Incidence of renal failure and nephroprotection by RAAS inhibition in heterozygous carriers of X-chromosomal and autosomal recessive Alport mutations. Kidney Int. 2012;81:779-783. [PMID: 22237748 DOI: 10.1038/ki.2011.452]

Phenotype-genotype correlations in patients with Alport syndrome from the Polish population

BACKGROUND

Alport syndrome (AS) is a rare inherited kidney disease associated with progressive renal failure and visual and hearing disorders. The purpose of this study was to find genetic variants in patients with suspected Alport syndrome from Central and Southwestern Poland and their association with the clinical course of the disease, and to evaluate the impact of Alport syndrome on pregnancy.

METHODS

Initially, 90 patients with suspected Alport syndrome were evaluated by molecular-based testing. Clinical analyses, including urinalysis, evaluation of serum parameters, ultrasound, ophthalmologic, cardiovascular and audiology examination, and genetic testing were performed using next-generation sequencing and the Sanger method.

RESULTS

Seventy-seven patients (40.26% male; 59.74% female) with a median age of 6 years were included in the study group, after receiving a diagnosis of Alport syndrome. Twenty pathogenic/potentially pathogenic variants within the COL4A3, COL4A4 and COL4A5 genes were identified in these patients. The c.1871G > A variant in the COL4A5 gene was the most common (53.25%). Isolated hematuria was the most common initial sign of Alport syndrome (70.8%). Genetic testing confirmed Alport syndrome in 85% of symptomatic patients and in 15% of asymptomatic patients. Sensorineural hearing loss (17%) and ocular abnormalities (6%) were also detected in patients in the study group. Isolated hematuria showed a significant association with COL4A5 gene variants (p < 0.001). Genetic variants showed an association with initial clinical symptoms and age at Alport syndrome manifestation.

CONCLUSIONS

Regular urinalysis and genetic testing should be considered in suspected cases of Alport syndrome for rapid diagnosis and effective patient management.

Protocol and rationale for a randomized controlled SGLT2 inhibitor trial in paediatric and young adult populations with chronic kidney disease: DOUBLE PRO-TECT Alport

BACKGROUND

Clinical trials have demonstrated positive cardiovascular and kidney outcomes of sodium-glucose co-transporter 2 (SGLT2) inhibitors in adult patients with diabetic and other chronic kidney diseases (CKDs). Whether benefits extend to children, teenagers and young adults with early-stage CKD is unknown. For this reason, the DOUBLE PRO-TECT Alport trial (NCT05944016) will study the progression of albuminuria in young patients with Alport syndrome (AS), the most common hereditary CKD, to assess the safety and efficacy of the SGLT2 inhibitor dapagliflozin. Patients living with AS and chronically elevated albuminuria have a high risk of kidney failure before the age of 50 years.

METHODS

DOUBLE PRO-TECT Alport is a multicentre, randomized, double-blind, placebo-controlled trial. Participants (ages 10-39 years) must have a diagnosis of AS by genetic testing or kidney biopsy, be on a stable (>3 months) maximum tolerated dose of a renin-angiotensin system inhibitor and have a urinary albumin:creatinine ratio (UACR) of >300 mg/g (paediatric) or >500 mg/g (adult).Eligible participants will be randomly assigned at a 2:1 ratio to 48 weeks of treatment with dapaglifozin 10 mg/day or matched placebo. Most participants are expected to be children with a normal estimated glomerular filtration rate (eGFR). In addition to safety, the primary (change in UACR from baseline to week 48) and key secondary (eGFR change from baseline to week 52) efficacy outcomes will be analysed with a mixed model repeated measures approach. Efficacy analyses will be performed primarily in the full analysis set according to the intention-to-treat principle. A sensitivity analysis will be performed using reference-based multiple imputation.

CONCLUSION

DOUBLE PRO-TECT Alport will assess whether SGLT2 inhibitors can safely reduce the UACR change from baseline as a marker for progression of CKD in young patients living with AS.

Alport syndrome: Expanding diagnosis and treatment

Alport syndrome (AS) is the second common monogenic cause of end-stage kidney disease (ESKD) worldwide and is caused by defective type 4 collagen due to pathogenic variants of COL4A3, COL4A4, or COL4A5. Type 4 collagen also exists in the eyes and ears, and thus ocular defects and hearing loss occur in AS. The understanding of AS has expanded over the past two decades due to greater availability of genetic testing and research on genotype-phenotype correlation. Patients previously diagnosed with idiopathic steroid resistant nephrotic syndrome or ESKD of unknown etiology may now be diagnosed as AS if pathogenic COL4A3-5 variants are identified. Some carriers of heterozygous COL4A3-5 variants may now be classified into females with X-linked AS or autosomal dominant AS, if there are typical pathologic changes in the glomerular basement membrane or if there is proteinuria and progression of kidney disease. Lastly, it has been recommended that renin-angiotensin-aldosterone system inhibition be started as soon as possible for selected AS patients for its long-term protective effect against kidney function deterioration. The purpose of this review is to introduce these important concepts to general pediatricians and pediatric nephrologists.

A Novel Deep Learning Approach for Analyzing Glomerular Basement Membrane Lesions in a Mouse Model of X-Linked Alport Syndrome

Alport syndrome is a rare kidney disease typically more severe in males due to its X-linked inheritance. However, female patients with heterozygous X-linked Alport syndrome (XLAS) can develop renal failure over time, necessitating accurate pathologic assessment for effective therapy. A key pathologic finding in female patients with XLAS is the mosaic pattern of partial loss of α5 chains of type IV collagen (COL4α5). This study, using a mouse model of XLAS with a nonsense mutation (R471∗) in the Col4a5 gene, analogous to human XLAS, aimed to examine the consistency of this pattern with the glomerular basement membrane (GBM) structure. A modified periodic acid-methenamine silver staining method was developed for clearer GBM visualization. The integrated images from COL4α5-stained fluorescence, periodic acid-methenamine silver, and low-vacuum scanning electron microscopy into a single-slide section and applied supervised deep learning to predict GBM lesions. Results showed significant individual variability in urinary protein levels and histologic lesions. Pathologic parameters, including crescent formation, focal segmental glomerulosclerosis, and the COL4α5/α2 ratio, correlated with clinical parameters like urinary protein and plasma creatinine levels. Integrated low-vacuum scanning electron microscopy analysis revealed dense GBM regions corresponded to areas where COL4α5 was preserved, whereas coarse GBM (basket-weave lesions) occurred in COL4α5-deficient regions. These advanced techniques can enhance biopsy-based diagnosis of Alport syndrome and aid in developing artificial intelligence diagnostic tools for diseases involving basement membrane lesions.

Clinical Implementation of Nephrologist-Led Genomic Testing for Glomerular Diseases in Singapore: Rationale and Protocol

INTRODUCTION

The early diagnosis and appropriate treatment of monogenic glomerular diseases can reduce kidney failure, avoid unnecessary investigations such as kidney biopsies and ineffective treatment with immunosuppressants, guide transplant decisions, and inform the genetic risks of their family members. Yet, genetic testing for kidney disease is underutilized in Singapore. We aimed to implement a nephrologist-led genetic service and evaluate the acceptance, adoption, utility, and cost-effectiveness of genetic testing for monogenic glomerular disease in Singapore.

