Prognostic Factors and Long-Term Outcome with ANCA-Associated Kidney Vasculitis in Childhood

BACKGROUND AND OBJECTIVES

ANCA-associated vasculitis is extremely rare in children. We report the clinicopathologic features, long-term outcomes, and prognostic factors of a large pediatric cohort of patients with ANCA-associated kidney vasculitis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective study included 85 consecutive patients with kidney biopsy specimen-proven ANCA-associated vasculitis from tertiary referral centers in Italy and Canada. Kidney biopsy specimens were categorized as focal, crescentic, sclerotic, or mixed, according to the Berden classification. The prognostic significance of baseline clinical, laboratory, and histologic findings was analyzed with respect to kidney failure or CKD stage 3-5/kidney failure.

RESULTS

A total of 53 patients had microscopic polyangiitis (62%), and 32 had granulomatosis with polyangiitis (38%). Rapidly progressive GN was the most frequent presentation (39%); a third of the patients also had nephrotic-range proteinuria. Kidney biopsy specimens were classified as focal in 21% of the patients, crescentic in 51%, sclerotic in 15%, and mixed in 13%. Remission-induction therapies included cyclophosphamide in 78% of patients. A total of 25 patients (29%) reached kidney failure. The median (interquartile range) time to kidney failure or last follow-up was 35 (6-89) months in the whole cohort, and 73 (24-109) months among the patients who did not reach this outcome. Patients whose biopsy specimens showed sclerotic histology had significantly shorter kidney survival (hazard ratio, 11.80; 95% confidence interval, 2.49 to 55.99) and survival free of CKD stage 3-5 (hazard ratio, 8.88; 95% confidence interval, 2.43 to 32.48), as compared with those with focal/mixed histology. Baseline eGFR, low serum albumin, hypertension, central nervous system complications, and sclerotic histology, which reflected severe kidney involvement, were associated with both kidney failure and CKD stage 3-5/kidney failure at unadjusted analysis; no independent prognostic factors emerged at multivariable analysis.

CONCLUSIONS

Children with ANCA-associated kidney vasculitis often have aggressive presentation; a third of such children progress to kidney failure and this usually occurs early during follow-up. A severe clinical presentation is associated with the development of CKD or kidney failure.

Different renal manifestations associated with very early onset pediatric inflammatory bowel disease: case report and review of literature

Background

Inflammatory bowel diseases are characterized by chronic inflammation of the gastrointestinal tract. In particular, Crohn disease and ulcerative colitis represent the two most common types of clinical manifestations. Extraintestinal manifestations of inflammatory bowel diseases represent a common complications, probably reflecting the systemic inflammation. Renal involvement is reported in 4–23% of cases. However, available data are limited to few case series and retrospective analysis, therefore the real impact of renal involvement is not well defined.

Case presentation

We report the case of a 10-years old male affected by very early onset unclassified-Inflammatory bowel diseases since he was 1-year old, presenting with a flare of inflammatory bowel diseases associated with acute kidney injury due to granulomatous interstitial nephritis. Of interest, at 7-year-old, he was treated for IgA nephropathy.

To our knowledge, no previous reports have described a relapse of renal manifestation in inflammatory bowel diseases, characterized by two different clinical and histological phenotypes.

Conclusions

The link between the onset of kidney injuries with flares of intestinal inflammation suggest that nephritis maybe considered an extra-intestinal manifestation correlated with active inflammatory bowel disease. However, if granulomatous interstitial nephritis represents a cell-mediated hypersensitivity reaction than a true extraintestinal manifestation of inflammatory bowel diseases is still not clarified. We suggest as these renal manifestations here described may be interpreted as extraintestinal disorder and also considered as systemic signal of under treatment of the intestinal disease.

Surgical validation of functional magnetic resonance urography in the study of ureteropelvic junction obstruction in a pediatric cohort

INTRODUCTION

Ureteropelvic junction obstruction (UPJO) is one of the most common urological diseases in children. The etiology can be intrinsic, extrinsic (crossing vessel [CV] or adhesions), or mixed. To date, ultrasonography and scintigraphy are considered gold-standard imaging techniques for the study of UPJO. Functional magnetic resonance urography (fMRU) combines anatomical and functional information and has been recently evaluated for the detection of CVs in UPJO.

OBJECTIVE

The objective of the study was to evaluate the concordance between fMRU and surgery in determining the etiology of UPJO and the presence of obstructing/non-obstructing CVs.

STUDY DESIGN

Patients with unilateral hydronephrosis who underwent surgery after an fMRU were included in the sample. Surgical data regarding the etiology of UPJO were compared with radiological results. The etiology was divided into intrinsic, extrinsic due to CV, extrinsic due to adhesions, and mixed or cicatricial (postoperative). The concordance was calculated by means of the Cohen's kappa coefficient.

RESULTS

The observed agreement between fMRU and surgical findings regarding the etiology and the presence of CV were 83.2% and 89.4%, respectively (with substantial Cohen's kappa coefficient). The sensitivity and specificity of fMRU were 0.84 and 0.93, respectively; the positive predictive value (PPV) and negative predictive value (NPV) were 0.889 and 0.897, respectively. The observed agreement regarding the type of vessel was 88.3% with a Cohen's kappa coefficient of 0.787 (substantial).

DISCUSSION

In children with hydronephrosis, it is very important for the surgeon to quantify the extent of dilation, define the etiology of the obstruction, and the presence or absence of CVs. fMRU is a 'one-stop-shop' technique which provides both anatomical and functional information showing a high concordance with surgical findings, avoiding radiation exposure.

CONCLUSIONS

fMRU should be considered a valid imaging technique in the study of pediatric UPJO, as it provides the surgeon with important information regarding the etiology of the obstruction for the preoperative planning.

Molecular and Cellular Mechanisms for Proteinuria in Minimal Change Disease

Minimal Change Disease (MCD) is a clinical condition characterized by acute nephrotic syndrome, no evident renal lesions at histology and good response to steroids. However, frequent recurrence of the disease requires additional therapies associated with steroids. Such multi-drug dependence and frequent relapses may cause disease evolution to focal and segmental glomerulosclerosis (FSGS) over time. The differences between the two conditions are not well defined, since molecular mechanisms may be shared by the two diseases. In some cases, genetic analysis can make it possible to distinguish MCD from FSGS; however, there are cases of overlap. Several hypotheses on mechanisms underlying MCD and potential molecular triggers have been proposed. Most studies were conducted on animal models of proteinuria that partially mimic MCD and may be useful to study glomerulosclerosis evolution; however, they do not demonstrate a clear-cut separation between MCD and FSGS. Puromycin Aminonucleoside and Adriamycin nephrosis are models of glomerular oxidative damage, characterized by loss of glomerular basement membrane polyanions resembling MCD at the onset and, at more advanced stages, by glomerulosclerosis resembling FSGS. Also Buffalo/Mna rats present initial lesions of MCD, subsequently evolving to FSGS; this mechanism of renal damage is clearer since this rat strain inherits the unique characteristic of overexpressing Th2 cytokines. In Lipopolysaccharide nephropathy, an immunological condition of renal toxicity linked to B7-1(CD80), mice develop transient proteinuria that lasts a few days. Overall, animal models are useful and necessary considering that they reproduce the evolution from MCD to FSGS that is, in part, due to persistence of proteinuria. The role of T/Treg/Bcells on human MCD has been discussed. Many cytokines, immunomodulatory mechanisms, and several molecules have been defined as a specific cause of proteinuria. However, the hypothesis of a single cell subset or molecule as cause of MCD is not supported by research and an interactive process seems more logical. The implication or interactive role of oxidants, Th2 cytokines, Th17, Tregs, B7-1(CD80), CD40/CD40L, c-Mip, TNF, uPA/suPAR, Angiopoietin-like 4 still awaits a definitive confirmation. Whole genome sequencing studies could help to define specific genetic features that justify a definition of MCD as a “clinical-pathology-genetic entity.”

