Absence of APOL1 risk variants protects against HIV-associated nephropathy in the Ethiopian population

Higher prevalence of kidney function impairment among older people living with HIV in Uganda

Background

People living with HIV (PLWH) are at risk of kidney function impairment due to HIV-related inflammation, antiretroviral therapy (ART), diabetes mellitus, and hypertension. Older persons may experience a higher burden of chronic kidney disease (CKD) as kidney function declines with increasing age. There is a paucity of data comparing the prevalence of kidney function impairment in older PLWH to that in HIV-uninfected people in sub-Saharan Africa.

Methods

We conducted a cross-sectional study among people aged ≥ 60 years living with and without HIV in Kampala, Uganda who were matched 1:1 by community location. We collected data on sociodemographics, comorbidities, and HIV-related clinical characteristics. We defined kidney function impairment as an estimated glomerular filtration rate(eGFR) < 60mls/min/1.73m2 with or without proteinuria. We constructed multivariable logistic regression models to study associations between participant characteristics and kidney function impairment.

Results

We enrolled 278 people (median age 66 years); 50% were PLWH, and 51.8% were female. Overall, the prevalence of kidney function impairment was 23.0% (95% CI:18.4%-28.4%); 33.1% (95% CI: 25.7%-41.4%) versus 12.9% (95% CI: 8.3%-19.7%) among people living with and without HIV (p-value < 0.01). The prevalence of proteinuria among PLWH versus people without HIV was 43.9% (95% CI:35.8%-52.3%) versus 19.4% (95% CI:13.6%-26.9%) p-value < 0.01. Living with HIV (OR = 3.89(95% CI: 2.04-7.41), p-value < 0.01), older age (OR = 1.13, (95% CI:1.07-1.20), p-value < 0.01), female sex (OR = 1.95, (95% CI:1.06-3.62), p-value = 0.03) and a prior diagnosis of hypertension (OR = 2.19(95% CI:1.02-4.67), p-value = 0.04) were significantly associated with kidney function impairment.

Conclusions

HIV infection is strongly associated with kidney function impairment among older PLWH. Prioritizing routine measurements of kidney function and proteinuria in older PLWH will enable early detection and institution of measures to reduce the progression of kidney disease.

The changing landscape of HIV-associated kidney disease

The HIV epidemic has devastated millions of people globally, with approximately 40 million deaths since its start. The availability of antiretroviral therapy (ART) has transformed the prognosis of millions of individuals infected with HIV such that a diagnosis of HIV infection no longer automatically confers death. However, morbidity and mortality remain substantial among people living with HIV. HIV can directly infect the kidney to cause HIV-associated nephropathy (HIVAN) - a disease characterized by podocyte and tubular damage and associated with an increased risk of kidney failure. The reports of HIVAN occurring primarily in those of African ancestry led to the discovery of its association with APOL1 risk alleles. The advent of ART has led to a substantial decrease in the prevalence of HIVAN; however, reports have emerged of an increase in the prevalence of other kidney pathology, such as focal segmental glomerulosclerosis and pathological conditions associated with co-morbidities of ageing, such as hypertension and diabetes mellitus. Early initiation of ART also results in a longer cumulative exposure to medications, increasing the likelihood of nephrotoxicity. A substantial body of literature supports the use of kidney transplantation in people living with HIV, demonstrating significant survival benefits compared with that of people undergoing chronic dialysis, and similar long-term allograft and patient survival compared with that of HIV-negative kidney transplant recipients.

Rationale and Design of the Diet, CKD, and Apolipoprotein L1 Study in Low-Income and Middle-Income Countries

Introduction

Diet, chronic kidney disease (CKD), and Apolipoprotein L1 (APOL1) (DCA) Study is examining the role of dietary factors in CKD progression and APOL1 nephropathy. We describe enrollment and retention efforts and highlight facilitators and barriers to enrollment and operational challenges, as well as accommodations made in the study protocol.

Methods

The DCA study is enrolling participants in 7 centers in West Africa. Participants who consented were invited to complete dietary recalls and 24-hour urine collections in year 1. We conducted focus groups and semistructured interviews among study personnel to identify facilitators and barriers to enrollment as well as retention and operational challenges in the execution of the study protocol. We analyzed emerging themes using content analyses.

Results

A total of 712 participants were enrolled in 18 months with 1256 24-hour urine and 1260 dietary recalls. Barriers to enrollment were the following: (i) a lack of understanding of research, (ii) the burden of research visits, and (iii) incorporating cultural and traditional nuances when designing research protocols. Factors facilitating enrollment were the following: (i) designing convenient research visits, (ii) building rapport and increased communication between the research team and participants, and (iii) cultural sensitivity - adapting research protocols for the populations involved. Offering home visits, providing free dietary counseling, reducing the volume of study blood collection, and reducing the frequency of visits were some changes made in the study protocol that increased participant satisfaction.

Conclusion

Adopting a participant-centered approach with accommodations in the protocol for cultural adaptability and incorporating participant feedback is vital for carrying out research in low-income and middle-income regions.

Parietal Epithelial Cell Behavior and Its Modulation by microRNA-193a

Glomerular parietal epithelial cells (PECs) have been increasingly recognized to have crucial functions. Lineage tracking in animal models showed the expression of a podocyte phenotype by PECs during normal glomerular growth and after acute podocyte injury, suggesting a reparative role of PECs. Conversely, activated PECs are speculated to be pathogenic and comprise extracapillary proliferation in focal segmental glomerulosclerosis (FSGS) and crescentic glomerulonephritis (CrescGN). The reparative and pathogenic roles of PECs seem to represent two sides of PEC behavior directed by the local milieu and mediators. Recent studies suggest microRNA-193a (miR193a) is involved in the pathogenesis of FSGS and CrescGN. In a mouse model of primary FSGS, the induction of miR193a caused the downregulation of Wilms' tumor protein, leading to the dedifferentiation of podocytes. On the other hand, the inhibition of miR193a resulted in reduced crescent lesions in a mouse model of CrescGN. Interestingly, in vitro studies report that the downregulation of miR193a induces trans-differentiation of PECs into a podocyte phenotype. This narrative review highlights the critical role of PEC behavior in health and during disease and its modulation by miR193a.

High risk APOL1 genotypes and kidney disease among treatment naïve HIV patients at Kano, Nigeria

Introduction

Racial disparities are known in the occurrence of kidney disease with excess risks found among people of African descent. Apolipoprotein L1 (APOL1) gene variants G1 and G2 are associated with kidney disease among HIV infected individuals of African descent in the USA as well as among black population in South Africa. We set out to investigate the prevalence of these high-risk variants and their effects on kidney disease among HIV infected patients in Northern Nigeria with hitherto limited information despite earlier reports of high population frequencies of these alleles from the Southern part of the country.

Methods

DNA samples obtained from the whole blood of 142 participants were genotyped for APOL1 G1 and G2 variants after initial baseline investigations including assessment of kidney function. Participants comprised 50 HIV positive patients with no evidence of kidney disease, 52 HIV negative individuals with no kidney disease and 40 HIV positive patients with chronic kidney disease (CKD) evidenced by persistent proteinuria and/or reduced eGFR, who also had a kidney biopsy. All the HIV positive patients were newly diagnosed and treatment naïve.

Results

The distribution of the APOL1 genotypes among the study participants revealed that 24.6% had a G1 risk allele and 19.0% a G2. The frequency of the High Risk Genotype (HRG) was 12.5% among those with CKD compared to 5.8% in the HIV negative group and zero in the HIV positive no CKD group. Having the HRG was associated with a higher odds for developing HIV Associated Nephropathy (HIVAN) (2 vs 0 risk alleles: OR 10.83, 95% CI 1.38–84.52; P = 0.023; 2 vs 0 or 1 risk alleles: OR 5.5, 95% CI 0.83–36.29; P = 0.07). The HRG was also associated with higher odds for Focal Segmental Glomerulosclerosis (FSGS) (2 vs 0 risk alleles: OR 13.0, 95% CI 2.06–81.91; P = 0.006 and 2 vs 0 or 1 risk alleles: OR 9.0, 95%CI 1.62–50.12; P = 0.01) when compared to the control group.

Conclusion

This study showed a high population frequency of the individual risk alleles of the APOL1 gene with higher frequencies noted among HIV positive patients with kidney disease. There is high association with the presence of kidney disease and especially FSGS and HIVAN among treatment naive HIV patients carrying two copies of the HRG.

