Autosomal Recessive Alport Syndrome Research Articles

Denovo glomerulonephritis associated with IgA anti-GBM alloantibodies after kidney transplantation in Alport syndrome: A case report with diagnostic implications

Alport syndrome (AS) is a hereditary disorder caused by pathogenic variants in COL4A3, COL4A4, or COL4A5 genes expressing α3, α4, and α5 chains of basement membrane type IV collagen (COL4). The triple-helical α3α4α5(IV) protomer is a major component of the mature glomerular basement membrane (GBM) whose defective formation in AS leads to structural GBM disruption and kidney dysfunction, often resulting in kidney replacement therapy. A genetically intact renal graft exposes the immune system to a non-tolerized α3α4α5(IV) component and an alloimmune response eventually ensues. So far, only IgG alloantibodies reacting against COL4 have been reported in AS alloimmune responses. Here, we report alloimmune glomerulonephritis mediated by IgA antibodies against the non-collagenous C-terminal domain 1 of the α5(IV) chain in a patient with autosomal recessive AS following a second kidney transplantation. The patient presented a not previously described biallelic variant in the COL4A4 gene. Immunological, diagnostic, and clinical implications are discussed.

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.

Development of CRISPR/Cas9-Based Mouse Models for X-linked Alport Syndrome

Intro: Alport Syndrome (AS) is a rare hereditary disorder characterized by progressive renal impairment and sensorineural hearing loss, resulting from mutations in the genes that encode COL4 synthesis. X-linked Alport Syndrome (XLAS) is the most common form of AS, comprising an estimated 80% of all human AS cases (the others being various forms of autosomal recessive or autosomal dominant AS), and is caused by various mutations on the COL4A5 gene. However, to date, there are no animal models of XLAS. Methods: To facilitate comprehensive preclinical investigations and therapeutic developments, we established two novel mouse models of XLAS using CRISPR/Cas9 technology. Leveraging the robust C57Bl/6J mouse strain, we precisely introduced the L1655R and C1570S mutations, which represent the predominant human variants of XLAS observed in the Western United States. Discussion: Our innovative mouse models not only serve as invaluable tools for elucidating the underlying mechanisms of XLAS pathogenesis but also provide a platform for evaluating the effcacy of potential therapeutic interventions. The establishment of these faithful genetic replicas of human XLAS marks a significant advancement in the field, offering unprecedented opportunities for in-depth mechanistic studies and the development of targeted therapeutic strategies for this debilitating renal and auditory disorder. This research is supported by the National Institutes of Health under Ruth L. Kirschstein National Research Service Award 5T32DK091317 from the National Institute of Diabetes and Digestive and Kidney Diseases and the National Kidney Foundation of Utah and Idaho. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Corneal endothelial cell morphology in children with autosomal recessive Alport syndrome: a longitudinal study

ABSTRACT Purpose To evaluate the corneal endothelial cell morphology in children with autosomal recessive Alport syndrome (ARAS). Methods This is a longitudinal, prospective cohort study that evaluated pediatric patients with genetically diagnosed ARAS. Fifty-eight eyes of 29 pediatric patients (12 patients, 17 controls) underwent a full ophthalmic examination. Corneal endothelial cell density (ECD) (cells/mm²), coefficient variation (CV) of cell area (polymegathism), the percentage of hexagonal cells (HEX) (pleomorphism), and central corneal thickness (CCT) were analyzed automatically using a noncontact specular microscopy. Results The mean ECD was 2904 ± 355.48 cell/mm² in the ARAS group and 3263.20 ± 261.71 cell/mm² in the control group (p = 0.004). In the ARAS group, the mean CV was 46.53 ± 10.43, which was significantly higher than that in controls (p = 0.026). The mean HEX was 48.86 ± 14.71 in the ARAS group and 59.06 ± 10.64 in the control group (p = 0.038). The mean CCT was 565.26 ± 39.77 µm in the ARAS group and 579.66 ± 31.65 µm in the control group (p = 0.282). The comparison of endothelial cell characteristic of the ARAS group with 1-year follow-up is as follows: The mean ECD decreased from 2904 ± 355.48 cell/mm² to 2735 ± 241.58 cell/mm² (p = 0.003). The mean CV increased from 46.53 ± 10.43 to 47.93 ± 10.50 (p = 0.471). The mean HEX decreased from 48.86 ± 14.71 to 48.50 ± 10.06 (p = 0.916). The mean CCT decreased from 565.26 ± 39.77 µm to 542.86 ± 40.39 µm (p = 0.000). Conclusion Measurement of ECD and percentage of hexagonality can also be used as an indicator of the health of the corneal endothelium. In this study, the mean ECD and HEX were significantly lower in ARAS group than in age-matched pediatric controls. Polymegathism, which reflects cellular stress, was statistically significantly higher in ARAS group. The mean ECD and CCT decreased significantly at 1-year follow-up. This study may demostrated that endothelial damages and stress in ARAS patients appear in childhood and show a rapid increase with age.