FCGR2A single nucleotide polymorphism confers susceptibility to childhood-onset idiopathic nephrotic syndrome

Childhood-onset idiopathic nephrotic syndrome affects 1.15-3.4 children/100,000 children/year in Western Countries. Immune-mediated mechanisms, particularly T cell-mediated, are thought to play a key pathogenic role. The genetic basis of the disease is still poorly understood. We tested the association between single nucleotide polymorphisms (SNPs) of four genes encoding Fc gamma receptors (FCGR2A, FCGR2B, FCGR3A, FCGR3B) and idiopathic nephrotic syndrome in a case-control study of paediatric patients. Children with idiopathic nephrotic syndrome (aged 1-16 years) were included. FCGR2A rs1801274 and FCGR3A rs396991 SNPs were genotyped using real-time PCR with the TaqMan method, while FCGR2B rs1050501 and FCGR3B NA1/NA2 were genotyped using Sanger sequencing. Fisher's exact test was used to explore genetic association. We enrolled 103 idiopathic nephrotic syndrome patients and 181 healthy controls. A significant association was found between idiopathic nephrotic syndrome and FCGR2A rs1801274 SNP (both with the T allele and the TT genotype, p value=0.0009, OR 1.81, 95% CI 1.27-2.59 and p value=0.0007, OR 2.39, 95% CI 1.44-3.99, respectively). No associations were found for the remaining SNPs. Fc gamma receptors might modulate response to rituximab; since 60 of the enrolled patients were treated with rituximab, we also tested the association between the studied SNPs and rituximab efficacy in this patient subgroup, but found only a weak association with FCGR2A CC genotype (p value=0.03). The FCGR2A rs1801274 SNP in the gene encoding the activating receptor CD32A confers susceptibility to idiopathic nephrotic syndrome.

Kidney Intragraft Homing of De Novo Donor-Specific HLA Antibodies Is an Essential Step of Antibody-Mediated Damage but Not Per Se Predictive of Graft Loss

Donor-specific HLA antibody (DSA)-mediated graft injury is the major cause of kidney loss. Among DSA characteristics, graft homing has been suggested as an indicator of severe tissue damage. We analyzed the role of de novo DSA (dnDSA) graft homing on kidney transplantation outcome. Graft biopsy specimens and parallel sera from 48 nonsensitized pediatric kidney recipients were analyzed. Serum samples and eluates from graft biopsy specimens were tested for the presence of dnDSAs with flow bead technology. Intragraft dnDSAs (gDSAs) were never detected in the absence of serum dnDSAs (sDSAs), whereas in the presence of sDSAs, gDSAs were demonstrated in 72% of biopsy specimens. A significantly higher homing capability was expressed by class II sDSAs endowed with high mean fluorescence intensity and C3d- and/or C1q-fixing properties. In patients with available sequential biopsy specimens, we detected gDSAs before the appearance of antibody-mediated rejection. In sDSA-positive patients, gDSA positivity did not allow stratification for antibody-mediated graft lesions and graft loss. However, a consistent detection of skewed unique DSA specificities was observed over time within the graft, likely responsible for the damage. Our results indicate that gDSAs could represent an instrumental tool to identify, among sDSAs, clinically relevant antibody specificities requiring monitoring and possibly guiding patient management.

Acquisition of C3d-Binding Activity by De Novo Donor-Specific HLA Antibodies Correlates With Graft Loss in Nonsensitized Pediatric Kidney Recipients

Alloantibody-mediated graft injury is a major cause of kidney dysfunction and loss. The complement-binding ability of de novo donor-specific antibodies (dnDSAs) has been suggested as a prognostic tool to stratify patients for clinical risk. In this study, we analyzed posttransplant kinetics of complement-fixing dnDSAs and their role in antibody-mediated rejection development and graft loss. A total of 114 pediatric nonsensitized recipients of first kidney allograft were periodically monitored for dnDSAs using flow bead assays, followed by C3d and C1q assay in case of positivity. Overall, 39 patients developed dnDSAs, which were C1q(+) and C3d(+) in 25 and nine patients, respectively. At follow-up, progressive acquisition over time of dnDSA C1q and C3d binding ability, within the same antigenic specificity, was observed, paralleled by an increase in mean fluorescence intensity that correlated with clinical outcome. C3d-fixing dnDSAs were better fit to stratify graft loss risk when the different dnDSA categories were evaluated in combined models because the 10-year graft survival probability was lower in patients with C3d-binding dnDSA than in those without dnDSAs or with C1q(+) /C3d(-) or non-complement-binding dnDSAs (40% vs. 94%, 100%, and 100%, respectively). Based on the kinetics profile, we favor dnDSA removal or modulation at first confirmed positivity, with treatment intensification guided by dnDSA biological characteristics.

Immunology of membranous nephropathy: from animal models to humans

Membranous nephropathy (MN), the leading cause of nephrotic syndrome in adults, is characterized by the deposition of subepithelial immune deposits that consist mainly of immunoglobulin (Ig)G and complement. Most of the cases are primary or idiopathic (iMN), while only approximately 25% of the cases are secondary to some known disease such as systemic lupus erythematosus, hepatitis B, drugs and malignancies. Most of our knowledge on the pathogenesis of iMN has relied upon old experimental models (i.e. Heymann nephritis) that have shown that immune deposits are formed in situ by the reaction of autoantibodies against the respective podocyte antigen. Recent findings indicate that podocyte proteins also act as an autoantigen in human iMN. The M-type phospholipase A2 receptor (PLA2R) has been identified as the main target antigen, as it can be found in approximately 70% of iMN patients but only rarely in other glomerulonephritides. Podocytes damage in the experimental model of Heymann nephritis is complement-mediated. In humans, the presence of complement within the subepithelial deposits is well established, but IgG4, which does not activate complement by classical or alternative pathways, represents the predominant subclass of IgG anti-PLA2R. Some evidence suggests that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin (MBL) and activate the lectin complement pathway. A genetic background for iMN has been demonstrated by genome-wide association studies that have shown highly significant associations of the PLA2R1 and the human leucocyte antigen (HLA)-DQA1 loci with iMN. In addition to their diagnostic value, anti-PLA2R antibodies may be useful to monitor disease activity and predict response to treatment.

