Conflicting reports exist as to whether sickle cell trait is a risk factor for the progression of nephropathy. In order to determine whether African Americans with sickle cell trait are at increased risk for kidney disease, we assessed the genetic association between sickle cell trait and end-stage renal disease (ESRD). Hemoglobin S, non-muscle myosin heavy chain 9 (MYH9), and apolipoprotein L1 (APOL1) risk variants were genotyped in 3258 unrelated African Americans: 1085 with non-diabetic ESRD, 996 with type 2 diabetes-associated ESRD, and 1177 controls. Since APOL1 is strongly associated with ESRD in African Americans, interactions between APOL1 and MYH9 risk variants and hemoglobin S were assessed using case-only and case-control centered two-way logistic regression interaction analyses. The sickle cell trait genotype frequencies were 8.7% in non-diabetic ESRD, 7.1% in type 2 diabetes-ESRD, and 7.2% in controls. There was no age-, gender-, and admixture-adjusted significance for sickle cell trait association with non-diabetic ESRD (odds ratio 1.16); type 2 diabetes-ESRD (odds ratio 1.01); or all-cause ESRD (combined non-diabetic and type 2 diabetic-ESRD patients compared to the controls; odds ratio 1.05) in dominant models. In addition, no evidence of APOL1 or MYH9 interactions with sickle cell trait was detected. Hence, sickle cell trait is not associated with diabetic or non-diabetic ESRD in a large sample of African Americans.
African American; APOL1; diabetes; end-stage kidney disease; hemoglobin S; hypertension
Despite intensive anti-hypertensive therapy there was a high incidence of renal end-points in participants of the African American Study of Kidney Disease and Hypertension (AASK) cohort. To better understand this, coding variants in the apolipoprotein L1 (APOL1) and the non-muscle myosin heavy chain 9 (MYH9) genes were evaluated for an association with hypertension-attributed nephropathy and clinical outcomes in a case-control study. Clinical data and DNA were available for 675 AASK participant cases and 618 African American non-nephropathy control individuals. APOL1 G1 and G2, and MYH9 E1 variants along with 44 ancestry informative markers were genotyped with allele frequency differences between cases and controls analyzed by logistic regression multivariable models adjusting for ancestry, age, and gender. In recessive models, APOL1 risk variants were significantly associated with kidney disease in all cases compared to controls with an odds ratio of 2.57. In AASK cases with more advanced disease, such as a baseline urine protein to creatinine ratio over 0.6 g/g or a serum creatinine over 3 mg/dL during follow-up, the association was strengthened with odds ratios of 6.29 and 4.61, respectively. APOL1 risk variants were consistently associated with renal disease progression across medication classes and blood pressure targets. Thus, kidney disease in AASK participants was strongly associated with APOL1 renal risk variants.
Polymorphisms in the non-muscle myosin IIA gene (MYH9) are associated with focal segmental glomerulosclerosis (FSGS) and non-diabetic end-stage renal disease (ESRD) in African Americans and FSGS in European Americans. We tested for association of single nucleotide polymorphisms (SNPs) in MYH9 with T2DM–ESRD in European Americans; additionally, three APOL1 gene variants were evaluated.
Fifteen MYH9 SNPs and two APOL1 SNPs plus a 6-bp deletion were genotyped in 1963 European Americans, 536 cases with T2DM–ESRD and 1427 non-nephropathy controls (467 with T2DM and 960 without diabetes).
Comparing T2DM–ESRD cases with the 467 T2DM non-nephropathy controls, single variant associations trending toward significance were detected with SNPs rs4821480, rs2032487 and rs4281481 comprising part of the major MYH9 E1 risk haplotype [P-values 0.053–0.055 recessive, odds ratio (OR) 6.08–6.14]. Comparing T2DM–ESRD cases to all 1427 non-nephropathy controls, we confirmed evidence of association in these three SNPs as well as in the fourth E1 SNP (rs3752462) (P-values 0.017–0.035, OR 1.41–3.72). APOL1 G1/G2 nephropathy risk variants were rare in individuals of European American heritage, present in 0.28% of chromosomes in T2DM–ESRD cases and 0.32% of controls.
MYH9 SNPs rs4821480, rs2032487, rs4281481 and rs3752462 are associated with T2DM–ESRD susceptibility in European Americans. The APOL1 risk variants are not present at appreciable frequency in this cohort with T2DM–ESRD. Therefore, polymorphisms in MYH9 appear to influence nephropathy risk in this sample.
