Position and configuration of the ureteral orifice and its relationship to renal scarring in adults

History of endoscopic treatment of vesicoureteral reflux

Since its first clinical application in 1984, the endoscopic subureteral injection of bulking agents has become an alternative to long-term antibiotic prophylaxis and open surgical intervention in the treatment of VUR in children. The 15 min day care endoscopic procedure has gained worldwide popularity in the management of VUR in children. Over the years, multiple studies have demonstrated safety and long-term efficacy of this minimally invasive outpatient procedure. Nowadays almost 90% of the surgical treatment of VUR in Sweden is done by endoscopic procedure. In the current article, our aim was to review how the endoscopic treatment of VUR developed.

Pathologic glomerular characteristics and glomerular basement membrane alterations in biopsy-proven thin basement membrane nephropathy

BACKGROUND

Thin basement membrane nephropathy (TBMN) is diagnosed by diffuse thinning of the glomerular basement membrane (GBM) without any clinical and pathologic findings of Alport syndrome and the other renal diseases. TBMN is characterized clinically by benign familial hematuria but rarely develops into end-stage renal disease.

METHODS

In 27 cases of biopsy-proven TBMN, we evaluated the pathologic characteristics of TBMN, and examined the correlation between these pathologic characterizations and renal dysfunction.

RESULTS

All patients had hematuria, and 21 patients (77.8%) had proteinuria. In six patients (28.6%) who were more than 50 years of age, the estimated glomerular filtration rate (eGFR) decreased from G3a to G4 in the chronic kidney disease stage. Pathologically, an irregular decrease in intensity of type IV collagen α5(IV) chain was seen in GBM, and irregular thinning with diffuse rough etched images was observed on the GBM surface with several sizes of holes by low-vacuum scanning electron microscopy. The glomerular morphology of TBMN was characterized by an increased number of small glomerular capillaries with an increased extracellular matrix (ECM). These characteristic morphologic alterations were evident from a young age in patients with TBMN, but were not correlated directly with the decrease of eGFR, the degree of hematuria, and proteinuria. The decrease of eGFR in patients with TBMN who were more than 50 years of age might be primarily mediated by arteriolosclerosis-associated glomerulosclerosis and interstitial fibrosis.

CONCLUSION

Characteristic pathological glomerular findings and GBM alterations occurred from a young age but were not associated directly with renal impairment in biopsy-proven TBMN.

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.

Anatomy and Physiology of the Urinary Tract: Relation to Host Defense and Microbial Infection

The urinary tract exits to a body surface area that is densely populated by a wide range of microbes. Yet, under most normal circumstances, it is typically considered sterile, i.e., devoid of microbes, a stark contrast to the gastrointestinal and upper respiratory tracts where many commensal and pathogenic microbes call home. Not surprisingly, infection of the urinary tract over a healthy person's lifetime is relatively infrequent, occurring once or twice or not at all for most people. For those who do experience an initial infection, the great majority (70% to 80%) thankfully do not go on to suffer from multiple episodes. This is a far cry from the upper respiratory tract infections, which can afflict an otherwise healthy individual countless times. The fact that urinary tract infections are hard to elicit in experimental animals except with inoculum 3-5 orders of magnitude greater than the colony counts that define an acute urinary infection in humans (105 cfu/ml), also speaks to the robustness of the urinary tract defense. How can the urinary tract be so effective in fending off harmful microbes despite its orifice in a close vicinity to that of the microbe-laden gastrointestinal tract? While a complete picture is still evolving, the general consensus is that the anatomical and physiological integrity of the urinary tract is of paramount importance in maintaining a healthy urinary tract. When this integrity is breached, however, the urinary tract can be at a heightened risk or even recurrent episodes of microbial infections. In fact, recurrent urinary tract infections are a significant cause of morbidity and time lost from work and a major challenge to manage clinically. Additionally, infections of the upper urinary tract often require hospitalization and prolonged antibiotic therapy. In this chapter, we provide an overview of the basic anatomy and physiology of the urinary tract with an emphasis on their specific roles in host defense. We also highlight the important structural and functional abnormalities that predispose the urinary tract to microbial infections.