Is there a dominant-negative effect in individuals with heterozygous disease-causing variants in COL4A3/COL4A4?

Alport syndrome (AS) shows a broad phenotypic spectrum ranging from isolated microscopic hematuria (MH) to end-stage kidney disease (ESKD). Monoallelic disease-causing variants in COL4A3/COL4A4 have been associated with autosomal dominant AS (ADAS) and biallelic variants with autosomal recessive AS (ARAS). The aim of this study was to analyze clinical and genetic data regarding a possible genotype-phenotype correlation in individuals with disease-causing variants in COL4A3/COL4A4. Eighty-nine individuals carrying at least one COL4A3/COL4A4 variant classified as (likely) pathogenic according to the American College of Medical Genetics guidelines and current amendments were recruited. Clinical data concerning the prevalence and age of first reported manifestation of MH, proteinuria, ESKD, and extrarenal manifestations were collected. Individuals with monoallelic non-truncating variants reported a significantly higher prevalence and earlier diagnosis of MH and proteinuria than individuals with monoallelic truncating variants. Individuals with biallelic variants were more severely affected than those with monoallelic variants. Those with biallelic truncating variants were more severely affected than those with compound heterozygous non-truncating/truncating variants or individuals with biallelic non-truncating variants. In this study an association of heterozygous non-truncating COL4A3/COL4A4 variants with a more severe phenotype in comparison to truncating variants could be shown indicating a potential dominant-negative effect as an explanation for this observation. The results for individuals with ARAS support the, still scarce, data in the literature.

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

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. 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. 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%. 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.

Sex Differences in Glomerular Protein Expression in Mice with Autosomal Recessive Alport Syndrome

Sex Differences in Glomerular Protein Expression in Mice with Autosomal Recessive Alport Syndrome

A Current Landscape on Alport Syndrome Cases: Characterization, Therapy and Management Perspectives.

Alport syndrome (AS) is a rare genetic disorder categorized by the progressive loss of kidney function, sensorineural hearing loss and eye abnormalities. It occurs due to mutations in three genes that encode for the alpha chains of type IV collagen. Globally, the disease is classified based on the pattern of inheritance into X-linked AS (XLAS), which is caused by pathogenic variants in COL4A5, representing 80% of AS. Autosomal recessive AS (ARAS), caused by mutations in either COL4A3 or COL4A4, represents 15% of AS. Autosomal dominant AS (ADAS) is rare and has been recorded in 5% of all cases due to mutations in COL4A3 or COL4A4. This review provides updated knowledge about AS including its clinical and genetic characteristics in addition to available therapies that only slow the progression of the disease. It also focuses on reported cases in Saudi Arabia and their prevalence. Moreover, we shed light on advances in genetic technologies like gene editing using CRISPR/Cas9 technology, the need for an early diagnosis of AS and managing the progression of the disease. Eventually, we provide a few recommendations for disease management, particularly in regions like Saudi Arabia where consanguineous marriages increase the risk.

Potential Founder Variants in COL4A4 Identified in Bukharian Jews Linked to Autosomal Dominant and Autosomal Recessive Alport Syndrome.

