Albuminuria and reduced eGFR associate with two apolipoprotein L1 gene (APOL1) variants in non-diabetic African Americans. Whether APOL1 associates with subclinical atherosclerosis and survival remains unclear. To determine this, 717 African American-Diabetes Heart Study participants underwent computed tomography to determine coronary artery, carotid artery, and aorta calcified atherosclerotic plaque mass scores in addition to the urine albumin:creatinine ratio (UACR), eGFR, and C-reactive protein. Associations between mass scores and APOL1 were assessed adjusting for age, gender, African ancestry, BMI, HbA1c, smoking, hypertension, use of statins and ACE inhibitors, albuminuria, and eGFR. Participants were 58.9% female with mean age 56.5 years, eGFR 89.5 ml/min/1.73m2, UACR 169.6 mg/g, coronary artery, carotid artery and aorta calcified plaque mass scores of 610, 171 and 5378, respectively. In fully adjusted models, APOL1 risk variants were significantly associated with lower levels of carotid artery calcified plaque (β −0.42, SE 0.18, dominant model), and marginally lower coronary artery plaque (β −0.36, SE 0.21; dominant model), but not with aorta calcified plaque, C-reactive protein, UACR, or eGFR. After a mean follow-up of 5.0 years, 89 participants died. APOL1 nephropathy risk variants were significantly associated with improved survival (hazard ratio 0.67 for 1 copy; 0.44 for 2 copies). Thus, APOL1 nephropathy variants associate with lower levels of subclinical atherosclerosis and reduced risk of death in African Americans with type 2 diabetes mellitus.
African Americans; apolipoprotein L1 gene (APOL1); atherosclerosis; calcified atherosclerotic plaque; diabetes mellitus; kidney disease
Two APOL1 nephropathy variants confer substantial risk for non-diabetic end-stage kidney disease (ESKD) in African Americans (AAs). Since not all genetically high-risk individuals develop ESKD, modifying factors likely contribute. Forty-two potentially interactive single nucleotide polymorphisms (SNPs) from a genome-wide association study in non-diabetic ESKD were tested for interaction with APOL1 to identify genes modifying risk for non-diabetic nephropathy.
SNPs were examined in an expanded sample of 1367 AA non-diabetic ESKD cases and 1504 AA non-nephropathy controls, with validation in an independent family-based cohort containing 608 first-degree relatives of index cases with non-diabetic ESKD. Logistic regression and mixed models were fitted to test for interaction effects with APOL1 on ESKD, estimated kidney function and albuminuria.
Among ESKD samples, 14 of 42 SNPs demonstrated suggestive APOL1 interaction with P-values <0.05. After Bonferroni correction, significant interactions with APOL1 were seen with SNPs in podocin (rs16854341; NPHS2, P = 8.0 × 10−4), in SDCCAG8 (rs2802723; P = 5.0 × 10−4) and near BMP4 (rs8014363; P = 1.0 × 10−3); with trends for ENOX1 (rs9533534; P = 2.2 × 10−3) and near TRIB1 (rs4457349; P = 5.7 × 10−3). The minor allele in NPHS2 markedly changed the APOL1-ESKD association odds ratio (OR) from 7.03 to 1.76 (∼50% reduction in effect per copy of the minor allele), rs2802723 changed the OR from 5.1 to 10.5, and rs8014363 increased the OR from 4.8 to 9.5. NPHS2 (P = 0.05) and SDCCAG8 (P = 0.03) SNPs demonstrated APOL1 interaction with albuminuria in independent family-based samples.
Variants in NPHS2, SDCCAG8 and near BMP4 appear to interact with APOL1 to modulate the risk for non-diabetic ESKD in AAs.
