Genetic differences between the determinants of lipid profile phenotypes in African and European Americans: the Jackson Heart Study

Influence of Obesity on the Relationship of Cardiometabolic Risks Factors With Cardiovascular Disease in Older African and European Americans

PURPOSE

This study evaluated the impact of obesity on cardiometabolic risk factors (CRF) interrelationships and predictive efficiency of CVD development in older African (AA) and European Americans (EA).

DESIGN

A comparative research design evaluated CRF risk profile differences between participant groups.

SETTING

Seven neighborhoods in a southern US city.

SUBJECTS

A sample of 179 older AA (n = 128) and EA (n = 51) adults.

MEASURES

Non-fasting blood samples were evaluated for lipids and lipoproteins, glycosylated hemoglobin, systolic -(SBP) and diastolic blood pressure (DBP), body mass index (BMI), body fat percentage (BF%) and physical function.

ANALYSIS

Data were analysis with descriptive statistics, t-tests, and correlations.

RESULTS

AA were heavier than EA although all had above average age-appropriate fitness. Means and relationships between CRF and other variables were different (P < .05) based on race. Both AA (41.3 + 5.8) and EA (38.6 + 6.4) BF% were CRF risks. Holding BMI constant, CRF were generally not related, and the relationships were different for AA and EA. AA had a range of 13.0 to 27.2% more favorable values for cholesterol, HDL-C, and triglyceride. EA had favorable A1c (EA 5.8 vs AA 6.2%) values.

CONCLUSIONS

A limitation of this report is the small sample size. Although further research is warranted, these findings suggest population specific CRF selections would improve CVD prediction in AA.

LPL rs264, PROCR rs867186 and PDGF rs974819 Gene Polymorphisms in Patients with Unstable Angina

BACKGROUND

Coronary artery disease is caused by changes in the coronary arteries due to the atherosclerotic process and thrombotic changes. A very important role in the development of the atherosclerotic process in the coronary vessels is played by the inflammatory process and the immune response. Due to the important role of lipids and the coagulation process in the atherosclerotic process, research has also focused on genes affecting lipid metabolism and the coagulation system. Lipoprotein lipase (LPL) is an enzyme that metabolises lipids, hydrolysing triglycerides to produce free fatty acids and glycerol. Protein C (PC) is an essential component of coagulation and fibrinolysis. It is activated on the endothelial surface by the membrane-bound thrombin-thrombomodulin complex. Platelet-derived growth factor (PDGF) has a number of important functions in processes related to fibroblast and smooth muscle cell function. Due to their influence on lipid metabolism and coagulation processes, LPL, PROCR (endothelial cell protein C receptor) and PDGF may affect the atherosclerotic process and, thus, the risk of coronary heart disease. The aim of the study was to examine the associations between the LPL rs264, PROCR rs867186 and PDGF rs974819 gene polymorphisms and the risk of unstable angina and selected clinical parameters.

METHODS

The study included 232 patients with unstable angina and 144 healthy subjects as the control group. Genotyping was performed using real-time PCR.

RESULTS

There were no statistically significant differences in the distribution of the polymorphisms tested between the patients with unstable angina and the control subjects. The results showed associations between the PROCR rs867186 and PDGF rs974819 polymorphisms and some clinical parameters in patients with unstable angina. In patients with the PDGF rs974819 CC genotype, there were increased values for cholesterol and LDL serum levels in comparison with patients with the PDGF rs974819 CT and TT genotypes. In patients with the PROCR rs867186 AA genotype, HDL serum levels were lower than in patients with the GA genotype.

CONCLUSIONS

The results of our study did not show that the LPL rs264, PROCR rs867186 and PDGF rs974819 gene polymorphisms were significant risk factors for unstable angina in our population. The results of the study suggest that PDGF rs974819 and PROCR rs867186 may be associated with some parameters of lipid metabolism.

Cardiometabolic risk factors and cardiovascular disease predictions in older African and European Americans

Cardiometabolic (CMO) risks factors do not provide similar cardiovascular disease (CVD) predictions in young African (AA) and European Americans (EA) adults. Whether CMO risk predictions contribute to this disparity in older adults is unclear. We hypothesize that older AA CMO clustering pattern will be different from EA clustering patterns when determine with non-fasting lipid and lipoproteins. The participants were 106 older adults (66 AA and 40 EA) from a working/middle class neighborhood (income $46,364 – $80,904) in an urban North Carolina community. The participants were evaluated for CMO risk factors (total cholesterol, high- (HDL) and low-density lipoproteins (LDL), triglyceride (TG), glycosylated hemoglobin (HbA1c), systolic –SBP- and diastolic blood pressures -DBP), body mass index (BMI), body fat % (BF%) and timed up and go test (assessed falls risk and physical function). The AA participants were heavier, had higher BMI, BF%, and timed up and go values (p < 0.01). The data were evaluated for differences (t-test) and Pearson correlations for relationships. If data differ by p < 0.05 the data were significantly different. The AA had a 17.6 % higher HDL (64.7 vs 55.1 mg/dL – p < 0.05) and 7.6 % higher HbA1c (5.8 vs 5.4 % – p < 0.01) than EA. Higher HDL values in EA indicate lower CVD risks. The HDL paradox for AA (AA had higher HDL values, but greater CVD risks) was observed and the HbA1c difference may be misleading, as similar glucose values in AA tend to have higher HbA1c values. Lipid, lipoprotein, and blood pressure was not different between the races. AA had higher body composition and HDL values. Although future research on this topic with larger samples, dietary data and detailed descriptions of participations medications is warranted to validate findings from this study. These data suggest older AA and EA adults with similar environmental conditions have similar CMO risks when measures with none fasting blood samples. Since AA have a greater prevalence of CVD, these finding suggests that population specific CMO risk factor clustering may be more effective predictors of CVD for AA.

Metabolic Syndrome Components in a Nondiabetic Afro-Caribbean Population: Influence of Gender and Age

Background: Our aim was to describe the prevalence of metabolic syndrome (MetS) and its components among Afro-Caribbean adults without diabetes and cardiovascular complications. Methods: Participants were recruited from a Health Center in Guadeloupe, French West Indies. MetS was defined according to the NCEP ATP III. Prevalence of MetS and MetS components were compared across age groups and sex. The odds ratios (ORs) and 95% confidence intervals were obtained using logistic regression. Results: There were 1011 participants (68.8% women, mean age 47.8 ± 11.8 years). Prevalence of MetS was 17.9% (21.1% women, 10.8% men) and increased by age in women. High blood pressure had the highest prevalence among men and among women ≥60 years. Prevalence of abdominal obesity (AbO) was higher in women than in men. High triglyceride levels were uncommon at all ages and, men and women <40 years, compared with the other groups had higher prevalence of low high-density lipoprotein cholesterol (HDL-C) levels. With multiple logistic regression, compared with adults <40 years, those ≥60 years had the highest OR for prevalent hypertension 7.8 (4.8-12.8); P < 0.001, AbO 2.1 (1.3-3.3); P = 0.002 and high fasting blood glucose levels 5.5 (3.1-9.8); P < 0.001. They also had lower odds for having low HDL-C than the younger ones (G1: age <40 years). Among persons ≥60 years, OR for MetS was 1.9 (1.1-3.6); P = 0.013 compared with the referent group. Compared with men, women had higher odds of MetS 2.2 (1.5-3.3); P < 0.001. Conclusion: Women were more likely to have MetS than men and persons ≥60 years were significantly more likely to have MetS than persons <40 years. Preventive measures are required to reduce the prevalence of MetS.

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.

Genetic association of LPL rs326 with BMI among the Kuwaiti population

Supplemental Digital Content is available in the text.

Lipoprotein lipase is a key enzyme in lipid metabolism with reported variants associated with obesity, hypertension, type 2 diabetes, and coronary heart disease. This study was performed to investigate the association between common lipoprotein lipase single nucleotide polymorphisms and metabolic disorders in a sample of Kuwaiti cohort (n = 494). Five lipoprotein lipase variants (rs1801177, rs295, rs326, ss2137497749, and ss2137497750) across the lipoprotein lipase gene were genotyped by real-time PCR employing the TaqMan allele discrimination assay. Genotype, allelic frequencies, and Hardy-Weinberg Equilibrium were determined for each variant in the cohort followed by multivariate and logistic regression analysis. A novel finding was observed for the G allele of single nucleotide polymorphism rs326 which was associated with increased BMI after adjusting for age and sex (β = 1.04; 95% confidence interval = 0.15–1.94; P = 0.02). Moreover, a significant difference in the distribution of the minor C allele of rs295 among coronary heart disease subjects compared with noncoronary heart disease, however, this significance was diminished after controlling for age, sex, and BMI. This study demonstrated that lipoprotein lipase rs326 may be indicative for the increased risk of obesity and possibly rs295 for coronary heart disease. The findings are also in agreement with other reports suggesting that intronic variants are important genetic markers in association studies. The findings warrant further studies in a large cohort to confirm and validate the results presented.