Alport syndrome is a hereditary disorder caused by pathogenic variants in the COL4A gene, which can be inherited in an autosomal recessive, dominant, or X-linked pattern. In the Bukharian Jewish population, no founder pathogenic variant has been reported in COL4A4. The cohort included 38 patients from 22 Bukharian Jewish families with suspected Alport syndrome who were referred the nephrogenetics clinic between 2012 and 2022. The study collected demographic, clinical, and genetic data from electronic medical records, which were used to evaluate the molecular basis of the disease using Sanger sequencing, and next-generation sequencing. Molecular diagnosis was confirmed in 20/38 patients, with each patient having at least one of the three disease-causing COL4A4 variants detected: c.338G<A (p.Gly113Asp), c.3022G>A (p.Gly1008Arg), and c.871-6T>C. In addition, two patients were obligate carriers. Overall, there were 17 heterozygotes, 2 compound heterozygotes, and 3 homozygotes. Each variant was detected in more than one unrelated family. All patients had hematuria with/without proteinuria at referral, and the youngest patient with proteinuria (age 5 years) was homozygous for the c.338G>A variant. End-stage renal disease was diagnosed in two patients at the age of 38 years, a compound heterozygote for c.338G>A and c.871-6T>C. Hearing deterioration was detected in three patients, the youngest aged 40 years, all of whom were heterozygous for c.338G>A. This study unveils three novel disease-causing variants, c.3022G>A, c.871-6T>C, and c.338G>A, in the COL4A4 gene that are recurrent among Jews of Bukharian ancestry, and cause Alport syndrome in both dominant and recessive autosomal inheritance patterns.

Genetic Modifiers of Mendelian Monogenic Collagen IV Nephropathies in Humans and Mice.

Familial hematuria is a clinical sign of a genetically heterogeneous group of conditions, accompanied by broad inter- and intrafamilial variable expressivity. The most frequent condition is caused by pathogenic (or likely pathogenic) variants in the collagen-IV genes, COL4A3/A4/A5. Pathogenic variants in COL4A5 are responsible for the severe X-linked glomerulopathy, Alport syndrome (AS), while homozygous or compound heterozygous variants in the COL4A3 or the COL4A4 gene cause autosomal recessive AS. AS usually leads to progressive kidney failure before the age of 40-years when left untreated. People who inherit heterozygous COL4A3/A4 variants are at-risk of a slowly progressive form of the disease, starting with microscopic hematuria in early childhood, developing Alport spectrum nephropathy. Sometimes, they are diagnosed with benign familial hematuria, and sometimes with autosomal dominant AS. At diagnosis, they often show thin basement membrane nephropathy, reflecting the uniform thin glomerular basement membrane lesion, inherited as an autosomal dominant condition. On a long follow-up, most patients will retain normal or mildly affected kidney function, while a substantial proportion will develop chronic kidney disease (CKD), even kidney failure at an average age of 55-years. A question that remains unanswered is how to distinguish those patients with AS or with heterozygous COL4A3/A4 variants who will manifest a more aggressive kidney function decline, requiring prompt medical intervention. The hypothesis that a subgroup of patients coinherit additional genetic modifiers that exacerbate their clinical course has been investigated by several researchers. Here, we review all publications that describe the potential role of candidate genetic modifiers in patients and include a summary of studies in AS mouse models.

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

Though 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. 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 GRADE assessment determined the certainty of evidence. 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; HR: 0.33; 95% CI: 0.24-0.45; moderate certainty evidence). After stratified by genetic types, a similar benefit was detected: male X-linked Alport syndrome (XLAS) (HR: 0.32; 95% CI: 0.22-0.48), autosomal recessive Alport syndrome (HR: 0.25; 95% CI: 0.10-0.62), female XLAS and autosomal dominant Alport syndrome (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. 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.

Abnormal mRNA Splicing Effect of COL4A3 to COL4A5 Unclassified Variants

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. 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. 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. 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.

A founder COL4A4 pathogenic variant resulting in autosomal recessive Alport syndrome accounts for most genetic kidney failure in Romani people.

Romani people have a high prevalence of kidney failure. This study examined a Romani cohort for pathogenic variants in the COL4A3, COL4A4, and COL4A5 genes that are affected in Alport syndrome (AS), a common cause of genetic kidney disease, characterized by hematuria, proteinuria, end-stage kidney failure, hearing loss, and eye anomalies. The study included 57 Romani from different families with clinical features that suggested AS who underwent next-generation sequencing (NGS) of the COL4A3, COL4A4, and COL4A5 genes, and 83 family members. In total, 27 Romani (19%) had autosomal recessive AS caused by a homozygous pathogenic c.1598G>A, p.Gly533Asp variant in COL4A4 (n = 20) or a homozygous c.415G>C, p.Gly139Arg variant in COL4A3 (n = 7). For p.Gly533Asp, 12 (80%) had macroscopic hematuria, 12 (63%) developed end-stage kidney failure at a median age of 22 years, and 13 (67%) had hearing loss. For p.Gly139Arg, none had macroscopic hematuria (p = 0.023), three (50%) had end-stage kidney failure by a median age of 42 years (p = 0.653), and five (83%) had hearing loss (p = 0.367). The p.Gly533Asp variant was associated with a more severe phenotype than p.Gly139Arg, with an earlier age at end-stage kidney failure and more macroscopic hematuria. Microscopic hematuria was very common in heterozygotes with both p.Gly533Asp (91%) and p.Gly139Arg (92%). These two founder variants contribute to the high prevalence of kidney failure in Czech Romani. The estimated population frequency of autosomal recessive AS from these variants and consanguinity by descent is at least 1:11,000 in Czech Romani. This corresponds to a population frequency of autosomal dominant AS from these two variants alone of 1%. Romani with persistent hematuria should be offered genetic testing.

