Renal tubular dysgenesis and microcolon, a novel association. Report of three cases

Renal tubular dysgenesis (RTD) is a developmental abnormality of the nephron characterized by fetal anuria, oligohydramnios, and severe postnatal hypotension. Genetic forms have an autosomal recessive inheritance and are caused by mutations in genes encoding key components of the renin-angiotensin pathway. We report three patients from two unrelated families with RTD due to pathogenic variants of the angiotensin-converting enzyme (ACE) gene, in whom RTD was associated with microcolon. We also detail key variations of the renin-angiotensin system in one of these infants. The severe intestinal developmental abnormality culminating in microcolon and early terminal ileum perforation/necrotizing enterocolitis is a novel finding not previously associated with RTD, which points to a role of the renin-angiotensin system in gut development.

Leucine-rich repeat kinase 2 (LRRK2)-deficient rats exhibit renal tubule injury and perturbations in metabolic and immunological homeostasis

Genetic evidence links mutations in the LRRK2 gene with an increased risk of Parkinson's disease, for which no neuroprotective or neurorestorative therapies currently exist. While the role of LRRK2 in normal cellular function has yet to be fully described, evidence suggests involvement with immune and kidney functions. A comparative study of LRRK2-deficient and wild type rats investigated the influence that this gene has on the phenotype of these rats. Significant weight gain in the LRRK2 null rats was observed and was accompanied by significant increases in insulin and insulin-like growth factors. Additionally, LRRK2-deficient rats displayed kidney morphological and histopathological alterations in the renal tubule epithelial cells of all animals assessed. These perturbations in renal morphology were accompanied by significant decreases of lipocalin-2, in both the urine and plasma of knockout animals. Significant alterations in the cellular composition of the spleen between LRRK2 knockout and wild type animals were identified by immunophenotyping and were associated with subtle differences in response to dual infection with rat-adapted influenza virus (RAIV) and Streptococcus pneumoniae. Ontological pathway analysis of LRRK2 across metabolic and kidney processes and pathological categories suggested that the thioredoxin network may play a role in perturbing these organ systems. The phenotype of the LRRK2 null rat is suggestive of a complex biology influencing metabolism, immune function and kidney homeostasis. These data need to be extended to better understand the role of the kinase domain or other biological functions of the gene to better inform the development of pharmacological inhibitors.

Renal tubular dysgenesis in Israel: pathologist's experience and literature review

BACKGROUND

Renal tubular dysgenesis is a rare lethal kidney abnormality clinically manifested by olighydramnios, anuria and respiratory distress. Most of the information on this entity is provided by case reports and short series.

OBJECTIVES

To evaluate the incidence and comparative frequency of clinical manifestations in different etiologic-pathogenic variants of RTD in Israel and in summarized published data.

METHODS

Stillborn and neonatal autopsy material from nine medical centers in northern and central Israel was studied. Information concerning pregnancy, labor and postnatal status and autopsy findings of cases with histologically, histochemically and immunohistochemically confirmed RTD were obtained from corresponding reports and from published material.

RESULTS

From the 1538 autopsies of fetuses (2 20 weeks gestation) and neonates that were performed between 1976 and 2007 we identified 12 cases of RTD (0.78%). Abnormality occurred more often (1.4%) in the Upper and Western Galilee than in Israel as a whole.

CONCLUSIONS

Our study and a review of the literature showed that the autosomal recessive variant of RTD was more frequent than twin-twin transfusion-induced. Most symptoms were similar in all variants of RTD, but their frequency was different in each of them.

Mode of Action: Oxalate Crystal-Induced Renal Tubule Degeneration and Glycolic Acid-Induced Dysmorphogenesis—Renal and Developmental Effects of Ethylene Glycol

Ethylene glycol can cause both renal and developmental toxicity, with metabolism playing a key role in the mode of action (MOA) for each form of toxicity. Renal toxicity is ascribed to the terminal metabolite oxalic acid, which precipitates in the kidney in the form of calcium oxalate crystals and is believed to cause physical damage to the renal tubules. The human relevance of the renal toxicity of ethylene glycol is indicated by the similarity between animals and humans of metabolic pathways, the observation of renal oxalate crystals in toxicity studies in experimental animals and human poisonings, and cases of human kidney and bladder stones related to dietary oxalates and oxalate precursors. High-dose gavage exposures to ethylene glycol also cause axial skeletal defects in rodents (but not rabbits), with the intermediary metabolite, glycolic acid, identified as the causative agent. However, the mechanism by which glycolic acid perturbs development has not been investigated sufficiently to develop a plausible hypothesis of mode of action, nor have any cases of ethylene glycol-induced developmental effects been reported in humans. Given this, and the variations in sensitivity between animal species in response, the relevance to humans of ethylene glycol-induced developmental toxicity in animals is unknown at this time.

