kidney disease

BACKGROUND

Microscopic nephrocalcinosis is a common pathological feature of chronic kidney disease (CKD) in cats. Detection of macroscopic nephrocalcinosis using ultrasonography and its implications remain unexplored.

OBJECTIVES

Identify risk factors associated with ultrasound-diagnosed nephrocalcinosis and evaluate the influence of nephrocalcinosis on CKD progression.

ANIMALS

Thirty-six euthyroid client-owned cats with CKD.

METHODS

Prospective cohort study. Cats with CKD with and without ionized hypercalcemia were enrolled for renal ultrasonography. Cats were categorized according to the presence or absence of ultrasound-diagnosed nephrocalcinosis. Binary logistic regression was performed to identify nephrocalcinosis risk factors. The influence of nephrocalcinosis on CKD progression was assessed using linear mixed models.

RESULTS

Ultrasound-diagnosed nephrocalcinosis was evident in 61% of CKD cats overall, with increased prevalence (81%) in those with hypercalcemia. At enrollment, higher blood ionized calcium concentration (odds ratio [OR], 1.27 per 0.1 mg/dL; P = .01), plasma phosphate concentration (OR, 1.16 per 0.1 mg/dL; P = .05), plasma creatinine concentration (OR, 1.29 per 0.1 mg/dL; P = .02) and alanine aminotransferase activity (OR, 2.08 per 10 U/L; P = .04) were independent nephrocalcinosis risk factors. The rate of change in log-transformed fibroblast growth factor-23 differed significantly between groups (P = .04). Cats with CKD and nephrocalcinosis had increasing plasma creatinine concentrations (.03 ± .01 mg/dL/month; P = .04) and phosphate concentrations (.06 ± .02 mg/dL/month; P < .001) and decreasing body weight (.02 ± .01 kg/month; P < .001) over time.

CONCLUSIONS AND CLINICAL IMPORTANCE

Nephrocalcinosis is prevalent in cats with CKD, especially in those with hypercalcemia. This pathological feature appears to be associated with CKD progression in cats.

Detection of nephrocalcinosis using ultrasonography, micro-computed tomography, and histopathology in cats

BACKGROUND

Identification of nephrocalcinosis in cats with chronic kidney disease (CKD) is of clinical interest but the ability of ultrasonography to detect nephrocalcinosis is uncertain.

OBJECTIVES

To compare ultrasonography, micro-computed tomography (μCT) and histopathology for identification of nephrocalcinosis.

ANIMALS

Twelve kidneys from 7 euthyroid client-owned cats with CKD.

METHODS

Descriptive study. Renal ultrasonography was performed ante-mortem for nephrocalcinosis detection. Kidneys were grouped based on nephrocalcinosis: present, suspected, or absent. When cats died, necropsy was performed. Renal tissue was evaluated using μCT for macroscopic nephrocalcinosis, and nephrocalcinosis volume-to-kidney tissue ratio (macro-VN:KT) and sagittal nephrocalcinosis area-to-kidney tissue ratio (macro-AN:KT) were calculated. Each kidney subsequently was bisected longitudinally, formalin-fixed, and paraffin-embedded for microscopic nephrocalcinosis assessment using von Kossa and Alizarin red staining with AN:KT (VK-micro-AN:KT and AR-micro-AN:KT) quantified using ImageJ. Data are presented as median (range). Relationships between macroscopic and microscopic AN:KT were assessed using Spearman's correlation.

RESULTS

Nephrocalcinosis by ultrasonography was considered to be absent in 3, suspected in 3, and present in 5 kidneys; 1 kidney had nephrolithiasis with nephrocalcinosis. The macro-VN:KT was 0.001%, 0.001%, and 0.019%, and the macro-AN:KT was 0.08%, 0.30%, and 1.47%, respectively. Histologically, VK-micro-AN:KT was 0.21%, 2.85%, and 4.56%, and AR-micro-AN:KT was 1.73%, 5.82%, and 8.90% for kidneys where ultrasonographic macro-nephrocalcinosis was absent, suspected, or present, respectively. A strong correlation was identified between macroscopic (macro-AN:KT) and microscopic (VK-micro-AN:KT) nephrocalcinosis (rs = 0.76; P = .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Ultrasonographically diagnosed nephrocalcinosis correlates well with macroscopic and microscopic nephrocalcinosis at necropsy despite their separation in time.

Clinical, genetic profile and therapy evaluation of 11 Chinese pediatric patients with Fanconi-Bickel syndrome

BACKGROUND

Fanconi-Bickel syndrome (FBS) is a rare autosomal recessive disorder characterized by impaired glucose and galactose utilization as well as proximal renal tubular dysfunction.

METHODS

Clinical, biochemical, genetic, treatment, and follow-up data for 11 pediatric patients with FBS were retrospectively analysed.

RESULTS

Hepatomegaly (10/11), short stature (10/11) and hypophosphataemic rickets (7/11) were the most common initial symptoms. At diagnosis, all patients had decreased fasting blood glucose (FBG), plasma bicarbonate (HCO3-) and serum phosphorus, as well as elevated liver transaminases, alkaline phosphatase (AKP) and proximal renal tubular dysfunction. Two infant patients were misdiagnosed with transient neonatal diabetes mellitus. After therapy with uncooked cornstarch and conventional rickets treatment, remission of hepatomegaly was observed in all patients, with significant improvements in pre-prandial blood glucose, liver transaminases, triglyceride, plasma HCO3- and AKP (p < 0.05). At the last follow-up, 5/7 patients with elevated AKP had nephrocalcinosis. The mean height standard deviation score (Ht SDS) of eight patients with regular treatment increased from - 4.1 to -3.5 (p = 0.02). Recombinant human growth hormone (rhGH) was administered to 4/9 patients, but their Ht SDS did not improve significantly (p = 0.13). Fourteen variants of the SLC2A2 gene were identified, with six being novel, among which one was recurrent: c.1217T > G (p.L406R) (allele frequency: 4/22, 18%). Patients with biallelic missense variants showed milder metabolic acidosis than those with null variants. Two of five patients from nonconsanguineous families with rare homozygous variations showed 5.3 Mb and 36.6 Mb of homozygosity surrounding the variants, respectively; a region of homozygosity (ROH) involving the entire chromosome 3 covering the SLC2A2 gene, suggesting uniparental disomy 3, was detected in one patient.

CONCLUSIONS

Early diagnosis of FBS is difficult due to the heterogeneity of initial symptoms. Although short stature is a major issue of treatment for FBS, rhGH is not recommended in FBS patients who have normal GH stimulation tests. Patients with biallelic null variants may require alkali supplementation since urine bicarbonate loss is genetically related. ROH is a mechanism for rare homozygous variants of FBS in nonconsanguineous families.

