Unravelling the genetics of vesicoureteric reflux: a common familial disorder

Dhavileswarapu AVL, Naik N, Karimi H, Hegde P, Rai BP, Somani BK. Big Data Analytics in urology: the story so far and the road ahead

Artificial intelligence (AI) has a proven record of application in the field of medicine and is used in various urological conditions such as oncology, urolithiasis, paediatric urology, urogynaecology, infertility and reconstruction. Data is the driving force of AI and the past decades have undoubtedly witnessed an upsurge in healthcare data. Urology is a specialty that has always been at the forefront of innovation and research and has rapidly embraced technologies to improve patient outcomes and experience. Advancements made in Big Data Analytics raised the expectations about the future of urology. This review aims to investigate the role of big data and its blend with AI for trends and use in urology. We explore the different sources of big data in urology and explicate their current and future applications. A positive trend has been exhibited by the advent and implementation of AI in urology with data available from several databases. The extensive use of big data for the diagnosis and treatment of urological disorders is still in its early stage and under validation. In future however, big data will no doubt play a major role in the management of urological conditions.

Estimation of the relationship between the polymorphisms of selected genes: ACE, AGTR1, TGFβ1 and GNB3 with the occurrence of primary vesicoureteral reflux

PURPOSE

Etiopathogenesis of VUR is composite and not fully understood. Many data indicate the importance of genetic predisposition. The aim of this study was to establish the relationship of selected polymorphisms: 14094 polymorphism of the ACE, polymorphism rs1800469 of TGFβ-1, rs5443 gene polymorphism of the GNB3 and receptor gene polymorphism rs5186 type 1 AGTR1 with the occurrence of the primary vesicoureteral reflux.

MATERIAL

The study included 190 children: 90 with the primary VUR confirmed with the voiding cystourethrogram and excluded secondary VUR and a control group of 100 children without a history of the diseases of the genitourinary tract.

METHODS

The study was planned in the scheme: "tested case versus control." Genomic DNA was isolated from the leukocytes of peripheral blood samples. The results were statistically analyzed in the Statistica 10 using χ ² test and analysis of the variance Anova.

RESULTS

Any of the four studied polymorphisms showed no difference in the distribution of genotypes between patients with primary vesicoureteral reflux and the control group. In patients with VUR and TT genotype polymorphism rs5443 GNB3 gene, the glomerular filtration rate was significantly higher than in patients with genotype CC or CT.

CONCLUSIONS

(1) No relationship was found between the studied polymorphisms (14094 ACE gene, rs1800469 gene TGFβ1, GNB3 gene rs5443, rs5186 AGTR1 gene) and the occurrence of primary vesicoureteral reflux. (2) TT genotype polymorphism rs5443 GNB3 gene may be a protective factor for the improved renal function in patients with primary vesicoureteral reflux in patients with genotype CC or CT.

Genetic Basis of Ureterocele

Congenital anomalies of the kidney and urinary tract (CAKUT) form a group of heterogeneous disorders that affect the kidneys, ureters and bladder, with frequent asynchronous presentations and multiple CAKUT associations in the same individual. Urinary tract formation is a complex process, dependent of the interaction of multiple genes and their sub-product. The same genic alterations can lead to different molecular expressions and different morphological anomalies. The ureterocele is a cystic dilation of the distal intramural ureter, resulting in obstruction of urine flow, dilation of the ureter and renal pelvis and loss of renal function. Two key steps in the urinary tract ontogenesis may be related to ureterocele development: formation and migration of the ureteric bud and its incorporation in the bladder. This review aims to describe the morphological, cellular and biochemical steps, as well as the genes involved in the occurrence of this anomaly.

The association of hypercalciuria and hyperuricosuria with vesicoureteral reflux in children

OBJECTIVES

One of the important complications of vesicoureteral reflux (VUR) is the development of urolithiasis. Identifying factors involved in development of urolithiasis in children with VUR is immensely important. This study was conducted to determine the association between hypercalciuria and hyperuricosuria with VUR in children.

METHODS

One-hundred children with VUR (case group) were compared to 100 healthy children (control group) in terms of hypercalciuria and hyperuricosuria. To measure these markers, random morning fasting urine samples were used. Data were analyzed using statistical tests.

RESULTS

Hypercalciuria and hyperuricosuria frequencies, and also urine calcium/creatinine (Ca/Cr) and urine uric acid/creatinine (UA/Cr) ratios were significantly higher in the case group compared to the control group (P < 0.05). A significant difference was found between hypercalciuria and hyperuricosuria in severity of VUR (P < 0.05). A positive correlation was observed between hypercalciuria and hyperuricosuria and severity of VUR (P < 0.05).

CONCLUSIONS

The present study showed that there is association between hypercalciuria, hyperuricosuria and VUR in children. It is recommended to adopt measures to prevent the development of urolithiasis in VUR patients.

Association of PAX2 and Other Gene Mutations with the Clinical Manifestations of Renal Coloboma Syndrome

BACKGROUND

Renal coloboma syndrome (RCS) is characterized by renal anomalies and optic nerve colobomas. PAX2 mutations contribute to RCS. However, approximately half of the patients with RCS have no mutation in PAX2 gene.

METHODS

To investigate the incidence and effects of mutations of PAX2 and 25 candidate genes, patient genes were screened using next-generation sequence analysis, and candidate mutations were confirmed using Sanger sequencing. The correlation between mutations and clinical manifestation was evaluated.