Inherited renal tubular dysgenesis: the first patients surviving the neonatal period

Renal tubular dysgenesis (RTD) is a clinical disorder either acquired during fetal development or inherited as an autosomal recessive condition. Inherited RTD is caused by mutations in the genes encoding the components of the renin-angiotensin system angiotensinogen, renin, angiotensin-converting enzyme and angiotensin II receptor type 1. Inherited RTD is characterized by early onset oligohydramnios, skull ossification defects, preterm birth and neonatal pulmonary and renal failure. The histological hallmark is the absence or poor development of proximal tubules. So far, all patients died either in utero or shortly after birth. We report the first patients with inherited RTD surviving the neonatal period and still being alive. Genetic and functional analysis of the renin-angiotensin system contributes to the diagnosis of RTD. In conclusion, the clinical diagnosis of inherited RTD is easily missed after birth without renal biopsy or information on affected family members. Genetic and functional analysis of the renin-angiotensin system contributes to correct diagnosis.

Dysgénésie tubulaire rénale autosomique récessive: étude morphologique et génétique de 2 nouveaux cas

Renal tubular dysgenesis (RTD) is a rare and severe nephropathy characterized by persistent fetal anuria leading to oligohydramnios with the Potter sequence, and perinatal death. The diagnosis is based on the histological finding of absence or paucity of proximal tubules. A consanguineous family is described in which 2 siblings, born after pregnancies complicated by oligohydramnios were affected with RTD. Patients were small for gestational age at birth. The first patient died after a few hours, the second after a few days of life, with persistent anuria unresponsive to treatment. Histologically, there was marked reduction in the number of proximal tubule sections and no renin was detected by immunohistochemistry. An homozygous mutation of the gene encoding renin was identified in both patients. This study underlines the interest of the histological examination of the kidney for the diagnostic of RTD in anuric fetuses and newborns, and the possibility of mutation analysis of RAS genes for genetic counselling and early prenatal diagnosis.

[Renal tubular dysgenesis and mutation in the renin gene]

Renal tubular dysgenesis is a severe and rare disorder of the renal development characterized by fetal anuria, oligohydramnios and early death from pulmonary hypoplasia and refractory arterial hypotension. We report on a female patient who presented with anuria in the neonatal period, requiring peritoneal dialysis until 5 months of age with unexpected diuresis recovery at 2 months of age. Clinical, histological and pathophysiological issues are discussed for this disease related to a mutation in the renin gene.

Renal tubular dysgenesis, a not uncommon autosomal recessive disorder leading to oligohydramnios: Role of the Renin-Angiotensin system

Renal tubular dysgenesis is a clinical disorder that is observed in fetuses and characterized by the absence or poor development of proximal tubules, early onset and persistent oligohydramnios that leads to the Potter sequence, and skull ossification defects. It may be acquired during fetal development or inherited as an autosomal recessive disease. It was shown recently that autosomal recessive renal tubular dysgenesis is genetically heterogeneous and linked to mutations in the genes that encode components of the renin-angiotensin system. This study analyzed the clinical expression of the disease in 29 fetus/neonates from 18 unrelated families and evaluated changes in renal morphology and expression of the renin-angiotensin system. The disease was uniformly severe, with perinatal death in all cases as a result of persistent anuria and hypoxia related to pulmonary hypoplasia. Severe defects in proximal tubules were observed in all fetuses from 18 gestational weeks onward, and lesions also involved other tubular segments. They were associated with thickening of the renal arterial vasculature, from the arcuate to the afferent arteries. Renal renin expression was strikingly increased in 19 of 24 patients studied, from 13 families, whereas no renal renin was detected in four patients from three families. Angiotensinogen and angiotensin-converting enzyme were absent or present in only small amounts in the proximal tubule, in correlation with the severity of tubular abnormalities. No specific changes were detected in angiotensin II receptor expression. The severity and the early onset of the clinical and pathologic expression of the disease underline the major importance of this system in fetal kidney function and development in humans. The identification of the disease on the basis of precise histologic analysis and the research of the genetic defect now allow genetic counseling and early prenatal diagnosis.

The anuric preterm newborn infant with a normal renal ultrasound: a diagnostic and ethical challenge

Diagnosis and treatment of an anuric premature infant with severe respiratory compromise and a normal renal ultrasound (US), is a difficult task that requires a multidisciplinary approach. A 29-week gestation premature male infant, born after 5 weeks of worsening oligohydramnios, was ventilated for respiratory distress and remained anuric. Intensive clinical investigations and pediatric nephrology consultation that predicted very poor prognosis were followed by progressive renal failure, electrolyte imbalance, respiratory failure, ventricular arrhythmia, and finally cardiac arrest and death on day 5. In view of the predicted poor outcome, and after discussion with the parents, a decision was made not to start peritoneal dialysis (PD), and to offer only palliative therapy, with comfort care alone. Pre and postnatal diagnosis lead, in this case, to an ethical challenge that focuses on the question of futility.

