APOL1 Long-term Kidney Transplantation Outcomes Network (APOLLO): Design and Rationale

APOL1 Nephropathy Risk Variants Through the Life Course: A Review

Two variant alleles of the gene apolipoprotein L1 (APOL1), known as risk variants (RVs), are a major contributor to kidney disease burden in those of African descent. The APOL1 protein contributes to innate immunity and may protect against Trypanosoma, HIV, Salmonella, and leishmaniasis. However, the effects of carrying 1 or more RVs contribute to a variety of disease processes starting as early as in utero and can be exacerbated by other factors (or "second hits"). Indeed, these genetic variations interact with environmental exposures, infections, and systemic disease to modify health outcomes across the life span. This review focuses on APOL1-associated diseases through the life-course perspective and discusses how early exposure to second hits can impact long-term outcomes. APOL1-related kidney disease typically presents in adolescents to young adults, and individuals harboring RVs are more likely to progress to kidney failure than are those with kidney disease who lack APOL-1 RVs. Ongoing research is aimed at elucidating the association of APOL1 RV effects with adverse donor and recipient kidney transplant outcomes. Unfortunately, there is currently no established treatment for APOL1-associated nephropathy. Long-term research is needed to evaluate the risk and protective factors associated with APOL1 RVs at different stages of life.

APOL1 Kidney Risk Variants and Long-Term Kidney Function in Healthy Middle-Aged Black Individuals: The Atherosclerosis Risk in Communities (ARIC) Study

Rationale & Objective

The effect of apolipoprotein L1(APOL1) genotype on future risk of kidney disease among middle-aged individuals with good kidney function is not well established.

Study Design

Longitudinal cohort study.

Setting & Participants

In total, 5,886 healthy individuals (45-64 years old) enrolled in the Atherosclerosis Risk in Communities study with creatinine-based estimated glomerular filtration rate ≥ 80 mL/min who would be suitable kidney donors.

Exposures

Race and APOL1 genotype.

Outcomes

Creatinine- and cystatin C-based estimated glomerular filtration rate (eGFRcr-cys) using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2021 equation, urinary albumin-creatinine ratio (UACR), proportion with chronic kidney disease (CKD) 3a or worse, end-stage kidney disease (ESKD), and death.

Analytical Approach

Participants grouped based on race and APOL1 genotype. Compared eGFRcr-cys and UACR across groups. Multinomial logistic regression models were used compare odds of CKD. Kaplan-Meier survival curves were created to compare rates of ESKD and death at last follow-up.

Results

There were 5,075 Whites (86%), 701 Blacks carrying the low-risk APOL1 genotype (12%), and 110 Blacks carrying the high-risk APOL1 genotype (2%). The mean age at baseline was 53 ± 6 years. At 10 years, White participants had lower eGFRcr-cys than low-risk and high-risk groups (89 ± 16 vs 91 ± 16 and 92 ± 15 mL/min/1.73 m2, respectively; P < 0.001). At 25 years, White participants continued to have lower eGFRcr-cys than the low-risk group (70 ± 18 vs 72 ± 19 mL/min/1.73 m2; P < 0.001) but not compared with the high-risk APOL1 genotype (67±23 mL/min/1.73 m2). There was no difference in UACR among groups at 10 and 25 years (P = 0.87 and 0.91, respectively). The odds of developing CKD stage 3a or worse were not different between low-risk and high-risk APOL1 group in both unadjusted and adjusted models (P = 0.26 and P = 0.39, respectively). At last follow-up, <5% developed ESKD, and 45% of individuals either died or reached ESKD with no difference in outcomes between the groups.

Limitations

Low ascertainment because of death and long follow-up.

Conclusions

Among middle-aged individuals, APOL1 genotype does not appear to be a major driver of future risk of kidney disease.

Reviewing Racial Disparities in Living Donor Kidney Transplantation: a Socioecological Approach

Despite kidney transplantation having superior outcomes to dialytic therapies, disparities continue to exist among rates of kidney transplantation between Black and non-Hispanic White patients, which cannot be explained by differences in individual characteristics. To better evaluate the persistent Black/White disparities in living kidney transplantation, we review the extant literature and include the critical factors and recent development in living kidney transplantation in the socioecological approach. We also emphasize the potential vertical and hierarchical associations among factors in the socioecological model. Specifically, this review explores the possibility that the relatively low living kidney transplantation among Blacks may be a consequence of individual, interpersonal, and structural inequalities in various social and cultural dimensions. At the individual level, the Black/White differences in socioeconomic conditions and transplant knowledge may account for the low transplantation rates among Blacks. Interpersonally, the relatively weak social support and poor communication between Black patients and their providers may contribute to disparities. At the structural level, the race-based glomerular filtration rate (GFR) calculation that is widely used to screen Black donors is a barrier to receiving living kidney transplantation. This factor is directly related to structural racism in the health care system but its potential impact on living donor transplantation is underexplored. Finally, this literature review emphasizes the current perspective that a race-free GFR should be considered and a multidisciplinary and interprofessional perspective is necessary to devise strategies and interventions to reduce the Black/White disparities in living donor kidney transplantation in the U.S.

Evaluating ApoL1 Genetic Testing Policy Options for Transplant Centers: A Delphi Consensus Panel Project with Stakeholders

BACKGROUND

Apolipoprotein L1 (ApoL1) variants G1 and G2 are associated with a higher risk of kidney disease. ApoL1 risk variants are predominantly seen in individuals with sub-Saharan African ancestry. In most transplant centers, potential organ donors are being selectively genetically tested for ApoL1 risk variants. Transplant programs have highly variable ApoL1 testing practices and need guidance on essential ApoL1 clinical policy questions.