Nephrocalcinosis in Neonates

Nephrocalcinosis occurs in as many as 40% of preterm neonates. Many causes and contributors predispose neonates to develop nephrocalcinosis, including metabolic, genetic, and iatrogenic factors. Because nephrocalcinosis can be a manifestation of an underlying genetic disorder, neonates with nephrocalcinosis must undergo an evaluation to identify and address contributors, to prevent further renal calcium deposition that can potentially lead to renal dysfunction. In this article, we review the epidemiology, pathogenesis, diagnosis, and evaluation of nephrocalcinosis in neonates. We also summarize the natural history of nephrocalcinosis of prematurity as well as the management of this condition.

Urinary Acidification Does Not Explain the Absence of Nephrocalcinosis in a Mouse Model of Familial Hypomagnesaemia with Hypercalciuria and Nephrocalcinosis (FHHNC)

Patients with mutations in Cldn16 suffer from familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC) which can lead to renal insufficiency. Mice lacking claudin-16 show hypomagnesemia and hypercalciuria, but no nephrocalcinosis. Calcium oxalate and calcium phosphate are the most common insoluble calcium salts that accumulate in the kidney in the case of nephrocalcinosis, however, the formation of these salts is less favored in acidic conditions. Therefore, urine acidification has been suggested to limit the formation of calcium deposits in the kidney. Assuming that urine acidification is causative for the absence of nephrocalcinosis in the claudin-16-deficient mouse model, we aimed to alkalinize the urine of these mice by the ablation of the subunit B1 of the vesicular ATPase in addition to claudin-16. In spite of an increased urinary pH in mice lacking claudin-16 and the B1 subunit, nephrocalcinosis did not develop. Thus, urinary acidification is not the only factor preventing nephrocalcinosis in claudin-16 deficient mice.

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.

Clinical outcomes of nephrocalcinosis in preschool-age children: association between nephrocalcinosis improvement and long-term kidney function

Background

We evaluated the long-term clinical outcomes of nephrocalcinosis (NC) according to etiology and grade in preschool-age children with NC.

Methods

We retrospectively analyzed the clinical outcomes and disease grade of children with NC classified into three groups according to etiology: prematurity, tubular disorders, and others.

Results

Overall, 67 children were diagnosed with NC [median age, 0.76 years; interquartile range (IQR) 0.46-2.14 years]. The etiologies of NC included prematurity (28.4%), tubular disorders (25.4%), and others (46.3%). Moreover, 56 (83.6%) children were asymptomatic and diagnosed accidentally through kidney ultrasonography. Newly diagnosed underlying diseases were greater in the tubular disorders group than in the other two groups (P = 0.001). Significantly more newly diagnosed NCs were grade 3 than grade 1 (P = 0.003). The median estimated glomerular filtration rate (eGFR) changed from 96.1 (IQR 68.8-119.2) ml/min/1.72 m2 at diagnosis to 90.9 (IQR 76.4-106.4) ml/min/1.72 m2 at the last follow-up, without a significant difference (P = 0.096). Changes in the kidney function did not differ according to etiology. However, patients without improvement in NC grade showed a decrease in eGFR from 98.1 (IQR 71.1-132.9) to 87.4 (IQR 74.0-104.1) ml/min/1.73 m2 (P = 0.023), while patients with improved NC grade did not show any change in the kidney function.

Conclusions

Early recognition, especially in NC grade 3, can help uncover further diagnoses, such as tubular disorders. Long-term kidney function depends on whether the NC grade improves.

Nephrocalcinosis in juvenile farmed Atlantic Salmon (Salmo salar) may be linked to osmoregulatory stress

Nephrocalcinosis is a widespread challenge in intensive production of salmon smolt. There is however no consensus on its aetiology, which makes it problematic to implement proper measures to limit its development. We performed a survey of nephrocalcinosis prevalence and environmental factors in 11 different hatcheries in Mid-Norway as well as a 6-month monitoring in one of the hatcheries. A multivariate analysis indicated that the most influencing factor for the prevalence of nephrocalcinosis was the supplementation of sea water during smolt production. In the 6-month monitoring, the hatchery introduced salinity in the production water prior to the change in day length. Mismatch in those environmental signals may increase the risk for developing nephrocalcinosis. Salinity fluctuations prior to smoltification can cause osmotic stress and result in unbalanced levels of ions in fish blood. This was clearly illustrated in our study, as the fish experienced chronic hypercalcaemia and hypermagnesaemia. Both magnesium and calcium are excreted over the kidneys and it is possible that their prolonged, elevated levels in plasma resulted in an oversaturation of the urine when finally excreted. This again could have led to the aggregation of calcium deposits within the kidney. This study indicates a relationship between osmotic stress induced by salinity changes in juvenile Atlantic salmon and the development of nephrocalcinosis. Other factors that may affect the severity of nephrocalcinosis are currently subjects for discussion.

Next-Generation Sequencing (NGS) Analysis Illustrates the Phenotypic Variability of Collagen Type IV Nephropathies

Mutations in COL4A3-A5 cause a spectrum of glomerular disorders, including thin basement membrane nephropathy (TBMN) and Alport syndrome (AS). The wide application of next-generation sequencing (NGS) in the last few years has revealed that mutations in these genes are not limited to these clinical entities. In this study, 176 individuals with a clinical diagnosis of inherited kidney disorders underwent an NGS-based analysis to address the underlying cause; those who changed or perfected the clinical diagnosis after molecular analysis were selected. In 5 out of 83 individuals reaching a molecular diagnosis, the genetic result was unexpected: three individuals showed mutations in collagen type IV genes. These patients showed the following clinical pictures: (1) familial focal segmental glomerulosclerosis; (2) end-stage renal disease (ESRD) diagnosed incidentally in a 49-year-old man, with diffuse cortical calcifications on renal imaging; and (3) dysmorphic and asymmetric kidneys with multiple cysts and signs of tubule-interstitial defects. Genetic analysis revealed rare heterozygote/compound heterozygote COL4A4-A5 variants. Our study highlights the key role of NGS in the diagnosis of inherited renal disorders and shows the phenotype variability in patients carrying mutations in collagen type IV genes.

Adjusting phosphate feeding regimen according to daily rhythm increases eggshell quality via enhancing medullary bone remodeling in laying hens

BACKGROUND

Body phosphorus metabolism exhibits a circadian rhythm over the 24-h daily cycle. The egg laying behavior makes laying hens a very special model for investigating phosphorus circadian rhythms. There is lack of information about the impact of adjusting phosphate feeding regimen according to daily rhythm on the phosphorus homeostasis and bone remodeling of laying hens.