RESULT

Thirty patients, including 26 patients (two families of five and two, 19 sporadic cases) with RCS, and 4 optic nerve coloboma only control cases were evaluated in the present study. Six PAX2 mutations in 21 probands [28%; two in family cohorts (n = 5 and n = 2) and in 4 out of 19 patients with sporadic disease] including four novel mutations were confirmed using Sanger sequencing. Moreover, four other sequence variants (CHD7, SALL4, KIF26B, and SIX4) were also confirmed, including a potentially pathogenic novel KIF26B mutation. Kidney function and proteinuria were more severe in patients with PAX2 mutations than in those without the mutation. Moreover, the coloboma score was significantly higher in patients with PAX2 gene mutations. Three out of five patients with PAX2 mutations had focal segmental glomerulosclerosis (FSGS) diagnosed from kidney biopsies.

CONCLUSION

The results of this study identify several new mutations of PAX2, and sequence variants in four additional genes, including a novel potentially pathogenic mutation in KIF26B, which may play a role in the pathogenesis of RCS.

Congenital anomalies of the kidney and urinary tract: a genetic disorder?

Congenital anomalies of the kidney and urinary tract (CAKUTs) occur in 3–6 per 1000 live births, account for the most cases of pediatric end-stage kidney disease (ESKD), and predispose an individual to hypertension and cardiovascular disease throughout life. Although CAKUTs are a part of many known syndromes, only few single-candidate causative genes have been implicated so far in nonsyndromic cases of human CAKUT. Evidence from mouse models supports the hypothesis that non-syndromic human CAKUT may be caused by single-gene defects. Because increasing numbers of children with CAKUT are surviving to adulthood, better understanding of the molecular pathogenesis of CAKUT, development of new strategies aiming at prevention of CAKUT, preservation of renal function, and avoidance of associated cardiovascular morbidity are needed. In this paper, we will focus on the knowledge derived from the study of syndromic and non-syndromic forms of CAKUT in humans and mouse mutants to discuss the role of genetic, epigenetic, and in utero environmental factors in the pathogenesis of non-syndromic forms of CAKUT in children with particular emphasis on the genetic contributions to CAKUT.

Urinary tract infection: clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months

OBJECTIVE

To revise the American Academy of Pediatrics practice parameter regarding the diagnosis and management of initial urinary tract infections (UTIs) in febrile infants and young children.

METHODS

Analysis of the medical literature published since the last version of the guideline was supplemented by analysis of data provided by authors of recent publications. The strength of evidence supporting each recommendation and the strength of the recommendation were assessed and graded.

RESULTS

Diagnosis is made on the basis of the presence of both pyuria and at least 50,000 colonies per mL of a single uropathogenic organism in an appropriately collected specimen of urine. After 7 to 14 days of antimicrobial treatment, close clinical follow-up monitoring should be maintained to permit prompt diagnosis and treatment of recurrent infections. Ultrasonography of the kidneys and bladder should be performed to detect anatomic abnormalities. Data from the most recent 6 studies do not support the use of antimicrobial prophylaxis to prevent febrile recurrent UTI in infants without vesicoureteral reflux (VUR) or with grade I to IV VUR. Therefore, a voiding cystourethrography (VCUG) is not recommended routinely after the first UTI; VCUG is indicated if renal and bladder ultrasonography reveals hydronephrosis, scarring, or other findings that would suggest either high-grade VUR or obstructive uropathy and in other atypical or complex clinical circumstances. VCUG should also be performed if there is a recurrence of a febrile UTI. The recommendations in this guideline do not indicate an exclusive course of treatment or serve as a standard of care; variations may be appropriate. Recommendations about antimicrobial prophylaxis and implications for performance of VCUG are based on currently available evidence. As with all American Academy of Pediatrics clinical guidelines, the recommendations will be reviewed routinely and incorporate new evidence, such as data from the Randomized Intervention for Children With Vesicoureteral Reflux (RIVUR) study.

CONCLUSIONS

Changes in this revision include criteria for the diagnosis of UTI and recommendations for imaging.

Genetics of vesicoureteral reflux

Primary vesicoureteral reflux (VUR) is the most common urological anomaly in children, affecting 1-2% of the pediatric population and 30-40% of children presenting with urinary tract infections (UTIs). Reflux-associated nephropathy is a major cause of childhood hypertension and chronic renal failure. The hereditary and familial nature of VUR is well recognized and several studies have reported that siblings of children with VUR have a higher incidence of reflux than the general pediatric population. Familial clustering of VUR implies that genetic factors have an important role in its pathogenesis, but no single major locus or gene for VUR has yet been identified and most researchers now acknowledge that VUR is genetically heterogeneous. Improvements in genome-scan techniques and continuously increasing knowledge of the genetic basis of VUR should help us to further understand its pathogenesis.

Concomitant vesicoureteral reflux and gastroesophageal reflux: an analytic cross-sectional study

PURPOSE

Vesicoureteral reflux (VUR) and Gastroesophageal reflux (GER) are both common disorders in children and could be associated with significant morbidities. Although they appear to be separate entities, their natural history and underlying pathophysiology are the same and they both tend to resolve over time. We aimed to appraise their concurrent occurrence and prevalence of GER in VUR patients to understand whether they can be considered different manifestations of a syndrome mainly caused by developmental delay resulting in dysfunction of the sphincters.

METHODS

Totally, 174 children ≤ 2 years of age were enrolled and 87 of them with primary VUR constituted patients group. The rest of the cases with the same age and sex distribution entered control group. All the study population underwent ultrasonographic evaluation to detect GER.

RESULTS

GER was more frequent in patients with primary VUR. GER was more prevalent in higher grades of VUR. We observed higher prevalence of GER and higher grades of VUR in younger infants demonstrating the tendency of both conditions to resolve overtime. Bilateral VUR was more prevalent among patients with higher grades of VUR. GER was more prevalent in patients with bilateral VUR and Prevalence of bilateral VUR decreased with increase in age. These findings show that the chance of concomitant GER and VUR is higher in children with more severe developmental defect of sphincters.

