Congenital anomalies of the kidney and urinary tract: An embryogenetic review

Spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) including renal parenchymal malformations during fetal life and the implementation of prenatal exome sequencing (WES)

OBJECTIVES AND BACKGROUND

Congenital malformations of the kidney and urinary tract (CAKUT) have a prevalence of 4-60 in 10,000 livebirths and constitute for 40-50% of all end stage pediatric kidney disease. CAKUT can have a genetic background due to monogenetic inherited disease, such as PKD or ciliopathies. They can also be found in combination with extra-renal findings as part of a syndrome. Upon detection of genitourinary malformations during the fetal anomaly scan the question arises if further genetic testing is required. The purpose of this study was to determine the phenotypic presentation of CAKUT cases and the results of exome analysis (WES).

METHODS

This is a retrospective analysis of 63 fetal cases with a diagnosis of CAKUT or DSD at a single center between August 2018 and December 2022.

RESULTS

A total of 63 cases (5.6%) out of 1123 matched CAKUT phenotypes including renal parenchyma malformations. In 15 out of 63 WES analysis a pathogenic variant was detected (23.8%). In fetuses with isolated CAKUT the rate of detecting a pathogenic variant on exome sequencing was five out of 44 (11.4%). Ten out of 19 fetuses (52.6%) that displayed extra-renal findings in combination with CAKUT were diagnosed with a pathogenic variant.

CONCLUSIONS

WES provides an increase in diagnosing pathogenic variants in cases of prenatally detected CAKUT. Especially in fetuses with extra-renal malformations, WES facilitates a gain in information on the fetal genotype to enhance prenatal counselling and management.

Does a Nonreassuring Fetal Heart Rate Pattern Impair Renal Function in Neonates Prenatally Diagnosed with Congenital Anomalies of the Kidneys and Urinary Tract?

OBJECTIVE

This study aimed to determine the effect of nonreassuring fetal heart rate (NRFHR) patterns in labor on the postnatal renal function of neonates with a prenatal diagnosis of congenital anomalies of the kidney and urinary tract (CAKUT).

STUDY DESIGN

A retrospective cohort study was conducted in a single tertiary referral center between 2012 and 2020. All cases with a prenatal diagnosis of CAKUT were extracted, and their fetal, maternal, obstetrical, and neonatal characteristics were analyzed. Cases of multiple gestations, preterm delivery, small for gestational age, major associated malformations or genetic aberrations, and prelabor acute obstetrical events were excluded from the analysis. The study group was comprised of patients who experienced NRFHR during labor. The control groups included (1) patients who had a trial of labor with a normal fetal heart rate pattern and (2) patients who delivered by elective cesarean section (CS). The primary outcome was abnormal serum creatinine levels in the perinatal period. For statistical purposes, the CAKUT cases were classified into a low and high estimated risk for an abnormal postnatal renal outcome. A subgroup analysis of the results was performed accordingly.

RESULTS

Two hundred and fifty-six fetuses diagnosed prenatally with CAKUT comprised the study group. Among these, 214 women (83%) opted for a labor trial, while 42 (17%) chose elective CS. Within the labor trial group, 21/214 patients (9.8%) experienced NRFHR during labor. Analysis of maternal and fetal characteristics revealed no statistically significant disparities between the groups. NRFHR patterns were not associated with a deterioration in neonatal serum creatinine compared with those with normal fetal monitoring or those born by an elective CS.

CONCLUSION

NRFHR patterns during labor and delivery did not impair neonatal renal function status in fetuses diagnosed prenatally with low- and high-risk CAKUT. Delivery can be managed according to standard obstetrical guidelines.

KEY POINTS

· Kidneys affected by CAKUT commonly display renal dysplasia and a reduction in nephron mass.. · Low Apgar scores and asphyxia are recognized as risk factors for perinatal acute kidney injury.. · Lack of research on NRFHR impact on perinatal renal function in prenatally diagnosed CAKUT.. · NRFHR patterns during labor did not impair neonatal renal function status in prediagnosed fetuses..