Apolipoprotein L1 High-Risk Genotypes and Albuminuria in Sub-Saharan African Populations

BACKGROUND AND OBJECTIVES

Recessive inheritance of African-specific APOL1 kidney risk variants is associated with higher risk of nondiabetic kidney disease, progression to kidney failure, and early-onset albuminuria that precedes eGFR decline. The effect of APOL1 risk variants on kidney disease in continental Africans is understudied. Objectives of this study were to determine APOL1 risk allele prevalence and associations between APOL1 genotypes and kidney disease in West, East, and South Africa.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This cross-sectional population-based study in four African countries included 10,769 participants largely aged 40-60 years with sociodemographic and health information, anthropometry data, and blood and urine tests for biomarkers of kidney disease. APOL1 risk alleles were imputed from the H3Africa genotyping array, APOL1 risk allele and genotype frequencies were determined, and genetic associations were assessed for kidney disease. Kidney disease was defined as the presence of eGFR <60 ml/min per 1.73 m², albuminuria, or a composite end point including eGFR <60 ml/min per 1.73 m² and/or albuminuria.

RESULTS

High G1 allele frequencies occurred in South and West Africa (approximately 7%-13%). G2 allele frequencies were highest in South Africa (15%-24%), followed by West Africa (9%-12%). Associations between APOL1 risk variants and albuminuria were significant for recessive (odds ratio, 1.63; 95% confidence interval, 1.25 to 2.12) and additive (odds ratio, 1.39; 95% confidence interval, 1.09 to 1.76) models. Associations were stronger for APOL1 G1/G1 genotypes versus G0/G0 (odds ratio, 3.87; 95% confidence interval, 2.16 to 6.93) compared with either G2/G2 (odds ratio, 1.65; 95% confidence interval, 1.09 to 2.51) or G1/G2 (odds ratio, 1.24; 95% confidence interval, 0.83 to 1.87). No association between APOL1 risk variants and eGFR <60 ml/min per 1.73 m² was observed.

CONCLUSIONS

APOL1 G1 and G2 alleles and high-risk genotype frequencies differed between and within West and South Africa and were almost absent from East Africa. APOL1 risk variants were associated with albuminuria but not eGFR <60 ml/min per 1.73 m². There may be differential effects of homozygous G1 and G2 genotypes on albuminuria that require further investigation.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_05_16_CJN14321121.mp3.

Predictors of renal impairment and proteinuria after commencement of antiretroviral therapy in a Zimbabwean HIV cohort

BACKGROUND

Renal disease prevalence varies widely amongst reported cohorts of people living with HIV (PLWHIV) in sub-Saharan Africa. Renal function testing is not routine in those commencing antiretroviral therapy (ART) in the region, however. Further data on renal disease prevalence and the change associated with ART use are therefore needed.

AIM

To explore changes in renal function and associated predictors after 1 year of ART in an adult cohort of PLWHIV from Zimbabwe.

METHODS

A retrospective analysis of patients who attended the Newlands Clinic between January 2007 and September 2019. Eligible patients were aged ≥18 years and had measures of serum creatinine at baseline and after 1 year of ART. Predictors of renal function change were assessed by multiple linear regression.

RESULTS

1729 patients were eligible for inclusion. Median age was 36 years (IQR 30-43) and 62.8% were female. After 1 year of ART, the proportion of patients with an estimated glomerular filtration rate (eGFR) <60 ml/min/1.73² did not significantly change (2.0% vs. 1.2%; p = 0.094), but there was a decrease in the proportion of patients with proteinuria (11.0% vs. 5.6%; p < 0.001). Hypertension (B = -6.43; 95% CI -8.97 to -3.89; p < 0.001) and baseline proteinuria (B = -7.33; 95% CI -10.25 to -4.42; p < 0.001) were negative predictors of change in eGFR from baseline, whereas diabetes status was not associated (p = 0.476).

CONCLUSION

Proteinuria was common, but its prevalence halved after 1 year of ART. Screening for hypertension could be a simple way to identify patients at risk of renal function decline.

Genetic Variants of APOL1 Are Major Determinants of Kidney Failure in People of African Ancestry With HIV

Introduction

Variants of the APOL1 gene are associated with chronic kidney disease (CKD) in people of African ancestry, although evidence for their impact in people with HIV are sparse.

Methods

We conducted a cross-sectional study investigating the association between APOL1 renal risk alleles and kidney disease in people of African ancestry with HIV in the UK. The primary outcome was end-stage kidney disease (ESKD; estimated glomerular filtration rate [eGFR] of <15 ml/min per 1.73 m2, chronic dialysis, or having received a kidney transplant). The secondary outcomes included renal impairment (eGFR <60 ml/min per 1.73 m2), albuminuria (albumin-to-creatinine ratio [ACR] >30 mg/mmol), and biopsy-proven HIV-associated nephropathy (HIVAN). Multivariable logistic regression was used to estimate the associations between APOL1 high-risk genotypes (G1/G1, G1/G2, G2/G2) and kidney disease outcomes.

Results

A total of 2864 participants (mean age 48.1 [SD 10.3], 57.3% female) were genotyped, of whom, 354 (12.4%) had APOL1 high-risk genotypes, and 99 (3.5%) had ESKD. After adjusting for demographic, HIV, and renal risk factors, individuals with APOL1 high-risk genotypes were at increased odds of ESKD (odds ratio [OR] 10.58, 95% CI 6.22-17.99), renal impairment (OR 5.50, 95% CI 3.81-7.95), albuminuria (OR 3.34, 95% CI 2.00-5.56), and HIVAN (OR 30.16, 95% CI 12.48-72.88). An estimated 49% of ESKD was attributable to APOL1 high-risk genotypes.

Conclusion

APOL1 high-risk genotypes were strongly associated with kidney disease in people of African ancestry with HIV and accounted for approximately half of ESKD cases in this cohort.

HIV-1 infection of the kidney: mechanisms and implications

People living with HIV are at higher risk for acute and chronic kidney disease compared with uninfected individuals. Kidney disease in this population is multifactorial, with several contributors including HIV infection of kidney cells, chronic inflammation, genetic predisposition, aging, comorbidities, and coinfections. In this review, we provide a summary of recent advancements in the understanding of the mechanisms and implications of HIV infection and kidney disease, with particular focus on the role of direct HIV infection of renal cells.

Renal function in a cohort of HIV-infected patients initiating antiretroviral therapy in an outpatient setting in Ethiopia

Aim

To evaluate the prevalence and associated factors of abnormal renal function among Ethiopian HIV-infected patients at baseline prior to initiation of antiretroviral therapy (ART) and during follow-up.

Methods

We conducted a retrospective observational cohort study of HIV infected patients who initiated ART at the outpatient ART clinic of Mehal Meda Hospital of North Shewa, Ethiopia from January 2012 to August 2018. Demographic and clinical data were abstracted from the medical records of patients. Renal function was assessed by estimated glomerular filtration rate (eGFR) calculated using the Modification of Diet in Renal Disease (MDRD) equation. Univariate and multivariate analysis were conducted to determine the factors associated with abnormal renal function at baseline and during follow-up.

Results

Among 353 patients, 70 (19.8%) had baseline eGFR <60 ml/min/1.73m² and 102 (28.9%) had eGFR = 60–89.9 ml/min/1.73m². Factors associated with baseline renal impairment (eGFR <60 ml/min/1.73m²) included female sex (AOR = 3.52, CI 1.75–7.09), CD4 count < 200 cells/mm³ (AOR = 2.75, CI 1.40–5.42), BMI < 25 Kg/m² (AOR = 3.04, CI 1.15–8.92), low hemoglobin (AOR = 2.19, CI 1.16–4.09) and high total cholesterol (AOR = 3.15, CI 1.68–5.92). After a median of 3.0 years of ART, the mean eGFR declined from 112.9 ± 81.2 ml/min/1.73m² at baseline to 93.9 ± 60.6 ml/min/1.73m² (P < 0.001). The prevalence of renal impairment increased from 19.8% at baseline to 22.1% during follow-up. Of 181 patients with baseline normal renal function, 49.7% experienced some degree of renal impairment. Older age (AOR = 3.85, 95% CI 2.03–7.31), female sex (AOR = 4.18, 95% CI 2.08–8.40), low baseline CD4 (AOR = 2.41, 95% CI 1.24–4.69), low current CD4 count (AOR = 2.32, 95% CI 1.15–4.68), high BMI (AOR = 2.91, 95% CI 1.49–5.71), and low hemoglobin (AOR = 3.38, 95% CI 2.00–7.46) were the factors associated with renal impairment during follow-up.

