Tauroursodeoxycholic acid ameliorates renal injury induced by COL4A3 mutation

COL4A3/A4/A5 mutations have been identified as critical causes of Alport syndrome and other genetic chronic kidney diseases. However, the underlying pathogenesis remains unclear, and specific treatments are lacking. Here, we constructed a transgenic Alport syndrome mouse model by generating a mutation (Col4a3 p.G799R) identified previously from one large Alport syndrome family into mice. We observed that the mutation caused a pathological decrease in intracellular and secreted collagen IV α3α4α5 heterotrimers. The mutant collagen IV α3 chains abnormally accumulated in the endoplasmic reticulum and exhibited defective secretion, leading to persistent endoplasmic reticulum stress in vivo and in vitro. RNA-seq analysis revealed that the MyD88/p38 MAPK pathway plays key roles in mediating subsequent inflammation and apoptosis signaling activation. Treatment with tauroursodeoxycholic acid, a chemical chaperone drug that functions as an endoplasmic reticulum stress inhibitor, effectively suppressed endoplasmic reticulum stress, promoted secretion of the α3 chains, and inhibited the activation of the MyD88/p38 MAPK pathway. Tauroursodeoxycholic acid treatment significantly improved kidney function in vivo. These results partly clarified the pathogenesis of kidney injuries associated with Alport syndrome, especially in glomeruli, and suggested that tauroursodeoxycholic acid might be useful for the early clinical treatment of Alport syndrome.

Effectiveness of renin-angiotensin-aldosterone system blockers in patients with Alport syndrome: a systematic review and meta-analysis

BACKGROUND

Although renin-angiotensin-aldosterone system (RAAS) blockers have been considered the primary treatment for patients with Alport syndrome (AS) for a decade, there is no comprehensive review with evidence-based analysis evaluating the effectiveness of RAAS blockers in AS.

METHODS

A systematic review and meta-analysis was performed of published studies that compared outcomes related to disease progression between patients with AS receiving RAAS blockers with those taking non-RAAS treatment. Outcomes were meta-analyzed using the random effects models. Cochrane risk-of-bias, Newcastle-Ottawa Scale and Grading of Recommendations Assessment, Development and Evaluation methodology (GRADE) assessment determined the certainty of evidence.

RESULTS

A total of eight studies (1182 patients) were included in the analysis. Overall, the risk of bias was low to moderate. Compared with non-RAAS treatment, RAAS blockers could reduce the rate of progression to end-stage kidney disease (ESKD) [four studies; hazard ratio (HR) 0.33, 95% confidence interval (CI) 0.24-0.45; moderate certainty evidence]. After stratified by genetic types, a similar benefit was detected: male X-linked AS (XLAS) (HR 0.32, 95% CI 0.22-0.48), autosomal recessive AS (HR 0.25, 95% CI 0.10-0.62), female XLAS and autosomal dominant AS (HR 0.40, 95% CI 0.21-0.75). In addition, RAAS blockers showed a clear gradient of benefit depending on the stage of disease at the initiation of treatment.

CONCLUSION

This meta-analysis suggested that RAAS blockers could be considered as a specific therapy to delay of ESKD for AS with any genetic type, especially at the early stage of the disease, and every further more-effective therapy would be advised to be applied on top of this standard of care.

Narrative update of clinical trials with antihypertensive drugs in children and adolescents

INTRODUCTION

To date, our knowledge on antihypertensive pharmacological treatment in children and adolescents is still limited because there are few randomized clinical trials (CTs), hampering appropriate management. The objective was to perform a narrative review of the most relevant aspects of clinical trials carried out in primary and secondary hypertension.

METHODS

Studies published in PubMed with the following descriptors: clinical trial, antihypertensive drug, children, adolescents were selected. A previous Cochrane review of 21 randomized CTs pointed out the difficulty that statistical analysis could not assess heterogeneity because there were not enough data. A more recent meta-analysis, that applied more stringent inclusion criteria and selected 13 CTs, also concluded that heterogeneity, small sample size, and short follow-up time, as well as the absence of studies comparing drugs of different classes, limit the utility.

RESULTS

In the presented narrative review, including 30 studies, there is a paucity of CTs focusing only on children with primary or secondary, mainly renoparenchymal, hypertension. In trials on angiotensin converting enzyme inhibitors (ACEI), angiotensin receptor blockers (ARBs), calcium channel blockers (CCBs) and diuretics, a significant reduction of both SBP and DBP in mixed cohorts of children with primary and secondary hypertension was achieved. However, few studies assessed the effect of antihypertensive drugs on hypertensive organ damage.

CONCLUSIONS

Given the increasing prevalence and undertreatment of hypertension in this age group, innovative solutions including new design, such as 'n-of-1', and optimizing the use of digital health technologies could provide more precise and faster information about the efficacy of each antihypertensive drug class and the potential benefits according to patient characteristics.