Multidisciplinary approaches for elucidating genetics and molecular pathogenesis of urinary tract malformations

Advances in clinical diagnostics and molecular tools have improved our understanding of the genetically heterogeneous causes underlying congenital anomalies of kidney and urinary tract (CAKUT). However, despite a sharp incline of CAKUT reports in the literature within the past 2 decades, there remains a plateau in the genetic diagnostic yield that is disproportionate to the accelerated ability to generate robust genome-wide data. Explanations for this observation include (i) diverse inheritance patterns with incomplete penetrance and variable expressivity, (ii) rarity of single-gene drivers such that large sample sizes are required to meet the burden of proof, and (iii) multigene interactions that might produce either intra- (e.g., copy number variants) or inter- (e.g., effects in trans) locus effects. These challenges present an opportunity for the community to implement innovative genetic and molecular avenues to explain the missing heritability and to better elucidate the mechanisms that underscore CAKUT. Here, we review recent multidisciplinary approaches at the intersection of genetics, genomics, in vivo modeling, and in vitro systems toward refining a blueprint for overcoming the diagnostic hurdles that are pervasive in urinary tract malformation cohorts. These approaches will not only benefit clinical management by reducing age at molecular diagnosis and prompting early evaluation for comorbid features but will also serve as a springboard for therapeutic development.

Evaluation of insertion/deletion (I/D) polymorphisms of ACE gene and circulating levels of angiotensin II in congenital anomalies of the kidney and urinary tract

BACKGROUND

Congenital Anomalies of the Kidney and the Urinary Tract (CAKUT) are defined as a heterogeneous group of anomalies that resulted from defects in kidney and urinary tract embryogenesis. CAKUT have a complex etiology. Genetic, epigenetic and environmental factors have been investigated in this context. Angiotensin II is a potent vasoconstrictor and exerts an important role in kidney embryogenesis. The angiotensin-converting enzyme (ACE) converts Angiotensin I into Angiotensin II (Ang II) and ACE gene has insertion/deletion (I/D) polymorphisms that have been evaluated in several nephropathies. This study aimed to evaluate whether the I/D polymorphisms of ACE gene and the circulating levels of Ang II are associated with any CAKUT phenotype or CAKUT in general.

METHODS AND RESULTS

Our study was performed with 225 pediatric patients diagnosed with CAKUT and 210 age-and-sex matched healthy controls. ACE I/D alleles were analysed by real-time polymerase chain reaction (RT-PCR). The distribution of ACE I/D polymorphisms were compared between CAKUT patients and healthy controls, as well between ureteropelvic junction obstruction (UPJO), vesicoureteral reflux (VUR), multicystic dysplastic kidney (MCDK) phenotypes and control group. No statistical association was detected between ACE I/D polymorphism and CAKUT and UPJO, VUR, and MCDK phenotypes. In a subset of 80 CAKUT patients and 80 controls, plasma levels of Ang II were measured. No significant differences were found between CAKUT patients and controls, even in regard to comparisons of UPJO, VUR and MCDK with control group.

CONCLUSION

Although CAKUT is a complex disease and the ACE gene may exert a role in kidney embryogenesis, CAKUT was not associated with any ACE I/D polymorphisms nor with differences in plasma levels of Ang II in this Brazilian pediatric population.

A Biallelic Frameshift Mutation in Nephronectin Causes Bilateral Renal Agenesis in Humans

BACKGROUND

Bilateral renal agenesis (BRA) is a lethal con genital anomaly caused by the failure of normal development of both kidneys early in embryonic development. Oligohydramnios on fetal ultrasonography reveals BRA. Although the exact causes are not clear, BRA is associated with mutations in many renal development genes. However, molecular diagnostics do not pick up many clinical patients. Nephronectin (NPNT) may be a candidate protein for widening diagnosis. It is essential in kidney development, and knockout of Npnt in mice frequently leads to kidney agenesis or hypoplasia.

METHODS

A consanguineous Han family experienced three cases of induced abortion in the second trimester of pregnancy, due to suspected BRA. Whole-exome sequencing (WES)-based homozygosity mapping detected underlying genetic factors, and a knock-in mouse model confirmed the renal agenesis phenotype.

RESULTS

WES and evaluation of homozygous regions in II:3 and II:4 revealed a pathologic homozygous frameshift variant in NPNT (NM_001184690:exon8:c.777dup/p.Lys260*), which leads to a premature stop in the next codon. The truncated NPNT protein exhibited decreased expression, as confirmed in vivo by the overexpression of WT and mutated NPNT. A knock-in mouse model homozygous for the detected Npnt mutation replicated the BRA phenotype.

CONCLUSIONS

A biallelic loss-of-function NPNT mutation causing an autosomal recessive form of BRA in humans was confirmed by the corresponding phenotype of knock-in mice. Our results identify a novel genetic cause of BRA, revealing a new target for genetic diagnosis, prenatal diagnosis, and preimplantation diagnosis for families with BRA.

