Genetic ancestry is associated with subclinical cardiovascular disease in African-Americans and Hispanics from the multi-ethnic study of atherosclerosis

High prevalence of subclinical atherosclerosis by carotid ultrasound among Mexican Americans: discordance with 10-year risk assessment using the Framingham risk score

BACKGROUND

Framingham risk scores (FRS) were validated in a mostly Caucasian population. Evaluation of subclinical atherosclerosis by carotid ultrasound may improve ascertainment of risk in nonwhite populations. This study aimed to evaluate carotid intima-media thickness (cIMT) and carotid plaquing among Mexican Americans, and to correlate these markers with coronary risk factors and the FRS.

METHODS/RESULTS

Participants (n = 141) were drawn from the Cameron County Hispanic Cohort. Carotid artery ultrasound was performed and cIMT measured. Carotid plaque was defined as areas of thickening >50% of the thickness of the surrounding walls. Mean age was 53.1 ± 11.7 years (73.8% female). Most were overweight or obese (88.7%) and more than half (53.2%) had the metabolic syndrome. One third (34.8%) had abnormal carotid ultrasound findings (either cIMT ≥75th percentile for gender and age or presence of plaque). Among those with abnormal carotid ultrasound, the majority were classified as being at low 10-year risk for cardiovascular events. Carotid ultrasound reclassified nearly a third of the cohort as being at high risk. This discordance between 10-year FRS and carotid ultrasound was noted whether risk was assessed for hard coronary events or global risk. Concordance between FRS and carotid ultrasound findings was best when long-term (30-year) risk was assessed and no subject with an abnormal carotid ultrasound was categorized as low risk by the 30-year FRS algorithm.

CONCLUSIONS

Integration of carotid ultrasound findings to coronary risk assessments and use of longer term prediction models may provide better risk assessment in this minority population, with earlier initiation of appropriate therapies.

Effect of race and genetics on vitamin D metabolism, bone and vascular health

The pathophysiology of chronic kidney disease-mineral and bone disorder accounts for an inverse relationship between bone mineralization and vascular calcification in progressive nephropathy. Inverse associations between bone mineral density (BMD) and calcified atherosclerotic plaque are also observed in individuals of European and African ancestry without nephropathy, suggesting a mechanistic link between these processes that is independent of kidney disease. Despite lower dietary calcium intake and serum 25-hydroxyvitamin D (25(OH)D) concentrations, African Americans have higher BMD and develop osteoporosis less frequently than do European Americans. Moreover, despite having more risk factors for cardiovascular disease, African Americans have a lower incidence and severity of calcified atherosclerotic plaque formation than do European Americans. Strikingly, evidence is now revealing that serum 25(OH)D and/or 1,25 dihydroxyvitamin D levels associate positively with atherosclerosis but negatively with BMD in African Americans; by contrast, vitamin D levels associate negatively with atherosclerosis and positively with BMD in individuals of European ancestry. Biologic phenomena, therefore, seem to contribute to population-specific differences in vitamin D metabolism, bone and vascular health. Genetic and mechanistic approaches used to explore these differences should further our understanding of bone-blood vessel relationships and explain how African ancestry protects from osteoporosis and calcified atherosclerotic plaque, provided that access of African Americans to health care is equivalent to individuals of European ethnic origin. Ultimately, in our opinion, a new mechanistic understanding of the relationships between bone mineralization and vascular calcification will produce novel approaches for disease prevention in aging populations.

