Genetic Markers Among the Israeli Druze Minority Population With End-Stage Kidney Disease.

RATIONALE & OBJECTIVE: Genetic etiologies have been identified among approximately 10% of adults with chronic kidney disease (CKD). However, data are lacking regarding the prevalence of monogenic etiologies especially among members of minority groups. This study characterized the genetic markers among members of an Israeli minority group with end-stage kidney disease (ESKD). STUDY DESIGN: A national-multicenter cross-sectional study of Israeli Druze patients (an Arabic-speaking Near-Eastern transnational population isolate) who are receiving maintenance dialysis for ESKD. All study participants underwent exome sequencing. SETTING & PARTICIPANTS: We recruited 94 adults with ESKD, comprising 97% of the total 97 Druze individuals throughout Israel being treated with dialysis during the study period. PREDICTORS: Demographics and clinical characteristics of kidney disease. OUTCOME: Genetic markers. ANALYTICAL APPROACH: Whole-exome sequencing and the relationship of markers to clinical phenotypes. RESULTS: We identified genetic etiologies in 17 of 94 participants (18%). None had a previous molecular diagnosis. A novel, population-specific, WDR19 homozygous pathogenic variant (p.Cys293Tyr) was the most common genetic finding. Other monogenic etiologies included PKD1, PKD2, type IV collagen mutations, and monogenic forms of noncommunicable diseases. The pre-exome clinical diagnosis corresponded to the final molecular diagnosis in fewer than half of the participants. LIMITATIONS: This study was limited to Druze individuals, so its generalizability may be limited. CONCLUSIONS: Exome sequencing identified a genetic diagnosis in approximately 18% of Druze individuals with ESKD. These results support conducting genetic analyses in minority populations with high rates of CKD and for whom phenotypic disease specificity may be low. PLAIN-LANGUAGE SUMMARY: Chronic kidney disease (CKD) affects many people worldwide and has multiple genetic causes. However, there is limited information on the prevalence of genetic etiologies, especially among minority populations. Our national-multicenter study focused on Israeli Druze patients. Using exome-sequencing, we identified previously undetected genetic causes in nearly 20% of patients, including a new and population-specific WDR19 homozygous pathogenic variant. This mutation has not been previously described; it is extremely rare globally but is common among the Druze, which highlights the importance of studying minority populations with high rates of CKD. Our findings provide insights into the genetic basis of end-stage kidney disease in the Israeli Druze, expand the WDR19 phenotypic spectrum, and emphasize the potential value of genetic testing in such populations.

Characterization of Alternative Splicing in High-Risk Wilms' Tumors.

The significant heterogeneity of Wilms' tumors between different patients is thought to arise from genetic and epigenetic distortions that occur during various stages of fetal kidney development in a way that is poorly understood. To address this, we characterized the heterogeneity of alternative mRNA splicing in Wilms' tumors using a publicly available RNAseq dataset of high-risk Wilms' tumors and normal kidney samples. Through Pareto task inference and cell deconvolution, we found that the tumors and normal kidney samples are organized according to progressive stages of kidney development within a triangle-shaped region in latent space, whose vertices, or "archetypes", resemble the cap mesenchyme, the nephrogenic stroma, and epithelial tubular structures of the fetal kidney. We identified a set of genes that are alternatively spliced between tumors located in different regions of latent space and found that many of these genes are associated with the epithelial-to-mesenchymal transition (EMT) and muscle development. Using motif enrichment analysis, we identified putative splicing regulators, some of which are associated with kidney development. Our findings provide new insights into the etiology of Wilms' tumors and suggest that specific splicing mechanisms in early stages of development may contribute to tumor development in different patients.

Characterization of Continuous Transcriptional Heterogeneity in High-Risk Blastemal-Type Wilms' Tumors Using Unsupervised Machine Learning.