METHODS

We conducted a Delphi consensus panel focused on ApoL1 clinical policy questions, including who gets tested, who decides whether testing occurs, how test results are shared, who receives test results, and how test results are used. A total of 27 panelists across seven stakeholder groups participated: living kidney donors ( n =4), deceased donor family members ( n =3), recipients of a deceased donor kidney ( n =4), recipients of a living donor kidney ( n =4), nephrologists ( n =4), transplant surgeons ( n =4), and genetic counselors ( n =4). Nineteen panelists (70%) identified as Black. The Delphi panel process involved two rounds of educational webinars and three rounds of surveys administered to panelists, who were asked to indicate whether they support, could live with, or oppose each policy option.

RESULTS

The panel reached consensus on one or more acceptable policy options for each clinical policy question; panelists supported 18 policy options and opposed 15. Key elements of consensus include the following: ask potential donors about African ancestry rather than race; make testing decisions only after discussion with donors; encourage disclosure of test results to blood relatives and organ recipients but do not require it; use test results to inform decision making, but never for unilateral decisions by transplant programs.

CONCLUSIONS

The panel generally supported policy options involving discussion and shared decision making among patients, donors, and family stakeholders. There was general opposition to unilateral decision making and prohibiting donation altogether.

Augmenting the Unites States transplant registry with external mortality data: A moving target ripe for further improvement

The Organ Procurement and Transplantation Network conducts a robust death verification process when augmenting the United States transplant registry with external sources of data. Process enhancements added over 35,000 externally verified deaths across waitlist candidates and transplant recipients for all organs beginning in April 2022. Ninety-four percent of added posttransplant deaths occurred beyond 5 years posttransplant, and over 74% occurred beyond 10 years. Deceased donor solid organ recipients transplanted from January 1, 2010, through October 31, 2020, were analyzed from January and July 2022 Organ Procurement and Transplantation Network Standard Transplant Analysis and Research and the Scientific Registry of Transplant Recipients Standard Analysis Files to quantify the impact of including vs excluding unverified deaths (not releasable to researchers) on posttransplant patient survival estimates. Across all organs, 1- and 5-year posttransplant survival rates were not substantially impacted; meaningful differences were observed in 10-year survival among kidney recipients. These findings bear important implications for anyone who utilized transplant registry data to examine long-term outcomes prior to the updated verification process. Users of transplant surveillance data should interpret results of long-term outcomes cautiously, particularly differences across subpopulations, and the transplant community should identify ways to improve data quality and minimize the reporting burden on transplant institutions.

Monogenic and polygenic concepts in chronic kidney disease (CKD)

Kidney function is strongly influenced by genetic factors with both monogenic and polygenic factors contributing to kidney function. Monogenic disorders with primarily autosomal dominant inheritance patterns account for 10% of adult and 50% of paediatric kidney diseases. However, kidney function is also a complex trait with polygenic architecture, where genetic factors interact with environment and lifestyle factors. Family studies suggest that kidney function has significant heritability at 35-69%, capturing complexities of the genome with shared environmental factors. Genome-wide association studies estimate the single nucleotide polymorphism-based heritability of kidney function between 7.1 and 20.3%. These heritability estimates, measuring the extent to which genetic variation contributes to CKD risk, indicate a strong genetic contribution. Polygenic Risk Scores have recently been developed for chronic kidney disease and kidney function, and validated in large populations. Polygenic Risk Scores show correlation with kidney function but lack the specificity to predict individual-level changes in kidney function. Certain kidney diseases, such as membranous nephropathy and IgA nephropathy that have significant genetic components, may benefit most from polygenic risk scores for improved risk stratification. Genetic studies of kidney function also provide a potential avenue for the development of more targeted therapies and interventions. Understanding the development and validation of genomic scores is required to guide their implementation and identify the most appropriate potential implications in clinical practice. In this review, we provide an overview of the heritability of kidney function traits in population studies, explore both monogenic and polygenic concepts in kidney disease, with a focus on recently developed polygenic risk scores in kidney function and chronic kidney disease, and review specific diseases which are most amenable to incorporation of genomic scores.

Emerging Preventive Strategies in Chronic Kidney Disease: Recent Evidence and Gaps in Knowledge

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is increasingly prevalent worldwide and is associated with increased cardiovascular risk. New therapeutic options to slow CKD progression and reduce cardiovascular morbidity and mortality have recently emerged. This review highlights recent evidence and gaps in knowledge in emerging CKD preventive strategies.

RECENT FINDINGS

EMPA-Kidney trial found that empagliflozin, a sodium-glucose co-transporter 2 inhibitor (SGLT2i) led to 28% lower risk of progression of kidney disease or death from cardiovascular causes, compared to placebo. This reinforced the previous findings from DAPA-CKD and CREDENCE trials and led to inclusion of SGLT2i as the cornerstone of CKD preventive therapy in both diabetic and non-diabetic CKD. Finerenone, a selective nonsteroidal mineralocorticoid receptor antagonist, slowed diabetic kidney disease progression by 23% compared to placebo in a pool analysis of FIDELIO-DKD and FIGARO-DKD trials. Non-pharmacological interventions, including low protein diet, and early CKD detection and risk stratification strategies based on novel biomarkers have also gained momentum. Ongoing efforts to explore the wealth of molecular mechanisms in CKD, added to integrative omics modeling are well posed to lead to novel therapeutic targets in kidney care. While breakthrough pharmacological interventions continue to improve outcomes in CKD, the heterogeneity of kidney diseases warrants additional investigation. Further research into specific kidney disease mechanisms will facilitate the identification of patient populations most likely to benefit from targeted interventions.