APOL1; diabetic nephropathy; end-stage renal disease; MYH9; type 2 diabetes mellitus
MYH9 has been proposed as a major genetic risk locus for a spectrum of nondiabetic end stage kidney disease (ESKD). We use recently released sequences from the 1000 Genomes Project to identify two western African-specific missense mutations (S342G and I384M) in the neighboring APOL1 gene, and demonstrate that these are more strongly associated with ESKD than previously reported MYH9 variants. The APOL1 gene product, apolipoprotein L-1, has been studied for its roles in trypanosomal lysis, autophagic cell death, lipid metabolism, as well as vascular and other biological activities. We also show that the distribution of these newly identified APOL1 risk variants in African populations is consistent with the pattern of African ancestry ESKD risk previously attributed to MYH9.
Mapping by admixture linkage disequilibrium (MALD) localized an interval on chromosome 22, in a region that includes the MYH9 gene, which was shown to contain African ancestry risk variants associated with certain forms of ESKD (Kao et al. 2008; Kopp et al. 2008). MYH9 encodes nonmuscle myosin heavy chain IIa, a major cytoskeletal nanomotor protein expressed in many cell types, including podocyte cells of the renal glomerulus. Moreover, 39 different coding region mutations in MYH9 have been identified in patients with a group of rare syndromes, collectively termed the Giant Platelet Syndromes, with clear autosomal dominant inheritance, and various clinical manifestations, sometimes also including glomerular pathology and chronic kidney disease (Kopp 2010; Sekine et al. 2010). Accordingly, MYH9 was further explored in these studies as the leading candidate gene responsible for the MALD signal. Dense mapping of MYH9 identified individual single nucleotide polymorphisms (SNPs) and sets of such SNPs grouped as haplotypes that were found to be highly associated with a large and important group of ESKD risk phenotypes, which as a consequence were designated as MYH9-associated nephropathies (Bostrom and Freedman 2010). These included HIV-associated nephropathy (HIVAN), primary nonmonogenic forms of focal segmental glomerulosclerosis, and hypertension affiliated chronic kidney disease not attributed to other etiologies (Bostrom and Freedman 2010). The MYH9 SNP and haplotype associations observed with these forms of ESKD yielded the largest odds ratios (OR) reported to date for the association of common variants with common disease risk (Winkler et al. 2010). Two specific MYH9 variants (rs5750250 of S-haplotype and rs11912763 of F-haplotype) were designated as most strongly predictive on the basis of Receiver Operating Characteristic analysis (Nelson et al. 2010). These MYH9 association studies were then also extended to earlier stage and related kidney disease phenotypes and to population groups with varying degrees of recent African ancestry admixture (Behar et al. 2010; Freedman et al. 2009a, b; Nelson et al. 2010), and led to the expectation of finding a functional African ancestry causative variant within MYH9. However, despite intensive efforts including re-sequencing of the MYH9 gene no suggested functional mutation has been identified (Nelson et al. 2010; Winkler et al. 2010). This led us to re-examine the interval surrounding MYH9 and to the detection of novel missense mutations with predicted functional effects in the neighboring APOL1 gene, which are significantly more associated with ESKD than all previously reported SNPs in MYH9.
Electronic supplementary material
The online version of this article (doi:10.1007/s00439-010-0861-0) contains supplementary material, which is available to authorized users.
African Americans (AA) disproportionately develop lupus nephritis (LN) relative to European Americans and familial clustering supports causative genes. Since MYH9 underlies approximately 40% of end-stage renal disease (ESRD) in AA, we tested for genetic association with LN.
Seven MYH9 single nucleotide polymorphisms (SNPs) and the E1 risk haplotype were tested for association with LN in three cohorts of AA.
A preliminary analysis revealed that the MYH9 E1 risk haplotype was associated with ESRD in 25 cases with presumed systemic lupus erythematosus (SLE)-associated ESRD, compared to 735 non-SLE controls (odds ratio 3.1; p = 0.010 recessive). Replication analyses were performed in 583 AA with SLE in the PROFILE cohort (318 with LN; 265 with SLE but without nephropathy) and 60 AA from the NIH (39 with LN; 21 with SLE but without nephropathy). Analysis of the NIH and larger PROFILE cohorts, as well as a combined analysis, did not support this association.
These results suggest that AA with ESRD and coincident SLE who were recruited from dialysis clinics more likely have kidney diseases in the MYH9-associated spectrum of focal segmental glomerulosclerosis. PROFILE and NIH participants, recruited from rheumatology practices, demonstrate that MYH9 does not contribute substantially to the development of LN in AA.
African Americans; Genetics; Lupus nephritis; Kidney; MYH9; Systemic lupus erythematosus
A region of chromosome 22 which includes APOL1 and MYH9 genes was recently identified as a risk locus for non-diabetic forms of kidney disease, including idiopathic and HIV associated focal segmental glomerular sclerosis and kidney disease clinically attributed to hypertension among African Americans. The purpose of the current study was therefore to examine the frequency of these variants and to determine whether they are associated with chronic kidney disease (CKD) among native Africans.
