Pathological and sonographic review of early isolated severe lower urinary tract obstruction and implications for prenatal treatment

OBJECTIVE

To identify favorable renal histology in fetuses with early severe lower urinary tract obstruction (LUTO) and determine the best timing and selection criteria for prenatal surgery.

METHODS

This multicenter, retrospective study included male fetuses with severe LUTO which died before 24 weeks of gestation during the period January 2000 to December 2018. Age-matched controls were used as reference standard for renal histology. Prenatal ultrasound features and fetal serum and/or urine β2microglobulin level were retrieved and kidney histology slides (hematein-eosin-safran and α-smooth-muscle-actin (αSMA) immunostaining) were prepared and reviewed. αSMA-positive staining of the blastema is due to its aberrant differentiation into myofibroblastic cells. Cases were sorted into histopathologic groups (favorable or unfavorable) according to the blastema's morphology and αSMA labeling and the data of these groups were compared.

RESULTS

Included in the study were 74 fetuses with a median gestational age at outcome of 17 + 6 (range, 13 + 0 to 23 + 5) weeks. Parenchymal organization was preserved in 48% of the kidneys. A blastema was present in 90% of the kidneys, but it was morphologically normal in only 9% and αSMA-negative in only 1% of them. Most (82%) fetuses had an unfavorable prognosis, and 36% of fetuses died ≤ 18 weeks and had severe renal lesions detected on histology (early unfavorable prognosis). A favorable renal prognosis was associated with an earlier gestational age (P = 0.001). Fetuses with LUTO had a significantly lower number of mature glomeruli (P < 0.001) compared with controls. However, there was no significant difference in the number of glomeruli generations between the early-unfavorable-prognosis group (≤ 18 weeks) and the group with a favorable prognosis (P = 0.19). A comparison of prenatal ultrasound features and biochemical markers between groups could not identify any prenatal selection criteria.

CONCLUSIONS

Before 18 weeks, around 30% of fetuses with severe LUTO still have potential for kidney development. Identification of these cases would enable them to be targeted for prenatal therapy. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

[Renal lesions in patients with Fabry's disease]

Kidney involvement is one of the main manifestations of Fabry's disease. In the absence of enzyme replacement therapy, hemizygous males and some heterozygous females progress to end stage renal failure. In hemizygous males, diffuse glycolipid accumulation is observed in all glomerular and vascular cells whereas distal tubular cells are focally involved. In heterozygous females, the glycolipid storage is irregular in glomeruli and vessels, some cells being massively involved, others being normal. In both sexes, degenerative changes occur, linked to the necrosis of overloaded mesangial and vascular smooth muscle cells. Their progression leads to unspecific arteriopathy and glomerulosclerosis not prone to reverse under enzymotherapy. Kidney biopsy is useful for confirming the diagnosis if clinical presentation of Fabry's disease is atypical. Moreover, histological analysis of renal tissue allows to assess the severity of degenerative changes and to evaluate the beneficial impact of enzyme replacement therapy.

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.

Autosomal dominant Alport's syndrome: study of a large Tunisian family

Alport's syndrome is a hereditary nephritis that may lead to end-stage renal disease (ESRD) in early adult life. It is a clinically and genetically heterogeneous nephropathy. Alport's syndrome is often associated with sensorineural deafness and/or ocular abnormalities. In contrast with the well-known X-linked phenotype, very little is known about the autosomal dominant form caused by mutations in COL4A3 and COL4A4 in the chromosome region 2q35-q37. We describe a Tunisian family with autosomal dominant Alport's syndrome in which males and females were equally affected. Two members reached ESRD at age 40 and 53 years, respectively. Three members experienced isolated microhematuria and one member experienced sensorineural deafness. No eye abnormalities were observed. Immunohistochemical studies showed a normal distribution of the alpha5 (type IV collagen) chain in the epidermal basement membrane. Genetic analysis demonstrated that a common haplotype co-segregated with the disease in the heterozygous state in all affected patients, thereby, confirming an autosomal dominant mode of inheritance. The same haplotype was observed in two asymptomatic children. We conclude that autosomal dominant Alport's syndrome, follows a rare mode of inheritance and exhibits a milder phenotype than usually observed in classic X-linked Alport's syndrome. The frequency of this mode of inheritance should be confirmed by a larger study.

Meckel-Grüber syndrome: sonography and pathology

OBJECTIVE

To define a specific sonographic pattern for the appearance of the kidneys in fetuses affected by Meckel-Grüber syndrome (MGS).

METHODS

This was a retrospective analysis of 30 cases, collected from five centers, with ultrasound features suggestive of MGS. Only fetuses with a confirmed diagnosis of MGS were finally included. Analysis included a detailed evaluation of the sonographic findings and comparison with pathological follow-up.

RESULTS

Seventeen cases met the pathological criteria for a diagnosis of MGS and were included in the study. In all cases, a typical sonographic pattern was seen: the kidneys were enlarged (mean, + 4.8 SD) and showed unusual corticomedullary differentiation, occurring as early as the first trimester. In most cases, the medullary areas appeared excessively large and mottled due to the presence of multiple small cysts.

CONCLUSIONS

The kidneys of fetuses with MGS are enlarged, cystic and have unusual corticomedullary differentiation. These features can be observed as early as the first and early second trimesters.