METHODS AND RESULTS

Two experiments were conducted. In Exp. 1, Hy-Line Brown laying hens (n = 45) were sampled according the oviposition cycle (at 0, 6, 12, and 18 h post-oviposition, and at the next oviposition, respectively; n = 9 at each time point). Diurnal rhythms of body calcium/phosphorus ingestions and excretions, serum calcium/phosphorus levels, oviduct uterus calcium transporter expressions, and medullary bone (MB) remodeling were illustrated. In Exp. 2, two diets with different phosphorus levels (0.32% and 0.14% non-phytate phosphorus (NPP), respectively) were alternately presented to the laying hens. Briefly, four phosphorus feeding regimens in total (each included 6 replicates of 5 hens): (1) fed 0.32% NPP at both 09:00 and 17:00; (2) fed 0.32% NPP at 09:00 and 0.14% NPP at 17:00; (3) fed 0.14% NPP at 09:00 and 0.32% NPP at 17:00; (4) fed 0.14% NPP at both 09:00 and 17:00. As a result, the regimen fed 0.14% NPP at 09:00 and 0.32% NPP at 17:00, which was designed to strengthen intrinsic phosphate circadian rhythms according to the findings in Exp. 1, enhanced (P < 0.05) MB remodeling (indicated by histological images, serum markers and bone mineralization gene expressions), elevated (P < 0.05) oviduct uterus calcium transportation (indicated by transient receptor potential vanilloid 6 protein expression), and subsequently increased (P < 0.05) eggshell thickness, eggshell strength, egg specific gravity and eggshell index in laying hens.

CONCLUSIONS

These results underscore the importance of manipulating the sequence of daily phosphorus ingestion, instead of simply controlling dietary phosphate concentrations, in modifying the bone remodeling process. Body phosphorus rhythms will need to be maintained during the daily eggshell calcification cycle.

OXGR1 is a candidate disease gene for human calcium oxalate nephrolithiasis

PURPOSE

Nephrolithiasis (NL) affects 1 in 11 individuals worldwide, leading to significant patient morbidity. NL is associated with nephrocalcinosis (NC), a risk factor for chronic kidney disease. Causative genetic variants are detected in 11% to 28% of NL and/or NC, suggesting that additional NL/NC-associated genetic loci await discovery. Therefore, we employed genomic approaches to discover novel genetic forms of NL/NC.

METHODS

Exome sequencing and directed sequencing of the OXGR1 locus were performed in a worldwide NL/NC cohort. Putatively deleterious, rare OXGR1 variants were functionally characterized.

RESULTS

Exome sequencing revealed a heterozygous OXGR1 missense variant (c.371T>G, p.L124R) cosegregating with calcium oxalate NL and/or NC disease in an autosomal dominant inheritance pattern within a multigenerational family with 5 affected individuals. OXGR1 encodes 2-oxoglutarate (α-ketoglutarate [AKG]) receptor 1 in the distal nephron. In response to its ligand AKG, OXGR1 stimulates the chloride-bicarbonate exchanger, pendrin, which also regulates transepithelial calcium transport in cortical connecting tubules. Strong amino acid conservation in orthologs and paralogs, severe in silico prediction scores, and extreme rarity in exome population databases suggested that the variant was deleterious. Interrogation of the OXGR1 locus in 1107 additional NL/NC families identified 5 additional deleterious dominant variants in 5 families with calcium oxalate NL/NC. Rare, potentially deleterious OXGR1 variants were enriched in patients with NL/NC compared with Exome Aggregation Consortium controls (χ2 = 7.117, P = .0076). Wild-type OXGR1-expressing Xenopus oocytes exhibited AKG-responsive Ca2+ uptake. Of 5 NL/NC-associated missense variants, 5 revealed impaired AKG-dependent Ca2+ uptake, demonstrating loss of function.

CONCLUSION

Rare, dominant loss-of-function OXGR1 variants are associated with recurrent calcium oxalate NL/NC disease.

Renal replacement therapy in sarcoidosis

Sarcoidosis is a systemic inflammatory disease of unknown etiology. Kidney involvement in sarcoidosis may be present in up 25-30% of cases. An early diagnosis and prompt treatment with corticosteroids can improve the prognosis but rarely renal sarcoidosis can lead to kidney failure needing renal replacement therapy (RRT). Acute kidney injury (AKI) in sarcoidosis may be caused by granulomatous interstitial nephritis (GIN) or hypercalcemia. These disorders are usually clinically silent and may lead end stage renal disease (ESKD) if not diagnosed or detected too late. In patients with ESKD, dialysis and renal transplantation can offer results comparable to those observed in patients with other causes of kidney failure. Based on a review of literature, we present an overview of RRT in patients with AKI or chronic kidney disease (CKD) caused by sarcoidosis.

Pathogenesis of Pulmonary Calcification and Homologies with Biomineralization in Other Tissues

Lungs often present tissue calcifications and even ossifications, both in the context of high or normal serum calcium levels. Precise mechanisms governing lung calcifications have not been explored. Herein, we emphasize recent advances about calcification processes in other tissues (especially vascular and bone calcifications) and discuss potential sources of calcium precipitates in the lungs, involvement of mineralization promoters and crystallization inhibitors, as well as specific cytokine milieu and cellular phenotypes characteristic for lung diseases, which may be involved in pulmonary calcifications. Further studies are necessary to demonstrate the exact mechanisms underlying calcifications in the lungs, document homologies in biomineralization processes between various tissues in physiological and pathologic conditions, and unravel any locally specific characteristics of mineralization processes that may be targeted to reduce or prevent functionally relevant lung calcifications without negatively affecting the skeleton.

Gene expression patterns in Atlantic salmon (Salmo salar) with severe nephrocalcinosis

Nephrocalcinosis is a common disorder in farmed Atlantic salmon, but the consequences for the fish physiology are not well understood. We performed a transcriptome study in kidneys of Atlantic salmon (Salmo salar) smolts without and with severe chronic nephrocalcinosis (NC). The study revealed that numerous genes are differentially expressed in fish with NC compared with healthy salmon. The most evident changes in gene expression patterns in the NC group were a massive downregulation of metabolism and energy production, upregulation of signalling pathways important for tissue repair and function maintenance and upregulation of inflammatory responses. Overall, the extensive tissue damage and the gene regulation responses that affect salmon with severe nephrocalcinosis are highly likely to have dramatic consequences on fish survival.

Nephrocalcinosis in a Transplanted Kidney: A New Sign of Chronic Tacrolimus Nephrotoxicity

Calcineurin inhibitors are potent immunosuppressive drugs in solid-organ transplantation and multiple autoimmune diseases. Their use is associated with the acute impairment of glomerular filtration and chronic interstitial fibrosis. The latter is mediated by the accumulation of matrix proteins. In this case report, we present a kidney transplant patient with chronic and progressive allograft failure that was associated with nephrocalcinosis. He did not have hypercalcemic-hypercalciuric states such as hyperparathyroidism, sarcoidosis, and hyper-vitaminosis D; normocalcemic-hypercalciuric states such as distal renal tubular acidosis, medullary sponge kidney, excessive use of high-dose loop diuretics, and beta-thalassemia; hyperphosphaturic conditions; and hyperoxaluria. Moreover, his calcifications were limited to the transplanted kidney and spared the native kidneys and extrarenal tissues, and his renal function had improved and stabilized for 6 months after discontinuation of prolonged-release tacrolimus (Advagraf), indicating a cause and an effect phenomenon. Nephrocalcinosis was suspected after ultrasonography and confirmed by computed tomography scanning. Hence, allograft nephrocalcinosis may indicate chronic tacrolimus nephrotoxicity.