METHODS

We will perform a prospective, multi-centre, type II hybrid effectiveness-implementation study with a post-design to evaluate both implementation and clinical outcomes of nephrologist-led genetic testing for suspected genetic glomerular kidney diseases. The multi-disciplinary implementation team will train "genetic nephrologists" to provide pre- and post-test counselling, order targeted exome panel sequencing for suspected glomerular kidney diseases (persistent microscopic haematuria and/or albuminuria or proteinuria in the absence of known causes, steroid-resistant primary nephrotic syndrome, apparent familial IgA nephropathy, or chronic kidney disease with no apparent cause), and interpret genetic test results; create workflows for patient referral, evaluation and management, and discuss genetic results at regular genomic board meetings. The outcomes are acceptance, appropriateness and adoption among patients and nephrologists, utility (proportion of patients who received genetic testing and have a confirmed diagnosis of genetic glomerular disease), and cost-effectiveness.

CONCLUSION

This study will create and evaluate a nephrologist-led genetic service, develop an efficient variant curation process, and inform future recommendations on the optimal referral and genetic testing strategy for monogenic glomerular disease in Singapore. This will facilitate the future mainstreaming of genetic testing that will enable precision medicine in kidney care.

Genotype-First Analysis in an Unselected Health System-Based Population and Phenotypic Severity of COL4A5 Variants

Background:

Our knowledge of X-linked Alport Syndrome comes mostly from selected cohorts with more severe disease.

Methods:

We examined the phenotypic spectrum of X-linked Alport Syndrome in males and females with a genotype-based approach using data from the Geisinger MyCode DiscovEHR study, an unselected health system-based cohort with exome sequencing and electronic health records. Patients with COL4A5 variants reported as pathogenic or likely pathogenic in ClinVar, or protein-truncating variants, were each matched with up to 5 controls without COL4A3/4/5 variants by sociodemographics, diabetes diagnosis, and year of first outpatient encounter. Phenotypes examined included dipstick hematuria, bilateral sensorineural hearing loss, proteinuria, decreased estimated glomerular filtration rate, and kidney failure.

Results:

Out of 170,856 patients, there were 29 hemizygous males (mean age 52 y [SD 20]) and 55 heterozygous females (mean age 59 y [SD 19]) with a pathogenic/likely pathogenic COL4A5 variant, including 48 with the hypomorphic variant p.Gly624Asp. Overall, penetrance (having any Alport Syndrome phenotypic feature) was highest for non-p.Gly624Asp variants (males: 94%, females: 85%), intermediate for p.Gly624Asp (males: 77%, females: 69%), compared to controls (males: 32%; females: 50%). The proportion with kidney failure was highest for males with non-p.Gly624Asp variants (44%), intermediate for males with p.Gly624Asp (15%) and females with non-p.Gly624Asp variants (10%), compared to controls (males: 3%, females 2%). Only 47% of individuals with COL4A5 had completed albuminuria screening, and a minority were taking renin-angiotensin aldosterone system inhibitors. Only 38% of males and 16% of females had a known diagnosis of Alport Syndrome or thin basement membrane disease.

Conclusions:

Using a genotype-first approach, we show that men and women with X-linked Alport Syndrome are at higher risk of related phenotypic features with a wider spectrum of severity than has been described previously and variability by genotype.

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.

Genotype-first analysis in an unselected health system-based population reveals variable phenotypic severity of COL4A5 variants

Introduction

Our knowledge of X-linked Alport Syndrome [AS] comes mostly from selected cohorts with more severe disease.

Methods

We examined the phenotypic spectrum of X-linked AS in males and females with a genotype-based approach using data from the Geisinger MyCode DiscovEHR study, an unselected health system-based cohort with exome sequencing and electronic health records. Patients with COL4A5 variants reported as pathogenic (P) or likely pathogenic (LP) in ClinVar, or protein-truncating variants (PTVs), were each matched with up to 5 controls without COL4A3/4/5 variants by sociodemographics, diabetes diagnosis, and year of first outpatient encounter. AS-related phenotypes included dipstick hematuria, bilateral sensorineural hearing loss (BSHL), proteinuria, decreased eGFR, and ESKD.

Results

Out of 170,856 patients, there were 29 hemizygous males (mean age 52.0 y [SD 20.0]) and 55 heterozygous females (mean age 59.3 y [SD 18.8]) with a COL4A5 P/LP variant, including 48 with the hypomorphic variant p.Gly624Asp. Overall, penetrance (having any AS phenotypic feature) was highest for non-p.Gly624Asp P/LP variants (males: 94%, females: 85%), intermediate for p.Gly624Asp (males: 77%, females: 69%), compared to controls (males: 32%; females: 50%). The proportion with ESKD was highest for males with P/LP variants (44%), intermediate for males with p.Gly624Asp (15%) and females with P/LP variants (10%), compared to controls (males: 3%, females 2%). Only 47% of individuals with COL4A5 had completed albuminuria screening, and a minority were taking renin-angiotensin aldosterone system (RAAS) inhibitors. Only 38% of males and 16% of females had a known diagnosis of Alport syndrome or thin basement membrane disease.

Conclusion

In an unselected cohort, we show increased risks of AS-related phenotypes in men and women compared to matched controls, while showing a wider spectrum of severity than has been described previously and variability by genotype. Future studies are needed to determine whether early genetic diagnosis can improve outcomes in Alport Syndrome.

Alport Syndrome: Clinical Utility of Early Genetic Diagnosis in Children

Alport syndrome (AS) is a hereditary glomerulopathy due to pathogenic variants in COL4A3, COL4A4, and COL4A5. Treatment with Renin-Angiotensin-Aldosterone System (RAAS) inhibitors can delay progression to end stage renal disease (ESRD). From 2018 until today, we performed Whole Exome Sequencing (WES) in 19 patients with AS phenotype with or without positive family history. Fourteen of these patients were children. Genetic testing was extended to family members at risk. All patients received a genetic diagnosis of AS: five X-linked AS (XLAS) males, five X-linked AS (XLAS) females, six autosomal dominant AS (ADAS), and one autosomal recessive AS (ARAS). After cascade screening four XLAS males and eight XLAS females, six ADAS and three ARAS heterozygotes were added to our initial results. Fifteen patients were eligible to start treatment with RAAS inhibitors after their diagnosis. All XLAS female patients, ARAS heterozygotes, and ADAS have been advised to be followed up, so that therapeutic intervention can begin in the presence of microalbuminuria. Genetic diagnosis of AS ensures early therapeutic intervention and appropriate follow up to delay progression to chronic kidney disease, especially in thet pediatric population.

Aberrant Splicing of COL4A5 Intronic Variant Contribute to the Pathogenesis of X-Linked Alport Syndrome: A Case Series

Introduction

X-linked Alport syndrome (XLAS) is caused by pathogenic variants in COL4A5 which lead to abnormalities of the glomerular basement membrane (GBM) structural and is characterized by progressive kidney disease, hearing loss, and ocular abnormalities. The aim of this study was to identify gene mutations in a Chinese family with XLAS by whole-exome sequencing (WES) and verified the pathogenicity of the mutation in vitro experiments.