Conclusion

Impaired renal function was common in HIV-infected patients initiating ART in an outpatient setting in Ethiopia, and there appears to be a high prevalence of renal impairment after a median ART follow-up of 3 years. There is a need for assessment of renal function at baseline before ART initiation and regular monitoring of renal function for patients with HIV during follow-up.

Renal function in Ethiopian HIV-positive adults on antiretroviral treatment with and without tenofovir

Background

Limited data are available on the effect of antiretroviral treatment (ART) or Tenofovir disoproxil fumarate (TDF) on renal function in Ethiopians. We aimed to assess factors associated with renal function changes during the first year of ART with special focus on TDF.

Methods

HIV positive persons who were ≥ 18 years of age and eligible for ART initiation were recruited. Creatinine measurement to estimate glomerular filtration rate (eGFR) and spot urine analyses were performed at baseline and after 3, 6 and 12 months of ART. Univariate and multivariate linear regression and univariate logistic regression were used to determine factors associated with eGFR as continuous and categorical variable respectively. A linear mixed model was used to assess 12 month eGFR difference in TDF and non-TDF based regimen.

Result

Of 340 ART-naïve HIV patients with baseline renal function tests, 82.3% (279/339) were initiated on a TDF based ART regimen. All patients were on non-nucleoside reverse transcriptase inhibitors (NNRTI) based ART regimen. The median (IQR) change in eGFR with 12 months of ART was 0.8 (− 11.1; 10.0) ml/min/1.73m². About 41 and 26.9% of HIV patients had a drop of greater than 3 and 10 mL/min/1.73 m² in eGFR at 12 month, respectively. However, none of the HIV patients declined to < 60 ml/min/1.73m² within 12 months. Moreover, none of the HIV patients had persistent proteinuria or glycosuria. Older HIV patients especially age > 45 years and those with unsuppressed viral load at 6 month of ART had a significantly lower eGFR at 12 months of ART initiation. However, there was no difference in 12 month eGFR between HIV patients initiated on TDF based regimen and non-TDF based regimen.

Conclusion

Renal function remained stable with no difference between HIV patients treated with TDF or non-TDF NNRTI based ART regimen over 12 months. However, older HIV patients and those with unsuppressed viral load deserve special focus on renal monitoring. Data on long-term safety of TDF (> 1 year) is still warranted in this population.

Association of Genetic Polymorphisms of TGF-β1, HMOX1, and APOL1 With CKD in Nigerian Patients With and Without HIV

RATIONALE & OBJECTIVE

Recent studies in the human immunodeficiency virus (HIV)-infected population have suggested that there are genetic predispositions to the development of chronic kidney disease (CKD) in this context. We investigated the association of genetic polymorphisms of the genes encoding apolipoprotein L1 (APOL1), transforming growth factor β1 (TGF-β1; a profibrotic cytokine), and heme oxygenase 1 (HMOX1) with prevalent CKD among adults with and without HIV infection.

STUDY DESIGN

Case-control study.

SETTING & PARTICIPANTS

West African adults including 217 HIV-infected patients with CKD (HIV⁺/CKD⁺ group), 595 HIV-infected patients without CKD (HIV⁺/CKD^- group), 269 with CKD and no HIV infection (HIV^-/CKD⁺ group), and 114 with neither CKD nor HIV (HIV^-/CKD^- group).

EXPOSURE

The genetic polymorphisms with reference single-nucleotide polymorphism (rs) identification numbers rs1800469 (TGF-β1), rs1800470 (TGF-β1), rs121918282 (TGF-β1); rs60910145 (APOL1 G1 risk allele), rs73885319 (APOL1 G1 risk allele), rs71785313 (APOL1 G2 risk allele), and rs743811 (HMOX1); HIV.

OUTCOME

CKD.

ANALYTICAL APPROACH

Single-nucleotide polymorphism (SNP) genotyping of rs1800469 (TGF-β1), rs1800470 (TGF-β1), rs121918282 (TGF-β1); rs60910145 (APOL1), rs73885319 (APOL1), rs71785313 (APOL1), and rs743811 (HMOX1) was performed. Hardy-Weinberg equilibrium was evaluated for all SNPs, and minor allele frequencies were reported. A case-control analysis was performed, and multivariable logistic regression was used to control for potential confounders.

RESULTS

Minor allele frequencies for TGF-β1 (rs1800469, rs1800470, and rs1800471), APOL1 (rs60910145, rs73885319, and rs71785313), and HMOX1 (rs743811) were 0.25, 0.46, 0.46, 0.44, 0.45, 0.17, and 0.14, respectively. Among HIV-positive individuals, only TGF-β1 rs1800470 (GG vs AA), APOL1 (in the recessive model), and hypertension were associated with prevalent CKD (adjusted ORs of 0.44 [95% CI, 0.20-0.97], 2.54 [95% CI, 1.44-4.51], and 2.17 [95% CI, 1.35-3.48], respectively). No SNP polymorphisms were associated with prevalent CKD among HIV-negative individuals.

LIMITATIONS

The lack of histopathology data for proper categorization of the type of HIV-related nephropathy.

CONCLUSIONS

APOL1 polymorphisms were highly prevalent in this population and among adult patients infected with HIV and were associated with increased CKD risk. The TGF-β1 (rs1800470) polymorphism was associated with reduced risk, and HMOX1 polymorphisms were unassociated with CKD.

Contemporary issues and new challenges in chronic kidney disease amongst people living with HIV

Chronic kidney disease (CKD) is a comorbidity of major clinical significance amongst people living with HIV (PLWHIV) and is associated with significant morbidity and mortality. The prevalence of CKD is rising, despite the widespread use of antiretroviral therapy (ART) and is increasingly related to prevalent non-infectious comorbidities (NICMs) and antiretroviral toxicity. There are great disparities evident, with the highest prevalence of CKD among PLWHIV seen in the African continent. The aetiology of kidney disease amongst PLWHIV includes HIV-related diseases, such as classic HIV-associated nephropathy or immune complex disease, CKD related to NICMs and CKD from antiretroviral toxicity. CKD, once established, is often relentlessly progressive and can lead to end-stage renal disease (ESRD). Identifying patients with risk factors for CKD, and appropriate screening for the early detection of CKD are vital to improve patient outcomes. Adherence to screening guidelines is variable, and often poor. The progression of CKD may be slowed with certain clinical interventions; however, data derived from studies involving PLWHIV with CKD are sparse and this represent an important area for future research. The control of blood pressure using angiotensin converting enzyme inhibitors and angiotensin receptor blockers, in particular, in the setting of proteinuria, likely slows the progression of CKD among PLWHIV. The cohort of PLWHIV is facing new challenges in regards to polypharmacy, drug-drug interactions and adverse drug reactions. The potential nephrotoxicity of ART is important, particularly as cumulative ART exposure increases as the cohort of PLWHIV ages. The number of PLWHIV with ESRD is increasing. PLWHIV should not be denied access to renal replacement therapy, either dialysis or kidney transplantation, based on their HIV status. Kidney transplantation amongst PLWHIV is successful and associated with an improved prognosis compared to remaining on dialysis. As the cohort of PLWHIV ages, comorbidity increases and CKD becomes more prevalent; models of care need to evolve to meet the new and changing chronic healthcare needs of these patients.

Variation of ApoL1 Testing Practices for Living Kidney Donors

INTRODUCTION

Tests exist for ApoL1 genetic variants to determine whether a potential donor's kidneys are at increased risk of kidney failure. Variants of the ApoL1 gene associated with increased risk are primarily found in people with West African ancestry. Given uncertainty about clinical implications of ApoL1 test results for living kidney donors and recipients and the lack of uniform guidelines for ApoL1 testing, transplant centers across the United States vary in ApoL1 testing practices.

RESEARCH QUESTIONS

(1) What approach do transplant centers take to determine whether prospective donors are of West African ancestry? (2)How do transplant centers engage potential donors during the ApoL1 testing process? (3) What do transplant centers identify as concerns and barriers to ApoL1 testing? and (4) What actions do transplant centers take when a potential donor has 2 ApoL1 risk variants?