Relationship Between Vesicoureteric Reflux and Nephrocalcinosis in Children: A Case-Control Study at a Tertiary Medical Center in Saudi Arabia

BACKGROUND

 Vesicoureteral reflux (VUR), one of the most common pediatric congenital urogenital abnormalities, refers to the abnormal backflow of urine from the urinary bladder back into the ureter or to the kidney. This causes urinary tract infections. Nephrocalcinosis (NC) refers to abnormal deposits of calcium within the renal parenchyma and/or in the renal cortex. Patients with NC are mostly asymptomatic and severe disease may progress to renal failure. Early diagnosis through examinations such as radiography, computed tomography, and ultrasonography, is crucial for therapeutic treatment. Ultrasonography is the preferred method for scanning and grading nephrocalcinosis in children, primarily because it emits no radiation. This study aimed to increase the body of knowledge regarding VUR and nephrocalcinosis by determining its prevalence and assessing the relationship between VUR and nephrocalcinosis in children presenting at our institution. ​​​​Methods:A case-control study was conducted using data from the medical records of 632 children younger than 14 years in a tertiary medical center in Riyadh, Saudi Arabia. Eligible participants were assigned to two groups: Group 1 consisted of 316 patients with VUR, while Group 2 consisted of 316 sex- and age-matched patients without VUR. The difference in the prevalence of nephrocalcinosis between the two groups was assessed. Frequency and percentage were used to present the categorical variables; Pearson product-moment correlation was utilized to establish the association between VUR and nephrocalcinosis. Statistical significance was established at p<0.05. ​​​​​Result: Only two cases in Group 1 were positive for nephrocalcinosis (0.63%, one male and one female), while four cases in Group 2 were positive for the condition (1.26%, two males and two females). There was no significant difference in the incidence of nephrocalcinosis between the two groups (p=0.873), indicating no relationship between VUR and nephrocalcinosis in children.

CONCLUSION

There is no relationship between VUR and nephrocalcinosis in children under the age of 14 years.

Prevalence and Predictors of Radiographically Apparent Upper Urinary Tract Urolithiasis in Eight Dog Breeds Predisposed to Calcium Oxalate Urolithiasis and Mixed Breed Dogs

Data on upper urinary tract (UUT) uroliths in dogs are important to understanding their etiology. The aim of this retrospective case-control study was to determine the prevalence and identify predictors of radiographically apparent UUT uroliths in dog breeds at increased risk for calcium oxalate uroliths (CaOx risk breeds) and mixed breed dogs. Radiologist reports of three-view abdominal radiographs were reviewed from 251 purebred dogs of 8 CaOx risk breeds and 68 mixed breed dogs. UUT uroliths were more common in CaOx risk breeds than mixed breed dogs (23% versus 6%, respectively; OR = 4.8, 95% confidence interval [CI] 1.7−18.9, p < 0.001). UUT uroliths were more common in dogs with lower urinary tract (LUT) uroliths (predominantly calcium-containing) than those without (41% versus 5%, respectively; OR = 13.6, 95% CI 6.3−33.1, p < 0.001), and LUT uroliths predicted the presence of UUT uroliths in the multivariable regression (OR = 6.5, 95% CI 2.8−16.7, p < 0.001). Increasing age (p < 0.001) and lower body weight (p = 0.0016) were also predictors of UUT urolith presence in the multivariable regression. The high prevalence of UUT uroliths in dogs with LUT uroliths supports a shared mechanism for their formation.

Genetic testing enables a precision medicine approach for nephrolithiasis and nephrocalcinosis in pediatrics: a single-center cohort

Objective

Hereditary factors are the main cause of pediatric nephrolithiasis (NL)/nephrocalcinosis (NC). We summarized the genotype–phenotype correlation of hereditary NL/NC in our center, to evaluate the role of genetic testing in early diagnosis.

Methods

The clinical data of 32 NL/NC cases, which were suspected to have an inherited basis, were retrospectively analyzed from May 2017 to August 2020. The trio-whole exome sequencing was used as the main approach for genetic testing, variants were confirmed by Sanger sequencing, and pathogenicity analysis according to protein function was predicted with custom-developed software.

Results

Causative monogenic mutations were detected in 24 of 32 NL/NC patients, and copy number variation was detected in one patient. A summary of manifestations in patients with inherited diseases revealed a significant degree of growth retardation, increased urinary excretion of the low-molecular weight protein, hypercalciuria, electrolyte imbalances, and young age of onset to be common in heredity disease. In addition, some patients had abnormal renal function (3 ppm 25). The most frequent pathology identified was distal renal tubular acidosis (with inclusion of SLC4A1, ATP6V1B1, and ATP6VOA4 genes), followed by Dent disease (CLCN5 and OCRL1 genes), primary hyperoxaluria (PH) (AGXT and HOGA1 genes) and Kabuki syndrome (KMT2D gene), which was more likely to present as NC or recurrent stone and having a higher correlation with a specific biochemical phenotype and extrarenal phenotype.

Conclusion

The etiology of NL/NC is heterogeneous. This study explored in depth the relationship between phenotype and genotype in 32 patients, and confirmed that genetic testing and clinical phenotype evaluation enable the precision medicine approach to treating patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00438-022-01897-z.

Extracellular DNA: A Missing Link in the Pathogenesis of Ectopic Mineralization

Although deoxyribonucleic acid (DNA) is the genetic coding for the very essence of life, these macromolecules or components thereof are not necessarily lost after a cell dies. There appears to be a link between extracellular DNA and biomineralization. Here the authors demonstrate that extracellular DNA functions as an initiator of collagen intrafibrillar mineralization. This is confirmed with in vitro and in vivo biological mineralization models. Because of their polyanionic property, extracellular DNA molecules are capable of stabilizing supersaturated calcium phosphate solution and mineralizing 2D and 3D collagen matrices completely as early as 24 h. The effectiveness of extracellular DNA in biomineralization of collagen is attributed to the relatively stable formation of amorphous liquid droplets triggered by attraction of DNA to the collagen fibrils via hydrogen bonding. These findings suggest that extracellular DNA is biomimetically significant for fabricating inorganic-organic hybrid materials for tissue engineering. DNA-induced collagen intrafibrillar mineralization provides a clue to the pathogenesis of ectopic mineralization in different body tissues. The use of DNase for targeting extracellular DNA at destined tissue sites provides a potential solution for treatment of diseases associated with ectopic mineralization.

Switching from conventional therapy to burosumab injection has the potential to prevent nephrocalcinosis in patients with X-linked hypophosphatemic rickets

OBJECTIVES

X-linked hypophosphatemic rickets (XLH) is a congenital fibroblast growth factor (FGF)23-related metabolic bone disease that is treated with active vitamin D and phosphate as conventional therapies. Complications of these therapies include nephrocalcinosis (NC) caused by excessive urine calcium and phosphate concentrations. Recently, an anti-FGF23 antibody, burosumab, was developed and reported to be effective in poorly-controlled or severe XLH patients. This study aimed to reveal the impact of switching treatments in relatively well-controlled XLH children with the Rickets Severity Scale less than 2.0.