[Immunohistochemistry contribution in Alport syndrome diagnosis]

Alport syndrome (AS) is an hereditary disease characterised by the association of progressive hematuria nephritis. The diagnosis is based on clinical genetic and ultrastructural findings. Nowadays, immunohistochemical technique is of great interest. It enables us to analyze the distribution of the different chains of the type IV collagen in renal basement membrane (RBM) and epidermal basement membrane (EBM) which appeared to be abnormal in 70% of cases.

METHODS

We report a prospective study of five families affected with AS. Six patients were investigated by immunohistochemical studies of kidney (3 cases) and skin (6 cases) frozen specimens. Monoclonal antibodies recognizing the collagenous domain of alpha1 (MAB1), alpha3 (MAB3) and alpha5 (MAB5) chains of type IV collagen were used. Two methods were performed: direct immunofluorescence and immunohistochemical (ultravision) analysis.

RESULTS

The different chains distribution of type IV collagen in the EBM and RBM was normal in four cases (4 men), abnormal in two patients (1 man and woman). Based on the clinical, genetical and immunohistochemical findings we established three transmission modes: autosomal recessive in two families, dominant X linked in two other familiales, and autosomal dominant in one family.

CONCLUSION

Immunohistochemical studies is a simple technique of an easy interpretation accomplished on kidney frozen specimen, or even on a simple cutaneous biopsy. It could be very useful for the diagnosis and enables us in addition to determine the mode of transmission of AS.

Sonographic findings in Beckwith–Wiedemann syndrome related toH19 hypermethylation

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with congenital malformations and tumour predisposition. BWS results from variable mutations or epigenetic modifications of imprinted genes in the 11p15 chromosomal region. We present a fetus with mild general overgrowth and bilateral enlarged echogenic kidneys with loss of the corticomedullary differentiation in which prenatal diagnosis of BWS was suspected. The rest of the fetal anatomy and the amniotic fluid volume appeared normal. After termination of the pregnancy, molecular analysis confirmed the diagnosis of BWS by showing an isolated hypermethylation of the H19 gene.

Prenatal diagnosis of bilateral isolated fetal hyperechogenic kidneys. Is it possible to predict long term outcome?

OBJECTIVE

To study perinatal and long term outcome following prenatal diagnosis of hyperechogenic kidneys.

DESIGN

Prospective observational cohort study.

SETTING

The Maternité Port-Royal Hôpital Cochin and at the Departments of Obstetrics and Paediatric Nephrology, Necker Enfants Malades in Paris, France.

POPULATION

Forty-three fetuses with isolated bilateral hyperechogenic kidneys.

METHODS

All patients referred with isolated bilateral hyperechogenic fetal kidneys were followed up prospectively up to 34-132 months. The following prenatal items were analysed: fetal kidney size, amniotic fluid volume, gestational age at diagnosis, family history and renal ultrasound in parents. Postmortem examination was carried out in cases with perinatal death. Postnatal follow up of survivors included postnatal ultrasound, blood pressure, serum creatinine, proteinuria, need for restricted diet, weight and height and renal biopsy when available.

MAIN OUTCOME MEASURES

Aetiology of hyperechogenicity, perinatal mortality and renal function in survivors.

RESULTS

The aetiology could be established by family history, postmortem or postnatal data, but not by prenatal ultrasound. There were 20 autosomal recessive, 8 autosomal dominant polycystic kidney diseases, 9 other renal disorders and 6 symptom-free survivors without aetiological diagnosis. There were 19 terminations of pregnancy, 5 neonatal deaths and 19 survivors, of whom 14 had normal renal function three had mild and two had end stage renal failure. None of those with severe oligohydramnios and fetal kidneys > 4 SD survived (n = 14, 10 terminations and 4 neonatal deaths), whereas of the 17 with normal amniotic fluid volume and kidneys < 4 SD, 14 survived, of whom 9 were symptom-free.

CONCLUSION

Aetiology could not be established prenatally in the absence of familial data. Kidney size and amniotic fluid volume were the best prenatal predictors of outcome.

[Contribution of genetics to knowledge and management of hereditary kidney diseases progressing to renal failure]

Genes of most of the hereditary renal diseases progressing to renal insufficiency are now identified. In the first part of this paper we describe their multi-faceted genetics. Genetic heterogeneity has been demonstrated in many of these diseases, such as Alport's syndrome and nephronophtisis. In some of them an allelic heterogeneity is present as in the X-linked form of Alport's syndrome (more than 300 different mutations have been described along the COL4A5 gene). Besides these classical mendelian diseases, mendelian subentities have been isolated within common diseases such as cortico-resistant nephrosis. Many diseases also demonstrate a variability of their phenotype resulting from allelic and/or genetic heterogeneity, or from modifier genes. In the second part of the paper we discuss the consequences of this explosion of knowledge with respect to epidemiology, genetic diagnosis, prenatal diagnosis and treatment.

Two splice variants of the Wilms' tumor 1 gene have distinct functions during sex determination and nephron formation

Alternative splicing of Wt1 results in the insertion or omission of the three amino acids KTS between zinc fingers 3 and 4. In vitro experiments suggest distinct molecular functions for + and -KTS isoforms. We have generated mouse strains in which specific isoforms have been removed. Heterozygous mice with a reduction of +KTS levels develop glomerulosclerosis and represent a model for Frasier syndrome. Homozygous mutants of both strains die after birth due to kidney defects. Strikingly, mice lacking +KTS isoforms show a complete XY sex reversal due to a dramatic reduction of Sry expression levels. Our data demonstrate distinct functions for the two splice variants and place the +KTS variants as important regulators for Sry in the sex determination pathway.