Wilms' tumors are pediatric malignancies that are thought to arise from faulty kidney development. They contain a wide range of poorly differentiated cell states resembling various distorted developmental stages of the fetal kidney, and as a result, differ between patients in a continuous manner that is not well understood. Here, we used three computational approaches to characterize this continuous heterogeneity in high-risk blastemal-type Wilms' tumors. Using Pareto task inference, we show that the tumors form a triangle-shaped continuum in latent space that is bounded by three tumor archetypes with "stromal", "blastemal", and "epithelial" characteristics, which resemble the un-induced mesenchyme, the cap mesenchyme, and early epithelial structures of the fetal kidney. By fitting a generative probabilistic "grade of membership" model, we show that each tumor can be represented as a unique mixture of three hidden "topics" with blastemal, stromal, and epithelial characteristics. Likewise, cellular deconvolution allows us to represent each tumor in the continuum as a unique combination of fetal kidney-like cell states. These results highlight the relationship between Wilms' tumors and kidney development, and we anticipate that they will pave the way for more quantitative strategies for tumor stratification and classification.

A multidisciplinary nephrogenetic referral clinic for children and adults-diagnostic achievements and insights.

BACKGROUND: Genetic kidney diseases contribute a significant portion of kidney diseases in children and young adults. Nephrogenetics is a rapidly evolving subspecialty; however, in the clinical setting, increased use of genetic testing poses implementation challenges. Consequently, we established a national nephrogenetics clinic to apply a multidisciplinary model. METHODS: Patients were referred from different pediatric or adult nephrology units across the country if their primary nephrologist suspected an undiagnosed genetic kidney disease. We determined the diagnostic rate and observed the effect of diagnosis on medical care. We also discuss the requirements of a nephrogenetics clinic in terms of logistics, recommended indications for referral, and building a multidisciplinary team. RESULTS: Over 24 months, genetic evaluation was completed for a total of 74 unrelated probands, with an age range of 10 days to 72 years. The most common phenotypes included congenital anomalies of the kidneys and urinary tract, nephrotic syndrome or unexplained proteinuria, nephrocalcinosis/nephrolithiasis, tubulopathies, and unexplained kidney failure. Over 80% of patients were referred due to clinical suspicion of an undetermined underlying genetic diagnosis. A molecular diagnosis was reached in 42/74 probands, yielding a diagnostic rate of 57%. Of these, over 71% of diagnoses were made via next generation sequencing (gene panel or exome sequencing). CONCLUSIONS: We identified a substantial fraction of genetic kidney etiologies among previously undiagnosed individuals which influenced subsequent clinical management. Our results support that nephrogenetics, a rapidly evolving field, may benefit from well-defined multidisciplinary co-management administered by a designated team of nephrologist, geneticist, and bioinformatician. A higher resolution version of the Graphical abstract is available as Supplementary information.

Human Kidney Spheroids and Monolayers Provide Insights into SARS-CoV-2 Renal Interactions.

BACKGROUND: Although coronavirus disease 2019 (COVID-19) causes significan t morbidity, mainly from pulmonary involvement, extrapulmonary symptoms are also major componen ts of the disease. Kidney disease, usually presenting as AKI, is particularly severe among patients with COVID-19. It is unknown, however, whether such injury results from direct kidney infection with COVID-19's causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or from indirect mechanisms. METHODS: Using ex vivo cell models, we sought to analyze SARS-CoV-2 interactions with kidney tubular cells and assess direct tubular injury. These models comprised primary human kidney epithelial cells (derived from nephrectomies) and grown as either proliferating monolayers or quiescent three-dimensional kidney spheroids. RESULTS: We demonstrated that viral entry molecules and high baseline levels of type 1 IFN-related molecules were present in monolayers and kidney spheroids. Although both models support viral infection and replication, they did not exhibit a cytopathic effect and cell death, outcomes that were strongly present in SARS-CoV-2-infected controls (African green monkey kidney clone E6 [Vero E6] cultures). A comparison of monolayer and spheroid cultures demonstrated higher infectivity and replication of SARS-CoV-2 in actively proliferating monolayers, although the spheroid cultures exhibited high er levels of ACE2. Monolayers exhibited elevation of some tubular injury molecules-including molecules related to fibrosis (COL1A1 and STAT6) and dedifferentiation (SNAI2)-and a loss of cell identity, evident by reduction in megalin (LRP2). The three-dimensional spheroids were less prone to such injury. CONCLUSIONS: SARS-CoV-2 can infect kidney cells without a cytopathic effect. AKI-induced cellular proliferation may potentially intensify infectivity and tubular damage by SARS-CoV-2, suggesting that early intervention in AKI is warranted to help minimize kidney infection.

