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
Common genetic variation frequently accounts for only a modest amount of inter-individual variation in quantitative traits and complex disease susceptibility. Circulating adiponectin, an adipocytokine implicated in metabolic disease, is a model for assessing the contribution of genetic and clinical factors to quantitative trait variation. The adiponectin locus, ADIPOQ, is the primary source of genetically-mediated variation in plasma adiponectin levels. This study sought to define the genetic architecture of ADIPOQ in the comprehensively phenotyped Hispanic (n=1151) and African American (n=574) participants from the Insulin Resistance Atherosclerosis Family Study (IRASFS). Through resequencing and bioinformatic analysis, rare/low frequency (<5% MAF) and common variants (>5% MAF) in ADIPOQ were identified. Genetic variants and clinical variables were assessed for association with adiponectin levels and contribution to adiponectin variance in the Hispanic and African American cohorts. Clinical traits accounted for the greatest proportion of variance (POV) at 31% (p=1.16×10−47) and 47% (p=5.82×10−20), respectively. Rare/low frequency variants contributed more than common variants to variance in Hispanics: POV=18% (p= 6.40×10−15) and POV=5% (p=0.19), respectively. In African Americans, rare/low frequency and common variants both contributed approximately equally to variance: POV=6% (p=5.44×10−12) and POV=9% (P=1.44×10−10), respectively. Importantly, single low frequency alleles in each ethnic group were as important as, or more important than, common variants in explaining variation in adiponectin. Cumulatively, these clinical and ethnicity-specific genetic contributors explained half or more of the variance in Hispanic and African Americans and provide new insight into the sources of variation for this important adipocytokine.
adiponectin; proportion of variation; rare variants; common variants; clinical traits
Adiponectin is an adipocytokine associated with a variety of metabolic traits. These associations in human studies, in conjunction with functional studies in model systems, have implicated adiponectin in multiple metabolic processes.
We hypothesize that genetic variants associated with plasma adiponectin would also be associated with glucose homeostasis and adiposity phenotypes.
Design and Setting
The Insulin Resistance Atherosclerosis Family Study was designed to identify the genetic and environmental basis of insulin resistance and adiposity in the Hispanic- (n=1,424) and African-American (n=604) population.
Main Outcome Measures
High quality metabolic phenotypes, e.g. insulin sensitivity (SI), acute insulin response (AIR), disposition index (DI), fasting glucose, body mass index (BMI), visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and waist circumference, were explored.
Based on association analysis of more than 40 genetic polymorphisms in the adiponectin gene (ADIPOQ), we found no consistent association of ADIPOQ variants with plasma adiponectin levels and adiposity phenotypes. However, there were two promoter variants, rs17300539 and rs822387, associated with plasma adiponectin levels (P=0.0079 and 0.021, respectively) in the Hispanic-American cohort that were also associated with SI (P=0.0067 and 0.013, respectively). In contrast, there was only a single promoter SNP, rs17300539, associated with plasma adiponectin levels (P=0.0018) and fasting glucose (P=0.042) in the African-American cohort. Strikingly, high impact coding variants did not show evidence of association.
The lack of consistent patterns of association between variants, adiponectin levels, glucose homeostasis, and adiposity phenotypes suggests a reassessment of the influence of adiponectin in these pathways.
adiponectin; single nucleotide polymorphisms; glucose homeostasis; adiposity; African Americans; Hispanic Americans
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
Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent condition, particularly among Hispanic Americans. A genetic variant in PNPLA3 (rs738409) has been identified as a strong predictor of hepatic fat content.
To confirm the association of this variant with NAFLD in two minority cohorts, Hispanic Americans and African Americans, in whom liver density was quantified by computed tomography (CT).
This analysis was conducted in the Insulin Resistance Atherosclerosis (IRAS) Family Study. Participants were recruited from the general community and included 843 Hispanic American and 371 African American adults aged 18–81 years. A single variant in PNPLA3 (rs738409) was genotyped. Liver density was calculated in Hounsfield Units from abdominal CT scans.
