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

Slowly progressive autosomal dominant Alport Syndrome due to COL4A3 splicing variant

Alport syndrome is a rare genetic kidney disease caused by variants in the COL4A3/A4/A5 genes. It's characterised by progressive kidney failure, though therapies targeting Renin-Angiotensin System can delay its progression. Additionally, extrarenal manifestations may sometimes coexist. Recent advances in genetic analysis and the necessity to better clarify genotype-phenotype correlations in affected patients raises the importance of detecting even cryptic splicing variants, lying in both canonical and non-canonical splice sites variants such as last exonic nucleotide variants. These variants, often, do not cause an amino acid change but alter the snRNP proteins binding. We studied a big Italian family with Alport syndrome showing a clear dominant pattern of transmission with younger family members having only haematuria and older individuals presenting with End-Stage Kidney Failure (ESKF). Kidney biopsy showed the typical disease hallmarks. We deeply mined the data for SNV and CNV through exome sequencing on DNA from both peripheral blood samples and patients' podocytes-lineage cells. We identified an already reported synonymous variant, c.765G>A (p.(Thr255Thr)), in the last exonic nucleotide of exon 13 of the COL4A3 gene. Employing the patient's podocytes we demonstrated that this variant results in exon skipping leading to an in-frame deletion of 28 amino acids without leaky effect. According to the pattern of transmission, to the kidney biopsy and to the exome data analysis we provided further evidence that autosomal dominant Alport syndrome is a well-defined clinical entity. We also confirmed the pathogenicity of the synonymous COL4A3 variant for the first time demonstrating its role in a dominant pattern of transmission.

Quantitative assessment of glomerular basement membrane collagen IV α chains in paraffin sections from patients with focal segmental glomerulosclerosis and Alport gene variants

Focal segmental glomerulosclerosis (FSGS) lesions have been linked to variants in COL4A3/A4/A5 genes, which are also mutated in Alport syndrome. Although it could be useful for diagnosis, quantitative evaluation of glomerular basement membrane (GBM) type IV collagen (colIV) networks is not widely used to assess these patients. To do so, we developed immunofluorescence imaging for collagen α5(IV) and α1/2(IV) on kidney paraffin sections with Airyscan confocal microscopy that clearly distinguishes GBM collagen α3α4α5(IV) and α1α1α2(IV) as two distinct layers, allowing quantitative assessment of both colIV networks. The ratios of collagen α5(IV):α1/2(IV) mean fluorescence intensities (α5:α1/2 intensity ratios) and thicknesses (α5:α1/2 thickness ratios) were calculated to represent the levels of collagen α3α4α5(IV) relative to α1α1α2(IV). The α5:α1/2 intensity and thickness ratios were comparable across all 11 control samples, while both ratios were significantly and markedly decreased in all patients with pathogenic or likely pathogenic Alport COL4A variants, supporting validity of this approach. Thus, with further validation of this technique, quantitative measurement of GBM colIV subtype abundance by immunofluorescence, may potentially serve to identify the subgroup of patients with FSGS lesions likely to harbor pathogenic COL4A variants who could benefit from genetic testing.

Whole exome sequencing approach for identification of the molecular etiology in pediatric patients with hematuria

BACKGROUND

Hematuria is a common condition in clinical practice of pediatric patients. It is related to a wide spectrum of disorders and has high heterogeneity both clinically and genetically, which contributes to challenges of diagnosis and lead many pediatric patients with hematuria not to receive accurate diagnosis and early management.

METHODS

In this single center study, 42 children with hematuria were included in Tianjin Children's Hospital between 2019 and 2020. We analyzed the clinical information and performed WES (Whole exome sequencing) for all cases. Then the classification of identified variants was performed according to the American College of Medical Genetics and Genomics (ACMG) guidelines for interpreting sequence variants. For the fragment deletion, qPCR was performed to validate and confirm the inherited pattern.