African American; APOL1; bone morphogenetic protein 4 (BMP4); kidney disease; podocin (NPHS2); serologically defined colon cancer antigen 8 (SDCCAG8)
Previous GWAS studies have reported significant associations between various common SNPs and prostate cancer risk using cases unselected for family history. How these variants influence risk in familial prostate cancer is not well studied. Here, we analyzed 25 previously reported SNPs across 14 loci from prior prostate cancer GWAS. The International Consortium for Prostate Cancer Genetics (ICPCG) previously validated some of these using a family-based association method (FBAT). However, this approach suffered reduced power due to the conditional statistics implemented in FBAT. Here, we use a case-control design with an empirical analysis strategy to analyze the ICPCG resource for association between these 25 SNPs and familial prostate cancer risk. Fourteen sites contributed 12,506 samples (9,560 prostate cancer cases, 3,368 with aggressive disease, and 2,946 controls from 2,283 pedigrees). We performed association analysis with Genie software which accounts for relationships. We analyzed all familial prostate cancer cases and the subset of aggressive cases. For the familial prostate cancer phenotype, 20 of the 25 SNPs were at least nominally associated with prostate cancer and 16 remained significant after multiple testing correction (p≤1E−3) occurring on chromosomal bands 6q25, 7p15, 8q24, 10q11, 11q13, 17q12, 17q24, and Xp11. For aggressive disease, 16 of the SNPs had at least nominal evidence and 8 were statistically significant including 2p15. The results indicate that the majority of common, low-risk alleles identified in GWAS studies for all prostate cancer also contribute risk for familial prostate cancer, and that some may be contribute risk to aggressive disease.
prostate cancer; pedigrees; familial disease; simulation; replication
Routine follow-up care is recommended to promote the well-being of cancer survivors, but financial difficulties may interfere. Rural-urban disparities in forgoing healthcare due to cost have been observed in the general population; however, it is unknown whether this disparity persists among survivors. The purpose of this study was to examine rural-urban disparities in forgoing healthcare after cancer due to cost.
We analyzed data from 7804 cancer survivors in the 2006–2010 National Health Interview Survey. Logistic regression models, adjusting for sociodemographic and clinical characteristics, were used to assess rural-urban disparities in forgoing medical care, prescription medications, and dental care due to cost, stratified by age (younger: 18–64, older: 65+).
Compared to urban survivors, younger rural survivors were more likely to forgo medical care (p<0.001) and prescription medications (p<0.001) due to cost; older rural survivors were more likely to forgo medical (p<0.001) and dental care (p=0.05). Rural-urban disparities did not persist among younger survivors in adjusted analyses; however, older rural survivors remained more likely to forgo medical (OR=1.66, 95%CI=1.11–2.48) and dental care (OR=1.54, 95%CI=1.08–2.20).
Adjustment for health insurance and other sociodemographic characteristics attenuates rural-urban disparities in forgoing healthcare among younger survivors, but not older survivors. Financial factors relating to healthcare utilization among rural survivors should be a topic of continued investigation.
Addressing out-of-pocket costs may be an important step in reducing rural-urban disparities in healthcare, especially for older survivors. It will be important to monitor how healthcare reform efforts impact disparities observed in this vulnerable population.
cancer; long-term survivors; rural population; healthcare disparities; health services accessibility
Rural US adults have increased risk of poor outcomes after cancer, including increased cancer mortality. Rural-urban differences in health behaviors have been identified in the general population and may contribute to cancer health disparities, but have not yet been examined among US survivors. We examined rural-urban differences in health behaviors among cancer survivors and associations with self-reported health and health-related unemployment.
We identified rural (n=1,642) and urban (n=6,162) survivors from the cross-sectional National Health Interview Survey (2006–2010) and calculated the prevalence of smoking, physical activity, overweight/obesity, and alcohol consumption. Multivariable models were used to examine the associations of fair/poor health and health-related unemployment with health behaviors and rural-urban residence.
The prevalence of fair/poor health (rural 36.7%, urban 26.6%), health-related unemployment (rural 18.5%, urban 10.6%), smoking (rural 25.3%, urban 15.8%), and physical inactivity (rural 50.7%, urban 38.7%) was significantly higher in rural survivors (all p<.05); alcohol consumption was lower (rural 46.3%, urban 58.6%), and there were no significant differences in overweight/obesity (rural 65.4%, urban 62.6%). All health behaviors were significantly associated with fair/poor health and health-related unemployment in both univariate and multivariable models. After adjustment for behaviors, rural survivors remained more likely than urban survivors to report fair/poor health (OR= 1.21, 95%CI 1.03–1.43) and health-related unemployment (OR= 1.49, 95%CI 1.18–1.88).
Rural survivors may need tailored, accessible health promotion interventions to address health compromising behaviors and improve outcomes after cancer.
cancer survivors; smoking; physical activity; health status; employment
We examined racial/ethnic disparities in healthcare receipt among a nationally representative sample of male cancer survivors.
We identified adult men (age 18+) from the 2006–2010 National Health Interview Survey who reported a history of cancer. Four self-reported measures assessed healthcare receipt: primary care visit, specialist visit, flu vaccination, and pneumococcal vaccination. We used hierarchical logistic regression modeling, stratified by age (younger: <65, older: 65+), to examine racial/ethnic disparities in healthcare receipt.