The Impact of Ethnicity on Research Authorization at the Time of Organ Donation: A Single-Center Experience Among Deceased Donor Kidney Transplantation

Objective

Research on deceased organ donors is needed to expand the donor organ supply. Little is known about the rate of research authorization among various groups. We aimed to determine the percentage of research authorization by the deceased donor family across different donor characteristics.

Materials and Methods

We performed a retrospective review of deceased donors referred to one U.S. institution for kidney transplantation over a 12-month period. Organs were offered from multiple organ procurement organizations (OPO) across the United States. Stepwise logistic regression was performed to determine the predictors of research authorization.

Results

From 10/2018 to 10/2019, 437 deceased donors were accepted for transplantation. 81.5% came from OPOs outside our donor service area and 18.5% from our local OPO. Overall, research authorization was declined in 24.0% of donors. Declined authorization was highest among Black donors (42.0%) compared to Whites (16.3%) and Hispanics (26.9%); p=0.000006. Donors <35 years had highest declined research authorization at 42.9% compared to older donors. There were no significant differences between individual OPOs.

Conclusion

Deceased donor research authorization declined at the time of organ donation is higher among Black and younger donors. There is an immediate need for the transplant and donor community to develop best-practices to eliminate barriers to research in organ transplantation.

Early recurrence of focal segmental glomerulosclerosis in a kidney transplant recipient with APOL1 one risk variant

Apolipoprotein 1 (APOL1) risk variants (G1 and G2) are associated with focal segmental glomerulosclerosis (FSGS) in patients of African ancestry. The prevalence of APOL1 two risk variants is lower in Hispanics and very rare in European and Asian populations. APOL1 two risk variants in donor kidneys is associated with recipient kidney graft loss, however the effect of recipient risk variant in the kidney transplant outcome is unclear. Here, we present a late adolescent male with FSGS and end stage renal disease with one APOL1 risk variant (G2) who had immediate recurrence of FSGS in the post-KT period. There was an excellent response to few sessions of plasmapheresis and Rituximab with no further recurrence of FSGS in the 1 year follow-up period. It needs to be seen whether the recipient APOL1 single risk variant causes increased susceptibility to kidney graft loss on a long run via recurrent or de novo pathologies.

A Primer in Precision Nephrology: Optimizing Outcomes in Kidney Health and Disease through Data-Driven Medicine

This year marks the 63rd anniversary of the International Society of Nephrology, which signaled nephrology's emergence as a modern medical discipline. In this article, we briefly trace the course of nephrology's history to show a clear arc in its evolution-of increasing resolution in nephrological data-an arc that is converging with computational capabilities to enable precision nephrology. In general, precision medicine refers to tailoring treatment to the individual characteristics of patients. For an operational definition, this tailoring takes the form of an optimization, in which treatments are selected to maximize a patient's expected health with respect to all available data. Because modern health data are large and high resolution, this optimization process requires computational intervention, and it must be tuned to the contours of specific medical disciplines. An advantage of this operational definition for precision medicine is that it allows us to better understand what precision medicine means in the context of a specific medical discipline. The goal of this article was to demonstrate how to instantiate this definition of precision medicine for the field of nephrology. Correspondingly, the goal of precision nephrology was to answer two related questions: ( 1 ) How do we optimize kidney health with respect to all available data? and ( 2 ) How do we optimize general health with respect to kidney data?

Time to Abolish Metrics That Sustain Systemic Racism in Kidney Allocation

This Viewpoint discusses how the Kidney Donor Profile Index (KDPI) in its current form is not fit to guide kidney allocation because it devalues organ donation by Black donors based on a weak association between donor race and kidney transplant failure.

Attitudes and beliefs regarding race-targeted genetic testing of Black people: A systematic review

Geographical ancestry has been associated with an increased risk of various genetic conditions. Race and ethnicity often have been used as proxies for geographical ancestry. Despite numerous problems associated with the crude reliance on race and ethnicity as proxies for geographical ancestry, some genetic testing in the clinical, research, and employment settings has been and continues to be race- or ethnicity-based. Race-based or race-targeted genetic testing refers to genetic testing offered only or primarily to people of particular racial or ethnic groups because of presumed differences among groups. One current example is APOL1 testing of Black kidney donors. Race-based genetic testing raises numerous ethical and policy questions. Given the ongoing reliance on the Black race in genetic testing, it is important to understand the views of people who identify as Black or are identified as Black (including African American, Afro-Caribbean, and Hispanic Black) regarding race-based genetic testing that targets Black people because of their race. We conducted a systematic review of studies and reports of stakeholder-engaged projects that examined how people who identify as or are identified as Black perceive genetic testing that specifically presumes genetic differences exist among racial groups or uses race as a surrogate for ancestral genetic variation and targets Black people. Our review identified 14 studies that explicitly studied this question and another 13 that implicitly or tacitly studied this matter. We found four main factors that contribute to a positive attitude toward race-targeted genetic testing (facilitators) and eight main factors that are associated with concerns regarding race-targeted genetic testing (barriers). This review fills an important gap. These findings should inform future genetic research and the policies and practices developed in clinical, research, public health, or other settings regarding genetic testing.

