The non-muscle Myosin heavy chain 9 gene (MYH9) is not associated with lupus nephritis in African Americans

Non-diabetic end-stage renal disease in Saudis associated with polymorphism of MYH9 gene but not UMOD gene

The prevalence of risk factors of chronic kidney disease in Saudi Arabia has augmented an already serious public health problem, therefore, determination of genetic variants associated with the risk of the disease presents potential screening tools that help reducing the incidence rates and promote effective disease management.The aim of the present study is to determine the association of UMOD and MYH9 genetic variants with the risk of non-diabetic end-stage renal disease (ESRD) in the Saudi population.Two single nucleotide polymorphisms (SNP), rs12917707 in gene UMOD and rs4821480 in gene MYH9 were genotyped in 154 non-diabetic ESRD Saudi patients and 123 age-matched healthy controls using Primers and Polymerase chain reaction conditions (PCR), Sanger sequencing, and TaqMan Pre-designed SNP Genotyping Assay. The association of these genetic variants with the risk of the disease and other renal function determinants was assessed using statistical tools such as logistic regression and One-way Analysis of Variance tests.The genotypic frequency of the two SNPs showed no deviation from Hardy-Weinberg equilibrium, the minor allele frequency of UMOD SNP was 0.13 and MYH9 SNP was 0.08. rs4821480 in MYH9 was significantly associated with the risk of non-diabetic ESRD (OR = 3.86; 95%CI: 1.38-10.82, P value .010), while, rs12917707 showed lack of significant association with the disease, P value .380. and neither of the 2 SNPs showed any association with the renal function determinants, serum albumin, and alkaline phosphatase enzyme.

I too, am America: a review of research on systemic lupus erythematosus in African-Americans

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disorder that can cause significant morbidity and mortality. A large body of evidence has shown that African-Americans experience the disease more severely than other racial-ethnic groups. Relevant literature for the years 2000 to August 2015 were obtained from systematic searches of PubMed, Scopus, and the EBSCOHost platform that includes MEDLINE, CINAHL, etc. to evaluate research focused on SLE in African-Americans. Thirty-six of the 1502 articles were classified according to their level of evidence. The systematic review of the literature reported a wide range of adverse outcomes in African-American SLE patients and risk factors observed in other mono and multi-ethnic investigations. Studies limited to African-Americans with SLE identified novel methods for more precise ascertainment of risk and observed novel findings that hadn't been previously reported in African-Americans with SLE. Both environmental and genetic studies included in this review have highlighted unique African-American populations in an attempt to isolate risk attributable to African ancestry and observed increased genetic influence on overall disease in this cohort. The review also revealed emerging research in areas of quality of life, race-tailored interventions, and self-management. This review reemphasizes the importance of additional studies to better elucidate the natural history of SLE in African-Americans and optimize therapeutic strategies for those who are identified as being at high risk.

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.

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.

End-stage renal disease in African Americans with lupus nephritis is associated with APOL1

OBJECTIVE

Lupus nephritis (LN) is a severe manifestation of systemic lupus erythematosus (SLE) that exhibits familial aggregation and may progress to end-stage renal disease (ESRD). LN is more prevalent among African Americans than among European Americans. This study was undertaken to investigate the hypothesis that the apolipoprotein L1 gene (APOL1) nephropathy risk alleles G1/G2, common in African Americans and rare in European Americans, contribute to the ethnic disparity in risk.

METHODS

APOL1 G1 and G2 nephropathy alleles were genotyped in 855 African American SLE patients with LN-ESRD (cases) and 534 African American SLE patients without nephropathy (controls) and tested for association under a recessive genetic model, by logistic regression.

