Outcomes of kidney transplantation in Alport syndrome compared with other forms of renal disease

Alport syndrome: an update

PURPOSE OF REVIEW

The recent widespread availability of genetic testing has resulted in the diagnosis of many more people with Alport syndrome. This increased recognition has been paralleled by advances in understanding clinical consequences, genotype-phenotype correlations and in the development of new therapies.

RECENT FINDINGS

These include the international call for a change of name to 'Alport spectrum' which better reflects the diverse clinical features seen with autosomal dominant and X-linked Alport syndrome; the demonstration of how common Alport syndrome is in people with haematuria, proteinuria, or kidney failure; the inability of current genetic testing to detect all pathogenic variants in suspected Alport syndrome; the different genotype-phenotype correlations for autosomal dominant and X-linked disease; and the novel treatments that are available including SGLT2 inhibitors for persistent albuminuria despite renin-angiotensin-aldosterone blockade, as well as early studies of gene-modifying agents.

SUMMARY

Autosomal dominant Alport syndrome is the commonest genetic kidney disease and X-linked Alport syndrome is the second commonest genetic cause of kidney failure. Both these diseases are frequently seen in the renal clinic, and clinicians should be aware of their likelihood in a person with persistent glomerular haematuria, proteinuria or kidney failure. Autosomal dominant Alport syndrome is so common that it also occurs coincidentally in other kidney diseases especially IgA nephropathy.

Alport Syndrome Presenting as Incidental Finding of Proteinuria on Pre-Employment Checkup: A Case Report

Introduction: Glomerulonephritis is a prominent cause of chronic kidney disease and encompasses a subset of renal diseases characterized by immune-mediated damage to the basement membrane, the mesangium, or the capillary endothelium. Symptoms in early stages are usually nonspecific and can be easily overlooked. Unfortunately, if not detected early, this may lead to end-stage renal disease. We present a case of a 23-year-old male patient with no family of kidney disease who had proteinuria on routine urinalysis. Case Presentation: A 23-year-old male, nonhypertensive and nondiabetic, with no family history of kidney disease coming in for proteinuria. During pre-employment checkup, patient was noted to have 4+ proteinuria on urinalysis. Creatinine was requested by company doctor with result of 1.05 mg/dL (eGFR: 104 mL/min/1.73 m2). Repeat urinalysis was done but still with 4+ proteinuria on urinalysis. Hence, advised consult with a nephrologist due to persistence of proteinuria. Upon consult, workups were done, which revealed hyperuricemia, urate crystals on urinalysis, persistence of 4+ proteinuria, and urine protein creatinine ratio of 2.8 (urine protein: 223.28 mg/dL and urine creatinine: 79.64 mg/dL). Patient was started on ACE inhibitor, hypouricemic agent, and advised kidney biopsy for further evaluation of proteinuria. The review of systems was pertinent for hearing impairment and blurring of vision. Kidney biopsy was done in which electron microscopy showed segmental podocyte foot process effacement. The glomerular basement membrane shows lamellation and alternate thickening and thinning. No definite electron-dense deposits are seen in glomerular basement membrane and mesangium. Mean glomerular basement membrane thickness is 299 nm (normal mean glomerular basement membrane thickness in adult males is 373 ± 42 nm). He was advised consult with an ophthalmologist and otolaryngologist. Regular checkup, monitoring of renal parameters, and appropriate medications were given. Conclusion: Although a rare cause of glomerulonephritis, Alport syndrome must be considered in patients presenting with subnephrotic range proteinuria and microscopic hematuria. Thorough history and physical examination and characteristic findings on kidney biopsy can help in the prompt diagnosis of the disease. Multidisciplinary care and early intervention can improve the quality of life and delay the progression to end-stage kidney disease among these patients.