Renal tubular dysgenesis associated with in utero exposure to Nimuselide

Maternal ingestion of the selective cyclo-oxygenase-2 (COX-2) inhibitor Nimuselide has been reported to be associated with the development of oligohydramnios and neonatal renal failure in some cases. We report a case of neonatal renal failure associated with maternal ingestion of Nimuselide in the third trimester of pregnancy. The neonate presented with metabolic acidosis and non-oliguric renal failure on the second day of life. The renal histopathology showed evidence of renal tubular dysgenesis. The child continues to have elevated serum creatinine and hypertension at 10 months of age.

Andersen-Tawil syndrome: New potassium channel mutations and possible phenotypic variation

OBJECTIVE

To evaluate clinical, genetic, and electrophysiologic features of patients with Andersen-Tawil syndrome (ATS) in the United Kingdom.

METHODS

Clinical and neurophysiologic evaluation was conducted of 11 families suspected to have ATS. Molecular genetic analysis of each proband was performed by direct DNA sequencing of the entire coding region of KCNJ2. Control samples were screened by direct DNA sequencing. The electrophysiologic consequences of several new mutations were studied in an oocyte expression system.

RESULTS

All 11 ATS families harbored pathogenic mutations in KCNJ2 with six mutations not previously reported. Some unusual clinical features including renal tubular defect, CNS involvement, and dental and phonation abnormalities were observed. Five mutations (T75M, D78G, R82Q, L217P, and G300D) were expressed, all of which resulted in nonfunctional channels when expressed alone, and co-expression with wild-type (WT) KCNJ2 demonstrated a dominant negative effect.

CONCLUSION

Six new disease-causing mutations in KCNJ2 were identified, one of which was in a PIP2 binding site. Molecular expression studies indicated that five of the mutations exerted a dominant negative effect on the wild-type allele. KCNJ2 mutations are an important cause of ATS in the UK.

Fish mesonephric model of polycystic kidney disease in medaka (Oryzias latipes) pc mutant

BACKGROUND

Polycystic kidney disease (PKD) is a common hereditary disease. A number of murine and zebrafish mutants have been generated and used for the study of PKD as metanephric and pronephric models, respectively. Here, we report a medaka (Oryzias latipes) mutant that develops numerous cysts in the kidney in adulthood fish in an autosomal-recessive manner as a mesonephric model of PKD.

METHODS

The phenotypes of the medaka pc mutant were described in terms of morphologic, histologic, and ultrastructural features. The pc see-through stock was produced by crossing a pc mutant and a fish from the see-through stock and used for observing the kidney through the transparent body wall of a live fish.

RESULTS

The mutant developed bilateral massive enlargement of the kidney in adulthood. They sexually matured normally within 2 months of age and died within 6 months of age. The affected kidney was occupied by numerous, fluid-filled cysts, which were lined by attenuated squamous epithelial cells. Developmentally, cystic formation began in the pronephros in 10-day-old fry and in the mesonephros in 20-day-old fry at the microscopic level. The pc see-through stock was useful in observing disease progression in live fish.

CONCLUSION

The kidney disorder that develops in the medaka pc mutant is a mesonephric counterpart of PKD, particularly an autosomal-dominant PKD, based on its morphologic, histologic, and ultrastructural features, and slow progression.

Mutations in genes in the renin-angiotensin system are associated with autosomal recessive renal tubular dysgenesis

Autosomal recessive renal tubular dysgenesis is a severe disorder of renal tubular development characterized by persistent fetal anuria and perinatal death, probably due to pulmonary hypoplasia from early-onset oligohydramnios (Potter phenotype). Absence or paucity of differentiated proximal tubules is the histopathological hallmark of the disease and may be associated with skull ossification defects. We studied 11 individuals with renal tubular dysgenesis, belonging to nine families, and found that they had homozygous or compound heterozygous mutations in the genes encoding renin, angiotensinogen, angiotensin converting enzyme or angiotensin II receptor type 1. We propose that renal lesions and early anuria result from chronic low perfusion pressure of the fetal kidney, a consequence of renin-angiotensin system inactivity. This is the first identification to our knowledge of a renal mendelian disorder linked to genetic defects in the renin-angiotensin system, highlighting the crucial role of the renin-angiotensin system in human kidney development.

Renal tubular dysgenesis-a case presentation

Renal tubular dysgenesis (RTD) is a lethal, developmental anomaly of the fetal kidney characterized by a defect in differentiation of the proximal and distal convoluted tubules. It is usually associated with oligohydramnios in later pregnancy and Potter's syndrome. A neonate with typical features who presented with mild respiratory distress, dysmorphic appearance and anuria is described. At the age of seven days, peritoneal dialysis was started and was continued until the death of the baby at the age of three months. The diagnosis was made on the bases of clinical and ultrasonographic findings confirmed by renal biopsy. A review of the literature showed that this is the first case of RTD reported in Turkey.