Crossed unfused renal ectopia with pelviureteric junction obstruction associated with nephrolithiasis: a rare troublesome triad managed by robotic surgery

We report a rare case of non-fused renal ectopia with pelviureteric junction obstruction and multiple pelvic and renal calculi thereby discussing vascular anatomy of the non-fused ectopic kidney along with robot assisted surgical management of this rare clinical entity which amounts for good preoperative workup for best surgical and clinical outcome.

Side predilection in congenital anomalies of the kidney, urinary and genital tracts

BACKGROUND

There appear to be various patterns of sidedness with relation to the common urogenital malformations observed in pediatric urology. The objective of this statistical review was to synthesize this data and to assess if these patterns are significant.

MATERIALS AND METHODS

Eighteen urogenital conditions were investigated and for each condition the five largest studies that noted laterality were included. The sidedness of each condition was then analysed for statistical significance.

RESULTS

Three conditions had a statistically significant higher proportion on the right side: palpable undescended testis (63%, p = 0.0002), inguinal hernia (59%, p = 0.0001) and hydrocele (60%, p = 0.003). Three conditions were significantly more common on the left side: impalpable undescended testis (59%, p = 0.0008), renal agenesis (54%, p = 0.02) and vesico-ureteric junction obstruction (71%, p < 0.0001) while both pelvi-ureteric junction obstruction (62%, p = 0.09) and absent vas deferens (61%, p = 0.11) were trending towards significance.

CONCLUSIONS

Various urogenital malformations display a predilection for one side. Proximal malformations tend to be more frequently seen on the left side, where as inguinoscrotal malformations are more frequently observed on the right. There is an increasing body of literature regarding aetiological factors for these conditions. However, our current understanding of the pathophysiology of these conditions does not completely explain this pattern of observation.

The association between gestational use of personal care products and neonatal urological abnormality at birth: The Japan Environment and Children's Study

Congenital anomalies of the kidney and urinary tract (CAKUT) include a broad group of birth defects. Exposure to endocrine disrupting chemicals (EDCs) is suspected to be one of the risk factors for CAKUT, and the use of personal care products (PCPs) is a source of EDC exposure. Therefore, this study aimed to investigate the relationship between CAKUT and the use of PCPs in a large birth cohort study. Data from 86,899 pregnant women included in the Japan Environment and Children's Study (JECS), an ongoing nationwide project, were analyzed. The prevalence of CAKUT in newborns was 0.25 % and almost 90 % of subjects used PCPs during mid-late pregnancy. No association was found between CAKUT and PCP use in a model adjusted for the following covariates: maternal age at delivery. The result was persistent after rigorous sensitivity analyses.

Embryology and Morphological (Mal)Development of UPJ

Kidney parenchyma and collecting system arise from two different embryologic units as a result of a close interaction between them. Therefore, their congenital abnormalities are classified together under the same heading named CAKUT (congenital abnormalities of the kidney and urinary tract). The pathogenesis of CAKUT is thought to be multifactorial. Ureteropelvic junction obstruction (UPJO) is the most common and most investigated form of CAKUT. Despite years of experimental and clinical research, and the information gained on the embryogenesis of the kidney; its etiopathogenesis is still unclear. It involves both genetic and environmental factors. Failure in development of the renal pelvis, failure in the recanalization of ureteropelvic junction, abnormal pyeloureteral innervation, and impaired smooth muscle differentiation are the main proposed mechanisms for the occurrence of UPJO. There are also single gene mutations like AGTR2, BMP4, Id2 proposed in the etiopathogenesis of UPJO.

Mouse Models of Congenital Kidney Anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects, which cause the majority of chronic kidney diseases in children. CAKUT covers a wide range of malformations that derive from deficiencies in embryonic kidney and lower urinary tract development, including renal aplasia, hypodysplasia, hypoplasia, ectopia, and different forms of ureter abnormalities. The majority of the genetic causes of CAKUT remain unknown. Research on mutant mice has identified multiple genes that critically regulate renal differentiation. The data generated from this research have served as an excellent resource to identify the genetic bases of human kidney defects and have led to significantly improved diagnostics. Furthermore, genetic data from human CAKUT studies have also revealed novel genes regulating kidney differentiation.