To investigate possible evidence of association between variants in these genes and non-diabetic CKD among West Africans, we performed a case/control analysis in a sample of 166 Nigerians without history of European admixture. Our study included a total of 9 variants on APOL1 (n=4) and MYH9 (n=5) genes.
We observed significantly strong associations with previously reported APOL1 variants rs73885319 and rs60910145 and their two-allele “G1” haplotype (P < 0.005). We did not observe significant evidence of association between non-diabetic CKD and any of the MYH9 variants or haplotypes after accounting for multiple testing in our sample.
In conclusion, APOL1 risk variants are associated with non-diabetic forms of CKD among Nigerians of Yoruba ethnicity. Further information on APOL1/MYH9 variants may lead to screening programs which could lead to earlier detection and interventions for non-diabetic kidney disease.
chronic kidney disease; APOL1; MYH9; genetic renal disease
A region of chromosome 22 which includes APOL1 and MYH9 genes was recently identified as a risk locus for non-diabetic forms of kidney disease, including idiopathic and HIV-associated focal segmental glomerular sclerosis and kidney disease clinically attributed to hypertension among African Americans. The purposes of the current study were, therefore, to examine the frequency of these variants and to determine whether they are associated with chronic kidney disease (CKD) among native Africans.
To investigate the possible evidence of association between variants in these genes and non-diabetic CKD among West Africans, we performed a case/control analysis in a sample of 166 Nigerians without history of European admixture. Our study included a total of 9 variants on APOL1 (n = 4) and MYH9 (n = 5) genes.
We observed significantly strong associations with previously reported APOL1 variants rs73885319 and rs60910145, and their two-allele “G1” haplotype (P < 0.005). We did not observe significant evidence of association between non-diabetic CKD and any of the MYH9 variants or haplotypes after accounting for multiple testing in our sample.
In conclusion, APOL1 risk variants are associated with non-diabetic forms of CKD among Nigerians of Yoruba ethnicity. Further information on APOL1/MYH9 variants may lead to screening programs, which could lead to earlier detection and interventions for non-diabetic kidney disease.
Chronic kidney disease; APOL1; MYH9; Genetic renal disease
Renal failure occurs in 5–18% of sickle cell disease (SCD) patients and is associated with early mortality. At risk SCD patients cannot be identified prior to the appearance of proteinuria and the pathobiology is not well understood. The MYH9 and APOL1 genes have been associated with risk for focal segmental glomerulosclerosis and end-stage renal disease in African Americans.
We genotyped 26 SNPs in MYH9 and 2 SNPs in APOL1 in 521 unrelated adult (18–83 years) SCD patients screened for proteinuria. Using logistic regression, SNPs were evaluated for association with proteinuria.
Eight MYH9 SNPs and one APOL1 SNP were nominally associated with proteinuria. Six SNPs remained significant after multiple testing correction (p < 0.0025), and a risk haplotype was associated with proteinuria (p=0.001). Using multiple regression, association with APOL1 diminished in the presence of MYH9 SNPs. Glomerular filtration rate was negatively correlated with proteinuria (p < 0.0001), and was nominally associated with MYH9 and APOL1 in age-adjusted analyses.
Our data provide insight into the pathobiology of renal dysfunction in SCD, suggesting that MYH9 is more strongly associated than APOL1. These data also provide the opportunity for early identification of patients at risk and new therapeutics.
sickle cell disease; nephropathy; genetics association; genetic modifier; proteinuria
Genetic variation at the MYH9 locus is linked to the high incidence of focal segmental glomerulosclerosis (FSGS) and non-diabetic end-stage renal disease among African Americans. To further define risk alleles with FSGS we performed a genome-wide association analysis using more than one million single nucleotide polymorphisms in 56 African and 61 European American patients with biopsy-confirmed FSGS. Results were compared to 1641 European and 1800 African Americans as unselected controls. While no association was observed in the cohort of European Americans; the case-control comparison of African Americans found variants within a 60kb region of chromosome 22 containing part of the APOL1 and MYH9 genes associated with increased risk of FSGS. This region spans different linkage disequilibrium blocks and variants associating with disease within this region are in linkage disequilibrium with variants which have shown signals of natural selection. APOL1 is a strong candidate for a gene that has undergone recent natural selection and is known to be involved in the infection by Trypanosome brucei, a parasite common in Africa that has recently adapted to infect human hosts. Further studies will be required to establish which variants are causally related to kidney disease, what mutations caused the selective sweep, and to ultimately determine if these are the same.