RESULTS

For the 42 patients, 16 cases had gross hematuria and 26 had microscopic hematuria. Molecular genetic causes were uncovered in 9 (21.4%) children, including 7 with Alport syndrome (AS), one with polycystic nephropathy and one with lipoprotein glomerulopathy. The genetic causes for other patients were not related with hematuria.

CONCLUSIONS

WES is a rapid and effective way to evaluate patients with hematuria. The analysis of genotype-phenotype correlations of patients with AS indicated that severe variants were associated with early kidney failure. Secondary findings were not rare in Chinese children, thus the clinician should pay more attention to the clinical interpretation of sequencing results and properly interaction with patients and their family.

Clinicopathological Features of Hereditary Nephritis in the Iranian Population: Analysis of a 14-Year Survey in Kidney Biopsies From a Large Referral Center

BACKGROUND

Hereditary nephritis (HN), including Alport syndrome (AS) and thin basement membrane nephropathy (TBMN), is a rare genetic cause of hematuria. A definitive diagnosis requires electron microscopy (EM). Therefore, the clinical characteristics of these conditions are less known. This study aimed to determine the percentage and clinicopathological features of HN in patients from a referral center in Iran.

METHODS

We checked kidney biopsy reports from 2007 to 2021 and extracted cases with HN. Fresh specimens of the cases diagnosed in the last two years were stained by immunofluorescence (IF) for collagen type IV alpha chains. EM findings in these cases were re-evaluated and categorized as diffuse glomerular basement membrane (GBM) thinning, definite, and suspicious features of AS.

RESULTS

We analyzed 3884 pathology reports of kidney biopsies from 2007 to 2021 and identified 210 patients (5.4%) with HN, with a mean age of 13.78±12.42 years old. Hematuria with proteinuria (53.3%), isolated hematuria (44.2%), and proteinuria with hematuria and increased creatinine (2.5%) were found in these patients. The re-evaluation of EM findings revealed GBM thinning, definite, and suspicious findings of AS in 37.5%, 43.8%, and 18.8% cases, respectively. The most common diagnosis in 32 cases after the IF study was X-linked AS (71.9%), and 6.2% of cases were autosomal recessive AS. TBMN and autosomal dominant AS remained the differential diagnoses in 21.9%.

CONCLUSION

It was found that EM is helpful for the primary diagnosis of patients with definite AS. Immunostaining improves the diagnostic sensitivity for the differentiation of those with suspicious EM findings and determines the inheritance pattern. However, a multidisciplinary approach for a subset of cases is required for the best diagnosis and management.

COL4A gene variants are common in children with hematuria and a family history of kidney disease

BACKGROUND

Inherited kidney diseases are a common cause of chronic kidney disease (CKD) in children. Identification of a monogenic cause of CKD is more common in children than in adults. This study evaluated the diagnostic yield and phenotypic spectrum of children who received genetic testing through the KIDNEYCODE sponsored genetic testing program.

METHODS

Unrelated children < 18 years of age who received panel testing through the KIDNEYCODE sponsored genetic testing program from September 2019 through August 2021 were included (N = 832). Eligible children met at least one of the following clinician-reported criteria: estimated GFR ≤ 90 ml/min/1.73 m2, hematuria, a family history of kidney disease, or suspected or biopsy confirmed Alport syndrome or focal segmental glomerulosclerosis (FSGS) in the tested individual or family member.

RESULTS

A positive genetic diagnosis was observed in 234 children (28.1%, 95% CI [25.2-31.4%]) in genes associated with Alport syndrome (N = 213), FSGS (N = 9), or other disorders (N = 12). Among children with a family history of kidney disease, 30.8% had a positive genetic diagnosis. Among those with hematuria and a family history of CKD, the genetic diagnostic rate increased to 40.4%.

