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

Multidisciplinary management improves the genetic diagnosis of hereditary kidney diseases in the next generation sequencing (NGS) era

BACKGROUND AND OBJECTIVE

Hereditary kidney diseases (HKD) are a frequent cause of chronic kidney disease, and their diagnosis has increased since the introduction of next generation sequencing (NGS). In 2018, the Multidisciplinary Unit for Hereditary Kidney Diseases of the Region of Murcia (UMERH-RM) was founded based on the genetic study of HKD. The objective of this study is to analyze the results obtained in the first 3 years of operation, and to analyze the clinical factors associated to a final genetic diagnosis.

MATERIALS AND METHODS

All the patients studied with the HKD gene panel were included. The characteristics between those who obtained a final genetic diagnosis and those who did not were compared.

RESULTS

A total of 360 patients were studied, detecting genetic variants in 164 not related patients (45.6%). 45 of these were variants of uncertain significance requiring a family co-segregation study, which was facilitated by the multidisciplinary unit. Overall, considering the results obtained with the NGS panel and the extended genomic studies, a final diagnostic yield of HRD of 33.3% (120/360) was achieved, and including incidental findings 35.6% (128/360). Two hundred and twenty-three patients with suspected Alport syndrome were studied. Diagnosis was confirmed in 28.5% (COL4A4 most frequent gene), more frequently women with an obvious compatible family history. They also had frequently microhematuria, although 5 patients without microhematuria confirmed the diagnosis. There were no differences in age, proteinuria, renal function, hearing loss, or ophthalmologic abnormalities. The most frequent finding in the renal biopsy was mesangial proliferation. We estimate that 39 patients avoided renal biopsy. A total of 101 patients with suspected PKD were also studied, 49.5% had a conclusive genetic result (most frequent gene PKD1), more frequently women, with larger kidney sizes (although 9 patients with normal kidney size confirmed diagnosis). Again, the most predictive characteristic of genetic outcome was family history.

CONCLUSIONS

The implementation of an NGS panel for HKD, together with the multidisciplinary approach to cases, has improved the diagnostic performance of HKD. In our sample, autosomal dominant Alport syndrome is of highest incidence. Ophthalmological and auditory examinations did not contribute to the diagnosis. We have seen a significant decrease in the indication of renal biopsies thanks to molecular diagnosis. The multidisciplinary approach, with the active participation of nephrologists, paediatricians, clinical and molecular geneticists, with insistence on adequate patient phenotyping and review of their family history, offers a better interpretation of genetic variants, allowing reclassification of the diagnosis of some nephropathies, thus improving their management and genetic advice.

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.

Treatment of Severe Atopic Dermatitis with Dupilumab in Three Patients with Renal Diseases

BACKGROUND

Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disease that can affect patients' quality of life. Dupilumab is the first biologic agent approved for the treatment of patients with inadequately controlled moderate-to-severe AD and its mechanism of action is based on the inhibition of the interleukin (IL)-4 and IL-13 signaling. There are only a few data on the safety of dupilumab in AD patients with comorbidities, including kidney disorders.

MATERIALS AND METHODS

Descriptive retrospective series of three patients with chronic kidney diseases (Alport syndrome, IgA nephropathy, and hypertensive nephrosclerosis, respectively) receiving dupilumab for their concomitant severe AD.

RESULTS

Treatment with a standard dosage of dupilumab caused a relevant improvement of AD in all patients without any adverse events or worsening of renal function. In a patient with severe renal failure, the drug was effective and well tolerated without the need for any dose adjustments, also after the initiation of peritoneal dialytic treatment.

CONCLUSION

Our case series suggests the use of dupilumab as an effective and safe treatment for AD patients suffering from renal diseases, although additional studies are required to confirm such preliminary findings.

Good maternal and fetal outcomes of three consecutive pregnancies in a Mediterranean woman with Alport syndrome: a case report

BACKGROUND

Alport syndrome is a rare inherited disorder affecting the glomerular basement membrane, manifested by hematuria and proteinuria that is commonly associated with ocular and hearing defects. There is limited information about the maternal and fetal outcomes of Alport syndrome in pregnancy.

CASE PRESENTATION

We describe a smooth course of pregnancy, a good maternal outcome, and a good fetal outcome in three consecutive pregnancies for a 35-year-old Mediterranean woman with Alport syndrome over a 10-year duration. Although there was a nephrotic range of progressive proteinuria in all her pregnancies, there was a prompt drop in proteinuria within 2 weeks of her deliveries. She has constantly shown a normal serum creatinine level and a normal serum protein level in all her pregnancies. Apart from a single episode of asymptomatic hypertension in her second pregnancy at 34 weeks of gestation that returned to a normal range immediately after delivery, she was normotensive antenatally and postnatally. She gave birth by cesarean section to three healthy newborns.

CONCLUSIONS

A normal prepregnancy creatinine level and a mild range of proteinuria in a patient with normotension, who is not on any medication, are associated with good maternal and fetal outcomes. Furthermore, successful pregnancy that is followed by a normal renal function test might suggest a favorable outcome for any future pregnancy.

Genetic Kidney Diseases (GKDs) Modeling Using Genome Editing Technologies

Genetic kidney diseases (GKDs) are a group of rare diseases, affecting approximately about 60 to 80 per 100,000 individuals, for which there is currently no treatment that can cure them (in many cases). GKDs usually leads to early-onset chronic kidney disease, which results in patients having to undergo dialysis or kidney transplant. Here, we briefly describe genetic causes and phenotypic effects of six GKDs representative of different ranges of prevalence and renal involvement (ciliopathy, glomerulopathy, and tubulopathy). One of the shared characteristics of GKDs is that most of them are monogenic. This characteristic makes it possible to use site-specific nuclease systems to edit the genes that cause GKDs and generate in vitro and in vivo models that reflect the genetic abnormalities of GKDs. We describe and compare these site-specific nuclease systems (zinc finger nucleases (ZFNs), transcription activator-like effect nucleases (TALENs) and regularly clustered short palindromic repeat-associated protein (CRISPR-Cas9)) and review how these systems have allowed the generation of cellular and animal GKDs models and how they have contributed to shed light on many still unknown fields in GKDs. We also indicate the main obstacles limiting the application of these systems in a more efficient way. The information provided here will be useful to gain an accurate understanding of the technological advances in the field of genome editing for GKDs, as well as to serve as a guide for the selection of both the genome editing tool and the gene delivery method most suitable for the successful development of GKDs models.