Regulatory T cells and minimal change nephropathy: in the midst of a complex network

Minimal change nephrosis (MCN) is an important cause of morbidity in children. In spite of successful therapies having been developed in the last three decades, most aspects related to pathogenesis still remain poorly defined. Evolution in basic immunology and results deriving from animal models of the disease suggest a complex interaction of factors and cells starting from activation of innate immunity and continuing with antigen presentation. Oxidants, CD80 and CD40/CD40L have probably a relevant role at the start. Studies in animal models and in human beings also suggest the possibility that the same molecules (i.e. CD80, CD40) are expressed by podocytes under inflammatory stimuli, representing a direct potential mechanism for proteinuria. B and T cells could play a relevant role this contest. Implication of B cells is suggested indirectly by studies utilizing anti-CD20 monoclonal antibodies as the main therapy. The role of regulatory T cells (Tregs ) is supported mainly by results in animal models of nephrotic syndrome (i.e. adriamycin, puromycin, lipopolysaccharide), showing a protective effect of direct Treg infusion or stimulation by interleukin 2 (IL-2). Limited studies have also shown reduced amounts of circulating Tregs in patients with active MCN cells. The route from bench to bedside would be reduced if results from animal models were confirmed in human pathology. The expansion of Tregs with recombinant IL-2 and new anti-CD20 monoclonal antibodies is the beginning. Blocking antigen-presenting cells with cytotoxic T lymphocyte antigen (CTLA-4)-Ig fusion molecules inhibiting CD80 and/or with blockers of CD40-CD40 ligand interaction represent potential new approaches. The hope is that evolution in therapies of MCN could fill a gap lasting 30 years.

Unbiased next generation sequencing analysis confirms the existence of autosomal dominant Alport syndrome in a relevant fraction of cases

The mode of inheritance of Alport syndrome (ATS) has long been controversial. In 1927, the disease was hypothesized as a dominant condition in which males were more severely affected than females. In 1990, it was considered an X-linked (XL) semidominant condition, due to COL4A5 mutations. Later on, a rare autosomal recessive (AR) form due to COL4A3/COL4A4 mutations was identified. An autosomal dominant (AD) form was testified more recently by the description of some large pedigrees but the real existence of this form is still questioned by many and its exact prevalence is unknown. The introduction of next generation sequencing (NGS) allowed us to perform an unbiased simultaneous COL4A3-COL4A4-COL4A5 analysis in 87 Italian families (273 individuals) with clinical suspicion of ATS. In 48 of them (55%), a mutation in one of the three genes was identified: the inheritance was XL semidominant in 65%, recessive in 4% and most interestingly AD in 31% (15 families). The AD form must therefore be seriously taken into account in all pedigrees with affected individuals in each generation. Furthermore, a high frequency of mutations (>50%) was shown in patients with only 1 or 2 clinical criteria, suggesting NGS as first-level analysis in cases with a clinical suspicion of ATS.

Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk for late antibody-mediated rejection

The emerging role of humoral immunity in the pathogenesis of chronic allograft damage has prompted research aimed at assessing the role of anti-HLA antibody (Ab) monitoring as a tool to predict allograft outcome. Data on the natural history of allografts in children developing de novo Ab after transplantation are limited. Utilizing sera collected pretransplant, and serially posttransplant, we retrospectively evaluated 82 consecutive primary pediatric kidney recipients, without pretransplant donor-specific antibodies (DSA), for de novo Ab occurrence, and compared results with clinical-pathologic data. At 4.3-year follow up, 19 patients (23%) developed de novo DSA whereas 24 had de novo non-DSA (NDSA, 29%). DSA appeared at a median time of 24 months after transplantation and were mostly directed to HLA-DQ antigens. Among the 82 patients, eight developed late/chronic active C4d+ antibody-mediated rejection (AMR), and four C4d-negative AMR. Late AMR correlated with DSA (p < 0.01), whose development preceded AMR by 1-year median time. Patients with DSA had a median serum creatinine of 1.44 mg/dL at follow up, significantly higher than NDSA and Ab-negative patients (p < 0.005). In our pediatric cohort, DSA identify patients at risk of renal dysfunction, AMR and graft loss; treatment started at Ab emergence might prevent AMR occurrence and/or progression to graft failure.

Circulating suPAR in two cohorts of primary FSGS

Overexpression of soluble urokinase receptor (suPAR) causes pathology in animal models similar to primary FSGS, and one recent study demonstrated elevated levels of serum suPAR in patients with the disease. Here, we analyzed circulating suPAR levels in two cohorts of children and adults with biopsy-proven primary FSGS: 70 patients from the North America-based FSGS clinical trial (CT) and 94 patients from PodoNet, the Europe-based consortium studying steroid-resistant nephrotic syndrome. Circulating suPAR levels were elevated in 84.3% and 55.3% of patients with FSGS patients in the CT and PodoNet cohorts, respectively, compared with 6% of controls (P<0.0001); inflammation did not account for this difference. Multiple regression analysis suggested that lower suPAR levels associated with higher estimated GFR, male sex, and treatment with mycophenolate mofetil. In the CT cohort, there was a positive association between the relative reduction of suPAR after 26 weeks of treatment and reduction of proteinuria, with higher odds for complete remission (P=0.04). In the PodoNet cohort, patients with an NPHS2 mutation had higher suPAR levels than those without a mutation. In conclusion, suPAR levels are elevated in geographically and ethnically diverse patients with FSGS and do not reflect a nonspecific proinflammatory milieu. The associations between a change in circulating suPAR with different therapeutic regimens and with remission support the role of suPAR in the pathogenesis of FSGS.