Single, Double and Triple Blockade of RAAS in Alport Syndrome: Different Tools to Freeze the Evolution of the Disease

Background: The goal of the treatment of Alport syndrome (AS) is to delay the progression of kidney damage. The current standard of care is the use of Renin Angiotensin Aldosterone System (RAAS) blockers: angiotensin-converting enzyme inhibition (ACEi), angiotensin receptor blockade, and, recently, spironolactone (SP). Aim of the study: the purpose of this retrospective study is to evaluate the efficacy (reduction of proteinuria and changes of glomerular function) and safety of a sequential introduction of RAAS blockers up to a triple RAAS blockade in pediatric proteinuric patients with AS. Methods: in this retrospective study (1995 to 2019), we evaluated proteinuria values in AS patients, during the 12 months following the beginning of a new RAAS blocker, up to a triple blockade. ACEi was always the first line of treatment; then ARB and SP were sequentially added if uPCR increased by 50% from the basal level in 2 consecutive samples during a 3-months observation period, or when uPCR ratio was >2 mg/mg. Results: 26 patients (mean age at treatment onset was 10.55 ± 5.02 years) were enrolled. All patients were on ACEi, 14/26 were started on a second drug (6/14 ARB, 8/14 SP) after a mean time of 2.2 ± 1.7 years, 7/26 were on triple RAAS blockade after a further period of 5.5 ± 2.3 years from the introduction of a second drug. Repeated Measure Anova analysis of log-transformed data shows that the reduction of uPCR values after Time 0 from the introduction of the first, second and third drug is highly significant in all three cases (p values = 0.0016, 0.003, and 0.014, respectively). No significant changes in eGFR were recorded in any group, apart from a 15-year-old boy with X-linked AS, who developed kidney failure. One patient developed mild hyperkaliemia, and one gynecomastia and symptomatic hypotension. No life-threatening events were recorded. Conclusions: double and triple RAAS blockade is an effective and safe strategy to reduce proteinuria in children with AS. Nevertheless, we suggest monitoring eGFR and Kaliemia during follow-up.

Organoprotective Effects of Spironolactone on Top of Ramipril Therapy in a Mouse Model for Alport Syndrome

Angiotensin-converting enzyme inhibitors (ACEi) delay progression of the inherited renal disease Alport syndrome. However, the effect of ACEis weakens gradually due to an “aldosterone escape”. Here, we investigate if an aldosterone antagonist can counteract loss of ACEi-efficacy. COL4A3−/− mice were treated with ramipril (ACEi), starting at 4.5 weeks of age, and spironolactone was added at 7 weeks of age. Lifespan until renal failure, as well as kidney function parameters, were investigated. Dual therapy decreased proteinuria levels compared to ACEi monotherapy. Matrix accumulation, as well as tubulointerstitial and glomerular scar-tissue formation, were significantly reduced compared to untreated mice and ACEi-monotherapy at 75 and 100 days. Lifespan in dual treated mice was extended compared to untreated mice. However, lifespan was not superior to ACEi monotherapy–despite improved urea-nitrogen levels in the dual therapy group. In conclusion, adding the aldosterone-antagonist spironolactone to ACEi therapy further improved kidney function and reduced proteinuria and fibrosis. However, survival was not improved further, possibly due to premature death from side effects of dual therapy such as hyperkalemia. Thus, dual therapy could offer an effective therapy option for Alport syndrome patients with progressive proteinuria. However, the risks of adverse events require close monitoring.

HMGB-1 and TGFβ-1 highlight immuno-inflammatory and fibrotic processes before proteinuria onset in pediatric patients with Alport syndrome

INTRODUCTION

Alport syndrome (ALP) is a rare genetic condition characterized by progressive involvement of the basal membranes and renal dysfunction. The purpose of the study was to evaluate urinary (u) and serum (s) levels of tumor growth factor (TGF)-beta(β) and high mobility group box (HMGB)-1 in ALP patients with normal renal function, albuminuria and proteinuria.

METHODS

A prospective, single-center study was performed with a follow-up period of 12 months, enrolling 11 pediatric ALP patients and 10 healthy subjects (HS). Normal values of serum creatinine, albuminuria and proteinuria, as well as unaltered estimated glomerular filtration rate (eGFR) were required at enrollment.

RESULTS

ALP patients had significantly higher levels of serum and urinary HMGB1 compared to HS. The same trend was observed for TGF-β1, with higher values in ALP patients than in HS. HMGB1 and TGF-β1 correlated with each other and with markers of renal function and damage. Urinary biomarkers did not correlate with eGFR, whereas sHMGB1 and sTGF-β1 were negatively related to filtration rate (r: - 0.66; p = 0.02, r: - 0.96; p < 0.0001, respectively). Using proteinuria as a dependent variable in a multiple regression model, only the association with sTGF-β1 (β = 0.91, p < 0.0001) remained significant.

CONCLUSIONS

High levels of HMGB1 and TGF-β1 characterized ALP patients with normal renal function, highlighting the subclinical pro-fibrotic and inflammatory mechanisms triggered before the onset of proteinuria. Further studies are needed to evaluate the role of HMGB1 and TGFβ-1 in ALP patients.