RESULTS

Ninety percent of the SLE patients were female. The mean ± SD age at SLE diagnosis was significantly lower in LN-ESRD cases than in SLE non-nephropathy controls (27.3 ± 10.9 years versus 39.5 ± 12.2 years). The mean ± SD time from SLE diagnosis to development of LN-ESRD in cases was 7.3 ± 7.2 years. The G1/G2 risk alleles were strongly associated with SLE-ESRD, with 25% of cases and 12% of controls having 2 nephropathy alleles (odds ratio [OR] 2.57, recessive model P = 1.49 × 10(-9)), and after adjustment for age, sex, and ancestry admixture (OR 2.72, P = 6.23 × 10(-6)). The age-, sex-, and admixture-adjusted population attributable risk for ESRD among patients with G1/G2 polymorphisms was 0.26, compared to 0.003 among European American patients. The mean time from SLE diagnosis to ESRD development was ∼2 years earlier among individuals with APOL1 risk genotypes (P = 0.01).

CONCLUSION

APOL1 G1/G2 alleles strongly impact the risk of LN-ESRD in African Americans, as well as the time to progression to ESRD. The high frequency of these alleles in African Americans with near absence in European Americans explains an important proportion of the increased risk of LN-ESRD in African Americans.

MYH9 and APOL1 gene polymorphisms and the risk of CKD in patients with lupus nephritis from an admixture population

MYH9 polymorphisms have been described to be associated with the risk of CKD in non-diabetic nephropathy, HIV nephropathy and FSGS. Predominating in black descendants, MHY9 genetic variants could partially explain the excess risk of CKD associated with African ancestry. However, recent data suggests that APOL1 gene co-segregate with MYH9, and could be the gene truly associated with CKD risk. In this study, we evaluated the role of MYH9 and APOL1 gene polymorphisms in the risk of CKD in Brazilian patients with lupus nephritis (LN). A retrospective analysis of 196 LN patients was done. MYH9 rs4821480, rs2032487, rs4821481 and rs3752462, APOL 1rs73885319, rs16996616, rs60910145, rs71785313, and APOL3 rs11089781 gene polymorphisms were determined. Genetic ancestry was ascertained both by autossomal ancestry and mitochondrial haplogroup. Primary outcome was defined as doubling of serum creatinine (DC) or end stage renal disease (ESRD). Sixty-two patients presented the PO. In our population, MYH9 and APOL1 were not in LD. None APOL polymorphism was associated with the PO, whereas rs3752462 MYH9 polymorphism showed a positive association (HR3.72, 95%CI 1.47–9.38, p = 0.005). When we analyzed the MYH9 E1 haplotype, the GCCT carriers (1 or 2 alelles present in 29.7% in the PO group vs. 18.5% in controls) showed a significant association to the risk of PO, even after adjustments for baseline estimated creatinine clearance and autossomal ancestry (HR 2.0, 95%CI 1.2–3.4, p = 0.01). Our results show that in our population MYH9, but not APOL1, gene polymorphisms confer an increased risk of CKD in LN patients, independently of race.

Background strain and the differential susceptibility of podocyte-specific deletion of Myh9 on murine models of experimental glomerulosclerosis and HIV nephropathy

We previously reported that podocyte-specific deletion of Myh9 (conventional myosin heavy chain 2A) in C57BL/6 mice does not cause spontaneous kidney disease but instead results in a predisposition to glomerulosclerosis in response to a second model of glomerular injury. In contrast, other investigators reported that podocyte-specific deletion of Myh9 (PodΔMyh9) resulted in spontaneous glomerulosclerosis in mice on a mixed background, suggesting that the glomerulosclerosis is dependent on background strain. In order to elucidate the cause of this strain dependent effect Podocin::Cre and Myh9(flox) alleles were backcrossed to mouse strain FVB/N, which is highly susceptible to glomerulosclerosis, with the aim of intercrossing susceptible FVB/N and resistant C57BL/6 mice in subsequent congenic analyses. However, after backcrossing mice to FVB/N and aging mice to 28 weeks, we found no evidence of glomerular disease in PodΔMyh9 mice vs control littermates (urine MAC ratio all p>0.05). We also tested C57BL/6 PodΔMyh9 mice for a predisposition to injury from models other than Adriamycin including HIV nephropathy (HIVAN), puromycin nephropathy, and sheep nephrotoxic serum. In the Tg26 model of HIVAN, we found that podocyte-specific deletion of Myh9 resulted in a modest hypersensitivity in adults compared to Tg26+ control littermates (urine MAC ratio, p<0.05 or less). In contrast, we found that PodΔMyh9 mice were not predisposed to injury in response to other injury models including puromycin nephropathy and sheep nephrotoxic serum. While the mechanism of injury in these models is not fully understood, we conclude that PodΔMyh9 results in a variable susceptibility to glomerulosclerosis in response to different models of glomerular injury. In addition, based on the lack of a spontaneous phenotype of glomerulosclerosis in both C57BL/6 and FVB/N mice, we propose that Myh9 is not absolutely required in adult podocytes.