What the Jackson Heart Study Has Taught Us About Diabetes and Cardiovascular Disease in the African American Community: a 20-year Appreciation

PURPOSE OF REVIEW

The burden of cardiometabolic diseases such as cardiovascular disease (CVD) and type 2 diabetes (T2D) is pronounced among African Americans. Research has shown that behavioral, social, metabolic, psychosocial, and genetic risk factors of CVD and T2D are closely interwoven. Approximately 20 years ago, the Jackson Heart Study (JHS) was established to investigate this constellation of risk factors.

RECENT FINDINGS

Findings from neighborhood studies emphasize the importance of social cohesion and physical environment in the context CVD and T2D risk. Socioeconomic status factors such as income and education were significant predictors for CVD and T2D. Behavioral studies indicate that modifiable risk factors such as smoking, physical inactivity, lack of sleep, and poor nutrition are associated with CVD risk and all-cause mortality. Mental health also was found to be associated with CVD and T2D. Genetic influences are associated with disease etiology. This review summarizes the joint contributions of CVD and cardiometabolic risk factors in an African American population.

Postprandial Metabolism and Physical Activity in Asians: A Narrative Review

The widespread benefits of physical activity in enhancing health and lowering the risk of non-communicable chronic diseases are well established across populations globally. Nevertheless, the prevalence of several lifestyle-related chronic diseases, including cardiovascular disease, varies markedly across countries and ethnicities. Direct ethnic comparative studies on the health benefits of physical activity are sparse and evidence-based physical activity guidelines are not ethnicity-specific. Indeed, physical activity guidelines in some Asian countries were developed primarily based on data from Western populations even though the magnitude of potential benefit may not be the same among different ethnic groups. Unfavorable diurnal perturbations in postprandial triglycerides and glucose are risk factors for cardiovascular disease. This narrative review summarizes differences in these risk factors primarily between individuals of Asian and white European descent but also within different Asian groups. Moreover, the variable effects of physical activity on mitigating risk factors among these ethnic groups are highlighted along with the underlying metabolic and hormonal factors that potentially account for these differences. Future ethnic comparative studies should include investigations in understudied ethnic groups, such as those of East Asian origin, given that the effectiveness of physical activity for ameliorating cardiovascular disease varies even among Asian groups.

FADS1 gene polymorphism(s) and fatty acid composition of serum lipids in adolescents

Polyunsaturated fatty acids (PUFA) influence many physiological functions. Associations have been found between single nucleotide polymorphisms (SNP) in the FADS1 (Fatty acid desaturase 1) gene and the relative abundance of PUFA in serum lipids. This study examines the relationship between two SNPs in the FADS1 gene (rs174546, rs174537) and the fatty acid (FA) composition of serum lipids in adolescents (13-18 years). We used DNA samples (670 children; 336 girls and 334 boys) from the Childhood Obesity Prevalence and Treatment (COPAT) project. Genomic DNA was extracted from peripheral blood leukocytes in whole blood samples. For genotype analysis, TaqMan SNP Genotyping assays (Applied Biosystems) were used. Fatty acid composition of serum lipids was assessed using gas chromatography. The T-statistic and regression were used for statistical evaluations. Minor allele T carriers in both SNPs had significant lower level of palmitic acid (16:0, phospholipids) and arachidonic acid (20:4[n-6], phospholipids) in both sexes. In girls, we found a significant positive association between minor allele T carriers and eicosadienoic acid (20:2[n-6], cholesteryl esters) in both SNPs. Being a minor allele T carrier was significantly positively associated with dihomo-γ-linolenic acid (20:3[n-6], phospholipids) in boys in both SNPs. SNPs (including rs174546, rs174537) in the FADS gene cluster should have impacted desaturase activity, which may contribute to different efficiency of PUFA synthesis.

Hypertension is associated with a variant in the RARRES2 gene in populations of Ouro Preto, Minas Gerais, Brazil: a cross-sectional study

BACKGROUND

Arterial hypertension (AH) is implicated in vascular health and contributes significantly to cardiovascular morbidity and mortality. In addition to the contribution of usual risk factors for AH, elucidating the influence of genetic factors is a promising area of investigation. Therefore, we evaluated the association between AH and cardiovascular risk factors (CVRFs) and genetic polymorphisms in communities in Southeast Brazil.

METHODS

A total of 515 adults aged 18-91 years, who were cross-sectionally assessed between 2015-2016, were included. Demographic, clinical, behavioral, anthropometric characteristics, and laboratory parameters and 12 single nucleotide polymorphisms in seven candidate genes involved in cardiovascular risk (RARRES2, AGT, NOS3, GNB3, APOE, APOB, APOC3, LDLR, and PPARG) were evaluated, with AH as the outcome. Sex, age, and laboratory parameters were considered the main confounding factors.

RESULTS

There was a significant association between age >60 years (odds ratio [OR] =6.74), alcohol dependence (OR=3.84), smoking (OR=1.74), overweight (OR=1.74), high plasma triglyceride (TG) levels (OR=1.98) and low high-density lipoprotein (HDL-c) (OR=6.22), diabetes (OR=3.68), and insulin resistance (OR=2.40) and AH. A significant association was observed between rs4721 in RARRES2 and AH. The T allele in homozygosis was a potent chance modifier for AH. The highest chance gradients for AH were characterized by the presence of the TT genotype and DMT2 (OR=9.70), high TG (OR=6.26), low HDL-c (OR=8.20), and age more than 60 years (OR=9.96).

CONCLUSION

The interaction of the T allele of the rs4721 polymorphism in RARRES2 with CVRFs may predispose carriers to a higher cardiovascular risk.

Common genetic variation in circadian clock genes are associated with cardiovascular risk factors in an African American and Hispanic/Latino cohort

Misalignment of the internal circadian time with external physical time due to environmental factors or due to genetic variantion in circadian clock genes has been associated with increased incidence of cardiovascular risk factors. Common genetic variation in circadian genes in the United States have been identified predominantly in European ancestry individuals. We therefore examined the association between circadian clock single nucleotide polymorphisms (SNPs) in Clock, Cry1, Cry2, Bmal1 and Per3 genes and cardiovascular risk factors in African Americans and Hispanic/Latinos. We analyzed 17 candidate circadian SNPs in 1,166 subjects who self-identified as African-American or Hispanic/Latino and were enrolled in the UIC Cohort of Patients, Family and Friends. We found significant differences in the minor allele frequencies between African American and Hispanic/Latino subjects. Our analyses also established ethnic-specific SNPs that are associated with cardiovascular risk factors. In Hispanic/Latinos, the rs6850524 in Clock was associated with increased risk for hypertension, meanwhile rs12649507, rs4864546, and rs4864548 reduced the risk, also rs8192440 (Cry1) reduced the risk for type 2 diabetes. In African Americans, the Clock rs1801260 and rs6850524 were negatively associated with the presence of obesity; Bmal1 rs11022775 reduced the risk for dyslipidemia; and the Cry2 rs2292912 increased the risk for dyslipidemia and diabetes. Genetic variations in candidate circadian-clock genes are associated with risk factors for cardiovascular disease in African-Americans and Hispanic/Latinos. Our findings may help to improve cardiovascular risk assessment as well as better understand how circadian misalignment impacts cardiovascular risk in diverse populations.

Identification of disease-associated loci using machine learning for genotype and network data integration

Motivation

Integration of different omics data could markedly help to identify biological signatures, understand the missing heritability of complex diseases and ultimately achieve personalized medicine. Standard regression models used in Genome-Wide Association Studies (GWAS) identify loci with a strong effect size, whereas GWAS meta-analyses are often needed to capture weak loci contributing to the missing heritability. Development of novel machine learning algorithms for merging genotype data with other omics data is highly needed as it could enhance the prioritization of weak loci.