CONCLUSIONS

Children with hematuria and a family history of CKD have a high likelihood of being diagnosed with a monogenic cause of kidney disease, identified through KIDNEYCODE panel testing, particularly COL4A variants. Early genetic diagnosis can be valuable in targeting appropriate therapy and identification of other at-risk family members. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

Investigation of the current situation regarding diagnosis and treatment of Alport syndrome in Asian countries: results of survey of the Asian Paediatric Nephrology association (AsPNA) tubular and inherited working group

BACKGROUND

Alport syndrome is one of the most common inherited kidney diseases worldwide. A genetic test or kidney biopsy is necessary for a definite diagnosis of this disease, and an accurate diagnosis system for this disease is highly desired in each country. However, the current situation in Asian countries is not clear. Therefore, the tubular and inherited disease working group of the Asian Pediatric Nephrology Association (AsPNA) aimed to assess the current situation of diagnosis and treatment for Alport syndrome in Asia.

METHODS

The group conducted an online survey among the members of AsPNA in 2021-2022. Collected data included the number of patients for each inheritance mode, availability of gene tests or kidney biopsy, and treatment strategies for Alport syndrome.

RESULTS

A total of 165 pediatric nephrologists from 22 countries in Asia participated. Gene test was available in 129 institutes (78%), but the cost was still expensive in most countries. Kidney biopsy was available in 87 institutes (53%); however, only 70 can access electron microscopy, and 42 can conduct type IV collagen α5 chain staining. Regarding treatment, 140 centers use renin-angiotensin system (RAS) inhibitors (85%) for Alport syndrome patients.

CONCLUSIONS

This study result might suggest that the system is underdeveloped enough to diagnose all Alport syndrome patients in most Asian countries. However, once diagnosed with Alport syndrome, most of them were treated with RAS inhibitors. These survey results can be used to address knowledge, diagnostic system, and treatment strategy gaps and improve the Alport patients' outcomes in Asian countries.

Case report: A case report of Alport syndrome caused by a novel mutation of COL4A5

Alport syndrome (#308940) is an X-linked genetic disease with clinical manifestations, such as hematuria, proteinuria, renal insufficiency, and end-stage renal disease. The disease is characterized by the thinning of the glomerular basement membrane in the early stages and the thickening of the glomerular basement membrane in the late stages and may be associated with ocular lesions and varying degrees of sensorineural deafness. Herein, we report a case of Alport syndrome caused by a de novo mutation in COL4A5. The patient was a young male with clinical manifestations of hematuria and massive proteinuria who was diagnosed with Alport syndrome based on renal pathology and genetic testing.

Abnormal mRNA Splicing Effect of COL4A3 to COL4A5 Unclassified Variants

Introduction

Genetic diagnosis of Alport syndrome (AS), which results from pathogenic variants in COL4A3, COL4A4, or COL4A5 genes, is hindered by large numbers of unclassified variants detected using next-generation sequencing (NGS). We examined the impact on splicing of variants of uncertain significance in COL4A3 to COL4A5.

Methods

Nine unrelated patients with clinical diagnosis or suspicion of AS were enrolled according to the criteria. Their clinical and genetic data were collected. Blood and urine samples were obtained from the patients and their family members. Sanger sequencing was used to confirm the 9 COL4A3 to COL4A5 unclassified variants identified by NGS. COL4A3 to COL4A5 mRNAs from urine were analyzed using targeted reverse transcription polymerase chain reaction and direct sequencing.

Results

Nine COL4A3 to COL4A5 unclassified variants were found to alter mRNAs splicing. Skipping of an exon or an exon fragment was induced by variants COL4A3 c.828+5G>A; COL4A4 c.3506-13_3528del; and COL4A5 c.451A>G (p. [Ile151Val]), c.2042-9 T>G, c.2689 G>C (p. [Glu897Gln]) and c.1033-10_1033-2delGGTAATAAA. Retention of an intron fragment was caused by variants COL4A3 c.3211-30G＞T, and COL4A5 c.4316-20T>A and c.1033-10 G>A, respectively. The 9 families in this study obtained genetic diagnosis of AS, including 3 with autosomal recessive AS and 6 with X-linked AS.

Conclusions

Our findings demonstrate that urine mRNA analysis facilitates the identification of abnormal splicing of unclassified variants in Alport genes, which provides evidence of routine use of RNA analysis to improve genetic diagnosis of AS.