focal segmental glomerulosclerosis; end stage kidney disease; genetic renal disease
Polymorphisms in the MYH9 and adjacent APOL1 gene region demonstrate a strong association with non-diabetic kidney disease in African-Americans. However, it is not known to what extent these polymorphisms are present in other ethnic groups. To examine the association of genetic polymorphisms in this region with chronic kidney disease (CKD; estimated glomerular filtration rate <60 ml/min/1.73 m2) in individuals of European ancestry, we examined rs4821480, an MYH9 single-nucleotide polymorphism (SNP) recently identified as associated with kidney disease in African-Americans, in 13 133 participants from the Framingham Heart Study (FHS) and Atherosclerosis Risk in Communities (ARIC) Study. In addition, we further interrogated the MYH9/APOL1 gene region using 282 SNPs for association with CKD using age-, sex- and center-adjusted models and performed a meta-analysis of the results from both studies. Because of prior data linking rs4821480 and kidney disease, we used a P-value of <0.05 to test the association with CKD. In the meta-analysis, rs4821480 (minor allele frequency 4.45 and 3.96% in FHS and ARIC, respectively) was associated with higher CKD prevalence in participants free of diabetes (odds ratio 1.44; 95% confidence interval 1.15–1.80; P = 0.001). No other SNPs achieved significance after adjusting for multiple testing. Results utilizing directly genotyped data confirmed the results of the primary analysis. Recently identified APOL1 risk variants were also directly genotyped, but did not account for the observed MYH9 signal. These data suggest that the MYH9 polymorphism rs4821480 is associated with an increased risk of non-diabetic CKD in individuals of European ancestry.
Background. Coding variants in the apolipoprotein L1 gene (APOL1) are strongly associated with non-diabetic nephropathy in African Americans. ApoL1 proteins associate with high-density lipoprotein (HDL) particles in the circulation. Plasma HDL particle subclass concentrations were compared in 73 African Americans based on APOL1 genotypes to detect differences potentially contributing to renal disease.
Methods. HDL subclass concentrations were measured using nuclear magnetic resonance spectroscopy in African American first-degree relatives of patients with non-diabetic end-stage renal disease. Participants had estimated glomerular filtration rates (GFRs) > 80 mL/min and lacked albuminuria. Additive effects of the number of APOL1 risk variants on natural logarithm-transformed HDL subclass concentrations were computed.
Results. Participants were 58.9% female with mean ± SD age 47.2 ± 13.3 years and GFR 92.4 ± 18.8 mL/min. The numbers with 2, 1 and 0 APOL1 nephropathy risk variants, respectively, were 36, 17 and 20. Mean ± SD medium-sized HDL concentrations were significantly lower for each additional APOL1 risk variant (2 versus 1 versus 0 risk variants: 9.0 ± 5.6 versus 10.1 ± 5.5 versus 13.1 ± 8.2 μmol/L, respectively; P = 0.0222 unadjusted; P = 0.0162 triglyceride- and ancestry adjusted).
Conclusions. Lower medium-sized HDL subclass concentrations are present in African Americans based on increasing numbers of APOL1 nephropathy risk variants. Potential mechanistic roles of altered medium HDL concentrations on APOL1-associated renal microvascular diseases should be evaluated.
APOL1; arteriolar nephrosclerosis; FSGS; HDL cholesterol; kidney
APOL1 gene variants are associated with end-stage renal disease in African Americans. Here we investigate the impact of recipient APOL1 (apolipoprotein L-1) gene distributions on kidney allograft outcomes. We conducted a retrospective analysis of 119 African American kidney transplant recipients, and found that 58 (48.7%) carried two APOL1 kidney disease risk variants. Contrary to the association seen in native kidney disease, there is no difference in allograft survival at 5 years post-transplant for recipients with high-risk APOL1 genotypes. Thus, we were able to conclude that APOL1 genotypes do not increase risk of allograft loss after kidney transplantations, and carrying 2 APOL1 risk alleles should not be an impediment to transplantation.
African-Americans; kidney graft survival; gene polymorphism
Coding variants in the apolipoprotein L1 gene (APOL1) are strongly associated with nephropathy in African Americans (AAs). The effect of transplanting kidneys from AA donors with two APOL1 nephropathy risk variants is unknown. APOL1 risk variants were genotyped in 106 AA deceased organ donors and graft survival assessed in 136 resultant kidney transplants. Cox proportional-hazard models tested for association between time to graft failure and donor APOL1 genotypes. Mean follow-up was 26.4 ± 21.8 months. Twenty-two of 136 transplanted kidneys (16%) were from donors with two APOL1 nephropathy risk variants. Twenty five grafts failed; eight (32%) had two APOL1 risk variants. A multivariate model accounting for donor APOL1 genotype, overall African ancestry, expanded criteria donation, recipient age and gender, HLA mismatch, CIT, and PRA revealed that graft survival was significantly shorter in donor kidneys with two APOL1 risk variants (hazard ratio [HR] 3.84; p=0.008) and higher HLA mismatch (HR 1.52; p=0.03), but not for overall African ancestry excluding APOL1. Kidneys from AA deceased donors harboring two APOL1 risk variants failed more rapidly after renal transplantation than those with zero or one risk variants. If replicated, APOL1 genotyping could improve the donor selection process and maximize long term renal allograft survival.