Long-term Medical Outcomes of Living Kidney Donors

Historically, to minimize risks, living kidney donors have been highly selected and healthy. Operative risks are well-defined, yet concern remains about long-term risks. In the general population, even a mild reduction in glomerular filtration rate (GFR) is associated with cardiovascular disease, chronic kidney disease, and end-stage kidney disease (ESKD). However, reduction in GFR in the general population is due to kidney or systemic disease. Retrospective studies comparing donors with matched general population controls have found no increased donor risk. Prospective studies comparing donors with controls (maximum follow-up, 9 years) have reported that donor GFR is stable or increases slightly, whereas GFR decreases in controls. However, these same studies identified metabolic and vascular donor abnormalities. There are a few retrospective studies comparing donors with controls. Each has limitations in selection of the control group, statistical analyses, and/or length of follow-up. One such study reported increased donor mortality; 2 reported a small increase in absolute risk of ESKD. Risk factors for donor ESKD are similar to those in the general population. Postdonation pregnancies are also associated with increased risk of hypertension and preeclampsia. There is a critical need for long-term follow-up studies comparing donors with controls from the same era, geographic area, and socioeconomic status who are healthy, with normal renal function on the date matching the date of donation, and are matched on demographic characteristics with the donors. These data are needed to optimize donor candidate counseling and informed consent.

Variant APOL1 protein in plasma associates with larger particles in humans and mouse models of kidney injury

BACKGROUND

Genetic variants in apolipoprotein L1 (APOL1), a protein that protects humans from infection with African trypanosomes, explain a substantial proportion of the excess risk of chronic kidney disease affecting individuals with sub-Saharan ancestry. The mechanisms by which risk variants damage kidney cells remain incompletely understood. In preclinical models, APOL1 expressed in podocytes can lead to significant kidney injury. In humans, studies in kidney transplant suggest that the effects of APOL1 variants are predominantly driven by donor genotype. Less attention has been paid to a possible role for circulating APOL1 in kidney injury.

METHODS

Using liquid chromatography-tandem mass spectrometry, the concentrations of APOL1 were measured in plasma and urine from participants in the Seattle Kidney Study. Asymmetric flow field-flow fractionation was used to evaluate the size of APOL1-containing lipoprotein particles in plasma. Transgenic mice that express wild-type or risk variant APOL1 from an albumin promoter were treated to cause kidney injury and evaluated for renal disease and pathology.

RESULTS

In human participants, urine concentrations of APOL1 were correlated with plasma concentrations and reduced kidney function. Risk variant APOL1 was enriched in larger particles. In mice, circulating risk variant APOL1-G1 promoted kidney damage and reduced podocyte density without renal expression of APOL1.

CONCLUSIONS

These results suggest that plasma APOL1 is dynamic and contributes to the progression of kidney disease in humans, which may have implications for treatment of APOL1-associated kidney disease and for kidney transplantation.

Treatment potential in APOL1-associated nephropathy

PURPOSE OF REVIEW

More than 5 million African-Americans, and millions more in Africa and worldwide, possess apolipoprotein L1 gene (APOL1) high-risk genotypes with an increased risk for chronic kidney disease. This manuscript reviews treatment approaches for slowing the progression of APOL1-associated nephropathy.

RECENT FINDINGS

Since the 2010 discovery of APOL1 as a cause of nondiabetic nephropathy in individuals with sub-Saharan African ancestry, it has become apparent that aggressive hypertension control, renin-angiotensin system blockade, steroids and conventional immunosuppressive agents are suboptimal treatments. In contrast, APOL1-mediated collapsing glomerulopathy due to interferon treatment and HIV infection, respectively, often resolve with cessation of interferon or antiretroviral therapy. Targeted therapies, including APOL1 small molecule inhibitors, APOL1 antisense oligonucleotides (ASO) and inhibitors of APOL1-associated inflammatory pathways, hold promise for these diseases. Evolving therapies and the need for clinical trials support the importance of increased use of APOL1 genotyping and kidney biopsy.

SUMMARY

APOL1-associated nephropathy includes a group of related phenotypes that are driven by the same two genetic variants in APOL1. Clinical trials of small molecule inhibitors, ASO, and inflammatory pathway inhibitors may improve outcomes in patients with primary forms of APOL1-associated nephropathy.

Clinical Utility in Adopting Race-free Kidney Donor Risk Index

Recent events of racial injustice prompted us to study potential impact of removing race from kidney donor risk index (KDRI) calculator.

Use of Machine Learning Consensus Clustering to Identify Distinct Subtypes of Black Kidney Transplant Recipients and Associated Outcomes

Importance

Among kidney transplant recipients, Black patients continue to have worse graft function and reduced patient and graft survival. Better understanding of different phenotypes and subgroups of Black kidney transplant recipients may help the transplant community to identify individualized strategies to improve outcomes among these vulnerable groups.

Objective

To cluster Black kidney transplant recipients in the US using an unsupervised machine learning approach.

Design, Setting, and Participants

This cohort study performed consensus cluster analysis based on recipient-, donor-, and transplant-related characteristics in Black kidney transplant recipients in the US from January 1, 2015, to December 31, 2019, in the Organ Procurement and Transplantation Network/United Network for Organ Sharing database. Each cluster's key characteristics were identified using the standardized mean difference, and subsequently the posttransplant outcomes were compared among the clusters. Data were analyzed from June 9 to July 17, 2021.

Exposure

Machine learning consensus clustering approach.

Main Outcomes and Measures

Death-censored graft failure, patient death within 3 years after kidney transplant, and allograft rejection within 1 year after kidney transplant.

Results

Consensus cluster analysis was performed for 22 687 Black kidney transplant recipients (mean [SD] age, 51.4 [12.6] years; 13 635 men [60%]), and 4 distinct clusters that best represented their clinical characteristics were identified. Cluster 1 was characterized by highly sensitized recipients of deceased donor kidney retransplants; cluster 2, by recipients of living donor kidney transplants with no or short prior dialysis; cluster 3, by young recipients with hypertension and without diabetes who received young deceased donor transplants with low kidney donor profile index scores; and cluster 4, by older recipients with diabetes who received kidneys from older donors with high kidney donor profile index scores and extended criteria donors. Cluster 2 had the most favorable outcomes in terms of death-censored graft failure, patient death, and allograft rejection. Compared with cluster 2, all other clusters had a higher risk of death-censored graft failure and death. Higher risk for rejection was found in clusters 1 and 3, but not cluster 4.