Clinical, histological and molecular characteristics of Alport syndrome in Chinese children

BACKGROUND

Alport syndrome is caused by COL4A3, COL4A4, or COL4A5 gene mutations. The present study aims to compare the clinicopathological features, gene mutations, and outcome of Chinese children with different forms of Alport syndrome.

METHODS

One hundred twenty-eight children from 126 families diagnosed with Alport syndrome through pathological and genetic examination between 2003 and 2021 were included in this single-center retrospective study. The laboratory and clinicopathological features of the patients with different inheritance patterns were analyzed. The patients were followed-up for disease progression and phenotype-genotype correlation.

RESULTS

Of the 126 Alport syndrome families, X-linked forms accounted for 77.0%, autosomal recessive for 11.9%, autosomal dominant for 7.1%, and digenic for 4.0%. Among the patients, 59.4% were males and 40.6% were females. Altogether, 114 different mutations were identified in 101 patients from 99 families by whole-exome sequencing, of which 68 have not been previously reported. The most prevalent type of mutation was glycine substitution, which was identified in 52.1%, 36.7%, and 60% of the patients with X-linked Alport syndrome, autosomal recessive and autosomal dominant Alport syndrome, respectively. At the end of a median follow up of 3.3 (1.8-6.3) years, Kaplan-Meier curves showed kidney survival was significantly lower in autosomal recessive compared to X-linked Alport syndrome (P = 0.004). Pediatric patients with Alport syndrome seldom presented extrarenal involvement.

CONCLUSIONS

X-linked Alport syndrome is the most frequent form found in this cohort. Progression was more rapid in autosmal recessive than in X-linked Alport syndrome.

Pathogenic variant detection rate by whole exome sequencing in Thai patients with biopsy-proven focal segmental glomerulosclerosis

The spectra of underlying genetic variants for various clinical entities including focal segmental glomerulosclerosis (FSGS) vary among different populations. Here we described the clinical and genetic characteristics of biopsy-proven FSGS patients in Thailand. Patients with FSGS pathology, without secondary causes, were included in our study. Clinical laboratory and pathological data were collected. Whole-exome sequencing (WES) was subsequently performed. 53 unrelated FSGS patients were recruited. 35 patients were adults (66.0%), and 51 patients were sporadic cases (96.2%). Clinical diagnosis before kidney biopsy was steroid-resistant nephrotic syndrome (SRNS) in 58.5%, and proteinuric chronic kidney disease in 32.1%. Using WES, disease-associated pathogenic/likely pathogenic (P/LP) variants could be identified in six patients including the two familial cases, making the P/LP detection rate of 11.3% (6/53). Of these six patients, two patients harbored novel variants with one in the COL4A4 gene and one in the MAFB gene. Four other patients carried previously reported variants in the CLCN5, LMX1B, and COL4A4 genes. Four of these patients (4/6) received immunosuppressive medications as a treatment for primary FSGS before genetic diagnosis. All four did not respond to the medications, emphasizing the importance of genetic testing to avoid unnecessary treatment. Notably, the mutation detection rates in adult and pediatric patients were almost identical, at 11.4% and 11.1%, respectively. In conclusion, the overall P/LP variant detection rate by WES in biopsy-proven FSGS patients was 11.3%. The most identified variants were in COL4A4. In addition, three novel variants associated with FSGS were detected.

Genetic testing and glomerular hematuria-A nephrologist's perspective

Alport syndrome is an inherited disorder of the kidneys that results from variants in three collagen IV genes-COL4A3, COL4A4, and COL4A5. Early diagnosis and pharmacologic intervention can delay the progression of chronic kidney disease and the onset of kidney failure in patients with Alport syndrome. This article describes the evolution of approaches to the diagnosis and early treatment of Alport syndrome.