In adjusted models, older African American and Hispanic survivors were approximately twice as likely as non-Hispanic Whites to not see a specialist (OR 1.78, CI 1.19–2.68 and OR 2.09, CI 1.18–3.70, respectively), not receive the flu vaccine (OR 2.21, CI 1.45–3.37 and OR 2.20, CI 1.21–4.01, respectively) and not receive the pneumococcal vaccine (OR 2.24, CI 1.54–3.24 and OR 3.10, CI 1.75–5.51, respectively).
Racial/ethnic disparities in healthcare receipt were evident among older, but not younger survivors, despite access to Medicare. This may have implications for their health and receipt of follow-up care if these survivors are less likely to see specialists, including oncologists, and get basic preventive care.
cancer; men; health care disparities; long-term survivors; health services
This study investigated the association of copy number variants (CNVs) in type 2 diabetes (T2D) and T2D-associated end-stage renal disease (ESRD) in African Americans. Using the Affymetrix 6.0 array, >900,000 CNV probes spanning the genome were interrogated in 965 African Americans with T2D-ESRD and 1029 non-diabetic African American controls. Previously identified and novel CNVs were separately analyzed and were evaluated for insertion/deletion status and then used as predictors in a logistic regression model to test for association. One common CNV insertion on chromosome 1 was significantly associated with T2D-ESRD (p=6.17×10−5, OR=1.63) after multiple comparison correction. This CNV region encompasses the genes AMY2A and AMY2B, which encode amylase isoenzymes produced by the pancreas. Additional common and novel CNVs approaching significance with disease were also detected. These exploratory results require further replication but suggest the involvement of the AMY2A/AMY2B CNV in T2D and/or T2D-ESRD, and indicate that CNVs may contribute to susceptibility for these diseases.
Copy number variation; African Americans; Diabetic nephropathy; End-stage renal disease; Genome-wide association study; Type 2 diabetes
While rural residents are more likely to be diagnosed with more advanced cancers and die of cancer, little is known about rural-urban disparities in self-reported health among survivors.
We identified adults with a self-reported cancer history from the National Health Interview Survey (2006–2010). Rural-urban residence was defined using US census definitions. Logistic regression with weighting to account for complex sampling was used to assess rural-urban differences in health status after accounting for differences in demographic characteristics.
Of the 7,804 identified cancer survivors, 20.8% were rural residents. This translates to a population of 2.8 million rural cancer survivors in the US. Rural survivors were more likely than urban survivors to be non-Hispanic white (p<.001), have less education (p<.001) and lack health insurance (p<.001). Rural survivors reported worse health in all domains. After adjustment for sex, race/ethnicity, age, marital status, education, insurance, time since diagnosis, and number of cancers, rural survivors were more likely to report fair/poor health [OR=1.39, 95%CI=1.20–1.62, psychological distress [OR=1.23, 1.00–1.50], ≥2 non-cancer comorbidities [OR=1.15, 1.01–1.32], and health-related unemployment [OR=1.66, 1.35–2.03].
We provide the first estimate of the proportion and number of US adult cancer survivors who reside in rural areas. Rural cancer survivors are at greater risk for a variety of poor health outcomes, even many years after their cancer diagnosis, and should be a target for interventions to improve their health and well-being.
cancer; survivors; rural health; health status; mental health; unemployment; comorbidity; health status disparities
The presence and severity of coronary artery calcified plaque (CAC) differs markedly between individuals of African and European descent, suggesting that admixture mapping (AM) may be informative for identifying genetic variants associated with subclinical cardiovascular disease (CVD).
Methods and Results
AM of CAC was performed in 1,040 unrelated African Americans with type 2 diabetes mellitus from the African American-Diabetes Heart Study (AA-DHS), Multi-Ethnic Study of Atherosclerosis (MESA), and Family Heart Study (FamHS) using the Illumina custom ancestry informative marker (AIM) panel. All cohorts obtained computed tomography scanning of the coronary arteries using identical protocols. For each AIM, the probability of inheriting 0, 1, and 2 copies of a European-derived allele was determined. Linkage analysis was performed by testing for association between each AIM using these probabilities and CAC, accounting for global ancestry, age, gender and study. Markers on 1p32.3 in the GLIS1 gene (rs6663966, LOD=3.7), 1q32.1 near CHIT1 (rs7530895, LOD=3.1), 4q21.2 near PRKG2 (rs1212373, LOD=3.0) and 11q25 in the OPCML gene (rs6590705, LOD=3.4) had statistically significant LOD scores, while markers on 8q22.2 (rs6994682, LOD=2.7), 9p21.2 (rs439314, LOD=2.7), and 13p32.1 (rs7492028, LOD=2.8) manifested suggestive evidence of linkage. These regions were uniformly characterized by higher levels of European ancestry associating with higher levels or odds of CAC. Findings were replicated in 1,350 AAs without diabetes and 2,497 diabetic European Americans from MESA and the Diabetes Heart Study.
