The Expanding Role of APOL1 Risk in Chronic Kidney Disease and Cardiovascular Disease

Trends in the epidemiology of childhood nephrotic syndrome in Africa: A systematic review

Background

Childhood nephrotic syndrome, if left untreated, leads to progressive kidney disease or death. We quantified the prevalence of steroid-sensitive nephrotic syndrome, steroid-resistant nephrotic syndrome, and histological types as the epidemiology of nephrotic syndrome in Africa remains unknown, yet impacts outcomes.

Methods

We searched MEDLINE, Embase, African Journals Online, and WHO Global Health Library for articles in any language reporting on childhood nephrotic syndrome in Africa from January 1, 1946 to July 1, 2020. Primary outcomes included steroid response, biopsy defined minimal change disease, and focal segmental glomerulosclerosis (FSGS) by both pooled and individual proportions across regions and overall.

Findings

There were 81 papers from 17 countries included. Majority of 8131 children were steroid-sensitive (64% [95% CI: 63-66%]) and the remaining were steroid-resistant (34% [95% CI: 33-35%]). Of children biopsied, pathological findings were 38% [95% CI: 36-40%] minimal change, 24% [95% CI: 22-25%] FSGS, and 38% [95% CI: 36-40%] secondary causes of nephrotic syndrome.

Interpretation

Few African countries reported on the prevalence of childhood nephrotic syndrome. Steroid-sensitive disease is more common than steroid-resistant disease although prevalence of steroid-resistant nephrotic syndrome is higher than reported globally. Pathology findings suggest minimal change and secondary causes are common. Scarcity of data in Africa prevents appropriate healthcare resource allocation to diagnose and treat this treatable childhood kidney disease to prevent poor health outcomes.

Funding

Funding was provided by the Canadian Institute for Health Research (CIHR) and the National Institute of Health (NIH) for the H3 Africa Kidney Disease Research Network. This research was undertaken, in part, from the Canada Research Chairs program.

Genetics of Cardiovascular Disease: How Far Are We from Personalized CVD Risk Prediction and Management?

Despite the rapid progress in diagnosis and treatment of cardiovascular disease (CVD), this disease remains a major cause of mortality and morbidity. Recent progress over the last two decades in the field of molecular genetics, especially with new tools such as genome-wide association studies, has helped to identify new genes and their variants, which can be used for calculations of risk, prediction of treatment efficacy, or detection of subjects prone to drug side effects. Although the use of genetic risk scores further improves CVD prediction, the significance is not unambiguous, and some subjects at risk remain undetected. Further research directions should focus on the “second level” of genetic information, namely, regulatory molecules (miRNAs) and epigenetic changes, predominantly DNA methylation and gene-environment interactions.

Beyond Panel-Based Testing: Exome Analysis Increases Sensitivity for Diagnosis of Genetic Kidney Disease

BACKGROUND

Next-generation sequencing (NGS) is a useful tool for evaluating patients with suspected genetic kidney disease. Clinical practice relies on the use of targeted gene panels that are ordered based on patient presentation. We compare the diagnostic yield of clinical panel-based testing to exome analysis.

METHODS

In total, 324 consecutive patients underwent physician-ordered, panel-based NGS testing between December 2014 and October 2018. Gene panels were available for four clinical phenotypes, including atypical hemolytic uremic syndrome (n=224), nephrotic syndrome (n=56), cystic kidney disease (n=26), and Alport syndrome (n=13). Variants were analyzed and clinical reports were signed out by a pathologist or clinical geneticist at the time of testing. Subsequently, all patients underwent retrospective exome analysis to detect additional clinically significant variants in kidney disease genes that were not analyzed as part of the initial clinical gene panel. Resulting variants were classified according to the American College of Medical Genetics and Genomics 2015 guidelines.

RESULTS

In the initial physician-ordered gene panels, we identified clinically significant pathogenic or likely pathogenic variants in 13% of patients (n=42/324). CFHR3-CFHR1 homozygous deletion was detected in an additional 13 patients with aHUS without a pathogenic or likely pathogenic variant. Diagnostic yield of the initial physician-ordered gene panel was 20% and varied between groups. Retrospective exome analysis identified 18 patients with a previously unknown pathogenic or likely pathogenic variant in a kidney disease gene and eight patients with a high-risk APOL1 genotype. Overall, retrospective exome analysis increased the diagnostic yield of panel-based testing from 20% to 30%.