Case Presentation

A five-generation pedigree with a total of 49 family members originating from Hainan province of China was investigated in this study. The proband was a 23-year-old male who developed microscopic hematuria, proteinuria and end-stage kidney disease (ESKD) at age 17. WES identified a novel splicing mutation c.321+5G>A of COL4A5, which cause exon skip. Further co-segregation analysis confirmed that this mutation exists in relatives who had renal abnormalities using Sanger sequencing. According to American College of Medical Genetics and Genomics guidelines (ACMG), the mutation was determined to be of uncertain significance (VUS). In vitro splicing experiments have shown that the COL4A5 variant induces aberrant mRNA splicing and transcript deletion.

Conclusion

We identified a novel intronic COL4A5 pathogenic mutation (c.321+5G>A) in a Chinese XLAS family and described the phenotypes of affected relatives. This study expands the mutation spectrum of COL4A5 gene in XLAS and demonstrates the importance of gene screening for AS.

A Novel COL4A5 Pathogenic Variant Joins the Dots in a Family with a Synchronous Diagnosis of Alport Syndrome and Polycystic Kidney Disease

Alport Syndrome (AS) is the most common genetic glomerular disease, and it is caused by COL4A3, COL4A4, and COL4A5 pathogenic variants. The classic phenotypic spectrum associated with AS ranges from isolated hematuria to chronic kidney disease (CKD) with extrarenal abnormalities. Atypical presentation of the disorder is possible, and it can mislead the diagnosis. Polycystic kidney disease (PKD), which is most frequently associated with Autosomal Dominant PKD (ADPKD) due to PKD1 and PKD2 heterozygous variants, is emerging as a possible clinical manifestation in COL4A3-A5 patients. We describe a COL4A5 novel familial frameshift variant (NM_000495.5: c.1095dup p.(Leu366ValfsTer45)), which was associated with AS and PKD in the hemizygous proband, as well as with PKD, IgA glomerulonephritis and focal segmental glomerulosclerosis (FSGS) in the heterozygous mother. Establishing the diagnosis of AS can sometimes be difficult, especially in the context of misleading family history and atypical phenotypic features. This case study supports the emerging genotypic and phenotypic heterogeneity in COL4A3-A5-associated disorders, as well as the recently described association between PKD and collagen type IV (Col4) defects. We highlight the importance of the accurate phenotyping of all family members and the relevance of next-generation sequencing in the differential diagnosis of hereditary kidney disease.

Alport Syndrome

Alport syndrome (AS) is characterized by progressive kidney failure, hematuria, sensorineural hearing loss, and ocular abnormalities. Pathogenic variants in the COL4A3-5 genes result in a defective deposition of the collagen IV α3α4α5 protomers in the basement membranes of the glomerulus in the kidney, the cochlea in the ear and the cornea, lens capsule and retina in the eye. The presence of a large variety of COL4A3-5 gene(s) pathogenetic variants irrespective of the mode of inheritance (X-linked, autosomal recessive, autosomal dominant, or digenic) with and without syndromic features is better defined as the "Alport spectrum disorder", and represents the most common cause of genetic kidney disease and the second most common cause of genetic kidney failure. The clinical course and prognosis of individuals with AS is highly variable. It is influenced by gender, mode of inheritance, affected gene(s), type of genetic mutation, and genetic modifiers. This review article will discuss the epidemiology, classification, pathogenesis, diagnosis, clinical course with genotype-phenotype correlations, and current and upcoming treatment of patients with AS. It will also review current recommendations with respect to when to evaluate for hearing loss or ophthalmologic abnormalities.

Alport syndrome and Alport kidney diseases - elucidating the disease spectrum

PURPOSE OF REVIEW

With the latest classification, variants in three collagen IV genes, COL4A3 , COL4A4 , and COL4A5 , represent the most prevalent genetic kidney disease in humans, exhibiting diverse, complex, and inconsistent clinical manifestations. This review breaks down the disease spectrum and genotype-phenotype correlations of kidney diseases linked to genetic variants in these genes and distinguishes "classic" Alport syndrome (AS) from the less severe nonsyndromic genetically related nephropathies that we suggest be called "Alport kidney diseases".

RECENT FINDINGS

Several research studies have focused on the genotype-phenotype correlation under the latest classification scheme of AS. The historic diagnoses of "benign familial hematuria" and "thin basement membrane nephropathy" linked to heterozygous variants in COL4A3 or COL4A4 are suggested to be obsolete, but instead classified as autosomal AS by recent expert consensus due to a significant risk of disease progression.

SUMMARY

The concept of Alport kidney disease extends beyond classic AS. Patients carrying pathogenic variants in any one of the COL4A3/A4/A5 genes can have variable phenotypes ranging from completely normal/clinically unrecognizable, hematuria without or with proteinuria, or progression to chronic kidney disease and kidney failure, depending on sex, genotype, and interplays of other genetic as well as environmental factors.

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.

Dual inhibition of the endothelin and angiotensin receptor ameliorates renal and inner ear pathologies in Alport mice

Alport syndrome (AS), a type IV collagen disorder, leads to glomerular disease and, in some patients, hearing loss. AS is treated with inhibitors of the renin-angiotensin system; however, a need exists for novel therapies, especially those addressing both major pathologies. Sparsentan is a single-molecule dual endothelin type-A and angiotensin II type 1 receptor antagonist (DEARA) under clinical development for focal segmental glomerulosclerosis and IgA nephropathy. We report the ability of sparsentan to ameliorate both renal and inner ear pathologies in an autosomal-recessive Alport mouse model. Sparsentan significantly delayed onset of glomerulosclerosis, interstitial fibrosis, proteinuria, and glomerular filtration rate decline. Sparsentan attenuated glomerular basement membrane defects, blunted mesangial filopodial invasion into the glomerular capillaries, increased lifespan more than losartan, and lessened changes in profibrotic/pro-inflammatory gene pathways in both the glomerular and the renal cortical compartments. Notably, treatment with sparsentan, but not losartan, prevented accumulation of extracellular matrix in the strial capillary basement membranes in the inner ear and reduced susceptibility to hearing loss. Improvements in lifespan and in renal and strial pathology were observed even when sparsentan was initiated after development of renal pathologies. These findings suggest that sparsentan may address both renal and hearing pathologies in Alport syndrome patients. © 2023 Travere Therapeutics, Inc and The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

What patients want to know about genetic testing for kidney disease

Previously, genetic kidney disease was often recognised when family members shared clinical features. Now, many genetic kidney diseases are diagnosed when testing demonstrates a pathogenic variant in a gene associated with the disease. Detection of a genetic variant also identifies the mode of inheritance, and suggests family members at risk. The genetic diagnosis has additional advantages for patients and their doctors even when no specific treatment is available since it often indicates likely complications in other organs, the clinical course, and management strategies. Generally, informed consent is required for genetic testing because the result provides "certainty" with implications for the patient, and their family, and possibly for employment, and for life and medical insurance, as well as having social, ethical, and financial consequences. Patients want to be provided with a copy of their genetic test result in a format that is comprehensible and to have the result explained. Their at-risk family members should be sought out and offered genetic testing too. Patients who allow the sharing of their anonymised results in registries help advance everyone's understanding of these diseases and expedite a diagnosis in other families. Patient Support Groups not only help normalise the disease but also educate patients, and update them on recent advances and new treatments. Some registries encourage patients to themselves submit their genetic variants, clinical features and response to treatment. More and more often, patients may volunteer for clinical trials of novel therapies including some that depend on a genetic diagnosis or variant type.