Prenatal genetic considerations of congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital anomalies of the kidney and urinary tract (CAKUT) constitute 20% of all congenital malformations occurring in one in 500 live births. Worldwide, CAKUT are responsible for 40% to 50% of pediatric and 7% of adult end-stage renal disease. Pathogenic variants in genes causing CAKUT include monogenic diseases such as polycystic kidney disease and ciliopathies, as well as syndromes that include isolated kidney disease in conjunction with other abnormalities. Prenatal diagnosis most often occurs using ultrasonography; however, further genetic diagnosis may be made using a variety of testing strategies. Family history and pathologic examination can also provide information to improve the ability to make a prenatal diagnosis of CAKUT. Here, we provide a comprehensive overview of genetic considerations in the prenatal diagnosis of CAKUT disorders. Specifically, we discuss monogenic causes of CAKUT, associated ultrasound characteristics, and considerations for genetic diagnosis, antenatal care, and postnatal care.

Congenital Anomalies of the Kidney and Urinary Tract: A Clinical Review

Purpose of review

This review highlights the most common congenital anomalies of the kidney and urinary tract (CAKUT) that are encountered in pediatric practices. CAKUT are the most common cause of prenatally diagnosed developmental malformations and encompass a spectrum of disorders impacting lower urinary tract development as well as kidney development and function. In pediatric and adolescent populations, developmental abnormalities are the leading cause of end-stage kidney disease. The goal of this review is to provide pediatric providers a framework for appropriate clinical management as well as highlight when referral to subspecialty care is needed.

Recent findings

While the exact etiologies of CAKUT are not completely defined, new evidence demonstrates that genetic and molecular changes impact embryonic kidney and urinary tract development. As a result, phenotypes and clinical outcomes may be affected.

Summary

Because pediatric providers provide front-line care to children and adolescents with developmental kidney and urinary tract anomalies, updated knowledge of CAKUT pathogenesis, embryology, clinical management, and patient outcomes is needed. This manuscript reviews CAKUT etiologies and essential diagnostic, prognostic, and management strategies.

Prevalence, types, and malformations in congenital anomalies of the kidney and urinary tract in newborns: a retrospective hospital-based study

Background

Congenital anomalies of the kidney and urinary tract (CAKUTs) are some of the most common birth defects affecting newborns. CAKUTs often have poor birth outcomes owing to the limited experience of physicians in developing countries regarding antenatal and postnatal diagnosis. We aimed to estimate the epidemiology of CAKUTs using data from a hospital-based registry in Zhejiang Province, China.

Methods

We included a total of 2790 newborns with CAKUTs, identified among 1,748,038 births during 2010–2016. The prevalence and type of CAKUTs, maternal and neonatal characteristics, and associated malformations were analyzed.

Results

The average prevalence of CAKUTs born to mothers overall and mothers aged ≥35 years were both around 1.60 per 1000 births (95% confidence interval (CI), 1.54–1.66; 95% CI, 1.44–1.83, respectively) during the study period. The prevalence of CAKUTs changed over time among all women and women of advanced maternal age, although no significant trends were observed. CAKUTs were more likely to occur in male than female newborns (odds ratio (OR) 1.28, 95% CI 1.18–1.38), in multiple births than singletons (OR 1.53, 95% CI 1.21–1.92) and in urban areas than rural areas (OR 1.27, 95% CI 1.18–1.37). The overall prenatal detection rate of CAKUTs was 73.87%. The average gestational age at antenatal diagnosis was 26.57 ± 8.70 weeks. A total 22.69% CAKUTs had associated malformations. Congenital heart defects were the most common anomalies, accounting for 8.89% of the whole population. The main proportion in subgroups was hydronephrosis, representing 31.79% of registered CAKUTs.

Conclusions

There was a nearly twofold increase in the prevalence of CAKUTs from 2010 to 2016 in Zhejiang Province. CAKUTs are strongly associated with male sex, multiple births, urban areas, and other nonurinary congenital malformations.