Vesico-ureteric reflux: using mouse models to understand a common congenital urinary tract defect

Vesico-ureteric reflux (VUR) is a common congenital urinary tract defect in which urine flows retrogradely from the bladder to the kidneys because of an abnormally formed uretero-vesical junction. It is associated with recurrent urinary tract infections, renal hypo/dysplasia, reflux nephropathy, hypertension, and end-stage renal disease. In humans, VUR is genetically and phenotypically heterogeneous, encompassing diverse renal and urinary tract phenotypes. To understand the significance of these phenotypes, we and others have used the mouse as a model organism and this has led to the identification of new candidate genes. Through careful phenotypic analysis of these models, a new understanding of the genetics and biology of VUR is now underway.

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.

The C3H/HeJ inbred mouse is a model of vesico-ureteric reflux with a susceptibility locus on chromosome 12

Vesico-ureteric reflux is the most common congenital anomaly of the urinary tract, characterized by a defective uretero-vesical junction with retrograde urine flow from the bladder toward the kidneys. Because there is strong evidence for a genetic basis for some cases of vesico-ureteric reflux, we screened 11 inbred mouse strains for reflux and kidney size and identified one strain, C3H/HeJ, that has a 100 percent incidence of vesico-ureteric reflux with otherwise normal kidneys at birth. These mice are predisposed to reflux as a result of a defective uretero-vesical junction characterized by a short intravesical ureter. This defect results from a delay in urinary tract development initially manifested by a ureteric bud arising from a more caudal location along the mesonephric duct. In contrast, C57BL/6J mice (resistant to reflux at birth) have long intravesical ureters, normally positioned ureteric buds, and no delay in urinary tract development. Genome-wide and additional fine mapping of backcross mice, derived from C3H/HeJ and C57BL/6J crosses, identified a significant reflux susceptibility locus, Vurm1, on chromosome 12 (peak logarithm of the odds=7.39). The C3H/HeJ mouse is a model of vesico-ureteric reflux without renal malformation, and further characterization of this model will allow for the identification of a pathway important for urinary tract development, a finding that will serve as a model for the human disorder.

Gene discovery and vesicoureteric reflux

Vesicoureteric reflux (VUR) is a congenital urinary tract defect caused by abnormal insertion of the ureter within the bladder wall. This leads to a defective ureterovesical junction in which urine flows retrogradely from the bladder to the kidneys. Although VUR is associated with recurrent urinary tract infections, renal malformations, hypertension, and reflux nephropathy, its relationship to each of these clinical entities is poorly understood. Mutations in genes expressed by the developing kidney and urinary tract can cause VUR in mice, and some of these same genes have been identified in humans with VUR. By discovering the genes that are associated with VUR, new hypotheses will be generated such that, eventually, the relationship between VUR and its complications will be understood.

Vesicoureteral reflux

Vesicoureteral reflux (VUR), the retrograde flow of urine from the bladder toward the kidney, is common in young children. About 30% of children with urinary tract infections will be diagnosed with VUR after a voiding cystourethrogram. For most, VUR will resolve spontaneously; 20% to 30% will have further infections, but few will experience long-term renal sequelae. Developmentally, VUR arises from disruption of complex signaling pathways and cellular differentiation. These mechanisms are probably genetically programmed but may be influenced by environmental exposures. Phenotypic expression of VUR is variable, ranging from asymptomatic forms to severe renal parenchymal disease and end-stage disease. VUR is often familial but is genetically heterogeneous with variability in mode of inheritance and in which gene, or the number of genes, that are involved. Numerous genetic studies that explore associations with VUR are available. The relative utility of these for understanding the genetics of VUR is often limited because of small sample size, poor methodology, and a diverse spectrum of patients. Much, if not all, of the renal parenchymal damage associated with end-stage disease is likely to be congenital, which limits the opportunity for intervention to familial cases where risk prediction may be available. Management of children with VUR remains controversial because there is no strong supportive evidence that prophylactic antibiotics or surgical intervention improve outcomes. Furthermore, well-designed genetic epidemiological studies focusing on the severe end of the VUR phenotype may help define the causal pathway and identify modifiable or disease predictive factors.