Pathogenesis of twin-twin transfusion syndrome: the renin-angiotensin system hypothesis

In spite of active perinatal management, twin-twin transfusion syndrome (TTTS) remains a severe disease with a high risk of neonatal mortality and morbidity. TTTS initially results from an unbalanced blood flow from a donor to a recipient twin. However, its pathogenesis remains unclear, although cardiovascular disturbances and regulation of fetal volemia and diuresis seem central in this syndrome. Previously, we demonstrated that the renin-angiotensin system (RAS) was up-regulated in donor twins as a consequence of hypovolemia, and down-regulated in recipients. This was the first evidence of the implication of the RAS in TTTS. We hypothesize that the RAS plays a key role in the pathogenesis of TTTS. In the donor, RAS up-regulation aggravates oligohydramnios and may increase arterial resistance, which could contribute to placental dysfunction leading to intrauterine growth restriction. In the recipient, paradoxical RAS activation, due to transfer of effectors such as angiotensin II through placental shunts, could explain fetal vascular disturbances and cardiomyopathy. According to our hypothesis, TTTS would appear similar to the classical model of hypertension referred to as '2 kidneys-1 clip' with a donor twin, comparable to the clipped kidney, intoxicating its cotwin, comparable to the normal kidney.

Glomerular extracellular matrix and growth factors in diffuse mesangial sclerosis

Diffuse mesangial sclerosis, isolated (IDMS) or observed in the context of Denys-Drash syndrome (DDS) due to WT1 mutation, is characterized by early onset nephrotic syndrome progressing to renal failure. A striking morphological feature is the rapid development of glomerulosclerosis.

THE AIMS OF OUR STUDY WERE

(1) to analyze the glomerular distribution of extracellular matrix (ECM) antigens at the early stage of DMS, (2) to determine the composition of the ECM accumulated within the mesangial areas and leading to glomerular sclerosis, and (3) to analyze the expression of growth factors, transforming growth factor-beta 1 (TGF beta 1) and platelet-derived growth factor A (PDGFA). In glomeruli of patients with IDMS and DDS, the glomerular basement membrane (GBM) expression of the heparan sulfate chain of heparan sulfate proteoglycan (HSPG) was decreased from the early stage of DMS, at a time when ECM proteins retained a normal distribution. In fully developed lesions, mesangial and subendothelial accumulation of collagenous and noncollagenous glycoproteins normally expressed in the mesangial area (types IV [alpha 1(IV)2 alpha 2(IV)] and VI collagen, beta 1 laminin, fibronectin, tenascin, and perlecan) increased with progression of mesangial sclerosis. This was associated with mesangial expression of proteins normally restricted to the GBM (agrin, alpha 1/alpha 5, beta 2, and gamma 1 laminin chains) and with accumulation of chondroitin sulfate proteoglycan. The distribution of the alpha 3-alpha 5 chains of type IV collagen was normal. Focal accumulation of types I, III, and V collagen was seen only in severely sclerotic glomeruli. Expression of growth factors TGF beta 1 and PDGFA was increased in 9 of 10 and 5 of 10 patients, respectively. Early decreased GBM expression of the heparan sulfate chain of HSPG could play a role in the proteinuria of DMS patients. Changes in the composition of the ECM accumulated within the mesangial areas are not specific. We speculate that deregulation of the expression of growth factors normally downregulated by WT1, is one of the factors responsible for the rapid and massive mesangial deposition of basement membrane material in DDS.

Detection of apoptosis in kidney biopsies of patients with D+ hemolytic uremic syndrome

In this study we have investigated the presence of apoptotic cells in renal biopsy material of seven patients with hemolytic uremic syndrome (HUS) by using an improved and stringent terminal deoxynucleotidyl nick-end labeling (TUNEL) technique. Renal biopsy material was taken in the second or third week after onset of the disease. Renal biopsy material of patients with minimal lesions nephrotic syndrome or thin basement syndrome were used as control. It has been reported that nonapoptotic cells can be labeled nonspecifically due to proteinase K pretreatment or a delay in fixation when only TUNEL technique is used. In post mortem material this delay in fixation is seen. Moreover, it has been described that mainly nonapoptotic cells that shows signs of active gene transcription can be labeled in this nonspecific way. For this reason we used the TUNEL technique in combination with a label for RNA synthesis and splicing factor (SC-35). Indeed, we found nonspecific labeling of nonapoptotic nuclei in biopsy material of HUS patients, but not in control biopsy material. By using co-labeling with RNA synthesis factor SC-35, we were able to identify true apoptotic cells. There was a significant increase (p < 0.05) in the presence of apoptotic cells in biopsy material of HUS patients compared with material of controls. About 80 % of apoptotic cells were detected in tubuli and only 20 % in glomeruli of the renal biopsies of HUS patients. Furthermore, most apoptotic cells were detected in those patients that had received peritoneal dialysis suggesting that there is a relationship between severity of the disease and amount of apoptotic cells. The finding of apoptotic cells suggest that apoptosis plays a role in HUS.