CONCLUSIONS

These results highlight the importance of a broad and collaborative approach between the clinical laboratory and their physician clients that employs additional analysis when a targeted panel of kidney disease-causing genes does not return a clinically meaningful result.

Phenome-wide association analysis suggests the APOL1 linked disease spectrum primarily drives kidney-specific pathways

The relationship between commonly occurring genetic variants (G1 and G2) in the APOL1 gene in African Americans and different disease traits, such as kidney disease, cardiovascular disease, and pre-eclampsia, remains the subject of controversy. Here we took a genotype-first approach, a phenome-wide association study, to define the spectrum of phenotypes associated with APOL1 high-risk variants in 1,837 African American participants of Penn Medicine Biobank and 4,742 African American participants of Vanderbilt BioVU. In the Penn Medicine Biobank, outpatient creatinine measurement-based estimated glomerular filtration rate and multivariable regression models were used to evaluate the association between high-risk APOL1 status and renal outcomes. In meta-analysis of both cohorts, the strongest phenome-wide association study associations were for the high-risk APOL1 variants and diagnoses codes were highly significant for "kidney dialysis" (odds ratio 3.75) and "end stage kidney disease" (odds ratio 3.42). A number of phenotypes were associated with APOL1 high-risk genotypes in an analysis adjusted only for demographic variables. However, no associations were detected with non-renal phenotypes after controlling for chronic/end stage kidney disease status. Using calculated estimated glomerular filtration rate -based phenotype analysis in the Penn Medicine Biobank, APOL1 high-risk status was associated with prevalent chronic/end stage kidney disease /kidney transplant (odds ratio 2.27, 95% confidence interval 1.67-3.08). In high-risk participants, the estimated glomerular filtration rate was 15.4 mL/min/1.73m²; significantly lower than in low-risk participants. Thus, although APOL1 high-risk variants are associated with a range of phenotypes, the risks for other associated phenotypes appear much lower and in our dataset are driven by a primary effect on renal disease.

Racial disparities in end-stage renal disease in a high-risk population: the Southern Community Cohort Study

Introduction

The Southern Community Cohort Study is a prospective study of low socioeconomic status (SES) blacks and whites from the southeastern US, where the burden of end-stage renal disease (ESRD) and its risk factors are high. We tested whether the 2.4-fold elevated risk of ESRD we previously observed in blacks compared to whites was explained by differences in baseline kidney function.

Methods

We conducted a case-cohort study of incident ESRD cases (n = 737) with stored blood and a probability sampled subcohort (n = 4238) and calculated estimated glomerular filtration rate (eGFR) from serum creatinine. 86% of participants were enrolled from community health centers in medically underserved areas and 14% from the general population in 12 states in the southeastern United States. Incident ESRD after entry into the cohort was ascertained by linkage of the cohort with the US Renal Data System (USRDS).

Results

Median (25th, 75th percentile) eGFR at baseline was 63.3 (36.0, 98.2) ml/min/1.73m² for ESRD cases and 103.2 (86.0, 117.9) for subcohort. Black ESRD cases had higher median (25th, 75th) eGFR [63.3 (35.9, 95.9)] compared to whites [59.1 (39.4, 99.2)]. In multivariable Cox models accounting for sampling weights, baseline eGFR was a strong predictor of ESRD risk, and an interaction with race was detected (P = 0.029). The higher ESRD risk among blacks relative to whites persisted (hazard ratio: 2.58; 95% confidence interval: 1.65, 4.03) after adjustment for eGFR.

Conclusion

In this predominantly lower SES cohort, the racial disparity in ESRD risk is not explained by differences in baseline kidney function.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1502-z) contains supplementary material, which is available to authorized users.

Incremental risk of cardiovascular disease and/or chronic kidney disease for future ASCVD and mortality in patients with type 2 diabetes mellitus: ACCORD trial

BACKGROUND

Cardiovascular disease (CVD) and chronic kidney disease (CKD) are complications of type 2 diabetes mellitus (DM). Current cholesterol guidelines recommend the same prevention strategy for patients with DM alone as patients with DM + CKD. However, the incremental risk of these common complications for incident cardiovascular disease and mortality has not been well studied.

METHODS

We compared the incremental risk of having DM + CKD, DM + CVD and DM + CVD + CKD in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial participants for incident CVD as the primary outcome and all-cause mortality.