Lin28 sustains early renal progenitors and induces Wilms tumor.

Wilms Tumor, the most common pediatric kidney cancer, evolves from the failure of terminal differentiation of the embryonic kidney. Here we show that overexpression of the heterochronic regulator Lin28 during kidney development in mice markedly expands nephrogenic progenitors by blocking their final wave of differentiation, ultimately resulting in a pathology highly reminiscent of Wilms tumor. Using lineage-specific promoters to target Lin28 to specific cell types, we observed Wilms tumor only when Lin28 is aberrantly expressed in multiple derivatives of the intermediate mesoderm, implicating the cell of origin as a multipotential renal progenitor. We show that withdrawal of Lin28 expression reverts tumorigenesis and markedly expands the numbers of glomerulus-like structures and that tumor formation is suppressed by enforced expression of Let-7 microRNA. Finally, we demonstrate overexpression of the LIN28B paralog in a significant percentage of human Wilms tumor. Our data thus implicate the Lin28/Let-7 pathway in kidney development and tumorigenesis.

Multicystic Dysplastic Kidney: Prenatal Compensatory Renal Growth Pattern.

OBJECTIVES: To assess the prenatal growth pattern of the normal kidney contralateral to a multicystic dysplastic kidney (MCDK). METHODS: A retrospective study was conducted in a single referral center over 4 years. Cases diagnosed prenatally as MCDK and confirmed postnatally constituted the study group. For creation of nomograms, only isolated cases of MCDK were included. RESULTS: Sixty-one fetuses had a diagnosis of an MCDK during the study period. After exclusion of cases with associated malformations, 47 fetuses remained, providing 94 measurements for creation of nomograms. The growth pattern of the normal kidney contralateral to an MCDK was linear throughout gestation (percentile = 20.01 + 1.5 gestational age; linear R2  = 0.753; r = 0.868) and was significantly higher during the third trimester (29-38 weeks' gestation) compared to the second trimester (22-28 weeks' gestation; P < .001). A comparison of the growth pattern of the normal kidney contralateral to the MCDK to the growth pattern of a solitary kidney revealed a significant higher compensatory trend during the third trimester (P < .0001). The mean kidney lengths at 22 and 38 weeks' gestation correlated with the 52nd and 88th and with the 84th and 90th percentiles for the normal kidney contralateral to the MCDK and a solitary kidney, respectively. CONCLUSIONS: According to our study, the normal kidney contralateral to an MCDK has a unique growth pattern during intrauterine life, with dominant growth during the third trimester. The exact mechanism for this pattern, in comparison to early renal hypertrophy shown in solitary kidneys, is currently not clear. These data provide relevant information for the multidisciplinary prenatal counseling of future parents regarding the future renal outcome.

Single-Cell RNA Sequencing Reveals mRNA Splice Isoform Switching during Kidney Development.

BACKGROUND: During mammalian kidney development, nephron progenitors undergo a mesenchymal-to-epithelial transition and eventually differentiate into the various tubular segments of the nephron. Recently, Drop-seq single-cell RNA sequencing technology for measuring gene expression from thousands of individual cells identified the different cell types in the developing kidney. However, that analysis did not include the additional layer of heterogeneity that alternative mRNA splicing creates. METHODS: Full transcript length single-cell RNA sequencing characterized the transcriptomes of 544 individual cells from mouse embryonic kidneys. RESULTS: Gene expression levels measured with full transcript length single-cell RNA sequencing identified each cell type. Further analysis comprehensively characterized splice isoform switching during the transition between mesenchymal and epithelial cellular states, which is a key transitional process in kidney development. The study also identified several putative splicing regulators, including the genes Esrp1/2 and Rbfox1/2. CONCLUSIONS: Discovery of the sets of genes that are alternatively spliced as the fetal kidney mesenchyme differentiates into tubular epithelium will improve our understanding of the molecular mechanisms that drive kidney development.