Regulation of innate immunity by the nucleotide pathway in children with idiopathic nephrotic syndrome

Activation of the oxidative burst and failure of CD4(+) CD25(+) cell regulation have been implicated in idiopathic nephrotic syndrome (iNS). The intimate mechanism is, however, unknown and requires specifically focused studies. We investigated reactive oxygen species (ROS) generation [di-chlorofluorescein-diacetate (DCFDA)] fluorescence assay and the regulatory adenosine 5'-triphosphate (ATP) pathways in the blood of 41 children with iNS, utilizing several agonists and antagonists of nucleotide/nucleoside receptors, including the addition of soluble apyrase. The CD4(+) CD25(+) CD39(+) /CD73(+) expression was determined in vivo in parallel during disease activity. Overall, we found that the percentage of CD39(+) CD4(+) CD25(+) was reduced markedly in iNS by 80% (3·43±0·04% versus 13·14±0·07% of total lymphocytes, P<0·001). In these patients, reactive oxygen species (ROS) generation by polymorphonuclear neutrophils (PMN) at rest was a function of apyrase (CD39) expressed by CD4(+) CD25(+) , with higher rates in patients with very low CD39(+) CD4(+) CD25(+) levels (<7·5%). Addition of apyrase reduced ROS generation by 40% in both iNS and controls and was mainly effective in patients. The quota of ROS surviving ATP elimination was higher still in iNS. In vitro studies to limit ROS generation with adenosine analogues (2'-chloroadenosine and 5'-N-ethylcarboxamidoadenosine) produced minor effects. At variance, antagonizing ATP efflux with carbenoxolone or by antagonizing ATP effects (Brilliant Blue G, KN62 and A437089) reduced ROS generation comparable to apyrase. These results confirm a key role of ATP in the regulation of innate immunity and minimize the effect of adenosine. Decreased CD39(+) CD4(+) CD25(+) expression in iNS highlights an impairment of ATP degradation in this pathology. However, high ROS surviving ATP consumption implies a major role of other regulatory pathways.

Failure of regulation results in an amplified oxidation burst by neutrophils in children with primary nephrotic syndrome

The mechanism responsible for proteinuria in non-genetic idiopathic nephrotic syndrome (iNS) is unknown. Animal models suggest an effect of free radicals on podocytes, and indirect evidence in humans confirm this implication. We determined the oxidative burst by blood CD15+ polymorphonucleates (PMN) utilizing the 5-(and-6)-carboxy-2',7'-dichlorofluorescin diacetate (DCF-DA) fluorescence assay in 38 children with iNS. Results were compared with PMN from normal subjects and patients with renal pathologies considered traditionally to be models of oxidative stress [six anti-neutrophil cytoplasmic autoantibody (ANCA) vasculitis, seven post-infectious glomerulonephritis]. Radicals of oxygen (ROS) production was finally determined in a patient with immunodeficiency, polyendocrinopathy, enteropathy X-linked (IPEX) and in seven iNS children after treatment with Rituximab. Results demonstrated a 10-fold increase of ROS production by resting PMN in iNS compared to normal PMN. When PMN were separated from other cells, ROS increased significantly in all conditions while a near-normal production was restored by adding autologous cells and/or supernatants in controls, vasculitis and post-infectious glomerulonephritis but not in iNS. Results indicated that the oxidative burst was regulated by soluble factors and that this regulatory circuit was altered in iNS. PMN obtained from a child with IPEX produced 100 times more ROS during exacerbation of clinical symptoms and restored to a near normal-level in remission. Rituximab decreased ROS production by 60%. In conclusion, our study shows that oxidant production is increased in iNS for an imbalance between PMN and other blood cells. Regulatory T cells (Tregs) and CD20 are probably involved in this regulation. Overall, our observations reinforce the concept that oxidants deriving from PMN are implicated in iNS.

Searching for IgA nephropathy candidate genes: genetic studies combined with high throughput innovative investigations

Idiopathic IgA Nephropathy (IgAN) is the most common biopsy-proven glomerulonephritis worldwide. All races with the exception of Blacks and Indians are involved. Families with two or more relatives affected by IgAN may be observed in 15-20% of pedigrees of IgAN patients. Genome wide linkage study has been considered the most promising approach to identify IgAN susceptibility genes. Therefore, some European investigators constituted the European IgAN Consortium which was initially funded by the European Union. Data from linkage analysis studies, family association studies and case-control association studies are reported. To date, the Consortium has identified two loci (located on chromosomes 4q26-31 and 17q12-22), in addition to the previous study which described the first IgAN locus on chromosome 6q22-23. The functional mapping of genes involved in the disease proceeds from the identification of susceptibility loci identified by linkage analysis (step 1) to the isolation of candidate genes within gene disease-susceptibility loci, after obtaining information by microarray analysis carried out on peripheral leukocytes and renal tissue samples (step 2). Then, the process will proceed from the design of RNA interferenceagents against selected genes (step 3) to the application of systematically tested effect of RNA agents on functional cellular assay (step 4). The above combined high-throughput technologies will give information on the pathogenic mechanisms of IgAN. In addition, these data may indicate potential targets for screening, prevention and early diagnosis of the disease and more appropriate and effective treatment.

Recurrent nephrotic syndrome in homozygous truncating NPHS2 mutation is not due to anti-podocin antibodies

Mutations in NPHS2 are a common cause of focal segmental glomerulosclerosis (FSGS). It was initially assumed that FSGS caused by a genetically defective protein in the native kidney would not recur after transplantation; however, description of three patients with NPHS2 missense mutations challenged the validity of this assumption. A possible mechanism of recurrence in cases with stop-codon mutations is the formation of auto-antibodies against the truncated protein. In this case report, we describe a 9-year-old girl with the R138X NPHS2 mutation who presented with recurrent nephrotic syndrome 4 years after renal transplantation from a deceased donor, and was treated with plasmapheresis with a partial response. Renal histology did not demonstrate glomerular immunoglobulin deposition and an extensive search for anti-podocin antibodies based on indirect Western blot with recombinant podocin, was negative, as was the test for glomerular permeability factor (Palb). Taken together these findings confirm the possibility of post transplantation nephrotic syndrome in patients with NPHS2 mutations. Lack of immunoglobulin deposition, absence of circulating anti-podocin antibodies, and normal Palb suggest that other, unknown pathogenetic mechanisms are implicated.

Podocin-Related Mechanisms in Posttransplantation Recurrence of Focal Segmental Glomerulsclerosis

Posttransplantation recurrence of focal segmental glomerulosclerosis (FSGS) is one of the most disarming events in human pathology with important social and psychological consequences. It usually occurs in 30% to 50% of patients affected by the primary form of the disease with an abrupt onset in the majority of cases occurring within 1 month of the transplantation. Prediction of recurrent cases and early therapy with plasmapheresis are the main goals of the therapy. Although the mechanism of posttransplantation recurrence is still obscure, it has been proposed to be of a multifactorial origin, in which plasma factors determine the shedding of proteins of the slit-diaphragm, such as nephrin and podocin, with structural alterations of the ultra-filtering unit of the glomerulus. Low resynthesis of podocin and/or haplo-insufficiency due to heterozygous mutations should represent significant predisposing factors to proteinuria. In this review, the role of podocin in posttransplantation recurrence will be evaluated focusing on the possibility that resynthesis of the protein could represent a key step also for stable normalization of the renal filter. The recent characterization of the podocin promoter cis- and trans- acting elements and the possibility to characterize low- and high-podocin producer haplotypes offer opportunities to evaluate the capacity for podocin resynthesis in the donor kidney. A review of the literature on posttransplantation recurrence of FSGS in patients originally carrying homozygous and/or heterozygous NPHS2 mutations supports the general idea of a multifactorial origin of the primary disease that can be extended to the pathogenesis of posttransplantation recurrence.