Cerebral white matter hyperintensity in African Americans and European Americans with type 2 diabetes

Previous studies involving inner city populations detected higher cerebral white matter hyperintensity (WMH) scores in African Americans (AAs) compared with European Americans (EAs). This finding might be attributable to the higher prevalence of cardiovascular disease (CVD) risk factors and poorer access to healthcare in AAs. Despite racial differences in CVD risk factor profiles, AAs have paradoxically lower levels of subclinical CVD. We hypothesized that AAs with diabetes and good access to healthcare would have comparable or lower levels of WMH as EAs. Racial differences in the distribution of WMH were analyzed in 46 AAs and 156 EAs with type 2 diabetes enrolled in the Diabetes Heart Study (DHS)-Mind, and replicated in a sample of 113 AAs and 61 EAs patients who had clinically indicated cerebral magnetic resonance imaging. Wilcoxon 2-sample tests and linear models were used to compare the distribution of WMH in AAs and EAs and to test for association between WMH and race. The unadjusted mean WMH score from the Diabetes Heart Study-Mind was 1.9 in AAs and 2.3 in EAs (P = .3244). Among those with clinically indicated magnetic resonance imaging, the mean WMH score was 2.9 in AAs and 3.9 in EAs (P = .0503). Adjustment for age and sex produced no statistically significant differences in WMH score between AAs and EAs. These independent datasets reveal comparable WMH scores in AAs and EAs, suggesting that disparities in access to healthcare and environmental exposures likely underlie the previously reported excess burden of WMH in AAs.

Genetic admixture is associated with plasma hemostatic factor levels in self-identified African Americans and Hispanics: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Epidemiologic studies report that self-identified African Americans typically have higher hemostatic factor levels than do self-identified Caucasians or Hispanics.

OBJECTIVE

To enhance understanding of phenotypic variation in hemostatic factor levels by race/ethnicity, we evaluated the relationship between genetic ancestry and hemostatic factor levels among Multi-Ethnic Study of Atherosclerosis (MESA) study participants.

PATIENTS/METHODS

Our sample included 712 African American and 701 Hispanic men and women aged 45 to 84 years. Individual global ancestry was estimated from 199 genetic markers using STRUCTURE. Linear regression models were used to evaluate the relationship between ancestry and hemostatic factor levels, adjusting for age, gender, education, income and study site.

RESULTS

Among African Americans, mean ± standard deviation (SD) ancestry was estimated as 79.9% ± 15.9% African and 20.1% ± 15.9% European. Each SD (16%) greater African ancestry was associated with 2.1% higher fibrinogen levels (P = 0.007) and 3.5% higher plasmin-antiplasmin (PAP) levels (P = 0.02). Ancestry among African Americans was not related to levels of factor (F)VIII or D-dimer. Mean ± SD estimated ancestry among Hispanics was 48.3% ± 23.8% Native American, 38.8% ± 21.9% European, and 13.0% ± 8.9% African. In Hispanics, each SD (19%) greater African ancestry was associated with 2.7% higher fibrinogen levels (P = 0.009) and 7.9% higher FVIII levels (P = 0.0002). In Hispanics, there was no relation between African ancestry and D-dimer or PAP levels, or between European ancestry and hemostatic factor levels.

CONCLUSIONS

Greater African ancestry among African Americans and Hispanics was associated with higher levels of several hemostatic factors, notably fibrinogen. These results suggest that genetic heterogeneity contributes, albeit modestly, to racial/ethnic differences in hemostatic factor levels.

Ethnic differences in the development of albuminuria: the DISTANCE study

OBJECTIVES

To determine whether ethnic differences in the incidence of albuminuria are present in patients with diabetes, and to identify social, behavioral, and provider factors that explain ethnic differences.

STUDY DESIGN

Survey follow-up design with a race-stratified baseline survey (2005-2006) in diabetic patients from a nonprofit, fully integrated healthcare system in Northern California. We followed the 10,596 respondents (30% whites, 20% blacks, 23% Hispanics, 14% Asians, and 13% Filipinos) without evidence of prevalent albuminuria at baseline.

METHODS

Incident albuminuria was defined by positive dipstick urinalysis (>1) or urine albumin to creatinine level (>30 mg/g), and confirmed with repeat testing at least 3 months later.

