New Insight Into the Association of Apolipoprotein E Genetic Variants With Carotid Plaques and Intima-Media Thickness

Extracranial carotid artery atherosclerotic plaque and APOE polymorphisms: a systematic review and meta-analysis

Introduction

Carotid atherosclerotic plaque is an important independent risk factor for stroke. Apolipoprotein E (APOE) influences cholesterol levels and certain isoforms are associated with increased carotid atherosclerosis, though the exact association between APOE and carotid plaque is uncertain. The study aimed to evaluate the association between APOE and carotid plaque.

Methods

A systematic review was performed to retrieve all studies which examined the association between carotid plaque and APOE. This study was conducted in accordance with the PRISMA guidelines. Independent readers extracted the relevant data from each study including the type of imaging assessment, plaque definition, frequency of APOE E4 carrier status and type of genotyping. Meta-analyses with an assessment of study heterogeneity and publication bias were performed. Results were presented in a forest plot and summarized using a random-effects model.

Results

After screening 838 studies, 17 studies were included for systematic review. A meta-analysis of 5 published studies showed a significant association between ε4 homozygosity and carotid plaque [odds ratio (OR), 1.53; 95% CI, 1.16, 2.02; p = .003]. Additionally, there was a significant association between patients possessing at least one ε4 allele, heterozygotes or homozygotes, and carotid plaque (OR, 1.25; 95% CI, 1.03, 1.52; p = .03). Lastly, there was no association between ε4 heterozygosity and carotid plaque (OR, 1.08; 95% CI, 0.93, 1.26; p = .30).

Conclusion

APOE ε4 allele is significantly associated with extracranial carotid atherosclerotic plaque, especially for homozygous individuals.

Involvement of APOE in Incidence of Revascularization in Patients Affected by Peripheral Arterial Disease: A Prospective Study from Southern Italy

INTRODUCTION

Atherosclerosis is a complex multifactorial disease and apolipoprotein E (APOE) polymorphism has been associated with cardiovascular events. The APOE gene, located on chromosome 19q13.2, has an important role in lipid metabolism, in particular on circulating cholesterol levels, implying further pleiotropic effects; from its polymorphism are derived three alleles (ε2, ε3 and ε4), which induce different phenotypes, while its impact on carotid and femoral atherosclerosis is still controversial.

OBJECTIVES

The aim of the study is to investigate the relationship between APOE genotypes and peripheral revascularization in a cohort of patients affected by advanced peripheral arterial disease (PAD) at a prolonged follow-up.

MATERIALS AND METHODS

Some 332 patients (259 males and 73 females; mean age 70.86 ± 7.95 years) with severe PAD were enrolled in a longitudinal study, with a 90.75 ± 32.25 month follow-up, assessing major adverse cardiovascular events (MACE).

RESULTS

As compared with ε3/ε3, in ε4 patients we observed a significant higher incidence of carotid (13.2% vs. 5.6%; HR = 2.485, 95% CI 1.062-5.814; p = 0.036) and lower limb (11.8% vs. 4.3%; HR = 2.765, 95% CI 1.091-7.008; p = 0.032) revascularizations and, accordingly, a higher incidence of total peripheral revascularizations (13.5% vs. 9.5%; HR = 2.705, 95% CI 1.420-5.151; p = 0.002). HR remained statistically significant even when adjusted for classic cardiovascular risk factors.

CONCLUSIONS

In our observational study, we confirm that the ε4 allele is associated with higher total peripheral revascularization in patients with advanced atherosclerotic vascular disease at prolonged follow-up.

Inflammation and endothelial function-related gene polymorphisms are associated with carotid atherosclerosis-A study of community population in Southwest China

OBJECTIVES

To investigate the relationships between 18 single nucleotide polymorphisms with carotid atherosclerosis and whether interactions among these genes were associated with an increased risk of carotid atherosclerosis.

METHODS

Face-to-face surveys were conducted with individuals aged 40 or older in eight communities. A total of 2377 individuals were included in the study. Ultrasound was used to detect carotid atherosclerosis in the included population. 18 loci of 10 genes associated with inflammation and endothelial function were detected. Gene-gene interactions were analyzed using generalized multifactor dimensionality reduction (GMDR).