Genetic background, recent advances in molecular biology, and development of novel therapy in Alport syndrome

Alport syndrome (AS) is a progressive inherited kidney disease characterized by hearing loss and ocular abnormalities. There are three forms of AS depending on inheritance mode: X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, which encodes type IV collagen α5 chain, while ADAS and ARAS are caused by variants in COL4A3 or COL4A4, which encode type IV collagen α3 or α4 chain, respectively. In male XLAS or ARAS cases, end-stage kidney disease (ESKD) develops around a median age of 20 to 30 years old, while female XLAS or ADAS cases develop ESKD around a median age of 60 to 70 years old. The diagnosis of AS is dependent on either genetic or pathological findings. However, determining the pathogenicity of the variants detected by gene tests can be difficult. Recently, we applied the following molecular investigation tools to determine pathogenicity: 1) in silico and in vitro trimer formation assay of α345 chains to assess triple helix formation ability, 2) kidney organoids constructed from patients’ induced pluripotent stem cells to identify α5 chain expression on the glomerular basement membrane, and 3) in vitro splicing assay to detect aberrant splicing to determine the pathogenicity of variants. In this review article, we discuss the genetic background and novel assays for determining the pathogenicity of variants. We also discuss the current treatment approaches and introduce exon skipping therapy as one potential treatment option.

COL4A3 mutation is an independent risk factor for poor prognosis in children with Alport syndrome

BACKGROUND

Alport syndrome (AS) is an inherited glomerular disease caused by mutations in COL4A3, COL4A4, or COL4A5. Associations between clinical manifestations and genotype are not yet well defined. Our study aimed to define clinical and genetic characteristics, establish genotype-phenotype correlations, and determine prognosis of AS in children.

METHODS

A total of 87 children with AS from 10 pediatric nephrology centers, whom had genetic analyses performed at the Hacettepe University Nephrogenetics Laboratory between February 2017 and February 2019, were included. Data regarding demographics, family history, clinical and laboratory characteristics, histopathological and genetic test results, treatments, and yearly follow-up results were retrospectively analyzed.

RESULTS

Of 87 patients, 16% presented with nephrotic syndrome. In patients with nephrotic syndrome, kidney biopsy findings showed focal segmental glomerulosclerosis (FSGS) in 79%, and COL4A3 mutations were the leading genetic abnormality (50%). Twenty-four percent of all patients progressed to chronic kidney disease (CKD). The rate of progression to CKD and the decline in the glomerular filtration rate of the patients with COL4A3 mutation were higher than other mutation groups (p < 0.001 and p = 0.04, respectively). In kidney survival analysis, nephrotic syndrome presentation, histopathology of FSGS, COL4A3 mutations, and autosomal recessive inheritance were found as independent risk factors for earlier progression to CKD. Cyclosporin A treatment did not improve kidney survival.

CONCLUSIONS

We emphasize that genetic testing is important for patients suspected as having AS. Furthermore, COL4A mutations should be considered in patients with FSGS and steroid-resistant nephrotic syndrome. This approach will shed light on the prognosis of patients and help with definitive diagnosis, preventing unnecessary and potentially harmful medications. Graphical abstract.

Genotype-phenotype correlations influence the response to angiotensin-targeting drugs in Japanese patients with male X-linked Alport syndrome

Early kidney failure in the hereditary type IV collagen disease, Alport syndrome, can be delayed by renin-angiotensin inhibitors. However, whether all patients and all different genotypes respond equally well to this kidney-protective therapy remains unclear. Here, we performed a retrospective study on 430 patients with male X-linked Alport syndrome to examine the relationships among kidney prognosis, genotype, and treatment effect in a large cohort of Japanese patients. We analyzed the clinical features, genotype-phenotype correlation, and kidney survival period for patients treated with or without renin-angiotensin inhibitors. As a result, the median kidney survival period of patients in this cohort was found to be at 35 years with a strong genotype-phenotype correlation. The median age at the onset of end stage kidney disease (ESKD) significantly differed between patients treated with and without renin-angiotensin inhibitors (over 50 years versus 28 years, respectively). Moreover, these drugs delayed the onset of ESKD in patients with truncating variants for 12 years, extending the median age from 16 years to 28 years. Thus, our results confirmed a strong genotype-phenotype correlation in patients with male X-linked Alport syndrome. Additionally, it was suggested that renin-angiotensin inhibitors could significantly delay ESKD progression. Despite these therapies, patients with truncating variants developed ESKD at the median age of 28 years.

New therapeutic options for Alport syndrome

Alport syndrome (AS) is the most frequent inherited kidney disease after autosomal dominant polycystic kidney disease. It has three different patterns of inheritance-autosomal dominant, autosomal recessive and X-linked-which in part explains the wide spectrum of disease, ranging from isolated microhaematuria to end-stage renal disease early in life. The search for a treatment for AS is being pursued vigorously, not only because of the obvious unmet need but also because AS is a rare disease and any drug approved will have an orphan drug designation with its various benefits. Moreover, AS patients are quite young with very few comorbidities, which facilitates clinical trials. This review identifies the particularities of each pattern of inheritance but focuses mainly on new drugs or therapeutic targets for the disease. Most treatment-related investigations are directed not at the main abnormality in AS, namely collagen IV composition, but rather at the associated inflammation and fibrosis. Thus, AS may serve as a proof of concept for numerous drugs of potential value in many diseases that cause chronic kidney disease.