FAT4 Fine-Tunes Kidney Development by Regulating RET Signaling

FAT4 mutations lead to several human diseases that disrupt the normal development of the kidney. However, the underlying mechanism remains elusive. In studying the duplex kidney phenotypes observed upon deletion of Fat4 in mice, we have uncovered an interaction between the atypical cadherin FAT4 and RET, a tyrosine kinase receptor essential for kidney development. Analysis of kidney development in Fat4^-/- kidneys revealed abnormal ureteric budding and excessive RET signaling. Removal of one copy of the RET ligand Gdnf rescues Fat4^-/- kidney development, supporting the proposal that loss of Fat4 hyperactivates RET signaling. Conditional knockout analyses revealed a non-autonomous role for Fat4 in regulating RET signaling. Mechanistically, we found that FAT4 interacts with RET through extracellular cadherin repeats. Importantly, expression of FAT4 perturbs the assembly of the RET-GFRA1-GDNF complex, reducing RET signaling. Thus, FAT4 interacts with RET to fine-tune RET signaling, establishing a juxtacrine mechanism controlling kidney development.

The copy number variation landscape of congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) are a major cause of pediatric kidney failure. We performed a genome-wide analysis of copy number variants (CNVs) in 2,824 cases and 21,498 controls. Affected individuals carried a significant burden of rare exonic (i.e. affecting coding regions) CNVs and were enriched for known genomic disorders (GD). Kidney anomaly (KA) cases were most enriched for exonic CNVs, encompassing GD-CNVs and novel deletions; obstructive uropathy (OU) had a lower CNV burden and an intermediate prevalence of GD-CNVs; vesicoureteral reflux (VUR) had the fewest GD-CNVs but was enriched for novel exonic CNVs, particularly duplications. Six loci (1q21, 4p16.1-p16.3, 16p11.2, 16p13.11, 17q12, and 22q11.2) accounted for 65% of patients with GD-CNVs. Deletions at 17q12, 4p16.1-p16.3, and 22q11.2 were specific for KA; the 16p11.2 locus showed extensive pleiotropy. Using a multidisciplinary approach, we identified TBX6 as a driver for the CAKUT subphenotypes in the 16p11.2 microdeletion syndrome.

Impact of next generation sequencing on our understanding of CAKUT

Congenital abnormalities of the kidney and urinary tract (CAKUT) form the leading cause of pediatric end-stage renal disease. Knowledge on the molecular mechanisms that underlie CAKUT leads to the improvement of DNA diagnostics and counseling regarding prognosis and recurrence risk estimation for CAKUT patients and their relatives. Implementation of next generation sequencing in research and diagnostic settings has led to the identification of the molecular basis of many developmental diseases. In this review, we summarize the efforts on next generation sequencing in CAKUT research and we discuss how next generation sequencing added to our understanding of CAKUT genetics. Although next generation sequencing has certainly proven to be a game changer in the field of disease gene identification and novel CAKUT-causing gene variants have been identified, most CAKUT cases still remain unsolved. Occurring with genetic and phenotypic heterogeneity along with incomplete penetrance, the identification of CAKUT etiology poses many challenges. We see great potential for combined -omics approaches that include next generation sequencing in the identification of CAKUT-specific biomarkers, which is necessary to optimize the care for CAKUT patients.

Evaluation of Renal Function in Children with Congenital Scoliosis and Congenital Anomalies of the Kidney and Urinary Tract

Background

The aim of this study was to compare renal function in children with congenital scoliosis and congenital anomalies of the kidney and urinary tract, with healthy children.

Material/Methods

Biochemical tests were performed before surgery (pre-therapy) and after surgery (post-therapy) in 16 children with congenital scoliosis and congenital anomalies of the kidney and urinary tract. Thirty-two healthy children were matched for age, sex, and weight (healthy controls). General renal function tests included serum electrolytes, creatinine, urea, cystatin C, and estimated glomerular filtration rate (eGFR). Tests for early renal changes included N-acetyl-beta-D-glucosaminidase (NAG), urine microalbumin, serum transferrin, immunoglobulin G (IgG), urinary alpha-1-microglobulin (A1M), and beta-2-microglobulin (B2M).

Results

Sixteen patients with congenital anomalies of the kidney and urinary tract included eight boys (mean age, 11.38±2.00 years) and eight girls (mean age, 11.00±2.78 years). There were no significant differences in renal function between the pre-therapy and post-therapy groups (P>0.05), or between the three groups (pre-therapy, post-therapy, and healthy controls). In the pre-therapy group, there were significant differences in IgG, A1M, NAG, and serum phosphate levels between boys and girls, urine microalbumin was significantly increased in girls, but not boys (P<0.05). There were no significant differences between the pre-therapy group and post-therapy group (P>0.05).

Conclusions

Routine tests of renal function were normal in children with congenital scoliosis and congenital anomalies of the kidney and urinary tract, but early changes in renal function occurred before surgical treatment, indicating long-term follow-up of renal function is recommended.