Congenital erythropoietic porphyria: prenatal diagnosis and autopsy findings in two sibling fetuses

Congenital erythropoietic porphyria is an autosomal recessive disease characterized by a deficiency of uroporphyrinogen III cosynthetase activity, with diffuse tissue accumulation of specific type I porphyrins. The diagnosis of this disease was made in two fetuses, who were siblings, and from a Caucasian nonconsanguinous family. The first fetus died in utero with hydrops fetalis and anemia, but without an etiopathogenic diagnosis. In the second case, the diagnosis was based on pink fluorescence of the amniotic fluid examined fortuitously in sunlight. DNA analysis showed that the fetus was heteroallelic for the mutation C73R. The autopsy showed brown skin, and at histological examination, porphyrin pigment was deposited in many tissues. Retrospectively, similar deposits were found in the tissues of the first fetus.

PAX2 mutations in oligomeganephronia

BACKGROUND

Oligomeganephronia (OMN) is a rare congenital and usually sporadic anomaly. It is characterized by bilateral renal hypoplasia, with a reduced number of enlarged nephrons. The mechanisms involved in this deficient nephrogenesis are unknown. The paired box transcription factor PAX2 plays a fundamental role in renal development. Heterozygous Pax2 mutants in mice are characterized by renal hypoplasia and retinal defects, and in humans, PAX2 mutations have been described in the renal-coloboma syndrome.

METHODS

To assess whether OMN could be related to PAX2, we searched for PAX2 mutations in nine patients presenting with sporadic and apparently isolated OMN.

RESULTS

Heterozygous PAX2 mutations were found in three patients. A limited optic nerve coloboma was secondarily detected in two cases and a very mild optic disk dysplasia in one patient. None of these patients had visual impairment.

CONCLUSIONS

Ocular anomaly and PAX2 mutations should be sought in all patients with OMN.

PAX2 mutations in renal-coloboma syndrome: mutational hotspot and germline mosaicism

The renal-coloboma syndrome (RCS, MIM 120330) is an autosomal dominant disorder caused by PAX2 gene mutations. We screened the entire coding sequence of the PAX2 gene for mutations in nine patients with RCS. We found five heterozygous PAX2 gene mutations: a dinucleotide insertion (2G) at position 619 in one sporadic RCS case, a single nucleotide insertion (619 + G) in three unrelated cases, and a single nucleotide deletion in a familial case. In this familial case, three affected sibs showed a striking ocular phenotypic variability. Each of the sibs carried a 619insG mutation, whilst unaffected parents did not, suggesting the presence of germline mosaicism. Interestingly, the 619insG mutation has been previously reported in several patients and is also responsible for the Pax21Neu mouse mutant, an animal model of human RCS. This study confirms the critical role of the PAX2 gene in human renal and ocular development. In addition, it emphasises the high variability of ocular defects associated with PAX2 mutations ranging from subtle optic disc anomalies to microphthalmia. Finally, the presence of PAX2 germline mosaicism highlights the difficulties associated with genetic counselling for PAX2 mutations.

[Prenatal diagnosis of autosomal recessive polycystic kidney disease]

OBJECTIVE

Prenatal ultrasonographic detection of autosomal recessive polycystic kidney disease (ARPKD) is of poor reliability, especially in early pregnancy. Molecular genetics allows earlier diagnosis, from 11 weeks of gestation; however, since only indirect diagnosis is possible--the ARPKD gene being localized on chromosome 6 but not identified--the feasibility of molecular diagnosis requires several conditions: definitive diagnosis in the index case, availability of index case and parents' DNA, genetic informativity of the family at the ARPKD locus. Results and limits of this method are analyzed, using a series of 56 requests for prenatal diagnosis.

RESULTS

In eight of the 56 families ARPKD was excluded on the basis of histological (seven cases) and/or genetic (two cases) criteria. Molecular study was impossible in three families due to the lack of index case's DNA, and two other families were non-informative. Among the 43 families in which prenatal diagnosis was feasible, analysis of the haplotype of 35 fetuses issued from 29 families showed that 11 fetuses with the same haplotypes as that of the index case were affected, while 24 were not. No false positive or false negative result was reported.

CONCLUSIONS

Early and reliable prenatal diagnosis of recessive polycystic kidney disease is possible in nearly 80% of affected families.

Glomerular expression of type IV collagen chains in normal and X-linked Alport syndrome kidneys

Alport syndrome is an inherited nephropathy characterized by alterations of the glomerular basement membrane because of mutations in type IV collagen genes. COL4A5 mutations, causing X-linked Alport syndrome, frequently result in the loss of the alpha5 chains of type IV collagen in basement membranes. This is associated with the absence of the alpha3(IV) and alpha4(IV) chains and increased amounts of alpha1(IV) and alpha2(IV) in glomerular basement membranes. The mechanisms resulting in such a configuration are still controversial and are of fundamental importance for understanding the pathology of the disease and for considering gene therapy. In this article we studied, for the first time, type IV collagen expression in kidneys from X-linked Alport syndrome patients, using in situ hybridization and immunohistochemistry. We show that, independent of the type of mutation and of the level of COL4A5 transcription, both COL4A3 and COL4A4 genes are actively transcribed in podocytes. Moreover, using immunofluorescence amplification, we were able to demonstrate that the alpha3 chain of type IV collagen was present in the podocytes of all patients. Finally, the alpha1(IV) chain, which accumulates within glomerular basement membranes, was found to be synthesized by mesangial/endothelial cells. These results strongly suggest that, contrary to what has been found in dogs affected with X-linked Alport syndrome, there is no transcriptional co-regulation of COL4A3, COL4A4, and COL4A5 genes in humans, and that the absence of alpha3(IV) to alpha5(IV) in glomerular basement membranes in the patients results from events downstream of transcription, RNA processing, and protein synthesis.