DESIGN

We explored the current practices of transplant centers by surveying nephrologists and transplant surgeons at transplant centers evaluating the majority of black living donors in the United States.

RESULTS

About half of these transplant centers offered ApoL1 testing. Of those who offered ApoL1 testing, only half involved the donor in decision-making about donation when the donor has 2 risk variants.

DISCUSSION

Unaddressed differences in the priorities of transplant centers and black living donors may stigmatize black donors and undermine trust in the health-care and organ donation systems. Variation in transplant center testing practices points to the critical need for further research and community engagement to inform the development of guidelines for ApoL1 testing.

Impact of Immigration on Body Mass Index and Blood Pressure Among Adolescent Males and Females: A Nationwide Study

Immigration from one cultural milieu to another has been associated with a greater risk for incident cardio-metabolic morbidity among adults. In this nationwide, population-based, cross-sectional study of data recorded from 1992 to 2016, we assessed the association between body mass index and blood pressure levels among adolescent immigrants, aged 16 to 19 years, of Ethiopian origin, and their secular trend of overweight and obesity. Adolescents of Ethiopian origin were classified as Israeli-born (n=16 153) or immigrants (N=23 487), with stratification by age at immigration. Adolescents whose fathers were at least 3 generations in Israel (n=277 789) served as a comparative group. Hypertensive-range blood pressure values adjusted for age, sex, and height served as outcome. Among adolescents of Ethiopian origin, overweight and obesity (body mass index ≥85th percentile), increased by 2.5 and 4-fold in males and females, respectively, during the study period, compared with a 1.5-fold increase among native Israeli-born males and females. The odds for hypertensive-range measurements increased with the length of residence in Israel: 7.3%, 10.6%, and 14.4% among males who immigrated at ages 12 to 19, 6 to 11.9, and 0 to 5.9 years, respectively; and 11.5%, 16.7%, and 19.3%, respectively, among females. Israeli-born Ethiopians had a significantly higher risk for hypertensive-range measurements at any body mass index level compared with native Israeli-born examinees, after adjusting for sociodemographic factors and health status. In conclusion, among Ethiopian Israeli adolescents, abnormal blood pressure correlates directly with the time-lapse since immigration. Immigrant populations require targeted surveillance and appropriate intervention.

APOL1 Genetic Testing in Living Kidney Transplant Donors

The presence of 2 apolipoprotein L1 gene (APOL1) risk variants is associated with increased risk for chronic kidney disease and end-stage kidney disease. Inferior allograft outcomes following transplantation with kidneys from donors with 2 risk variants have also been reported. These data, coupled with anecdotal case reports and a recent cohort study of living donors, raise important questions about the potential increased kidney disease risk for living donors with APOL1 risk variants and the need for testing as part of the standard living donor evaluation process. We identify a series of questions that are central to the development of clinical policy regarding APOL1 testing of potential living kidney donors given the current uncertainty over the clinical implications of having 2 risk variants. We explore the ethical challenges that arise when determining when and to whom APOL1 testing should be offered, what potential donors should be told about APOL1 testing, how test results should be used to determine suitability for donation, if and when recipients should have access to results, and how clinical policy regarding APOL1 testing should be established.

Serum creatinine and estimated glomerular filtration rates in HIV positive and negative adults in Ethiopia

BACKGROUND

Glomerular filtration rate estimating equations using serum creatinine are not validated in most African settings. We compared serum creatinine and estimated glomerular filtration rate (eGFR) in HIV positive and negative adults and assessed the performance of eGFR equations ((Cockcroft and Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)) compared to 24-hour creatinine clearance in HIV positive adults.

METHODS

Data were collected on demographic, anthropometric, body composition, clinical parameters and serum creatinine in HIV positive and negative adults. 24-hour urine was collected from some of the HIV positive adults who volunteered. Bias was calculated as mean difference between 24-hr creatinine clearance and eGFR (eGFR- 24 hour creatinine clearance) and the accuracy of each eGFR equation was calculated as the percentage of estimates within 30% of creatinine clearance.

RESULTS

A total of 340 HIV positive and 100 HIV negative adults were included in this study. Creatinine clearance was determined for 46 of HIV positive adults. Serum creatinine increased with increasing age, weight, height, body surface area, fat free mass and grip strength in both HIV positive and negative adults (P<0.05). No difference was observed in eGFR between HIV positive and HIV negative adults. For all eGFR equations, the correlation between eGFR and 24-hr creatinine clearance was 0.45-0.53 and the accuracy within 30% of 24-hr creatinine clearance was 24-46%. Removing ethnic coefficient reduced the bias and improved accuracy of the CKD-EPI and the MDRD estimates.

CONCLUSION

Ethiopian HIV positive adults in the present study had good kidney function at the initiation of antiretroviral treatment. However, all eGFR equations overestimated 24-hr creatinine clearance in the study population. Creatinine based eGFR equations that accounts for low muscle mass and body surface area are needed.

Reduced Kidney Function in Tenofovir Disoproxil Fumarate Based Regimen and Associated Factors: A Hospital Based Prospective Observational Study in Ethiopian Patients

Purpose

Tenofovir disoproxil fumarate (TDF), a drug broadly used in combination antiretroviral therapy, is associated with renal dysfunction but the prevalence varied from country to country and it is not known in Ethiopia. The objectives of this study were to assess the prevalence of renal dysfunction and risk factors associated with it and the mean change in estimated glomerular filtration rate in human immunodeficiency virus infected patients receiving TDF based antiretroviral regimen at Tikur Anbessa Specialized Hospital.

Method

It was a hospital based prospective cohort study. The study participants were treatment naïve HIV infected patients initiating TDF containing combination antiretroviral therapy or switched to it because of adverse events. Multivariable logistic analysis was used to identify variables which have significant association.

Result

A total of 63 study participants were studied, 16 (25.4%) of whom had fall in eGFR greater than 25% relative to baseline. Only age greater than 50 years, baseline CD4 count less than 200 cells/mm³, and baseline proteinuria were significantly associated with renal dysfunction in multivariable logistic regression. There was -8.4 ml/min/1.73m² mean change in estimated glomerular filtration rate relative to baseline at six months of study.

Conclusion

The renal dysfunction (defined as decline in eGFR greater than 25%) was found in a quarter of the study population. The long term impact and the clinical implication of it are not clear. Future prospective study is required with large sample size and long duration to ascertain the prevalence of decline greater than 25% in estimated glomerular filtration rate and its progression to chronic kidney disease.

An African perspective on the genetic risk of chronic kidney disease: a systematic review

BACKGROUND

Individuals of African ethnicity are disproportionately burdened with chronic kidney disease (CKD). However, despite the genetic link, genetic association studies of CKD in African populations are lacking.

METHODS

We conducted a systematic review to critically evaluate the existing studies on CKD genetic risk inferred by polymorphism(s) amongst African populations in Africa. The study followed the HuGE handbook and PRISMA protocol. We included studies reporting on the association of polymorphism(s) with prevalent CKD, end-stage renaldisease (ESRD) or CKD-associated traits. Given the very few studies investigating the effects of the same single nucleotide polymorphisms (SNPs) on CKD risk, a narrative synthesis of the evidence was conducted.

RESULTS

A total of 30 polymorphisms in 11 genes were investigated for their association with CKD, ESRD or related traits, all using the candidate-gene approach. Of all the included genes, MYH9, AT1R and MTHFR genes failed to predict CKD or related traits, while variants in the APOL1, apoE, eNOS, XPD, XRCC1, renalase, ADIPOQ, and CCR2 genes were associated with CKD or other related traits. Two SNPs (rs73885319, rs60910145) and haplotypes (G-A-G; G1; G2) of the apolipoprotein L1 (APOL1) gene were studied in more than one population group, with similar association with prevalent CKD observed. The remaining polymorphisms were investigated in single studies.

CONCLUSION

According to this systematic review, there is currently insufficient evidence of the specific polymorphisms that poses African populations at an increased risk of CKD. Large-scale genetic studies are warranted to better understand susceptibility polymorphisms, specific to African populations.