CONCLUSIONS

Regarding the higher prevalence of GER among VUR patients and correlation of VUR severity with co-occurrence of GER, besides the natural tendency of both conditions to resolve overtime, they may be considered parts of developmental delay syndrome of sphincters.

Vesicoureteric reflux deterioration in monozygotic twins

Primary vesicoureteric reflux (VUR) is the most common inherited structural urinary tract disorder, conforming closely to autosomal dominant transmission. A pair of monozygotic siblings is described exhibiting a remarkably parallel clinical course. VUR grade II was diagnosed in girl A during urinary tract infection at the age of 2 yr; screening of her asymptomatic sister (girl B) revealed the same. Renal cortical scintigraphy unveiled unilateral hypo-dysplasia in both the twins. Despite trimethoprime-sulfamethoxazole prophylaxis, infection recurred in girl A after 7 months, while girl B had a first episode 2 months later that prompted regimen switch to nitrofurantoin. Follow-up at the age of 4 depicted bilateral reflux deterioration; an urodynamics study that followed revealed functional bladder instability in both girls and the oral antispasmodic oxybutynin was initiated with good results. Evaluation for reflux should be prompt in infants with urinary infection. Patient siblings display a higher relative reflux risk, being highest in identical twins. Heredity issues, the impact of age and dysfunctional voiding in the clinical course, and the contribution of nuclear medicine in VUR management are discussed.

A genome-wide scan for genes involved in primary vesicoureteric reflux

BACKGROUND

Vesicoureteric reflux (VUR) is the retrograde flow of urine from the bladder into the ureters. It is the most common urological anomaly in children, and a major cause of end-stage renal failure and hypertension in both children and adults. VUR is seen in approximately 1-2% of Caucasian newborns and is frequently familial.

OBJECTIVE AND METHODS

In order to search for genetic loci involved in VUR, we performed a genome-wide linkage scan using 4710 single-nucleotide polymorphisms (SNPs) in 609 individuals from 129 Irish families with >1 affected member.

RESULTS

Nonparametric linkage (NPL) analysis of the dataset yielded moderately suggestive linkage at chromosome 2q37 (NPL(max) = 2.67, p<0.001). Analysis of a subset without any additional features, such as duplex kidneys, yielded a maximum NPL score of 4.1 (p = 0.001), reaching levels of genome-wide statistical significance. Suggestive linkage was also seen at 10q26 and 6q27, and there were several smaller peaks.

CONCLUSION

Our results confirm the previous conclusion that VUR is genetically heterogeneous, and support the identification of several disease-associated regions indicated by smaller studies, as well as indicating new regions of interest for investigation.

Disruption of ROBO2 is associated with urinary tract anomalies and confers risk of vesicoureteral reflux

Congenital anomalies of the kidney and urinary tract (CAKUT) include vesicoureteral reflux (VUR). VUR is a complex, genetically heterogeneous developmental disorder characterized by the retrograde flow of urine from the bladder into the ureter and is associated with reflux nephropathy, the cause of 15% of end-stage renal disease in children and young adults. We investigated a man with a de novo translocation, 46,X,t(Y;3)(p11;p12)dn, who exhibits multiple congenital abnormalities, including severe bilateral VUR with ureterovesical junction defects. This translocation disrupts ROBO2, which encodes a transmembrane receptor for SLIT ligand, and produces dominant-negative ROBO2 proteins that abrogate SLIT-ROBO signaling in vitro. In addition, we identified two novel ROBO2 intracellular missense variants that segregate with CAKUT and VUR in two unrelated families. Adult heterozygous and mosaic mutant mice with reduced Robo2 gene dosage also exhibit striking CAKUT-VUR phenotypes. Collectively, these results implicate the SLIT-ROBO signaling pathway in the pathogenesis of a subset of human VUR.

Embryology and genetics of primary vesico-ureteric reflux and associated renal dysplasia

Congenital anomalies of the kidney and urinary tract, as well as primary vesico-ureteric reflux (VUR) and associated renal dysplasia, are the most relevant causes of end-stage renal failure in the pediatric population. In vivo and in vitro experimental studies have allowed the identification of several genes involved both in ureteric bud branching, ureteric elongation and insertion into the bladder, and in nephrogenesis. It has been proposed that both renal and ureteral abnormalities, as well as the associated renal hypo-dysplasia, may derive from a common mechanism as the result of a dysregulation of the normal developmental program. The large homologies between mice and the human genome suggest that the same genes could be involved both in rodent and human VUR. Furthermore, epidemiological observations suggest that not only syndromic but also isolated VUR is an inherited trait. Linkage analysis for homologous mouse genes in humans, genome-wide linkage studies in multigenerational families and association studies by polymorphisms support the hypothesis that VUR is genetically heterogeneous and is caused by a number of different genes acting with random environmental effects. The present teaching paper is an overview of the embryology and genetics of primary VUR and associated congenital reflux nephropathy.

Familial Vesicoureteral Reflux: Influence of Sex on Prevalence and Expression

PURPOSE

Familial clustering of vesicoureteral reflux implies that genetic factors have an important role in the pathogenesis of vesicoureteral reflux. We investigated the impact of sex on familial vesicoureteral reflux.

MATERIALS AND METHODS

Between 1998 and 2003 we identified 159 white families with at least 2 children (range 2 to 5) with vesicoureteral reflux confirmed by a voiding cystourethrogram. Families were divided into 3 groups, including group 1 with only boys affected (29 or 18%), group 2 with only girls affected (57 or 36%) and group 3 with boys and girls affected (73 or 46%). Clinical characteristics, reflux grade and associated renal anomalies in these 3 groups were compared using the Mann-Whitney U and chi-square tests for statistical analysis.