Posttransplant recurrence of proteinuria in a case of focal segmental glomerulosclerosis associated with WT1 mutation

Posttransplant recurrence of inherited focal segmental glomerulosclerosis (FSGS) is still an enigma owing to the evident paradox of the molecular origin of proteinuria. A young girl with FSGS for WT1 mutation (IVS9+4C>T) and Frasier syndrome received a renal transplant at the age of 11 years. After an initial good outcome with recovery of renal function, proteinuria re-appeared after 7 days and steadily increased up to a nephrotic range. Determination of plasma permeability activity showed concomitant high Palb (0.7). At this point, plasmapheresis was started and after nine cycles with 1500 mL exchange and albumin re-infusion, proteinuria decreased to normal range and is still normal after 3 years. This is the first description of posttransplant recurrence of proteinuria in Frasier syndrome that should be included in potential outcome of renal transplant in this category of patients. This observation confirms the concept that recurrence of proteinuria may occur in inherited forms of FSGS so far reported only for patients carrying NPHS2 mutations and reinforces the idea on multifactorial origin of the disease.

Nephronophthisis type 1 deletion syndrome with neurological symptoms: prevalence and significance of the association

Type 1 nephronophthisis (NPHP) with homozygous deletions of nephrocystin [NPHP1, DEL] has been considered a pure renal disorder, but co-occurrence of extrarenal symptoms, mainly retinitis pigmentosa, is observed in a subset of patients. Recently, [NPHP1, DEL] has been detected in three patients with Joubert syndrome-related disorders (JSRDs), who associated neurological signs with a peculiar neuroradiological malformation known as the 'molar tooth sign' (MTS). To define the frequency of JSRD spectrum in NPHP1 patients, we re-examined 56 cases with [NPHP1, DEL] and found an overall incidence of 8.9% (five out 56 patients). All had small hyperechoic kidneys and had developed advanced renal failure within 15 years. Two patients presented the complete features of JSRD with cerebello-renal-retinal association and MTS. Two others showed, instead, severe intentional tremor and thick superior cerebellar peduncles on brain magnetic resonance imaging (MRI), and one of them had associated retinopathy. The fifth patient presented with hypotonia, developmental delay, central deafness, and ataxia associated with Leber congenital amaurosis and liver fibrosis but with normal brain MRI. Marked intrafamilial variability of associated extrarenal symptoms was observed in familial cases. Deletion extension did not differ in patients with isolated renal phenotype and in those with associated neurological symptoms. In conclusion, neurological defects varying from subtle involvement of cerebellum with thickened peduncle to both JSRD and diffuse central hypotonia are frequent in [NPHP1, DEL] patients. Prevalence of such association may justify systematic neurological and neuroradiological evaluation.

Cis and trans regulatory elements in NPHS2 promoter: implications in proteinuria and progression of renal diseases

Podocin (NPHS2) expression in podocytes is associated with variable degrees of proteinuria and progression to renal failure in different glomerular diseases that suggests different expression profiles in NPHS2 promoter. Three functional polymorphisms in NPHS2 promoter (-51T, -116T, and -535 insCTTTTTT(3)) were found determining strong downregulation (-73, -59, and -82%, respectively) of the reporter gene expression when transfected in podocytes. Electrophoretic mobility shift assay experiments showed that all wild-type variants (-51G, -116C, and -535 insCTTTTTT(2)) formed specific DNA-protein complexes with podocyte nuclear extracts that were abolished by the presence of the rare forms (-51T, -116T, and -535 insCTTTTTT(3)). In the case of -51G, upstream stimulatory factor-1 (USF1) was identified as the specific trans element in accord to binding inhibition experiments and USF1 RNAi silencing. Haplotype analysis of 204 normal controls and 545 patients with renal diseases (308 immunoglobulin (Ig)A nephropathy and 237 focal segmental glomerulosclerosis) evidenced that -116/-51 and -535/P2OL formed two blocks in strong linkage disequilibrium in both normal and pathological cohorts. The high NPHS2 promoter profile -116C/-51G haplotype was more frequent in patients with IgA nephropathy (P-value=0.005) and was associated with a better clinical outcome in terms of proteinuria and creatinine levels. Overall our study describes functional variants of NPHS2 promoter and characterizes trans-acting elements that modulate podocin expression in the kidney. High producer NPHS2 promoter haplotypes seem protective in patients with chronic glomerular diseases.

Glomerular clusterin is associated with PKC-alpha/beta regulation and good outcome of membranous glomerulonephritis in humans

Mechanisms for human membranous glomerulonephritis (MGN) remain elusive. Most up-to-date concepts still rely on the rat model of Passive Heymann Nephritis that derives from an autoimmune response to glomerular megalin, with complement activation and membrane attack complex assembly. Clusterin has been reported as a megalin ligand in immunodeposits, although its role has not been clarified. We studied renal biopsies of 60 MGN patients by immunohistochemistry utilizing antibodies against clusterin, C5b-9, and phosphorylated-protien kinase C (PKC) isoforms (pPKC). In vitro experiments were performed to investigate the role of clusterin during podocyte damage by MGN serum and define clusterin binding to human podocytes, where megalin is known to be absent. Clusterin, C5b-9, and pPKC-alpha/beta showed highly variable glomerular staining, where high clusterin profiles were inversely correlated to C5b-9 and PKC-alpha/beta expression (P=0.029), and co-localized with the low-density lipoprotein receptor (LDL-R). Glomerular clusterin emerged as the single factor influencing proteinuria at multivariate analysis and was associated with a reduction of proteinuria after a follow-up of 1.5 years (-88.1%, P=0.027). Incubation of podocytes with MGN sera determined strong upregulation of pPKC-alpha/beta that was reverted by pre-incubation with clusterin, serum de-complementation, or protein-A treatment. Preliminary in vitro experiments showed podocyte binding of biotinilated clusterin, co-localization with LDL-R and specific binding inhibition with anti-LDL-R antibodies and with specific ligands. These data suggest a central role for glomerular clusterin in MGN as a modulator of inflammation that potentially influences the clinical outcome. Binding of clusterin to the LDL-R might offer an interpretative key for the pathogenesis of MGN in humans.

The IgA nephropathy Biobank. An important starting point for the genetic dissection of a complex trait

Background

IgA nephropathy (IgAN) or Berger's disease, is the most common glomerulonephritis in the world diagnosed in renal biopsied patients. The involvement of genetic factors in the pathogenesis of the IgAN is evidenced by ethnic and geographic variations in prevalence, familial clustering in isolated populations, familial aggregation and by the identification of a genetic linkage to locus IGAN1 mapped on 6q22–23. This study seems to imply a single major locus, but the hypothesis of multiple interacting loci or genetic heterogeneity cannot be ruled out. The organization of a multi-centre Biobank for the collection of biological samples and clinical data from IgAN patients and relatives is an important starting point for the identification of the disease susceptibility genes.