APOL1 risk variants and kidney disease: what we know so far

There are striking differences in chronic kidney disease between Caucasians and African descendants. It was widely accepted that this occurred due to socioeconomic factors, but recent studies show that apolipoprotein L-1 (APOL1) gene variants are strongly associated with focal segmental glomerulosclerosis, HIV-associated nephropathy, hypertensive nephrosclerosis, and lupus nephritis in the African American population. These variants made their way to South America trough intercontinental slave traffic and conferred an evolutionary advantage to the carries by protecting against forms of trypanosomiasis, but at the expense of an increased risk of kidney disease. The effect of the variants does not seem to be related to their serum concentration, but rather to local action on the podocytes. Risk variants are also important in renal transplantation, since grafts from donors with risk variants present worse survival.

APOL1 Nephropathy: A Population Genetics and Evolutionary Medicine Detective Story

Common DNA sequence variants rarely have a high-risk association with a common disease. When such associations do occur, evolutionary forces must be sought, such as in the association of apolipoprotein L1 (APOL1) gene risk variants with nondiabetic kidney diseases in populations of African ancestry. The variants originated in West Africa and provided pathogenic resistance in the heterozygous state that led to high allele frequencies owing to an adaptive evolutionary selective sweep. However, the homozygous state is disadvantageous and is associated with a markedly increased risk of a spectrum of kidney diseases encompassing hypertension-attributed kidney disease, focal segmental glomerulosclerosis, human immunodeficiency virus nephropathy, sickle cell nephropathy, and progressive lupus nephritis. This scientific success story emerged with the help of the tools developed over the past 2 decades in human genome sequencing and population genomic databases. In this introductory article to a timely issue dedicated to illuminating progress in this area, we describe this unique population genetics and evolutionary medicine detective story. We emphasize the paradox of the inheritance mode, the missing heritability, and unresolved associations, including cardiovascular risk and diabetic nephropathy. We also highlight how genetic epidemiology elucidates mechanisms and how the principles of evolution can be used to unravel conserved pathways affected by APOL1 that may lead to novel therapies. The APOL1 gene provides a compelling example of a common variant association with common forms of nondiabetic kidney disease occurring in a continental population isolate with subsequent global admixture. Scientific collaboration using multiple experimental model systems and approaches should further clarify pathomechanisms further, leading to novel therapies.

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

Variants of the APOL1 gene, found primarily in individuals of African descent, are associated with various forms of kidney disease and kidney disease progression. Recent studies evaluating the association of APOL1 with cardiovascular disease have yielded conflicting results, and the potential role in cardiovascular disease remains unclear. In this review, we summarize the observational studies linking the APOL1 risk variants with chronic kidney and cardiovascular disease among persons of African descent.

Kidney disease in the setting of HIV infection: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

HIV-positive individuals are at increased risk for kidney disease, including HIV-associated nephropathy, noncollapsing focal segmental glomerulosclerosis, immune-complex kidney disease, and comorbid kidney disease, as well as kidney injury resulting from prolonged exposure to antiretroviral therapy or from opportunistic infections. Clinical guidelines for kidney disease prevention and treatment in HIV-positive individuals are largely extrapolated from studies in the general population, and do not fully incorporate existing knowledge of the unique HIV-related pathways and genetic factors that contribute to the risk of kidney disease in this population. We convened an international panel of experts in nephrology, renal pathology, and infectious diseases to define the pathology of kidney disease in the setting of HIV infection; describe the role of genetics in the natural history, diagnosis, and treatment of kidney disease in HIV-positive individuals; characterize the renal risk-benefit of antiretroviral therapy for HIV treatment and prevention; and define best practices for the prevention and management of kidney disease in HIV-positive individuals.

HIV-Associated Nephropathy in Africa: Pathology, Clinical Presentation and Strategy for Prevention

The human immunodeficiency virus (HIV) infection can lead to progressive decline in renal function known as HIV-associated nephropathy (HIVAN). Importantly, individuals of African ancestry are more at risk of developing HIVAN than their European descent counterparts. An in-depth search on Google Scholar, Medline and PubMed was conducted using the terms "HIVAN" and "pathology and clinical presentation", in addition to "prevalence and risk factors for HIVAN", with special emphasis on African countries for any articles published between 1990 and 2017. HIVAN is characterized by progressive acute renal failure, proteinuria and enlarged kidneys. A renal biopsy is necessary to establish definitive diagnosis. Risk factors are male gender, low CD4 counts, high viral load and long use of combined antiretroviral medication (cART). There is a wide geographical variation in the prevalence of HIVAN as it ranges from 4.7% to 38% worldwide and little published literature is available about its prevalence in African nations. Microalbuminuria is a common finding in African populations and is significantly associated with severity of HIV disease progression and CD4 count less than 350 cells/µL. Other clinical presentations in African populations include acute kidney injury (AKI), nephrotic syndrome and chronic kidney disease. The main HIV-associated renal pathological lesions were focal segmental glomerulosclerosis, mainly the collapsing form, acute interstitial nephritis (AIN), and immune complex-mediated glomerulonephritis (ICGN). HIV infection-induced transcriptional program in renal tubular epithelial cells as well as genetic factors is incriminated in the pathogenesis of HIVAN. This narrative review discusses the prevalence, presentation, pathogenesis and the management of HIVAN in Africa. In low resource setting countries in Africa, dealing with HIV complications like HIVAN may add more of a burden on the health system (particularly renal units) than HIV medication itself. Therefore, the obvious recommendation is early use of cART in order to decrease risk factors that lead to HIVAN.

APOL1 renal risk variants have contrasting resistance and susceptibility associations with African trypanosomiasis

Reduced susceptibility to infectious disease can increase the frequency of otherwise deleterious alleles. In populations of African ancestry, two apolipoprotein-L1 (APOL1) variants with a recessive kidney disease risk, named G1 and G2, occur at high frequency. APOL1 is a trypanolytic protein that confers innate resistance to most African trypanosomes, but not Trypanosoma brucei rhodesiense or T.b. gambiense, which cause human African trypanosomiasis. In this case-control study, we test the prevailing hypothesis that these APOL1 variants reduce trypanosomiasis susceptibility, resulting in their positive selection in sub-Saharan Africa. We demonstrate a five-fold dominant protective association for G2 against T.b. rhodesiense infection. Furthermore, we report unpredicted strong opposing associations with T.b. gambiense disease outcome. G2 associates with faster progression of T.b. gambiense trypanosomiasis, while G1 associates with asymptomatic carriage and undetectable parasitemia. These results implicate both forms of human African trypanosomiasis in the selection and persistence of otherwise detrimental APOL1 kidney disease variants.

DOI:http://dx.doi.org/10.7554/eLife.25461.001

African-Americans have a greater risk of developing chronic kidney disease than Americans with European ancestry. Much of this increased risk is explained by two versions of a gene called APOL1 that are common in people with African ancestry. These two versions of the gene, known as G1 and G2, suddenly became much more common in people in sub-Saharan Africa in the last 10,000 years. One theory for their rapid spread is that they might protect against a deadly parasitic disease known as African sleeping sickness. This disease is caused by two related parasites of a species known as Trypanosoma brucei, one of which is found in East Africa, while the other affects West Africa.

Laboratory studies have shown that blood from individuals who carry the G1 and G2 variants is better at killing the East African parasites. However, it is not clear if these gene versions help people living in the rural communities, where African sleeping sickness is common, to fight off the disease.

Now, Cooper, Ilboudo et al. show that G1 and G2 do indeed influence how susceptible individuals in these communities are to African sleeping sickness. Individuals with the G2 version were five-times less likely to get the disease from the East African parasite. Neither version could protect individuals from infection with the West African parasite, but infected individuals with the G1 version had fewer parasites in their blood and were less likely to become severely ill. The ability of the G1 version to control the disease and prolong life could explain why this gene version has become so common amongst people in West Africa.

Unexpectedly, the experiments also revealed that people with the G2 version were more likely to become severely unwell when they were infected by the West African parasite. This indicates that whether this gene variant is helpful or harmful depends on where an individual lives. The next step following on from this work will be to investigate exactly how the G1 version reduces the severity of the West African disease. This may aid the development of new drugs for African sleeping sickness and kidney disease.