Acute renal failure: definitions, diagnosis, pathogenesis, and therapy

Acute renal failure (ARF), characterized by sudden loss of the ability of the kidneys to excrete wastes, concentrate urine, conserve electrolytes, and maintain fluid balance, is a frequent clinical problem, particularly in the intensive care unit, where it is associated with a mortality of between 50% and 80%. In this review, the epidemiology and pathophysiology of ARF are discussed, including the vascular, tubular, and inflammatory perturbations. The clinical evaluation of ARF and implications for potential future therapies to decrease the high mortality are described.

Renal tubular dysgenesis and neonatal hemochromatosis without pulmonary hypoplasia

Renal tubular dysgenesis is a rare disorder of differentiation of the fetal kidney. The condition has previously been reported as a postmortem diagnosis in infants who have had oligohydramnios commencing after 20 weeks gestation and have died of renal or respiratory failure shortly after birth with a clinical description of Potter sequence. The absence of clinically significant pulmonary hypoplasia in our case serves to emphasize that renal tubular dysgenesis, fetal anuria and long-standing oligohydramnios can occur without pulmonary insufficiency. The coexistence of renal tubular dysgenesis with neonatal hemochromatosis has been previously described in four published cases. The link between these two rare conditions is clinically important if dialysis or liver transplantation is considered in infants with hepatic and renal failure. Antemortem diagnosis by renal biopsy in our case enabled parental counseling and avoided the inappropriate use of peritoneal dialysis.

Renal tubular dysgenesis with hypoplastic calvaria: report of two cases

Renal tubular dysgenesis (RTD), a rare, lethal, autosomal recessive disorder, is characterized by short and poorly differentiated proximal tubules and associated with hypoplastic calvaria. We report two cases of RTD with hypoplasia of the calvaria. Microscopically, proximal tubules in the kidneys were not seen on routine H&E stain. Almost all tubules in the cortex were stained for epithelial membrane antigen (EMA), confirming the absence of proximal tubule differentiation. The autopsy findings, microscopic features and the etiology of this rare condition is discussed and compared with literature data.

Perturbed medullary tubulogenesis in neonatal rat exposed to renin-angiotensin system inhibition

BACKGROUND

Pharmacological interruption of the angiotensin II type-1 receptor (AT(1)) signalling during nephrogenesis in rats induces irreversible abnormalities in kidney morphology, comprising papillary atrophy and tubulointerstitial damage, which are characterized by tubular dilatation/atrophy and interstitial inflammation/fibrosis. This study determined the time course for development of tubular structural and inflammatory changes and possible cytokine production in the renal medulla of newborn rats exposed to angiotensin-converting enzyme (ACE) inhibition. Additionally, medullary expression of E-cadherin, a marker for tubular formation, was investigated in ACE-inhibited rats.

METHODS

Newborn rats were exposed (postnatal days 0-12) to ACE inhibitor enalapril and killed at days 1, 2, 4, 9 and 13. One kidney was used for morphological evaluation and the other for immunohistochemistry, using antibodies directed against monocytes/macrophages, T cells and E-cadherin on frozen sections. In a separate experiment, rats were treated for 9 days and had their kidneys processed for western immunoblot and immunohistochemistry, where antibodies directed against monocyte chemoattractant protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha) were used on paraffin sections.

RESULTS

In renal medulla from enalapril-treated rats, volume fractions of tubular lumens and interstitium were increased from postnatal days 2 and 4, respectively, while that of tubular cells was decreased from 4 days of age. Concomitant loss and/or reduction in E-cadherin expression (from day 2) was observed in dilated medullary tubules of enalapril-treated rats. Furthermore, in the medulla of enalapril-treated rats, the increased number of ED2+ (resident macrophages) cells, followed by the increase in ED1+ (monocytes/macrophages) and CD4+ T cells, was observed at days 9 and 13, respectively. This was accompanied by increased medullary expression of TNF-alpha at day 9.

CONCLUSIONS

Neonatal ACE inhibition perturbs medullary tubulogenesis, as indicated by tubular dilatation and a lack of E-cadherin expression in these tubules. Macrophage/monocyte-mediated immune response is a secondary event, coincidentally associated with the up-regulation of TNF-alpha.

The Rho family of small GTPases is involved in epithelial cystogenesis and tubulogenesis

BACKGROUND

Epithelial cyst and tubule formation represent critical processes for the development of many mammalian organs and involve transient, highly choreographed changes in cell polarity. The Rho family of small GTPases, whose prototypes are RhoA, Rac1, and Cdc42, regulate many biologic processes, including cell polarization and morphogenesis. The exocyst is a conserved eight-subunit protein complex involved in the biogenesis of polarity; in yeast, it is a downstream effector for several Rho family proteins, and, in mammals, plays a central role in cystogenesis and tubulogenesis.

METHODS

Inducible cell lines expressing mutant forms of RhoA, Rac1, and Cdc42 and an in vitro model of cystogenesis and tubulogenesis were used to examine the effects of Rho family proteins on cyst and tubule formation. A series of pulse-chase assays, using basolateral, apical, and secretory proteins, were performed to examine the synthesis and membrane trafficking profile of the various Rho family mutant proteins.