Results

We developed cNMTF (corrected non-negative matrix tri-factorization), an integrative algorithm based on clustering techniques of biological data. This method assesses the inter-relatedness between genotypes, phenotypes, the damaging effect of the variants and gene networks in order to identify loci-trait associations. cNMTF was used to prioritize genes associated with lipid traits in two population cohorts. We replicated 129 genes reported in GWAS world-wide and provided evidence that supports 85% of our findings (226 out of 265 genes), including recent associations in literature (NLGN1), regulators of lipid metabolism (DAB1) and pleiotropic genes for lipid traits (CARM1). Moreover, cNMTF performed efficiently against strong population structures by accounting for the individuals’ ancestry. As the method is flexible in the incorporation of diverse omics data sources, it can be easily adapted to the user’s research needs.

Availability and implementation

An R package (cnmtf) is available at https://lgl15.github.io/cnmtf_web/index.html.

Supplementary information

Supplementary data are available at Bioinformatics online.

High levels of chemerin associated with variants in the NOS3 and APOB genes in rural populations of Ouro Preto, Minas Gerais, Brazil

Chemerin is an adipokine that has been associated with components of metabolic syndrome. It has been described to affect adipocyte metabolism and inflammatory responses in adipose tissue, as well as the systemic metabolism of lipids and glucose. Few epidemiological studies have evaluated classical and genetics cardiovascular risk factors (CVRFs) in the mixed adult rural population in Brazil. Therefore, the present study explored possible associations between CVRFs and chemerin. This cross-sectional study included 508 adults from the rural localities of Lavras Novas, Chapada, and Santo Antônio do Salto in Ouro Preto, Minas Gerais, Southeast Brazil. Demographic, behavioral, clinical, biochemical, anthropometric variables, and 12 single nucleotide polymorphisms (SNPs) linked with metabolic syndrome phenotypes were evaluated for associations with chemerin level. There was a significant association of high triglyceride levels [odds ratio (OR)=1.91, 95%CI: 1.23-2.98], insulin resistance (OR=1.82, 95%CI: 1.03-3.22), age (OR=1.64, 95%CI: 1.08-2.49), and sex (OR=1.99, 95%CI: 1.35-2.95) with high levels of chemerin. High chemerin levels were significantly associated with the genetic polymorphisms rs693 in the APOB gene (OR=1.50, 95%CI: 1.03-2.19) and rs1799983 in the NOS3 gene (OR=1.46, 95%CI: 1.01-2.12) for the AA and GT+TT genotypes, respectively. In the concomitant presence of genotypes AA of rs693 and GT+TT of rs1799983, the chance of presenting high levels of chemerin showed a 2.21-fold increase (95%CI: 1.25-3.88) compared to the reference genotype. The development of classical CVRFs in this population may be influenced by chemerin and by two risk genotypes characteristic of variants in well-studied genes for hypertension and dyslipidemia.

Minority-centric meta-analyses of blood lipid levels identify novel loci in the Population Architecture using Genomics and Epidemiology (PAGE) study

Lipid levels are important markers for the development of cardio-metabolic diseases. Although hundreds of associated loci have been identified through genetic association studies, the contribution of genetic factors to variation in lipids is not fully understood, particularly in U.S. minority groups. We performed genome-wide association analyses for four lipid traits in over 45,000 ancestrally diverse participants from the Population Architecture using Genomics and Epidemiology (PAGE) Study, followed by a meta-analysis with several European ancestry studies. We identified nine novel lipid loci, five of which showed evidence of replication in independent studies. Furthermore, we discovered one novel gene in a PrediXcan analysis, minority-specific independent signals at eight previously reported loci, and potential functional variants at two known loci through fine-mapping. Systematic examination of known lipid loci revealed smaller effect estimates in African American and Hispanic ancestry populations than those in Europeans, and better performance of polygenic risk scores based on minority-specific effect estimates. Our findings provide new insight into the genetic architecture of lipid traits and highlight the importance of conducting genetic studies in diverse populations in the era of precision medicine.

Genomics of Reproductive Traits and Cardiometabolic Disease Risk in African American Women

BACKGROUND

Age at menarche and age at natural menopause occur significantly earlier in African American women than in other ethnic groups. African American women also have twice the prevalence of cardiometabolic disorders related to the timing of these reproductive traits.

OBJECTIVES

The objectives of this integrative review were to (a) summarize the genome-wide association studies of reproductive traits in African American women, (b) identify genes that overlap with reproductive traits and cardiometabolic risk factors in African American women, and (c) propose biological mechanisms explaining the link between reproductive traits and cardiometabolic risk factors.

METHODS

PubMed was searched for genome-wide association studies of genes associated with reproductive traits in African American women. After extracting and summarizing the primary genes, we examined whether any of the associations with reproductive traits had also been identified with cardiometabolic risk factors in African American women.

RESULTS

Seven studies met the inclusion criteria. Associations with both reproductive and cardiometabolic traits were reported in or near the following genes: FTO, SEC16B, TMEM18, APOE, PHACTR1, KCNQ1, LDLR, PIK3R1, and RORA. Biological pathways implicated include body weight regulation, vascular homeostasis, and lipid metabolism.

DISCUSSION

A better understanding of the genetic basis of reproductive traits in African American women may provide insight into the biological mechanisms linking variation in these traits with increased risk for cardiometabolic disorders in this population.

Genetic association of LPL rs1121923 and rs258 with plasma TG and VLDL levels

Lipoprotein lipase (LPL) is a rate-limiting enzyme for the hydrolysis of triglycerides (TG). Hundreds of genetic variants including single nucleotide polymorphisms have been identified across the 30Kb gene locus on chromosome 8q22. Several of these variants have been demonstrated to have genetic association with lipid level variation but many remain unresolved. Controversial reports on the genetic association of variants among different populations pose a challenge to which variants are informative. This study aimed to investigate "common" LPL variants (rs1121923, rs258, rs328, rs13702) and their possible role in plasma lipid level. Genotyping was performed using Realtime PCR. Based on the observed genotypes, the minor allele frequencies were A: 0.065 for rs1121923; C: 0.379 for rs258; G: 0.087 for rs328 and C: 0.337 for rs13702. Using linear regression, a lowering effect of rs1121923 (p = 0.024) on TG levels (-0.14 B coefficient: CI: -0.27--0.019) and rs258 (p = 0.013) on VLDL levels (B: -0.046; CI: -0.082--0.009) was observed indicating a "protective" role for the two variants. Moreover, the findings indicate the potential for including rs1121923 and rs258 in diagnostic panels for use as an estimator of "risk" scores for dyslipidemia.

Nutrigenetic Contributions to Dyslipidemia: A Focus on Physiologically Relevant Pathways of Lipid and Lipoprotein Metabolism

Cardiovascular disease (CVD) remains the number one cause of death worldwide, and dyslipidemia is a major predictor of CVD mortality. Elevated lipid concentrations are the result of multiple genetic and environmental factors. Over 150 genetic loci have been associated with blood lipid levels. However, not all variants are present in pathways relevant to the pathophysiology of dyslipidemia. The study of these physiologically relevant variants can provide mechanistic understanding of dyslipidemia and identify potential novel therapeutic targets. Additionally, dietary fatty acids have been evidenced to exert both positive and negative effects on lipid profiles. The metabolism of both dietary and endogenously synthesized lipids can be affected by individual genetic variation to produce elevated lipid concentrations. This review will explore the genetic, dietary, and nutrigenetic contributions to dyslipidemia.

Genetic variants influencing lipid levels and risk of dyslipidemia in Chinese population

Recently, several human genetic and genomewide association studies (GWAS) have discovered many genetic loci that are associated with the concentration of the blood lipids. To confirm the reported loci in Chinese population, we conducted a crosssection study to analyse the association of 25 reported SNPs, genotyped by the ABI SNaPshot method, with the blood levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG) in 1900 individuals by multivariate analysis. Logistic regression was applied to assess the association of the genetic loci with the risk of different types of dyslipidemia. Our study has convincingly identified that 12 of 25 studied SNPs were strongly associated with one or more blood lipid parameters (TC, LDL, HDL and TG). Among the 12 associated SNPs, 10 significantly influence the risk of one or more types of dyslipidemia.We firstly found four SNPs (rs12654264 in HMGCR; rs2479409 in PCSK9; rs16996148 in CILP2, PBX4; rs4420638 in APOE-C1-C4-C2) robustly and independently associate with four types of dyslipidemia (MHL, mixed hyperlipidemia; IHTC, isolated hypercholesterolemia; ILH, isolated low HDL-C; IHTG, isolated hypertriglyceridemia). Our results suggest that genetic susceptibility is different on the same candidate locus for the different populations. Meanwhile, most of the reported genetic variants strongly influence one or more plasma lipid levels and the risk of dyslipidemia in Chinese population.