RESULTS

The 27,292 person-years of observation yielded 981 incident albuminuria events. Agestandardized rates of albuminuria (per 1000 person-years) ranged from 13.6 (95% confidence interval [CI] 10.5-17.0) in whites to 27.8 (CI 18.2- 38.3) in blacks. In fully adjusted Cox models, the hazard ratio for blacks (1.22, 95% CI 1.09-1.38), Asians (1.35, 95% CI 1.13-1.61), and Filipinos (1.93, 95% CI 1.61-2.32), but not Hispanics, was significantly greater than it was for whites. In some cases, point estimates changed markedly from the base model when fully adjusted for potential confounders. Moreover, adjustment for an array of potentially mediating factors explained only a small proportion of the observed ethnic disparities.

CONCLUSIONS

Despite uniform medical care coverage, Filipinos, blacks, and Asians with diabetes developed albuminuria at higher rates than white and Hispanic adults.

Association of self-reported race/ethnicity and genetic ancestry with arterial elasticity: the Multi-Ethnic Study of Atherosclerosis (MESA)

African Americans have a disproportionate burden of hypertension compared with white, whereas data on Hispanics is less well-defined. Mechanisms underlying these differences are unclear, but could be in part because of ancestral background and vascular function. We studied 660 African Americans and 635 Hispanics from the Multi-Ethnic Study of Atherosclerosis (MESA) with complete data on genetic ancestry, pulse pressure (PP), and large and small arterial elasticity (LAE, SAE). LAE and SAE were obtained using the HDI PulseWave CR-2000 Research CardioVascular Profiling Instrument. Among African Americans, higher European ancestry was marginally associated with higher LAE (P = .05) and lower PP (P = .05); results for LAE were attenuated after adjustment for potential mediators (P = .30). Among Hispanics, higher Native American ancestry was associated with higher SAE (P = .0006); higher African ancestry was marginally associated with lower SAE (P = .07). Ancestry was not significantly associated with LAE or PP in Hispanics. Among African Americans, higher European ancestry may be associated with less large artery damage, as measured by LAE and PP, although these associations warrant further study. Among Hispanics, ancestry is strongly associated with SAE. Future studies should consider genetic ancestry when studying hypertension in race/ethnic minorities, particularly among Hispanics.

Effects of race on albuminuria and risk of cardiovascular and kidney disease

The literature describing the relationship between urinary protein excretion and risk of cardiovascular disease and renal disease is rapidly proliferating. Several studies have demonstrated racial differences in the relationship between albuminuria and associated disorders. The purpose of this article is to summarize the effects of race on the relationship between albuminuria and renal and cardiovascular disease risk, propose explanatory hypotheses, and suggest directions for future investigation.

Correlates of coronary artery calcified plaque in blacks and whites with type 2 diabetes

PURPOSE

To examine whether the relationship between cardiovascular disease risk factors and coronary artery calcification (CAC) is modified by race among those with diabetes.

METHODS

Data were pooled data from three studies (Multi-Ethnic Study of Atherosclerosis, Family Heart Study, Diabetes Heart Study) for a total of 835 blacks and 1122 whites with diabetes. CAC was quantified by cardiac computed tomography and risk factors were obtained using standard methods. Regression models examined the relationship between risk factors and presence and quantity of CAC.

RESULTS

The average age of the cohort was 60 years; 57% were women. Presence of CAC was lower in blacks compared to whites (odds ratio = 0.22 for men, 0.57 for women, p <0.01). Hemoglobin A1c, duration of diabetes, low-density lipoprotein, smoking, and body mass index were independently associated with presence of CAC; high-density lipoprotein, triglycerides, and C-reactive protein were not. Race did not modify these associations. Adjustment for multiple risk factors did not explain the race disparity in CAC.

CONCLUSIONS

CAC was reduced in blacks compared to whites in persons with diabetes. This effect was most pronounced in men. The relationship between risk factors and CAC did not differ between races. Racial differences in CAC are likely due to unmeasured risk factors and/or genetic susceptibility.