Current and Future Therapeutical Options in Alport Syndrome

Alport syndrome (AS) is a hereditary kidney disease caused by pathogenic variants in COL4A3 and COL4A4 genes with autosomal recessive or autosomal dominant transmission or in the COL4A5 gene with X-linked inheritance. Digenic inheritance was also described. Clinically it is associated with microscopic hematuria, followed by proteinuria and chronic renal insufficiency with end-stage renal disease in young adults. Nowadays, there is no curative treatment available. The inhibitors of RAS (renin-angiotensin system) since childhood slow the progression of the disease. Sodium-glucose cotransporter-2 inhibitors seem to be promising drugs from DAPA-CKD (dapagliflozin-chronic kidney disease) study, but only a limited number of patients with Alport syndrome was included. Endothelin type A receptor and angiotensin II type 1 receptor combined inhibitors, and lipid-lowering agents are used in ongoing studies in patients with AS and focal segmental glomerulosclerosis (FSGS). Hydroxychloroquine in AS is studied in a clinical trial in China. Molecular genetic diagnosis of AS is crucial not only for prognosis prediction but also for future therapeutic options. Different types of mutations will require various types of gene, RNA, or protein therapy to improve the function, the of final protein product.

Alport Syndrome: Clinical Spectrum and Therapeutic Advances

Alport syndrome is a hereditary disorder characterized by kidney disease, ocular abnormalities, and sensorineural hearing loss. Work in understanding the cause of Alport syndrome and the molecular composition of the glomerular basement membrane ultimately led to the identification of COL4A3, COL4A4 (both on chromosome 2q36), and COL4A5 (chromosome Xq22), encoding the α3, α4, and α5 chains of type IV collagen, as the responsible genes. Subsequent studies suggested that autosomal recessive Alport syndrome and males with X-linked Alport syndrome have more severe disease, whereas autosomal dominant Alport syndrome and females with X-linked Alport syndrome have more variability. Variant type is also influential-protein-truncating variants in autosomal recessive Alport syndrome or males with X-linked Alport syndrome often present with severe symptoms, characterized by kidney failure, extrarenal manifestations, and lack of the α3-α4-α5(IV) network. By contrast, mild-moderate forms from missense variants display α3-α4-α5(IV) in the glomerular basement membrane and are associated with protracted kidney involvement without extrarenal manifestations. Regardless of type, therapeutic intervention for kidney involvement is focused on early initiation of angiotensin-converting enzyme inhibitors. There are several therapies under investigation including sodium/glucose cotransporter 2 inhibitors, aminoglycoside analogs, endothelin type A antagonists, lipid-modifying drugs, and hydroxychloroquine, although targeting the underlying defect through gene therapy remains in preclinical stages.

Incorporation of Genetic Studies in the Kidney Transplant Evaluation Clinic: The Value of a Multidisciplinary Approach

BACKGROUND

Recent studies identified underlying genetic causes in a proportion of patients with various forms of kidney disease. In particular, genetic testing reclassified some focal segmental glomerulosclerosis (FSGS) cases into collagen type 4 (COL4)-related nephropathy. This knowledge has major implications for counseling prospective transplant recipients about recurrence risk and screening biologically related donors. We describe our experience incorporating genetic testing in our kidney transplant multidisciplinary practice.

METHODS

Patients' DNA was analyzed using whole exome sequencing for a comprehensive kidney gene panel encompassing 344 genes associated with kidney diseases and candidate genes highly expressed in the kidney. Results were correlated with phenotype by a multidisciplinary committee of nephrologists, renal pathologists, geneticists, and genetic counselors. Between October 2018 and July 2020, 30 recipient and 5 donor candidates completed testing.

RESULTS

Among recipient candidates, 24 (80%) carried the diagnosis of FSGS, 2 (6.7%) tubulointerstitial nephritis, and 1 (3.3%) nephrolithiasis, and 3 (10%) had an unknown cause of kidney disease. The yield for pathogenic/likely pathogenic variants was 43.3%, with majority being COL4 variants (53.8%). Among those with FSGS diagnosis, the yield was 10 of 24 (41.6%), with 29% reclassified into a COL4-related nephropathy. Family history of kidney disease was the only clinical characteristic difference between recipients with positive and negative results (76.9 versus 29.4%; P = 0.025). One of 5 donors tested positive for a pathogenic/likely pathogenic variant and was excluded from donation.

CONCLUSIONS

We conclude that thoughtful use of genetic testing can be valuable for kidney donor selection and transplant recipient management.

Approach to genetic testing to optimize the safety of living donor transplantation in Alport syndrome spectrum

Alport syndrome spectrum can be considered as a group of genetic diseases affecting the major basement membrane collagen type IV network in various organs including the ear, eye, and kidney. The living donor candidate evaluation is an ever-changing landscape. Recently, next-generation sequence (NGS) panels have become readily available and provide opportunities to genetically screen recipient and donor candidates for collagen network gene variants. In this review, our aim is to provide a comprehensive update on the role of genetic testing for the evaluation of potential living kidney donors to kidney candidates with Alport syndrome spectrum. We examine the utility of genetic testing in the evaluation of potential donors for recipients with Alport syndrome spectrum, and discuss risks and unresolved challenges. Suggested algorithms in the context of related and unrelated donation are offered. In contemporary practice, an approach to the evaluation of living donor candidates for transplant candidates with Alport syndrome spectrum can incorporate genetic testing in algorithms tailored for donor-recipient relationship status. Ongoing research is needed to inform optimal practice.

Novel Therapies for Alport Syndrome

Alport syndrome (AS) is a hereditary kidney disease associated with proteinuria, hematuria and progressive kidney failure. It is characterized by a defective glomerular basement membrane caused by mutations in type IV collagen genes COL4A3/A4/A5 which result in defective type IV collagen α3, α4, or α5 chains, respectively. Alport syndrome has three different patterns of inheritance: X-linked, autosomal and digenic. In a study of CKD of unknown etiology type IV collagen gene mutations accounted for the majority of the cases of hereditary glomerulopathies which suggests that AS is often underrecognized. The natural history and prognosis in patients with AS is variable and is determined by genetics and environmental factors. At present, no preventive or curative therapies exist for AS. Current treatment includes the use of renin-angiotensin-aldosterone system inhibitors which slow progression of kidney disease and prolong life expectancy. Ramipril was found in retrospective studies to delay the onset of ESKD and was recently demonstrated to be safe and effective in children and adolescents, supporting that early initiation of Renin Angiotensin Aldosterone System (RAAS) blockade is very important. Mineralocorticoid receptor blockers might be favorable for patients who develop "aldosterone breakthrough." While the DAPA-CKD trial suggests a beneficial effect of SGLT2 inhibitors in CKD of non-metabolic origin, only a handful of patients had Alport in this cohort, and therefore conclusions can't be extrapolated for the treatment of AS with SGLT2 inhibitors. Advances in our understanding on the pathogenesis of Alport syndrome has culminated in the development of innovative therapeutic approaches that are currently under investigation. We will provide a brief overview of novel therapeutic targets to prevent progression of kidney disease in AS. Our review will include bardoxolone methyl, an oral NRf2 activator; lademirsen, an anti-miRNA-21 molecule; sparsentan, dual endothelin type A receptor (ETAR) and angiotensin 1 receptor inhibitor; atrasentan, oral selective ETAR inhibitor; lipid-modifying agents, including cholesterol efflux transporter ATP-binding cassette A1 (ABCA1) inducers, discoidin domain receptor 1 (DDR1) inhibitors and osteopontin blocking agents; the antimalarial drug hydroxychloroquine; the antiglycemic drug metformin and the active vitamin D analog paricalcitol. Future genomic therapeutic strategies such as chaperone therapy, genome editing and stem cell therapy will also be discussed.