WT1 splice-site mutations are rarely associated with primary steroid-resistant focal and segmental glomerulosclerosis

BACKGROUND

Donor splice-site de novo heterozygous mutations in intron 9 of the Wilms' tumor gene (WT1) have been reported in Frasier syndrome, which is defined by the association of focal and segmental glomerulosclerosis (FSGS), male pseudohermaphroditism, and gonadoblastoma. These splice-site mutations alter the WT1 alternative splicing leading to two WT1 isoforms, with (+) or without (-) three amino acids, lysine-threonine-serine (KTS), between zinc fingers 3 and 4. The aim of this work was to investigate the possibility that some cases of primary steroid-resistant nephrotic syndrome associated with FSGS may be caused by WT1 splice-site mutations.

METHODS

We analyzed WT1 exons 8 and 9 and the surrounding exon/intron boundary DNA sequences in 37 children with nonfamilial primary steroid-resistant nephrotic syndrome. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the relative ratio of +KTS/-KTS transcripts from immortalized lymphocyte RNA.

RESULTS

One boy with FSGS and associated pathologies (diaphragmatic hernia, proximal hypospadias, and unilateral testicular ectopia) was found to carry the heterozygous 1228 +4 C-->T splice-site mutation. RT-PCR quantitation of the +KTS/-KTS transcripts from immortalized lymphocyte RNA of this patient showed a diminution of the +KTS/-KTS isoform ratio (0.43), which is identical to that reported in patients with Frasier syndrome. Using the same approach, healthy control subjects have +KTS/-KTS ratios ranging from 1.50 to 2.00.

CONCLUSIONS

This study expands the range of the phenotypic presentation of the intron 9 splice-site WT1 mutations and adds to the already reported heterogeneity of primary steroid-resistant nephrotic syndromes. We suggest that these mutations are not likely to be a common cause of isolated steroid-resistant nephrotic syndrome, and recommend a WT1 exon 9/intron 9 splice-site study in children with primary steroid-resistant nephrotic syndrome if genital or diaphragmatic anomalies are associated. The identification of such WT1 mutations has practical implications for the management of these patients.

Alport syndrome and diffuse leiomyomatosis. Clinical aspects, pathology, molecular biology and extracellular matrix studies. A synthesis

The Alport syndrome-diffuse leiomyomatosis association can be defined as a hereditary disease of type IV collagen combining features of Alport syndrome (hematuric nephropathy, deafness and ocular abnormalities: anterior lenticonus, maculopathy) and leiomyomatosis involving oesophagus (diffuse type), tracheobronchial tree, and genitals (only in women). This entity is transmitted as an X-linked dominant trait. Mutations of both the COL4A5 and COL4A6 genes, located head to head in Xq22 encoding the alpha 5 and alpha 6(IV) chains are responsible for the abnormalities. Molecular studies have shown deletions of the 5' end of both COL4A5 and COL4A6 including the intergenic region. The breakpoint in COL4A6 is always located within intron 2. Immunohistochemistry has shown significant alterations of basement membranes in the kidney and esophageal leiomyomas. Leiomyomas lack alpha 5 and alpha 6(IV) chains, fibronectin and laminin beta 1 chains in the muscle basement membranes where they are normally expressed. The tumors also show myocyte anomalies: irregular expression of the alpha 5 integrin subunits, and disorganization of actin and desmin filaments. It is hypothesized that a third as yet unknown gene, situated within the large intron 2 in a critical 90 kb region, is responsible for the smooth muscle proliferation. Abnormalities of the basement membranes could destabilize interactions between muscular cells and the extracellular matrix.

Genetics of the nephrotic syndrome

There are a large number of glomerular diseases that may be responsible for a nephrotic syndrome, the most frequent in childhood being minimal change disease. In the past few years, the molecular genetic basis of several conditions that may cause a nephrotic syndrome have been identified. Denys-Drash syndrome and Frasier syndrome are related diseases caused by mutations in the WT1 gene. Familial forms of idiopathic nephrotic syndrome with focal and segmental glomerular sclerosis/hyalinosis have been identified with an autosomal dominant or recessive mode of inheritance and linkage analysis have allowed to localize several genes on chromosomes 1, 11 and 17. The gene responsible for the Finnish type congenital nephrotic syndrome has been identified. This gene, named NPHS1, codes for nephrin, which is located at the slit diaphragm of the glomerular podocytes and is thought to play an essential role in the normal glomerular filtration barrier.

NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome

Familial idiopathic nephrotic syndromes represent a heterogeneous group of kidney disorders, and include autosomal recessive steroid-resistant nephrotic syndrome, which is characterized by early childhood onset of proteinuria, rapid progression to end-stage renal disease and focal segmental glomerulosclerosis. A causative gene for this disease, NPHS2, was mapped to 1q25-31 and we report here its identification by positional cloning. NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family. We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier.