African Americans; APOL1; focal segmental glomerulosclerosis; graft survival; kidney donor; kidney transplantation
Recently, an association was found between non-diabetic kidney disease in African Americans and two independent sequence variants in the APOL1 gene, encoding apolipoprotein L1. In this study we determined the frequency of APOL1 risk variants in patients with biopsy-proven HIV-associated nephropathy (HIVAN) and distinctive pathological characteristics potentially driven by those risk variants. Among 76 patients with HIVAN, 60 were successfully genotyped for APOL1 G1 and G2 polymorphisms. In this cohort, 37 had two risk alleles, 18 were heterozygous and 5 had neither risk variant. There were no differences in the pathological findings of HIVAN and the number of APOL1 risk alleles. Further, the progression to end stage kidney disease or death did not differ by the number of risk alleles. Median renal survival was 9.3 months in patients with none or one risk allele compared to 11.7 months in patients with two APOL1 risk alleles. Thus, our study suggests that although the majority of African American patients with HIVAN have two APOL1 risk alleles, other as yet unknown factors in the host including genetic risk variants and environmental or viral factors may influence the development of this disorder in those with none or one APOL1 risk allele.
Familial clustering of disparate kidney diseases including clinically diagnosed hypertensive and diabetic nephropathy, idiopathic focal segmental glomerulosclerosis (FSGS) and Human Immunodeficiency Virus-associated nephropathy are often observed in African Americans. Admixture mapping recently identified the non-muscle myosin heavy chain 9 gene (MYH9) as a susceptibility factor strongly associated with several non-diabetic etiologies of end-stage renal disease (ESRD) in African Americans, less strongly with diabetes-associated ESRD. MYH9-associated nephropathies reside in the spectrum of FSGS/focal global glomerulosclerosis. The renal histology in proteinuric African Americans homozygous for MYH9 risk variants with longstanding type 2 diabetes mellitus is unknown. We report a case of coincident idiopathic FSGS, collapsing variant; and diabetic nephropathy in an African American homozygous for the MYH9 E1 risk haplotype. This case demonstrates that diabetic African Americans with overt proteinuria can have mixed renal lesions, including those in the spectrum of MYH9-associated nephropathy. Careful interpretation of kidney biopsies in proteinuric African Americans with diabetes is necessary to exclude coincident non-diabetic forms of nephropathy, precisely define etiologies of kidney disease, and determine the natural history and treatment response in mixed lesions of diabetes-associated and MYH9-associated kidney disease.
We report a case of coincident idiopathic FSGS, collapsing variant; and diabetic nephropathy in an African American homozygous for the MYH9 E1 risk haplotype.
African American; collapsing variant focal segmental glomerulosclerosis; diabetes; diabetic nephropathy; MYH9
Human apolipoprotein L1 (ApoL1) possesses both extra- and intra-cellular functions crucial in host defense and cellular homeostatic mechanisms. Alterations in ApoL1 function due to genetic, environmental, and lifestyle factors have been associated with African sleeping sickness, atherosclerosis, lipid disorders, obesity, schizophrenia, cancer, and chronic kidney disease (CKD). Importantly, two alleles of APOL1 carrying three coding-sequence variants have been linked to CKD, particularly in Sub-Saharan Africans and African Americans. Intracellularly, elevated ApoL1 can induce autophagy and autophagy-associated cell death, which may be critical in the maintenance of cellular homeostasis in the kidney. Similarly, ApoL1 may protect kidney cells against renal cell carcinoma (RCC). We summarize the role of ApoL1 in RCC and CKD, highlighting the critical function of ApoL1 in autophagy.