Fine mapping these regions will likely identify novel genetic variants that contribute to CAC and clarify racial differences in susceptibility to subclinical CVD.
ancestry; cardiovascular disease risk factors; type 2 diabetes; admixture mapping
African Americans (AAs) are predisposed to non-diabetic (non-DM) end-stage renal disease (ESRD) and studies have shown a genetic component to this risk. Rare mutations in ACTN4 (α-actinin-4) an actin binding protein expressed in podocytes cause familial focal segmental glomerulosclerosis.
We assessed the contribution of coding variants in ACTN4 to non-DM ESRD risk in AAs. Nineteen exons, 2800 bases of the promoter and 392 bases of the 3’ untranslated region of ACTN4 were sequenced in 96 AA non-DM ESRD cases and 96 non-nephropathy controls (384 chromosomes). Sixty-seven single nucleotide polymorphisms (SNPs) including 51 novel SNPs were identified. The SNPs comprised 33 intronic, 21 promoter, 12 exonic, and 1 3’ variant. Sixty-two of the SNPs were genotyped in 296 AA non-DM ESRD cases and 358 non-nephropathy controls.
One SNP, rs10404257, was associated with non-DM ESRD (p<1.0E-4, odds ratio (OR)=0.76, confidence interval (CI)=0.59–0.98; additive model). Forty-seven SNPs had minor allele frequencies less than 5%. These SNPs were segregated into risk and protective SNPs and each category was collapsed into a single marker, designated by the presence or absence of any rare allele. The presence of any rare allele at a risk SNP was significantly associated with non-DM ESRD (p = 0.001, dominant model). The SNPs with the strongest evidence for association (n = 20) were genotyped in an independent set of 467 non-DM ESRD cases and 279 controls. Although, rs10404257 was not associated in this replication sample, when the samples were combined rs10404257 was modestly associated (p=0.032, OR=0.78, CI=0.63–0.98; dominant model). SNPs were tested for interaction with markers in the APOL1 gene, previously associated with non-DM ESRD in AAs and rs10404257 was modestly associated (p = 0.0261, additive model).
This detailed evaluation of ACTN4 variation revealed limited evidence of association with non-DM ESRD in AAs.
ACTN4; non-diabetic ESRD; FSGS; kidney; hypertensive nephrosclerosis; African Americans
PPP2R2A, mapped to 8p21.2, encodes for the α isoform of the regulatory B55 subfamily of the protein phosphatase 2 (PP2A). PP2A is one of the four major Ser/Thr phosphatases and is implicated in the negative control of cell growth and division. Because of its known functions and location within a chromosomal region where evidence for linkage and somatic loss of heterozygosity was found, we hypothesized that either somatic copy number changes or germline sequence variants in PPP2R2A may increase prostate cancer (PCa) risk. We examined PPP2R2A deletion status in 141 PCa samples using Affymetrix SNP arrays. It was found that PPP2R2A was commonly (67.1%) deleted in tumor samples including a homozygous deletion in 3 tumors (2.1%). We performed a mutation screen for PPP2R2A in 96 probands of hereditary prostate cancer (HPC) families. No high risk mutations were identified. Additionally, we reanalyzed 10 SNPs of PPP2R2A in sporadic PCa cases and controls. No significant differences in the allele and genotype frequencies were observed among either PCa cases and controls or PCa aggressive and non-aggressive cases. Taken together, these results suggest that a somatic deletion rather than germline sequence variants of PPP2R2A may play a more important role in PCa susceptibility.
PPP2R2A; homozygous deletion; prostate cancer
In spite of intensive efforts, understanding of the genetic aspects of familial prostate cancer remains largely incomplete. In a previous microsatellite-based linkage scan of 1233 prostate cancer (PC) families, we identified suggestive evidence for linkage (i.e. LOD≥1.86) at 5q12, 15q11, 17q21, 22q12, and two loci on 8p, with additional regions implicated in subsets of families defined by age at diagnosis, disease aggressiveness, or number of affected members.