Using Full Genomic Information to Predict Disease: Breaking Down the Barriers Between Complex and Mendelian Diseases

While sequence-based genetic tests have long been available for specific loci, especially for Mendelian disease, the rapidly falling costs of genome-wide genotyping arrays, whole-exome sequencing, and whole-genome sequencing are moving us toward a future where full genomic information might inform the prognosis and treatment of a variety of diseases, including complex disease. Similarly, the availability of large populations with full genomic information has enabled new insights about the etiology and genetic architecture of complex disease. Insights from the latest generation of genomic studies suggest that our categorization of diseases as complex may conceal a wide spectrum of genetic architectures and causal mechanisms that ranges from Mendelian forms of complex disease to complex regulatory structures underlying Mendelian disease. Here, we review these insights, along with advances in the prediction of disease risk and outcomes from full genomic information.

Joint Influence of SNPs and DNA Methylation on Lipids in African Americans From Hypertensive Sibships

INTRODUCTION

Plasma concentrations of lipids (i.e., total cholesterol, high-density cholesterol, low-density cholesterol, and triglycerides) are amenable to therapeutic intervention and remain important factors for assessing risk of cardiovascular diseases. Some of the observed variability in serum lipid concentrations has been associated with genetic and epigenetic variants among cohorts with European ancestry (EA). Serum lipid levels have also been associated with genetic variants in multiethnic populations.

METHODS

The purpose of this study was to determine whether single-nucleotide polymorphisms (SNPs) and DNA methylation (DNAm) differences contribute to lipid variation among African Americans ([AAs], N = 739) in the Genetic Epidemiology Network of Arteriopathy (GENOA) study.

RESULTS

Previous meta-analyses identified 161 SNPs that are associated with lipid traits in populations of EA. We evaluated these SNPs and 66 DNAm sites within the genes containing the SNPs in the GENOA cohort using linear mixed-effects modeling. We did not identify any significant associations of SNPs or DNAm with serum lipid levels. These results suggest that the SNPs identified as being significant for lipid levels through the EA genome-wide association studies may not be significant across AA populations.

CONCLUSIONS

Reductions in morbidity and mortality due to variation in lipids among AAs may be achieved through a better understanding of the genetic and epigenetic factors associated with serum lipid levels for early and appropriate screening. Further large-scale studies specifically within AA and other non-EA populations are warranted.

A novel LPL intronic variant: g.18704C>A identified by re-sequencing Kuwaiti Arab samples is associated with high-density lipoprotein, very low-density lipoprotein and triglyceride lipid levels

The role interethnic genetic differences play in plasma lipid level variation across populations is a global health concern. Several genes involved in lipid metabolism and transport are strong candidates for the genetic association with lipid level variation especially lipoprotein lipase (LPL). The objective of this study was to re-sequence the full LPL gene in Kuwaiti Arabs, analyse the sequence variation and identify variants that could attribute to variation in plasma lipid levels for further genetic association. Samples (n = 100) of an Arab ethnic group from Kuwait were analysed for sequence variation by Sanger sequencing across the 30 Kb LPL gene and its flanking sequences. A total of 293 variants including 252 single nucleotide polymorphisms (SNPs) and 39 insertions/deletions (InDels) were identified among which 47 variants (32 SNPs and 15 InDels) were novel to Kuwaiti Arabs. This study is the first to report sequence data and analysis of frequencies of variants at the LPL gene locus in an Arab ethnic group with a novel “rare” variant (LPL:g.18704C>A) significantly associated to HDL (B = -0.181; 95% CI (-0.357, -0.006); p = 0.043), TG (B = 0.134; 95% CI (0.004–0.263); p = 0.044) and VLDL (B = 0.131; 95% CI (-0.001–0.263); p = 0.043) levels. Sequence variation in Kuwaiti Arabs was compared to other populations and was found to be similar with regards to the number of SNPs, InDels and distribution of the number of variants across the LPL gene locus and minor allele frequency (MAF). Moreover, comparison of the identified variants and their MAF with other reports provided a list of 46 potential variants across the LPL gene to be considered for future genetic association studies. The findings warrant further investigation into the association of g.18704C>A with lipid levels in other ethnic groups and with clinical manifestations of dyslipidemia.

Clinical and Histologic Characterization of Nonalcoholic Steatohepatitis in African American Patients

OBJECTIVE

There has been a widespread misconception among physicians that African Americans are protected from developing nonalcoholic steatohepatitis (NASH). However, a formal histologic and metabolic comparison against well-matched Caucasians has never been performed.

RESEARCH DESIGN AND METHODS

Sixty-seven African American patients were matched 2:1 to Caucasians (n = 134) for age, sex, BMI, hemoglobin A_1c, and prevalence of type 2 diabetes mellitus (T2DM). Screening for NASH included measurement of intrahepatic triglyceride content by proton MRS (¹H-MRS), followed by a liver biopsy if patients had hepatic steatosis. Insulin resistance was estimated during an oral glucose tolerance test using the Matsuda Index.

RESULTS

Compared with Caucasians, African American patients had a lower intrahepatic triglyceride content (mean ± SD 6.1 ± 6.8% vs. 9.4 ± 7.5%, P = 0.007) and the presence of nonalcoholic fatty liver disease (NAFLD) was less common (25.0% vs. 51.9%, P = 0.003). However, prevalence of NASH was not different between ethnicities in patients with NAFLD (57.1% vs. 73.3%, P = 0.12). Moreover, they showed similar severity in each of the individual histologic parameters (inflammation, ballooning, and fibrosis). Among patients with NAFLD, insulin resistance was similar between both ethnic groups (Matsuda Index: 3.3 ± 1.8 vs. 3.1 ± 1.9, P = 0.61; adipose tissue insulin resistance [Adipo-IR] index: 5.7 ± 4.6 vs. 6.4 ± 4.7 mmol/L ⋅ µU/mL, P = 0.53) but appeared to be worse in African American versus Caucasian patients without NAFLD (Matsuda Index: 4.9 ± 3.6 vs. 7.0 ± 4.9, P = 0.11; Adipo-IR: 3.9 ± 2.8 vs. 2.7 ± 2.3 mmol/L ⋅ µU/mL, P = 0.06). African American patients also had lower plasma triglycerides and higher HDL cholesterol, independent of the severity of intrahepatic triglyceride.

CONCLUSIONS

Although African Americans have lower intrahepatic triglyceride accumulation, once NAFLD develops, NASH occurs as frequently, and as severe, as in Caucasian patients. Therefore, African Americans with NAFLD should be screened for NASH with the same degree of clinical resolve as in Caucasian patients.

Lipoprotein Lipase Expression in Chronic Lymphocytic Leukemia: New Insights into Leukemic Progression

Lipoprotein lipase (LPL) is a central enzyme in lipid metabolism. Due to its catalytic activity, LPL is involved in metabolic pathways exploited by various solid and hematologic malignancies to provide an extra energy source to the tumor cell. We and others described a link between the expression of LPL in the tumor cell and a poor clinical outcome of patients suffering Chronic Lymphocytic Leukemia (CLL). This leukemia is characterized by a slow accumulation of mainly quiescent clonal CD5 positive B cells that infiltrates secondary lymphoid organs, bone marrow and peripheral blood. Despite LPL being found to be a reliable molecular marker for CLL prognosis, its functional role and the molecular mechanisms regulating its expression are still matter of debate. Herein we address some of these questions reviewing the current state of the art of LPL research in CLL and providing some insights into where currently unexplored questions may lead to.

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.

Subtypes of Native American ancestry and leading causes of death: Mapuche ancestry-specific associations with gallbladder cancer risk in Chile

Latin Americans are highly heterogeneous regarding the type of Native American ancestry. Consideration of specific associations with common diseases may lead to substantial advances in unraveling of disease etiology and disease prevention.

Here we investigate possible associations between the type of Native American ancestry and leading causes of death. After an aggregate-data study based on genome-wide genotype data from 1805 admixed Chileans and 639,789 deaths, we validate an identified association with gallbladder cancer relying on individual data from 64 gallbladder cancer patients, with and without a family history, and 170 healthy controls. Native American proportions were markedly underestimated when the two main types of Native American ancestry in Chile, originated from the Mapuche and Aymara indigenous peoples, were combined together. Consideration of the type of Native American ancestry was crucial to identify disease associations. Native American ancestry showed no association with gallbladder cancer mortality (P = 0.26). By contrast, each 1% increase in the Mapuche proportion represented a 3.7% increased mortality risk by gallbladder cancer (95%CI 3.1–4.3%, P = 6×10⁻²⁷). Individual-data results and extensive sensitivity analyses confirmed the association between Mapuche ancestry and gallbladder cancer. Increasing Mapuche proportions were also associated with an increased mortality due to asthma and, interestingly, with a decreased mortality by diabetes. The mortality due to skin, bladder, larynx, bronchus and lung cancers increased with increasing Aymara proportions. Described methods should be considered in future studies on human population genetics and human health. Complementary individual-based studies are needed to apportion the genetic and non-genetic components of associations identified relying on aggregate-data.