METHODS

The effects of the two treatments in eight relatively well-controlled XLH children with a mean age of 10.4 ± 1.9 years were compared retrospectively for the same treatment duration (31 ± 11 months) before and after the baseline.

RESULTS

Actual doses of alfacalcidol and phosphate as conventional therapy were 150.9 ± 43.9 ng/kg and 27.5 ± 6.3 mg/kg per day, respectively. Renal echography revealed spotty NC in 8/8 patients, but no aggravation of NC was detected by switching treatments. Switching treatments increased TmP/GFR (p=0.002) and %TRP (p<0.001), and improved the high urine calcium/creatinine ratio to the normal range (p<0.001) although both treatments controlled disease markers equally. Additionally, low intact parathyroid hormone during conventional therapy was increased within the normal range by switching treatments.

CONCLUSIONS

Our results suggest that a high dose of alfacalcidol was needed to control the disease, but it caused hypercalciuria and NC. We concluded that switching treatments in relatively well-controlled XLH children improved renal phosphate reabsorption and decreased urine calcium extraction, and may have the potential to prevent NC.

Renal complications in patients with chronic hypoparathyroidism on conventional therapy: a systematic literature review : Renal disease in chronic hypoparathyroidism

A systematic literature review was performed to summarize the frequency and nature of renal complications in patients with chronic hypoparathyroidism managed with conventional therapy. Methodology was consistent with the recommendations outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Peer-reviewed journal articles with specified medical subject heading terms were identified using the PubMed, EMBASE, and Cochrane databases. Data were extracted from eligible articles based on prespecified parameters for clinical outcomes of renal calcifications and disease. Because of the heterogeneity of the data, a meta-analysis could not be conducted. From 1200 potentially relevant articles, data were extracted from 13 manuscripts that reported data for ≥1 of the 19 predefined renal outcomes for ≥10 adult patients (n = 11 manuscripts) or pediatric patients (n = 2 manuscripts). The collective data provide evidence that adult and pediatric patients with chronic hypoparathyroidism and treated with conventional therapy (oral calcium and active vitamin D) had an increased risk of renal complications. The reported rate of nephrolithiasis was up to 36%, with the lowest rates in studies reporting shorter duration of disease. The rate of nephrocalcinosis was up to 38%. Some studies reported a combined nephrolithiasis/nephrocalcinosis outcome of 19% to 31%. Data for renal disease that encompassed a range of renal insufficiency to chronic kidney disease were reported in 10 articles; the reported rates ranged from 2.5% to 41%. In patients who receive long-term treatment with oral calcium and active vitamin D, chronic hypoparathyroidism may be associated with an increased risk of renal complications compared with the general population.

[18F]-sodium fluoride autoradiography imaging of nephrocalcinosis in donor kidneys and explanted kidney allografts

Nephrocalcinosis is present in up to 43% of kidney allograft biopsies at one-year after transplantation and is associated with inferior graft function and poor graft survival. We studied [¹⁸F]-sodium fluoride ([¹⁸F]-NaF) imaging of microcalcifications in donor kidneys (n = 7) and explanted kidney allografts (n = 13). Three µm paraffin-embedded serial sections were used for histological evaluation of calcification (Alizarin Red; Von Kossa staining) and ex-vivo [¹⁸F]-NaF autoradiography. The images were fused to evaluate if microcalcification areas corresponded with [¹⁸F]-NaF uptake areas. Based on histological analyses, tubulointerstitial and glomerular microcalcifications were present in 19/20 and 7/20 samples, respectively. Using autoradiography, [¹⁸F]-NaF uptake was found in 19/20 samples, with significantly more tracer activity in kidney allograft compared to deceased donor kidney samples (p = 0.019). Alizarin Red staining of active microcalcifications demonstrated good correlation (Spearman’s rho of 0.81, p < 0.001) and Von Kossa staining of consolidated calcifications demonstrated significant but weak correlation (0.62, p = 0.003) with [¹⁸F]-NaF activity. This correlation between ex-vivo [¹⁸F]-NaF uptake and histology-proven microcalcifications, is the first step towards an imaging method to identify microcalcifications in active nephrocalcinosis. This may lead to better understanding of the etiology of microcalcifications and its impact on kidney transplant function.

Point-of-care ultrasound for evaluating intra-abdominal calcification in the pediatric emergency department: case series and review of literature

Background

The presence of intra-abdominal calcification in the pediatric population can be due to a wide range of conditions. Calcification in the abdomen can be seen in normal or abnormal anatomical structures. In some patients, abnormal calcification points towards the pathology; whereas in others, calcification itself is the pathology. After a thorough history and clinical examination, point-of-care ultrasound (POCUS) would complement the assessment of acute abdominal pain, based on the list of differentials generated as per the abdominal region. The main objective of this article is to review commonly encountered causes of intra-abdominal calcifications in the pediatric population and help in clinical decision-making in a Pediatric Emergency Department.

Case presentation

We describe a series of pediatric patients who presented to the Pediatric Emergency Department with acute abdominal pain, in whom point-of-care ultrasound helped expedite the diagnosis by identifying varying types of calcification and associated sonological findings. For children who present to the Pediatric Emergency Department with significant abdominal pain, a rapid distinction between emergencies and non-emergencies is vital to decrease morbidity and mortality.

Conclusions

In a child presenting to the Pediatric Emergency Department with abdominal pain, POCUS and the findings of calcifications can narrow or expand the differential diagnosis when integrated with history and physical exam, to a specific anatomic structure. Integrating these findings with additional sonological findings of an underlying pathology might raise sufficient concerns in the emergency physicians to warrant further investigations for the patient in the form of a formal radiological ultrasound and assist in the patient's early disposition. The use of POCUS might also help to categorize the type of calcification to one of the four main categories of intra-abdominal calcifications, namely concretions, conduit wall calcification, cyst wall calcification, and solid mass-type calcification. POCUS used thoughtfully can give a diagnosis and expand differential diagnosis, reduce cognitive bias, and reduce physician mental load. By integrating the use of POCUS with the history and clinical findings, it will be possible to expedite the management in children who present to the Pediatric Emergency Department with acute abdominal pain.

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.

Nephrocalcinosis: A Review of Monogenic Causes and Insights They Provide into This Heterogeneous Condition

The abnormal deposition of calcium within renal parenchyma, termed nephrocalcinosis, frequently occurs as a result of impaired renal calcium handling. It is closely associated with renal stone formation (nephrolithiasis) as elevated urinary calcium levels (hypercalciuria) are a key common pathological feature underlying these clinical presentations. Although monogenic causes of nephrocalcinosis and nephrolithiasis are rare, they account for a significant disease burden with many patients developing chronic or end-stage renal disease. Identifying underlying genetic mutations in hereditary cases of nephrocalcinosis has provided valuable insights into renal tubulopathies that include hypercalciuria within their varied phenotypes. Genotypes affecting other enzyme pathways, including vitamin D metabolism and hepatic glyoxylate metabolism, are also associated with nephrocalcinosis. As the availability of genetic testing becomes widespread, we cannot be imprecise in our approach to nephrocalcinosis. Monogenic causes of nephrocalcinosis account for a broad range of phenotypes. In cases such as Dent disease, supportive therapies are limited, and early renal replacement therapies are necessitated. In cases such as renal tubular acidosis, a good renal prognosis can be expected providing effective treatment is implemented. It is imperative we adopt a precision-medicine approach to ensure patients and their families receive prompt diagnosis, effective, tailored treatment and accurate prognostic information.