European genetic ancestry is associated with a decreased risk of lupus nephritis

OBJECTIVE

African Americans, East Asians, and Hispanics with systemic lupus erythematosus (SLE) are more likely to develop renal disease than are SLE patients of European descent. This study was undertaken to investigate whether European genetic ancestry protects against the development of lupus nephritis, with the aim of exploring the genetic and socioeconomic factors that might explain this effect.

METHODS

This was a cross-sectional study of SLE patients from a multiethnic case collection. Participants were genotyped for 126 single-nucleotide polymorphisms (SNPs) informative for ancestry. A subset of participants was also genotyped for 80 SNPs in 14 candidate genes for renal disease in SLE. Logistic regression was used to test the association between European ancestry and renal disease. Analyses were adjusted for continental ancestries, socioeconomic status (SES), and candidate genes.

RESULTS

Participants (n = 1,906) had, on average, 62.4% European, 15.8% African, 11.5% East Asian, 6.5% Amerindian, and 3.8% South Asian ancestry. Among the participants, 656 (34%) had renal disease. A 10% increase in the proportion of European ancestry estimated in each participant was associated with a 15% reduction in the odds of having renal disease, after adjustment for disease duration and sex (odds ratio 0.85, 95% confidence interval 0.82-0.87; P = 1.9 × 10(-30) ). Adjustment for other genetic ancestries, measures of SES, or SNPs in the genes most associated with renal disease (IRF5 [rs4728142], BLK [rs2736340], STAT4 [rs3024912], and HLA-DRB1*0301 and DRB1*1501) did not substantively alter this relationship.

CONCLUSION

European ancestry is protective against the development of renal disease in SLE, an effect that is independent of other genetic ancestries, candidate risk alleles, and socioeconomic factors.

Target organ damage in African American hypertension: role of APOL1

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 from 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.

Role of MYH9 and APOL1 in African and non-African populations with lupus nephritis

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by autoantibody production and organ damage. Lupus nephritis (LN) is one of the most severe manifestations of SLE. Multiple studies reported associations between renal diseases and variants in the non-muscle myosin heavy chain 9 (MYH9) and the neighboring apolipoprotein L 1 (APOL1) genes. We evaluated 167 variants spanning MYH9 for association with LN in a multiethnic sample. The two previously identified risk variants in APOL1 were also tested for association with LN in European-Americans (EAs) (N = 579) and African-Americans (AAs) (N = 407). Multiple peaks of association exceeding a Bonferroni corrected P-value of P < 2.03 × 10(-3) were observed between LN and MYH9 in EAs (N = 4620), with the most pronounced association at rs2157257 (P = 4.7 × 10(-4), odds ratio (OR) = 1.205). A modest effect with MYH9 was also detected in Gullah (rs8136069, P = 0.0019, OR = 2.304). No association between LN and MYH9 was found in AAs, Asians, Amerindians or Hispanics. This study provides the first investigation of MYH9 in LN in non-Africans and of APOL1 in LN in any population, and presents novel insight into the potential role of MYH9 in LN in EAs.