Conclusions and Relevance

In this cohort study using an unsupervised machine learning approach, the identification of clinically distinct clusters among Black kidney transplant recipients underscores the need for individualized care strategies to improve outcomes among vulnerable patient groups.

The evolving role of diagnostic genomics in kidney transplantation

Monogenic forms of heritable kidney disease account for a significant proportion of chronic kidney disease (CKD) across both pediatric and adult patient populations and up to 11% of patients under 40 years reaching end-stage kidney failure (KF) and awaiting kidney transplant. Diagnostic genomics in the field of nephrology is ever evolving and now plays an important role in assessment and management of kidney transplant recipients and their related donor pairs. Genomic testing can help identify the cause of KF in kidney transplant recipients and assist in prognostication around graft survival and rate of recurrence of primary kidney disease. If a gene variant has been identified in the recipient, at-risk related donors can be assessed for the same and excluded if affected. This paper aims to address the indications for genomic testing in the context for kidney transplantation, the technologies available for testing, the conditions and groups in which testing should be most often considered, and the role for the renal genetics multidisciplinary team in this process.

Apolipoprotein L1 Opinions of African American Living Kidney Donors, Kidney Transplant Patients, and Nonpatients

INTRODUCTION

The discovery of apolipoprotein L1 (ApoL1) has raised important ethical and clinical questions about genetic testing in the context of living and deceased kidney donation. Largely missing from this discussion are the perspectives of those African Americans (AA) most likely to be impacted by ApoL1 testing.

METHODS

We surveyed 331 AA potential and former living kidney donors (LKDs), kidney transplant candidates and recipients, and nonpatients at three United States transplant programs about their ApoL1 testing attitudes.

RESULTS

Overall, 72% felt that transplant programs should offer ApoL1 testing to AA potential LKDs. If a potential LKD has the high-risk genotype, 79% felt that the LKD should be allowed to make their own donation decision or participate in shared decision-making with transplant doctors. More than half of the potential LKDs (58%) would undergo ApoL1 testing and 81% of former LKDs would take the test now if offered. Most transplant candidates expressed a low likelihood of accepting a kidney from a LKD (79%) or a deceased donor (67%) with the high-risk genotype.

CONCLUSIONS

There is strong support among LKDs and transplant patients for ApoL1 testing when evaluating potential kidney donors of African ancestry. Inclusion of AA stakeholders in developing guidelines and educational programs for ApoL1 testing is critical.

How Genetics Can Improve Clinical Practice in Chronic Kidney Disease: From Bench to Bedside

Chronic kidney disease (CKD) is considered a major global health problem with high socio-economic costs: the risk of CKD in individuals with an affected first degree relative has been found to be three times higher than in the general population. Genetic factors are known to be involved in CKD pathogenesis, both due to the possible presence of monogenic pathologies as causes of CKD, and to the role of numerous gene variants in determining susceptibility to the development of CKD. The genetic study of CKD patients can represent a useful tool in the hands of the clinician; not only in the diagnostic and prognostic field, but potentially also in guiding therapeutic choices and in designing clinical trials. In this review we discuss the various aspects of the role of genetic analysis on clinical management of patients with CKD with a focus on clinical applications. Several topics are discussed in an effort to provide useful information for daily clinical practice: definition of susceptibility to the development of CKD, identification of unrecognized monogenic diseases, reclassification of the etiological diagnosis, role of pharmacogenetics.

Employment status at transplant influences ethnic disparities in outcomes after deceased donor kidney transplantation

Background

African American (AA) recipients of deceased-donor (DD) kidney transplants (KT) have shorter allograft survival than recipients of other ethnic groups. Reasons for this disparity encompass complex interactions between donors and recipients characteristics.

Methods

Outcomes from 3872 AA and 19,719 European American (EA) DDs who had one kidney transplanted in an AA recipient and one in an EA recipient were analyzed. Four donor/recipient pair groups (DRP) were studied, AA/AA, AA/EA, EA/AA, and EA/EA. Survival random forests and Cox proportional hazard models were fitted to rank and evaluate modifying effects of DRP on variables associated with allograft survival. These analyses sought to identify factors contributing to the observed disparities in transplant outcomes among AA and EA DDKT recipients.

Results

Transplant era, discharge serum creatinine, delayed graft function, and DRP were among the top predictors of allograft survival and mortality among DDKT recipients. Interaction effects between DRP with the kidney donor risk index and transplant era showed significant improvement in allograft survival over time in EA recipients. However, AA recipients appeared to have similar or poorer outcomes for DDKT performed after 2010 versus before 2001; allograft survival hazard ratios (95% CI) were 1.15 (0.74, 1.76) and 1.07 (0.8, 1.45) for AA/AA and EA/AA, compared to 0.62 (0.54, 0.71) and 0.5 (0.41, 0.62) for EA/EA and AA/EA DRP, respectively. Recipient mortality improved over time among all DRP, except unemployed AA/AAs. Relative to DDKT performed pre-2001, employed AA/AAs had HR = 0.37 (0.2, 0.69) versus 0.59 (0.31, 1.11) for unemployed AA/AA after 2010.

Conclusion

Relative to DDKT performed before 2001, similar or worse overall DCAS was observed among AA/AAs, while EA/EAs experienced considerable improvement regardless of employment status, KDRI, and EPTS. AA recipients of an AA DDKT, especially if unemployed, had worse allograft survival and mortality and did not appear to benefit from advances in care over the past 20 years.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02631-4.