Description

The IgAN Consortium organized a Biobank, recruiting IgAN patients and relatives following a common protocol. A website was constructed to allow scientific information to be shared between partners and to divulge obtained data (URL: ). The electronic database, the core of the website includes data concerning the subjects enrolled. A search page gives open access to the database and allows groups of patients to be selected according to their clinical characteristics. DNA samples of IgAN patients and relatives belonging to 72 multiplex extended pedigrees were collected. Moreover, 159 trios (sons/daughters affected and healthy parents), 1068 patients with biopsy-proven IgAN and 1040 healthy subjects were included in the IgAN Consortium Biobank. Some valuable and statistically productive genetic studies have been launched within the 5^th Framework Programme 1998–2002 of the European project No. QLG1-2000-00464 and preliminary data have been published in "Technology Marketplace" website: .

Conclusion

The first world IgAN Biobank with a readily accessible database has been constituted. The knowledge gained from the study of Mendelian diseases has shown that the genetic dissection of a complex trait is more powerful when combined linkage-based, association-based, and sequence-based approaches are performed. This Biobank continuously expanded contains a sample size of adequately matched IgAN patients and healthy subjects, extended multiplex pedigrees, parent-child trios, thus permitting the combined genetic approaches with collaborative studies.

Circulating anti-actin and anti-ATP synthase antibodies identify a sub-set of patients with idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome (iNS) with resistance or dependence to steroids is a common disease in children but in spite of an increasing clinical impact its pathogenesis is unknown. We screened for the presence of circulating antibodies against glomerular (podocytes, mesangium) and tubular cells (tubular epithelia) a cohort of 60 children with iNS including 8 patients with a familial trait of iNS or with proven mutation of NPHS1-NPHS2 and 12 with good sensitivity to steroids. Positive sera were found in 8 cases, all belonging to the category without familial trait/molecular defects. The targets of antibodies were characterized with Western blot and MALDI-Mass utilizing beta-hexyl cell extracts separated with two-dimensional electrophoresis. In all cases antibodies of the IgM class were directed against ATP synthase beta chain alone (4 cases) or in combination with actin (3 cases); one child presented IgG against aldose reductase. The clinical picture was nephrotic syndrome with steroid resistance or dependence and variable cyclosporin sensitivity; 3 patients developed end stage renal failure. The basic pathology picture was focal segmental glomerulosclerosis (FSGS) in 4 cases and mesangial proliferative glomerulonephrites with deposition of IgM in 2. Overall, patients with circulating auto-antibodies could not be readely differentiated on clinical grounds with the exception of 3 children who developed positivity for antinuclear antibodies during the follow-up. Affinity-purified IgM from one patient who underwent plasmapheresis for therapeutical pourposes (but not from a normal pool) induced proteinuria in Sprague-Dawley rats and concomitant human IgM deposition within glomeruli. This is the first report of circulating anti-actin/ATP synthase beta chain antibodies in a subset of patients with iNS. Both pathological significance and clinical impact given by the presence of these antibodies and the relationship with other conditions such as lupus-erythematosus, characterized by their presence, must be defined.

Humoral permeability factors in the nephrotic syndrome: a compendium and prospectus

The concept that increased glomerular albumin permeability in steroid-resistant nephrotic syndrome is induced by circulating humoral factors is not new. Zimmermann (1) was among the first to demonstrate that serum from a renal transplant patient with recurrent focal segmental glomerulosclerosis (FSGS) could provoke increased albumin excretion when infused in the aorta of intact rats. Unfortunately, the experiment was not easily reproducible, and the possibility that human serum could induce serum sickness in rats was a serious limitation of the original experiment. We now know that inhibitors of permeability activity are present in both normal human and rat serum (see below), which explains the difficulty in replicating the disease in intact animals. In 1974 Shalhoub (2) theorized that a disordered clone of T lymphocytes, present in both minimal change disease and FSGS, secreted a circulating lymphokine "toxic" to the glomerular barrier. In support of this hypothesis, Koyama et al (3) formed hybridomas from T cells from four patients with minimal change disease and three control subjects. The hybridomas of the patients produced a substance that induced proteinuria when injected intravenously into normal rats. However, the study utilized stimulated and not quiescent T cells, and therefore the relevance to the pathogenesis of FSGS is unknown. Hoyer and colleagues first described recurrence of idiopathic nephrotic syndrome after renal transplantation in 1972 (4). Numerous subsequent reports have established the rate of recurrence as being about 30%. Timely plasmapheresis associated with aggressive immunosuppression resolves the proteinuria and disease progression in a large proportion of cases (5). FSGS not only recurs after renal transplantation, but the diseased kidney can also recover when kept protected from the pathological milieu. Rea et al (6) demonstrated that kidneys from a donor with FSGS transplanted into two uremic recipients were free from proteinuria, and that renal function was normal after one year. Ethical and legal considerations aside, recurrence of FSGS after transplantation is strong evidence supporting the role of a humoral factor in the pathogenesis of the disease.

IgA nephropathy, the most common cause of glomerulonephritis, is linked to 6q22-23

End-stage renal disease (ESRD) is a major public health problem, affecting 1 in 1,000 individuals and with an annual death rate of 20% despite dialysis treatment. IgA nephropathy (IgAN) is the most common form of glomerulonephritis, a principal cause of ESRD worldwide; it affects up to 1.3% of the population and its pathogenesis is unknown. Kidneys of people with IgAN show deposits of IgA-containing immune complexes with proliferation of the glomerular mesangium (Fig. 1). Typical clinical features include onset before age 40 with haematuria and proteinuria (blood and protein in the urine), and episodes of gross haematuria following mucosal infections are common; 30% of patients develop progressive renal failure. Although not generally considered a hereditary disease, striking ethnic variation in prevalence and familial clustering, along with subclinical renal abnormalities among relatives of IgAN cases, have suggested a heretofore undefined genetic component. By genome-wide analysis of linkage in 30 multiplex IgAN kindreds, we demonstrate linkage of IgAN to 6q22-23 under a dominant model of transmission with incomplete penetrance, with a lod score of 5.6 and 60% of kindreds linked. These findings for the first time indicate the existence of a locus with large effect on development of IgAN and identify the chromosomal location of this disease gene.

Localisation of the gene responsible for fechtner syndrome in a region <600 Kb on 22q11-q13

Fechtner syndrome is an autosomal dominant disorder which has been thought to be a variant of Alport syndrome. It is characterised by nephritis, sensorineural hearing loss and eye abnormalities, as well as by macrothrombocytopenia and polymorphonuclear inclusion bodies. Recently, the Fechtner syndrome has been mapped in a 5.5 Mb region on the long arm of chromosome 22 by linkage analysis in an extended Israeli family. We describe here the genetic refinement of the Fechtner critical interval to a region less than 600 Kb by linkage analysis performed in a large Italian pedigree. The presence of several recombination events allowed the disease gene to be localised between markers D22S278 and D22S426, in a region containing only two non-recombinant markers, D22S1173 and D22S283. This interval, spanning <600 Kb on genomic DNA, has been entirely sequenced and contains six known and three putative genes.