RESULTS

Sisters of index female patients were at significantly higher risk for vesicoureteral reflux than brothers (p <0.01). Boys in group 1 had a significantly higher grade of vesicoureteral reflux than boys in group 3, and girls in groups 3 and 2 (p = 0.018, <0.001 and <0.0001, respectively). Severe renal scarring was present in 7% of boys in group 1, 6.6% of boys in group 3, 1.3% of girls in group 3 and 1.9% of girls in group 2. Duplex kidneys were present in 15.3% of boys in group 1 but only in 2.3% of boys in group 3 (p <0.01), 5.7% of girls in group 3 and 5.8% of girls in group 2. Age at diagnosis was not significantly different among boys in groups 1 and 3, and girls in group 2 (median 0.9, 0.6 and 1.9 years, respectively).

CONCLUSIONS

The risk and severity of vesicoureteral reflux in siblings depends on the sex of the affected child. Brothers of index male patients have higher grade of reflux and higher rate of associated duplex systems. This has implications for genetic counseling and for modeling the inheritance of vesicoureteral reflux.

Renal Scarring in Familial Vesicoureteral Reflux: Is Prevention Possible?

PURPOSE

Detailed knowledge about risk factors for renal scarring in familial reflux is necessary to decide whether these factors could be influenced by early screening and treatment of siblings. We evaluated the prevalence of and risk factors influencing renal scarring in familial vesicoureteral reflux.

MATERIALS AND METHODS

We reviewed the medical records and dimercapto-succinic acid scans of 306 children with familial vesicoureteral reflux. Scarring was classified as mild, moderate and severe. The impact of urinary tract infections, patient sex, reflux grade and age at diagnosis on renal scarring was evaluated.

RESULTS

The prevalence of renal scarring was identical at 36% in 142 index patients and 74 siblings presenting with urinary tract infection but it was only 10% in 87 asymptomatic siblings (p <0.001) The difference between siblings with and without urinary tract infection was only statistically significant for mild scarring (23% vs 4.6%, p <0.001). It did not attain significance in those with moderate to severe scarring (13.5% vs 5.7%). Moderate to severe scarring was significantly more common in grade V than in grade IV refluxing units (43% vs 10%, p <0.0001) and in male than in female siblings (15.8% vs 3.4%, p = 0.012). Mild scarring was not significantly associated with reflux grade or patient sex. Children diagnosed before age 3 years showed significantly less scarring than patients diagnosed later (23% vs 41%, p <0.002).

CONCLUSIONS

The development of mild renal scarring seems to mainly depend on urinary tract infections, while moderate and severe scarring are also associated with high grade reflux and male sex. Early detection and treatment may prevent further urinary tract infections as well as reflux related kidney damage.

A locus for renal malformations including vesico-ureteric reflux on chromosome 13q33-34

Congenital anomalies of kidney and urinary tract (CAKUT), including vesico-ureteric reflux (VUR), are major causes of ESRD in childhood. Herein is reported evidence for a locus on 13q33q34 associated with CAKUT. Deletion mapping of chromosome 13q was performed in four children with CAKUT using 31 microsatellite markers on peripheral blood genomic DNA that was obtained from the patients and their parents. mRNA expression of the positional candidate genes was compared with sequences in electronic databases in silico and also studied in adult and fetal mouse kidneys using reverse transcription-PCR. The children (three girls; age range 5 to 17 yr) had varying severity of developmental delay and other organ system involvement. The spectrum of CAKUT included high-grade VUR (n = 2), renal dysplasia (n = 2), and hydronephrosis (n = 1). Both the children with VUR had evidence of renal failure with one of them developing ESRD. Deletion mapping identified a 7-Mb critical region flanked by markers D13S1311 and D13S285. There are 33 genes (12 known; 21 computer predicted) in this region. In silico expression studies showed matches for 14 of these genes in the kidneys and 10 in the bladder expressed sequenced tags databases. Mouse kidney studies showed that of the 24 genes examined, several had variable expression through the different stages of renal development, whereas five of the genes were not expressed at all. Herein is reported a new locus on chromosome 13q33q34 that can be associated with VUR with several genes showing mRNA expression patterns that suggest their potential for involvement in renal/urinary tract developmental anomalies.

Multicystic dysplastic kidney and variable phenotype in a family with a novel deletion mutation of PAX2

The renal coloboma syndrome (OMIM 120330) is caused by mutations in the PAX2 gene. Typical findings in these patients include renal hypoplasia, renal insufficiency, vesicoureteric reflux, and optic disc coloboma. A family with a novel heterozygous 10-bp deletion in exon 2 of the PAX2 gene leading to a truncating mutation and variable phenotype across three generations is reported. The first presentation of multicystic dysplastic kidney in this syndrome is reported. The possibility that abnormal PAX2 protein in this case may cause a dominant negative effect also is discussed. The finding of multicystic dysplastic kidney in renal coloboma syndrome could suggest that PAX2 may play a role in early ureteric obstruction and subsequent renal maldevelopment.

Uroplakin III is not a major candidate gene for primary vesicoureteral reflux

Vesicoureteral reflux (VUR) is the retrograde flow of urine from the bladder into the ureter and towards the kidneys. VUR is the most common cause of end stage renal failure in both children and adults and it is a major cause of severe hypertension in children. VUR is seen in approximately 1-2% of newborn Caucasians. Substantial evidence exists that VUR is a genetic disorder. Uroplakins are integral membrane proteins found in the bladder wall. Knockout studies in mice have suggested uroplakin III (UPK3) as a candidate gene for VUR. We have used parametric and nonparametric linkage analysis and tests for association, to investigate this possibility in a cohort of 126 sibling pairs affected with primary VUR. None of the analyses showed any substantial evidence for linkage or association of markers at the UPK3 locus to VUR. Our results do not support a role for UPK3 in primary VUR.