RESULTS

Among the 2377 subjects, 445 (18.7%) subjects had increased intima-media thickness in the common carotid artery (CCA-IMT), and 398 (16.7%) subjects were detected with vulnerable plaque. In addition, NOS2A rs2297518 polymorphism was associated with increased CCA-IMT, IL1A rs1609682, and HABP2 rs7923349 polymorphisms were associated with vulnerable plaque. Besides, GMDR analysis showed significant gene-gene interactions among TNFSF4 rs1234313, IL1A rs1609682, TLR4 rs1927911, ITGA2 rs1991013, NOS2A rs2297518, IL6R rs4845625, ITGA2 rs4865756, HABP2 rs7923349, NOS2A rs8081248, HABP2 rs932650.

CONCLUSION

The prevalences of increased CCA-IMT and vulnerable plaque were high in Southwestern China's high-risk stroke population. Furthermore, inflammation and endothelial function-related gene polymorphisms were associated with carotid atherosclerosis.

Cardiorespiratory fitness decreases the odds for subclinical carotid plaques in apolipoprotein e4 homozygotes

Some studies suggest that being an apolipoprotein e4 (APOE e4) carrier increases the risk of atherosclerosis, and others suggest that cardiorespiratory fitness (CRF) could play a key role in atherosclerotic prevention. Our aim was to analyze the association of APOE e4 with carotid atherosclerosis and the association of CRF with atherosclerosis in APOE e4 carriers. A cross-sectional analysis based on a subsample of 90 participants in the Aragon Workers' Health Study was carried out. Ultrasonography was used to assess the presence of plaques in carotid territory; the submaximal Chester Step Test was used to assess CRF; and behavioral, demographic, anthropometric, and clinical data were obtained by trained personnel during annual medical examinations. APOE e4e4 participants were categorized into Low-CRF (VO_2max < 35 mL/kg/min) and High-CRF (VO_2max ≥ 35 mL/kg/min) groups. After adjusting for several confounders, compared with APOE e3e3, those participants genotyped as APOE e3e4 and APOE e4e4 showed an OR = 1.60 (95% CI 0.45, 5.71) and OR = 4.29 (95% CI 1.16, 15.91), respectively, for carotid atherosclerosis. Compared to Low-CRF APOE e4e4 carriers, the odds of carotid plaque detection were 0.09 (95% CI 0.008, 0.98) times lower among High-CRF APOE e4e4 carriers. The APOE e4e4 genotype was associated with increased carotid atherosclerosis. However, CRF is a modifiable factor that may be targeted by APOE e4e4 to decrease the elevation of atherosclerotic risk due to this genetic condition.

Genetic susceptibility to cerebrovascular disease: A systematic review

Investigation of genetic susceptibility to cerebrovascular disease has been of growing interest. A systematic review of human studies assessing neurogenomic aspects of cerebrovascular disease was performed according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. Any association study exploring genetic variants located in the exome associated with one of the major cerebrovascular diseases with at least 500 subjects was eligible for inclusion. Of 6874 manuscripts identified, 35 studies met the inclusion criteria. Most studies of interest focused on ischemic stroke and cerebrovascular occlusive disease. Large cohort genetic association studies on hemorrhagic cerebrovascular disease were less common. In addition to rare, well-established monogenic conditions with significant risk for cerebrovascular disease, a number of genetic variants are also relevant to cerebrovascular pathogenesis as part of a multifactorial process. The 45 polymorphisms identified were located in genes involved in processes related to endothelial and vascular health (15 (33.4%) variants), plasma lipid metabolism (10 (22.2%) variants), inflammation (9 (20%) variants), coagulation (3 (6.7%) variants), and blood pressure modulation (2 (4.4%) variants), and other (6 (13.3%) variants). This work represents a comprehensive overview of genetic variants in the exome relevant to ischemic and hemorrhagic stroke pathophysiology.