RESULTS

We show that expression of mutant RhoA, Rac1, and Cdc42 proteins all result in abnormal cyst and tubule formation. Furthermore, with respect to cystogenesis and tubulogenesis, the phenotypic effects of expressing each mutant Rho family protein are different. Specifically, cyst and, therefore, tubule formation is completely inhibited in the presence of constitutively active RhoA and tubulogenesis is inhibited in the presence of dominant negative Rac1. Reversal of cyst polarity is seen in the presence of dominant negative RhoA, dominant negative Rac1, and both dominant negative and constitutively active Cdc42. The series of synthesis and delivery assays, using basolateral, apical, and secretory proteins, revealed that Rho family mutant proteins display an exocyst-like trafficking profile.

CONCLUSION

The differential effects suggest that RhoA, Rac1, and Cdc42 all act to control cyst and tubule formation and may act in concert to control these higher-order processes. The exocyst-like membrane trafficking profile displayed by the Rho family mutant proteins raises the possibility that Rho family proteins interact, either directly or indirectly, with the exocyst to control cyst and tubule formation.

Renal tubular dysgenesis in siblings

Renal tubular dysgenesis is a recently recognized autosomal recessive condition characterized by absence or poor development of proximal convoluted tubules, clinical presentation of oligohydromnios, Potter sequence, and neonatal respiratory failure. Only a few cases of renal tubular dysgenesis have been diagnosed. We report 2 cases from a single family. Histologically, the renal cortices showed crowding of the glomeruli and primitive tubules, most of which demonstrated positive cytoplasmic staining for epithelial membrane antigen and peanut lectin. Electron microscopy of the kidneys of the second baby revealed absence of differentiated characteristics of the proximal tubules.

Congenital nephrosis of the Finnish type: overview of placental pathology and literature review

Congenital nephrosis of the Finnish type (CNF) is a rare, autosomal recessive disorder of glomerular filtration that results in massive proteinuria, edema, and ascites. Although previous studies describe the classic renal lesions characterizing this disorder, there are few documenting in detail the associated placental alterations. In this context, we present a case of CNF with emphasis on the placental pathology and compare our findings to what has been previously reported in the literature. A 36-year-old G2P1 with no significant medical history developed persistently elevated amniotic fluid alpha-fetoprotein in the absence of neural tube defects. Because of a clinical suspicion of CNF, she electively terminated the pregnancy at 19 weeks. Postmortem examination revealed characteristic renal changes, confirmed by electron microscopy, as well as significant placental villous edema. Although the placenta was not enlarged, the villi appeared profoundly hydropic. Extensive cystic vacuolar change was documented in both stem villi and tertiary villi, affecting 95% of the villi present. Since the fetus was not grossly edematous, the placental findings may represent the first sign of systemic hypoproteinemia.

A deletion of the paracellin-1 gene is responsible for renal tubular dysplasia in cattle

Various hereditary diseases analogous to particular human heritable diseases have been identified in cattle. Investigation of these cattle diseases will provide useful information regarding the pathogenesis of the corresponding human diseases. Renal tubular dysplasia is an autosomal recessive disease of Japanese black cattle characterized by renal failure and growth retardation. We have previously mapped the locus responsible for the disease within a region on bovine chromosome 1. In the present study, we further typed additional markers in this region and found that a genomic segment of bovine chromosome 1 including the microsatellite marker BMS4009 was deleted in the affected animals. Construction of a physical map covering this region with BAC clones and comparison of the nucleotide sequences of this region between normal and affected animals revealed that a region of 37 kb including exons 1 to 4 of the bovine paracellin-1 gene was deleted in the affected animals. The paracellin-1 gene, which is the causative gene for human renal hypomagnesemia with hypercaciuria and nephrocalcinosis, encodes a tight junction protein of renal epithelial cells. Therefore, we concluded that deletion of the paracellin-1 gene is responsible for renal tubular dysplasia of cattle, and the cattle disease could be a good model for the human disease.

A recessive contiguous gene deletion causing infantile hyperinsulinism, enteropathy and deafness identifies the Usher type 1C gene

Usher syndrome type 1 describes the association of profound, congenital sensorineural deafness, vestibular hypofunction and childhood onset retinitis pigmentosa. It is an autosomal recessive condition and is subdivided on the basis of linkage analysis into types 1A through 1E. Usher type 1C maps to the region containing the genes ABCC8 and KCNJ11 (encoding components of ATP-sensitive K + (KATP) channels), which may be mutated in patients with hyperinsulinism. We identified three individuals from two consanguineous families with severe hyperinsulinism, profound congenital sensorineural deafness, enteropathy and renal tubular dysfunction. The molecular basis of the disorder is a homozygous 122-kb deletion of 11p14-15, which includes part of ABCC8 and overlaps with the locus for Usher syndrome type 1C and DFNB18. The centromeric boundary of this deletion includes part of a gene shown to be mutated in families with type 1C Usher syndrome, and is hence assigned the name USH1C. The pattern of expression of the USH1C protein is consistent with the clinical features exhibited by individuals with the contiguous gene deletion and with isolated Usher type 1C.