RESULTS

After a mean (SD) follow up of 4.7(1.4) years, 1,046(10%) participants developed CVD. DM +vCKD, DM + CVD, and DM + CKD + CVD had a significantly increased risk of the primary outcome compared to DM alone [adjusted hazard ratio(95%CI): 1.41 (1.06-1.89), p = 0.02; 2.20 (1.92-2.53), p < 0.001); 2.35 (1.81-3.04), p < 0.001), respectively]. All-cause mortality had a graded increased risk compared to the reference group [adjusted hazard ratio(95%CI): 1.39 (1.01-1.90), p = 0.04; 1.29 (1.51-2.12), p < 0.0001; 2.36 (1.75-3.13), p < 0.0001), respectively].

CONCLUSION

Our post hoc analysis shows an incremental graded risk for CVD outcomes and all-cause mortality with the development of CKD and/or CVD in individuals with DM.

Genetics, Genomics, and Precision Medicine in End-Stage Kidney Disease

Recent advances in genetics of renal disease have deepened our understanding of progressive kidney disease. Here, we review genetic variants that are of particular importance to progressive glomerular disease that result in end-stage kidney disease (ESKD). Some of the most striking findings relate to APOL1 genetic variants, seen exclusively in individuals of sub-Saharan African descent, that create a predisposition to particular renal disorders, including focal segmental glomerulosclerosis and arterionephrosclerosis. We also review the genetics of cardiovascular disease in ESKD and note that little work has been published on the genetics of other ESKD complications, including anemia, bone disease, and infections. Deeper understanding of the genetics of ESKD and its complications may lead to new therapies that are tailored to an individual patient's genetic profile or are discovered based on genetic approaches that identify novel pathways of renal cell injury and repair.

Advances in molecular diagnosis and therapeutics in nephrotic syndrome and focal and segmental glomerulosclerosis

PURPOSE OF REVIEW

The widespread adoption of next-generation sequencing by research and clinical laboratories has begun to uncover the previously unknown genetic basis of many diseases. In nephrology, one of the best examples of this is seen in focal and segmental glomerulosclerosis (FSGS) and nephrotic syndrome. We review advances made in 2017 as a result of human and molecular genetic studies as it relates to FSGS and nephrotic syndrome.

RECENT FINDINGS

There are more than 50 monogenic genes described in steroid-resistant nephrotic syndrome and FSGS, with seven reported in 2017. In individuals presenting with FSGS or nephrotic syndrome before or at the age of 18 years, the commonest genes in which a mutation is found continues to be limited to only a few including NPHS1 and NPHS2 based on multiple studies. For FSGS or nephrotic syndrome that presents after 18 years, mutations in COl4A3/4/5, traditionally associated with Alport syndrome, are increasingly being reported. Despite the extensive genetic heterogeneity in FSGS, there is evidence that some of these genes converge onto common pathways. There are also reports of in-vivo models exploring apolipoprotein 1 biology, variants in which account for part of the increased risk of nondiabetic kidney disease in African-Americans. Finally, genetic testing has several clinical uses including clarification of diagnosis and treatment; identification of suitable young biologic relatives for kidney donation; and preimplantation genetic diagnosis. CRISPR gene editing is currently an experimental tool only, but the recent reports of excising mutations in embryos could be a therapeutic option for individuals with any monogenic disorder in the future.

SUMMARY

Sequencing efforts are bringing novel variants into investigation and directing the efforts to understand how these lead to disease phenotypes. Expanding our understanding of the genetic basis of health and disease processes is the necessary first step to elaborate the repertoire of therapeutic agents available for patients with FSGS and nephrotic syndrome.

Apolipoprotein L1 nephropathies: 2017 in review

PURPOSE OF REVIEW

To review publications relating to apolipoprotein L1 (APOL1) renal risk variants published 2017.

RECENT FINDINGS

The study of APOL1 variants continues to be highly active; 24 articles published in 2017 were selected to highlight. These include clinical studies of kidney disease, kidney transplantation, hypertension, cardiovascular disease, and genetic diversity. Laboratory studies included APOL1 association with vesicle-associated membrane soluble N-ethylmaleimide-sensitive factor activating protein receptor protein and with soluble urokinase-type plasminogen activator receptor, mitochondrial dysfunction, endolysosomal dysfunction, and inflammasome activation.

SUMMARY

Our understanding of the role of APOL1 genetic variants and the mechanisms for renal toxicity continues to deepen. It is not yet clear which pathways are most relevant to human disease, and so, the most relevant drug targets remain to be defined.