Familial Vesicoureteral Reflux: Testing Replication of Linkage in Seven New Multigenerational Kindreds

Vesicoureteral reflux (VUR) (OMIM %193000), a common cause of childhood renal failure, is strongly influenced by hereditary factors. Familial VUR most closely conforms to autosomal-dominant inheritance, but because of variable penetrance and expressivity, large multigenerational pedigrees tractable to linkage analysis have been difficult to ascertain. A single genome-wide study of familial VUR has demonstrated linkage to chromosome 1p13, with 78% locus heterogeneity. Previous studies in humans have also suggested loci on chromosomes 6p21, 10q26, and 19q13, whereas mutations in ROBO2 were recently reported in some patients with VUR. Replication of these studies was attempted in seven previously undescribed families from Italy and the United States. Simulation studies, assuming 50% locus heterogeneity, showed that these kindreds had 85% power to replicate linkage and 53% power to achieve genome-wide significance at candidate intervals. Thirty-five markers on chromosomes 1p13, 3p12, 6p21, 10q26, and 19q13 were genotyped and analysis of linkage under a variety of models was performed. Parametric analysis excluded linkage to all candidate loci under genetic homogeneity; moreover, the data did not support statistically significant linkage under models of locus heterogeneity. Similarly, nonparametric, allele-sharing analysis did not reveal any evidence of linkage at any of the loci tested. Thus, despite sufficient power, linkage of familial VUR to previously reported candidate intervals could not be replicated. These data demonstrate substantial genetic heterogeneity of VUR and suggest that mapping strategies relying on a large number of kindreds or single "loaded" pedigrees will be most effective to achieve replication or detection of linkage.

Lack of major involvement of human uroplakin genes in vesicoureteral reflux: implications for disease heterogeneity

BACKGROUND

Primary vesicoureteral reflux (VUR) is a hereditary disorder characterized by the retrograde flow of urine into the ureters and kidneys. It affects about 1% of the young children and is thus one of the most common hereditary diseases. Its associated nephropathy is an important cause of end-stage renal failure in children and adults. Recent studies indicate that genetic ablation of mouse uroplakin (UP) III gene, which encodes a 47 kD urothelial-specific integral membrane protein forming urothelial plaques, causes VUR and hydronephrosis.

METHODS

To begin to determine whether mutations in UP genes might play a role in human VUR, we genotyped all four UP genes in 76 patients with radiologically proven primary VUR by polymerase chain reaction (PCR) amplification and sequencing of all their exons plus 50 to 150 bp of flanking intronic sequences.

RESULTS

Eighteen single nucleotide polymorphisms (SNPs) were identified, seven of which were missense, with no truncation or frame shift mutations. Since healthy relatives of the VUR probands are not reliable negative controls for VUR, we used a population of 90 race-matched, healthy individuals, unrelated to the VUR patients, as controls to perform an association study. Most of the SNPs were not found to be significantly associated with VUR. However, SNP1 of UP Ia gene affecting a C to T conversion and an Ala7Val change, and SNP7 of UP III affecting a C to G conversion and a Pro154Ala change, were marginally associated with VUR (both P= 0.08). Studies of additional cases yielded a second set of data that, in combination with the first set, confirmed a weak association of UP III SNP7 in VUR (P= 0.036 adjusted for both subsets of cases vs. controls).

CONCLUSION

Such a weak association and the lack of families with simple dominant Mendelian inheritance suggest that missense changes of uroplakin genes cannot play a dominant role in causing VUR in humans, although they may be weak risk factors contributing to a complex polygenic disease. The fact that no truncation or frame shift mutations have been found in any of the VUR patients, coupled with our recent finding that some breeding pairs of UP III knockout mice yield litters that show not only VUR, but also severe hydronephrosis and neonatal death, raises the possibility that major uroplakin mutations could be embryonically or postnatally lethal in humans.

Overexpression of RET leads to vesicoureteric reflux in mice

RET, a tyrosine kinase receptor essential for kidney development, has recently been shown to be important for the formation of the urinary tract. When RET is overexpressed in the HoxB7/Ret transgenic mouse, kidneys are small and cystic, and in some of the mice, the ureters are grossly dilated. Here, we report that the observed ureteral dilatation is associated with the urinary tract abnormality vesicoureteric reflux (VUR), in which urine flows retrogradely from the bladder to the ureter. Reflux was determined in vitro by injecting methylene blue into the bladders of HoxB7/Ret and wild-type mice. At postnatal day 1, 30% of HoxB7/Ret mice had VUR compared with 4% of wild-type mice (P < 0.05). The length of the intravesical ureteral tunnel was shorter in HoxB7/Ret mice compared with wild-type mice, on both the right and the left sides (P < 0.05), suggesting a basis for the higher incidence of VUR in these mutants. At embryonic day 11, the ureteric bud was found to exit more caudally from the mesonephric duct in HoxB7/Ret mice, and this may predispose them to VUR (P < 0.05). Wild-type and HoxB7/Ret mice were tested for reflux at embryonic day 17, and both showed a high frequency of VUR (59 and 75%, respectively). These results suggest that VUR may occur transiently during normal urinary tract development before the ureter has completed its insertion into the bladder. In the HoxB7/Ret mouse, overexpression of RET appears to delay the maturation of the distal ureter, resulting in postnatal VUR. The HoxB7/Ret mouse is thus an important model in which to examine how vesicoureteric reflux arises during urinary tract development.

Familial vesicoureteral reflux

PURPOSE

Vesicoureteral reflux is known to occur in families. We summarized worldwide data on the incidence and nature of vesicoureteral reflux in siblings of children with vesicoureteral reflux.