A lot of attention has been paid to Latino heterogeneity related to individual proportions of Native American, European and African ancestry. The importance of the type of Native American ancestry for health, however, has hardly been studied. Here we examined genetic data from 2,039 admixed Chileans to investigate possible associations between top causes of death and the two major types of Native American ancestry in Chile. Our findings demonstrate the necessity of suitable surrogates for ancestry estimation which mirror the actual composition of the study population, and the advantage of considering fine-scale Latino heterogeneity for unraveling of disease etiology and personalized healthcare.

Genetic architecture of age-related cognitive decline in African Americans

OBJECTIVE

To identify genetic risk factors associated with susceptibility to age-related cognitive decline in African Americans (AAs).

METHODS

We performed a genome-wide association study (GWAS) and an admixture-mapping scan in 3,964 older AAs from 5 longitudinal cohorts; for each participant, we calculated a slope of an individual's global cognitive change from neuropsychological evaluations. We also performed a pathway-based analysis of the age-related cognitive decline GWAS.

RESULTS

We found no evidence to support the existence of a genomic region which has a strongly different contribution to age-related cognitive decline in African and European genomes. Known Alzheimer disease (AD) susceptibility variants in the ABCA7 and MS4A loci do influence this trait in AAs. Of interest, our pathway-based analyses returned statistically significant results highlighting a shared risk from lipid/metabolism and protein tyrosine signaling pathways between cognitive decline and AD, but the role of inflammatory pathways is polarized, being limited to AD susceptibility.

CONCLUSIONS

The genetic architecture of aging-related cognitive in AA individuals is largely similar to that of individuals of European descent. In both populations, we note a surprising lack of enrichment for immune pathways in the genetic risk for cognitive decline, despite strong enrichment of these pathways among genetic risk factors for AD.

The future of n-3 polyunsaturated fatty acid therapy

PURPOSE OF REVIEW

This article focuses on the potential role by which a complex mixture of omega-3 fatty acids (OM3-FAs) may beneficially modify cardiovascular risk by modifying the cholesterol composition of atherogenic lipoproteins. This hypothesis is being tested in the STRENGTH trial, which is enrolling 13 000 patients on statins at high cardiovascular risk with hypertriglyceridemia and low HDL cholesterol (HDL-C) treated with an OM3-carboxylic acid.

RECENT FINDINGS

Complex mixtures of OM3-FAs containing predominately eicosapentanoic acid and docosahexanoic acid in combination with statins lowers non-HDL by reducing triglyceride-rich lipoprotein cholesterol (TRL-C) while shifting small LDL cholesterol (LDL-C) to large LDL-C. Recent genomic and epidemiological studies have implicated TRL-C and small LDL-C as causal for cardiovascular disease. Therefore OM3-FAs containing both eicosapentanoic acid and docosahexanoic acid in combination with statins may beneficially modify the high residual risk for patients with hypertriglyceridemia and low HDL-C.

SUMMARY

Although outcome trials are underway, subgroup analyses of data from previous randomized controlled trials are suggestive of a reduction in coronary artery disease and atherosclerotic cardiovascular disease event rates with triglyceride and TRL-C lowering therapies, particularly if accompanied by low HDL-C. Although the limitations of such data are acknowledged, clinicians must make treatment decisions while awaiting more definitive results from well-designed large-scale randomized controlled trials.

Genetic and Environmental Biomarkers Associated with Triglyceride Levels in Two Groups of Slovak Women

OBJECTIVE

This study analyzed the association between the MLXIPL gene polymorphism (rs3812316) and triglyceride (TG) levels and selected environmental biomarkers in Slovak women at risk for cardiovascular disease compared to a reference sample.

MATERIALS AND METHODS

The studied sample consisted of 200 women at cardiovascular risk (mean age 52.96 ± 6.01 years) and 244 healthy women (mean age 47.52 ± 5.34 years). Participants gave details of their health and lifestyle during their medical examination, and peripheral blood samples were used for biochemical analyses and DNA genotyping. A nested polymerase chain reaction-restriction fragment length polymorphism assay was used to detect the rs 3812316 SNP.

RESULTS

We determined that there were significantly different genotype distributions in two TG categories: (1) subjects with normal TG values had a significantly higher G allele frequency than those with elevated TG levels (χ² = 6.1556, df = 2, p = 0.046); and (2) the rare G allele frequency was 0.11 in the cardiovascular risk group and 0.15 in the reference group. Binary regression analysis showed that women with at least one G allele had a significantly lower relative risk of hypertriglyceridemia than women with the CC genotype (OR = 0.399, p = 0.022, 95% CI = 0.182-0.876).

CONCLUSION

This cross-sectional study suggests that MLXIPL rs3812316 genotypes may be associated with TG levels. However, further analysis is advisable because of study limitations.

Dyslipidemia according to gender and race: The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

BACKGROUND

There is little information regarding lipid profiles of racially mixed populations. Differently from other Latin American countries, the proportion of African ancestry is much higher in Brazil.

OBJECTIVE

Verify whether there are differences in the lipid profile between black and white subjects and if people with mixed ancestry have a pattern more closely resembling whites or blacks.

METHODS

A total of 15,105 civil servants aged 35-74 years from the ELSA-Brasil study had their fasting lipid profile determined. Race/skin color was self-reported as white, mixed, black, Asian, or indigenous. Dyslipidemia subtypes were classified as high triglycerides (TG) (≥150 mg/dL), low HDL-C (<40 [men] and <50 [women] mg/dL), and high LDL-C (≥130 mg/dL or ever taking lipid-lowering agents). The adjusted odds ratios (95% confidence interval) for dyslipidemia were calculated for each racial group using white participants as the reference group by logistic regression.

RESULTS

Elevated concentrations in LDL-C and TG and low-HDL-C had a lower prevalence in the black group compared with whites after multivariate adjustment including adiposity and socioeconomic status. For women and men, respectively, the odds ratios (95% confidence interval) for high LDL-C are 0.94 (0.89-0.99) and 0.93 (0.87-0.99); for high TG, 0.63 (0.54-0.74) and 0.92 (0.84-1.00); and for low HDL-C, 0.77 (0.66-0.91) and 0.78 (0.64-0.94). The mixed race group presented a pattern of dyslipidemia closer to white than to black subjects.

CONCLUSIONS

Blacks in comparison with whites had lipid concentrations that are associated with a lower risk of atherosclerotic cardiovascular disease. The mixed racial group had lipid concentrations closer to the white grouping.

Vitamin D Receptor Gene Polymorphisms Are Associated with Abdominal Visceral Adipose Tissue Volume and Serum Adipokine Concentrations but Not with Body Mass Index or Waist Circumference in African Americans: The Jackson Heart Study

BACKGROUND

The biological actions of vitamin D are mediated through the vitamin D receptor (VDR). Single-nucleotide polymorphisms (SNPs) in the VDR gene have been previously associated with adiposity traits. However, to our knowledge, few studies have included direct measures of adiposity and adipokine concentrations.

OBJECTIVE

We examined the association of tagging SNPs in the VDR gene with multiple adiposity measures, including waist circumference (WC), body mass index (BMI), body fat percentage, subcutaneous and visceral adipose tissue (VAT) volume, and serum adipokine (adiponectin and leptin) concentrations in adult African Americans (AAs).

METHODS

Data from 3020 participants (61.9% women; mean age, 54.6 y) from the Jackson Heart Study were used for this analysis. Forty-five tag SNPs were chosen with the use of genotype data from the International HapMap project. We used linear regression to test the associations of imputed VDR SNPs with each of the traits, adjusted for age, sex, educational status, physical activity, smoking, alcohol intake, serum vitamin D concentration, European ancestry, and multiple testing.

RESULTS

The G allele of the SNP rs4328262 remained associated with increased VAT volume after multiple testing correction (β = 45.7; P < 0.001). The A allele of another SNP (rs11574070) was nominally associated with body fat percentage (β = 0.96; P = 0.002). None of the VDR SNPs analyzed showed any link with WC or BMI. The A allele of rs2228570 (β = 0.08; P = 0.001) for men and the T allele of rs2853563 (β = 0.04; P < 0.001) for women remained positively associated with serum adiponectin concentrations after multiple testing correction.