In an attempt to replicate these findings and increase linkage resolution, we used the Illumina 6000 SNP linkage panel to perform a genome-wide linkage scan of an independent set of 762 multiplex PC families, collected by 11 ICPCG groups.
Of the regions identified previously, modest evidence of replication was observed only on the short arm of chromosome 8, where HLOD scores of 1.63 and 3.60 were observed in the complete set of families and families with young average age at diagnosis, respectively. The most significant linkage signals found in the complete set of families were observed across a broad, 37 cM interval on 4q13-25, with LOD scores ranging from 2.02 to 2.62, increasing to 4.50 in families with older average age at diagnosis. In families with multiple cases presenting with more aggressive disease, LOD scores over 3.0 were observed at 8q24 in the vicinity of previously identified common PC risk variants, as well as MYC, an important gene in PC biology.
These results will be useful in prioritizing future susceptibility gene discovery efforts in this common cancer.
African Americans (AAs) have increased susceptibility to non-diabetic nephropathy relative to European Americans.
Follow-up of a pooled genome-wide association study (GWAS) in AA dialysis patients with nondiabetic nephropathy; novel gene-gene interaction analyses.
Setting & Participants
Wake Forest sample: 962 AA nondiabetic nephropathy cases; 931 non-nephropathy controls. Replication sample: 668 Family Investigation of Nephropathy and Diabetes (FIND) AA nondiabetic nephropathy cases; 804 non-nephropathy controls.
Individual genotyping of top 1420 pooled GWAS-associated single nucleotide polymorphisms (SNPs) and 54 SNPs in six nephropathy susceptibility genes.
APOL1 genetic association and additional candidate susceptibility loci interacting with, or independently from, APOL1.
The strongest GWAS associations included two non-coding APOL1 SNPs, rs2239785 (odds ratio [OR], 0.33; dominant; p = 5.9 × 10−24) and rs136148 (OR, 0.54; additive; p = 1.1 × 10−7) with replication in FIND (p = 5.0 × 10−21 and 1.9 × 10−05, respectively). Rs2239785 remained significantly associated after controlling for the APOL1 G1 and G2 coding variants. Additional top hits included a CFH SNP(OR from meta-analysis in above 3367 AA cases and controls, 0.81; additive; p = 6.8 × 10−4). The 1420 SNPs were tested for interaction with APOL1 G1 and G2 variants. Several interactive SNPs were detected, the most significant was rs16854341 in the podocin gene (NPHS2) (p = 0.0001).
Non-pooled GWAS have not been performed in AA nondiabetic nephropathy.
This follow-up of a pooled GWAS provides additional and independent evidence that APOL1 variants contribute to nondiabetic nephropathy in AAs and identified additional associated and interactive non-diabetic nephropathy susceptibility genes.
African American; APOL1; CFH; end-stage renal disease; FIND; FSGS; hypertension
Multiple prostate cancer (PCa) risk-related loci have been discovered by genome-wide association studies (GWAS) based on case–control designs. However, GWAS findings may be confounded by population stratification if cases and controls are inadvertently drawn from different genetic backgrounds. In addition, since these loci were identified in cases with predominantly sporadic disease, little is known about their relationships with hereditary prostate cancer (HPC). The association between seventeen reported PCa susceptibility loci was evaluated with a family-based association test using 1,979 hereditary PCa families of European descent collected by members of the International Consortium for Prostate Cancer Genetics, with a total of 5,730 affected men. The risk alleles for 8 of the 17 loci were significantly over-transmitted from parents to affected offspring, including SNPs residing in 8q24 (regions 1, 2 and 3), 10q11, 11q13, 17q12 (region 1), 17q24 and Xp11. In subgroup analyses, three loci, at 8q24 (regions 1 and 2) plus 17q12, were significantly over-transmitted in hereditary PCa families with five or more affected members, while loci at 3p12, 8q24 (region 2), 11q13, 17q12 (region 1), 17q24 and Xp11 were significantly over-transmitted in HPC families with an average age of diagnosis at 65 years or less. Our results indicate that at least a subset of PCa risk-related loci identified by case–control GWAS are also associated with disease risk in HPC families.