Genotype-Phenotype Correlations for Pathogenic COL4A3–COL4A5 Variants in X-Linked, Autosomal Recessive, and Autosomal Dominant Alport Syndrome

Alport syndrome is inherited as an X-linked (XL), autosomal recessive (AR), or autosomal dominant (AD) disease, where pathogenic COL4A3 – COL4A5 variants affect the basement membrane collagen IV α3α4α5 network. About 50% of pathogenic variants in each gene (major rearrangements and large deletions in 15%, truncating variants in 20%, splicing changes in 15%) are associated with “severe” disease with earlier onset kidney failure, and hearing loss and ocular abnormalities in males with XL inheritance and in males and females with AR disease. Severe variants are also associated with early proteinuria which is itself a risk factor for kidney failure. The other half of pathogenic variants are missense changes which are mainly Gly substitutions. These are generally associated with later onset kidney failure, hearing loss, and less often with major ocular abnormalities. Further determinants of severity for missense variants for XL disease in males, and in AD disease, include Gly versus non-Gly substitutions; increased distance from a non-collagenous interruption or terminus; and Gly substitutions with a more (Arg, Glu, Asp, Val, and Trp) or less disruptive (Ala, Ser, and Cys) residue. Understanding genotype-phenotype correlations in Alport syndrome is important because they help predict the likely age at kidney failure, and the need for early and aggressive management with renin-angiotensin system blockade and other therapies. Genotype-phenotype correlations also help standardize patients with Alport syndrome undergoing trials of clinical treatment. It is unclear whether severe variants predispose more often to kidney cysts or coincidental IgA glomerulonephritis which are recognized increasingly in COL4A3-, COL4A4 - and COL4A5-associated disease.

What the Adult Nephrologist Should Know About Alport Syndrome

Recent trends in the diagnosis, treatment, and classification of collagen IV-associated kidney disease are likely to result in increasing numbers of people in adult nephrology practices who have a confirmed diagnosis of Alport syndrome. These trends include the increasing use of genetic testing in the diagnostic evaluation of people with hematuria, focal segmental glomerulosclerosis, and chronic kidney disease of unknown etiology; early treatment with inhibitors of the renin-angiotensin-aldosterone system to delay kidney failure; and application of an expanded definition of Alport syndrome based on genotype rather than phenotype. This commentary discusses these trends and their implications for the adult nephrologist.

Identification of Four Novel COL4A5 Variants and Detection of Splicing Abnormalities in Three Chinese X-Linked Alport Syndrome Families

Chronic renal disease associated with X-linked Alport syndrome (XLAS) is relatively rare. However, due to the lack of specificity in the pathologic and clinical manifestations of the disease, it is easy to be misdiagnosed. In this study, we included three Chinese families with XLAS and used targeted NGS to find gene variants. In family X1, the 36-year-old male proband had hematuria, massive proteinuria, sensorineural deafness and ESRD at 33. In silico prediction showed the novel c.1424-4C > G variant reduced the score of the normal 3’ splice site from 0.47 to 0.00 (according to BDGP). Transcriptional analysis from his peripheral blood cells indicated that it caused the insertion of an amino acid [p.(Lys474_Gly475insVal)]. In family X2, the proband was a 32-year-old male, who had hematuria, proteinuria, hypertension, hearing loss and progressed into ESRD at 30 years. He carried a novel missense variant c.2777G > T p.(Gly926Val). In family X3, the proband, a 16-year-old male, had hematuria, massive proteinuria, sensorineural deafness and ESRD; the results of renal pathological findings were consistent with AS. He carried a novel variant c.4529-2A > T, so did his mother with ESRD and probable XLAS. Bioinformatic analysis with BDGP showed that it abolished the acceptor site from 0.83 to 0.00. RT-PCR analysis from his kidney tissue indicated that it caused exon 50 skipping and exon 50 skipping along with inserting a cryptic exon derived from intron 49 p.[Gly1510Aspfs*11, Gly1510Alafs*35]. Another novel missense variant c.1552G > A p.(Gly518Arg) was identified in his mother and his aunt. No skewed X-chromosome inactivation was involved in these two female patients. In conclusion, four novel variants in COL4A5 were identified and transcriptional analysis is essential to investigate the pathogenicity of intronic variants. Thus we found a rare event in a female patient with XLAS caused by two COL4A5 variants in trans.

Multidisciplinary approaches for elucidating genetics and molecular pathogenesis of urinary tract malformations

Advances in clinical diagnostics and molecular tools have improved our understanding of the genetically heterogeneous causes underlying congenital anomalies of kidney and urinary tract (CAKUT). However, despite a sharp incline of CAKUT reports in the literature within the past 2 decades, there remains a plateau in the genetic diagnostic yield that is disproportionate to the accelerated ability to generate robust genome-wide data. Explanations for this observation include (i) diverse inheritance patterns with incomplete penetrance and variable expressivity, (ii) rarity of single-gene drivers such that large sample sizes are required to meet the burden of proof, and (iii) multigene interactions that might produce either intra- (e.g., copy number variants) or inter- (e.g., effects in trans) locus effects. These challenges present an opportunity for the community to implement innovative genetic and molecular avenues to explain the missing heritability and to better elucidate the mechanisms that underscore CAKUT. Here, we review recent multidisciplinary approaches at the intersection of genetics, genomics, in vivo modeling, and in vitro systems toward refining a blueprint for overcoming the diagnostic hurdles that are pervasive in urinary tract malformation cohorts. These approaches will not only benefit clinical management by reducing age at molecular diagnosis and prompting early evaluation for comorbid features but will also serve as a springboard for therapeutic development.

X-Linked Kidney Disorders in Women

A number of genes that cause inherited kidney disorders reside on the X chromosome. Given that males have only a single active X chromosome, these disorders clinically manifest primarily in men and boys. However, phenotypes in female carriers of X-linked kidney conditions are becoming more and more recognized. This article reviews the biology of X inactivation as well as the kidney phenotype in women and girls with a number of X-linked kidney disorders including Alport syndrome, Fabry disease, nephrogenic diabetes insipidus, X-linked hypophosphatemic rickets, Dent disease, and Lowe syndrome.

Population-based studies reveal an additive role of type IV collagen variants in hematuria and albuminuria

Specific variants in genes that encode the α3α4α5 chains of type IV collagen cause Alport syndrome (AS), which encompass a clinical spectrum from isolated hematuria to multisystem disease affecting sight, hearing and kidney function. The commonest form is X-linked Alport syndrome (XLAS; COL4A5) with autosomal AS (COL4A3 and COL4A4) comprising a minority of cases. While historic data estimates the frequency of AS at 1:5000-10,000, recent population-based genetic studies suggest the prevalence is considerably higher. Genome-wide association studies (GWAS) have been performed in the Icelandic (deCODE) and UK (UK Biobank) populations, demonstrating an association of type IV collagen gene variants with AS relevant kidney traits. In the Icelandic population, 1 in 600 carries a 2.5-kb COL4A3 coding deletion or a COL4A3 missense variant (rs200287952[A], Gly695Arg), both of which are strongly associated with hematuria and albuminuria (P values = 1.9 × 10^-5 to 2.5 × 10^-20). In the UK Biobank, COL4A4 rs35138315 (Ser969X; carrier frequency 0.13%) is strongly associated with both hematuria and albuminuria (P = 1.5 × 10^-73). Thus, the frequency for autosomal AS is 5-16 times higher than the historic prevalence of all forms of the disorder. Furthermore, COL4A4 rs3518315 (Ser969X) is also a reported founder mutation in families with autosomal dominant focal and segmental glomerulosclerosis and autosomal recessive forms of AS. This supports an additive mode of inheritance for specific variants, wherein a number of copies of a mutation influence disease severity in a cumulative fashion. These studies did not include the X chromosome, excluding analysis of COL4A5, which represents an area for future study.