Mutations in MYH9 result in the May-Hegglin anomaly, and Fechtner and Sebastian syndromes. The May-Heggllin/Fechtner Syndrome Consortium

The autosomal dominant, giant-platelet disorders, May-Hegglin anomaly (MHA; MIM 155100), Fechtner syndrome (FTNS; MIM 153640) and Sebastian syndrome (SBS), share the triad of thrombocytopenia, large platelets and characteristic leukocyte inclusions ('Döhle-like' bodies). MHA and SBS can be differentiated by subtle ultrastructural leukocyte inclusion features, whereas FTNS is distinguished by the additional Alport-like clinical features of sensorineural deafness, cataracts and nephritis. The similarities between these platelet disorders and our recent refinement of the MHA (ref. 6) and FTNS (ref. 7) disease loci to an overlapping region of 480 kb on chromosome 22 suggested that all three disorders are allelic. Among the identified candidate genes is the gene encoding nonmuscle myosin heavy chain 9 (MYH9; refs 8-10), which is expressed in platelets and upregulated during granulocyte differentiation. We identified six MYH9 mutations (one nonsense and five missense) in seven unrelated probands from MHA, SBS and FTNS families. On the basis of molecular modelling, the two mutations affecting the myosin head were predicted to impose electrostatic and conformational changes, whereas the truncating mutation deleted the unique carboxy-terminal tailpiece. The remaining missense mutations, all affecting highly conserved coiled-coil domain positions, imparted destabilizing electrostatic and polar changes. Thus, our results suggest that mutations in MYH9 result in three megakaryocyte/platelet/leukocyte syndromes and are important in the pathogenesis of sensorineural deafness, cataracts and nephritis.

A DNA element in the alpha1 type III collagen promoter mediates a stimulatory response by angiotensin II

BACKGROUND

Angiotensin II (Ang II) plays an important role in extracellular matrix deposition and tissue scarring in the kidney and the heart. The mechanism for extracellular matrix stimulation by Ang II is currently hypothetical, with one possibility pointing to a direct effect on cell synthesis of specific collagens.

METHODS

We studied the molecular mechanism for activation of type III collagen synthesis by Ang II in an in vitro cell model of myofibroblasts by evaluating (1) alpha1(III) collagen mRNA expression; (2) alpha1(III) collagen promoter activity; (3) DNA/protein binding with characterization of binding sites; (4) expression of transcription factors; and (5) the role of a short DNA segment as Ang II responsive element.

RESULTS

We found a specific dose-dependent stimulation of alpha1(III) collagen mRNA expression and a parallel effect on alpha1(III) collagen promoter activity. Transfection of constructs containing alpha1(III) collagen promoter fragments of different lengths localized the site of activation within the shortest 178 bp construct. By gel-retardation experiments, we observed the formation of a DNA-protein complex with crude extracts from Ang II-stimulated cells and an oligonucleotide spanning the 3 to 20 sequence. This complex was due to a sequence-specific interaction and was abolished by a 3 bp substitution mutation. The introduction of this mutation into the 178 bp construct abolished the stimulatory effect of Ang II.

CONCLUSIONS

These results demonstrate that Ang II stimulates the expression of alpha1(III) collagen mRNA in myofibroblasts in vitro by activating the alpha1(III) collagen promoter at the level of a factor recognition site localized immediately downstream of the transcription start site. This mechanism could be involved in Ang II-induced renal and heart fibrosis.

Evidence of further genetic heterogeneity in autosomal dominant medullary cystic kidney disease

BACKGROUND

Autosomal dominant medullary cystic kidney disease is a genetically heterogeneous nephropathy with clinical and morphological features similar to recessively inherited juvenile nephronophthisis. Recently, a second gene locus on chromosome 16p12, MCKD2 has been mapped [1] in addition to the known locus on chromosome 1q21 (MCKD1) [2]. In a previous study we have excluded linkage for three caucasian families to the MCKD1 locus [3].

METHODS

Haplotype analysis was performed on 72 individuals (including 24 affected subjects), using a set of seven microsatellite markers spanning the critical region on chromosome 16p12-p13 of about 10.5 cM.

RESULTS

We report on haplotype analysis of closely linked markers to the MCKD2 locus in the previously studied families and two additional families.

CONCLUSION

In all five families the association of MCKD2 with the disease was excluded by a multipoint LOD score <-2, thus suggesting the involvement of a third MCKD locus.

Characterization of a DNA binding site that mediates the stimulatory effect of cyclosporin-A on type III collagen expression in renal cells

BACKGROUND

Previous work from our laboratory demonstrated upregulation of type III collagen by cyclosporin A (CsA) in a cellular model of renal fibroblasts 'in vitro', suggesting that a mechanism of gene transcriptional activation might be responsible for collagen accumulation in renal fibrosis resulting from chronic CsA treatment.

METHODS

We analysed in the same cellular model: (i) COL3A1 mRNA expression by RT-PCR; (ii) COL3A1 promoter activity by transfection of renal fibroblasts with constructs containing promoter fragments of different length fused to a reporter gene; (iii) expression of transcription factors by western blot analysis; (iv) DNA-protein binding by gel retardation assays with nuclear extracts from CsA-treated and untreated cells; and (v) site-directed mutagenesis of COL3A1 promoter to verify the role of a short DNA segment as CsA responsive element.

RESULTS

CsA induced a 3-5-fold increase in COL3A1 mRNA that was paralleled by a stimulation of the COL3A1 promoter. Degradation of COL3A1 mRNA was comparable in CsA-treated and -untreated cells. The target region was first limited to a 178 bp fragment from -117 to +61 (pFV1). By gel retardation, utilizing several oligonucleotides that covered the whole length of pFV1, we detected a factor able to bind the promoter DNA (oligo 31) in nuclear extracts after 3 h treatment with CsA. The binding was absent in untreated cells and it was not detected when a 10-base mutation was introduced in oligonucleotide 31. Finally, the same substitution mutation at the site of binding of this factor abolished the stimulatory effect of CsA on COL3A1 promoter. Some transcription factors, whose potential binding sites are included in the above promoter fragment, were induced by CsA treatment either soon (3 h) or late (24-72 h) after treatment and were detected by western blot analysis.

CONCLUSIONS

CsA induces the synthesis of type III collagen by stimulating a pathway leading to activation of COL3A1 promoter and upregulation of COL3A1 mRNA. A short promoter fragment, proximal to the transcription start site, is the target of CsA stimulation.