Crossed Unfused Ectopic Pelvic Kidneys: A Case Illustration

Crossed unfused ectopia constitutes a very rare variant of ectopic kidneys, with an approximate incidence of 1 : 75000. We hereby describe a rare case of an incidental finding of crossed unfused ectopic kidneys, in a 45-year-old gentleman incidentally found to have a bladder lesion. The unique blood supply of his kidneys has also been described. The present case also highlights the different subtypes of renal ectopia, the different embryological hypotheses behind their presentation, and the various systematic anomalies, associated with them. Variations in vasculature of ectopic kidneys have been only described in case reports and are crucial to recognize in case any further intervention is needed.

Renal development in the fetus and premature infant

Congenital abnormalities of the kidney and urinary tract (CAKUT) are one of the leading congenital defects to be identified on prenatal ultrasound. CAKUT represent a broad spectrum of abnormalities, from transient hydronephrosis to severe bilateral renal agenesis. CAKUT are a major contributor to chronic and end stage kidney disease (CKD/ESKD) in children. Prenatal imaging is useful to identify CAKUT, but will not detect all defects. Both genetic abnormalities and the fetal environment contribute to CAKUT. Monogenic gene mutations identified in human CAKUT have advanced our understanding of molecular mechanisms of renal development. Low nephron number and solitary kidneys are associated with increased risk of adult onset CKD and ESKD. Premature and low birth weight infants represent a high risk population for low nephron number. Additional research is needed to identify biomarkers and appropriate follow-up of premature and low birth weight infants into adulthood.

Interkinetic nuclear migration in the mouse embryonic ureteric epithelium: Possible implication for congenital anomalies of the kidney and urinary tract

Interkinetic nuclear migration (INM) is a phenomenon in which progenitor cell nuclei migrate along the apico-basal axis of the pseudostratified epithelium, which is characterized by the presence of apical primary cilia, in synchrony with the cell cycle in a manner of apical mitosis. INM is suggested to regulate not only stem/progenitor cell proliferation/differentiation but also organ size and shape. INM has been reported in epithelia of both ectoderm and endoderm origin. We examined whether INM exists in the mesoderm-derived ureteric epithelium. At embryonic day (E) 11.5, E12.5 and E13.5, C57BL/6J mouse dams were injected with 5-bromo-2'-deoxyuridine (BrdU) and embryos were killed 1, 2, 4, 6, 8, 10 and 12 h later. We immunostained transverse sections of the ureter for BrdU, and measured the position of BrdU (+) nuclei in the ureteric epithelia along the apico-basal axis at each time point. We analyzed the distribution patterns of BrdU (+) nuclei in histograms using the multidimensional scaling. Changes in the nucleus distribution patterns suggested nucleus movement characteristic of INM in the ureteric epithelia, and the mode of INM varied throughout the ureter development. While apical primary cilia are related with INM by providing a centrosome for the apical mitosis, congenital anomalies of the kidney and urinary tract (CAKUT) include syndromes linked to primary ciliary dysfunction affecting epithelial tubular organs such as kidney, ureter, and brain. The present study showed that INM exists in the ureteric epithelium and suggests that INM may be related with the CAKUT etiology via primary ciliary protein function.

Genetics of Vesicoureteral Reflux

Vesicoureteral reflux (VUR) is the retrograde passage of urine from the bladder to the upper urinary tract. It is the most common congenital urological anomaly affecting 1-2% of children and 30-40% of patients with urinary tract infections. VUR is a major risk factor for pyelonephritic scarring and chronic renal failure in children. It is the result of a shortened intravesical ureter with an enlarged or malpositioned ureteric orifice. An ectopic embryonal ureteric budding development is implicated in the pathogenesis of VUR, which is a complex genetic developmental disorder. Many genes are involved in the ureteric budding formation and subsequently in the urinary tract and kidney development. Previous studies demonstrate an heterogeneous genetic pattern of VUR. In fact no single major locus or gene for primary VUR has been identified. It is likely that different forms of VUR with different genetic determinantes are present. Moreover genetic studies of syndromes with associated VUR have revealed several possible candidate genes involved in the pathogenesis of VUR and related urinary tract malformations. Mutations in genes essential for urinary tract morphogenesis are linked to numerous congenital syndromes, and in most of those VUR is a feature. The Authors provide an overview of the developmental processes leading to the VUR. The different genes and signaling pathways controlling the embryonal urinary tract development are analyzed. A better understanding of VUR genetic bases could improve the management of this condition in children.