DOI:http://dx.doi.org/10.7554/eLife.25461.002

HIV associated kidney diseases: Clarifying concordance between renal failure in HIV infection and histopathologic manifestations at kidney biopsy

Patients with HIV infection have a wide spectrum of renal diseases. Some are known to be the direct effect of the viral infection while others are renal diseases that also occur in uninfected populations. HIV associated nephropathy (HIVAN) is considered to be a subtype of primary focal and segmental glomerulosclerosis that is distinct in HIV infected patients. It is more frequent in the African-American population and associated with mutations of the apolipoprotein L1 (APOL1) gene. HIV associated immune complex kidney disease (HIVICD) encompasses a spectrum of HIV associated renal diseases characterized by the presence of immune complex deposition within glomeruli. Thrombotic microangiopathy (TMA) is a complication of HIV infection that presents with hemolytic anemia, thrombocytopenia, and renal failure. TMA in HIV patients is associated with very high mortality. Lastly, the multitude of antiretroviral drugs used for treatment of HIV infections can result in nephrotoxicity. Although a kidney biopsy may not be the first line study for renal disease, knowledge of the different histopathologic features of HIV-associated and unassociated diseases is of paramount importance in the treatment and subsequent outcome of renal function in HIV infected patients. In this review we will describe the histopathologic features and discuss the pathophysiology of the entities previously named.

Most ApoL1 Is Secreted by the Liver

Two coding sequence variants in the APOL1 gene (G1 and G2) explain much of the increased risk for FSGS, HIV-associated nephropathy, and hypertension-attributed ESRD among people of recent African ancestry. The ApoL1 protein is expressed in a wide variety of cell tissues. It has been assumed that the majority of circulating ApoL1 is produced by the liver, but this has not been shown. Using mass spectrometry, we genotyped and quantified the circulating ApoL1 in two liver transplant recipients whose native APOL1 genotype differed from the genotype of the deceased donors, allowing us to differentiate liver- from nonliver-produced ApoL1. Our findings confirm that the liver is indeed the main source of circulating ApoL1. However, the liver is not the sole source of circulating ApoL1, because we found that residual amounts of native ApoL1 continued to circulate in the blood, even after the liver transplant.

Pharmacogenomic implications of the evolutionary history of infectious diseases in Africa

As the common birthplace of all human populations, modern humans have lived longer on the African continent than in any other geographical region of the world. This long history, along with the evolutionary need to adapt to environmental challenges such as exposure to infectious agents, has led to greater genetic variation in Africans. The vast genetic variation in Africans also extends to genes involved in the absorption, distribution, metabolism and excretion of pharmaceuticals. Ongoing cataloging of these clinically relevant variants reveals huge allele-frequency differences within and between African populations. Here, we examine Africa's large burden of infectious disease, discuss key examples of known genetic variation modulating disease risk, and provide examples of clinically relevant variants critical for establishing dosing guidelines. We propose that a more systematic characterization of the genetic diversity of African ancestry populations is required if the current benefits of precision medicine are to be extended to these populations.

Update on current management of chronic kidney disease in patients with HIV infection

The prevalence of HIV-associated chronic kidney disease (CKD) varies geographically and depends on the definition of CKD used, ranging from 4.7% to 38% globally. The incidence, however, has decreased with the use of effective combined antiretroviral therapy (cART). A wide variety of histological patterns are seen in HIV-associated kidney diseases that include glomerular and tubulointerstitial pathology. In resource-rich settings, there has been a plateau in the incidence of end-stage renal disease secondary to HIV-associated nephropathy (HIVAN). However, the prevalence of end-stage renal disease in HIV-positive individuals has risen, mainly due to increased longevity on cART. There is a disparity in the occurrence of HIVAN among HIV-positive individuals such that there is an 18- to 50-fold increased risk of developing kidney disease among HIV-positive individuals of African descent aged between 20 and 64 years and who have a poorer prognosis compared with their European descent counterparts, suggesting that genetic factors play a vital role. Other risk factors include male sex, low CD4 counts, and high viral load. Improvement in renal function has been observed after initiation of cART in patients with HIV-associated CKD. Treatment with an angiotensin-converting enzyme inhibitor/angiotensin receptor blocker is recommended, when clinically indicated in patients with confirmed or suspected HIVAN or clinically significant albuminuria. Other standard management approaches for patients with CKD are recommended. These include addressing other cardiovascular risk factors (appropriate use of statins and aspirin, weight loss, cessation of smoking), avoidance of nephrotoxins, and management of serum bicarbonate and uric acid, anemia, calcium, and phosphate abnormalities. Early diagnosis of kidney disease by screening of HIV-positive individuals for the presence of kidney disease is critical for the optimal management of these patients. Screening for the presence of kidney disease upon detection of HIV infection and annually thereafter in high-risk populations is recommended.

The African diaspora: history, adaptation and health

The trans-Atlantic slave trade brought millions of Africans to the New World. Advances in genomics are providing novel insights into the history and health of Africans and the diasporan populations. Recent examples reviewed here include the unraveling of substantial hunter-gatherer and 'Eurasian' admixtures across sub-Saharan Africa, expanding our understanding of ancestral African genetics; the global ubiquity of mixed ancestry; the revealing of African ancestry in Latin Americans that likely derived from the slave trade; and understanding of the ancestral backgrounds of APOL1 and LPL found to influence kidney disease and lipid levels, respectively, providing specific insights into disease etiology and health disparities.

Genetic risk variants for membranous nephropathy: extension of and association with other chronic kidney disease aetiologies

Background

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Previous genome-wide association studies (GWAS) of 300 000 genotyped variants identified MN-associated loci at HLA-DQA1 and PLA2R1.

Methods

We used a combined approach of genotype imputation, GWAS, human leucocyte antigen (HLA) imputation and extension to other aetiologies of chronic kidney disease (CKD) to investigate genetic MN risk variants more comprehensively. GWAS using 9 million high-quality imputed genotypes and classical HLA alleles were conducted for 323 MN European-ancestry cases and 345 controls. Additionally, 4960 patients with different CKD aetiologies in the German Chronic Kidney Disease (GCKD) study were genotyped for risk variants at HLA-DQA1 and PLA2R1.

Results

In GWAS, lead variants in known loci [rs9272729, HLA-DQA1, odds ratio (OR) = 7.3 per risk allele, P = 5.9 × 10^-27 and rs17830558, PLA2R1, OR = 2.2, P = 1.9 × 10^-8] were significantly associated with MN. No novel signals emerged in GWAS of X-chromosomal variants or in sex-specific analyses. Classical HLA alleles (DRB1*0301-DQA1*0501-DQB1*0201 haplotype) were associated with MN but provided little additional information beyond rs9272729. Associations were replicated in 137 GCKD patients with MN (HLA-DQA1: P = 6.4 × 10^-24; PLA2R1: P = 5.0 × 10^-4). MN risk increased steeply for patients with high-risk genotype combinations (OR > 79). While genetic variation in PLA2R1 exclusively associated with MN across 19 CKD aetiologies, the HLA-DQA1 risk allele was also associated with lupus nephritis (P = 2.8 × 10^-6), type 1 diabetic nephropathy (P = 6.9 × 10^-5) and focal segmental glomerulosclerosis (P = 5.1 × 10^-5), but not with immunoglobulin A nephropathy.

Conclusions

PLA2R1 and HLA-DQA1 are the predominant risk loci for MN detected by GWAS. While HLA-DQA1 risk variants show an association with other CKD aetiologies, PLA2R1 variants are specific to MN.

APOL1 Risk Variants Are Strongly Associated with HIV-Associated Nephropathy in Black South Africans

APOL1 variants are associated with HIV-associated nephropathy and FSGS in African Americans. The prevalence of these variants in African populations with CKD in HIV-1 infection has not been investigated. We determined the role of APOL1 variants in 120 patients with HIV-associated nephropathy and CKD and 108 controls from a South-African black population. Patients with CKD were selected on the basis of histology. Genotypes were successfully determined for APOL1 G1 and G2 variants and 42 single nucleotide polymorphisms, including 18 ancestry informative markers, for 116 patients with CKD (96.7%; 38 patients with HIV-associated nephropathy, 39 patients with HIV-positive CKD, and 39 patients with HIV-negative CKD), and 108 controls (100%). Overall, 79% of patients with HIV-associated nephropathy and 2% of population controls carried two risk alleles. In a recessive model, individuals carrying any combination of two APOL1 risk alleles had 89-fold higher odds (95% confidence interval, 18 to 912; P<0.001) of developing HIV-associated nephropathy compared with HIV-positive controls. Population allele frequencies were 7.3% for G1 and 11.1% for G2. APOL1 risk alleles were not significantly associated with other forms of CKD. These results indicate HIV-positive, antiretroviral therapy-naïve South-African blacks with two APOL1 risk alleles are at very high risk for developing HIV-associated nephropathy. Further studies are required to determine the effect of APOL1 risk variants on kidney diseases in other regions of sub-Saharan Africa.