Apolipoprotein L (ApoL); ApoL1; ApoL6; ApoA1; Autophagy; Apoptosis; ESKD; FSGS; Genetics; GSGS; HIVAN; Kidney transplantation
Single nucleotide polymorphisms (SNPs) in MYH9 and APOL1 on chromosome 22 (c22) are powerfully associated with non-diabetic end-stage renal disease (ESRD) in African Americans (AAs). Many AAs diagnosed with type 2 diabetic nephropathy (T2DN) have non-diabetic kidney disease, potentially masking detection of DN genes. Therefore, genome-wide association analyses were performed using the Affymetrix SNP Array 6.0 in 966 AA with T2DN and 1,032 non-diabetic, non-nephropathy (NDNN) controls, with and without adjustment for c22 nephropathy risk variants. No associations were seen between FRMD3 SNPs and T2DN before adjusting for c22 variants. However, logistic regression analysis revealed seven FRMD3 SNPs significantly interacting with MYH9—a finding replicated in 640 additional AA T2DN cases and 683 NDNN controls. Contrasting all 1,592 T2DN cases with all 1,671 NDNN controls, FRMD3 SNPs appeared to interact with the MYH9 E1 haplotype (e.g., rs942280 interaction p-value = 9.3E−7 additive; odds ratio [OR] 0.67). FRMD3 alleles were associated with increased risk of T2DN only in subjects lacking two MYH9 E1 risk haplotypes (rs942280 OR = 1.28), not in MYH9 E1 risk allele homozygotes (rs942280 OR = 0.80; homogeneity p-value = 4.3E−4). Effects were weaker stratifying on APOL1. FRMD3 SNPS were associated with T2DN, not type 2 diabetes per se, comparing AAs with T2DN to those with diabetes lacking nephropathy. T2DN-associated FRMD3 SNPs were detectable in AAs only after accounting for MYH9, with differential effects for APOL1. These analyses reveal a role for FRMD3 in AA T2DN susceptibility and accounting for c22 nephropathy risk variants can assist in detecting DN susceptibility genes.
African Americans have high rates of kidney disease attributed to type 2 diabetes mellitus. However, approximately 25% of patients are misclassified and have non-diabetic kidney disease on renal biopsy. The APOL1-MYH9 gene region on chromosome 22 is powerfully associated with non-diabetic kidney diseases in African Americans. Therefore, we tested for interactions between single nucleotide polymorphisms across the genome with APOL1 and MYH9 non-diabetic nephropathy risk variants in African Americans with presumed diabetic nephropathy. Markers in FRMD3, a gene associated with type 1 diabetic nephropathy in Caucasians, appeared to interact with MYH9; however, increased nephropathy risk was seen in diabetic cases lacking two MYH9 risk haplotypes, and protective effects were seen in those with two MYH9 risk haplotypes. Stratified analyses based on the chromosome 22 nephropathy risk haplotypes demonstrated that FRMD3 variants were associated with diabetic nephropathy risk in cases without two MYH9 (or APOL1) risk haplotypes. It appears that African Americans with diabetes and kidney disease who are not chromosome 22 nephropathy risk variant homozygotes are enriched for the presence of diabetic nephropathy and FRMD3 risk alleles. This genetic dissection ultimately allowed for detection of the FRMD3 diabetic nephropathy gene association in a subset of cases enriched for this disorder.
Apolipoprotein L1 (APOL1) gene association studies and results of the African American Study of Kidney Disease and Hypertension are disproving the longstanding concept that mild to moderate essential hypertension contributes substantially to end-stage renal disease susceptibility in African Americans. APOL1 coding variants underlie a spectrum of kidney diseases, including that attributed to hypertension (labeled arteriolar or hypertensive nephrosclerosis), focal segmental glomerulosclerosis, and HIV-associated nephropathy. APOL1 nephropathy risk variants persist because of protection afforded by the parasite that causes African sleeping sickness. This breakthrough will lead to novel treatments for hypertensive African Americans with low-level proteinuria, for whom effective therapies are lacking. Furthermore, APOL1 nephropathy risk variants contribute to racially variable allograft survival rates after kidney transplantation and assist in detecting nondiabetic forms of nephropathy in African Americans with diabetes. Discovery of APOL1-associated nephropathy was a major success of the genetics revolution, demonstrating that secondary hypertension is typically present in nondiabetic African Americans with nephropathy.
African American; African sleeping sickness; Arteriolar nephrosclerosis; APOL1; Chronic kidney disease; Dialysis; End-stage renal disease; ESRD: Focal segmental glomerulosclerosis; Genetics; Glomerulosclerosis; Hypertension; Hypertensive nephrosclerosis; Kidney disease; Kidney donors; MYH9; Nondiabetic nephropathy; Racial differences; Trypanosoma brucei rhodesiense; Transplantation
Familial aggregation of non-diabetic end stage renal disease (ESRD) is found in African Americans and variants in the apolipoprotein L1 gene (APOL1) contribute to this risk. To detect genetic associations with milder forms of nephropathy in high-risk families, analyses were performed using generalized estimating equations to assess relationships between kidney disease phenotypes and APOL1 variants in 786 relatives of 470 families. Adjusting for familial correlations, 23.1, 46.7, and 30.2 percent of genotyped relatives possessed two, one, or no APOL1 risk variants, respectively. Relatives with two compared to one or no risk variants had statistically indistinguishable median systolic blood pressure, urine albumin to creatinine ratio, estimated GFR (MDRD equation) and serum cystatin C levels. After adjusting for age, gender, age at ESRD in families, and African ancestry, significant associations were detected between APOL1 with overt proteinuria and estimated GFR (CKD-EPI equation), with a trend toward significance for quantitative albuminuria. Thus, relatives of African Americans with non-diabetic ESRD are enriched for APOL1 risk variants. After adjustment, two APOL1 risk variants weakly predict mild forms of kidney disease. Second hits appear necessary for the initiation of APOL1-associated nephropathy.