Congenital anomalies of the kidney and the urinary tract: A murmansk county birth registry study

BACKGROUND

Congenital anomalies of the kidney and the urinary tract (CAKUTs) are relatively common birth defects. The combined prevalence in Europe was 3.3 per 1000 in 2012. The risk factors for these anomalies are not clearly identified. The aims of our study were to calculate the birth prevalences of urinary malformations in Murmansk County during 2006 to 2011 and to investigate related prenatal risk factors.

METHODS

The Murmansk County Birth Registry was the primary source of information and our study included 50,936 singletons in the examination of structure, prevalence and proportional distribution of CAKUTs. The multivariate analyses of risk factors involved 39,322 newborns.

RESULTS

The prevalence of CAKUTs was 4.0 per 1000 newborns (95% confidence interval [CI], 3.4-4.5) and did not change during the study period. The most prevalent malformation was congenital hydronephrosis (14.2% of all cases). Diabetes mellitus or gestational diabetes (odds ratio [OR] = 4.77; 95% CI, 1.16-19.65), acute infections while pregnant (OR = 1.83; 95% CI, 1.14-2.94), the use of medication during pregnancy (OR = 2.03; 95% CI, 1.44-2.82), and conception during the summer (OR = 1.75; 95% CI 1.15-2.66) were significantly associated with higher risk of CAKUTs.

CONCLUSION

The overall fourfold enhancement of the occurrence of urinary malformations in Murmansk County for the 2006 to 2011 period showed little annual dependence. During pregnancy, use of medications, infections, pre-existing diabetes mellitus, or gestational diabetes were associated with increased risk of these anomalies, as was conception during summer. Our findings have direct applications in improving prenatal care in Murmansk County and establishing targets for prenatal screening and women's consultations.

Epithelial cell fate in the nephron tubule is mediated by the ETS transcription factors etv5a and etv4 during zebrafish kidney development

Kidney development requires the differentiation and organization of discrete nephron epithelial lineages, yet the genetic and molecular pathways involved in these events remain poorly understood. The embryonic zebrafish kidney, or pronephros, provides a simple and useful model to study nephrogenesis. The pronephros is primarily comprised of two types of epithelial cells: transportive and multiciliated cells (MCCs). Transportive cells occupy distinct tubule segments and are characterized by the expression of various solute transporters, while MCCs function in fluid propulsion and are dispersed in a "salt-and-pepper" fashion within the tubule. Epithelial cell identity is reliant on interplay between the Notch signaling pathway and retinoic acid (RA) signaling, where RA promotes MCC fate by inhibiting Notch activity in renal progenitors, while Notch acts downstream to trigger transportive cell formation and block adoption of an MCC identity. Previous research has shown that the transcription factor ets variant 5a (etv5a), and its closely related ETS family members, are required for ciliogenesis in other zebrafish tissues. Here, we mapped etv5a expression to renal progenitors that occupy domains where MCCs later emerge. Thus, we hypothesized that etv5a is required for normal development of MCCs in the nephron. etv5a loss of function caused a decline of MCC number as indicated by the reduced frequency of cells that expressed the MCC-specific markers outer dense fiber of sperm tails 3b (odf3b) and centrin 4 (cetn4), where rescue experiments partially restored MCC incidence. Interestingly, deficiency of ets variant 4 (etv4), a related gene that is broadly expressed in the posterior mesoderm during somitogenesis stages, also led to reduced MCC numbers, which were further reduced by dual etv5a/4 deficiency, suggesting that both of these ETS factors are essential for MCC formation and that they also might have redundant activities. In epistatic studies, exogenous RA treatment expanded the etv5a domain within the renal progenitor field and RA inhibition blocked etv5a in this populace, indicating that etv5a acts downstream of RA. Additionally, treatment with exogenous RA partially rescued the reduced MCC phenotype after loss of etv5a. Further, abrogation of Notch with the small molecule inhibitor DAPT increased the renal progenitor etv5a expression domain as well as MCC density in etv5a deficient embryos, suggesting Notch acts upstream to inhibit etv5a. In contrast, etv4 levels in renal progenitors were unaffected by changes in RA or Notch signaling levels, suggesting a possible non-cell autonomous role during pronephros formation. Taken together, these findings have revealed new insights about the genetic mechanisms of epithelial cell development during nephrogenesis.