CONCLUSION

Although we did not find any association for anthropometric measures, we did observe associations of VDR variants with serum adipokines and with the more metabolically active fat, VAT. Therefore, our findings demonstrate a possible role of VDR variants in regulating adipose tissue activity and adiposity among AAs.

Trimethylamine N-Oxide and Cardiovascular Events in Hemodialysis Patients

Cardiovascular disease causes over 50% of the deaths in dialysis patients, and the risk of death is higher in white than in black patients. The underlying mechanisms for these findings are unknown. We determined the association of the proatherogenic metabolite trimethylamine N-oxide (TMAO) with cardiovascular outcomes in hemodialysis patients and assessed whether this association differs by race. We measured TMAO in stored serum samples obtained 3-6 months after randomization from a total of 1232 white and black patients of the Hemodialysis Study, and analyzed the association of TMAO with cardiovascular outcomes using Cox models adjusted for potential confounders (demographics, clinical characteristics, comorbidities, albumin, and residual kidney function). Mean age of the patients was 58 years; 35% of patients were white. TMAO concentration did not differ between whites and blacks. In whites, 2-fold higher TMAO associated with higher risk (hazard ratio [95% confidence interval]) of cardiac death (1.45 [1.24 to 1.69]), sudden cardiac death [1.70 (1.34 to 2.15)], first cardiovascular event (1.15 [1.01 to 1.32]), and any-cause death (1.22 [1.09 to 1.36]). In blacks, the association was nonlinear and significant only for cardiac death among patients with TMAO concentrations below the median (1.58 [1.03 to 2.44]). Compared with blacks in the same quintile, whites in the highest quintile for TMAO (≥135 μM) had a 4-fold higher risk of cardiac or sudden cardiac death and a 2-fold higher risk of any-cause death. We conclude that TMAO concentration associates with cardiovascular events in hemodialysis patients but the effects differ by race.

Causal Role of Alcohol Consumption in an Improved Lipid Profile: The Atherosclerosis Risk in Communities (ARIC) Study

INTRODUCTION

Health benefits of low-to-moderate alcohol consumption may operate through an improved lipid profile. A Mendelian randomization (MR) approach was used to examine whether alcohol consumption causally affects lipid levels.

METHODS

This analysis involved 10,893 European Americans (EA) from the Atherosclerosis Risk in Communities (ARIC) study. Common and rare variants in alcohol dehydrogenase and acetaldehyde dehydrogenase genes were evaluated for MR assumptions. Five variants, residing in the ADH1B, ADH1C, and ADH4 genes, were selected as genetic instruments and were combined into an unweighted genetic score. Triglycerides (TG), total cholesterol, high-density lipoprotein cholesterol (HDL-c) and its subfractions (HDL2-c and HDL3-c), low-density lipoprotein cholesterol (LDL-c), small dense LDL-c (sdLDL-c), apolipoprotein B (apoB), and lipoprotein (a) (Lp(a)) levels were analyzed.

RESULTS

Alcohol consumption significantly increased HDL2-c and reduced TG, total cholesterol, LDL-c, sdLDL-c, and apoB levels. For each of these lipids a non-linear trend was observed. Compared to the first quartile of alcohol consumption, the third quartile had a 12.3% lower level of TG (p < 0.001), a 7.71 mg/dL lower level of total cholesterol (p = 0.007), a 10.3% higher level of HDL2-c (p = 0.007), a 6.87 mg/dL lower level of LDL-c (p = 0.012), a 7.4% lower level of sdLDL-c (p = 0.037), and a 3.5% lower level of apoB (p = 0.058, poverall = 0.022).

CONCLUSIONS

This study supports the causal role of regular low-to-moderate alcohol consumption in increasing HDL2-c, reducing TG, total cholesterol, and LDL-c, and provides evidence for the novel finding that low-to-moderate consumption of alcohol reduces apoB and sdLDL-c levels among EA. However, given the nonlinearity of the effect of alcohol consumption, even within the range of low-to-moderate drinking, increased consumption does not always result in a larger benefit.

Bioanalytical techniques in nontargeted clinical lipidomics

Lipidomic analysis aims at comprehensive characterization of molecular lipids in biological systems. Due to the central role of lipid metabolism in many devastating diseases, lipidomics is being increasingly applied in biomedical research. Over the past years, advances in analytical techniques and bioinformatics enabled increasingly comprehensive and accurate coverage of lipids both in tissues and biofluids, yet many challenges remain. This review highlights recent progress in the domain of analytical lipidomics, with main emphasis on non-targeted methodologies for large scale clinical applications, as well as discusses some of the key challenges and opportunities in this field.

Multiple microRNA regulation of lipoprotein lipase gene abolished by 3'UTR polymorphisms in a triglyceride-lowering haplotype harboring p.Ser474Ter

BACKGROUND

Lipoprotein lipase (LPL) is a key enzyme in triglyceride (TG) metabolism. LPL gene single nucleotide polymorphisms (SNPs) are associated with TG concentrations however the functionality of many of these SNPs remains poorly understood. MicroRNAs (miR) exert post-transcriptional down-regulation and their target sequence on the 3'UTR may be altered by SNPs. We therefore investigated whether LPL 3'UTR SNPs could modulate plasma TG concentration through the alteration of miR binding-sites.

METHODS AND RESULTS

We performed genetic association studies of LPL 3'UTR SNPs with TG concentrations in 271 type 2 diabetic patients and in general population samples (2997 individuals). A specific LPL haplotype (Hap4) was associated with lower plasma TG concentration (TG-0.18, IC95% [-0.30, -0.07] mmol/L or logTG-0.13, IC95% [-0.18, -0.08], p = 4.77·10(-8)) in the meta-analysis. Hap4 comprises seven 3'UTR SNP minor alleles and p.Ser474Ter (rs328) a well-documented nonsense mutation associated with low TG concentration although by an unknown mechanism so far. Bio-informatic studies identified several putative miRNA binding-sites on the wild-type Hap1 haplotype, lost on Hap4. Functional validation performed in HEK-293T cells using luciferase expression constructs with various LPL 3'UTR allele combinations demonstrated a binding of miR-29, miR-1277 and miR-410 on Hap1, lost on Hap4. This loss of specific miR binding-site in presence of Hap4 was independent of the allelic variation of p.Ser474Ter (rs328).

CONCLUSIONS

We report the regulation of LPL by the miR-29, miR-1277 and miR-410 that is lost in presence of Hap4, a specific LPL TG-lowering haplotype. Consequently p.Ser474Ter association with TG concentration could be at least partially explained by its strong linkage disequilibrium with these functional 3'UTR SNPs.

Mapping asthma-associated variants in admixed populations

Admixed populations arise when two or more previously isolated populations interbreed. Mapping asthma susceptibility loci in an admixed population using admixture mapping (AM) involves screening the genome of individuals of mixed ancestry for chromosomal regions that have a higher frequency of alleles from a parental population with higher asthma risk as compared with parental population with lower asthma risk. AM takes advantage of the admixture created in populations of mixed ancestry to identify genomic regions where an association exists between genetic ancestry and asthma (in contrast to between the genotype of the marker and asthma). The theory behind AM is that chromosomal segments of affected individuals contain a significantly higher-than-average proportion of alleles from the high-risk parental population and thus are more likely to harbor disease-associated loci. Criteria to evaluate the applicability of AM as a gene mapping approach include: (1) the prevalence of the disease differences in ancestral populations from which the admixed population was formed; (2) a measurable difference in disease-causing alleles between the parental populations; (3) reduced linkage disequilibrium (LD) between unlinked loci across chromosomes and strong LD between neighboring loci; (4) a set of markers with noticeable allele-frequency differences between parental populations that contributes to the admixed population (single nucleotide polymorphisms (SNPs) are the markers of choice because they are abundant, stable, relatively cheap to genotype, and informative with regard to the LD structure of chromosomal segments); and (5) there is an understanding of the extent of segmental chromosomal admixtures and their interactions with environmental factors. Although genome-wide association studies have contributed greatly to our understanding of the genetic components of asthma, the large and increasing degree of admixture in populations across the world create many challenges for further efforts to map disease-causing genes. This review, summarizes the historical context of admixed populations and AM, and considers current opportunities to use AM to map asthma genes. In addition, we provide an overview of the potential limitations and future directions of AM in biomedical research, including joint admixture and association mapping for asthma and asthma-related disorders.