Basement membrane collagens and disease mechanisms

Basement membranes (BMs) are specialised extracellular matrix (ECM) structures and collagens are a key component required for BM function. While collagen IV is the major BM collagen, collagens VI, VII, XV, XVII and XVIII are also present. Mutations in these collagens cause rare multi-systemic diseases but these collagens have also been associated with major common diseases including stroke. Developing treatments for these conditions will require a collective effort to increase our fundamental understanding of the biology of these collagens and the mechanisms by which mutations therein cause disease. Novel insights into pathomolecular disease mechanisms and cellular responses to these mutations has been exploited to develop proof-of-concept treatment strategies in animal models. Combined, these studies have also highlighted the complexity of the disease mechanisms and the need to obtain a more complete understanding of these mechanisms. The identification of pathomolecular mechanisms of collagen mutations shared between different disorders represent an attractive prospect for treatments that may be effective across phenotypically distinct disorders.

[Analysis of Alport syndrome induced by type IV collagen alpha 5 gene mutation in two families]

OBJECTIVE

To investigate genetic characteristics of Alport syndrome.

METHODS

High-throughput sequencing-based whole exome sequencing was performed in two patients with recurrent unexplained abnormal urinalysis. The pathogenicity of the genetic variations, type of Mendelian genetics, and clinical phenotypes were analysed, and the disease-cause mutations were confirmed in the family members using Sanger sequencing.

RESULTS

Two heterozygous splice site mutations of COL4A5 gene c.2147-2A > T (IVS27) and c.646-2A > G (IVS11) (NM_033380) were found in patients of the two families, which showed a co-segregation association with the affected members of the families.

CONCLUSIONS

Alport syndrome is mainly inherited from direct female patients, and prenatal genetic screening based on amniotic fluid testing can effectively prevent birth defects in patients with a family history of this characteristic phenotype.

Advances in molecular diagnosis and therapeutics in nephrotic syndrome and focal and segmental glomerulosclerosis

PURPOSE OF REVIEW

The widespread adoption of next-generation sequencing by research and clinical laboratories has begun to uncover the previously unknown genetic basis of many diseases. In nephrology, one of the best examples of this is seen in focal and segmental glomerulosclerosis (FSGS) and nephrotic syndrome. We review advances made in 2017 as a result of human and molecular genetic studies as it relates to FSGS and nephrotic syndrome.

RECENT FINDINGS

There are more than 50 monogenic genes described in steroid-resistant nephrotic syndrome and FSGS, with seven reported in 2017. In individuals presenting with FSGS or nephrotic syndrome before or at the age of 18 years, the commonest genes in which a mutation is found continues to be limited to only a few including NPHS1 and NPHS2 based on multiple studies. For FSGS or nephrotic syndrome that presents after 18 years, mutations in COl4A3/4/5, traditionally associated with Alport syndrome, are increasingly being reported. Despite the extensive genetic heterogeneity in FSGS, there is evidence that some of these genes converge onto common pathways. There are also reports of in-vivo models exploring apolipoprotein 1 biology, variants in which account for part of the increased risk of nondiabetic kidney disease in African-Americans. Finally, genetic testing has several clinical uses including clarification of diagnosis and treatment; identification of suitable young biologic relatives for kidney donation; and preimplantation genetic diagnosis. CRISPR gene editing is currently an experimental tool only, but the recent reports of excising mutations in embryos could be a therapeutic option for individuals with any monogenic disorder in the future.

SUMMARY

Sequencing efforts are bringing novel variants into investigation and directing the efforts to understand how these lead to disease phenotypes. Expanding our understanding of the genetic basis of health and disease processes is the necessary first step to elaborate the repertoire of therapeutic agents available for patients with FSGS and nephrotic syndrome.

A review of clinical characteristics and genetic backgrounds in Alport syndrome

Alport syndrome (AS) is a progressive hereditary renal disease that is characterized by sensorineural hearing loss and ocular abnormalities. It is divided into three modes of inheritance, namely, X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, while ADAS and ARAS are caused by those in COL4A3/COL4A4. Diagnosis is conventionally made pathologically, but recent advances in comprehensive genetic analysis have enabled genetic testing to be performed for the diagnosis of AS as first-line diagnosis. Because of these advances, substantial information about the genetics of AS has been obtained and the genetic background of this disease has been revealed, including genotype-phenotype correlations and mechanisms of onset in some male XLAS cases that lead to milder phenotypes of late-onset end-stage renal disease (ESRD). There is currently no radical therapy for AS and treatment is only performed to delay progression to ESRD using nephron-protective drugs. Angiotensin-converting enzyme inhibitors can remarkably delay the development of ESRD. Recently, some new drugs for this disease have entered clinical trials or been developed in laboratories. In this article, we review the diagnostic strategy, genotype-phenotype correlation, mechanisms of onset of milder phenotypes, and treatment of AS, among others.