Vesico-ureteric reflux and urinary tract development in the Pax2 1Neu+/- mouse

Vesico-ureteric reflux (VUR) is a urinary tract abnormality that affects roughly one-third of patients with renal-coloboma syndrome, an autosomal dominant condition caused by a mutation in PAX2. Here, we report that a mouse model with an identical mutation, the Pax2 1Neu+/- mouse, has a 30% incidence of VUR. In VUR, urine flows retrogradely from the bladder to the ureter and is associated with urinary tract infections, hypertension, and renal failure. The propensity to reflux in the Pax2 1Neu+/- mouse is correlated with a shortened intravesical ureter that has lost its oblique angle of entry into the bladder wall compared with wild-type mice. Normally, the kidney and urinary tract develop from the ureteric bud, which grows from a predetermined position on the mesonephric duct. In Pax2 1Neu+/- mice, this position is shifted caudally while surrounding metanephric mesenchyme markers remain unaffected. Mutant offspring from crosses between Pax2 1Neu+/- and Hoxb7/GFP+/- mice have delayed union of the ureter with the bladder and delayed separation of the ureter from the mesonephric duct. These events are not caused by a change in apoptosis within the developing urinary tract. Our results provide the first evidence that VUR may arise from a delay in urinary tract maturation and an explanation for the clinical observation that VUR resolves over time in some affected children.

Vesicoureteric reflux and renal malformations: a developmental problem

Vesicoureteric reflux (VUR) is a congenital urinary tract defect caused by the failure of the ureter to insert correctly into the bladder. It occurs in up to 1% of the general population and is associated with recurrent urinary tract infections and renal failure. Despite treatment of affected children for the past 40 years, the incidence of end-stage renal disease secondary to VUR has not decreased. Twin and family studies reveal that VUR has a genetic basis. Some of the gene candidates that have been identified regulate the position of ureteric budding, a critical step in both kidney and urinary tract development. Analysis of data from humans and mice suggests that some of the renal damage associated with VUR is congenital and is due to a kidney malformation. Therefore, in these cases, the association of VUR and renal failure may be caused by a genetic defect affecting the formation of the kidney and the urinary tract.

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.

Developmental renal pathology: its past, present, and future

Congenital anomalies of the kidney and urinary tract are responsible for approximately 40% of cases of childhood end-stage renal failure in the United States. This article describes the spectrum of developmental renal lesions in children (including renal agenesis, dysplasias, hereditary hydronephrosis, autosomal recessive and dominant polycystic kidneys, vesicoureteral reflux, diabetic embryopathy, some teratogenic drugs affecting renal development, and syndromes associated with renal dysplasias). The article quotes some historic references that established the foundation for further studies; reviews the embryology, pathology, postnatal renal development, and its possible consequences of renal function; as well as recent advances in fetal ultrasonography and molecular biology with some novel treatment and diagnostic modalities. Finally, an attempt is made to predict several future avenues in pharmacogenetics that are being built currently and that will allow a better prognosis for many children with congenital renal conditions.

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.

Unravelling the genetics of vesicoureteric reflux: a common familial disorder

Primary vesicoureteric reflux (VUR) is one of the more common genetic disorders. Little is yet known about the genetics of this potentially manageable childhood condition, which is characterised by regurgitation of urine from the bladder to the kidney. The VUR phenotype is associated with shortness of the submucosal segment of the ureter due to congenital lateral ectopia of the ureteric orifice. VUR is found in 30-50% of infants and young children with a urinary tract infection. A serious concern in families with an affected patient is that approximately one half of siblings or offspring will be affected, but up to a half of these affected siblings and offspring may be asymptomatic in childhood. If left untreated, these patients may present later in life with proteinuria, hypertension or renal failure. VUR is the commonest cause of end-stage renal failure in children, and an important cause in adults. As the kidney damage resulting from severe VUR is preventable, early detection is desirable. The techniques for clinical diagnosis are invasive and costly, reinforcing the importance of identification of a gene for VUR to facilitate genetic screening. Although family studies suggest a major dominant gene, the inheritance pattern is still a matter of debate. In rare instances, VUR occurs in association with other diseases, such as the coloboma-ureteric-renal syndrome, which is caused by a PAX2 gene mutation. In this review, we present evidence that this common disorder may be caused by mutations in the developmental pathway of which the PAX2 gene forms a part.