Lipoprotein lipase SNPs rs13702 and rs301 correlate with clinical outcome in chronic lymphocytic leukemia patients

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western world and is characterized by a heterogeneous clinical course. This variability in clinical course has spiked the search for prognostic markers able to predict patient evolution at the moment of diagnosis. Markers demonstrated to be of value are the mutation status of the immunoglobulin heavy chain variable region genes (IGHV) and lipoprotein lipase (LPL) expression. High LPL mRNA expression has been associated with short treatment free (TFS) and decreased overall survival (OS) in CLL. The LPL SNPs rs301 (T<C), rs328 (C<G) and rs13702 (T<C) have been associated with various metabolic disorders, but the association with CLL evolution is unknown. Here, in a cohort of 248 patients, we show that patients with the LPL SNP rs13702 wild-type T/T genotype had significantly shorter OS than patients with C/C and T/C genotypes (median time until CLL related death: 90 and 156 months respectively, p=0.008). The same was observed for LPL SNP rs301 (median time until CLL related death T/T: 102 and C/C, T/C: 144 months, p=0.03). Both SNPs rs301 and rs13702 were significantly associated with each other and notably, no association was found between IGHV status and presence of the SNP genotypes, indicating that these LPL SNPs are reliable prognostic markers that could add extra prognostic and predictive information to classical markers and help to improve the management of CLL.

Genetics and causality of triglyceride-rich lipoproteins in atherosclerotic cardiovascular disease

Triglycerides represent 1 component of a heterogeneous pool of triglyceride-rich lipoproteins (TGRLs). The reliance on triglycerides or TGRLs as cardiovascular disease (CVD) risk biomarkers prompted investigations into therapies that lower plasma triglycerides as a means to reduce CVD events. Genetic studies identified TGRL components and pathways involved in their synthesis and metabolism. We advocate that only a subset of genetic mechanisms regulating TGRLs contribute to the risk of CVD events. This "omic" approach recently resulted in new targets for reducing CVD events.

Resequencing of LPL in African Blacks and associations with lipoprotein-lipid levels

Genome-wide association studies have identified several loci associated with plasma lipid levels but those common variants together account only for a small proportion of the genetic variance of lipid traits. It has been hypothesized that the remaining heritability may partly be explained by rare variants with strong effect sizes. Here, we have comprehensively investigated the associations of both common and uncommon/rare variants in the lipoprotein lipase (LPL) gene in relation to plasma lipoprotein-lipid levels in African Blacks (ABs). For variant discovery purposes, the entire LPL gene and flanking regions were resequenced in 95 ABs with extreme high-density lipoprotein cholesterol (HDL-C) levels. A total of 308 variants were identified, of which 64 were novel. Selected common tagSNPs and uncommon/rare variants were genotyped in the entire sample (n=788), and 126 QC-passed variants were evaluated for their associations with lipoprotein-lipid levels by using single-site, haplotype and rare variant (SKAT-O) association analyses. We found eight not highly correlated (r(2)<0.40) signals (rs1801177:G>A, rs8176337:G>C, rs74304285:G>A, rs252:delA, rs316:C>A, rs329:A>G, rs12679834:T>C, and rs4921684:C>T) nominally (P<0.05) associated with lipid traits (HDL-C, LDL-C, ApoA1 or ApoB levels) in our sample. The most significant SNP, rs252:delA, represented a novel association observed with LDL-C (P=0.002) and ApoB (P=0.012). For TG and LDL-C, the haplotype analysis was more informative than the single-site analysis. The SKAT-O analysis revealed that the bin (group) containing 22 rare variants with MAF≤0.01 exhibited nominal association with TG (P=0.039) and LDL-C (P=0.027). Our study indicates that both common and uncommon/rare LPL variants/haplotypes may affect plasma lipoprotein-lipid levels in general African population.

Genome-wide association study of metabolic syndrome in koreans

Metabolic syndrome (METS) is a disorder of energy utilization and storage and increases the risk of developing cardiovascular disease and diabetes. To identify the genetic risk factors of METS, we carried out a genome-wide association study (GWAS) for 2,657 cases and 5,917 controls in Korean populations. As a result, we could identify 2 single nucleotide polymorphisms (SNPs) with genome-wide significance level p-values (<5 × 10^-8), 8 SNPs with genome-wide suggestive p-values (5 × 10^-8 ≤ p < 1 × 10^-5), and 2 SNPs of more functional variants with borderline p-values (5 × 10^-5 ≤ p < 1 × 10^-4). On the other hand, the multiple correction criteria of conventional GWASs exclude false-positive loci, but simultaneously, they discard many true-positive loci. To reconsider the discarded true-positive loci, we attempted to include the functional variants (nonsynonymous SNPs [nsSNPs] and expression quantitative trait loci [eQTL]) among the top 5,000 SNPs based on the proportion of phenotypic variance explained by genotypic variance. In total, 159 eQTLs and 18 nsSNPs were presented in the top 5,000 SNPs. Although they should be replicated in other independent populations, 6 eQTLs and 2 nsSNP loci were located in the molecular pathways of LPL, APOA5, and CHRM2, which were the significant or suggestive loci in the METS GWAS. Conclusively, our approach using the conventional GWAS, reconsidering functional variants and pathway-based interpretation, suggests a useful method to understand the GWAS results of complex traits and can be expanded in other genomewide association studies.

Lipoprotein lipase variants interact with polyunsaturated fatty acids for obesity traits in women: replication in two populations

BACKGROUND AND AIMS

Lipoprotein lipase (LPL) is a candidate gene for obesity based on its role in triglyceride hydrolysis and the partitioning of fatty acids towards storage or oxidation. Whether dietary fatty acids modify LPL associated obesity risk is unknown.

METHODS AND RESULTS

We examined five single nucleotide polymorphisms (SNPs) (rs320, rs2083637, rs17411031, rs13702, rs2197089) for potential interaction with dietary fatty acids for obesity traits in 1171 participants (333 men and 838 women, aged 45-75 y) of the Boston Puerto Rican Health Study (BPRHS). In women, SNP rs320 interacted with dietary polyunsaturated fatty acids (PUFA) for body mass index (BMI) (P = 0.002) and waist circumference (WC) (P = 0.001) respectively. Higher intake of PUFA was associated with lower BMI and WC in homozygotes of the major allele (TT) (P = 0.01 and 0.005) but not in minor allele carriers (TG and GG). These interactions were replicated in an independent population, African American women of the Atherosclerosis Risk in Communities (ARIC) study (n = 1334).

CONCLUSION

Dietary PUFA modulated the association of LPL rs320 with obesity traits in two independent populations. These interactions may be relevant to the dietary management of obesity, particularly in women.

Dyslipidemia patterns among Hispanics/Latinos of diverse background in the United States

BACKGROUND

The prevalence and determinants of dyslipidemia patterns among Hispanics/Latinos are not well known.

METHODS

Lipid and lipoprotein data were used from the Hispanic Community Health Study/Study of Latinos—a population-based cohort of 16,415 US Hispanic/Latinos ages 18-74 years. National Cholesterol Education Program cutoffs were employed. Differences in demographics, lifestyle factors, and biological and acculturation characteristics were compared among those with and without dyslipidemia.

RESULTS

Mean age was 41.1 years, and 47.9% were male. The overall prevalence of any dyslipidemia was 65.0%. The prevalence of elevated low-density lipoprotein cholesterol was 36.0%, and highest among Cubans (44.5%; P < .001). Low high-density lipoprotein cholesterol (HDL-C) was present in 41.4% and did not significantly differ across Hispanic background groups (P = .09). High triglycerides were seen in 14.8% of Hispanics/Latinos, most commonly among Central Americans (18.3%; P < .001). Elevated non-HDL-C was seen in 34.7%, with the highest prevalence among Cubans (43.3%; P < .001). Dominicans consistently had a lower prevalence of most types of dyslipidemia. In multivariate analyses, the presence of any dyslipidemia was associated with increasing age, body mass index, and low physical activity. Older age, female sex, diabetes, low physical activity, and alcohol use were associated with specific dyslipidemia types. Spanish-language preference and lower educational status were associated with higher dyslipidemia prevalence.

CONCLUSION

Dyslipidemia is highly prevalent among US Hispanics/Latinos; Cubans seem particularly at risk. Determinants of dyslipidemia varied across Hispanic backgrounds, with socioeconomic status and acculturation having a significant effect on dyslipidemia prevalence. This information can help guide public health measures to prevent disparities among the US Hispanic/Latino population.