Prostate cancer has a strong familial component but uncovering the molecular basis for inherited susceptibility for this disease has been challenging. Recently, a rare, recurrent mutation (G84E) in HOXB13 was reported to be associated with prostate cancer risk. Confirmation and characterization of this finding is necessary to potentially translate this information to the clinic. To examine this finding in a large international sample of prostate cancer families, we genotyped this mutation and 14 other SNPs in or flanking HOXB13 in 2,443 prostate cancer families recruited by the International Consortium for Prostate Cancer Genetics (ICPCG). At least one mutation carrier was found in 112 prostate cancer families (4.6 %), all of European descent. Within carrier families, the G84E mutation was more common in men with a diagnosis of prostate cancer (194 of 382, 51 %) than those without (42 of 137, 30 %), P = 9.9 × 10−8 [odds ratio 4.42 (95 % confidence interval 2.56–7.64)]. A family-based association test found G84E to be significantly over-transmitted from parents to affected offspring (P = 6.5 × 10−6). Analysis of markers flanking the G84E mutation indicates that it resides in the same haplotype in 95 % of carriers, consistent with a founder effect. Clinical characteristics of cancers in mutation carriers included features of high-risk disease. These findings demonstrate that the HOXB13 G84E mutation is present in ~5 % of prostate cancer families, predominantly of European descent, and confirm its association with prostate cancer risk. While future studies are needed to more fully define the clinical utility of this observation, this allele and others like it could form the basis for early, targeted screening of men at elevated risk for this common, clinically heterogeneous cancer.
Electronic supplementary material
The online version of this article (doi:10.1007/s00439-012-1229-4) contains supplementary material, which is available to authorized users.
PTEN (phosphatase and tensin homolog deleted on chromosome 10) functions as a major tumor suppressor gene and is frequently deleted in different types of tumors including prostate cancer (PCa). It was hypothesized that germ-line genetic changes of PTEN affect susceptibility to PCa. Both common (with a minor allele frequency ≥5%) and rare (with a minor allele frequency <5%) germ-line variants of PTEN were comprehensively evaluated. A total of 15 germ-line variants were identified by re-sequencing the PTEN gene, including 5′ untranslated region, all nine exons, exon-intron junctions and 3′ untranslated region, in 188 probands of hereditary prostate cancer (HPC) families recruited from Johns Hopkins Hospital. Two microsatellite markers surrounding PTEN were used to test the co-segregation of 10 rare variants, which may give rise to highly penetrant in HPC. Two common single nucleotide polymorphisms (SNPs) were evaluated in the 188 HPC families using a family-based association study approach. To study low penetrant SNPs in PCa susceptibility, 33 SNPs covering PTEN were selected from the whole genome-wide association studies (GWAS) from our available case-control studies in Sweden (Cancer of the Prostate in Sweden (CAPS)) and the publicly available cancer genetic markers of susceptibility (CGEMS) study. Germ-line copy-number variations (CNVs) in PTEN were assessed in CAPS. Co-segregation of germ-line variants and PCa was not observed among HPC families and no significant differences in the allele frequencies were observed in sporadic cases and controls, aggressive and non-aggressive PCa (P >0.05). These results suggest that germ-line variants in PTEN do not have an important role in PCa susceptibility.
co-segregation; family-based association; population-based association; prostate cancer; PTEN; sequencing
African-Americans (AAs) with diabetes have high incidence rates of end-stage renal disease (ESRD) with associated high mortality. Genetic factors modulating the risk of mortality on dialysis are poorly understood. Meth ods: A genome-wide association study was performed in 610 AAs with type 2 diabetes (T2D) and ESRD on dialysis, using the Affymetrix 6.0 platform (868,155 SNPs). Time to death was assessed using Cox proportional hazards model adjusting for ancestry and other confounding variables. Cases were censored at kidney transplant or (if living) at study conclusion.
Mean follow-up was 5.4 ± 3.5 years; 434 deaths were recorded. Five SNPs were associated with time to death at p < 1.00 × 10−6: rs2681019 (HR = 2.58, PREC = 8.00 × 10−8), rs815815 in CALM2 (HR = 1.51, PADD = 6.50 × 10−7), rs926392 (HR = 2.37, PREC = 4.80 × 10−7), and rs926391 (HR = 2.30, PREC = 7.30 × 10−7) near DHX35, and rs11128347 in PDZRN3 (HR = 0.57, PADD = 6.00 × 10−7). Other SNPs had nominal associations with time to death (p < 1.00 × 10−5).
Genetic variation may modify the risk of death on dialysis. SNPs in proximity to genes regulating vascular extracellular matrix, cardiac ventricular repolarization, and smoking cessation are associated with dialysis survival in AAs with T2D. These results warrant replication in other cohorts and races.