Homozygosity mapping of the locus responsible for renal tubular dysplasia of cattle on bovine chromosome 1

Renal tubular dysplasia is a hereditary disease of Japanese black cattle showing renal failure and growth retardation with an autosomal recessive trait. In the present study, we mapped the locus responsible for the disease (RTD) by linkage analysis with an inbred paternal half-sib pedigree obtained from commercial herds. By analyzing segregation of microsatellite markers in the half-sibs, significant linkage was observed between the RTD locus and markers on bovine Chromosome (Chr) 1 with the highest lod score of 11.4. Homozygosity mapping with the inbred pedigree further defined the localization of the RTD locus in a 4-cM region between microsatellite markers BMS4003 and INRA119. Mapping of the RTD locus on bovine Chr 1 will facilitate cloning and characterization of the gene responsible for this disease.

The malformed kidney: disruption of glomerular and tubular development

Renal malformations are the major cause of renal failure during early childhood. They are found in approximately 100 genetic syndromes. We review the embryologic development of the kidney and its molecular control. Important new information has been derived from mutational analysis in humans and mice. We describe how mutations in nine transcription factors, 12 signaling molecules and nine gene products involved in a variety of other cellular functions disrupt renal morphogenesis. The information presented provides a template for integrating new discoveries on the molecular basis of renal development, for classifying renal malformations observed in the clinical setting, and for identifying defective genes in affected patients.

Abnormal urinary acidification in infants with hydronephrosis

Distal renal tubular abnormalities have been observed in patients with dilated urinary tract disorders. The present study was undertaken to look for patterns in urinary acidification in infants with varying degrees of hydronephrosis due to either reflux or obstruction and occurring as unilateral or bilateral disease. Three groups of infants (mean age 3.7+/-3.8 months) were studied prospectively. Groups IA and IB included patients with hydronephrosis who were acidotic and non-acidotic, respectively. Group II served as controls and consisted of patients with diarrhea and secondary metabolic acidosis with no known renal disease. Serum electrolytes, creatinine, and urine pH were measured in all patients. Urinary titratable acidity, ammonium (NH4), and net acid excretion (NAE) were measured by the titrimetric method. Infants with hydronephrosis demonstrated lower urinary buffering capacity, reflected in low NAE in the face of acidosis. Deficiencies were noted in both titratable acid and NH4 excretion compared with control infants. Acidosis was as common in unilateral as in bilateral disease, regardless of severity score. These data confirm a defect in distal urinary acidification in infants with hydronephrosis, whether unilateral or bilateral. Immaturity and endogenous acid load may play a significant role in the manifestation of metabolic acidosis with unilateral disease.

Renal tubular dysgenesis, absent nipples, and multiple malformations in three brothers: a new, lethal syndrome

We report on three brothers with renal tubular dysgenesis and absent nipples, each also had other malformations including pre-auricular pits and a preauricular tag, branchial clefts, choanal atresia, pulmonary lobation anomaly, ventricular septal defect, type IIB interrupted aortic arch, absent gallbladder, absent thymus, parathyroid gland, accessory spleen, imperforate anus, clinodactyly, and broad digits and small nails. All three infants died neonatally. This pattern of clinical malformations appears to be a previously unreported syndrome.

[Renal tubular dysgenesis in upper and western Galilee]

Renal tubular dysgenesis (RTD) is a very rare malformation. 48 cases have been described, mostly in North America, Europe and Israel. Histopathological examination plays a key role in its diagnosis of RTD. We present the results of a retrospective study documenting the frequency, clinical manifestations and pathological findings in RTD in the Upper and Eastern Galilee. In 343 perinatal autopsies performed in Safed and Nahariya Hospitals between 1974 and 1997, there were 5 cases with RTD. All were men, 3 were Druze and 2 were Jews. The parents of the Druze patients were first cousins; 2 cases were twins of whom 1 had RTD; intrauterine growth retardation was documented in 2 and oligohydramnios in 3 cases. Life span of 4 newborns ranged from 1.1 to 49 hours and was complicated by severe respiratory failure and anuria. Ultrasound and postmortem examinations revealed no pathology of the kidney and urinary tracts. Absence of the proximal tubules was supported by immunohistochemistry for epithelial membrane antigen. Our previous assumption about the importance of lysozyme immunostaining for diagnosis of RTD was confirmed by this larger series of cases and by statistical analysis. Because RTD is considered an autosomal recessive phenotype with a recurrence rate of 25%, there should be genetic counseling of the family in every case of RTD.