Hydroxychloroquine Ameliorates Hematuria in Children with X-Linked Alport Syndrome: Retrospective Case Series Study.

As a rare collagen type IV hereditary kidney disease, X-linked Alport syndrome (XLAS) is the most common form of Alport syndrome, the prevalence of which is estimated at 1:10,000 of the population, four times higher than the prevalence rate of autosomal recessive Alport syndrome. To describe a series of eight XLAS children with persistent hematuria and proteinuria and the clinical outcomes after hydroxychloroquine (HCQ) treatment to assess its efficacy as early intervention. The study retrospectively analysed 8 patients with persistent hematuria and proteinuria at different onset ages who were diagnosed with XLAS and been treated with HCQ. The urinary erythrocyte count, urinary albuminn were measured. Descriptive statistics were used to estimate the patients' responses to HCQ treatment after one month, three months, and six months. After the first month, the three months, and the six months of HCQ treatment, the urinary erythrocyte counts of four, seven, and eight children were significantly reduced; the decreasing proteinuria was found in two, four, and five children. Only one child with increasing proteinuria was found after 1-month HCQ treatment. This proteinuria was maintained after 3-month HCQ treatment but decreased to minor after 6-month HCQ treatment. We present the first potential efficacy of HCQ treatment in XLAS with hematuria and persistent proteinuria. It suggested that HCQ could be an effective treatment to ameliorate hematuria and proteinuria.

Digenic Alport Syndrome.

Digenic Alport syndrome refers to the inheritance of pathogenic variants in COL4A5 plus COL4A3 or COL4A4 or in COL4A3 plus COL4A4 Where digenic Alport syndrome includes a pathogenic COL4A5 variant, the consequences depend on the sex of the affected individual, COL4A5 variant "severity," and the nature of the COL4A3 or COL4A4 change. A man with a pathogenic COL4A5 variant has all his collagen IV α3α4α5-heterotrimers affected, and an additional COL4A3 or COL4A4 variant may not worsen disease. A woman with a pathogenic COL4A5 variant has on average 50% of her heterotrimers affected, which is increased to 75% with a further COL4A3 or COL4A4 variant and associated with a higher risk of proteinuria. In digenic Alport syndrome with pathogenic COL4A3 and COL4A4 variants, 75% of the heterotrimers are affected. The COL4A3 and COL4A4 genes occur head-to-head on chromosome 2, and inheritance is autosomal dominant when both variants affect the same chromosome (in cis) or recessive when they affect different chromosomes (in trans). This form of digenic disease results in increased proteinuria and a median age of kidney failure intermediate between autosomal dominant and autosomal recessive Alport syndrome. Previous guidelines have suggested that all pathogenic or likely pathogenic digenic variants should be identified and reported. Affected family members should be identified, treated, and discouraged from kidney donation. Inheritance within a family is easier to predict if the two variants are considered independently and if COL4A3 and COL4A4 variants are known to be inherited on the same or different chromosomes.

New Insights into Renal Failure in a Cohort of 317 Patients with Autosomal Dominant Forms of Alport Syndrome: Report of Two Novel Heterozygous Mutations in COL4A3.