End-stage reflux nephropathy

Forty-two of 371 patients (11.3%) entering a dialysis-transplant program had end-stage reflux nephropathy. Thirteen of these 371 patients were under 16 years of age, with 6 of them having reflux nephropathy. Most patients presented with severely impaired renal function, hypertension, and proteinuria. Documented urinary tract infections occurred in only 4 of the 18 male and 14 of the 24 female patients. Thirty-five patients had hypertension, which in 22 had not been detected before presentation. Five presented with accelerated hypertension. Eight of the 24 women presented during a pregnancy. Twenty-nine patients are still alive, 20 with a functioning renal transplant. Reflux nephropathy is an important cause of end-stage renal failure, particularly in younger people. All patients presenting with renal insufficiency and proteinuria, with or without urinary tract infections or hypertension, should have reflux nephropathy excluded.

Vesicoureteric reflux and renal injury

Renal injury associated with the intrarenal reflux (IRR) of urine that is either infected, under high pressure, or both, is a major cause of severe hypertension during childhood and adolescence and of chronic renal insufficiency in patients less than 30 years of age. Many, but not all, adolescent and adult patients with reflux nephropathy (RN) give a history of urinary tract infection (UTI) or unexplained fevers in infancy or early childhood, when the kidney is thought to be at greatest risk of injury. Although vesicoureteric reflux (VUR) is observed more commonly in infants than children with UTI, it is rare in uninfected patients at any age and should never be considered a normal finding during human development. Renal scarring may not be obvious in radiographic or radionuclear studies to medical management alone, no definite benefit of one over the other was observed, regardless of the grade of VUR. Moreover, progressive renal injury in scarred kidneys has been noted even after VUR had been corrected, when infection had been prevented, and while hypertension had been controlled satisfactorily. Focal glomerular sclerosis, a lesion found in patients with proteinuria and RN, has been identified not only in scarred kidneys, but also may be seen in contralateral, unscarred kidneys without VUR, which might suggest a humoral factor or, perhaps, a hyperfiltration phenomenon. RN is one of the most frequent causes of end-stage renal disease (ESRD) in children, adolescents, and young adults, which is potentially preventable. However, prevention will depend on early identification of patients at risk--infants and young children after the first UTI and siblings of patients with VUR--aggressive and effective treatment of UTI, minimizing intravesical pressure, and education of patients, parents, and physicians.

Urinary infections in children 1985

Images

Pyelonephritic scarring in 213 patients with upper and lower urinary tract infections: long-term followup

Of 213 patients more than 3 years old with recurrent urinary tract infections new pyelonephritic scars formed only among those with a combination of urinary tract infection and vesicoureteral reflux. Of 61 patients with that combination new renal pyelonephritic scars developed in 7 (11.48 per cent) and severe clubbing in 2. Of 40 patients with vesicoureteral reflux who underwent an antireflux operation new scars formed in 5 and progressive renal damage occurred in 1. Most renal scars (58) were present at initial examination. Neither number of urinary tract infections, number of upper urinary tract infections localized by the bladder washout technique nor attacks of flank pain and fever were seen more often in patients who suffered new scars, and grade of reflux was not a factor. Patients in whom new scars developed during our prospective followup were younger than those who did not have new scars. However, new scars formed after an initial normal excretory urogram in only 1 patient with vesicoureteral reflux and urinary tract infection compared to 4 after an antireflux operation.

Renal clubbing and scarring in adults: a retrospective study of 110 cases

A urographic pattern of renal clubbing and scarring was found in 182 scarred kidneys of 110 adult patients. Homolateral vesicoureteric reflux was demonstrated by reliable techniques in 90/135 scarred kidneys. Urinary tract infections occurred in 75 patients. Hypertension developed in 20 patients with normal renal function and was not related to the extent of scarring. Chronic renal failure occurred in 30 patients with diffuse bilateral scarring. Four patients showed histologic changes of chronic pyelonephritis. Two hypertensive patients had a typical histologic pattern of Ask-Upmark kidney (segmental hypoplasia). Development of renal scars in adulthood was demonstrated in 2 cases.