A review of clinical characteristics and genetic backgrounds in Alport syndrome

Alport syndrome (AS) is a progressive hereditary renal disease that is characterized by sensorineural hearing loss and ocular abnormalities. It is divided into three modes of inheritance, namely, X-linked Alport syndrome (XLAS), autosomal recessive AS (ARAS), and autosomal dominant AS (ADAS). XLAS is caused by pathogenic variants in COL4A5, while ADAS and ARAS are caused by those in COL4A3/COL4A4. Diagnosis is conventionally made pathologically, but recent advances in comprehensive genetic analysis have enabled genetic testing to be performed for the diagnosis of AS as first-line diagnosis. Because of these advances, substantial information about the genetics of AS has been obtained and the genetic background of this disease has been revealed, including genotype–phenotype correlations and mechanisms of onset in some male XLAS cases that lead to milder phenotypes of late-onset end-stage renal disease (ESRD). There is currently no radical therapy for AS and treatment is only performed to delay progression to ESRD using nephron-protective drugs. Angiotensin-converting enzyme inhibitors can remarkably delay the development of ESRD. Recently, some new drugs for this disease have entered clinical trials or been developed in laboratories. In this article, we review the diagnostic strategy, genotype–phenotype correlation, mechanisms of onset of milder phenotypes, and treatment of AS, among others.

Renal, auricular, and ocular outcomes of Alport syndrome and their current management

Alport syndrome is a hereditary glomerular basement membrane disease caused by mutations in the COL4A3/4/5 genes encoding the type IV collagen alpha 3-5 chains. Most cases of Alport syndrome are inherited as X-linked dominant, and some as autosomal recessive or autosomal dominant. The primary manifestations are hematuria, proteinuria, and progressive renal failure, whereas some patients present with sensorineural hearing loss and ocular abnormalities. Renin-angiotensin-aldosterone system blockade is proven to delay the onset of renal failure by reducing proteinuria. Renal transplantation is a curative treatment for patients who have progressed to end-stage renal disease. However, only supportive measures can be used to improve hearing loss and visual loss. Although both stem cell therapy and gene therapy aim to repair the basement membrane defects, technical difficulties require more research in Alport mice before clinical studies. Here, we review the renal, auricular, and ocular manifestations and outcomes of Alport syndrome and their current management.

Clinical Aspects of WT1 and the Kidney

For more than 30 years, WT1 mutations have been associated with complex developmental syndromes involving the kidney. Acting as a transcription factor, WT1 is expressed throughout the nephron and controls the reciprocal interactions and phenotypic changes required for normal renal development. In the adult, WT1 expression remains extremely high in the renal podocyte, and at a lower level in the parietal epithelial cells. Wt1-null mice are unable to form kidneys [1]. Unsurprisingly, WT1 mutations lead to significant abnormalities of the renal and genitourinary tract, causing a number of human diseases including syndromes such as Denys-Drash syndrome, Frasier syndrome, and WAGR syndrome. Recent methodological advances have improved the identification of WT1 mutations, highlighting its importance even in nonsyndromic renal disease, particularly in steroid-resistant nephrotic syndrome. This vast spectrum of WT1-related disease typifies the varied and complex activity of WT1 in development, disease, and tissue maintenance.

Phenotype variability in a large Spanish family with Alport syndrome associated with novel mutations in COL4A3 gene

Background

Alport syndrome is an inherited renal disorder characterized by glomerular basement membrane lesions with hematuria, proteinuria and frequent hearing defects and ocular abnormalities. The disease is associated with mutations in genes encoding α3, α4, or α5 chains of type IV collagen, namely COL4A3 and COL4A4 in chromosome 2 and COL4A5 in chromosome X. In contrast to the well-known X-linked and autosomal recessive phenotypes, there is very little information about the autosomal dominant. In view of the wide spectrum of phenotypes, an exact diagnosis is sometimes difficult to achieve.

Methods

We investigated a Spanish family with variable phenotype of autosomal dominant Alport syndrome using clinical, histological, and genetic analysis.

Results

Mutational analysis of COL4A3 and COL4A4 genes showed a novel heterozygous mutation (c. 998G > A; p.G333E) in exon 18 of the COL4A3 gene. Among relatives carrying the novel mutation, the clinical phenotype was variable. Two additional COL4A3 mutations were found, a Pro-Leu substitution in exon 48 (p.P1461L) and a Ser-Cys substitution in exon 49 (p.S1492C), non-pathogenics alone.

Conclusion

Carriers of p.G333E and p.P1461L or p.S1492C mutations in COL4A3 gene appear to be more severely affected than carriers of only p.G333E mutation, and the clinical findings has an earlier onset. In this way, we could speculate on a synergistic effect of compound heterozygosity that could explain the different phenotype observed in this family.

Early RAAS Blockade Exerts Renoprotective Effects in Autosomal Recessive Alport Syndrome

Alport syndrome is a progressive renal disease caused by mutations in COL4A3, COL4A4, and COL4A5 genes that encode collagen type IV alpha 3, alpha 4, and alpha 5 chains, respectively. Because of abnormal collagen chain, glomerular basement membrane becomes fragile and most of the patients progress to end-stage renal disease in early adulthood. COL4A5 mutation causes X-linked form of Alport syndrome, and two mutations in either COL4A3 or COL4A4 causes an autosomal recessive Alport syndrome. Recently, renin-angiotensin-aldosterone system (RAAS) blockade has been shown to attenuate effectively disease progression in Alport syndrome. Here we present three Japanese siblings and their father all diagnosed with autosomal recessive Alport syndrome and with different clinical courses, suggesting the importance of the early initiation of RAAS blockade. The father was diagnosed with Alport syndrome. His consanguineous parents and his wife were healthy. All three siblings showed hematuria since infancy. Genetic analysis revealed that they shared the same gene mutations in COL4A3 in a compound heterozygous state: c.2330G>A (p.Gly777Ala) from the mother and c.4354A>T (p.Ser1452Cys) from the father. Although RAAS blockade was initiated for the older sister and brother when their renal function was already impaired, it did not attenuate disease progression. In the youngest brother, RAAS blockade was initiated during normal renal function stage. After the initiation, his renal function has been normal with the very mild proteinuria to date at the age of 17 years. We propose that in Alport syndrome, RAAS blockade should be initiated earlier than renal function is impaired.