APOL1 risk variants in kidney transplantation: a modulation of immune cell function

APOL1 G1 and G2 variants are established risk factors for nondiabetic kidney disease. The presence of two APOL1 risk variants in donor kidneys negatively impacts kidney allograft survival. Because of evolutionary pressure, the APOL1 risk variants have become common in people from Africa and in those with recent African ancestry. APOL1 risk variant proteins are expressed in kidney cells and can cause toxicity to these cells. In this issue of the JCI, Zhang, Sun, and colleagues show that recipient APOL1 risk variants negatively affect kidney allograft survival and T cell-mediated rejection rates, independent of donor APOL1 genotype or recipient ancestry. The authors provide evidence that APOL1 risk variants play an immunomodulatory role in T cells and NK cells in the setting of kidney transplantation. These findings have important clinical implications that require further investigation.

Recurrent Glomerular Disease after Kidney Transplantation: Diagnostic and Management Dilemmas

Recurrent glomerular disease after kidney transplant remains an important cause of allograft failure. Many of the different entities post-transplant still suffer from incomplete knowledge on pathophysiology, and therefore lack targeted and effective therapies. In this review, we focus on specific clinical dilemmas encountered by physicians in managing recurrent glomerular disease by highlighting new insights into the understanding and treatment of post-transplant focal segmental glomerulosclerosis, membranous nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, amyloid light-chain (AL) amyloidosis, and IgA nephropathy.

Recipient APOL1 risk alleles associate with death-censored renal allograft survival and rejection episodes

Apolipoprotein L1 (APOL1) risk-alleles in donor kidneys associate with graft loss but whether recipient risk-allele expression impacts transplant outcomes is unclear. To test whether recipient APOL1 risk-alleles independently correlate with transplant outcomes, we analyzed genome-wide SNP genotyping data of donors and recipients from two kidney transplant cohorts, Genomics of Chronic Allograft Rejection (GOCAR) and Clinical Trials in Organ Transplantation (CTOT1/17). We estimated genetic ancestry (quantified as proportion of African ancestry or pAFR) by ADMIXTURE and correlated APOL1 genotypes and pAFR with outcomes. In the GOCAR discovery set, we observed that the number of recipient APOL1 G1/G2 alleles (R-nAPOL1) associated with increased risk of death-censored allograft loss (DCAL), independent of ancestry (HR = 2.14; P = 0.006), and within the subgroup of African American and Hispanic (AA/H) recipients (HR = 2.36; P = 0.003). R-nAPOL1 also associated with increased risk of any T cell-mediated rejection (TCMR) event. These associations were validated in CTOT1/17. Ex vivo studies of peripheral blood mononuclear cells revealed unanticipated high APOL1 expression in activated CD4+/CD8+ T cells and natural killer cells. We detected enriched immune response gene pathways in risk-allele carriers vs. non-carriers on the kidney transplant waitlist and among healthy controls. Our findings demonstrate an immunomodulatory role for recipient APOL1 risk-alleles associating with TCMR and DCAL. This finding has broader implications for immune mediated injury to native kidneys.

Outcomes of Kidney Transplant Recipients with Sickle Cell Disease: An Analysis of the 2000-2019 UNOS/OPTN Database

Background: Lower patient survival has been observed in sickle cell disease (SCD) patients who go on to receive a kidney transplant. This study aimed to assess the post-transplant outcomes of SCD kidney transplant recipients in the contemporary era. Methods: We used the OPTN/UNOS database to identify first-time kidney transplant recipients from 2010 through 2019. We compared patient and allograft survival between recipients with SCD (n = 105) vs. all other diagnoses (non-SCD, n = 146,325) as the reported cause of end-stage kidney disease. We examined whether post-transplant outcomes improved among SCD in the recent era (2010–2019), compared to the early era (2000–2009). Results: After adjusting for differences in baseline characteristics, SCD was significantly associated with lower patient survival (HR 2.87; 95% CI 1.75–4.68) and death-censored graft survival (HR 1.98; 95% CI 1.30–3.01), compared to non-SCD recipients. The lower patient survival and death-censored graft survival in SCD recipients were consistently observed in comparison to outcomes of recipients with diabetes, glomerular disease, and hypertension as the cause of end-stage kidney disease. There was no significant difference in death censored graft survival (HR 0.99; 95% CI 0.51–1.73, p = 0.98) and patient survival (HR 0.93; 95% CI 0.50–1.74, p = 0.82) of SCD recipients in the recent versus early era. Conclusions: Patient and allograft survival in SCD kidney recipients were worse than recipients with other diagnoses. Overall SCD patient and allograft outcomes in the recent era did not improve from the early era. The findings of our study should not discourage kidney transplantation for ESKD patients with SCD due to a known survival benefit of transplantation compared with remaining on dialysis. Urgent future studies are needed to identify strategies to improve patient and allograft survival in SCD kidney recipients. In addition, it may be reasonable to assign risk adjustment for SCD patients.

Transcriptome-Wide Association Study of Blood Cell Traits in African Ancestry and Hispanic/Latino Populations

BACKGROUND

Thousands of genetic variants have been associated with hematological traits, though target genes remain unknown at most loci. Moreover, limited analyses have been conducted in African ancestry and Hispanic/Latino populations; hematological trait associated variants more common in these populations have likely been missed.