Renal tubular dysgenesis in twins

In a fetal autopsy series, we have explored the occurrence of renal tubular dysgenesis in twins. Renal tubular dysgenesis was found exclusively among those monozygotic twins with evidence of twin transfusion syndrome, particularly in those donor twins with oligohydramnios and growth restriction. We infer that hypotension in the donor twin of the twin transfusion syndrome pair is responsible for the failure of proximal convoluted tubule differentiation, and the disturbance of renal function is manifested as oligohydramnios prenatally, and either oliguria or tubular dysfunction postnatally.

Cerebral defects and nephrogenic diabetes insipidus with the ARC syndrome: additional findings or a new syndrome (ARCC-NDI)?

We report on 4 children from 2 unrelated families who appear to have the lethal ARC syndrome (arthrogryposis, renal tubular dysfunction, and cholestasis) together with the additional findings of nephrogenic diabetes insipidus and cerebral anomalies, including deafness. With increased survival time in our patients, paucity of the intrahepatic bile ductules and cholestasis progressed to cirrhosis, growth was severely impaired, and severe mental retardation became apparent. No evidence was found for peroxisomal, chromosomal, or mitochondrial disorders. We propose to amend the ARC mnemonic to ARCC-NDI (A-Arthrogryposis, R-renal Fanconi, C-cerebral, C-cholestasis, NDI-nephrogenic diabetes insipidus) to name the major manifestations of this syndrome, several of which have not been appreciated.

Renal tubular dysgenesis with microcephaly

Renal tubular dysgenesis, a rare, lethal, autosomal recessive disorder, is characterized by short and poorly differentiated proximal convoluted tubules associated with oligohydramnios, Potter sequence, and neonatal death due to respiratory failure. Abnormalities of the skull may occur in some cases. We report an infant born of a consanguineous union who also had microcephaly, among other features. A history of oligohydramnios with or without skull abnormalities and a lethal outcome without obvious explanation should occasion renal histological study aimed at precise diagnosis and genetic counselling.

Congenital renal tubular dysplasia and skull ossification defects similar to teratogenic effects of angiotensin converting enzyme (ACE) inhibitors

An apparently autosomal recessive syndrome of congenital renal tubular dysplasia and skull ossification defects is described in five infants from two separate, consanguineous, Pakistani Muslim kindreds. The clinical, pathological, and radiological features are similar to the phenotype associated with fetal exposure to angiotensin converting enzyme (ACE) inhibitors: intrauterine growth retardation, skull ossification defects, and fetal/ neonatal anuric renal failure associated with renal tubular dysplasia. There was no fetal exposure to ACE inhibitors in the affected infants. Phenotypic similarities between these familial cases and those associated with ACE inhibition suggest an abnormality of the "renin-angiotensin-aldosterone" system (RAS). It is postulated that the molecular pathology in this uncommon autosomal recessive proximal renal tubular dysgenesis could be related to mutations of the gene systems governing the RAS.

Glomerular number and size following chronic angiotensin II blockade in the postnatal rat

Chronic angiotensin-converting enzyme (ACE) inhibition with enalapril or angiotensin II (Ang II) receptor antagonism with either losartan (specific for Ang II type-1 receptor, AT1) or PD 123319 (specific for the Ang II type-2 receptor, AT2) were effected between postnatal days 3 and 21 in the rat. Following quantitative analysis of the kidneys using recently developed unbiased stereological techniques we found that none of the treatments resulted in changes in glomerular number or size. This implies that inhibition of Ang II activity had no effect on postnatal nephron induction or glomerular development. However, following both chronic ACE inhibition and AT1 antagonism, abnormalities of tubules and their associated vessels were evident throughout the kidney and were accompanied by an increased proportion of interstitium. The structural abnormalities were most prominent in the outer medulla and were consistent with interruption of descent of the loops of Henle and vasa rectae. In contrast, no renal morphological abnormalities were observed following chronic AT2 antagonism.

Renal tubular abnormalities in hydrops fetalis: a histological and immunohistochemical study

An immunohistochemical study of renal tubule cell differentiation in hydrops fetalis was performed using antibodies against lysozyme, CD15, keratin, epithelial membrane antigen and Leu-7, and formalin-fixed, paraffin-embedded sections of tissue that was obtained at autopsy. In 3 cases among 17 cases of hydrops fetalis (17.6%) there was a marked decrease in the number of cells stained positively for lysozyme, suggesting abnormal differentiation of the cells of the proximal convoluted tubules. This is the first report concerning the abnormalities of the renal tubular epithelium in hydrops fetalis.

Renal tubular dysgenesis: a report of two cases

Renal tubular dysgenesis, a congenital disorder of renal tubular development, was diagnosed in two newborns with oligohydramnios and Potter phenotype. Renal tubular dysgenesis (RTD) is a recently recognized congenital disorder of renal tubular development associated with oligohydramnios, Potter phenotype, and neonatal respiratory and renal failure. We report two newborn siblings with typical clinical and anatomic features of RTD. The diagnosis was proven by autopsy in one child. The pediatrician should consider the diagnosis of RTD in a child with congenital anuria and structurally normal kidneys on ultrasound, especially if a maternal history of late trimester oligohydramnios is present.