Genetic ancestry and lower extremity peripheral artery disease in the Multi-Ethnic Study of Atherosclerosis

Using self-report of race/ethnicity, African Americans consistently have a higher prevalence of peripheral artery disease (PAD) compared to other ethnic groups. We aimed to determine the associations between estimated genetic admixture and PAD among African and Hispanic Americans. We studied the association between genetic ancestry and PAD among 1417 African and Hispanic American participants in the Multi-Ethnic Study of Atherosclerosis who were genotyped for ancestry informative markers (AIMs). PAD was defined as an ankle-brachial index (ABI) < 0.90. The overall prevalence of PAD among the 712 self-identified African American subjects was 15.2% and 4.6% among the 705 self-identified Hispanic Americans. A one standard deviation increment in European ancestry was associated with non-significant reductions in the odds for PAD among African (OR: 0.96 [95% CI: 0.78-1.18]) and Hispanic Americans (0.84 [0.58-1.23]), while the same increment in Native American ancestry was significantly associated with a lower odds of PAD in Hispanic Americans (0.56 [0.36-0.96]). Adjustment for demographic variables, field center, cardiovascular disease (CVD) risk factors and inflammatory markers strengthened the odds for European ancestry among African (0.85 [0.66-1.10]) and Hispanic Americans (0.68 [0.41-1.11]). The magnitude of the association for Native American ancestry among Hispanic Americans did not materially change (0.56 [0.29-1.09]). In conclusion, a higher percent Native American ancestry in Hispanics is associated with a lower odds of PAD while in both Hispanics and African Americans, greater European ancestry does not appear to be associated with lower odds for PAD.

Ethnic differences in the relationship between pericardial adipose tissue and coronary artery calcified plaque: African-American-diabetes heart study

BACKGROUND

Calcified atherosclerotic plaque (CP) is less prevalent and less severe in African-Americans (AA), relative to European Americans (EA). Because pericardial adipose tissue (PAT) is associated with CP in the neighboring coronary arteries, we explored ethnic-specific relationships between PAT and CP.

METHODS

PAT volume and coronary and aortic CP were measured in 561 EA and 575 AA subjects with type 2 diabetes using single and multidetector computed tomography. Generalized estimating equations with exchangeable correlation and the sandwich estimator of the variance were used to test for associations between PAT and CP.

RESULTS

Mean (sd) ages of AA and EA participants were 56.7 (9.5) and 62.0 (8.9) yr, respectively; diabetes duration was 10.5 (8.1) and 10.1 (7.3) yr; and PAT volume was 86.9 (38.6) and 131.7 (55.3) cm3/45 mm. In AA and EA participants, respectively, mean (sd) coronary CP mass scores were 803 (1,889) and 1,465 (2,847) mg calcium; and aortic CP, 5,407 (10,651) and 10,090 (15,087) mg calcium. Adjusting for age, gender, body mass index, blood pressure, height, smoking, lipid-lowering medications, C-reactive protein, albuminuria, high-density lipoprotein-cholesterol, and triglycerides, parameter estimates for the relationship between PAT and log(coronary CP+1) were 0.012 in AA (P<0.0001) and 0.003 (P=0.24) in EA, with a significant ethnic difference (P=0.019). No significant relationships or ethnic differences were observed between PAT and aortic CP (P=0.24, fully adjusted model).

CONCLUSIONS

Pericardial adiposity is strongly associated with coronary atherosclerosis in AA with type 2 diabetes. Novel cardiovascular disease risk factors such as PAT may contribute to ethnic disparities in susceptibility to development of coronary atherosclerosis.

Review of the Diabetes Heart Study (DHS) family of studies: a comprehensively examined sample for genetic and epidemiological studies of type 2 diabetes and its complications