MATERIALS AND METHODS

We searched MEDLINE using the words siblings vesicoureteral reflux, familial vesicoureteral reflux, offspring vesicoureteral reflux and vesicoureteral reflux screening. All articles that we identified that were published from 1972 to 2002 were analyzed for the incidence of renal damage in siblings of patients with vesicoureteral reflux.

RESULTS

Siblings of patients with vesicoureteral reflux have a much higher incidence of reflux than the normal population. There is a direct relationship of patient age to the incidence and severity of reflux. Most investigators advocate screening asymptomatic siblings of patients with vesicoureteral reflux.

CONCLUSIONS

The incidence of sibling reflux is significant. When vesicoureteral reflux is discovered in symptomatic siblings, it is usually high grade and associated with a high incidence of reflux nephropathy. Randomized controlled studies are needed to compare renal damage in patients with reflux detected through screening to renal damage in those diagnosed after urinary tract infection to establish how much renal damage may be prevented by screening in asymptomatic siblings.

Angiotensin II type 2 receptor gene is not responsible for familial vesicoureteral reflux

PURPOSE

The renin-angiotensin system has an important role in the development of the kidney and ureter. It has been reported that disruption of the angiotensin II type 2 receptor (AT2) gene leads to congenital anomalies of the kidney and ureter in mice, including vesicoureteral reflux. In humans a single base A to G transition at position -1332 in intron 1 (A-1332G) of the AT2 gene has been reported to occur significantly more often in patients with ureteropelvic junction obstruction and primary obstructive megaureter than in controls. We investigate the incidence of A-1332G transition in patients with primary familial vesicoureteral reflux to determine if AT2 gene is involved in pathogenesis of this disease.

MATERIALS AND METHODS

We evaluated the incidence of A-1332G transition in 82 male and 110 female patients, 111 male and 124 female nonaffected family members from 88 families in which 2 or more members had primary vesicoureteral reflux, and 106 male and 107 female controls with no unselected for reflux status. Genomic DNA was extracted from whole blood samples. Polymerase chain reaction method modified for fluorescent detection was used to type all samples for the A-1332G variant. Furthermore, to identify mutations in the coding sequence of the AT2 gene, we selected 61 patients from different families as well as 15 controls with no vesicoureteral reflux status.

RESULTS

The incidence of A-1332G transition in male patients with primary familial vesicoureteral reflux and controls was 33% (27 of 82 patients) and 38% (41 of 106 controls), respectively, and, the incidence of A-1332G substituted allele in female patients and controls was 47% (104 of 220 total alleles) and 50% (107 of 214 total alleles), respectively. Moreover, the transmission/disequilibrium test revealed no significant skewing of genotype transmission from mother to children. None of the 61 patients or 15 controls carried by mutations or polymorphisms in the coding sequence of the AT2 gene.

CONCLUSIONS

Although the AT2 gene has been reported to have a role in developmental anomalies of the kidney and ureter, our data indicate that it is not involved in the pathogenesis of primary familial vesicoureteral reflux.

Scintigraphic screening for renal damage in siblings of children with symptomatic primary vesico-ureteric reflux

OBJECTIVE

To define prospectively the incidence of renal parenchymal lesions in the siblings of patients treated at one institution for primary vesico-ureteric reflux (VUR).

PATIENTS AND METHODS

From January 1997 to October 1998, a prospective study including renal scintigraphy (using dimercaptosuccinic acid, DMSA) and a radionuclide cystogram was proposed systematically to the asymptomatic siblings of children treated for primary VUR. The radionuclide cystograms were interpreted as showing the presence or absence of VUR and the DMSA scan as symmetrical or asymmetrical differential function, with or with no renal defect.

RESULTS

Fifty-five families gave informed consent, of whom 46 completed the study (eight refused secondarily and one was omitted by exclusion criteria), representing 46 symptomatic patients and 65 siblings. There were 17 siblings with VUR (26%) including two of 13 infants and 15 of 52 children aged > 18 months. One radionuclide cystogram failed. Of the 17 refluxing siblings, four had a history of symptomatic urinary tract infection; 62 of the 65 siblings had a DMSA scan, of which 56 were normal and six (10%) showed abnormalities (five asymmetrical differential function and one parenchymal defect). Only one of these six patients had VUR at the time of the evaluation and only one had a small kidney detected by ultrasonography on one side (and no VUR). There were no adverse effects associated with screening.

CONCLUSION

This study confirms a significant overall incidence of VUR (26%) in the asymptomatic siblings of patients treated for primary VUR. From the results of the DMSA scan (only one sibling had a parenchymal defect), the systematic screening of asymptomatic siblings does not appear to be beneficial.

Genetic evidence for a novel gene(s) involved in urogenital development on 10q26

BACKGROUND

Although the frequent association between distal 10q monosomy and urogenital anomalies suggests the presence of a gene(s) for urogenital development on distal 10q, molecular deletion mapping has not been performed for the putative gene(s). In this study, we examined genotype-phenotype correlations in patients with distal 10q monosomy.

METHODS

This study consisted of six karyotypic males (cases 1 through 6) and four karyotypic females (cases 7 through 10) with 10q26 monosomy. Cases 3 through 5 and 7 through 10 had urinary anomalies such as vesicoureteral reflux and hypoplastic kidney, and cases 1 through 6, 8, and 9 exhibited genital anomalies such as micropenis, hypospadias, cryptorchidism, and hypoplastic labia majora. Fluorescence in situ hybridization (FISH) for 10q telomere, whole chromosome 10 painting, and microsatellite analysis for 35 loci on distal 10q were performed in cases 1 through 8.