Guidelines for Genetic Testing and Management of Alport Syndrome

Genetic testing for pathogenic COL4A3-5 variants is usually undertaken to investigate the cause of persistent hematuria, especially with a family history of hematuria or kidney function impairment. Alport syndrome experts now advocate genetic testing for persistent hematuria, even when a heterozygous pathogenic COL4A3 or COL4A4 is suspected, and cascade testing of their first-degree family members because of their risk of impaired kidney function. The experts recommend too that COL4A3 or COL4A4 heterozygotes do not act as kidney donors. Testing for variants in the COL4A3-COL4A5 genes should also be performed for persistent proteinuria and steroid-resistant nephrotic syndrome due to suspected inherited FSGS and for familial IgA glomerulonephritis and kidney failure of unknown cause.

The basement membrane in the cross-roads between the lung and kidney

The basement membrane (BM) is a specialized layer of extracellular matrix components that plays a central role in maintaining lung and kidney functions. Although the composition of the BM is usually tissue specific, the lung and the kidney preferentially use similar BM components. Unsurprisingly, diseases with BM defects often have severe pulmonary or renal manifestations, sometimes both. Excessive remodeling of the BM, which is a hallmark of both inflammatory and fibrosing diseases in the lung and the kidney, can lead to the release of BM-derived matrikines, proteolytic fragments with distinct biological functions. These matrikines can then influence disease activity at the site of liberation. However, they are also released to the circulation, where they can directly affect the vascular endothelium or target other organs, leading to extrapulmonary or extrarenal manifestations. In this review, we will summarize the current knowledge of the composition and function of the BM and its matrikines in health and disease, both in the lung and in the kidney. By comparison, we will highlight, why the BM and its matrikines may be central in establishing a renal-pulmonary interaction axis.

Clinical Manifestations of Alport Syndrome-Diffuse Leiomyomatosis Patients With Contiguous Gene Deletions in COL4A6 and COL4A5

Alport syndrome-diffuse leiomyomatosis is a rare type of X-linked Alport syndrome resulting from contiguous deletions of 5′ exons of COL4A5 and COL4A6. Studies have suggested that the occurrence of diffuse leiomyomatosis is associated with the characteristic localisation of the COL4A6 gene deletion break point. An electronic database was searched for all studies accessing AS-DL to analyze the clinical characteristics, gene deletion break points of patients with AS-DL, and the pathogenesis of AS-DL. It was found that the proportion of de novo mutations of AS-DL was significantly higher in female probands than male probands (78 vs. 44%). Female patients with AS-DL had a mild clinical presentation. The incidence of proteinuria and ocular abnormalities was much lower in female probands than in male probands, and there was generally no sensorineural hearing loss or chronic kidney disease (CKD), which progressed to Stage 3 in female probands. The contiguous deletion of the 5' exons of COL4A5 and COL4A6, with the break point within the intron 3 of COL4A6, was the critical genetic defect causing AS-DL. However, the pathogenesis of characteristic deletion of COL4A6 that contributes to diffuse leiomyomatosis is still unknown. In addition, characteristic contiguous deletion of COL4A5 and COL4A6 genes in AS-DL may be related to transposed elements (TEs).

Functional assessment of a novel COL4A5 splicing site variant in a Chinese X-linked Alport syndrome family

Background

Chronic kidney disease caused by X-linked Alport syndrome (XLAS) is relatively rare. However, due to the nonspecific pathologic and clinical manifestations of this disease, it is easily misdiagnosed. Genetic testing is crucial in identifying suspected cases. In addition, the results of genetic testing are an important indicator of patient prognosis. This study demonstrated a novel pathogenic COL4A5 splicing site variant in a Chinese family with XLAS.

Methods

Targeted next generation sequencing (NGS) was performed to identify the gene variant in the family members, and the gene mutation site was confirmed by Sanger sequencing. We then further analyzed the consequences of this gene mutation on the translated protein of this variant using in silico and in vitro approaches.

Results

A novel splice region variant, c.1033-2(IVS 18) A>G, in COL4A5 intron 18 was identified in the affected family members. Sanger sequencing confirmed that this variant is segregated with disease. In silico analysis, this variant led to frame-shift and premature termination on the translation of the nucleic acid, and this result was verified by RNA splicing analysis in a cell model. Unexpectedly, we still observed positive immunohistology staining of collagen IV α5 in the glomerular basement membrane (GBM) of the index patient, which implied that another potential transcription or translation mechanism skipping the mutated site might exist.

Conclusions

Our present finding expands the mutational spectrum for the COL4A5 gene associated with XLAS and highlights the genotype-phenotype correlations in this disease.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Alport Syndrome: A Primer for Clinicians

Alport syndrome is a genetic and hereditary disease, caused by mutations in the type IV collagen genes COL4A3, COL4A4 and COL4A5, that affects the glomerular basement membrane of the kidney. It is a rare disease with an underestimated prevalence. Genetic analysis of population cohorts has revealed that it is the second most common inherited kidney disease after polycystic kidney disease. Renal involvement is the main manifestation, although it may have associated extrarenal manifestations such as hearing loss or ocular problems. The degree of expression of the disease changes according to the gene affected and other factors, known or yet to be known. The pathophysiology is not yet fully understood, although some receptors, pathways or molecules are known to be linked to the disease. There is also no specific treatment for Alport syndrome; the most commonly used are renin–angiotensin–aldosterone system inhibitors. In recent years, diagnosis has come a long way, thanks to advances in DNA sequencing technologies such as next-generation sequencing (NGS). Further research at the genetic and molecular levels in the future will complete the partial vision of the pathophysiological mechanism that we have, and will allow us to better understand what is happening and how to solve it.

Pathogenic Variants in the Genes Affected in Alport Syndrome (COL4A3-COL4A5) and Their Association With Other Kidney Conditions: A Review

Massively Parallel Sequencing identifies pathogenic variants in the genes affected in Alport syndrome (COL4A3 - COL4A5) in up to 30 % of individuals with focal and segmental glomerulosclerosis (FSGS), 10 % of those with kidney failure of unknown cause and 20 % with familial IgA glomerulonephritis. FSGS associated with COL4A3 - COL4A5 variants is usually present by kidney failure onset and may develop because the abnormal glomerular membranes result in podocyte loss and secondary hyperfiltration. The association of COL4A3 - COL4A5 variants with kidney failure or IgA glomerulonephritis may be coincidental and not pathogenic. However, since some of these variants occur more often than they should by chance, some may be pathogenic. COL4A3 - COL4A5 variants are sometimes also found in cystic kidney diseases after autosomal dominant polycystic kidney disease (ADPKD) has been excluded. COL4A3 - COL4A5 variants should be suspected in individuals with FSGS, kidney failure of unknown cause, or familial IgA glomerulonephritis, especially where there is persistent haematuria, and a family history of haematuria or kidney failure.