RAAS inhibition and the course of Alport syndrome

Alport syndrome (AS) is a hereditary progressive glomerulonephritis with a high life-time risk for end-stage renal disease (ESRD). Most patients will reach ESRD before the age of 30 years, while a subset of them with milder mutations will do so at older ages, even after 50 years. Frequent extrarenal manifestations are hearing loss and ocular abnormalities. AS is a genetically heterogeneous collagen IV nephropathy, with 85% of the cases caused by mutations in the X-linked COL4A5 gene and the rest by homozygous or compound heterozygous mutations in either the COL4A3 or the COL4A4 gene on chromosome 2q36-37. There is no radical cure for the disease and attempts to use various stem cell therapies in animal models have been met with ambiguous success. However, effective treatment has been accomplished with pharmacological intervention at the renin-angiotensin-aldosterone system (RAAS), first in animal models of AS and more recently in humans. Angiotensin converting enzyme inhibitors (ACEis) and angiotensin receptor blockers (ARBs) have been shown to significantly delay the progression of chronic kidney disease and the onset of ESRD. Also, renin inhibitors and aldosterone blockade were used with positive results, while the combination of ACEis and ARBs was met with mixed success. An important study, the EARLY-PROTECT, aims at evaluating the efficacy of ACEis when administered very early on in children with AS. Novel therapies are also tested experimentally or are under design in animal models by several groups, including the use of amniotic fluid stem cells and synthetic chaperones.

Long-term treatment by ACE inhibitors and angiotensin receptor blockers in children with Alport syndrome

BACKGROUND

The aim of this study was to analyze the long-term efficacy and safety of angiotensin-converting enzyme inhibitor (ACEi) and ACEi + angiotensin receptor blocker (ARB) treatments in a cohort of children with Alport syndrome (AS).

METHODS

This was a respective review of 79 Chinese children with AS who received ACEi alone or combined ACEi + ARB therapy.

RESULTS

The mean age of the pediatric patients with AS at onset of treatment was 8.6 ± 4.1 (range 1.5-16.3) years. The mean duration of follow-up was 2.5 ± 1.8 (range 0.5-7.8) years. For analysis, we separated the children into three groups according to proteinuria level before treatment, namely, <25, 25-50, and ≥50 mg/kg/day, respectively; after 1 year of treatment the proteinuria had decreased from 11.0 to 9.7 mg/kg/day, from 34.6 to 15.2 mg/kg/day, and from 73.0 to 50.0 mg/kg/day in each group, respectively. Proteinuria decreased significantly during the first 2 years of treatment and was stable from the third to fifth years of treatment. There was no statistically significant difference in the antiproteinuric effect of the ACEi and ACEi + ARB treatments in patients with severe or less severe mutations after 1 year of therapy. Five children stopped the ACEi + ARB treatment due to a decline in creatinine clearance.

CONCLUSION

Our findings demonstrate that early and long-term ACEi and ARB treatments in children with AS is efficient and well tolerated. The antiproteinuric effect of ACEi and ARB is of equal value in children with severe and less severe mutations in the COL4An gene.

Coinheritance of COL4A5 and MYO1E mutations accentuate the severity of kidney disease

BACKGROUND

Mutations in podocyte and basement membrane genes are associated with a growing spectrum of glomerular disease affecting adults and children. Investigation of familial cases has helped to build understanding of both normal physiology and disease.

METHODS

We investigated a consanguineous family with a wide clinical phenotype of glomerular disease using clinical, histological, and new genetic studies.

RESULTS

We report striking variability in severity of nephropathy within an X-linked Alport syndrome (XLAS) family. Four siblings each carried a mutant COL4A5 allele, p.(Gly953Val) and p.(Gly1033Arg). Two boys had signs limited to hematuria and mild/moderate proteinuria. In striking contrast, a sister presented with end-stage renal disease (ESRD) at 8 years of age and an infant brother presented with nephrotic syndrome, progressing to ESRD by 3 years of age. Both were subsequently found to have homozygous variants in MYO1E, p.(Lys118Glu) and p.(Thr876Arg). MYO1E is a gene implicated in focal segmental glomerulosclerosis and it encodes a podocyte-expressed non-muscle myosin. Bioinformatic modeling demonstrated that the collagen IV-alpha3,4,5 extracellular network connected via known protein-protein interactions to intracellular myosin 1E.

CONCLUSIONS

COL4A5 and MYO1E mutations may summate to perturb common signaling pathways, resulting in more severe disease than anticipated independently. We suggest screening for MYO1E and other non-COL4 'podocyte gene' mutations in XLAS when clinical nephropathy is more severe than expected for an individual's age and sex.