Genetics of ischaemic stroke in young adults

Background

Stroke may be a clinical expression of several inherited disorders in humans. Recognition of the underlined genetic disorders causing stroke is important for a correct diagnosis, for genetic counselling and, even if rarely, for a correct therapeutic management. Moreover, the genetics of complex diseases such the stroke, in which multiple genes interact with environmental risk factors to increase risk, has been revolutionized by the Genome-Wide Association Study (GWAS) approach.

Scope of review

Here we review the single-gene causes of ischemic stroke, bringing the reader from the candidate gene method toward the exciting new horizons of genetic technology.

Major conclusions

The aetiological diagnosis of ischemic stroke in young adults is more complex than in the elderly. The identification of a genetic cause is important to provide appropriate counseling and to start a correct therapy, when available. The advent of GWAS technology, such as for other complex pathological conditions, has contributed enormously to the understanding of many of these genetic bases. For success large, well phenotyped case cohorts are required, and international collaborations are essential.

General significance

This review focuses on the main causes of genetically-based ischemic stroke in young adults, often classified as indeterminate, investigating also the recent findings of the GWAS, in order to improve diagnostic and therapeutic management.

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The aetiological diagnosis of stroke in young adults needs a different and more complex diagnostic work up than in older adults.

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Stroke may be a clinical expression of several inherited disorders in humans.

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The most common genetic causes of stroke are CADASIL, Fabry and mitochondrial diseases.

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Recognition of the underlined genetic disorders causing stroke is important for the correct management of the patient.

Plasma β-amyloid 40 levels are positively associated with mortality risks in the elderly

BACKGROUND

We evaluated if plasma β-amyloid (Aβ) levels were associated with mortality risks in a subsample of the French Three-City (3C) prospective cohort study.

METHODS

Analyses were based on 1254 participants randomly selected from the initial 3C cohort stratified by center, sex, and age in the context of a nested case-cohort study to investigate biological variables. Associations between plasma Aβ and mortality were assessed with the Cox regression model with delayed entry including various potential confounding factors and testing possible mediators.

RESULTS

A relationship between high plasma Aβ1-40 concentrations and risk of mortality (hazards ratio, 1.15; 95% confidence interval, 1.01-1.31, P = .03) was unveiled independently of age, educational level, vascular risk factors, diet, physical activity, cognitive impairment, or frailty status. It was only modified when we included cystatin C levels.

CONCLUSIONS

Further investigations are needed to determine precisely the pathophysiological roles of plasma Aβ1-40 and cystatin C and before envisioning any future clinical applications.

APOE ϵ 2 allele is an independent risk factor for vulnerable carotid plaque in ischemic stroke patients

BACKGROUND AND AIMS

The data about apolipoprotein E gene (APOE) genotype and the risk of stroke are inconsistent. The APOE genotype is expected to influence the development of carotid plaques. Our aim was to look for association between APOE genotype and carotid plaque morphology in ischemic stroke patients.

METHODS AND RESULTS

Data of ischemic stroke patients was collected prospectively for 2 years. The degree of stenosis and plaque echogenicity and surface were assessed with ultrasound. Subsequent APOE genotypes were compared: APOE ϵ 3/ϵ 3 (E3--reference), APOE ϵ 2/ϵ 3 (E2 group) and APOE ϵ 3/ϵ 4, APOE ϵ 4/ϵ 4 (E4 group). We included 388 patients with acute ischemic stroke. Patients in E2 group had more often hypoechogenic, ulcerated plaques and severe stenosis comparing to E3 patients. On logistic regression analysis, ϵ 2 genotype remained an independent risk factor for vulnerable carotid plaque (OR  =  2.3 for <60% stenosis and OR  =  2.7 for ≥60% stenosis; 95% CI).

CONCLUSIONS

This study suggests that ϵ 2 allele is an independent risk factor for echolucent and ulcerated carotid plaque.

APOE polymorphism and carotid atherosclerosis in Korean population: the Dong-gu Study and the Namwon Study

OBJECTIVE

We evaluated the association between APOE polymorphism and carotid atherosclerosis in two large independent cohorts from South Korea.