Single nucleotide polymorphism (SNP) rs738409 was strongly associated with reduced liver density (i.e. NAFLD) in Hispanic Americans (1.18 × 10−9) and in African Americans (P = 4.99 × 10−6). The association followed an additive genetic model with the G allele conferring risk. The allele was two times more common in Hispanic Americans than in African Americans (40 vs 19%), consistent with the greater prevalence of NAFLD in Hispanic Americans (24 vs 9%). The SNP explained 4.4 and 5.6% of the variance of the adjusted liver density outcome in Hispanic Americans and African Americans, respectively.
We confirmed the association of a PNPLA3 variant with NAFLD in Hispanic Americans and African Americans, suggesting that PNPLA3 contributes to the variation in NAFLD across multiple ethnicities. This study adds to the growing evidence that some of the ethnic variation in NAFLD is genetic.
African Americans; computed tomography; genetic epidemiology; hepatic steatosis; Hispanic Americans; non-alcoholic fatty liver disease; PNPLA3
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.
Recently, a genome-wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic-American cohort. Multiple single-nucleotide polymorphisms (SNPs) in the G-protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar-laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat-laden food intake.
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
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
Haptoglobin (HP) is an acute phase protein that binds to freely circulating hemoglobin. HP exists as two distinct forms, HP1 and HP2. The longer HP2 form has been associated with cardiovascular (CVD) events and mortality in individuals with type 2 diabetes (T2DM).
This study examined the association of HP genotypes with subclinical CVD, T2DM risk, and associated risk factors in a T2DM-enriched sample. Haptoglobin genotypes were determined in 1208 European Americans (EA) from 473 Diabetes Heart Study (DHS) families via PCR. Three promoter SNPs (rs5467, rs5470, and rs5471) were also genotyped.
Analyses revealed association between HP2-2 duplication and increased carotid intima-media thickness (IMT; p = 0.001). No association between HP and measures of calcified arterial plaque were observed, but the HP polymorphism was associated with triglyceride concentrations (p = 0.005) and CVD mortality (p = 0.04). We found that the HP2-2 genotype was associated with increased T2DM risk with an odds ratio (OR) of 1.49 (95% CI 1.18-1.86, p = 6.59x10-4). Promoter SNPs were not associated with any traits.
This study suggests association between the HP duplication and IMT, triglycerides, CVD mortality, and T2DM in an EA population enriched for T2DM. Lack of association with atherosclerotic calcified plaque likely reflect differences in the pathogenesis of these CVD phenotypes. HP variation may contribute to the heritable risk for CVD complications in T2DM.
Haptoglobin; Genetic polymorphism; Cardiovascular disease; Type 2 diabetes
Multiple single nucleotide polymorphisms (SNPs) associated with type 2 diabetes (T2D) susceptibility have been identified in predominantly European-derived populations. These SNPs have not been extensively investigated for individual and cumulative effects on T2D risk in African Americans.
RESEARCH DESIGN AND METHODS
Seventeen index T2D risk variants were genotyped in 2,652 African American case subjects with T2D and 1,393 nondiabetic control subjects. Individual SNPs and cumulative risk allele loads were assessed for association with risk for T2D. Cumulative risk was assessed by counting risk alleles and evaluating the difference in cumulative risk scores between case subjects and control subjects. A second analysis weighted risk scores (ln [OR]) based on previously reported European-derived effect sizes.
Frequencies of risk alleles ranged from 8.6 to 99.9%. Eleven SNPs had ORs >1, and 5 from ADAMTS9, WFS1, CDKAL1, JAZF1, and TCF7L2 trended or had nominally significant evidence of T2D association (P < 0.05). Individuals carried between 13 and 29 risk alleles. Association was observed between T2D and increase in risk allele load (unweighted OR 1.04 [95% CI 1.01–1.08], P = 0.010; weighted 1.06 [1.03–1.10], P = 8.10 × 10−5). When TCF7L2 SNP rs7903146 was included as a covariate, the risk score was no longer associated with T2D in either model (unweighted 1.02 [0.98–1.05], P = 0.33; weighted 1.02 [0.98–1.06], P = 0.40).