The population genetics of chronic kidney disease: insights from the MYH9-APOL1 locus

Many rare kidney disorders exhibit a monogenic, Mendelian pattern of inheritance. Population-based genetic studies have identified many genetic variants associated with an increased risk of developing common kidney diseases. Strongly associated variants have potential clinical uses as predictive markers and may advance our understanding of disease pathogenesis. These principles are elegantly illustrated by a region within chromosome 22q12 that has a strong association with common forms of kidney disease. Researchers had identified DNA sequence variants in this locus that were highly associated with an increased prevalence of common chronic kidney diseases in people of African ancestry. Initial research concentrated on MYH9 as the most likely candidate gene; however, population-based whole-genome analysis enabled two independent research teams to discover more strongly associated mutations in the neighboring APOL1 gene. The powerful evolutionary selection pressure of an infectious pathogen in West Africa favored the spread of APOL1 variants that protect against a lethal form of African sleeping sickness but are highly associated with an increased risk of kidney disease. We describe the data sources, process of discovery, and reasons for initial misidentification of the candidate gene, as well as the lessons that can be learned for future population genetics research.

[Podocyte research in rheumatic diseases]

Podocytes are glomerular visceral epithelial cells, which function as molecular sieve with foot process (FT) and slit diaphragm (SD) spanning FT, not to allow high molecular weight protein to be filtrated through glomerular capillary loop. Pathological proteinuria is caused by discoordinated tertiary podocyte structure such as disappearance of FT and/or SD, and irreversible glomeular sclerosis is caused by podocyte loss due to cell death and/or detachment from capillary wall. With recent advance of nephrological research technology such as podocyte cell culture system, genetically engineered transgenic mice with podocyte-specific regulation of gene expression, podocyte-associated biomarkers, the new isolation method of glomeruli, laser capture microdissection, multiphoton imaging and extracellular flux analyzer, new findings of pathogenesis of glomerular lesions will be expected, not only in primary glomerulonephritis, but also in secondary glomerulonephritis or glomerulopathy due to rheumatic diseases.

Admixture mapping of end stage kidney disease genetic susceptibility using estimated mutual information ancestry informative markers

BACKGROUND

The question of a genetic contribution to the higher prevalence and incidence of end stage kidney disease (ESKD) among African Americans (AA) remained unresolved, until recent findings using admixture mapping pointed to the association of a genomic locus on chromosome 22 with this disease phenotype. In the current study we utilize this example to demonstrate the utility of applying a multi-step admixture mapping approach.

METHODS

A multi-step case only admixture mapping study, consisted of the following steps was designed: 1) Assembly of the sample dataset (ESKD AA); 2) Design of the estimated mutual information ancestry informative markers (n = 2016) screening panel 3); Genotyping the sample set whose size was determined by a power analysis (n = 576) appropriate for the initial screening panel; 4) Inference of local ancestry for each individual and identification of regions with increased AA ancestry using two different ancestry inference statistical approaches; 5) Enrichment of the initial screening panel; 6) Power analysis of the enriched panel 7) Genotyping of additional samples. 8) Re-analysis of the genotyping results to identify a genetic risk locus.

RESULTS

The initial screening phase yielded a significant peak using the ADMIXMAP ancestry inference program applying case only statistics. Subgroup analysis of 299 ESKD patients with no history of diabetes yielded peaks using both the ANCESTRYMAP and ADMIXMAP ancestry inference programs. The significant peak was found on chromosome 22. Genotyping of additional ancestry informative markers on chromosome 22 that took into account linkage disequilibrium in the ancestral populations, and the addition of samples increased the statistical significance of the finding.

CONCLUSIONS

A multi-step admixture mapping analysis of AA ESKD patients replicated the finding of a candidate risk locus on chromosome 22, contributing to the heightened susceptibility of African Americans to develop non-diabetic ESKD, and underscores the importance of using mutual information and multiple ancestry inference approaches to achieve a robust analysis, using relatively small datasets of "affected" only individuals. The current study suggests solutions to some limitations of existing admixture mapping methodologies, such as considerations regarding the distribution of ancestry information along the genome and its effects on power calculations and sample size.