Chronic renal failure after Puumala virus infection

Chronic renal failure has never been described after Puumala hantavirus infection, which usually causes acute renal failure with spontaneous full recovery. We report a 15-year-old boy who presented with Puumala hantavirus infection and initial severe acute renal failure. His renal function gradually improved, but more than 2 years after the acute episode it was still moderately impaired, with a creatinine clearance of about 60 ml/min per 1.73 m(2)

Crescentic glomerulonephritis in hyper IgD syndrome

The hyperimmunoglobulinemia D syndrome (HIDS) is a well-defined entity resembling familial Mediterranean fever. HIDS is a systemic inflammatory disease associated with stimulation of T-cell-mediated immunity. These patients are at low risk for amyloidosis and are not known to develop nephropathy. We report a boy of Mediterranean ancestry who exhibited typical HIDS and end-stage renal failure. Kidney biopsy revealed pauci-immune crescentic glomerulonephritis (cGN). We hypothesized that the glomerular involvement was secondary to the cytokine network activation observed in HIDS. Thus, cGN should be considered as part of the syndrome, and kidney biopsy should be performed early in the course of the renal disease in patients with HIDS.

WT1 and PAX-2 podocyte expression in Denys-Drash syndrome and isolated diffuse mesangial sclerosis

Denys-Drash syndrome is a rare disorder of urogenital development characterized by the association of early onset glomerulopathy caused by diffuse mesangial sclerosis, gonadal dysgenesis leading to pseudohermaphroditism in males, and a high risk of developing Wilms' tumor. The syndrome is caused by dominant negative point mutations in the WT1 gene that encodes a tumor suppressor transcription factor normally expressed in podocytes. Mutations usually affect the zinc fingers of the WT1 protein. The basic defect is unknown in most cases of isolated diffuse mesangial sclerosis, a disease characterized by the same glomerular changes as in Denys-Drash syndrome but possibly transmitted as an autosomal recessive trait. Here we show that the distribution of WT1 is abnormal in most patients with Denys-Drash syndrome : WT1 nuclear staining of podocytes is decreased or absent. This finding is consistent with the decreased DNA binding capacity of the mutated protein. One target gene of WT1 is PAX2, the expression of which is down-regulated in podocytes during early stages of nephrogenesis. We demonstrate that WT1 mislocalization is associated with abnormal podocyte expression of PAX2 protein and RNA. We suggest that persistent expression of PAX2 is likely to result from the loss of WT1 dependent transcriptional repression and may participate in the pathological mechanisms leading to glomerular dysfunction. Abnormal distribution of WT1 and PAX2 was also observed in isolated diffuse mesangial sclerosis suggesting that a defect in WT1 could also be operative in isolated diffuse mesangial sclerosis. Primary involvement of PAX2 is an alternative hypothesis because persistent expression of PAX2 in transgenic mice is associated with the occurrence of early and severe glomerulopathy.

Diffuse leiomyomatosis of the esophagus: disorder of cell-matrix interaction?

Diffuse leiomyomatosis (DL) is rare condition characterized by proliferation of smooth muscle in the upper gastrointestinal tract. Most cases are associated with X-linked Alport syndrome and have partial deletions in the genes encoding both the alpha5 and alpha6 chains of collagen type IV. We studied aspects of cell-matrix interaction of myocytes in an esophagogastrectomy specimen from a 12-year-old patient with DL. Myocytes had central areas of cytoplasmic rarefaction, which were actin positive and desmin poor, with the reverse pattern of staining at the cell periphery. Electron microscopy (EM) showed that the areas of rarefaction consisted of disorganized aggregates of filaments. The basement membranes ranged from thickened to thinned or absent. Immunohistochemical staining for the alpha1-alpha4 chains of collagen type IV, the alpha1, alpha2, beta2, and gamma1 chains of laminin, nidogen, type VI collagen, and fibronectin was normal. There was loss of the alpha5 and alpha6 chains of collagen type IV and the beta1 chain of laminin. Normal staining for alpha1, alpha2, alpha3, alpha4, alpha6, alpha8, and beta1 integrins was noted. Staining for alpha5 integrin varied from normal to reduced or negative in different cells. In DL, a primary abnormality of basement membrane may be associated with disorganization of the contractile apparatus and alterations of certain integrins. This may reflect a disturbance of cell-matrix interactions that play a role in cell differentiation and internal organization.

Determination of the genomic structure of the COL4A4 gene and of novel mutations causing autosomal recessive Alport syndrome

Autosomal recessive Alport syndrome is a progressive hematuric glomerulonephritis characterized by glomerular basement membrane abnormalities and associated with mutations in either the COL4A3 or the COL4A4 gene, which encode the alpha3 and alpha4 type IV collagen chains, respectively. To date, mutation screening in the two genes has been hampered by the lack of genomic structure information. We report here the complete characterization of the 48 exons of the COL4A4 gene, a comprehensive gene screen, and the subsequent detection of 10 novel mutations in eight patients diagnosed with autosomal recessive Alport syndrome. Furthermore, we identified a glycine to alanine substitution in the collagenous domain that is apparently silent in the heterozygous carriers, in 11.5% of all control individuals, and in one control individual homozygous for this glycine substitution. There has been no previous finding of a glycine substitution that is not associated with any obvious phenotype in homozygous individuals.