The Diabetes Heart Study (DHS) is a genetic and epidemiological study of 1,443 European American and African American participants from 564 families with multiple cases of type 2 diabetes. Initially, participants were comprehensively examined for measures of subclinical cardiovascular disease (CVD) including computed tomography measurement of vascular calcified plaque, ultrasound imaging of carotid artery wall thickness, and electrocardiographic intervals. Subsequent studies have investigated the relationship between bone mineral density and vascular calcification, measures of adiposity, and biomarkers. Ongoing studies are carrying out an extensive evaluation of cerebrovascular disease using magnetic resonance imaging and cognitive assessment. A second, parallel study, the African American DHS, has expanded the sample of African Americans to investigate marked racial differences in subclinical CVD between European Americans and African Americans. Studies in development will evaluate the impact of social stress during the lifecourse on CVD risk, and the prevalence of gastroparesis in this diabetes enriched sample. In addition, the ongoing high mortality rate in DHS participants provides novel insights into the increased risks for type 2 diabetes affected individuals. A comprehensive genetic analysis of the sample is underway using the genome-wide association study (GWAS) approach. Data from this GWAS survey will complement prior family-based linkage data in the analysis of genetic contributors to the wide range of traits in the sample. To our knowledge the DHS family of studies has created the most comprehensively examined sample of individuals with type 2 diabetes yet available, and represents a unique resource for the study people with type 2 diabetes. The aim of this review is to provide a collective overview of the major results from the DHS family of studies, and relate them to the larger body of biomedical investigations of diabetes and its complications.

Genomes, populations and diseases: ethnic genomics and personalized medicine

This review discusses the progress of ethnic genetics, the genetics of common diseases, and the concepts of personalized medicine. We show the relationship between the structure of genetic diversity in human populations and the varying frequencies of Mendelian and multifactor diseases. We also examine the population basis of pharmacogenetics and evaluate the effectiveness of pharmacotherapy, along with a review of new achievements and prospects in personalized genomics.

Potential effects of MYH9-associated nephropathy on dialysis and kidney transplant outcomes

Several related disorders comprise the spectrum of nonmuscle myosin heavy chain 9-associated (MYH9) nephropathy. The contribution of variants in this single MYH9 gene to ethnic differences in the incidence rates of end-stage renal disease is now clearly established. The importance of recognizing the role of MYH9 in these inherited kidney disorders goes beyond simple disease association; there may well be effects on clinical outcomes in patients on dialysis and after kidney transplantation. MYH9 polymorphisms may affect treatment outcomes in severe kidney disease and such gene effects are rarely encountered in practice.

Differences in albuminuria between Hispanics and whites: an evaluation by genetic ancestry and country of origin: the multi-ethnic study of atherosclerosis

BACKGROUND

Reports show higher prevalence of albuminuria among Hispanics compared with whites. Differences by country of origin or genetic background are unknown.

METHODS AND RESULTS

In Multi-Ethnic Study of Atherosclerosis, we studied the associations of both genetic ancestry and country of origin with albumin to creatinine ratio among 1417 Hispanic versus white participants using multivariable linear regression and back transforming beta coefficients into relative difference (%RD, 95% CI). Percentage European, Native American, and African ancestry components for Hispanics were estimated using genetic admixture analysis. The proportions of European, Native American, and African genetic ancestry differed significantly by country of origin (P<0.0001); Mexican/Central Americans had the highest Native American (41+/-13%), Puerto Ricans had the highest European (61+/-15%), and Dominicans had the highest African (39+/-21%) ancestry. Hispanic ethnicity was associated with higher albumin/creatinine ratio compared with whites, but the association varied with the country of origin (adjusted P interaction=0.04). Mexican/Central Americans and Dominicans had higher albumin/creatinine ratio compared with whites after adjustment (RD 19%, 2% to 40% and RD 27%, 1% to 61%), but not Puerto Ricans (RD 8%, -12% to 34%). Higher Native American ancestry was associated with higher albuminuria after age and sex adjustment among all Hispanics (RD 11%, 1% to 21%) but was attenuated after further adjustment. Higher European ancestry was independently associated with lower albumin/creatinine ratio among Puerto Ricans (-21%, -34% to -6%) but not among Mexican/Central Americans and Dominicans.

CONCLUSIONS

Hispanics are a heterogeneous group with varying genetic ancestry. Risks of albuminuria differ across the country of origin groups. These differences may be due, in part, to differences in genetic ancestral components.