APOL1 genetic variants, chronic kidney diseases and hypertension in mixed ancestry South Africans

Background

The frequencies of apolipoprotein L1 (APOL1) variants and their associations with chronic kidney disease (CKD) vary substantially in populations from Africa. Moreover, available studies have used very small sample sizes to provide reliable estimates of the frequencies of these variants in the general population. We determined the frequency of the two APOL1 risk alleles (G1 and G2) and investigated their association with renal traits in a relatively large sample of mixed-ancestry South Africans. APOL1 risk variants (G1: rs60910145 and rs73885319; G2: rs71785313) were genotyped in 859 African mixed ancestry individuals using allele-specific TaqMan technology. Glomerular filtration rate (eGFR) was estimated using the Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

Results

The frequencies of rs73885319, rs60910145 and rs71785313 risk alleles were respectively, 3.6 %, 3.4 %, and 5.8 %, resulting in a 1.01 % frequency of the APOL1 two-risk allele (G1:G1 or G1:G2 or G2:G2). The presence of the two-risk allele increased serum creatinine with a corresponding reduction in eGFR (either MDRD or CKD-EPI based). In dominant and log-additive genetic models, significant associations were found between rs71785313 and systolic blood pressure (both p ≤ 0.025), with a significant statistical interaction by diabetes status, p = 0.022, reflecting a negative non-significant effect in nondiabetics and a positive effect in diabetics.

Conclusions

Although the APOL1 variants are not common in the mixed ancestry population of South Africa, the study does provide an indication that APOL1 variants may play a role in conferring an increased risk for renal and cardiovascular risk in this population.

Translational Genomics in Low- and Middle-Income Countries: Opportunities and Challenges

Translation of genomic discoveries into patient care is slowly becoming a reality in developed economies around the world. In contrast, low- and middle-income countries (LMIC) have participated minimally in genomic research for several reasons including the lack of coherent national policies, the limited number of well-trained genomic scientists, poor research infrastructure, and local economic and cultural challenges. Recent initiatives such as the Human Heredity and Health in Africa (H3Africa), the Qatar Genome Project, and the Mexico National Institute of Genomic Medicine (INMEGEN) that aim to address these problems through capacity building and empowerment of local researchers have sparked a paradigm shift. In this short communication, we describe experiences of small-scale medical genetics and translational genomic research programs in LMIC. The lessons drawn from these programs drive home the importance of addressing resource, policy, and sociocultural dynamics to realize the promise of precision medicine driven by genomic science globally. By echoing lessons from a bench-to-community translational genomic research, we advocate that large-scale genomic research projects can be successfully linked with health care programs. To harness the benefits of genomics-led health care, LMIC governments should begin to develop national genomics policies that will address human and technology capacity development within the context of their national economic and sociocultural uniqueness. These policies should encourage international collaboration and promote the link between the public health program and genomics researchers. Finally, we highlight the potential catalytic roles of the global community to foster translational genomics in LMIC.

Sequencing rare and common APOL1 coding variants to determine kidney disease risk

A third of African Americans with sporadic focal segmental glomerulosclerosis (FSGS) or HIV-associated nephropathy (HIVAN) do not carry APOL1 renal risk genotypes. This raises the possibility that other APOL1 variants may contribute to kidney disease. To address this question, we sequenced all APOL1 exons in 1, 437 Americans of African and European decent, including 464 patients with biopsy-proven FSGS/HIVAN. Testing for association with 33 common and rare variants with FSGS/HIVAN revealed no association independent of strong recessive G1 and G2 effects. Seeking additional variants that might have been under selection by pathogens and could represent candidates for kidney disease risk, we also sequenced an additional 1, 112 individuals representing 53 global populations. Except for G1 and G2, none of the 7 common codon-altering variants showed evidence of selection or could restore lysis against trypanosomes causing human African trypanosomiasis. Thus, only APOL1 G1 and G2 confer renal risk and other common and rare APOL1 missense variants, including the archaic G3 haplotype, do not contribute to sporadic FSGS and HIVAN in the United States population. Hence, in most potential clinical or screening applications, our study suggests that sequencing APOL1 exons is unlikely to bring additional information compared to genotyping only APOL1 G1 and G2 risk alleles.

Exon 4-encoded sequence is a major determinant of cytotoxicity of apolipoprotein L1

The apolipoprotein L1 (APOL1) gene (APOL1) product is toxic to kidney cells, and its G1 and G2 alleles are strongly associated with increased risk for kidney disease progression in African Americans. Variable penetrance of the G1 and G2 risk alleles highlights the significance of additional factors that trigger or modify the progression of disease. In this regard, the effect of alternative splicing in the absence or presence of G1 or G2 alleles is unknown. In this study we investigated whether alternative splicing of non-G1, non-G2 APOL1 (APOL1 G0) affects its biological activity. Among seven APOL1 exons, exons 2 and 4 are differentially expressed in major transcripts. We found that, in contrast to APOL1 splice variants B3 or C, variants A and B1 demonstrate strong toxicity in human embryonic kidney (HEK293T) cells. Subsequently, we established that exon 4 is a major determinant of toxicity of variants A and B1 and that extracellular release of these variants is dispensable for their cytotoxicity. Although only variants A and B1 induced nuclear translocation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy, exon 4-positive and -negative APOL1 variants stimulated perinuclear accumulation of unprocessed autophagosomes. Knockdown of endogenous TFEB did not attenuate APOL1 cytotoxicity, indicating that nuclear translocation of TFEB is dispensable for APOL1 toxicity. Our findings that a human podocyte cell line expresses exon 4-positive and -negative APOL1 transcripts suggest that these variants may play a differential role in podocyte pathology. In summary, we have identified exon 4 as a major determinant of APOL1 G0 cytotoxicity.

HIV-associated nephropathies: epidemiology, pathology, mechanisms and treatment

HIV is a highly adaptive, rapidly evolving virus, which is associated with renal diseases including collapsing glomerulopathy-the classic histomorphological form of HIV-associated nephropathy. Other nephropathies related to viral factors include HIV-immune-complex kidney disease and thrombotic microangiopathy. The distribution of HIV-associated kidney diseases has changed over time and continues to vary across geographic regions worldwide. The reasons for this diversity are complex and include a critical role of APOL1 variants and possibly other genetic factors, disparities in access to effective antiviral therapies, and likely other factors that we do not yet fully understand. The mechanisms responsible for HIVAN, including HIV infection of podocytes and tubular epithelial cells, the molecules responsible for HIV entry, and diverse mechanisms of cell injury, have been the focus of much study. Although combined antiretroviral therapy is effective at preventing and reversing HIVAN, focal segmental glomerulosclerosis, arterionephrosclerosis and diabetic nephropathy are increasingly common in individuals who have received such therapy for many years. These diseases are associated with metabolic syndrome, obesity and premature ageing. Future directions for HIV-related kidney disease will involve regular screening for drug nephrotoxicity and incipient renal disease, as well as further research into the mechanisms by which chronic inflammation can lead to glomerular disease.

APOL1 nephropathy: from gene to mechanisms of kidney injury

The contribution of African ancestry to the risk of focal segmental glomerulosclerosis and chronic kidney disease has been partially explained by the recently described chromosome 22q variants in the gene apolipoprotein L1 (APOL1). The APOL1 variants appear at a high allele frequency in populations of West African ancestry as a result of apparent adaptive selection of the heterozygous state. Heterozygosity protects from infection with Trypanosoma brucei rhodesiense. This review will describe the role of the approaches in population genetics for the description of APOL1-associated nephropathies and draw inferences as to the biologic mechanisms from genetic epidemiology findings to date. Modifier loci can influence APOL1 risk for the development of kidney disease. 'Second hits', both viral and non-viral, may explain the discrepancy between the remarkably high odds ratios and the low lifetime risks of kidney disease in two allele carriers of APOL1 risk variants. Therapeutic strategies for APOL1-associated nephropathies will require the prevention and treatment of these 'second hits' and the development of drugs to protect the APOL1 downstream renal injury pathways.