Familial renal tubular dysgenesis: a disorder not isolated to proximal convoluted tubules

The autopsy findings of a newborn with renal tubular dysgenesis, born to first cousins of Moslim Arab descent, are described. Hypocalvaria and hyperflexible joints were noted in addition to the renal lesion. A microdissection study demonstrated marked shortening of all the nephron segments from the glomeruli to the collecting tubules, rather than an isolated abnormality of the proximal convoluted tubules.

Renal tubular dysgenesis: evidence of abnormality in the renin-angiotensin system

Renal tubular dysgenesis is an autosomal recessive condition characterized by short, abnormally developed cortical tubules that lack proximal differentiation. Despite the lack of normal proximal tubules, the major site of water resorption in the kidney, the principal clinical manifestations are caused by fetal and neonatal oliguria. The kidneys in three cases of neonatal renal tubular dysgenesis were found to contain large amounts of immunohistochemically reactive renin in preglomerular arterioles, glomerular hilums, and glomerular mesangial areas, far exceeding the intensity of staining and the numbers of sites stained in control kidneys. The increased accumulation of renin may reflect strong local vasoconstriction, which is responsible for reduced glomerular perfusion. This accumulation suggests faulty feedback control of renin secretion, the basis of which is still to be identified.

Renal tubular dysgenesis present in a newborn with meconium ileus

The combination of renal tubular dysgenesis (RTD) and meconium ileus in a native Israeli is presented for the first time. The clinical diagnosis was oligohydramnios and abruptio placentae, respiratory failure, and anuria refractory to treatment. The autopsy revealed meconium ileus and meconium peritonitis. RTD was established by the detection of a monomorphous undifferentiated population of tubules, absence of proximal tubules, and dense epithelial membrane antigen immunoreactivity of all tubules. The lack of alpha 1-antitrypsin- and lysozyme-immunoreactive tubules was first revealed in the kidney with RTD. These findings extend the possibilities of RTD detection.

Renal and biliary abnormalities in a new murine model of autosomal recessive polycystic kidney disease

Current models of autosomal recessive polycystic kidney disease (ARPKD) fail to demonstrate biliary abnormalities in association with renal cysts. We therefore studied a new murine model of ARPKD in which dual renal tubular and biliary epithelial abnormalities are present. Affected homozygous animals typically die 1 month postnatally in renal failure with progressively enlarged kidneys. Renal cysts shift in site from inner cortical proximal tubules at birth to collecting tubules 20 days later, as determined by segment-specific lectin binding. Increased numbers of mitosis were demonstrated in proximal and collecting tubular cysts. In addition, epithelial hyperplasia was demonstrated morphometrically in the intra- and extrahepatic biliary tract of affected animals. The number of intrahepatic biliary epithelial cells was increased by 50% on postnatal day 5 and by 100% on postnatal day 25 (P < 0.01). Despite an increased frequency of "chaotic" portal areas in mice with renal cysts, no intrahepatic cysts or shape abnormalities of the biliary lumen were detected using biliary casts and morphometry. Additionally there was nonobstructive hyperplastic dilatation of the extrahepatic biliary tract which was linked in all animals to the presence of renal cysts. The hyperplastic abnormalities in both renal and biliary epithelium make this new mouse strain a good model for the study of the dual organ cellular pathophysiology of ARPKD.

Renal tubular dysgenesis: a description of early renal maldevelopment in siblings

A family is described in which three siblings, born after pregnancies complicated by oligohydramnios, developed renal abnormalities. In the first infant, of 38 weeks gestation, histologic changes were nearly identical to those found in renal tubular dysgenesis (RTD), a recently identified disorder characterized by the absence of recognizable renal proximal tubules. Additional findings include bilateral renal vein thrombosis and marked calvarial bone hypoplasia. The other two gestations were 20 and 22 weeks long. Renal histology in these cases showed nonspecific abnormalities with focal tubular dilatation, decreased tubule formation, and increased interstitial connective tissue. Clearly recognizable proximal tubules were present, though decreased in number. The latter two gestations described herein are the earliest examined in a family with RTD and the renal abnormalities may represent early changes seen in this disorder.

Effect of ACE inhibition on the fetal kidney: decreased renal blood flow

The kidneys of nine fetuses whose mothers were chronically hypertensive were examined microscopically. Three of these mothers used antihypertensive agents throughout pregnancy including one who used an angiotensin-converting enzyme (ACE) inhibitor. The tubular defects found in these kidneys were compared to the kidneys of 20 normal controls, 13 fetuses with various multiple malformation syndromes and six cases of the twin to twin transfusion syndrome. Evidence from these cases as well as the literature suggest that the primary mechanism by which ACE inhibitors affect development of the fetal kidney is through decreased renal blood flow.