RESULTS

FISH and whole chromosome painting confirmed distal 10q monosomy in cases 1 through 8. Microsatellite analysis revealed that hemizygosity for the region distal to D10S186 was shared by cases with urinary anomalies and that for the region distal to D10S1248 was common to cases with genital anomalies. Furthermore, it was indicated that PAX2, GFRA1, and EMX2 on distal 10q, in which the deletions could affect urinary and/or genital development, were present in two copies in cases 1 through 8.

CONCLUSIONS

The results suggest that a novel gene(s) for urinary development and that for genital development reside in the approximately 20 cM region distal to D10S186 and in the approximately 10 cM region distal to D10S1248, respectively, although it remains to be determined whether the two types of genes are identical or different.

Ablation of uroplakin III gene results in small urothelial plaques, urothelial leakage, and vesicoureteral reflux

Urothelium synthesizes a group of integral membrane proteins called uroplakins, which form two-dimensional crystals (urothelial plaques) covering >90% of the apical urothelial surface. We show that the ablation of the mouse uroplakin III (UPIII) gene leads to overexpression, defective glycosylation, and abnormal targeting of uroplakin Ib, the presumed partner of UPIII. The UPIII-depleted urothelium features small plaques, becomes leaky, and has enlarged ureteral orifices resulting in the back flow of urine, hydronephrosis, and altered renal function indicators. Thus, UPIII is an integral subunit of the urothelial plaque and contributes to the permeability barrier function of the urothelium, and UPIII deficiency can lead to global anomalies in the urinary tract. The ablation of a single urothelial-specific gene can therefore cause primary vesicoureteral reflux (VUR), a hereditary disease affecting approximately 1% of pregnancies and representing a leading cause of renal failure in infants. The fact that VUR caused by UPIII deletion seems distinct from that caused by the deletion of angiotensin receptor II gene suggests the existence of VUR subtypes. Mutations in multiple gene, including some that are urothelial specific, may therefore cause different subtypes of primary reflux. Studies of VUR in animal models caused by well-defined genetic defects should lead to improved molecular classification, prenatal diagnosis, and therapy of this important hereditary problem.

Pregnancy outcome in women with reflux nephropathy and the inheritance of vesico-ureteric reflux

In women with reflux nephropathy, we investigated whether pre-existing hypertension and impaired renal function influence the rates of preeclampsia, renal function deterioration and preterm birth. The infants were investigated for vesico-ureteric reflux (VUR). A prospective audit of 54 pregnancies in 46 women with reflux nephropathy was performed. Preeclampsia complicated 24% of pregnancies and was increased in women with pre-existing hypertension (42%) compared with normotensive women (14%), (RR 3.0 (95% CI 1.1-7.8)). Nine (18%) women experienced deterioration in renal function during pregnancy Women with mild or moderate renal impairment were at increased risk of renal function deterioration (RR 12.7 (95% CI 1.6-98.5); RR 19.8 (95% CI 2.6-155)), respectively A third of infants were delivered preterm. The risk of preterm birth was increased if the mother had pre-existing hypertension (p = 0.01) or moderate renal impairment (p = 0.002). Seventeen (43%) of the 40 infants who underwent micturating cystourethrography had VUR, consistent with autosomal dominant inheritance with reduced penetrance. In reflux nephropathy, pre-existing hypertension was associated with an increased risk of preeclampsia and pre-existing renal impairment with deterioration in renal function. Infants of women with reflux nephropathy should be screened for VUR.

A molecular and genetic view of human renal and urinary tract malformations

Malformations of the kidney and lower urinary tract are common causes of chronic renal failure in infants and young children, but little is known about the molecular pathogenesis of these disorders. In animal experiments, the main causes of malformation are mutations, chemical and pharmaceutical teratogens, obstruction of fetal urinary flow, and alterations of maternal nutrition. The focus of this review is to consider how mutations and other alterations of gene expression during development cause human urinary tract malformations. Some of these disorders are associated with congenital anomalies in multiple organ systems, and two such syndromes are considered in detail: first, the renal-coloboma syndrome, in which mutations of the PAX2 transcription factor cause partial failure of urinary tract growth; second, Kallmann's syndrome, in which mutations of a cell-signaling molecule are associated with the absence of the urinary tract. In patients seen by nephrologists and urologists, however, most urinary tract malformations occur in isolation, and in some of these individuals, a genetic pathogenesis is strongly suggested by a positive family history and genetic linkage studies. One common example is primary vesicoureteric reflux. Furthermore, sporadic malformations have been shown to be associated with polymorphisms of genes expressed during construction of the urinary tract. In the long term, an understanding of the genetic aspects of human urinary tract malformations will help to unravel the pathogenesis of these disorders and may facilitate the design of genetic screening tests with a view to early diagnosis.

Recent advances in the understanding and management of primary vesicoureteral reflux and reflux nephropathy

Vesicoureteral reflux and reflux nephropathy continue to be active areas of clinical investigation. There is conclusive evidence that vesicoureteral reflux is inherited. Prenatal diagnosis offers the opportunity for early recognition and intervention that may reduce the incidence of complications of vesicoureteral reflux such as pyelonephritis episodes and the development of reflux nephropathy.

How they begin and how they end: classic and new theories for the development and deterioration of congenital anomalies of the kidney and urinary tract, CAKUT

CAKUT are problems that often require surgical intervention or, in the worst case, lead to renal failure and the need for dialysis and/or renal transplantation. It is believed that these anomalies share a common genetic cause and to date there has been no good animal model with which to study these abnormalities. Although the abnormal interaction between the ureteral bud and metanephric blastema leads to renal hypodysplasia, vesicoureteral reflux, and ectopic ureters to name a few, the genetic and biochemical modulation of urinary tract development is not understood. Studies using the mouse strain mutant for angiotensin type 2 (AT2) receptors have given new insight into this mystery. The animals show defective apoptosis of undifferentiated mesenchymal cells in the area surrounding the developing kidney and urinary tract. This abnormal apoptosis may well interfere with the normal interaction between the ureteral bud and metanephric blastema resulting in CAKUT. This abnormal interaction would theoretically lead to preexisting intrinsic abnormalities of the kidney, which are programmed and take effect early in embryonic development. In the worst cases, the renal abnormalities would lead to progressive deterioration of renal function. Undoubtedly, there are more genes and biochemical modulators involved in this process other than the RAS and AT2 receptors. Our current animal model gives new and unique possibilities with which to study development of the kidney and urinary tract and ultimately seek ways of preventing an often debilitating disease process.