Successful Introduction of Human Renovascular Units into the Mammalian Kidney.

BACKGROUND: Cell-based therapies aimed at replenishing renal parenchyma have been proposed as an approach for treating CKD. However, pathogenic mechanisms involved in CKD such as renal hypoxia result in loss of kidney function and limit engraftment and therapeutic effects of renal epithelial progenitors. Jointly administering vessel-forming cells (human mesenchymal stromal cells [MSCs] and endothelial colony-forming cells [ECFCs]) may potentially result in in vivo formation of vascular networks. METHODS: We administered renal tubule-forming cells derived from human adult and fetal kidneys (previously shown to exert a functional effect in CKD mice) into mice, alongside MSCs and ECFCs. We then assessed whether this would result in generation of "renovascular units" comprising both vessels and tubules with potential interaction. RESULTS: Directly injecting vessel-forming cells and renal tubule-forming cells into the subcutaneous and subrenal capsular space resulted in self-organization of donor-derived vascular networks that connected to host vasculature, alongside renal tubules comprising tubular epithelia of different nephron segments. Vessels derived from MSCs and ECFCs augmented in vivo tubulogenesis by the renal tubule-forming cells. In vitro coculture experiments showed that MSCs and ECFCs induced self-renewal and genes associated with mesenchymal-epithelial transition in renal tubule-forming cells, indicating paracrine effects. Notably, after renal injury, renal tubule-forming cells and vessel-forming cells infused into the renal artery did not penetrate the renal vascular network to generate vessels; only administering them into the kidney parenchyma resulted in similar generation of human renovascular units in vivo. CONCLUSIONS: Combined cell therapy of vessel-forming cells and renal tubule-forming cells aimed at alleviating renal hypoxia and enhancing tubulogenesis holds promise as the basis for new renal regenerative therapies.

[THE BIG CHALLENGES OF PEDIATRIC NEPHROLOGY AT THE OUTSET OF THE THIRD DECADE OF THE 21ST CENTURY].

INTRODUCTION: Over the past few decades, there have been tremendous advancements in the field of nephrology due to developments in genetics and molecular biology, such as the ability to pinpoint the causative mutations in congenital syndromes involving the kidneys, animal models of kidney disease and an array of tools for manipulating nucleic acids. However, despite these achievements, in most cases, these sophisticated technologies have yet to translate into improved outcomes. Thus, there are still several important challenges in the field of pediatric nephrology, the most important of which are reviewed herein. These include: 1. Better understanding of the association between a specific genotype and disease phenotype in congenital anomalies of the kidney and urinary tract, and development of effective treatments for these anomalies. 2. Deeper understanding of the pathophysiology of genetic kidney diseases. 3. Application of the available molecular tools for the purpose of genetic treatments of congenital kidney disease. 4. Uncovering the underlying mechanisms of renal fibrosis and establishment of effective means of halting/preventing it. Advancements in any of these areas have a great potential to influence the prognosis of children with kidney diseases, and considering the fast pace in which new knowledge is acquired and technologies are developed, it is expected that at least some of these challenges will be met in the foreseeable future.

Prenatal diagnosis and postnatal outcome of anterior urethral anomalies.