METHODS

The datasets were from the Dong-gu Study (N = 9056) and the Namwon Study (N = 10,158). Carotid ultrasonography was performed to measure carotid intima-media thickness (IMT) and the presence of carotid plaques. The APOE polymorphism was determined by PCR-RFLP. We performed combined and separate analyses for the two datasets.

RESULTS

In the combined analysis, individuals with E2E2 or E2E3 genotype had a lower common carotid IMT compared with individuals with E3E3 genotype (0.684 mm vs. 0.736 mm, p = 0.007; 0.718 mm vs. 0.736 mm, p < 0.001, respectively). This association was very slightly attenuated but remained statistically significant after adjustment for blood lipids (0.690 mm vs. 0.736 mm, p = 0.033; 0.725 mm vs. 0.736 mm, p = 0.005, respectively). Compared with individuals with E3E3 genotype, individuals with E2E3 genotype had lower risk for carotid plaque (odds ratio (OR) = 0.83, 95% confidence interval (CI) = 0.75-0.93), while individuals with E3E4 genotype had a higher risk for carotid plaque (OR = 1.09, 95% CI = 1.00-1.20). After adjustment for blood lipids, ORs of E2E3 genotype for carotid plaque was slightly attenuated but remained significant (OR = 0.87 95% CI = 0.78-0.97), while OR of E3E4 genotype were slightly attenuated and not significant (OR = 1.08, 95% CI, 0.99-1.18).

CONCLUSIONS

We found that APOE polymorphism is associated with carotid atherosclerosis and this association was partly mediated through blood lipid. Our results suggest that APOE polymorphism may influence atherosclerosis through non-lipid pathways.

Genetics of stroke

Stroke is the second most common cause of death and the most common cause of disability in developed countries. Stroke is a multi-factorial disease caused by a combination of environmental and genetic factors. Numerous epidemiologic studies have documented a significant genetic component in the occurrence of strokes. Genes encoding products involved in lipid metabolism, thrombosis, and inflammation are believed to be potential genetic factors for stroke. Although a large group of candidate genes have been studied, most of the epidemiological results are conflicting. Studies of stroke as a monogenic disease have made huge progress, and animal models serve as an indispensable tool to dissect the complex genetics of stroke. In the present review, we provide insight into the role of in vivo stroke models for the study of stroke genetics.

Apolipoprotein E Genotype and Cardiovascular Diseases in the Elderly

The apolipoprotein E (APOE) genotype is a genetic risk factor for dementia, Alzheimer’s disease, and cardiovascular disease (CVD). It includes three alleles (e2, e3, e4) that are located on chromosome 19q3.2. The e3 allele is the most common and is more common in people of Northern European ancestry and less common in those of Asian ancestry. Those with at least one e4 allele are at increased risk for CVD outcomes. It is well established that the presence of an e4 allele is linked to higher low-density lipoprotein cholesterol levels, even at young ages. Even though most CVD occurs in older people, there are few studies of the effects of APOE on CVD in older people. This review addresses recent research on the links between APOE, CVD, and vascular mechanisms by which APOE may affect CVD in the elderly.

Fractalkine receptor/ligand genetic variants and carotid intima-media thickness

BACKGROUND AND PURPOSE

The fractalkine ligand/receptor (CX3CL1/CX3CR1) complex is important in inflammatory responses and has been associated with vascular disease. We determined whether genetic variants in CX3CL1 and CX3CR1 are associated with carotid atherosclerosis in 2 large European populations.

METHODS

18 polymorphisms in CX3CL1 and CX3CR1 were genotyped in 2763 German community individuals (CAPS). Positive results were tested for replication on 6049 French community individuals (3C Study).

RESULTS

In CAPS we found associations of common carotid artery (CCA)-IMT with 2 CX3CL1 (rs170364, rs614230) and 1 CX3CR1 (rs3732378) variants, and significant interactions of CX3CR1 rs11129820, rs3732378, and rs614230 variants with smoking and alcohol consumption in relation with CCA-IMT. None of these were replicated in 3C. In 3C only there was a borderline significant association of rs3732378 with carotid plaques.