Renal-coloboma syndrome: a multi-system developmental disorder caused by PAX2 mutations

Optic nerve coloboma combined with renal disease, also called renal-coloboma syndrome ( # 120330 in McKusick's Mendelian Inheritance in Man Online, OMIM), a relatively recently characterized syndrome, results from autosomal dominant mutations in the PAX2 gene. Although renal-coloboma syndrome involves both ocular and renal anomalies, some patients are affected with vesico-ureteral reflux (VUR), high frequency hearing loss, central nervous system (CNS) anomalies, and/or genital anomalies, consistent with the expression of PAX2 in these tissues during development. We review here the clinical features of patients with renal-coloboma syndrome and PAX2 mutation. We also review the PAX2 mutations that have been reported to date, and discuss the possible effect of PAX2 mutations on normal development.

Angiotensin II, type 2 receptor in the development of vesico-ureteric reflux

OBJECTIVE

To investigate if mutation of the angiotensin II (Ang II) receptors AT2 is involved in primary vesico-ureteric reflux (VUR) in humans.

PATIENTS AND METHODS

Genetic polymorphisms in the AT1 and AT2 receptors was evaluated in 23 patients having the most common congenital urological abnormality, namely primary congenital VUR. The occurrence of the A1166C transition in the AT1 receptor gene and the A-1332G transition in the AT2 receptor gene were evaluated and compared with the incidence in normal controls with no urological abnormalities.

RESULT

The distribution of the AT1 receptor genotypes was no different between patients with VUR and healthy controls. Furthermore, 10 of 23 (44%) patients with VUR and seven of 19 (42%) controls carried the AT2 receptor gene variation. These results contrast with our previous finding of an association between the A-1332G transition in the AT2 receptor gene and primary obstructive megaureter, and pelvi-ureteric junction obstruction.

CONCLUSIONS

We propose that while the AT2 receptor is crucial for the normal development of the ureter, it does not contribute to the processes which culminate in VUR, which is primarily an abnormality in the bladder trigone.

The prevalence of PAX2 mutations in patients with isolated colobomas or colobomas associated with urogenital anomalies

The PAX2 gene is mutated in patients with ocular colobomas, vesicoureteral reflux (VUR), and kidney anomalies (renal-coloboma syndrome, OMIM 120330). The three abnormalities which make up this syndrome also occur in isolation, but the causal genes are not known. PAX2 encodes a transcription factor of the paired box class of DNA binding proteins, important for the development of the urogenital tract, optic nerve and adjacent retina, inner ear, and CNS. In this paper we have investigated the prevalence of PAX2 mutations in patients with ocular colobomas, microphthalmos, or retinal anomalies, either in isolation or with associated urogenital anomalies. Using PCR-SSCP, most or all exons of PAX2 were examined in blood DNA from 99 patients who have either ocular anomalies alone or a combination of ocular and urogenital conditions. PAX2 mutations were not detected in patients with ocular colobomas, either in isolation or with associated abnormalities, except in one patient with typical renal-coloboma syndrome. We conclude that PAX2 mutations are unlikely to be common in patients with ocular colobomas in isolation or in patients with ocular colobomas and associated anomalies, except for patients with typical renal-coloboma syndrome where PAX2 is known to be the aetiological cause.

Urinary tract infection and renal damage in sibling vesicoureteral reflux

PURPOSE

Siblings of index patients with vesicoureteral reflux are known to have an increased incidence of reflux. Previously reported studies have evaluated vesicoureteral reflux in asymptomatic siblings of children who were previously proved to have reflux. We determine the incidence and nature of vesicoureteral reflux in symptomatic siblings of children with documented vesicoureteral reflux.

MATERIALS AND METHODS

Between January 1990 and December 1996, 624 patients were diagnosed with vesicoureteral reflux during the investigation of documented urinary tract infections. All patients were evaluated for reflux by contrast voiding cystourethrography and reflux was graded according to the international reflux study. 99mTechnetium dimercapto-succinic acid nuclear renal scans were performed to detect renal scarring. The medical records and voiding cystourethrograms of the 624 consecutive patients with vesicoureteral reflux were retrospectively reviewed to identify siblings with vesicoureteral reflux.

RESULTS

Vesicoureteral reflux was noted in 85 siblings (134 refluxing ureters) of the 624 index patients (13.6%), including 1 and 2 siblings of 38 and 3 patients, respectively. Mean age at presentation of the 37 boys and 48 girls was 2.5 years. Reflux was unilateral in 36 siblings and bilateral in 49. Reflux was grades I to V in 8, 9, 51, 55 and 11 ureters, respectively. Nuclear scan revealed reflux nephropathy in 22 of the 77 tested siblings (28.5%).

CONCLUSIONS

When vesicoureteral reflux is discovered in symptomatic siblings, it is usually high grade and associated with a higher incidence of reflux nephropathy. Of further interest are the findings that refluxing symptomatic siblings of index patients are usually younger and boys are as commonly affected as girls. Screening for vesicoureteral reflux in asymptomatic siblings is recommended to decrease the incidence of reflux nephropathy.