Whole exome sequencing identifies monogenic forms of nephritis in a previously unsolved cohort of children with steroid-resistant nephrotic syndrome and hematuria

BACKGROUND

Alport syndrome (AS), atypical hemolytic-uremic syndrome (aHUS), and fibronectin-glomerulopathy (FG) are rare forms of glomerular diseases that manifest in a combination of proteinuria, hematuria, and hypertension, referred to as nephritic syndrome. Due to phenotypic overlays, steroid-resistant nephrotic syndrome (SRNS) and nephritic syndrome have been difficult to discern diagnostically. SRNS is more common than nephritic syndrome and is the second leading cause of childhood-onset CKD. Fourteen monogenic causes of AS, aHUS, and FG and 60 monogenic causes of SRNS have been identified. As whole exome sequencing (WES) allows for unequivocal molecular genetic diagnostics, we hypothesize to be able to identify causative mutations in genes known to cause nephritic syndrome in patient cohorts with a clinical diagnosis of SRNS.

METHODS

We identified patients with hematuria and steroid-resistant proteinuria in an international patient cohort that we had submitted to WES and who were unsolved for known monogenic causes of SRNS. These 70 patients from 65 individual families were subsequently analyzed for causative mutations in 14 AS, aHUS, or FG causing genes. WES data were compared to a control cohort of 76 patients from 75 families that were diagnosed with nephronophthisis-related ciliopathies (NPHP-RC) and to a control cohort of 83 individuals from 75 families with SRNS, but without hematuria.

RESULTS

We detected likely pathogenic genetic variants in 3 of 65 families (4.6%) in 2 of the 14 genes analyzed.

CONCLUSIONS

We confirmed that in cohorts of childhood-onset SRNS, patients with nephritic syndrome can be discerned by WES. The findings highlight the importance of clinical genetic testing for therapeutic and preventative measures in patients with proteinuria. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

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 27 Novel Variants in Genes COL4A3, COL4A4, and COL4A5 in Lithuanian Families With Alport Syndrome

Introduction:

Alport syndrome (AS) is an inherited disorder characterized by hematuria, proteinuria, and kidney function impairment, and frequently associated with extrarenal manifestations. Pathogenic variants in COL4A5 usually cause X-linked Alport syndrome (XLAS), whereas those in the COL4A3 or COL4A4 genes are associated with autosomal dominant (AD) or recessive (AR) inheritance. To date, more than 3000 different disease-causing variants in COL4A5, COL4A3, and COL4A4 have been identified. The aim of this study was to evaluate the clinical and genetic spectrum of individuals with novel, pathogenic or likely pathogenic variants in the COL4A3-A5 genes in a previously unstudied cohort.

Methods

In this study molecular analysis by next generation sequencing (NGS) was performed on individuals from a Lithuanian cohort, with suspected AS. The presence of AS was assessed by reviewing clinical evidence of hematuria, proteinuria, chronic kidney disease (CKD), kidney failure (KF), a family history of AS or persistent hematuria, and specific histological lesions in the kidney biopsy such as thinning or lamellation of the glomerular basement membrane (GBM). Clinical, genetic, laboratory, and pathology data were reviewed. The novelty of the COL4A3-A5 variants was confirmed in the genetic variant databases (Centogene, Franklin, ClinVar, Varsome, InterVar). Only undescribed variants were included in this study.

Results

Molecular testing of 171 suspected individuals led to the detection of 99 individuals with 44 disease causing variants including 27, previously undescribed changes, with the frequency of 9/27 (33,3%) in genes COL4A5, COL4A3 and COL4A4 equally. Three individuals were determined as having digenic AS causing variants: one in COL4A3 and COL4A4, two in COL4A4 and COL4A5. The most prevalent alterations in genes COL4A3-5 were missense variants (n = 19), while splice site, frameshift, unknown variant and stop codon changes were detected more in genes COL4A4 and COL4A5 and accounted for 3, 3, 1 and 1 of all novel variants, respectively.

Conclusion

Genotype-phenotype correlation analysis suggested that some variants demonstrated intra-familial phenotypic variability. These novel variants represented more than half of all the variants found in a cohort of 171 individuals from 109 unrelated families who underwent testing. Our study expands the knowledge of the genetic and phenotypic spectrum for AS.

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.

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.