Interethnic Variation in Lipid Profiles: Implications for Underidentification of African-Americans at risk for Metabolic Disorders

Ancestral and environmental patterns in the association between triglycerides and other cardiometabolic risk factors

BACKGROUND

West Africans and African Americans with substantial (∼80%) West African ancestry are characterized by low levels of triglycerides (TG) compared to East Africans and Europeans. The impact of these varying TG levels on other cardiometabolic risk factors is unclear. We compared the strength of association between TG with hypertension, blood pressure, BMI, waist circumference, type 2 diabetes (T2D), and fasting glucose across West African (WA), East African (EA), and European (EU) ancestry populations residing in three vastly different environmental settings: sub-Saharan Africa, United States, and Europe.

METHODS

We analysed data from four cross-sectional studies that included WA in sub-Saharan Africa (n = 7201), the U.S. (n = 4390), and Europe (n = 6436), EA in sub-Saharan Africa (n = 781), and EU in the U.S. (n = 8670) and Europe (n = 4541). Linear regression analyses were used to test the association between TG and cardiometabolic risk factors.

FINDINGS

Higher adjusted regression coefficients were observed in EU compared with WA ancestry for TG on hypertension (EU β [95% CI]: 0.179 [0.156, 0.203], WA β [95% CI]: 0.102 [0.086, 0.118]), BMI (EU β [95% CI]: 0.028 [0.027, 0.030], WA β [95% CI]: 0.015 [0.014, 0.016]), and waist circumference (EU β [95% CI]: 0.013 [0.013, 0.014], WA β [95% CI]: 0.009 [0.008, 0.009) (all ancestry × trait interaction P-values <0.05), irrespective of environmental differences within ancestry groups. Less consistency was observed among EA. Associations of TG with T2D did not follow ancestry patterns, with substantial variation observed between environments.

INTERPRETATION

TG may not be an equally strong associated with other established cardiometabolic risk factors in West and East Africans in contrast to European ancestry populations. The value of TG for identifying individuals at high risk for developing metabolic disorders needs to be re-evaluated for African ancestry populations.

FUNDING

National Institutes of Health, European Commission, Dutch Heart Foundation, Netherlands Organization for Health Research and Development, Centers for Disease Control and Prevention.

Targeted Lipidomics To Measure Phospholipids and Sphingomyelins in Plasma: A Pilot Study To Understand the Impact of Race/Ethnicity in Alzheimer's Disease

The number of people suffering from Alzheimer's disease (AD) is increasing rapidly every year. One aspect of AD that is often overlooked is the disproportionate incidence of AD among African American/Black populations. With the recent development of novel assays for lipidomics analysis in recent times, there has been a drastic increase in the number of studies focusing on changes of lipids in AD. However, very few of these studies have focused on or even included samples from African American/Black individuals samples. In this study, we aimed to determine if the lipidome in AD is universal across non-Hispanic White and African American/Black individuals. To accomplish this, a targeted mass spectrometry lipidomics analysis was performed on plasma samples (N = 113) obtained from cognitively normal (CN, N = 54) and AD (N = 59) individuals from African American/Black (N = 56) and non-Hispanic White (N = 57) backgrounds. Five lipids (PS 18:0_18:0, PS 18:0_20:0, PC 16:0_22:6, PC 18:0_22:6, and PS 18:1_22:6) were altered between AD and CN sample groups (p value < 0.05). Upon racial stratification, there were notable differences in lipids that were unique to African American/Black or non-Hispanic White individuals. PS 20:0_20:1 was reduced in AD in samples from non-Hispanic White but not African American/Black adults. We also tested whether race/ethnicity significantly modified the association between lipids and AD status by including a race × diagnosis interaction term in a linear regression model. PS 20:0_20:1 showed a significant interaction (p = 0.004). The discovery of lipid changes in AD in this study suggests that identifying relevant lipid biomarkers for diagnosis will require diversity in sample cohorts.

Genetic European Ancestry and Incident Diabetes in Black Individuals: Insights From the SPRINT Trial

BACKGROUND

Black individuals have high incident diabetes risk, despite having paradoxically lower triglyceride and higher HDL (high-density lipoprotein) cholesterol levels. The basis of this is poorly understood. We evaluated the participants of SPRINT (Systolic Blood Pressure Intervention Trial) to assess the association of estimated European genetic ancestry with the risk of incident diabetes in self-identified Black individuals.