OBJECTIVES: Anterior urethral anomalies (AUA) which present as anterior urethral valve, stenosis or atresia, are a rare cause for congenital urinary tract obstruction. We present our AUA prenatal diagnosis case series. METHODS: Fetuses presenting with prenatal findings suggestive for AUA according to postnatal reported clinical and imaging signs (urinary tract dilatation, dilated bladder, enlarged edematous fetal penis, dilatation of the fetal urethra and diverticula) were followed prospectively. RESULTS: Six fetuses were diagnosed with AUA. Diagnosis was confirmed upon examination of the neonate or the abortus. All cases presented with variable degrees of urinary tract dilatation. Four fetuses who presented with additional congenital anomalies of the kidneys and urinary tract (CAKUT) developed intra-uterine or early postnatal renal failure, while two isolated AUA cases have a normal renal outcome. CONCLUSIONS: AUA is a rare diagnosis. However, high index of suspicion and careful sonographic assessment of the male fetal urethra in cases referred for urinary tract dilatation may enable appropriate parent counseling, optimal prenatal surveillance and timed postnatal urological intervention. As in other lower urinary tract obstructions, future renal function seems to correlate with associated CAKUT, therefore close follow up throughout pregnancy and meticulous sonographic assessment is recommended.

Fetal Pancake Kidney: Prenatal Diagnosis and Postnatal Follow-up.

Bilateral failure of the kidneys to ascend during embryonic life may lead to fusion of the two renal masses, resulting in a round mass known as pancake kidney. Reviewing the literature, we did not encounter any reports of prenatal diagnosis of pancake kidneys. We present 6 cases of a pancake kidney diagnosed prenatally. Extrarenal associated anomalies included an aberrant right subclavian artery, nonvisualization of the uterus, consistent with Mayer-Rokitansky-Küster-Hauser syndrome, and a sequence of early-onset growth restriction, hypospadias, and syndactyly, suspected as Smith-Lemli-Opitz syndrome. On postnatal follow-up, all infants had a normal renal outcome.

Renal lineage cells as a source for renal regeneration.

The mammalian kidney is a highly complex organ, composed of various cell types within a unique structural framework. Nonetheless, in recent years, giant leaps in our understanding of nephrogenesis and the origin of new cells in the adult kidney have resulted in novel routes to regenerate damaged nephrons. While several strategies can be envisioned to achieve this aim, one common theme is the reliance on renal lineage cells, as extrarenal cells, such as bone marrow-derived cells, have been shown to be devoid of renal differentiation capacity. Herein, we will present the main motivation for the pursuit for cell-based therapies, which is the ever growing problem of chronic kidney disease (CKD), and discuss different strategies toward replenishing the damaged renal parenchyma. These include transplantation of fetal kidney grafts or fetal kidney stem cells, directed differentiation of pluripotent stem cells into kidney epithelia, establishment of renal progenitors from the adult kidney, and genetic reprogramming of mature kidney cells into a progenitor state. Taken together with novel techniques recapitulating the three-dimensional developmental environment, these advances are expected to take the field into a new era, bringing us closer than ever to the day when kidney stem cell-based therapy becomes a viable therapeutic option.

Severe fetal hydronephrosis: the added value of associated congenital anomalies of the kidneys and urinary tract (CAKUT) in the prediction of postnatal outcome.

OBJECTIVE: The aim of this study was to focus on fetuses diagnosed with severe hydronephrosis and correlate prenatal sonographic characteristics with postnatal outcome. METHODS: Cases presenting prenatally with severe hydronephrosis (anterior-posterior renal pelvic diameter >15 mm) were collected retrospectively over a period of 11 years and divided into 2 groups: (1) isolated hydronephrosis and (2) those associated with congenital anomalies of the kidney and urinary tract (CAKUT). RESULTS: A total of 83 fetuses comprised the study group: 35 fetuses had isolated severe hydronephrosis and 48 had associated CAKUT. The mean anterior-posterior renal pelvic diameter was 22.6 ± 8.5 mm (range 15.0-66.0 mm). The CAKUT group was associated with a significantly increased incidence of postnatal need for surgery (17.6% vs 44.2%, P = .014), dysplastic kidney (0% vs 14%, P = .023), and total abnormal outcome (52.9% vs 86%, P = .001) in comparison with isolated severe prenatal hydronephrosis. CONCLUSIONS: Severe fetal hydronephrosis has a wide postnatal clinical spectrum, which is mainly influenced by the presence of associated sonographic CAKUT findings. These clinical data have biological relevance: a genetic or environmental defect that influences multiple renal developmental processes leads to hydronephrosis but also to concomitant malformations (CAKUT) and critically influences renal prognosis. A more selective abnormal developmental process that results in isolated enlarged pelvis even to a severe extent has less influence on renal prognosis.