METHODS

To derive gene expression prediction models, we used ancestry-stratified datasets from the Multi-Ethnic Study of Atherosclerosis (MESA, including n = 229 African American and n = 381 Hispanic/Latino participants, monocytes) and the Depression Genes and Networks study (DGN, n = 922 European ancestry participants, whole blood). We then performed a transcriptome-wide association study (TWAS) for platelet count, hemoglobin, hematocrit, and white blood cell count in African (n = 27,955) and Hispanic/Latino (n = 28,324) ancestry participants.

RESULTS

Our results revealed 24 suggestive signals (p < 1 × 10-4) that were conditionally distinct from known GWAS identified variants and successfully replicated these signals in European ancestry subjects from UK Biobank. We found modestly improved correlation of predicted and measured gene expression in an independent African American cohort (the Genetic Epidemiology Network of Arteriopathy (GENOA) study (n = 802), lymphoblastoid cell lines) using the larger DGN reference panel; however, some genes were well predicted using MESA but not DGN.

CONCLUSIONS

These analyses demonstrate the importance of performing TWAS and other genetic analyses across diverse populations and of balancing sample size and ancestry background matching when selecting a TWAS reference panel.

Diagnosis, Education, and Care of Patients with APOL1-Associated Nephropathy: A Delphi Consensus and Systematic Review

BACKGROUND

APOL1 variants contribute to the markedly higher incidence of ESKD in Blacks compared with Whites. Genetic testing for these variants in patients with African ancestry who have nephropathy is uncommon, and no specific treatment or management protocol for APOL1-associated nephropathy currently exists.

METHODS

A multidisciplinary, racially diverse group of 14 experts and patient advocates participated in a Delphi consensus process to establish practical guidance for clinicians caring for patients who may have APOL1-associated nephropathy. Consensus group members took part in three anonymous voting rounds to develop consensus statements relating to the following: (1) counseling, genotyping, and diagnosis; (2) disease awareness and education; and (3) a vision for management of APOL1-associated nephropathy in a future when treatment is available. A systematic literature search of the MEDLINE and Embase databases was conducted to identify relevant evidence published from January 1, 2009 to July 14, 2020.

RESULTS

The consensus group agreed on 55 consensus statements covering such topics as demographic and clinical factors that suggest a patient has APOL1-associated nephropathy, as well as key considerations for counseling, testing, and diagnosis in current clinical practice. They achieved consensus on the need to increase awareness among key stakeholders of racial health disparities in kidney disease and of APOL1-associated nephropathy and on features of a successful education program to raise awareness among the patient community. The group also highlighted the unmet need for a specific treatment and agreed on best practice for management of these patients should a treatment become available.

CONCLUSIONS

A multidisciplinary group of experts and patient advocates defined consensus-based guidance on the care of patients who may have APOL1-associated nephropathy.

Apolipoprotein L1 and mechanisms of kidney disease susceptibility

PURPOSE OF REVIEW

Allelic variants in the gene for apolipoprotein L1 (APOL1), found only in individuals of African ancestry, explain a majority of the excess risk of kidney disease in African Americans. However, a clear understanding how the disease-associated APOL1 variants cause kidney injury and the identity of environmental stressors that trigger the injury process have not been determined.

RECENT FINDINGS

Basic mechanistic studies of APOL1 biochemistry and cell biology, bolstered by new antibody reagents and inducible pluripotent stem cell-derived cell systems, have focused on the cytotoxic effect of the risk variants when APOL1 gene expression is induced. Since the APOL1 variants evolved to alter a key protein-protein interaction with the trypanosome serum resistance-associated protein, additional studies have begun to address differences in APOL1 interactions with other proteins expressed in podocytes, including new observations that APOL1 variants may alter podocyte cytoskeleton dynamics.

SUMMARY

A unified mechanism of pathogenesis for the various APOL1 nephropathies still remains unclear and controversial. As ongoing studies have consistently implicated the pathogenic gain-of-function effects of the variant proteins, novel therapeutic development inhibiting the synthesis or function of APOL1 proteins is moving toward clinical trials.

Integrating Patient Priorities with Science by Community Engagement in the Kidney Precision Medicine Project

The Kidney Precision Medicine Project (KPMP) is a multisite study designed to improve understanding of CKD attributed to diabetes or hypertension and AKI by performing protocol-driven kidney biopsies. Study participants and their kidney tissue samples undergo state-of-the-art deep phenotyping using advanced molecular, imaging, and data analytical methods. Few patients participate in research design or concepts for discovery science. A major goal of the KPMP is to include patients as equal partners to inform the research for clinically relevant benefit. The purpose of this report is to describe patient and community engagement and the value they bring to the KPMP. Patients with CKD and AKI and clinicians from the study sites are members of the Community Engagement Committee, with representation on other KPMP committees. They participate in KPMP deliberations to address scientific, clinical, logistic, analytic, ethical, and community engagement issues. The Community Engagement Committee guides KPMP research priorities from perspectives of patients and clinicians. Patients led development of essential study components, including the informed consent process, no-fault harm insurance coverage, the ethics statement, return of results plan, a "Patient Primer" for scientists and the public, and Community Advisory Boards. As members across other KPMP committees, the Community Engagement Committee assures that the science is developed and conducted in a manner relevant to study participants and the clinical community. Patients have guided the KPMP to produce research aligned with their priorities. The Community Engagement Committee partnership has set new benchmarks for patient leadership in precision medicine research.