Multidisciplinary Management of Alport Syndrome: Current Perspectives

Alport syndrome is a multisystem disorder that universally affects the kidney and frequently involves the inner ear and the eye. Over the course of a lifetime, addressing the health care needs of a person with Alport syndrome and their family entails the services of primary providers, nephrologists, genetic counselors, audiologists, ophthalmologists, transplant physicians, kidney dieticians, and social workers as well as other healthcare professionals. This article attempts to provide context and guidance regarding the multidisciplinary care of Alport syndrome based on the natural history of the condition.

Clinical and Genetic Features of Autosomal Dominant Alport Syndrome: A Cohort Study

RATIONALE & OBJECTIVE

Alport syndrome is a common genetic kidney disease accounting for approximately 2% of patients receiving kidney replacement therapy (KRT). It is caused by pathogenic variants in the gene COL4A3, COL4A4, or COL4A5. The aim of this study was to evaluate the clinical and genetic spectrum of patients with autosomal dominant Alport syndrome (ADAS).

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

82 families (252 patients) with ADAS were studied. Clinical, genetic, laboratory, and pathology data were collected.

OBSERVATIONS

A pathogenic DNA variant in COL4A3 was identified in 107 patients (35 families), whereas 133 harbored a pathogenic variant in COL4A4 (43 families). Digenic/complex inheritance was observed in 12 patients. Overall, the median kidney survival was 67 (95% CI, 58-73) years, without significant differences across sex (P=0.8), causative genes (P=0.6), or type of variant (P=0.9). Microhematuria was the most common kidney manifestation (92.1%), and extrarenal features were rare. Findings on kidney biopsies ranged from normal to focal segmental glomerulosclerosis. The slope of estimated glomerular filtration rate change was-1.46 (-1.66 to-1.26) mL/min/1.73m² per year for the overall group, with no significant differences between ADAS genes (P=0.2).

LIMITATIONS

The relatively small size of this series from a single country, potentially limiting generalizability.

CONCLUSIONS

Patients with ADAS have a wide spectrum of clinical presentations, ranging from asymptomatic to kidney failure, a pattern not clearly related to the causative gene or type of variant. The diversity of ADAS phenotypes contributes to its underdiagnosis in clinical practice.

Long-term outcome among females with Alport syndrome from a single pediatric center

BACKGROUND

Alport syndrome (AS) is a multisystem condition which can result in progressive kidney disease, hearing loss, and ocular changes. X-linked inheritance is observed in 85% of affected individuals. As a result, most prior studies have focused on males. Girls with AS can also be symptomatic although historically thought to have few clinical manifestations in childhood. The objective of the study was to describe the clinical presentation and course of females with AS.

METHODS

A single-center retrospective study of all young females with AS between January 1, 1987, and May 20, 2019. Subjects were identified using ICD-9/10 diagnosis codes for AS, familial hematuria, or nephritis. Clinical data were extracted by retrospective chart review.

RESULTS

Thirty-six female patients were included in the analysis. Mean age at presentation was 5.58 ± 3.0 years, and mean follow-up was 5.9 ± 3.9 years. Twenty-nine patients (80%) had a family history of AS. At end of the follow-up period, gross hematuria was observed in 15 patients (42%), 20 (56%) developed proteinuria, and 2 (6.7%) had an estimated glomerular filtration rate (eGFR) < 90 ml/min/1.73m² with one patient developing stage 5 chronic kidney disease. Four of the twenty-seven (14.8%) who underwent audiologic testing had an abnormal exam.

CONCLUSIONS

Known family histories of AS or gross hematuria were the most common reasons for the initial presentation in our cohort. Development of proteinuria, eGFR < 90 ml/min/1.73m², and abnormal audiology exam are not exceptional findings, suggesting that close monitoring of young females into adulthood is warranted.

Clinical practice recommendations for the diagnosis and management of Alport syndrome in children, adolescents, and young adults-an update for 2020

In 2013, we published a set of clinical practice recommendations for the treatment of Alport syndrome in this journal. We recommended delaying the initiation of angiotensin-converting enzyme inhibition until the onset of overt proteinuria or, in some cases, microalbuminuria. Developments that have occurred over the past 7 years have prompted us to revise these recommendations. We now recommend the initiation of treatment at the time of diagnosis in males with X-linked Alport syndrome and in males and females with autosomal recessive Alport syndrome. We further recommend starting treatment at the onset of microalbuminuria in females with X-linked Alport syndrome and in males and females with autosomal dominant Alport syndrome. This article presents the rationale for these revisions as well as recommendations for diagnostic tactics intended to ensure the early diagnosis of Alport syndrome.

Genotype-phenotype correlations and nephroprotective effects of RAAS inhibition in patients with autosomal recessive Alport syndrome

BACKGROUND

Autosomal recessive Alport syndrome (ARAS) is caused by pathogenic variants in both alleles of either COL4A3 or COL4A4 genes. Reports on ARAS are rare due to small patient numbers and there are no reports on renin-angiotensin-aldosterone system (RAAS) inhibition therapy in ARAS.

METHODS

Retrospective study in 101 patients with ARAS from Chinese Registry Database of Hereditary Kidney Diseases and European Alport Registry. Genotype-phenotype correlations and nephroprotective effects of RAAS inhibition in ARAS were evaluated.

RESULTS

Median age was 15 years (range 1.5-46 years). Twelve patients progressed to stage 5 chronic kidney disease (CKD5) at median age 20.5 years. Patients without missense variants had both higher prevalence and earlier onset age of hearing loss, nephrotic-range proteinuria, more rapid decline of eGFR, and earlier onset age of CKD5 compared to patients with 1 or 2 missense variants. Most patients (79/101, 78%) currently are treated with RAAS inhibitors; median age at therapy initiation was 10 years and mean duration 6.5 ± 6.0 years. Median age at CKD5 for untreated patients was 24 years. RAAS inhibition therapy delayed CKD5 onset in those with impaired kidney function (T-III) to median age 35 years, but is undefined in treated patients with proteinuria (T-II) due to low number of events. No treated patients with microalbuminuria (T-I) progressed to CKD5. ARAS patients with 1 or 2 missense variants showed better response to treatment than patients with non-missense-variants.

CONCLUSIONS

Our study provides the first evidence for early use of RAAS inhibition therapy in patients with ARAS. Furthermore, genotype in ARAS correlates with response to therapy in favor of missense variants.

Integration of genetic and histopathology data in interpretation of kidney disease

For many years renal biopsy has been the gold standard for diagnosis in many forms of kidney disease. It provides rapid, accurate and clinically useful information in most individuals with kidney disease. However, in recent years, other diagnostic modalities have become available that may provide more detailed and specific diagnostic information in addition to, or instead of, renal biopsy. Genomics is one of these modalities. Previously prohibitively expensive and time consuming, it is now increasingly available and practical in a clinical setting for the diagnosis of inherited kidney disease. Inherited kidney disease is a significant cause of kidney disease, in both the adult and paediatric populations. While individual inherited kidney diseases are rare, together they represent a significant burden of disease. Because of the heterogenicity of inherited kidney disease, diagnosis and management can be a challenge and often multiple diagnostic modalities are needed to arrive at a diagnosis. We present updates in genomic medicine for renal disease, how genetic testing integrates with our knowledge of renal histopathology and how the two modalities may interact to enhance patient care.