A Dominant Mutation in Nuclear Receptor Interacting Protein 1 Causes Urinary Tract Malformations via Dysregulation of Retinoic Acid Signaling.

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of CKD in the first three decades of life. However, for most patients with CAKUT, the causative mutation remains unknown. We identified a kindred with an autosomal dominant form of CAKUT. By whole-exome sequencing, we identified a heterozygous truncating mutation (c.279delG, p.Trp93fs*) of the nuclear receptor interacting protein 1 gene (NRIP1) in all seven affected members. NRIP1 encodes a nuclear receptor transcriptional cofactor that directly interacts with the retinoic acid receptors (RARs) to modulate retinoic acid transcriptional activity. Unlike wild-type NRIP1, the altered NRIP1 protein did not translocate to the nucleus, did not interact with RARα, and failed to inhibit retinoic acid-dependent transcriptional activity upon expression in HEK293 cells. Notably, we also showed that treatment with retinoic acid enhanced NRIP1 binding to RARα RNA in situ hybridization confirmed Nrip1 expression in the developing urogenital system of the mouse. In explant cultures of embryonic kidney rudiments, retinoic acid stimulated Nrip1 expression, whereas a pan-RAR antagonist strongly reduced it. Furthermore, mice heterozygous for a null allele of Nrip1 showed a CAKUT-spectrum phenotype. Finally, expression and knockdown experiments in Xenopus laevis confirmed an evolutionarily conserved role for NRIP1 in renal development. These data indicate that dominant NRIP1 mutations can cause CAKUT by interference with retinoic acid transcriptional signaling, shedding light on the well documented association between abnormal vitamin A levels and renal malformations in humans, and suggest a possible gene-environment pathomechanism in this disease.

Fetal Renal to Abdominal Ratio: A Constant Measurement Throughout Gestation.

BACKGROUND: Sonographic assessment of the fetal kidneys is an integral part of the prenatal anatomical survey. OBJECTIVES: To evaluate the fetal renal to abdominal (RTA) ratio throughout pregnancy and to investigate whether this ratio can be a potential diagnostic landmark for congenital anomalies of the kidney and urinary tract (CAKUT). METHODS: Measurements of the anterior-posterior diameters of the fetal kidney and fetal abdomen (APAD) were obtained prospectively. The RTA was calculated as the ratio between them in in two groups: normal population vs. CAKUT cases. RTA in CAKUT cases was compared to RTA in a normal population. RESULTS: The study group was comprised of 210 women. The mean gestational age for the fetuses was 31 ± 5.6 weeks (range 14-40 weeks). Fetal RTA ratio was found to be 0.28 ± 0.03 throughout pregnancy from early second trimester to term, with high reproducibility of measurements. During the study period the RTA was evaluated in nine cases referred for suspected CAKUT. All cases demonstrated a different ratio according to the renal anomaly. High ratio was observed in one case of overgrowth syndrome (Beckwith Wiedenmann syndrome; 0.47), three cases of infantile polycystic kidney (0.45-0.47), and three cases of a solitary kidney (0.31-0.35), while cases of dysplastic kidneys revealed a low ratio (0.14-0.18). CONCLUSIONS: Prenatal RTA ratio is constant throughout gestation. An abnormal ratio should lead to meticulous renal investigation to rule out kidney disease.

A rare variant in the FHL1 gene associated with X-linked recessive hypoparathyroidism.