The trend of increase in risk for T2D with increasing risk allele load is similar to observations in European-derived populations; however, these analyses indicate that T2D genetic risk is primarily mediated through the effect of TCF7L2 in African Americans.
Several genome scans have explored the linkage of chronic kidney disease phenotypes to chromosomic regions with disparate results. Genome scan meta-analysis (GSMA) is a quantitative method to synthesize linkage results from independent studies and assess their concordance.
We searched PubMed to identify genome linkage analyses of renal function traits in humans, such as estimated glomerular filtration rate (GFR), albuminuria, serum creatinine concentration and creatinine clearance. We contacted authors for numerical data and extracted information from individual studies. We applied the GSMA nonparametric approach to combine results across 14 linkage studies for GFR, 11 linkage studies for albumin creatinine ratio, 11 linkage studies for serum creatinine and 4 linkage studies for creatinine clearance.
No chromosomal region reached genome-wide statistical significance in the main analysis which included all scans under each phenotype; however, regions on Chromosomes 7, 10 and 16 reached suggestive significance for linkage to two or more phenotypes. Subgroup analyses by disease status or ethnicity did not yield additional information.
While heterogeneity across populations, methodologies and study designs likely explain this lack of agreement, it is possible that linkage scan methodologies lack the resolution for investigating complex traits. Combining family-based linkage studies with genome-wide association studies may be a powerful approach to detect private mutations contributing to complex renal phenotypes.
albuminuria; chronic kidney disease; glomerular filtration rate; linkage scans; meta-analysis
The hepatocyte nuclear factor 4-α (HNF4α) gene codes for a transcription factor which is responsible for regulating gene transcription in pancreatic beta cells, in addition to its primary role in hepatic gene regulation. Mutations in this gene can lead to maturity-onset diabetes of the young (MODY), an uncommon, autosomal dominant, non-insulin dependent form of diabetes. Mutations in HNF4α have been found in few individuals, and infrequently have they segregated completely with MODY in families. In addition, due to similarity of phenotypes, it is unclear what proportion of type 2 diabetes (T2DM) in the general population is due to MODY or HNF4α mutations specifically. In this study, 27 documented rare and common variants were genotyped in a European American population of 1270 T2DM cases and 1017 controls from review of databases and literature implicating HNF4α variants in MODY and T2DM. Seventeen variants were found to be monomorphic. Two cases and one control subject had one copy of a 6-bp P2 promoter deletion. The intron 1 variant (rs6103716; MAF = 0.31) was not significantly associated with disease status (p>0.8) and the missense variant Thr130Ile (rs1800961; MAF = 0.027) was also not significantly different between cases and controls (p>0.2), but showed a trend consistent with association with T2DM. Four variants were found to be rare as heterozygotes in small numbers of subjects. Since many variants were infrequent, a pooled chi-squared analysis of rare variants was used to assess the overall burden of variants between cases and controls. This analysis revealed no significant difference (P=0.22). We conclude there is little evidence to suggest that HNF4α variants contribute significantly to risk of T2DM in the general population, but a modest contribution cannot be excluded. In addition, the observation of some mutations in controls suggests they are not highly penetrant MODY-causing variants.
Type 2 Diabetes; HNF4A; Rare variants
Monocyte chemoattractant protein-1 (MCP-1) plays important roles in kidney disease susceptibility and atherogenesis in experimental models. Relationships between serum MCP-1 concentration and early nephropathy and subclinical cardiovascular disease (CVD) were assessed in African Americans (AAs) with type 2 diabetes (T2D).
Serum MCP-1 concentration, urine albumin:creatinine ratio (ACR), estimated glomerular filtration rate (eGFR), and atherosclerotic calcified plaque (CP) in the coronary and carotid arteries and infrarenal aorta were measured in 479 unrelated AAs with T2D. Generalized linear models were fitted to test for associations between MCP-1 and urine ACR, eGFR, and CP.