Diagnosis of Alport syndrome--search for proteomic biomarkers in body fluids

BACKGROUND

The hereditary kidney disease Alport syndrome (AS) has become a treatable disease: intervention with angiotensin-converting enzyme (ACE)-inhibitors delays end stage renal failure by years. The efficiency of ACE inhibition depends on the onset of therapy-the earlier the better. Therefore, early diagnosis has become increasingly important. To date, robust diagnosis requires renal biopsy and/or expensive genetic analysis, which is mostly performed late after onset of the profound clinical symptoms of this progressive renal disease. Thus, disease biomarkers enabling low-invasive screening are urgently required.

METHODS

Fourteen potential proteomic candidate markers (proteins) identified in a previous study in sera from patients exhibiting manifest AS were evaluated in the plasma, serum, and urine collected from a cohort of 132 subjects, including patients with AS and other nephropathies and healthy controls. Quantitation was performed by immunoassays.

RESULTS

The serum and plasma levels of none of the 14 proteins evaluated were significantly different among the three groups and therefore could not be used to discriminate between the groups. In contrast, the levels of various biomarker combinations in the urine were significantly different between AS patients and healthy controls. Importantly, some combinations had the potential to discriminate between AS and other nephropathies.

CONCLUSIONS

These findings open a window of opportunity for the sensitive and specific early diagnosis of AS. Our results increase the potential for larger scale evaluation of an increased number of patients.

Alport syndrome: the effects of spironolactone on proteinuria and urinary TGF-β1

BACKGROUND

Alport syndrome (AS) is a progressive hereditary glomerular disease. Recent data indicate that aldosterone promotes fibrosis mediated by the transforming growth factor-β1 (TGF-β1) pathway, which may worsen proteinuria. Spironolactone (SP) antagonizes aldosterone and this study aimed to evaluate the efficacy of SP in reducing proteinuria and urinary TGF-β1 excretion in proteinuric AS patients.

METHODS

The study involved ten children with AS, normal renal function, and persistent proteinuria (>6 months; uPr/uCr ratio >1). SP 25 mg once a day for 6 months was added to existing ACE inhibitor treatment with or without angiotensin-II receptor blockade. Urine and blood samples were examined monthly. Urinary TGF-β1 levels were measured twice before and three times during SP treatment. Plasma renin activity (PRA) and serum aldosterone levels were also measured. In eight patients, uProt/uCreat was also assessed after 9 months and 12 months of SP treatment.

RESULTS

After beginning SP therapy, all patients showed significant decrease in mean uProt/uCreat ratio (1.77 ± 0.8 to 0.86 ± 0.6; p < 0.001) and mean urinary TGF-β1 levels (104 ± 54 to 41 ± 20 pg/mgCreatinine; p < 0.01), beginning after 30 days of treatment and remaining stable throughout SP administration. PRA remain unchanged, and mean serum aldosterone increased from 105 ± 72 pg/ml to 303 ± 156 pg/ml (p < 0.001). The only side effect was gynecomastia in an obese boy. After 1 year of therapy, mean uProt/uCreat remains low (0.82 ± 0.48).

CONCLUSIONS

Addition of SP to ACE-I treatment with or without angiotensin II receptor blokers (ARB) significantly reduced proteinuria. This was mediated by decreased urinary TGF-β1 levels and not associated with major side effects.

An update on the pathomechanisms and future therapies of Alport syndrome

Alport Syndrome (AS) is an inherited progressive disease that is caused by mutations of the genes encoding the key collagen chains, α3, α4, and α5, which are necessary for the composition of collagen type IV to form a robust glomerular basement membrane (GBM), capable of withstanding the significant biomechanical strain to which the glomerulus is subjected. Progressive loss of the filtration barrier allows excessive proteinuria, which ultimately leads to end-stage kidney disease (ESKD). The evidence for a beneficial renoprotective effect of renin-angiotensin-aldosterone system (RAAS) blockade by angiotensin-converting enzyme (ACE) inhibition and/or angiotensin receptor blockers (ARBs) is well established in AS and recent evidence has shown that it can significantly delay the time to onset of renal replacement therapy and ESKD. Future potential treatments of AS disease progression are evaluated in this review.

Losartan and enalapril are comparable in reducing proteinuria in children with Alport syndrome

BACKGROUND

A previous subgroup analysis of a 12-week, double-blind study demonstrated that losartan significantly lowered proteinuria versus placebo and amlodipine and was well tolerated in children (1-17 years old) with proteinuria secondary to Alport syndrome. The present subgroup analysis of the open-label, extension phase of this study assessed the long-term efficacy and tolerability of losartan versus enalapril.

METHODS

Patients who had completed the double-blind study were re-randomized to losartan or enalapril and followed for proteinuria and renal function for up to 3 years.

RESULTS

Twenty-seven patients with Alport syndrome were randomized to losartan (0.44-2.23 mg/kg/day; n = 15) or enalapril (0.07-0.72 mg/kg/day; n = 12). The least-squares (LS) mean percent change from week 12 in urinary protein to creatinine ratio (UPr/Cr was +1.1 % in the losartan group versus a further 13.9 % reduction in the enalapril group (GMR [95 % CI] = 1.2 [0.7, 2.0]); the LS mean change from week 12 in estimated glomerular filtration rate (eGFR) was -6.4 ml/min/1.73 m(2) in the losartan group versus -9.1 ml/min/1.73 m(2) in the enalapril group. The adverse event incidence was low and comparable in both treatment groups.