Isolated familial hypoparathyroidism is an extremely rare disorder, which to date has been linked to several loci including mutations in CASR, GCM2, and PTH, as well as a rare condition defined as X-linked recessive hypoparathyroidism, previously associated with a 1.5 Mb region on Xq26-q27. Here, we report a patient with hypocalcemia-induced seizures leading to the diagnosis of primary hypoparathyroidism. Mutations in CASR, GCM2, and PTH were ruled out, while whole exome sequencing of the family suggested FHL1, located on chromosome Xq26, as the most likely causative gene variant (FHL1, exon 4, c.C283T, p.R95W). Since FHL1 has not been linked to calcium regulation before, we provide evidence for its functional role in hypoparathyroidism by: (i) bioinformatics analysis coupling its action to known modulators of PTH function; (ii) observing strong expression of fhl1b in Corpuscles of Stannius, gland-like aggregates in zebrafish that function in calcium regulation similar to mammalian PTH; and (iii) implicating fhl1b and FHL1 as regulators of calcium homeostasis in zebrafish and human cells, respectively. Altogether, our data suggest that FHL1 is a novel regulator of calcium homeostasis and implicate it as the causative gene for X-linked recessive hypoparathyroidism.

Crossed ectopic kidney: prenatal diagnosis and postnatal follow-up.

OBJECTIVE: The objective of this study is to investigate prenatal diagnosis and postnatal outcome of fetuses with crossed ectopic kidney. METHOD: Cases referred for an empty renal fossa and diagnosed with crossed ectopic kidney confirmed postnatally were analyzed retrospectively over a period of 10 years. Prenatal diagnosis was established following the detection of one kidney in a normal position and a second ipsilateral kidney fed by abnormal blood vessels on Doppler flow RESULTS: Between 2005 and 2015, 185 fetuses were referred for an empty renal fossa. Crossed ectopic kidney was diagnosed in 10 of them. Associated congenital urological anomalies included two cases of double collecting system and bilateral hydronephrosis in one. Associated extra renal findings were single umbilical artery (4/10), ventricular septal defects (1/10), and persistent left superior vena cava (1/10). On postnatal follow-up, bilateral vesicoureteral reflux was diagnosed in a case who presented prenatally with bilateral hydronephrosis and two cases of mild hydronephrosis. All cases were managed conservatively. CONCLUSION: Crossed ectopic kidney should be suspected in cases presenting with an empty renal fossa and a normal positioned kidney. Thorough anatomical scan should be performed as well as periodic follow-up throughout pregnancy. Postnatal nephrological follow-up is recommended. © 2017 John Wiley & Sons, Ltd.

Autosomal-Recessive Mutations in SLC34A1 Encoding Sodium-Phosphate Cotransporter 2A Cause Idiopathic Infantile Hypercalcemia.

Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D catabolizing enzyme 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)2D3. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)2D3 with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.

Kidney stem cells in development, regeneration and cancer.

The generation of nephrons during development depends on differentiation via a mesenchymal to epithelial transition (MET) of self-renewing, tissue-specific stem cells confined to a specific anatomic niche of the nephrogenic cortex. These cells may transform to generate oncogenic stem cells and drive pediatric renal cancer. Once nephron epithelia are formed the view of post-MET tissue renal growth and maintenance by adult tissue-specific epithelial stem cells becomes controversial. Recently, genetic lineage tracing that followed clonal evolution of single kidney cells showed that the need for new cells is constantly driven by fate-restricted unipotent clonal expansions in varying kidney segments arguing against a multipotent adult stem cell model. Lineage-restriction was similarly maintained in kidney organoids grown in culture. Importantly, kidney cells in which Wnt was activated were traced to give significant clonal progeny indicating a clonogenic hierarchy. In vivo nephron epithelia may be endowed with the capacity akin to that of unipotent epithelial stem/progenitor such that under specific stimuli can clonally expand/self renew by local proliferation of mature differentiated cells. Finding ways to ex vivo preserve and expand the observed in vivo kidney-forming capacity inherent to both the fetal and adult kidneys is crucial for taking renal regenerative medicine forward. Some of the strategies used to achieve this are sorting human fetal nephron stem/progenitor cells, growing adult nephrospheres or reprogramming differentiated kidney cells toward expandable renal progenitors.