HIV-associated renal and genitourinary comorbidities in Africa

With the recent massive scale-up of access to antiretroviral therapy (ART) in resource-limited countries, HIV has become a chronic disease with new challenges. There is mounting evidence of an increased burden of renal and genitourinary diseases among HIV-infected persons caused by direct HIV viral effects and/or indirectly through the development of opportunistic infections, ART medication-related toxicities, and other noncommunicable diseases (NCDs). We review the epidemiology of HIV-associated renal and urogenital diseases, including interactions with kidney-related NCDs such as hypertension, diabetes mellitus, and cardiovascular disease. We also examine the current evidence regarding the impact of HIV infection on the development of urogenital diseases. Highly advisable in sub-Saharan Africa are the establishment of renal disease registries, reviews of existing clinical practice including cost-effectiveness studies, and the adoption and use of HIV-related NCD management, with training for different cadres of health providers. Epidemiological research priorities include prospective studies to evaluate the true prevalence and spectrum of HIV-related renal disease and their progression. Simple diagnostics tools should be evaluated, including urinary dipsticks and point-of-care urea and creatinine tests to screen for kidney injury in primary care settings. Study of urological manifestations of HIV can help determine the extent of disease and outcomes. As patients live longer on ART, the burden of renal and genitourological complications of HIV and of ART can be expected to increase with a commensurate urgency in both discovery and evidence-based improvements in clinical management.

APOL1 kidney risk alleles: population genetics and disease associations

APOL1 kidney disease is a unique case in the field of the genetics of common disease: 2 variants (termed G1 and G2) with high population frequency have been repeatedly associated with nondiabetic CKDs, with very strong effect size (odds ratios 3-29) in populations of sub-Saharan African descent. This review provides an update on the spectrum of APOL1 kidney disease and on the worldwide distribution of these kidney risk variants. We also summarize the proper way to run a recessive analysis on joint and independent effects of APOL1 G1 and G2 kidney risk variants.

The impact of APOL1, CAV1, and ABCB1 gene variants on outcomes in kidney transplantation: donor and recipient effects

Dramatic improvements have been seen in short-term kidney allograft survival over recent decades with introduction of more potent immunosuppressant medications and regimens. Unfortunately, improvements in long-term graft survival have lagged behind. The genomics revolution is providing new insights regarding the potential impact of kidney donor genotypes on long-term graft survival. Variation in the donor apolipoprotein L1 (APOL1), caveolin 1 (CAV1), and multi-drug resistance 1 encoding P-glycoprotein genes (ABCB1) are all associated with graft survival after kidney transplantation. Although the precise mechanisms whereby these donor gene variants confer risk for graft loss have yet to be determined, these findings provide novel opportunities for modifying interactive environmental factors and optimizing kidney allocation with the ultimate goal of improving long-term graft survival rates.

[Hypertension, chronic kidney disease and genetics in patients with African ancestry]

The incidence and prevalence of hypertension is markedly elevated in Afro-American populations vs Caucasians. The development of end-stage renal disease is also more frequent in Afro-American subjects, independently of blood pressure control. As compared to Caucasians, Afro-American subjects have a higher risk of end-stage renal disease when they are infected with HIV or have lupus. For decades, these data remained mysterious. Within the last 3 years, results from studies in the field of genetics and infectious diseases have transformed our view on this problem. The aim of this paper is to explain how these results have changed our understanding of hypertension and its consequences in Afro-American subjects.

APOL1 and nephropathy progression in populations of African ancestry

Marked familial aggregation of chronic kidney disease suggests that inherited factors play a major role in nephropathy susceptibility. Molecular genetics analyses have identified a number of genes reproducibly associated with a broad range of renal phenotypes. Most associations show polygenic inheritance patterns with limited effect size. In contrast, genetic association between the apolipoprotein L1 (APOL1) gene and several severe nondiabetic forms of kidney disease in African Americans approach Mendelian inheritance patterns and account for a large proportion of glomerulosclerosis in populations of African ancestry. Emerging data support an important role for APOL1 in the progression of diverse etiologies of kidney disease, in concert with requisite environmental (gene*environment) and inherited (gene*gene) interactions. This article reviews the current status of APOL1-associated nephropathy and discusses research questions under active investigation in the search for a cure for these severe and often progressive kidney diseases.

Research capacity. Enabling the genomic revolution in Africa

H3Africa is developing capacity for health-related genomics research in Africa

Gene-gene and gene-environment interactions in apolipoprotein L1 gene-associated nephropathy

Molecular genetics have revolutionized the understanding of susceptibility to the broad spectrum of kidney diseases with light microscopic appearance of FSGS, particularly in populations with recent African ancestry. These disorders include idiopathic FSGS, HIV-associated nephropathy, severe lupus nephritis, sickle cell nephropathy, and the primary kidney disorder focal global glomerulosclerosis, which had historically been ascribed to systemic hypertension. FSGS was once thought to include a multitude of unrelated disorders with similar histologic appearance. However, variation in the apolipoprotein L1 gene locus is now known to account for the vast majority of such cases in African Americans as well as nearly all the excess risk for FSGS and related forms of progressive nondiabetic nephropathy in populations with recent African ancestry, relative to European ancestry. Inheriting two coding apolipoprotein L1 gene nephropathy risk variants is necessary for susceptibility to CKD; however, these variants alone are insufficient to produce disease. This work reviews the evidence supporting second hits or modifying factors that affect risk for apolipoprotein L1 gene-associated nephropathy and produce the protean manifestations of this common and complex syndrome. Targeting modifiable second factors will lead to preventive therapies for slowing progression of nondiabetic nephropathy in many patients possessing two apolipoprotein L1 gene risk variants. This model of genetic risk coupled with modifiable second hits will serve as a paradigm applicable to patients with CKD of various etiologies as well as a host of other complex disorders.

APOL1 risk variants enhance podocyte necrosis through compromising lysosomal membrane permeability

Development of higher rates of nondiabetic glomerulosclerosis (GS) in African Americans has been attributed to two coding sequence variants (G1 and G2) in the APOL1 gene. To date, the cellular function and the role of APOL1 variants (Vs) in GS are still unknown. In this study, we examined the effects of overexpressing wild-type (G0) and kidney disease risk variants (G1 and G2) of APOL1 in human podocytes using a lentivirus expression system. Interestingly, G0 inflicted podocyte injury only at a higher concentration; however, G1 and G2 promoted moderate podocyte injury at lower and higher concentrations. APOL1Vs expressing podocytes displayed diffuse distribution of both Lucifer yellow dye and cathepsin L as manifestations of enhanced lysosomal membrane permeability (LMP). Chloroquine attenuated the APOL1Vs-induced increase in podocyte injury, consistent with targeting lysosomes. The chloride channel blocker DIDS prevented APOL1Vs- induced injury, indicating a role for chloride influx in osmotic swelling of lysosomes. Direct exposure of noninfected podocytes with conditioned media from G1- and G2-expressing podocytes also induced injury, suggesting a contributory role of the secreted component of G1 and G2 as well. Adverse host factors (AHFs) such as hydrogen peroxide, hypoxia, TNF-α, and puromycin aminonucleoside augmented APOL1- and APOL1Vs-induced podocyte injury, while the effect of human immunodeficiency virus (HIV) on podocyte injury was overwhelming under conditions of APOLVs expression. We conclude that G0 and G1 and G2 APOL1 variants have the potential to induce podocyte injury in a manner which is further augmented by AHFs, with HIV infection being especially prominent.

The changing epidemiology of HIV-related chronic kidney disease in the era of antiretroviral therapy

The epidemiology of kidney disease in HIV-infected individuals has changed significantly since the introduction of combination antiretroviral therapy (cART) in the mid 1990s. HIV-associated nephropathy (HIVAN), an aggressive form of collapsing focal segmental glomerulosclerosis (FSGS) caused by direct HIV infection of the kidney in a genetically susceptible host, emerged early in the HIV epidemic as a leading cause of end-stage renal disease. With the widespread use of cART, HIVAN is increasingly rare in populations with access to care, and the spectrum of HIV-related chronic kidney disease now reflects the growing burden of comorbid disease in the aging HIV population. Nonetheless, available data suggest that both HIV infection and cART nephrotoxicity continue to contribute to the increased risk of chronic kidney disease in HIV-infected individuals in the United States and Europe. Despite the genetic susceptibility to HIVAN in individuals of West African descent, limited data are available to define the prevalence and spectrum of HIV-related kidney disease in sub-Saharan Africa, which is home to two-thirds of the world's HIV population. In this mini-review, we characterize the changing epidemiology of HIV-related chronic kidney disease in Western nations and in sub-Saharan Africa.