Synergistic toxicity of compound heterozygous mutations in the COL4A3 gene causes end-stage renal disease in A large family of Alport syndrome

Alport syndrome (AS) is a genetic disorder characterized by kidney disease and hearing/vision abnormalities, resulting from mutations in the COL4A3, COL4A4, or COL4A5 genes. While numerous mutations have been identified in AS cases, the precise molecular mechanisms, particularly for compound mutations, remain under investigation. This study investigated the molecular mechanisms of AS in a proband with end-stage kidney disease (ESKD) using whole exome sequencing, which identified two compound heterozygous COL4A3 missense mutations: NM_000091.5:c.1354G > A (p.G452R) and NM_000091.5:c.4793 T > G (p.L1598R). Sixteen family members of the proband were genotyped, and further analyses, including in silico structural prediction, molecular docking, and in vitro co-immunoprecipitation assays, revealed that the p.G452R mutation disrupted the collagen triple helical structure, associated with hematuria in carriers, while the p.L1598R mutation interfered with the interaction between the NC1 domains of COL4A3 and COL4A4 proteins, crucial for collagen trimerization. These findings demonstrate a synergistic loss-of-function effect of the two mutations, contributing to the AS pathogenesis in the proband, and emphasize the importance of genetic screening and personalized treatment strategies for AS.

Explaining Alport syndrome-lessons from the adult nephrology clinic

Alport syndrome is a genetic kidney disease that causes worsening of kidney function over time, often progressing to kidney failure. Some types of Alport syndrome cause other symptoms and signs, including hearing loss and eye abnormalities. Research now indicates that Alport syndrome (autosomal dominant inheritance) is the most common form. Alport syndrome can have X-linked or a rare form of autosomal recessive inheritance. Traditionally, a kidney biopsy was used to diagnose Alport syndrome, but genetic testing provides a more precise and less invasive means of diagnosis and reveals the underlying pattern of inheritance. At present, there are no specific curative treatments for Alport syndrome however there is a strong international effort in pursuit of future therapies. Currently, angiotensin-converting enzyme inhibitors (ACEi), or an angiotensin receptor blocker (ARB) if a patient cannot tolerate an ACEi, slow down the progression of kidney disease and can delay the onset of kidney failure by years. There are other potential treatments in research that potentially can help delay the onset of kidney issues. Early treatment of patients and identification of their at-risk relatives is a priority. People living with Alport syndrome and their doctors now benefit from an active international research community working on translating further treatments into clinical practice and providing up-to-date clinical guidelines.

A case report and literature study on Alport syndrome featuring nephrotic syndrome as its primary manifestation

BACKGROUND

Historically, due to the lack of distinct clinical symptoms, Alport syndrome, a hereditary kidney disease prevalent in children and a leading cause of kidney failure, has often been misdiagnosed as other kidney conditions.

CASE DESCRIPTION

This article presents a comprehensive review and analysis of clinical data concerning a child diagnosed with Alport syndrome, where nephrotic syndrome served as the primary manifestation. The male child in this case exhibited symptoms starting at the age of 6, initially diagnosed as nephrotic syndrome. Consequently, oral steroid medication was administered, proving ineffective. Due to persistent proteinuria and microscopic hematuria, a renal biopsy was performed. Immunofluorescence staining revealed no abnormal expression of the α3, α4, and α5 chains of type IV collagen. Notably, electron microscopy revealed the basement membrane to be partially torn and arachnoid. Genetic testing indicated a hemizygous COL4A5 acceptor-splice-site mutation c.4707-1(IVS50)G > A, inherited from his mother.

CONCLUSION

This specific mutated locus, being the first of its kind reported, adds valuable information to the existing gene mutation spectrum of Alport syndrome. Consequently, it emphasizes the importance for clinicians to deepen their understanding of rare kidney diseases, contributing to enhanced diagnostic accuracy and improved patient care.