Chronology of renal scarring in males with Alport syndrome

We investigated the onset of renal scarring in 62 males (aged 4-26 years) with Alport syndrome by measuring cortical interstitial volume fraction [Vv (interstitium/cortex)] and percentage global glomerular sclerosis in kidney biopsies. Male pediatric (n = 9) and adult (n = 7) donor kidneys served as controls. Creatinine clearance at the time of biopsy was available for 43 Alport patients. A statistically insignificant correlation between age and Vv (interstitium/cortex) was observed in normal subjects (r = +0.47, slope = 0.0009, P = 0.07). In the Alport patients, age was significantly correlated with Vv (interstitium/cortex (r = +0.49, slope = 0.01, P = 0.001) and global glomerular sclerosis (r = +0.41, P = 0.01), and inversely correlated with creatinine clearance (r = -0.33, P = 0.04). Creatinine clearance was inversely correlated with Vv (interstitium/cortex) (r = -0.78, P = 0.001) and global glomerular sclerosis (r = -0.74, P = 0.001). The correlation with creatinine clearance was especially strong for Vv (interstitium/cortex) values above the normal range, i.e., > 0.2 (r = -0.82, P = 0.001), and was absent for Vv (interstitium/cortex) < 0.2 (r = -0.119, P = 0.55). Creatinine clearance values less than 80 ml/min per 1.73 m2 occurred more frequently in patients with Vv (interstitium/cortex) values > 0.2 (P < 0.0001) and in patients with > 10% globally sclerosed glomeruli (P < 0.001). Patients < or = or > 10 years of age differed in Vv (interstitium/cortex) [0.13 +/- 0.09 (mean +/- SD) vs. 0.24 +/- 0.026, P < 0.001], the frequency of Vv (interstitium/cortex) > 0.2 (3/32 vs. 15/31, P < 0.0001), the frequency of > 10% globally sclerosed glomeruli (3/33 vs. 11/30, P < 0.05), mean creatinine clearance (113 +/- 7 vs. 84 +/- 10 ml/min per 1.73 m2, P = 0.057), and the frequency of creatinine clearance < 80 ml/min per 1.73 m2 (1/20 vs. 11/23, P < 0.01). Thus, reduced creatinine clearance in males with Alport syndrome is associated with Vv (interstitium/cortex) > 0.2 and > 10% globally sclerosed glomeruli. These are frequently detectable in the 2nd decade. We hypothesize that most Alport males will require intervention during the 1st decade for optimal preservation of kidney function.

Identification of constitutional WT1 mutations, in patients with isolated diffuse mesangial sclerosis, and analysis of genotype/phenotype correlations by use of a computerized mutation database

Constitutional mutations of the WT1 gene, encoding a zinc-finger transcription factor involved in renal and gonadal development, are found in most patients with Denys-Drash syndrome (DDS), or diffuse mesangial sclerosis (DMS) associated with pseudohermaphroditism and/or Wilms tumor (WT). Most mutations in DDS patients lie in exon 8 or exon 9, encoding zinc finger 2 or zinc finger 3, respectively, with a hot spot (R394W) in exon 9. We analyzed a series of 24 patients, 10 with isolated DMS (IDMS), 10 with DDS, and 4 with urogenital abnormalities and/or WT. We report WT1 heterozygous mutations in 16 patients, 4 of whom presented with IDMS. One male and two female IDMS patients with WT1 mutations underwent normal puberty. Two mutations associated with IDMS are different from those described in DDS patients. No WT1 mutations were detected in the six other IDMS patients, suggesting genetic heterogeneity of this disease. We analyzed genotype/phenotype correlations, on the basis of the constitution of a WT1 mutation database of 84 germ-line mutations, to compare the distribution and type of mutations, according to the different symptoms. This demonstrated (1) the association between mutations in exons 8 and 9 and DMS; (2) among patients with DMS, a higher frequency of exon 8 mutations among 46, XY patients with female phenotype than among 46,XY patients with sexual ambiguity or male phenotype; and (3) statistically significant evidence that mutations in exons 8 and 9 preferentially affect amino acids with different functions.

Familial juvenile nephronophthisis

Familial juvenile nephronophthisis (NPH) is an autosomal recessive interstitial nephritis leading to terminal renal failure around puberty. Associations with extrarenal symptoms have been reported, mainly with Leber amaurosis (termed Senior-Løken syndrome). By means of linkage analysis a gene NPH1 for the purely renal form of NPH has been localized to chromosome 2. Genetic heterogeneity has been shown between NPH and Senior-Løken syndrome and also within the group of isolated NPH cases. Further characterization of the NPH1 region led to the isolation of large homozygous deletions in approximately 70% of patients with NPH. The detection of these deletions by PCR represents a simple noninvasive method for precise diagnosis in the majority of patients suspected of having NPH.

Somatic deletion of the 5' ends of both the COL4A5 and COL4A6 genes in a sporadic leiomyoma of the esophagus

Leiomyomata of the esophagus are sporadic benign tumors of unknown etiology. We studied a collection of nine tumors for the expression of extracellular matrix components and found the same aberrant expression pattern as previously observed in inherited diffuse leiomyomatosis. We demonstrate here the occurrence of a somatic deletion at the COL4A5/COL4A6 locus at Xq22 in a frozen leiomyoma sample. These data confirm the hypothesis that the same underlying etiology is responsible for circumscribed smooth muscle proliferation in sporadic leiomyomata as for diffuse smooth muscle cell proliferation in inherited diffuse leiomyomatosis.