Rare genetic causes of complex kidney and urological diseases

Although often considered a single-entity, chronic kidney disease (CKD) comprises many pathophysiologically distinct disorders that result in persistently abnormal kidney structure and/or function, and encompass both monogenic and polygenic aetiologies. Rare inherited forms of CKD frequently span diverse phenotypes, reflecting genetic phenomena including pleiotropy, incomplete penetrance and variable expressivity. Use of chromosomal microarray and massively parallel sequencing technologies has revealed that genomic disorders and monogenic aetiologies contribute meaningfully to seemingly complex forms of CKD across different clinically defined subgroups and are characterized by high genetic and phenotypic heterogeneity. Investigations of prevalent genomic disorders in CKD have integrated genetic, bioinformatic and functional studies to pinpoint the genetic drivers underlying their renal and extra-renal manifestations, revealing both monogenic and polygenic mechanisms. Similarly, massively parallel sequencing-based analyses have identified gene- and allele-level variation that contribute to the clinically diverse phenotypes observed for many monogenic forms of nephropathy. Genome-wide sequencing studies suggest that dual genetic diagnoses are found in at least 5% of patients in whom a genetic cause of disease is identified, highlighting the fact that complex phenotypes can also arise from multilocus variation. A multifaceted approach that incorporates genetic and phenotypic data from large, diverse cohorts will help to elucidate the complex relationships between genotype and phenotype for different forms of CKD, supporting personalized medicine for individuals with kidney disease.

Clinical Genetic Screening in Adult Patients with Kidney Disease

Expanded accessibility of genetic sequencing technologies, such as chromosomal microarray and massively parallel sequencing approaches, is changing the management of hereditary kidney diseases. Genetic causes account for a substantial proportion of pediatric kidney disease cases, and with increased utilization of diagnostic genetic testing in nephrology, they are now also detected at appreciable frequencies in adult populations. Establishing a molecular diagnosis can have many potential benefits for patient care, such as guiding treatment, familial testing, and providing deeper insights on the molecular pathogenesis of kidney diseases. Today, with wider clinical use of genetic testing as part of the diagnostic evaluation, nephrologists have the challenging task of selecting the most suitable genetic test for each patient, and then applying the results into the appropriate clinical contexts. This review is intended to familiarize nephrologists with the various technical, logistical, and ethical considerations accompanying the increasing utilization of genetic testing in nephrology care.

A novel frameshift mutation of COL4A5 in a Chinese family with presumed IgA nephropathy and chronic glomerulonephritis

BACKGROUND

Alport syndrome (ATS) is a hereditary nephritis with hereditary and clinical heterogeneity; the early clinical symptoms are atypical, which can easily lead to misdiagnosis. The proband, a 6-year-old girl, was found to have microscopic hematuria, proteinuria, and visual impairment at about 5 years old; the results of renal pathological examination revealed mesangial hyperplasia and IgA deposition. The proband's father exhibited gross hematuria, eye swelling, and bilateral hearing loss after the age of 5, renal function progressively decreased, and he underwent right renal allograft at the age of 23 due to renal failure. The proband and her father were clinically diagnosed as IgA nephropathy and chronic glomerulonephritis, respectively.

METHODS

For proband, targeted exome capture sequencing was performed using the Targeted Exome Capture Kit; this kit targets 162 genes known to cause renal diseases. The identified mutation was confirmed and analyzed for cosegregation by Sanger sequencing in other family members whose gDNA was available.

RESULTS

Targeted exome capture sequencing revealed a novel heterozygous variant (NM_000495, c.697delG, p.G233fs) in the COL4A5 gene of the proband; the variant was inherited from her father. The variant was likely pathogenic according to the criteria of the American College of Medical Genetics and Genomics.

CONCLUSION

In this study, we first report a c.697delG mutation of COL4A5 in two patients presumed IgA nephropathy and chronic glomerulonephritis. This study emphasizes on the diagnostic value of next-generation sequencing for hereditary kidney diseases to help in their timely and cost-effective diagnosis, determine appropriate treatments, and promote genetic counseling.

Alport Syndrome Classification and Management

Alport syndrome affects up to 60,000 people in the United States. The proposed reclassification of thin basement membrane nephropathy and some cases of focal segmental glomerulosclerosis as Alport syndrome could substantially increase the affected population. The reclassification scheme categorizes Alport syndrome as 3 distinct diseases of type IV collagen α3/4/5 based on a genetic evaluation: X-linked, autosomal, and digenic. This approach has the advantage of identifying patients at risk for progressive loss of kidney function. Furthermore, the shared molecular cause of Alport syndrome and thin basement membrane nephropathy arises from mutations in the COL4A3, COL4A4, and COL4A5 genes, which contribute to downstream pathophysiologic consequences, including chronic kidney inflammation. Recent evidence indicates that chronic inflammation and its regulation through anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2) and proinflammatory nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) transcription factors plays a central role in renal tubular and glomerular cell responses to injury. Crosstalk between the Nrf2 and NF-κB pathways is important in the regulation of inflammation in patients with chronic kidney disease; moreover, there is evidence that an insufficient Nrf2 response to inflammation contributes to disease progression. Given the association between type IV collagen abnormalities and chronic inflammation, there is renewed interest in targeted anti-inflammatory therapies in Alport syndrome and other forms of progressive chronic kidney disease.

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.

Alport Syndrome: Achieving Early Diagnosis and Treatment

Alport syndrome is a genetically and phenotypically heterogeneous disorder of glomerular, cochlear, and ocular basement membranes resulting from mutations in the collagen IV genes COL4A3, COL4A4, and COL4A5. Alport syndrome can be transmitted as an X-linked, autosomal recessive, or autosomal dominant disorder. Individuals with Alport syndrome have a significant lifetime risk for kidney failure, as well as sensorineural deafness and ocular abnormalities. The availability of effective intervention for Alport syndrome-related kidney disease makes early diagnosis crucial, but this can be impeded by the genotypic and phenotypic complexity of the disorder. This review presents an approach to enhancing early diagnosis and achieving optimal outcomes.

SGLT2 inhibitors - a potential treatment for Alport syndrome

Alport syndrome is a rare genetic disease that results in disordered basement membrane type IV collagen resulting in occular and auditory defects as well of progressive kidney disease. Although no 'cure' currently exists, therapeutic blockade of the renin-angiotensin-aldosterone system can slow the progression to end-stage kidney disease (ESKD). Clinical trials for treatments in preventing chronic kidney disease have largely been negative over the last two decades until recent trials have shown positive cardiovascular and renal outcomes of sodium-glucose co-transporter-2 (SGLT2) inhibitors in patients with diabetes mellitus. Although marketed as medications for Type 2 diabetes, SGLT2 inhibitors have been found to have additional properties that are nephroprotective which makes them a potential candidate for treatment for those with other forms of progressive kidney disease. This review discusses the evidence for the use of SGLT2 inhibitors as a potential treatment in Alport syndrome that may slow the progression of chronic kidney disease and prevent patients reaching ESKD.

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.