African-Americans; Diabetes mellitus; Dialysis; Genome-wide association study; Survival
A genome-wide association study was performed using the Affymetrix 6.0 chip to identify genes associated with diabetic nephropathy in African Americans. Association analysis was performed adjusting for admixture in 965 type 2 diabetic African American patients with end-stage renal disease (ESRD) and in 1029 African Americans without type 2 diabetes or kidney disease as controls. The top 724 single nucleotide polymorphisms (SNPs) with evidence of association to diabetic nephropathy were then genotyped in a replication sample of an additional 709 type 2 diabetes-ESRD patients and 690 controls. SNPs with evidence of association in both the original and replication studies were tested in additional African American cohorts consisting of 1246 patients with type 2 diabetes without kidney disease and 1216 with non-diabetic ESRD to differentiate candidate loci for type 2 diabetes-ESRD, type 2 diabetes, and/or all-cause ESRD. Twenty-five SNPs were significantly associated with type 2 diabetes-ESRD in the genome-wide association and initial replication. Although genome-wide significance with type 2 diabetes was not found for any of these 25 SNPs, several genes, including RPS12, LIMK2, and SFI1 are strong candidates for diabetic nephropathy. A combined analysis of all 2890 patients with ESRD showed significant association SNPs in LIMK2 and SFI1 suggesting that they also contribute to all-cause ESRD. Thus, our results suggest that multiple loci underlie susceptibility to kidney disease in African Americans with type 2 diabetes and some may also contribute to all-cause ESRD.
Recent genome-wide association studies (GWAS) have identified multiple novel loci associated with obesity in Europeans but results in other ethnicities are less convincing. Here, we report a two-stage GWAS of BMI in African Americans. The GWAS was performed using the Affymetrix 6.0 platform in 816 nondiabetic and 899 diabetic nephropathy subjects. 746,626 single-nucleotide polymorphisms (SNPs) were tested for association with BMI after adjustment for age, gender, disease status, and population structure. Sixty high scoring SNPs that showed nominal association in both GWAS cohorts were further replicated in 3,274 additional subjects in four replication cohorts and a meta-analysis was computed. Meta-analysis of 4,989 subjects revealed five SNPs (rs6794092, rs268972, rs2033195, rs815611, and rs6088887) at four loci showing consistent associations in both GWAS (P < 0.0001) and replication cohorts (P < 0.05) with combined P values range from 2.4 × 10−6 to 5 × 10−5. These loci are located near PP13439-TMEM212, CDH12, MFAP3-GALNT10, and FER1L4 and had effect sizes between 0.091 and 0.167 s.d. unit (or 0.67–1.24 kg/m2) of BMI for each copy of the effect allele. Our findings suggest the presence of novel loci potentially associated with adiposity in African Americans. Further replication and meta-analysis in African Americans and other populations will shed light on the role of these loci in different ethnic populations.
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
African Americans are disproportionately affected by type 2 diabetes (T2DM) yet few studies have examined T2DM using genome-wide association approaches in this ethnicity. The aim of this study was to identify genes associated with T2DM in the African American population. We performed a Genome Wide Association Study (GWAS) using the Affymetrix 6.0 array in 965 African-American cases with T2DM and end-stage renal disease (T2DM-ESRD) and 1029 population-based controls. The most significant SNPs (n = 550 independent loci) were genotyped in a replication cohort and 122 SNPs (n = 98 independent loci) were further tested through genotyping three additional validation cohorts followed by meta-analysis in all five cohorts totaling 3,132 cases and 3,317 controls. Twelve SNPs had evidence of association in the GWAS (P<0.0071), were directionally consistent in the Replication cohort and were associated with T2DM in subjects without nephropathy (P<0.05). Meta-analysis in all cases and controls revealed a single SNP reaching genome-wide significance (P<2.5×10−8). SNP rs7560163 (P = 7.0×10−9, OR (95% CI) = 0.75 (0.67–0.84)) is located intergenically between RND3 and RBM43. Four additional loci (rs7542900, rs4659485, rs2722769 and rs7107217) were associated with T2DM (P<0.05) and reached more nominal levels of significance (P<2.5×10−5) in the overall analysis and may represent novel loci that contribute to T2DM. We have identified novel T2DM-susceptibility variants in the African-American population. Notably, T2DM risk was associated with the major allele and implies an interesting genetic architecture in this population. These results suggest that multiple loci underlie T2DM susceptibility in the African-American population and that these loci are distinct from those identified in other ethnic populations.