METHODS

Self-identified non-Hispanic Black SPRINT participants free of diabetes at baseline were included. Black participants were stratified into tertiles (T1-T3) of European ancestry proportions estimated using 106 biallelic ancestry informative genetic markers. The multivariable-adjusted association of European ancestry proportion with indices of baseline metabolic syndrome (ie, fasting plasma glucose, triglycerides, HDL cholesterol, body mass index, and blood pressure) was assessed. Multivariable-adjusted Cox regression determined the risk of incident diabetes (fasting plasma glucose ≥126 mg/dL or self-reported diabetes treatment) across tertiles of European ancestry proportion.

RESULTS

Among 2466 Black SPRINT participants, a higher European ancestry proportion was independently associated with higher baseline triglyceride and lower HDL cholesterol levels (P<0.001 for both). European ancestry proportion was not associated with baseline fasting plasma glucose, body mass index, and blood pressure (P>0.05). Compared with the first tertile, those in the second (hazard ratio, 0.64 [95% CI, 0.45-0.90]) and third tertiles (hazard ratio, 0.61 [95% CI, 0.44-0.89]) of the European ancestry proportion had a lower risk of incident diabetes. A 5% point higher European ancestry was associated with a 29% lower risk of incident diabetes (hazard ratio, 0.71 [95% CI, 0.55-0.93]). There was no evidence of a differential association between the European ancestry proportion tertiles and incident diabetes between those randomized to intensive versus standard blood pressure treatment.

CONCLUSIONS

The higher risk of incident diabetes in Black individuals may have genetic determinants in addition to adverse social factors. Further research may help understand the interplay between biological and social determinants of cardiometabolic health in Black individuals. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01206062.

African genetic diversity and adaptation inform a precision medicine agenda

The deep evolutionary history of African populations, since the emergence of modern humans more than 300,000 years ago, has resulted in high genetic diversity and considerable population structure. Selected genetic variants have increased in frequency due to environmental adaptation, but recent exposures to novel pathogens and changes in lifestyle render some of them with properties leading to present health liabilities. The unique discoverability potential from African genomic studies promises invaluable contributions to understanding the genomic and molecular basis of health and disease. Globally, African populations are understudied, and precision medicine approaches are largely based on data from European and Asian-ancestry populations, which limits the transferability of findings to the continent of Africa. Africa needs innovative precision medicine solutions based on African data that use knowledge and implementation strategies aligned to its climatic, cultural, economic and genomic diversity.

Genomic ancestry and metabolic syndrome in individuals with type 1 diabetes from an admixed population: a multicentre, cross-sectional study in Brazil

AIMS

To evaluate the relationship between self-reported colour-race, genomic ancestry, and metabolic syndrome in an admixed Brazilian population with type 1 diabetes.

METHODS

We included 1640 participants with type 1 diabetes. The proportions of European, African and Amerindian genomic ancestries were determined by 46 ancestry informative markers of insertion deletion. Two different sets of analyses were performed to determine whether self-reported colour-race and genomic ancestry were predictors of metabolic syndrome.

RESULTS

Metabolic syndrome was identified in 29.8% of participants. In the first model, the factors associated with metabolic syndrome were: female gender (odds ratio 1.95, P < 0.001); diabetes duration (odds ratio 1.04, P < 0.001); family history of type 2 diabetes (odds ratio 1.36, P = 0.019); and acanthosis nigricans (odds ratio 5.93, P < 0.001). Colour-race was not a predictive factor for metabolic syndrome. In the second model, colour-race was replaced by European genomic ancestry. The associated factors were: female gender (odds ratio 1.95, P < 0.001); diabetes duration (odds ratio 1.04, P < 0.001); family history of type 2 diabetes (odds ratio 1.39, P = 0.011); and acanthosis nigricans (odds ratio 6.12, P < 0.001). Physical exercise (≥3 times a week) was a protective factor (odds ratio 0.77, P = 0.041), and European genomic ancestry was not associated with metabolic syndrome but showed an odds ratio of 1.77 (P = 0.05).

CONCLUSIONS

Although a higher level of European genomic ancestry was observed among participants with metabolic syndrome in the univariate analysis, this association did not persist after multivariable adjustments. Further prospective studies in other highly admixed populations remain necessary to better evaluate whether the European ancestral component modulates the development of metabolic syndrome in type 1 diabetes.