APOL1 at 10 years: progress and next steps

APOL1 kidney risk variants (RVs) were identified in 2010 as major drivers of glomerular, tubulointerstitial, and renal microvascular disease in individuals with sub-Saharan African ancestry. In December 2020, the "APOL1 at Ten" conference summarized the first decade of progress and discussed controversies and uncertainties that remain to be addressed. Topics included trypanosome infection and its role in the evolution of APOL1 kidney RVs, clinical phenotypes in APOL1-associated nephropathy, relationships between APOL1 RVs and background haplotypes on cell injury and molecular mechanisms initiating disease, the role of clinical APOL1 genotyping, and development of novel therapies for kidney disease. Future goals were defined, including improved characterization of various APOL1 RV phenotypes in patients and experimental preclinical models; further dissection of APOL1-mediated pathways to cellular injury and dysfunction in kidney (and other) cells; clarification of gene-gene and gene-environment interactions; and evaluation of the role for existing and novel therapies.

Donor Family History of ESKD and Long-term Outcomes Among African American Living Kidney Donors: A Retrospective Cohort Study

RATIONALE & OBJECTIVE

Live kidney donation is associated with a small increased risk for kidney disease and hypertension in African American donors. We investigated a possible association between donor family history of end-stage kidney disease (ESKD) and their postdonation kidney function and the development of hypertension. We tested whether this association was modified by kidney donation.

STUDY DESIGN

Retrospective cohort.

SETTING & PARTICIPANTS

Former African American live kidney donors between 1993 and 2010. Healthy nondonors were selected from the Coronary Artery Disease in Young Adults (CARDIA) Study.

EXPOSURE

Family history of ESKD in a first-degree relative.

OUTCOMES

Kidney function and blood pressure ≥ 140/90 mm Hg or use of antihypertensive medications at follow-up.

ANALYTICAL APPROACH

Donors were grouped based on family history of ESKD. Outcomes were first compared between donor groups and then between donors and healthy nondonors matched for demographics, follow-up time, and family history. A mixed-effect model was used to compare outcomes.

RESULTS

Of 179 donors, 139 (78%) had a first degree relative with ESKD. Predonation characteristics were similar between the 2 groups. At a median follow-up of 11 years postdonation, there was no difference in postdonation estimated glomerular filtration rates (68 ± 19 vs 69 ± 13 mL/min/1.73 m2; P = 0.71) and the presence of albuminuria (P = 0.16). There was a trend toward a higher incidence of hypertension (51% vs 35%; P = 0.08) among donors with a family history of ESKD than for those without. Although there was no difference in annual change in estimated glomerular filtration rate (P = 0.17), the risk for hypertension was higher in donors than nondonors (relative risk, 2.44 [95% CI, 1.56-3.84]), but there was no interaction by family history (P = 0.11).

LIMITATIONS

Retrospective small study. Lack of data across donor-recipient specific biological relationship.

CONCLUSIONS

Family history of ESKD is not associated with postdonation kidney function among African American kidney donors. Live kidney donation is associated with an increased risk for hypertension among African Americans, independent of donor family history of ESKD.

COVID-19-Associated Glomerular Disease

BACKGROUND

Studies have documented AKI with high-grade proteinuria in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In some patients, biopsies have revealed collapsing glomerulopathy, a distinct form of glomerular injury that has been associated with other viruses, including HIV. Previous patient reports have described patients of African ancestry who developed nephrotic-range proteinuria and AKI early in the course of disease.

METHODS

In this patient series, we identified six patients with coronavirus disease 2019 (COVID-19), AKI, and nephrotic-range proteinuria. COVID-19 was diagnosed by a positive nasopharyngeal swab RT-PCR for SARS-CoV-2 infection. We examined biopsy specimens from one transplanted kidney and five native kidneys. Three of the six patients underwent genetic analysis of APOL1, the gene encoding the APOL1 protein, from DNA extracted from peripheral blood. In addition, we purified genomic DNA from paraffin-embedded tissue and performed APOL1 genotype analysis of one of the native biopsies and the donor kidney graft.

RESULTS

All six patients were of recent African ancestry. They developed COVID-19-associated AKI with podocytopathy, collapsing glomerulopathy, or both. Patients exhibited generally mild respiratory symptoms, and no patient required ventilator support. Genetic testing performed in three patients confirmed high-risk APOL1 genotypes. One APOL1 high-risk patient developed collapsing glomerulopathy in the engrafted kidney, which was transplanted from a donor who carried a low-risk APOL1 genotype; this contradicts current models of APOL1-mediated kidney injury, and suggests that intrinsic renal expression of APOL1 may not be the driver of nephrotoxicity and specifically, of podocyte injury.

CONCLUSIONS

Glomerular disease presenting as proteinuria with or without AKI is an important presentation of COVID-19 infection and may be associated with a high-risk APOL1 genotype.

Apolipoprotein L1: role in the evaluation of kidney transplant donors

PURPOSE OF REVIEW

To summarize the current state of evidence regarding the role of apolipoprotein L1 (APOL1) genotyping in evaluating donors for kidney transplantation.

RECENT FINDINGS

African ancestry is associated with an increased risk of kidney failure following living donation. Moreover, kidney transplants from African ancestry deceased donors have an increased risk of graft failure. Preliminary evidence suggests that APOL1 genotype may mediate at least a portion of this racial variation, with high-risk APOL1 genotypes defined by presence of two renal risk variants (RRVs). A pilot study 136 African ancestry living donors found that those with APOL1 high-risk genotypes had lower baseline kidney function and faster rates of kidney function decline after donation. To date, three retrospective studies identified a two-to-three times greater risk of allograft failure associated with kidneys from donors with high-risk APOL1 genotype. Active research initiatives seek to address unanswered questions, including reproducibility in large national samples, the role of 'second hits' injuries, and impact of recipient genotype, with a goal to build consensus on applications for policy and practice.

SUMMARY

As evidence evolves, APOL1 genotyping may have applications for organ quality scoring in deceased donor kidney allocation, and for the evaluation and selection of living donor candidates.