Background. Non-diabetic forms of nephropathy commonly lead to end-stage renal disease (non-DM ESRD). Previous studies have demonstrated that African Americans are more susceptible to non-DM ESRD compared to other ethnic groups, and this risk has a strong genetic component. A genome-wide scan for ESRD in African American families enriched for non-DM ESRD showed evidence for linkage in chromosome 13q33.3, and a candidate gene in this region, klotho, was selected for a detailed analysis in a follow-up case-control association study.
Methods. Thirty-four single-nucleotide polymorphisms (SNPs) in the klotho gene were genotyped in 317 unrelated African American non-DM ESRD cases and 354 non-nephropathy controls, including 12 SNPs identified by re-sequencing a region around exon 4.
Results. Two SNPs demonstrated modest admixture-adjusted evidence of association with non-DM ESRD, rs650439 (P = 0.013, recessive model) and rs643780 (P = 0.017, recessive model), while rs17643698 approached significance (P = 0.0953, two degrees of freedom test). Eight of the most significant SNPs were tested for replication in a second case-control collection (557 African American non-DM ESRD cases and 187 controls), and there was no evidence of association in replicate cases and controls; nor when the samples were combined for a total of 874 non-DM cases and 541 controls. Cox proportional hazards models were computed to test for association between polymorphisms in klotho and age at onset of ESRD. A three-SNP haplotype, rs526906, rs525014 and rs571118 (T/T/A), was associated with age of onset of ESRD [P = 0.007, recessive model; hazard ratio (HR) = 0.70]. Subjects homozygous for this haplotype had a mean 4 years later onset of ESRD, suggesting a slower disease progression. HapMap subjects homozygous for this haplotype had increased expression of klotho, further supporting a protective role of this variant in ESRD.
Conclusion. We conclude that three SNPs in intron 1 of the klotho gene are associated with delayed age at onset of non-DM ESRD in African Americans.
genetics; klotho; non-diabetic ESRD
Chromosome 20q12-q13.1 has been linked to type 2 diabetes (T2D) in multiple populations. We examined the influence of genes in this region on T2D and BMI in two European American case-control populations. SNPs were genotyped in 300 diabetic patients and 310 controls. A subset of 72 SNPs were further genotyped in 470 cases and 442 controls. All genes examined showed evidence of association with T2D in the initial sample (additive P-value [Pa] =0.00090–0.045). SNPs near PREX1 were also associated in the second case-control population (Pa=0.017–0.042). The combined analysis resulted in the same SNPs, among others, associated with T2D (Pa=0.0013–0.041). Stratification analysis by T2D status showed that association with BMI was observed solely in cases (Pa=0.0018–0.041). Mediation testing revealed 30–40% of the effects of these SNPs on T2D were significantly mediated by BMI. SNPs near PREX1 may contribute to T2D susceptibility mediated through effects of adiposity in European Americans
association; type 2 diabetes; genetics; adiposity; mediation analysis
African Americans have increased susceptibility to non-diabetic (non-DM) forms of end-stage renal disease (ESRD) and extensive evidence supports a genetic contribution. A genome-wide association study (GWAS) using pooled DNA was performed in 1,000 African Americans to detect associated genes. DNA from 500 non-DM ESRD cases and 500 non-nephropathy controls was quantified using gel electrophoresis and spectrophotometric analysis and pools of 50 case and 50 control DNA samples were created. DNA pools were genotyped in duplicate on the Illumina HumanHap550-Duo BeadChip. Normalization methods were developed and applied to array intensity values to reduce inter-array variance. Allele frequencies were calculated from normalized channel intensities and compared between case and control pools. Three SNPs had p values of <1.0E–6: rs4462445 (ch 13), rs4821469 (ch 22) and rs8077346 (ch 17). After normalization, top scoring SNPs (n = 65) were genotyped individually in 464 of the original cases and 478 of the controls, with replication in 336 non-DM ESRD cases and 363 non-nephropathy controls. Sixteen SNPs were associated with non-DM ESRD (p < 7.7E–4, Bonferroni corrected). Twelve of these SNPs are in or near the MYH9 gene. The four non-MYH9 SNPs that were associated with non-DM ESRD in the pooled samples were not associated in the replication set. Five SNPs that were modestly associated in the pooled samples were more strongly associated in the replication and/or combined samples. This is the first GWAS for non-DM ESRD in African Americans using pooled DNA. We demonstrate strong association between non-DM ESRD in African Americans with MYH9, and have identified additional candidate loci.
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.