Cardiometabolic Dysfunction Among U.S. Adolescents and Area-Level Poverty: Race/Ethnicity-Specific Associations

PURPOSE

To examine race/ethnicity-specific associations between area-level poverty and cardiometabolic dysfunction among U.S. adolescents.

METHODS

Data were from 10,415 adolescents aged 12-19 in the National Health and Nutrition Examination Survey (1999-2012), linked with census tract data on area-level poverty (the percent population living in poverty, grouped into race/ethnicity-specific quartiles). Cardiometabolic dysfunction was parameterized by summing z-scores of six cardiometabolic biomarkers, grouped into quintiles. Hierarchical ordinal models estimated overall and race/ethnicity specific associations. Posthoc analysis explored associations between area-level poverty and family poverty-to-income ratio.

RESULTS

Overall, compared to adolescents residing in areas with the lowest area-level poverty (i.e., first quartile), residents in third (OR 1.32, 95% CI 1.13, 1.53) and fourth (OR 1.27, 95% CI 1.08, 1.50) quartiles of area-level poverty experienced elevated odds of cardiometabolic dysfunction. Area-level poverty predicted cardiometabolic dysfunction between non-Hispanic white and Mexican American adolescents, but not between non-Hispanic black adolescents.

CONCLUSIONS

We found race/ethnicity-specific associations between area-level poverty and cardiometabolic dysfunction among U.S. adolescents, highlighting the moderating effect of race-ethnicity. Among non-Hispanic black adolescents, neither higher area-level nor family-level socioeconomic status is associated with cardiometabolic health, in contrast to non-Hispanic white adolescents. Similar associations among non-Hispanic white and Mexican American groups aligns with evidence of the Hispanic Paradox. Future studies of effect of area-level determinants of cardiometabolic dysfunction may consider race/ethnicity-specific associations.

Population specific genetic heterogeneity of familial hypercholesterolemia in South Africa

PURPOSE OF REVIEW

To describe the prevalence and population-specific genetic heterogeneity of familial hypercholesterolemia in South Africa.

RECENT FINDINGS

This review highlights the paucity of data on familial hypercholesterolemia in South Africa, and the urgent need to uncover the mutation profiles in lipid-associated genes, causing an increase in LDL-cholesterol in the different ethnic groups. Case reports and small studies have shown that familial hypercholesterolemia, although apparently uncommon, is present in black Africans.

SUMMARY

Local founder effects have led to an increased prevalence of familial hypercholesterolemia in several South African populations: Afrikaner founder mutations (c.681 C>G, c.1285 G>A, c.523 G>A), Ashkenazi founder mutation (c.654_656del) and possible Indian founder mutation (c.2054 C>T). Preliminary data in black Africans with elevated LDL-cholesterol identified a possible common mutation, c.137_142del. The South African multiethnic society and well described founder effects emphasize the need for differential approaches to diagnosis and management of familial hypercholesterolemia. Studies involving larger cohorts and inclusive of different ethnicities are paramount to establishing an accurate prevalence of familial hypercholesterolemia in black Africans, not only in South Africa but in the Sub-Saharan African region. It is clear that the estimated world prevalence of one in 250 cannot be generally applied across African populations.

Diversity and inclusion in genomic research: why the uneven progress?

Conducting genomic research in diverse populations has led to numerous advances in our understanding of human history, biology, and health disparities, in addition to discoveries of vital clinical significance. Conducting genomic research in diverse populations is also important in ensuring that the genomic revolution does not exacerbate health disparities by facilitating discoveries that will disproportionately benefit well-represented populations. Despite the general agreement on the need for genomic research in diverse populations in terms of equity and scientific progress, genomic research remains largely focused on populations of European descent. In this article, we describe the rationale for conducting genomic research in diverse populations by reviewing examples of advances facilitated by their inclusion. We also explore some of the factors that perpetuate the disproportionate attention on well-represented populations. Finally, we discuss ongoing efforts to ameliorate this continuing bias. Collaborative and intensive efforts at all levels of research, from the funding of studies to the publication of their findings, will be necessary to ensure that genomic research does not conserve historical inequalities or curtail the contribution that genomics could make to the health of all humanity.