CONCLUSIONS

In almost 9000 subjects, we found no replicable associations of CX3CL1 and CX3CR1 polymorphisms with CCA-IMT or plaque.

Relation of apolipoprotein E polymorphism to markers of early atherosclerotic changes in young adults--the Cardiovascular Risk in Young Finns Study

BACKGROUND

Carotid artery intima-media thickness (IMT), which is measured by ultrasound, is used in the assessment of early atherosclerotic changes, and has been associated with apolipoprotein E (APOE) polymorphism in many studies comprising elderly subjects. However, results are still inconclusive and data relating to young adults are missing. Whether common APOE polymorphism is related to carotid IMT was studied in a population of young adults. Also brachial flow-mediated dilatation (FMD) and carotid artery compliance (CAC) were determined to clarify their relation to this genetic factor.

METHODS AND RESULTS

A total of 1,188 young adults (aged 24-39 years) participating in the Cardiovascular Risk in Young Finns Study with complete data of common APOE polymorphism underwent a carotid and brachial ultrasound. Patients' lipid levels and blood pressure were also examined. There was no significant association between the APOE phenotypes and carotid IMT, brachial FMD or CAC either in young men or in young women. The results were similar for systolic and diastolic blood pressure. In the same population, the well-known association between APOE phenotypes and lipids was seen.

CONCLUSIONS

Common APOE polymorphism does not seem to be an independent genetic determinant of carotid IMT, brachial FMD or CAC.

Association between apolipoprotein E genotype and carotid intima-media thickness may suggest a specific effect on large artery atherothrombotic stroke

BACKGROUND AND PURPOSE

Apolipoprotein E genotype (APOE) influences cholesterol levels and ischemic heart disease. Although there is no convincing overall association with ischemic stroke, APOE may influence large artery (atherothrombotic) stroke, for which carotid intima-media thickness (CIMT) is an informative intermediate phenotype. We therefore performed a systematic review and meta-analysis of the association between APOE and CIMT.

METHODS

We sought all published studies assessing the association between APOE and CIMT. From each study, we extracted available data on study methods, subjects' characteristics, and mean (and standard deviation) CIMT for each genotype or genotype group. We calculated study-specific and random effects pooled differences in mean CIMT between genotype groups, and assessed heterogeneity between studies and predefined subgroups using I(2) and chi(2) statistics.

RESULTS

Meta-analysis of 22 published studies (30,879 subjects) showed a significant association between APOE and CIMT (pooled mean difference epsilon 4- versus epsilon 2-allele containing genotypes 46 microm, 95% CI 29 to 62, P<0.00001). We found evidence of small study (mainly publication) bias, with a diminished (but still highly statistically significant) association in studies of >1000 subjects (pooled mean difference 17 microm, 95% CI 12 to 23, P<0.00001). The association was larger among high vascular risk and eastern Asian populations, but this may simply reflect the smaller size of these studies.

CONCLUSIONS

Our results show a clear association of APOE with CIMT, even though publication bias means that this is overestimated by the published literature. These findings suggest the possibility of a specific association with large artery ischemic stroke.

A common VLDLR polymorphism interacts with APOE genotype in the prediction of carotid artery disease risk

The genetic factors associated with carotid artery disease (CAAD) are not fully known. Because of its role in lipid metabolism, we hypothesized that common genetic variation in the very low density lipoprotein receptor (VLDLR) gene is associated with severe CAAD (>80% stenosis), body mass index (BMI), and lipid traits in humans. VLDLR was resequenced for variation discovery in 92 subjects, and single nucleotide polymorphisms (tagSNPs) were chosen for genotyping in a larger cohort (n = 1,027). Of the 17 tagSNPs genotyped, one tagSNP (SNP 1226; rs1454626) located in the 5' flanking region of VLDLR was associated with CAAD, BMI, and LDL-associated apolipoprotein B (apoB). We also identified receptor-ligand genetic interactions between VLDLR 1226 and APOE genotype for predicting CAAD case status. These findings may further our understanding of VLDLR function, its ligand APOE, and ultimately the pathogenesis of CAAD in the general population.