Renal Ca2+ and Water Handling in Response to Calcium Sensing Receptor Signaling: Physiopathological Aspects and Role of CaSR-Regulated microRNAs

Calcium (Ca²⁺) is a universal and vital intracellular messenger involved in a diverse range of cellular and biological processes. Changes in the concentration of extracellular Ca²⁺ can disrupt the normal cellular activities and the physiological function of these systems. The calcium sensing receptor (CaSR) is a unique G protein-coupled receptor (GPCR) activated by extracellular Ca²⁺ and by other physiological cations, aminoacids, and polyamines. CaSR is the main controller of the extracellular Ca²⁺ homeostatic system by regulating parathyroid hormone (PTH) secretion and, in turn, Ca²⁺ absorption and resorption. Recent advances highlight novel signaling pathways activated by CaSR signaling involving the regulation of microRNAs (miRNAs). miRNAs are naturally-occurring small non-coding RNAs that regulate post-transcriptional gene expression and are involved in several diseases. We previously described that high luminal Ca²⁺ in the renal collecting duct attenuates short-term vasopressin-induced aquaporin-2 (AQP2) trafficking through CaSR activation. Moreover, we demonstrated that CaSR signaling reduces AQP2 abundance via AQP2-targeting miRNA-137. This review summarizes the recent data related to CaSR-regulated miRNAs signaling pathways in the kidney.

Living Kidney Donation in a Type 1 Dent's Disease Patient from His Mother

INTRODUCTION

Dent's disease is a rare X-linked recessive disorder that manifests in childhood or early adulthood and can lead to end-stage renal disease (ESRD). It occurs in males, who are hemizygous. In patients who develop ESRD, a deceased donor kidney transplant cures the disease. Females are obligate carriers of the mutated gene, and some show a mild Dent's disease phenotype. There may be reason for concern when considering a female obligate carrier (i.e., the mother) for kidney donation because of the risk of kidney function deterioration.

CASE PRESENTATION

We describe the first successful kidney transplantation involving a patient with type 1 Dent's disease and ESRD given a kidney by an obligate carrier of the gene mutation, his mother.

CONCLUSIONS

After careful assessment of the female obligate carriers, intrafamilial kidney donation in Dent's disease type 1 is feasible. No deteriorating renal function in the donor was observed.

The role of the gasotransmitter hydrogen sulfide in pathological calcification

Calcification is the deposition of minerals, mainly hydroxyapatite, inside the cell or in the extracellular matrix. Physiological calcification is central for many aspects of development including skeletal and tooth growth; conversely, pathological mineralization occurs in soft tissues and is significantly associated with malfunction and impairment of the tissue where it is located. Various mechanisms have been proposed to explain calcification. However, this research area lacks a more integrative, systemic, and global perspective that could explain both physiological and pathological processes. In this review, we propose such an integrated explanation. Hydrogen sulfide (H₂ S) is a newly recognized multifunctional gasotransmitters and tis actions have been studied in different physiological and pathological contexts, but little is known about its potential role on calcification. Interestingly, we found that H₂ S promotes calcification under physiological conditions and has an inhibitory effect on pathological processes. This makes H₂ S a potential therapy for diseases related to pathological calcification. LINKED ARTICLES: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Mice with a Brd4 Mutation Represent a New Model of Nephrocalcinosis

Nephrolithiasis (NL) and nephrocalcinosis (NC), which comprise renal calcification of the collecting system and parenchyma, respectively, have a multifactorial etiology with environmental and genetic determinants and affect ∼10% of adults by age 70 years. Studies of families with hereditary NL and NC have identified >30 causative genes that have increased our understanding of extracellular calcium homeostasis and renal tubular transport of calcium. However, these account for <20% of the likely genes that are involved, and to identify novel genes for renal calcification disorders, we investigated 1745 12-month-old progeny from a male mouse that had been treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) for radiological renal opacities. This identified a male mouse with renal calcification that was inherited as an autosomal dominant trait with >80% penetrance in 152 progeny. The calcification consisted of calcium phosphate deposits in the renal papillae and was associated with the presence of the urinary macromolecules osteopontin and Tamm-Horsfall protein, which are features found in Randall's plaques of patients with NC. Genome-wide mapping located the disease locus to a ∼30 Mbp region on chromosome 17A3.3-B3 and whole-exome sequence analysis identified a heterozygous mutation, resulting in a missense substitution (Met149Thr, M149T), in the bromodomain-containing protein 4 (BRD4). The mutant heterozygous (Brd4^+/M149T ) mice, when compared with wild-type (Brd4^+/+ ) mice, were normocalcemic and normophosphatemic, with normal urinary excretions of calcium and phosphate, and had normal bone turnover markers. BRD4 plays a critical role in histone modification and gene transcription, and cDNA expression profiling, using kidneys from Brd4^+/M149T and Brd4^+/+ mice, revealed differential expression of genes involved in vitamin D metabolism, cell differentiation, and apoptosis. Kidneys from Brd4^+/M149T mice also had increased apoptosis at sites of calcification within the renal papillae. Thus, our studies have established a mouse model, due to a Brd4 Met149Thr mutation, for inherited NC. © 2019 American Society for Bone and Mineral Research.

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.

Advances in the treatment of hypoparathyroidism with PTH 1-34

Hypoparathyroidism is a rare disorder of calcium metabolism which is treated with calcium and vitamin D analogs. Although conventional therapy effectively raises serum calcium, it bypasses the potent calcium reabsorption effects of PTH on the kidney which leads to hypercalciuria and an increased risk of nephrocalcinosis and renal insufficiency. Twenty-five years ago, we launched the first systematic investigation into synthetic human PTH 1-34 replacement therapy in both adults and children. These studies led to our current understanding of the complex nature of PTH 1-34 therapy and to the challenges we still face in our pursuit of a safe and effective physiologic replacement therapy for hypoparathyroidism. The normalization and minimal fluctuation of serum and urine calcium levels were the primary management goals. As the frequency of PTH 1-34 injections increased, the total daily dose required to normalize calcium homeostasis decreased and episodes of hypercalcemia and hypercalciuria diminished, producing a more physiologic biochemical profile. Twice-daily injections achieved simultaneous normalization of serum and urine calcium levels in many patients but the persistent elevation of bone markers and the difficulty in reducing urine calcium to normal levels in the more severe cases, suggested an alternative to PTH 1-34 injections was needed. The studies with PTH 1-34 delivered by insulin pump represent an important advance in the management of hypoparathyroidism. PTH 1-34 delivered by insulin pump normalized serum and urine calcium and markers of bone turnover. Additionally, pump delivery of PTH 1-34 produced stable magnesium values within the normal range and reduced magnesium excretion. Currently, PTH 1-34 delivery by pump is the only alternative to PTH injections that has been tested in both adults and children and proven to achieve a physiologic biochemical profile.