"Stasis"--a test for vesico-ureteric orifice competence in children with reflux

Intravenous radionuclide cystography (IVRNC) with one injection on 99m-Tc-DTPA measures renal function and detects vesico-renal reflux [1, 2, 3]. This paper describes a possible means of detecting incompetent ureteric orifices during IVRNC examinations. In some patients a hold-up of material in the renal areas (stasis) was observed which suddenly cleared at micturition. A prospective study of 58 patients who had IVRNC and cystoscopy within 28 days of each other revealed that 76.3% had anatomically abnormal ureteric orifices on the same side as the stasis. This contrasted with only 12.8% of abnormal uretic orifices found in patients not showing stasis (p less than 0.005). As incompetent ureteric orifices are recognised as the major aetiological factor in vesico-renal reflux [4, 5, 6] this additional information gained at IVRNC could be of clinical use and perhaps avoid some cystoscopies.

Reflux nephropathy

The whole subject of reflux nephropathy, which may affect 1 in every 300 of the white female population, and is the second most common disease of the kidney in the young, is still bedevilled by a lack of information regarding many of its important aspects, and the absence of any coordinated action to obtain it. What is required above all else is a means of its early detection in very young children, so that it may be prevented, at least in its more severe forms. Its financial cost can only be surmised, but the treatment of its end-stages is likely to be in the region of a hundred million dollars a year. The cost in wastage involving, as it does, young people, particularly females, is incalculable.

Renal vein renin concentration in the hypertension of unilateral reflux nephropathy

Hypertension is a frequent complication of reflux nephropathy. The cause of this hypertension is unknown. Our study was undertaken to assess the possible role of the renin-angiotensin system in the hypertension associated with unilateral reflux nephropathy. We selected for study 17 normotensive and 12 hypertensive patients with strictly unilateral reflux nephropathy. There were 3 normotensive and 2 hypertensive patients with a renal vein renin ratio exceeding 1.5. Of these 3 normotensive patients 1 had evidence from divided renal function studies to suggest functional renal ischemia. No consistent evidence was obtained to support the concept that the renin-angiotensin system has a primary role in the non-malignant hypertension of unilateral reflux nephropathy.

Disappearance of vesicoureteric reflux during long-term prophylaxis of urinary tract infection in children

Seventy-five children aged 3 weeks to 12 years and found on investigation of symptomatic urinary infection to have vesicoureteric reflux were managed conservatively with continuous low-dose prophylaxis. Serial cystographic and renal growth studies were performed during seven to 15 years' follow-up. Reflux disappeared spontaneously in 53 children (71%) and from 79% of the affected ureters. This occurred at any age and not only in infancy or at puberty. The initial severity or reflux was the most important factor affecting the outcome. Reflux disappeared from 85% of ureters of normal calibre but from only 41% of dilated ureters. Gross reflux associated with existing severe renal scarring was least likely to disappear. Nevertheless, reflux stopped in 12 of the 19 initially scarred renal units (63%). Reflux was as likely to disappear in children who had a recurrence of urinary infection as in those who had no further infection. Renal growth appeared to be normal in 93% of kidneys and fresh or extending scarring was seen in only two children. Management programmes for children with vesicoureteric reflux should take into account the self-limiting nature of three-quarters of the reflux found on investigating uncomplicated urinary tract infection.

The interrelationship between vesico-ureteric reflux, trigonal abnormalities and a bifid pelvicalyceal collecting system: a family study

3 investigations have been undertaken to study the interrelationship between a bifid pelvicalyceal collecting system, vesico-ureteric reflux and lateral ectopia of the ureteric orifice. Firstly, in 30 families investigated to confirm the familial incidence of bifid and double ureters there were 3 families in which siblings were found with primary reflux. Secondly, reflux was found in 62 of 110 patients investigated with a duplex pelvicalyceal system. Reflux was to the ipsilateral kidney in 48 patients but occurred to the contralateral kidney, unaffected by duplicity, in 14. This high incidence of reflux is related to lateral ectopia of the ureteric orifice which may be either bilateral or unilateral. Thirdly, the incidence of a bifid pelvicalyceal system was determined in the parents and siblings of a series of 32 patients with primary reflux. The results support the hypothesis that primary reflux may be inherited by an autosomal dominant gene of variable penetrance in a manner similar to the inheritance of a duplex urinary tract. Thus there is a direct genetic relationship between primary vesico-ureteric reflux, lateral ectopia of the ureteric orifices and a duplex pelvicalyceal system.