Participants were 57% female, with mean ± SD (median) age 55.6±9.5 (55.0) years, diabetes duration 10.3±8.2 (8.0) years, urine ACR 149.7±566.7 (14.0) mg/g, CKD-EPI eGFR 92.4±23.3 (92.0) ml/min/1.73m2, MCP-1 262.9±239.1 (224.4) pg/ml, coronary artery CP 280.1±633.8 (13.5), carotid artery CP 47.1±132.9 (0), and aorta CP 1616.0±2864.0 (319.0). Adjusting for age, sex, smoking, HbA1c, BMI, and LDL, serum MCP-1 was positively associated with albuminuria (parameter estimate 0.0021, P=0.04) and negatively associated with eGFR (parameter estimate −0.0003, P=0.001). MCP-1 remained associated with eGFR after adjustment for urine ACR. MCP-1 levels did not correlate with the extent of CP in any vascular bed, HbA1c or diabetes duration, but were positively associated with BMI. No interaction between BMI and MCP-1 was detected on nephropathy outcomes.
Serum MCP-1 levels are associated with eGFR and albuminuria in AAs with T2D. MCP-1 was not associated with subclinical CVD in this population. Inflammation appears to play important roles in development and/or progression of kidney disease in AAs.
African Americans; Albuminuria; Atherosclerotic calcified plaque; Diabetes; GFR; MCP-1
Over the past 50 years, increases in dietary n-6 polyunsaturated fatty acids (PUFAs), such as linoleic acid, have been hypothesized to cause or exacerbate chronic inflammatory diseases. This study examines an individual’s innate capacity to synthesize n-6-long chain PUFAs (LC-PUFAs), with respect to the fatty acid desaturase (FADS) locus in Americans of African and European descent with diabetes/metabolic syndrome. Compared to European Americans (EAm), African Americans (AfAm) exhibited markedly higher serum levels of arachidonic acid (AA) (EAm 7.9±2.1; AfAm 9.8±1.9 % of total fatty acids, mean ± sd; p<2.29×10−9) and the AA to n-6-precursor fatty acid ratio, which estimates FADS1 activity (EAm 5.4±2.2, AfAm 6.9±2.2; p=1.44×10−5). Seven single nucleotide polymorphisms (SNP) mapping to the FADS locus revealed strong association with AA, eicosapentaenoic acid (EPA) and dihomogamma-linolenic acid (DGLA) in the EAm. Importantly, EAm homozygous for the minor allele (T) had significantly lower AA levels (TT: 6.3±1.0; GG: 8.5±2.1; p=3.0×10−5) and AA/DGLA ratios (TT: 3.4±0.8; GG: 6.5±2.3; p=2.2×10−7) but higher DGLA levels (TT: 1.9±0.4; GG: 1.4±0.4; p=3.3×10−7) compared to those homozygous for the major allele (GG). Allele frequency patterns suggest that the GG genotype at rs174537 (associated with higher circulating levels of AA) is much higher in AfAm (0.81) compared to EAm (0.46). Similarly, marked differences in rs174537 genotypic frequencies were observed in HapMap populations. These data suggest that there are likely important differences in the capacity of different populations to synthesize LC-PUFAs. These differences may provide a genetic mechanism contributing to health disparities between populations of African and European descent.
SNP; FADS; arachidonic acid synthesis
Non-alcoholic fatty liver disease (NAFLD) is commonly diagnosed in patients with obesity and type 2 diabetes mellitus (T2DM), and has been associated with the single nucleotide polymorphism (SNP) rs738409 in the PNPLA3 gene. This association remains to be investigated in African Americans with T2DM, a group at lower risk for hepatic steatosis relative to European Americans with T2DM.
We examined 422 African Americans with T2DM (40.3% male; age: 56.4 ± 9.6 years; BMI: 35.2 ± 8.2 kg/m2), all with measures of liver density reflecting hepatic fat content on abdominal computed tomography, and blood glucose and lipid profiles. Associations between rs738409 and phenotypes of interest were determined using SOLAR, assuming an additive model of inheritance with covariates age, sex, BMI and use of lipid-lowering medications.
Mean ± SD liver density was 55.4 ± 10.2 Hounsfield Units. SNP rs738409 in PNPLA3 was significantly associated with liver density (P=0.0075) and hepatic steatosis (P=0.0350), but not with blood glucose, HbA1c, total cholesterol, triglycerides, high-density or low-density lipoprotein levels or liver function tests (P=0.15–0.96).