African American; APOL1; end-stage renal disease; FSGS; kidney; screening
This manuscript reviews the controversial relationship between hypertension and initiation of kidney disease. We focus on ethnic differences in renal histopathology and associated gene variants comprising the spectrum of MYH9-nephropathy.
Purpose of review
Treating mild to moderate essential hypertension in non-diabetic African Americans fails to halt nephropathy progression; while hypertension control slows nephropathy progression in European Americans. The pathogenesis of these disparate renal syndromes is reviewed.
The non-muscle myosin heavy chain 9 gene (MYH9) is associated with a spectrum of kidney diseases in African Americans, including idiopathic focal global glomerulosclerosis historically attributed to hypertension, idiopathic focal segmental glomerulosclerosis, and the collapsing variant of focal segmental glomerulosclerosis (HIV-associated nephropathy). Risk variants in MYH9 likely contribute to the failure of hypertension control to slow progressive kidney disease in non-diabetic African Americans.
Early and intensive hypertension control fails to halt progression of “hypertensive nephropathy” in African Americans. Genetic analyses in patients with essential hypertension and nephropathy attributed to hypertension, FSGS and HIVAN reveal that MYH9 gene polymorphisms are associated with a spectrum of kidney diseases in this ethnic group. Mild to moderate hypertension may cause nephropathy in European Americans with intra-renal vascular disease improved by the treatment of hypertension, hyperlipidemia and smoking cessation.
African Americans; CHGA; focal segmental glomerulosclerosis; genetics; hypertensive nephrosclerosis; MYH9
Among African-Americans, genome wide association revealed a strong correlation between the G1 and G2 alleles of APOL1 (apolipoproteinL1, also called trypanolytic factor) and kidney diseases including focal and segmental glomerulosclerosis, HIV-associated nephropathy and hypertensive nephrosclerosis. In the prevailing hypothesis, heterozygous APOL1 G1 and G2 alleles increase resistance against Trypanosoma that cause African sleeping sickness, resulting in positive selection of these alleles, but when homozygous the G1 and G2 alleles predispose to glomerulosclerosis. While efforts are underway to screen patients for G1 and G2 alleles and to better understand “APOL1 glomerulopathy,” no data prove that these APOL1 sequence variants cause glomerulosclerosis. G1 and G2 correlate best with glomerulosclerosis as recessive alleles, which suggests a loss of function mutation for which proof of causality is commonly tested with homozygous null alleles. This test cannot be performed in rodents as the APOL gene cluster evolved only in primates. However, there is a homozygous APOL1 null human being who lives in a village in rural India. This individual and his family offer a unique opportunity to test causality between APOL1 null alleles and glomerulosclerosis.
Methods and Findings
We obtained clinical data, blood and urine from this APOL1 null patient and 50 related villagers. Based on measurements of blood pressure, BUN, creatinine, albuminuria, genotyping and immunoblotting, this APOL1 null individual does not have glomerulosclerosis, nor do his relatives who carry APOL1 null alleles.
This small study cannot provide definitive conclusions but the absence of glomerulosclerosis in this unique population is consistent with the possibility that African-American glomerulosclerosis is caused, not by loss of APOL1 function, but by other mechanisms including a subtle gain of function or by the “genetic hitchhiking” of deleterious mutations in a gene linked to APOL1 G1 and G2.
Nowadays diabetic nephropathy (DN) is the most common cause of end-stage renal disease (ESRD). Recent studies have demonstrated that the myosin, heavy chain 9, non-muscle (MYH9) gene is associated with ESRD in African Americans. In this study, we tested the hypothesis that a common single nucleotide polymorphism rs16996677 in the MYH9 gene may contribute to the etiology of DN in type 2 diabetes (T2D) in a Taiwanese population with T2D. There were 180 T2D patients diagnosed with DN and 178 age- and sex-similar T2D without DN controls. Single locus analyses showed no significant main effects of MYH9 rs16996677 on the risk of DN in T2D. The results suggest that the rs16996677 SNP in MYH9 may not contribute to the risk of DN in T2D in Taiwanese T2D patients.