Association of Candidate Gene Polymorphisms With Chronic Kidney Disease: Results of a Case-Control Analysis in the Nefrona Cohort

Chronic kidney disease (CKD) is a major risk factor for end-stage renal disease, cardiovascular disease and premature death. Despite classical clinical risk factors for CKD and some genetic risk factors have been identified, the residual risk observed in prediction models is still high. Therefore, new risk factors need to be identified in order to better predict the risk of CKD in the population. Here, we analyzed the genetic association of 79 SNPs of proteins associated with mineral metabolism disturbances with CKD in a cohort that includes 2,445 CKD cases and 559 controls. Genotyping was performed with matrix assisted laser desorption ionization–time of flight mass spectrometry. We used logistic regression models considering different genetic inheritance models to assess the association of the SNPs with the prevalence of CKD, adjusting for known risk factors. Eight SNPs (rs1126616, rs35068180, rs2238135, rs1800247, rs385564, rs4236, rs2248359, and rs1564858) were associated with CKD even after adjusting by sex, age and race. A model containing five of these SNPs (rs1126616, rs35068180, rs1800247, rs4236, and rs2248359), diabetes and hypertension showed better performance than models considering only clinical risk factors, significantly increasing the area under the curve of the model without polymorphisms. Furthermore, one of the SNPs (the rs2248359) showed an interaction with hypertension, being the risk genotype affecting only hypertensive patients. We conclude that 5 SNPs related to proteins implicated in mineral metabolism disturbances (Osteopontin, osteocalcin, matrix gla protein, matrix metalloprotease 3 and 24 hydroxylase) are associated to an increased risk of suffering CKD.

Human proximal tubular cells can form calcium phosphate deposits in osteogenic culture: role of cell death and osteoblast-like transdifferentiation

Nephrocalcinosis is a clinicopathological entity characterized by microscopic calcium crystals in the renal parenchyma, within the tubular lumen or in the interstitium. Crystal binding to tubular cells may be the cause underlying nephrocalcinosis and nephrolithiasis. Pathological circumstances, such as acute cortical necrosis, may induce healthy cells to acquire a crystal-binding phenotype. The present study aimed to investigate whether human renal proximal tubular cells (HK-2 cells) can form calcium phosphate deposits under osteogenic conditions, and whether apoptosis and/or osteogenic-like processes are involved in cell calcification. HK-2 cells were cultured in standard or osteogenic medium for 1, 5, and 15 days. Von Kossa staining and ESEM were used to analyze crystal deposition. Apoptosis was investigated, analyzing caspase activation by in-cell Western assay, membrane translocation of phosphotidylserine by annexin V-FITC/propidium iodide staining, and DNA fragmentation by TUNEL assay. qRT/PCR, immunolabeling and cytochemistry were performed to assess osteogenic activation (Runx2, Osteonectin, Osteopontin and ALP), and early genes of apoptosis (BAX, Bcl-2). HK-2 cell mineralization was successfully induced on adding osteogenic medium. Calcium phosphate deposition increased in a time-dependent manner, and calcified cell aggregates exhibited characteristic signs of apoptosis. At 15 days, calcifying HK-2 cells revealed osteogenic markers, such as Runx2, ALP, osteonectin and osteopontin. Monitoring the processes at 1, 5, and 15 days showed apoptosis starting already after 5 days of osteogenic induction, when the first small calcium phosphate crystals began to appear on areas where cell aggregates were in apoptotic conditions. The cell death process proved caspase-dependent. The importance of apoptosis was reinforced by the time-dependent increase in BAX expression, starting from day 1. These findings strongly support the hypothesis that apoptosis triggered HK-2 calcification even before any calcium phosphate crystal deposition or acquisition of an osteogenic phenotype.

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.

Calcium-sensing receptor: evidence and hypothesis for its role in nephrolithiasis

Calcium-sensing receptor (CaSR) is a plasma-membrane G protein-coupled receptor activated by extracellular calcium and expressed in kidney tubular cells. It inhibits calcium reabsorption in the ascending limb and distal convoluted tubule when stimulated by the increase of serum calcium levels; therefore, these tubular segments are enabled by CaSR to play a substantial role in the regulation of serum calcium levels. In addition, CaSR increases water and proton excretion in the collecting duct and promotes phosphate reabsorption and citrate excretion in the proximal tubule. These CaSR activities form a network in which they are integrated to protect the kidney against the negative effects of high calcium concentrations and calcium precipitates in urine. Therefore, the CaSR gene has been considered as a candidate to explain calcium nephrolithiasis. Epidemiological studies observed that calcium nephrolithiasis was associated with polymorphisms of the CaSR gene regulatory region, rs6776158, located within the promoter-1, rs1501899 located in the intron 1, and rs7652589 in the 5'-untranslated region. These polymorphisms were found to reduce the transcriptional activity of promoter-1. Activating rs1042636 polymorphism located in exon 7 was associated with calcium nephrolithiasis and hypercalciuria. Genetic polymorphisms decreasing CaSR expression could predispose individuals to stones because they may impair CaSR protective effects against precipitation of calcium phosphate and oxalate. Activating polymorphisms rs1042636 could predispose to calcium stones by increasing calcium excretion. These findings suggest that CaSR may play a complex role in lithogenesis through different pathways having different relevance under different clinical conditions.

Predictors of Renal Function and Calcifications in Primary Hyperparathyroidism: A Nested Case-Control Study

CONTEXT

Some patients with primary hyperparathyroidism (PHPT) develop renal calcifications. Investigation of urinary and nonurinary risk factors are essential.

OBJECTIVE

We aimed to study the prevalence and potential biochemical predictors of renal calcifications.

DESIGN

Nested case-control study.

SETTING

University hospital.

PARTICIPANTS

We identified 792 patients with PHPT from 2005 to 2015. We used biochemical data to validate the diagnosis of PHPT.

MAIN OUTCOME MEASURES

The prevalence of renal calcifications defined as nephrolithiasis or nephrocalcinosis assessed by a routine CT scan at the time of diagnosis.

RESULTS

A total of 792 patients with PHPT were identified among whom 617 patients (78%) had a CT scan preformed. We found a prevalence of renal calcifications of 23%, equally frequent between sexes. A total of 76 patients (12%) had nephrolithiasis and 75 patients (12%) had nephrocalcinosis where 7 patients (1%) had both nephrolithiasis and nephrocalcinosis. Compared with patients without renal calcifications, patients with renal calcifications had significantly higher levels of ionized calcium, parathyroid hormone, and 24-hour calcium excretion (Pall < 0.01). Patients with nephrocalcinosis had higher plasma levels of phosphate and a higher calcium-phosphate product compared with patients with nephrolithiasis (Pall < 0.05). Impaired renal function (estimated glomerular filtration rate <60 mL/min) was observed in 12% of patients. However, no differences in renal function were observed between those with and without renal calcifications.