These findings provide evidence that the PNPLA3 SNP rs738409 contributes to risk for increased liver fat content in African Americans with T2DM, an effect that appears to be independent from serum lipids. Although African Americans are less susceptible to fatty liver than European Americans, PNPLA3 appears to be a risk locus for hepatic steatosis in diabetic African Americans.
type 2 diabetes; genetics; fatty liver disease; African American
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
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
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
In diabetes, it remains unclear whether the coronary artery calcium (CAC) score provides additional information about total mortality risk beyond traditional risk factors.
RESEARCH DESIGN AND METHODS
A total of 1,051 participants, aged 34–86 years, in the Diabetes Heart Study (DHS) were followed for 7.4 years. Subjects were separated into five groups using baseline computed tomography scans and CAC scores (0–9, 10–99, 100–299, 300–999, and ≥1,000). Logistic regression was performed adjusting for age, sex, race, smoking, and LDL cholesterol to examine the association between CAC and all-cause mortality. Areas under the curve with and without CAC were compared. Natural splines using continuous measures of CAC were fitted to estimate the relationship between observed CAC and mortality risk.
A total of 17% (178 of 1,051) of participants died during the follow-up. In multivariate analysis, the odds ratios (95% CIs) for all-cause mortality, using CAC 0–9 as the reference group, were CAC 10–99: 1.40 (0.57–3.74); CAC 100–299: 2.87 (1.17–7.77); CAC 300–999: 3.04 (1.32–7.90); and CAC ≥1,000: 6.71 (3.09–16.87). The area under the curve without CAC was 0.68 (95% CI 0.66–0.70), and the area under the curve with CAC was 0.72 (0.70–0.74) (P = 0.0001). Using splines, the estimated risk (95% CI) of mortality for a CAC of 0 was 6.7% (4.6–9.7), and the risk increased nearly linearly, plateauing at CAC ≥1,000 (20.0% [15.7–25.2]).
In diabetes, CAC was shown to be an independent predictor of mortality. Participants with CAC (0–9) were at lower risk (0.9% annual mortality). The risk of mortality increased with increasing levels of CAC, plateauing at approximately CAC ≥1,000 (2.7% annual mortality). More research is warranted to determine the potential utility of CAC scans in diabetes.
A carotid artery calcified plaque (CarCP) linkage peak on chromosome 16p (LOD 4.39 at 8.4cM) in European American (EA) families with type 2 diabetes mellitus (T2DM) from the Diabetes Heart Study (DHS) has been refined by fine-mapping and candidate genes and SNPs evaluated for association with subclinical CVD. Fine-mapping was based on 104 SNPs in 937 subjects from 315 families, including 45 SNPs in six candidate genes (CACNA1H, SEPX1, ABCA3, IL32, SOCS1, and KIAA0350). Linkage and association analyses using variance components analysis (SOLAR; adjusting for age, gender, BMI, and T2DM status) refined the original CarCP linkage into two distinct linkage regions (LOD scores: 3.89 at 6.9cM and 4.86 at 16.0cM). Evidence of linkage for coronary calcified plaque (LOD: 2.27 at 19cM) and a vascular calcification principle component (LOD: 3.71 at 16.0cM) was also observed. The strongest evidence for association with CarCP was observed with SNPs in the A2BP1 gene region (rs4337300 p=0.005) with modest evidence of association with SNPs in CACNA1H (p=0.010–0.033). Bayesian Quantitative Trait Nucleotide analysis identified a SNP, rs1358489, with either a functional effect on CarCP or in linkage disequilibrium with a functional SNP. This study refined the 16p region contributing to vascular calcification. Although the causal variants remain to be identified the results are consistent with a linkage peak which is due to multiple common variants, though rare variants cannot be excluded.
type 2 diabetes; subclinical cardiovascular disease; fine mapping
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
A new report suggests that differences in albuminuria might contribute to disparities in susceptibility to nephropathy in African American and white individuals. Interpretation of this finding requires consideration of renal histology, clinical trials and genetic studies. These factors indicate that a far more complex scenario is likely to exist than previously thought.