Alport syndrome (AS) is a clinically and genetically heterogeneous disorder with a wide phenotypic spectrum, onset, and progression. X-linked AS (XLAS) and autosomal recessive AS (ARAS) are severe conditions, whereas the severity of autosomal dominant AS (ADAS) may vary from benign familial hematuria to progressive renal disease with extra-renal manifestations. In this study, we collated information from the literature and analyzed a cohort of 317 patients with ADAS carrying heterozygous disease-causing mutations in COL4A3/4 including four patients from two unrelated families who carried two novel variants in COL4A3. Regarding the age of onset of the disease, 80% of patients presented urinalysis alterations (microhematuria, hematuria, and/or proteinuria) before the age of 40 years. The cumulative probability of suffering adverse renal events was mainly observed between 30 and 70 years, without statistical differences between COL4A3 and COL4A4. We observed statistically significant differences between the sexes in the age of developing ESKD in cases affected by mutations in COL4A3/4 (p value = 0.0097), suggesting that males begin experiencing earlier deterioration of renal function than women. This study supports the importance of follow-up in young patients who harbor pathogenic mutations in COL4A3/4. We update the knowledge of ADAS, highlighting differences in the progression of the disease between males and females.

Bilateral Macular Retinoschisis Caused by Autosomal Recessive Alport Syndrome

A 76-year-old female with hearing loss and microhematuria without renal dysfunction presented with bilateral macular retinoschisis related to autosomal recessive Alport syndrome, representing the first case of macular retinoschisis in autosomal recessive disease.

Presumed COL4A3/COL4A4 Missense/Synonymous Variants Induce Aberrant Splicing.

BackgroundThe incorrect interpretation of missense and synonymous variants can lead to improper molecular diagnosis and subsequent faulty genetic counselling. The aim of this study was to evaluate the pathogenicity of presumed COL4A3/COL4A4 missense and synonymous variants detected by next-generation sequencing to provide evidence for diagnosis and genetic counselling.MethodsPatients' clinical findings and genetic data were analysed retrospectively. An in vitro minigene assay was conducted to assess the effect of presumed COL4A3/COL4A4 missense and synonymous variants on RNA splicing.ResultsFive unclassified COL4A3/COL4A4 variants, which were detected in five of 343 patients with hereditary kidney diseases, were analysed. All of them were predicted to affect splicing by Human Splicing Finder. The presumed COL4A3 missense variant c.4793T > G [p. (Leu1598Arg)] resulted in a loss of alternative full-length transcript during the splicing process. The COL4A3 transcript carried synonymous variant c.765G > A [p. (Thr255Thr)], led to an in-frame deletion of exon 13. Nevertheless, variants c.3566G > A [p. (Gly1189Glu)] in COL4A3 and c.3990G > A [p. (Pro1330Pro)], c.4766C > T [p. (Pro1589Leu)] in COL4A4 exhibited no deleterious effect on splicing. Among the five patients harbouring the abovementioned COL4A3/COL4A4 variants, three patients were genetically diagnosed with autosomal recessive Alport syndrome, one patient was highly suspected of having thin basement membrane nephropathy, and the other patient was clinically diagnosed with Alport syndrome.ConclusionsCOL4A3 presumed missense variant p. (Leu1598Arg) and synonymous variant p. (Thr255Thr) affect RNA splicing, which highlights the prime importance of transcript analysis of unclassified exonic sequence variants for better molecular diagnosis and genetic counselling. Meanwhile, the reliability of splicing predictions by predictive tools for exonic substitutions needs to be improved.

Analysis of genetic variant in a child with autosomal recessive Alport syndrome

To explore the genetic basis for a pedigree affected with Alport syndrome. Next generation sequencing and Sanger sequencing was applied to detect potential variants of the COL4A3, COL4A4 and COL4A5 genes among members from the pedigree and 100 unrelated healthy controls. The proband and his twin brother were found to carry two novel variants, namely c.4953G>A and c.4623C>A, of the COL4A4 gene, which were respectively inherited from her father and mother. The same variants were not detected among the 100 healthy controls and medical literature. Based on the guidelines of the American College of Medical Genetics and Genomics, both the c.4953G>A and c.4623C>A variants were predicted to be pathogenic (PVS1+PM2_supporting+PP1). The c.4953G>A and c.4623C>A variants of the COLA4A gene probably underlay the Alport syndrome in this pedigree. Above finding has enriched the spectrum of COLA4A gene variants.

Genotype\u2013phenotype correlations and nephroprotective effects of RAAS inhibition in patients with autosomal recessive Alport syndrome

BackgroundAutosomal 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.MethodsRetrospective 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.ResultsMedian 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.ConclusionsOur 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.