CONCLUSIONS

In children with proteinuria secondary to Alport syndrome, losartan maintained proteinuria reduction, and enalapril produced a further proteinuria reduction over the 3-year study period. Both agents were generally well tolerated.

Effect of enalapril on glomerular filtration rate and proteinuria in children with chronic kidney disease: a randomized controlled trial

OBJECTIVE

To evaluate the efficacy of enalapril treatment on decline in glomerular filtration rate and reduction in proteinuria in children with chronic kidney disease (CKD).

DESIGN

Open-label, randomized controlled trial.

SETTING

Pediatric nephrology clinic at a tertiary-care referral hospital.

INTERVENTION

Children with GFR between 15-60 mL/min/1.73 m2 were randomized to receive either enalapril at 0.4 mg/kg /day or no enalapril for 1 year.

OUTCOME MEASURES

Change in GFR using 99mTc-DTPA and urine protein to creatinine ratio. Secondary outcomes included occurrence of composite outcome (30% decline in GFR or end stage renal disease) and systolic and diastolic blood pressure SDS during the study period.

RESULTS

41 children were randomized into two groups; 20 received enalapril while 21 did not receive enalapril. During 1 year, GFR decline was not different in the two groups (regression coefficient (r) 0.40, 95% CI -4.29 to 5.09, P=0.86). The mean proteinuria reduction was 65% in the enalapril group, significantly higher than control group. The difference was significant even after adjustment for blood pressure was 198.5 (CI 97.5, 299.3; P<0.001). 3 (17.6%) patients in enalapril and 7 (36.8%) in non-enalapril group attained the composite outcome.

CONCLUSIONS

Enalapril is effective in reducing proteinuria in children with CKD and might be renoprotective in proteinuric CKD.

Clinical practice recommendations for the treatment of Alport syndrome: a statement of the Alport Syndrome Research Collaborative

We present clinical practice recommendations for the treatment of children with Alport syndrome who are not enrolled in clinical trials. Our goal is to promote early initiation of a standard therapeutic approach that will facilitate assessment of the safety and efficacy of the protocol. The treatment protocol is based on the reduction of proteinuria, intraglomerular pressure, and renal fibrosis via interference with the renin-angiotensin-aldosterone system.

Challenge in pathologic diagnosis of Alport syndrome: evidence from correction of previous misdiagnosis

Background

Pathologic studies play an important role in evaluating patients with Alport syndrome besides genotyping. Difficulties still exist in diagnosing Alport syndrome (AS), and misdiagnosis is a not-so-rare event, even in adult patient evaluated with renal biopsy.

Methods

We used nested case–control study to investigate 52 patients previously misdiagnosed and 52 patients initially diagnosed in the China Alport Syndrome Treatments and Outcomes Registry e-system.

Results

We found mesangial proliferative glomerulonephritis (MsPGN, 26.9%) and focal and segmental glomerulosclerosis (FSGS, 19.2%) were the most common misdiagnosis. FSGS was the most frequent misdiagnosis in female X-linked AS (fXLAS) patients (34.8%), and MsPGN in male X-linked AS (mXLAS) patients (41.2%). Previous misdiagnosed mXLAS patients (13/17, 76.5%) and autosomal recessive AS (ARAS) patients (8/12, 66.7%) were corrected after a second renal biopsy. While misdiagnosed fXLAS patients (18/23, 78.3%) were corrected after a family member diagnosed (34.8%) or after rechecking electronic microscopy and/or collagen-IV alpha-chains immunofluresence study (COL-IF) (43.5%) during follow-up. With COL-IF as an additional criterion for AS diagnosis, we found that patients with less than 3 criteria reached have increased risk of misdiagnosis (3.29-fold for all misdiagnosed AS patients and 3.90-fold for fXLAS patients).

Conclusion

We emphasize timely and careful study of electronic microscopy and COL-IF in pathologic evaluation of AS patients. With renal and/or skin COL-IF as additional criterion, 3 diagnosis criteria reached are the cutoff for diagnosing AS pathologically.

Alport syndrome--insights from basic and clinical research

In 1927, Arthur C. Alport first published his description of a triad of symptoms in a family with hereditary congenital haemorrhagic nephritis, deafness and ocular changes. A few years after his death, this group of symptoms was renamed Alport syndrome. To this day, Alport syndrome still inevitably leads to end-stage renal disease and the need for renal replacement therapy, starting in young adulthood. During the past two decades, research into this rare disease has focused on the effects of mutations in collagen type IV and the role of changes in podocytes and the glomerular basement membrane that lead to early kidney fibrosis. Animal models of Alport syndrome also demonstrate the pathogenetic importance of interactions between podocytes and the extracellular matrix. Such models might also help researchers to answer basic questions about podocyte function and the development of fibrosis, and to develop new therapeutic approaches that might be of use in other kidney diseases. In this Review, we discuss the latest basic and clinical research on Alport syndrome, focusing on the roles of podocyte pathology and the extracellular matrix. We also highlight early diagnosis and treatment options for young patients with this disorder.