Clinical and molecular heterogeneity of juvenile nephronophthisis in Italy: insights from molecular screening

Autosomal recessive nephronophthisis (NPH) is a renal disorder histologically characterized by tubulointerstitial lesions that are, in some cases, associated with extrarenal manifestations such as tapeto-retinal degeneration or liver fibrosis. The disease is usually pauci-symptomatic in an early phase but invariably evolves to end-stage renal failure in childhood or early adulthood. The recent discovery of the NPHP1 gene (nephrocystin) has prompted research into putative genotype-phenotype correlations. We screened a population of 68 Italian children (10 multiplex families, 47 sporadic cases) with a clinical and histopathologic picture of NPH and found a large homozygous deletion at 2q13 involving nephrocystin in 30 cases, and heterozygous deletion associated with new point mutations at exons 15 (Tyr518Ter) and 17 (Arg585Ter) of the gene in two other cases. The remaining 36 children had no apparent molecular defects of nephrocystin. In spite of this genetic heterogeneity, the two groups, with and without detectable molecular defects of nephrocystin, showed similar renal defects and comparable cumulative survival considering the start of dialysis as an end-point. The unique difference observed was a less frequent requirement of dialysis in NPH1 patients with pure renal form. Finally, tapeto-retinal degeneration was associated with renal lesions in seven cases presenting deletion of the nephrocystin gene and in five sporadic cases without molecular defects. These data show that a molecular defect of nephrocystin is involved in approximately 50% of patients with NPH, and another 50% require further molecular characterization. Research therefore should now be aimed at characterizing a new locus. In spite of the molecular heterogeneity, NPH in children presents similar renal and extrarenal manifestations, thus suggesting the involvement of common pathological routes.

Disseminated autoimmune disease during levamisole treatment of nephrotic syndrome

Side effects such as cutaneous vasculitis, which occur during prolonged levamisole treatment, may discourage the utilization of the drug in relapsing nephrotic syndrome. We describe a child who developed disseminated vasculitis during prolonged treatment with levamisole. The acute phase was characterized by hepatosplenomegaly, hemolytic anemia, IgM anticardiolipin and p-antineutrophil cytoplasmic antibodies. One month after withdrawal of therapy all symptoms had disappeared and tests normalized. This case report, together with other reports on cutaneous vasculitis, suggest caution and close monitoring during prolonged levamisole therapy.

N-(4-hydroxyphenyl) retinamide inhibits cystogenesis by polycystic epithelial cell lines in vitro

Primary tubular epithelial cells develop spherical monolayered cysts when cultured in collagenI matrix, a model that has been used to study the mechanism of cystogenesis. In an attempt to block cystogenesis, we have evaluated the effect of N-(4-hydroxyphenyl) retinamide (HPR), a synthetic derivative of retinoic acid, on both formation and growth of cysts in a human model of polycystic kidney cells. Number, dimension and submicroscopical characteristics of cysts were evaluated after 2 and 4 weeks from treatment with HPR. A marked inhibitory effect of HPR on cystogenesis was found at concentration of 1 microM, while a complete block was observed at concentration between 5 and 10 microM. Furthermore, treatment with HPR of already formed cysts resulted in their disruption. HPR at 10 microM also induced apoptosis of several tubular epithelial cell models suggesting a correlation between the two phenomena. Taken together these observations demonstrate that HPR blocks cystogenesis by polycystic kidney cells "in vitro" and that it also reverts the fate of already formed cysts. Apoptosis may be the mechanism which mediates the inhibitory effect on cystogenesis in this model.

Identification of a new locus for medullary cystic disease, on chromosome 16p12

Autosomal dominant medullary cystic disease (ADMCKD) is an interstitial nephropathy that has morphologic and clinical features similar to autosomal recessive nephronophthisis. The typical renal dysfunction associated with ADMCKD results mainly from a defect in urinary concentration ability, although results of urinalysis are normal. Recently, a locus on chromosome 1 was associated with ADMCKD, in DNA from two large Cypriot families, and genetic heterogeneity was inferred. We describe the genomewide linkage mapping of a new locus for medullary cystic disease, ADMCKD2, on chromosome 16p12 in a four-generation Italian pedigree. The family with ADMCKD2 fulfills the typical diagnostic criteria of ADMCKD, complicated by hyperuricemia and gouty arthritis. Marker D16S3036 shows a maximum two-point LOD score of 3.68, and the defined critical region spans 10.5 cM, between D16S500 and SCNN1B1-2. Candidate genes included in the critical region are discussed.

Renal-retinal syndromes: association of retinal anomalies and recessive nephronophthisis in patients with homozygous deletion of the NPH1 locus

Tapeto-retinal degeneration is frequent in patients with nephronophthisis. Association of the most severe forms of tapeto-retinal dystrophy with NPH identifies a syndrome described first by Senior et al and Loken et al. This syndrome is distinct on molecular grounds from pure renal nephronophthisis (NPH1), which has its gene locus mapped on chromosome 2q13. We describe three families with large homozygous deletion of the NPH1 locus in which mild to moderate ocular lesions due to tapeto-retinal degeneration coexisted and were correlated to renal defects. This new association of NPH1 with retinal dystrophy is characterized by focal lesions of retina and is pauci-symptomatic in clinical presentation. For this reason it may remain unrecognized in most NPH1 patients.

Transforming growth factor beta blocks cystogenesis by MDCK epithelium in vitro by enhancing the paracellular flux: implication of collagen V

Transforming growth factor beta (TGFbeta) determines a nearly complete inhibition of cystogenesis by MDCK cells grown in collagen I-enriched matrices in vitro. In order to elucidate the mechanism implicated in this phenomenon, we performed a series of experiments aimed at discovering a relevant role of extracellular matrix. TGFbeta (2 ng/ml) played a marked stimulatory effect on the expression of extracellular matrix by MDCK with a selective effect on collagen V (three to fourfold increase of protein and mRNA) and in parallel inhibited cystogenesis by 95%. Cotreatment with TGFbeta and anti-collagen V antibodies restored a normal cystogenesis. In analogy, when MDCK cells were grown in three-dimensional matrices containing collagen I and minor (10%) amounts of collagen V, cystogenesis was once again inhibited by 95%. To characterize the molecular mechanism activated by TGFbeta and collagen V, we looked at the electrophysiological characteristics of MDCK monolayers and found a drastic fall of transepithelial electrical resistance (TER) in both conditions. In parallel with the decrease in TER, TGFbeta and collagen V also induced the leakage of two high molecular weight tracers, i.e., [3H]-inulin and 150 kD FITC-Dextran, suggesting a perturbation of the paracellular permeability. Finally, TGFbeta at the relevant concentration did not stimulate apoptosis in our cellular model, as judged by propidium iodide staining and by in situ end labeling of DNA fragments. These observations suggest that TGFbeta inhibits cystogenesis by MDCK cells in vitro by altering the collagenic composition of the three-dimensional milieu where MDCK cells grow and form cysts. The molecular mechanism responsible for inhibition of cystogenesis is the increase of paracellular flux which overcomes the active transport of solutes and water inside cysts.