Interethnic Differences in Serum Lipids and Implications for Cardiometabolic Disease Risk in African Ancestry Populations

African Americans generally have a healthier lipid profile (lower triglycerides and higher high-density lipoprotein cholesterol concentration) compared with those of other ethnicities. Paradoxically, African Americans do not experience a decreased risk of the cardiometabolic diseases that serum lipids are expected to predict. This review explores this mismatch between biomarker and disease among African ancestry individuals by investigating the presence of interethnic differences in the biological relationships underlying the serum lipids-disease association. This review also discusses the physiologic and genomic factors underlying these interethnic differences. Additionally, because of the importance of serum lipids in assessing disease risk, interethnic differences in serum lipids have implications for identifying African ancestry individuals at risk of cardiometabolic disease. Where possible, data from Africa is included, to further elucidate these ancestral differences in the context of a different environmental background.

Stress Measured by Allostatic Load Score Varies by Reason for Immigration: The Africans in America Study

OBJECTIVE

Reason for immigration as a biological stress has not been studied in Africans. Our goal was to determine in African immigrants, if biological stress measured by allostatic load score (ALS) varies by reason for immigration.

METHODS

Using an ALS which had been previously developed with the National Health and Nutrition Examination Survey (NHANES) data to assess stress due to racism and nativity, ALS was calculated in 85 African immigrants (67% male, age 42 ± 10 years). For confirmation, we tested five additional ALS also built from NHANES.

RESULTS

The two reasons for immigration which consistently had the lowest ALS were family reunification and lottery winner for self and immediate family. The other reasons for immigration such as study, asylum/refugee, and work had higher ALS. As reasons for immigration with the lowest ALS promoted family unity, they were combined (group 1) and the Africans who came for other reasons were combined (group 2). ALS in group 1 vs. group 2 was 1.96 ± 1.40 vs. 2.94 ± 1.87, P = 0.03.

CONCLUSIONS

Biological stress varies by reason for immigration and appears to be mitigated by maintaining family unity. Overall, reason for immigration is an important biographical data likely to influence health.

Gene-based sequencing identifies lipid-influencing variants with ethnicity-specific effects in African Americans

Although a considerable proportion of serum lipids loci identified in European ancestry individuals (EA) replicate in African Americans (AA), interethnic differences in the distribution of serum lipids suggest that some genetic determinants differ by ethnicity. We conducted a comprehensive evaluation of five lipid candidate genes to identify variants with ethnicity-specific effects. We sequenced ABCA1, LCAT, LPL, PON1, and SERPINE1 in 48 AA individuals with extreme serum lipid concentrations (high HDLC/low TG or low HDLC/high TG). Identified variants were genotyped in the full population-based sample of AA (n = 1694) and tested for an association with serum lipids. rs328 (LPL) and correlated variants were associated with higher HDLC and lower TG. Interestingly, a stronger effect was observed on a "European" vs. "African" genetic background at this locus. To investigate this effect, we evaluated the region among West Africans (WA). For TG, the effect size among WA was the same in AA with only African local ancestry (2-3% lower TG), while the larger association among AA with local European ancestry matched previous reports in EA (10%). For HDLC, there was no association with rs328 in AA with only African local ancestry or in WA, while the association among AA with European local ancestry was much greater than what has been observed for EA (15 vs. ∼ 5 mg/dl), suggesting an interaction with an environmental or genetic factor that differs by ethnicity. Beyond this ancestry effect, the importance of African ancestry-focused, sequence-based work was also highlighted by serum lipid associations of variants that were in higher frequency (or present only) among those of African ancestry. By beginning our study with the sequence variation present in AA individuals, investigating local ancestry effects, and seeking replication in WA, we were able to comprehensively evaluate the role of a set of candidate genes in serum lipids in AA.

Genetic epidemiology of type 2 diabetes and cardiovascular diseases in Africa

The burdens of type 2 diabetes (T2D) and cardiovascular diseases (CVD) are increasing in Africa. T2D and CVD are the result of the complex interaction between inherited characteristics, lifestyle, and environmental factors. The epidemic of obesity is largely behind the exploding global incidence of T2D. However, not all obese individuals develop diabetes and positive family history is a powerful risk factor for diabetes and CVD. Recent implementations of high throughput genotyping and sequencing approaches have advanced our understanding of the genetic basis of diabetes and CVD by identifying several genomic loci that were not previously linked to the pathobiology of these diseases. However, African populations have not been adequately represented in these global genomic efforts. Here, we summarize the state of knowledge of the genetic epidemiology of T2D and CVD in Africa and highlight new genomic initiatives that promise to inform disease etiology, public health and clinical medicine in Africa.