CONCLUSION

Renal calcifications are frequent in patients with PHPT and are associated with the severity of the disease. Impaired renal function is also common in PHPT, but renal function was not associated with renal calcifications.

Focal segmental glomerulosclerosis and medullary nephrocalcinosis in children with ADCK4 mutations

BACKGROUND

Mutations in the AarF domain containing kinase 4 gene (ADCK4), one of the novel genes causing steroid-resistant nephrotic syndrome (SRNS), usually manifest as isolated adolescent-onset focal segmental glomerulosclerosis (FSGS). ADCK4 interacts with components of the coenzyme Q10 (CoQ10) biosynthesis pathway.

METHODS

The incidence and phenotypes of patients with ADCK4 mutations were investigated in a cohort of Korean pediatric patients with SRNS.

RESULTS

Among the 53 patients enrolled in the study the incidence of ADCK4-associated FSGS was 7.5% (n = 4) in children aged 5 years and older with multidrug-resistant FSGS. Two additional patients were included for phenotype analyses, one detected by family screening and the other with cyclosporine-responsive FSGS. These six patients presented proteinuria without overt nephrotic syndrome at a median age of 110 (range 60-153) months, of whom five progressed to end-stage renal disease within a median period of 46 (range 36-79) months after onset. Renal biopsies revealed mitochondrial abnormalities in podocytes and tubular cells of all patients. Notably, all patients showed accompanying medullary nephrocalcinosis. None of the patients showed other extrarenal manifestations.

CONCLUSIONS

ADCK4 mutations should be considered in older children presenting with steroid resistant FSGS. An early diagnosis of ADCK4 mutations is essential because the condition is treatable with CoQ10 supplementation at an early stage. The association with medullary nephrocalcinosis may be an additional diagnostic indicator.

Renal involvement in lysinuric protein intolerance: contribution of pathology to assessment of heterogeneity of renal lesions

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disease caused by mutations in the SLC7A7 gene encoding the light subunit of a cationic amino acid transporter. Symptoms mimic primary urea cycle defects but dysimmune symptoms are also described. Renal involvement in LPI was first described in the 1980s. In 2007, it appeared that it could concern as much as 75% of LPI patients and could lead to end-stage renal disease. The most common feature is proximal tubular dysfunction and nephrocalcinosis but glomerular lesions are also reported. However, very little is known regarding histological lesions associated with LPI. We gathered every kidney biopsy of LPI-proven patients in our highly specialized pediatric and adult institution. Clinical, biological, and histological information was analyzed. Five LPI patients underwent kidney biopsy in our institution between 1986 and 2015. Clinically, 4/5 presented with proximal tubular dysfunction and 3/5 with nephrotic range proteinuria. Histology showed unspecific tubulointerstitial lesions and nephrocalcinosis in 3/5 biopsies and marked peritubular capillaritis in one child. Glomerular lesions were heterogeneous: lupus-like-full house membranoproliferative glomerulonephritis (MPGN) in one child evolved towards monotypic IgG1κ MPGN sensitive to immunomodulators. One patient presented with glomerular non-AA non-AL amyloidosis. Renal biopsy is particularly relevant in LPI presenting with glomerular symptoms for which variable histological lesions can be responsible, implying specific treatment and follow-up.

Dent Disease in Chinese Children and Findings from Heterozygous Mothers: Phenotypic Heterogeneity, Fetal Growth, and 10 Novel Mutations

OBJECTIVE

To characterize the phenotypes of Dent disease in Chinese children and their heterozygous mothers and to establish genetic diagnoses.

STUDY DESIGN

Using a modified protocol, we screened 1288 individuals with proteinuria. A diagnosis of Dent disease was established in 19 boys from 16 families by the presence of loss of function/deleterious mutations in CLCN5 or OCRL1. We also analyzed 16 available patients' mothers and examined their pregnancy records.

RESULTS

We detected 14 loss of function/deleterious mutations of CLCN5 in 15 boys and 2 mutations of OCRL1 in 4 boys. Of the patients, 16 of 19 had been wrongly diagnosed with other diseases and 11 of 19 had incorrect or unnecessary treatment. None of the patients, but 6 of 14 mothers, had nephrocalcinosis or nephrolithiasis at diagnosis. Of the patients, 8 of 14 with Dent disease 1 were large for gestational age (>90th percentile); 8 of 15 (53.3%) had rickets. We also present predicted structural changes for 4 mutant proteins.

CONCLUSIONS

Pediatric Dent disease often is misdiagnosed; genetic testing achieves a correct diagnosis. Nephrocalcinosis or nephrolithiasis may not be sensitive diagnostic criteria. We identified 10 novel mutations in CLCN5 and OCRL1. The possibility that altered CLCN5 function could affect fetal growth and a possible link between a high rate of rickets and low calcium intake are discussed.

Ways of calcium reabsorption in the kidney

The role of the kidney in calcium homeostasis has been reshaped from a classic view in which the kidney was regulated by systemic calcitropic hormones such as vitamin D3 or parathyroid hormone to an organ actively taking part in the regulation of calcium handling. With the identification of the intrinsic renal calcium-sensing receptor feedback system, the regulation of paracellular calcium transport involving claudins, and new paracrine regulators such as klotho, the kidney has emerged as a crucial modulator not only of calciuria but also of calcium homeostasis. This review summarizes recent molecular and endocrine contributors to renal calcium handling and highlights the tight link between calcium and sodium reabsorption in the kidney.

Osteopontin protects against high phosphate-induced nephrocalcinosis and vascular calcification

Pathologic calcification is a significant cause of increased morbidity and mortality in patients with chronic kidney disease. The precise mechanisms of ectopic calcification are not fully elucidated, but it is known to be caused by an imbalance of procalcific and anticalcific factors. In the chronic kidney disease population, an elevated phosphate burden is both highly prevalent and a known risk factor for ectopic calcification. Here we tested whether osteopontin, an inhibitor of calcification, protects against high phosphate load-induced nephrocalcinosis and vascular calcification. Osteopontin knockout mice were placed on a high phosphate diet for 11 weeks. Osteopontin deficiency together with phosphate overload caused uremia, nephrocalcinosis characterized by substantial renal tubular and interstitial calcium deposition, and marked vascular calcification when compared with control mice. Although the osteopontin-deficient mice did not exhibit hypercalcemia or hyperphosphatemia, they did show abnormalities in the mineral metabolism hormone fibroblast growth factor-23. Thus, endogenous osteopontin plays a critical role in the prevention of phosphate-induced nephrocalcinosis and vascular calcification in response to high phosphate load. A better understanding of osteopontin's role in phosphate-induced calcification will hopefully lead to better biomarkers and therapies for this disease, especially in patients with chronic kidney disease and other at-risk populations.