Targets of alloantibodies in Alport anti-glomerular basement membrane disease after renal transplantation

A minority of patients with Alport syndrome develop anti-GBM disease in their allografts after renal transplantation. Clinically, the renal disease appears indistinguishable from Goodpasture's disease of native kidneys, in which the target of autoantibodies had been identified as the NC1 domain of the alpha 3 chain of type IV collagen, alpha 3(IV)NC1. However, in the majority of cases, Alport syndrome is due to mutations in the gene encoding the alpha 5 chain of type IV collagen, located on the X chromosome. Neither chain is detectable in the glomerular basement membrane (GBM) of most patients with Alport syndrome. We investigated the targets of the alloantibodies of 12 Alport patients who developed post-transplant anti-GBM disease by Western blotting onto recombinant NC1 domains made in insect cells. Binding to these antigens, for both typical Goodpasture and Alport anti-GBM antibodies, was strong and conformation-sensitive. Nine antibodies showed selective binding to alpha 5(IV)NC1. This specificity was confirmed by the demonstration of binding to a 26 kDa band of collagenase-solubilized human GBM, and/or binding to normal epidermal as well as renal basement membranes by indirect immunofluorescence. One antibody showed binding to alpha 5 and alpha 3(IV)NC1, while two showed predominant binding to alpha 3(IV)NC1. All seven patients whose pedigree or mutation analysis showed X-linked inheritance had predominant anti-alpha 5 reactivity. One with predominant anti-alpha 3 reactivity had a COL4A3 mutation. These findings show that human anti-GBM disease can be associated with antibodies directed towards different molecular targets. Alpha 5(IV)NC1 is the primary target in most patients with X-linked Alport syndrome who develop post-transplant anti-GBM disease.

Novel COL4A5/COL4A6 deletions and further characterization of the diffuse leiomyomatosis-Alport syndrome (DL-AS) locus define the DL critical region

Diffuse leiomyomatosis (DL) with Alport syndrome (AS) has been shown to be associated with contiguous gene deletions of the COL4A5 and COL4A6 genes, with the COL4A6 breakpoint of the deletions invariably located in the large intron 2 of the gene. We describe four YAC clones covering the locus and a refined restriction map of the entire COL4A6 gene. These resources have allowed us to make a precise estimate of the size of COL4A6 introns 2 and 3, as well as the size of the gene itself. We also describe five novel deletions which, in conjunction with previous reports, allow the definition of a 90-kb critical region in which to search for a gene or other entity involved in the pathogenesis of DL.

Donor splice-site mutations in WT1 are responsible for Frasier syndrome

Frasier syndrome (FS) is a rare disease defined by male pseudo-hermaphroditism and progressive glomerulopathy. Patients present with normal female external genitalia, streak gonads and XY karyotype and frequently develop gonadoblastoma. Glomerular symptoms consist of childhood proteinuria and nephrotic syndrome, characterized by unspecific focal and segmental glomerular sclerosis, progressing to end-stage renal failure in adolescence or early adulthood. No case of Wilms' tumour has been reported, even in patients with extended follow-up. In contrast with FS patients, most individuals with Denys-Drash syndrome (DDS; refs 6,7) have ambiguous genitalia or a female phenotype, an XY karyotype and dysgenetic gonads. Renal symptoms are characterized by diffuse mesangial sclerosis, usually before the age of one year, and patients frequently develop Wilms' tumour. Mutations of the Wilms'-tumour gene, WT1, cause different pathologies of the urogenital system, including DDS. WT1 is composed of ten exons and encodes a protein with four zinc-finger motifs and transcriptional and tumour-suppressor activities. Alternative splicing generates four isoforms: the fifth exon may or may not be present, and an alternative splice site in intron 9 allows the addition of three amino acids (KTS) between the third and fourth zinc fingers of WT1 (ref. 17). Here we demonstrate that FS is caused by mutations in the donor splice site in intron 9 of WT1, with the predicted loss of the +KTS isoform. Examination of WT1 transcripts indeed showed a diminution of the +KTS/-KTS isoform ratio in patients with FS.

A novel gene that encodes a protein with a putative src homology 3 domain is a candidate gene for familial juvenile nephronophthisis

Familial juvenile nephronophthisis (NPH) is an autosomal recessive, genetically heterogeneous disorder, representing the most frequent inherited cause of chronic renal failure in children. One of the responsible loci, NPH1 , has been mapped to 2q13. The presence of large homozygous deletions of approximately 250 kb in the majority of affected patients allowed us to define a minimal deletion interval for NPH1 . A BAC contig covering this interval was established. Combination of large scale genomic sequencing, cDNA selection and computer-aided analysis led to the characterization of two transcriptional units. One encodes the already known BENE protein, and the other encodes a novel protein of at least 732 amino acids containing a putative src homology 3 domain. In two patients carrying the large deletion of the NPH1 region on only one allele, two mutations were detected in two independent exons of the novel gene. One consists of a single base deletion, causing a frameshift, and the other is a G-->A substitution in the consensus 5' splice donor site. Both mutations thus potentially generate null mutants. One of these mutations was found to segregate with the disease in the family, and the second appeared to be a de novo mutation. We therefore conclude that this novel gene is a strong candidate for NPH.

[Familial hematuric nephropathies]

Alport syndrome is a hereditary hematuric nephritis progressing to end-stage renal failure, often associated with hearing loss and specific ocular changes. It is characterized by the presence of thickening and splitting of the glomerular basement membrane. Defects in type IV collagen, the main component of basement membranes, are responsible for the disease. The prevalence rate of Alport syndrome is 1/5,000 and it is the cause of about 2% of end-stage renal failure. The disease is heterogenous both at the clinical and genetic level. In most kindreds, it is transmitted as an X-linked dominant trait: males are severely affected whereas most females have a benign disease. The genes coding the different chains of type IV collagen have been cloned and several mutations have been characterized. Since prenatal counselling is now possible, the recognition of this severe familial under-diagnosed disease is of the upmost importance.