Genetic association of APOB polymorphisms with variation in serum lipid profile among the Kuwait population

BACKGROUND

Several studies have identified APOB as a candidate gene predisposing individuals to dyslipidemia. Polymorphisms including the signal peptide (rs11279109), codon 2488 XbaI (rs1042031), codon 3611 MspI (rs693), codon 4154 EcoRI (rs1801701) and the 3' variable number of tandem repeats have been reported to be associated with dyslipidemia in several populations. With limited studies on Arabs, this study aimed to investigate the genetic association of APOB polymorphisms and assess the potential influence of minor and rare alleles on serum lipid levels in the Kuwaiti population.

METHODS

A total of 795 Kuwaiti subjects, documented with phenotypic data and fasting serum lipid levels, were genotyped for the five polymorphisms using PCR, PCR-RFLP and gene fragment analysis. Genotype and allele association with variation in serum lipid levels as well as haplotypes were analyzed using chi-square test, univariate and logistic regression analysis.

RESULTS

Analysis of the genotype and allele frequencies distribution revealed a significant positive association between the APOB signal peptide and 3611 MspI polymorphisms with increased levels of triglycerides (statistical power of 80%). Haplotype analysis further supported the findings by showing that carriers of haplotypes (IX-M-E+M) had significantly lower mean (SD) TG levels (0.86 ± 0.07) as compared to non-carriers (1.01 ± 0.02). Significance was also observed with regards to positive family history of hypercholesterolemia.

CONCLUSION

The results imply a "protective role" for two alleles (rs11279109 and rs1801701) in which logistic regression analysis showed a significant half-fold decrease in the risk for heterozygotes of rs11279109 and an 8.8 fold decrease in the risk for homozygous M-M- of rs1801701 of having lower TG levels (<1.70 mmol/L) in individuals. This suggests that genetic interaction between various polymorphisms at different gene loci act in linkage disequilibrium to affect serum TG levels. Apo B genotyping may be a useful adjunct for the identification of individuals at risk of developing dyslipidemia in order to provide them with lifestyle modifications and/or pharmacological intervention to mitigate the effects of gene interaction and environmental influence.

Genome-wide admixture and association study of serum iron, ferritin, transferrin saturation and total iron binding capacity in African Americans

Iron is an essential component of many important proteins and enzymes, including hemoglobin, which is responsible for carrying oxygen to the cells. African Americans (AAs) have a greater prevalence of iron deficiency compared with European Americans. We conducted genome-wide admixture-mapping and association studies for serum iron, serum ferritin, transferrin saturation (SAT) and total iron binding capacity (TIBC) in 2347 AAs participating in the Jackson Heart Study (JHS). Follow-up replication analyses for JHS iron-trait associated SNPs were conducted in 329 AA participants in the Healthy Aging in Neighborhoods of Diversity across the Life Span study (HANDLS). Higher estimated proportions of global African ancestry were significantly associated with lower levels of iron (P = 2.4 × 10(-5)), SAT (P = 0.0019) and TIBC (P = 0.042). We observed significant associations (P < 5 × 10(-8)) between serum TIBC levels and two independent SNPs around TF on chromosome 3, the first report of a genome-wide significant second independent signal in this region, and SNPs near two novel genes: HDGFL1 on chromosome 6 and MAF on chromosome 16. We also observed significant associations between ferritin levels and SNPs near GAB3 on chromosome X. We replicated our two independent associations at TF and our association at GAB3 in HANDLS. Our study provides evidence for both shared and unique genetic risk factors that are associated with iron-related measures in AAs. The top two variants in TF explain 11.2% of the total variation in TIBC levels in AAs after accounting for age, gender, body mass index and background ancestry.

MicroRNA-410 regulated lipoprotein lipase variant rs13702 is associated with stroke incidence and modulated by diet in the randomized controlled PREDIMED trial

BACKGROUND

MicroRNAs have emerged as important epigenetic regulators in cardiovascular diseases (CVDs). Using an observational meta-analysis design, we previously characterized a gain-of-function microRNA-410 target site polymorphism (rs13702T>C) in the 3'untranslated region of the lipoprotein lipase (LPL) gene. The C allele was associated with lower triglycerides, and this association was modulated by fat intake.

OBJECTIVES

We aimed to extend our findings by assessing the interaction between the rs13702 polymorphism and fat intake on triglycerides at baseline and longitudinally by using a dietary intervention design. We also examined as a primary outcome the association of this variant with CVD incidence and its modulation by the Mediterranean diet (MedDiet).

DESIGN

We studied 7187 participants in the PREDIMED (Prevención con Dieta Mediterránea) randomized trial that tested a MedDiet intervention compared with a control diet, with a median 4.8-y follow-up. LPL polymorphisms and triglycerides were determined and CVD assessed. Gene-diet interactions for triglycerides were analyzed at baseline (n = 6880) and after a 3-y intervention (n = 4131). Oxidative stress parameters were investigated in a subsample.

RESULTS

The rs13702T>C polymorphism was strongly associated with lower triglycerides in C allele carriers and interacted synergistically with dietary monounsaturated (P = 0.038) and unsaturated fat intake (P = 0.037), decreasing triglycerides at baseline. By 3 y, we observed a gene-diet interaction (P = 0.025) in which the C allele was associated with a greater reduction in triglycerides after intervention with MedDiet, high in unsaturated fat. Although the polymorphism was associated with lower stroke risk (HR: 0.74; 95% CI: 0.57, 0.97; P = 0.029 per C allele), this association reached statistical significance only in the MedDiet intervention (HR: 0.58; 95% CI: 0.37, 0.91; P = 0.019 in C compared with TT carriers), not in the control group (HR: 0.94; 95% CI: 0.55, 1.59; P = 0.805).

CONCLUSION

We report a novel association between a microRNA target site variant and stroke incidence, which is modulated by diet in terms of decreasing triglycerides and possibly stroke risk in rs13702 C allele carriers after a high-unsaturated fat MedDiet intervention.

APOε4 is associated with enhanced in vivo innate immune responses in human subjects

BACKGROUND

The genetic determinants of the human innate immune response are poorly understood. Apolipoprotein (Apo) E, a lipid-trafficking protein that affects inflammation, has well-described wild-type (ε3) and disease-associated (ε2 and ε4) alleles, but its connection to human innate immunity is undefined.

OBJECTIVE

We sought to define the relationship of APOε4 to the human innate immune response.

METHODS

We evaluated APOε4 in several functional models of the human innate immune response, including intravenous LPS challenge in human subjects, and assessed APOε4 association to organ injury in patients with severe sepsis, a disease driven by dysregulated innate immunity.

RESULTS

Whole blood from healthy APOε3/APOε4 volunteers induced higher cytokine levels on ex vivo stimulation with Toll-like receptor (TLR) 2, TLR4, or TLR5 ligands than blood from APOε3/APOε3 patients, whereas TLR7/8 responses were similar. This was associated with increased lipid rafts in APOε3/APOε4 monocytes. By contrast, APOε3/APOε3 and APOε3/APOε4 serum neutralized LPS equivalently and supported similar LPS responses in Apoe-deficient macrophages, arguing against a differential role for secretory APOE4 protein. After intravenous LPS, APOε3/APOε4 patients had higher hyperthermia and plasma TNF-α levels and earlier plasma IL-6 than APOε3/APOε3 patients. APOE4-targeted replacement mice displayed enhanced hypothermia, plasma cytokines, and hepatic injury and altered splenic lymphocyte apoptosis after systemic LPS compared with APOE3 counterparts. In a cohort of 828 patients with severe sepsis, APOε4 was associated with increased coagulation system failure among European American patients.

CONCLUSIONS

APOε4 is a determinant of the human innate immune response to multiple TLR ligands and associates with altered patterns of organ injury in human sepsis.

Genetics of lipid traits: Genome-wide approaches yield new biology and clues to causality in coronary artery disease

A wealth of novel lipid loci have been identified through a variety of approaches focused on common and low-frequency variation and collaborative metaanalyses in multiethnic populations. Despite progress in identification of loci, the task of determining causal variants remains challenging. This work will undoubtedly be enhanced by improved understanding of regulatory DNA at a genomewide level as well as new methodologies for interrogating the relationships between noncoding SNPs and regulatory regions. Equally challenging is the identification of causal genes at novel loci. Some progress has been made for a handful of genes and comprehensive testing of candidate genes using multiple model systems is underway. Additional insights will be gleaned from focusing on low frequency and rare coding variation at candidate loci in large populations. This article is part of a Special Issue entitled: From Genome to Function.