diabetic nephropathy; end-stage renal disease; single nucleotide polymorphisms; type 2 diabetes
African Americans have high incidence rates of end-stage renal disease (ESRD) labeled as due to hypertension. As recent studies showed strong association with idiopathic and HIV-related focal segmental glomerulosclerosis and non-muscle myosin heavy chain 9 (MYH9) gene polymorphisms in this ethnic group, we tested for MYH9 associations in a variety of kidney diseases. Fifteen MYH9 single-nucleotide polymorphisms were evaluated in 175 African Americans with chronic glomerulonephritis-associated ESRD, 696 African Americans reportedly with hypertension-associated ESRD, and 948 control subjects without kidney disease. Significant associations were detected with 14 of the 15 polymorphisms in all 871 non-diabetic patients with ESRD. In hypertension-associated ESRD cases alone, significant associations were found with 13 MYH9 polymorphisms and the previously reported E1 haplotype. Thus, hypertension-associated ESRD in African Americans is substantially related to MYH9 gene polymorphisms and this may explain the poor response to blood pressure control in those diagnosed with hypertensive nephrosclerosis. It is possible that many African Americans classified as having hypertension-associated ESRD have occult MYH9-associated segmental or global glomerulosclerosis. Our study shows that gene-environment and/or gene–gene interactions may initiate kidney disease in genetically susceptible individuals, because African Americans homozygous for MYH9 risk alleles do not universally develop kidney disease.
African American; end-stage renal disease; focal segmental glomerulosclerosis; hypertension; hypertensive nephrosclerosis; MYH9
Though single nucleotide polymorphisms (SNPs) in the non-muscle myosin gene (MYH9) have been reported to explain most of the excess risk of nondiabetic chronic kidney disease (CKD), in African-Americans, some studies have also shown associations with diabetic end-stage renal disease. We investigated the association of MYH9 SNPs with renal traits in a mixed-ancestry South African population prone to diabetes.
Research Design and Methods
Three SNPs known to be associated with CKD (rs4821480, rs5756152 and rs12107) were genotyped using Taqman assay in 716 adults (198 with diabetes) from the Bellville-South community, Cape Town. Glomerular filtration rate was estimated (eGFR) and urinary albumin/creatinine ratio (ACR) assessed. Multivariable regressions were used to relate the SNPs with renal traits.
Mean age was 53.6 years, with the expected differences observed in characteristics by diabetic status. Significant associations were found between rs575152 and serum creatinine, and eGFR in the total population, and in diabetic participants (all p≤0.003), but not in non-diabetics (all p≥0.16), with significant interactions by diabetes status (interaction-p≤0.009). The association with ACR was borderline in diabetic participants (p = 0.05) and non-significant in non-diabetics (p = 0.85), with significant interaction (interaction p = 0.02). rs12107 was associated with fasting-, 2-hour glucose and HbA1c in diabetic participants only (interaction-p≤0.003), but not with renal traits.
MYH9 SNPs were associated with renal traits only in diabetic participants in this population. Our findings and other studies suggest that MYH9 may have a broader genetic risk effect on kidney diseases.
Admixture mapping recently identified MYH9 as a susceptibility gene for idiopathic focal segmental glomerulosclerosis (FSGS), HIV-associated nephropathy (HIVAN) and end-stage kidney disease attributed to hypertension (H-ESKD) in African Americans (AA). MYH9 encodes the heavy chain of non-muscle myosin IIA, a cellular motor involved in motility. A haplotype and its tagging SNPs spanning introns 12–23 were most strongly associated with kidney disease (OR 2–7; P < 10−8, recessive). To narrow the region of association and identify potential causal variation, we performed a dense-mapping study using 79 MYH9 SNPs in AA populations with FSGS, HIVAN and H-ESKD (typed for a subset of 46 SNPs), for a total of 2496 cases and controls. The strongest associations were for correlated SNPs rs5750250, rs2413396 and rs5750248 in introns 13, 14 and 15, a region of 5.6 kb. Rs5750250 showed OR 5.0, 8.0 and 2.8; P = 2 × 10−17, 2 × 10−10 and 3 × 10−22, respectively, for FSGS, HIVAN and H-ESKD; OR 5.7; P = 9 × 10−27 for combined FSGS and HIVAN, recessive. An independent association was observed for rs11912763 in intron 33. Neither the highly associated SNPs nor the results of resequencing MYH9 in 40 HIVAN or FSGS cases and controls revealed non-synonymous changes that could account for the disease associations. Rs2413396 and one of the highly associated SNPs in intron 23, rs4821480, are predicted splicing motif modifiers. Rs5750250 combined with rs11912763 had receiver operator characteristic (ROC) C statistics of 0.80, 0.73 and 0.65 for HIVAN, FSGS and H-ESKD, respectively, allowing prediction of genetic risk by typing two SNPs.