Association of Primary Kidney Disease Type and Donor Relatedness With Live Donor Kidney Transplant Outcomes: An Analysis of ANZDATA

RATIONALE & OBJECTIVE

There is limited information about the association between primary kidney disease and donor relatedness with transplant outcomes. This study addresses this gap by evaluating clinical outcomes after kidney transplantation in recipients of living donor kidneys as a function of primary kidney disease type and donor relatedness in Australia and New Zealand.

STUDY DESIGN

Retrospective observational study.

SETTING & PARTICIPANTS

Kidney transplant recipients who received allografts from living donors between January 1, 1998, and December 31, 2018, as recorded in the Australian and New Zealand Dialysis and Transplant Registry (ANZDATA).

EXPOSURES

Primary kidney disease type categorized as majority monogenic, minority monogenic, or other primary kidney disease based on disease heritability as well as donor relatedness.

OUTCOME

Primary kidney disease recurrence, graft failure.

ANALYTICAL APPROACH

Kaplan-Meier analysis and Cox proportion hazards regression to generate hazard ratios for primary kidney disease recurrence, allograft failure, and mortality. Partial likelihood ratio test was used to examine possible interactions between primary kidney disease type and donor relatedness for both study outcomes.

RESULTS

Among 5,500 live donor kidney transplant recipients, majority monogenic (adjusted HR, 0.58, P<0.001) and minority monogenic primary kidney diseases (adjusted HR, 0.64, P<0.001) were associated with reduced primary kidney disease recurrence compared with other primary kidney diseases. Majority monogenic primary kidney disease was also associated with reduced allograft failure (adjusted HR, 0.86, P=0.04) compared with other primary kidney diseases. Donor relatedness was not associated with primary kidney disease recurrence nor graft failure. No interaction was detected between primary kidney disease type and donor relatedness for either study outcome.

LIMITATIONS

Potential misclassification of primary kidney disease type, incomplete ascertainment of primary kidney disease recurrence, unmeasured confounding.

CONCLUSIONS

Monogenic primary kidney disease is associated with lower rates of primary kidney disease recurrence and allograft failure. Donor relatedness was not associated with allograft outcomes. These results may inform pretransplant counseling and live donor selection.

PLAIN-LANGUAGE SUMMARY

There are theoretical concerns that live-donor kidney transplants may be associated with increased risks of kidney disease recurrence and transplant failure due to unmeasurable shared genetic factors between the donor and the recipient. This study analyzed data from the Australia and New Zealand Dialysis and Transplant (ANZDATA) registry and showed that, although disease type was associated with the risk of disease recurrence and transplant failure, donor relatedness did not impact transplant outcomes. These findings may inform pretransplant counseling and live donor selection.

Uncovering Modifier Genes of X-Linked Alport Syndrome Using a Novel Multiparent Mouse Model

BACKGROUND

Mutations in COL4A5 are responsible for 80% of cases of X-linked Alport Syndrome (XLAS). Although genes that cause AS are well characterized, people with AS who have similar genetic mutations present with a wide variation in the extent of kidney impairment and age of onset, suggesting the activities of modifier genes.

METHODS

We created a cohort of genetically diverse XLAS male and female mice using the Diversity Outbred mouse resource and measured albuminuria, GFR, and gene expression. Using a quantitative trait locus approach, we mapped modifier genes that can best explain the underlying phenotypic variation measured in our diverse population.

RESULTS

Genetic analysis identified several loci associated with the variation in albuminuria and GFR, including a locus on the X chromosome associated with X inactivation and a locus on chromosome 2 containing Fmn1. Subsequent analysis of genetically reduced Fmn1 expression in Col4a5 knockout mice showed a decrease in albuminuria, podocyte effacement, and podocyte protrusions in the glomerular basement membrane, which support the candidacy of Fmn1 as a modifier gene for AS.

CONCLUSION

With this novel approach, we emulated the variability in the severity of kidney phenotypes found in human patients with Alport Syndrome through albuminuria and GFR measurements. This approach can identify modifier genes in kidney disease that can be used as novel therapeutic targets.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

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

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